Yvonne M.Purdy10.01.08
Imagine using bicycle parts to create an external bone fixation device. In the 1950s, breakthroughs in orthopedic care were the result of that kind of creativity. Today, the same kind of creativity produces advancements in machining capabilities that keep the orthopedic device industry on the cutting edge of technology.
In a few short decades, the orthopedic device industry has gone from quaint to quintessential in the delivery of life-enhancing treatment options. The fairly recent days of splints and traction are the archaic history of the industry. Today, surgical options are the norm, which puts an enormous pressure on manufacturers to produce devices of flawless form and function.
The importance of manufacturing capabilities in the realization of innovative ideas gives OEMs a central role in the advancement of medical science. Innovations in arthroscopy, implants and joint replacements are accomplished as much by the device manufacturer as by the surgeon. Therefore, the capabilities of manufacturers must keep pace with the needs of medical product innovators.
Of course, continual process development is a major focus in the contract manufacturing industry. Most processes are improved and refined to reflect the needs of OEMs and designers. As an example, grinding capabilities have evolved to become extremely versatile in the manufacturing of precision parts and components. Grinding is one of the oldest methods of metal fabrication-in its basic function, an ancient technology. Early hand grinding and pedal-operated wheels gave way to mechanized systems, computer-controlled systems and, eventually, electrochemical grinding (ECG). Each innovation advanced the precision, speed and efficiency of the method.
For orthopedic device manufacturers, new manufacturing capabilities can present exciting opportunities for innovation. With advanced technology, the ability to tap the potential of new materials is especially important to the development of high-performance, longer-lasting orthopedic implants.
Demographic trends bode well for future growth. A longer-lived baby boomer population will make significant demands on the market. In addition, a younger demographic is choosing orthopedic options to maintain activity and lifestyle. Many patients are opting for procedures that will prevent or forestall the need for treatment at an older age.
In any case, the invasive nature of these types of procedures makes wear-resistance and performance life of implants critical. Both are determined by the material used to produce them. Currently, metal implants last 10-15 years. Research is ongoing to identify new materials that may prolong product life to 20 years or longer. Harder, lighter and more durable materials are the key to manufacturing products that will improve the quality of life for orthopedic patients-and the bottom line for OEMs.
Over the years, significant changes have taken place in the realm of orthopedic devices. New or refined manufacturing methods, engineered materials and emerging science have enabled the development of products with increasingly complex applications and performance standards. Yet, the innovations themselves sometimes produce their own challenges and limitations. For instance, some exotic metals exhibit characteristics that are well suited for new generations of biomedical applications. However, the use of these materials in manufacturing often is made more difficult by the very characteristics that distinguish them. For example, ultra-hard or heat-sensitive super-alloys with exceptional promise may be underutilized because they are difficult to machine or grind with conventional methods.
A material such as zirconium may be a better choice than titanium for joint replacement. It is lightweight and more wear-resistant than titanium, making it ideal for orthopedic applications. However, it is more difficult to machine. Conventional grinding of zirconium produces a "gunpowder" effect resulting from the heat generated by the grinding action. Finding a suitable process to produce long-lasting implants from materials such as this has been a major focus of the device industry for years.
To keep pace with material developments, new grinding methods must be developed to overcome these high hurdles and expand the range of materials options available to designers and engineers. One such development is the Molecular Decomposition Process (MDP) developed by Oberg Industries, headquartered in Freeport, PA. MDP is used across the various industries the company serves, including medical. Some of the innovations of this grinding process are that it produces no thermals, no mechanical stresses and no burrs. In addition, it can be used to create precision parts in a single pass from hard, heat-sensitive, exotic metals and super-alloys without the need for secondary operations, such as polishing or de-burring.
In the development of new technology, innovators must identify the limitations and inefficiencies of current systems to improve them. New grinding technology is no different, and any improvements compared with current grinding processes increase the potential of that technology for OEMs. MDP was developed to address the concerns of OEMs for precision, efficiency and safety in grinding methods, according to Oberg. These improvements enhance the versatility of grinding and expand the materials options available to device designers. An overview of this process as it relates to ECG and conventional grinding illustrates these features.
