Last updated: 2026-09-05 · 5 min read
Design Freeze in Injection Molding — What Does It Mean, Why Must the Part Design Be Locked Before the Mold Is Cut, and What Happens If You Change It After?
Design freeze is the point at which the part drawing is finalized and no further changes are allowed — the mold maker begins cutting steel based on this frozen geometry. Changes after freeze cost $1,000–$15,000 per revision (steel welding, re-machining, re-polish) and delay the project 1–4 weeks. The earlier the freeze, the lower the mold cost.
- Design freeze triggers three parallel activities: (1) mold design (cavity layout, cooling circuits, ejection system) is finalized, (2) mold flow analysis runs with the frozen geometry, and (3) steel is ordered from the mill. Once steel arrives (2–4 weeks lead time), cutting begins. Any change after steel is ordered requires a new steel order if the cavity size changes — this adds 2–4 weeks. Any change after cutting begins requires welding the old geometry, re-machining the new geometry and re-polishing the surface — each step takes 3–7 days.
- The cost of a design change escalates at each stage. Before steel order: $0 (just update the CAD). After steel order but before cutting: $200–$500 (update the mold design drawing). After cutting begins: $1,000–$5,000 (weld + re-machine a cavity insert). After T1 sampling: $5,000–$15,000 (modify the assembled mold, re-polish, re-texture, re-run T1). The rule of 10: each stage costs 10× the previous stage to fix the same change. This is why design freeze exists — it prevents expensive late-stage changes.
- Design freeze does not mean the design is perfect — it means the design is good enough to proceed, and remaining changes are accepted as cost risks. The DFM review (before freeze) identifies issues: draft angle too small, wall too thin, undercut requiring a slide. The DFM review should resolve all known issues before freeze. Changes after freeze are either “must-fix” (part does not function) or “nice-to-have” (cosmetic). Must-fix changes are made regardless of cost. Nice-to-have changes are usually deferred to the next mold revision.
What Checklist Items Must Be Complete Before Design Freeze?
| Item | Status Required | Who Confirms | Cost If Missed |
|---|---|---|---|
| 3D model finalized | All features complete | Product engineer | $2,000–$10,000 rework |
| 2D drawing with GD&T | Critical dims tolled | Design engineer | $1,000–$5,000 re-machining |
| Resin selected | Grade and supplier confirmed | Material engineer | $3,000–$8,000 (shrinkage change) |
| DFM review complete | All issues resolved | Mold maker + designer | $5,000–$15,000 mold rework |
| Mold flow analysis | Gate, weld, warpage OK | Simulation engineer | $2,000–$5,000 gate relocation |
| Press match confirmed | Platen, tonnage, bolt pattern | Production engineer | $5,000–$20,000 new mold base |
Design freeze is a formal milestone — both the customer and the mold maker sign off on the frozen drawing. After freeze, any change request must go through a change order process: the mold maker quotes the change cost and time impact, the customer approves (or withdraws the request), and the change is executed. This formal process prevents informal “can you just…” requests that bypass cost control.
Rule of 10 — each project stage costs 10× the previous stage to fix the same design change. Before steel order: $0. After order, before cutting: $200–$500. After cutting: $1,000–$5,000. After T1: $5,000–$15,000. The exponential cost curve is why design freeze exists — it prevents expensive late-stage changes. The file requirements guide lists what must be finalized before freeze.
What Three Rules Minimize Post-Freeze Changes?
- Complete the DFM review before freeze — this catches 80% of design issues before steel is cut. The DFM review checks: draft angles (minimum 1° for textured, 0.5° for polished), wall thickness uniformity (±0.3mm), rib thickness (50–60% of nominal wall), boss diameter (2× wall thickness), and undercut elimination (slides or lifters needed). Each issue found in DFM costs $0 to fix (just update the CAD). Each issue found at T1 costs $5,000–$15,000 to fix in the mold. The DFM review is the highest-ROI activity in the mold development process.
