The New World of Micromanufacturing
Small is profitable
By Robert B. Aronson
Making very small parts is a new, but growing industry. It's so new that even the definitions vary considerably. The two terms most often heard are "nano" and "micro." A nanometer is one billionth of a meter and a micrometer is one millionth of a meter. As a reference, a human hair is about 100 micrometers in diameter.
Both have been subjects of research for decades. The "nano" area is often concerned with items made of molecules or even atoms. This work has attracted a lot of media attention as well as venture capital financing because of the "gee whiz" nature of the projects involved. Medical breakthroughs are the main interest for the "nano" portion of this market.
Closer to Home. The "micro area" is more closely related to established cutting, fabricating, and joining techniques: milling, drilling, turning, grinding, EDM, stamping, and welding. Several trends are driving this market.
- Harder materials. Many very small parts are molded from polymers and softer metals such as brass. But some manufacturers have found that these materials are not durable enough to meet the increasing demand for reliability and long life. They are therefore switching to harder metals in many cases, which require processes that can make products from the harder materials.
- Miniaturization. There is a growing demand to make existing products smaller. This is particularly true in the medical and electronics industries. Cell phones are an obvious example. In their short history, they have become physically smaller while greatly increasing the number of functions they offer. Medical devices, because of the key requirement to function within the human body have similar miniaturization demands.
- Something new. Some newer products would not be feasible unless small elements are available. Consumers want more features on home entertainment products and more conveniences on personal vehicles. At the same time, industry wants to know more about how products function, and how best to maintain them. This requires a new generation of miniature sensors and data transmission equipment.
Cutting Tools. In many micromanufacturing applications, the issue is not smaller machine tools, but smaller cutting tools and machine setup time. Many of the major cutting tool manufacturers now have specific programs aimed at this market. Space is limited with the Swiss-type machines often used in this work, so toolmakers have designed tools, and toolholding systems to meet this new challenge.
According to Bob Jeffreys, product manager for Micro-Machining Tooling Systems, Kennametal (Latrobe, PA). "Micromanufacturing is an important area to the cutting tool makers, particularly supplying products for the Swiss-type machines." Kennametal has addressed the Swiss-style machine market with its KM Micro quick-change tooling system that is similar in design to the systems used on more conventional equipment. A typical design consists of a clamping unit and a quick-change cutting unit attached to the gang plate like a conventional Swiss-style toolholder. The operator indexes the inserts in a cutting unit off line while the machine is running. When inserts need indexing, one cutting unit is exchanged for another. Quick-change toolholders substantially reduce setup time from 30 to 5 minutes.
"The KM micro line includes 12 and 16 mm and 1/2 and 5/8" [13 and 16-mm] tools designed specifically for Swiss-type machines," says Jeffreys.
Iscar Metals Inc. (Arlington, TX) has been offering products for the last four years. Medical and electronics components are major product lines the company is working on, particularly shallow face grooves. Seats for miniature 0-rings on hydraulic components and holes in high-speed computer printers are typical products.
"When considering micromanufacturing, we need the sharpest possible tool so the coatings are chiefly PVD because the CVD generally have some edge rounding to them," explains Andy Pitsker, business development manager, Sandvik Coromant Co. (Fairlawn, NJ).
With the Swiss-type machines you can do more in one setup. Before they were usually turning only with form tools. Initially, they got their higher volume by using multiple spindles under cam operation. Now, they are available with CNC control, multitasking, and with one to three live spindles to do drilling, milling, and grinding. Contouring is handled by small end mills.
"Cuts are relatively deeper because of the demands for high-volume production, often as much as 0.160" [4 mm] per pass," says Pitsker. "But the cuts are so clean it is often possible to avoid finish grinding."
Many of the parts being machined are still made of traditions steels and stainless steels, but we are seeing more applications in the harder alloys, ceramics or metal matrix composites being machined in Swiss applications.
"Currently we offer a full assortment of indexable turning tools with small shanks, indexable inserts focused on these machining applications along with drills down to 3 mm [0 .118"]and end mills of .04 mm [.016"]and less," says Pitsker.
Most of the sales action is with the smaller companies, often with no more than 20 machines, of which one to three are Swiss type. Many of the parts are the harder alloys, ceramics or metal matrix composites. They are for parts that can't be formed and have to be cut.
