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The Process is Key

Accurate, efficient application of material is now a defining characteristic of robots for the paint shop.

Accurate, efficient application of material is now a defining characteristic of robots for the paint shop. It’s not the arm that’s important—it’s what it can do.

Fanuc Robotics (Rochester Hills, MI) actually has its North American roots in the auto industry: when it began, it was known as GMFanuc with the “GM” referring to, well, GM. What’s more, the initial product that really established the vendor in the auto industry was a painting robot. Consequently, one could argue—as Jon Karr, vp of the firm’s Paint Shop Automation Group, does—that the company has a solid background in providing paint automation to automotive.

Interesting enough, however, Karr says that today, the emphasis isn’t as much on the robot arm per se as it is on the process. The arm is a given; what the arm can actually do is what matters most. So the technical developments in this area tend to be focused on improving the process: painting robots are designed around the dictates of the process. (Yes, this may seem obvious today, but remember that sometimes the apparent glitz of the technology blinds one from seeing the obvious.)

From a macro sense, one of the goals in automotive paint facilities—one that is undoubtedly more critical today than ever before—relates to what Karr calls “economies of application.” In other words, there is a focus on putting the paint where it is needed: on the vehicle. Not only does the paint cost money, but it is also expensive to deal with the waste that results when the paint doesn’t go where it is supposed to. The process objective is to improve transfer efficiency. One of the ways this is being realized is through the utilization of rotary bell sprayers that operate at comparatively high rates (40,000 rpm and higher) and provide efficient application of the paint material.

Charged Up. One trend that has been gaining momentum over the last several years is the use of water-borne paint. Karr notes that there is a particular difficulty in the switch from solvent-based to water-based, which is that of charging the paint for purposes of electrostatic application. Water is, after all, highly conductive. An apparent problem is that the electrical charge can go up into the system (following the stream of paint back to its source) or that the charge will be dissipated in the fluid. Working with its partner Sames Corp., Fanuc Robotics is offering what’s called the “AquaBell,” which is a direct-charge paint applicator for electrostatic application of water-borne paint.

The unit has two main components. The rotary bell head and a paint gun voltage block system (called “AccuStat”). The paint is actually contained in a reservoir within the body of the applicator. Because it is contained and charged, there isn’t the problem with the charge going anywhere other than where it needs to be. There is also a benefit to this setup from the standpoint of material conservation. The amount of paint material is loaded into the canister based on the specific requirements of the task to be performed. What happens is that the robot positions the AquaBell at a docking station. The gun is cleaned, and then the required amount of paint is put into the reservoir. The robot then proceeds with the painting operation. In the mean time, the control system determines what color will be required next so that it is prepared for when the robot returns with the gun.

On Track. According to Karr, there are two different approaches that are typically used in automotive paint shops: stop stations and line tracking. In European automotive assembly plants, there apparently is a combination of the two: when it comes to painting cut-ins (e.g., inside doors, the decklid, hood), the moving line stops. Karr says that while a paint shop is typically automated, performing cut-in painting is where there are still manual operations to be found. That’s because the closure panels need to be opened and closed. So to automate this and to have a moving line it is necessary to have a device (e.g., a three-axis opening robot) that opens the door and a painting robot that “knows” where the vehicle is in space as it moves along and then paints it. Once the painting is complete, then the other device shuts the closure panel. When the vehicle is stopped, this is pretty straightforward. But Karr says that with demands for high hourly throughput (e.g., 50 jobs per hour), the tracking line is the most efficient, especially when the tremendous cost of paint booths are taken into account. (E.g., to get the same type of throughput as tracking with stop stations, it would be necessary to have multiple stations. This means multiple robots, air handling systems, etc.)

Another area where robots are finding application is in repair areas. In this situation, painted bodies are inspected with a vision system. If a flaw is detected, coordinate information defining its location is sent to the robot control. The robot then goes to that position and sands the area in question. The vehicle is then sent to the repair area. Karr says that this system is meant to minimize the number of flaws that might pass undetected when the job is done manually.

And with the continued popularity of pickup trucks, there is another area that robots are finding use in finishing applications: spraying bed liner material into the pickup box.—GSV