Small Batch Production With FDM: What Changes Above 50 Parts

A prototype has to be right once. A small batch has to be right every time, on different machines, with different filament lots, over weeks. That is a different problem and it is where most FDM batch orders go wrong.

When FDM beats injection molding

A mould costs a four to five figure sum and several weeks before the first part exists. FDM has no tooling cost, so the crossover point decides. For parts of moderate size, FDM is usually the cheaper total cost up to somewhere between a few hundred and a few thousand units, and it stays cheaper indefinitely when the geometry is still changing or when you need several variants in parallel.

Lock the process, not just the file

For a batch we freeze more than the STEP file: nozzle diameter, layer height, wall count, infill, orientation on the plate, chamber temperature and the drying regime for the filament. Any of those changing mid batch changes the mechanical behaviour and the fit. If a customer reorders six months later, this recorded parameter set is what makes part 500 identical to part 1.

Design for the batch, not for the first print

• Remove support-dependent overhangs: supports are the largest source of surface variation and manual labour per part
• Give critical bores machining allowance and ream them, instead of chasing printed tolerances
• Use threaded inserts instead of printed threads for anything that gets assembled repeatedly
• Keep wall thickness a whole multiple of the extrusion width so every part fills the same way
• Orient the part once, for load direction and for surface, then keep that orientation for the whole batch

Inspection that scales

Measuring every part is not economical above a few dozen units and measuring nothing is not acceptable. We agree a small number of critical dimensions with the customer, check the first article against them, then sample within each build. Parts that carry load also get a visual layer adhesion check, because a delaminated part can be dimensionally perfect.

Cost per part in a batch

Machine time dominates, so cost per part falls mainly through nesting more parts per build and reducing print time, not through cheaper filament. Shortening a part by a few millimetres in height or removing a support-heavy feature often saves more than switching material. Send the geometry and we will tell you which change moves the price.

We produce batches from 50 up to several thousand parts, with a documented parameter set and a first article you approve before the batch runs.