January 19, 2009
by Bennett Brumson
High prices for metals and energy are squeezing manufacturers, but one way to help keep these expenses in line is to automate material removal processes. Buffing, polishing, grinding, deburring, de-flashing, water-jet cutting, sanding, drilling and milling of manufactured parts are difficult to do manually, but experts from robotics manufacturers and integrators say deploying robotics provides labour savings while reducing scrap parts, consumables and repetitive injury claims.
Robots ensure there are fewer mistakes, which means less scrap and they help hold the line on consumable media costs by being more consistent. That leads to savings in sanding belts, grinding wheels, polishing paste and buffing paste,” says Dominique Lalut, operations manager with Stäubli Corp. in Duncan, SC.
Here are some points to consider when setting up material removal systems.
Material removal segments
Robots cover five different areas. The largest is cutting and trimming. Next is surface finishing and polishing applications that remove rough edges from a metal part after it’s formed, or smooths the finish on metal castings and composites. A third type is plastic edge finishing, which cleans up a rough parting line after the injection moulding process. The fourth is stripping and cleaning. “Periodically the dimensional coating on parts used in products such as aircraft jet engines needs to be taken off and reapplied. In addition, moulds in some metal and composite moulding processes need to be cleaned regularly,” explains Roberta Zald, director of market planning and communications at KMT Robotic Solutions Inc. in Auburn Hills, Mich. The fifth and newest segment is milling, where a robot creates a shape out of a block of material.
Work cell design
When designing a robotic material removal work cell, Doug Niebruegge, segment manager for foundry applications at ABB Inc. in Auburn Hills, Mich., says keep the importance of path performance in mind (especially when cutting holes into a plastic or metal part) to ensure you get a circular hole rather than an oval one. “In robotic surface finishing applications, knowing where the part is in space is vital for repeatability. Having a repeatable robot is necessary when de-flashing a cast part because knowing where the flash is and knowing how that flash can vary from part to part is important.”
Repeatability and variances are major concerns for Virgil Wilson, senior engineer for material removal with FANUC Robotics America Inc. in Rochester Hills, Mich. Variability comes from several sources, such as robot repeatability, part repeatability and process variability. Robot repeatability will range from 0.02 millimetres for smaller robots to 0.40 millimetres for very large ones.
“This variance should consider what is achievable in the part’s finish requirements,” says Wilson. “Variance can be substantial or insignificant, depending on the process. Sand cast parts usually have the most variance, while machined parts have the least.”
He says part variability can be addressed with vision technology to measure the part’s location relative to the robot. Process variability involves the size of the gate, flash, welds and burrs. To manage these variables, the system provides feedback that allows the robot to react dynamically. Wilson suggests using feedback from a force control sensor or from the spindle motor.
The complexity of parts that must be properly gripped—especially those with many contours—poses a challenge, says Lalut. “Precision is required, particularly when the robot moves a lot within the work cell. Parts such as watch bezels, medical implants and aerospace turbine blades require a high-quality finish, without any nicks or grooves.”