Scrap Rate / Rejection Rate
Scrap rate measures the percentage of production that is irreparably defective and must be discarded. It directly impacts material cost, OEE quality factor, and environmental waste.
Scrap rate is the ratio of rejected (non-reworkable) units to total production. Unlike rework, which can be corrected, scrap represents a total loss: The material, energy, labor, and machine time invested are all wasted.
Scrap rate directly affects the quality factor in OEE: Quality = Good Parts / Total Parts Produced. High scrap means low quality performance, even if the machine runs at full speed with high availability.
The cost of scrap extends beyond the material value: It includes processing costs up to the point of rejection, disposal costs, the opportunity cost of machine time that produced nothing sellable, and potential delivery delays if scrap reduces available output.
Effective scrap reduction requires understanding where and why defects occur. Process capability analysis (Cp, Cpk) identifies whether the process is fundamentally capable, while defect tracking identifies specific failure modes for targeted improvement.
Formula
Scrap Rate = Scrapped Units / Total Units Produced x 100%
Practical Example
A die-casting operation produces 2,400 parts per shift. Average scrap: 168 parts (7% scrap rate). Material cost per part: 4.50 EUR. Direct scrap cost: 756 EUR per shift, 181,440 EUR per year. After implementing process monitoring and die maintenance schedules, scrap drops to 2.8% -- saving 121,000 EUR annually.
How Leanshift Helps
Leanshift records production quantities and defect events, automatically calculating scrap rate per shift, machine, and product. Trend visualization shows whether quality measures are working and where the next improvement should focus.
Frequently Asked Questions
What is the difference between scrap and rework?
Scrap cannot be fixed and must be discarded (total loss). Rework can be corrected but requires additional processing time and cost. Both are quality losses, but scrap has a higher cost impact per unit.
How do you reduce scrap rate?
Start with Pareto analysis of defect types. Apply root cause analysis (5-Why, Ishikawa) to the top causes. Implement Poka-Yoke and process controls. Monitor with SPC to catch drift before it creates scrap.
Is zero scrap achievable?
In theory, yes. In practice, near-zero scrap is achievable for many processes through robust design, process control, and error-proofing. The economic optimum balances scrap reduction cost against scrap cost savings.
Related Terms
OEE (Overall Equipment Effectiveness)
OEE is the key metric for machine and equipment productivity. It combines availability, performance, and quality into a single percentage value.
Poka-Yoke (Error Proofing)
Poka-Yoke is a design approach that makes errors impossible or immediately detectable. It builds quality into the process rather than relying on inspection after the fact.
First Pass Yield (FPY)
First Pass Yield measures the percentage of units that pass through a process correctly the first time, without any rework, repair, or rejection. It reveals the true quality of a process.