Every stage of the entire process from the signing of precision mold production order information to the delivery of qualified mold shells to customers is likely to endanger the quality of mold shells. The entire process of precision mold production and manufacturing is controlled according to engineering projects, and every stage must be controlled, which is a prerequisite for precision mold production and manufacturing. The guiding principle for the processing of mold parts is to develop corresponding processing process plans for different mold parts, materials, and technical standards. The general processing process of mold parts includes: pre preparation of rough embryos - rough machining - semi precision machining - heat treatment process (heat treatment, heat treatment) - high-precision grinding - electrical machining - milling worker repair and surface processing. According to the operation of various technological processes throughout the entire processing process, achieve the specified machining precision.
1. Raw materials and heat treatment process control
The heat treatment process of mold parts not only ensures that the parts obtain the necessary raw material strength, but also ensures that the entire process and specifications of the parts can be stable after processing. For different materials and structural characteristics of the parts, there are different heat treatment methods. It is necessary to manipulate the thermal stress of the heat treatment process of the parts. The formulation of heat treatment methods should take into account the cutting performance of the raw materials, forced superheat sensitivity, and carburization sensitivity, For thick walled parts, press quenching processing technology should be used.
(1) The raw materials used for precision molds are:
In addition to using CrWMn, Cr12, 40Cr, GCr15, Cr12MoV, 9Mn2V hard alloy cutting tools, for some cavities and mold seats with high working strength and strict bearing capacity, carbon steel S2, S3, V10, APS23S1, G2, G3, G4, G8 with high heat resistance and excellent mechanical conditions can be used.
(2) Remove crustal stress after heat treatment:
After heat treatment, all workpieces retain thermal stress, which is very easy to cause the specification change or even crack of workpieces after finishing. Therefore, after heat treatment, the crustal stress of parts should be removed during heat quenching. For workpieces with complicated appearance and many internal and external corners, quenching cannot remove the crustal stress of heat treatment. Before finishing, crustal stress quenching or several quenching and tempering treatments should be carried out to fully release crustal stress.
2. High precision grinding operation
Grinding is an important process flow in precision mold processing. Precision machining grinding requires strict control of grinding deformation and the occurrence of grinding cracks, and even manipulation of microscopic cracks on the surface of the workpiece. When formulating high-precision grinding processes, the following aspects should be considered.
(1) Select grinding wheel blades:
For high tungsten, high vanadium, high molybdenum, and high aluminum alloys used as raw materials for precision molds, PA manganese steel jade sand wheel sheets and GC green silicon carbide sand wheel sheets can be used for their high toughness characteristics; When machining hard alloy cutting tools and materials with high heat treatment strength, diamond saw blades with organic chemical bonding agents are selected. The organic chemical bonding agent sand wheel blades have good self grinding performance, and the precision of the polished workpiece is above IT5. The surface roughness can reach the regulation of Ra=0.16um. CBN boron nitride sand wheel pieces are used for precision machining on CNC machine tool forming CNC grinding machines, coordinate CNC grinding machines, and CNC internal grinding machines, and the actual effect is better than other types of sand wheel pieces. When grinding, it is necessary to immediately repair the sandwheel to maintain its sharpness. After passivation treatment, the sandwheel slides, scratches, and extrudes on the surface of the workpiece, causing burns, microscope cracks, or pipe grooves on the surface of the workpiece, which endangers the machining accuracy.
(2) Selection of cutting amount:
The cutting amount for high-precision grinding should be small, and the cooling during grinding should be sufficient. Refrigerant materials should be selected as much as possible, and parts with a processing capacity within 0.01mm should be temperature controlled for grinding.
