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Micromanufacturing: The New frontier

 

The old manufacturing rules don't apply in the microworld

 

By Robert Aronson
Senior Editor 

 

Micromanufacturing is a growing part of the industrial scene driven chiefly by the needs of the medical market and the constant demand for ever smaller electronic products.

Companies now involved in micromanufacturing originally came from three sources. First, a number of companies have been successful partners in the micromarket for some time, such as those involved with Swiss turning. The second group consists of manufacturers who have modified their equipment to meet the special needs of micromanufacturing. For example, many tool builders have generated lines of small tools fairly recently. Third are the entrepreneurs who, in the last few years, introduced totally new products for the micromarket such as desktop machine tools and robots that assist surgeons.

And what are these companies doing? Let's begin by looking at a company that builds high-tech medical products.

Intuitive Surgical (Sunnyvale, CA) designs, manufactures, and markets the da Vinci Surgical System. All of Intuitive's products are designed for minimally invasive surgical (MIS) procedures, a term used interchangeably with laparoscopy or endoscopic surgery. This surgery is performed through dime-sized (1–2-cm) incisions—or operating ports. This approach is dramatically different than the much larger incisions employed in traditional, open surgery, which are often as large as 6–12" (152–305-mm) long.

The system has been successfully used for radical prostatectomy and mitral valve repairs, among other procedures. In use, the da Vinci Surgical System seamlessly translates the surgeon's natural hand movements on instrument controls at a console into corresponding micromovements of instruments positioned inside the patient via small puncture incisions, or ports. It provides the surgeon with the intuitive control, range of motion, fine tissue manipulation capability, and 3-D visualization characteristic of open surgery, while simultaneously allowing the surgeon to work through the small ports of MIS.

Actually, the da Vinci Surgical System cannot—in any manner—run on its own. Instead, the System is designed to seamlessly replicate the movement of the surgeon's hands with the tips of microinstruments.

While seated at the console, the surgeon views a 3-D image of the surgical field. The surgeon's fingers grasp the master controls below the display, with hands and wrists naturally positioned relative to his or her eyes. Utilizing a master/slave model, the system translates the surgeon's hand, wrist, and finger movements into precise, real-time movements of surgical instruments inside the patient. The patient-side cart provides either three or four robotic arms—two or three instrument arms and one endoscope arm—that execute the surgeon's commands. A full range of proprietary EndoWrist instruments are available to support the surgeon during an operation. The instruments are designed with seven degrees of motion that mimic the dexterity of the human hand and wrist. Each instrument has a specific surgical mission, such as clamping, suturing, and tissue manipulation. Quick-release levers speed instrument changes during surgical procedures.

The InSite Vision System, with highdefinition, high-resolution 3-D endoscope and image-processing equipment, provides the true-to-life, 10x magnified, 3-D images of the operating field. Cutting tools have to be modified to do a job in the microarena. "While conventional CNC machines use big motors designed with enough force and horsepower to run large, rugged tools, these characteristics can be devastating to fragile, small tools," explains Walter Schnecker, president, Datron Dynamics Inc. (Milford, NH). "Efficient use of small tools to produce many medical parts requires both the foresight to employ equipment specifically designed for them, and a willingness to deviate from standard machining practices."

High-speed machining technology uses high-rpm rates, taking a smaller stepover, but with significantly increased feed rates. With microtooling, the system moves fast, and there's insufficient time for heat to feed back into the part and cause problems.

Datron's medical industry customers find that the company's 60,000-rpm spindle reduces the chip load in many instances to less than 0.005" (0.127 mm). This chip load significantly reduces the forces between the tool and the material, thus reducing heat and tool deflection, and allowing the machining of thinner-walled workpieces.

Datron's technology delivers precision and accuracy (a resolution of ±0.00008" (0.002 mm), absolute accuracy of ±0.0005" (0.0127 mm), and relative accuracy of ±0.00002" (0.0005 mm). This performance addresses the user's need to machine in close proximity to fine traces, and even on populated PCBs.

