Die Casting vs CNC Machining vs Injection Moulding — A Process Comparison

CNC machining has no tooling and starts tomorrow, but every part pays full machine time — unbeatable for prototypes and low volumes, expensive forever at scale. Die casting buys a steel die once and then produces aluminum parts in seconds — the tooling hurts once, the unit cost rewards you on every piece. Injection moulding follows die casting's logic in plastic: mould cost up front, very low unit cost after, in ABS/PP rather than metal. The right process is the one whose cost curve crosses your real lifetime volume at the lowest total — and whose geometry and material your part can live with.

Cost comparisons are meaningless until a process can actually make the part. Die casting needs draft, reasonably uniform walls and a shape that ejects from a die; it rewards complexity that is castable — ribs, bosses, thin walls in ADC12/A380. Machining makes almost any geometry in aluminum or stainless, including the thick sections and undercuts casting hates, at the price of time and swarf. Injection moulding makes complex plastic shapes with snap-fits and fine detail that metal processes cannot match economically, in ABS/PP.

Start the comparison on the drawing, not the spreadsheet: classify the part's geometry and material first, and usually only one or two processes survive to the costing stage. Our blog runs the companion piece on the injection-moulding-versus-die-casting question in Q&A form; this page keeps the three-way comparison.

Because all three processes live here, an enquiry can be quoted comparatively in a way single-process shops cannot offer: the same drawing priced as a casting (tooling + unit), as a machined part (unit, no tooling), and — where plastic is conceivable — as a moulding. The crossover volume is shown, not asserted. Buyers regularly discover their assumed process is the second-best one; discovering that at quotation costs nothing, and discovering it after tooling costs the tooling.

Send the drawing with honest volume expectations — trial, first year, lifetime — and ask for the comparison explicitly. It is the question this factory's structure was built to answer.

Programmes here share one skeleton whatever the process: a drawing review that routes each component to its best process, tooling where the process needs it, production under one quality system, finishing as specified, and CMM-backed inspection before release. Two habits keep programmes healthy. First, state volumes honestly — trial, first year, lifetime — because tooling and routing decisions hang on them, and a programme quoted on fantasy volumes is mispriced in both directions. Second, keep one channel for changes: drawing revisions sent with a note about what changed functionally let production re-plan operations and inspection in one pass.

Buyers transferring existing work should say so at enquiry. A proven part with tooling, a part needing new tooling, and a part being re-specified from a sample are three different projects with three different first steps, and the review will name which one you have before quoting anything.