(Almost) everything you wanted to know about deburring but were afraid to ask
It’s a sad fact of practically all metal removal operations that, no matter how sharp the tool or free-machining the material, there are going to be burrs, hanging chads, ragged corners, and other edge quality issues that must be dealt with before calling the workpiece complete. The good news is there’s no shortage of methods to address these problems.
The bad news? Determining which is most effective often comes down to a “let’s give this a try” approach.
Sometimes this tactic works quite well—machinists, sheet metal fabricators, and additive manufacturers are largely a talented and knowledgeable lot, each enjoying a firm grip on mechanical problem-solving. Other times, however, the educated guess approach to burr removal comes up short, leaving big piles of money on the table in the highest stakes card game of all: manufacturing.
Advice from the Master
LaRoux Gillespie, a writer, industry consultant, and expert on all things deburring, will tell you there are 124 distinct processes available for burr removal and edge finishing, with roughly half of them used every day in shops around the world.
Some of the more common of these deburring processes are vibratory finishing, electropolishing, abrasive blasting, brush deburring, chamfer and radius cutters, and that old standby, hand deburring with files, abrasive pads, and scraper knives. The problem with most (but not all) of these, Gillespie said, is that they can affect more than the burr.
“When determining which one is most effective, shops must assess a variety of factors, including the burr height and thickness, workpiece material, allowable edge radius, maximum stock loss in the surrounding area, required surface finish, and, of course, the number of parts that will be produced and therefore the economics,” he said. “For many of today’s commercial products, any negative effects of the deburring process are small enough that they can be ignored, but for precision parts, it is essential to evaluate these impacts early on in the manufacturing planning stage.”
How does one know the difference between commercial products and those requiring a higher level of precision? Gillespie pointed to the work of another deburring expert, one-time Toshiba engineer Dr. Koya Takazawa, who decades ago defined the six classes of edge finishing, E0 through E5. The most stringent of these—E0—describes a maximum radius of 0.0002 mm, generated via diamond microtome knives and measurable only through electron microscopy. On the other end of the spectrum, E5 is specified as a “dull edge,” suitable for sheet metal and similar hardware grade components.
Though they might not be familiar with the terminology, most machinists typically work within the E3 to E4 specification, equal to an edge break of 0.2 mm to 0.5 mm radius, respectively. Chamfers and radii in this range, Gillespie noted, are easily measured with a microscope, optical comparator, or vision-based inspection system, and can be created through a variety of mechanical or abrasive means, manually or otherwise.
“Many parts today are inspected under magnification (up to 400X in one instance) to assure desired quality levels, and while this may seem excessive, it’s interesting to note that miniature watch parts have been produced and inspected at 30X magnification, tolerances of ±0.000050" (0.00127 mm), and surface finishes of 8 μin Ra (0.2 μm Ra) since at least the 1960s,” he said. “These include precision gears, pins, microscopic holes, wafer-thin shims and other metal components, all of which have for decades been produced to these requirements.”
Keeping Holes Clean
Holemaking is perhaps the most commonly performed of all metalworking operations. Thanks to the relatively high cutting forces generated when punching a tool through metal, however, and the commensurately larger burr thus formed, holes are often one of the most challenging part features to make burr-free. This is especially true on parts with intersecting holes, such as hydraulic manifolds and valve bodies, where it can be difficult or even impossible to reach the target area with traditional deburring tools.
Abrasive Flow Machining, or AFM, is one solution. It uses a viscoelastic (putty-like) abrasive-filled media that is pressurized and made to flow through holes and internal part channels, removing burrs and polishing surfaces as it passes. Developed by Extrude Hone Corp. in the 1960s, it has become a favorite for finishing automotive fuel nozzles, turbine blades, and medical components such as heart valves, which obviously require a smooth surface and must be perfectly burr-free. AFM requires specialty equipment, however, and is typically reserved for complex workpieces where no other option exists.
Cutting Potato Chips
A more general-purpose solution comes from J.W. Done Corp., Hayward, Calif., maker of the ORBITOOL Cross Hole deburring tool. General Manager Stan Kroll described the ORBITOOL as a hemispherical cutter with a polished disk on one side and a flexible shaft on the other—picture a Tootsie Pop with the upper half cut away, and the disc sitting atop the flat surface.
