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Precision machining process control of die parts

Return list Reffer:NITONI Click number:- Release time:2018-01-06

Each mold is made up of many parts, some of which are process parts, and the other part is structural parts.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 empirical methods worth reference.

Precision machining process control of die parts

Process control of die finishing

The processing of mould parts, the general guideline is to adapt to different mold parts, different materials, different shapes and different technical requirements.However, through the control of the process, the best processing effect and economy is our focus.According to the appearance of mould parts, the parts can be divided into three categories: axial, disc, plate and shaped.The process of these three kinds of parts is generally: rough machining - semi - precision machining - (quenching and conditioning) - precision grinding - electroprocessing - fitter finishing - assembly machining.

1. Heat treatment of mould 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.Its process is to consider economy, material hardenability, quenching, heat 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.Such materials have high thermal stability and good organizational status.After quenching, the general workpiece has the internal stress, which can lead to the cracking in the following finishing or work. After the parts are quenched, it should be hot tempered to eliminate the quenching stress.The workpiece with complex shape and more inner and outer corner is not sufficient to eliminate the quenching stress, and the stress annealing or multiple aging treatment should be carried out before finishing, and the stress can be fully released.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 guarantee the hardness of the workpiece and reduce the deformation of the workpiece, which is widely used in the complex deformation of the workpiece.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 mould parts

There are three main types of grinding machine tool: surface grinding machine, internal and external cylindrical grinding machine and tool forming grinding machine.It is necessary to strictly control the appearance of grinding and grinding cracks when grinding and grinding, even if it is a microscopic crack in the workpiece surface, it will gradually show up in the subsequent work.Accordingly, the feed knife of precision grinding should be small, the cooling should be sufficient in grinding, choose coolant medium as far as possible, the part that the processing allowance is in 0.01mm should be kept as constant as possible grinding.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 machining of plate and plate parts is mainly used in surface grinding machine, and it is difficult to process long thin sheet.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, through the grinding method of as mentioned above can improve most of the flatness of workpiece, such as through a grinding process to reach the ideal effect of flatness, can you repeat the above process 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 characteristics of shaft parts are composed of multiple rotary surfaces, and the ultimate precision machining method of modern enterprises is generally used for grinding of internal and external cylindrical grinding machines.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.

3. Electric machining of mold parts

Modern mold enterprise, almost has no shortage of machining, because electric processing can be of different types, and various types of mold processing or high hardness parts effectively and therefore have become an indispensable of mould manufacturing and metal processing industries processing means.The processing technology of the slow-moving silk thread is obtained from the information of the feedback from the enterprise: the precision can be reached plus or minus 0.002 mm, and the roughness Ra= 0.4mu m.For machining precision, at the beginning to check the status of the wedm, to see the ionized water deionization degree, ionized water temperature, wire cutting, wire verticality, tension, cutting wire, cut the workpiece material, and other factors, to ensure good processing speed and accuracy.For linear cutting processing, it is a whole piece of billet in a processing of resection or cutting material, so the original stress balance is destroyed in the process of machining, cause stress concentration around the corner, when the corner radius R < 0.2, should suggest improving the structure of the mould design department.Processing method of stress concentration, but by using the principle of the vector translation, finish machining allowance for 0.8 ~ 0.9 mm, before rehearsals cavity rough shape, and then to heat treatment, machining stress release before finishing, as far as possible to ensure that the thermal stability.The cutting of the cutting filaments should be considered carefully when machining the convex mold.Selecting the position of the holding billet should be in the first time after the input, the workpiece is not the wall shape, always make the workpiece stressed state good, does not affect the subsequent several times processing;For the high requirement of the punch, can be perforated through the raw material, the processing effect is better.The high precision workpiece is widely used to ensure the quality of parts.When die thickness direction to be part of the taper machining, in the pursuit of efficient processing, usually for the first time rough machining straight edge, and the second time taper machining, the third time to finish straight, such a process is characterized by, no longer need to taper edge of existing vertical finishing, just finish machining of blade section straight edge, the fourth times refinement straight edge again.The machining of edm is to make coarse and fine electrode.The machining electrode requires the shape of the cavity to be good, and the good fine electrode has been finished by CNC CNC machine.Electrode material selection, the copper electrode is mainly used for general steel parts processing;Cu - W alloy electrode, comprehensive performance is good, especially in the process of machining electrode wastage is smaller than copper electrode obviously, under the condition of good chip removal, and cross section shape of complex parts finishing for difficult-to-machine materials have very well;The electrode performance of Ag-W alloy electrode is better than that of Cu-W alloy electrode.And graphite electrode, has been widely used, there are domestic graphite and graphite, graphite import with low loss, high hardness, fast electric erosion, low surface roughness, advantage, has been applied in many complex pieces of finishing.When the electrode is designed, the clearance volume of the electrode and the number of electrodes are calculated.When the large area or heavy electrode is processed, the workpiece and electrode clamping should be firm, with certain strength, preventing the process from loosening.But after the edm surface is much more difficult than ordinary mechanical processing or the surface of the heat treatment after grinding, so fine gauge should be used before the end of edm dressing, remove the surface hardening thin layer.

4. Surface treatment of mould parts

Forming the content of the surface treatment, include steel pore-free, uniform hardness, low anisotropy characteristic difference is small, inclusions and leave a mark, when machining parts surface grinding marks such as stress concentration area.Therefore, after finishing the processing, the surface of the parts should be strengthened, through mechanical polishing, grinding, polishing and processing of the hidden trouble.The workpiece is useless edge, acute Angle, hole is obtuse.Generally, machining surface of metamorphic hardening layer 6 ~ 10 microns, are pale color, and the brittle layer and residual stress, before use to fully eliminate the hardening layer, method for surface polishing, grind hardened layer.Want to obtain high-quality polishing effect, workpiece material, shape, hardness as well as the machining surface quality to have sufficient consideration, must have a high quality of the polishing tools, high-quality polishing material, polishing process of the right, rigorous of personnel quality, good clean environment.

5. Assembly of mould parts

In grinding processing, machining process, the workpiece can be magnetized, with weak magnetic, easy adsorption of small sundry, so before assembly, shall make sufficient demagnetization of the workpiece, and acetic acid ethyl ester to clean the surface.In the process of assembly: (1) first understand the assembly drawing and match all kinds of parts;(2) list the assembly sequence of each component;(3) check the dimension accuracy of each part and make clear the requirements of the matching;(4) assemble the required tools and then set about assembling the mould;(5) the lead guide sleeve of the die frame part and the assembly of the components of the cavity forming block;(6) combination of the set plate and the convex die and the concave mold, and the position of each plate in the microadjustment;(7) open the mould and check whether the mold action is reliable.

Numerous practice proves that mould enterprises pay attention to the process control of the precision machining process, which is the long-term and effective way of survival and development of mold enterprises.The process control can minimize the difference and scrap of the parts, so as to effectively improve the life of the mould in the production and use, and the stable product quality has profound significance.

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