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A Machining Process That's Hard to "Resist"
Photo chemical etching is well suited for mechanical components, such as shims, spacers, gaskets, pointers, dials, clips, diaphragms, and springs, among others.
Photo courtesy of Conard Corp.
Connecticut company makes incredibly intricate and small metal parts with a stencil-like photo chemical process that rivals traditional stamping, punching, and laser cutting methods
How is it possible get 40,000 delicate and complex parts made out of only one thin square foot piece of metal?
The answer could save OEMs a lot of money, enable more design freedom, as well as get finished parts delivered in three to five days rather than weeks. But don't look to stamping, punching, or laser and water jet processes.
It's called "photo chemical etching" and it just might be the answer for design engineers looking for a manufacturing process for their parts that allows for more complexity, inexpensive tooling, and consistency. Not only that, but photo chemical etching or "photo chemical machining" (PCM) results in no burrs or deformations and offers up pristinely clean parts because no lubricants or cutting fluids are used.
As opposed to mechanical cutting operations that tackle one part at a time, photo chemical etching produces parts as simple as a disc or as complex as a screen, by dissolving metal with acid using a stencil-like approach. And parts are made all at once, unlike the "boom, boom, boom" process of some traditional methods that stamp or punch parts out one at a time. The PCM process is like putting a batch of cookies into an oven.
"We make parts like you were baking cookies—you put a whole bunch of parts in the oven and they all come out done in the end. So if you need to make a million simple parts, you probably want to stamp it, but if you want to make 100,000 or more complex parts, you might want to look into photo etching them," said Kathy Stillman, director of sales and marketing for Conard Corporation. "Granted, a laser can be very fast, but if it has to stop and start again and again, you lose a lot of time," explained Stillman.
Why bake cookies one at a time?
Because parts are made by metal being dissolved using etching chemistry, many parts can be made all at once, especially extremely complex parts that would be impossible or impractical to produce by stamping or laser cutting.
"And with the photo chemical process we don't induce any stress — we don't mechanically change the metal at all," said Conard's general manager, Art Long. "There are a lot of other processes that do have an influence on the mechanics of the metal, so that's a big advantage to us. For us, there are large volume parts that the only way they can be made is through chemical etching."
At Conard Corp. (www.conardcorp.com), in Glastonbury, Conn., photo chemical machining (PCM) is all that they do, and they are experts and innovators in the field, Stillman said, adding that the company works with a long list of popular metals and alloys, including aluminum, which is very difficult to etch. The company is involved in developing capabilities with using other difficult metals for photo etching, such as magnesium and titanium, which should be available within the next year, she said.
Photo chemical etching or "photo chemical machining" (PCM) results in no burrs or deformations and offers up pristinely clean parts because no lubricants or cutting fluids are used.
Photo courtesy of Conard Corp.
Although Conard Corp. can produce simple parts as large as 60 inches by 24 inches, PCM is optimal for very thin, tiny parts that either have complex geometries or contain many holes or internal cut-outs, as with screens. The company can process materials as thin as 0.0005-inch thick and there's "nothing else out there that would attempt to do this," Stillman said. The smallest part the company ever produced was a 19 thousandths (0.019) inch diameter washer with a 0.012 inch hole. And to think a credit card is 20 thousandths of an inch thick, that's quite a small feat. The metal thickness for PCM generally ranges from 0.001 inch to 0.080 inch, depending on the type of metal used.
Making thousands of holes all at once in a part can be extremely beneficial for making screens — everything from a pulp screen for orange juice to fire detection equipment, as well as screens that go into medical and scientific instrumentation. About 10 percent of Conard's business involves screening, as well as metal grids, meshes, filters, separators, micro filters, grilles, lighting diffusers, and other perforated metal applications for the industrial and architectural industries.
