Micromanufacturing is Growing
Don't miss the "small opportunity"
By Robert B. Aronson
Many industries have been making parts with micron dimensions for some time, but in the last few years, the market for miniaturization has expanded. The demand is not only for small parts, but also for small complex features on larger parts. This is due chiefly to the switch to modules in which the functions of several parts or subsystems are not handled by a single complex unit.
The medical and electronic industries are the most active in this area. In both cases the incentives are the same: making smaller parts with more capabilities. The cell phone is an obvious example. Its size has gone from that of a fairly large handset to less-than-palm size in a short time. Now the goal is to cram more features into these units.
The goals are similar in the medical industry. The human body has a limited capacity to take "extra" equipment, so units for various repair and pain-relief devices must be small. Also, physicians want instruments that are less intrusive so there is less chance for infection, and faster healing time.
Many industries are also interested in micromanufacturing. Aerospace is looking at fasteners, fittings, sensors, and various flow-control devices. Automotive wants these parts chiefly for the many convenience, entertainment, and safety items being introduced. For example many of these features require very small motors and actuators. And on the more practical side, there is a need for complex fuel injection and control elements. Fluidics, a topic that dropped from popularity a few years ago, is seeing revival of interest because of the availability of small flow-control devices.
Jun Ni, director of the S.M. Wu Manufacturing Center, College of Engineering, University of Michigan (Ann Arbor) notes, "The Japanese are the current world leaders in microfactory development, based on an early realization that there are significant possible economic benefits in moving towards the microfactory paradigm. It has been estimated that the size of the replacement market for micromachine tools in Japan will reach $1.1 billion in 2015, Similar market growth is being projected for America, driven by the rapid expansion of the biomedical industry that continues to remain the fastest-growing sector in the American economy, at 16% per year."
Because micromanufacturing is a fairly new industry, definitions are not yet firm. Three terms are commonly linked to these developments: micro (one millionth of a unit), nano (one billionth of a unit) and meso (generally bigger than micro).
Most "small parts" that can be manufactured by conventional means (milling, drilling, turning, and grinding) are in the micro/meso size areas. Products in the "nano" area are at the atomic and molecular level. This is the area now getting a lot of publicity, and attracting both venture capital and Federal research support. These are the far-out projects that may possibly create small machines that may be introduced into the body and carry out repairs. One of the projects that seems to be the closest to reality is molecular-size computer memories. The electronics industry is trying to go beyond the limits imposed by lithographic circuit manufacturing techniques, and find methods for cramming even more circuitry and memory elements into computers.
On the lower fringes of the micro area are Micro-Electro-Mechanical Systems (MEMS) which integrate mechanical elements, sensors, actuators, and electronics on a single, usually silicon, device. This area also does not utilize many conventional machining operations, but uses a version of stereolithograpy commonly used by many rapid prototyping systems, and specialty plating processes to make parts.
Micromanufacturing equipment development, the emphasis of this article, is found in two areas. First, manufacturers are adapting existing products to handle micromanufacturing tasks. This involves scaling down some units to handle smaller parts or adding options that can handle the micromanufacturing applications.
The other thrust is a new generation of machine tools designed specifically for micromanufacturing. Much of this work is still in the research stage, but some units are on the market.
In considering the modification of larger equipment, it's important to note there is a limit to how far conventional machining processes can be scaled down. Beyond certain dimensions, factors that can be ignored in conventional machining suddenly play a big part. Vibration, temperature, tool offset, rigidity, and chip removal are more important because these factors have a much greater influence on a part's ultimate size.
Part handling and fixturing take on a new significance as well. Since the parts are quite fragile, special attention is necessary to ensure that the process does not damage the part. Hold down and transfer by vacuum is more common.
Conventional probes and gages are often too large to use for small part monitoring. Often measuring systems must use air, light, or other noncontacting scanning methods to evaluate a part.
| MicroECM Technology
Electrochemical micromachining is a process in which metal is removed from metallic workpieces by controlled dissolution of surface atoms without direct contact between the tool and the workpiece material. Material removal follows Faraday's law of electrolysis, that is, the amount of material removed is proportional to the time and intensity of an electrical current flow between tool and workpiece. The workpiece is not exposed to mechanical or thermal stress, hence there is no change in the physical or chemical properties of the material.
The microECM process can produce internal features a few microns deep by 10s to 100s of microns wide, or external features as small as a few microns in some applications. In general, the process is limited by the ability to produce the cathode tool required to machine the desired features.
A significant advantage of the microECM technology is the ability to machine features in bores. In one application, we were able to put over 40 grooves in a 0.200" (5-mm) diam bore. The machining time to produce these grooves was 3.5 sec.
The ability of the process to meet requirements for full-form, high-volume machining, with nonconsumed tooling, is very attractive to manufacturing. These microECM production systems have demonstrated unique capabilities with respect to micromachining.
Donald Risko General Manager Extrude Hone Corp. ECX Division Irwin, PA
Research Efforts Accelerate
Research into various areas of micromanufacturing has been going on for some time, but in the last few years it has have become more varied, and in more places. And in a few instances coming closer to practical applications.
The S.M. Wu Manufacturing Research Center at the University of Michigan. Ann Arbor, MI has an active micromanufacturing program. According to Jun Ni, director, "Micro/meso-scale components inherent within all these technologies have nominal feature sizes within the range of tens of microns to several millimeters." Their work, which has been going on since 1988, falls into four general categories.
*Basic research into the micro cutting process.
"We are investigating the mechanisms of micromachining. That includes such factors as cutting forces, DOC, relation between feed and chip ejection, and cutting tool edge radius. This is a big concern because it may often be equal to the DOC.
"Understanding the fundamental mechanisms of the micromilling process requires accepting some different ideas," says Ni. "For example, the assumption of homogeneity of the workpiece material breaks down because the depth of cut used in micromilling is often less than the grain size of the material, e.g., most aluminum alloys have average grain sizes in the order of 10 - 15 µm. In addition, the stiffness of the cutting tool scales linearly, and the reduced stiffness at the micromilling level has a dominant effect in the chip-formation mechanism. The mechanism of chip formation at the micro-scale differs substantially from the conventional process in that a chip may not form with every tooth pass. When the depth of cut is comparable to the radius of the tool edge, material plowing plays an important role in cutting mechanics, along with the shearing operation removing a chip."
