Tooling and Cavitation
MIM tools are built like plastic injection tools but must be oversized for sintering shrinkage, commonly in the range of roughly 15 to 20 percent linear, and the shrink factor is specific to the feedstock lot behavior and part geometry. Tool cost scales with cavity count, side actions and surface requirements. More cavities cut molding cost per piece but raise the tooling investment and the risk of cavity-to-cavity dimensional variation after sintering.
Amortize tooling over expected lifetime volume, not the first order, and decide whether the customer pays tooling up front or it is recovered in the piece price. Include tool maintenance and an allowance for a shrink-correction rework, since first articles often need a tool adjustment.
Feedstock, Runners and Regrind
Feedstock is metal powder mixed with a binder system, bought as a compounded pellet or made in house. The part weight understates feedstock use because the shot includes sprues and runners. Cold runner regrind can often be reused in a controlled percentage, but the allowed ratio depends on the feedstock, the customer spec and your process validation.
Cost the net material: shot weight times price, minus the credit for regrind that is genuinely reused. Because the binder is later removed, material cost per sintered part is computed on shot weight, while the sintered mass is far lower. Mixing these bases is a frequent estimating error.
- Shot weight including runner versus sintered part weight
- Regrind reuse ratio allowed by process validation
- Feedstock price per kilogram by alloy, such as 17-4PH or 316L
- Powder price changes passed through in quotes
Debinding and Sintering: The Real Bottleneck
After molding, binder is removed by solvent, catalytic or thermal debinding, then parts are sintered in a batch furnace, often in vacuum or controlled atmosphere, with cycles that can run for many hours. Furnace capacity, not press capacity, usually caps output. Cost per part is furnace cycle cost divided by the number of good parts in the load, so setter tray design and load density matter as much as the cycle length.
Track parts per load, cycle hours and energy. A sintering profile is validated per part family, so changing furnace assignment is not free. Estimators who price furnace time as a flat per-hour number miss the effect of loading density.
Try it here, free
Bar Stock Yield and Material Cost per Part Calculator
Work out how many parts come from each bar after cutoff and end loss, how many bars to buy, and the true material cost per part.
Secondary Operations and Yield
Many MIM parts need sizing or coining to tighten dimensions, machining of critical features, heat treatment such as H900 aging for 17-4PH, passivation, plating, or tumbling. Each carries labor, and outsourced steps carry minimum lot charges. Yield loss accumulates through molding defects, debinding cracks, sintering distortion and final inspection, so quote on a cumulative yield rather than an assumed 100 percent.
Customers in medical and firearms markets often require lot traceability and dimensional capability data, which adds inspection time. Use yield history by part family from your records to set the allowance rather than a fixed percentage across the board.
When MIM Is Not the Right Quote
If annual volume is low, a part is large, or the geometry is simple enough to machine or press and sinter conventionally, the tool investment will not amortize and the honest advice is to recommend another process. Likewise, if a part fits within a conventional powder metallurgy envelope, the cost per piece may be lower. A quoting process that can compare process routes, MIM, press and sinter, machining and additive, for the same print saves the customer from a bad choice and protects your reputation.
Frequently asked questions
How many parts are needed before MIM tooling pays off?
It depends on tooling cost, cavity count and the alternative process, but MIM is generally considered for runs in the tens of thousands per year and above for small complex parts. Below that, machining or additive may be cheaper. Compare total landed cost over the expected program life, including tooling amortization, not piece price alone.
Why is sintering the bottleneck in MIM?
Sintering cycles are long and run in batch furnaces, so output depends on furnace count and parts per load. Molding presses run much faster than furnaces can absorb. That is why load density, setter design and cycle scheduling directly affect cost per piece and delivery performance.
What yield should I use when quoting MIM?
Use cumulative yield from your own history, split by molding, debinding, sintering and inspection, for the specific part family. A mature simple geometry may yield far better than a new thin-wall design. Quote first articles with more conservative yield and revise after process capability is established.
If you quote MIM from spreadsheets with flat furnace rates, Netray can help you ground the next draft in actual cycle, load density and yield history from your ERP.