Injection molding
Injection molding is a molding process for plastics: molten plastic is injected under pressure into a steel mold and solidifies there. The mold must be polishable, dimensionally stable, and corrosion-resistant – quite different requirements than in die casting.
What injection molding is
In injection molding, thermoplastic is melted, injected under pressure into a closed steel mold, and cools there to form the finished part. Cycle after cycle, identical parts are produced.
What the mold has to do
The injection mold has to do one thing above all: deliver a perfect surface. It is polished to a gloss so the plastic parts shine clean. Plus dimensional accuracy, good machinability for the engravings, and – with aggressive plastics – corrosion resistance.
Difference from die casting
In injection molding, the thermal shock is much milder: plastic comes in at 200–300 °C, not over 600 °C like aluminum in die casting. But the molds are often huge and need steels that polish and machine well – like 1.2738, 1.2311, or 1.2316.
When welding
Injection molds need filler metals that match the base structure and special protection for the polished surfaces when welding. Preheat according to the material, but the thermal load is overall gentler than in die casting.