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What factors are related to the machining accuracy of cnc machining center dies

December 8, 2022

What factors are related to the machining accuracy of cnc machining center dies
In the process of mold processing, the machining center has higher and higher requirements for precision and surface processing quality. In order to ensure the mold processing quality, we should consider the selection of machine tools, tool handles, tools, processing schemes, program generation, operator requirements, etc.

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1. High precision and high speed machining center
With the improvement of product design requirements and the development of high-speed and high-precision processing technology, the quality of mold NC processing has been greatly improved, the mold processing speed has been greatly improved, the processing process has been reduced, the mold production cycle and clamping times have been shortened, and sometimes the time-consuming bench worker repair work can be eliminated. High speed and high precision machining of molds has gradually become one of the important contents of technological transformation of mold manufacturers. It is inevitable that high-speed CNC machining centers replace traditional low-speed machining, and the development of mold manufacturing technology will also bring us more rich product experience.

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2. Use appropriate tool handle structure
The use of high-speed and high-precision machining centers will also drive the updating of related process equipment. In particular, the impact of tools on NC machining quality and tool shank will become prominent. In the rotary cutting tool processing system, the chuck is closely connected with the machine tool (or its combination) to ensure the realization of the tool processing performance. The interfaces between machine tools and tool handles commonly used include HSK hollow tool handles and BT tool handles. The taper of the taper shank interface between the machine tool spindle and the BT tool shank is 24:7. This kind of tool shank connection mode is suitable for traditional low-speed machining. Because the BT tool shank and the machine tool spindle are only tapered, under the action of high speed centrifugal force, the taper clearance will increase, which will affect the quality of NC machining. Generally, when the spindle speed exceeds 16000 rpm, we will need to use the HSK hollow handle. The HSK cutter bar positioning structure is over positioning, providing standard connection with the machine tool. Under the pull of the machine tool, ensure that the short cone and end face of the cutter bar are closely matched with the machine tool.

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3. Select a suitable tool for machining
The rational use and selection of cutting tools will be an important factor affecting the quality of NC machining. Cemented carbide tools are more and more widely used. In high-speed machining, coated cemented carbide will replace most of the sharp steel tools, including simple tools such as reamers, ball cutters, and boring cutters. Coated cemented carbide will play an important role in high-speed machining tool materials and be applied to most conventional machining fields.
Generally, we know that we will use large diameter tools for rough machining. In order to save costs and reduce the difficulty of tool manufacturing, we will use machine clamped carbide inserts to make rough machining as much as possible; In semi finish machining, the insert cutter with high speed and high feed is used to make the semi finish machining run fast; When finishing, try to use high-precision round mirror blade and carbide cutter bar to ensure the strength of the tool and cutter bar, which will save the expensive cost of using integral alloy cutter while maintaining the machining accuracy. During processing, we also need to pay attention to that the radius of the inner contour fillet on the finishing part must be greater than or equal to the radius of the tool. The tool with a radius smaller than the corner fillet radius is selected for processing in the way of circular interpolation or oblique interpolation, which can avoid the phenomenon of over cutting caused by linear interpolation and ensure the quality of the die finishing.

4. NC process plan
In high-speed and high-precision machining, the importance of the design of NC process plan has been raised to a higher position. The whole process of machining must be controlled. Any mistakes will have a serious impact on the quality of the mold. Therefore, the process plan will play a decisive role in the processing quality. NC machining process planning can be considered as the state control of a system process plan from the blank to the part processing and molding.
A good process plan is difficult in the whole design process, and it can only be obtained after continuous practice summary and modification. A large amount of information needs to be considered in the design process, and the relationship between the information is extremely complex, which must be guaranteed by the actual work experience of the programmer. Therefore, the design quality of process plan mainly depends on the experience and level of technicians.

Generally, a complete NC machining process planning includes the following contents:
1) CNC machine tool selection.
2) Processing method selection.
3) Determine the clamping method of the part and select the fixture.
4) Positioning method.
5) Inspection requirements and methods.
6) Select the tool.
7) Error control and tolerance control in machining.
8) Define NC operation.
9) Numerical control process sequencing.
10) Cutting parameter selection.
11) Prepare NC process program sheet.
5. CAM software
A good software can also improve the mold processing quality and efficiency. For example, UniGraphics and CIMIAMTRON are good mold processing software. In particular, the two kinds of software are rich in practical and different processing strategies. They are widely used in NC milling programming, turning programming, and WEDM programming. The mutual complementation has greatly improved the quality and efficiency of NC processing.
CIMIAMTRON can add the screw function when removing rough machining in the offset area, which will make the actual cutting more stable, eliminate the sudden change of the feed direction connected between adjacent tool paths, reduce the acceleration and deceleration of the cutting feed, maintain a more stable cutting load, extend the tool life, and also play a good role in protecting the machine tool.
Software is also just a tool. An excellent programmer has rich on-site machining experience and theoretical knowledge. At the same time, NC programmers who are proficient in software functions are the decisive factors in mold NC processing, playing a key role in the quality and efficiency of NC processing. To this end, a sound training system for programmers should be established. First of all, the designers should practice in the position of NC operation for a period of time, and the training of NC program design can only be carried out after passing the strict operation examination. In order to ensure the quality of the die NC processing, it is necessary to have a good NC program.
6. Operator
The operators of machining centers are the executors of NC machining, and their control over the quality of NC machining is also obvious. They have the best understanding of the real-time status of machine tools, tool handles, tools, processing technology, software and cutting parameters in the process of performing processing tasks. Their operations have the most direct impact on NC processing, so the skills and sense of responsibility of the machining center operators are also the key factors to improve the quality of NC processing!
Conclusion: Although hardware equipment such as machining center is critical, talent is the decisive factor affecting the quality of NC machining, because the professional ethics, skill level and sense of responsibility of programmers and machine tool operators determine how effective various advanced equipment can be. We must pay attention to all aspects of processing, especially human factors, so that the CNC machining center mold processing is more and more extensive.