This grinding process is similar to (ECG) and cutting. It can be used to grind or cut any conductive material. As with ECG, it employs an abrasive wheel combined with a steady supply of electrolyte solution. While ECG uses alternating current (AC) power, MDP uses direct current (DC) power passed between a specially formulated grinding wheel (cathode) and the conductive metal work piece (anode). The resultant formation of non-conductive oxides and hydroxides on the work piece then is removed, or "wiped away," by the grinding wheel in a reverse plating process. Precision cuts and grinds can be achieved with a single pass with less abrasive action. Also, this heat-free system prevents the degradation of the metal work-piece during manufacturing, making the process well suited to the grinding of memory metals such as Nitinol.
As with any advanced manufacturing method, precision and repeatability rely on the operator's expertise in setting values for key functions of the machine. In this case, a fuzzy logic/neural-network control system provides precise monitoring of work-piece position, conductivity and rate of stock removal. This technology assures the coordination of the three essential control elements: electrical, chemical and mechanical. Each has been designed to allow the greatest control possible to ensure the precision, efficiency and safety of the system.
Because DC is used, the power supply is stable throughout production, unlike processes that rely on AC power. The use of DC power eliminates power spikes or brown outs. This type of fluctuation is a problem, as it affects the accuracy and repeatability of tolerances and is a drawback of conventional ECG. DC power not only resolves this issue, but it uses less power to do so (an additional "green" benefit of the process). With special algorithms, the wattage and volts are precisely determined and controlled to maintain consistent levels throughout production. The power control capabilities available also provide a higher level of safety for the operator, equipment and the product. When certain parameters are exceeded during MDP grinding, the grinding operation is suspended, and the machine retracts to a safe position instead of crashing and causing potential damage to the equipment and injury to the operator.
The chemical formulations for both the electrolytic solution and the grinding wheel itself also play an important role. An electrolytic solution has been developed that optimizes the flow of current and the interaction between cathodic wheel and anodic work piece. Conductivity is precisely controlled, allowing optimal performance during grinding operations. The composition of the grinding wheels is another key factor in the synergy of the electrochemical and mechanical systems. Research has yielded a formulation that is applied to the construction of each wheel based on the material being ground that maximizes conductivity and removes the material with only 10% of the abrasiveness created in conventional grinding, according to process developers. That, in turn, results in the absence of thermal and mechanical stress in the work piece and reduced wear on the wheel.
The mechanical functions in this system, including platforms (horizontal and vertical), grinding wheels, spindles, filters and electrolyte delivery are customizable. Research and experience have generated continually updated, on-file data of optimal control parameters relevant to specific materials, geometries and tolerances.
This process can achieve precision tolerances of better than +/-0.0005 inch, and sub-micron tolerances are also possible. (The typical accuracy of ECG is 0.002 inch and on certain applications may be down to 0.001 inch. Traditional grinding can reach tolerances equivalent to MDP but does not offer burr-free, stress-free and heat-free advantages.) Much of this precision is due to the grinding wheel formulated to control the abrasive concentration and type, conductivity and interaction with electrolytes. These wheels are monolithic and are made based on material requirements and compatibility to promote an efficient interface between the anode and the cathode. They are customized to conform to required part geometries. With this wheel technology, grinding wheel pressure is reduced by 90% as compared with conventional grinding wheel pressure. Therefore, wheel re-dressing is diminished or unnecessary.
This new grinding process creates no heat or thermal deformation and does not discriminate in its effectiveness on dissimilar material combinations. It can grind thin-walled components without damage or distortion. It is appropriate for grinding thin geometries, deep or shallow slots, wide or narrow slots, complex configurations, tubing as well as round and flat stock. It can be used to create, for example, specialty needles, guidewire tips, specialty blades, orthopedic nails, probes, cannulas and biopsy products.
With this new process, there is no plowing or sliding during machining. These two effects are common concerns with conventional grinding and cutting because either effect can cause or mask flaws in the material. This is especially true in alloys that combine easily machined material with a difficult-to-machine material. Titanium carbide is a case in point. Traditional milling, grinding or turning of this alloy may result in smearing and carbide plowing that leaves voids or porosity in the titanium. This grinding process is capable of uniform cutting through both substances without any surface or internal distortion. Maintaining the structural integrity of the work-piece material is essential for biomedical devices.
