Machining Medicine: Insights into Precision and Laser Machining Demands

As orthopedic instruments and devices become increasingly complex with smaller configurations, precision and laser machining take on greater roles for creating these high-precision products. And, as these products become more challenging to build, medical device manufacturers (MDMs) are more intent on quality assurance—for example, precise dimensions, tight tolerances, surface finishes, and validated performance. This requires advanced machining equipment, operated by skilled workers with deep knowledge about material behavior and the intricacies (and limits) of the machines they run. Mistakes can truly be a matter of life and death—critical dimensions that don’t meet spec could negatively impact product performance and perhaps even harm patients.

“High-precision machining includes computer numerical control (CNC) machining, electrical discharge machining (EDM machining), wire cutting, and laser etching,” said Angel Wong, marketing manager of AC Mould Engineering, a China-based contract manufacturer of orthopedic braces. “Dimensions, structures, interfaces, fittings, and surface finishes must all be precisely done in the molds in order to make quality parts that meet required tolerances. Achieving this also requires highly-skilled equipment operators.”

Of course, price breaks and fast delivery times are always top expectations for MDMs. Delivery pressure is constant, even for mission-critical and complex components. In the past, complex projects with multiple bills of materials, ultra-precise machining, complex work holding, and inspections had lead times of 12-20 weeks, which was considered acceptable. Today customers are demanding three- to four-week lead times for similar projects, even for highly complex products with multi-component assemblies that have never been made before. To stay at the top of the preferred vendor list, machining companies constantly strive to improve their manufacturing processes and knowledge base so they stay ahead of the technology curve.

However, with machining and machine tool technology advancing so rapidly, there is a notable lack of knowledge regarding basic measuring techniques, material performance, geometric dimensioning and tolerancing (GD&T), and manufacturing on the customer side, which hampers communication and slows down turnaround time.

“In years past,” said John MacDonald, president of AIP Precision Machining, a Daytona Beach, Fla.-based provider of precision machining services for the medical industry, “this knowledge was common at the OEM level, since these types of companies were born out of manufacturing organizations themselves. When OEMs maintain a strong manufacturing knowledge based on experience, it makes manufacturing translations and inspection parity between customer and vendor much easier.”

As devices get smaller, more complex, and multifunctional, an increasing number of MDMs are turning toward design for manufacturing (DFM) to be certain they are doing everything they can to maximize quality, reduce risk, and control costs. DFM has actually moved beyond the early-adopter stage and into widespread industry use. MDMs realize that, to get their products to market faster without sacrificing quality, they need DFM—an integral part of which is machining.

“The process ideally starts with the technical teams in design, but new machine tool technology is also helping,” said Philip Allen, director of sales and marketing for Lowell, a Minneapolis, Minn.-based contract manufacturer of complex implants for the orthopedic and cardiovascular markets. “We can create more complex components with greater accuracy, which contributes to a quicker time to market. The sourcing and regulatory teams also get involved early. Their guidance is critical for performing ‘what if’ scenarios and putting together validation plans.”

Precision GD&T and profile tolerancing are essential for maintaining quality. Allen indicates that many device drawings have too many features labeled as critical. “If all features are critical, then none really are,” he said. “We’ve learned over the years to focus on complex features and, most importantly, reduce measured tolerances to the critical few.”

Output from profile tolerancing software, in an easy-to-interpret 3D CAD model, allows machinists and inspectors to tell, at a glance, if a device’s machined features or dimensions conform to the drawing. This ability reduces setup, in-process, and final inspection times. “If problems are not identified early in setup or in-process inspection, hundreds of out-of-tolerance parts that may have already been made must be discarded,” added Allen.

Machining Systems Continue to Advance
CNC Swiss machines (as high as 13-axis) are ideal for complex part geometries. They provide highly precise machine movements that can be easily programmed for optimal speeds and feeds, resulting in faster cycle times. Multiple spindle machining can complete parts in a single setup. Other capabilities include turning with live tooling and wire EDM. Programming and engineering creativity continues to be reflected in the new machines coming into the market, including improved tooling and cutter designs. High-speed machining software, in conjunction with higher spindle speeds, can achieve better surface finishing results. This reduces or eliminates additional finishing operations, reducing costs and speeding up time to market. 

The role of laser machining continues to expand. As medical device specifications get more complex, more MDMs and their contract manufacturers rely on laser systems to produce highly precise components at very high levels of speed and accuracy—for example, tolerances of ±0.0001 inch over the entire production run. Components can be laser machined from tubular and flat stock in a wide variety of materials for specialized products such as vascular stents and other neurovascular devices. Athermal, ultra-short pulse (USP) lasers can cut highly precise features in any material, including sensitive materials such as bioabsorbable polymers, without producing heat-affected zones (HAZ) (areas of cracking or weakening that can result from the heat of conventional lasers). Laser-welding technologies enable the connection of a variety of dissimilar materials, including exotic-grade metals, which are normally difficult to join. This is especially useful for thin-walled, tubular medical components.

