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.

Summary

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.

Conclusion

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.

Conventional end mills have the following drawbacks under high-efficiency cutting conditions:

1.To reduce cutting forces and facilitate chip evacuation, the end edges of corner radius end mills typically feature a concave design with a high edge at the tip and a low center. This means that only the tip participates in cutting during face milling, resulting in high stress and a tendency for chipping.

2.The cutting edge of ball-end mills exhibits both negative rake angles and low-speed cutting inefficiencies, leading to a low metal removal rate.

3.Cutting forces are primarily radial, with the main cutting forces directed along the X and Y axes, causing tool chatter under high-efficiency cutting conditions.

To address these issues, the tool’s end edge shape is optimized by incorporating an arc design for edge protection. The concave straight edge is replaced with an arc edge where the tip is lower and the center is higher. The benefits include:

1.Increased cutting edge length, reducing the cutting load per unit, and distributing the cutting allowance and cutting force across the entire edge shape.

2.The bottom arc design, with a larger radius and smaller main cutting angle, reduces cutting forces and cutting-induced vibrations.

End Mill Cutter Shape Design and Analysis

Taking a φ10 four-flute end milling cutter as an example, the optimized arc-shaped milling cutter blade outperforms conventional end mills (corner radius and ball-end mills) in terms of effective cutting edge shape and length Le (black thick line) at the same cutting depth (0.5mm), as shown in Figure 1 and Table 1. The arc-shaped milling cutter has the longest effective cutting edge length, followed by the ball-end milling cutter, with the corner radius end milling cutter having the shortest. To comprehensively evaluate the performance of arc-shaped milling cutters compared to conventional end mills under high-efficiency machining conditions, both cutting simulations and cutting experiments were conducted for comparison.

During the cutting simulation, both the end milling cutter and the workpiece were simplified and precisely configured to ensure accurate calculations. A 10mm section of the end mill was selected as the simulation cutting portion, with detailed settings applied only to the cutting edge area. The total rotation angle of the tool during simulation was set to 190°, ensuring complete data for tool entry and exit points. The cutting parameters were set based on relatively large values commonly used in the mold industry: vc= 120m/min，fz=0. 4mm ／z，ap = 0. 5mm，ａe =10mm. The workpiece material selected was hardened steel (SKD11, with a hardness of HRC58), and the tool material chosen was carbide. The milling method used was climb milling. The cutting simulation model and the cutting conditions are shown in Figure 2.

Comparison of Cutting Forces

Cutting force is a crucial indicator of cutting performance. Excessive cutting force significantly impacts tool life. The cutting forces in the X, Y, and Z directions were directly extracted using the AdvantEdge post-processing program, showing how cutting forces fluctuate over time (see Figure 3).

From the figure, it is evident that the corner radius end milling cutter exhibits relatively stable cutting behavior. In contrast, the ball-end mill shows significant fluctuations in cutting force. This instability is attributed to the ball-end mill’s two-flute connection at the center, where long and short teeth alternate during milling. The variation in the number of active cutting edges leads to changes in the effective cutting edge length, resulting in substantial fluctuations in cutting force. The optimized arc-shaped end milling cutter initially encounters a larger cutting allowance when it begins to engage with the workpiece, resulting in higher cutting forces. As the cutting progresses deeper into the workpiece, the cutting allowance is uniformly removed radially along the tool, causing the cutting force to decrease and stabilize.

Comprehensive Comparison

The average values of the simulated cutting forces and cutting temperatures were calculated (see Table 1). It can be observed that the ball-end mill operates at a lower cutting temperature but experiences greater fluctuations in cutting force. The corner radius end milling cutter, with its shorter effective cutting edge, generates smaller cutting forces. The optimized arc-shaped end milling cutter produces higher cutting forces, predominantly in the axial direction.

Since the cutting edges involved in the process are concentrated on the end edges, they can be considered as simultaneously engaged in cutting. The resultant cutting force ftotalf_{total}ftotal? and the cutting force in the axial plane fxyf_{xy}fxy? per unit length of the cutting edge are shown in Table 2. The corner radius end mill exhibits the highest cutting force per unit length, indicating that under these conditions, the tool’s cutting edge experiences a higher cutting load, making it more prone to chipping and cutting vibrations. The optimized arc-shaped end milling cutter has the lowest cutting force per unit length, suggesting a more reasonable distribution of the cutting load.

Cutting Experiment Analysis

To comprehensively evaluate the cutting performance of the tools, the experiment was conducted to verify both cutting force and tool durability.

The experimental material, SKD11 with a hardness of HRC61, was the same as that used in the cutting simulation. The machining was performed on a MIKRON UCP1000 machining center using climb milling and dry cutting. The cutting process and parameters were consistent with those used in the cutting simulation.

Cutting Force Experiment

The cutting force sensor used was a Swiss Kistler 9265B three-component piezoelectric dynamometer, along with a charge amplifier and a corresponding data acquisition and processing system. After filtering, the cutting force values are shown in Table 3. The results indicate that the optimized arc-shaped end milling cutter generates a larger overall cutting force, but the cutting load per unit length is the smallest, consistent with the conclusions drawn from the cutting force simulation.

Cutting Performance Experiment for End Milling Cutter

Cutting hardened steel typically results in significant tool wear and short tool life, especially under high-efficiency cutting conditions, where differences in tool performance become more apparent. As shown in Figure 4, after machining a single groove (cutting length of 130mm), the optimized arc-shaped end mill exhibited normal wear, while the corner radius end mill and ball-end milling cutter both experienced edge chipping, leading to tool failure. The optimized arc-shaped end mill only showed edge chipping and failure after a cutting distance of 10 meters, which is more than ten times the tool life of conventional corner radius end mills and ball-end mills.

Analysis of Experimental Results

The experimental results indicate that cutting hardened steel leads to significant tool wear. Under high-efficiency cutting conditions, tools face extreme situations where only those that meet the machining demands can be used; otherwise, they are unsuitable. The optimized arc-shaped end milling cutter, with its modified blade shape, redistributes the cutting forces, reduces the cutting load per unit length on the effective cutting edge, and improves the tool’s cutting performance, thereby meeting the demands of high-efficiency cutting.

Conclusion

This study focused on modifying the tool blade shape to meet the high-efficiency cutting requirements for hardened steel. Through general cutting simulations and cutting experiments, the following conclusions were drawn:

1.Cutting simulations and cutting force experiments revealed that the optimized arc-shaped end mill generates greater cutting forces, particularly in the axial direction, compared to conventional corner radius and ball-end mills. However, it has a lower cutting force per unit length, with cutting temperatures comparable to those of the corner radius end mill.

