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Optimizing Automatic Deburring

May 18, 2009
Flexible deburring tool helps an aluminum diecaster use robotics more effectively to remove flashing economically and safely.

TPi/Arcade is a different sort of diecaster: it specializes in producing a range of premium-finish, tight-tolerance aluminum products using the VProcess, a metalcasting technique that uses vacuum technology to shape a mold around a pattern. There’s another distinction for the Arcade, NY, producer of components for instrumentation, computers, and medical devices, as well as RVs, heavy equipment, and automobiles: it has solved a particular problem in finishing finished castings.

The Flexdeburr tool has a rigid outer housing and an internal motor/spindle assembly that allows it to achieve close tolerance cleaning of complex castings.

“Flashing on diecast parts must be removed for operational, safety, and aesthetic reasons,” explains Tom Wittmeyer, process technician for TPi Arcade, “but how this chore is completed has always come under considerable scrutiny by manufacturing engineers and more important OSHA regulators.

“With the Flexdeburr™ tool we have cleared the hurdle,” Wittmer reveals, “cutting the deburring time in half and minimizing employee involvement. The automated tool allows us to robotically remove the flashing quickly and efficiently while virtually eliminating the operator’s manual deburring and exposure to casting dust.”

The Flexdeburr RC-660 that Wittmer describes was supplied by ATI Industrial Automation.

“We have always looked for ways to robots to perform these routine and repetitive deburring tasks,” Wittmeyer continues. “However, we were somewhat restricted when programming the robot. Typically, robotic programming moves the deburring tool along a path defined by discrete points, and that path may not exactly coincide with the shape or contour of the surface to be deburred due to variations in the part itself or to differences between the part edge and the exact path the robot has interpolated.”

Implementing Flexdeburr solved that problem. The patented, flexible deburring tool uses a “pivoting” motor and spindle arrangement to achieve radial compliance, which allows it to accommodate differences between the part edge and the actual tool path. “The tool is designed to follow the part profile, accommodating surface variations, and more than satisfying our initial application,” Wittmeyer reports. “We intend to use it in the future.”

The V-Process
TPi Arcade Inc. is a 50,000-ft2 aluminum foundry that, in addition to the V-Process, performs permanent and semi-permanent mold casting. It specializes in rapid prototyping and low-volume production with the V-Process, which is capable of quick turnaround and high-quality production.

In the V-Process, a thin plastic film is heated and placed over a pattern. A vacuum draws the film over the pattern, which is then surrounded by a flask. The flask is filled with fine, unbonded sand, and the mold is vibrated so that the sand packs tightly around the pattern. A second sheet of film is placed on the flask, and then a vacuum draws out the air. Then the completed mold is stripped from the pattern.

This is done to produce each half of a mold. Then, aluminum is poured furnace into the closed halves, and the mold is held under vacuum to retain its shape. After the mold cools, the vacuum is released and the sand and completed castings are unmolded.

Some of the advantages of the V-process are: 0° draft, which reduces weight and minimizes machining on finished castings; thin wall thicknesses (0.125-inch over large areas and 0.09-inch in small areas); tolerances that are up to twice as accurate as sand-casting can achieve; unlimited pattern life; 150 RMS finish, as compared to 250- 550 for sand casting, and 200-500 for permanent mold casting; and excellent molding integrity for maintaining repeatability of all casting dimensions.

Some of the parts that TPi has produced include engine casings, primary covers, and transmission covers for Harley Davidson; alternator housings for Delphi Automotive; snowmobile drive covers for Polaris; and engine oil pans for John Deere.

Wittmeyer explains: “When the aluminum casting comes out of the V-Process there are minor flashings that need to be removed. We use ATI’s Flexdeburr model RC-660 mounted in a stationary position and a robot to maneuver the part for deburring. We started running the V-Process in 1979 and all of the deburring operations were done manually until we implemented the Flexdeburr a few years ago.

“Our first installation of Flexdeburr resulted in a 90% reduction in deburring operations and an overall bench time reduction of 60%,” Wittmeyer says now. “Also, the reduced deburring time significantly lowers the employees’ exposure to aluminum dust and other contaminants. This initial success has convinced us to look at other applications that can benefit from robotic finishing operations.”

Deburring problems
Problematical burrs, residual material on parting lines and flashing on diecast parts must be removed for operational, safety, and aesthetic reasons. Traditionally, deburring was done manually, with handheld tools, but this lead to several health and safety problems. These included carpal tunnel syndrome and permanent numbness ("white fingers") thanks to constant vibrations, high contact forces, and the necessarily contorted positions that are characteristic for workers using hand-held deburring tools. Metal, fiberglass, and other hazardous particles introduced into the workers’ environment pose health risks, too. In addition, the tedious task of manual deburring often results in inconsistent quality for finished parts.

