The main body of the part is a weak stiffness structure, which is prone to instability during mechanical machining, especially when machining the outer wall of the ring and clamping the thin-walled ring.

Machining Analysis

The morphology of the typical weak thin-walled ring with a composite structure of bilateral axial supporting parts after machining with general mechanical machining techniques is shown in Figure 2. The following deficiencies are observed:

（1）Obvious tool marks in the middle of the bilateral axial supporting parts. The upper and lower parts of the bilateral axial supporting parts are formed during two separate machining steps: milling the shape of the thin-walled ring and milling the shape of the bilateral axial supporting parts. Due to the non-coincidence of the process benchmarks between the two steps, obvious tool marks appear in the middle of the bilateral axial supporting parts.

（2）Prominent vibration marks in the middle of the thin-walled ring shape. The wall thickness of the middle part of the ring body is 2mm, which results in significantly insufficient stiffness. During the machining of the thin-walled ring shape, the middle part is prone to instability, leading to the formation of obvious vibration marks. The superposition of these issues collectively results in the machining instability problem becoming a production bottleneck.

Process Optimization

To address the deficiencies of general mechanical machining techniques, a series of compound machining measures have been adopted, including the conversion control of process benchmarks to “bore-face-contour,” the gradual reduction of workpiece stiffness during machining, the reinforcement of stiffness combined with damping and vibration absorption, and the maximization of clamping area and stiffness. These measures aim to achieve stable machining of the weak thin-walled ring with the composite structure of bilateral axial supporting parts.

Precision Conversion of Process Benchmarks

(1) After rough machining the inner shape and end face, precision turn the inner circle and end face to form the process benchmark “bore-face.”

(2) The specific steps for milling the contour positioning benchmark are as follows.

1）Clamp the fixture in the vise (see Figure 3). The bottom surface of the fixture is aligned with the workpiece end face, and the cylindrical surface of the fixture is aligned with the axial direction of the workpiece inner circle. Use a dial indicator to align the fixture bottom surface with a flatness of ≤0.01mm and then secure it.

2) Clamp the workpiece on the fixture (see Figure 4). The workpiece end face and inner bore are tightly against the fixture’s positioning surface and are clamped with a pressure plate.

3)Symmetrically machine two identical precision milling positioning steps on the workpiece contour (see Figure 5). The step height is 20mm, which converts the process benchmark from “bore-face” to “contour.”

Steady-state Machining Control

(1) The specific steps for milling the thin-walled ring contour are as follows.

1）Clamp the workpiece with a vice on the precision milling positioning step (see Figure 6).

2) Embed polytetrafluoroethylene or nylon washers into the internal thread relief groove of the workpiece, and then use an external thread mandrel to screw into the internal thread of the workpiece to enhance the stiffness of the annular body cavity.

3) Machine the round corners of the bilateral supporting parts and the shape of the thin-walled ring (see Figure 7).

(2) The specific steps for milling the shape of the bilateral axial supporting parts are as follows.

Turn the workpiece around, and use an external thread mandrel (see Figure 8) to screw into the internal thread of the workpiece to enhance the stiffness of the annular body cavity.

Clamp the workpiece with a clamping block (see Figure 9), and secure it with a flat-nose pliers.

Perform finish machining on the shape of the bilateral axial supporting parts (see Figure 10).

(3) The specific steps for milling the outer step of the bilateral supporting parts?are as follows.

Clamp the fixture with a flat-nose pliers (see Figure 11).

Axially compress the thin-walled ring body of the workpiece with the fixture (see Figure 12).

Press the expanding ring into the inner circle of the workpiece’s thin-walled ring and align the inner circle of the expanding ring with the edge finder.

Machine the structures such as the outer side of the bilateral supporting parts, the step, chamfer, and thread to completion.

Machining Process

According to the optimized process plan, the specific machining process is as follows.

(1) Milling the profile positioning reference: The milling process for the profile positioning reference is shown in Figure 13.

(2) Milling the shape of the thin-walled ring: The shape of the thin-walled ring after milling is shown in Figure 14.

Currently, in mechanical manufacturing, due to the rapid updating and upgrading of products, there are higher requirements for the selection of parts. Particularly in the manufacturing of industries such as aerospace, large power stations, and ships, some difficult-to-machine materials like high-temperature alloys, titanium alloys, heat-resistant stainless steels, and composite materials have been widely used. Among them, the efficient processing of widely used and commonly employed high-temperature alloy materials has received more attention.

Using high-performance high-speed steel bimetal saw blades (with M42 as the edge material) to cut difficult-to-machine high-temperature alloys results in low cutting efficiency and a very short service life. Subsequently, saw blades made of cemented carbide with high hardness were chosen. Through testing and practical application, cemented carbide saw blades have achieved significant results in the blanking processing of high-temperature alloys, meeting the requirements of production schedules.

Design and Selection of Cemented Carbide Saw Blades

Cemented carbide saw blades have different materials and structures. In practical applications, we have found that not every type of cemented carbide saw blade can achieve good results in the blanking processing of high-temperature alloys. Only by making reasonable choices and using them properly can the desired results be obtained. Therefore, we have selected and compared four aspects: the structure of the saw blade, the form of the tooth shape, the material, and the reasonable selection of cutting parameters. The details are as follows:

Tool Structure

Cemented carbide saw blades typically adopt a tipped and welded structure. The tips of the teeth on cemented carbide saw blades have the advantages of high hardness, high wear resistance, and high fatigue resistance. However, their main drawbacks are brittleness, low strength, and poor resistance to impact.

After testing and comparative application (especially based on the final sawing blanking data comparison results), we believe that for the blanking of high-temperature alloys, the saw blade structure is best suited with coarse teeth and variable pitch cemented carbide saw blades. The reason we believe this is optimal is that during the sawing blanking of high-temperature alloys (particularly nickel-based high-temperature alloys), the chips have strong adhesion, making it difficult for the chips to be discharged smoothly. The intermittent formation and disappearance of built-up edge can easily cause the cutting edge to chip and the tool’s flank wear to intensify. Choosing coarse teeth not only increases the strength of the cutting edge but also enlarges the chip space, facilitating the use of a larger feed rate to improve cutting efficiency. The adoption of variable pitch can reduce cutting noise and vibration, making the cutting process more stable, which is beneficial for improving the durability of the tool. A schematic diagram of the variable pitch saw blade structure can be seen in Figure 1.

Selection of Tool Tooth Shape

Common tooth shapes for saw blades include standard teeth, hook-shaped teeth, and trapezoidal teeth, as shown in Figure 2.

1. Standard teeth have a cutting approach angle g=0°, with the tooth face perpendicular to the substrate, and the tooth slots are deep and narrow.
2. Hook-shaped teeth have a cutting approach angle g=5°～10°, with the tooth slots deep and wide.
3. Trapezoidal teeth have a cutting approach angle g=10°～15° and a back angle a=6°～8°, providing high tooth strength, suitable for heavy cutting.

For the processing of high-temperature alloy materials, in addition to selecting high-strength cemented carbide materials for the saw blades, the choice of tooth shape is also very important. Trapezoidal teeth have sufficient strength and are less prone to chipping during cutting. Due to the larger approach angle, the cutting resistance is also smaller than that of standard straight teeth. Practical verification has also proven that the choice of trapezoidal teeth results in better cutting performance compared to the other two tooth shapes.

