Mark Crawford, Contributing Writer04.01.15
Numerous injection molding technologies are used to manufacture orthopedic implants, instruments and other related products. Molders are constantly being challenged by smaller devices, more complex designs and high-performance polymers that are engineered to provide enhanced physical characteristics, such as stiffness and chemical and temperature resistance.
Although these advanced materials allow designers to be more innovative in their product designs, they also are more expensive and more challenging to mold.
The type of molding technology used to make an orthopedic part or product depends on a number of factors, including end use and operational environment, selected materials, product design, aesthetic appeal, budget and size of the production run.
Common technologies are thermoplastic injection molding, two-shot molding, insert molding, overmolding, gas-assist injection molding and high-temperature molding.
Although plastic is the most common material, metal and liquid silicone rubber (LSR) also can be injection molded. Products include spinal implants, surgical instruments, disposable devices, implant trial devices, bone anchors and staples, surgical handles, case and tray components and surgical cutting guides.
What OEMs Want
Orthopedic device companies want more precision, more speed and, of course, lower costs—with no price increases. This puts continuous pressure on molders to find new ways to meet these demands, without compromising quality or performance—which is especially challenging when making miniaturized complex parts.
One way hospitals can control costs is by using less-expensive, single-use surgical instruments and related products. Many healthcare networks today are struggling to control rising costs, as well as reduce the transfer of infections. Common instruments such as hemostats and forceps are becoming increasingly expensive to purchase and use—this total cost also includes the increasing expense of instrument sterilization.
“When you also consider that single-use instruments help minimize the transfer of infections, it is no surprise that many OEMs are looking to replace previously reusable devices made of metal with single-use instruments made of high-performance plastics,” said Jim Hicks, technical marketing engineer for Alpharetta, Ga.-based Solvay Specialty Polymers, a provider of engineered polymers for the medical industry.
For single-use products, the overall challenge is reducing manufacturing costs while maintaining structural integrity requirements. For example, with femoral and tibial trials, extremely tight tolerances are required because the parts mimic the actual machined implants. Some are in the 0.0005-inch profile range over complex geometries.
“To successfully mold such tight tolerances, a molder has to understand scientific injection molding, as well as how to build a tool that will mold with very tight tolerances controlled by geometric dimensioning and tolerancing,” said Dwalin DeBoer, business unit director for Mack Molding, an Arlington, Vt.-based provider of custom injection molding, manufacturing and assembly services for the medical industry. “We have been able to create several hundred item numbers using less than ten tools, by starting with an all-inclusive tool and refining it as the process and part requirements allow.”
Selecting the right resin and molding process—and understanding end use—are critical for achieving performance expectations and product longevity. For example, some orthopedic products are heavily impacted in the surgical suite, so the resin must have adequate impact-resistance properties.
“And while we take some cost out by changing the molding process to internal gas-assist or structural foam, that can also affect the strength of the resin through wall thickness or foam,” said DeBoer. “So it is imperative the right process is used with the right resin and part design.”
Building the mold and tooling typically is the largest production expense. Therefore, medical device manufacturers consistently look for ways to reduce tooling investment. One way is by running different classes of resins within the same tool steel. Another strategy for reducing tooling costs is to use standard mold bases and standard mold parts, as well as making multiple parts in one mold, experts told Orthopedic Design & Technology.
“Instead of making 10 molds to manufacture 10 different parts, we can make one mold with ten cavities, one for each of those parts,” said Kenny Wang, managing director for Kaiser Technology Company in Taiwan. “Multiple cavities in one tool for different parts requires less tooling investment. This can reduce tooling costs by as much as 50 percent and tooling lead time by as much as two-thirds.”
Pushing the Limits of Design
As orthopedic parts and products become smaller, the demand for micro-molding is increasing. OEMs are on the hunt for crisp geometries, high manufacturing precision, finer edge quality and no radii in their miniaturized products. Tolerances can be as tight as a few microns.
“Miniaturization of micro components with high resolution of features is one the most important considerations for OEMs when they are looking for a micro-molder,“ said Lindsay Mann, project manager for MTD Micro Molding, a Charlton, Mass.-based molder of micro components for the medical industry.