*Development of a new generation of small machine tools specifically for micromanufacturing.
The target scale of the individual micro tools has been defined as maximum cubic volume, with a major dimension of 200 mm in all axes, which is roughly the size of a typical shoebox. According to Rhett Mayor, assistant research scientist with the S.M. Wu center. "The goal is micro/meso-scale machine tools [mMTs] capable of producing micro features with submicron accuracy. We have developed several prototype systems. Our current mMt platform, which would fit inside a shoebox, is a three-axis system with a 2" [50-mm] cube working volume and uses a 100,000-rpm air spindle. Positioning is achieved with high-precision ballscrews with submicron resolution. The chief problem is maintaining precision on longer strokes. One answer is the development of a piezoelectric stage."
A review of meso and micro measuring systems for this work is necessary because part features are often too big to use a profilometer or laser. "But, we are developing a laser system that can simultaneously measure six degrees of freedom using a meso-scale laser head. It should be able to perform error measurement on mMT platforms."
"All the work is not theoretical," explains Mayor. "Among other projects, we are developing a micro free-piston engine. It has a total mass of 150 grams, but delivers 20-W continuous power. The ultimate goal is to use such a device to replace batteries. The system needs high-precision, meso-scale components that can be fabricated using micromanufacturing techniques."
There has been a major collaborative effort in micro/meso-scale machining and machine tool systems research among the University of Illinois at Urbana-Champaign, Northwestern University, and the University of Michigan-Ann Arbor for about the last four years, funded primarily by the National Science Foundation. Among the prototypes already built is a shoebox size, three-axis CNC milling machine, programmable in G code and driven with a Delta Tau controller.
Speaker grille has thousands of precision holes made by Makino's EDM system with a precise surface finish with a 30% reduction in molding cycle time over the previous method.
"Conventional machine tool positioning devices are not the best alternative at this size scale job so researchers are borrowing from the electronics industry," explains Richard DeVor, Research Professor at the University of Illinois in Urbana. "In one of our prototypes, the machine tool's X-Y-Z stages are positioned by devices based on voice-coil actuation technology, used for high-speed scanning applications that include tissue scanning and laser and optical scanning where fast acceleration and high positioning resolution are required. In another, a piezoelectric-based actuation system is being used."
"To get the spindle speeds needed, spindle technologies used in dental drills such as air turbines are being employed, which can operate at 200,000 - 500,000 rpm. But reducing runout is a major challenge. Solid carbide end mills used in the micromachines under development are commercially available in diameters as small as 10 microns, but edge radii are large relative to the feed rates used so the cutting mechanism is altered from conventional machining."
Among the other issues DeVor notes when machining at this scale is that the material's microstructure-grain sizes are of the same order of magnitude as the tool. Therefore, the different phases of ferrous material such as ferrite and pearlite machine as two dissimilar materials.
"In conventional machining, you consider the workpiece as a homogeneous material. But in microcutting operations, the cutter's diameter may be the same size as the grain. So you are moving from one material [pearlite] to another [ferrite] along the toolpath. Therefore, we must consider that the cutting process performance metrics, including forces, vibrations and stability, and surface generation, all have strong components driven by the microstructure. For example, there is burr formation at the pearlite/ferrite grain boundaries. It's like face milling across the deck of an aluminum block with cast iron cylinder liners."
"We are also looking at 'the micro-factory' concept as an important manufacturing paradigm of the future," explains DeVor. "That is, the linking of several miniature machine tool, material handling, assembly, and measurement devices to make a product. Suitcase-sized microfactories were first made by the Japanese in the mid and late 1990s. Now in Europe and other locations in the Pacific Rim such as Korea, are getting active in this area. We really need to accelerate efforts in the US in this area."
Because there are already a number of desktop milling machines, researchers at MIT decided to work on developing a miniature grinding machine. To date a design has been completed and a prototype unit is being built by Basaran Grinders Corp. (Long Island, NY). It will be called the LT-100 and is expected to be on the market by this summer.
The machine is a workbench-sized ID/OD grinder designed to make parts with diameters from 0.5 to 100 mm. According to MIT Professor Alex Slocum who developed the design with student Murat Basaran, "If you are going to grind small parts, you need to use a small dedicated machine rather than modify an existing larger machine. A unique feature of this design is that it uses the attractive force of a linear motor to preload the machine's air bearings."
The work envelope is about 100 x 100 mm and its slides are powered by a 2000-N linear motor. It is capable of using CBN technology as well as being fully adaptable with manufacturing line automation. The control resolution is 0.01 µm (0.0000004") and grinding accuracy is about 2.5 µm ("0.00010") under full load.
Laser and EDM
The big advantage of all EDM is that it is a noncontact manufacturing process. The process does not create conventional stresses, and you can do things you can't do with a cutter.
Commenting on horizontal wire EDM machines from Makino (Auburn Hills, MI) John Shanahan, EDM product manager notes the following developments.
- Wire diams as small as 0.00078" (0.02 mm).
- Integrated work changers.
- EDM drilling of high-precision holes having a 100:1 length-to-diam ratio. RAM EDM is required for this operation.
- Low-vibration direct tool-change spindles that eliminate toolholder variation and spindle speeds to 170,000 rpm.
- Closed-loop feedback systems down to 2 nm.
"Much the same type of improvement has been occurring with sinker machines. A lot of this micro work is for mold manufacturing, and we can make the tooling to do that."
Shanahan notes that, "Micromanufacturing has been with us for some time under various names, and has only recently begun to become somewhat formalized. But, I expect this trend to continue as demand for ever-smaller precision parts continues to grow. This industry is user-driven. When a need arises, we will make the machines to meet it.
"In the future we will have to pay more attention to environmental conditions because of the small dimensions involved," he explains. "Electronic compensation is not enough, besides a sound mechanical structure, considerations for thermal control must be inherent in the design."
The design must also account for the possibility of adverse external vibration outside the plant.
For making small holes with EDM, Makino offers its Edge 2. "It was designed as a conventional CNC EDM sinker machine, but with options for small-hole applications. It can make 20 µm holes," explains John Bradford, technical specialist.
"It has a built-in rotating axis on the table that allows the part to be flipped 180º to allow a much deeper hole," says Bradford. "That is, the hole is burned part way, then flipped and drilled from the other side. The unit is capable of creating holes of at least 100 times electrode diam. There is also an optional 4th and 5th axis for more complex holemaking assignments."