Kyocera (Irvine, CA) specializes in microtools from 1/4 to 0.0015" (6.4–0.4 mm) with the majority of their expertise in tools less than 1/8" (3.2-mm) diam. "In the world of micromachining, we classify tools 0.020–0.001" [0.3-mm] diam as micro," explains Michael D. Tibbet, senior development engineer. "Machining with tools down to 0.010" [0.3-mm] is relatively easy, but with tools under 0.010", the task becomes 'very challenging'."

Typical markets for microtooling include electronics, medical, dental, and component manufacturing for automotive and aerospace industries. "In the case of electronics, every aspect of their products is getting smaller," says Tibbet. "This drives tolerances as tight as 0.00004" [0.001 mm] for key components.

"In some cases, deep holes under 0.0200" [0.5-mm] diam and 0.750 in. [19-mm] deep," he explains. "Medical device manufacturers also use micro end mills down to 0.005" [0.13 mm] diam with the added problem of requiring a very high surface finish."

One example of meeting such requirements was a medical tubing application requiring 0.0120". (0.3-mm) diam, burr-free holes and slots. Kyocera engineers produced these features with a 0.010" diam, down/up, cut-end mill. "First, we plunge into a 0.0160" [0.4-mm] OD tube with 0.0030" [0.08-mm] wall thickness. The end mill uses minimal circular interpolation to produce features simultaneously through both walls. The only burr occurs on the outside of the tube and is removed by tumbling, he concludes.

Tapping also takes special evaluation. Carbide microtaps are primarily used where the accuracy of the thread to be tapped exceeds the capability of an HSS tap. In general, it's easier to produce a precision carbide tap than an HSS tap with equal accuracy, particularly in the size range of microtaps. The six-axis CNC620XS made by Rollomatic Inc. (Mundelein, IL) is suited for grinding microtaps in both HSS and in carbide. Control software allows all operations on a tap to be done in one clamping, including thread grinding, flutes, body relief, gun points, lead angle, and any other point geometry needed.

Tapping operations also need consideration. On the Rollomatic Grind-Smart, a special tailstock has been designed for small taps. It has a pressure-adjustable center and it's automatic, allowing it to swing out of position for automatic loading and unloading. The CNC Fanuc i control Panel on the GrindSmart has a scale feedback on the linear axes of 50 nm. An on-board rotary dresser is a CNCdriven rotary dresser with programmable and controlled rotary speed. It's used to dress the shape of the thread. Usually, the shape is 60° inclusive with a corner radius that will produce the bottom of the thread form. A software module available on the GrindSmart lets the programmer choose the shape of the thread form.

Once a part is made, the job isn't over. Metrology is a critical part of the work. Is the part you made the one you want? Answering that question requires precise metrology. For example, comparators from The L.S. Starrett Co. (Athol, MA) use 0.00005" (0.0013-mm) resolution Heidenhain scales. Such scale precision ensures that the production line is holding its tolerances, ±0.0001" (0.003 mm) within 1°. Their optical comparators use 50 or 100-power lenses, depending on the size of the microparts. When sorting is required, a template helps complete the full inspection quickly.

"Carl Zeiss IMT Corp. [Maple Grove, MN] has designed a machine specifically to address the metrology challenge. It has the ability to measure part geometry using a tactile probe, and can even scan using the tactile sensor," says Gerrit deGlee, new product manager, precision products. "The difference here is that the force of the sensor is approximately 100 times less than that exerted by standard CMMs. This reduction results in both the ability to use lower fixturing forces, and ensures that there is no part deformation because of the probe contact."

The probe sensor on this machine, the Zeiss F25, can be a 0.12-mm diam sphere. Its small size allows access to many micromachined part features, that could not otherwise be probed. "Some microparts have geometry that can be measured using optical methods," says deGlee. "This machine includes the ability to use optical edge detection. Continuous reduction of part tolerances means that the accuracy of the gage must also improve. The F25 machine delivers a guaranteed measurement uncertainty not to exceed 250 nm. This is expressed according to ISO 10360.