OEMs are turning more to insert molding for small components to reduce assembly steps and mitigate the risks of utilizing adhesives. MTD Micro Molding recently worked with an injectable drug-delivery systems company that was struggling with the traditional manufacturing approach for its drug-delivery device. The process included a series of high-risk, cumbersome steps to manually assemble four micro components to combine the cannula and housing, which drove up labor costs. The company wanted to streamline this process and reduce costs. An initial mold-flow analysis showed that all the components could be micro-molded together at the same time. This process eliminated three assembly steps (considered to be the industry norm for this kind of product), resulting in a significant cost savings.
“The geometry-rich cannula was micro-molded at 10 cents a unit, in contrast with making four separate components at a cost of over $1.50 for the set, excluding assembly costs,” said Mann. “In addition, with the assembly steps largely contributing to the main failure mode in the final device, molding the device as a single unit removed all possibilities for functional failures.”
To take advantage of the qualities of both metal and plastic, more orthopedic design engineers are developing hybrid devices that incorporate both. This requires an in-depth knowledge of not only how these materials behave individually, but how they react and bond with each other—both during production and in the end-use environment. For example, more aluminum sterilization cases are being built with plastic brackets, trays and lid. These plastic components not only reduce the overall weight and cost of the delivery system, but are also engineered to withstand repeated steam sterilization.
“Hybrid systems have been growing in popularity,” said Hicks. “Even though all-metal systems are lower cost, they don't always provide the best protection for increasingly delicate instruments. Plastics provide better protection, but can cost more. Combining the attributes of metal and plastic provides a broader level of design freedom that can lower manufacturing costs when plastic parts are produced via injection molding.”
Sometimes injection molding isn’t always the answer. Some products may require 3-D printing or other additive manufacturing technologies that complement injection molding. For example, an additive process like direct metal laser sintering (DMLS) or metal machining works well for initial prototyping before increasing part production with a process like metal injection molding (MIM).
This is especially true for products such as surgical instruments, scanning equipment and handheld devices. Three-dimensional printing also provides more advanced material choices, such as polyether ether ketone (PEEK) and Ultem.
“Three-dimensional printing is often thought of as a one-off process, but the equipment is getting faster, material properties are approaching those we are accustomed to in machining and molding and processes are more robust,” said Rob Bodor, vice president and general manager of the Americas Division of Proto Labs, an injection molding and CNC machining facility in Maple Plain, Minn. “Stereolithography, for example, can produce parts with features down to 0.002 inches wide and 0.001 inches tall.”
DMLS is one of the most cutting-edge additive manufacturing technologies available for medical device manufacturing. It involves fusing a bed of metal powder into thousands of thin layers that eventually become prototypes and even production parts.
“On OEM requests that have organic or extremely challenging geometries, or designs that are impossible to manufacture with traditional methods, DMLS can be used,” said Bodor. “DMLS is also leveraged to combine multiple metal components on a device into one part, which reduces bill of materials.”
Advanced Materials
There is growing interest by medical product designers in engineering materials that not only have enhanced physical characteristics, but are also easier to mold in the production environment. This means faster and higher-quality parts for designers and engineers. For example, Proto Labs has partnered with material manufacturers such as Cool Polymers and Dow Corning to provide thermally conductive plastics and medical and optical liquid silicone rubber.
“These advanced injection molding materials help us better serve customers who are looking for the latest in advanced material offerings,” said Bodor. “Medical- and optical-grade LSR are frequently used in device applications. Their ability to be sterilized sets them apart from many traditional soft-touch materials.”
Medical design engineers continue to find new ways to use PEEK and PEEK varieties, which are becoming popular for orthopedic applications because of their strength and durability. Because it is an approved implant material, PEEK also has the advantage of offering biostability data. However, PEEK is very challenging to mold because extremely high heat and precise temperature control are required to achieve highly crystalline parts. Also, extremely small parts tend to shift and move in the mold cavity, posing another challenge.