Tool Material Grades

The grades of cemented carbide suitable for cutting high-temperature alloy materials mainly fall into two categories: Type M and Type K according to the ISO standard (now recommended as Type S). Based on the results of sawing comparison tests, the improvement in cutting efficiency between the two types of tool grades is not significant. However, in terms of sawing service life, the saw blades made of material equivalent to grade M15-M30 have a 15%～20% longer life span compared to those made of material equivalent to grade K05-K20 (when processing high-temperature alloys of the same specification and grade).

Selection of Cutting Parameters

The rational selection of cutting parameters is crucial for the blanking of high-temperature alloys. Proper cutting parameters ensure normal blanking of workpieces, significantly improve cutting efficiency and tool life, and also reduce the harsh noise generated by the adhesion and friction of chips between the tool and the workpiece during blanking. Based on our experimental application results for various nickel-based high-temperature alloy grades (considering efficiency and tool life comprehensively), the selected rational cutting parameters are as follows:

Cutting linear speed: 15～20 m/min

Feed rate (material removal rate): 6～8 cm2/min

The above cutting parameters have been determined through long-term experimental applications and are considered to be economically viable.

Actual Tool Benefits

Through the aforementioned four aspects of work, the use of cemented carbide saw blades for processing high-temperature alloys has achieved significant economic effects in the steam turbine factory:

After testing and comparing multiple data results, the current cemented carbide saw blades used for processing high-temperature alloys have improved the cutting efficiency by 5 to 8 times compared to the previously used bimetal saw blades. For example, when processing a GH4169 nickel-based high-temperature alloy blank with dimensions of 140×245, the original M42 bimetal saw blade took about 6 to 8 hours to blank one piece. However, with the selected cemented carbide saw blade for processing high-temperature alloys, the blanking time for one workpiece is only about 1 hour. Moreover, what is more prominent is the improvement in tool life.

When processing blanks of the above-mentioned grades and specifications, the original M42 bimetal saw blade could only blank one piece, whereas the current cemented carbide saw blade can generally blank 20 to 24 pieces (under reasonable cutting parameters and proper operation, one saw blade can even blank 40 to 50 pieces). Although the price of the current cemented carbide saw blade is about 5 times higher than that of the bimetal saw blade, in terms of cost-performance ratio and comprehensive economic benefits (especially as demonstrated by the comparison of the above typical example), using cemented carbide saw blades to process high-temperature alloys is very cost-effective. It achieves the goal of low cost, high tool life, and efficient processing.

Use of Cemented Carbide Saw Blades
Using cemented carbide saw blades for sawing and blanking high-temperature alloy materials is an efficient and ideal process method. However, improper use can lead to rapid wear of the saw blade’s teeth and even cause the saw belt to break, which not only fails to achieve the expected results but may also result in significant losses. Therefore, the correct use of cemented carbide saw blades is very important. There are strict requirements for using saw blades, which are mainly in the following three aspects:

Requirements for the Machine Tool
a. The sawing machine must have good rigidity and a certain level of accuracy to meet the requirements for stable processing with cemented carbide saw blades.
b. Select a sawing machine with a suitable power and specification based on the diameter (cutting area) of the workpiece.
c. The machine tool must be equipped with a good chip removal, cooling system, and saw blade guiding device.

Requirements for Operating the Use of Cemented Carbide Saw Blades
a. The workpiece must be clamped securely, and after clamping, check whether the clamping points (surfaces) are in the middle and upper part of the workpiece to ensure stability during processing.
b. Break-in of the saw blade: New saw blades must go through a break-in period before normal cutting to prevent premature damage to the teeth. After the break-in process, the teeth will wear normally; without it, the teeth will be destroyed prematurely. The feed rate during the break-in period should be 20%～30% of the normal feed rate.
c. Selection of tension force:Excessive tension can cause the saw belt to break; insufficient tension can damage the saw belt or cause cutting deviation. When using a cemented carbide band saw, the tension must be adjusted to 2200～2500 kg/m2.
d. Cooling and chip flushing during cutting: When using a cemented carbide band saw to blank high-temperature alloy materials, in order to reduce the cutting temperature, cutting resistance, and extend the life of the band saw, water-based extreme pressure cutting fluid must be continuously applied during sawing. Additionally, the chips produced during sawing should be cleaned synchronously with a steel brush.

Rational Selection of Cutting Parameters
For blanking high-temperature alloy blanks, the selection of cutting parameters directly ensures the normal progress of sawing. Reasonable cutting parameters also achieve higher cutting efficiency and tool life. Due to the poor machinability of high-temperature alloy materials, the cutting parameters should be much lower compared to other alloy steel materials. Practice has proven that the cutting parameters recommended in the above examples are more reasonable. If the feed rate (material removal rate) is too low, the wear on the flank of the tool will increase. Moreover, increasing the cutting speed and feed rate will also increase the cutting force and cause the chip slot to clog, leading to chipping and reduced tool life.

The Functions of the Different Parts of the Turning Tool

?Rake angle

The rake angle is the angle between the cutting face and the reference plane; it is an important indicator of how the cutting edge participates in the cutting process. The rake angle of the blade itself is usually a positive rake angle, and the shape of the cutting face can be a circular arc, chamfer, or flat surface. The size and sign (positive or negative) of the rake angle will affect the tool strength, cutting force, the tool’s finish machining capability, vibration tendencies, and chip formation. The rake angle has a significant impact on cutting force, chip evacuation, cutting heat, and tool life.

Impact of rake angle?size on cutting

1.A larger positive rake angleresults in a sharper cutting edge, but the strength of the cutting edge decreases.

2. A larger positive rake angle?reduces the cutting force; an excessively large negative rake angle?increases the cutting force.

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Applications of different rake?angle sizes

Relief angle

The relief angle has the function of avoiding the friction between the back tool face and the workpiece and making the tool tip cut into the workpiece freely.

Relief angle size and back tool face wear diagram

?Influence of relief angle size on turning tools

The relief angle is large, and the rear tool surface is worn less, but the strength of the tool tip is decreased, and the reverse is true when the relief angle is small.

Application of different size relief angle

Secondary rake angle

The secondary rake angle affects the mitigation of impact force, the size of the feed force component, the size of the back force component, and the chip thickness.

Impact of the size of the secondary rake angle on cutting

① When the feed rate is the same, a larger secondary rake angle increases the length of contact between the insert and the chip, resulting in a thinner chip thickness. This disperses the cutting force over a longer cutting edge, thereby improving the tool life.

② A larger secondary rake angle leads to an increase in the component force a’, which can cause bending when machining slender workpieces.

③ A larger secondary rake angle results in poorer chip handling performance.

④ A larger secondary rake angle leads to a thinner chip thickness and an increased chip width, making it difficult for the chip to break.

Secondary clearance angle

The angle designed to avoid interference between the machined surface and the tool (secondary cutting edge). It is usually between 5° and 15°.

Impact of the secondary clearance angle

① A smaller secondary clearance angle increases the strength of the cutting edge, but the tool tip is prone to heating.

② A smaller secondary clearance angle increases the back force, which can cause vibration during cutting.

③ For rough machining, a smaller secondary clearance angle is preferable; for finish machining, a larger secondary clearance angle is more suitable.

Inclination Angle

The inclination angle is the angle at which the cutting face is tilted. During heavy cutting, the tool tip at the starting point of the cut bears a significant impact force. To prevent the tool tip from being damaged by this force due to brittleness, an inclination angle for the cutting edge is necessary. In turning operations, it is generally set to 3°-5°;

① When the inclination angle is negative, the chips flow towards the workpiece.

When the inclination angle is positive, the chips are discharged in the opposite direction.

② When the inclination angle is negative, the cutting edge strength increases, but the cutting back force also increases, which can easily cause vibration.

