Marking Metal Parts
Permanently marked metal components offer medical, aerospace, and automotive companies true traceability
By Patrick Waurzyniak
From NASCAR to the operating room, metal components used in many industries require precise, permanent markings that can accurately trace a part's serial number and other vital statistics that are key to recalls, medical liability cases, and even supply-chain or quality-control issues. Lasers and many impact-type 2-D data matrix marking methods available today offer users a wide array of options for true cradle-to-grave traceability of metal components.
Manufacturers need permanent marks on parts through which components can be easily traced from cradle to grave, and these part markings must be able to withstand the rigors of the manufacturing process. The marks also must be in a format that can instantly validate parts, such as with human readable and vision-readable UID 2-D markings by which any component's history can easily be extracted with vision system scanners.
Aerospace leads the way. Aerospace, automotive, medicine, and even racing teams face growing requirements to access key product identification data, such as serial numbers, batch numbers, and manufacturing dates for traceability on quality control, warranty, or other factors. Automotive manufacturers require traceability for such reasons, and so do racing teams like Wegner Motorsports, which needed a part-marking system offering instant validation of engine components (see the Shop Solutions "NASCAR Spec Engine Is On Its Mark" in the October 2007 issue of Manufacturing Engineering.)
Aerospace/defense manufacturers have extensively deployed direct part marking technologies far longer than most other companies, partly due to the Department of Defense (DoD) mandates requiring parts be marked on mission-critical rotating components in aircraft engines, as well as other military equipment. Automotive builders also are early adopters because of federally mandated traceability requirements for recalling defective components. In contrast, medical systems have lagged those industries in adopting part-marking technology, with some observers noting that there are relatively few standards for manufacturers of medical parts. In veterinary medicine, standards are evolving for the traceability of animal medicines in veterinary care.
"Data matrix is the most highly used 2-D symbology for direct part marking, and that's basically what we deal with," says Rick Pentz, vice president, business development, Dapra Corp. (Bloomfield, CT). "We're not involved with selling tags or labels or printing 1-D bar codes—most of the tracking we deal with is involved with data matrix.
"The leading organization that has really pushed this whole issue of direct part marking and data matrix codes is the Department of Defense," Pentz states. "They have an initiative that's been out now quite a few years that's called UID, Unique Identification. Basically, their parameters are if your parts fall under certain characteristics—if they have to be serialized or if they cost a certain amount—you're going to have to provide parts that can be tracked. If you're marking an engine block, for example, you're not going to put a paper label on it, because it's not going to last. Identification information has to be directly marked into the part."
Technologies for part-marking/traceability include lasers, dot-peen marking systems, air-impact markers, and even hand-stamping with hammers, a crude but cost-effective way of marking. "We do everything from the hand stamp to the laser, and everything in between," says Tom Phipps, CEO of Columbia Marking Tools (Chesterfield Township, MI). "We do everything for direct part marking. We are not classified as a cosmetic house. A lot of people either do laser, or they'll do pinstamp, or they'll do CO2 marking, which is more cosmetic and would be used to do laser images on some parts."
The latest lasers used in marking applications are air-cooled, fiber-pulsed or fiber-diode lasers that supply variable power levels, and require little maintenance compared to CO2 lasers, Phipps notes. "The pulse-fiber diode has 50,000 to 100,000 hours of duty cycle," he says. "Typically, in a high-production medical application using lasers, actual marking time might be a total of 1000 hr in a year. The laser's only on for 10 sec here and there. If you ran 1000 hr, you could see where it would be 50 to 100 years before the actual fiber diode laser source has to be replaced. Instead of spending $3000–$4000 to keep fixing your laser every six months or so with the water chillers on the YAGs, now you go into pulse-fiber diode, and they're so efficient that they don't use any water cooling, they're all air-cooled, and last forever. They're very, very fast, and they can mark very deep."
While laser marking has become popular in medical, using lasers can create heat-affected zones that impact the structural integrity of metal parts. As an alternative, many industries instead opt for 2-D UID data-matrix methods, such as Columbia's patented 2-D/UID Square Dot peen marking process, which includes a machine control and a handheld vision reader. Columbia also offers a DPS (Dot-Peen- Scribe) CNC marking system equipped with a CNC stepper-motor-driven marking spindle that can provide ultrafast dot-peen marks as well as Square Dot silent scribe marks. The system's marking depth control is adjustable, and the unit can mark metals to RC 55 with a carbide marking pin, and harder metals exceeding RC 55 with a special diamond 2-D UID marking pin.
"We were specified by NASCAR to do whole engines, where every single part in and outside the engine has to have your new 2-D code on it," Phipps states. "A bar code will hold up to 18 digits, and it's scanning the thickness of the line and the distance between the lines. The combination above the lines makes up the matrix that comprises an 18-digit part number. It takes a lot of real estate, and it's very limited, with only 18 characters you can put in there. If you're measuring the width of the line and the thickness of the line, the scanner would have to follow the shortest path across the lines, to be accurate. If you skew it on an angle, they can't get it to read. If you've been to Home Depot or anywhere else where they end up picking up the product and typing the number in, that's because their scanner couldn't read it.
