Deburring, rounding and polishing techniques are becoming more important as manufacturers strive for ever more precise parts
Burrs, sharp edges, and rough surfaces plague even the most precise metal-cutting or forming process. Deburring and finishing can often be treated as the step-child of a manufacturing process, but its importance is growing as tolerances get tighter and precision devices become the norm. Many of the reasons for deburring have also changed in just the last few years. “For a long time, deburring was related to safety, especially handling parts,” explained Adam Mutschler, sales manager for Cleveland Deburring Machine Co. (Cleveland). He bases his comment on his 10 years of experience in the family owned business. “Before, you might have a part that was razor sharp and operators would be assembling parts and cutting themselves,” he said. Now, with the growth of automation in assembly, burrs, sharp edges, and other imperfections have become more of a functionality issue. “In a variable cam timing component used in an engine, a small burr could create havoc in the finished assembly,” he said.
He emphasizes that these needed post-machining operations are not simply removing burrs—reducing sharp edges also increases robustness by eliminating stress concentrations. Sharp edges can fail. There is also a vast array of deburring technologies and choices available. “Every technology has its advantages, and disadvantages,” he said. Cleveland Deburring concentrates on mechanical forms of deburring, especially in brushes, various forms of abrasive deburring, and hard tooling usually with parts that are fixtured.
Mutschler also notes the increasing emphasis on automated solutions. “Manual deburring and refinishing is certainly not dead yet, but sometimes it seems to be trending that way,” he explained. In response, Cleveland has become a FANUC authorized integrator of robots, mostly for material handling within dedicated deburring cells. “The move towards automation, I think, has to do with trying to eliminate human error,” he said, as well as cost reduction.
The company’s offerings include a wide range of equipment, from portable deburring machines to dedicated equipment for bevel gear and ring gear deburring. He stated their most popular equipment are through-feed deburring machines, the CDMC Mag series. Using a series of magnetic conveyors, the parts are presented to the brush sets in the proper orientation. The first set of brushes approach from above and the second from below. An optional de-magnetizer removes residual magnetism induced by the conveyors. “These can process up to 1200 parts per hour,” he said.
Others are joining in. In perhaps a sign of the growing importance of deburring, ARKU (Cincinnati) announced in a press release provided to Manufacturing Engineering that it is entering the “smoothness business” with its new EdgeBreaker deburring and rounding machine. Known for its flatness and parts leveling technology, the EdgeBreaker is designed specifically to debur plates with greater thickness. The Edgebreaker is a dry processing application and can perform double-sided deburring and rounding, according to the press release. For aluminum, steel or titanium, the oscillating roller equipped EdgeBreaker removes unwanted burrs, while transverse-running rounding units equipped with rounding locks, simultaneously round the edges on both sides.
Walther Trowal (Grand Rapids, MI) is one of the oldest companies, starting its business in Germany in 1931, to provide deburring and finishing equipment, especially mass finishing techniques. “The problems of deburring are the same as they were when we started, but the issues around deburring are worse,” stated Ken Raby sales manager for the company. He agrees that there is a move towards more automation, spurred by the difficulties in training skilled operators for hand deburring and finishing. Also, individual operators in workcells are being asked to do more multitasking, making it more difficult for them to master the craftsmanship of hand deburring while performing other tasks, he said.
More automation translates into an increased need for what Raby describes as higher energy mass finishing equipment. According to Raby, mass finishing generally refers to any deburring, edge breaking or surface conditioning process in which the workpieces, although confined in a chamber, are not fixtured. This could include vibratory bowls, tumbling barrels, centrifugal barrels and centrifugal disk machines that tumble parts with some type of media to remove burrs, polish, and round edges. Media is often abrasives, water and soap, though dry media is an option as well. Examples of each category are offered in Walther Trowal’s extensive equipment catalog.
The parts themselves are getting smaller, more precise and more intricate. “To meet today’s market, we developed the multi vibrator, or MV, line of equipment,” he said. “The MV machine can now do parts that could not be done in the past, coming close in my opinion to what an operator can do with hand sanding,” he said. Walther Trowal offers three sizes of the MV machine, MV21, MV25, and the newest MV32. Unlike a typical mass finishing device, workpieces are mounted onto a clamping device located at the bottom of the work bowl. Once the workpieces are in place the work bowl is filled with media and energized by two or three vibratory motors. He describes these machines as one of the more popular choices in North America.