Chamfering and blunting of the cutting edge

Chamfering and blunting of the cutting edge are treatments applied to the cutting edge to ensure its strength. Typically, this involves rounding or chamfering the cutting edge. The chamfer is a narrow band-like surface set along the cutting face or the back face. Usually, the grinding width is half the feed rate.

Influence of cutting edge grinding width on turning tools

① High cutting edge strength, reduced chance of chipping, and improved tool life.

② The wear on the flank face is likely to spread, resulting in a lower tool life. The width has no effect on the wear of the cutting face.

③ Increased cutting force, which can easily cause vibration.

Application of different tip widths

Tip radius

The tip radius is a key factor in turning operations. It has a significant impact on the strength of the tip and the roughness of the machined surface. The specific choice depends on the cutting depth and feed, and it will affect surface quality, chip breaking, and blade strength.

Influence of tip radius

Advantages of a larger tip radius:

① Improved surface roughness.

② Increased blade strength, less prone to chipping.

③ Reduced wear on the front and back of the tool.

Disadvantages of an excessively large tip radius:

① Increased cutting force, prone to vibration.

② Poor chip handling performance.

Application of different tool tip corner radius sizes

In addition, when selecting turning tools and parameters, it is necessary to consider factors such as the nature of the material being machined, the required precision, and the production volume.

Embracing the trend of three-dimensional parametric design technology, we have shifted to a new model of “parametric design (CAD) – grinding simulation (CAE) – cutting simulation analysis (CAE).” Designers no longer need to physically manufacture prototypes; instead, they can create the three-dimensional solid model of the tool by adjusting geometric parameters. Subsequently, cutting simulation technology is used to evaluate the performance of the design parameters, thereby optimizing the structural parameters of the tool. This transformation has significantly reduced research and development costs and cycles, injecting formidable competitiveness into tool manufacturing companies. Therefore, delving into the research of tool parametric design technology is of self-evident significance.

Techniques and Research Status Related to the Parametric Design of end milling?Cutters

The parametric design of integral end milling?cutters refers to the automatic and rapid generation of a three-dimensional solid model of the end milling?cutter by inputting structural dimension parameters such as the tool’s front angle, back angle, helix angle, diameter, and cutting edge length. To achieve the three-dimensional parametric design of end milling?cutters within a computer, it is necessary to first establish a mathematical description model of the cutter’s structural features. By employing theories and methods related to computational geometry, computer graphics, and Boolean operations, the modeling, display, and storage of the end milling?cutter in the computer are realized. Finally, the development of the parametric design software system is completed through the creation of a user interface and database. Therefore, the main research content of the parametric design of integral end milling?cutters includes the establishment of mathematical models and the software implementation.

The mathematical modeling of integral end milling?cutters involves using mathematical expressions of points, lines, or surfaces to describe the dimensional structure and topological relationships of each spatial structure of the end milling?cutter. The description method will directly determine the precision of the end milling?cutter model and the ease of software implementation. Currently, research on the mathematical modeling of end milling?cutters primarily includes structures such as bar stock, helical cutting edges, and chip flute cross-section lines.

Bar Stock Mathematical Model

As the manufacturing blank for integral end milling?cutters, the bar stock determines the basic structural parameters of the cutter, such as diameter and cutting edge length, as well as the selection of the tool holder. The mathematical model of the bar stock mainly includes two parts: the detailed modeling of the shank and the modeling of the cutter’s rotational contour. By dividing the end milling?cutter body into the shank, neck, and working parts (including the stem and head), and considering the features of the cutter’s shank (taper shank, straight shank, presence or absence of a positioning slot) and head features (rounded, ball-end, chamfered), a general mathematical model for the end milling?cutter bar stock is obtained based on the universal rotational body mathematical model, as shown in Figure 1.

Helical Cutting Edge Mathematical Model

The helical cutting edge curve of an integral end milling?cutter can alter the chip flow direction, increase the actual cutting rake angle, and extend the length of the cutting edge involved in cutting simultaneously, thereby improving the surface machining quality of the workpiece and the tool life. Therefore, the design of the cutting edge curve plays a crucial role in the design of end milling?cutters. The cutting edge curve of an integral end milling?cutter mainly consists of two parts: the peripheral cutting edge curve and the bottom cutting edge curve (for ball-end mills).

The helical cutting edges of end milling?cutters mainly come in three forms:

1.Constant pitch helical cutting edges, where the helix angle with the generatrix is a constant value, and the helix angle with the axis is also a constant value.

2.Based on the concept of helical motion, the method for establishing the geometric equations of constant pitch helices is discussed.

3.Using the velocity method and according to the theory of generalized helical motion of points and lines on any rotational surface, a generalized helix angle mathematical model is proposed, which relates the tangential velocity of a point undergoing helical motion to the angle between the generatrix of the rotating body, as well as the generalized helical line mathematical model. Furthermore, the mathematical models for constant pitch, constant helix angle, and general helical cutting edge curves on conical, spherical, and planar surfaces are derived, as shown in Figure 2.

From Figure 2, the general mathematical model for the helical cutting edge can be obtained:

where p(x) can be determined based on the shape of the milling cutter’s outer contour, and p(x) takes different values depending on the type of helix:

For equal-pitch cutting edges,?P is the pitch, and φ0 is the initial angle.

β is the angle between the helix and the generator of the cutter’s rotational body.

The bottom cutting edge curve of a ball-end end milling?cutter mainly includes three forms: straight cutting edge, equal helix angle edge, and orthogonal helical edge (equal pitch edge).

① A straight cutting edge refers to the cutting edge along the axial direction of the cutter’s ball-end portion being in a “straight line” shape. The straight cutting edge has a simple shape and is easy to sharpen, but during machining, it tends to have poor cutting stability due to sudden engagement and disengagement, and the cutting speed at the top of the edge is zero, which can lead to the formation of built-up edge at the top of the cutting edge. Therefore, in actual production, the bottom cutting edge of ball-end end milling?cutters often uses a helical cutting edge, as shown in Figure 3.

Based on the first fundamental form of the spherical surface, the equation for the equal helix angle helical cutting edge on the ball-end portion is obtained:

Where R? is the parameter and β is the helix angle. When the cutting edge curve is at the top of the ball-end mill, i.e., R = R?, the above equation does not hold, and a separate smooth curve that connects to the vertex needs to be designed.

An orthogonal helical cutting edge refers to the intersection line between the orthogonal helical surface formed by the straight generatrices always perpendicular to the axis of the mill and the spherical surface. Based on the equation of the spherical surface and the equation of the orthogonal helical surface, the equation for the orthogonal helical cutting edge is obtained:

Here, β represents the helix angle of the circumferential cutting edge, θ is the parameter, with 0 ≤ θ ≤ tanβ.

Mathematical Model of Radial Section Lines for end milling?Cutters

The actual chip flute of a end milling?cutter is produced by the grinding wheel moving in a helical path around the cutter’s axis, resulting in a space helical surface. The shape of the radial section line is influenced by the shape of the grinding wheel, its relative position and posture to the cutter, and the relative motion trajectory, making it difficult to precisely describe the section line shape with a mathematical model.

To simplify the calculation, during the parametric modeling of the cutter, the chip flute section line is divided into several parts: the cutting face, the flute bottom, the transition face, and the back face. The cutting face is simplified to a straight line segment, the flute bottom and the transition face are simplified to two arcs, and the back face is simplified to a straight line segment. Among these, the arc representing the flute bottom is tangent to the straight line segment of the cutting face, the core circle, and the transition face. The transition face is tangent to both the arc of the flute bottom and the straight line segment of the back face, as shown in Figure 4.

