Heat treatment process of automobile injection mold parts

1. Heat treatment characteristics of automobile injection molds

(1) Heat treatment characteristics of carburized steel plastic molds

1. For plastic molds with high hardness, high wear resistance and high toughness requirements, carburizing steel should be used to manufacture, and carburizing, quenching and low temperature tempering should be used as the final heat treatment.

2. Requirements for the carburized layer, generally the thickness of the carburized layer is 0.8 ~ 1.5mm, when pressing plastics containing hard fillers, the thickness of the carburized layer in the mold is required to be 1.3 ~ 1.5mm, and the carburized layer when pressing soft plastics. The thickness is 0.8 to 1.2 mm. The carbon content of the carburized layer is preferably 0.7% to 1.0%. If carbon and nitriding are used, the wear resistance, corrosion resistance, oxidation resistance and anti-stickiness are better.

3. The carburizing temperature is generally 900-920°C, and the medium-temperature carbonitriding at 840-860°C is preferable for small molds with complex cavities. The carburizing holding time is 5-10h, which should be selected according to the requirements of the thickness of the carburizing layer. The carburizing process is preferably a graded carburizing process, that is, the high temperature stage (900 ~ 920 ℃) is mainly to rapidly infiltrate the surface of the part; the medium temperature stage (820 ~ 840 ℃) is mainly to increase the thickness of the carburized layer, so that in the A uniform and reasonable carbon concentration gradient distribution is established in the carburized layer, which is convenient for direct quenching.

4. The quenching process after carburizing is different according to the steel type. After carburizing, it can be used separately: reheating and quenching; direct quenching after graded carburizing (such as alloy carburized steel); direct quenching after medium temperature carbonitriding (such as industrial Small precision molds formed by cold extrusion of pure iron or low carbon steel); air-cooled quenching after carburizing (such as large and medium-sized molds made of high-alloy carburized steel).

(2) Heat treatment of hardened steel plastic mold

1. For molds with complex shapes, heat treatment is performed after rough machining, and then finishing is performed to ensure that the deformation during heat treatment is small. For precision molds, the deformation should be less than 0.05%.

2. The surface requirements of the plastic mold cavity are very strict, so during the quenching and heating process, it is necessary to ensure that the surface of the cavity is not oxidized, decarburized, corroded, or overheated. It should be heated in a protective atmosphere furnace or a salt bath furnace after strict deoxidation. If an ordinary box-type resistance furnace is used for heating, a protective agent should be applied to the surface of the mold cavity, and the heating speed should be controlled at the same time. Cooling medium, control the cooling speed to avoid deformation, cracking and scrapping during the quenching process. Generally, hot bath quenching is preferred, and pre-cooling quenching can also be used.

3. After quenching, it should be tempered in time. The tempering temperature should be higher than the working temperature of the mold. The tempering time should be sufficient. The length depends on the mold material and section size, but it should be at least 40 to 60 minutes.

(3) Heat treatment of pre-hardened steel plastic mold

1. Pre-hardened steel is supplied in a pre-hardened state and generally does not require heat treatment, but sometimes it needs to be re-forged, and the die blank after re-forging must be heat-treated.

2. The pre-heat treatment of pre-hardened steel usually adopts spheroidizing annealing, the purpose is to eliminate the forging stress, obtain a uniform spherical pearlite structure, reduce the hardness, improve the plasticity, and improve the cutting performance or cold extrusion forming performance of the die blank.

3. The pre-hardening process of pre-hardened steel is simple, most of which are quenched and tempered, and tempered sorbite is obtained after quenching and tempering. The high temperature tempering has a wide temperature range and can meet various working hardness requirements of the mold. Due to the good hardenability of this type of steel, oil cooling, air cooling or nitrate graded quenching can be used during quenching.

(4) Heat treatment of age-hardening steel plastic molds

1. The heat treatment process of age-hardening steel is divided into two basic steps. First, solution treatment is carried out, that is, the steel is heated to a high temperature to dissolve various alloy elements into austenite, and after the austenite is completed, the martensite structure is obtained by quenching. The second step is aging treatment, and the mechanical properties required after Z are achieved by aging strengthening.

2. The solution treatment heating is generally carried out in a salt bath furnace and a box furnace. The heating time is respectively 1min/mm and 2～2.5min/mm. The quenching adopts oil cooling, and the steel with good hardenability can also be air-cooled. If the final forging temperature can be accurately controlled when forging the die blank, solution quenching can be carried out directly after forging.

3. The aging treatment is carried out in a vacuum furnace. If it is carried out in a box furnace, in order to prevent the surface of the mold cavity from being oxidized, a protective atmosphere must be introduced into the furnace, or alumina powder, graphite powder, and cast iron chips should be used to protect the box. Aging below. Packing protection heating should properly prolong the holding time, otherwise it is difficult to achieve the aging effect.