Surface finishes of less than 1 RA are achievable, even on very hard materials, with no recast layer. This surface finish is comparable to the best that can be achieved with conventional grinding. Parts ground are free of micro-cracks, fissures and burrs and are, in fact, finished. No additional processes are needed to finish or polish the piece.
This technology has been developed to include environmental safety features. Filtering of the electrolyte, a simple salt compound that mixes easily with tap water, prolongs the life of the solution to six months, as compared with 40 hours for standard ECG equipment, without the creation of hexavalent chrome, a heavy metal, toxic byproduct of the typical ECG process. Waste materials such as suspended solids, metal chips, swarfs, oxides and grinding wheel residues are filtered, collected and converted into a non-toxic, semi-dry "cake." These features, along with the lower power required for the system, make this a "green" technology.
The MDP has undergone extensive testing and development since it was introduced in 2002. At that time, the process was an evolving technology that promised the capability to remove material without inducing stress. For OEMs, this capability means greater flexibility in using materials that can enhance the performance life and quality of their products. Now, a heat-free, stress-free process can offer consistent, precision grinding of parts and components made from conductive materials.
Practical applications trials were performed after developing chemistries for electrolytic solutions and wheel formulations. Outcomes showed that the process achieved specified geometries, surface finishes and tolerances, according to Oberg.
Process Speed: Process speed rates were consistently faster than conventional methods because much more material (as much at 0.250 inch) can be removed in one pass with burr-free results. This process typically can achieve extremely precise dimensions or required surface quality with fewer grinding passes than traditional ECG.
Roundness and Finish: Testing produced a consistent dimensional accuracy to 0.0003 mm on round parts ground from full hard, stainless steel. MDP achieved a surface finish of 0.05 RA um, with a Six Sigma quality, on these same parts. The roundness and finish were produced concurrently and required no secondary operations to achieve either outcome.
Burring: Burr comparison tests show the process removing 0.030 inch on a bundle of stock tube in a single pass with no burrs and a very minimal edge break. Using conventional grinding, 0.030 inch was removed from the opposite side, taking 0.0005 inch per pass and resulting in significant burring at the edges.
Thin Material Grinding: Burr-free sharps have been produced from 0.004-inch thick, 300 series stainless steel, blanked and formed. This technology can be used to produce needles, sharps, trocars and biopsy products. Traditionally, these products are made in a series of manufacturing processes. They typically are ground first and then de-burred in a separate operation mechanically, with grit blasting, or by electropolishing. MDP can produce edges that are more well defined than any other technique using multiple manufacturing processes, according to Oberg.
Alloy Integrity: Test cuts in titanium carbide (90% titanium/10% carbide) produced slots as wide as 0.250 x 0.300 inch deep, feeding at 1.5 inches per minute without adverse affect to either material. Ongoing testing of this alloy is projected to allow grinding of material having a ratio of 60% titanium/40% carbide.
Nitinol Tube and Wire: Nitinol grinding capabilities were tested on an 18-inch tube with incremental grinds over its entire length. With an outer diameter (OD) of 0.068 inch and a wall thickness of 0.0105 inch, the process produced 0.055-inch wide grooves around the diameter, leaving a wall thickness of only 0.006 inch. Nitinol wire with a supplied OD of 0.014 inch also was ground to a print specification requiring a 0.008-inch diameter +/-0.0002 inch, with a 30-degree angle and a full capped radius.
Slotting: Experiments with Inconel 617, 0.010-inch thick, specified a finished product cut with 0.003-inch wide x 0.003-inch deep slots, 0.003 inch apart. At a feed rate of 1.5 ipm, 106 slots (212 linear inches) were cut with a single wheel without re-dressing.
These results illustrate the potential of new technologies development for medical device OEMs. Speed, precision, cost effectiveness and materials versatility are important considerations for manufacturers that look for time-to-market advantages without sacrificing quality.
With new technologies, the impediments to using some of the most promising new alloys and compounds are disappearing. In their place are exciting opportunities for products that advance both the manufacturing and medical care industries using materials such as Nitinol, titanium carbide and ultra-hard specialty alloys. Someday, a completely new alloy may become the standard for long-lasting, high-performance implants. But that also will depend on machining capabilities.
