Casting Yield and Scrap Cost: Getting Them Right in Your Quote

Yield, Melt Loss and Scrap Are Three Different Numbers

Yield describes how much of the metal you pour ends up in the finished casting, with the rest returning as gates, risers, runners and overflows. In sand foundries that return metal is remelted, but it still costs energy, melt loss and handling. Melt loss is metal lost to oxidation and slag, which differs for aluminum, ductile iron, steel and copper alloys.

Scrap is rejected castings, split into internal scrap caught in-house and external returns from customers. Mixing these into one number hides the real problem. A plant can show decent overall yield while a single part number loses money to a specific defect.

• Yield: finished weight over pour weight, driven by gating and riser design
• Melt loss: oxidation and dross, alloy dependent
• Internal scrap: rejected before shipping, with a cost that grows the later it is caught
• External returns: the most expensive scrap, including freight and customer chargebacks

Cost of Scrap Depends on Where It Is Caught

A casting scrapped at shakeout costs the metal, molding and core labor. One scrapped after cleaning adds grinding and blast hours. One scrapped after machining adds machine time, and one rejected by the customer adds freight and sorting.

A flat scrap percentage applied to the whole cost stack misses this. Better practice records scrap quantity, defect code and the operation where it was found, then values each at accumulated cost at that point. That gives you a scrap cost curve per part and shows whether you should invest in earlier inspection such as radiography or pressure testing before machining.

Common Defects and the Data You Need

Sand foundries see shrinkage, gas porosity, sand inclusions, misruns, cold shuts, mismatch and dimensional rejects. Die casters see porosity, cold shuts, flash, soldering, heat checking marks, and dimensional drift as the die wears. Each defect has a different root cause and cost.

To quote and improve, you need defect codes consistent across shifts, quantity by code per job, and the link back to heat, die, machine and operator. Without that, scrap becomes a single line in the production report and the ERP can only report a percentage.

• Use a controlled defect code list, not free-text reasons
• Record the operation where the defect was found
• Link scrap to heat number, die number or pattern, and shift
• Report scrap cost, not just scrap quantity

Feeding Real Scrap Into the Estimate

The practical step is to compute trailing scrap and yield per part family from actual jobs, weighted toward recent runs, and use those as quote defaults. Flag first-time parts as higher risk, because trial runs rarely match steady state, and add a risk allowance until you have three or more production runs. In ERP terms, this means the production reporting screen must capture good quantity and scrap by reason at each operation, and your costing method must carry scrap into job cost.

Whether you use standard or actual costing, the variance between quoted and actual yield should be reviewed monthly by part number.

When Detailed Scrap Tracking Is Overkill

If your product mix is a handful of stable parts with scrap well under control and customers accept your price, a plant-level scrap report may suffice. Detailed defect-by-operation tracking pays off when mix is high, new parts are frequent, or a few part numbers consume most of the scrap dollars. Run a Pareto of last quarter's scrap dollars by part number first.

If the top five parts are not a majority of the loss, deeper tracking will not change your quotes much.