When we talk plastic molding, most mold engineers default to injection—and rightly so, since it covers over 60% of thermoplastic parts. But limiting yourself to that one process leaves money on the table. The full landscape includes 23 core methods, each with its own tooling constraints, cycle-time economics, and material compatibility. For instance, blow molding demands split-cavity designs with pinch-off lands, while rotational molding requires thin-shell cores that can handle biaxial rotation at 8–12 rpm. Even within injection, you have variants like gas-assist (for hollow sections) and insert molding (for overmolded metal or PCB assemblies). Knowing when to switch from a standard two-plate mold to a three-plate or hot-runner system can cut scrap by 15–20% on high-cavitation jobs.

Beyond the mainstream, compression and transfer molding still dominate thermoset and high-glass-fill applications. Compression molds need precise charge-weight control—typically ±1%—to avoid flash or short shots, and they run at 150–180°C with clamp pressures around 200–400 bar. Transfer molding offers better dimensional stability for intricate inserts, but the pot and plunger add tooling cost. On the foam side, structural foam molding uses a low-pressure (20–40 bar) nitrogen or chemical blowing agent to create a cellular core, which reduces part weight by 10–30% while maintaining stiffness. The catch: tool surfaces must be hardened to resist the abrasive flow of foaming resin, and you need venting channels that are 0.05–0.1 mm deep to let gas escape without leaving witness marks.

For a mold shop, the real value lies in matching the process to the part geometry and annual volume. Thin-wall packaging? High-speed injection with hardened H13 or S7 tooling. Large hollow tanks? Rotomolding with bismuth-tin or aluminum molds. Microcellular foaming? You'll need a specialized screw and accumulator setup. Don't overlook secondary steps like in-mold labeling or overmolding, which can add 5–10% to the piece price but eliminate assembly labor. Each method has its own shrinkage rates, draft-angle requirements, and cooling-line layouts—get those wrong and you're chasing warpage for weeks. For a deeper dive into tooling specs, cycle-time benchmarks, and cost-estimation templates across these 23 processes, visit MoldWorld (www.moldw.com) for sourcing guides and supplier comparisons.