low volume bridge tooling

Choosing between CNC machining and injection molding is a volume decision before it is a technical one. Both processes turn a CAD model into an accurate plastic part, and both can hold the tolerances a drawing calls out, but they reach those tolerances on completely different cost curves. Machining bills spindle time per part, so its unit price stays nearly flat as volume rises; injection molding front-loads the cost into a steel mold and then produces parts far more cheaply. The crossover volume decides most projects. Below it, machining wins on lead time and design freedom; above it, molding wins on unit cost, repeatability and cosmetic consistency. This article sets out the volumes, tolerances, materials and lead times at which each process is the right answer, and how to bridge the two...