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

◆ complexity of size and shape,

◆ processed materials,

◆ Durability requirements or design life.

Cold work die steel

(1) Divided into five groups: Group W, Group O, Group A, Group D, and Group S.

◆ Group W is water-quenched mold steel. There are 11 steel types and 7 carbon mold steels. The carbon content is from 0.7% to 1.3%.

◆ Group O is oil-quenched cold-working die steel (commonly known as oil steel). There are 4 steel types with a carbon content of 0.85% -1.55%.

◆ Group A is an air-quenched medium alloy cold work die steel. There are 9 steel grades with carbon content from 0.5% to 2.25%.

◆ Group D is high-carbon and high-chromium cold-working die steel. There are 7 steel types with a carbon content of 0.9% -2.5%.

◆ Group S is impact-resistant tool steel. There are 7 steel types with a carbon content of 0.4% -0.6%.

Also used in cold work molds are high-speed steel (HSS group) and ultra-high-speed steel (SHSS group), cobalt-based cemented carbide and steel-bonded cemented carbide (HA group), powder steel and engineering ceramics (PIM group), carbon tungsten Tool steel (group F), special purpose tool steel (group L).

(2) Selection of cold-rolled die steel

The main series of cold-rolled die steel is high-hard cold work, which is mainly used for molds that require high compression resistance and wear resistance. The hardness is higher than HRC60-62. For molds that require impact resistance and high toughness, the hardness is lower than HRC60-62. Type S and some types of A and the most common quenched and tempered steel, spring steel, hot work mold or base steel are mainly used. For large stamping dies, such as automotive stamping parts, cast iron is mainly used. Zinc-based alloys or polymer composites are simple or have a small life.

The use of high-speed steel and ultra-high-speed steel in cold work molds has grown rapidly. This is mainly due to the high "compressive strength / hardness" ratio. And hardness can be selected between HRC60-70.

Powder mold steel has excellent abrasion resistance, hardness is not high, HRC60-62, and there are quite a lot of applications.

Carbon tool steel still has a certain range of applications in punches or soft material stamping dies with a life of 100,000 pieces.

Hot rolled die steel

American hot-rolled mold steel is divided into two categories: hot-rolled mold steel, and super hot-strength alloys.

Because hot-rolled molds work under the conditions of temperature, the materials are required to have thermal strength and thermal wear resistance. In order to ensure the service life of the molds, the molds must be cooled. The hot-cooled alternate molds will crack, that is, thermal fatigue cracks. It also requires crack resistance and thermal fatigue resistance.

Material selection according to the main series of heat resistance:

Low alloy quenched and tempered die steel (6G, 6F2, 6F3) → medium chromium hot work die steel (H11, H12, H13) → tungsten hot work die steel (H21, H22).

Non-standard hot work die steel: such as age hardened 6H4 for hot upset dies. When H11, H12, and H13 are not used to meet the thermal wear resistance, you can choose 6H1, 6H2.

When the mold is required to be hot-wear-resistant, D2, D4 → M2, M4 → powder steel can be selected. The high temperature abrasion resistance of steel-bonded cemented carbide and cobalt-based cemented carbide is very high, but its thermal fatigue resistance (that is, cold and hot anti-fatigue cracks) is poor, and it cannot be used under rapid cooling and hot conditions.

Plastic mold steel

The United States is the earliest country to list special steel for plastic molds in tool steel. It is mainly represented by P, which is divided into five categories.

◆ Carburized plastic mold steel: P1, P2, P3, P4, P5, P6. The carbon content of this type of steel is very low, mainly in the early United States and by extrusion molding. It requires good cold plasticity and high extrusion performance. After carburizing, the surface is carburized and quenched to increase surface hardness and have a long service life. Ultra-low carbon in the core minimizes deformation during quenching.

◆ Tempered and tempered plastic mold: P20, P21. The amount of P20 in plastic molds is large and has become the main body. Most of them are used in the pre-hardened state.

◆ Medium carbon alloy tool steel is used for thermosetting plastic mold. Steel grades are H13, while L2 and S7, O1 and A2 are also used. The characteristics of this category are:

(1) Basically belongs to secondary hardening gold steel, with good heat strength at 500-600oC.

(2) High chromium content and 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.

◆ Aging steel is obtained through aging treatment to obtain high performance. There are two types, one is P21 low-carbon Ni-A1 aged steel; the other is 18Ni martensitic aged 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 that require high mechanical properties, dimensional accuracy, smoothness and corrosion resistance.

Selection of plastic mold steel

For thin-walled plastic boxes, when the production batch is less than 100,000 pieces, P20 and P21 are used in the pre-hardened state (HB250 ～ 300), and 414L is used when the corrosion is strong.

Ordinary plastic mold with high life, using P6 or P20, hardness after HCC54-58 after carburizing and quenching; when the plastic parts are not too large, O1, S7 can be used. Use 420 for strong corrosion.

Non-high temperature thermoset molds P6 and P20 are used after carburizing and quenching. Highly corrosive with 420.

H13 and S7 or carburized steel P4 are used for high temperature thermosetting plastic molds. These chromium-containing materials have good tempering resistance and high temperature oxidation resistance.

Plastic mold steel

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 categories

Quality distribution of plastic mold steel

The mold types are divided into the following types according to the American SPI-SPE standard.

One, Type 101 mold (SPI-SPE standard 1,000, 000 or more beer, long-term precision production mold)

1. Need detailed mold structure drawing.

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

3. The inner mold steel with glue level must be hard to 48 ~ 50HRC. Other parts such as row position, pressure lock, pressure strip, etc. should also be hardware.

4. The ejector pin should have a guide post.

5. There should be hard film in the row position.

6. If required, the upper mold, lower mold and row position must be temperature controlled.

7. For all water transportation channels, it is recommended to use electroless nickel or 420 stainless steel as the template. This prevents rust and cleans up the trash.

8. Straight lock or oblique lock is required.

Second, class 102 modules. (No more than 1,000,000 beers, mass-produced molds.)

1. Need detailed mold structure drawing.

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

3. The inner mold steel with rubber position should be as hard as 48 ~ 52HRC, and other useful parts should be treated the same.

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

5. The following items may or may not be needed. It depends on the final production quantity. It is recommended to check if the following items are used when quoting:

A. Thimble plate guide post.

B, row bit hard film.

C, electroplating water delivery hole.

D. Plating cavity.

Three, Type 103 mold (less than 500,000 beer, medium production mold.)

1. Need detailed mold structure drawing.

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

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

4. The remaining requirements depend on the needs.

Four, 104 types of mold (less than 100,000 beer, a small number of production molds)

1. Need mold structure drawing.

2. Mould material P20 (28 ~ 32HRC) can use soft steel or aluminum. (1040 steel)

3. The inner mold can be made of aluminum, mild steel or other approved metals.

4. The remaining requirements depend on the needs.

Five, 105 types of mold. (Less than 500 beers, first mold or test mold)

Aluminum cast iron or epoxy resin or any material can be used as long as it has sufficient strength to produce the minimum number of tests.