Don’t overlook advanced technology available for removing the gnarliest burrs from parts large or small
Precision product finishing has come a long way from the days when the principal options for burr removal were manual deburring or high-volume tumbling. Both of those options play an important role in helping manufacturers meet their finishing requirements, especially with the variety of equipment and media available to meet most any part requirement. There are, however, a wide variety of deburring techniques and equipment that also enable manufacturers to take advantage of the increased use of automation. In industries as diverse as automotive, aerospace, and medical, where part size and part requirements vary from the smallest to the largest, identifying and defining the scope of deburring process required is essential. Based on considerations of part type, material, part volume, and manufacturing process used, solutions can be found that will address just about any part processing requirement, efficiently and cost effectively. And with today’s emphasis on lean manufacturing with single-product, flow-type processing, solutions can take advantage of automated robotic and in-machine deburring processes, and include processes that work equally well in manual or automated machine tool applications.
What’s a Burr and How Do You Process It?
“Our response to this question was to develop a burr standard that was easy to understand and apply in the field,” said Mike Akuszewski, application engineer for Osborn, a unit of Jason Inc. The Brooklyn Heights, Ohio, supplier of surface treatment solutions and finishing tools put its engineers to work to develop a standard for classifying burrs to facilitate finding “standard solutions for a nonstandard manufacturing problem. Once the standard was adopted by manufacturers and distribution channels, Osborn’s application engineers could simply ask two questions to get an idea of the manufacturer’s need. First, what material is the manufacturer working with? Secondly, what burr class is the manufacturer trying to remove,” said Akuszewski.
Osborn found that there are few problems removing steel and aluminum burrs, which are typically class 1 and class 2 burrs according to its standard. (See Standard Fig. 1, p. 66) They can be removed with standard silicon carbide ATB brushes (Advanced Technology Brushing). For class 3 and 4 burrs, a more aggressive product is needed. “We had some success with short-trim wheel brushes, and we also added bridles to disk brushes, which controlled flare and shortened the trim of a disk brush to make it more aggressive when working on steel applications,” said Akuszewski. To process exotic materials such as hardened steel, Inconel, Hastelloy, stainless steel, and titanium, Osborn developed a ceramic line of ATB brushes, called the CG product line. The ceramic grit of this line has a sharp, jagged grain that provides a deeper cut to remove material faster. “For Class 3 and 4 burrs, which are larger, well attached and require a significant amount of energy to remove, a tougher filament and a harder ceramic are able to cut deeper and remove a heavier burr faster.
In Osborn’s classification standard, Class 5 burrs are also known as “extruded burrs.” They aren’t actually burrs but a deformation of extruded or displaced base material resulting from drilling. Although they are commonly called “burr” and classified as such, they indicate a problem resulting from a process such as a too-high drilling speed or material feed. Class 5 burrs require preconditioning with a chamfer or carbide cutting tool to remove the burr, which will leave a residual burr that can be removed with a brush tool.
Automation and Certain Industry Considerations
“Automation of finishing is accomplished by integrating products into robotic cells that mimic the movement of the human hand, CNC machines, and custom deburring machines,” said Akuszewski. “In-machine deburring has become a new standard in the aerospace industry, which is adopting the automotive production style of manufacturing and doing away with hand deburring. New aerospace standards are creating the need for much higher precision for deburring, tighter tolerances, and exact production quantities. These automated processes are being put in place to keep manufacturing in-house and to maintain tighter process control,” said Akuszewski.
“Manufacturers are pushing their tooling harder and use in-machine deburring, rather than using secondary machines to precondition larger burrs on materials such as ductile iron and compact graphite iron (CGI). As a result, Osborn developed a product that is both aggressive and compliant with a new filament that can conform to a complex shape. The new line also has products that work well on large burrs on Inconel and other high-nickel materials, typically found in the aerospace industry.”
“Certain industries are running into problems with surface finishes being too smooth after deburring with an ATB brush. For example, in the automotive industry, if the surfaces of some components are too smooth, gaskets will not seal properly. This translates into a component that won’t perform correctly. Certain parts need to have the same surface roughness after burrs are removed, or actually need to have a rougher surface. Stainless steel wire disk brushes are ideal for deburring where roughing is required,” said Akuszewski.
