When customers ask which process fits their part, I start with the mold itself. Injection molding uses a closed steel mold with a machined cavity and core, typically P20 or 718H, running 20–120°C depending on resin. Cycle times range from 15–60 seconds, wall thickness stays between 0.8–3 mm, and tooling costs run high—often $10,000 to $100,000+—but the payoff is tight tolerances of ±0.05 mm and millions of cycles. For anything needing ribs, bosses, snap-fits, or insert molding, this is the only real option.

Blow molding splits into extrusion and injection blow. Extrusion blow uses a two-half mold with pinch-off edges and a parison die head; the mold is cheaper and often aluminum or beryllium copper for cooling. Injection blow gives better neck finish and no flash, which matters for pharmaceutical bottles. Typical wall thickness is 0.5–3 mm, cycle times 20–90 seconds, and tolerances are looser at ±0.25 mm. Vacuum forming is the simplest tooling—a single cavity with vacuum holes, often cast aluminum or even epoxy for prototypes. It handles sheets from 0.5–6 mm, but you only get one finished surface, draw ratios stay under 1:1, and trimming is a secondary operation.

From a tooling standpoint, the decision comes down to volume, geometry, and surface requirements. Injection molds justify their cost above roughly 10,000 parts; blow molds suit hollow parts from 50 ml to 200 L; vacuum forming wins for large panels and short runs under 5,000 pieces. Watch cooling channel layout and draft angles—1–2° for injection, 3–5° for vacuum forming—because they drive cycle time and part quality more than most people expect. For more mold sourcing and process guidance, visit MoldWorld at www.moldw.com.