"What 2-D code does is, it's an ingenious matrix that you can put in about a half-inch square probably about 300 characters, anywhere from 250–400, in a much smaller space," Phipps adds. "We put codes down to 3/16" [4.8-mm] square where we'll put like 40 or 50 characters in; that 2-D code has what they call finder bars—one the shape of an L, one is latitude and longitude—it measures up and over for every dot in the code. Because of the camera, the vision system can see it easily and it automatically adjusts radially to find the L-shaped finder bars, and then it reads from there. It doesn't care what angle you put it on."
Two-dimensional UID direct part marking has worked so well that the federal government has mandated that as of January 1, 2010, all military products will have this 2-D code direct part marked into them, according to Phipps, who notes that as of September 2007, any military part over $5000 in value had to have such 2-D codes.
"In the medical industry, the 2-D code, I believe, would revolutionize product identification. They should grab it with both hands and run with it," Phipps adds. "The 2-D code is pretty standard, so they can mark a product, read it, and they can know everything about it, especially in the medical industry. It'll give all the history. You can include a lot of information—when it was made, who made it, where it was made, what engineering-revision level, or medical-revision level it is, lot numbers, or serial numbers.
"I've got the brand new gizmo I'm sticking inside your chest here, and there was a recall on it, is this the right one? Part marking can answer that question. So it should actually help the liability insurance issues, because you'll have better traceability and know that you're not using something that has been recalled. And that's the main purpose of direct part marking."
Permanent part marks are critical in all metal-component marking applications. "The military calls it cradle-tograve," Phipps adds. "From the time the part's born to the time it goes out of service, the mark's always with it. You can utilize it through production and distribution, and the final end user always has the mark with the product." Compared to barcodes, 2-D marking technology offers great advantages, notes Carl Gerst, senior director and business unit manager for ID Products at vision systems supplier Cognex Corp. (Natick, MA). Bar codes are like a picket fence, and the information is based on the width and spaces between characters. "The technology works great on paper, but it was never conducive to marking on metal," Gerst says of bar codes.
"What we focus on is traceability, and that started predominantly in automotive," Gerst says. Data matrix is considered 2-D, he notes, and it looks more like a checkerboard. Data matrix is read by vision-system cameras and with hand-held scanners. "One of the differences is subtle. Is the square red, or black, or white? You're taking a picture of it, and the cameras that we use are eight-bit grayscale cameras that view it in 256 shades of gray."
Tracing medical components has grown in importance in recent years, as medical system integrators and hospitals implement systems for marking medical implants and surgical instruments. "We're seeing more of it," Gerst says. "One of our largest integrators is marking surgical instruments, and traceability within the hospital is a real challenge." The Cognex integrator, Censis Technologies Inc. (Franklin, TN), has a surgical instrument tracking system, called Censitrac, that uses laser technology to permanently mark medical tools with a standard mark size of about 2.5 x 2.5-mm that's suitable for most instruments.
Many medical implants and surgical instruments are marked with laser-etch processes, Gerst notes, although permanent marks can be chemically etched, dot-peened, or laser etched. Cognex recently added its new DataMan 700 handheld ID readers, which are said to be capable of reading any code, on any surface, made by any marking method. The company offers a broad range of imagebased ID readers and code-quality verifiers used on marks from printed barcodes on labels to the most challenging 2-D codes directly marked on metal parts.
The DataMan 700 series includes two new readers: The DataMan 750 model is electrostatic discharge (ESD) safe, making it suitable for reading 1-D and 2-D codes in electronics and medical-device industries. It uses Cognex's IDMax decoding software to handle code degradations that result from differences in material types and surfaces. Another new model, the DataMan 710, features the company's IDQuick decoding software for fast, consistent reading of high-quality 1-D and 2-D codes, as well as low-contrast codes on uniform backgrounds, and also high performance when reading labels and other well-marked codes.
"Any time you mark on metal it's a very challenging application," notes Gerst. "Picture your standard digital camera—and you're going to see a big hotspot. One of the challenges is arranging the light so that you can actually see the metal."
"Laser would typically provide the highest quality mark, and in the medical industry that's almost what you'd need," Gerst says. "I'm not sure there's a spec out there. It's up to the manufacturer or the integrator. The resolution or the size of the mark is usually in mils or thousandths."
Traceability guidelines from the FDA and other agencies are not highly developed. "In terms of the medical side, I'm not aware of any standard," says Gerst, noting that the aerospace/defense industry's milspec standards are very well established. "There's a new standard from the International Federation for Animal Health (IFAH) being used by veterinarians, the GS1 guidelines for animal health products. Much like the DoD, they want to make sure that each code is marked.
"This all started within companies' own four walls, in order to understand inventory and processes," says Gerst. "What you'll see is the exact same thing that's used in ISO for application ID's. It's an open standard. In medical, we've had tremendous growth in our products. But the majority of all the scanned marking and reading is predominantly within manufacturers' four walls. There's a huge cost savings to the manufacturer. It helps them understand bottlenecks and costs."