2.Cutting experiments demonstrated that due to the modified blade shape, the cutting load per unit length of the cutting edge is reduced. As a result, the optimized arc-shaped end milling cutter outperforms conventional corner radius and ball-end mills under high-efficiency and heavy-load cutting conditions in mold manufacturing.

High-Speed Cutting Milling Equipment

1.High Stability of Machine Bed Components

The bed and support components of a high-speed cutting machine must exhibit excellent dynamic and static stiffness, thermal rigidity, and optimal damping characteristics. Most machines use high-quality, high-rigidity gray cast iron for these components, with some manufacturers incorporating high-damping polymer concrete into the base to enhance vibration resistance and thermal stability. This not only ensures stable machine accuracy but also prevents tool chatter during cutting. Measures such as closed bed designs, integral casting of the machine bed, symmetric bed structures, and dense ribbing are also crucial for enhancing machine stability.

2.Machine Spindle

The spindle performance of high-speed machines is crucial for achieving high-speed cutting. High-speed cutting spindles typically operate at speeds ranging from 10,000 to 100,000 RPM, with spindle power greater than 15 kW. Spindle axial gaps between the tool holder and spindle are controlled to be no more than 0.005 mm using compressed air or cooling systems. Spindles are required to have rapid acceleration and deceleration capabilities, meaning they must have high angular acceleration and deceleration rates.

High-speed spindles often use liquid static pressure bearings, air static pressure bearings, hot-pressed silicon nitride (Si3N4) ceramic bearings, or magnetic suspension bearings. Lubrication is commonly achieved with oil-air lubrication or spray lubrication, and spindle cooling typically involves internal water or air cooling.

3.Machine Drive System

To meet the demands of high-speed mould processing, the drive system of a high-speed milling machine should have the following characteristics:

High Feed Speed: Research indicates that increasing spindle speed and feed per tooth is beneficial for reducing tool wear, especially for small-diameter tools. Common feed speed ranges are 20-30 m/min, with large lead ball screws allowing speeds up to 60 m/min and linear motors achieving up to 120 m/min.

High Acceleration: High-speed milling of complex 3D surfaces requires a drive system with good acceleration characteristics, with drivers providing high-speed feed (fast feed rate of about 40 m/min and 3D profile processing speed of 10 m/min) and accelerations and decelerations ranging from 0.4 m/s2 to 10 m/s2.

Most machine manufacturers use closed-loop position servo control with small lead, large-size, high-quality ball screws or large lead multi-head screws. Advances in motor technology have led to the development and successful application of linear motors in CNC machines. Linear motor drives eliminate issues such as mass inertia, overshooting, lag, and vibrations, speeding up servo response, improving servo control accuracy, and enhancing machine processing precision.

4.CNC System

Advanced CNC systems are key to ensuring the quality and efficiency of high-speed processing of complex mould surfaces. Basic requirements for CNC systems in high-speed cutting include:

High-Speed Digital Control Loop: Includes 32-bit or 64-bit parallel processors and hard drives with over 1.5 GB; extremely short linear motor sampling times.

Speed and Acceleration Feedforward Control: Digital drive systems with jerk control.

Advanced Interpolation Methods: Such as NURBS-based spline interpolation for good surface quality, precise dimensions, and high geometric accuracy.

Look-Ahead Function: Requires a large capacity buffer register to pre-read and check multiple program segments (e.g., up to 500 segments for DMG machines, and 1000-2000 segments for Siemens systems) to adjust feed speeds and avoid over-cutting when surface shapes (curvatures) change.

Error Compensation Functions: Includes compensation for thermal errors due to linear motors and spindles, quadrant errors, measurement system errors, etc. Additionally, high data transmission speeds are required.

Data Interfaces: Traditional data interfaces like RS232 serial ports transmit at 19.2 kb, while many advanced milling centers now use Ethernet for data transmission at speeds up to 200 kb.

5.Cooling and Lubrication

High-speed milling uses coated carbide tools and operates without cutting fluids, resulting in higher cutting efficiency. This is because the high centrifugal forces of the rotating spindle make it difficult for cutting fluids to reach the cutting zone, and even if they do, the high temperatures may cause the fluids to evaporate, reducing cooling effectiveness. Additionally, cutting fluids can cause rapid temperature changes at the tool edge, leading to cracking. Thus, dry cutting with oil/air cooling is employed. This method quickly blows away the cutting heat with high-pressure air, and atomized lubrication oil forms a thin protective film on the tool edge and workpiece surface, effectively extending tool life and improving surface quality.

Tools for High-Speed Cutting

Tools are one of the most critical factors in high-speed cutting, directly impacting processing efficiency, manufacturing costs, and product precision. High-speed cutting tools must withstand high temperatures, pressures, friction, impact, and vibrations. They should have good mechanical properties and thermal stability, including impact resistance, wear resistance, and thermal fatigue resistance. The development of high-speed cutting tools has been rapid, with common materials including diamond (PCD), cubic boron nitride (CBN), ceramic tools, coated carbide, and titanium carbide (TiC) and titanium nitride (TiN) hardmetals.

For cutting cast iron and alloy steel, carbide is the most commonly used tool material due to its good wear resistance, although its hardness is lower than CBN and ceramics.

To improve hardness and surface finish, coating technologies such as titanium nitride (TiN) and aluminum titanium nitride (TiAlN) are employed. Coating technology has evolved from single-layer to multi-layer and multi-material coatings, becoming a key technology for enhancing high-speed cutting capabilities. Carbide inserts with titanium carbonitride coatings in the diameter range of 10-40 mm can process materials with Rockwell hardness below 42, while titanium aluminum nitride-coated tools can handle materials with Rockwell hardness of 42 or higher.

For high-speed cutting of steel, tools made from heat-resistant and fatigue-resistant P-class carbide, coated carbide, CBN, and CBN composite materials (WBN) are preferred. For cutting cast iron, fine-grain K-class carbide should be used for roughing, and composite silicon nitride ceramics or polycrystalline CBN (PCBN) tools for finishing.

For precision milling of non-ferrous metals or non-metallic materials, polycrystalline diamond (PCD) or CVD diamond-coated tools are recommended. When selecting cutting parameters, attention should be given to the effective diameter for round blades and ball end mills. High-speed milling tools should be designed with dynamic balancing, and the cutting edge angles should be adjusted compared to conventional tools.

