MOULDING AND EXTRUSION
 |
Cleanroom injection moulding is a good match for an array of medical applications. Pictured here are medical devices moulded on Arburg equipment.
|
Manufacturers of moulding and extrusion equipment are doing well these days, and the medical field is a major contributor to their success. The reasons for injection moulding’s popularity are numerous: the procedure offers high manufacturing flexibility, it can eliminate surface finishing operations, and, in addition, injection-moulded parts are usually lighter and cheaper than machined metal alternatives. Similarly, the medical field’s continually strong demand for tubing and other extruded parts supports the growth of the extrusion industry. But as moulding and extrusion firms grow to accommodate rising demand, so do the pressures put on them by medical device firms, seeming to always request smaller parts and tubing made to tighter tolerances than were previously possible. On the moulding front, liquid silicone rubber (LSR) moulding and multicomponent moulding are popular because they can meet the rigorous demands of the medical device industry. Manufacturers of extrusion equipment are also keeping up with the needs of medical device firms by developing machines with expanded capability in producing miniature tubing with multiple layers and lumens.
LSR moulding is a rapidly growing area for all kinds of medical applications, according to Arburg president Friedrich Kanz. Much of LSR’s popularity stems from the apparent ease with which liquid silicone can be moulded into parts with tight tolerances. It is easier than most materials to mould into complicated shapes, and the process typically yields parts with minimal flash or burrs. In addition, LSR requires a short curing time and the process eliminates the risk of contamination because the material is pumped directly into the machine.
LSR parts are particularly well suited for medical device applications, owing to the material’s biocompatibility and durability. According to silicone specialist Nusil (Sophia Antipolis, France), silicone is among the most extensively researched biomaterials on the market. Offering long-term resistance to environmental extremes, the material does not support bacteria growth and adapts well to tissue and body fluids. The material is also durable, which makes it attractive to medical device OEMs. It resists acids, bases, chemicals, oils, and water, and withstands multiple autoclave cycles. Additionally, LSR is often used for moulding handheld medical devices that require a soft and comfortable surface. Medical devices coated with the material are also easier for physicians to grip when they are covered with blood or other bodily fluids.
LSR can be processed using conventional moulding machines. “It is not a difficult procedure to put into operation,” Kanz explains. “Basically, all of the Arburg machines have silicone moulding capability,” he adds. “Setting up a machine for LSR moulding is mainly a matter of modifying the machine to provide the desired characteristics of the part that is to be moulded.” To ensure the quality of parts made using LSR moulding, Kanz stresses the importance of high-quality moulds. “I would say that having a well-designed, structurally sound mould is more important for silicone moulding than with other materials,” he explains.
Continued growth of multicomponent moulding
Another trend that has experienced rapid growth is multicomponent moulding—also known as multishot or multimaterial moulding. “It’s a proven technology,” explains Anthony Pagliaro, marketing manager of the healthcare division of Saint Gobain Performance Plastics (Saint-Quentin Fallavier, France). “I believe the product design flexibility, lower product cost, and improved product quality that the moulding technique offers are very attractive features for the highly competitive [medical device] market.” The growth of multicomponent moulding in recent years has been an important development in the field of automation because it can simplify moulding operations for complicated parts made of multiple materials. Multicomponent moulding can be used to make production more efficient by reducing several moulding processes to a single cycle on one machine. For high-volume applications, the procedure can curb part costs by eliminating downstream assembly steps. The procedure may not be cost efficient for low-volume use, however, because of the high upfront costs associated with multishot moulding equipment.
Multishot moulding can be used to create parts with a range of material properties and colours. In addition, materials deposited by a second shot can provide devices with functional features such as shock absorption, vibration dampening, or soft-touch handles. The simplified production process improves the lot-to-lot consistency of products, often reducing the need for quality-control inspection. In addition, this leads to less component handling, which can lower contamination risks. “Although not every product is right for multimaterial moulding, the cost savings that are generated for the right design will accelerate interest and acceptance in the process,” predicts Pagliaro, giving the company’s two-shot moulding services as an example. “By replacing traditional moulding plus assembly, multimaterial moulding will streamline procurement, development, and manufacturing, reduce part cost, and improve part performance by enabling more robust component design.”
Extrusion trends
Demand for custom and small-diameter tubing is fuelling innovation in extrusion equipment. As a result, the industry has developed machinery that can make progressively smaller and more complex tubing. “The main trends we are seeing from medical device companies are reductions in the size of tubing and increased pressure to hold wall tolerances of the tubing,” says Steve Blanche, sales manager at Guill Extrusion (West Warwick, RI, USA). Extrusion firms have kept up with the demand for tubing with a diameter the size of a human hair by offering machines that can extrude 0.0025-in.-diam tubing with tolerances down to 0.0005 in. “Tubes of this size are being used alone or in conjunction with another tube to administer drugs using a needle,” he explains. “These tubes also can be used as a drain for certain applications,” he adds.
Another trend that Blanche observes in the medical field is growing demand for multilumen and multilayer tubes. “There are companies asking for multilumen tubing with anywhere from 2 to 12 holes,” he says. “These lumens can be used for inserting wires, cameras, or fluids,” he explains. Recent growth in multilayer technology is mainly the result of a surge in invasive applications. Multilayer tubing can help hospitals control costs because it incorporates relatively inexpensive materials in its inner layers without sacrificing the properties of the external layers. “The outer layers generally have properties such as high lubricity that can be useful in invasive procedures,” Blanche explains.
A procedure that is the extrusion equivalent of multicomponent moulding can produce multimaterial silicone tubing by switching between material feeders during extrusion. A typical example of a product made using this method is a catheter tube with a flexible distal end and a rigid proximal end. During extrusion, a pigment can be added to one of the tubing ends to enable physicians to distinguish the two ends visually.
