When a customer sends over a part drawing, the first decision on my desk is never the mold steel or the gate type — it's which molding process the part actually belongs to. The five mainstream routes are injection, compression, extrusion, transfer, and blow molding, and each has hard boundaries. Injection molding dominates complex, high-volume parts with tight tolerances, and it's where most of our tooling work sits: multi-cavity layouts, hot runner systems, and cycle times measured in seconds. Compression molding still earns its place for large, flat, or reinforced parts — think SMC/BMC components and phenolic parts — where you want low shear on the material and can accept longer cycles. Extrusion runs a continuous profile through a die rather than a closed tool, so the "mold" is a die head, and the engineering focus shifts to die land length, drawdown, and cooling calibration.
Transfer molding sits between injection and compression: the charge is loaded into a pot and pushed into a closed cavity, which suits thermosets and encapsulated inserts where you need better dimensional control than compression but can't use a screw. Blow molding is its own animal — extrusion blow, injection blow, and stretch blow all start from a parison or preform, and the mold only shapes the outer skin, so wall thickness control lives in the parison programming, not the cavity. In practice, the selection logic comes down to three matching checks: part geometry (wall thickness uniformity, undercuts, inserts), production volume (tool life and cycle economics), and material melt flow (how far and how thin the melt will travel before it freezes). Get one of those wrong and no amount of mold polishing saves the project.
From a tooling standpoint, that means the process choice drives everything downstream — draft angles, shrinkage allowance, ejection strategy, and venting all change with the route you pick. A part that looks like a natural injection job can turn into a compression or transfer job the moment the material is a filled thermoset or the volume drops below the point where a hardened multi-cavity tool pays back. My advice: settle the process before you quote the tool, not after. For more mold sourcing and process selection information, visit MoldSo at www.moldso.com.