Extrusion customers want tighter tolerances, better performance and lower cost.
Keeping the customer satisfied” is unquestionably sound business strategy—yet it is also harder to do,
The increased trend in miniaturized medical devices has emphasized the criticality of tooling and materials on the extrusion process. Photo courtesy of Interface Catheter Solutions.
especially in an uncertain economy, as customer expectations continue to rise. Better precision, greater strengths, new materials, smaller sizes and better quality are all in high demand these days (and expected at a lower cost, of course).
“Clients are requesting tighter tolerances, greater function, thinner profiles and faster lead times,” said Krissi Heard, a technical sales representative with MicroLumen in Tampa, Fla., a producer of polyimide tubing and custom co-extrusions. “They also want tubing with multi-functionality. We can manufacture a tube with a multi-durometer shaft that’s PTFE (polytetrafluoroethylene)-lined, braid-reinforced with stainless steel and has a laser-ablated outer diameter (OD). The biggest challenge for us is meeting an unrealistic due date as the design engineers needed parts yesterday. One flaw in one part of the process can have a trickle-down effect that slows everything else down.”
Extruded balloon tubing is another product that’s becoming more challenging to make—customers want longer lengths and larger diameters while maintaining wall thickness consistency to prevent inconsistent compliance percentages, burst values and fatigue life.
“This increases the demand and requirements on the tubing to reach the optimal balloon production yields, which means the extrusion process must have more consistent mechanical properties along with tighter tensile and elongation tolerances,” said Kenny Mazzarese, director of balloon development and extrusion for Interface Catheter Solutions in Laguna Niguel, Calif.
Increased complexity in the extrusion process also is a result of the trend toward miniaturized medical products—invasive devices for vascular applications continue to reach deeper into the anatomy with more therapeutic technology, requiring ever smaller and more precisely extruded components. “Miniaturization, combined with more complex procedures, requires more process control to achieve new tolerances, shorten lead times and make sure the manufacturing process is meeting customer specifications,” said Byron Flagg, product manager for PolyMedex Discovery Group in Putnam, Conn., which extrudes thermoplastic profile tubing for minimally invasive medical devices.
Extruders who desire strategic relationships with customers need to provide a greater range of capabilities than ever before. Full-service extrusion providers must be capable of everything from complex multilumens smaller than 3Fr to coil-reinforced components to longer than 1 inch in diameter.
More customers are asking their extruders to perform statistical analyses on their production lines to ensure quality control and tight tolerances. Photo courtesy of Coeur Inc.
The trends toward medical device miniaturization and stronger regulation have increased the need for more sophisticated and repeatable inspection technologies. “Once dominated by pin gauges and rulers, the inspection technology required to accurately measure miniature medical device components now involves automated non-contact vision systems and laser scanners,” Flagg continued. “These systems allow miniature component geometries to be inspected quickly and accurately, reducing costs and providing a more complete quality record.”
More customers are asking their extruders to regularly perform statistical analyses on their production lines to ensure quality control and tight tolerances. “The extrusion process requires attention to detail and a full understanding of melt rhelogy and material attributes to improve products,” Daniel Cykana, principle consultant for Extrusion Solutions LLC in Sheboygan Falls, Wis., told Medical Product Outsourcing. “Equipment must be certifiable with the ability to replicate capability for high-quality products.”
The use of more statistical process control is driven both by U.S. Food and Drug Administration (FDA) standards and customer expectations.
“In some cases it may be due to a finding from the FDA that our customers want for their records, but mostly it is to ensure that our processes match their specifications,” according to Paul Mazelin, marketing manager for Specialty Silicone Fabricators in Paso Robles, Calif., which produces silicone extrusions. Because of tightened tolerances, Specialty Silicone Fabricators relies on gauge R & R (repeatability and reproducibility) studies to ensure they are measuring parts the same way their customers do. “This can sometimes be challenging, trying to get the customer to buy off on the time required to perform these tests on their end,” Mazelin said.
