Precision mold manufacturing method and control process

Every link in the process from the signing of the precision mold manufacturing order to the delivery of qualified molds to the customer may affect the quality of the mold. The precision mold manufacturing process is controlled by system engineering, and every link must be controlled, which is the prerequisite of precision mold manufacturing.

The guiding ideology of mold parts processing is to formulate corresponding process plans for different mold parts, different materials, different shapes and different technical requirements. The general process of mold parts is: blank preparation-rough machining-semi-finish machining-heat treatment (quenching, quenching and tempering)-precision grinding-electrical machining-fitter finishing and surface processing. Through the control of each process in the processing process, the required processing accuracy is achieved.

1. Material and heat treatment control

The heat treatment of mold parts makes the parts obtain the required material hardness, and at the same time, the processing process and the size and shape of the parts can be stabilized. According to the different materials of the parts and the structural characteristics of the parts, there are different heat treatment methods, and the internal stress of the parts must be heat treated. To control and formulate the heat treatment process, full consideration should be given to the hardenability, overheat sensitivity and decarburization sensitivity of the material, and the press quenching process should be used for thin-walled parts.

(1) Selection of precision mold materials: In addition to the selection of CrWMn, Cr12, 40Cr, GCr15, Cr12MoV, 9Mn2V cemented carbide, for some concave molds and convex molds with high working strength and severe stress, high thermal stability can be selected Alloy steel S2, S3, V10, APS23S1, G2, G3, G3, G4, G8, etc. with good properties and good organization.

(2) Stress relief treatment after quenching: all the workpieces after quenching retain internal stress, which may easily cause the size of the workpiece to change or even crack after the subsequent finishing. Therefore, the parts should be tempered while hot after quenching to eliminate the quenching stress. The shape is complicated and the internal and external corners are large. For the workpiece, tempering is not enough to eliminate the quenching stress. Stress relief annealing or multiple aging treatments are required before finishing to fully release the stress.

2. Precision grinding process control

Grinding is a key process in precision mold processing. Finishing grinding must strictly control the appearance of grinding deformation and grinding cracks, and even control the micro-cracks on the surface of the workpiece. The following aspects should be considered when formulating precision grinding processes

(1) Choose grinding wheel: For the characteristics of high tungsten, high vanadium, high molybdenum, high alloy and high hardness of the mold material, PA chrome steel jade grinding wheel and GC green silicon carbide grinding wheel can be selected; when processing hard alloy, quenching For high-hardness materials, use organic binder diamond grinding wheels. The organic binder grinding wheels have good self-grinding properties. The precision of the ground workpiece is above IT5, and the roughness can reach the requirement of Ra=0.16um. CBN cubic boron nitride grinding wheels are used for finishing on CNC forming grinders, coordinate grinders, and CNC internal and external cylindrical grinders, and the effect is better than other types of grinding wheels. In the grinding process, the grinding wheel should be trimmed in time to keep the grinding wheel sharp. When the grinding wheel is passivated, it will slip, scratch, and squeeze on the surface of the workpiece, causing burns, micro cracks or grooves on the surface of the workpiece, which will affect the processing accuracy.

(2) Selection of feed rate: The feed rate of precision grinding should be small, the cooling should be sufficient during grinding, and the coolant medium should be selected as much as possible. Parts with machining allowance within 0.01 mm should be ground at a constant temperature.

(3) Workpiece clamping: Shaft parts are characterized by multiple rotating surfaces. The precision machining method is generally used in the grinding process of internal and external cylindrical grinders, using the grinding machine chuck and tailstock center to clamp and position the workpiece or use the head and tail Two centers locate the workpiece. At this time, the connection between the chuck and the center of the center is the center line of the workpiece after grinding. If the center line jumps, the coaxiality of the processed workpiece cannot meet the requirements, so make the chuck before processing For the concentric inspection of the center and the centering inspection of the center and the center of the center, the clamping technology table should be considered when grinding the inner hole of the book wall, that is, a thick wall part is left during the turning process, and the inner hole is cut after the grinding is completed.

3. EDM control

(1) Wire cutting preparation: Wire cutting uses precision slow-moving wire cutting machine tools, with a machining accuracy of ±0.001mm, roughness Ra=0.2um, and a high deionization degree of deionized water wire cutting wire. The verticality meets the requirements of processing accuracy. The material of the wire used for cutting with moderate tightness is compatible with the material of the workpiece to be cut to ensure a reasonable processing speed.

(2) Machining route design: wire cutting process destroys the original stress balance of the material during the process, causing stress concentration at the corners. The method to deal with stress concentration is to use the vector translation principle, and leave 0.8~0.9 mm before finishing. For the margin, the rough shape of the cavity is pre-processed, and then heat treatment is performed to release the processing stress as much as possible before finishing to ensure thermal stability. 4 cuts are used when processing the punch. The cutting position and path of the cutting wire should be determined reasonably. The position of the clamping blank should be selected after the first pass. The workpiece is not in a hanging state, and the workpiece is always in a good state of force without affecting it. Subsequent processing; perforating and threading on the blank, the processing effect is better than the shape cutting.

(3) EDM processing technology: EDM processing requires the production of coarse and fine electrodes respectively. The precision electrode is processed by CNC machine tools. Cu-W alloy electrode has good overall performance, and the electrode loss is less than copper electrode. Under good chip removal conditions, it can process difficult-to-machine materials and parts with complex cross-sectional shapes; Ag-W alloy electrode It has better performance than Cu-W alloy electrode and is used for precision processing; graphite electrode is imported graphite with low loss, high hardness, high corrosion rate and low surface roughness. Before the end of EDM, arrange precise trimming to remove the hardened thin layer formed on the surface.

4. Surface treatment and mold assembly

(1) Surface treatment: After finishing the surface treatment, the surface of the workpiece has no pores, uniform hardness, small differences in characteristics, low inclusions, and no tool marks or wear marks left on the surface of the parts where stress concentration is left during processing. Use polishing, grinding, and fitter polishing to blunt the useless edge of the workpiece and the sharp-angled orifice. After the electric machining, the surface is grayish white. The 6-10 m modified hardened layer is removed. This layer is brittle with residual stress. The hardening should be fully eliminated before use. Floor.

(2) Mold assembly: Before assembly, the workpiece should be fully demagnetized, and the surface should be cleaned with ethyl acetate. During the grinding process, the workpiece will be magnetized, with weak magnetic force, and easy to absorb some small debris. In the process: fully understand the structure and technical requirements of the assembly drawing, and complete all kinds of parts; correctly list the assembly sequence of each part; check the dimensional accuracy of each part, and clarify the matching requirements; Assembly tools; first install the guide post and guide sleeve of the mold base part and the assembly of the cavity forming block assembly; combine the assembly template with the convex mold and the concave mold to adjust the position of each plate; open and close the mold to check whether the mold action is accurate and reliable.