The possibilities for exponential, innovative changes in the quality of orthopedic care are made more real with processes that eliminate production barriers. And, as production capabilities evolve, so do the visionary ideas of medical researchers and practitioners. Innovative processes will add an entirely new dimension to the realm of orthopedic device technology.
Perhaps in the near future, a cobalt-chrome knee will seem as quaint as a device made from bicycle parts.
In a few short decades, the orthopedic device industry has gone from quaint to quintessential in the delivery of life-enhancing treatment options. The fairly recent days of splints and traction are the archaic history of the industry. Today, surgical options are the norm, which puts an enormous pressure on manufacturers to produce devices of flawless form and function.
The importance of manufacturing capabilities in the realization of innovative ideas gives OEMs a central role in the advancement of medical science. Innovations in arthroscopy, implants and joint replacements are accomplished as much by the device manufacturer as by the surgeon. Therefore, the capabilities of manufacturers must keep pace with the needs of medical product innovators.
Of course, continual process development is a major focus in the contract manufacturing industry. Most processes are improved and refined to reflect the needs of OEMs and designers. As an example, grinding capabilities have evolved to become extremely versatile in the manufacturing of precision parts and components. Grinding is one of the oldest methods of metal fabrication-in its basic function, an ancient technology. Early hand grinding and pedal-operated wheels gave way to mechanized systems, computer-controlled systems and, eventually, electrochemical grinding (ECG). Each innovation advanced the precision, speed and efficiency of the method.
Market Factors
For orthopedic device manufacturers, new manufacturing capabilities can present exciting opportunities for innovation. With advanced technology, the ability to tap the potential of new materials is especially important to the development of high-performance, longer-lasting orthopedic implants.
Demographic trends bode well for future growth. A longer-lived baby boomer population will make significant demands on the market. In addition, a younger demographic is choosing orthopedic options to maintain activity and lifestyle. Many patients are opting for procedures that will prevent or forestall the need for treatment at an older age.
In any case, the invasive nature of these types of procedures makes wear-resistance and performance life of implants critical. Both are determined by the material used to produce them. Currently, metal implants last 10-15 years. Research is ongoing to identify new materials that may prolong product life to 20 years or longer. Harder, lighter and more durable materials are the key to manufacturing products that will improve the quality of life for orthopedic patients-and the bottom line for OEMs.
New Technology for New Challenges
Over the years, significant changes have taken place in the realm of orthopedic devices. New or refined manufacturing methods, engineered materials and emerging science have enabled the development of products with increasingly complex applications and performance standards. Yet, the innovations themselves sometimes produce their own challenges and limitations. For instance, some exotic metals exhibit characteristics that are well suited for new generations of biomedical applications. However, the use of these materials in manufacturing often is made more difficult by the very characteristics that distinguish them. For example, ultra-hard or heat-sensitive super-alloys with exceptional promise may be underutilized because they are difficult to machine or grind with conventional methods.
A material such as zirconium may be a better choice than titanium for joint replacement. It is lightweight and more wear-resistant than titanium, making it ideal for orthopedic applications. However, it is more difficult to machine. Conventional grinding of zirconium produces a "gunpowder" effect resulting from the heat generated by the grinding action. Finding a suitable process to produce long-lasting implants from materials such as this has been a major focus of the device industry for years.
To keep pace with material developments, new grinding methods must be developed to overcome these high hurdles and expand the range of materials options available to designers and engineers. One such development is the Molecular Decomposition Process (MDP) developed by Oberg Industries, headquartered in Freeport, PA. MDP is used across the various industries the company serves, including medical. Some of the innovations of this grinding process are that it produces no thermals, no mechanical stresses and no burrs. In addition, it can be used to create precision parts in a single pass from hard, heat-sensitive, exotic metals and super-alloys without the need for secondary operations, such as polishing or de-burring.
Developing a Different Method
In the development of new technology, innovators must identify the limitations and inefficiencies of current systems to improve them. New grinding technology is no different, and any improvements compared with current grinding processes increase the potential of that technology for OEMs. MDP was developed to address the concerns of OEMs for precision, efficiency and safety in grinding methods, according to Oberg. These improvements enhance the versatility of grinding and expand the materials options available to device designers. An overview of this process as it relates to ECG and conventional grinding illustrates these features.
