The Many Challenges of Extrusion
Matching product needs to supplier capabilities and anticipating variables is key to successfully navigating this difficult discipline.
Extrusion is one of the trickier processes in medical device manufacturing. The right combination of materials, temperature and controls is necessary. But there is less room to play around with those than there used to be, because recent designs tend to call for tighter tolerances and thinner walls. The margin for error is slim and the chances of a failed process is great if all the variables are not thought out properly.
This is why it is essential that medical device OEMs do extensive homework when choosing an extrusion partner. Extra care must be taken to ensure that the partner has experience working with the materials the OEM intends to use, that it is capable of making the kinds of products the OEM designs, and that it understands the documentation and process requirements.
Asking the Right Questions
Requirements for medical tubing are not the same as requirements for other kinds of tubing, so the first thing an OEM should learn from a potential partner is how much experience it has with serving the medical device industry, according to Apur Lathiya, vice president and general manager for thermoplastics at Vesta Inc., a medical extrusion firm based in Franklin, Wis.
Once this is established, the OEM must then ask “what materials do you extrude most frequently, and what is the experience level of your technical staff,” he said. Each material behaves very differently under the extrusion process, so general experience with medical device extrusion is no substitute for experience with specific materials.
The OEM then must get a sense of what kind of systems the potential partner has in place. To make the product is one thing; to also provide operations that support themaking of it is another.
How extensive its operations are in a specific type of extrusion and to what extent it might be able to offer advice during the design phase are facts that should be determined, added Bill Woinowski, engineering manager for new silicone technologies at Vesta.
“You need to ask, do you have systems in place to develop, inspect, and validate this extrusion?” Woinowski said.
Specifically in regard to systems, Bill Shedd, marketing communications manager at Eldon James Corp., a Loveland, Colo.-based maker of tubing and connector parts, said one first must ask:
• What is the production capacity of the facility relative to the demand of the client?
• Can the supplier deliver documentation capabilities if the project requires U.S. Food & Drug Administration (FDA) approvals? These requirements have become more demanding in the past five years, he notes.
• Are the products manufactured ina cleanroom?
Also, Woinowski said, “validation is key. Downstream inspection devices have peaked customer interest, but the basics still apply.”
Mike Badera, president of Glens Falls, N.Y.-based Precision Extrusion Inc., said that lead times are another important issue to ask about.
“In recent years, OEMs are expecting shorter lead times for extrusion projects, so they need to ask suppliers about their typical lead times,” he said.
If the partner is going to support the product development process, an OEM needs to know if it has an internal tool-making capability, said Dan Lazas, executive vice president for marketing and sales for Putnam Plastics Co., an extrusion provider in Dayville, Conn., that is part of PolyMedix Discovery Group.
“In order to move at the pace device companies want to move at, they need to generate prototypes quickly and do iterations in house,” he said.
If the partner is going to consult on product development, then it should have experience with a wide range of materials and processes, otherwise it might try to force a manufacturing strategy that is not for the best, Lazas added.
“If they only have one thing to offer, they will try to solve it with that,” he said. “But if they have multiple capabilities, for example thermoplastics, fluoroplastics, braiding, and co-extrusion, that gives them a bigger toolbox to provide solutions. Every material has a different work-around to it. It also helps if they have secondary operations such as RF (radio frequency) welding available.”
Similarly, he said, the ideal partner will have “experienced extrusion engineers available to do development.”
Indeed, said Geary Havran, president of NDH Medical Inc., a St. Petersburg, Fla.-based extrusion provider, participation inproduct development is one of three major requirements that medical device companies are seeking from their partners that they weren’t five years ago, at least not to the same extent. The other two are “comprehensive data collection and analysis for process control and validation, and materials expertise for medical device applications,” he said.
The OEM also needs to get a sense of what resins are involved in a partner’s extrusion process, Shedd said. Certain potentially toxic components traditionally used in tubing are now banned throughout various parts of the world.
“Do the resins contain any toxic components such as vinyl chloride, phthalates or other plasticizers?” he asks. “Are the materials animal-derivative free, if that is a criterion?”
Of course, OEMs must ask if the partner’s systems can achieve the tighter tolerances demanded of today’s extrusion projects, said Mark Erson, QA director of Sil-Pro LLC, a Delano, Minn.-based provider of extrusion for silicone medical products.