Results need to be reproducible and predictable. For balloon tubing extrusion, that means proving dimensional capability in the tenths of thousandths and being able to maintain tensile characteristics within 5 percent. “As an example, we have used other commercially available tubing and have seen significant variation in lot-to-lot tensile properties, up to as much as 40 percent,” said Mazzarese. “By specifically targeting this property and controlling the extrusion process we can achieve ± 5 percent variation.”
Meeting this goal requires specialized equipment and tooling, but a new extruder is only half of the battle—the rest is incorporating effective pre- and post-processes to ensure extrusion performance and stability. The company has on-site materials lab capabilities for testing and evaluating tubing characteristics, as well as inline monitoring of the extrusion-forming process.
“These pre- and post-processes involve both common sense approaches as well as specialized techniques derived from fundamental understanding of the tubing required,” Mazzarese continued. “For example, excessive moisture and or insufficient elongation results in medical balloons with fish eyes, which can lead to lower burst pressures or reduced fatigue. Some pre-extrusion processes we use include cleaning the external surface of the resin and incorporating in-line filters. We’ve developed the pre- and post-methods we need to extrude tubing with the mechanical and dimensional properties our customers want.”
There is no doubt very high-quality/top-performing tubing for medical devices can be produced on an extruder with discrete instruments. “However, if a company wants to repeat that quality consistently, retain exact records of the process and have long-term savings, a central control device is needed,” advised Peter Rinaudo of Petrin Consulting in Waterford, Conn.
Some companies rely on a few instruments to read out barrel temperatures, screw speed, drive load and barrel pressure. Downstream equipment is only looked at to check the line speed. “But there is a lot more going on in the complete extrusion system that can throw off the quality of the product,” Rinaudo continued. “A central extrusion system control (CESC) computer system is able to monitor, control and record the entire extrusion system in real time.”
If, for example, the quality control department finds a previous shift of product below standards, the system can identify the exact time the problem occurred. It also will show the device on the line that caused the problem. “If tubing is being extruded, the CESC is picking up the inner diameter (ID)/OD/wall with a non-contact laser gauge at a rate of hundreds of times a minute,” he said. “There are extrusion lines operating today that if CESC picks a tube running out of spec, the operator is notified. The tube is sorted to a waste bin automatically. If corrective action is not taken, the line will shut down and an alarm will sound.”
The latest extrusion technologies center on new screw and die designs and more sophisticated software-based control systems. These improvements adapt to the inconsistencies inherent in polymer resins to stabilize the extrusion process and produce components with tighter tolerances. Post-extrusion or downstream equipment continues to change to meet product requirements by relying on better controls. Newer equipment has smaller footprints, site glass windows and access for ease of cleaning.
The increased trend in miniaturized medical devices has emphasized the criticality of tooling and materials on the extrusion process. “Miniaturization requires smaller extruders with specially designed
While device designers keep specifying smaller components with tighter tolerances, polymer manufacturers have made little to no improvements to their raw materials. Photo courtesy of Helix Medical.
screws and with more precise instrumentation to validate the process,” said Cykana. MicroLumen’s process and tooling allows it to specialize in small diameter tubing (ID < 0.0100”) with tolerances of 0.0002” (Conventional extrusion is typically double these tolerances with much thicker wall profiles).
The key to improving the extrusion process is developing the proper screw that will optimize the specific thermoplastic developed for a given product. “An extruder with a two-inch screw is not ideal to produce extrusion with an ID of 0.015” and a 0.005” wall thickness,” Mazzarese said. “Among other issues this creates increased stagnation which can result in overheating. Micro-extrusion demands a micro-extruder.”
Regarding miniaturizing tubing, Rinaudo has noticed a trend with some extrusion manufacturers who think they should use smaller extruders to make smaller tubing. “But over the long run going with an extruder less than one inch in size could be asking for more of a challenge,” he said. “When an extruder size is below one inch, the root strength of the screw is much reduced. And with a slight change in barrel temperatures the screw could bend or break. Also with a screw below the one-inch size, the standard plastic pellet does not carry forward as well in the feed section of the extruder. Yes, you could get mini-pellets, but that is an added cost. And in some cases the mini-pellet adds another heat history to the material that we don’t want. I would rather use a one-inch extruder with a well designed low-output screw. Another plus to a well-designed one-inch screw is the reduction of dwell time in the extruder barrel.”
