Micro components continue to shrink in size, demanding ever-greater precision and improved handling of parts with sub-micron-sized features. New approaches in micro machining technology include higher-precision systems from traditional micro machining developers, as well as techniques using additive manufacturing processes and semiconductor wafer-scale technology on the smallest of micro parts.
With micro machining and molding techniques, manufacturers can create an astounding array of extremely small parts for medical uses including catheters, surgical tools, and implants made from a variety of materials including metals, ceramics, silicon and PEEK polymers. Micro components also increasingly power the latest high-tech devices with the small batteries, connectors, LEDs and IC chips found in smartphones and iPads, and some of the tiny devices being used in aerospace and defense applications by the military.
“The industry is definitely getting smaller and smaller, in terms of the size of the component, and the precision of the components they require. We are approaching nano in feature size and tolerance, and the envelope is being pushed further in that direction every day,” said Donna Bibber, president and CEO of Micro Engineering Solutions (MES; Charlton City, MA), a manufacturer and developer of micro machined and micro molded parts.
Metrology, Part Handling Obstacles
As micro components become smaller and more precise, manufacturers face more difficulties in combining materials, which can be either metal or plastic pieces, to make an assembly, Bibber noted. Problems also can arise in measuring and testing sub-micron parts. “The testing and the metrology is as important as anything,” she added. “You’ve probably heard the saying ‘You can’t make it if you can’t measure it.’ At this level of small, that is even more important.”
A recent MES project involved making an endoscope measuring 5 mm in diameter by 20-mm long in which there are 18 different metal components working together, so the endoscope can move and rotate a needle 360º, Bibber recalled. “You can imagine how much of a stack-up tolerance, literally microns, in this instance,” she said. “We can’t always scale up to the tolerance needed from machined parts to molded parts, but we have to plan for scale up from part one in terms of stack-up tolerances.”
Another major issue is the trend toward more challenging part geometries. “The trends are small features, small parts, and small assemblies,” Bibber said. “The challenges are mostly in handling, and metrology. The bulk of the cost of the assemblies are really in how you handle the components, and how they’re measured.”
Additive Micro Process
Combining aspects of 3-D printing and semiconductor manufacturing techniques, Microfabrica Inc. (Van Nuys, CA) has developed an additive manufacturing process enabling the development of complex, sub-millimeter metal components and subassemblies. MICA Freeform, the company’s proprietary volume production process, can achieve 1 to 2-µm tolerances with 20-µm feature sizes, using a materials palette that includes nickel-cobalt, palladium, rhodium, and copper, covering a broad range of mechanical and electromechanical needs.
“One of the most promising manufacturing technologies as a whole is 3-D printing,” said Eric Miller, CEO of Microfabrica. “Today, the majority of 3-D printing is relegated to prototype development.
However, with the advent of new processes and materials, production opportunities for 3-D printing are emerging.
“The constant and sometimes relentless drive to miniaturization is pushing conventional micro-machining processes forward, and we see a lot of exciting things going on with laser machining and micro EDM, as they continue to be able to create more complex components and parts at a smaller and smaller scale,” Miller said. “That said, most of these subtractive processes struggle in the millimeter and sub-millimeter range, and many struggle with high-volume production.”
The MICA Freeform process combines aspects of both 3-D printing and semiconductor scale manufacturing. It’s an additive manufacturing process, allowing designers to achieve virtually any conceivable geometry, no matter how complex, Miller said. “Wafer-scale manufacturing principles allow us to achieve extreme precision, at the sub-millimeter scale, and leverage these attributes in a volume production process.”
Microfabrica’s 40,000 ft2 (3720-m2) Van Nuys headquarters includes its manufacturing fab and the company also has a medical device development office in Santa Clara, CA. “Additive manufacturing in its simplest form is building in layers,” Miller said, “so we’ll take any designer’s 3-D CAD model and put it through our proprietary software called Layerize, which separates the design into layers. This prepares the design for our fabrication process. We produce a photomask for each layer and then electrochemically deposit each structural layer until the entire device or component is built up on the wafer. The last step is to chemically etch away the sacrificial material to resolve the design and release the component from the wafer.”