With the ORBITOOL inside the hole, the spindle is engaged at speeds up to 10,000 rpm and the shaft moved sideways, driving the disk against the hole wall. It then rides along the surface until reaching the intersecting hole, at which point the pre-loaded shaft forces the cutter to spring outwards, engaging the elliptical “potato chip-shaped” geometry at the intersection. The cutter continues to advance, removing material until the burr is completely gone.
It sounds complicated, but a quick look at the J.W. Done website illustrates that it’s actually a straightforward process. The ORBITOOL can be used as just described in a hand grinder or live-tool CNC lathe, or in machining centers and transfer machines, in which case a helical “just like a thread mill” motion must be programmed. Tool diameters from 0.055-0.375" (1.39-9.52 mm) in diameter and up to 12" (304.8 mm) long are available, as are double-sided (full lollipop) ORBITOOLs for cross-type intersections.
Clothespins and Flippers
Another company with a long history of hole deburring is Camden, S.C.-based Cogsdill Tool Products Inc. Don Aycock, vice president of sales and marketing, said the company offers a range of mechanical deburring tools, including the spring-loaded Burraway and Micro Burraway, the single-piece “clothespin” style Burr-Off, the Ellipti-Bur for curved or angled surfaces, and more. There’s also the Flipcut, which uses a centrifugally-activated, self-extending blade to spot-face the backside of a hole.
Most of these tools employ a simple in-and-out action to deburr and/or chamfer both sides of a hole in a single pass, and most use a disposable HSS or carbide blade, with material-specific geometries available. All are offered in a range of sizes and lengths—the flagship Burraway, for example, deburrs holes from 0.093" (2.36 mm) up to 2.0" (50.8 mm), while the Micro Burraway tackles holes down to 0.040" (1 mm) in diameter. Aycock is quick to point out that special orders are not a problem.
As with the ORBITOOL, Cogsdill tools can be used manually, in a CNC machine tool, or even robotically. In one notable example, a California-based aerospace customer employed robots to drill hundreds of different diameter holes in a titanium ring measuring 10' (3 m) in diameter, roughly a foot wide, and with a wall thickness of “a quarter inch or so.” When they were done, the robot used Cogsdill Burraway tools to deburr each of the holes. “We also do a lot of work with composite materials, removing the frayed edges around drilled holes in various aerospace components,” said Aycock.
He and J.W. Done’s Stan Kroll agree on one crucial aspect of any deburring operation, and that’s to minimize burrs as much as possible. This means keeping cutting tools sharp, carefully managing their life, using the appropriate tool, and having clearly defined standards for acceptable burr size.
“We were working with one customer and asked them to describe their guideline for when to change the drill,” said Kroll. “Their answer was, ‘When the burr gets so big that the guys in the deburring department start to gripe about it.’” He laughed. “I don’t care how good the deburring tool is, that’s just not good machine shop practice.”
The Rest of the Story
If this article were about hole deburring, that would be the end of the story, but as any machinist or sheet metal worker can attest, there’s far more to manufacturing than holemaking. As LaRoux Gillespie mentioned earlier, there are more than 100 ways to skin the deburring cat, and I’m sorry to say we’re not going to discuss even a fraction of them. This is why Gillespie and other experts strongly recommend that shops learn all they can about this often overlooked but exceedingly important part of the manufacturing process.
Bernhard Kerschbaum is one of them. The CEO at Rosler Metal Finishing USA LLC, Battle Creek, Mich., he added that one of the best ways to become knowledgeable about deburring is to speak with a finishing expert and do so sooner rather than later. “For a lot of shops, deburring is an afterthought,” he said. “This is particularly true with 3D printing, where seemingly simple factors like part orientation and support structures can play a huge role in optimizing the entire manufacturing process.”
Kerschbaum doesn’t care whether a part is made additively or subtractively, stamped, formed, cast, or forged. It’s his and his team’s job to develop the most effective method to remove burrs (or support structures in the case of 3D-printed parts) and provide surface finishes that meet or exceed customer requirements. They accomplish this through a variety of means, including wet blasting, shot blasting, high energy disc systems, plunge and drag grinding, and especially vibratory finishing. All can be operated in manual mode for lower volume work, but are in most cases automated for maximum efficiency.
