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Three principles of mold material selection

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Mold selection is an important process in plastic injection molding. For best results, it is important to understand the principles of mold selection. This article discusses three of these principles.

By understanding these principles, you can make better decisions when selecting molds for your project. Stay tuned for more information on this topic!

1. The mold meets the requirements of working conditions

Wear resistance

When the blank is plastically denatured in the mold cavity, it flows and slides along the surface of the cavity, causing severe friction between the surface of the cavity and the blank, resulting in the failure of the injection mold 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.

Strong toughness

Most of the working conditions of the injection mold are very harsh, and some often bear large impact loads, resulting in brittle fractures.

To prevent sudden brittle fracture of injection molded 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 organizational state of the material.

Fatigue fracture performance

During the working process of the mold, under the action of cyclic stress, it often leads to fatigue fracture. Its forms include small energy multiple impact fatigue fracture, tensile fatigue fracture, contact fatigue fracture, and bending fatigue fracture.

The fatigue fracture performance of the injection mold mainly depends on its strength, toughness, hardness, and the content of inclusions in the material.

High-temperature performance

When the working temperature of the mold is high, the hardness and strength will decrease, resulting in early wear or plastic deformation of the mold and failure.

Therefore, the mold material should have high stability against tempering to ensure that the injection mold has high hardness and strength at working temperature.

Cold and heat fatigue resistance

Some molds are in the state of repeated heating and cooling during the working process, so that the surface of the cavity is subjected to tension, pressure, and stress, causing surface cracks and peeling, increasing friction, hindering plastic deformation, and reducing dimensional accuracy, resulting in Mold failure.

Cold and heat fatigue is one of the main forms of failure of hot work dies, and the molds for supporting pictures should have high resistance to cold and heat fatigue.

Corrosion resistance

When some molds such as plastic injection molds are working, due to the presence of chlorine, fluorine, and other elements in the plastic, they decompose and decompose strong corrosive gases such as HCI and HF after heating, which erodes the surface of the mold cavity, increases its surface roughness, and aggravates wear and tear failure.

2. The mold meets the process performance requirements

The manufacture of injection molds generally goes through several processes such as forging, cutting, and heat treatment.

To ensure the manufacturing quality of the mold and reduce the production cost, the material should have good forge ability, machinability, hardenability, hardenability and grind ability; it should also have small oxidation, decarburization sensitivity, and quenching Deformation cracking tendency.

Forgeability

It has low hot forging deformation resistance, good plasticity, a wide forging temperature range, a low tendency of forging cracking, cold cracking, and precipitation of network carbides.

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.

Machinability

The cutting amount is large, the tool loss is low, and the machined surface roughness is low.

Sensitivity to oxidation and decarburization

When heated at high temperatures, it has good anti-oxidation capacity, slow decarburization speed, insensitive to heating medium, and has little pitting tendency.

Hardenability

After quenching, it has a uniform and high surface hardness.

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 cracking sensitivity and is insensitive to quenching temperature and workpiece shape.

Grindability

The grinding wheel is relatively small in loss, and the amount of grinding without a burn limit is large. It is not sensitive to the quality of the grinding wheel and cooling conditions, and it is not easy to cause abrasion and grinding cracks.

3. The mold meets the economic requirements

When selecting mold materials, the principle of the economy must be considered to reduce injection molding industry manufacturing costs as much as possible.

Therefore, under the premise of satisfying the use performance, first, choose the one with a lower price, if carbon steel can be used, alloy steel is not used, and if the material produced by pictures can be used, there is no need to import the material.

In addition, the injection molding process production and supply situation of the market should also be considered when selecting materials, and the selected steel types should be as few as possible and concentrated, and easy to purchase.

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