Precision Machining Process Control of Mould parts


Each set of molds is made up of many parts, one of which is a process part, the other is a structural part. Craft parts directly affect molding product quality, process the final quality of parts in the present mould processing enterprises finish machining method to finally complete, how to control the precision machining process is related to die life and forming products can be delivered.

In mould manufacturing enterprise, the finishing stage except by wire cutting, cutting more than one repair technology method, the other methods is after semi-finishing grinding machining and heat treatment on the basis at this stage to control the deformation and internal stress of part, many technical parameters such as shape tolerance and dimensional accuracy. In the specific production practice, the operation is more difficult, but there are still many effective experience methods worth learning.

I. process control of mold finishing
The general guiding idea of mould parts processing is to carry out adaptive processing for different mould parts, different materials, different shapes and different technical requirements. However, through the control of the processing process, to achieve the best processing effect and economy is our focus. According to the appearance shape of mould parts, parts can be divided into three categories: shaft, disc, plate and forming parts. The process of these three types of parts is generally: roughing -- semi-finishing -- (quenching, tempering) -- precision grinding -- electrical processing -- fitter dressing -- assembly processing.

(1) heat treatment of mold parts
Mold parts to obtain the required heat treatment hardness, necessary to control stress in heat-treatment, make the parts processing and processing after the size tolerance, form tolerance can be stable, in view of the different material parts, have different ways of heat treatment. The process should consider economy, material hardenability, hardenability, overheat sensitivity and decarbonization sensitivity. With the development of the mould industry in recent years, the materials used in a lot of more phyletic, besides CrWMn, Cr12, 40 cr, GCr15, Cr12MoV, 9 mn2v carbide, for some working intensity big, stress demanding concave die and punch, can choose new materials of powder alloy steel, such as S2, S3, V10, APS23S1, G2, and G3, G4, the G8, and so on. This kind of material has high thermal stability and good tissue state.

Generally, the internal stress of the workpiece remains after quenching, which is easy to lead to subsequent finishing or cracking in work. For the workpiece with complex shape and many internal and external rotating angles, tempering is sometimes not enough to eliminate the quenching stress. Before finishing, it is necessary to carry out stress-relieving annealing or multiple aging treatment to fully release the stress. Take different approaches according to different requirements. For Cr12 material parts as example, the quenching treatment after rough machining, when the quenching cooling alone are: air cooling (puts the artifacts of the heated air cooling, this method is simple, small deformation, but the hardness is low, easy oxidation of the surface. Suitable for small size, high precision, uneven thickness of the workpiece), oil cooling (puts the workpiece heated oil, cooled to 300 ℃ ~ 200 ℃, remove the cooling in the air. This method is simple, the workpiece hardness is higher, but the deformation is bigger, is easy to produce deformation of workpiece, is suitable for the larger size, shape, simple artifacts), plate clamp (cooled in the air after heating the workpiece on compaction, between two pieces of iron or copper cooling in the air. Synthetic process is relatively complex, but the workpiece deformation is small, only suitable for some special shape of the workpiece), interrupted quenching (heat the workpiece rear nitrate than Ms point temperature, stay time, DaiGong parts inside and outside temperature are basically identical, remove the cooling in the air. This method can not only guarantee the hardness of the workpiece, but also reduce the deformation of the workpiece. It is widely used for the workpiece with complex shape and small deformation requirements. Powder alloy steel parts, such as the V10, APS23 because its can bear high temperature tempering, quenching can be adopted when the secondary hardening process, 1040 ℃ ~ 1080 ℃ quenching, with 490 ℃ ~ 520 ℃ high temperature tempering and for many times, can obtain higher impact toughness and stability, to collapse as the main failure forms of blade mould.

(2) grinding and processing of mold parts
There are three main types of machine tools used in grinding: surface grinding machine, internal and external circular grinding machine and tool forming grinding machine. In precision grinding, grinding deformation and grinding cracks should be strictly controlled, even microscopic cracks on the workpiece surface, otherwise they will gradually appear in subsequent work. Therefore, in precision grinding, the amount of feed knife should be small, the cooling should be sufficient during grinding, the coolant medium should be selected as far as possible, and the parts with the machining allowance within 0.01mm should be grinded at a constant temperature as far as possible.
When grinding the workpiece must be cautious to choose grinding wheel: in view of the die steel with high tungsten, vanadium, molybdenum, the condition of high alloy, the characteristics of high hardness of workpiece, can choose PA chrome steel and GC green silicon carbide grinding wheel; When processing hard alloy, high quenching hardness of the material, the priority of using organic binder of diamond grinding wheel, organic binder grinding wheel since sharpen and grinded workpiece precision above IT5, roughness of Ra = 0.16 microns. With the use of new materials in recent years, the application of CBN cubic nitride borax wheel, showed a good processing effect, both inside and outside the nc forming grinding, jig grinding machine, CNC grinding machine on finishing, even better than other kinds of grinding wheel. To timely dressing grinding wheel in grinding process, keep the wheel sharp, when grinding wheel after passivation can slip on the workpiece surface wipe, score, extrusion, surface caused by burn, microscopic cracks or producing grooves, to significantly reduce the use of utility in the future.

The processing of disc and plate parts is mostly made by surface grinding machine. It is difficult to process long and thin sheet parts. Before processing under the force of grinding magnetic table, there is some original bending stress produced deformation, flat against the surface of workbench, after grinding, the workpiece and the original stress under the action of deformation response, measure the thickness of panel is displayed when is consistent, but as a result of deformation response, flatness, could not reach the requirements of the mould parts should be before the solution is grinding with high iron mat underneath the artifacts, walking around with stop blocking artifacts to prevent, when grinding head grinding feed quantity is smaller, feeding mode had been used to complete the first datum plane, after the first reference plane processing good side, you can use this reference plane adsorption on the magnetic table, The grinding method mentioned above can improve the planeness of most workpieces. For example, if a grinding process cannot achieve the desired planeness effect, the above process can be repeated again. After a few such grinding can in flatness shall conform to the requirements, but for the thickness of the panel size have strict requirements, must according to the workpiece material, shape, material, machining means, comprehensive factors such as heat treatment method, add put appropriate thickness allowance.

The characteristic of shaft parts is that they are composed of several turning surfaces. During processing, the use of grinding machine clamp head and tail top positioning clamping work-piece or two thimbles with fore and aft positioning the workpiece, the chuck and the center of the thimble attachment is the center of the workpiece after grinding if the center line of the beating, the workpieces can produce different heart problems, therefore before processing to chuck and top concentric detection and fore and aft to check in. If it is to use thimble clamping chuck with the center axis positioning a grinding steps, is before this time grinding to the clamping part x advanced grinding, once through the clamping can centering position during grinding. Book clamping process should consider when wall inner hole grinding machine, namely the more you deliberately in machined part a thick wall, left for grinding inner hole after complete resection, if not process machine clamping force is too large, otherwise easy to produce in the workpiece circular "triangle" deformation, every time the same grinding feed quantity is smaller, by eligibility requirements can feed grinding out many times, and grinding coolant should fully in the process of spray to be grinding position, in order to make the iron filings and abrasive grinding out dust particles can smooth discharge grinding area.