1. Cast iron bed structure, machine tool spindle with heat dissipation function
Cast iron has high rigidity and heat dissipation characteristics, so it is the most stable material for manufacturing machine tool structural parts. For any machine tool used for milling large parts, it must have very strong cast iron structure and equipped with a spindle with heat dissipation function.
As far as the spindle of machine tool is concerned, it must adopt the built-in cooling technology to cool the spindle from the outside of the bearing, so as to ensure that the spindle itself will not be burnt out or accuracy loss caused by thermal expansion in the long-time processing. These factors are very important, because the processing of large mold takes a long time, and under heavy cutting conditions, it will increase the heat and stress of the mold. Therefore, the structural parts of the machine tool must have good rigidity and heat dissipation characteristics, which is the premise of processing large-scale high-quality mold. Therefore, it is necessary to limit the vibration of the machine tool in the machining process to a large extent, and quickly diffuse the heat generated in the machining process. Choosing the appropriate machine tool and cutting tool can achieve a win-win situation of cost and cycle.
2. Thermal stabilization technology
Due to the long injection processing time, the influence of ambient temperature must also be considered. For example, when the ambient temperature changes by 10 ℃ when processing large mold on ordinary machine tool, it will lead to the temperature change of 6 ℃ on the machine tool column, which will cause the parallelism of spindle angle plate to change by 0.07mm. Therefore, the design of the machine tool must take into account the effect of environmental temperature to avoid the influence of environmental temperature on the accuracy of processing parts.
For a large die machining center with fast moving stroke, the spindle speed of the large die machining machine should be at least 20000 R / min, and the metal cutting speed should be 762 ~ 20000 mm / min.
Precision control runs through all stages of mold processing. If it is necessary to realize rough machining and finish machining of large mold in a machining center, the positioning accuracy and repeated positioning accuracy of the machine tool must be strictly controlled. Generally, the positioning accuracy of the special machining center for large mold can reach ± one point five μ m. Repeat positioning accuracy should reach ± one μ m。 At the same time, the pitch accuracy should be kept at 5 μ Within 5 m.
5. Feedback solutions
For high-precision surface machining, the feedback resolution of machine tool itself is very important for detecting the accuracy of machined parts. In the standard 1 μ Under the condition of m-feedback resolution, the results usually obtained are not very satisfactory. If the resolution can reach 0.05 μ m. The results show that there are almost no defects. In addition, by controlling the resolution of the machine tool, proportional feedback and small pitch ball screw, the machining quality of the part surface can be further improved.
The spindle used in the injection mold processing center must meet the requirements of rough machining, semi finishing and high quality finishing. As a reference standard, the surface processing quality that can be realized should be controlled at 2 μ M level. Usually, it is very important to finish the closed surface and parting line of die. However, in traditional technology, many mold manufacturers have to use manual polishing to make up for the problem of insufficient machining precision. Because, the cost of large-scale machining machine tools is very expensive. If multi-function machine tools are purchased for this process, it is obviously not practical.
In addition, a reasonable spindle design must be able to extend the service life of the tool to a large extent, so that it can work continuously with low vibration and low temperature rise in the processing cycle. When the injection mold is used to process the automobile instrument panel mold, if the 16mm CBN inlaid blade finishing tool is used, the processing speed can reach 8m / min, the service life can exceed 30h, and the surface quality can be controlled within 0.336 ~ 3.2 μ m。 It can be seen that, considering the increase of tool cost when processing large mold, the use of specially designed large mold processing machine tool can not only extend the tool life, but also greatly save the tool cost of processing each mold.
7. Mobile multi axis machining head
Because of the limitation of the size and weight of the injection mold, it usually takes a long time to clamp the workpiece. Therefore, the use of 3-axis linkage machining center not only reduces the number of debugging and clamping of the workpiece, but also does not affect the machining accuracy of the machine tool, thus greatly improving the production capacity of workshop processing large mold.
The movable multi axis machining head can be used to process large molds with extremely complex structure. The machining head designed according to the variable geometry can allow three-axis linkage machining. With only one clamping of the workpiece, the deep molds and cooling holes can be milled, and many other parts with complex geometry can be machined. For example, when the spindle is tilted at a Zui angle, the proximity of the machining head to the milling point can be improved, so that the multi axis machining head can be used to complete the machining of the inclined hole.
In addition, because the multi axis machining head processes the surface of the workpiece, the radius of the tool is used to replace the front end of the tool, so the surface roughness can be improved.
8. Chip management
Metal cutting will produce a lot of chips, if not eliminated in time, it will inevitably lead to secondary cutting, and cause the temperature rise of machine tool structural components or workpiece surface. There are usually 18 chip removal holes under the worktable of large die machining center. No matter where the worktable moves, the chip can be removed reliably. There are four built-in hinged chip conveyor belts on the machine tool, which discharge chips to the front of the machine tool at a high speed.
9. High pressure coolant
High pressure coolant plays a very important role in injection mold processing. For example, when the 2 + 3 axis machining method is used to drill the inclined hole, the coolant with a pressure of 1000PSI (1psi = 6890pa) is needed to effectively remove the chips and achieve higher precision cutting. If there is no such high-pressure coolant, additional machine tools and secondary clamping are needed to reduce the machining accuracy and increase the cycle cost. According to the above analysis, it can be seen that the machine tool needs more and better functions to realize the simple processing of large mold.
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