Another line of automated equipment is the AV line of continuous vibrators. These move parts through a trough-shaped work bowl. The company believes it is best used for robust small and medium sized parts such as stampings or die castings, and designed for 24/7 operation with little or no human intervention.
He offers advice to engineers. “Be prepared to do testing,” he advises. “No off-the-shelf product can be ready in 10 minutes. To do the right process takes time.” He notes that Walther Trowal has provided him with a wide range of test equipment and analytical software to help. “Unfortunately, deburring and finishing is not taught in any university, so getting help is critical,” he said.
High Energy Applications
For high-precision, high-value parts, the deburring process needs to be consistent, said Ken Bagdasarian, CEO of United Surface Solutions (Santa Fe Springs, CA). “For example, big aerospace companies are using $5 million five-axis CNC machines to produce parts with tolerances in the millionths of an inch. They might get up to 40% rejection of parts if they try deburring with vibratory bowls, or even by hand,” he said. He also said that some of the more common mechanical deburring equipment, like tumblers, vibratory bowls, centrifugal disk, or drag finishers provide from 1 to 1.5 g’s of force.
In contrast, United Surface specializes in providing what Bagdasarian described as high-end solutions in the form of centrifugal barrel finishing machines. “These are very aggressive mass finishing machines. They produce upwards of 30 g’s of force in the deburring process, which provides two benefits—speed and consistency,” he stated. He cited timing comparisons where a centrifugal barrel machine could produce smooth parts in 10 minutes where a vibratory bowl might take three hours. “It is also much more consistent, up to 100%,” he said. He also noted that the high g forces mean manufacturers can use much smaller media and still get acceptable results, so smaller IDs and features in precision parts are now available. “Centrifugal barrel is not new technology. It has been known since the early1900s. But it is only in the last few decades have we introduced it,” he said, as high-precision technology made its benefits attractive. “We have done parts with our machines where the parts cost $50,000 each.”
He also cites the growing importance of automation for his customers. “Our machines have a number of controls, accessed through PLCs and touch screens and all are programmable with sensors to aid in the process,” he said. Precise control of high energy deburring is critical. If a process runs too long, 30 g’s can reduce a part to scrap quite easily. Their newest machine he pointed to was the company’s CPC4000. It is advertised as capable of small parts and large, up to 27.5” (70cm) long with an optional automated elevator and fill system. Larger machines are also available.
Applications Diverse, Critical, Ubiquitous
“Deburring and finishing has always been of high, critical importance in manufactured goods,” stated John Thompson national technical sales manager of Pferd Inc. (Milwaukee), manufacturer of various end-item abrasives such as files, grinding and cut-off wheels, along with impregnated brushes. From extending the life of automotive transmissions to preventing small particulates in food-handling equipment, deburring is critical. While providing tools for on-hand or off-hand applications, he agrees that automated off-hand deburring seems to be increasing, according to Thompson. “We build the components that go into deburring equipment,” he explained. Each application still requires careful thought. Designing a deburring technique is not an exact science, with help from component providers like Pferd.
As manufacturing processes improve, he has noted some shifts in technology. “Much of the post-processing work that once was needed is no longer required,” he explained. “We get more calls per day on fine finishing than coarse preparation. The efficiency of the process itself has improved, so it requires far less post-work.” For example, the precision of band saws has improved so much in recent years that kerfs are finer, waste is less. “You simply do not have as much deburring to do,” he said.
In his practice, Thompson has noted a trend towards the use of nonmetallic abrasives. “These give you significantly more contact area than other types of brushes,” he explained. This has been driven by the use of more nonferrous metals in practically every application, according to Thompson. Aluminum, magnesium, titanium, stainless steels and alloys, as well as composites are all ideally deburred with nonmetallic abrasive. Pferd’s M-BRAD abrasive filament brushes, using a 6.12 nylon monofilament evenly encapsulates abrasive grit particles. “Contamination is much less of an issue than with a metallic filament, the impact is greater and the overall life with nonmetallic filament is much greater,” he explained. The nonmetallic abrasive could include ceramic, silicon carbide, aluminum oxide or diamond, embedded in the nylon filament. The company noted that M-BRAD is suitable for both wet and dry applications and they claim it will not degrade the dimensions of the workpiece. “I can control filament size as well, allowing more options for designing the process,” he said.