"Currently we offer drills down to 3 mm and end mills of 1 mm and less," he says. "Much of our work now is on a new family of holders."
Holemaking. For micro products, holemaking is done by drill bit, EDM, and laser. Which process to use is application dependent: workpiece material, hole diameter and depth, access to the work area, surface finish, and production volume all play a part in the decision.
Drill bits. The bit material is an essential element ranging from HSS to carbide. Those made of HSS are more resistant to breaking, while carbide is stiffer, but is more brittle. There are intermediate materials that offer a compromise between the two extremes.
Minitool Inc. (Los Gatos, CA) offers drills in diameters from 0.001 to 0.020" (0.025 - 0.5 mm). Most are made from micrograin carbide, although there is a line of HSS drills for softer materials. Hole depth can be 5 - 10 times drill diameter. "In the range from 0.001 to 0.005" [.025 - 0.13 mm] we recommend a spade, rather than spiral tip, says General Manager Dave Healey. "The spade configuration creates its own center and is less likely to "walk around" than the spiral type.
Although any of the drills can be used in conventional machine tools Minitool has its own design. The drill is made with a pulley on its shaft and the shaft is mounted on V-shaped diamond bearings. Because of the more exact alignment, runout is virtually eliminated.
Lubricant, a water and kerosene mixture, can be applied as a spray or by flushing. In situations where it is necessary to observe the hole during drilling, the lubricant may be manually applied with a brush. Drilling is done with a pecking action so chips don't accumulate in the hole. Healy says despite the hype given high rpm drilling, they have found that speeds around 3500 rpm are best, with 5000-rpm max. This eliminates error-causing vibration, and when you are dealing with dimensions in the millionths of an inch, that's a consideration.
Lasers and EDM. "We have seen an expanding EDM market in this area," says Gisbert Ledvon of Charmilles Technologies (Itasca, IL). "This occurs as we take over products made by conventional drilling and machining as well as the manufacture of totally new components where EDM is the only way to cut small, detailed, highly accurate shapes. But we are in the early stages of this industry and many of those who want to become involved don't know the capabilities of the available manufacturing equipment, particularly EDM. So the initial job is education."
According to Ledvon, "Our EDMs have made gears as small as 800 µin. diam and holes as small as 0.004" [0.1 mm] with aspect ratios as high as 10 to one, or 0.004" [0.1-mm-diam hole] 0.04" [1-mm] deep.
In describing his company's EDM capabilities, Steve Nunez, applications engineer Mitsubishi EDM (Cypress, CA) comments, "we machine small holes using a guide arm attachment on either our EA or VA series sinker machines. The smallest hole we have made, without dressing the electrode, is 0.0030" [0.08 mm]. This was done using our VA10 machine through 0.040" [1.0-mm] thick carbide. For holes smaller than this we use the EDM process to turn down the electrode in the machine against a block of copper tungsten. We have made electrodes down to 0.0004" [0.01-mm] diam, which gives a 0.0007" [0.18-mm] diam hole through 0.005" [0.13-mm] thick stainless steel."
The hole depth possible changes with hole diameter. Mitsubishi EDM equipment normally can make holes that are about 50 times diameters of the wire. Holes 2" (51-mm) deep have been made 0.040" (1 mm) in diam.
"Most of our micromanufacturing work is done with a VA 10 with a high-speed spindle unit," says Nunez. "The guide assembly allows us to use the orbital feature of the machine so that we can produce diameters that are in-between guide sizes. Recently we offered a new generator circuit called Nanopulse. It reduces the amount of on time down from microseconds into the nanosecond range to reduce surface roughness." Surface finishes from 0.5 to 2µin. are possible using the Nanopulse circuit.
One of the other major players in the micromanufacturing area, lasers have been doing fine work since their introduction in the 1960s. This initially included welding and cutting, then later marking and heat treating. The main changes as this technique has evolved are smaller, hotter beams, simpler operation, and the ability to operate in a shop-floor environment.
"We have developed lasers with smaller spot sizes capable of delivering high-intensity beams to a small spot to meet high-production demands," explains Clive Grafton-Reed, product line manager, Nd:YAG lasers GSI Lumonics (Rugby, England). "For example, weld spot size has dropped from 300 to less than 200 µin. [5µm] diam.