This grinding process is similar to (ECG) and cutting. It can be used to grind or cut any conductive material. As with ECG, it employs an abrasive wheel combined with a steady supply of electrolyte solution. While ECG uses alternating current (AC) power, MDP uses direct current (DC) power passed between a specially formulated grinding wheel (cathode) and the conductive metal work piece (anode). The resultant formation of non-conductive oxides and hydroxides on the work piece then is removed, or "wiped away," by the grinding wheel in a reverse plating process. Precision cuts and grinds can be achieved with a single pass with less abrasive action. Also, this heat-free system prevents the degradation of the metal work-piece during manufacturing, making the process well suited to the grinding of memory metals such as Nitinol.
|
MDP is suitable for applications that require highly polished weight bearing and articulating surfaces free of micro-cracks, fissures and burrs. Free-form geometry or a multi-axis approach has not been fully commissioned at this time, according to Oberg Industries, the developer of this process. Photo courtesy of Oberg Industries. |
Because DC is used, the power supply is stable throughout production, unlike processes that rely on AC power. The use of DC power eliminates power spikes or brown outs. This type of fluctuation is a problem, as it affects the accuracy and repeatability of tolerances and is a drawback of conventional ECG. DC power not only resolves this issue, but it uses less power to do so (an additional "green" benefit of the process). With special algorithms, the wattage and volts are precisely determined and controlled to maintain consistent levels throughout production. The power control capabilities available also provide a higher level of safety for the operator, equipment and the product. When certain parameters are exceeded during MDP grinding, the grinding operation is suspended, and the machine retracts to a safe position instead of crashing and causing potential damage to the equipment and injury to the operator.
The chemical formulations for both the electrolytic solution and the grinding wheel itself also play an important role. An electrolytic solution has been developed that optimizes the flow of current and the interaction between cathodic wheel and anodic work piece. Conductivity is precisely controlled, allowing optimal performance during grinding operations. The composition of the grinding wheels is another key factor in the synergy of the electrochemical and mechanical systems. Research has yielded a formulation that is applied to the construction of each wheel based on the material being ground that maximizes conductivity and removes the material with only 10% of the abrasiveness created in conventional grinding, according to process developers. That, in turn, results in the absence of thermal and mechanical stress in the work piece and reduced wear on the wheel.
The mechanical functions in this system, including platforms (horizontal and vertical), grinding wheels, spindles, filters and electrolyte delivery are customizable. Research and experience have generated continually updated, on-file data of optimal control parameters relevant to specific materials, geometries and tolerances.
This process can achieve precision tolerances of better than +/-0.0005 inch, and sub-micron tolerances are also possible. (The typical accuracy of ECG is 0.002 inch and on certain applications may be down to 0.001 inch. Traditional grinding can reach tolerances equivalent to MDP but does not offer burr-free, stress-free and heat-free advantages.) Much of this precision is due to the grinding wheel formulated to control the abrasive concentration and type, conductivity and interaction with electrolytes. These wheels are monolithic and are made based on material requirements and compatibility to promote an efficient interface between the anode and the cathode. They are customized to conform to required part geometries. With this wheel technology, grinding wheel pressure is reduced by 90% as compared with conventional grinding wheel pressure. Therefore, wheel re-dressing is diminished or unnecessary.
This new grinding process creates no heat or thermal deformation and does not discriminate in its effectiveness on dissimilar material combinations. It can grind thin-walled components without damage or distortion. It is appropriate for grinding thin geometries, deep or shallow slots, wide or narrow slots, complex configurations, tubing as well as round and flat stock. It can be used to create, for example, specialty needles, guidewire tips, specialty blades, orthopedic nails, probes, cannulas and biopsy products.
|
Grinding fine detail in small-diameter memory alloys (0.014-inch diameter ground to 0.008 inch with a 30-degree angle and full capped radius) can be achieved with MDP technology, according to its developer. (Note: Photo shown at 40x magnification). Photo courtesy of Oberg Industries. |
Surface finishes of less than 1 RA are achievable, even on very hard materials, with no recast layer. This surface finish is comparable to the best that can be achieved with conventional grinding. Parts ground are free of micro-cracks, fissures and burrs and are, in fact, finished. No additional processes are needed to finish or polish the piece.