Extruders have been innovative in developing their own advanced in-house tooling capabilities and adopting new laser machining and electrical discharge machining, or EDM, capabilities to produce the tooling required for complex and miniaturized extrusions. “The increased radiopaque filler loading required for visibility of smaller devices under fluoroscopy can compromise material properties and impact the extrusion process,” Flagg said. “In addition to understanding the impact increased filler levels have on their process, extruders also need to foster close relationships with custom compounders to ensure optimal filler dispersion and lot-to-lot consistency.”
Future breakthroughs in extrusion technology will involve the integration of value-added operations that currently take place after the extrusion is complete such as marker bands, electronic components, coil and braid reinforcement, material combinations and graphic artwork.
Two major trends affecting extrusion are the turnover in polymer grades available for medical device use and the lagging of polymer material properties behind an increasingly demanding medical device industry. Right now, extrusion technology is driven primarily by the need to utilize alternative polymers and to mitigate the inherent variability in polymer resins.
The selection of medical-grade polymers available for extrusion is turning over as new polymers are introduced and others are eliminated. New materials are being designed by many major resin suppliers utilizing nanotechnology to improve physical characteristics such as modulus without sacrificing impact qualities. Medical device manufacturers are developing new applications for bioresorbable polymers, either as temporary implantable structures within the body or for drug delivery.
“Some of the more exotic materials are PLA (polylactic acid), PCL (polycaprolactone) and other specialty bioresorbables, fluoropolymers, thin-walled balloon extrusions, flexible olefins and TPEs (thermoplastic elastomers),” according to Len Czuba, president of Czuba Enterprises in Lombard, Ill. New techniques must be developed to reliably process the bioresorbable polymers while preserving their unique properties.
Long-standing favorite polymers in the medical industry are being eliminated from the market because of possible health concerns. There is growing support within the European Union and the United States to legally ban the use of polyvinyl chloride (PVC); some polymer manufacturers are refusing to sell their products into the medical industry due to liability risks. New polymers are being developed to fill these voids, but in the meantime extruders must learn to use alternatives to meet the needs of their customers. “The newer flexible olefins and in particular TPEs have become a good way for companies to offer non-PVC products,” added Czuba.
Even utilizing long-standing polymer grades is becoming challenging as device designers continue to specify smaller components with tighter tolerances while polymer manufacturers have made little to no improvements to their raw materials. (Even if suppliers did make improvements, regulatory requirements would likely preclude their use unless the device manufacturers went through the expensive and time-consuming process of re-qualifying the new materials.)
“Extrusion is an extremely dynamic process in which any variation within the process creates a ripple effect that increases the variation downstream,” said Flagg. “Over the years, the precision of the extrusion equipment has improved. However the polymer raw materials continue to exhibit the same significant variations in properties as they have for decades. So, while tighter device tolerances are demanding more and more stable extrusion processes, consistency and homogeneity of the polymer raw materials to be extruded have improved little over the years. Extrusion companies are now caught in the middle, and some of the most significant technological improvements in recent years have been focused on this very challenge.”
Searching for greater tensile properties for small-diameter vascular applications, device designers have increasingly adopted the use of engineering polymers such as PEEK and thermoset polyimide. Their impact and fatigue resistance make them a suitable or even superior option to metal in some applications. In other applications such as guidewires, advanced stainless steel and Nitinol alloys will continue to be commonplace.
“In the case of engineering materials, some extrusions can and do replace metals in specific applications,” said Czuba. “For example, this is especially true for products that may have use in MRI suites where any ferrous metals would be a big problem because of the strong magnetic fields.”
Although all these changes—tighter tolerances, more quality control, smaller parts, new materials—add value to the customer experience, they also add expense. Companies must carefully evaluate every step of their process and apply Lean manufacturing principles to keep costs down and remain competitive.
