Today’s medical device original equipment manufacturers (OEMs) and their customers demand high-quality, aesthetically appealing surfaces. The surface quality of the plastic component for medical applications is important from both a functional and aesthetic perspective. The properties of the thermoplastic, the mold surface finish, and the molding process all play a role in the final component surface quality.
Polycarbonates and polycarbonate acrylonitrile butadiene styrene (PC+ABS) blends offer remarkable thermal and mechanical properties, enabling these robust materials to be suitable for a wide variety of medical applications. The optical clarity and transparency of polycarbonate resins make them excellent candidates for medical parts that require glass-like transparency. Polycarbonate resins and PC+ABS blends can be pre-colored to achieve different colors and special effects to meet the requirements of a wide range of medical applications.
Due to its fast cycle time, excellent part-to-part repeatability, and ability to produce large quantities from a single injection mold, this has been the primary technology for mass production of polycarbonate parts for the medical industry. This allows engineers and designers to craft polycarbonate components of nearly any shape with tight tolerances and varying geometric complexity. Medical device OEMs must also consider disinfectant compatibility, sterilization requirements, and regulatory fulfillment when qualifying a material.
To meet changing medical application and market requirements, injection molding technology continues to evolve. A new advancement in injection molding called rapid heating and cooling (RH&C) helps medical device OEMs and their customers enhance surface appearance for medical housings with the opportunity to reduce manufacturing costs.
Rapid heating & cooling
During the typical injection molding process, a thin frozen skin layer is formed due to the temperature difference between the mold tool surface and the plastic melt, as they come into contact during melt injection. A large temperature difference does not allow the molten plastic to fully replicate the mold surface, which can cause poor surface quality and highly visible weld lines in some instances.
Weld lines on a medical device can be considered unacceptable in some applications from both a visual and structural integrity perspective. To improve part surface quality, a mold temperature closer to the softening point of the polymer is needed. However, this can lead to longer cycle times and poor part quality using conventional molding and cooling technology.
Medical OEMs and their customers continue to search for ways to improve part aesthetics and optimize production to meet performance and cost challenges. While injection molding has traditionally been the primary technology for mass production of polycarbonate parts in the medical industry, RH&C is an emerging technology that has positive implications for the medical device market.
With RH&C technology, it is possible to eliminate surface defects to deliver high-quality surfaces on thin-wall, complex designs that offer medical OEMs and molders countless possibilities and cost savings.
About the authors: Mark Matsco is director of application development, polycarbonates – Covestro North America. Jessica Boyer is application development engineer, polycarbonates – Covestro North America. Questions can directed to Matsco or Boyer at firstname.lastname@example.org.
Recently developed 4- and 5-layer coextruded tubing can reduce medical device manufacturing costs up to 50%, while retaining, or even expanding, performance.
Developed by Natvar, the tubing is an alternative for applications currently relying on monolayer materials, as well as some 2- and 3-layer structures. The technology also provides a more cost-effective alternative to braided tubes for higher-pressure delivery systems.
Key tubing attributes include flexibility, clarity, and the ability to be solvent- and UV-adhesive bondable. Additional desired characteristics could include UV protection and moisture/oxygen barrier.
Drugs delivered at higher pressures, such as contrast media, could benefit from the technology. Traditional 3-layer tubes with a polyethylene inner layer can handle (based on application) up to 1,200psi.
NEMA 34 series integrated stepper motors with Profinet Industrial Ethernet capabilities are available in torque ratings of 30N-m (26.6 lb-in), 60N-m (53.1 lb-in), 90N-m (79.7 lb-in), and 120N-m (106.2 lb-in). They include all necessary electronics within the housing, and connect to Ethernet bus systems such as EtherCat, Ethernet I/P, Powelink, ModbusTCP, Sercos III, and Profinet. Bluetooth, ZigBee, WLAN, PLC, RS485, and CANbus are available with an optional SMC85 controller. Options include electronic gearing, 9.53mm (0.375") or 14mm (0.551") diameter shafts, absolute mini-turn encoder, and planetary gear heads.
Spring-energized seals for reciprocating, static/face applications
A technical catalog from Bal Seal Engineering Inc. provides information about how spring-energized seals can be used to address reciprocating and static/face sealing challenges.
The 28-page catalog, “Bal Seal spring-energized seal: Solutions for Reciprocating and Static/Face Applications,” describes the company’s range of reciprocating and static/face Bal Seal spring-energized seals can increase the performance, safety, and reliability of products designed for low-friction, high-pressure, and prolonged service sealing applications.
