Surface roughness is one of the most important evaluation indexes in machine cutting. In order to analyze how the tool path affects the roughness of the surface after milling, series of simulations are implemented in MasterCAM. We set up the same processing conditions with same parameters such as speed, material and feed rate etc. in these simulations, but different processing paths are used. We choose three paths: the parallel milling along the X-Y axis direction, the parallel milling along the Z-X or Z-Y axis direction and the streamline processing in the simulations. At the same time, end miller, arc miller and ball miller are respectively selected in the software. So there are totally 9 simulations of the milling process that are performed. Then the experimental cutting processes are performed correspondingly and the surface roughness and the accuracy are measured. The results show that the milling effect of the arc is better and the waste is minimal in the parallel milling along the Z-X or Z-Y axis direction with the end mills.
The processing of the injection mold needs milling, grinding, EDM, and light etching process, etc., but the CNC milling process is still the fastest and the most economical way of achieving the main structure and shape of the molds. Lots of papers are focusing on the milling processing of the injection mold, for example, many researches are devoted to studying the relations between the processing quality and the machining speed and feed rate [1-3], and also many studies are devoted to analyzing the difference of the dry milling and wet milling, which can markedly affect the processing quality [
This paper focuses on the finish milling of the mold surfaces, the comprehensive analysis and comparison of the surface milling by using different processing paths that are performed to achieve the high precision and the machining quality. Research achievements will be used in the milling of the inner fillet of master mold or the outer arc of the mold heart. The analysis and comparison realized by experimental machining and measurement can prove that the high precision and quality can be obtained in the injection mold milling.
In the computer-aided manufacturing software such as Master CAM, the effects of the different processing paths are compared in the same speed, tools, materials and other conditions.
1) Setting the basic operating parameters
The size of workpiece and the coordinate frame are set already which can determine the moving scope of the physical tool; correspondingly, the boundary, NC machining scope and the working scope can be determined by the setting of the original point and corner. The work setting dialog box in Master CAM is shown in
2) Parameters setting of surface finish
Surface finish is the final cutting process which can definitively determine the quality. The most important cutting parameters are the tool form, the feed rate, the tool lifting speed, the tool down speed and the spindle speed, etc. In addition, the setting of the finishing parameters consists of the maximum cutting distance and the overall cutting error settings. The tool parameter settings of the surface finishing are shown in
| Parameter | Values |
|---|---|
| Tool size | Φ 8 mm |
| Feed rate | 300 mm /min |
| Down speed | 100 mm /min |
| Lifting speed | 600 mm /min |
| Spindle speed | 2500 rpm |
| Maximum cutting distance | 0.1 mm |
| Overall error | 0.02 mm |
Using the different tools, the simulations are carried out according to various processing paths in Master CAM, such as the parallel milling along the X-Y axis, the parallel milling along the Z-X or Z-Y axis to the milling and the streamline processing. After the processing surfaces and the processing parameters are set, the tool paths are automatically calculated by MasterCAM. The path planning graph is shown in
According to the simulation results, the best three methods, the parallel milling along the X-Y axis, the parallel milling along the Z-X or Z-Y axis and the streamline processing are chosen as shown in
All the cutting processes are simulated successfully, so the NC programs can be obtained by using the MasterCAM according to the corresponding parameters set in the simulations. The code generated by MasterCAM is shown in
By use of a surface profiler, the roughness of the samples obtained from the practical cutting processes is measured. The measurement results are shown in
According to the measurement results of the surface profiler machined by using the program generated by Master CAM, the path of parallel milling along Z-X axis can obtain the best surface roughness. But
| Sample | Processing conditions |
|---|---|
| Sample 1 | Parallel milling of end mill along Z-X axis |
| Sample 2 | Parallel milling of end mill along Z-Y axis |
| Sample 3 | Streamline processing of end mill |
| Sample 4 | Parallel milling of ball mill along Z-X axis |
| Sample 5 | Parallel milling of the ball mill along Z-Y axis |
| Sample 6 | Streamline processing of ball mill |
| Sample 7 | Parallel milling of arc mill along Z-X axis |
| Sample 8 | Parallel milling of arc mill along Z-Y axis |
| Sample 9 | Streamline processing of arc mill |
| First measured value | Second measured value | Third measured value | average value | |
|---|---|---|---|---|
| Sample 1 | 22.617 | 20.577 | 23.442 | 22.212 |
| Sample 2 | 9.840 | 9.383 | 9.924 | 9.716 |
| Sample 3 | 1.569 | 1.801 | 1.575 | 1.648 |
| Sample 4 | 0.587 | 0.469 | 0.510 | 0.522 |
| Sample 5 | 2.733 | 2.529 | 3.132 | 2.798 |
| Sample 6 | 5.049 | 4.742 | 4.921 | 4.904 |
| Sample 8 | 2.269 | 2.011 | 2.347 | 2.209 |
| Sample 8 | 4.513 | 4.146 | 4.318 | 4.326 |
| Sample 9 | 5.642 | 5.881 | 5.672 | 5.732 |
the simulation results show that the machining process will result in over-cutting if the processing condition in Case 4 is selected. Because the Master CAM calculates the processing path without the consideration of the cutter radius of the ball mill, this processing condition is not preferred. Therefore, by use of the parallel milling of the end mill along the Z-X or Z-Y axis, the arc quality is better than others, and the waste is minimal. These research results can guide the practices in milling of the inner fillet of the master mold, the outer arc of the mold heart and the injection mold, which can greatly benefit the precision and quality.
The financial support of the project by Shenzhen Science and Technology Plan (No. JCYJ20170817112916883; JCYJ20160307101647019) and Shenzhen Institute of Information and Technology Project (No. ZY201708) is acknowledged.
The authors declare no conflicts of interest regarding the publication of this paper.