Sin categoría
In production testing, validation, and quality control, correctly defining tolerance limits is one of the most critical factors to ensure reliability, repeatability, and yield (FPY). The test tolerance represents the acceptable margin of variation between the measured value and the expected nominal value, taking into account natural imperfections of the process and instruments.

In production testing, validation, and quality control, correctly defining the tolerance limits is one of the most critical factors to ensure reliability, repeatability, and yield (FPY). The test tolerance represents the acceptable margin of variation between the measured value and the expected nominal value, taking into account natural imperfections of the process and instruments.

🔍 Why is defining tolerances essential?

Without well-defined limits, a test can:

  • Approve defective products (false negative – NDF)
  • Reject good products (false positive – waste)
  • Compromise quality indicators like FPY, PPM, Cpk and OEE
  • Generate unnecessary rework and loss of confidence in production
  • Conceal problems of calibration or process instability

🎯 How to strategically define tolerances?

The correct definition of test tolerance should consider the following factors:

  1. Technical specifications of the product
    • What is the actual functional range allowed?
    • Is the performance limited by regulatory standards?
  2. Process capability (Cpk, Ppk)
    • Is the manufacturing process stable enough to produce within tolerance?
  3. Uncertainty of measurement instruments
    • The tolerance should be significantly greater than the uncertainty (rule 4:1 or 10:1)
  4. Test objective (End-of-Line, validation, screening)
    • Final tests require tighter limits than screening tests
  5. Statistical analysis of previous data
    • Use of histograms, trend analysis, standard deviation calculation

🛠️ How AJOLLY Testing supports tolerance definition

AJOLLY Testing applies precise methodologies to ensure your test tolerances are safe and productive:

  • Analysis of historical measurement distribution (histogram, standard deviation)
  • Automatic limit calculation based on 3σ, 4σ or target Cpk
  • Statistical validation reports with charts and outlier analysis
  • Simulations in TestStand and LabVIEW to anticipate limit failures
  • Traceability tools integrated with MES and dashboards (Power BI)

✅ Best practices for defining tolerances

  • Always validate limits with real production data
  • Reevaluate tolerances after process, supplier, or firmware changes
  • Include a safety margin based on the natural variability of the process
  • Avoid extreme (tight) limits without statistical validation
  • Use asymmetric tolerances when applicable

⚠️ Beware of “standard tolerance”

Avoid applying generic limits for convenience. Each test should have limits defined based on technical criteria and real data, avoiding long-term quality and reliability issues.

With AJOLLY Testing, your test tolerances are defined based on data, engineering, and reliability — so that no product is approved by chance and no good product is discarded.