"Aerospace applications are one of our major successes. Lasers can cut the nickel and cobalt alloys often used. They can get into areas where drills cannot access, and they are faster than EDM. In addition, in some aircraft designs hole quality is an issue, that is, they are considering flow characteristics though the hole rather than just the shape. Some configurations require tapered or fan-shaped holes that are more easily done by a laser than other processes. Typically these aerospace applications require holes from 0.8 mm down to 200µin. [5.0µm]."
"Another emerging market for lasers is in the automotive area. Designers are asking for 'fine lubrication' that is getting small quantities of lubricant to certain areas of the engine and transmission," according to Grafton-Reed.
Fix the Planes. A potentially more attractive market is repairing aircraft elements. Refurbishing dies by welding is a long established technique. First a layer of weld material is built up on the worn area, then it is machined to the required finish. The same technique can be used to add new features to the die or mold. The laser system follows similar steps but in a much smaller space. It is possible to work on jet engine blades and rivet holes down to 0.100" (2.5 mm) with sheet metal 0.20 to 0.40" (5 - 10-mm) thick.
This method is being used to rework worn fastener holes. Vibration is a big enemy of aircraft. After some hours of flight, wear occurs in almost all mating components. One area of particular concern is fastener holes. Rivets and threaded fasteners begin to loosen. Using the laser system, the hole can be relined and the fastener replaced in a secure hole or threaded area.
One of the conditions driving the interest in lasers for small feature work is the EPA fuel economy mandates on the diesel automotive industry, and a good way to meet the new requirements is cleaner, more complete combustion. This can be achieved with better atomization of the fuel as it is forced into the cylinder through an injector. This means smaller holes in the injector. Currently, holes are 150 µin. (3.8µm) in diam. In the near future, they will have to be 75 µin. (1.9µm) or less.
"With our lasers we can make 50 µin. [1.3µm] holes 1-mm deep repetitively and with high accuracy," says Mike Herglin of Lambda Physik (Ft. Lauderdale, FL). "We have been in this market for some time using our lasers to make holes for components in semiconductor parts and in ink-jet printers. The printers each have about 200 25 µin. [0.6µm] diam holes which are all made in a 1.5-sec cycle. In another application, we made 1-mm diam washers with 39µin.[1.0µm] holes.
"At the same time, our lasers have become smaller and more reliable. We now offer a 'toaster-oven size' unit with a solid-state, diode-pumped laser of very high reliability. Time between maintenance checks is about 20,000 hr and it's a cutting tool that never dulls."
Die Making. Another growing market is micromanufacturing of small precision dies using lasers. In the system offered by DMG (Chicago) controls automatically convert CAD data to position the cutting head and determine the intensity of the laser beam's cut. The technology is replacing some EDM operations, and could be expanded to replace some die machining.
"We have developed a laser system for making small, intricate dies," says Pat Ofenlach, milling product manager. "They are used chiefly for prototype work and low-volume production. The idea is that manufacturers don't want to go to the expense of making trial EDM dies, and so make a prototype with their laser system."
These systems are used chiefly in production of jewelry, small toys, and other products of great complexity and detail. The main disadvantage is that the process can be time consuming, depending on the depth of cut and part complexity.
"Currently, our machines use a 100-W, pulsed YAG laser," say Ofenlach. "Accuracy is around 0.0005" [0.013 mm], depending on material being cut and accuracy and speed needed.
"We have products that supplement conventional machining with low heat input processes that work well with the miniature parts we have been processing," says Steve Roy, YAG product manager for Trumpf Laser Division (Plymouth, MI). "For welding we use laser beam diameters down to 100µin. (2.5µm) for micro-electronics. For cutting and drilling, laser beams below 50µin. [1.3µm] are used in industrial applications.
"The big advantage of using a laser in these applications is low heat input to the product. Because the materials are usually quite thin, often only a few millimeters thick, distortion is a big potential problem. But with short pulses, this issue is all but eliminated. Trumpf lasers have a pulse time of 1 to 20 µsec for a spot weld.
"We have drilled holes for diesel injectors to about 140µin. (3.6µm) in diam to a depth of 1 mm," says Roy. "Noncontact drilling is preferred by many manufacturers because of the consistancy and reliability of such a process."