High-Speed Milling Processes and Strategies

High-speed machining includes roughing, semi-finishing, finishing, and mirror finishing to remove excess material and achieve high-quality surface finishes and fine structures.

Roughing

The primary goal of mould roughing is to maximize material removal rate per unit time and prepare the geometric profile of the workpiece for semi-finishing. The process plan for high-speed roughing involves a combination of high cutting speeds, high feed rates, and small cutting depths. The most commonly used CAM software employs methods like spiral contouring and Z-axis contouring, which generate continuous, smooth tool paths in a single pass without retracting the tool, using arc entry and exit methods. Spiral contouring avoids frequent tool retraction and approach, minimizing the impact on surface quality and machine wear. Steep and flat areas are processed separately, with optimized tool paths generated using spiral methods with minimal retraction to achieve better surface quality. In high-speed milling, it is essential to use arc entry and exit methods and maintain a consistent tool path to minimize machine wear and achieve higher material removal rates.

Semi-Finishing

The semi-finishing process focuses on improving surface quality and dimensional accuracy, bridging the gap between roughing and finishing. The cutting speeds are higher than those used in traditional milling but lower than those in finishing. The primary goal is to achieve a better surface finish and precision by using a reduced depth of cut and controlling feed rates. Advanced CAM systems generate tool paths using techniques like trochoidal milling and adaptive clearing, which adaptively change cutting parameters based on the workpiece geometry and tool path. This method enhances tool life and surface quality while reducing cutting forces and thermal stresses.

Finishing

Finishing operations aim to achieve the final surface quality and dimensional accuracy. High-speed finishing involves higher cutting speeds and lower depths of cut, using techniques such as high-speed finishing cuts with constant engagement to ensure a smooth and uniform surface. Tool paths are optimized using advanced CAM software to achieve the desired surface finish and accuracy. Techniques like high-speed trochoidal milling and constant chip load milling are used to achieve excellent surface finishes and tight tolerances.

Mirror Finishing

Mirror finishing is the final step to achieve an exceptionally smooth and reflective surface. High-speed mirror finishing processes often involve special tools and techniques, including abrasive tools and polishing compounds. The key is to minimize surface irregularities and achieve a mirror-like finish with high precision. Techniques such as high-speed burnishing, polishing, and super-finishing are employed to achieve the desired surface quality.

Conclusion

High-speed milling technology has revolutionized the mould manufacturing industry by significantly enhancing machining efficiency, precision, and surface quality. The integration of advanced machining equipment, CNC systems, tooling technologies, and innovative milling strategies has enabled the production of complex mould cavities with high accuracy and reduced processing times. As technology continues to advance, high-speed milling will play an increasingly crucial role in meeting the evolving demands of the mould manufacturing industry.

Structural Types

carbide?face milling cutters can be categorized into three types: integral welding type, mechanical clamping ?type, and indexable type.

The diagram 1 below illustrates an integral welding type face milling cutter. This type has a compact structure and is relatively easy to manufacture. However, if the teeth are damaged, the entire milling cutter must be discarded, so its usage has decreased.

As shown in the above diagram is the mechanical clamping welding type face milling cutter. This cutter welds carbide?inserts onto small cutter heads, which are then mechanically clamped into slots on the cutter body. When the inserts are worn out, they can be replaced with new ones, thereby extending the cutter body’s service life.

As shown in Figure 2, the commonly used indexable face milling cutter consists of components such as the cutter body (5), insert (1), tightening screws (3), cutter blade (6), wedge block (2), and eccentric pin (4). The insert (1) is clamped onto the cutter body using the wedge block (2) and tightening screws (3). Before tightening the screws, the eccentric pin (4) is rotated to adjust the axial runout of the insert within a specified range at the axial support point. Once the cutter blade (6) is mounted on the insert, it is clamped in place by the wedge block (2) and tightening screws (3). The eccentric pin (4) also prevents excessive axial forces on the insert during cutting, thereby preventing axial movement.

Compared to high-speed steel face milling cutters, carbide?face milling cutters offer higher milling speeds, better processing efficiency, and improved surface quality. They are capable of machining workpieces with hardened surfaces and layers, demonstrating significant advantages in enhancing product quality and processing efficiency.

Face Milling Cutter Main Structural Parameters

(1) Diameter and Number of Teeth

Diameter and number of teeth are the two main structural parameters of a face milling cutter. To accommodate different cutting requirements, face milling cutters of the same diameter are classified into coarse, medium, and fine types based on the number of teeth. Taking a 100 mm diameter cutter as an example, the number of teeth for coarse, medium, and fine types are 5 teeth, 6 teeth, and 8 teeth respectively.

(2) Geometric Angles

Indexable face milling cutters have key geometric angles including the lead angle κr, rake angle γp, and clearance angle γf. The lead angle κr is available in 45°, 60°, 75°, and 90° variants, with 75° being the most commonly used. When machining flat surfaces with shoulders or thin-walled workpieces, a 90° lead angle is typically chosen.

The rake angle γp and clearance angle γf can be combined into positive rake, negative rake, and positive-negative rake configurations. Positive rake angles are used for machining general materials; for instance, γp=7° and γf=0° are common for milling mild steel and cast iron, while γp=18° and γf=11° are used for milling aluminum alloys. Negative rake angles are employed for machining cast steel and hard materials, often set at γp=-7° and γf=-6°. Positive-negative rake angles offer good impact resistance and chip removal properties, suitable for milling general steel and cast iron, commonly used on machining centers with values like γp=12° and γf=-8°.

How to Select a Face Milling Cutter?

Selection of Face Milling Cutter Diameter

(1) When the machining area is not large, it is important to choose a tool or milling cutter with a diameter larger than the width of the plane. This allows for single-pass face milling. When the width of the face milling cutter is 1.3 to 1.6 times the width of the machining area, it effectively ensures proper chip formation and removal.

(2) For machining large surface areas, it is necessary to select a milling cutter with an appropriate diameter and perform multiple passes for face milling. Due to machine limitations, cutting depth, width, and the dimensions of the cutter and inserts, the diameter of the milling cutter may be constrained.

