Machining & Laser Processing: A Matter of Microns

When it comes to machining and laser processing, it is all about speed—getting the job done faster, without sacrificing precision and accuracy. This translates into less time, less labor, more precision and fewer chances for something to go wrong or slow things down. Process reliability and repeatability are improved. Tight tolerances can be maintained within a few microns, ensuring top performance. Lower operational costs and faster time to market also improve customer satisfaction.

Medical device manufacturers want this kind of speed and accuracy that result from advanced, integrated processes, such as multi-axis, high-speed micro machining and femtosecond laser technology. OEMs are seeking tighter tolerances, faster cycle times and cleaner parts with fewer secondary operations.

“Advances in machining and laser processing now make it possible to deliver smaller and highly accurate features burr-free, something that is in high demand for precious metal machining,” said Jyrki Calderon Larjanko, account manager for Johnson Matthey, a San Diego, Calif.-based provider of medical device components. “It is also possible to go from prototyping to high-volume production with minimum changeovers and optimal process capability index.”

A popular trend in laser processing is the development of production-worthy, compact, high-power ultrafast lasers—both picosecond and femtosecond lasers where the temporal pulse (the amount of time the laser light is in contact with the material) is three to six orders of magnitude shorter than conventional lasers. Lasers are now reaching megahertz repetition rates that lead to higher cutting speeds.

“The initial promise of the ultrafast lasers is the laser micromachining of metals as life-sciences companies continue to reduce post-processing steps such as grinding, de-burring and electro-polishing after laser-cutting products like metal stents, hypotubes, nitinol and precious metal-based devices,” said Glenn Ogura, senior vice president of market development for Resonetics, a Nashua, N.H.-based provider of laser micromachining solutions for the medical device and life sciences markets.

When ultrafast lasers were first introduced, the wavelengths were in the infrared and visible regime. In the the past few years, however, ultrafast lasers have become available in the shorter ultraviolet wavelength.

“This opens up opportunities to machine polymers such as bioabsorbable scaffolds or fluoro-based polymers such as polytetrafluoroethylene (PTFE), Teflon and fluorinated ethylene propylene (FEP), as well as silicone,” added Ogura.

Closed-loop process controls, including in-situ monitoring, increasingly are used to maximize yields and efficiencies. Endpoint detection techniques correct for variations in coating thickness, extrusion wall thickness and geometry. In-situ monitoring is the real-time inspection of critical dimensions during the laser machining process.

“For example,” said Ogura, “as the laser is stripping the polymer coating off the wire, the strip length and strip location are measured and the presence/absence of the coating is detected. We can laser strip tiny wires in a reel-to-reel format and perform real-time monitoring of the amount of polymer coating remaining on the wire.” 

Laser Capabilities
OEMs want a lower cost per part, but with faster process times and more parts per hour. Demands for tight-tolerance components with complex features requiring above 1.33 CPK (a measure of process capability) make it even more challenging to fulfill those customer needs. There are also material challenges—for example, “laser technology can now process polymer and adhesive materials with optimum edge fidelity,” said Thomas J. Daul, manager for the MicroMed Solutions Group of LasX Industries, a White Bear Lake, Minn.-based provider of laser cutting machines and services. “We have had edges compared to match metal die-cut edges.”

Lasers also can machine hybrid components comprised of layers of metal and polymers. For example, lasers can cut metal braid from a shaft without damaging the underlying PTFE liner. Lasers can also drill through a polymer-coated metal without any burning or melting.

“This is actually a challenging problem to solve,” noted Ogura. “If the laser is intense enough to cut through the metal, then it will undoubtedly melt the polymer. If the laser is gentle enough not to melt the polymer, it will not penetrate through the metal. The solution is selecting a laser with an ultrashort pulse length to minimize burrs, a short wavelength to cleanly ablate the polymer and optimized process parameters and environment.”

With an emphasis on better product performance with lower costs, OEMs are pushing for multiple part formats such as web handling, reel-to-reel and part handling automation. As parts keep getting smaller, handling micro parts becomes more challenging. For every laser micromachining process, Resonetics identifies three key steps: part handling, laser processing and inspection. “The overall tact time of all three steps influences the overall cost of manufacturing,” explained Ogura. “Tight control over the three steps influences the quality of manufacturing.”

Laser micromachining of polymer-based components is especially well-suited for the life-sciences industry. Products include balloons, catheters, heart valves, stents, laser singulate sensors/devices from sheets or wafers and laser strip wires/cables/braided shafts or laser etch blind holes or channels, as well as shaping ceramic material for dental implants.

A relatively new application is molecular diagnostics for the point-of-care market. Feature sizes are dropping below 1 micron as the feature sizes mimic the dimensions of cells or DNA fragments, used for DNA sequencing and infectious and genetic disease detection. Customized optics with high numerical apertures play a significant role in creating micron or sub-micron features as well as customized optical inspection systems to measure the tiny features.

Laser machining also shows promise for processing bio-absorbable materials and devices—for example, implantable bioabsorbable scaffolds for tissue growth. One of the biggest advantages is that ultrashort-pulse lasers deliver a very precise concentration of light over such short duration that no heat damage occurs to the surrounding material—a process called athermal laser ablation. This results in very clean microscale machined features that are free of burrs and thermal defects.  Therefore, the process is a good solution for making bioabsorbable stents and other polymer-based devices, which are heat-sensitive.

Integrated Technologies
Lasers are being integrated with other conventional manufacturing technologies to increase functionality, such as lasers combined with powder metal deposition and lasers combined with water-jet cutting.

