One, the difference between fine die and ordinary die
We often say fine blanking mold, refers to the strong pressure plate fine blanking. PR- gear ring force, PS- hidden force, pg-back pressure. The basic principle of fine blanking is to use special structure of the mold, in the pressure machine, under the action of strong force, the material produces plastic deformation, so as to obtain high quality fine blanking parts.
Fine die and ordinary die in the structure of the difference is: fine die structure than ordinary die to much more robust, much higher precision, much smaller gap. The precision die has a v-ring blanking ring in which the material is blanked under the clamping of the blanking ring and the die, the reverse pressing plate and the punch. This process requires that the blanking force and back pressure are greater than the unloading force and the top pressure, so the force of the precision mold is larger than the ordinary mold, and the rigidity is higher.
Crl2MoV steel is usually chosen as the material of the fine die, and W6Mo5Cr4V2 high speed steel can be used when the thickness is greater than 4mm. P/m steel or cemented carbide can be used for high volume, complex shape and poor stress conditions of fine die, or in recent years introduced several new steel materials, such as YG20 cemented carbide, 7Cr4Mo2VSi steel, GT35 cemented carbide and CG2 fine die materials need to be treated before use. Concrete is:
I forging technique
Taking Crl2MoV billet as an example, the forging of fine die billet requires carbide uniformity of more than 3 grades, so the bar with better quality should be selected as the die billet. The forging process is preheated to 880 ~ 900℃ and the holding time is 1min/mm. It was heated at 1080 ~ 1100℃ for 1.5min/mm. During the forging process, up forging and drawing lengths were carried out 6 times. Forgings are completed at 900 ° c and insulated at 550 ° c.
Heat treatment process
Taking Crl2MoV steel die as an example, stress relief annealing should be carried out after rough machining to eliminate the stress of die head and reduce its deformation. The quenching temperature is 30 ~ 50℃ higher than normal, the high-temperature tempering process is (720 ~ 760) ℃× (4 ~ 6) h, and the furnace is cooled to 500℃ before air cooling. When the cutting edge shape of Crl2MoV steel die is simple and the blanking tool is thin (≤3mm), the final heat treatment can adopt one-step hardening process; If the blade shape is complex and the workpiece is thick (> 3mm), a secondary hardening process is used.
For heat treatment of W6Mo5Cr4V2 high speed steel, low temperature quenching should be adopted to obtain higher mechanical properties of fine blanking die.
Surface strengthening technique
Fine mold requires high blanking accuracy, high hardness, high wear resistance and high service life. There are three methods of surface reinforcement:
The first method is to change the chemical composition of the die surface, such as metal, carburizing, nitriding, boron and TD treatment. The second method does not change the chemical composition of the die surface, such as laser quenching, low temperature and ultra-low temperature treatment; The third method is to form hardened layers on the surface, such as hard chrome plating, thermal spraying, VCD, PVD, etc., to form TiC, TiN and other superhard substances on the surface of the mold.
After surface strengthening treatment, the fine die can obtain good internal toughness, high surface hardness, wear resistance, heat resistance, corrosion resistance, bite resistance and high fatigue resistance and other special comprehensive performance, can improve the service life of finishing mill.