Microfabrica works with industries requiring extreme precision at a very small scale, Miller said, including aerospace/defense, semiconductor test, and medical devices. “For example, we fabricate a very complex metal composite for a micro-contact application in the semiconductor test industry,” he said, “and we’re working with a very large aerospace/defense contractor to develop a fuse for the military. We’re also engaged in developing a micro tissue removal device with a large medical manufacturer.”
In late October, Microfabrica announced it had signed an exclusive sales and marketing agreement with Johnson Matthey Medical (West Chester, PA), a supplier of specialty and precious metal machined parts, tubing, wire and Nitinol to the medical device industry.
The Johnson Matthey deal enables Johnson Matthey to introduce its customer base to the MICA Freeform technology. “It literally extends their capabilities to an entirely new scale, allowing their customers to march further down the path to miniaturization.
“Our sweet spot is in the sub-millimeter scale,” Miller said. “Based on the semiconductor manufacturing aspects of our process, we can achieve extremely tight tolerances, ±2 µm, for these devices. The minimum feature size that we can create is 20 µm.”
Low-Friction Microsurfacing Technology
Another key trend in micro manufacturing is reducing cost by creating surface microstructures on low-cost materials that give them the performance of a high-cost material, said Andrew H. Cannon, R&D manager, Hoowaki LLC (Pendleton, SC), a developer of microstructures for commercially available extruded products. Hoowaki focuses on transforming surface structures of parts via engineered microstructures. “For example, we are enabling nylon and HDPE [high-density polyethylene] products to outperform PTFE [polytetrafluoroethylene],” Cannon noted. “Another trend is enhancing the performance of the current product via surface microstructure engineering. Sometimes we can enhance the performance while reducing manufacturing cost.”
Hoowaki has developed proprietary processes to impart engineered microstructures onto the surfaces of curved and flat tools, Cannon said. “Our application development and modeling efforts have produced a database of hundreds of micro designs validated and tested for specific product performance. We utilize existing designs where we can and adapt the designs as needed.”
With its technology, Hoowaki has created 400-nm structures over a 30-cm-long half cylinder mold insert, he added. “This is very different than high tolerances and often means creating the right microstructures to get the desired performance regardless of microstructure geometry consistency,” Cannon said. “Some of the major process difficulties in micro manufacturing are maintaining micro-size structures over macro areas at a reasonable cost. Hoowaki provides tools to its customers so that they can leverage low-cost, high-volume molding and extrusion processes in creating the products with enhanced surface properties.”
The medical industry, for example, is leveraging Hoowaki’s microstructured extrusion technology to reduce sliding friction in catheters. “The medical industry is also reducing the stickiness of low-durometer materials with Hoowaki technology,” Cannon said, “and the wire and cable industry is using our technology to make wire installation easier.
“We have a customer who is reducing the friction of their current catheter by 80% by using a die and mandrel that Hoowaki micro machined. They sent us their extrusion die and mandrel, we micro machined the die and mandrel with a design that creates low friction surfaces on extruded products, and they extruded their catheters with the micro-machined die and mandrel,” Cannon added. “We delivered 100% of what our customer needed to extrude their next-generation catheter.”
Conventional Micro Machining
More conventional micro machining systems like the iQ300 VMC from Makino Inc. (Mason, OH) are targeting precision micro machining, noted Bill Howard, Makino product line manager, Vertical Machines. The iQ300 Precision Micromachining Center offers the latest in Makino’s machine and spindle design. The VMC features a 45,000-rpm HSK-E32 spindle equipped with the company’s patented core cooling, under-race and jacket spindle temperature control system, which virtually eliminates thermal growth, deflection or vibration during high-speed machining.