- Run mold flow analysis before freeze — this predicts fill, weld lines and warpage before the mold exists. The simulation identifies: gate location (is the proposed gate causing a weld line at a high-stress area?), air traps (trapped gas causing burn marks at flow end?), and warpage (does predicted deformation exceed tolerance?). If the simulation reveals a problem, the gate can be relocated or part design modified — at zero steel cost. After the mold is cut, moving a gate requires welding the old location and machining a new one — $2,000–$5,000.
- Freeze the design at 95% complete — do not wait for 100% perfection. Waiting for 100% perfection delays the mold start by weeks while the product team debates minor features (cosmetic fillet radius, text engraving depth, snap fit retention force). These changes can be made as post-mold modifications (after T1) at lower risk than delaying the entire project. Freeze at 95% — the critical dimensions and functional features are locked, and the remaining 5% (cosmetic details) can be adjusted after T1 sampling reveals the actual part quality.
Change order — a formal document issued after design freeze when a change is requested. The mold maker quotes the fix cost and time impact, the customer approves or withdraws, and the change is executed only after written sign-off. Change orders prevent informal requests that bypass cost control. The mold flow analysis guide shows what can be predicted before freeze to reduce change orders.
Design freeze: part drawing locked, mold cutting begins. Changes after freeze: $1k–$15k per revision, 1–4 week delay. Rule of 10: each stage costs 10× the previous. DFM + mold flow before freeze catches 80% of issues. Freeze at 95% — don’t wait for 100%.
- 3D model finalized — all features complete, no pending changes.
- 2D drawing with GD&T — critical dims tolled, datum frame set.
- Resin grade confirmed — shrinkage factor locked, data sheet attached.
- DFM review signed off — draft, wall, ribs, bosses, undercuts resolved.
- Mold flow results approved — gate, weld, warpage within spec.
Frequently Asked Questions
What if I discover a functional defect after design freeze?
Functional defects (part does not fit, snap or seal) must be fixed regardless of cost. The change order process still applies: mold maker quotes fix cost and time, customer approves, change is executed. The key question: can the fix be made by modifying the existing mold, or does it require a new insert? A surface change (add 0.5mm to a wall) can be made by machining existing steel — $1,000–$3,000. A geometry change (move a boss 5mm) requires welding and re-machining — $5,000–$10,000.
How do I handle cosmetic changes after the mold is textured?
Texture changes after the mold is textured are the most expensive changes — the texture must be removed (by polishing), the steel modified, and the texture re-applied. Cost: $3,000–$8,000 per cavity, plus 2–3 weeks lead time (the mold must be sent to a texture shop). For cosmetic changes: wait until after T1 sampling to evaluate the actual texture appearance on molded samples. If the texture is too coarse or too fine, adjust at that point — after the functional dimensions are confirmed.
Can I make changes during T1 sampling without stopping production?
Minor changes (vent depth, ejector pin position, gate vestige size) can be made during T1 without stopping — these are process adjustments, not geometry changes. Major changes (wall thickness, boss location, snap fit geometry) require mold modification — the mold must be removed from the press, modified, re-installed and re-sampled. This adds 1–3 weeks per iteration. To minimize T1 iterations: complete the DFM review and mold flow analysis before freeze.
Key Takeaways
- Design freeze: drawing locked, steel cutting begins.
- Changes after freeze: $1k–$15k, 1–4 week delay.
- DFM + mold flow before freeze catches 80% of issues.
- Freeze at 95% — don’t wait for 100% perfection.
Send the part drawing and DFM review results — the review confirms the design is ready for freeze, identifies any remaining issues that should be resolved before steel is cut, and specifies the change order process for any post-freeze modifications.
Sources: Plastics Technology — Design Freeze and Change Management in Mold Building · Plastics Technology Online — DFM Review Before Design Freeze · Society of Plastics Engineers (SPE) — Design for Manufacturability Technical Papers · ASTM — Design Guidelines for Injection Molded Parts · ISO 10303 — STEP Standard for Product Data Exchange
— Arthur, Tooling Engineer at aCatMould