“For example, multiple lasers can be integrated in line with roll handling equipment to build intricate patterned multilayer fluidic devices for the point-of-care medical device industry,” stated Daul. “This technique can perform intricate patterning while holding feature tolerances to +/- 25 microns. The inline roll fed process allows companies to scale to high volume production cost-effectively.”

Okay Industries Inc., a New Britain, Conn.-based manufacturer of components and subassemblies for the medical device market, is co-developer of the Accu-LaserSwiss laser machining process, which fully integrates a six-axis precision CNC lathe with a fully enabled laser-cutting module. This eliminates the need to move between machines, which increases accuracy, reduces cycle time and cuts costs.

“OEMs are demanding smaller parts with higher accuracies at lower costs,” stated Joe Lovotti, director of laser technologies for Okay Industries. “Accu-LaserSwiss manufacturing allows us to combine design attributes that in the past would have required multiple components separately manufactured and welded together into a single low-cost component.”

“With this technology we have successfully combined all the attributes of conventional Swiss turning with a fully integrated laser cutter,” added Sean Stowick, business development executive for Okay Industries. “This allows us to choose the best technology for a given part on a feature by feature basis.”

It also simplifies the design process for the customer, who no longer has to design for a specific technology, or layer one process on top of another. A good example would be turning a small tubular component and holding machining tolerances of +/-.0005 inches and then, without losing registration of the part, adding laser cuts as small as .0015 inches wide, all at full processing speed with no secondary cleaning operations.

“Customers can now design components that, just a year ago, would have been judged too expensive to produce, or apply tolerances to a component that previously would have been judged impossible,” said Lovotti.

Laser cutting and precision forming also can be automated in a robotic cell.

“For example, we have added material load and unload automation, allowing unmanned machine operation over multiple shifts,” said Brian Gallivan, laser/automation consultant for Amada America, a Buena Park, Calif.-based provider of sheet metal equipment. “This allows the end user to produce parts at a lower cost with the reduction of labor. These automation systems are modular and can be expanded to include more automation and additional laser machines, if needed.”

Customized Solutions
Resonetics developed a proprietary, closed-loop laser micromachining process that enables selective material removal on multi-layer wire consisting of different materials. Having completed process development, design and fabrication of a custom laser workstation, process optimization and a rigorous validation, this 24/7 work cell produces millions of wire sensors for a Class III medical device.  

The engineering team determined that a single laser beam with mechanical rotation of the wire was the most robust process for uniformly laser ablating the entire circumference of the wire in selected regions. Several types of lasers were evaluated and the optimal wavelength was chosen to meet the technical specifications and quality requirements. They also discovered that raw material variability provided challenges for development of a laser skiving process, specifically non-concentricity of the wire cross section due to non-uniform layer thickness of the coatings.

“A laser process with closed-loop control was needed to compensate for material thickness variation and to selectively ablate different material layers to achieve a uniformly stripped wire,” said Ogura. “A patented ‘end point detection’ technology for in-situ monitoring of plasma plumes generated by laser ablation of different materials was developed. Laser parameters were optimized via characterization through a scanning electron microscope and fluorescence microscopy.”

Automated handling of the wire material also presented its own set of technical challenges and a reel-to-reel system with tension control was developed for wire transport. The wire handling system was designed so that the wire could be rotated back and forth in opposite directions during laser ablation for custom exposure of areas with varying layer thickness. For singulation of wire sensors, a separate reel-to-cut system was designed to place cut wire sensors into vials, featuring wire grippers, a blade assembly and a vision system for automated sorting of rejected parts.

A company contacted Okay Industries looking for cost reductions on an existing two-component assembly. Using its Accu-LaserSwiss technology, Okay engineers were able to redesign the product to be a single component, where one of the components was integrated into the body of the part using fine laser cutting to create the flexibility that previously required a second component and assembly. In another example, a customer wanted to simplify a three-piece welded assembly.

“It required two laser cut tubes and a cable, welded into a three-piece machined assembly,” said Lovotti. “We were successful in converting that assembly made of three individually manufactured components, which required secondary welding and machining operations, into a single flexible component.”

Amada America recently collaborated with a client who approached the company with a high-volume, smaller-sized part request. They used laser programming software to create multiple parts that were “nano-joined” together. These parts were removed together in individual groups of four. They were then taken to the press brake, bent twice, and then separated.

“The customer used nesting software and common line cutting to use 95 percent of stainless steel material blank and, with the use of multiple shelf automation, the customer was able to process 39,000 parts in 24 hours,” said Gallivan.

Parting Advice
OEMs need to consider feature aspect ratio with the material thickness, as well as tolerancing, when designing a component. Even the simplest geometry can drive high costs or become almost impossible to manufacture by narrowing and tightening tolerances when not needed. For best results, apply design-with-intent practices and consider process performance for high volume scenarios—customer sourcing representatives appreciate this approach.

“The equipment is as good as the process engineering put into the operation,” said Larjanko. “By engineering complex tooling and fixtures that can hold a high volume of components, and combining these with smart and efficient program code, we can deliver a capable process for a low operational cost.” 

Most OEMs do not fully understand the capabilities of laser micromachining. They are not aware of the variety and depth of laser technology and how a laser that is meant for machining a metal is not the best solution for polymers—therefore getting machinists involved early in the design process is critical for developing a product that is easy to design and manufacture.

“It is important to continue to invest in technologies that we see as long-term solutions for our OEM customers,” said Stowik. “We understand the need to ensure the financial success of our customer’s programs over their life cycles. Whether it is laser processing, machining, stamping, tubing or finished assemblies, developing tooling and automation strategies will drive the innovation that we need to support our customer’s quality and cost goals.”  

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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. Contact him at [email protected].