A Discolored Area Measuring Only a Few Hundredths of a Millimeter—Yet Appearing in Nearly 20% of Units During DVT
May 12,2026
Recently, we encountered an interesting challenge in a medical device OEM project.
The initial prototypes showed no issues. The pilot production run also proceeded normally. However, once the project entered the Design Verification Testing (DVT) stage, slight yellowing began to appear intermittently on a section of heat-shrink tubing.
The affected area measured only a few hundredths of a millimeter, yet the occurrence rate was close to 20%.
Why did the issue appear only during DVT?
Rather than immediately attributing it to the material or the operators, the Diagsensor engineering team reassessed every potential variable in the process, including:
- The heat-shrink tubing supplier’s raw materials and manufacturing process
- Our heat-shrinking temperature and process parameters
- Differences between operators
- The actual heating position and duration
- Changes in material batches and production conditions
After multiple rounds of single-factor and comparative testing, we identified the root cause:
The issue was not caused by a single material defect. It resulted from intermittent process variation created by the combined effects of temperature and manual heating time.
Under the original operating method, even when the specified process parameters remained unchanged, slight differences could still occur in the actual heating position and duration. When these variations accumulated beyond a certain point, localized yellowing could appear.
Once the cause was identified, we did not simply ask operators to “be more careful.”
If process consistency depends on an operator’s attention and experience, the process itself still has room for improvement.
We therefore introduced a dedicated fixture to control the critical operating position and process, reducing variation caused by manual operation.
Following implementation and continued verification, no further yellowing was observed.
As production volume increases from prototyping and pilot runs to DVT, low-probability variations hidden within manual operations are more likely to emerge.
The value of contract manufacturing is not simply producing a successful prototype. It lies in continuously identifying variables that depend on individual experience—and converting them, through process optimization and dedicated tooling, into controlled, repeatable manufacturing processes.
#MedicalDevice #ContractManufacturing #OEM #DVT #ProcessEngineering #ProcessValidation #QualityControl #MedicalDeviceManufacturing
May 12,2026
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