The photo etching process produces consistent, burr-free holes as small as 0.004 inch in 0.002-inch thick material, Stillman said. As a general rule, she said, minimum hole size is 110 percent of the thickness of the material, i.e., on 0.010 inch material, the smallest hole would be 0.011 inch. Photochemical machining leaves the material free of burrs and of mechanical or thermal stress or deformation, she said. Metal meshes can be photo etched in a wide variety of alloys, like steel and nickel, and holes can be made in a variety of shapes and sizes at no additional cost in tooling.
The AS9100-certified company also does a hefty amount of work for the aerospace industry, making aircraft components like heat sinks, airframe stiffeners, and satellite batteries. The aerospace industry is well-served by photo chemical etching, according to general manager, Art Long, because Conard has the ability to produce complex parts that are free of burrs and distortion in very thin gauges of metal. Many aerospace components are produced in aluminum to save weight, and photo etching aluminum is challenging because it is a very reactive metal that readily oxidizes, Long explained.
Quick Glimpse into the Photo Etching Process
- A stencil, or "photo tool" creates images of the part on both sides of metal sheet
- Metal coated with light-sensitive and acid-resistant material, called "resist"
- Images of parts developed and uncured "resist" is washed away
- Acid etching chemistry dissolves metal around the part
- Parts are rinsed multiple times and dried on a turbo dryer
In the 1960s, the founder of the company, Richard Huttinger, a metallurgist who previously worked for Boeing and Pratt & Whitney, developed a proprietary method for precision chemical milling of aluminum for jet engine components on propeller hubs. Photochemical machining is exempt from Nadcap because the process does not alter any of the properties of the metal.
Other contract manufacturing companies subcontract their aluminum work to Conard Corp. because it's so difficult to work with and because Conard has such an experienced and expert history with working with it, Stillman said.
"They don't want to be bothered (with aluminum)," she said. "If you don't know what you're doing with aluminum, it's just a giant pain, so it's easier for them to ship it to us to do it because we're set up to do aluminum every single day. There's no one else in the industry that does aluminum as well as we do."
Photo chemical etching can produce photo-etched copper and aluminum circuit board heat sinks for commercial and military applications. Component-side heat sinks are photo-chemically machined, precision drilled, conversion coated, dielectric epoxy coated, and silk-screened. Heat sinks and other photo-etched parts can be found in electronic engine controls, guidance and navigation systems, and environmental systems, and weapon systems that can be found on U.S. Navy ships and NASA's Space Shuttle fleet.
According to Long, photo chemical etching is an effective solution for producing heat transfer and dissipation components that are used in LED lighting, chilling systems, RF and microwave power circuits, and printed circuit boards.
Photo chemical machining (PCM) is optimal for very thin, tiny parts that either have complex geometries or contain many holes or internal cut-outs, as with screens.
Photo courtesy of Conard Corp.
Photo chemical etching is "exceptionally" well suited for mechanical components, such as shims, spacers, gaskets, pointers, dials, clips, diaphragms, and springs, among others, Stillman said.
"Items with complex geometries in odd shapes or with lots of holes are often far more cost effective to produce by PCM than by stamping, punching, laser cutting, or wire EDM," she said. "In PCM, the part emerges from the metal all at once as the etchant simultaneously etches through all unmasked areas of the plate. CNC punching, laser, and EDM affect only a small, localized area at a time, and so the more complex the part, the more time it takes."
Conard does a fair amount of work for the medical industry, making parts for instrumentation and for sensor-type devices used in diagnosis, Long said. The company also makes parts for many types of microsurgery blades, flexible sensors, detectors, and circuits.
Decorative arts, everything from jewelry to book marks and giftware, also comprises about 10 percent of the company's business. Photo etching enables intricate designs to be created in brass, copper, aluminum, or steel. Finishing options include plating in nickel, flash gold, or imitation rhodium, and color can be added with hand enameling, glass fusing, or full-color, digital inkjet.
