Regarding the small plastic molds, due to the high cost of production and the low cost of materials, it is preferable to use steel with good process performance, stable performance and long service life in the process of using small plastic molds. Let’s explain in detail the requirements for the selection of steel for small plastic molds.
1. Adhesion. Due to the interdiffusion or single-phase diffusion of two metal atoms, the surface of industrial mold parts tends to adhere to the processed metal, especially the surface of some cutting, shearing tools and stamping tools may cause adhesion or crusting. This will affect the sharpness of the cutting edge and the change of local tissue and chemical composition, causing the blade to partially crack or adhere to the metal to scratch the mold, making the surface of the workpiece rough, so good anti-adhesion is very important.
2. Wear resistance. When the part is formed, the material moves relative to the surface of the mold cavity, causing wear on the surface of the cavity, which causes the dimensional accuracy, shape and surface roughness of the mold to change and fail. Wear is a complicated process, and there are many influencing factors. In addition to the external conditions acting on the mold, it depends to a large extent on the chemical composition inhomogeneity, microstructure, and mechanical properties of the steel.
3. Good quenching performance. Most of the cavity parts of the deformed small plastic mold need to be heat treated, which requires the steel to have good hardenability and little deformation. Generally, the mold for thermoplastic molding can be quenched and tempered, pre-hardened, and thermosetting. The mold for plastic molding needs to be hardened.
4. Fatigue performance. With the alternating stress of mechanical impact and thermal shock during the mold running, the thermal alternating stress causes the mold to be thermally cracked, which is caused by the stress and temperature gradient, which is often caused by cracks. The surface of the cavity forms shallow and thin cracks. Its rapid propagation and expansion lead to mold failure, chemical composition of steel and uneven structure. Metallurgical defects in steel are like non-metallic inclusions. The fatigue strength is reduced because under the action of alternating stress, fatigue cracks are first generated in these weak areas and developed into fatigue failure.
In order to maintain the small plastic molds under good running state and prolong the mould service life, we have to do daily maintenance work for them to ensure molds work better and longer.