Researchers continue to find new ways to use lasers in medical device manufacturing. For example, as reported in the May 2017 issue of Optics and Laser Technology,¹ researchers achieved rounded edges on a nitinol biliary stent using a femtosecond laser system with a galvano-mirror scanner. The radius of the edges was significantly enhanced from 9 µm to 42.5 µm. These results show that edges of nitinol biliary stents can be successfully modified from squared edges to rounded-shaped edges with precise dimension, clean surface morphology, and a minimal heat-affected zone. Also, after femtosecond laser micromachining and rounding was completed, the stent did not require any further post-processing to remove heat-related damage, or to further finish the edges.

The lower price and faster delivery constraints levied by MDMs are pushing contract manufacturers to invest in automation. Not only does automation increase efficiency and productivity, it provides higher rates of unattended machine time and therefore, almost free capacity. To stay competitive, machining companies are finding new ways to maximize the automation of their machines/facilities every year to boost efficiency and throughput.

“In our factory, all CNC/EDM/wire cut/laser machines are computerized,” said Wong. “We simply input the programming and the machines run automatically until the process is completed. Some advanced machines—for example, Mori-Seiki high-speed CNC and Agie Charmilles EDM—create highly controlled, precise dimensions and smooth machined surfaces, often eliminating the need for secondary polishing work.”

Automated inspection equipment monitors every step of the machining process to verify it is performing with precision. “We used to take the parts off the machine, go to the QC room for coordinate measuring machine inspection, verify the part is okay, then re-load it for the next machining process, and then repeat the unloading, inspection, and reloading,” said Wong. “Now, with our CNC online inspection system, parts are inspected directly and automatically on the machine after the CNC machining is finished, which saves time and reduces risk of error in repeated loading and centering.”

“Hybrid” laser-Swiss equipment is becoming more popular as a way to speed up production and reduce the number of steps required to make a part or product. Hybrid equipment combines Swiss turning, laser cutting, and laser welding operations into a single setup, so parts can be completed at a single station.

“This type of integration of previously separate technologies into a single machining center is an ever-evolving trend,” said John Cross, senior manager of research, development, and engineering for Micro, a Somerset, N.J.-based contract manufacturer of medical devices and sub-assemblies. “For example, we have the first commercially placed Citizen Swiss style screw machine combined with a 400w fiber laser cutter. This hybrid ‘laser Swiss’ system gives Micro the ability to both laser cut and traditionally machine features into customer parts from raw bar or tube stock, reducing setup time and handling costs while also increasing throughput. This allows us to produce delicate parts that require the utmost in precision.”

Another recent trend is the push to merge multi-axis CNC machining with laser sintering, a process known as “hybrid manufacturing.” This term describes combining additive manufacturing and subtractive manufacturing in a single machine system. “In this process, the machine essentially creates its own near net part shape with on-board laser sintering,” said Cross. “Then the part is precision machined into dimensional tolerance with the CNC portion of the machine. This can be thought of in terms of 3D metal meets CNC machine.”

Other Precision Machining Applications
Contract manufacturers can improve their machining efficiencies and reduce costs by developing their own custom machining tools. “Developing our own tools helps us unlock more capabilities in our CNC machines and ensures high-quality tools for our processes,” said Allen. “This leads to faster production and better results for complex projects.”

For example, Lowell no longer has to wait on order times for custom tools, which accelerates turnaround time and therefore, a customer’s time to market. And, because Lowell is designing a tool for a specific purpose or feature, the tool does exactly what it needs to do to ensure the end results meet specifications. “With the correct surface treatments, custom tools can last longer too, meaning fewer broken tools and change overs,” said Allen.

Machining is also required to finish up products made by methods such as metal injection molding (MIM) or additive manufacturing. MIM uses fine metal powders (typically less than 20 micrometers) that are custom formulated with a binder into a feedstock that is then fed into the cavities of an injection molding machine. In the medical device market, near net shape MIM is gaining traction, especially for smaller, highly complex parts. This is when parts are made near net shape with MIM, but require tighter tolerances than the MIM process can deliver. Once the MIM part is recovered from the mold, hole locations, bearing surfaces, or other features can be enhanced with machining to conform to tighter tolerance ranges. “This combines the advantages of high-volume MIM pricing with the tight tolerances on critical surfaces done with machining,” said Cross. “As a result, making MIM components for various medical device applications, combined with precision machining, is a useful design option for designers and manufacturers.”

The same holds true for additively manufactured parts that still need touching up to meet specifications. As more MDMs use additive manufacturing, more contract manufacturers are receiving requests for precision machining to finish near net components that were created with the process. Depending on the part, certain features or characteristics cannot be achieved with 3D printing; these 3D-printed components then require additional secondary machining for completion.

“It could be as simple as tapping a thread for better tolerances, or adding a secondary milled surface for fitment,” said David Cabral, president of Five Star Companies, a New Bedford, Mass.-based orthopedic contract manufacturer specializing in high-precision machining. “For example, components of an instrument assembly that need precise surface tolerances for fitment with the other mating part. The biggest challenge is actually figuring out how to hold these complex parts during the secondary process.”

