The life of the mold refers to the number of production times (stamping times, forming times) that the mold can achieve under the premise of ensuring the quality of the parts, that is, the number of parts that can be formed. This includes repeated sharpening and replacement of wear parts until the main part of the mold replaces the total number of good parts formed. The following is a detailed analysis of the life of the mold:
First, the classification of mold life
Mold service life: the number of times the mold has been produced.
Mold normal life: the number of qualified products produced before the mold fails normally. The number of qualified products produced before the mold repair is called life; The number of qualified products produced after one repair of the mold and before the next repair is called the repair life. Mold life is the sum of the life and the life of each repair.
Grinding life: The mold cannot punch out the qualified parts due to normal wear and tear, and must be re-sharpened. The total number of parts stamped during the two sharpening periods is the grinding life.
Second, the factors that affect the life of the mold
Mold material: The properties of the mold material have a great impact on the life of the mold, including strength, impact toughness, wear resistance, corrosion resistance, hardness, thermal stability and thermal fatigue resistance. The type of mold material also has a great impact on the life of the mold, such as the same workpiece, using different mold materials for bending test, the results will be very different.
Surface roughness: The reduction of surface roughness can reduce the flow resistance of the blank and reduce the wear rate of the mold cavity on the one hand; On the other hand, it can reduce surface defects (such as knife marks, electromechanical melt spots, etc.) and the tendency to crack. For example, when the surface roughness of 6Cr3SiV steel refrigeration extrusion die is R1.6~1.8um, its life is about 30,000 pieces; If the surface roughness of fine polishing reaches R0.2~1.0um, the service life can be increased to 45,000~50,000 pieces.
Mold hardness: The hardness of the working parts of the mold also has a great impact on the life of the mold, but it is not that the higher the hardness, the longer the life of the mold. The hardness of the mold must be determined according to the forming properties and failure mode, and the hardness, strength, toughness, wear resistance, fatigue resistance, etc. should be matched to meet the required forming.
Mold heat treatment and surface treatment: under the condition that the mold structure, materials and use conditions remain unchanged, ensuring the quality of heat treatment and the heat treatment process adopted are the key to giving full play to the potential of mold materials and improving the service life of molds. The purpose of mold surface strengthening treatment is to obtain the effect of external hardness and internal toughness, so as to obtain a good combination of hardness, wear resistance, toughness and fatigue strength.
Mold assembly accuracy: the adjustment of the amount and uniformity of the mold clearance, increasing the contact between the mating bearing surface and the clamping surface, and ensuring the consistency of the force center of the punch and the die can improve the assembly accuracy of the mold, thereby improving the life of the mold.
The use of the mold: including the characteristics of the forging equipment (such as the accuracy and stiffness of the press), the properties of the processed material (such as the surface state, strength, hardness of the blank), the operation procedures and maintenance of the mold (such as the hot work die should be preheated before work, and the shutdown should be insulated to prevent cracking caused by thermal stress), etc., will affect the service life of the mold.
3. The life of different types of molds
Stamping die: the hardness is generally between HRC58~62, and the service life of the die depends on the hardness of the stamping. If the hardness of the material is high, the service life of the mold will not be long. If the stamping material is mild steel, the service life of the die can reach hundreds of thousands of times. Generally speaking, the life standard of stamping dies should be more than 1 million times, and some high-quality molds can even reach more than 10 million times. The mold materials of punches and dies are in the order of SKS→ SKD→ powder high-speed steel → cemented carbide, and the mold life gradually increases.
Injection mold: the design life is generally about 10 years, and the service life is generally between tens of thousands and hundreds of thousands of injection cycles. The lifespan of a plastic mold is determined by a number of factors, including material selection, design quality, usage conditions, and maintenance.
Foaming mold: the design life is about 300,000 times.
Welding mold: such as ultrasonic welding mold, the structure is simple, generally does not need to be replaced, and the service life is more than 1 million times.