Swiss-Type Machines. While much of the machine tool industry continues in the doldrums, sales of Swiss-type machine are more encouraging. According to one estimate, worldwide sales of Swiss-type machines were 8500 in the year 2000, will be 10,000 this year, and may be as high as 20,000 by 2007.
Much of the work done in micromanufacturing is conventional turning, drilling, and machining done on these machines. Designed for high-volume production of small parts, these units have been available for almost a century. They had their origins in regions of Switzerland, Germany, and France where cottage industries developed for the manufacture of clocks, music boxes, and mechanical toys.
Swiss-type machines are characterized by a moveable headstock and a support bushing. With this arrangement it is possible to support the part near the cutting zone so there is less workpiece deflection. Workpiece size is limited by the bushing diameter.
"We have been doing a lot with miniature medical and aerospace components for some years, typically parts with dimensions from 0.008 to 1 5/8" [0.0.2 - 42.3 mm]," says John Jones of Swiss-Tech Inc. (Delavan, WI). "We do a lot with type 410 stainless. One of our toughest jobs is an 8" long X 0.0025" diam [2032 X 0.06-mm] tungsten piece that is used for spinal surgery.
"We have to worry about light chip load. You don't want to distort the part through cutting tool load. Also we have to be very clean, with no impurities left on the part. Holding these parts is one of our specialties. We make our own fixtures."
Also heat is an issue. It is important not to introduce heat that will change the material properties or result in distortion.
"We do a lot of our work on a Brothers VMC with twin pallets and indexing head and Ken Wah turning machine," says Jones.
The machines from Ken Wah (Pewaukee, WI) are rigid, eight-axis units. The smallest can handle 12-mm-diam parts and the largest 32 mm. They specialized in long, small diameter parts.
Marubeni Citizen-Cincom Inc. (Allendale, NJ) is reportedly selling about 500 machines a year. And the company sees a lot of growth potential. "We plan to convert a lot of CNC users to Swiss-type machines," according to Bill Papp, regional manager. "They are more versatile, minimize setup time, and adjust to a variety of production volumes."
The company offers a series of machines for small part work, the unit that handles the smallest parts is the R04 Swiss turning center. It can make parts to a maximum of 0.157" (4 mm) in diam. Main spindle speed is 20,000 rpm and it can handle up to 13 tools, including two live spindles. Footprint is only 22 X 48 X 56" (5588 X 1219 X 1422 mm). Because conventional handling devices have problems with small parts, the unit has an optional vacuum system to remove finished parts.
Initially these machines were designed to make electrical connectors, but they have found a home in the medical parts industry making such things as surgical screws and dental implants.
Tru Tech Systems Inc. (Mt. Clemens, MI) designed a machine for grinding to millionths of an inch. When the company was approached to grind some specialized micro parts for a medical company, their grinding unit was a perfect match for the application, as conventional grinding equipment did not have the needed capabilities. Since then, business has been growing at a rate of 25 - 30% a year. Tru Tech now provides grinding services to the aerospace, medical, and electronics industries, mainly wire and tubing products as small as 0.0005" (0.13-mm) diam. Often, operators must use microscopes fitted to the machines to see the parts being ground. Materials used include tungsten, stainless steel, ceramics, ruby, and exotic metals.
"We do a lot of products with diameters down to 0.002" [0.05-mm] diam," says company president Steve Smarsh. "Our machine has a runout of 5 - 10 millionths of an inch and can achieve surface finishes of 2 - 4 µin."
United Grinding Technologies Inc. (Miamisburg, OH) offers a number of machines suitable for micromanufacturing applications. A recent introduction is the Ewag seven-axis CNC Rotoline. These machines are designed for ultra-precise grinding of highly complex tools, inserts, and other parts, with applications in the watch, medical/dental, and electronic industries.
Another machine designed more specifically for small-part manufacture is the six-axis Ewamatic. It typically works with parts down to 1 mm in diam and recently supplied Rolex watch with a 0.3-mm-diam mill for watch case manufacture.
"When working on these projects it is usually not a matter of selling a machine off-the-shelf," says Ulrich Buchs, who works with the company's Ewag line. "Meeting the customer's needs often requires special modifications such as fixturing, part finish, and handling. They give us the specs on what they want to make and the materials used, then we come up with the machine that will do the job."
This article was first published in the April 2003 edition of Manufacturing Engineering magazine.
Published Date : 4/1/2003