“We have experienced a trend toward tighter tolerances, smaller tubing, thinner walls, and more stringent visual requirements,” he said. “With tolerances changing from a typical +/- .005 inches for silicone to sometimes down to +/- .0005 inches for wall thickness requirements and +/- .002 inches for inner diameters (ID) and outer diameters (OD), it becomes much more critical to have good process controls and highly skilled operators.”
And we all know that no screening process can be complete without a discussion of costs.
“Tooling, material and labor costs all are cost drivers, especially in development of new products, so these have to be talked about,” said Lathiya.
This is especially true for custom projects, which are harder to bid, according to Shedd.
“It is difficult to project the amount of scrap for custom projects because you generally don’t know what obstacles you might encounter in achieving process stability,” he said. “Like everything else, cost comes down with volume. Tooling is always a major up-front cost on any custom project, so it is beneficial if that can be spread out over higher volumes. This is usually not that difficult with medical products because many are disposable. That, however, creates environmental concerns, which, along with human health issues, are driving companies towards low-toxicity substitutes to replace PVC and other higher toxicity resins; and most of these low toxicity substitutes are currently more expensive. Also, all plastics are tied to the cost of oil, which has fluctuated dramatically in the past several years, making cost projection difficult.”
Processing capabilities and support services always must be discussed in the context of cost. “Validation expenses verses process and design flexibility are in constant tension,” Havran said.
Lazas agreed. “There is a competing agenda: OEMs want more out of the process, but they want it for less,” he said.
Given how many variables go in to the extrusion process, there are a number of obstacles that can present themselves. Working with a partner who has experience dealing with as many of these as possible can give a medical device company the confidence that issues will be dealt with effectively or, better yet, anticipated and prevented before theyever happen.
Perhaps the greatest challenge is “lot-to-lot consistency in raw materials,” said Lathiya. The substances used to make tubing are not uniform in how they are made by different manufacturers. In some cases, there can be inconsistencies in lots from the same manufacturer. This variation must be accounted for and documented.
This is especially true for silicones, according to Erson.
“For silicone extrusion, the biggest obstacle is the material itself,” he said. “Between production runs, the largest variable is differences in the raw material. The stiffness of the material (measured as plasticity) can vary greatly depending on the manufacturer and the type of material it is. This change in the viscosity of the material can affect the extrusion rate, the surface finish on the tubing, the cure rate, the puller wheel speeds, and other things. It is important to use multiple lots of material during development if possible so this process variation can be more fully defined prior to production release.”
These issues are compounded the farther away one gets from basic silicone, said Woinowski. “Some of the exotic materials require a different mindset from traditional silicones,” he said.
Tooling geometry also can present problems, Erson explained. In fact, he calls “tooling geometry for tubing that is not straight ID/OD tubing” the second-biggest obstacle to a successful extrusion process, after materials consistency.“For multi-lumen and unsymmetrical geometries, it often takes more than one tooling set to get it right,” he said.
Problems also occur when too many technologies are employed at once, making the process more complex than it used to be, Lazas explained. “Some clients want you to put more stuff in the extrusion. Lumens are getting larger, more torque is needed, more pressure is needed, but at the same time, wall thickness is being reduced and demand on tolerances is being increased,” he said. “If you combine, for example, coextrusion of multilumens with braiding on the outside, the capability may just not be there to handle that, and the result is overextrusion.”
Mistakes also can be made if the team is charged with developing complex extrusions in a short amount of time, Lazas said. The OEM and the supplier need to determine in advance what might be a realistic lead time that gives the project the best chance to meet both quality demands and the marketing timetable.
Shedd noted that OEMs and providers sometimes forget that “downstream processes and equipment have significant impact on the quality and stability of the process.”
And sometimes, an operator is just not capable of running a process correctly. Havran noted that having properly trained, educated, and experienced operators is very important, but sometimes they can be hard to find. Extrusion is not a process where one can just press a button and have everything turn out the same every time. There are too many inherent inconsistencies in the process, and operators have to know how to adjust for them.
“The operator must be very good at not only running an established process, but also good at developing processes and knowing what inputs affect what outputs,” said Erson. “Reacting to differences in materials in the correct way is critical.”
A lot of these issues can be overcome with proper planning.
“The supplier must understand all the product requirements on the front end of the development process,” said Lazas. “The more knowledge we can get on the front end, the more we can help you with product planning, and the better able we are to meet your requirements and timetable. And the supplier must make available qualified extrusion engineers to work on new projects.”