Cabral noted, though, that this important but secondary machining role will likely diminish over time as 3D printing and related software become more sophisticated.

Moving Forward
Automation and robotics are two technologies that are driving rapid change throughout the orthopedic market. They have been a major focus at industry events over the last several years, and more of these technology vendors are rolling out advanced machines with greater functionality as well as easier-to-use software and user interfaces on a regular basis. Contract manufacturers must keep up and invest in this equipment to meet ever-increasing customer demands for tight tolerances, quality, and speed. And although mastering new advances in technology is a must, so is having the knowledge, creativity, and savvy to combine existing technologies to push the edge of the technology envelope—where science starts to merge with “art” in making materials and equipment work together to achieve something that hasn’t been done before.

For example, products that AIP typically machines are low-volume orders that require extreme levels of precision (high-volume jobs tend to be done with injection molding, rather than machining). “Therefore, we need to be in and out of our jobs quickly in order to meet the customer’s goals of quality, delivery, and price,” said MacDonald. “This is all accomplished before we have time to truly optimize run time and automate manufacturing process to the level needed for high-rate production. This is where the value of our team’s experience provides crucial value. Many times, the process is unique to a particular component for a particular customer. However, we shift what we learn from each project and apply it to the next project when and where applicable, which results in a streamlined process.”

What Five Star has found to be of greatest value, observed Cabral, is its ability to change its culture and deepen its knowledge regarding the products it  manufactures. “How can we modify our process to lower cycle times, increase productivity, and elevate a level of quality that reduces inspection and makes us more competitive?” said Cabral. “Speed and cost are the drivers in this industry; quality is not negotiable. If we are looking to bring manufacturing back into the U.S., we must continuously research new methods of improving upon all aspects of the process.”

In MacDonald’s opinion, the most critical issue facing the machining industry today “is the imminent need for a manufacturing ‘bench’ team,” he said. “This team is needed to fill the coming void in manufacturing experience as the current craftsmen approach retirement over the next decade.”

The medical device industry is struggling to recruit capable young machinists, noted MacDonald. The learning curve to become a precision machinist, especially for plastics, can be arduous. The current entry-level workforce was raised in a time of readily available information and generally lacks the patience or desire to master the skills they need. This is a setback to shops trying to internally develop the next generation of talent to the machining profession. “It is almost like a fine wine,” said MacDonald. “You cannot rush it, but if you wait, the reward is worth it.” The recruiting problem today also suffers from parental pressure on children to work toward cleaner white-collar jobs, rather than manufacturing. These challenges are also coupled with fighting the impression that a career in manufacturing is not attractive or rewarding.

But those who do persevere will be welcomed into a constantly evolving, high-tech world of manufacturing that makes life-changing products that better society.

“At AIP we could be machining a self-expanding polyetheretherketone (PEEK) skull plate bridge one day, which allows the brain to swell and retract after surgery or a traumatic injury, or next-generation porous PEEK spinal implants the next,” said MacDonald. “These promote bone in-growth and fusion faster than legacy titanium or non-porous PEEK implants, allowing people to live free of back pain and regain mobility they thought they had lost forever. Or we can machine precision polycarbonate components that adjust shunt valves implanted in the skulls of pediatric patients with hydrocephalus. If these tools are not machined to strictly specified tolerances, then they will not function properly and patients could die. It is extremely rewarding to make such life-improving and critically important medical products, especially as they become more structurally complex and challenging to make.”  

References

1. http://bit.ly/odt101750

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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. 

Saving Time and Money with Swiss-Laser Hybrids An example provided below by Micro, a Somerset, N.J.-based contract manufacturer of medical devices, illustrates the benefits of using a hybrid Swiss-laser system for an existing product being made with traditional methods. After being received and inspected in Building 2, 10-foot tubes are then sent to the shipping area by material handlers, loaded into a diesel truck, and driven to Building 1, where they are cut to length, cleaned, and hand-delivered to a stamping press station. Once the holes are formed, the tubes are driven back to Building 2, where a CNC lathe cuts three equidistant grooves 0.003 inches deep on each tube. The tubes then come back to Building 1 for cleaning before being shipped to Building 2 for packaging and shipping to the customer. “This represents an excruciating amount of movement and work for simple, thin-walled tubes with four holes and three grooves,” said John Cross, senior manager of research, development, and engineering for Micro. However, since Micro acquired its Laser System L2000 from Marubeni Citizen-Cincom (a Citizen L20 Swiss style bar-fed turning center combined with a 400w fiber laser-cutting system), the process is greatly shortened. Now, after the 10-foot tubes go through incoming inspection in Building 2, they are brought to the L2000 and loaded in the bar feeder. The L2000 precision machines the grooves and laser cuts the holes, completing the entire process in less than 30 seconds. The parts are then cleaned, packaged, and shipped to the customer, all in the same building. “This machine technology advancement has significantly aided our lean efforts to compress our value stream, and brings additional revenue and capability into the organization,” said Cross. “The impacts are felt throughout the organization by simplifying the value stream map and increasing throughput; shareholders benefit from additional bottom-line revenue generation.”  — M.C.