The catalog presents data on the seals’ properties, including pressure limits, cross section ranges, and inside diameter ranges. A detailed table describes available seal jacket materials and their characteristics, including temperature range, wear resistance, pressure/extrusion resistance, and shaft abrasion.
Type MPP microPEM self-clinching pins for micro positioning and alignment applications in compact electronic assemblies clinch permanently into stainless or other metal sheets as thin as 0.5mm (0.020"). The chamfered end of the pin offers easy mating-hole alignment, and the head of the installed pin will be flush in the host sheet to present a smooth appearance. The pins can be installed automatically and are available in diameters as small as 1mm (0.040") and in lengths as short as 2mm (0.080"). The precipitation-hardened stainless steel pins offer corrosion resistance.
In a proof-of-concept experiment, Australian researchers have used a handheld 3D printing pen to draw human stem cells in freeform patterns with high survival rates. The device was developed in collaboration with ARC Centre of Excellence for Electromaterials Science (ACES) researchers and orthopedic surgeons at St. Vincent’s Hospital, Melbourne, to allow surgeons to sculpt customized cartilage implants during surgery.
The pen delivers a cell-survival rate of more than 97%. A hydrogel bio-ink carries and supports living human stem cells, and a low-powered light source solidifies the ink. Bioprinters have the potential to revolutionize tissue engineering, as they can be used to print cells, layer-by-layer, building artificial tissues for implantation.
In some applications, such as cartilage repair, the exact geometry of an implant cannot be precisely known prior to surgery, making it difficult to prepare an artificial cartilage implant. The pen treats defects by filling them with custom scaffolds.
“The development of this type of technology is only possible with interactions between scientists and clinicians to identify the problem and scientists to develop a solution,” says Professor Peter Choong, director of orthopedics at St. Vincent’s Hospital.
The team developed the pen with surgical constraints in mind and fabricated it using 3D-printed, medical-grade plastic and titanium. The device is small, lightweight, ergonomic, and sterilizable. A low-powered light source is fixed to the device and solidifies the inks during dispensing.
“The biopen project highlights both the challenges and exciting opportunities in multidisciplinary research,” says Professor Gordon Wallace, ACES director. “When we get it right, we can make extraordinary progress at a rapid rate.” www.electromaterials.edu.au; svhm.org.au
Commercial CLIP-based additive manufacturing
The M1 commercial 3D printer uses continuous liquid interface production (CLIP) technology and engineering-grade materials. The printer offers high-resolution parts with the engineering-grade mechanical properties and surface finish required for functional prototyping and production-quality parts. Internet-connected and data-rich, the M1 collects more than 1 million process-control data points per day, allowing remote diagnostics, assistance with print optimization, and improved print quality. The M1 has seven proprietary resins, enabling the use of complex chemistries to create parts with a range of mechanical properties. www.carbon3D.com
Fathom and Nano Dimension introduce 3D printer
Fathom and Nano Dimension willcollaborate on the introduction of the DragonFly 2020 3D printer to Silicon Valley and the greater West Coast area.
“Both companies share the same vision of changing the way products are designed and manufactured,” says Michelle Mihevc, Fathom principal and co-founder. “Nano Dimension is leading the way in the 3D printed electronics space.”
Mihevc and her partner Rich Stump started Fathom in 2008.
“Fathom will help bring us even closer to our key customers because it is well-known as one of the most creative and best performing 3D printing services companies in the country,” says Simon Fried, Nano Dimension CBO. www.nano-di.com; www.studiofathom.com
High-strength PETG based 3D material
A high strength polyethylene terephthalate glycol-modified based material, guidel!ne, from taulman3D offers high temperature printing capabilities and addresses the difficulty of printing small features of some parts due to thermal build-up. The material is also a starting point for developers wishing to obtain FDA/CE certification for a device, knowing that the raw material is listed with the FDA and has passed FDA testing.
Sold as a raw material, guidel!ne is extruded in a way that keeps contaminates out of the soft material during cooling, where contaminates and bacteria could be embedded. In addition, pH and ORP levels are monitored and adjusted to maintain acceptable levels.
Information provided to the guidel!ne user will be in sync with the FDA’s “Technical Considerations for Additive Manufactured Devices Draft Guidance for Industry and Food and Drug Administration Staff, Section C, Material Controls.” While certificate of authenticity will be the responsibility of the end user, taulman3D will provide information to support such efforts. www.taulman3d.com
Metal medical miracles
Features - Metal Cutting
Medical grade metals may be difficult to cut, but given the right tooling and cutting fluid, productive machining is within reach.