“An issue with PEEK is that temperatures are so high that the part doesn’t exhibit optimal mechanical properties, so it distorts very easily,” said Mann. “With micro-molding, temperature control is highly critical. Because the part doesn’t have cold strength during the molding process, it may stick in the cavity. PEEK parts are often so thin they don’t have the strength that a thicker part would have, making it hard to predict which half of the tool it will stay on. This makes it more challenging to de-mold properly without distortion. The mold temperature needs to be 350 degrees [Fahrenheit] or higher to crystallize PEEK so the final product will have the physical characteristics that are expected.”
Another critical challenge with molding PEEK is the optimization of the flow path the polymer takes to get to the cavity. A challenge for micro parts is getting the PEEK from the injection unit into the cavity, while still maintaining its orientation and properties. This requires the runner, sprue and coldslug to release properly and cooperate with robotic automation and camera presentation.
“Although mold design and temperature control are extremely important for successfully molding PEEK, so is the design of these mold features,” said Mann.
Polyaryletherketone (PAEK) is also being used more in the orthopedic market. This resin family offers both unfilled and glass or carbon fiber-reinforced thermoplastics (for more strength) with high-temperature stability and high mechanical strength.
“With 30 percent glass, for example, PAEK offers good chemical resistance, high-heat resistance for various sterilization techniques, biocompatibility, high stiffness and strength, radiation resistance and radio-translucency so it can be used during an MRI. It also offers improved part economics compared to 30-percent glass fiber-reinforced PEEK, another high-heat resin,” said Michael Hansen, senior technical development engineer for Mack Molding.
For ultra polymers such as modified PEEK and PAEK materials, temperatures can be as high as 700 degrees Fahrenheit, which create safety challenges for the operators and technicians who handle this equipment.
“As the temperatures and duration of sterilization processes for these products increase, so do the heat and chemical resistance requirements of the materials,” said Hansen. “The ripple effect of higher heat properties in resins is higher mold, melt and drying temperatures, resulting in increasingly stringent safety precautions on the molding room floor.”
Getting Creative
Considering plastics for medical devices that have been traditionally made from metal can be a major challenge for design engineers, who have grown accustomed to working with and designing with metals. To help them see the benefits of advanced plastics, Solvay Specialty Polymers conducted an in-depth study on end-use performance, biological safety and the economics of replacing metal with plastic and developed a practical seven-step metal replacement plan. The study used Solvay’s PARA resin to replace metal in the traditional metal Hohmann retractor, a popular device used in surgical procedures. The retractor was selected because of its challenging performance requirements, including high mechanical loads. For single-use applications, PARA was used because of its strength and stiffness, excellent surface finish and compatibility with gamma radiation sterilization.
“The high-performance polymer provided the same level of strength and rigidity as some metals at ambient temperatures,” said Hicks. “High-performance polymers also deliver cost benefits, enhanced aesthetics and ergonomic improvements. They can also be colored, thus enabling the production of devices in a variety of sizes that can be easily and quickly identified in the operating room.”
A recent Mack Molding project involved manufacturing a high part number mix at low volumes for a tibial trial program. Tibial trials are the plastic instruments used during knee replacement surgery that mimic the final implant and help surgeons determine the proper size and thickness needed for a correct fit. Traditionally, these products are CNC-machined. In this case, the OEM was looking for a more cost-effective method for producing the required 420 tibial trial configurations. The OEM had already designed a spacer or shim that allowed parts to be stacked to create multiple thicknesses, which was a good start.
“This reduced the part number count to 258,” said DeBoer. “Yet developing injection-molding tools for such a large number of parts cost competitively was still a challenge.”
While individual dies were needed for each of the top surface parts, because they had various articulating surface conditions, the bottom surfaces were virtually identical for all parts of a particular size group. To further reduce part count, Mack Molding used the master-unit-die tool concept, where standard prefabricated bases are inserted with custom core/cavity units. This solution allowed them to produce 24 different part numbers using only four complete modular dies, five additional cavities and two core sub-inserts.