(3) When machining small plane areas or dispersed workpieces, a smaller diameter end mill should be selected for milling. To achieve optimal efficiency, the milling cutter should have contact with the workpiece equal to 2/3 of its diameter, which means the milling cutter diameter should be 1.5 times the width of the cut. Properly using this ratio of cutter diameter to cutting width ensures the milling cutter approaches the workpiece at an ideal angle. If the machine’s power cannot sustain cutting at this ratio, axial cutting thickness can be divided into two or more passes to maintain the ratio of cutter diameter to cutting width as much as possible.

Selection of Number of Teeth on the Milling Cutter

When selecting a milling cutter for machining, the number of teeth is an important consideration. For example, a coarse-toothed milling cutter with 6 teeth has a diameter of 100 mm, whereas a fine-toothed milling cutter with 8 teeth also has a diameter of 100 mm. The density of teeth affects both production efficiency and product quality. Dense teeth improve efficiency and quality but may hinder chip removal. Depending on the diameter of the teeth, they can be categorized as sparse teeth, fine teeth, and dense teeth.

Sparse teeth are used for rough machining of workpieces, with 1 to 1.5 inserts per 25.4 mm diameter, providing ample space for chips. Such tools are suitable for continuous chip formation in soft materials, using long blades and wide cuts. Dense teeth are advantageous for stable machining conditions, typically used for rough machining of cast iron, shallow and narrow cuts in high-temperature alloys, and when chip space is not required.

Dense teeth are applied in fine milling, with axial cutting depths ranging from 0.25 to 0.64 mm per tooth, minimizing cutting loads and power requirements, suitable for machining thin-walled materials.

Selection of Milling Inserts

The choice of milling inserts for flat milling is a critical factor to consider. In certain machining scenarios, pressed inserts are more suitable, while in others, ground inserts are preferred.

For rough machining

Pressed inserts are often preferred as they lower machining costs. Pressed inserts have lower dimensional accuracy and edge sharpness compared to ground inserts. However, they offer better edge strength, making them suitable for rough milling tasks. They can withstand higher impact and accommodate larger depths of cut and feed rates. Pressed inserts typically feature chip grooves on the front face, reducing cutting forces and friction with the workpiece and chips, thereby lowering power requirements. However, their surface finish is less compact than ground inserts, resulting in varying heights among insert tips on the milling cutter body. Due to their cost-effectiveness, pressed inserts find widespread use in production.

For fine milling

Ground inserts are preferable due to their superior dimensional accuracy. This high precision ensures precise positioning of the cutting edge during milling, leading to higher machining accuracy and lower surface roughness values. Moreover, the trend in ground milling inserts for fine machining includes forming large positive rake cutting edges with chip grooves, allowing the inserts to handle small feed rates and depths of cut effectively. In contrast, carbide?inserts without sharp rake angles may experience friction with the workpiece during fine machining with small feed rates and depths of cut, reducing tool life.

What are CNC Turning Tools?

A turning tool is a tool with a cutting part used for CNC turning. It is one of the most commonly used tools in CNC milling. The working part of the turning tool is the part that generates and processes chips, including the cutting edge, the structure that breaks or curls the chips, the space for chip removal or storage, and the channel for cutting fluid.

Types of Lathe Cutting Tools:

Lathe cutting tools are basically divided into two types based on their usage:

A) Based on the Tool’s Usage Method

B) Based on the Method of Application Feed

A) Based on the Tool’s Usage Method:

There are 11 types of tools:

1.Thread Cutting Tools

They come in two types:

External Thread Tools: Also known as threading tools, used to machine external threads on workpieces.

Internal Thread Tools: Used to machine internal threads inside workpieces.

2.Chamfering Tools

Chamfering tools are used to design bevels or grooves on bolts, chamfering the corners of workpieces. Specific chamfering tools with side cutting angles are needed for extensive chamfering work.

3.Turning Tools

There are usually two types of turning tools:

Rough Turning Tools: Used to remove large amounts of metal in a short time with clear cutting angles that can withstand maximum cutting force.

Finishing Turning Tools: Used to remove small amounts of metal, with polished cutting angles to produce very smooth and precise surfaces.

4.Grooving Tools

Grooving tools are used to create narrow cavities of certain depths on the cone, cylinder, or surface of parts. The specific shape of the grooving tool depends on the shape of the groove (square, round, etc.).

5.Facing Tools

Facing tools are used to cut planes perpendicular to the axis of rotation of the workpiece, reducing the length of the workpiece by providing a vertical cut to the lathe axis. The cutting edge should be set at the same height as the center of the workpiece.

6.Boring Tools

Boring tools are used to enlarge existing holes. When you want to enlarge an existing hole, you need to use a boring bar that can easily enter the pre-drilled hole and expand its diameter.

7.Forming Lathe Tools

Forming tools are used to create different shapes on workpieces. Special types of holders are used to fix forming tools, allowing operations such as making internal and external radii.

8.Reaming Tools

Reaming tools are used to enlarge and position the sleeve heads of screws or bolts, creating pre-drilled holes or holes on the workpiece.

9.Reaming Tools

Reaming tools are used for finishing and ensuring dimensional tolerances of drilled or reamed holes.

10.Undercutting? Lathe Tools

Undercutting tools are similar to grooving tools, used to bore large holes at a fixed distance from the end of the hole, often for creating clearance in internal threads.

11.Drilling Tools

Drilling tools are used to machine cylindrical holes on workpieces, typically fixed on the tailstock drill frame and completed by the tailstock spindle’s movement.

B) Based on the Method of Application Feed:

There are three types:

12.Round Nose Tools

Used for finish turning, round nose tools have no side or back rake angles and can cut in other directions.

13.Right-Hand Tools

These tools remove material when moving from right to left (with the cutting face on top in the top view). Named by analogy to the right hand, the primary cutting edge is on the left side.

14.Left-Hand Tools

Opposite to right-hand tools, these remove material when moving from left to right (with the cutting face on top in the top view). Named by analogy to the left hand, the primary cutting edge is on the right side.

How to Choose Lathe Tools

Selecting lathe tools requires understanding certain factors related to the equipment. Here are crucial factors to consider:

Type of Material: The type of material you’re cutting determines the type of lathe tools you can use. Important properties to note include hardness, wear resistance, toughness, and stiffness. Extremely hard materials may require carbide or diamond tools.

Shape of the Tool: The shape of the lathe tool is another factor to consider, with the cutting edge’s position determining the cutting direction (right-hand, left-hand, or round nose tools).

Shape of the Workpiece: Each type of lathe tool leads to specific shapes. You must integrate the desired shape into the lathe tool. Due to the complexity of most CNC machined products, you may need a combination of several lathe tools.

