Robotic deburring cell: removes parting lines and flashing in hard-to-reach places.
The conventional approach to automation is a fixed part and a robot that travels along a rigid, programmed path. Inconsistency occurs when the part may be slightly misaligned in the workholding device and the robot follows its predetermined path. Without tool compliance, the deburring tip may gouge the part, leave unwanted burrs on the edge, or, in a worst-case scenario, the tip will break requiting immediate repair.
Robotic deburring and chamfering are extremely difficult to perform with the required degree of quality. The complexity of the part and the 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 robot movements is dependent on the complexity of the part, and complex parts require significant programming time to achieve acceptable robot paths.
"We are always looking for new ways of performing deburring tasks," explains Bob Howard, systems integrator for Fanuc Robotics Southeast, Charlotte, NC. Fanuc Robotics is a worldwide robotics systems integrator that engineers, builds, integrates, services, and supports customer needs focused on "turnkey" integrated systems. Fanuc has been successful in supplying deburring cells that use conventional deburring tools.
One new way that Fanuc has tried with success is the Flexdeburr from ATI Industrial Automation. The Flexdeburr robotic deburring tool was developed to deburr parting lines or flash by closely mimicking the methodology of manual deburring. It uses a "floating" motor and spindle arrangement that provides [+ or -]0.31" (8 mm) of radial compliance, which accommodates differences between the part edge and the actual tool path. The tool is also designed to be easily maneuvered around protrusions and into small cavities, satisfying nearly 100 percent of all robotic and automated deburring applications.
The Flexdeburr is a high-speed, airturbine-driven tool for deburring aluminum, plastic, and steel. 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 deburring tool has a rigid outer housing and an internal motor/spindle assembly that provides the compliance. The pneumatic motor/spindle assembly is mounted on a pivot bearing mounted to the tool housing. This allows the pneumatic motor to move with the pivot bearing independently of the housing. The radial "compliance field" is created by a ring of small pneumatic pistons located near the front of the tool housing. The compliance force can be exerted on the spindle/tool in any direction (360 degrees) radially from the tool.
The inherent compliance at the deburring tip saves robot programming time. Programmers can program fewer path points since the tool compliance will accommodate deviations between the robot path and the part edge. The robot path does not have to precisely follow the part edge. Programming savings are multiplied in applications where multiple passes are necessary in order to achieve a desired finish.
Removing rough edges
The Flexdeburr also uses ATI's patented force control system that provides very high stiffness in the path direction, and low stiffness in the contact force direction. This feature avoids chattering, a common problem with robotic deburring. The extremely low inertia of the floating rotary file allows fast robot motions, resulting in greatly reduced cycle time. Deburring can be as fast as 1" to 3" per second on hard materials, 3" to 12" per second on soft materials. The deburring tool spins at a constant 40,000 rpm when in operation.
The pneumatically-driven 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 floating head provides the constant force needed to produce a good quality chamfer. The tool is extremely light, allowing it to hug the workpiece edge at a constant force even as the robot moves as fast as 12" per second along the edge of the part. Additionally, the long, thin envelope of the "working" end of Flexdeburr allows deburring in tight, deep, and generally hard-to-reach places.
"We are convinced that the Flexdeburr will provide a 35 to 40 percent gain in productivity due to improvements in the deburring process," says Howard. "The first successful application is an automotive parts manufacturer in the southeast that had a very complex part. The application needed the flexibility of the deburring tip to access several crevices that were hard to reach, even with manual deburring systems. We can now maneuver the tip to reach all areas of the part and at a pace of two parts every 190 seconds."
Programming the robot path is achieved by mounting either a dowel pin of the same diameter as the cutting tool, or a pointed teaching tool, in place of the actual cutting tool. The robot is manually moved to a point where the dowel or pointed tool is touching the edge of a finished part, and the point is recorded. This is repeated at intervals along the edge of the part and the robot controller uses these recorded points to define the path to be followed.
The cutting force is also adjustable "on-the-fly" allowing the programmer to increase the cutting force in areas having larger burrs or where more material must be removed. The motor maintains a high spindle speed of 40,000 rpm and the entire tool weighs only 2.6 pounds. The tool uses standard tungsten-carbide industrial bits that allow for adaptation to changing assembly lines and part requirements. Also, the bits can be easily changed from one operation to the next.
"Creating a deburring cell that can satisfy more than 90 percent of all industrial applications is our goal," says Howard. "We must exhibit the ability to handle both large and small burrs and have the built-in compliance and flexibility to satisfy the most challenging jobs.
"Most large manufacturing companies have a number of deburring needs that warrant the purchase of a robotic cell. The key to success is to assure that the automated deburring operation can satisfactorily and repeatedly perform the deburring task."
ATI Industrial Automation, www.rsleads.com/412tp-238
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|Title Annotation:||parts finishing|
|Publication:||Tooling & Production|
|Date:||Dec 1, 2004|
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