(3) Workpiece clamping:
The characteristics of shaft parts are composed of several rotating surfaces. High precision machining methods generally use internal grinding machines to grind the entire process, using CNC grinding machines to hold and accurately locate the workpiece with the top clamp and tailstock, or using the top two clamps of the head and tail to accurately locate the workpiece. At this time, the connection between the clamp and the top management center is the axis of the ground workpiece. If the axis trembles, the parallelism of the processed workpiece cannot meet the requirements, Therefore, before processing, it is necessary to carry out the same boat inspection of the collet and top level, as well as the alignment inspection of the head and tail top level. When grinding the inner holes of the wall, it is necessary to consider the use of a clamping processing technology platform, that is, to leave an extra section of thick wall pipe during turning and remove it after grinding the inner thread.
3. Spark discharge machining operation
(1) Preparation in advance for wire cutting processing:
The wire cutting machine adopts a high-precision slow wire cutting machine tool, with a machining accuracy of ± 0.001mm and a surface roughness of Ra=0.2um. The double steam water wire cutting machine selected to improve the degree of removal of positive ions has a flatness that meets the requirements of machining precision. The tension distance is appropriate, and the wire material used for laser cutting is consistent with the material of the cut workpiece, ensuring effective machining speed.
(2) Processing circuit design scheme:
Wire cutting process destroys the original crustal stress balance of raw materials to a certain extent in the whole process of processing, causing stress at the corner. The way to solve the stress is to apply the basic principle of vector material movement. Before finishing, 0.8~0.9mm capacity is reserved, and the general shape of the concave mold is pre processed. Then, heat treatment process is carried out to make the processing crustal stress released as far as possible before finishing to ensure heat resistance. When processing the mold base, four passes of laser cutting should be used. The entry location and path of the laser cutting wire should be effectively formulated to select the clamping position of the blank material. After the first pass of cutting, the workpiece should not be suspended from the wall, and the load-bearing condition of the workpiece should be excellent from beginning to end, without harming the subsequent processing; Cutting holes and threading on the embryo material results in better processing results than cutting in the appearance design.
(3) Spark discharge forming process:
Spark discharge forming machining requires the production of both coarse and fine electrical grades. The precision electrical level is processed using CNC numerical control lathes, and the Cu-W aluminum alloy electrical level has good comprehensive performance. The electrical level loss rate is smaller than that of copper electrodes. Under excellent milling surface standards, it is difficult to process raw materials and complex parts with cross-sectional shapes; Ag W aluminum alloy has superior electrical properties compared to Cu W aluminum alloy, making it suitable for high-precision machining; Graphite electrodes use imported high-purity graphite with low wear, high strength, faster corrosion rate, and low surface roughness. Before the completion of spark discharge machining, a precise and accurate adjustment is assigned to remove the hard substrate layer generated on the surface.
4. Surface solution and precision mold assembly
(1) Surface solution:
After finishing, the surface of the workpiece is treated to address areas where there are no air holes, uniform strength, small differences in anisotropy, low impurities, and no stress such as knife marks or scratches left on the surface of the part during machining. According to the polishing, grinding and milling, the workpiece is not blunted with edge obtuse angle nozzle. After the electric machining, the surface is gray, 6~10m, and the mildew hardened bottom layer is removed. This layer is brittle and contains residual crustal stress. The hard bottom layer should be fully removed before application.
(2) Precision mold assembly:
Before assembly, sufficient demagnetization should be performed on the workpiece and the surface should be cleaned with formic acid ethyl ester. During the entire process of grinding, machining, and electrical machining, the workpiece will be magnetized to a certain extent and have very weak magnetism, making it easy to absorb some small dirt. Throughout the assembly process, it is necessary to have a sufficient understanding of the structure and technical standards of CAD part drawings, and complete various parts; Properly list the installation sequence between each component and each other; Check the specifications and precision of each component, and establish various mutual cooperation regulations; Complete the required installation special tools; Firstly, install a part of the mold guide pillar and assemble the concave mold forming block components to form a mold; Integrate the tower template with the mold base cavity to adjust the positions of each plate; Open and close the mold shell to check if the posture of the precision mold is accurate and reliable.
