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What is Finishing End Mill? What role does it Play in Machining?
Finishing end mill is a tool designed for processes that require high surface accuracy and finish. It is often used for the final cut of the workpiece to achieve the ideal surface finish and dimensional accuracy. Compared with traditional roughing milling cutters, finishing end mills typically use more cutting edges (such as 4-edge, 6-edge, or even multi-edge designs). They also feature a smaller helix angle and optimized cutting edge geometry to reduce tool vibration and achieve a smoother cutting trajectory.
Made mostly from solid carbide, finishing end mills offer excellent wear resistance and thermal stability, making them ideal for high-speed milling and micro-cutting operations. Finishing end mills are often coated with materials such as TiAlN and AlCrN to improve heat resistance and prevent chipping, making them perfect for machining materials with high hardness or prone to built-up edges, like mold steel, stainless steel, and titanium alloys.
In practical applications, finishing end mills are widely used in precision parts manufacturing, the mold industry, and mirror processing for parts requiring extremely high surface quality. By choosing the right tool geometry, material, and cutting parameters, engineers can achieve a mirror-like surface directly without the need for secondary polishing, greatly improving both efficiency and product quality.
Difference From Roughing End Mill
Although finishing end mills and roughing are both types of end mills, they are essentially different in design concept and application purpose. Roughing end mills are mainly used to remove a large amount of excess material, emphasizing cutting efficiency and tool strength. Wave edge or chip breaker design is often used to achieve a greater cutting depth and feed rate. At the same time, the chip removal ability is enhanced and the cutting resistance is reduced.
In contrast, finishing end mills are mainly aimed at improving surface finish and dimensional accuracy. Its cutting edge is usually sharper, with a high helix angle or polishing treatment to reduce chatter marks and burrs generated during processing. In addition, the cutting load of the finishing end mill is small, which is suitable for the last machining process to finely trim the workpiece contour or surface, but not suitable for rough machining tasks with large cutting volume.
In short, the roughing end mill is responsible for efficient material removal, while the finishing mill is the key tool to achieve the final surface quality and precision control. The two are usually used together to achieve an efficient and high-quality overall machining strategy.
Key Factors Affecting Surface Finish in CNC Machining
When using a finishing end mill for precision machining, the ability to achieve a high-quality surface finish depends on multiple factors. These include tool geometry, material coating, cutting parameters, and machine tool rigidity. Below is a breakdown of how to optimize each factor for the best surface finish:
Tool Geometry Parameters
Flute Count and Its Impact on Finish
The number of flutes directly affects the cutting volume per revolution and chip removal space. For finishing applications, a multi-edge design (such as 4-edge or 6-edge) provides a smoother cutting trajectory and reduces tool marks, resulting in a flatter surface. However, for soft materials like aluminum alloys, having too many flutes can hinder chip evacuation and reduce surface quality.
Helix Angle and Cutting Edge Design
Finishing end mills with high helix angles (e.g., 45° or 55°) are commonly used for high-surface-quality applications. These tools can reduce cutting resistance and improve chip evacuation efficiency, making them ideal for stainless steel and softer metals. A sharp cutting edge with polishing treatment further helps to reduce burrs and chatter marks, which are crucial for achieving a mirror-finish surface.
Tool Material and Coating Selection
Advantages of Solid Carbide Finishing End Mills
Solid carbide finishing end mills are excellent for high-speed cutting and fine finishing due to their exceptional wear resistance, thermal stability, and rigidity. These tools are especially suitable for precision operations in industries such as mold cavity machining, medical parts, and aerospace components.
Coating Comparison: TiAlN / DLC / Mirror Coating
- TiAlN Coated Finishing End Mill: High heat resistance, suitable for high-temperature processing and dry cutting, especially for steel or hardened materials.
- DLC Coated End Mill: With an extremely low friction coefficient, it is ideal for high-gloss finishes on soft metals like aluminum and copper.
- Mirror-Polished Coating: Enhances chip removal efficiency and reduces edge buildup on the tool, often used for applications requiring mirror-like finishes, such as optical mold processing.
Choosing the right coating not only impacts tool life but also directly influences the final surface quality.
Cutting Parameter Setting
Recommended Speed (RPM) and Feed Rate
In the finishing stage, using higher spindle speed and lower feed rate is a common optimization strategy. Setting the right RPM and feed rate for finishing operations can significantly reduce tool marks and surface waviness. It is recommended to dynamically adjust according to the material and tool diameter instead of using fixed values.
Tips for Controlling the Minimum Amount of Ccutting
In the finishing process, too shallow a cutting depth can easily cause “empty cutting” or tool slippage, thereby scratching the workpiece surface. Maintaining the minimum effective cutting amount is essential for achieving stable cutting and good finish.