Perceptions and Uses
Mike Radaelli, director of product management of Thin Wheels & Construction Products for Norton Abrasives Saint Gobain (Worcester, MA), noted the widespread use of deburring in both MRO operations and especially in original part fabrication. Like others interviewed for this article, he sells deburring abrasives for a wide range of industries, from aircraft turbine blades to golf clubs. Castings need to be deflashed, edges blended, surfaces made shiny in practically every field. “The trend overall, in the last 10–20 years, is what we call manual-to-machine,” said Radaelli. “Even today, many customers continue to do these operations by hand.”
While Norton Abrasives Saint Gobain sells the end-item abrasives that are used in deburring operations, hand held or automatic, Radaelli has found value in deploying their own applications engineering department to help customers develop the right process. “Even though we do not sell the machines, we make sure the customer gets the automation solution they need,” he said. This manual-to-machine movement is worldwide, he said. He related how this is true even in low-cost labor markets. For example, Norton helped a supplier of golf clubs in southeast Asia install an automated deburring solution. They had done this primarily by hand, but wanted to improve the ergonomic workload on its employees as well as improve throughput.
“The move to automation, while increasing speed, lowering costs, and improving quality and consistency requires better abrasives,” he stated. For example, he noted his company’s development of ceramic abrasives, both treated and shaped. These engineered ceramic grits are versatile, giving the designers of abrasives the freedom to bond them as particles into a sphere that can then go into a coated abrasive or into a grinding wheel. “This gives it a three-dimensional cutting action, increasing lifetime and throughput,” he said.
New products, Radaelli noted, from Norton that incorporate these technical trends include Norton Quantum3 grinding wheels, Norton Blaze stripping discs and Norton Vortex nonwovens. “The Norton Vortex technology can help you skip steps, eliminating the need go from rough metal removal to polishing in six steps to three,” he said, through the advanced cutting action. “People for a hundred years have used coated abrasives and it has become familiar to them. But a faster way is with what we call nonwoven products, taking a synthetic like nylon and making a convolute, Rapid Finish wheel. You can pass many more parts through that than a belted coated abrasive,” he said.
Variety and Prevention
“There are 124 different ways to deburr,” stated LaRoux Gillespie, a noted SME expert and consultant in the field of deburring. However, he stressed that the best solution is to not create one in the first place, or at the very least minimize them as much as possible. “The machinist [operating the cutting tool] has the ability to minimize the size of the burr and in some cases can take off the majority of the burr right there,” he said, by using a chamfering cutter or deburring brush in a second pass. While preventing them altogether might be the best way, it is not always the most economic, he admits. “In about 5% of my consulting practice, I can help customers actually prevent a burr,” he said, “so I spend most of the time helping minimize the burr and finding the most effective removal processes.” Toolpaths, cutter design and sharpness and other machining parameters can be chosen to greatly reduce burr size.
“Brushing off the burr on the cutting machine is one of the most cost-effective approaches you can use for typical burrs. The typical burr size in normal industry is 0.003″ [0.076 mm] thick, about the diameter of a human hair,” he explained. “There are three or four major companies that make a variety of brushes that reach into almost any geometry” and eliminate burrs of that size.
He predicts that the manufacturing world will pay more attention to burrs and surface finish in the future. “We have done surveys, and most people calculate [deburring] to cost about 3–10% the cost of making the part,” he said. “In today’s world, these are significant enough costs to warrant worrying about.” He also cautioned that deburring can eat up clock time if not cost, with parts waiting to be deburred before shipping. “Economics are important. Before you improve you have to understand and quantify your end goal for reducing the cost of deburring. That is one key,” he stated.
This article was first published in the October 2016 edition of Manufacturing Engineering magazine.