For high-volume, untended operation, the unit has an automatic electrode change. When one is worn, a fresh electrode is automatically inserted.
To date, the machine has been used chiefly for optical connectors and other electronic parts. And often wire EDM is used to make special features on the original holes. Positioning and repeatability are guaranteed at ±1 µm.
"We are seeing an increase in sales for machines dedicated to micro products, but customers want a multipurpose machine that can use both large and small wires with automatic changeover," says Gisbert Ledvon, Charmilles Technologies (Lincolnshire, IL).
The company is adapting its machines to meet the new micromanufacturing requirements. "Our latest EDM machines have the ability to cut smaller holes and also thread and change wire automatically," says Ledvon. "The manpower cost for handwork is a problem, but with the automated systems customers are more willing to take on the more challenging smaller-piece cutting.
"We have gone to a smaller 0.0008" [0.020 mm] wire. The machine has an 0.0010" [0.03 mm] wire for rough cutting, then automatically switches to the 0.0008" wire for finishing. The main focus is still on the use of wire EDM for medical."
When deciding among EDM and various lasers, there are a number of variables to consider beyond initial cost, such as setup time, production speed, and production volume.
Prima North America Inc.'s Laserdyne Systems Div. (Champlin, MN) is the leading manufacturer of high-precision Nd:YAG and CO2 laser machining systems. One of the major applications of the company's products is precision drilling of holes in a wide range of components for aircraft jet engines and turbines used for power generation. Parts drilled on Laserdyne equipment include turbine blades, nozzle guide vanes, shrouds, and combustors. For these applications, the goal of the turbine engine builders is to achieve consistent air flow through the cooling holes and across the surfaces of the components. Too much air flow adversely affects fuel efficiency. Too little flow and the components overheat, shortening their lives.
"Currently we are investing in ways to further improve the consistency of air flow through laser drilled holes," explains Terry VanderWert, vice president. "Holes for turbine engine applications are typically 0.02" [0.5 mm] and larger, produced in high-temperature, nickel-cobalt-chromium alloys. Smaller holes, approximately 0.006" [0.15-mm] diam, can be produced in these materials, and even smaller holes can be produced in a wide range of other materials.
"We are also continuing to demonstrate and add to our capability for drilling 'shaped holes,' an increasingly popular design approach being used to improve cooling of engine components. As a soft-tooled process, laser drilling has significant flexibility in the shapes it can produce and the ease with which the shapes can be modified."
The Laserdyne Model 790 BeamDirector is a five-to-nine-axis system that has a PC-based CNC process control, designed specifically for multiaxis laser systems. It has an optical focus control to position the laser beam relative to the workpiece surface on both metals and nonmetals, including ceramic-coated metals.
"We are now working to extend to other applications the capability developed from working to meet the very demanding turbine engine applications," says VanderWert. "Typical nonaerospace applications involve parts with many small holes in metals or nonmetals, including ceramic-coated metals. Lasers can produce these holes at compound angles as low as 12º to the surface."
"We specialize in UV lasers both solid-state and excimer," says Jeffrey Sercel, president, JPSALaser (Hollis, NH). "Solid-state UV lasers have an easily steered, pinpoint beam down to and below 5 µm. There you get the cool advantage with the direct-write techniques. IR YAG and CO2 lasers are like mini blowtorches where they vaporize materials.
"Generally, UV uses less power than other lasers, and has a limited or no heat-affected zone. We are able to make submicron features."
UV lasers tend to be more exact and have less heat and melting effects. They have large area beams that are very uniform over these larger areas. This allows the use of projection lithographic techniques to image photo masks. For instance large arrays of holes, lines spots, squares, etc.
"The excimer laser generates a wider beam, about 1 X 1/2" (25 X 13 mm) that creates a product in a single shot," according to Sercel. "For example, you could make 10,000 holes simultaneously. The operator makes the product in 3-D as opposed to burning it out with a point source. With UV you use less power and achieve better, heat-free results. As an example of its lack of heat generation, it is used for eye surgery.
"How the laser beam reacts to the workpiece material is critical and testing is always an important first step," Sercel explains. "In some cases they will only work with material that has specific absorption characteristics. But with an excimer you can machine any material because materials absorb more UV energy. They don't reflect it. For that reason you can work with thermally sensitive polymers, quartz, or glass.
"Our excimer lasers are available in a wide variety of wave lengths to match a variety of materials," says Sercel. "In operation, the excimer laser removes from 1/10 to 1/2 µm per pass. Most of the materials we work with are quite thin, usually up to 0.5 mm. In some cases we can handle material up to 2-mm thick.
"I don't consider our lasers as competitors for EDM. We both have unique niches. Generally EDM does the thick stuff and we handle the thin. Neither do we compete with conventional machining. If you can machine it, you don't need a laser," he concludes.
"Everybody wants things smaller; customers are asking, 'What's the smallest thing I can work with?' " says Steve Roy, YAG product manager for Trumpf Laser Division (Plymouth, MI). "We are seeing a lot of activity. But we are not making laser systems specifically for this market. Our systems can be adapted to most customer requests."
The three areas where lasers are called on for micromanufacturing tasks are cutting, welding, and drilling. "Minimum drilling requirements have held at around 50 µm for some time," explains Roy. "For welding applications, we are now in the 50 µm range in some cases. These jobs are chiefly for microelectronics. For cutting, requests go down to the 20 µm area. In many cases there is a trend to lower, better controlled power. Lower laser energy is needed as the laser beam gets smaller."
GSI Lumonics. "Micromanufacturing continues to be an increasingly important area for laser processing applications," says Mohammed Naeem, materials processing development manager, (Rugby, England). "The increasing complexity of microelectronics/ engineering devices and the requirement for higher yields and automated production systems place stringent demands on the assembly techniques and performance requirements of materials, machining, and joining techniques. This has led to increasing interest in the use of low-power lasers for machining, welding, soldering and marking of small assemblies. Of particular interest to microcomponent industries is the ability of such lasers to apply controlled amounts of energy in precise areas, utilizing extremely low heat input, resulting in very low distortion, and coupled with the ability to operate at high production rates in a flexible manner. These characteristics are critical to applications such as:
- Micromachining [two and three-dimensional cutting, drilling, surfacing, rapid prototyping];
- Assembly [welding, soldering, brazing, forming]
- Repair [rework/replacement of damaged or faulty components];
- Marking [engraving, color change, surface modification, topcoat removal];
- Material transformation [surface and bulk].