Cutting Depth vs. Width: Affecting the Texture Direction
Reasonable planning of the depth and width distribution in the cutting path helps control the texture direction and the uniformity of the overlapping area. For large curved surface processing, it is recommended to use a strategy of small step distance and large overlap rate to obtain a more consistent surface texture.
Machine Tool and Spindle Rigidity
High-speed Machining Center vs. Ordinary Vertical Mill
High-speed machining centers are usually equipped with higher-precision spindles and stronger system rigidity, which are suitable for high-speed and low-cutting force operations in finishing end mills. In contrast, ordinary vertical mills are prone to tool vibration due to their weak spindle rigidity and precision, affecting surface quality.
Importance of Shock-absorbing Structure
One of the most common problems in finishing is tool runout and resonance, which will be directly reflected as surface vibration or reduced finish. Using a tool holder with an internal shock-absorbing structure (such as a hydraulic chuck or a heat-shrink tool holder) can effectively improve the rigidity of the system and improve the overall processing stability.
How do you Choose a Suitable Finishing End Mill When Processing Different Materials?
Different materials exhibit completely different physical properties during the cutting process, such as thermal conductivity, ductility, hardness, adhesion, etc., which will directly affect the surface finish and tool life. Therefore, choosing a finishing end mill for high surface finish suitable for specific materials is the key to improving processing efficiency and quality. The following introduces targeted tool selection and processing strategies based on three common materials.
Processing Aluminum Alloys
Key Points for Achieving Mirror Effects
Aluminum alloys have good machinability and thermal conductivity and are suitable for high-speed finishing. To achieve mirror finish on aluminum parts, it is necessary to control the cutting temperature and reduce the formation of built-up edge. Tools with blunt edges or rough surfaces should be avoided to avoid scratching the workpiece surface.
Polishing Groove Design & High Helix Angle Tool Selection
For aluminum finishing, a finishing end mill with polished cutting edge and high helix angle (such as 45°~55°) should be selected to optimize chip evacuation and improve cutting smoothness. This type of high helix carbide end mill for aluminum can effectively reduce chatter marks and improve surface reflectivity. DLC coated or uncoated tools can avoid surface adhesion and improve finish when processing soft metals.
Processing Stainless Steel / Titanium Alloy
Cooling Strategy (Coolant vs. Air Cooling)
Stainless steel and titanium alloy are low thermal conductivity, easy to work hardening materials, easy to form built-up edge at the front of the tool and increase tool wear. When performing finishing operations on stainless steel or titanium, a reasonable cooling method is crucial. It is recommended to use a high-pressure coolant system to reduce cutting temperature and prevent material adhesion; air cooling or minimal lubrication (MQL) can also be used in some delicate occasions to avoid affecting the workpiece surface.
Coating and Shock Absorption are Particularly Critical
It is recommended to use coated tools with high hardness and oxidation resistance, such as TiAlN, AlTiN or nano-coating finishing end mills, to resist wear in high temperature environments. In addition, this type of material has high cutting resistance, and a tool system with strong shock absorption (such as using thermal expansion chucks or hydraulic chucks) should be used to reduce tool deflection and vibration, and ensure surface stability and processing accuracy.
Processing Hardened Steel/Die Steel
Use of Small Diameter Tools and High-hardness Coatings
When processing die steel above 45HRC or heat-treated workpieces, the use of solid carbide finishing end mill with nano-coating is a basic requirement. This type of tool has sufficient red hardness and wear resistance to complete detail finishing under high load. Usually a small-diameter, multi-edge design (such as Φ1Φ6mm, 4/6 edges) is used to reduce single-edge cutting force and improve contour accuracy.
Advantages of Multi-axis Machining
In finishing of complex cavities, curved surfaces or internal corner root cleaning, 5-axis simultaneous finishing strategy can not only optimize the tool contact angle, but also avoid interference and reduce the number of tool changes, thereby improving the overall surface consistency. Especially on hard materials, multi-axis linkage with short overhang and high rigidity tools is an effective solution to improve mold quality and life.
Practical Tips for Improving Surface Quality
Even if the right F finishing end mill is selected, it is still difficult to obtain the ideal surface finish without a reasonable machining strategy. In the finishing process, in addition to the control of the tool itself, the optimization of the machining path, cutting method and parameter details will also have a direct impact on the final result. The following are some practical tips to help achieve high-quality surfaces without polishing in actual applications.
