Every day lost in validation costs you more than time. Based on years of experience supporting medical and high-precision molding programs, PTI has identified the 12 most common reasons validation stalls—and practical ways to avoid them.
Use this guide to improve planning, streamline documentation, and keep your launch on schedule.
12 things that will delay your molding validation.
Delay Cause
Recommended Action
1. Scope Changes
Ambiguous or shifting validation scope (e.g., 100% layout vs full IQ/OQ/PQ) can derail timelines.
Establish the complete scope of validation early in the project—ideally before the tool design phase. Create a Master Validation Plan that clearly defines all required deliverables, such as IQ, OQ, PQ, PPAP, or dimensional layouts.
Confirm mutual understanding between your team and your molding partner to eliminate ambiguity. If any scope adjustments become necessary, implement a formal change process with documented impact analysis to prevent rework and lost time downstream.
2. Protocol / Report Review and Approvals
Having too many people involved or not reviewing document templates ahead of time leads to bottlenecks.
Streamline documentation by identifying a small, dedicated approval team—ideally no more than two individuals. Ensure everyone understands their specific responsibilities and timelines for review. Use standard templates for protocols and reports to maintain consistency and reduce administrative back-and-forth.
Sharing templates early allows the customer to align expectations before validation begins, saving multiple review cycles and keeping the project on schedule.
3. Quality System Alignment
Mismatch in quality systems or standards (e.g., OEM vs molder) causes wasted time negotiating.
Use supplier’s registered standards (e.g., ISO 13485, FDA CFR 820) to your advantage. Confirm up-front that all parties align on the required quality system and documentation.
4. Excessive Critical Dimensions
Specifying too many “critical dimensions” increases measurement, analysis and delays.
Limit the number of “critical” dimensions to those truly affecting form, fit, and function. Focus validation efforts on three to five dimensions that reflect the process’s overall capability.
Overloading your validation plan with dozens of critical features adds unnecessary measurement work, statistical studies, and documentation time. A leaner approach maintains regulatory compliance while accelerating qualification and decision-making.
5. Critical Dimensions with GD&T Callouts
Using sophisticated GD&T (especially surface profiles) complicates measurement, tooling tweaks, and slows the qualification processing.
Avoid using advanced GD&T callouts—especially surface profiles—for process validation whenever possible.
These measurements often require specialized equipment, complex data analysis, and repeated CMM work. Instead, rely on simpler linear dimensions that can still demonstrate process control. If GD&T features are critical to product function, plan extra time for setup, inspection correlation, and data interpretation early in the project.
6. Dimensions Out of Tolerance
Discovering out-of-spec dimensions during validation triggers decisions (drawing change or tooling fix) that delay work.
Have a predefined decision-making protocol for out-of-tolerance results.
Determine ahead of time who has the authority to approve drawing revisions, tooling adjustments, or deviation requests. When nonconformances occur, assess whether they truly impact function before committing to costly steel or design changes. Fast, informed decision paths minimize downtime and help maintain project momentum.
7. Dimensions not meeting Cpk Requirements or Normality
When key dimensions lack statistical capability or normal distribution, the route forward is unclear.
When capability or normality targets aren’t met, work collaboratively with your molder to evaluate functional impact.
Not all Cpk misses are critical—some may be statistically insignificant or can be addressed through minor specification updates. Establish a risk-based decision process that weighs functional performance over pure statistical perfection. This approach prevents unnecessary re-validation and allows projects to proceed confidently when parts are performing as intended.
8. Excessively Tight Dimensional Tolerances
Unrealistic tolerance specs for plastic parts increases cost, complexity, and delays.
Design with the realities of plastic in mind. Use SPI or industry-standard tolerance guidelines appropriate to part size and resin type. Unreasonably tight tolerances increase cost, slow validation, and may require unnecessary tool rework.
If ultra-tight tolerances are truly essential, discuss options for design compensation, steel-safe conditions, or alternate materials early in development. Aligning expectations on achievable precision helps prevent delays later in the process.
9. Bringing Part Dimensions into Spec by Pushing Process Limits
Trying to force tooling/process to hit specs shrinks process window and opens risk of other failures.
Avoid adjusting molding parameters to artificially bring parts into spec. This practice narrows the process window and increases the risk of instability or defects during production. Instead, evaluate whether the part still meets functional requirements within a slightly broader tolerance.
If so, revise the drawing accordingly. Protecting a robust, repeatable process is far more valuable than forcing conformance to an unrealistic specification.
10. Cosmetic Standards not Achievable or Exceed Capabilities of Material or Molding Process
Setting subjective or unrealistic cosmetic specs (e.g., “no bubbles, no scratches”) delays consensus and approval.
Define cosmetic expectations using objective, industry-recognized standards such as SPI surface finish grades.
Eliminate subjective terms like “no blemishes” or “perfect appearance,” which lead to disagreement and reinspection delays.
During design reviews, discuss the realistic cosmetic limits of the chosen material and molding process. Set achievable, measurable criteria that align with end-use requirements, not personal interpretation.
11. Customer and Molder Inspection Data not Aligned
Different inspection methods between customer and molder (e.g., CT scan vs CMM vs linear) cause reinspection and delay.
Agree on measurement methods, equipment, and data formats before validation begins.
Whether using CMM, vision, or CT scanning, ensure both customer and molder follow identical procedures and report structures. Early alignment prevents discrepancies that trigger re-measurement and debate over “whose data is correct.” Document the approved inspection approach within the protocol to keep the entire team consistent.
12. CT Scan Required for Inspection
Requiring CT scans adds cost, huge data sets, and time for data review/scrubbing—often more than required for validation.
Reserve CT scanning for parts where internal geometry, wall thickness, or void analysis is essential. For standard dimensional validation, stick to conventional measurement techniques like CMM or optical inspection. CT data sets are massive and require expert interpretation, often leading to extended review cycles.
By using CT strategically rather than routinely, you reduce cost, data overload, and unnecessary delay while still achieving reliable validation outcomes.
Watch our Device Talks!
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