Research Status of Parametric Design Software for Integral end milling?Cutters

Parametric design software for integral end milling?cutters requires a user-friendly human-machine interface as well as the capability to display and store three-dimensional models of the cutters. Currently, there are mainly two development approaches: secondary development technology based on existing 3D CAD software and development technology based on the OpenGL graphics interface.

By utilizing the secondary development interfaces provided by software such as UG, SolidWorks, CATIA, Pro/Engineer, and AutoCAD, and calling library functions for modeling, transformation, and Boolean operations, the parametric design of end milling?cutters can significantly reduce the programming difficulty of the software system. To date, universities such as Shandong University, Southwest Jiaotong University, Northwestern Polytechnical University, Harbin University of Science and Technology, Xihua University, Northeastern University, and Xiamen University have conducted extensive research on the parametric design of end milling?cutters based on secondary development technology of 3D CAD software.

Parametric Design of Cutters Based on UG Secondary Development Technology

Shandong University has established a parametric design system for solid carbide end milling?cutters based on the grinding and manufacturing process of the cutters. They used UG/Open MenuScript to create system menus, UG/Open UIStyler to create a user interface in the UG style, and UG/Open GRIP along with UG/Open API for secondary development functions to create the three-dimensional solid model of the end milling?cutter. They compiled the program using VC++ and completed the development. Subsequently, they studied the modeling methods for detailed structures such as the tip radius and relief grooves and completed the development of two-dimensional engineering drawings. They also established three-dimensional models for milling cutters with unequal pitch. Northeastern University, based on the theory of helical lines and helical surfaces, completed the parametric design of end milling?cutters and forming cutters for machining chip flutes after classifying and analyzing the characteristics of CNC helical milling cutters. Northwestern Polytechnical University conducted parametric design for indexable cutters and flat-end end milling?cutters. Harbin University of Science and Technology established mathematical models for the helical lines and chip flute section lines of ball-end end milling?cutters and carried out parametric design for integral ball-end end milling?cutters. Xiamen University added a model for relief grooves, achieving the design of tapered ball-end milling cutters.

Parametric Design of Cutters Based on SolidWorks Secondary Development Technology

Xihua University and others, to meet the needs of Zigong Cemented Carbide Co., Ltd., have developed an object-oriented three-dimensional parametric cutter CAD system using SolidWorks as the development platform and VC++ as the development tool. By utilizing SolidWorks API for secondary development functions, combining dynamic link library technology, Oracle database technology, and ADO (ActiveX Data Objects) database connection technology, and based on the cross-sectional model of end milling?cutters, they have achieved parametric design for chip flutes, four-edge ball-end end milling?cutters, and indexable ball-end end milling?cutters.

Parametric Design of Cutters Based on CATIA Secondary Development Technology

Southwest Jiaotong University, with the assistance of CATIA/API functions and OLE Automation technology, has chosen Visual Basic (VB) as the development tool to develop a parametric design system for end milling?cutters. This system can realize parametric design for five major types of end milling?cutters, including ball-end end milling?cutters, conventional end milling?cutters, CNC end milling?cutters, high-speed end milling?cutters, and end mills. It can also achieve parametric modeling of solid blanks, cylindrical teeth, ball teeth, end teeth, transition teeth, and other detailed cutter structures.

Parametric Design of Cutters Based on AutoCAD Secondary Development Technology:

Northeastern University has chosen VB as the development tool for secondary development of AutoCAD, completing the development of standardized CAD/CAPP software. This software uses a method of disassembly and simplification, modularizing the structural features of end milling?cutters, and achieving computer-aided design for titanium alloy machining end milling?cutters through the invocation of various sub-modules.

Parametric Design of Cutters Based on Pro/E Secondary Development Technology

Lanzhou University of Technology has used the Pro/Toolkit tool for secondary development of Pro/E. Based on the mathematical models of the cutting edge curve, peripheral flute surface, peripheral relief surface, relief groove surface, and the main spiral?slot, relief surface, and spiral secondary groove surface of the ball-end end milling?cutter, they have achieved parametric design of the ball-end end milling?cutter by using surface merging, arraying, and solidification techniques. Tianjin University of Technology and Shanghai Jiao Tong University have established a parametric design system for two-tooth ball-end end milling?cutters, which includes design tools for the cutter body, chip flute, peripheral relief angle, end tooth rake angle, standard Gash, and end tooth relief angle.

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Structure of a Three-Sided Edge Mill Cutter

A three-sided edge mill has a circular shape, with cutting edges evenly distributed around the outer circumference in a serrated pattern, and a center bore for the installation of the cutter.

The main cutting edge of a three-sided edge mill is distributed on the cylindrical surface of the cutter, while the secondary cutting edges are distributed on the end faces of both ends. All three cutting edges have a relief angle, hence the name “three-sided edge mill cutter.”

Three-Sided Edge Mill Cutter Types

Classification by Tooth Shape: Three-sided edge mill? can be classified into two types by tooth shape: straight teeth and staggered teeth.

Straight Tooth Three-Sided Edge Mill Cutter

Characteristics: The blades are arranged in a straight line.

Applications: Straight teeth are used for milling shallow fixed-size grooves and can also mill general slots, step faces, and side finishing processes.

Staggered Tooth Three-Sided Edge Mill Cutter

Characteristics: The blades are distributed in an interleaved pattern, which helps to achieve smooth feed and reduce vibration.

Applications: Suitable for milling deeper slots or occasions that require a higher surface finish.

Classification by Structure: Three-sided edge mills can be classified into solid three-sided edge mill cutters, carbide three-sided edge mill cutters, and indexable three-sided edge mills.

Solid Three-Sided Edge Mill Cutter

Characteristics: The surface is treated with a special coating to improve tool life and cutting performance.

Applications: Enhanced heat resistance and wear resistance, suitable for high-speed cutting and difficult-to-machine materials.

Carbide Three-Sided Edge Mill Cutter

Characteristics: The blades are made of carbide welding, offering higher hardness and wear resistance.

Applications: Suitable for machining materials with higher hardness, such as cast iron and steel.

Indexable Three-Sided Edge Mill Cutter

Characteristics: Uses replaceable blades, which is convenient for maintenance and cost control.

Applications: Widely used for rough and semi-finish machining of various materials.

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Applications of Three-Sided Edge Mill Cutters

Three-sided edge mills are widely used in mechanical machining. The common usage is to mount them on the arbor of a horizontal milling machine for machining, or they can also be installed on other vertical machines (such as machining centers, vertical milling machines, etc.) for machining grooves, steps, and side faces.

Plane (Side) and Step Milling?

Depending on the product structure, three-sided edge mill cutters with different diameters and custom tool holders can be selected to machine multiple faces in one operation.

This combined machining method, due to the simultaneous machining of multiple faces, results in greater cutting forces. Therefore, it is necessary to carefully select the diameter and length (overhang) of the tool holder to ensure its strength. Additionally, it is important to set the cutting parameters reasonably and ensure the stable clamping of the fixture and workpiece. Otherwise, it may lead to tool damage or product scrap.

Slot milling

Used for machining slots of various widths and depths.

Other special machining

such as T-slot, circular arc slot, etc.

The above are the structural features and applications of the three-fluted end mill. When using it, the appropriate type of cutting tool should be selected based on factors such as the size of the product to be machined and the hardness of the material.