“Using combinations of trials and spacers, they were able to cover 420 tibial trial configurations with 258 unique molded part numbers, including 48 spacer molds, 48 complete tibial trial molds and an additional 162 cavities,” said DeBoer. “This approach reduced the total number of complete modular inserts by 210 and cut total tooling costs in half. Additionally, converting from conventional CNC-machined trials to injection-molded replacements reduced part cost by nearly 75 percent.”
A top priority in almost all job requests is speed—however, for some projects, how fast a job gets done should not necessarily be the priority. With some equipment, slower is better—and even cheaper—compared to traditional methods. For example, Sarix milling equipment is well-known for its high quality and precision—however, it takes longer than traditional milling and even electrical discharge machining (EDM).
“EDM is 100 percent slower than traditional milling and Sarix is 100 percent slower than that,” said Mann. “For example, we recently had the Sarix create 36 needle features, which consisted of 72 needle-halves. This process took about four weeks of 24 [hours]/7 [days a week] unattended time to complete. The perception may be that this is a more expensive tooling technique because of the high-tech equipment and time needed, but it isn’t due the unattended nature of the process.”
Sarix allows micro-machinists to create fine details with very little electrode wear. While graphite electrodes can machine sharp corners with .001- to .0015-inch corner radii, Sarix has such minimal wear that corners can measure at 5 microns (.0002 inches), with a tolerance resolution of .000004 inches and glass-like surface finish (Ra 0.05).
“Sarix micro EDM capability enables us to make edge features that were not possible before, with finishes that are mirror-smooth and perfectly detailed corners, edges and surfaces,” said Mann. “This capability gives our customers more flexibility for making more innovative, complex product designs.”
Moving Forward
OEMs and contract manufacturers continue to work together to push the limits of technology. Costly metal instruments can be replaced with high-performance plastics that can withstand repeated steam sterilization cycles and autoclave temperatures up to 273 degrees Fahrenheit (134 degrees Celsius). As these high-temperature plastics become better known and tested in the medical-device industry (they have been used for years in aerospace and automotive), more products that were traditionally made from metal—including cutting instruments—are now being produced in plastic.
“Clearly the use of plastic for cutting or other material-removal instruments such as broaches or rasps will depend on the end use of the device and how long it is expected to perform,” said Hicks. “In several cases, customers are looking at metal/plastic hybrids to reduce cost by having a simpler metal-cutting surface embedded into a rigid plastic substrate. Cost reduction can be significant—depending on device and unit volume, a three- to four-fold reduction is not uncommon.”
“Replacing anything made from metal, which can cost in the hundreds of dollars per part, with an appropriate resin, which can cost in the tens of dollars per part, results in major cost savings for OEMs, roughly 80-90 percent of cost,” added DeBoer.
But just as the appeal of metal starts to fade because of cost and machining time, technology improvements—including additive manufacturing and metal injection molding—are making metal competitive again. For example, metal injection molding involves a multi-step debinding and sintering process to create parts in metals like steel and stainless steel.
“It’s a process that is most commonly used in manufacturing when large-scale production is needed for hundreds of thousands of parts,” said Bodor. However, it can be used for low-volume production as well. We can produce a dozen MIM parts, or tens of thousands. This volume is something that is rarely seen at manufacturing facilities and it’s a capability that probably comes as a pleasant surprise to some. We can also ship parts in as little as five days, and the molds only cost a few thousand dollars.”
What brings all this technology and expertise together is working with highly experienced supply chain partners in the earliest stages of a project—this is where the greatest design gains will be realized through the exchange of in-depth production and material knowledge. This minimizes mistakes, maximizes efficiency and speeds up time to market. And the more vertically integrated a supplier is, the more expertise it can bring to the table—shortening the supply chain and improving communication and response time.
“Vertical integration of services includes providing extensive engineering services very early in the product design process, as well as prototyping, injection molding, sheet metal fabrication, machining and total product manufacturing,” said DeBoer. “Vertical integration allows us to control cost, quality and lead time.”