At Zeiss, the F25 was designed for micropart inspection. The company's Calypso software is fully integrated with this machine. "But," cautions deGlee, "to meet these inspection needs, a user must have an accurate machine, a reliable control system, a microsensor, optical sensor, and the right software to be able to interface with the technology, plus an organization to support the entire package."

Robots are important to the micromanufacturing industry because they are becoming smaller, more reliable, and less costly. Fanuc Robotics America Inc. (Rochester Hills. MI) has a line of six-axis table top units. They offer an iRVision integrated robot vision option for the new Fanuc R-J3iC controller. This system is the company's first built-in vision package, and provides customers a single source for robot guidance or process feedback. It's a ready-to-use robotic vision package.

The latest robot is the LR mate 200 IC. It's faster than previous units. The unit's weight has been cut from 45 kg to 27 kg, and it operates with high repeatability.

According to Richard Johnson, general manager, material handling, a major change in the Fanuc design philosophy is to include vision systems on every robot. "This reduces system cost because you need less equipment than with a blind robot so the part has to be positioned accurately initially," says Johnson. The vision system tells the robot where the part is so you need little or no fixturing. In operation, the system snaps a picture, processes the data, and sends signals to control robot action. If required, the robot can pick up the part and present it to the camera to check for specific features, or present the part to a gage.

PCs that ran earlier vision systems were not always reliable in an industrial environment. But the Fanuc control is within the robot. The camera system is virtually plug-and-play.

Adapting to the micro role has not been a problem for some well-established machine tool builders. Makino (Auburn Hills, MI) has focused on die and mold production, chiefly for the plastics industry. "I find there has been a transition in US industry to very large and very small parts as companies try to find their own niche," comments Lee Richmond, micromarket showroom manager for Makino. "And both are asking for really tight tolerances. Our machines have evolved to fit the microarena. We have a series of machines. The V22 has a 40,000-rpm spindle, a good work stroke, and works well with both large and small manufacturing details.

On the EDM side, Makino offers the EDAC 1 which is capable of small, sharp corners and details, while providing high accuracy.

In addition to making small parts, the task is often making small features on large parts. "We had a client who needed progressive dies to work with material 0.005" [0.13-mm] thick or less. He allowed only 0.0001" [0.002 mm] in clearance between punch and die on a job that would normally allow 0.0005" [0.013 mm]. The customer originally did the work with a combination of EDM and grinding, but wanted to get the job done in a single setup. He now machines it in one setup."

EDM is a special favorite of micromanufacturers. Sarix (Losone, Switzerland) offers the Micro EDM machine line. The SX-100/200 series is designed for semi-medium-volume production of high-precision microinstruments, microcomponents, and microinjection molding of microfluidics cavities.

Both machines are combined with advanced Micro EDM technology incorporated on a Micro Fine Pulse Shape (MFPS) generator, allowing new possibilities for smaller, deeper, more precise, perfectly round holes. This enables the equipment to achieve drill holes with diameters from 1 mm down to 10µm with surface finish as fine as Ra 0.05 µm.

Using a built-in microscale wire-EDM device for electrode microgrinding, the unit can machine intricately shaped forms, thin walls, and microstructures using up to four simultaneous axes. It provides depth control of less than 1 µm. The Micro-EDM unit can provide sinking and drilling to ±0.5 µm in materials such as Nitinol, titanium, platinum, polycrystalline diamond, and solid carbide, without material alteration.