"Processes such as these are currently being applied to a wide range of metallic and non-metallic materials, including ceramics, silicon, polymers, glass and precious stones.
"GSI Lumonics manufactures a range of low-power lasers suited for micromachining, including Nd:YAGs, excimers and CO2 lasers. One of our new pulsed JK series twin-rod Nd:YAGs will be used at the Nanoscience Research Center at one of the US National Laboratories."
| Making Micromolds
We specialize in the design and manufacture of micromolds. These molds weigh fractions of a gram, have wall thickness of less than 0.005" (0.0.13 mm), and are made to tolerances of 0.0001 - 0.0002" (0.003 - 0.008 mm). Frequently their geometry can be seen only by using a microscope.
Sizes achievable in micromolding can be as low as 0.5 µm and 50 µm-length "channels" can be interconnected in a flow pattern. Finish requirements are optical in nature and measured in Angstroms for optical components. Average surface finishes in steel vary by manufacturing method.
Micromold costs range from $1500 for a cavity insert up to $550,000 and higher for intricate geometry and multicavity micromolds. Lead time ranges from two to 14 weeks, depending on part complexity. The tolerance possible depends on the project. Generally, we will build steel to 25% of part tolerance, leaving 75% for the molding-process window. If the tolerances are less than 0.0005" (0.013 mm), we really end up "engineering a process" that allows us to meet tolerances to give us the most repeatable results. Tolerances of less than 0.0005" (0.013 mm) require us to build the mold around those particular areas and make them steel-safe to be able to adjust if necessary. One example of a very tight tolerance is a mold we just finished for an eight-cavity surgical instrument with a U-shaped "tooth" part. We made a side-action tool with stepped and jumped parting line with 132 pieces of steel in the mold that stacked up to an intentional offset of 0.0005" ±0.0002" (0.0127 mm ±0.005 mm) across the parting line.
Microsensor part (the gear-like part) has 0.002" (0.051-mm) double-edge-gates. Slots on the back of the part are 0.003" (0.12 mm).
Many markets have a need for micromolded components, the largest being the medical market. The automotive market employs many "behind the dash" applications such as GPS/Navigation System sensors and air bag sensors. Another market is microfluidics, which employs lab-on-a-chip applications for assay testing, drug discovery, and environmental testing in research laboratories and pharmaceutical and biomedical applications. Lastly, micromolds are assisting researchers with the "here and now" to achieve nanotechnology futuristic applications. President Bush has approved a 17% increase over last year to fund nanotechnology research. Nanotechnology is 10-9, but micromolding is serving the 10-5 or 10-6 market at this time.
We use a variety of methods to make the tooling. EDM, LIGA, laser, hot embossing, and ion machining. EDM is noncontact manufacturing and the tiny pieces of steel require a hardened, stress-free machining method that EDM offers. We have also used LIGA techniques, where surface finish is required to be near-mirror or SEM (scanning electron microscope) quality.
To ensure accuracy and monitor sizes, we mount tooling microscopes right in the EDM tanks to see the setups. Both steel and plastic are measured with video microscopes with one more decimal-point resolution than the specification calls for. In the case of submicron features, we use external sources that have certified equipment For example, if 0.0001" (0.0025 mm) is the specification, 0.00001" (0.00025 mm) measurement resolution is required.
Some of these parts are so small that the toothpick-sized runners are used as handling devices in some cases to assemble the microscopic pieces. In other cases, parts are placed on blister-packed reeled tape so they do not get lost. Static electricity is a very large problem with dust-sized parts, and static eliminators are used throughout the manufacturing process.
Donna Bibber Vice President Miniature Tool & Die Inc. Charlton, MA
Micro Machine Tools
The early manufacture of clocks and watches in Switzerland stimulated the development of machine tools capable of making the necessary small parts. The ability of these machines to support the workpiece close to the cutting tool gave the necessary precision. Once called Swiss turning units, these machines have evolved into Swiss-type machining centers with milling, drilling, and boring capabilities. These newer machines often have the ability to finish a part in a single setup, which because of handling challenges with very small parts, is a major advantage. Plus, because of the relatively low cost of the machines, they are attractive to both big and small operators.
Citizen."We have been doing micromanufacturing for some time," says John Antignani, executive vice president, Marubeni Citizen Cincom (Allendale, NJ). "Although our machines were initially for turning only, today's units have subspindles and live-tool capability, along with drilling and milling features. Initially parts up to 1.25" [32 mm] in diam were considered small. Now parts are much smaller and more precise. We are now looking more at subminiature parts, down to 0.5 mm in diam. Recently, we announced a new spindle to handle that size."
Currently the machine that can handle the smallest parts is the RO4. It has a 20,000-rpm spindle and can take work 4 mm in diam and smaller. The machine has ceramic bearings and linear guideways.
"There are a great many medical and electronic applications," says Antignani. "In automotive we work on parts for fuel injection and ABS. For aerospace work it's mainly sensors and instrumentation.
"Initially there were not many tool suppliers for our type of machine. We had no choice but to buy carbide and grind our own. Now there is a good library of tools from suppliers. Currently we are looking for boring bars that better meet our needs.
"Our big advantage is that we can make a small complex part in one machine. Currently we do not offer a grinding option, but when finish is the issue, we can usually provide what is needed by turning, and avoid grinding."
Stock loading can be an issue. Handling 1-mm bar stock can be a problem, for example. To meet this need, the company has developed a bar feeder that can handle stock down to 0.7 mm. Parts handling is difficult with parts so small they can be lost in the chips. The RO4 has a vacuum system that delivers parts segregated from the chips.
Makino. Micromachining is definitely a distinct industry and it's growing, says Brett Hopkins, senior applications engineer, Makino (Auburn Hills, MI). Key uses are in the medical, electronic, automotive, and aerospace areas.
This is a technology in which Makino has long been active. In fact, Makino manufactures a range of machining centers for this market including the Hyper and V-series machines.
