Every scrapped part wastes material, machine time, labour and energy. Every reworked part consumes capacity that could make new products. Yet in many factories, scrap is accepted as normal, recorded loosely at month end and rarely analysed. Reducing scrap and rework is one of the most direct ways to improve margins — and the first step is simply seeing it clearly.
Step 1: Capture defects at source
Record scrap and rework where they occur: by part, operation, machine, shift, operator and defect type. Month-end stock adjustments tell you scrap happened, not where or why. Tablets at operations or inspection stations with clear defect codes make recording quick. See designing reason codes — the same principles apply to defect codes.
Step 2: Value scrap correctly
A part scrapped at the final operation costs far more than one scrapped at the first: it carries all the material, machine time and labour added along the way. Value scrap at accumulated cost to the point of rejection. Add rework labour, re-inspection, disposal and any customer costs. This is the cost of poor quality — often much larger than management assumes.
Step 3: Pareto analysis
Rank scrap cost by part, defect type and operation. Typically, a few combinations account for most of the cost. Focus improvement on these rather than spreading effort across everything.
Step 4: Find root causes
For each priority defect, investigate systematically: when does it occur, on which machines, materials, shifts? What changed? Use 5 Why, fishbone diagrams and data analysis. Distinguish common-cause variation (inherent in the process) from special causes (specific events). See 5 Why analysis.
Step 5: Implement controls
- Process parameters: define and monitor critical settings.
- First-off approval: verify setups before running. See first article inspection.
- In-process checks and SPC: catch drift before parts go out of tolerance.
- Error-proofing: fixtures and checks that prevent defects physically.
- Standard work: clear instructions with photos.
- Material control: incoming inspection and supplier quality.
- Tool and maintenance management: prevent wear-related defects.
Step 6: Catch defects earlier
A defect found at the operation that caused it is cheapest to fix. Found at final inspection, it may have affected many parts. Found by the customer, it's most expensive. Moving detection upstream — operator self-checks, in-process inspection — reduces the cost of each defect.
Step 7: Manage rework properly
Rework should follow defined instructions, be recorded, and reworked parts re-inspected. Uncontrolled rework creates quality risks and hides the true defect rate. Track rework hours as a cost and a capacity loss.
Step 8: Track and sustain
Monitor scrap and rework weekly by priority defect. Review in daily or weekly meetings. When a defect is reduced, update control plans and work instructions so the improvement sticks, then move to the next priority.
Scrap from setups and start-ups
A significant share of scrap occurs during setups, warm-ups and restarts. Recording start-up scrap separately shows how much is lost at each changeover and strengthens the case for setup reduction and better process settings. See the six big losses.
Supplier-related defects
Some scrap originates in purchased material: wrong hardness, dimensional variation, contamination. Recording supplier and material lot against defects shows when a supplier is the cause, supporting claims, incoming inspection changes and supplier development. See supplier scorecards.
An example: machined castings
A machining company processing castings had high scrap at final inspection. When defects were recorded by operation and casting lot, the Pareto showed that porosity found during machining and bore dimensional errors accounted for most scrap cost. Porosity linked to specific casting lots and suppliers, leading to supplier corrective action and incoming checks. Bore errors linked to tool wear and thermal drift, solved with tool life limits and in-process gauging. Scrap cost fell substantially within a few months.
Getting started
Introduce defect codes and source recording on your highest-scrap line, value scrap at accumulated cost and run a Pareto after four weeks. Form a small team to attack the top defect, and review progress weekly.
Common mistakes
- Recording scrap only at month end.
- Valuing scrap at material cost only.
- Trying to fix every defect at once.
- Blaming operators instead of improving processes.
- Uncontrolled rework that hides problems.
How software helps
Quality and shop floor software capture defects at source, value scrap, produce Pareto charts, drive NCR and CAPA workflows and track results over time. See quality management software.
Talk to us about reducing scrap in your factory.
Involving operators
Operators often know the causes of recurring defects — a fixture that loosens, a material batch that machines differently, a setting that drifts after lunch. Sharing scrap data with them in daily meetings and asking for their ideas brings causes to light faster than analysis alone, and builds ownership of the solutions.
Frequently asked questions
How do we know how much scrap costs us?
Record scrap and rework quantities by part and operation, then value them at accumulated cost to that point — material, machine time and labour — plus disposal and rework labour.
Where should we start?
With a Pareto of scrap cost by part and defect type. A few defects usually account for most of the cost.
Is rework better than scrap?
Rework saves material but costs labour, capacity and sometimes quality risk. Both are waste; prevention is better than either.
Do operators need to record every defect?
Recording defects by type at the operation where they're found is essential. Tablets with defect codes and quick entry make this practical.
How long does it take to see results?
Early wins often come within weeks from obvious causes. Sustained reduction comes from systematic root cause work and controls.
