In the customization of hardware structural parts, prototyping failure is the norm rather than the exception. Industry-standard mold trials typically involve three rounds: T1 (identifying major issues), T2 (confirming repairs), and T3 (verifying mass production stability). Receiving a non-conforming sample does not mean the project has failed; the key lies in how the situation is handled—documenting evidence, identifying root causes, implementing corrective actions, and re-inspecting.
By executing each step correctly, the sample can transition from “NOK” (Not OK) to “OK.”
This article outlines the standard procedure for handling prototyping failures.
1.
Step One: Documenting Evidence and Rapid Verification
Upon receiving the sample, first take photos to document the evidence (outer packaging, sample condition, and specific defect locations). This serves as crucial evidence for subsequent liability determination; photos taken later cannot prove whether the issue existed upon receipt or occurred during use. Next, use measuring tools to verify two or three key mating dimensions against the blueprints and compare them with the values in the accompanying inspection report. If key dimensions are within tolerance, other aspects are likely fine; if they are out of tolerance, you have concrete data to support further communication.
Issues should be reported to the manufacturer within 24 hours, accompanied by photos and measurement data, to pinpoint the problem immediately.
2.
Step Two: Categorizing Defects—Rework vs. Scrap
Standard industry quality control classifies defects into two categories: “Scrap” (irreparable dimensional deviations, structural errors, or incorrect materials, requiring a complete remake) and “Rework” (cosmetic issues or repairable dimensional deviations, requiring rework).
It is also essential to distinguish between “part failure” and “requirement failure”: Did the sample fail to meet blueprint specifications, or did it meet the specifications but fail to satisfy actual application needs?
The former points to manufacturing issues on the supplier’s end, while the latter may indicate flaws in the blueprint design itself.
III. Step 3: Root Cause Analysis and Assignment of Responsibility
Require the supplier to provide a detailed Root Cause Analysis (RCA) and Corrective and Preventive Action (CAPA) plan, clearly identifying the source of the issue: mold errors, improper process parameters, or design flaws?
Common stamping prototyping issues have specific countermeasures: springback can be addressed by polishing the binder surface, adding locating features, or pre-bending; cracking often stems from insufficient material elongation, excessive blank holder force, or small corner radii—solutions include adjusting the blank holder force, increasing the draw bead radius, or reducing the blank size; if persistent dimensional deviations cannot be corrected even within a wide process window, the mold steel itself requires modification.
The assignment of responsibility directly impacts costs: if the issue arises from the supplier’s process errors, rework should be free of charge; if it stems from the customer’s design, the customer bears the cost of mold modification.
IV.
Step 4: Written Rectification and Re-inspection (Closing the Loop)
Document all modification requirements item by item: specify color differences using Pantone codes, annotate dimensional issues on drawings, and clearly list structural changes; both parties should retain records once the plan is finalized. Clearly define the scope of free modifications and the criteria for price adjustments per instance to prevent hidden charges.
Conduct a step-by-step re-inspection after rectification: verify each item against the previous issue list and issue a new inspection report. Major structural changes (wall thickness, profile, assembly structure) will likely incur costs for re-prototyping and mold revision; for multiple significant adjustments, weigh the cost-effectiveness of simply building a new mold.
Mass production may only proceed once new samples pass all checks and receive written approval.
V.
Prevention: Stopping Failure Before Prototyping
The root cause of frequent prototyping failures often lies in the DFM (Design for Manufacturability) stage: overly tight tolerances, poor structural manufacturability, and improper material selection often only manifest as critical issues during mold trials.
Industry best practices recommend conducting a DFM (Design for Manufacturability) review before mold fabrication, using simulation to anticipate risks such as springback and cracking. Material samples should be verified prior to the initial prototyping run to avoid misjudgments based solely on tactile feel.
Additionally, the contract should clearly stipulate the number of prototype iterations, associated costs, and liability for design revisions.
Industry experts advise viewing a failed prototype as a cost-free opportunity for process validation: the earlier issues are exposed, the fewer pitfalls will be encountered during mass production.