Some of these machines are available in the US but many have only been available in the growing Japanese market. The V22, for example, has a 40,000-rpm spindle, and travels of 12.6 X 11.3 X 11.8" (320 X 287 X 300 mm). It is not just a scaled-down version of a conventional machining center, but a unique design with special attention to rigidity and accuracy.
"When dealing with cutting tools as small as 0.004" [0.1 mm] very small deviations due to vibration or runout are disastrous. It is technologies like this that will allow manufacturers in high-cost markets to maintain their competitive edge," Hopkins says.
According to Hopkins, Japan is about 10 years ahead of the US in implementing micromanufacturing, which has driven the design of these unique machines. Japan has a more complete knowledge of accuracy issues than the US based on this historical head start. A much broader understanding of environmental control, tooling, fixturing, and CAD/CAM techniques are required. It is Makino's mission to develop this understanding in customers who invest in advanced technologies.
Mori Seiki (Irving, TX) is approaching the micromanufacturing issue through innovative, high-accuracy designs. First the design of its latest machines stresses high precision with the capability of handling the smaller tools. The NV4000 DCG, while not classed as a micromanufacturing machine, is proficient at small die and mold work.
According to Daniel O'Connor, training manager, Mori Seiki USA, Inc., "We looked at all those details that can add that extra bit of precision. We are looking at that last 1%. For example, we have our DCG [driven at the center of gravity] concept. In this configuration the ballscrew drives the table or head at the center of its mass, not from an offset position. So, there is no distorting leveling action during acceleration and deceleration. The result is better part finish and accuracy.
"The drive motors use million pulse per revolution encoders. Feedback of this accuracy keeps better track of the machine's position. It's no good to be able to cut if you don't know exactly where you are. These motors give that information."
The spindle has also been redesigned. It's more compact and delivers more torque, which means faster positioning and more rapid acc and dec.
"The machine easily has the capability to machine features measured in microns with the proper tooling and fixturing installed," says O'Connor. The smallest part would be determined by the fixturing attached to the work table and tooling size.
This new design also takes advantage of the company's "digital design" philosophy. "Before, we would build about four functioning prototypes to check out a new machine. With virtual digital designs we can try 200 or more designs without cutting metal," he concludes.
Mikron. Another manufacturer offering machine tools suitable for micromanufacturing is Mikron Corp. (Holliston, MA). In considering the design of these machines, company vice president Mal Sudhaker notes, "Many high-speed machining centers have not allowed for ease of automation, and issues such as thermal growth and vibration have inhibited users from operating in a truly unmanned mode."
Mikron offers high-speed machining centers designed for automation that address these problems. One model, their HSM400, has a table chuck with a palletizing system and a seven-position pallet changer as standard features. The modified bridge design of the machine allows the operator to access the machine from the front and permits the use of a pallet-changing device from the rear. The machine can also be served by a robot in place of the pallet changer.
To address specific issues of high-speed machining, the machines have several hardware and software modules, called "smart machine" modules, that improve process reliability.
One such module, the Advanced Process System, has a built-in vibration sensor in the spindle together with a spindle diagnostic module. The sensor measures the vibration levels at the bearings during the cutting process, and the spindle diagnostic module records the information. The vibration level scan may also be displayed on the monitor of the CNC control. Limit values can be set relating to the vibration level, and if the values reach certain levels a warning can be issued or at higher vibration levels the cutting process can be stopped, preventing damage to the machine and workpiece.
A new "smart machine" module labeled Intelligent Thermal Control addresses the issue of thermal growth. It has built-in intelligence on the thermal behavior of the machine and compensates automatically for thermal drift for all operating conditions. With this module, a warm-up phase or pre-heat cycles are no longer necessary, and machining can be carried out with a high level of confidence in a fully unmanned mode.
Hardinge. A number of machine manufacturers are adapting machines from their existing product line to meet micromanufacturing needs. For example, Hardinge (Elmira, NY) has a gang tool lathe, the Quest GT27SP, that is suited for micro work. It typically produces parts with a 5:1 length-to-diam ratio while maintaining high-precision tolerances.
"Spindle design is the key to our advantage," says Brian Ferguson, applications engineer. "With our collet-ready spindle, holding size, finish, and part roundness is much easier. This spindle design has no need for a gap between the collet and stock. Typical micro parts have tight tolerances, and our Super Precision machine provides an offset of 0.000010" [0.0003 mm]. For holding the part, we provide standard collets as small as 0.016" [0.406-mm] diam."
Precitec. Small size and extreme precision requirements made optics an early application of micromanufacturing. One company active in this work is Precitech (Keene, NH). "We consider that many of our machine are used to make products in the meso-scale range [1 - 20 mm]," explains Jay Roblee, vice president, engineering. "These machines are configured much like conventional two-axis lathes, but are much more precise. Normally, they are used to make lenses or lens molds by turning with single-point diamond tools to a precision of 50 nm or better.
"Commonly used materials for molds are plated nickel-phosphorous alloys. For these jobs, surface finish is a big issue. We need to get 2 nm, Ra. But we want to do this by just turning and eliminate polishing.
"Some of these molds are used to make precision contact lenses, including aspherical lenses to correct special vision problems. We also make intraoccular lenses. They are replacements for the cornea and inserted within the eye. We also make small lenses a few microns in diam for missiles, cameras, cell phones, and DVD players.
"Because our diamond tools cut a fraction of a micron at a time, keeping them sharp is a challenge. We use diamonds that have been shaped by focused ion beams. Tolerances are in the 100-nm range using a 50,000-rpm spindle for diamond-flycutting a freeform shape on our three-axis machines.
"Instead of mounting tools on a conventional slide, we use a piezoelectric device that can move the tool 600 times a second with amplitudes of 10 µm."
UGT. Often grinding is the only way to work with small parts made of very hard materials such as ceramics. United Grinding Technologies (Miamisburg, OH) offers a machine that can be adapted to this type of work, the Jung S-320 profile grinder. It is unique in that is uses a pendulum or pecking technique to grind parts. The grinding machines table is driven by a linear motor that rapidly cycles the head in and out of the part.
In one application, a carbide part had to be ground into a comb-like punch having a series of slots 0.0006" (0.2-mm) wide and 1/8" (3-mm) deep every 0.3 mm. The table was cycled at a rate of 600 strokes per minute. They used a 600-grit diamond wheel. "This form of reciprocal grinding is necessary to cool the part," added Reinhard Koppen, UGT's applications engineering manager, "Constant pressure would build up too much heat. Cycling allows fluid to cascade over the wheel and part and control heat build up."