Super strong metals that make jet engines spin faster, submarines dive deeper, and nuclear power plants safer to operate, are also responsible for most of today’s lifesaving implants and medical instruments. Heat resistant super alloys (HRSA) such as titanium and cobalt-chrome alloys comprise the lion’s share of bone screws, pins, fusion cages, and joint replacements; while trocars, shears, and hemostats made of 316L and other stainless steels – high in nickel and chromium – are common in any surgical theater.
These tough metals are biocompatible, fatigue and wear resistant, and very hard. And while these attributes make them desirable for use in the human body, they also present a variety of manufacturing obstacles, including poor and unpredictable tool life during machining. Sharp, positive-rake cutting tools and inserts are the rule when cutting titanium and other medical grade materials, but it takes the right blend of carbide, coating, and edge prep for tools to survive when battling HRSAs.
Plenty of choices
For finishing operations, Sandvik Coromant recommends a PVD-coated carbide such as 1105 grade – a multiphase TiAlN coating applied over a hard, wear-resistant substrate that resists cratering and abrasion while retaining the sharp cutting edge needed for effective machining. These types of PVD-coated tools also work well for the light depths of cut (DOC) and moderately high feedrates typical of the trochoidal, constant-engagement toolpaths used when roughing and semi-finishing HRSAs. Heavy roughing or interrupted cutting operations may require a tougher grade – a PVD-coated 1115, an uncoated H13A, or CVD-coated 2025 – all of which perform well against mechanical shock that is common when machining difficult materials.
Pocketing and slotting operations often benefit by using a roughing end mill designed for such work. Compared to the old-fashioned corn cob roughers most veteran machinists are familiar with, many solid carbide roughing tools are ground with varying pitch and helix angles to break up the harmonics that lead to chatter under heavy machining loads, while specially prepared flutes prevent edge chipping that is common when cutting tough medical materials. Don’t be scared off by what at first glance seems a steep price tag for these cutters – investment in high quality tools is the name of the game with HRSAs, and dropping an extra 25% (or more) for one that’s capable of Kung Fu-like cutting performance might be what it takes to turn a loser job into a winner.
One HRSA cutting tool option that may surprise some industry experts is ceramic. Known for extreme hardness and wear resistance, aluminum oxide and silicon nitride-based cutting tools have long been a favorite of the automotive industry for high volume machining of gray cast iron. But, these cutting tools are generally too brittle for superalloys. However, the addition of silicon carbide whiskers makes this material ideal for machining nickel-based materials, even under heavy roughing conditions. Silicon alumina nitride (SiAlON), for example, cuts cobalt chrome and similar super metals at speeds 20x to 30x greater than carbide. However, light feed rates must be used, generally less than 0.0039"/tooth (0.1mm/tooth), and round inserts are recommended due to SiAlON’s tendency to notch at the depth of cut line. Also, ceramic must be run without cutting fluid, and cannot be used to cut titanium due to chemical reactivity between the two materials.
Stick to the plan
These are all good starting recommendations, but unfortunately there’s no such thing as a general purpose carbide grade or cutting tool suitable for the entire range of HRSA machining. Shops can see significant productivity gains by working with a knowledgeable application specialist to fine tune their processes – someone with sufficient carbide grades and tooling geometries up his or her sleeve to cover the full spectrum of the shop’s materials and processes. The goal here should be development of a predictable tooling strategy rather than maximizing tool life or part output – better to change a cutter before it fails than to push too hard and scrapping out an expensive workpiece, or risk damaging an even more expensive machine tool.
Always perform test cuts on any new material, cutter, or machine tool to determine baseline feed rates, spindle speeds, and depths of cut. This may seem like a waste of machine time, but the effort is well worth it and helps maximize tool life and avoid scrapped parts. Follow the cutting tool manufacturer’s recommendations when starting out, but don’t be afraid to break the rules – if a certain insert grade is supposed to run between 300sfm to 600sfm with a chip load of 0.005ipr to 0.008ipr in titanium, go ahead and kick it up a notch if you’re getting good tool life, provided you can maintain predictable results. Pushing the boundaries is the best way to get ahead in this competitive machining environment.
The FMB Turbo 5-55, 5-65, and Turbo 8-80 are automatic magazine style bar feeders for processing bars in the diameter ranges of 5mm to 55mm, 5mm to 65mm, and 8mm to 80mm and in lengths from 12ft to 14ft on CNC lathes. Quick change polyurethane guide channels allow for quiet operation at high rpm while feeding round, square, or hex bar stock. The product line is compatible with all kinds of fixed headstock lathes, and Swiss-type synchronization is also available.