Medical molding shares similarities and differences with injection molding for other industries. Other life-critical industries such as food, auto, and aerospace bring their own specialized requirements. Poor quality can have an adverse impact on the health, safety, and mortality of the end user. The medical industry has established its own approach and terminology to managing those risks. We will explore that approach and how it applies to the injection molding process.
The establishment of a reliable and repeatable process serves as the overarching aim of medical molding. Medical molding moves away from inspecting quality into the parts and moves toward inspecting the process. Inspecting the process ensures that it produces quality parts.
With medical molding, Step One establishes a quality process up front. Step Two inspects the process on an ongoing basis. We will explain how this works below.
Step One – Establish a Quality Process
The establishment of a quality process in the general area of medical manufacturing happens during the verification stage. This is referred to as IQ/OQ/PQ, which stands for Installation Qualification/Operational Qualification/Performance Qualification. In medical molding this translates into:
- IQ - Qualifying the equipment such as the injection molding press and mold construction,
- OQ - Qualifying the operation of the mold by establishing a process that produces quality parts, and
- PQ - Qualifying the performance of the mold in runs that simulate production.
In medical molding, OQ earns the title of most intensive qualification step. Medical molding best achieves OQ by using the methods of Scientific Processing. Scientific Processing uses a DOE to establish the processing window. You can read more about how we employed Scientific Processing here, and you can read a Case Study about using DOE here. This entire processing window produces quality parts. In other words, rather than just creating a single process that works, Scientific Processing defines the tolerances around those processing parameters.
Step Two – Inspect the Process
After establishing the quality processing window, we know the process can vary within that window and still produce quality parts. If the process varies beyond that processing window, we venture into the unknown. The unknown brings risk. With medical molding we want to reduce risk.
Those parts produced when the process ventures outside the processing window might actually be good parts. If inspected, they might pass. Other industries might inspect and accept parts that deviate from the qualified processing window. Medical molding generally does not by default accept those parts on the fly. Companies certified to ISO 13485, the medical device standard, might require reverification and/or revalidation activities.
Medical molding can inspect the process through the injection molding press. Newer presses allow for integrated programming so the processing engineer can enter the nominal process as well as the tolerances around that process directly into the machine. On each shot, the machine knows whether it has exceeded the allowable tolerances around cycle time, temperature, and pressure. If it exceeded any tolerances, the robot places the shot in the reject bin rather than on the conveyor.
Medical molding’s second option for inspecting the process resides in real-time machine monitoring. Modern ERP systems give the process engineer a dashboard that tracks the processes at all presses. If any process at any press falls outside the established process parameter, the system alerts the process engineer.
The best medical molding incorporates continual improvement. This includes managing the variation in everything from the product design to the manufacturing process. In medical molding, we want to understand that variation exists even within parts that meet specifications. Some of the variation within the specs might be unacceptable. Variation beyond the original specifications might actually improve the product.
Remember that development teams initially define specifications using judgment calls. Reality sets in over the life of the product, and manufacturers discover specifications need to change. This happens whether the defined tolerance tightens, loosens, or shifts. Overly tight tolerances can unnecessarily increase costs.
We want to look at that variation relative to the entire system. Inspecting the process instead of inspecting the parts can improve both quality and cost. In some cases, medical molding would find 100% inspection desirable. Recent advances in automation have made 100% inspection more economically feasible.
As the pioneers of quality such as Shewhart, Deming, and Taguchi have taught us, we want to manage variation. We do not aim to eliminate variation at the expense of the overall system. We do want to understand variation to optimize performance toward the aim of the system.