Use Side Milling Instead of Face Milling as Much as Possible
In the finishing stage, side milling can maintain a more stable cutting force direction and contact angle than face milling, significantly reducing tool vibration and surface tool marks. Finishing end mill for smooth side wall finishing can provide a more uniform surface texture under continuous cutting of the side edge, which is particularly suitable for processing mold cavities, outer contours of mold lines, etc.
Processing Path Optimization: Climb Milling vs. Reverse Milling
When using the finishing end mill for surface finishing, the use of Climb milling can usually obtain better surface quality. Climb milling can make the cutting force direction downward, press the workpiece surface, reduce tearing, burrs and material stretching; while reverse milling is prone to surface burrs and wear marks because the tool gradually “cuts into” the material.
For high-precision surface processing, climb milling strategy for finishing is one of the most recommended path optimization methods.
Comparison of Multiple Shallow Cuts vs. One-time Deep Cuts
During the finishing process, the use of multiple shallow cuts can effectively disperse the cutting load, reduce heat accumulation and tool deflection, and finally obtain a smoother surface effect. On the contrary, although one-time deep cuts can improve efficiency in rough processing, they are prone to tool offset and chatter marks in the finishing stage, affecting contour accuracy.
When using the finishing end mill for high surface quality, the shallow cutting strategy with small feed should be given priority, especially on hard materials or thin-walled parts.
Process Cases without Secondary Polishing after Processing
In the mold industry and precision machining, more and more companies are beginning to adopt the post-polishing free finish process, that is, by optimizing the tool path and tool parameters, the workpiece can directly reach the “usable” surface after processing without additional polishing. For example, when machining mold steel or aluminum alloy surfaces, using a high number of flutes + high helix angle finishing end mill, combined with fine step tool path control, can obtain a mirror-like processing effect, greatly improving production efficiency and consistency.
Finishing Ppath Transition Skills: Small Step, Large Overlap Rate
In three-dimensional surface finishing, controlling the overlap between tool paths is the key to avoiding scallop marks. It is recommended to adopt a small step and large overlap rate (overlap > 80%) strategy to make the transition between tool cutting paths smooth and reduce surface texture mutations.
Especially in freeform surface finishing or large cavity finishing, the combination of ball-end finishing end mill and high-precision CAM toolpath can effectively eliminate tool marks and achieve uniform surface finish without visible tool marks.
FAQ
Why are There Chatter Marks on the Surface During Machining?
Chatter marks are often caused by tool vibration during machining. To reduce vibration:
- Use short flute finishing end mills with anti-vibration features.
- Shorten the tool extension (L/D ratio).
- Optimize cutting parameters, reduce feed rate, and adjust spindle speed to avoid resonance.
- Switch to climb milling to minimize reverse cutting impacts.
How to Avoid Tool Chipping or Surface Scratches?
Tool chipping and workpiece surface scratches are common in the following situations:
- Tool materials or geometric designs that are not suitable for finishing are used.
- Workpiece materials with high viscosity (such as stainless steel and copper alloys) cause built-up edge adhesion.
- Coating mismatch or insufficient cooling leads to high-temperature wear.
- Cutting force is too large and feed is unstable.
Recommendations:
- Choose fine edge geometry and mirror-polished flute finishing end mills for smoother cutting.
- Use highly lubricating coatings such as TiAlN and DLC to suppress chip sticking.
- Ensure a stable cooling system (high-pressure cooling or minimal lubrication).
- Avoid tool path designs with low speed and high load or sudden changes in feed direction.
Can Roughing Tools be Used for Finishing?
Although some roughing end mills have certain geometric versatility, it is not advisable to use roughing and finishing together from a process perspective, especially when pursuing high surface quality. Roughing tools usually have chip breakers, rough edges and stronger cutting angles, which are prone to tool marks, heat accumulation and hair pulling during the finishing stage.
- It is recommended to use a finishing end mill for superior surface finish, with sharper edges and more uniform contact areas.
- Use a design with more than 4 edges to balance the cutting forces.
- The finishing path should avoid repeated passes of roughing residual material.
Why do my Tools have a Short Life and an Unsatisfactory Finish?
This is usually the result of multiple factors, such as:
- The tool material or coating is not suitable for the target material.
- Improper cutting parameter settings lead to increased wear.
- The spindle or tool holder of the processing equipment is not accurate.
- The tool is not adequately shockproof, resulting in chipping or rough processing surface.
- Inferior or counterfeit tools are used.
For These Problems:
- Choose a reputable brand and use a solid carbide finishing end mill bit with wear-resistant coating. For example, choose CNC tools from SAMHO.
- Check whether the tool holder uses thermal expansion or hydraulic structure to ensure clamping rigidity.
- Refer to the cutting parameters provided by the manufacturer for reasonable matching.
- Periodically check the spindle runout and tool concentricity.