Mark Crawford is a full-time freelance business and marketing/communications writer based in Madison, Wis. His clients range from startups to global manufacturing leaders. He also writes a variety of feature articles for regional and national publications and is the author of five books. Contact him at mark.crawford@charter.net.
Although these advanced materials allow designers to be more innovative in their product designs, they also are more expensive and more challenging to mold.
The type of molding technology used to make an orthopedic part or product depends on a number of factors, including end use and operational environment, selected materials, product design, aesthetic appeal, budget and size of the production run.
Common technologies are thermoplastic injection molding, two-shot molding, insert molding, overmolding, gas-assist injection molding and high-temperature molding.
Although plastic is the most common material, metal and liquid silicone rubber (LSR) also can be injection molded. Products include spinal implants, surgical instruments, disposable devices, implant trial devices, bone anchors and staples, surgical handles, case and tray components and surgical cutting guides.
What OEMs Want
Orthopedic device companies want more precision, more speed and, of course, lower costs—with no price increases. This puts continuous pressure on molders to find new ways to meet these demands, without compromising quality or performance—which is especially challenging when making miniaturized complex parts.
One way hospitals can control costs is by using less-expensive, single-use surgical instruments and related products. Many healthcare networks today are struggling to control rising costs, as well as reduce the transfer of infections. Common instruments such as hemostats and forceps are becoming increasingly expensive to purchase and use—this total cost also includes the increasing expense of instrument sterilization.
“When you also consider that single-use instruments help minimize the transfer of infections, it is no surprise that many OEMs are looking to replace previously reusable devices made of metal with single-use instruments made of high-performance plastics,” said Jim Hicks, technical marketing engineer for Alpharetta, Ga.-based Solvay Specialty Polymers, a provider of engineered polymers for the medical industry.
For single-use products, the overall challenge is reducing manufacturing costs while maintaining structural integrity requirements. For example, with femoral and tibial trials, extremely tight tolerances are required because the parts mimic the actual machined implants. Some are in the 0.0005-inch profile range over complex geometries.
“To successfully mold such tight tolerances, a molder has to understand scientific injection molding, as well as how to build a tool that will mold with very tight tolerances controlled by geometric dimensioning and tolerancing,” said Dwalin DeBoer, business unit director for Mack Molding, an Arlington, Vt.-based provider of custom injection molding, manufacturing and assembly services for the medical industry. “We have been able to create several hundred item numbers using less than ten tools, by starting with an all-inclusive tool and refining it as the process and part requirements allow.”
Selecting the right resin and molding process—and understanding end use—are critical for achieving performance expectations and product longevity. For example, some orthopedic products are heavily impacted in the surgical suite, so the resin must have adequate impact-resistance properties.
“And while we take some cost out by changing the molding process to internal gas-assist or structural foam, that can also affect the strength of the resin through wall thickness or foam,” said DeBoer. “So it is imperative the right process is used with the right resin and part design.”
Building the mold and tooling typically is the largest production expense. Therefore, medical device manufacturers consistently look for ways to reduce tooling investment. One way is by running different classes of resins within the same tool steel. Another strategy for reducing tooling costs is to use standard mold bases and standard mold parts, as well as making multiple parts in one mold, experts told Orthopedic Design & Technology.
“Instead of making 10 molds to manufacture 10 different parts, we can make one mold with ten cavities, one for each of those parts,” said Kenny Wang, managing director for Kaiser Technology Company in Taiwan. “Multiple cavities in one tool for different parts requires less tooling investment. This can reduce tooling costs by as much as 50 percent and tooling lead time by as much as two-thirds.”
Pushing the Limits of Design
As orthopedic parts and products become smaller, the demand for micro-molding is increasing. OEMs are on the hunt for crisp geometries, high manufacturing precision, finer edge quality and no radii in their miniaturized products. Tolerances can be as tight as a few microns.
“Miniaturization of micro components with high resolution of features is one the most important considerations for OEMs when they are looking for a micro-molder,“ said Lindsay Mann, project manager for MTD Micro Molding, a Charlton, Mass.-based molder of micro components for the medical industry.