The photo tools used in the PCM process run off CAD files provided by the customer. Tooling costs vary with design and complexity, but usually range from $250 to $350 for sheets of about 24 inches x 30 inches and are usually available in 24 hours. Because photo tools are inexpensive, long-lived, and easily regenerated, it is easy for a customer to re-order parts. Tooling charges are one-time, unless the customer changes physical dimensions of the part.
Also affecting costs are the metals or alloys chosen; common alloys and gauges of copper, steel, or aluminum run between about $5 and $10 per pound. Dimensional tolerances also affect the sheet size for photo etching, as the tolerance variance from the center of the sheet to the edges increases with the distance. So, even a simple part with tight tolerances might have to be produced on a very small sheet. Tight tolerances also affect etching costs because the production yield of parts within tolerance decreases.
Conard Corp.'s Photo Etching Benefits:
- No burrs or deformations
- Fast, flexible, and inexpensive
- Photo tools replace conventional steel tools and dies
- Tight, consistent tolerances
- Quantities from handfuls to 100,000s
- Parts completed in 3 to 5 days
- Immensely intricate parts
- No mechanical stresses on metal substrates
- Inexpensive tooling usually available in 24 hours
- Ideal for parts that contain many holes or internal cut-outs
- Exempt from Nadcap
Educating the Masses
For Stillman, as sales and marketing director, getting the word out to those customers who can really benefit from this technology is her biggest challenge. There is only one college-level program in the country that has even a mention of photo chemical machining as a manufacturing process, she said.
"We actually did a program over at Central Connecticut State University several years ago to present photo etching to a class of manufacturing/engineering students and they looked at us like we had two heads," Stillman recalled.
The company has recently started attending trade shows, and at the end of an aisle tucked inside the Mfg4 trade show in Hartford last spring, Stillman stood behind the company's booth and waited hopefully.
The photo etching process produces consistent, burr-free holes as small as 0.004 inch in 0.002-inch thick material.
Photo courtesy of Conard Corp.
"A lot of people just stumble into us," she said. "That's the biggest challenge our industry faces—it's making our capabilities more widely known."
And it doesn't help that photo chemical machining (PCM) is such a small industry segment, with barely a hundred companies who do photo etching in the U.S. and about 400 worldwide, she said.
"There are probably more injection molders in Connecticut than there are photo etchers in the country," Stillman said.
One of the reasons Conard Corp. exhibited at the Mfg4 2014 trade show is because the company is starting a new "electro forming" line, which actually takes the opposite approach to photo etching, but is just as obscure a process.
"It will allow us to go even smaller because we're seeing more applications that are getting smaller and smaller, especially in medical instrumentation, such as with tiny apertures in root canal procedures,'' Stillman explained.
General manager Art Long described the new electro-forming process that the company introduced last June as the "oldest additive manufacturing process" because it involved growing a part. A metal substrate is electro formed by putting the resist pattern on in reverse and then starting to plate nickel onto the substrate.
"You're growing a part versus etching metal away," Long explained. "What that allows us to do is get better aspect ratios; for instance, you can have a two thousandths (0.002) diameter hole on four thousandths (0.004) thick nickel."
The part is "grown" at a rate of 1.2 microns per minute, which is like millionths of an inch, Stillman said.
"So you're putting down very thin layers at a time," she said. "We think we can make small things with photo etching; well, we can make even smaller things in electro forming,' Stillman said.
And as parts trend smaller, the variety of work coming in from customers has grown in intricacy and with a greater demand for quality. These elements have created a reshoring effect where customers who had left to work with Asian companies have now returned, mostly because of quality issues, Stillman said.
Long added that the company also is involved with export work to Asia due to companies wanting to protect their intellectual property. U.S-based customers are having Conard produce components and then ship those to Asia for assembly.
Customers are also reshoring due to language concerns, time-zone issues, and delivery and logistics.
"We'll go ahead and put material on the shelf for these customers so that if they have a sudden surge, we're able to ship within a day or two," Long added.
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