Summary

In practical cutting processes, familiarity with CNC machining and turning processes, along with extensive practical experience, will make choosing the right type of lathe tool more manageable and effective.

Classification of Cutting Fluids

We all know that cutting fluids are mainly divided into two major categories: oil-based and water-based.

Based on their functions, they can be arranged as follows:

Lubricity: Cutting oil > Emulsified fluid, Semi-synthetic cutting fluid > Fully synthetic

Cooling: Fully synthetic > Semi-synthetic cutting fluid > Emulsified fluid > Cutting oil

Rust Prevention: Cutting oil > Water-based cutting fluids (Emulsified fluid, Semi-synthetic cutting fluid, Fully synthetic)

Cleaning: Water-based cutting fluids (Emulsified fluid, Semi-synthetic cutting fluid, Fully synthetic) > Cutting oil

How to Select Cutting Fluids Rationally

There are many types of cutting fluids with different performances. The selection of cutting fluids should be based on factors such as workpiece material, tool material, machining method, and processing requirements.

Rough Machining

1.For rough turning or rough milling of carbon steel workpieces with high-speed steel tools, a low-concentration emulsified fluid (e.g., 3%–5% emulsified fluid) or a synthetic cutting fluid should be used.

2.For rough turning or rough milling of aluminum and its alloys, copper and its alloys with high-speed steel tools, use an emulsified fluid with 5%–7% concentration.

3.When rough turning or rough milling cast iron, due to the presence of graphite, which acts as a solid lubricant to reduce friction, cutting fluids are generally not used. Oil-based cutting fluids may cause the cutting chips and abrasive particles to stick together, acting as abrasives and causing wear to the tools and machine guides.

4.For modern carbide blades, cutting fluids are generally not used because insufficient or uneven cutting fluid flow can cause uneven heating and cooling of the carbide blades, leading to cracking and tool failure.

However, for processing certain high-hardness, high-strength, and poor thermal conductivity special materials (especially heavy cutting), cutting fluids that are sufficient in flow, uniform, and primarily for cooling, such as 2%–5% emulsified fluid or synthetic cutting fluids, should be used to significantly lower the cutting area temperature and extend tool life.

If using a spray application method for the cutting fluid, the cutting effect will be better. When using cutting fluids with carbide tools, continuous application from the beginning to the end is essential to avoid affecting tool life and the quality of the machined surface.

5.For low-speed cutting, where tool wear is mainly due to hard particles, cutting oils focusing on lubrication are preferred. For higher-speed cutting, where tool wear is primarily thermal, cutting fluids with good cooling performance, such as emulsified fluids or water-soluble solutions, should be selected.

Finishing

Finishing requires high surface roughness and machining accuracy. In addition to considering tool material, workpiece material, and machining methods, cutting speeds should also be considered, and cutting fluids with different properties should be selected.

1.For finishing carbon steel workpieces with high-speed steel tools, the cutting fluid should have good penetration, lubrication, and some cooling properties. At lower cutting speeds (less than 10 m/min), mechanical wear is predominant, so the cutting fluid should have good lubrication and flowability to quickly penetrate the cutting area, reduce friction and adhesion, inhibit chip build-up and burrs, improve workpiece precision, and extend tool life. Use 10%–15% emulsified fluid or 10%–20% extreme-pressure emulsified fluid.

2.For finishing carbon steel workpieces with carbide tools, no cutting fluid may be used, or 10%–25% emulsified fluid or 10%–20% extreme-pressure emulsified fluid can be used.

3.For finishing copper and its alloys, aluminum and its alloys, to achieve a low surface roughness and high quality, 10%–20% emulsified fluid or kerosene can be used.

4.For finishing cast iron, 7%–10% emulsified fluid or kerosene should be used to reduce the surface roughness of the workpiece.

Difficult-to-Machine Materials by applying cutting fluid

Difficult-to-machine materials are those that are harder to process than easier materials, often due to their composition or heat treatment processes. Typically, materials containing elements like chromium, nickel, molybdenum, manganese, titanium, vanadium, aluminum, niobium, tungsten, etc., are considered difficult-to-machine.

These materials have hard particles, high mechanical abrasion, low thermal conductivity, and are prone to chip dispersion. Therefore, cutting fluids for these materials must have high lubrication and cooling properties.

1.For cutting difficult-to-machine materials with high-speed steel tools, use 10%–15% extreme-pressure emulsified fluid or extreme-pressure cutting oil.

2.For cutting difficult-to-machine materials with carbide tools, use 10%–20% extreme-pressure emulsified fluid or sulfurized cutting oil.

Recommendation: Although animal and vegetable oils can be used for difficult-to-machine materials and achieve good cutting effects, they increase costs. Therefore, we should minimize or avoid using animal and vegetable oils as cutting fluids.

Closed or Semi-Closed Cutting Processes

In processes such as drilling, tapping, reaming, and broaching, where chip removal is done in a closed or semi-closed manner, chip removal is difficult, and the heat generated by friction between the tool and chips cannot be dissipated quickly, which can cause burning of the cutting edge and significantly affect the surface roughness of the workpiece. This issue is more prominent when cutting high-hardness, high-strength, and tough materials with significant cold-hardening.

Cutting fluids with good cooling, lubrication, and cleaning properties are needed to reduce heat generated by tool-chip friction and effectively remove chips. For deep hole drilling, broaching, tapping, and reaming, 10%–15% emulsified fluid, 15%–20% extreme-pressure emulsified fluid, mineral oil, or extreme-pressure cutting oil should be used.

Precautions for Using Cutting Fluids

To ensure that cutting fluids achieve the desired effects, the following points should be observed:

Oil-based emulsified fluids must be diluted with water before use.

Cutting fluid flow should be sufficient and maintain a certain pressure. The cutting fluid must be applied to the cutting area.

When using cutting fluids with carbide tools, the fluid must be applied continuously from start to finish to avoid causing cracks in the hard alloy blades due to sudden cooling.

Cutting fluids should be kept clean and impurities should be minimized. Expired cutting fluids should be replaced in a timely manner.

Common Problems and Solutions for Cutting Fluids

Summary

Choosing the right cutting fluid involves understanding its functions and the specific requirements of the machining process. By considering factors like material properties, cutting conditions, and process specifics, you can select the most suitable cutting fluid to achieve optimal performance in different machining scenarios.

Effective cutting chip control should avoid causing damage to the workpiece, tools, and operators; prevent production interruptions; and eliminate chip disposal issues.