Waterjet. Another cutting operation to consider for holemaking and small parts is waterjet. As this technology has matured, suppliers have been able to achieve finer detail through developments such as better control software, fine nozzles, and higher-pressure pumps. A big advantage of this process is that it does not generate a heat-affected zone.
According to Joe Cisar, senior applications technician, Bystronic Inc. (Hauppauge, NY) Bystronic has cut holes as small as 1.1 mm on their waterjet cutting system, Byjet. In recent tests, they cut a 1.2-mm diameter hole in 4-mm thick stainless steel, and a 1.3-mm hole in 5-mm-thick aluminum. Currently, the unit most often used for this work is the Byjet 3015 which features the BJD50 70-hp (52.5-kW) pump.
Cutting fluids."One of the main advantages is that all the fluids we supply work well together," explains Joseph Gentile, product manager, Hangsterfer Laboratories (Mantus, NJ) "This includes our way oils, tapping oils and cutting oils which are all compatible with each other. The products have a longer life because they contain no solvents or volatile organic compounds that can evaporate in a short time.
"Our oils all have a very light viscosity, which does not change characteristics quickly. Also, there are long-chain chlorinated paraffins which have the benefit of being nontoxic, highly effective extreme pressure additives. When machining metals like titanium or very small threads that makes a major difference, because these extreme pressure additives are not found in many competitor products with this light a viscosity."
Special Spindle."In general, there is a demand for smaller machines to make these smaller parts," says John Easley, Precise Corp. (Racine, WI). "For some time customers wanted an all-purpose machine, one machine that could make everything. Now it's a matter of right-sizing the equipment for the job. For smaller parts, often the work envelope is a 12in.3 [305 mm3] cube, usually to make precision molds.
"At the same time the customer wants the precision that will let them eliminate extra steps or hand finishing. One of the goals, chiefly among researchers, is the 500,000-rpm spindle, for high-speed holemaking. We see that as possible, but some time from now. Currently, our maximum speed for an air-bearing spindle is 180,000 rpm, and for a conventional ball-bearing spindle it's 160,000 rpm. It's a 60-mm spindle with a 1/8" [3 mm] collet capacity. But we are pushing the envelope to increase speed.
"In the design of ball-bearing spindles, power is rapidly increasing due to a couple of developments. First, permanent magnet motor design is improving. They offer a significant increase in power compared to typical ac-induction motors. Designers have found ways to keep the magnets on the shaft at higher speeds. The other improvement is the thermally stable shaft. There is a much smaller temperature difference in the shaft between idle and full-load operating conditions. The reduced temperature fluctuation means a more stable tool.
"At the same time there have been improvements in grease lubricants and bearing materials combining nitrogen steels and ceramic balls. They can operate at high speeds using grease lubrication, eliminating the need for oil and its complex supply system."
Nonmachining Processes. Much of the interest in micromanufacturing involves processes other than modifications of conventional machining. Some deal in manufacturing processes akin to those used in rapid-prototyping operations. For example, Microfabrica (Burbank, CA) manufactures parts measuring from 100 µm to a few millimeters. "Typical micromechanical devices are in three application areas: sensors [i.e. pressure and accelerometers], actuators [i.e. solenoids and valves], and microstructures [i.e. ink-jet nozzles and connectors]," explains Chris Bang, Microfabrica's vice president of design and applications engineering.
Their manufacturing process combines photolithography with a metal-plating operation. A CAD program is first converted to a program that defines small "slices" of the end product. Then each slice is created as a thin metal-plating on a substrate. Two metals are used, one that will become the final part, and a bracing or interconnecting metal. When the part is finally built up, usually in 20 to 30 layers, the bracing metal is etched away, leaving the finished product. Parts can be made individually or in batches. Most are made of nickel alloys, but other metals are being researched, including copper, platinum, and steel.
Sensors are a major area of research. According to Bang, "Survivability is an important issue for sensors in applications such as machine-tool performance and turbine-engine monitoring. Therefore we are looking into the possibility of incorporating the sensor into the metal of the product or process being evaluated, instead of just attaching it in some way."
| High-Speed Machining with Microtooling
We offer tools for high-speed machining with microtooling operations with a diam of 0.250" (6 mm) or less, when dealing with nonferrous metals and plastics. Spindle speeds are usually 25,000 rpm or more. Conventional CNC equipment using tools smaller than 1/2" (6 mm) diam at 10,000 rpm or less usually results in unfavorable feed rates and costly tool breakage. To attempt machining with microtooling, conventional machines must run very slowly, and have a tendency to easily break the fragile tools.
Smaller tools, on the other hand, are fragile and more susceptible to breakage. Improper chip evacuation is a major cause of tool breakage. In fact, more small tools break because of inadequate chip removal than they do because of incorrect machining parameters.
Chips must be removed from the cutting channel in order to minimize breakage possibilities. Small tools require high spindle speeds, but they need to go even faster to kick the chips out.
The best approach to efficiently machine with small tooling is a threefold process. The three interrelated elements are:
- Micro-tooling design,
- Low-viscosity coolant,
- High-speed machining technology.
Tooling requirements change when tool diam decreases and spindle speed increases. Conventional tooling using inserts is not appropriate for microtooling applications. This is primarily due to the required higher rpm rate rather than the tool diams involved. Increased rpm rates require a properly balanced tool with significantly increased chip room to ensure proper chip removal and to prevent chip burn-up. The geometry of microtooling, together with high-speed spindles and proper coolant, can totally eliminate deburring as a secondary operation.
Microtooling needs a lubricating agent with a viscosity lower than that of water. Lower viscosity is needed because the coolant needs to make it to the cutting edge of the tool at the high spindle speeds involved. Emulsion-based coolants have a higher viscosity than water, and thus are ineffective as a lubricant for high-speed machining with microtooling.
Available microvolume coolant spray systems can use ethanol. Ethanol is ideal for nonferrous metals and some plastics. However, steel-based materials require an oil-based coolant. Thus the advantages of ethanol coolant are not available for ferrous machining. This is because carbide tooling on steel surfaces can cause sparks, which could create a rather highly dynamic situation if exposed to an alcohol-based coolant.
