Raw Material Selection

Fig. 3 – Looking downstream, away from the extruder.
Raw material sources for custom extrusion companies can be categorized into three basic groups:

  • Resin manufacturers (e.g. Lubrizol, Arkema, Ticona, Bayer, etc.)
  • Compounding companies (e.g. Polyone, New England Urethane, Foster, etc.)
  • Customer-supplied custom resins

With resin manufacturers, the custom extruder can have a problem with the customarily small amounts purchased. The parts to be extruded are small and even hundreds of thousands of parts can be made with just a couple hundred pounds of resin. Often there are minimum order requirements, repacking charges for small order quantities with significant up charges. However, with resin manufacturers, the biggest problem custom extruders face is availability. The reason for this varies. For example, in 2010, an explosion caused a severe shortage of Nylon 12-based resins worldwide and a force majeure was issued. As a result, all Nylon 12 resins were placed on allocation, which meant new product development using Nylon 12- based resins had to look for alternatives or stop. In 2014, an issue with the supply of polyetherimide left custom medical extruders scrambling for alternative materials. It is evident that the quantities purchased by extruders do not gain much respect from the suppliers despite their use for medical applications.

Custom medical extruders have a far closer relationship with custom compounding companies. Like the custom extrusion houses, custom compounders also have their individual strengths and weaknesses. Quality and consistency is the primary driver when selecting a compounder. Although lead time is important to use, it does not displace quality, even with a significantly less expensive price. Responsiveness of the custom compounders is generally very good and that helps the extruder when problems arise and on the small lot custom compounding one needs to anticipate a problem from time to time.

The custom compound supplied by a customer is often produced in very small batches in laboratory settings. Lot-to-lot consistency is always the issue and extruders have had projects stopped because of this issue.

The custom extruder’s reliance on its raw material sources cannot be understated. With raw material quality largely out of our direct control, extruders do take steps at incoming inspection to assess the material’s suitability for medical extrusion, but most resin or compound defects do not reveal themselves until extruded and drawn down into a tiny medical tube. For this reason, relationships with compounding houses and ongoing proactive and strategic communication with them to ensure quality lots is extremely important.

Producing the Part

The day before extrusion of the part, the extrusion technician sets up the specified machines and tooling. The extrusion technician reviews the work order and special work instructions. If exceptions are taken to certain specifications on the customer drawing, the early tech review of the purchase order has made it clear what the extrusion technician should focus on and prioritize.

The next morning, the part extrudes. As a prototype (first run part), start up gets a bit more attention than usual production. Engineering is on hand and the other extrusion technicians have looked over the new set up and inquired about the new jigs installed on the line. An hour after turning on the extruder, the technician determines the extruder heats to be optimized: pressure is steady, the OD trend chart is nearly a flat line. A short while later, after adjustment to several of the IDs, the technician sends parts to the Quality Department for verification of specified dimensions and parts are being saved. (See Figure 3)

Customer Service is notified by Manufacturing of the successful extrusion run and the customer is notified by e-mail or phone and sent a digital image of the part’s profile. With complex profiles, first run success is not always anticipated and, in some cases, multiple attempts are made before the part is allowed to go to final inspection. Under these circumstances, having an in-house machine shop saves valuable time and also enables the custom extrusion house to dial in the extrusion by tweaking the tooling, sometimes even having the tool off the machine fine-tuned and back on the machine in the same day. When tooling is finessed in this way for complex profiles, the custom extruder needs to work with the client to produce parts that are functional as a minimum on these early runs. Work then goes forward based upon the terms of the quote/purchase order.

Once the part is successfully extruded and shipped to the customer, the extrusion house typically follows up to learn critical feedback from the customer on the conforming part. This conversation is important as there is always room for improvement, so if the extrusion house does not contact the customer, the customer should not hesitate to provide any and all feedback to the extrusion house.

Producing medical devices is a complex process of working with suppliers of components of the device. Complex extruded parts can be the most difficult of all the parts to source and consequently tend to create strong relationships or “partnerships” between the device maker and the extrusion house.

Selection of an extrusion house that best fits the requirements of the part to be made is a key to success. Open communication between the device maker and the extrusion house is a must. Both parties must listen and be open to each other’s recommendations remembering change is where innovation starts and both the device maker and the extrusion house have a stake in the project’s success.

This article was written by Timothy W. Steele, CEO/Founder, Microspec Corporation, Peterborough, NH. For more information, Click Here .