Introduction of concave-convex die processing technology

Concave-convex die is a key part in stamping die, and its processing technology directly affects the quality of die and the precision of stamping parts. The following is the general process of concave-convex die processing:

Design and process planning

Product design: according to the shape, size, precision requirements and production batch of stamping parts, a reasonable concave-convex die structure is designed. Using CAD software, the two-dimensional drawing of the mold is drawn, and the technical requirements such as size, tolerance and surface roughness of each part are marked.

Process planning: according to the mold design drawings, make a detailed processing route. Considering the material, shape complexity, accuracy requirements and other factors of the parts, the processing method, sequence, required equipment and tools of each process are determined.

Raw material preparation

Material selection: according to the use requirements and performance characteristics of the die, choose the appropriate die steel material. Common materials used for concave-convex dies are Cr12MoV, SKD11, etc. These materials have high hardness, high wear resistance and good toughness.

Inspection and blanking: inspect the purchased steel, including checking whether the hardness of the material meets the requirements and whether there are cracks, sand holes and other defects. Then, according to the size requirements of the die parts, the steel is cut into suitable blanks by sawing machine or flame cutting machine, and the blank size should consider the machining allowance.

forge

In order to improve the internal structure of steel and improve the comprehensive performance of the die, it is usually necessary to forge the blank for some large concave-convex dies or dies that bear large impact load. Forging can make the fiber structure of steel more compact and uniform, and improve the strength, toughness and wear resistance of the die. In the forging process, the forging ratio and forging temperature should be well controlled. Generally, the forging ratio is between 3 and 5, and the forging temperature is around 1050-1200℃ according to different materials.

heat treatment

Pre-heat treatment: Generally, the forged blank should be pre-heat-treated, such as spheroidizing annealing, to reduce the hardness of the material, improve the machinability, and prepare for the subsequent quenching treatment. Generally, the temperature of spheroidizing annealing is about 750-800℃, and the holding time depends on the material thickness and furnace charging.

Final heat treatment: the rough-machined concave-convex die parts need final heat treatment such as quenching and tempering to improve the hardness, strength and wear resistance of the die. For example, for Cr12MoV steel, the quenching temperature is generally 1020-1050℃, oil-cooled quenching, tempering temperature is between 550-650℃, and tempering times are usually 2-3 times.

Mechanical processing

Rough machining: Use CNC milling machine, lathe and other equipment to rough the blank, remove most of the allowance, and leave a machining allowance of 0.5-1mm for subsequent finishing. In the process of rough machining, attention should be paid to selecting suitable tools and cutting parameters to improve machining efficiency and reduce machining cost.

Finishing: After rough machining, high-precision equipment such as CNC machining center is used for finishing. For the concave-convex die surface, high-speed milling or EDM are usually used to ensure the dimensional accuracy and surface quality of the die surface. For example, in high-speed milling, the cutting speed can reach 1000-3000m/min, and the feed rate is between 0.05-0.1mm/z to obtain the surface roughness of Ra 0.8-1.6 μ m..

EDM: EDM is a common machining method for some concave-convex dies with complex shapes, especially those with narrow slits and deep grooves. It can remove metal by the high temperature generated by the pulse discharge between the electrode and the workpiece, and process various complex shapes, and the processing accuracy can reach within 0.01 mm.

surface treatment

In order to further improve the surface hardness, wear resistance and corrosion resistance of concave-convex die, it is usually necessary to carry out surface treatment on the die. Common surface treatment methods include hard chromium plating, nitriding and PVD coating. Hard chromium plating can improve the hardness and smoothness of the die surface and reduce the friction coefficient, which is beneficial to the demoulding of stamping parts. Nitriding treatment can form a nitride layer with high hardness and good wear resistance on the surface of the die, which improves the wear resistance and corrosion resistance of the die; PVD coating can coat a layer of coating with high hardness, high wear resistance and low friction coefficient on the surface of the mold, such as TiN, TiAlN and so on, which can effectively improve the service life of the mold.

quality test

Appearance inspection: mainly check whether there are cracks, sand holes, air holes and other defects on the surface of the mold, and whether the surface roughness meets the requirements. For dies coated with hard chromium or PVD coating, it is also necessary to check whether the coating is uniform and peeling off.

Dimensional accuracy measurement: Measure the key dimensions of the die with precision measuring equipment such as three-coordinate measuring instrument, including the external dimensions, profile dimensions and gap dimensions of the concave-convex die, so as to ensure that the dimensional deviation is within the tolerance range required by the design. For example, the clearance tolerance of concave-convex die is generally controlled within 0.05 mm.

Hardness testing: Hardness testing is carried out on different parts of the mold with a hardness tester to check whether the hardness meets the requirements after heat treatment. Uneven hardness may lead to local wear or deformation of the mold during use.

Inspection: Ultrasonic inspection, magnetic particle inspection and other methods are used to inspect the mold to check whether there are cracks and other defects inside, so as to ensure the quality and safety of the mold.

Assembly and debugging

Parts cleaning: clean the processed concave-convex die parts to remove the residual impurities such as oil, iron filings and dust during processing, and ensure the surface of the parts to be clean. After cleaning, antirust agent can be used for protection to prevent parts from rusting.

Die assembly: Assemble all parts of the concave-convex die according to the assembly process requirements. In the assembly process, attention should be paid to ensuring the accurate installation position and uniform clearance of parts. For example, by adjusting the gasket or grinding, the gap between concave and convex dies is evenly distributed, and the deviation is controlled within 0.05 mm. At the same time, it is necessary to ensure that all parts of the die are firmly installed and reliably connected to avoid problems such as looseness and displacement during stamping.

Debugging optimization: after the assembly is completed, debug the mold. First, carry out no-load debugging to check whether the opening and closing movement of the mold is smooth and whether there is interference between the parts. Then, try to debug the die, and check whether the dimensional accuracy, shape accuracy and surface quality of stamping parts meet the requirements by trying to punch a small number of stamping parts. According to the test results, the necessary adjustment and optimization are made to the die, such as adjusting the gap between the concave and convex die and correcting the stamping process parameters, until the die can stably produce qualified stamping parts.