Environmentally Safe
This technology has been developed to include environmental safety features. Filtering of the electrolyte, a simple salt compound that mixes easily with tap water, prolongs the life of the solution to six months, as compared with 40 hours for standard ECG equipment, without the creation of hexavalent chrome, a heavy metal, toxic byproduct of the typical ECG process. Waste materials such as suspended solids, metal chips, swarfs, oxides and grinding wheel residues are filtered, collected and converted into a non-toxic, semi-dry "cake." These features, along with the lower power required for the system, make this a "green" technology.
Testing
The MDP has undergone extensive testing and development since it was introduced in 2002. At that time, the process was an evolving technology that promised the capability to remove material without inducing stress. For OEMs, this capability means greater flexibility in using materials that can enhance the performance life and quality of their products. Now, a heat-free, stress-free process can offer consistent, precision grinding of parts and components made from conductive materials.
Practical applications trials were performed after developing chemistries for electrolytic solutions and wheel formulations. Outcomes showed that the process achieved specified geometries, surface finishes and tolerances, according to Oberg.
Conventional grinding (top photo) of 304 stainless steel removing 0.03 inch of stock at 0.0005 inch per pass produces burrs, as compared with 0.03 inch of stock removed with MDP grind in a single pass without burrs (bottom photo). Photos courtesy of Oberg Industries. |
Roundness and Finish: Testing produced a consistent dimensional accuracy to 0.0003 mm on round parts ground from full hard, stainless steel. MDP achieved a surface finish of 0.05 RA um, with a Six Sigma quality, on these same parts. The roundness and finish were produced concurrently and required no secondary operations to achieve either outcome.
Burring: Burr comparison tests show the process removing 0.030 inch on a bundle of stock tube in a single pass with no burrs and a very minimal edge break. Using conventional grinding, 0.030 inch was removed from the opposite side, taking 0.0005 inch per pass and resulting in significant burring at the edges.
Thin Material Grinding: Burr-free sharps have been produced from 0.004-inch thick, 300 series stainless steel, blanked and formed. This technology can be used to produce needles, sharps, trocars and biopsy products. Traditionally, these products are made in a series of manufacturing processes. They typically are ground first and then de-burred in a separate operation mechanically, with grit blasting, or by electropolishing. MDP can produce edges that are more well defined than any other technique using multiple manufacturing processes, according to Oberg.
Alloy Integrity: Test cuts in titanium carbide (90% titanium/10% carbide) produced slots as wide as 0.250 x 0.300 inch deep, feeding at 1.5 inches per minute without adverse affect to either material. Ongoing testing of this alloy is projected to allow grinding of material having a ratio of 60% titanium/40% carbide.
Nitinol Tube and Wire: Nitinol grinding capabilities were tested on an 18-inch tube with incremental grinds over its entire length. With an outer diameter (OD) of 0.068 inch and a wall thickness of 0.0105 inch, the process produced 0.055-inch wide grooves around the diameter, leaving a wall thickness of only 0.006 inch. Nitinol wire with a supplied OD of 0.014 inch also was ground to a print specification requiring a 0.008-inch diameter +/-0.0002 inch, with a 30-degree angle and a full capped radius.
Slotting: Experiments with Inconel 617, 0.010-inch thick, specified a finished product cut with 0.003-inch wide x 0.003-inch deep slots, 0.003 inch apart. At a feed rate of 1.5 ipm, 106 slots (212 linear inches) were cut with a single wheel without re-dressing.
These results illustrate the potential of new technologies development for medical device OEMs. Speed, precision, cost effectiveness and materials versatility are important considerations for manufacturers that look for time-to-market advantages without sacrificing quality.
Looking Ahead
With new technologies, the impediments to using some of the most promising new alloys and compounds are disappearing. In their place are exciting opportunities for products that advance both the manufacturing and medical care industries using materials such as Nitinol, titanium carbide and ultra-hard specialty alloys. Someday, a completely new alloy may become the standard for long-lasting, high-performance implants. But that also will depend on machining capabilities.
The possibilities for exponential, innovative changes in the quality of orthopedic care are made more real with processes that eliminate production barriers. And, as production capabilities evolve, so do the visionary ideas of medical researchers and practitioners. Innovative processes will add an entirely new dimension to the realm of orthopedic device technology.
Perhaps in the near future, a cobalt-chrome knee will seem as quaint as a device made from bicycle parts.
