Designed and iterated CNC-manufactured test fixtures to test safety syringes, applying exact constraint theory and GD&T to meet tight tolerance and clearance requirements.
3D model of initial fixture design in SolidWorks
Summary
During my co-op at Instron, I designed custom test fixtures to allow a specific brand of safety syringe to be tested on the autoinjector test system.
Design Challenges
The biggest challenge was balancing CNC manufacturability and tight clearances between the upper and lower grips during operation. Specifically, to inject medicine from the syringe, the upper grips must be lowered between the lower grips.
Furthermore, the grips needed to attach onto the existing autoinjector pneumatic grip fingers, while also interacting with the safety syringe in specific set zones to avoid damage.
Approach
Exact Constraint
I applied exact constraint principles, using pin holes and slots to ensure the grips are precisely attached onto the existing pneumatic grips to maintain repeatable positioning between testing rounds.
Design for Manufacturing
When developing the grips, I purposely designed them to minimized the number of CNC setups to make shorten manufacturing time. Furthermore, I implemented GD&T to set tighter tolerances when needed.
Validation and Verification Testing
I performed repeated tests on demo autoinjectors using 3D printed nylon and carbon fiber prototyped grips to verify grip performance. Initial testing results indicated inadequate grip force during safety syringe cap removal. To solve this, we proposed applying a thin rubber layer on the inner grip surface. This resulted in a vastly improved testing success rate.
V&V testing of safety syringe test fixtures
Results
Successfully developed safety syringe testing fixtures from initial concept through prototyping. Although, the final production design was changed after my co-op ended.
Skills Applied
- SolidWorks (configurations, assemblies, exploded views)
- GD&T
- Exact Constraint
- Design for Manufacturing