Whatever the technology, Kerschbaum said achieving consistent results depends on the development of the correct “recipe” for a given workpiece or family of workpieces. This means determining the correct media type, size, and abrasive level, whether to use finishing compounds and other chemical additives, and what machine to use (in some cases multiple machines) along with operating parameters such as cycle time and speed.
“There are a dozen or so different values that must be considered if you’re to develop a repeatable process,” Kerschbaum said. “Some customers choose to do this development work in-house, but it’s often easier and faster to just send us some parts or come visit us at our test lab here in Battle Creek, particularly if they’re trying to optimize a specific part.”
Design for Manufacturing
Process optimization extends well beyond which stones to use or how fast to run the machine, Kerschbaum added. When determining what type of deburring equipment to use, shops should look at their existing universe of parts and group them by workpiece material, minimum hole or slot size, and surface finish requirements (among other requirements) and use this to develop “part finishing families” that can each use the same size and shape of abrasive media. This approach minimizes the number of machines that must be purchased and discrete processes developed.
They might also talk to the customer or their own engineering department to assure that the product design supports efficient deburring and finishing operations, and that these steps are an integral part of the manufacturing process.
“Again, a lot of people overlook this aspect until it’s too late, especially on the additive side,” Kerschbaum warned. “With traditional manufacturing, the machinist or programmer intuitively knows that by running a chamfer tool around the part, they might save hours on hand-deburring later. This isn’t the case with 3D-printed parts, where the people programming the machines often have limited experience with deburring, or with metal removal in general.”
Don’t Forget the Abrasives
Another thing that’s overlooked is the abrasives. Mike Shappell, senior application engineer at Norton | Saint-Gobain Abrasives, Worcester, Mass., suggested that the status quo is too often alive and well when it comes to abrasive selection, adding that companies should call in a product expert every three years to help them evaluate “what’s new” in the industry, and how it can improve their operations.
“That’s a good rule of thumb for any metalworking process, but abrasives are often overlooked in this respect,” he said. “Take our Vortex technology, which didn’t even exist five years ago. I visited a shop recently that was using a non-woven abrasive disc for a deburring operation, and they were perfectly content to replace it every 15 minutes. They’d been doing it that way for years, so never thought to question whether there was a better way. I handed the operator a Vortex disc, he ran it for 30 minutes, and was about to throw it away when I had him dress the disc with a piece of 36-grit sandpaper, after which he got another 30 minutes out of it. People don’t seem to realize that abrasive technology is advancing all the time, just like everything else in manufacturing.”
Norton | Saint-Gobain has a massive catalog, and Shappell can talk for hours about flap wheels, abrasive grains, resin bonds, and much more. In fact, there’s virtually no abrasive-related problem that he can’t remedy. The one thing he can’t fix, however, is the attitude that the best abrasives are the cheapest abrasives. “That shop I worked with is an excellent example of this,” he said. “Every 15 minutes they were throwing away a $3.50 disc, but by switching to a $6.00 Vortex, they quadrupled their abrasive life. This situation is all too common if you buy on price alone.”
There’s also the unfortunate attitude that anything goes with abrasives, and that cutting speeds and other machining parameters don’t apply. Shappell emphasized that operators should be thoroughly trained on abrasives use. They should be taught that just because an air tool can be made to spin at 7,200 rpm doesn’t mean the wheel is safe to run at that speed, or that it will cut effectively. And they need to recognize that process control and consistency are just as important when deburring a part as they are when machining it. As Rosler’s Kerschbaum said, lean on the experts and learn all you can from them, especially considering the shortage of qualified workers.
Not Enough People
It’s mainly because of this shortage that automation is on the rise, even in smaller shops. Shappell said he’s worked on multiple projects lately where robots have been brought in to deburr parts, frequently doubling throughput and increasing part quality to boot. Similarly, Norton | Saint-Gobain customers are beginning to use the company’s “waterproof” unified and convolute wheels in their CNC machine tools to break edges and smooth surfaces, saving countless hours of secondary operations.
“It isn’t just the big automotive and aerospace companies that are moving in this direction, but the 50-person job shops that are running high-mix, low-volume work,” he said. “They can almost always justify a small robot for part deburring on repeat jobs, and provided they have a good filtration system on their CNC machines, it’s no problem at all using abrasive wheels just like they would any other cutting tool. And once they get a taste of automation, they start to get good at it, and pretty soon, they’re looking for other jobs to automate. We see it all the time.”