Plastic molds include thermoplastic molds and thermosetting plastic molds. Plastic mold steel requires a certain strength, hardness, wear resistance, thermal stability and corrosion resistance and other properties. In addition, it is also required to have good manufacturability, such as small heat treatment deformation, good processing performance, good corrosion resistance, good grinding and polishing performance, good repair welding performance, high roughness, good thermal conductivity, and stable size and shape of working conditions Wait. Under normal circumstances, injection molding or extrusion mold can choose hot die steel; thermosetting forming and requiring high wear resistance, high strength mold can choose cold die steel.

The United States according to the mold service conditions will die steel is divided into four categories, the American Institute of Metal Tool Steel Committee listed: cold work die steel, hot work die steel, plastic mold steel, plastic mold steel and other four categories. Among them, cold work die steel is divided into 12 sub-categories, hot work die steel 9 sub-categories, plastic die steel 2 sub-categories, plastic die steel 5 sub-categories. The selection of each subclass depends on three main factors:

The complexity of size and shape,

◆ The material being processed,

◆ Durability requirements or design life.

The United States is the first in the tool steel listed in the plastic mold special steel countries, to P to represent the main, divided into five categories.

◆ Carburized plastic mold steel: P1,P2,P3,P4,P5,P6. This kind of steel carbon content is very low, mainly in the early United States and extrusion molding method, requires good cold plasticity, high extrusion performance, after forming surface carburizing quenching to improve surface hardness, long service life. The ultra-low carbon core can minimize the amount of deformation during quenching.

◆ tempered plastic mold: P20,P21. The amount of P20 in the plastic mold is very large and has become the main body, most of which are used in the pre-hardened state.

◆ Medium carbon alloy tool steel is used for thermosetting plastic mold. Steel grade H13, while L2 and S7,O1 and A2 also have applications. Features of this class are:

(1) It is basically a secondary hardening gold steel with good thermal strength at 500-600oC.

(2) high chromium content, good atmospheric corrosion.

(3) Excellent hardenability, suitable for large modules.

◆ Stainless steel is used for plastic molds with high corrosion resistance requirements. The main steel grades are 420,414L,440,416.

The aging steel is through aging treatment to obtain high performance. There are two kinds, one is P21 low carbon Ni-A1 aging steel; the other is 18Ni maraging steel. The latter is a carbon-free high-purity, high-strength, high-toughness material used in the aerospace industry. It is used in plastic molds with high mechanical properties, dimensional accuracy, smoothness and corrosion resistance.

Selection of plastic mould steel

For thin-walled plastic boxes, when the production batch is less than 100000 pieces, P20 and P21 are used in pre-hardened state (HB 250~300), and 414L is used when the corrosion is strong.

High life of ordinary plastic mold, with P6 or P20, after carburizing quenching hardness in HRC54-58; plastic parts are not too large, available O1,S7. Use 420 when corrosive.

Non-high temperature thermosetting mold with P6,P20 after carburizing quenching use. Strong corrosive 420.

High temperature thermosetting plastic mold with H13 and S7 or carburized steel P4. These chromium-containing higher have good tempering resistance and high temperature oxidation resistance.

Plastic mold steel is divided into pre-hardened ordinary plastic mold steel, pre-hardened high-quality plastic mold steel, pre-hardened high-hardness plastic mold steel, pre-hardened anti-corrosion mirror plastic mold steel, anti-corrosion mirror plastic mold steel 5 small types of plastic mold steel quality grade distribution

The mold category is divided into the following categories according to the American SPI-SPE.

1. 101 type mold (SPI-SPE standard 1,000,000 beer or above, long-term precision production mold)

1. Detailed mold structure diagram is required.

2. The lowest hardness of mold blank material is 280BN. (DME #2 steel/4140 steel)

3. The inner module steel with glue position must be hard to 48 ~ 50HRC. Other parts such as row position, press lock, press strip, etc. shall also be hardware.

4. The thimble plate shall have guide posts.

5, the row position should have hard film.

6, if necessary, the upper mold, lower mold and row position should have temperature control.

7. For all waterways, it is recommended to use electroless nickel immersion or 420 stainless steel as formwork. This will prevent rust and clean up rubbish.

8, need straight body lock or oblique lock.

2. 102 class module. (No more than 1,000,000 beer, mass production mold.)

1. Detailed mold structure diagram is required.

2. The minimum hardness of mold blank material is 280BHN. (DME #2 steel/4140 steel)

3. The steel of the inner module with glue position shall be hard to a minimum of 48 ~ 52HRC, and other useful parts shall also be treated in the same way.

4. It is recommended to use straight body lock or oblique lock.

The following items may or may not be required. Depending on the final production quantity. It is suggested that if the following items are used in quotation, check whether it is necessary:

A, thimble plate guide post.

B, row bit hard film.

C, electroplating water transport hole.

D, electroplating mold cavity.

3. 103 models (less than 500,000 beer, medium production models.)

1. Detailed mold structure diagram is required.

2. The minimum hardness of mold blank material is 165BHN. (DME #1 steel/1040 steel)

The inner mold steel is P20(28 ~ 32HRC) or high hardness (36 ~ 38HRC).

4. The remaining requirements depend on the needs.

4. 104 models (less than 100,000 beer, a small number of production models)

1. Mold structure diagram is required.

2. Mold blank material P20(28 ~ 32HRC) can be mild steel or aluminum. (1040 steel)

3. The inner module can be aluminum, mild steel or other approved metal.

4. The remaining requirements depend on the needs.

5. 105 class module. (Less than 500 beer, first mold or test mold)

Aluminum cast iron or epoxy resin or any material with sufficient strength to produce the minimum number of tests may be used.