Currently, TiN is the primary coating used for cutting tools; however, traditional nitride coatings like TiN have low hardness, poor wear resistance, and particularly weak thermal stability, which limits their application in dry cutting tools. Improvements in TiN coatings have focused on developing new TiN-based alloys and multi-component composite layers, aiming to achieve wear-resistant, high-temperature coatings through the introduction of alloying elements (such as Al, Zr, Cr, V) into the TiN coating. This forms a new multi-element coating system that enhances coating hardness and improves wear resistance and thermal stability. The novel TiAlN coating, formed by implanting Al atoms into the TiN lattice, has become one of the most widely used tool coatings in global manufacturing.

In recent years, to further enhance the high-temperature hardness and oxidation resistance of tool coatings, as well as to improve the bonding strength between the coating and the substrate, research has shifted towards multi-element and multilayer composite coating systems. This paper employs unbalanced magnetron sputtering to prepare composite coatings such as TiN, TiAlN, TiN-MoS?, and CrAlTiN on carbide?tools. It conducts cutting comparison tests on TiN and its composite-coated tools under dry cutting conditions, investigating the mechanical and cutting performance of TiN-based composite coated tools. This research is significant for the further development and promotion of coated tools.

Experimental Methods

Composite coatings of TiN, TiAlN, TiN-MoS?, and CrAlTiN were deposited on YT14 carbide?tools using the closed-field unbalanced magnetron sputtering ion plating equipment from Teer. The nano-hardness and elastic modulus of the coatings were measured using a Nano Test 600 nano-hardness tester with a diamond tip under a load of 3 mN. To minimize experimental errors, the hardness and elastic modulus values reported are the averages of five measurements. Additionally, Vickers microhardness testing was conducted to validate the hardness measurements.

The morphology and phase structure of the tool coatings were analyzed using scanning electron microscopy (SEM) and an Advance 8 X-ray diffractometer (XRD). Cutting tests on the coated tools were performed in a CNC machining center, with the workpiece material being PCrNi3MoVA steel. The wear of the cutting edge was observed and measured using a 30x tool microscope. The tool life was evaluated based on the wear land width (VBc) on the flank face exceeding 0.6 mm as the criterion for tool lifespan, allowing for a comparison of the cutting life of the tools.

Experimental Results and Analysis

Hardness and Elastic Modulus Testing of Coatings

Figure 1 shows the loading-unloading curve obtained during the nano-hardness measurement of the CrAlTiN composite coating. This curve allows us to determine both the hardness and elasticity of the CrAlTiN film. The elastic recovery coefficient

R=(hmax-hres)/hmax ?is defined, where hmax?is the indentation depth at maximum load, and

hres?is the residual depth after unloading. A higher R value indicates greater elasticity. From the nano-indentation curve in Figure 2, the hardness of the CrAlTiN film is found to be 33 GPa, with an elastic modulus of 675 GPa.

Figure 2 also compares the nano-hardness of TiN, TiAlN, TiN-MoS?, and CrAlTiN coatings. The measured nano-hardness values are 18 GPa for TiN, 30 GPa for TiAlN, 15 GPa for TiN-MoS?, and 33 GPa for CrAlTiN. The order of nano-hardness for the four coatings is: CrAlTiN > TiAlN > TiN > TiN-MoS?. The addition of composite elements significantly alters the hardness of the TiN coating; in particular, the incorporation of Al increases the hardness by 12 GPa, while the addition of Cr and Al collectively raises the nano-hardness by 15 GPa. This indicates that Cr and Al form hard phases within the composite coating, enhancing its hardness. Conversely, the combination of TiN with MoS?results in a 3 GPa decrease in nano-hardness, suggesting that the MoS?phase exists as a soft phase within the coating, reducing hardness. However, this lubricating phase significantly improves the coating’s lubrication properties and lowers its friction coefficient.

Figure 3 presents the measured elastic modulus values for each coating. From the figure, it can be observed that the elastic modulus of the TiN coating is 214 GPa, that of the TiAlN coating is 346 GPa, the TiN-MoS? coating has an elastic modulus of 164 GPa, and the CrAlTiN coating reaches 675 GPa. The order of elastic modulus for the four coatings is CrAlTiN > TiAlN > TiN > TiN-MoS?. This indicates that the elastic modulus of the coatings is directly proportional to their hardness. Notably, the CrAlTiN coating shows the greatest relative increase in elastic modulus, with a value significantly higher than the other coatings at 675 GPa. This demonstrates that the deposited CrAlTiN coating possesses both high hardness and high elasticity.

At the same time, Vickers microhardness tests were conducted on each tool coating using a Vickers hardness tester, with an applied load of 15 g for 10 seconds. The results are shown in Figure 4. Although the testing principles of the Vickers microhardness and nano-indentation methods differ, a comparison of the nano-hardness values in Figure 2 and the microhardness values in Figure 4 reveals that the trends in microhardness for each coating are consistent with those of nano-hardness. Notably, the CrAlTiN coating exhibits the highest Vickers microhardness, measuring HV1560.

Drilling Tests

The four types of coated carbide?tools—TiN, TiAlN, TiN-MoS?, and CrAlTiN—were used to process the same material, PCrNi3MoVA steel, and the wear of the tools was evaluated to compare the durability of the different coated tools. The surface morphology of the coatings for the TiN, TiAlN, TiN-MoS?, and CrAlTiN tools is shown in Figure 5, all at a magnification of 600x. The figure illustrates significant differences in surface morphology among the four coatings, indicating that the incorporation of composite elements has greatly altered the crystallization state of the TiN compound.

The TiN coating shows a uniform surface microstructure with relatively small grains. In contrast, the TiAlN coating has a rougher surface morphology with larger grain structures. The addition of Al results in numerous bright white hard particles of aluminum oxide or aluminum nitride appearing in the TiN lattice. The TiN-MoS? coating features a substantial distribution of flake-like mixed structures, mainly composed of MoS? uniformly dispersed within the TiN/MoS?coating, contributing to its self-lubricating properties. The CrAlTiN coating exhibits relatively fine grains and a dense, uniform structure with a significant presence of hard particles on the surface.

The cutting test conditions for the coated tools are shown in Table 1. During the experiments, the conditions were kept constant, and the cutting time was recorded until the wear land width (VBc) on the flank face exceeded 0.6 mm, which was used as the criterion for tool life evaluation. The comparison of cutting life for the tools is presented in Figure 6.

From Figure 6, the ranking of cutting life for the four coated tools is as follows: CrAlTiN > TiN-MoS? > TiAlN > TiN. This indicates that the Cr and Al elements in the TiN coating form hard phases, and the addition of Al is beneficial for the formation of aluminum oxides, which helps prevent further oxidation during the cutting process, thereby enhancing the tool’s oxidation resistance and contributing to an increase in cutting life. Additionally, the MoS? lubricating phase helps reduce the friction coefficient and improve the wear resistance of the tools, further extending their service life.

In summary, the analysis indicates that the multi-component composite coatings effectively leverage the advantages of various coating materials, resulting in enhanced overall performance, excellent wear resistance, toughness, and reduced friction. This helps to minimize built-up edge formation while providing resistance to mechanical and thermal shocks, significantly extending tool life. Therefore, it is anticipated that the usage of multi-component composite coated tools will continue to increase in the future.

XRD Analysis

XRD analysis was conducted on the CrAlTiN tool coating, which exhibited the best cutting performance, with the results shown in Figure 8. The XRD patterns reveal that at room temperature, the crystalline phases of the coating are primarily composed of Cr, CrN, Cr?N, and TiN, with no amorphous phases detected. Further high-resolution scanning of the coating surface shows a significant distribution of hard phase particles. Combined with X-ray diffraction analysis, it is evident that these hard phases mainly consist of Cr, CrN, Cr?N, and TiN grains. These hard grains contribute to the improved cutting life of the coated tools.