 

When Microns Matter

Medical device, electronics, and biopharmaceutical manufacturers need new products that create tinier, less invasive, fluid-induced, and/or space-saving microdevices. These products require integrated micro and automated solutions to ensure their success out of the gate. The tiniest parts in an assembly are the ones most likely to be a problem, and are also usually the enabling component of the entire device. Many challenges exist in micromolding and micromolding systems and include:

  • Modeling of Microcomponents — There is a limited understanding of the fundamental physics at the micro scale, and improved understanding is necessary to develop reliable models. Much more research is required to perfect the modeling software, materials specifications, reliability models, and simulation models for mold flow for micro-molded components. 
  • Environment — One degree of temperature change can affect precision when machining at the submicron level, so many micromolders and micromachining experts enclose the entire machine and/or inspection area to create a controlled working environment. 
  • Metrology/Inspection Techniques — Inspection techniques in measuring very small micro-molded parts requires customized vises, tweezers, and fixturing. Inspecting steel measurements usually provides a flat, robust surface that can be measured with noncontact means or in some cases contact measurement. These same surfaces that make the molded components can be used to "certify" the dimensions much closer in repeatability and reproducibility than attempting the same corresponding measurement in the micromolded components. It's not uncommon for first-article inspection to consume as much time, if not more time, than the entire micro-moldmaking and micromolding project combined. In addition, a low vibration and low noise environment are needed to capture micro-molded feature images accurately. 
  • Validation — Gage R&R from client to vendor requires duplicate fixturing and exact methods of inspection technique to repeat the results to near-micron tolerances. A select few sources of inspection equipment exist that are capable of measuring to submicron tolerances and extremely clean and hepa-filtered aircontrolled rooms are necessary to the environment needed for repeatable measurements. It is also common in macro components, and specifically with medical devices to insist on 1.33 Cpk or better with respect to performance to drawing dimensions or tolerance. The 1.33 Cpk on 0.0001" (0.003-mm) tolerances requires a mathematical impossibility in some cases when the gage R&R and operator R&R are taken into account. Component manufacturers and micromolders require similar inspection machines with identical fixtures to validate tolerances in microcomponents. 
  • Properly sized machines — Commonly, micro-molded components have sprue and runner systems amount to 75% or more of the total shot. A common practice for creating microcomponents is referred to as the "work-around." Micro-molding parts in larger shot size machines and/or with multiple cavities is commonly attempted with varying levels of success. Dustspeck-sized parts cannot be molded in this manner due to the long residence times and corresponding degradation that occurs with oversized screw and barrel combinations. The use of conventional auxiliary equipment (i.e. dryers, moisture analyzers, hot runner manifolds, temperature controllers) are also not recommended for microcomponents. Customized auxiliary equipment is necessary until equipment manufacturers develop micro-sized equipment for drying, handling, weighing, analyzing, quantifying, and controlling microprocesses. 
  • Standardization — Many of the rules of molding accepted in the macroworld do not apply to micromolding. An extra element of shear and extreme injection pressures and velocities are inflicted in micromolding that change the viscosity of the material and many of the "rules" of general-purpose molding and the predictability values that we once knew in theory and practice.
  • Part Handling/Static — Part handling can be challenging. Many micromolders use edge-gated runners to carry their parts from one location to another and many are used as part of the automation process. If parts cannot be edge-gated, customized end-of-arm tooling, vacuum systems, reel-to-reel take-up equipment, and blister packs are utilized accordingly.
  • Static electricity is a common micro-molders' nightmare. Parts as small as dust can easily become airborne if proper grounding of part collection systems, robotics, packaging, and inspection systems is not accomplished. Static guns, wands, air curtains, and grounding mats are commonplace in micromolding facilities.
  • Micromanufacturing Processes — Micromachining and microtooling/molds hold the key for the development of micro-molding processes and also for other critical tolerance-based processes. These processes include LIM (Liquid Silicone Molding), MIM (Metal Injection Molding, and CIM (Ceramic Injection Molding). LIM requires extreme precision tooling with proper venting resulting in no flash. CIM requires extreme precision tooling for green-state components to eject from the mold properly. Micro MIM tooling requires extreme precision tooling for tiny features to be filled during processing. While each of these processes is vastly different in their processing, the tooling is the enabling component to developing the process. Because the sizes of the components are so small, bidirectional shrinkage within the cavities is minimal resulting in plastic, silicone, or metal matching very closely with that of the original tooling size.

Donna Bibber
President
Micro Engineering Solutions
Charlton City, MA

  


Published Date : 5/1/2007

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