“We are fortunate to have the resources, expertise and experience of our parent (Freudenberg-NOK) who has been practicing Lean principles and Six Sigma in the automotive and general industry markets for over 18 years,” said Thomas M. Vassallo, executive vice president of global business development for Helix Medical LLC in Carpentaria, Calif., which produces silicone extrusions for the medical device industry. “Lean is an enterprise philosophy, a way of life—it doesn’t happen overnight. At Helix Medical we incorporate Lean thinking throughout the corporate culture. We have assigned the responsibility for the implementation, training and ongoing practice of Lean to a divisional-level director whose sole responsibility is the execution of Lean principles and practices throughout our healthcare products division.”
Lean focuses on the reduction of waste and the elimination of non-value-added steps in every step of the manufacturing process. In a validated production environment the significant source of scrap is the changeover and startup process. Double inspection is another example of waste that can be removed from a process.
“Quick change and quick set-up are both things we have performed value stream mapping on and are continuing to ‘lean out’ the process to remove waste,” Mazelin said. “Set-up time does not add any value for our customers. We have improved our manufacturing techniques for die and mandrel fabrication and sped up the changeover of dies/mandrel. This yields better and more consistent product out the head of the extruder.”
Compared to injection molding or metal stamping, the extrusion process is inherently efficient in nature, with essentially 100 percent of the material consumed going into the finished product. “Therefore rapid changeover and startup are essential in minimizing the cost of material waste, which can be considerable given the cost of advanced medical polymer compounds and formulations,” Flagg explained. “Real-time, non-contact inspection technologies such as ultrasonic wall thickness measurement have cut down on start-up times by providing real-time process feedback and eliminating time-consuming offline measurements.”
During development, the greatest cost reduction is achieved by reducing the number of iterations required to establish a validated production process. As extrusion geometries become more complex, the number of development iterations required to refine tooling and processes increases, a situation that medical device designers cannot afford. “
In response,” said Flagg, “leading extruders have turned to finite element analysis software modeling to conduct development iterations in the digital realm. Considerable development can now be conducted virtually, before cutting steel for tooling or wasting polymer in prototype lots. This saves both time and material resources for the extruder and ultimately for medical device manufacturers.”
Customers are asking extruders to help them with their design and development as a way to streamline production and reduce costs. “Lead times are shorter than they were in the past, and our customers are looking for value engineering/cost savings,” said Ken Zander, director of OEM sales for Coeur Inc. in Lebanon, Tenn., which specializes in a variety of extrusions. “Most of our customers have realized that we can offer significant savings by providing them with engineering support and design of complex tube assemblies, whereas in the past that work was done by their own staff in-house.”
Heard indicated MicroLumen communicates with design engineers to target what functions are the most important in a tube’s design. “Once we know these,” she said, “we isolate specific properties or traits and focus on manufacturing a tube that meets those needs.
An example would be a tube that needs to have a specific flexibility at the distal end (for steering the device in the body) and a different amount of flexibility at the proximal end (so the administer can properly maneuver the device). Knowing that ahead of time allows us to properly manufacture a tube that meets that specific function.”
Specialty Silicone Fabricators is now extruding thermoplastic materials in addition to thermoset materials. “This has been a big addition to our product line,” Mazelin said. “We are expanding our capability to offer one-stop shopping to our customers. There are many thermoplastic extruders out there, and we are not attempting to compete with those folks; we are simply trying to assist our customers by providing a wider range of materials they may consider in their product designs.”
Successful extruders need to invest meaningful time developing intimate relationships with their customers to manage increasingly complex communications. As medical devices become more complicated, device designers need to communicate more complex requirements to their manufacturers, and extruders need to add value by rigorously advocating for design for manufacturability.
“Tough communications like this can easily become adversarial unless they take place within an intimate and healthy relationship,” Flagg said. “Such relationships are fostered by a considerable investment in one-on-one interaction, developing a deeper understanding and knowledge of people’s needs and showing genuine concern for those needs. It takes a real commitment from upper management to empower their sales teams and engineers to spend this much time up front with customers, but the payoffs in the long run are indispensable."