Application Prospects

Coating technology for tools has proven to be an effective way to enhance the cutting performance of carbide?tools, improve cutting efficiency, and reduce processing costs. Since its introduction in the late 1970s, it has rapidly developed and been adopted worldwide. By the late 1980s, the proportion of complex carbide?tools using coatings in industrialized countries exceeded 60%, significantly improving cutting efficiency and yielding notable economic benefits. Currently, over 80% of carbide?tools used in CNC machines in Japan and Germany are coated, and the adoption of coatings in countries like Russia is also increasing.

However, the usage of coated tools in China remains limited, with even high-performance CNC machines often relying on standard carbide?tools with inferior cutting performance. This restricts the full potential of expensive equipment. Therefore, developing composite coating processes for carbide?tools is crucial for shifting China away from its reliance on imported high-performance tools and advancing the local coating technology.

Although coated carbide?tools are priced 50% to 100% higher than standard tools, their superior cutting performance, longer tool life, and higher production efficiency lead to lower costs per part compared to uncoated tools. This is particularly beneficial for complex tools with longer manufacturing cycles, such as gear cutters and broaches, where using coated tools not only offsets the coating costs but also provides significant economic benefits and better machining quality

Furthermore, coated tools facilitate dry cutting, eliminating the increased production costs and environmental pollution associated with cutting fluids, thus protecting worker health. Therefore, from both economic and social benefit perspectives, using coated carbide?tools is advantageous. In the future, as research into multi-component and multilayer composite coating technologies progresses, the lifespan of coated carbide?tools will further improve, significantly lowering manufacturing costs and broadening the application of these coatings.

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This study utilized the closed-field unbalanced magnetron sputtering PVD coating process to prepare composite coatings such as TiN, TiAlN, TiN-MoS?, and CrAlTiN. Comparative tests of the mechanical and cutting performance of these coatings yielded the following results:

1.Nano-indentation analysis showed the order of nano-hardness for the four tool coatings as follows: CrAlTiN > TiAlN > TiN > TiN-MoS?. The elastic modulus was found to be proportional to hardness, and Vickers microhardness measurements further validated the accuracy of the nano-indentation tests.

2.Under dry cutting conditions while drilling PCrNi3MoVA steel, the cutting life of the coated tools ranked as: CrAlTiN > TiN-MoS? > TiAlN > TiN, indicating that multi-component composite coatings offer significantly better cutting performance than standard TiN coatings, marking a promising direction for the future development of coated tools.

Surface Roughness Symbol

a?、a?— symbols and values for the roughness height

parameters (unit is μm);

b — machining requirements, plating, coating, surface treatment, or other descriptions;

c — sampling length (in millimeters) or waviness (in micrometers);

d — symbol for the direction of the machining texture;

e — machining allowance (in millimeters);

f — roughness spacing parameter (in millimeters) or profile support length ratio.

?Other Annotation Descriptions

• Sampling Length: The length range selected when measuring roughness, used to calculate roughness parameters.
• Evaluation Length: The total sum of the sampling lengths, used to assess surface roughness.
• Machining Method: Indicates the machining method by which the surface roughness is achieved, such as turning, grinding, etc.
• Other Requirements: For example, surface treatment (such as sandblasting, polishing, etc.), texture direction, etc.

Roughness Code

Arithmetic Mean Roughness Ra

Arithmetic mean roughness is the most commonly used roughness parameter, representing the arithmetic average of the absolute values of the profile peaks and valleys within the sampling length. When selecting the reference length in the direction of the mean line from the roughness curve, using the direction of the mean line of the selected part as the X-axis and the direction of the vertical magnification as the Y-axis, if the roughness curve is represented as y=f(x), the value obtained from the following formula, when expressed in micrometers (μm), is called the arithmetic mean roughness Ra.

Arithmetic Mean ????? Ra

Note: The arithmetic mean roughness Ra is the most commonly used expression for roughness. Unless otherwise specifically noted, roughness generally refers to Ra.

From the roughness curve, a reference length is selected in the direction of the mean line. From the values measured in the direction of the vertical magnification from the mean line of the selected part, the sum of the average absolute values of the peak elevations (Yp) from the highest peak to the fifth peak and the average absolute values of the valley elevations (Yv) from the lowest valley to the fifth valley is calculated. This sum is referred to as the value expressed in micrometers (μm).

Maximum Height Ry

The maximum profile height, which represents the vertical distance between the highest profile peak and the deepest valley within the sampling length. From the roughness curve, a reference length is selected in the direction of the mean line. The interval between the peak line and the valley line of the selected part is measured in the direction of the vertical magnification of the roughness curve, and this value is called the micrometer value (μm).

Note: When determining Ry, the reference length should be selected from a section of the curve that is free of cracks and extreme peaks and valleys.

Labeling Example

Label the upper limit value of Ra

• Control the surface roughness to within 25μm by any means.
• Control the surface roughness to within 6.3μm by material removal methods.
• Control the surface roughness to within 25μm without removing material.

Label the direction of the machining texture

Note: The direction of the machined tool texture is perpendicular to the projection plane marked with symbols.

Label the upper and lower limits of Ra

Control the surface roughness to a minimum of 1.6μm and a maximum of 6.3μm by removing material. Generally, the upper and lower limit values are marked for oil seal installation holes, as roughness that is too large or too small can affect the sealing effect of the oil seal.

Label the machining method

Marking Machining Method

Attention Points Marking Position: The roughness symbol is usually annotated above or below the dimension line, close to the surface being marked.

Direction Guide Line: The direction guide line should point towards the surface being marked and be parallel or perpendicular to the surface.

Value Unit: The ????? values are typically expressed in micrometers (μm).

Development of High-Grade Carbide?Tools

China has become the world’s manufacturing center and the largest market for cutting tools. During the 11th Five-Year Plan, domestic tools accounted for over 65% of the market share, but these products primarily fall in the mid to low-end categories, necessitating significant imports of high-grade tools. In 2010, China’s tool consumption was about 33 billion yuan, with approximately 11 billion yuan spent on imported high-grade tools, while domestically developed high-grade tools accounted for only about 1 billion yuan in sales. This situation results in a significant consumption of tungsten resources with low added value.

Developing high-grade carbide?tools is crucial for reducing tungsten resource consumption and promoting sustainable development. For example, indexable CNC blades not only inherit the features of high-end solid carbide?tools but also showcase integration in design and manufacturing, excellent chip-breaking designs, and diverse coating options. Compared to solid carbides, indexable blades significantly increase material utilization; for instance, Seco’s DOUBLE OCTOMILL has 16 cutting edges, while Iscar’s H400 olive-shaped blade can be used over 10 times.

Improving the Utilization of Carbide?Tool Materials

Cutting tools often show minimal wear when they reach normal wear standards; directly classifying these tools as waste leads to significant tungsten resource wastage. Advanced regrinding and recoating technologies can remanufacture such tools, allowing them to maintain cutting performance multiple times and thus improving the utilization of carbide?tool materials.

Regrinding of carbide?tools involves classifying regrindable tools based on the extent of edge damage, determining suitable regrinding plans, and completing the process through rough grinding, fine grinding, and edge reinforcement. After rough and fine grinding, the cutting edge may have defects like micro-chipping and micro-cracking. Appropriate edge reinforcement methods can eliminate these defects, increasing edge strength and tool lifespan. Regrinded tools can also be coated again as needed.

