Introduction to the Challenge
When a client reached out to us, they were ramping up low volume production of their health monitoring device and facing an urgent and critical issue: in just three weeks they were set to begin manufacturing the next batch but had received reports from customers of high failure rates in the previous batch.
The problem? The ultrasonic weld that joined the two halves of the casework was failing, jeopardising the product integrity.
Acting quickly was essential. They needed to confirm the root cause of the failures and implement an improved manufacturing process to ensure the quality of their upcoming batch.
Ultrasonic welding process diagram
Our Approach
To meet the tight deadline, we pursued a parallel approach: analysing failed products while developing a robust, repeatable test protocol, all while working closely on-site with the manufacturer to improve the welding process.
1) Understanding the failed products and the process that produced them
We inspected samples that had failed, sectioned them and inspected the welds under a microscope. We pushed, poked and sat on them. We conducted a flash audit of the manufacturing process to observe each step first hand and identify potential areas of concern. While other areas for improvement emerged, ultrasonic welding (specifically, under-welding) had the largest impact on part quality.
2) Developing a Reliable Testing Protocol
Creating a quick, repeatable, and representative test was critical for delivering results on time. We decided on a compressive test, where the casework was stressed until the weld seam split. This approach was preferred over impact or drop tests due to its:
- Ease of setup and repeatability
- Continuous force measurement, providing richer data than a simple pass/fail result
This method allowed us to test minimal devices per category while still yielding statistically significant findings.
We designed a custom test jig tailored to the part’s geometry for accuracy, with compliant inserts to ensure force was applied consistently while allowing the part to deform and split along the weld seam. Each test measured peak force before failure, gave insight into stiffness and deflection, and pre- and post-test inspections recorded defects and variations in weld geometry.
3) Optimising the Welding Process
a) Mapping the Process Window
To check that under-welding was the issue, we produced test samples at varying weld settings, visually inspecting for cracks and casing damage while testing failure force using our newly-developed compression test.
By adjusting clamping pressure and welding time, we mapped out the process window—illustrated below:
b) Identifying Optimal Process Points
After careful analysis, we identified 11 process points across the process window, focusing on deeper, stronger welds. We then manufactured 8 parts at each setting to gauge repeatability.
Results
Our efforts paid off. We identified an optimized process point that was 50% stronger than the existing weld, all while using the same material.
Beyond quickly improving weld strength for the next batch, our insights into component design and assembly allowed us to recommend modifications to:
- Design changes to improve weldability and structural integrity
- Process improvements to enhance consistency in the welding process by refining the welding jig and setup checks, and
- Process trials to refine the process point and improve process capability for volume manufacture.
Conclusion
In just three weeks, we:
✔ Designed and manufactured a custom test jig
✔ Mapped out the welding process window
✔ Tested and validated an improved process point
As a result, the client manufactured their next batch with significantly fewer failures.
Additionally, we proposed further quality control and product design enhancements to boost long-term robustness for volume manufacture.
If your business faces urgent manufacturing challenges, we specialize in fast, actionable solutions. Get in touch to see how we can help.