Design of Process Research Scheme

a) Before Ultra-precision Machining

b) After Ultra-precision Machining

Figure 2　Micro-morphology of Tool Cutting Edge Before and After Micro-finishing

Cutting Tests of General-purpose Milling Tools

Milling Test for TC4 Material

1. Test Object: Solid cemented carbide end mill with specifications of φ20mm×R0.5mm.
2. Test Objective: Improve and extend the service life of the end mill through micro-finishing technology.
3. Test Environment: The part material selected for the test is TC4, which is a difficult-to-cut material. The blank of the TC4 part is shown in Figure 3. It can be seen that the rough machining allowance of the part is relatively large. The process scheme adopts high-feed tools for rough machining of the blank, and then uses a φ20mm×R0.5mm solid cemented carbide end mill for finish milling of the outer contour (see Figure 4). This cutting tool is prone to wear and has high consumption.

Figure 3　Blank of TC4 Part

Figure 4　Finish Milling of Part Outer Contour

4. Improvement Effect: Under the same cutting parameters, only the tool was subjected to micro-finishing. The test data of the TC4 machining tool before and after micro-finishing are shown in Table 1. Comparison of the test data shows that the micro-finishing technology effectively extends the cutting tool life by 253%, and also improves the surface quality of the parts.

Milling Test for 38CrMoAlA Material

1. Test Object: Solid cemented carbide end mill with specifications of φ20mm×R1mm.
2. Test Objective: Improve and extend tool life and enhance part surface machining quality through micro-finishing technology.
3. Test Environment: The machining content includes the inner cavity and bottom surface of process 225 (see Figure 5) and the inner cavity and bottom surface of process 235 (see Figure 6). The flatness requirement of the bottom surface is 0.02mm, and the parallelism requirement is 0.05mm. The physical object of the finished 38CrMoAlA part is shown in Figure 7. The nitrided surface hardness of the machined part is ≥58HRC, which is a difficult-to-cut material. During machining, the cutting tool wears severely, has a short service life and high consumption.

Figure 5　Machining of Inner Cavity and Bottom Surface of Process 225

Figure 6　Machining of Inner Cavity and Bottom Surface of Process 235

Figure 7　Physical Object of Finished 38CrMoAlA Part

5. Improvement Effect: The application of micro-finishing technology effectively extends the tool life, reduces the waiting time caused by tool changes during machining and the risk of part unqualified rate due to tool wear. At the same time, the surface quality of the machined parts is also improved. The test data of the 38CrMoAlA machining tool before and after micro-finishing are shown in Table 2. The service life of the improved tool is increased by 500%.

Milling Test for TM210A Material

1. Test Object: Solid cemented carbide end mill with specifications of φ10mm×R0mm.
2. Test Objective: Improve and extend cutting tool life through micro-finishing technology.
3. Test Environment: The hardness of the part is 51～58HRC. A φ10mm×R0mm solid cemented carbide end mill is used to machine two φ15H8 bushing holes on the part. The position of the milled holes is shown in Figure 8, with machining allowance reserved. TM210A is an ultra-high-strength steel, which is a difficult-to-cut material. In addition, the φ10mm×R0mm solid cemented carbide end mill is a high-consumption tool.

4. Improvement Effect: The test data of the TM210A machining tool before and after micro-finishing are shown in Table 3. The service life of the improved tool is increased by 100%, and the surface quality of the machined parts is also improved.

Milling Test for 30CrMnSiA Material

1. Test Object: Solid cemented carbide end mill with specifications of φ8mm×R1mm.
2. Test Objective: Improve and extend the service life of the end mill through micro-finishing technology.
3. Test Environment: The machining content includes the outer hexagon and two boss features on the outer circle of the part (see Figure 9). Restricted by the spatial distance between the outer hexagon and the right end face, a φ8mm×R1mm end mill is preferred for machining the outer hexagon surface. This cutting tool has severe wear, insufficient rigidity and short service life. The main machining difficulty is large material removal, and the end mill is a high-consumption tool.

4. Improvement Effect: Under the same cutting parameters, only the tool was subjected to micro-finishing. The application of micro-finishing technology effectively extends the tool life. The test data of the 30CrMnSiA machining tool before and after micro-finishing are shown in Table 4. The service life of the improved tool is increased by 200%. The physical object of the finished 30CrMnSiA part is shown in Figure 10.

Table 4　Test Data of 30CrMnSiA Machining Tool Before and After Micro-finishing

Figure 10　Physical Object of Finished 30CrMnSiA Part

Process Tests of Special-purpose Milling Tools

Milling Test of Sphere Socket Feature

1. Test Object: Solid cemented carbide ball nose end mill with specifications of φ14mm (see Figure 11).

   

   Figure 11　φ14mm Solid Cemented Carbide Ball Nose End Mill

2. Test Objective: Extend tool life and improve surface quality through micro-finishing technology.
3. Test Environment: The machining material is TM210A with hardness of 35～40HRC. The surface roughness measuring equipment is an integrated roughness and contour measuring instrument. The machining of the sphere socket (see Figure 12) is a difficult process. The roughing, semi-finishing and finishing processes must ensure the dimensional requirements. This cutting tool is a high-consumption tool, which is prone to wear and has large consumption. After machining, manual polishing is required to meet the surface roughness requirements. However, manual polishing is time-consuming, and may cause dimensional deviation and sphere socket deformation during the polishing process, resulting in low machining efficiency. Therefore, this process is a bottleneck procedure.

4. Improvement Effect: The application of micro-finishing technology on the tool for sphere socket parts effectively extends the tool life. The test data of the φ14mm solid cemented carbide ball nose end mill before and after micro-finishing are shown in Table 5. The service life of the improved tool is increased by 220%, the surface quality of the sphere socket is improved by 2 precision grades, and the workload of manual polishing is reduced.

Milling Test of Ball Raceway Feature

1. Test Object: Solid cemented carbide ball nose end mill with specifications of φ10mm (see Figure 13).

   Figure 13　φ10mm Solid Cemented Carbide Ball Nose End Mill

2. Test Objective: Extend tool life and enhance part surface quality through micro-finishing technology.
3. Test Environment: The part material is 38CrMoAlA with hardness of 30～37HRC. The machining surface quality requirement is very high. The roughing, semi-finishing and finishing processes are required to ensure the final dimensional requirements. This cutting tool is a high-consumption tool, which is prone to wear and has large consumption. After machining, manual polishing is required to ensure the surface quality of the ball raceway. However, manual polishing is inefficient, and may cause dimensional deviation and part deformation during the polishing process. Therefore, this has always been a difficult machining feature.
4. Improvement Effect: The application of micro-finishing technology effectively extends the tool life. The test data of the φ10mm solid cemented carbide ball nose end mill before and after micro-finishing are shown in Table 6. The service life of the improved tool is increased by 220%, the surface quality of the parts is improved by 2 precision grades, the workload of manual polishing is drastically reduced, and the machining efficiency is significantly improved. The comparison of the surface quality of the parts machined by the tool before and after improvement is shown in Figure 14.

a) Before Tool Improvement

b) After Tool Improvement

Figure 14　Comparison of Surface Quality of Parts Machined by  Cutting Tool Before and After Improvement

Conclusion