Plastic Mold Parts. Heat Treatment Process
Using different kinds of steel as plastic molds, their chemical composition and mechanical properties are different, so the manufacturing process is different; Similarly, different types of plastic die steel use different heat treatment process. This section mainly introduces the manufacturing process of plastic mold and the characteristics of heat treatment process.
Heat treatment characteristics of carburized carbon steel plastic die
1. For high hardness, high wear resistance and high toughness requirements of the plastic mold, to choose carburizing steel to manufacture, and carburizing, quenching and low temperature tempering as the final heat treatment.
2. For the carburized layer, the thickness of the general carburized layer is 0.8~1.5mm. When pressing the hard filler, the thickness of the carburized layer of the plastic mold is 1.3~1.5mm, and the thickness of the carburized layer of the pressed soft plastic is 0.8~1.2mm. The carburized layer content is 0.7% to 1.0%. If carbon, nitrogen, abrasion resistance, corrosion resistance, oxidation resistance, and anti-sticking are used.
3. Carburizing temperature in general 900 ~ 920℃, complex cavity of small mold can be 840 ~ 860℃ medium temperature carburizing. Carburizing heat preservation time is 5 ~ 10h, specific should be based on the thickness of the layer to choose. Carburizing process to use a graded carburizing process is appropriate, that is, high temperature stage (900 ~ 920℃) to quickly infiltrate carbon into the surface of the parts
4. Carburizing after the quenching process according to different steel, carburizing can be used: re-heating quenching; Stage carburizing followed by direct quenching (such as alloy carburizing steel); Carburizing after air cooling quenching (such as high alloy carburizing steel manufacture of large, medium die).
Heat treatment of hardened steel plastic molds
1. For molds with complex shapes, heat treatment should be carried out after roughing, and then finishing can ensure minimum deformation during heat treatment. For precision molds, the deformation should be less than 0.05%.
2. The surface of the plastic cavity is very strict, so it is necessary to ensure that the surface of the cavity does not oxidize, decarburize, corrode, or overheat during the quenching process. If ordinary box type resistance furnace is used for heating, protective agent should be coated on the cavity surface, and heating speed should be controlled. When cooling, a relatively mild cooling medium should be selected to control the cooling speed, so as to avoid deformation, cracking and scrap in the quenching process. Generally, hot bath quenching is preferred, and pre-cooling quenching can also be used.
3. After quenching, temper should be timely, the tempering temperature should be higher than the working temperature of the mold, the tempering time should be sufficient, long and short depending on the mold material and section size, but at least in 40 ~ 60min above.
Heat treatment of pre-hardened steel plastic molds
1. Pre-hard steel is supplied in pre-hard state, generally without heat treatment, but sometimes it needs to be forged, and the die blank after forging must be heat treated.
2. The preliminary heat treatment of pre-hard steel usually adopts spheroidal annealing, which aims to eliminate the forging stress, obtain uniform spherical pearlite structure, reduce hardness, improve plasticity, and improve the cutting performance or cold extrusion forming performance of die blank.
3. The prehardening process of pre-hardening steel is simple, and most of them adopt quenching and tempering treatment. After quenching and tempering, the tempered soxite structure is obtained. High temperature tempering temperature range is very wide to meet the requirements of various working hardness of the mold. Because this kind of steel hardenability is good, quenching can be used oil cooling, air cooling or nitrate grade quenching.
Heat treatment of aging hardening steel plastic molds
1. The heat treatment process of aging hardening steel is divided into two basic steps. Firstly, the steel is heated to a high temperature to dissolve various alloy elements into austenite, and the martensite structure is obtained by quenching after completion of austenite. In the second step, aging treatment is carried out to strengthen the mechanical properties required by aging.
2. Solid solution heating is generally carried out in salt bath furnace, box furnace, heating time can be: 1min/mm, 2 ~ 2.5min/mm, quenching using oil cooling, quenching steel can also be air cooling. If the final forging temperature can be controlled accurately during forging, the solid quenching can be carried out directly after forging.
3. Aging treatment is best carried out in a vacuum furnace, if carried out in a box furnace, in order to prevent oxidation of mold cavity surface, the furnace must be filled with a protective atmosphere, or use aluminum oxide powder, graphite powder, cast iron scrap, aging under the condition of box protection. Packing protection heating should be appropriately extended insulation time, otherwise it is difficult to achieve aging effect. plastic mold.