Conventional flood-coolant is petroleum-based. Such coolants need to be properly disposed of, with attendant costs. Ethanol doesn't need to be disposed of or recycled, because it simply evaporates.
High-frequency spindles with speed ranges from 6000 to 60,000 rpm are ideal for milling, drilling, thread milling, and engraving using microtooling. They move fast so there's insufficient time for heat to feed back into the part and cause issues. About 60% of the heat is inside the chip. High-speed machining tries to evacuate the bulk of the heat with the chip, providing for a cleaner cut. The better machining quality is based on cooler tooling, lower machining forces, and therefore less vibration.
Walter Schnecker, PhD President Datron Dynamics Milford, NH Cover blurb
Cutting Tools Go Micro
Iscar. Several of the major cutting tool manufacturers have fairly recently offered tool lines specifically for the micromanufacturing market. John Steward, product specialist, Iscar (Arlington, TX) notes, "Our solutions for this type of manufacturing have grown exponentially in the past 20 years. For instance, in 1984 our catalog offered tools such as the SGTHR 9.5-2, a part-off toolholder with a 0.375" [10-mm] shank that utilized coated carbide inserts as narrow as 0.087" [2.2 mm]. In 1994, we had grown to include tools such as the GHMR 12.7, which holds multidirectional grooving inserts as narrow as 0.041" [1 mm]. In 2004, we offer such tools as the Picco MFT, a multidirectional, multi-functional threading tool that drills, bores, profiles, and threads holes as small as 0.157" [4 mm]."
Iscar also offers miniature carbide coolant-fed drills; the Passport System, which includes miniature face-grooving tools that trepan diams as small as 0.236" (6 mm); the MiniCham, an indexable boring bar that offers multidirectional grooving inserts as narrow as 0.0197" (0.5 mm); and Shrink-In, a system of thermal shrinking holders that accommodate round tools as small as 3.0 mm. "We are continually pushing the limits of micromachining, producing smaller holders than we have ever manufactured before, like the SwissTurn and SwissCut tooling, which are ISO turning tools that offer shanks as small as 0.375" [10 mm] and innovative indexing techniques that allow the user to index inserts in Swiss machines without having to remove the toolholder," says Steward.
Kennametal. To reduce the time and cost of either replacing worn cutting tools or reconfiguring the tooling package on a machine tool, Kennametal Inc. (Latrobe, PA) developed the KM quick-change tooling system. The system was designed to replace square-shank tools with a shank dimension of 1" (25 mm) and larger. In recent years, Swiss-type machine tools have become an increasing part of the manufacturing environment. The conventional KM product cannot be adapted to the Swiss-type of machine due to its size. The layout of Swiss-type machines makes it difficult to access the turning tools for insert changes and tooling package reconfigurations. Existing tooling designs address the problem by utilizing special toolholder and insert designs, making it somewhat easier to access the insert holding mechanism. Kennametal's approach to the problem was to develop a quick-change mechanism, with all of the features of its KM design, capable of fitting into square and round shank toolholders from 3/8 to 5/8" (10 - 16 mm). The mechanism had to be capable of supplying sufficient rigidity to endure the forces developed in metalcutting as well as repeatability in three axes to allow for pre-gaging. It also had to be simple and robust. The final design concept has been named KM Micro.
KM Micro allows all insert changes to be performed offline. The worn insert is replaced with an identical cutting unit and insert that has been pre-gaged. The access screw to the mechanism is placed in the best possible orientation and location allowed by the Swiss-type tooling blocks. Since an insert can easily be indexed or changed once out of the machine tool, standard inserts can be used. The tooling package can be reconfigured in the same way that worn inserts are replaced. Machine downtime is greatly reduced by using the KM Micro system.
"The system has been designed to perform all types of machining operations including turning, boring, cut-off, and drilling," explains Robert Erickson, Kennametal consulting engineer. The machine operator changes a pre-gaged cutting unit and insert rather than undertaking the more difficult task of changing the individual cutting insert to which the operator has limited access.
"The system consists of a clamping unit and a cutting unit. The clamping unit can be a square shank or a round shank. Bolt-on flanges are also available to be used with special mounting blocks. The use of special mounting blocks with bolt-on flanges often makes it possible to add one or more additional tooling positions in the existing tooling envelope. The benefits realized in machine uptime through the use of using a quick-change tooling system on Swiss-type machines are especially relevant when considering the demand for these machines is increasing at a rate of 25 - 40%.
"The KM Micro system is not designed solely for Swiss-type machines," explains Erickson. "Square shanks and round shanks can be used in any tool slot, turret, or block with a dimension matching the system size. The system is currently available in 16 (5/8", 16 mm] and 12 [1/2", 12 mm] sizes. KM Micro sizes 10 [3/8", 10 mm] and 20 [3/4", 20 mm] are being developed. It is believed that a KM Micro 8 [5/16", 8 mm] mechanism is the smallest possible from a practical standpoint."
Mitsubishi Materials [Irvine, CA) has recently introduced a new line of "Swiss/Small" tools. They are designed to work with Swiss-style other small equipment.
"These tools are specially designed to work in a wide variety of applications, especially where light cutting pressure is needed for small part work. The inserts can also handle large DOCs because of limited toolholder locations on the machine," explains Chris Wills, turning products specialist. "They also have to handle higher rpm, because part diameters are relatively small and maximum rpm is reached at lower fpm."
Called the "Up Sharp" line, the smallest tool nose radius is 0.0002" (0.005 mm) which is offered as a ground insert, either coated or uncoated. The Up Sharp name comes from the high positive shear angle of the breaker. Mitsubishi also offers a line of coated microdrills with coolant-through-holes, starting at 1-mm diam, and solid-carbine end mills starting at 0.1-mm diam.
Sandvik. "Small-part manufacturing is definitely a growing market," says product manager Brent Godfrey, Sandvik Coromant (Fairlawn, NJ). "There are more and more small-- 0.5" [13 mm] and smaller--components that have to be machined to meet extremely tight dimensional tolerances. Usually, the most important goals are reduced cycle time and good quality, often in high-volume operations."
The industries most heavily involved are medical, automotive, aerospace, and electrical, with typical products being medical-bone screws, air-bag components, steering components, computer elements, and rivets.
