Current status of the use technology of cemented carbide molds

　1.Application status of non-standard cemented carbide die blanks The so-called non-standard refers to special-shaped blanks that are not listed in the national standard.In this regard,non-magnetic molds,progressive molds,etc.are more commonly used.Non-magnetic molds are generally made of YGl5 or YG2O cemented carbide.For example,the Sichuan 899 Factory uses YGl5 to make soft magnetic stampers.Jiangxi Optical Instrument Factory uses YG2O and YG2OC as soft magnetic mirror punching molds.When the nickel-based alloy IJ5O is punched,the parallelism of the mirror surface is<0.0O5mm,and the roughness Ra<0.2Um.After using the punching technology,the machining efficiency is dozens of times higher than that of the grinding process.The No.1 Radio Factory of Zigong uses YWC non-magnetic hard alloy as the soft magnetic material forming mold,with a life span of 500,000 to 1 million times.Whether it is a single-station or multi-station progressive die,most of them choose YGl5,YG2O and YG2OC as the main ones,and some choose steel and gold.For example,the progressive die of the split wheel assembly made by the Shanghai Watch Factory made of cemented carbide has worked 2.16 million times at a stroke speed of 300-400 times/min and produced 4 million high-precision qualified products.The stator progressive die also produces nearly 1 million qualified products at a rate of 300 times/min.The stator and rotor core punching dies of Nanjing Changjiang Machinery Factory can be sharpened 500,000 times once,with a total life of 50-60 million times.The hard alloy multi-station progressive die of Jiangsu Huajing Electronics Group punches lead frame materials at a punching speed of 400-600 times/min,with a total life of about 50 million times.The progressive blanking die for electrical plug-in products of Dalian Electric Machinery Factory,after using domestic cemented carbide,has a service life of more than 70 million times and a time of more than 2 years.In recent years,cemented carbide materials have also begun to be used for powder metallurgy products forming molds.For example,the YG8 forming die can press 700,000 pieces of products per pair,while the steel die is only 1,000 times factory vice and high chromium steel vice.Huzhou Changjiang Machinery Factory uses YG8 as a bimetallic shaft sleeve shaping mold,with a life of more than 100 square parts,while the life of GCrl5 steel mold is only 1,000 pieces.

　　2.Development of new hard mold materials

　　In the development of new cemented carbide materials,the replacement of cobalt with iron and nickel has become a hot topic in the past few years.For example,the high strength and toughness cemented carbides equivalent to YG15,YG2O and YG25 developed by Hunan Metallurgical Materials have achieved good results in cold heading dies,cold extrusion dies,etc.Tianjin Cemented Carbide Research Institute also uses iron Nickel to cobalt has developed a cemented carbide die material equivalent to GY(15-20),which is equivalent to YG2O in rolling forging of standard parts and cold forging of steel balls.In recent years,new research hotspots are fine-grained,ultra-fine-grained,and even nanocrystalline cemented carbide and gradient cemented carbide.Gradient cemented carbide has composition gradients,structural gradients,etc.In addition,molten metal infiltration treatment methods are also used to produce gradient cemented carbides,such as gradient cemented carbide top hammers.Fine-grained and ultra-fine-grained cemented carbides are also available.For example,the fine-grained YG8 wire drawing die is 3 times that of the general wire drawing die when drawing steel wires less than 1mm.In addition,there are hot work molds for inlay casting and inlaid hard alloy,which have achieved good results in rolling pipes and wire rods.Cemented carbide blanks of the material,after being processed into molds,have a long service life and some have a short service life.After anatomical analysis,it was found that the problem lies in the design,processing,assembly,and welding.

　　1.Technical status of cemented carbide die design

　　The wire drawing die is a die with a relatively simple structure.Before the 1980s,our country had always used the"straight line"theory design of the former Soviet Union.Only after the 1980s,some manufacturers used the"smooth transition"technical theory proposed in the 1950s.

　　In recent years,Chinese scholars have carried out angle design and theoretical analysis of ring groove wear on drawing dies,put forward the concept of maximum and minimum drawing angles,and analyzed the mechanism of uneven wear of metal in the process of tensile deformation.Researchers from Guangdong Institute of Technology conducted anatomical analysis of hard alloy molds for cold-heading small-size screws,and found that domestic molds have low life(2-4 million cycles)and Japanese molds have high life(9-10 million cycles).,Its key technology is the design of the angle.That is,the Japanese mold adopts a double-convex design at the contact part between the bottom of the mold core and the bottom surface of the inner hole of the mold sleeve.Its advantage is that the central part with the greatest force can be pressed tightly,and the space left around can be used to store the excess metal extruded from the hole wall when the interference fit.The cemented carbide die used for cold pier Ml2 nuts was changed from the original hexagonal design to six-petal braided inserts and used by Shenyang Bridge Factory.Its average life span is 500,000 pieces/mold,and as high as 1.2 million pieces/I think this design is more reasonable.First,it saves cemented carbide than the overall structure design mold;second,it is easy to assemble;third,mold replacement is easy.The damaged one can be replaced.

　　2.The influence of processing and assembly technology on cemented carbide molds

　　The dimensional accuracy and shape and position accuracy of cemented carbide molds are achieved by grinding.Because the grinding force of cemented carbide is 2-3 times that of general steel.Therefore,the grinding machine is required to have high power and high rigidity.As far as my country's current machine tool level is concerned,there is no special grinding machine for processing cemented carbide.Therefore,machining errors are often caused,and the cumulative effect of errors will seriously damage the service life of the mold.In the process of EDM,because the mold material is subjected to high temperature up to 10000℃and the action of the liquid medium at the moment of discharge,the surface layer will undergo changes in the metallographic structure,and there may be carburization(carbon in the working fluid).Metal infiltration(copper-tungsten electrode),and even the appearance of micro-cracks,will undoubtedly affect the life.The insert is to make the alloy can withstand greater impact and extrusion load.Whether it is hot-pressed inserts or cold-pressed inserts,the clearance requirements are very strict.Generally,the interference of 0.03-0.05mm is selected for cold press inserts,0.08-0.1Omm for hot press inserts,700-800℃for cavity sleeve heating,and 300℃for cemented carbide.After the hot pressing is completed,it is placed in a 600 box furnace for 2 hours to eliminate stress.

　　Cemented carbide welding is also a key technology.Generally,brazing is often used.Hunan Institute of Metallurgical Materials once developed a nickel-based brazing filler metal for Xi’an Aircraft Engine Manufacturing Company,which has achieved good results in brazing hard alloys in a vacuum furnace.