Due to the standardized and modular nature of indexable blades, the regrinding process can also be standardized. Table 1 outlines the main regrinding processes and characteristics for indexable blades. After proper regrinding and recoating, the cutting performance of carbide?tools during rough machining is about 50% to 80% of new tools, while during finishing, it is about 85% to 90%. Through advanced regrinding and recoating technologies, carbide?tools can repeatedly demonstrate their cutting performance, thus enhancing material utilization and reducing tungsten resource consumption.

Table 1: Main Regrinding Processes and Characteristics of Indexable Inserts

Recycling and Utilization of Carbide?Tool Materials

Tungsten resources in tungsten ore are primary, non-renewable resources, while tungsten resources in carbide?tool materials are secondary, renewable resources. As the supply of tungsten resources becomes increasingly tight, awareness of recycling tungsten resources from old carbide?tools is growing. Currently, the main methods for recycling tungsten resources from carbide?tool materials include melting, mechanical crushing, and electrolytic methods, with melting methods encompassing both niter and zinc melting methods. Zinc melting and electrolytic methods are currently the most widely used. Table 2 outlines the main methods and characteristics for recycling tungsten resources in carbide?materials. Additionally, other methods for recycling tungsten resources in carbides include high-temperature treatment and acid leaching.

Table 2: Main Methods and Characteristics of Tungsten Resource Recovery in Hard Alloy Materials

Foreign tool companies have long conducted research and application work on the recycling of worn carbide?tool materials. Sandvik Tooling has launched a recycling initiative aimed at recovering and reusing worn carbide?blades and solid carbide?tools. Reports indicate that approximately one-third of Sandvik’s carbide?products come from recycled materials each year. Similarly, Hitachi Tools in Japan is actively promoting the recycling of worn carbide?materials nationwide.

As a major consumer of carbide?tools, China has the potential to create favorable conditions for the recycling of tungsten resources. While many domestic companies, such as Heyuan Fuma carbide?Co., Ltd. and Xiamen Jinlu Special Alloy Co., Ltd., have begun recycling carbide?tool materials, overall awareness of tungsten resource recycling remains low, with a relatively low recycling rate and the quality of recycled tungsten resources needing further improvement.

Research and Development of New Carbide?Tool Material?

With the continuous emergence of new processing materials and technologies, new tool materials are also being developed. The research of carbide?tool materials with lower tungsten content plays a positive role in the conservation and sustainable development of tungsten resources. Currently, steel-bonded carbide?materials and functionally graded carbide?materials are two major research hotspots.

Steel-bonded carbide?is a new type of carbide?material developed in recent years. It consists of one or more carbides (such as TiC, WC) as the hard phase (about 30% to 50% content) and high-speed steel or alloy steel as the bonding phase, made through powder metallurgy. Steel-bonded carbides inherit the advantages of both carbides and steel, offering high hardness and wear resistance while also providing high strength, ductility, and weldability typical of steel. This material fills the gap between the two. Steel-bonded carbides can be used to manufacture complex tools like drill bits, milling cutters, pull tools, and hob cutters, showing significant effects in machining stainless steel, heat-resistant steel, and non-ferrous alloys.

Functionally graded carbide?materials are also a hot research topic globally and represent the future direction of modern carbides. These materials exhibit a systematic and uneven distribution of chemical composition across different sections, utilizing compositional gradients to endow different parts of the material with varying properties. This helps to resolve the inherent conflict between hardness and toughness in carbides, resulting in superior comprehensive performance.

The application of steel-bonded carbide?materials and functionally graded carbide?materials in tool fields has achieved remarkable results. For instance, the “Christmas tree” milling cutter used for machining turbine rotor grooves is made of steel-bonded carbide. Sandvik’s functionally graded carbide?materials have been widely used in products such as coating blades and mining alloys, which operate under very harsh conditions. Although China has researched steel-bonded carbide?and functionally graded carbide?materials for over a decade, breakthroughs in core technologies and equipment are still needed, making this a focus for future research.

Promotion of Other Tool Material?

Despite the strong versatility and broad applicability of carbide?tools, no universal tool exists; each type of tool material has its limitations. Promoting the use of other tool materials in their respective fields can reduce dependence on and excessive use of carbide?tools, contributing positively to the sustainable development of tungsten resources in the carbide?tool industry.

In addition to carbide?materials, other tool materials include high-speed steel, ceramic tools, and superhard materials. High-speed steel, especially high-performance powder metallurgy high-speed steel, remains important in complex forming tools; ceramic tools excel in machining cast iron and hardened steel; diamond PCD tools show clear advantages in processing non-ferrous metals and non-metallic materials; PCBN tools are primarily used for machining steel and cast iron materials.

Foreign tool application companies are far ahead of China in the use of other tool materials. For example, GE in the U.S. has achieved milling speeds of 4000 m/min when using PCD face mills on aluminum engine cylinder heads.? In recent years, the development of foreign ceramic tools has been particularly rapid; Sandvik has achieved significant success with whisker and alumina ceramic tools in high-feed turning and milling of high-temperature alloys.

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China’s tungsten resource supply is becoming increasingly scarce. To reduce tungsten resource consumption and ensure sustainable development in the carbide?tool industry, it is essential to actively develop high-grade carbide?tools, enhance tool performance, improve material utilization rates, recycle worn carbide?tool materials, and continuously research new carbide?tool materials. Additionally, there should be strong promotion of the use of other tool materials in relevant application fields.

Generally, compared to traditional insert end mills, solid carbide end mills offer significantly higher machining precision. This fact holds true specifically for the performance of the tool during cutting operations. Although both types of tools may have the same dimensional precision grade, the rigidity of solid carbide material is much higher than that of a steel tool holder with insert blades. This means that solid carbide end bit mills are less likely to undergo deflection or deformation under cutting forces, leading to higher machining precision.

Base Material of Solid Carbide End Mills

The machining performance of solid carbide end mills largely depends on the type of carbide base material used. The base material is crucial because it must support the cutting edges of the tool, endure significant cutting forces, and prevent any form of tool damage.

To ensure that end mills have sufficient toughness and provide good dynamic resistance, solid carbide end mills typically use micro-grain carbide as the base material (see Figure 2). This base material offers higher hardness and better edge sharpness while maintaining good toughness. However, compared to conventional grain-sized carbide, micro-grain carbide has relatively poorer thermal conductivity (its ability to dissipate heat from the cutting area). This means that heat generated during cutting tends to remain on the tool surface. Therefore, the cutting edges of solid carbide end mills must be able to withstand this cutting heat and manage the contact arc length, which is an important consideration when selecting solid carbide end mills.

Coating and Cutting Edge Preparation of Solid Carbide End Mills

To enhance tool wear resistance and isolate the cutting zone, which generates heat, from the tool base (since heat accumulation in the base material can shorten tool life), solid carbide end mills are typically coated. Additionally, because the cutting edges of solid carbide end bit mills are quite sharp, appropriate adhesion between the tool base and the coating is also crucial (see Figure 3). This is especially important for smaller diameter solid carbide end mills, where the sharpness of the cutting edges is a key factor in the tool’s machining performance.

The Ideal Cutting Edge for Solid Carbide End Mills

The ideal cutting edge of a solid carbide end mill should have as high a hardness as possible while minimizing the risk of chipping. This goal can be partially achieved through proper cutting edge preparation. Generally, different solid carbide end mills may employ various cutting edge preparation methods, edge geometries, and sharpness levels depending on the required machining quality and tool life.