OEMs are turning more to insert molding for small components to reduce assembly steps and mitigate the risks of utilizing adhesives. MTD Micro Molding recently worked with an injectable drug-delivery systems company that was struggling with the traditional manufacturing approach for its drug-delivery device. The process included a series of high-risk, cumbersome steps to manually assemble four micro components to combine the cannula and housing, which drove up labor costs. The company wanted to streamline this process and reduce costs. An initial mold-flow analysis showed that all the components could be micro-molded together at the same time. This process eliminated three assembly steps (considered to be the industry norm for this kind of product), resulting in a significant cost savings.
“The geometry-rich cannula was micro-molded at 10 cents a unit, in contrast with making four separate components at a cost of over $1.50 for the set, excluding assembly costs,” said Mann. “In addition, with the assembly steps largely contributing to the main failure mode in the final device, molding the device as a single unit removed all possibilities for functional failures.”
To take advantage of the qualities of both metal and plastic, more orthopedic design engineers are developing hybrid devices that incorporate both. This requires an in-depth knowledge of not only how these materials behave individually, but how they react and bond with each other—both during production and in the end-use environment. For example, more aluminum sterilization cases are being built with plastic brackets, trays and lid. These plastic components not only reduce the overall weight and cost of the delivery system, but are also engineered to withstand repeated steam sterilization.
“Hybrid systems have been growing in popularity,” said Hicks. “Even though all-metal systems are lower cost, they don't always provide the best protection for increasingly delicate instruments. Plastics provide better protection, but can cost more. Combining the attributes of metal and plastic provides a broader level of design freedom that can lower manufacturing costs when plastic parts are produced via injection molding.”
Sometimes injection molding isn’t always the answer. Some products may require 3-D printing or other additive manufacturing technologies that complement injection molding. For example, an additive process like direct metal laser sintering (DMLS) or metal machining works well for initial prototyping before increasing part production with a process like metal injection molding (MIM).
This is especially true for products such as surgical instruments, scanning equipment and handheld devices. Three-dimensional printing also provides more advanced material choices, such as polyether ether ketone (PEEK) and Ultem.
“Three-dimensional printing is often thought of as a one-off process, but the equipment is getting faster, material properties are approaching those we are accustomed to in machining and molding and processes are more robust,” said Rob Bodor, vice president and general manager of the Americas Division of Proto Labs, an injection molding and CNC machining facility in Maple Plain, Minn. “Stereolithography, for example, can produce parts with features down to 0.002 inches wide and 0.001 inches tall.”
DMLS is one of the most cutting-edge additive manufacturing technologies available for medical device manufacturing. It involves fusing a bed of metal powder into thousands of thin layers that eventually become prototypes and even production parts.
“On OEM requests that have organic or extremely challenging geometries, or designs that are impossible to manufacture with traditional methods, DMLS can be used,” said Bodor. “DMLS is also leveraged to combine multiple metal components on a device into one part, which reduces bill of materials.”
Advanced Materials
There is growing interest by medical product designers in engineering materials that not only have enhanced physical characteristics, but are also easier to mold in the production environment. This means faster and higher-quality parts for designers and engineers. For example, Proto Labs has partnered with material manufacturers such as Cool Polymers and Dow Corning to provide thermally conductive plastics and medical and optical liquid silicone rubber.
“These advanced injection molding materials help us better serve customers who are looking for the latest in advanced material offerings,” said Bodor. “Medical- and optical-grade LSR are frequently used in device applications. Their ability to be sterilized sets them apart from many traditional soft-touch materials.”
Medical design engineers continue to find new ways to use PEEK and PEEK varieties, which are becoming popular for orthopedic applications because of their strength and durability. Because it is an approved implant material, PEEK also has the advantage of offering biostability data. However, PEEK is very challenging to mold because extremely high heat and precise temperature control are required to achieve highly crystalline parts. Also, extremely small parts tend to shift and move in the mold cavity, posing another challenge.