The pneumatically driven tool uses one air line to power the deburring process, and a second air line to apply radial force to the motor/spindle assembly.

As an alternative, many metalcasters have adopted automated, or robotic, deburring. But typically, robotic deburring and chamfering has been difficult to perform with the required degree of quality. The complexity of the part and a robot’s limitation to generate a path exactly equivalent to the part edge make it difficult for the deburring operations to meet overall quality goals. Also, programming of a robot’s movements is dependent on the complexity of the part, and complex parts require significant programming time to achieve acceptable robot paths.

ATI’s Flexdeburr tools were designed to address these difficulties and to improve deburring effectiveness, while reducing robot-programming time. (It was developed to perform automated deburring tasks that could not be accomplished by a previous product, the Speedeburr. The Speedeburr tool is used for light, high-speed cleaning of burrs produced by machining operations and on diecastings.)

The Flexdeburr is a durable, air-turbinedriven tool for deburring aluminum, steel, or other materials at high speed, even in tough to reach places. While spinning at high speeds the lightweight, rotary tool has radial compliance supported by air pressure applied to the shaft, allowing the tool to perform consistently on irregular part patterns. The “pivoting” motor and spindle arrangement achieves radial compliance up to +/-0.31-inch (8 mm), and maintains a constant deburring force.

The deburring tool has a rigid outer housing and an internal motor/spindle assembly that provides the compliance. The pneumatic spindle is supported by a pivot bearing secured to the tool’s rear housing. This allows the spindle and cutting file to articulate freely and to follow the part profile independent of the housing. The “compliance field” is created by a circular array of small pistons at the front of the tool housing, thus allowing free spindle motion radially in any direction (360°) around the tool.

The Flexdeburr achieves high stiffness from its pneumatically adjustable compliance force, which minimizes a common problem with robotic deburring — chattering. Deburring can be completed as fast as 1 to 3 in./sec. (2.54 to 7.62 cm/sec) on hard materials; 3 to 12 in./sec (7.62 to 30.5 cm/ sec) on soft materials.

The pneumatically powered tool has one air line to spin the cutting file, and a second air line to apply force radially to the motor/ spindle assembly. Regulated air pressure on the pivoting spindle provides the constant force needed to produce a quality finish. The tool is very light, allowing it to adhere to the workpiece edge at a constant force even as the robot moves as fast as 12 in./sec. along the part profile. Additionally, the long, thin envelope of the Flexdeburr’s “working” end allows deburring in tight, deep, and generally hard-to-reach places.

Easy programming
The inherent compliance at the deburring tip saves robot-programming time. Programmers can install fewer path points because the tool compliance will accommodate deviations between the robot path and the part profile. The robot path does not have to follow the part edge precisely. Programming savings are multiplied in applications where multiple passes are necessary in order to achieve a desired finish.

Programming the robot path is easily achieved by temporarily mounting a dowel pin the same diameter as the desired cutting tool in the spindle. Then, the robot is moved to a point where the dowel touches the edge of a finished workpiece and the point is recorded. This is repeated at intervals along the part. A small tool offset is then programmed into the robot controller to account for part profile variations.

ATI Industrial Automation describes the patented Flexdeburr as a compliant deburring tool that satisfies nearly 100% of all robotic and automated deburring applications. It has a “pivoting” motor and spindle arrangement that provides the deburring tip’s radial compliance to perform consistently on irregular part profiles.

Mounted to a robot or CNC machine, the Flexdeburr has a quiet air turbine motor that requires clean, dry, filtered, non-lubricated air that can be directly vented into the workplace. It uses two air connections — one at 90 psi to spin the cutting file, and a second variable supply at up to 60 psi to apply the compliance force.

The motor’s internal governor maintains high speeds up to 65,000 rpm, depending on the Flexdeburr model. Adjusting the compliance air pressure between 5 and 60 psi sets the compliance force between 0.7- 9.5 lb (3.1 to 43.2 N), depending on the Flexdeburr model. The tool uses standard tungsten-carbide industrial bits, so it can be adapted to changing assembly lines and part requirements. Also, the bits are simple to change from one operation to the next.

Robotic deburring using Flexdeburr solves some of the most persistent problems and challenging jobs. The compliance built into the tool inherently provides the answers to work-piece tolerances and robot inaccuracies. It permits robots to succeed by giving manufacturers more choices to resolve their specific deburring needs.