Robots on the Grindstone: Material Removal Robotics

In an era of historically high prices for metals and energy, manufacturers are feeling the pinch. To ease the effect of increasing costs of these products, industry is taking a close look at ways of keeping energy and material expenses in line. Investing in robotics for material removal can be part of a mix of strategies to keep costs down by more efficiently using materials, time and energy.

“Many manufactures use material removal robotics for labor savings. Also, manufacturers see reductions in scrap parts, consumables and repetitive injury claims. These reductions can add up to significant savings,” says Virgil Wilson, Senior Engineer for Material Removal with FANUC Robotics America Inc., Rochester Hills, Michigan.

Removal Tasks
Material removal processes, which include buffing, polishing, grinding, deburring, de-flashing, water-jet cutting, sanding, drilling and milling of manufactured parts, are difficult to do manually. With ergonomic risks, consistency issues and the high cost of materials, the flexibility that robots offer make for a wise investment.

“Robots used for material removal can be split into five different segments,” asserts Roberta Zald, Director of Market Planning and Communications at KMT Robotic Solutions Inc., Auburn Hills, Michigan. “The largest segment, cutting and trimming, has the perimeter of parts and/or features cut by the robot.”

The next largest segment involves “surface finishing and polishing applications that have robots removing rough edges from a metal part after it is formed or smoothing the finish on metal castings or composites.” Zald continues, “A third type of material removal is plastic edge finishing, which has robots cleaning up a rough parting line after the injection molding process.”

According to Zald, the fourth largest category of material removal robotics is stripping and cleaning. “Periodically the dimensional coating on parts used in products such as aircraft jet engines needs to taken off and reapplied. In addition, molds in some metal and composite molding processes need to be cleaned regularly,” Zald explains.

Milling represents the fifth largest segment, according to Zald. “Milling takes a
block of material and creates a shape out of it. Unlike cutting and trimming where the part is already formed, robotic milling creates the shape of the part. This is the newest area of robotic material removal applications.”

When designing a robotic material removal work cell, integrators need to keep in mind that path performance is fundamental for a successful application. “When cutting holes into a plastic or metal part, accuracy of the path is important so you get circular hole rather than an oval hole.” stresses Doug Niebruegge, Segment Manager for Foundry Applications at ABB Inc., Auburn Hills, Michigan. “Path performance is critical when doing material removal.”

“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”, Niebruegge adds.

Repeatability is a major concern to FANUC’s Wilson, who contends that variability is an issue in material removal robotics. “Variability can come from several sources, such as robot repeatability, part repeatability, and process variability. Robot repeatability can range from 0.02 mm, for smaller robots to 0.40 mm for very large robots,” reports Wilson. “This variance should be considered what is achievable in the part’s finish requirements.” In short, end-users cannot expect to achieve a finish tolerance that is less than the robot’s repeatability, Wilson concludes.

In addressing part variability, Wilson says, “Variance can be substantial or insignificant, depending on the process. Sand cast parts usually have the most variance, while machined parts have the least.” Wilson observes that, “Part variability can be addressed by using vision to measure the part’s location relative to the robot.”

Wilson turns his attention to process variability. “The size of the gate, flash, welds, and burrs are examples of process variability. To manage these variables, the system gives feedback to the robot to allow the robot to dynamically react to the process.” Wilson suggests that using feedback from a force control sensor or from the spindle motor are among the strategies integrators use to deal with variability in the material removal process.

The complexity of parts that must be properly gripped in robotic material removal poses a challenge to integrators. “Some parts are difficult to grip because they have many contours,” says Dominique Lalut, Operations Manager with Stäubli Corp., Duncan, South Carolina. “Precision is required for complex parts, particularly when the robot moves a lot within the work cell. Parts like watch bezels, medical implants, and aerospace turbine blades require a high-quality finish, without any nicks or grooves.”

Deploying an appropriate robot for material removal tasks is another crucial consideration for integrators. “Many robots are not designed for the rigors of grinding or other material removal tasks that manipulate a tool over the part’s surface or contours,” says Greg Garmann, Software and Controls Technology Leader with Motoman Inc., West Carrollton, Ohio. Garmann believes in using a robust robot specifically designed with the rigidity needed for material removal applications.

“One challenge is finding the balance between process quality and cycle time,” says Ted Warnecke, Senior Application Specialist at Motoman. “Testing is required to verify the material removal process and cycle time.” Warnecke continues by saying, “Robotic material removal systems are often required to perform multiple tasks, including cutting and deburring or sanding and polishing. Integrators take one of two approaches: multiple spindles or spindles that can change material removal media or tools.” The method used is generally determined by the process, maintains Warnecke.

