A mold is composed of many parts. The quality of the parts directly affects the quality of the mold, and the final quality of the parts is guaranteed by the finishing. Therefore, it is important to control the finishing. Most mold manufacturing companies generally use grinding, electrical machining and fitter processing in the finishing stage. At this stage, it is necessary to control many technical parameters such as part deformation, internal stress, shape tolerance and dimensional accuracy. In the specific production practice, the operation is more difficult, but there are still many effective empirical methods that are worth learning.
Process control of mold finishing
The processing of mold parts can achieve good processing results by controlling the processing. According to the different appearance and shape of the parts, the parts can be roughly divided into three categories: shafts, plates and special-shaped parts. The common process is roughly: rough machining-heat treatment (quenching, quenching and tempering)-fine grinding-electric Processing-fitter (surface treatment)-assembly processing.
Heat treatment of parts
In the heat treatment process of the parts, while obtaining the required hardness of the parts, it is also necessary to control the internal stress to ensure the dimensional stability of the parts during processing. Different materials have different treatment methods. With the development of the mold industry in recent years, the types of materials used have increased. In addition to Cr12, 40Cr, Cr12MoV, and cemented carbide, for some convex and concave molds with high working strength and severe stress, new materials powder alloy steel can be used. , Such as V10, ASP23, etc., this kind of material has high thermal stability and good organization state.
For parts made of Cr12MoV, quenching is performed after rough machining. After quenching, the workpiece has a large residual stress, which is easy to cause cracks during finishing or work. After quenching, the parts should be tempered while hot to eliminate quenching stress. The quenching temperature is controlled at 900-1020℃, then cooled to 200-220℃, air-cooled, and then quickly returned to the furnace for tempering at 220℃. This method is called a primary hardening process, which can obtain higher strength and wear resistance. The mold that is the main failure mode works better.
For powder alloy steel parts such as V10, APS23, etc., because they can withstand high temperature tempering, the secondary hardening process can be used during quenching, 1050-1080℃ quenching, and then 490-520℃ high temperature tempering many times to obtain higher Impact toughness and stability are very suitable for molds with chipping as the main failure mode. The cost of powder alloy steel is relatively high, but its performance is good, and it is forming a trend of widespread use.
Grinding of parts
There are three main types of machine tools used in grinding: surface grinders, internal and external cylindrical grinders and tool abrasives. During finishing grinding, grinding deformation and grinding cracks must be strictly controlled. Even very small cracks will be exposed in the subsequent processing and use. Therefore, the feed of the fine grinding should be small, not large, the coolant should be sufficient, and the parts with the size tolerance within 0.01mm should be ground as much as possible at a constant temperature. From the calculation, it can be seen that for a 300mm long steel, when the temperature difference is 3℃, the material will have a change of about 10.8μm, 10.8=1.2×3×3 (1.2μm/℃ per 100mm deformation), and each finishing process needs to fully consider this The influence of one factor.
Practice has proved that good precision machining process control can effectively reduce the over-tolerance and scrapping of parts, and effectively improve the first-time success rate and service life of the mold.
Post time: Aug-14-2021