What factors affect chip formation?

Good chip formation can produce spiral short chips, which are generally believed to ensure longer tool life, easier chip handling and disposal, higher surface quality of machined parts, and a stable, reliable, and efficient cutting process. Simply put, ideal chips should be of a manageable size and require minimal effort during their formation.

In practice, numerous factors influence chip formation, including the shape of the tool, cutting conditions, material of the part, and cooling method.

Factors related to part material include the hardness and tensile strength of the workpiece, ductility, and structural considerations. These factors cannot be modified, but their impact on cutting chip formation must be considered.

The influence of the cooling system on chip formation is quite variable. Key tool characteristics include rake angle, cutting edge angle, tool nose radius, and the geometry of the cutting edge and chip breaker groove. Larger rake angles, lower cutting edge angles, and larger tool nose radii tend to produce longer chips. The effect of the coating type on chip formation is not easily defined.

Cutting conditions can intuitively affect chip formation, and altering these conditions is both easy and effective. The primary cutting condition to adjust is the chip thickness ratio or aspect ratio. When the chip thickness ratio is too low, so-called square cutting chips are produced, which impose excessive load on the tool tip, significantly limiting tool life. An excessively high chip thickness ratio results in long, ribbon-like cutting chips that are difficult to break into shorter pieces.

The chip thickness ratio is defined as the cutting width divided by the chip thickness. For a given feed rate, the cutting depth should be sufficiently large to avoid excessively low or high chip thickness ratios. Small cutting depths combined with certain feed rates produce square chips. Conversely, excessively small feed rates can lead to unbreakable ribbon-like chips.

In practical operations, cutting depth is usually fixed. In this case, the feed rate becomes crucial for good chip formation. Avoiding excessively low feed rates prevents long ribbon-like chips, while avoiding excessively high feed rates prevents the formation of square chips.

Chip Morphology

Cutting chips can be defined into four different types based on their cross-section:

Serrated, segmented, or discontinuous chips

Serrated or segmented cutting chips, also known as discontinuous chips, are semi-continuous chips with large areas of low shear strain and localized, small areas of high shear strain. This type of chip is commonly observed when machining materials with low thermal conductivity and strong strain-hardening characteristics. For example, when machining materials like titanium, the strength of the material increases under stress, especially under the combined effects of high temperature and stress. The appearance of these cutting chips is characterized by a serrated pattern.

Continuous cutting chips

Continuous chips are typically produced when machining ductile materials, such as low-carbon steel, copper, and aluminum alloys. Continuous cutting chips are difficult to handle and dispose of, as they can form very long spirals or coils around the workpiece and tool, posing a potential hazard to operators when they break. The prolonged contact time with the tool surface generates more frictional heat. Using chip breakers can effectively address this issue.

Built-up edge chips

When small particles of the workpiece material adhere to the cutting edge of the tool, a so-called built-up edge (BUE) is formed. This primarily occurs with soft and ductile workpiece materials, especially when forming continuous cutting chips. BUE can affect the cutting performance of the tool. These accumulations are very hard and brittle, and as layers of material build up, their stability decreases. When the BUE eventually breaks off, part of it is carried away with the chips to the tool surface, while another part remains on the machined surface, increasing surface roughness.

By increasing the cutting speed, using tools with a positive rake angle and sharper edges, applying coolant, and selecting cutting materials with lower chemical affinity to the workpiece material, the formation of BUE can be effectively reduced.

Shear chips

Shear chips or short chips, also known as discontinuous chips, consist of small segments that are separated from each other. These chips typically form when machining brittle materials such as bronze, hard brass, gray cast iron, and materials that are very hard or contain hard inclusions and impurities. Brittle materials lack sufficient ductility for significant plastic deformation during chip formation, leading to repeated fracturing that limits the extent of chip deformation.

Short chips

In less stable machine tools, short cutting chips may cause micro-vibrations during the machining process due to their intermittent formation. One advantage of these chips is that they are easier to handle and clean. When these chips form in brittle materials, such as bronze and gray cast iron, they often result in good surface finish, lower power consumption, and reasonable tool life. However, for ductile materials, discontinuous chips can lead to poorer surface finish and increased tool wear.

Cross-sections of different chip forms

Examples of chip and built-up edge (BUE) formations under different cutting speeds and chip forms in various workpiece materials:

1.Continuous Chips in Carbon Steel

2.Serrated Chips in Duplex Stainless Steel

3.Built-Up Edge (BUE) in Carbon Steel

4.Carbon steel can develop built-up edge (BUE) chip

Discontinuous Chips in Cast Iron

Cast iron typically forms discontinuous cutting chips, consisting of fragmented segments. This occurs due to the brittle nature of cast iron, limiting its ability to form continuous chips during machining.

Geometric Shapes of Chip Breakers

Long and continuous cutting chips can adversely affect machining efficiency and pose risks of damaging tools, workpieces, and machine tools. Moreover, issues with cutting chip disposal can lead to unnecessary downtime during production and pose safety hazards to operators. To ensure safety, facilitate chip handling, and prevent damage to machine tools and workpieces, it’s crucial to break these long cutting chips into smaller segments.

Chips bend or curl during formation due to various factors, including:

1.Stress distribution within primary and secondary shear zones.

2.Thermal effects.

3.Strain-hardening characteristics of the workpiece material.

4.Geometric shape of the cutting tool.

The influence of the cooling system also plays a role to some extent.

In essence, reducing the rake angle (using tools with a negative rake angle) tightens the curvature of the cutting chips, making them shorter and more prone to fracture. The function of a chip breaker is to reduce the curvature radius of the cutting chip, thereby promoting the fracture of cutting chips into shorter segments.

Basic principles of chip breaker groove geometry

The chip break diagram (refer to the diagram below) illustrates the relationship between workpiece material, cutting conditions, chip breaker type, and cutting chip morphology. This diagram indicates factors to consider when selecting cutting depths and feeds to use specific chip breaker types for machining workpiece materials.

The horizontal axis represents the feed rate, which must always be greater than a certain minimum value (the width of the T-land geometry) and should be less than a maximum value (not exceeding half of the tool nose radius). The vertical axis shows the cutting depth, which should always be greater than the tool nose radius to promote good chip formation and avoid square chip issues. Additionally, the cutting depth should not exceed the cutting edge length. In the latter case, a safety factor is recommended, depending on the strength of the cutting edge. For blades, these safety factors vary between 75% of the cutting edge length (for square or rhombic blades) and 20% (for replica blades with smaller top angles).