“Product design flexibility can aid in automated finishing with the ability to add flow-through coolant that provides an ideal working environment for ATB products and has many finishing benefits for the manufacturer. Coolant keeps the nylon filament rigid for consistent finishing and aids in achieving a finer surface finish. Coolant also lowers the risk of warping and distorting parts, especially in applications where smaller or thinner parts are being processed,” said Akuszewski.
Sizing Up Upstream Production for Parts Deburring
It’s a bit of a conundrum: Burrs are produced in upstream processes that are performed by cutting tools that, due to wear, produce burrs that change size over time. At the same time, deburring tools, like brushes, also wear. “One of the first questions we ask is, what is the upstream process and what are the best and worst-case burr geometries that are likely to be produced by that upstream process,” said John Sockman, director, industrial production, Weiler Corp. (Cresco, PA).
“Once we have a good understanding of that operating window from best to worst case, we evaluate parts in our application laboratory to select tools, operating parameters, and develop wear compensation scenarios. For example, the brush will work this way when it’s new, but we have to know how it will work when it’s 10% worn or 30% worn. We have to build a wear compensation system that is robust enough to handle the wear of the media and the fact that the upstream process is producing a burr that itself will vary over time. When the cutting tools are new, the burrs are small. But when the cutting tools wear, the burrs get larger,” said Sockman. “And you can be sure that production parts will not mimic the parts which were used for process development. This fact needs to be considered when the process is prototyped.”
In addition to planning for the variation introduced by the upstream process, another critical element of process design is the selection of operating parameters. This selection is not intuitive. “Inexperienced machine builders will commonly select operating parameters, speeds, feeds, and the brushing equivalent of depth-of-cut incorrectly. Another common mistake is thinking that smaller parts require the use of smaller media. That’s rarely a good decision. Generally, the largest media with the highest filament density that is allowed by the part geometry is the best solution. That’s the way to develop the most robust process with the lowerst cost per part. The smaller products tend to wear faster, resulting in more machine downtime, so using larger tools is almost always better,” said Sockman.
Aerospace, Automotive Automate in Different Ways
“Today, we are seeing a lot of automation projects in factories that are bringing work back from Asia, as well as for new programs that would have been sent overseas a decade ago. The economic benefits of having a shorter supply chain and bringing production closer to the end market are trumping lower labor costs,” said Sockman. Weiler gets involved in three different types of automation.
“In the aircraft engine market, most of the deburring systems involve robotics. In the automotive engine market, the deburring process is being integrated into inline CNC systems where deburring is simply a step in the machining process. A third type of automation involves the use of dedicated deburring machines. This type of deburring automation is more common in Tier 1 plants that make engine, transmission, steering, and suspension components and involves machines that are designed to process a particular part in a very high volume,” said Sockman.
“The segment of the auto industry we deal with most is making their investments in flexible systems for engine and transmissions that readily accept on-machine deburring. In the aircraft industry, for example, we put a robot right at the tail end of three grinders and those four machines work together in the cell. They have a single takt time and basically operate under a completely lean single parts flow-type operation. As soon as you take a mass finishing approach then you’ve lost single part flow and you’re back in batch and queue.”
Tool Works in Any Rotating Spindle
Brush Research Manufacturing (BRM: Los Angeles) supplies a complete line of surface finishing solutions for inner diameter (ID) and outer diameter (OD) applications. “For ID surface improvement and burr removal, BRM’s Flex-Hone tool can be used equally well as a hand-held tool or fixtured in a machine tool to remove burrs and improve the surface finish of cylinder walls,” said Michael Miller, vice president, Global Sales. “The Flex-Hone tool features a self-centering, self-aligning design similar to that of a bottle brush. The tool features abrasive globules laminated to flexible nylon filaments and are manufactured in 10 different abrasive types and 11 grit options in standard sizes from 4 mm to 36″ (914 mm).
The Flex-Hone is a low-rpm tool that’s suitable for most any rotating spindle, including drill presses, milling machines, lathes, CNC equipment, robotic arms and machining centers. Built with a twisted-wire metal stem, Ballhones are secured in a chuck, collet, or similar holding device. For CNC equipment machining centers, Flex-Hones use a Jacobs-style chuck or collet. Although not designed for heavy-duty or high-precise metal removal, Flex-Hone tools can be used in any size or type of cylinder in a hole that needs a finish improved or deburring operation.