“An issue with PEEK is that temperatures are so high that the part doesn’t exhibit optimal mechanical properties, so it distorts very easily,” said Mann. “With micro-molding, temperature control is highly critical. Because the part doesn’t have cold strength during the molding process, it may stick in the cavity. PEEK parts are often so thin they don’t have the strength that a thicker part would have, making it hard to predict which half of the tool it will stay on. This makes it more challenging to de-mold properly without distortion. The mold temperature needs to be 350 degrees [Fahrenheit] or higher to crystallize PEEK so the final product will have the physical characteristics that are expected.”
Another critical challenge with molding PEEK is the optimization of the flow path the polymer takes to get to the cavity. A challenge for micro parts is getting the PEEK from the injection unit into the cavity, while still maintaining its orientation and properties. This requires the runner, sprue and coldslug to release properly and cooperate with robotic automation and camera presentation.
“Although mold design and temperature control are extremely important for successfully molding PEEK, so is the design of these mold features,” said Mann.
Polyaryletherketone (PAEK) is also being used more in the orthopedic market. This resin family offers both unfilled and glass or carbon fiber-reinforced thermoplastics (for more strength) with high-temperature stability and high mechanical strength.
“With 30 percent glass, for example, PAEK offers good chemical resistance, high-heat resistance for various sterilization techniques, biocompatibility, high stiffness and strength, radiation resistance and radio-translucency so it can be used during an MRI. It also offers improved part economics compared to 30-percent glass fiber-reinforced PEEK, another high-heat resin,” said Michael Hansen, senior technical development engineer for Mack Molding.
For ultra polymers such as modified PEEK and PAEK materials, temperatures can be as high as 700 degrees Fahrenheit, which create safety challenges for the operators and technicians who handle this equipment.
“As the temperatures and duration of sterilization processes for these products increase, so do the heat and chemical resistance requirements of the materials,” said Hansen. “The ripple effect of higher heat properties in resins is higher mold, melt and drying temperatures, resulting in increasingly stringent safety precautions on the molding room floor.”
Getting Creative
Considering plastics for medical devices that have been traditionally made from metal can be a major challenge for design engineers, who have grown accustomed to working with and designing with metals. To help them see the benefits of advanced plastics, Solvay Specialty Polymers conducted an in-depth study on end-use performance, biological safety and the economics of replacing metal with plastic and developed a practical seven-step metal replacement plan. The study used Solvay’s PARA resin to replace metal in the traditional metal Hohmann retractor, a popular device used in surgical procedures. The retractor was selected because of its challenging performance requirements, including high mechanical loads. For single-use applications, PARA was used because of its strength and stiffness, excellent surface finish and compatibility with gamma radiation sterilization.
“The high-performance polymer provided the same level of strength and rigidity as some metals at ambient temperatures,” said Hicks. “High-performance polymers also deliver cost benefits, enhanced aesthetics and ergonomic improvements. They can also be colored, thus enabling the production of devices in a variety of sizes that can be easily and quickly identified in the operating room.”
A recent Mack Molding project involved manufacturing a high part number mix at low volumes for a tibial trial program. Tibial trials are the plastic instruments used during knee replacement surgery that mimic the final implant and help surgeons determine the proper size and thickness needed for a correct fit. Traditionally, these products are CNC-machined. In this case, the OEM was looking for a more cost-effective method for producing the required 420 tibial trial configurations. The OEM had already designed a spacer or shim that allowed parts to be stacked to create multiple thicknesses, which was a good start.
“This reduced the part number count to 258,” said DeBoer. “Yet developing injection-molding tools for such a large number of parts cost competitively was still a challenge.”
While individual dies were needed for each of the top surface parts, because they had various articulating surface conditions, the bottom surfaces were virtually identical for all parts of a particular size group. To further reduce part count, Mack Molding used the master-unit-die tool concept, where standard prefabricated bases are inserted with custom core/cavity units. This solution allowed them to produce 24 different part numbers using only four complete modular dies, five additional cavities and two core sub-inserts.