Cutting depth and feed rate (referred to as chip thickness ratio) must be kept within certain limits. The maximum chip thickness ratio should be maintained below a certain maximum value to avoid excessively long ribbon-like chips. The chip thickness ratio should also be maintained above a minimum value to prevent square chips from forming. These limits are depicted in the diagram with two diagonal lines. The minimum and maximum values of the chip thickness ratio depend on the workpiece material. To minimize cutting edge damage, cutting forces should not be too high. This constraint is represented by a curved line in the diagram.

Within the blue region of the diagram, every combination of feed rate and cutting depth can produce properly shaped chips. Choosing combinations outside the blue region will result in improper chip formation and may lead to excessively long or square chips, or excessive cutting edge damage.

The diagram above illustrates the influence of cutting speed on chip formation. The horizontal axis represents the feed rate, and the vertical axis represents the type of chip. Typically, as the feed rate increases, chips tend to become shorter, especially at low cutting speeds. However, as cutting speed increases, the relationship between feed rate and chip formation diminishes.

Five Methods for Optimizing Chip Control

1.Determine the priority criterion for process optimization: productivity or cost considerations.

2.If the chip shape is acceptable, go to step 5.

If the chips are too long, go to step 3.

If the chips are too short, go to step 4.

3.If productivity is key, increase the feed rate.

If cost efficiency is key, switch to a stronger chip breaker.

Keep the feed rate within the chip breaker’s range.

Go to step 5.

4.If productivity is key, switch the chip breaker to a sharper one.

If cost considerations are key, reduce the feed rate.

Keep the feed rate within the chip breaker’s range.

Go to step 5.

5.If cost considerations are prioritized, reduce the cutting speed.

If productivity is prioritized, increase the cutting speed.

Characteristics of Medical Industry Parts

The medical industry specializes in producing various medical devices to address a range of health protection issues. These devices comprise numerous parts of different sizes, precision, materials, and complex shapes. To manufacture these parts, the medical industry employs various technical processes, with machining still playing a vital role. The general principles for machining medical device parts are no different from those for similar non-medical parts. However, some parts require complex machining processes. These processes are challenging and necessitate new process flows, essential machining equipment, and the correct selection of cutting tools. Tool manufacturers are dedicated to developing unique tools to ensure high productivity and high profitability in the production of medical parts.

Machining Requirements for Medical Industry Parts

Orthopedic and dental surgical components are typical complex parts with high machining requirements. Typical implant materials, such as titanium alloys, cobalt-chromium (CoCr) alloys, and stainless steel, are challenging to cut. Many implant parts have complex shapes requiring multi-axis machine tool processing. Implant components and their corresponding parts are usually small in size, demanding strict dimensional tolerances and excellent surface roughness.

Modern high-performance small to medium-sized multi-tasking machines, Swiss-type lathes, and lathes with live tooling are the most efficient machines for machining implant parts. To maximize cutting capacity, the machines must be equipped with suitable tools. When developing cutting tools for machining implant parts, tool manufacturers consider the aforementioned characteristics to ensure the right solutions are proposed.

Artificial Acetabulum

Artificial hip joints typically consist of four independent parts: the femoral stem, the ball head, the acetabulum (or cup), and the ultra-high molecular weight polyethylene liner embedded in the acetabulum. As joint prostheses, these materials must have high strength, reliable chemical stability and safety, low friction but high wear resistance, and excellent biocompatibility; thus, medical-grade materials and hard-to-machine materials like surgical stainless steel, titanium, or cobalt-chromium are widely used.

Challenges in Machining

Demand for increased machining efficiency.

Ensuring process safety while improving tool life and tool wear predictability.

Minimizing vibration when using long overhangs and challenging workpieces and fixtures to achieve high-quality surface accuracy.

Machining Solutions with High-Precision Cutting Tools

The inner and outer rotary surfaces of the artificial acetabulum, including the inner and outer cylindrical surfaces, conical surfaces, and spherical surfaces, can be machined by turning methods. The tool insert substrate can be made of carbide material with good thermal conductivity, coated with AlTiN. The chip breaker structure of the tool insert should facilitate easy chip formation and removal, so a large rake angle with curved cutting edges should be chosen. Metal cup inner spherical turning is generally difficult, but using a large rake angle insert can ensure smooth chip and heat discharge. Drilling titanium alloys and other difficult-to-machine materials involves poor cutting and heat dissipation conditions. Holes in prosthetic parts can be machined with solid carbide drills with a wavy main cutting edge, which balances sharpness and wear resistance by eliminating the negative rake angle structure near the center. Ground with triple relief surfaces, the drill has zero chisel edge length, reducing flank friction and wear while enhancing centering ability, making it both sharp and durable. The dual-curvature helical flute ensures smooth chip removal, and our ball nose end mills can be used for inner spherical machining. Made from ultra-fine grain carbide with a high-hardness, ultra-wear-resistant monolayer nano-coating, these tools offer a hardness of HV3700, oxidation resistance up to 1300°C, and a friction coefficient of only 0.48 at 800°C against high-hardness steel, significantly improving wear resistance and damage resistance for high and stable machining quality.

Production of Surgical Tools

Complex surgical procedures require high-precision, specialized tools. These instruments range from simple scalpels and scissors to complex mechanical arms for minimally invasive surgery. These tools must be manufactured with high precision. High-precision cutting tools play a crucial role in producing surgical tools needed for various medical procedures. CNC machines can achieve complex geometries and strict tolerances, making them ideal for producing intricate surgical tool designs. For instance, robotic-assisted surgical instruments can be machined using CNC technology to ensure the highest accuracy, allowing surgeons to perform complex procedures with greater precision and fewer complications.

Electronic Medical Devices

Many medical devices, such as MRI scanners, heart rate monitors, and X-ray machines, are equipped with thousands of electronic components requiring high-precision cutting tools. Examples include switches, buttons, and control levers, as well as electronic housings and enclosures.

Unlike implants and surgical tools, these medical devices do not need to be biocompatible, as they do not come into direct contact with the patient’s internal systems. However, the manufacturing of these parts is still heavily regulated and controlled by multiple regulatory agencies. Failure to comply with the standards set by these regulatory bodies can result in hefty fines (and sometimes imprisonment) for machining shops. There have been instances where involved medical professionals have had their licenses revoked. Therefore, choosing medical device manufacturers wisely is essential.

