Case Study
Solving a Persistent Manufacturing Quality Problem
overview
Resolving a persistent 15% defect rate in a critical home appliance component after previous investigations failed to identify the causes. A targeted Lean Six Sigma assessment traced the problem to injection molding and robotic assembly, leading to corrective actions across both processes.
15% → 1.8%
Defect rate
$350K
Annual cost savings
-18%
Assembly cycle time improvement
The Situation
A home appliances manufacturer was facing a persistent 15% defect rate in a critical component made from short-glass-fiber-filled polypropylene.
The defects escaped standard in-line quality checks and became apparent only after final assembly, resulting in significant quality-related costs and rework.
Previous investigations by the company's R&D team and external Lean consultants had failed to identify the root causes or resolve the problem.
The Findings
The investigation identified two contributing causes across injection molding and automated assembly.
Injection molding: The mold design caused rapid shrinkage of freshly molded components, affecting their dimensional stability.
Robotic assembly: Programming inconsistencies occasionally caused microscopic damage to components during assembly.
Existing quality controls failed to detect these defects before the components reached final assembly.
The Work
The project began with a one-week on-site technical assessment covering injection molding, component quality and automated assembly. Production observations, process measurements and operating data were used to examine the relationship between component geometry, material behavior and manufacturing conditions.
The engineering review included an assessment of the injection mold design, cooling system configuration and dimensional stability of the molded components. Particular attention was given to shrinkage behavior and its impact on subsequent assembly operations. In parallel, the robotic assembly sequence, programming parameters and component handling were examined to identify sources of mechanical damage.
Over the following months, the work continued remotely, focusing on corrective engineering measures and process optimization. This included reviewing modifications to the mold cooling channels, developing revised injection molding parameters and refining robotic assembly settings to reduce component stress and improve process consistency.
The implementation was supported by ongoing technical discussions, production data reviews and evaluation of results as corrective measures were introduced. The objective was to achieve a stable, repeatable manufacturing process rather than rely on additional quality inspections to contain defects.
The Results
The implemented corrective measures reduced the component defect rate from 15% to 1.8%, resolving a longstanding quality issue that previous improvement initiatives had failed to address.
The project also delivered an 18% improvement in assembly cycle time and $350,000 in annual cost savings through reduced defects and improved manufacturing efficiency.
Beyond the immediate results, the changes improved process stability across injection molding and automated assembly, addressing the technical causes of defects rather than relying on additional downstream inspection.
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