With the rapid development of the industry, the demand for various molds is growing rapidly, and designers are continually increasing the size and complexity of such mold products. Therefore, the production of various molds has become a new field for many processing companies to seek opportunities for global competition. However, it is not an easy task to enter this field. Under the backward processing technology, the machine feed rate is slow, the operator needs to perform multiple debugging and clamping on the workpiece, and it takes several hours to manually polish the work, so the processing cycle is very long. Therefore, more advanced processing techniques must be sought for the processing of high-end molds.
The mobile phone mold shown in Figure 1 is the first edition of a famous mobile phone brand in China. The product has high precision requirements and is difficult to process. It is processed by traditional common equipment, the process and fixture are complicated, the processing quality is unstable, and the production efficiency is low. For this reason, the use of machining centers for processing is undoubtedly the best solution. This paper is based on MasterCAM9.1+HSM high-speed plug-in for 1-process processing. It introduces the case of processing the mobile phone front mold (static mode) with CNC machining center, including the specific process and processing parameters.
1. Mold process analysis
The mold has the following characteristics: 1The processing content is too much, and the machine tool and the tool need to be replaced frequently. 2 The processing precision is high, and the processing quality of ordinary machine tools is difficult to guarantee. Due to the long process flow and the number of turnovers, the production efficiency is difficult to improve. 3 shape is complicated. Machining with CNC machining center, thanks to the machining center's own precision and processing efficiency, rigidity and automatic tool change. As long as the process is well-designed and the design uses reasonable special fixtures and tools, the above problems can be solved.
2. Tool selection
All use of carbide tools to improve processing quality and production efficiency.
Milling cutter: It adopts carbide machine to clamp the insert milling cutter, which can realize high-speed milling and improve production efficiency.
Drill bit: It adopts advanced three-cutting carbide drill bit with high self-centering function to ensure the accuracy of drilling position.
3. Machining center processing
The numerical control machining program is shown in Table 1. According to the processing program card, the machining center is used to process the mold. The details are as follows:
(1) Workpiece milling and roughing
As the first step of processing, due to the large machining allowance, if the small tool is selected, the efficiency is not high. Therefore, the φ 16mm flat milling cutter is selected as the roughing tool. Here, the HSM high-speed plugging is mainly used.
HSM high-speed external plugging is much more refined than the original machining path of MasterCAM in the surface processing, with uniform processing level and reasonable path. The specific settings are shown in Figure 2.
The processing route is shown in Figure 3. Seen from the machining path, the program generates a uniform tool path and can remove the blank in large quantities, laying a solid foundation for future processing.
(2) Surface secondary roughing Now, the workpiece has been removed a large amount of machining allowance, and the purpose of this machining is to use a small tool to perform secondary clearance of the margin so that the margin is closer to the target image. This time, the contour is roughed.
(3) The diversion hole, the roughing diversion hole of the diversion groove and the diversion groove are the most important weights of the mold processing. If there is a slight error, it will bring serious consequences, such as flash and mold pattern error. , a full set of mold scrap, and so on. But this shows the processing advantages of the machining center, which is not the case with traditional machining.
Here, the M3 ball cutter is mainly used with the spiral descending 2D roughing, and the spiral descending can significantly improve the tool life and the dimensional accuracy of the workpiece.
A very common machining method for mold processing is used here. The size and shape of the machining ball cutter are very close to those of the guide groove, so the material can be uniformly removed during processing, and the precision is also higher. The software setting is shown in Fig. 4. This is the accumulated experience of the author's long-term experience, which can make the processing more effective.
The program filter must be hooked up, and many unnecessary tool paths can be filtered during the machining process, so that the tool path is more stable and uniform. The settings are shown in Figure 5. The descending oblique insertion setting is shown in Figure 6.
The descending oblique insertion mainly sets various settings when the oblique insertion is performed. If the setting is reasonable, the cutting path can be made smooth and the amount of the knife is evenly distributed.
According to the above settings, the obtained tool path is more uniform and stable than the software default setting, and the precision of the mold processing is better. Processing time is also reduced by 1/3. The most important thing is to reduce the problems that many diversion troughs are prone to, such as flashing, leaking, etc.
(4) Surface semi-finishing This semi-finishing is mainly for semi-finishing of some small shapes in the cavity of the mold. Since the shape of the cavity is small, the φ 6mm flat milling cutter is used for processing.
The processing method here is high-precision machining such as 2D processing composite. The composite use of the knife path can play the role of double auxiliary and double bearing, and it has a significant help to the processing precision and efficiency. The contour finishing settings are shown in Figure 7.
Optimized cutting must be hooked up so that our tool path sequence is smoother and smoother, then the “Advanced Settings” need to be reset, as shown in Figure 8.
The original default setting is "automatic calculation", so that the processed surface will appear rough and no streamline where the working surface meets. Now we change to "All Surface Edges". This processing can be processed to all the boundaries, and the intersection of the surfaces will be smoothly smoothed, thus improving the accuracy of the mold. Figure 9 shows the tool path, which shows that the tool path is simple and uniform.
(5) Finishing of the guide hole Here, the finishing of the guide hole is mainly performed.
(6) Surface roughing Because there are some slopes and irregular surfaces on the surface of the mold. Conventional machining must be performed by means of a jig. If a jig is used, the number of times of clamping is undoubtedly increased, and the error in machining is accumulated. And if you use a machining center for processing. This allows bevels and irregular surfaces to be machined as normal surfaces. Then start the above processing in one setup (see Figure 10).
(7) Semi-finishing and finishing of the guide groove The guide groove is one of the core parts of the mold. Therefore, the R1.75mm and R1mm ball-end knives are used for semi-finishing and finishing to obtain the target precision.
(8) Surface finishing This step is mainly for finishing the surface of the workpiece. Here, the round nose knife is used for processing. The round nose knife has the characteristics of both the flat knife and the ball cutter. As the finishing of this surface is undoubtedly the best choice. This is also the use of 2D processing composite contour finishing.
(9) Minor feature finishing We process some small shapes to complete the processing of the entire front mold.
4. Experience and technical summary
This machining is mainly based on small-diameter tools (with a diameter of 6 mm or less). The smaller the diameter, the worse the strength and the shallower the depth of machining. According to the past experience, the author summarizes the parameters of the infeed as shown in Table 2.
The mold has a very high requirement on the surface roughness. Therefore, when roughing, the machining allowance of the blank must be evenly distributed, and if necessary, the opening can be increased twice. Since the finishing is mainly based on small tools, in order to obtain the required surface roughness, a small cutting amount, a high rotation speed, and a high feed speed should be selected. The general speed is not less than 2 800 r/min, and the feed speed is not less than 2 000 mm/min to ensure the surface roughness.
In terms of tools, in the processing of the mold from blank to finished product, from roughing to semi-finishing and finishing, the cutting time takes about 3/4, and the choice of the tool is crucial to the processing time. The role and importance of the tool is also obvious. If cheap tools are used, the machining time will be extended in addition to the surface roughness and accuracy. Therefore, the machining uses a carbide machine clamp milling cutter to achieve high-speed milling and improve production efficiency.
5 Conclusion
Using the machining center to process the front mold of the mobile phone, the processing time is about 12h, which is only 1/6 of the past processing time, and the processing efficiency is greatly improved. In addition, due to the guarantee of the precision of the machine tool, the tooling marks are completely eliminated, and the matching precision is also effectively guaranteed, so that the processing quality is significantly improved and a good application effect is obtained.
