How to control the deformation of the mold during machining?

To control the deformation in mold processing, we need to take corresponding measures from process design, processing, heat treatment and other links. The following are specific methods:

Process design

Reasonable planning of machining route: follow the principle of roughing first and then finishing, remove most of the allowance during rough machining, and leave a machining allowance of 0.5-1mm for finishing to reduce cutting force and deformation during finishing. For complex molds, layered milling or multi-step machining can be used to gradually approach the final shape to avoid cutting too much material at one time.

Optimize the clamping mode: select appropriate clamping points and clamping forces, and use multiple evenly distributed support points or clamps to disperse the pressure, so as to prevent local stress from causing deformation. For thin-plate molds, vacuum sucker can be used for clamping, which can not only provide uniform adsorption force, but also avoid the local extrusion of the workpiece by traditional fixtures.

Processing aspect

Select appropriate cutting tools and cutting parameters: Choose cutting tools according to die materials and processing requirements, such as using cemented carbide tools or CBN tools when processing high-hardness die steel. Reasonably adjust cutting parameters, appropriately reduce cutting speed and feed, increase cutting times, and reduce cutting force and cutting heat. For example, cutting speed can be controlled at 100-300m/min and feed is between 0.05-0.15mm/r..

Adequate cooling and lubrication: use cutting fluid to fully cool and lubricate, reduce cutting temperature and thermal deformation. Select the appropriate cutting fluid type, such as oily cutting fluid is suitable for processing die steel with high hardness, and water-based cutting fluid has good cooling performance and is suitable for high-speed cutting.

Heat treatment

Pre-heat treatment: Pre-heat treatment such as annealing and normalizing is carried out on the die material before rough machining to eliminate the residual stress inside the material, improve the cutting performance of the material and reduce the deformation risk during machining. For example, for medium carbon steel dies, normalizing treatment can be used to refine grains and improve hardness uniformity.

Quenching and tempering: control the heating speed and cooling speed during quenching, and adopt methods such as step quenching and isothermal quenching to reduce quenching stress. Tempering is the key process to eliminate quenching stress, and the tempering temperature and time should be strictly controlled. Generally, the tempering temperature is between 500-650℃ and the tempering time is 2-4 hours. The tempering times are determined according to the size and material of the die, usually 2-3 times.

In terms of post-processing

Stress relief treatment: after the machining is completed, the die is subjected to stress relief annealing or vibration aging treatment to further eliminate the residual stress generated in the machining process, stabilize the die size and prevent deformation in the subsequent use. Stress relief annealing temperature is generally between 550-650℃, and the holding time depends on the die size and material.

Surface treatment: according to the use requirements of the mold, choose the appropriate surface treatment process, such as nitriding, hard chromium plating and so on. Surface treatment can not only improve the wear resistance, corrosion resistance and demoulding performance of the mold, but also compensate the dimensional change in the machining process to some extent, and improve the accuracy and stability of the mold.

Quality inspection and monitoring

Process inspection: During the machining process, measuring tools (such as calipers, micrometers, coordinate measuring instruments, etc.) are regularly used to inspect the key dimensions and form and position tolerances of the mold, so as to find out the deformation trend in time and adjust the machining parameters or clamping methods. For high-precision molds, it can be tested every 1-2 hours.

Finished product inspection: After machining, conduct a comprehensive quality inspection on the mold, including appearance, dimensional accuracy, shape and position tolerance, surface roughness and other indicators. The test results are analyzed, and the deformation laws and reasons are summarized, which provides experience reference for the subsequent mold processing and continuously optimizes the processing technology.