The iQ300’s design also includes a cast-iron Meehanite construction base for rigidity, linear motors instead of ballscrew design, precision roller ways and a 10-nm, 0.005-µm scale feedback, Howard said. “The reason for the linear motors is that you can remove all of the lost motion and backlash for much smoother motion,” Howard said. “All of those elements are working together to allow us to get down to positioning accuracy of ±1 micron, and repeatability of a half a micron.”
Along with advanced temperature control, the machine’s rigidity helps maintain precision for micro-machining applications, he added. “Everything we build is a cast-iron Meehanite type casting. Part of the reason for the massiveness of the casting is that it serves as a heat sink providing a thermal constant, if you will. It takes a long time for that mass to change temperature. Now, realistically, anybody who’s considering an iQ 300 machine is already looking at putting that into a controlled environment.”
The system also features temperature control through an Oilmatic unit that regulates the temperature of the spindle and the machine’s linear motors, Howard added, to maintain the system’s high precision machining. Temperature is controlled to about ±1.8ºF [±-17ºC] with the Oilmatic, a commercially available chiller. “We actually put a thermocouple in the bed of the machine so that we can monitor the temperature of the bed, and then we have this Oilmatic unit cycle on and off to maintain the lubrication that we send through the spindle and to maintain the temperature of the spindle and the linear motors so that everything is the same temperature—the castings, the chilling of the linear motors, and the temperature of the spindle. In essence, we’re creating an ambient manufacturing zone among all the major machine tool elements.
“This is such a new area of technology, people are approaching it from two different ways,” Howard said. “We’re approaching it from the traditional machine tool builder in that we’re removing metal to get to a tolerance. Other people are adding chemical deposition layers and literally building a part from nothing to get to those tolerances. They’re literally building the tolerance by an atom or a layer at a time.”
Many customers use micro machining technology for very small components, such as battery technology in cell phones, he added, as well as for diaphragms, pumps and stents in medical applications, just for starters. “There’s also a lot of it that’s in R&D applications and for military and proprietary technology,” Howard noted. “In some cases, we work with the customer to develop processes specific to their part designs. In other cases, design details may be so sensitive that all processing is handled internally by R&D labs.”
Micro Fills a Niche
More companies today are trying to find their niche by turning to producing smaller and smaller, high-end products, enabling them to stand apart from others in their fields, noted Danny Haight, MC Milling national product manager, MC Machinery Systems Inc. (Wood Dale, IL), a subsidiary of Mitsubishi Corp. and the importer of the Roku-Roku micro machining line as well as Mitsubishi EDM, Mitsubishi Laser, MC Waterjet, MC Press Brakes and MC Milling equipment.
“We always educate our customers to realize that buying a small cutter does not constitute micro manufacturing,” Haight said. “Obviously you must be working with a well-built, rigid and stable machine. The machine must also have a reliable, high-speed, low run-out spindle and the right CNC for a controlled toolpath.”
Toolholders have to be critically balanced, with minimal run-out, Haight advised, and cutters should be high-quality carbide with the proper coating and geometry to match the material being machined, with extreme accuracy and repeatability from cutter to cutter. “Having software that can produce complex high-speed toolpaths and minimize tool burial is imperative,” he added. “Environment is often overlooked, as manufacturers are being asked to hold tighter and tighter tolerances and produce smaller and smaller parts—maintaining a stable environment is key factor.”
With Roku-Roku’s micro machining technology, it is not uncommon to machine tool steel with a 0.004″ (0.102-mm) ball end mills, Haight added. “Our applications department in Japan has successfully drilled 0.0004″ (0.0102-mm) holes in machinable ceramic,” he noted, “and we can achieve position-to-position accuracy of less than 0.00002″ (0.00051 mm) with the proper machine.” ME
This article originally appeared in the January 2013 issue of Manufacturing Engineering.