Warnecke conveys a note of caution when he spells out a common error when setting up a material removal work cell. “Integrators must take into account the possibility that parts that can be in a different state than when finished.” Warnecke illustrates his point by citing an example. “Parts that are still hot from a die cast or injection mold can cause process and fixturing problems. These problems stem from not selecting the proper combination of spindles, cutting tools or media to meet cycle time, tool life and process requirements of the work cell.” An experienced and knowledgeable robot integrator is the best way to avoid these pitfalls.

Removed Material
Integrators must be mindful of managing the waste material when putting together material removal work cells. ABB’s Niebruegge points out, “In the design of the material removal system, integrators need to make provisions for getting the waste out. Usually this is done by having the debris fall by gravity and channeled onto a conveyor that will take the waste away.”

KMT’s Zald speaks of waste extraction in water-jet applications. “We have a method of using a high- volume vacuum that holds the part in position and removes the waste that is generated in water-jet cutting.” Zald also mentions that as new materials are being developed for use by industry, new pressures arise to come up with material removal processes while also protecting workers and the environment.

Flexibility and Efficiency
The inherent flexibility of robotics is very apparent in material removal applications as other processes and procedures can be combined with it. “Material removal can be combined with part unloading, die casting, injection molding, blow molding, thermoforming, and deburring applications, if cycle time permits,” says Warnecke of Motoman.

Likewise, “When the robot is polishing or deburring, we suggest having the robot carry the part so it can do additional operations like washing, cleaning, testing or palletizing,” says Lalut of Stäubli. When possible, Lalut advises having the robot present parts undergoing material removal procedures to other machines for inspection, dispensing, and material handling. Combining different applications in a single work cell saves on cycle times and floor space.

In a similar vein, FANUC’s Wilson believes material removal can be combined with other applications to add value to the manufacturing process. “During machine loading and unloading applications, the robot may have idle time between operations. This is a perfect time for a value-added application like material removal.”

KMT’s Zald observes that, “End-users want to add a material handling robot upstream, or dispense an adhesive for assembly tasks downstream from the material removal process.” Similarly, “Material removal is often combined with material handling applications because it is very time-efficient to take the part to different abrasive tools to perform material removal,” says ABB’s Niebruegge, “

By having an accurate and repeatable robot, fewer mistakes are made in the material removal process than if the task is performed manually. Fewer mistakes yield less scrap, which makes the production process more efficient and profitable.

Robots can help hold the line on consumable media costs.  Stäubli’s Lalut sketches out how robots help save on media use. “Robots use material removal media more consistently which leads to savings in sanding belts and grinding wheels as well as polishing and buffing paste.” He states that when material removal is performed manually, people vary the amount of pressure they apply, which leads to an inconsistent finish on the part and a less-efficient use of consumable media. “A precise robot applies constant pressure on parts all of the time,” Lalut affirms.

Removing On
“The past few years have seen major advances in the robot’s path performance so that it is able to follow a path very accurately. Also, the emergence of force control is making a big impact on material removal applications,” remarks Niebruegge of ABB. “More advanced vision systems will look at a part and be able to tell the robot exactly where to remove material based on what the part looks like compared to what the part should look like.”

Motoman’s Warnecke also sees more powerful sensors that will perfect robotic material removal. “I expect to see additional development of software and control devices that perform surface finishing. This will include sensors to reliably answer how smooth or how shiny or a part ‘feels’ or ‘looks.’ These sensors will be able to avoid over-sanding or polishing parts and reduce the need for manual touch-ups after the automated process.”

Editor’s Note:
This article has been reviewed by members of the RIA Editorial Advisory Group.

For more information, you may contact any of the experts listed in this article or visit RIA’s Info Center on Robotics Online.

Greg Garmann, Software & Controls Technology Leader, Motoman Inc., 937-440-2668, [email protected]

Dominique Lalut, Operations Manager, Stäubli Corp., 864-433-1980, [email protected]

Douglas Niebruegge, Segment Manager for Foundry Applications, ABB Inc., 414-870-3700, [email protected]

Ted Warnecke, Senior Application Specialist, Motoman Inc., 937-847-3443, [email protected]

Virgil Wilson, Senior Engineer for Material Removal, FANUC Robotics America Inc., 248-276-4240, [email protected]

Roberta Zald, Director of Market Planning and Communications, KMT Robotic Solutions Inc., 248- 829-2854, [email protected]