Customized Prosthetics

Personalization is becoming increasingly important in healthcare, particularly in prosthetics. Patients need prosthetic devices that perfectly fit their bodies, and traditional mass production techniques often fall short of meeting these needs. High-precision cutting tools are transforming the field of prosthetics, enabling the production of customized devices based on each patient’s unique physiological characteristics. Using 3D scanning and CAD modeling, prosthetics can be manufactured with intricate details and high-precision dimensions, ensuring optimal function and comfort for patients.

Small Orthopedic Hardware

Orthopedic devices such as plates, screws, and rods are widely used in the medical field to repair or replace damaged bones and joints. Given the critical role these devices play in patient recovery, their manufacturing must be of the highest precision and quality. High-precision cutting tools are essential in the production of these orthopedic devices. These tools can machine complex geometries with high precision, making them ideal for producing such equipment. Additionally, high-precision cutting tools can handle a variety of biocompatible materials, including titanium and stainless steel, commonly used in orthopedic devices.

Prototyping Medical Devices

Before any medical device goes into mass production, creating prototypes for testing and validation is crucial. High-precision cutting tools provide a fast and cost-effective solution for producing medical device prototypes. With the ability to quickly generate multiple iterations of a design, engineers can test and refine devices to ensure their safety, efficacy, and regulatory compliance. This capability is vital in the fast-paced medical device development field, where the ability to quickly bring new products to market can be a significant competitive advantage. High-precision cutting tools also enable the production of small batch prototypes, minimizing waste and saving material costs during development.

Dental Tools and Implants

High-precision cutting tools are essential for providing high-quality dental care by creating custom dental tools and implants. Dentists worldwide rely on advanced CNC technology for precise treatments. This technology is ideal for producing durable instruments such as drills, scalers, probes, and forceps, which are essential for various procedures.

Producing these instruments requires exceptional durability to withstand sterilization while ensuring patient safety. High-precision cutting tools offer repeatability and strict quality control, ensuring that each tool meets rigorous standards. Dental implants provide a long-term solution for missing teeth and require precise customization using high-precision cutting tools. These implants are created based on digital scans, ensuring an accurate and personalized fit for each patient. High-precision cutting tools have revolutionized the production of dental restorations, improving treatment outcomes.

Challenges in Medical Part Machining

Medical part machining is a rapidly developing branch of modern manufacturing that incorporates new engineering materials, such as composite materials, and new technologies like 3D printing. Modern machining solutions involve not only the production of orthopedic and dental parts but also medical equipment, medical device parts, and micromachining of medical devices. New trends present new challenges to the medical industry, requiring solutions from other fields related to medical product processing. Tool manufacturers, in particular, need to stay abreast of ever-changing industry trends. By keeping up with these changes, tool manufacturers will be able to provide ultimate solutions for machining complex medical parts.

Website of International Medical Devices Exhibition: http://www.chinaylqxexpo.com/

I. Key Fundamental Knowledge on Thread Machining

Terminology Definitions

① Root② Flank③ Crest

What is the Helix Angle?

• The helix angle depends on the diameter and pitch of the thread.
• Adjust the flank clearance angle of the insert by changing the shim.
• The rake angle is denoted as γ. The most common rake angle is 1°, corresponding to the standard shim in the tool holder.

Cutting Forces During Thread Insertion and Exit

• The highest axial cutting force in the thread machining process occurs during the tool’s entry and exit from the workpiece.
• Excessive cutting parameters may cause the insert to move if it is not securely clamped.

Function of the Rake Angle

The rake angle can be set by using a shim underneath the insert in the tool holder. You can refer to the charts in the tool catalog to choose which shim to use. All tool holders come equipped with a standard shim that sets the rake angle to 1°.

Selecting Shims Based on the Rake Angle

The rake angle is influenced by the workpiece diameter and thread pitch. As shown in the diagram below, for a workpiece with a diameter of 40mm and a pitch of 6mm, the required shim must have a 3° rake angle (the standard shim cannot be used).

Marking of Threading Inserts and Shims

Thread Forms and Their Applications

II. Types of Threading Inserts and Clamping Solutions

Multi-Tooth Inserts

Advantages:

• Reduces the number of tooling passes.
• Extremely high productivity.

Disadvantages:

• Requires stable clamping.
• Requires sufficient tool retraction space after thread machining.

Full-tooth cutter

Advantages:

• Better control of thread shape.
• Fewer burrs.

Disadvantages:

• Each blade can only cut one pitch.

V-tooth cutter.

Advantages:

• Flexibility, as the same type of blade can be used for machining several pitches. Disadvantages:
• May result in burr formation, requiring deburring.

Ⅲ.three different types of feed methods

The feed method plays an important role in the thread machining process. It affects cutting control, blade wear, thread quality, and tool life.

Improved lateral feed

This feed method is commonly used in most CNC machine tools through a looping program.

• Chips are easier to form and guide compared to traditional turning types;
• Axial cutting forces reduce the risk of vibration;
• The chips are thicker but only contact one side of the blade;
• Heat transfer to the blade is reduced;
• Preferred for most thread machining processes.

Radial feed

This is the most commonly used method and also one of the earliest methods that non-CNC lathes could employ.

• Produces hard “V”-shaped chips.
• Uniform blade wear.
• Blade holder exposed to high temperatures, limiting the depth of cut.
• Suitable for machining fine-pitch threads.
• May result in vibration and poor chip control when machining coarse-pitch threads.
• Preferred for machining hardened materials.

Alternating feed of thread machining

• Recommended for large pitches.
• Enables uniform blade wear and maximizes tool life when machining threads with extremely large pitches.
• Chips are guided in two directions, making control difficult.

Ⅳ.Methods for Improving Machining Results

Left: Step-down cutting depth (Constant chip area) Achieves a constant chip area, which is the most common method used in CNC programs.

• The first pass cuts the deepest.
• Follow the recommended values ??on the feed table in the sample.
• Balances chip area more evenly.
• The final pass actually measures around 0.07mm.

Right: Constant cutting depth Regardless of the number of passes, the depth of cut remains the same each time.

• Requires higher demands on the blade.
• Ensures optimal chip control.
• Not applicable for pitches greater than TP1.5mm or 16TP.

Utilizing additional allowance for thread crest finishing: Before machining threads, there’s no need to turn the blank to an exact diameter; utilize additional allowances/material for finishing the thread crest. For finishing crest inserts, leave 0.03~0.07mm of material from the preceding turning process to shape the crest correctly.