“Using combinations of trials and spacers, they were able to cover 420 tibial trial configurations with 258 unique molded part numbers, including 48 spacer molds, 48 complete tibial trial molds and an additional 162 cavities,” said DeBoer. “This approach reduced the total number of complete modular inserts by 210 and cut total tooling costs in half. Additionally, converting from conventional CNC-machined trials to injection-molded replacements reduced part cost by nearly 75 percent.”
A top priority in almost all job requests is speed—however, for some projects, how fast a job gets done should not necessarily be the priority. With some equipment, slower is better—and even cheaper—compared to traditional methods. For example, Sarix milling equipment is well-known for its high quality and precision—however, it takes longer than traditional milling and even electrical discharge machining (EDM).
“EDM is 100 percent slower than traditional milling and Sarix is 100 percent slower than that,” said Mann. “For example, we recently had the Sarix create 36 needle features, which consisted of 72 needle-halves. This process took about four weeks of 24 [hours]/7 [days a week] unattended time to complete. The perception may be that this is a more expensive tooling technique because of the high-tech equipment and time needed, but it isn’t due the unattended nature of the process.”
Sarix allows micro-machinists to create fine details with very little electrode wear. While graphite electrodes can machine sharp corners with .001- to .0015-inch corner radii, Sarix has such minimal wear that corners can measure at 5 microns (.0002 inches), with a tolerance resolution of .000004 inches and glass-like surface finish (Ra 0.05).
“Sarix micro EDM capability enables us to make edge features that were not possible before, with finishes that are mirror-smooth and perfectly detailed corners, edges and surfaces,” said Mann. “This capability gives our customers more flexibility for making more innovative, complex product designs.”
Moving Forward
OEMs and contract manufacturers continue to work together to push the limits of technology. Costly metal instruments can be replaced with high-performance plastics that can withstand repeated steam sterilization cycles and autoclave temperatures up to 273 degrees Fahrenheit (134 degrees Celsius). As these high-temperature plastics become better known and tested in the medical-device industry (they have been used for years in aerospace and automotive), more products that were traditionally made from metal—including cutting instruments—are now being produced in plastic.
“Clearly the use of plastic for cutting or other material-removal instruments such as broaches or rasps will depend on the end use of the device and how long it is expected to perform,” said Hicks. “In several cases, customers are looking at metal/plastic hybrids to reduce cost by having a simpler metal-cutting surface embedded into a rigid plastic substrate. Cost reduction can be significant—depending on device and unit volume, a three- to four-fold reduction is not uncommon.”
“Replacing anything made from metal, which can cost in the hundreds of dollars per part, with an appropriate resin, which can cost in the tens of dollars per part, results in major cost savings for OEMs, roughly 80-90 percent of cost,” added DeBoer.
But just as the appeal of metal starts to fade because of cost and machining time, technology improvements—including additive manufacturing and metal injection molding—are making metal competitive again. For example, metal injection molding involves a multi-step debinding and sintering process to create parts in metals like steel and stainless steel.
“It’s a process that is most commonly used in manufacturing when large-scale production is needed for hundreds of thousands of parts,” said Bodor. However, it can be used for low-volume production as well. We can produce a dozen MIM parts, or tens of thousands. This volume is something that is rarely seen at manufacturing facilities and it’s a capability that probably comes as a pleasant surprise to some. We can also ship parts in as little as five days, and the molds only cost a few thousand dollars.”
What brings all this technology and expertise together is working with highly experienced supply chain partners in the earliest stages of a project—this is where the greatest design gains will be realized through the exchange of in-depth production and material knowledge. This minimizes mistakes, maximizes efficiency and speeds up time to market. And the more vertically integrated a supplier is, the more expertise it can bring to the table—shortening the supply chain and improving communication and response time.
“Vertical integration of services includes providing extensive engineering services very early in the product design process, as well as prototyping, injection molding, sheet metal fabrication, machining and total product manufacturing,” said DeBoer. “Vertical integration allows us to control cost, quality and lead time.”
Mark Crawford is a full-time freelance business and marketing/communications writer based in Madison, Wis. His clients range from startups to global manufacturing leaders. He also writes a variety of feature articles for regional and national publications and is the author of five books. Contact him at mark.crawford@charter.net.