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Three principles of mold selection
发布日期:2021-11-12  阅读量: 338次
(1) The mold meets the requirements of working conditions
 
  1, abrasion resistance
 
   When the blank is plastically deformed in the mold cavity, it flows and slides along the surface of the cavity, causing violent friction between the surface of the cavity and the blank, which causes the mold to fail due to wear. Therefore, the wear resistance of the material is one of the most basic and important properties of the mold.
 
   Hardness is the main factor affecting wear resistance. In general, the higher the hardness of the mold parts, the smaller the amount of wear and the better the wear resistance. In addition, wear resistance is also related to the type, quantity, shape, size and distribution of carbides in the material.
 
  2, toughness
 
  The working conditions of molds are mostly very bad, and some of them are often subjected to large impact loads, which leads to brittle fracture. In order to prevent sudden brittle fracture of mold parts during work, the mold must have high strength and toughness. The toughness of the mold mainly depends on the carbon content, grain size and organization state of the material.
 
  3, fatigue fracture performance
 
  During the working process of the mold, under the long-term action of cyclic stress, it often leads to fatigue fracture. Its forms include low-energy multiple impact fatigue fracture, tensile fatigue fracture, contact fatigue fracture, and bending fatigue fracture. The fatigue fracture performance of the mold mainly depends on its strength, toughness, hardness, and the content of inclusions in the material.
 
  4, high temperature performance
 
   When the working temperature of the mold is higher, the hardness and strength will decrease, leading to early wear of the mold or plastic deformation and failure. Because the mold material should have high anti-tempering stability, to ensure that the mold has a high hardness and strength at the working temperature.
 
  5, resistance to cold and heat fatigue
 
Some molds are in a state of repeated heating and cooling during the working process, which causes the surface of the cavity to be pulled and pressure to change the stress, causing surface cracks and peeling, increasing friction, hindering plastic deformation, and reducing dimensional accuracy. Mold failure. Hot and cold fatigue is one of the main forms of failure of hot work molds. This type of mold should have high resistance to cold and heat fatigue.
 
  6, corrosion resistance
 
  When some molds such as plastic molds are in operation, due to the presence of chlorine and fluorine in the plastic, strong corrosive gases such as hci and hf will be resolved after heating, which will erode the surface of the mold cavity, increase its surface roughness, and aggravate wear failure.
 
   (2) The mold meets the process performance requirements
 
   Mold manufacturing generally involves several processes such as forging, cutting, and heat treatment. In order to ensure the quality of mold manufacturing and reduce production costs, the material should have good forgeability, machinability, hardenability, hardenability and grindability; it should also have small oxidation, decarburization sensitivity and quenching Deformation and cracking tendency.
 
  1, malleability
 
   has low hot forging deformation resistance, good plasticity, wide forging temperature range, low forging cold cracking and low tendency to precipitate network carbides.
 
  2, annealing process
 
   The spheroidizing annealing temperature range is wide, the annealing hardness is low and the fluctuation range is small, and the spheroidizing rate is high.
 
  3. Machinability
 
   Large cutting amount, low tool loss, low surface roughness.
 
  4, oxidation, decarburization sensitivity
 
   Good anti-oxidation performance when heated at high temperature, slow decarburization speed, insensitive to heating medium, and low tendency of pitting.
 
   5. Hardenability
 
   has uniform and high surface hardness after quenching.
 
   6, hardenability
 
  After quenching, a deeper hardened layer can be obtained, and it can be hardened by using a mild quenching medium.
 
  7, quenching deformation cracking tendency
 
   The volume change of conventional quenching is small, the shape is warped, the distortion is slight, and the tendency of abnormal deformation is low. Conventional quenching has low sensitivity to cracking, and is insensitive to quenching temperature and workpiece shape.
 
   8. Grindability
 
   The grinding wheel is relatively low wear, and the non-burn limit grinding consumption is large. It is not sensitive to the quality of the grinding wheel and the cooling conditions, and it is not easy to cause abrasion and grinding cracks.
 
   (3) Mold meets economic requirements
 
  When selecting materials for the mold, the principle of economy must be considered, and the manufacturing cost must be reduced as much as possible. Therefore, under the premise of satisfying the performance, the first choice is the lower price, carbon steel can be used without alloy steel, and domestic materials can be used without imported materials.
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