Process & QC — Shot Weight Consistency (Cpk)
Shot Weight Consistency (Cpk) for injection molding process control.
Part weight is the molding process's vital sign — every pressure, temperature and check-ring problem eventually shows up on the scale. A weight Cpk above 1.67 means the process is stable enough that dimensional Cpk has a chance; below 1, stop measuring dimensions and fix the process.
Formula
Note: Starting-point process values — the resin grade's datasheet and an in-mold study govern. Verify with a gate-seal study and a cooling-time ladder on the actual tool.
Shot Weight Consistency (Cpk) for injection molding process control. A free injection molding cycle & process tool — no sign-up, no upload, instant results in your browser.
About Process & QC — Shot Weight Consistency (Cpk)
Process & QC — Shot Weight Consistency (Cpk) computes the governing relationship Cpk = min[(USL−µ), (µ−LSL)] / 3σ live as you type. Part weight is the molding process's vital sign — every pressure, temperature and check-ring problem eventually shows up on the scale. A weight Cpk above 1.67 means the process is stable enough that dimensional Cpk has a chance; below 1, stop measuring dimensions and fix the process. Defaults are pre-filled with realistic values for this exact scenario, and the worked example substitutes your numbers step by step so the math is never a black box.
How to use Process & QC — Shot Weight Consistency (Cpk)
- 1Enter your values — Mean part weight, Standard deviation, Lower spec, Upper spec (sensible defaults are pre-filled).
- 2Read the live results: Cpk.
- 3Check the "with your numbers" line to see Cpk = min[(USL−µ), (µ−LSL)] / 3σ substituted step by step.
- 4Adjust inputs until the scenario matches yours, then copy or share the result.
Why use Process & QC — Shot Weight Consistency (Cpk)?
- ✓Instant, free and private — every calculation runs client-side in your browser; nothing is uploaded
- ✓Built on the stated formula Cpk = min[(USL−µ), (µ−LSL)] / 3σ with authoritative sources cited on the page (Rosato, Injection Molding Handbook, 3rd ed.; Osswald & Hernández-Ortiz, Polymer Processing — Modeling and Simulation)
- ✓Part weight is the molding process's vital sign — every pressure, temperature and check-ring problem eventually shows up on the scale.
- ✓Niche-specific defaults give a meaningful worked answer the moment the page loads
Frequently asked questions
What formula does the process & qc — shot weight consistency (cpk) use?+
It evaluates Cpk = min[(USL−µ), (µ−LSL)] / 3σ, exactly as published. Sources: Rosato, Injection Molding Handbook, 3rd ed.; Osswald & Hernández-Ortiz, Polymer Processing — Modeling and Simulation. The substituted worked example on the page lets you verify every step against the textbook.
How should I read the result — and how far can I trust it?+
Part weight is the molding process's vital sign — every pressure, temperature and check-ring problem eventually shows up on the scale. Starting-point process values — the resin grade's datasheet and an in-mold study govern. Verify with a gate-seal study and a cooling-time ladder on the actual tool.
When is this calculator the right tool for the job?+
Shot Weight Consistency (Cpk) for injection molding process control. A free injection molding cycle & process tool. A weight Cpk above 1.67 means the process is stable enough that dimensional Cpk has a chance; below 1, stop measuring dimensions and fix the process. For neighbouring scenarios, the related tools below cover the same engine with different presets.
Do I need to install anything or create an account?+
No. The tool is pure client-side JavaScript: open the page and it works, offline once loaded, with no account, no quota and no data leaving your device.
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