The cutting edge is the intersection line between the tool’s rake face and flank face. By grinding these faces, a sharp cutting edge can be obtained. However, if a PVD coating is deposited directly on a sharp cutting edge, it can create high internal stresses within the coating. These high internal stresses can cause the coating to crack and peel off during cutting, thereby shortening the tool’s life. The quality and effectiveness of the coating depend on its ability to withstand and/or reduce the wear rate during cutting. To ensure that the coating adheres more firmly to the cutting edge and to prevent edge damage, it is necessary to perform edge reinforcement (or blunting) treatment (see Figure 4). In other words, to ensure machining stability and achieve coating functionality, a certain degree of edge sharpness must be sacrificed, which in turn extends tool life.

It can even be said that the importance of cutting edge preparation for solid carbide end bit mills outweighs that of base material type and coating technology. Logically, this has a significant impact on the regrinding of solid carbide end mills. After regrinding, if the cutting edge is not re-blunted to restore its initial condition, the full potential of the tool repair cannot be realized. Therefore, considering the high initial cost of solid carbide end mills, it is crucial for the original tool manufacturer or its qualified service centers to handle tool regrinding services.

Machining Strategies for Solid Carbide End Mills

Solid carbide end mills can be categorized into several major types based on their size and geometry, and further subdivided into many specialized subcategories according to different machining ranges. In various tool application areas, design features such as flute geometry, cutting edge angles, rake and relief angles, and helix angles play crucial roles in differentiating among the types of solid carbide end bit mills. This classification guides the selection of both end mills and machining strategies.

So, which machining strategy is the best choice? This depends on the overall machining goals: is your primary aim to maximize productivity and part output, or to minimize tool costs and simplify tool types? Additionally, it also depends on the workpiece and various related factors: is the tool used for slotting, side milling, or a combination of both?

A final consideration is constraints, such as: what is the potential machining capability of the machine tool? How rigid is the workpiece clamping? These factors might become limiting constraints, preventing the use of more advanced machining strategies or more efficient specialized solid carbide end mills.

The correct choice of solid carbide end bit mill depends on multiple factors, with the most important being the adoption of the correct machining strategy. In practice, many constraints cannot be changed: the machining machine, CAM system, and the material, size, tolerance, and shape of the workpiece are fixed constants. However, within the existing machining system framework, machining results can still be influenced by formulating the right machining strategy and using various methods, and by optimizing cutting conditions through adjustments to feed rate, cutting speed, and cutting depth according to the overall machining goals.

Based on the selected focus and technical strategy, appropriate solid carbide end mills can be chosen. There are two obvious ways to select tools:

1. Performance-Based Selection:Choose specialized end mills with specific applications (such as side milling, slotting, or 3D profiling) to achieve optimal performance.
2. Versatility-Based Selection:Choose general-purpose end bit mills with a wider range of applications but fewer types.

Regardless of the selection method, users need to further narrow down the options within the available varieties and specifications of solid carbide end mills.

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The material, size, tolerance, and shape of the machined parts are given constants. However, within the existing machining system framework, machining results can still be influenced by formulating the correct machining strategy and employing various methods. Additionally, cutting conditions can be optimized by adjusting feed rate, cutting speed, and cutting depth according to the overall machining goals.

Based on the chosen focus and technical strategy, appropriate solid carbide end mills can be selected. There are two clear approaches to tool selection:

1. Performance-Based Selection:Choose specialized end mills designed for specific applications (such as side milling, slotting, or 3D profiling) to achieve the best performance.
2. Versatility-Based Selection:Choose general-purpose end mills that, while fewer in types, offer a wider range of applications.

Regardless of the selection method, users need to further narrow down the choices within the available varieties and specifications of solid carbide end mills.

With the rapid development of China’s automotive industry, especially in the booming new energy vehicle sector, lightweighting has become a core topic. The key to lightweighting is changing traditional materials. Aluminum alloys, with their high strength and low weight, are essential for achieving vehicle lightweighting. The complex geometric shapes of automotive parts and the increasing proportion of die-cast aluminum alloy parts in vehicles have led to a growing demand for CNC machining of die-cast parts.

CNC machining of aluminum alloy automotive parts requires high efficiency, stable continuous production, and decreasing costs, necessitating more detailed control and planning of the entire production process.

Tool Build-Up

Aluminum’s inherent property of low melting point causes it to become “sticky” during cutting. Due to this characteristic and inadequate cooling in actual conditions, the heat generated by friction during the microscopic cutting process cannot be released in time or effectively. This results in aluminum melting and adhering to the tool’s cutting edges and chip flutes. Upon cooling, the aluminum solidifies and sticks to the tool, forming build-up. This phenomenon, commonly referred to in the industry as “easy tool sticking,” leads to tool failure.

Tools are consumables in CNC machining processes and represent a significant cost component. Generally, cutting tools for aluminum alloys need to be sharper, with chip flutes specially polished and coated with aluminum-specific coatings to improve chip removal efficiency. The automotive industry’s push for high efficiency increases feed rates and cutting speeds, which raises the heat generated during cutting and the risk of aluminum melting and sticking to the tool, thereby increasing costs due to tool failure from build-up.

With environmental regulations, minimal quantity lubrication (MQL) is widely used as a cutting fluid alternative in aluminum alloy CNC machining. However, the low melting point of aluminum exacerbates the reduced cooling effect of MQL, further promoting build-up. Tools that fail due to sticking account for about 40% of conventional tool failures. Traditional methods of dealing with build-up, such as tapping or striking, rarely restore tools for reuse. Thus, a new solution is proposed.

Treatment Measures

The new solution involves the following steps:

1. Remove the tool with build-up.
2. Obtain solid NaOH, dilute it with water, and place it in a ceramic container.
3. Once diluted into NaOH solution, immerse the tool with aluminum build-up in the solution. Ensure that the build-up areas are fully submerged and maintain immersion for 2 hours, or adjust based on practical conditions. Table 1 compares traditional and new treatment methods.

Chemical Principles

Using A1Si7Mg material commonly found in automotive parts as an example, where A1 content is approximately 93.5%, Si content is 6.5%, and Mg content is 0.25%. Both Al and Si react with NaOH solution. Immersion in NaOH solution removes the primary A1 component from the tool. The principle involves the reaction between metal and NaOH, producing bubbles (H?), which eventually causes the adhered aluminum to detach.

Chemical reaction equations are as follows:

1. Si reacts with NaOH: Si + 2NaOH + H?O → Na?SiO? + 2H?↑
2. Al reacts with NaOH: 2Al + 2NaOH + 2H?O → 2NaAlO? + 3H?↑

The final result is the removal of aluminum, making the tool reusable.

Experimental Validation for Reducing Build-up

The theoretical method was tested using a tap. Taps are valuable tools in aluminum alloy machining, requiring a longer lifespan and featuring complex geometric shapes. Once aluminum adhesion occurs, physical removal is nearly impossible, making this test more significant and representative.

Due to high heat generated during machining and possible inadequate cooling, aluminum melts instantly and adheres to the flutes rendering the tap unusable due to damaged threads.

The test involved immersing the tap with aluminum build-up in NaOH solution.

The test conclusion: The tap, after complete immersion in NaOH, showed that the build-up had completely detached. Residual aluminum slag was found in the test container. The treated tap was used for further machining, and the workpiece threads met the required specifications. The tap was successfully restored for reuse.

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The automotive parts industry, characterized by mass production, requires extensive cutting validation during the initial equipment and tool design phase. Common issues such as build-up during validation due to parameter mismatches, equipment adjustments, and operator experience can significantly increase trial costs and production cycles. This method effectively addresses build-up issues, greatly reducing tool costs and processing time, extending tool life, and substantially lowering production costs.