Influence of Process and Assembly Technique on Tungsten Carbide Moulds
The size and geometry tolerances of the tungsten carbide moulds are achieved by grinding process.As the grinding force on the carbide moulds is 2~3 times more than the normal steel parts,which requires the grinding machines with large power and high rigidity,thus we do not have the special machine to grind the tungsten carbide parts basing on current machine technology.Therefore,it is inevitable that the tolerance deviated,especially with accumulation of deviated tolerance,resulted in serious damage to the moulds' service life.In electricity discharge blink of the EDM process,the carbide mould material is effected integratedly by up to about 10000℃ high temperature and liquid medium,leading to the change of surface metallurgical structure,carburization, metallic cementation,even micro-cracks emerged,that influence its service life certainly.
In order to make the tungsten carbide moulds bearing more shocking and extruding load,they are inlayed with steel sleeves,but no matter it is hot-press or cold-press inlaying,there is very strict clearance requirement,usually for the cold-pressing process,it is 0.03~0.05mm interference amount,but is 0.08~0.1mm for hot one with 700-800℃ heated on the steel body and around 300℃ on the carbide part.After hot-press work,they have to be put in the box type furnace with temperature 600 ℃ for 2 hours,so as to eliminate stress.
