The procedure for validating the medical injection molding process is critical to verify that the system offers repeatability, assurance of accuracy, and a high degree of quality. It’s important to receive validation for medical injection molding so it’s consistent and traceable. To meet these requirements, manufacturers use a three-step validation process described as:
- Installation Qualification (IQ)
- Operation Qualification (OQ)
- Performance Qualification (PQ).
These procedures help qualify Tooling, Materials, Equipment, Systems and Processes. The goal is to validate that the entire life cycle of the medical injection molding process is repeatable and traceable with a high confidence level that the quality repeats from lot to lot and year to year.
The Medical Injection Molding Process
There are four major variables that control the process: melt temperature, fill speed, pack pressure and cooling rate.
- Melt Temperature: The temperature at which the polymer will begin to melt
- Fill Speed: The time it takes to fill the mold with polymer
- Pack Pressure: The pressure applied to the melt to pack in the polymer and to force more of it into the mold
- Cooling Rate: When there is no more pressure being applied, how long it takes for the melted polymer to cool
Three of the variables are easy to duplicate from run to run. However, measuring melt temperature has always been a mystery, as it is difficult to measure accurately. Molders agree that melt temperature measurement remains one of the “last frontiers” of medical injection molding process control.
“You can’t control what you can’t measure” is a fundamental axiom, and the problem here is the lack of an accurate, repeatable, practical, and generally accepted method of measuring the melt temperature.
Why is it important to control melt temperature?
Melt temperature influences the plastic’s viscosity or resistance to flow (thinness or thickness), which is critical in obtaining optimal part dimensional control. Consistent viscosity allows for repeatable filling of mold with consistent cavity pressure, and less part to part and lot to lot variation. You will get a tighter “bell curve” on dimensional variation.
A revolutionary new system has been in development for the last 4 ½ years called the Melt Temperature Measurement System (MTMS). There are two major principles that define the system.
- An insulated cup is used to keep the purge molten so it can be measured before it solidifies.
- There is a defined flow path in the system that forces the molten material over the thermocouple probe.
A high-speed pyrometer records the peak temperature. It is fast, repeatable and easy to use. Gage R&R studies have been successfully completed.
Start Validating Your Medical Injection Molding
OEM Medical Companies should ask in-house molders and contract molders if they are monitoring and documenting melt temperatures. Contract or custom molders should be monitoring and documenting melt temperature as a Standard Operating Procedure (SOP) to improve your medical injection molding validation process.