"For these operations, the major challenges are chip control, tool life, and tool selection," says Godfrey. "This is complicated by the fact that often difficult-to-machine materials are involved, including brass, copper, alloy steel, stainless, titanium, heat-resistant superalloys, aluminum, and precipitation-hardened alloys. Even polymers and composites are involved.
"Chip control is critical since most of the high-volume parts are produced in automated environments. For the same reason tool life is critical. In many small-part applications the inserts have to tolerate demanding cutting data for the sake of minimizing cycle time," Godfrey explains.
Tool selection becomes more critical as parts get smaller. Some parts demand a radius of 0.001" (0.03 mm). Others need a 16 Ra surface finish. Some parts have thin walls and long overhangs so cutting forces need to be minimal. Some parts need internal machining down to 1- mm bore. Others have grooves 0.020" (0.5-mm) wide and extremely fine pitch threads. In many cases the insert must be extremely sharp, and some parts need the insert to have a dead-sharp corner.
"Sandvik Coromant has been providing tools for the small-part industry for several years," says Godfrey. "This year, we will introduce CoroTurn XS. CoroTurn XS is a program of boring inserts and holders designed for turning, copying, grooving, pre-parting, profiling, and threading of components with bores down to 1 mm. In addition, Sandvik will introduce a number of external tools capable of doing the same operations on extremely small parts.
"Among the new tools for micromachining we are offering are the VCEX inserts designed for both axial turning and back-turning. They have an extremely sharp edge to keep cutting forces low, and a ground surface behind the main cutting edge to provide good surface finish on almost any material. For parting and grooving there is CoroCut Swiss. This system utilizes our smallest, sharpest, and thinnest CoroCut inserts, and has a 45º mounted screw for easy access in a gang-tool setup. For threading we now have U-Lock and Top-Lok Swiss. Both of these systems are designed for threading small parts in a gang-tool setup. The CoroMill Plura solid end mill program has end mills as small as 0.016" [0.4-mm] diam, and the Delta C solid drill program will introduce 0.059" [1.5-mm] drills very soon."
Magafor. [Milford NH) provides a standard tool from stock for special microreaming applications. "Magafor offers a wide range of solid micrograin carbide K15 Micro Reamers," explains Harly B. Savage, general manager. "The right-hand cut/left-hand spiral design results in fine finish. The company's series #8600 is standard from 0.0236 to 0.1476" [0.6 - 4.0 mm], and stocked every 0.0004" [0.01 mm]. This range has recently been extended into the series #8610 starting at 0.00787 to 0.0234" [0.2 - 0.001 mm] and stocked every 0 .00004" [0.001 mm]. The reinforced 3-mm shank on the series #8610 offers the greater stability necessary to the success of these high-precision tools."
MA Ford. Some cutting tool manufacturers have been offering small precision tools for some time, such as M.A. Ford (Davenport, IA). They offer off-the-shelf drills down to 0.0039" (0.1-mm) diam and can make drills down to 0.002" (0.05-mm) diam by special order. The smallest item in their new die-mold ball end mill line is 0.0156" (0.4-mm) diam, while with traditional end mills the standard product offering starts at 0.0050" (0.12 mm) diam for a four-flute end mill.
A typical application for these die-mold end mills is cell phone body molds, while the drills are used in the manufacture of heart surgery stents.
There are also special requests, comments Gary Schmidt, technical applications engineer. "A racing team engineer had us drill a 0.004" [0.102-mm] hole in the bottom of a standard hydraulic lifter in a motor to provide better lubrication as it runs on the cam. This resulted in less friction and therefore, better engine performance.
"Most of the small MA Ford tools are made with a standard shank generally larger then the actual tool," explains Schmidt. "The size most commonly used is 0.125" or 3 mm. Most customers use precision collets to hold the tools, which may give runouts in the 0.0001 - 0.0003" [0.003 - 0.008-mm] range.
"Features unique to the design of these tools include a variable helix on the drills. This allows for a strong point geometry. Then, as the drill goes deeper into the material the helix changes to eject the chip better. On die-mold ball end mills, the design uses a slow helix to produce a stronger cutting edge because the goal is not to remove a lot of stock with these tools. The concern is for cutting edge strength.
"In the hard-to-machine materials like stainless and Inconel you should use the shortest flute length and strongest tools available. When calculating your DOC, be aware cut depths are greatly reduced for smaller end mills. Typically you would run a 1/2" [12 mm] end mill to a depth for slotting of one diam deep where with a 0.020" [0.5-mm] diam end mill it would only be 25% of the diam depth.
"When small-hole drilling in these material, use a pilot drill that has a very short flute length, but has a point angle the same as the long drill with which you will finish the hole. This will help with hole-registration tolerances. M.A. Ford's microdrills have two to three flute lengths available. Always start the hole with the shorter of the flute lengths and finish with a flute length suited for your requirements," concludes Schmidt.
Mitsubishi: Providing Solutions
Mitsubishi Materials USA Corp. was founded in 1984 with a charter to provide solutions in manufacturing process technologies to companies in North America. The company's corporate investment in R&D programs focuses on market-driven businesses. Focused, and steadily increased capital expenditures on fabricated metal products business ensures a continued premier position in technology, supported by world-class manufacturing process capabilities.
The three-diamond logo of Mitsubishi Materials stands for what a discerning customer can expect from our materials, products, services, and the people who represent the company. We serve a number of industries, such as automotive, heavy machinery, aerospace, electronics, oil, mining, construction, and general manufacturing.
Continuing our mission to solve our customers' process problems, Mitsubishi Carbide now introduces the M-Star line of solid carbide end mills in metric sizes from 0.1 to 6 mm and in a range of geometries. Also from Mitsubishi Carbide, Diamond Star solid carbide end mills are available with inch sizes and a wide range of geometries.
With their micrograin carbide substrates, M-Star and Diamond Star end mills achieve long tool life at high speeds and feeds. Both end mill lines employ the exclusive MS coating, which offers heat resistance and coating bond strength, thus making the coating harder and tougher. The coating permits users to operate at faster speeds and higher feed rates. Diamond Star and M-Star end mills are intended for machining materials such as Inconel, titanium alloys, and stainless. These high-performance tools are meant for the aerospace, medical, and die and mold industries.
This article was first published in the April 2004 edition of Manufacturing Engineering magazine.