When a customer asks which process fits their part, I start with wall thickness and annual volume. Injection molding handles walls from 0.5 mm to 4 mm with tolerances around ±0.05 mm, but a hardened steel mold with a hot runner system can run $30,000 to $80,000 and take 8–12 weeks to build. Cycle times sit at 15–60 seconds depending on part weight. Blow molding is different: the parison wall is stretched unevenly, so you get ±0.3 mm at best, yet a 20 L HDPE jerrycan mold costs roughly $8,000–$15,000 and cycles in 40–90 seconds. Vacuum forming is the cheapest tooling route—an aluminum or epoxy tool for a 1 m × 2 m ABS shell might cost $2,000–$5,000 and run a 30–60 second cycle, but you are limited to draw ratios under 1:1 and wall thinning at corners.

From a mold maintenance view, injection tools need hardened cores and sliders for glass-filled resins; blow molds need pinch-off inserts and cooling channels near the neck; vacuum form tools need vacuum holes drilled at 0.5–1.0 mm and often a temperature-controlled platen. I have seen vacuum form tools warp after 50,000 shots if the aluminum grade is wrong. Injection molds routinely hit 500,000 cycles with proper steel like P20 or H13. Blow molds usually last 100,000–300,000 cycles. The real trap is choosing vacuum forming for a part that needs a snap-fit boss—you cannot form a 3 mm boss on a 1.5 mm sheet without secondary bonding.

So the selection logic is simple: tight tolerances and high volume go to injection; hollow, thick-wall containers go to blow; large, shallow panels with low volume go to vacuum forming. I always ask for a 3D part file and annual quantity before quoting a mold. For more mold sourcing data and supplier comparisons, visit MoldWorld at www.moldw.com.