To understand and deal with materials inconsistency, it is essential that the provider document its history with each material, and make this information available to the OEM, according to Woinowski. “This way, you can identify the true obstacles and overcome them via a joint effort with the material supplier and the customer,” he said.
Erson agrees. “Testing multiple lots of material is the best way to identify and overcome the obstacles related to material,” he said.
Material suppliers are helping in this area too.
“Some material suppliers are more willing to customize compounds in smaller volumes,” Woinowski said. “Identification and characterization of some material anomalies are gaining more interest.”
Based on that work, the team then can establish raw material parameters, Lathiya said, adding, “With thermoplastics, this must be with respect to gel count and melt index, also known asintrinsic viscosity.”
Planning also comes into play when addressing tooling and geometry issues, Erson said.
“Tooling changes can be made to correct geometry issues. It is best to have extra tooling partially processed on difficult projects so the time required for a second or third tooling iteration can be shortened,” he said.
Shedd noted that everyone involved in the process also must understand that extruded products are becoming less of an off-the-shelf commodity, particularly in the medical sector.“Medical customers frequently want a specialized component that will interface with an application or product,” he said. “This means cut-to-length sizes, multi-lumen, co-extrusion and other special requirements, all of which have to be handled a little differently. Having state-of-the-art downstream equipment and operators that understand and know how make adjustments to these processes is important.”
Taking the time to find the right operators also makes abig difference.
“Operator training will only go so far,” Erson said. “The people running the extrusion process need to be skilled operators that can do much more than put in a program and press start. The key is to find someone with processing ability and proven ability to solve problems and then train that individual in the extrusion process and all the nuances that go with it.”
Most importantly, according to Badera, everyone has to understand that patience is essential to overcoming these obstacles. Extrusion is an art as much as it is a science.
Helping the Cause
Just as medical device innovation never ceases, the same is true for innovation in extrusion materials and processes. There is a ton of activity developing solutions that can tackle the challenges that vex those who need tubing in their products.
Lathiya told Medical Product Outsourcing that important work has taken place recently in improving the controls of the extrusion process.
“Most advances have been in the controls of the extruder and downstream equipment such as gauging and flaw detection,” he said. “We can expect further advances in extruder control and gauging to address the tighter tolerances that OEMs are requiring.”
Shedd agreed, noting that new downstream technologies are also greatly helping OEMs and suppliers with the documentation that FDA will want to see during an inspection. “I believe most of the advances arein the downstream processes, which are being increasingly microprocessor-driven,” he said. “This in turn lends itself to monitoring and records that can be stored andmaintained electronically.”
Another advance is online measurement technology, according to Erson.
“Online measurements with a laser micrometer give OD dimensions, but online measurements using a scope are much more important now than they were five years ago and sometimes are required many times throughout a run in order to produce tubing that meets the requirements for ID features and wall thickness,” he said. “Setups are more critical and multiple adjustments or start-ups are often necessary to make the tubing within the tighter tolerances. With thinner walls down to .002 inches in silicone, material selection becomes critical if there are requirements limiting the appearance of gels or bubbles. Some of the lower durometer materials have more gels in them than the higher durometer materials.”
Advances in inspection technology, especially those that can be incorporated into the extrusion line, also are helping suppliers detect problems that may have gone unnoticed before.
“Devices like the Pixargus cosmetic inspection as well as the Sikora X-ray profile inspection taking place online are new to us,” Woinowski said.
Havran identified three significant advances that have made everyone’s lives easier:
•Improved measuring systems for real-time process monitoring and control;
•Improved machine control and drive systems; and
•Continued polymer development to improve properties, add active functions, and reduce size of components withoutsacrificing performance.
Newer materials are emerging every day to improve medical devices and the ways in which they are processed, according to Lazas. “We are seeing MRI-compliant, metal-replacing resorbable polymers and durable elastomers that don’t require reinforcement come on the market,” he said.
Extrusion is a process that demands extensive planning in order to execute properly. If medical device manufacturers involve their extrusion partners at the earliest stages of product development, the numerous challenges inherent in the process will be much easier to tackle. It all starts with the OEM having a strong sense of what it needs to know about potential extrusion partners in order to find the right one. Then it proceeds with the OEM and its partner hashing out how the process will work well in advance, so that all potential problems can be anticipated and fixed early on.
Erik Swain is a freelance writer based in Phillipsburg, N.J. He hascovered the medical device industry for 13 years.