Regulations in the medical industry are still evolving, according to Ralph Villiotti of Telesis Technologies Inc. (Circleville, OH). "There's been no true push to enforce the regulations," he says, noting the FDA, Health Industry Business Communications Council (HIBCC), and other agencies have drafted guidelines for part marking and traceability. "It's definitely in its infancy."
Telesis offers turnkey laser systems for medical including its 100-W RoboLase system for part marking. Medical applications usually call for laser marking, Villiotti notes, with processes that won't degrade the integrity of metal used in implanted devices. "There has to be some kind of man-readable information on there, and that information has to go into a database," he adds. "From the medical side, it really is laser marking because you have issues with corrosives, and if you were to go onto the metal, like ink marking, that could flake off."
In aerospace, there are only certain technologies that are feasible for marking any type of rotating part, adds Villiotti, and either pinstamp or dot-peen marking will suffice. "There have been issues with acid etch and laser," he says. "For rotating parts, it's more about the possible failure of laser-marked parts. The concern is it may create a heat-affected zone, but the technology and laser-pulse characteristics have evolved to where it can be controlled."
Lasers and 2-D data matrix technologies have become popular for medical applications. "Medical industry is highly involved in laser—dot peens or roll markings are a little too invasive," notes Dave Noonan, laser product manager, Schmidt Marking Systems, Geo. T. Schmidt Inc. (Niles, IL), which supplies wide range of permanent marking systems. "They deform the materials. The laser is a way of marking the material without really distorting it. You can get an annealed appearance, which is a dark mark you can see, but you really can't feel it."
With Schmidt's MicroLase fiber or diode-laser markers, users can choose between methods of generating light that will be controlled by a scan head that marks a part, notes Noonan. "The fiber is a newer tool lineup, and we've found it to be a very powerful laser, where people are actually able to mark more information faster, which results in shorter cycle times, so they can put more parts through. And that is the name of the game for manufacturing. It's all about throughput."
Prices for laser-based marking systems have been falling, leading more manufacturers to adopt the technologies, Noonan says, noting that Schmidt offers lamppumped as well as diode and fiber-laser systems. The systems offer the traceability that's key to many industrial applications. "It's certainly paramount to aerospace, automotive, and medical," Noonan asserts. "They need to be able to trace implantable materials going into your body. They need to be able to trace that part back to the company that made the steel, to who machines it, to what machines it was run on, and when; so for traceability, they need 100% readable marks. Aerospace as well. When there's a failure in an aircraft—it doesn't have to be a plane crash—but when there's a failure they need to be able to trace that to look back at the lots, see whatever parts were run there, see where they are, and get those parts back."
Fiber-based lasers offer stable, consistent part marking, allowing for traceability in medical applications, notes Bob Henry, product manager, Epilog Laser (Golden, CO). Epilog Laser recently introduced its FiberMark laser-based part marking system aimed specifically at medical applications, including marking surgical instruments and implantable medical devices.
"The system is based on a well-proven line of laser systems we've manufactured that incorporate CO2 laser sources," notes Henry. "We've made some design modifications for incorporation of the fiber laser manufactured by IPG Photonics, so while the FiberMark is a new product for us, it's built on a very well-proven platform. The laser source itself has proven to be quite stable, and it works very well with the beam delivery system we have, which we call gantry-style, or flying optics."
For medical, the Epilog system offers permanent marks on metal parts for traceability. "There are instruments that are used for surgery, and implantable parts, that are being marked," Henry says. "If you can imagine a replacement hip, that item will be serialized and it will be marked, typically through a laser process. The laser effectively changes the surface of a given material. You then have a contrast, you have a readable type of mark. You'll find laser marking on tools, on instruments, again for both implantable and for surgical tools."
The wavelength of light is very versatile on both the YAG lasers and the terbium fiber lasers that Epilog offers, he adds. "They all have the same light wavelength, and you're going to fundamentally get the same type of mark from all of these sources," Henry says. "There are different types of marks—annealed, polished—depending on the material, but mostly with metals, we really can produce different types of marks, and etch is actually where we're scribing into, and we're abraiding the surface of the steel. Now that affects a color change in the metal, and you get a really nice mark doing that. That's more for industrial parts. We typically don't see such marks being called for in the medical sector."
Most users in the medical device industry want an annealed or a polished mark, Henry states. "With those, we change the color of the steel at the surface, there's no abrasion, there's no actual etching into the steel; hence, there's no opportunity for bacteria to become embedded in that etch, in that abrasion, and possibly cause problems down the road. An annealed mark is definitely the preferred type of mark. Again, some materials will anneal, some won't. Annealing is done through the carbon content in the steel, and of course if you're marking a titanium or aluminum, there's no carbon in it, thus you really don't get an annealed type of mark."
Offering automated operation, Epilog's Fiber-Mark features a gantry system with a 24 x 12" (610 x 305-mm) marking envelope in the X-Y axes. "With our gantry-style system, on smaller parts you can load up the entire bed of the laser system," Henry says. "You set up the artwork accordingly, load up the bed of the laser, start the job, and walk away and do other things."
This article was first published in the May 2008 edition of Manufacturing Engineering magazine.
Published Date : 5/1/2008