“Different types of abrasives and our proprietary adhesives make it possible to process workpieces in industries as diverse as nuclear, medical, and aerospace and on a wide variety of materials. One of our largest industry customers is the aerospace industry where we finish difficult materials including all high-nickel alloy stainless steel, titanium, and other difficult-to-machine metals. The key to success is having the right abrasive type available,” said Miller. Cross hole deburring is another major application area for the tool. “With the Flex-Hone tool, cross hole deburring can be done within the main bore and deburr all the cross holes at once.” In automotive applications, the Flex-Hone tool can produce a cross hatch finish in a cylinder bore for oil retention. “The oil and gas industry is another major market for our products where we are routinely asked to process tubular goods 18–24″ [457–610 mm] diameter, which are standard sizes for us.”
“Brush Research has other tools to process external surfaces. BRM’s Nampower nylon abrasive material series of disk-shaped tools have an abrasive impregnated nylon filament densely packed into a disk-type tool. It’s designed to be used with a flow through coolant holder on machine tools which allows coolant to be applied from the center of the tool. The Nampower brush combines two different abrasive types in the same tool; a ceramic filament is designed for material removal and a silicon carbide filament to provide a better finish which allows us to rough and finish a part at the same time,” said Miller.
Micro-Blasting for Small Precision Parts
As today’s manufacturing processes have enabled the fabrication of smaller and more intricate parts, traditional deburring methods using hand tools to carefully remove burrs have proven to be no longer adequate. For deburring small parts, Micro-Abrasive Blasting from Comco Inc. (Burbank, CA) has proven to be an effective method for removing fine burrs on small parts with complex geometries without causing dimensional changes to the part. Typical parts include medical devices, including hypodermic needles and stents, as well as fuel injectors, gear splines, hydraulic valves, mold cavities, nozzles, and electronic components.
The micro-abrasive blasting process involves finding the right combination of abrasive, nozzle size and air pressure to quickly cut off the burr. Abrasive particles are projected through a small nozzle at roughly a quarter of the speed of sound and directed to burrs by hand or when arrayed in semiautomated systems for high-volume production. When deburring complex parts like manifolds or injections, it’s important to be able to reach down inside a part. Because these types of parts have intricate shapes that are difficult to deburr using hand tools, Comco has developed a variety of extended and right-angle nozzles that enable the operator to blast burrs from these hard to reach areas. Typical materials that can be deburred with micro-abrasive blasting include Nitinol, titanium, tungsten carbide, aluminum, brass, Kovar, PEEK, stainless steel, Delrin, and others. For high-production applications, micro-abrasive blasting can be integrated into semiautomated systems.
Mass Finishing is “Finding a Better Way”
“More and more automation is being included in our traditional rotary vibratory bowl or vibratory tubs processing, often combining material handling and drying,” said Tim Gibson, general sales manager, Rosler Metal Finishing (Battle Creek, MI). “When we discuss a possible solution with our customers we want to know the scope of the program, what’s the throughput, whether deburring, polishing or smoothing a part, or descaling is involved. Looking at the geometry of the part helps us marry a mass finishing vibratory process, whether it’s drag finishing, traditional tumbling, or high-energy disk machining to the solution. We also offer shot blasting equipment, on the other side of the business,” said Gibson.
“A deburring or finishing solution includes equipment, automation, and consumables. We manufacture the consumable media, which people call stones, in Battle Creek. Media can be as diverse as ceramic, plastic, steel, and even glass beads, and include the soap and compound. Selection depends on the requirements of the part being processed. Our mass finishing equipment comprises rotary vibrators, tub vibrators, high-energy disk machines, which are typically 10 times more aggressive than the standard bowl, and drag machines which are 40 times more aggressive than a standard bowl. The drag machines are used for applications where sensitive parts can’t touch one another and we’re trying to remove a lot of material,” said Gibson.
“Mass finishing or shot blasting has been around for years. We continuously make improvements to the features of our equipment, but the biggest advancements are coming from the consumable side of the business where the media and the compounds are getting more and more advanced in terms of cutting performance, or wear performance, as well as preventing rust. One piece of new equipment is a wet blaster with an air-driven nozzle that shoots media, like glass beads, that are basically carried by water and cushioned when hitting the part, so you have no impingement. This equipment has made inroads in processing medical implants,” said Gibson. ME
This article was first published in the October 2014 edition of Manufacturing Engineering magazine.