How to Reduce MIM and PM Tooling and Unit Costs

Separate tooling cost from unit cost

Treating "the price" as a single number makes cost reduction difficult, because tooling and unit cost are driven by different things and trade off against each other. A design change that reduces tooling complexity may increase cycle time, and vice versa.

The useful discipline is to ask which component dominates for this part. On a short program at moderate volume, tooling dominates and the design should favour a simpler tool. On a long program at high volume, unit cost dominates and it is worth spending more on tooling to reduce cycle time or eliminate an operation.

Simplify geometry without losing function

The largest available saving usually comes from geometry. Every feature that requires a tool action, a core pin or a secondary machining step adds cost to both the tool and the part.

• Move features to directions the die can form. A cross-hole that could run parallel to the mould opening direction instead of across it may eliminate a side action.
• Consolidate parts. Two pressed or moulded components that could be one formed part remove an assembly step and a set of tolerances from the stack.
• Remove features that exist for convenience rather than function. Chamfers, grooves and cosmetic steps that no one inspects are still tool features that must be cut and maintained.
• Standardise across the family. If three variants share a bore, a boss pattern or an outer profile, designing them to share tool elements reduces both tool cost and setup time.

Let volume guide the process

Process choice is a cost decision, and it should be revisited when volume assumptions change. A part tooled for MIM at 5,000 units a year may be better served by PM if the geometry permits, or vice versa if a design change added three-dimensional detail.

The relevant calculation is tooling divided by per-part saving, checked against program life. That number should be recomputed whenever the volume forecast or the drawing changes, because a plan that was correct at 20,000 units a year can be wrong at 6,000.

Where volume is uncertain, there is a middle path worth considering: tool for the process the volume justifies at the lower end, and use a hybrid route (formed blank plus machined critical features) to bridge the gap. It costs more per part than a fully optimised forming route, but less than tooling for volume that never arrives.

Control tolerance and inspection scope

Tolerance structure is the second-largest lever, and it works in two directions: it determines which features need machining, and it determines which features must be measured.

• Apply as-sintered tolerance to general dimensions. Roughly ±0.3–0.5% is comfortable on most part sizes; specifying something tighter on a cosmetic or clearance dimension buys nothing.
• Reserve tight tolerances for features that carry function. Fits, bores, sealing faces and bearing journals. These are where a finishing operation earns its cost.
• Ask what is measured, and how often. A drawing with a tight tolerance on a feature nobody checks still adds cost, because the supplier must build the capability to hold it.
• Consider reducing inspection frequency where capability is demonstrated. Once a process is shown to hold a feature, sampling at a reduced rate is a legitimate cost reduction that does not reduce quality.

Choose material for the property, then the price

The cheapest grade that meets the requirement is the correct grade, but "meets the requirement" is doing real work in that sentence. Choosing a low-alloy steel to replace 316L saves material cost and then adds a plating operation — which may cost more per part than the material difference, and introduces a coating that can chip.

Two specific traps are worth avoiding. First, specifying a hardenable grade for a part that does not need to be hard, which adds a heat treatment operation for no functional benefit. Second, specifying a soft grade for a wear surface, which reduces the part's life and produces a bigger cost later.

The reliable sequence is: identify the property that governs — corrosion, wear, strength, magnetic response — select the least expensive grade that delivers it, and only then look at whether a coating could replace an expensive alloy. Occasionally it can; often it cannot, because the coating introduces its own cost and its own failure modes.

Audit secondary operations

Secondary operations are where unit cost quietly accumulates, because each one carries not only machine time but also handling, fixturing and inspection. It is worth listing every operation a part undergoes between sintering and packing, and asking what each one is for.

• Machining of a feature that could be formed. Sometimes a bore is machined out of habit when the mould could hold it to the required tolerance.
• Deburring of a feature that no longer needs to be sharp. A radius added at design stage removes the operation.
• Tumbling to a cosmetic standard that the customer no longer specifies. Appearance requirements often persist after the product has changed.
• Coating a surface that is no longer visible or no longer exposed. Design changes frequently leave coating specifications behind.
• Final inspection of features that capability data has shown to be stable. Sampling may replace full inspection only when permitted by the customer requirement and agreed control plan.

Design for tooling efficiency

Tooling cost responds to a small number of design decisions, and most of them are visible on the drawing.

• Uniform wall sections reduce the cooling and sintering variation the tool must accommodate, and reduce the risk of a tool correction after first article.
• Avoiding side actions where possible — each one adds a moving element to the tool that must be manufactured, fitted and maintained.
• Sensible draft on walls parallel to the opening direction reduces ejection force and tool wear.
• Radii at corners rather than sharp internal features, which are stress raisers in the part and wear points in the tool.
• A cavity count matched to volume. More cavities reduce cycle time per part but increase tool cost; the right number depends on volume and part size.

Cost levers at a glance

Prepare a cost-ready RFQ

None of the levers above can be applied by a supplier working from a bare drawing and a quantity. The enquiry that produces cost-reduction suggestions includes: the drawing with tolerance tiers marked, the STEP model, the material and property requirement, the annual volume and program life, the current process and its cost where the part already exists, the finish requirements with the function of each surface, and a note on which tolerances are functional and which are historical.

That last item is the one most likely to generate savings. Suppliers routinely see tolerances that are tight for reasons no longer present, and they can only suggest relaxing them if they know which ones are negotiable.

Conclusion

Cost reduction in MIM and PM happens mostly on the drawing. Tooling follows geometry complexity; unit cost follows cycle time, secondary operations and inspection scope; and material should be selected for the property rather than the price alone.

The most productive single exercise is to list every operation a part undergoes and ask what each one is for. Operations that exist for superseded requirements, features that are machined out of habit, and tolerances that are tight without reason are all removals that reduce cost at both the tooling and unit level — without changing what the part does.

Related component families

These pages show where the leverage tends to be greatest by component type.