GM's iron finishing automation: GM's Defiance casting plant saw what aluminum casting facilities were doing in their automatic finishing departments and applied it to iron.
Finishing departments in metalcasting facilities often are the most labor-heavy portions of an operation. It was no different at General Motors (GM) Powertrain Defiance Castings, Defiance, Ohio, where the finishing department for its green sand molding line consistently notched the most work-related injuries in the plant.
But safety wasn't the only issue. The finishing department was a manual ending to an otherwise automated molding operation. When the GM Defiance management team used value-stream mapping to figure out how to improve its casting operation, the finishing department was identified as an ideal candidate for a redesign.
"We have to do everything we can to be the casting supplier to the world," said Brian Rees, manufacturing general supervisor. "We wanted to be more competitive, improve safety, reduce cost and improve quality."
To do this, automating the finishing line was a no-brainer.
Except, automation wasn't so simple. GM Defiance casts blocks and heads in excess of 200 lbs. on its Plant 1 green sand molding line. In order to automate the high-volume finishing department, robots would be needed for metal removal. But a robotic finishing cell for iron castings had never been installed in North America. GM Defiance also wanted the robotic system to be used for several different parts, rather than be a dedicated line. The no-brainer turned into a brain teaser.
GM Defiance produces seven iron engine blocks and four cylinder heads in its Plant 1 facility, which operates in three shifts. Both its Plant 1 and Plant 2 ship more than 250,000 tons of castings a year to assembly plants in Michigan, New York, Ohio, Canada and Mexico. Although it is a captive metalcasting facility, GM Defiance must still prove its competitiveness against other engine makers. Redesigning the finishing line helped strengthen its case.
Prior to the new line, pneumatic air hammers and chisels were used to degate and deburr the castings. The finishing department historically reported that plant's worst safety performance as the source of eye injuries, strains and sprains. Exposure to dust, noise and vibrating tools were safety concerns, as well. Additionally, because it was so manual, consistency between one casting and the next was difficult to maintain.
The finishing department also required a lot of workers. The department had five ceils, each with five people working, three shifts a day. Minimizing labor and increasing productivity would help reduce competition from domestic and global casting suppliers.
GM Defiance had examined using robotics with dedicated lines in the past, but this time around, the firm knew it wanted a system that could be used on a range of parts and be able to adjust seamlessly from one part to the next. And, of course, the robots had to be able to handle castings up to 315 lbs. The automotive casting supplier worked with engineering firm Foundry Solutions and Design (FS&D) to come up with a solution.
"What was unique about the installation was it was the first automated iron block finishing/inspection in North America," said Ralph Perkul, president, FS&D. "A lot of robots are used for material handling, pick and place. But metal removal, such as grinding, was different. Facilities are doing this for aluminum, but not iron."
A few things had changed in robotics in recent years that made GM's robotic finishing possible. Robots with higher payloads had just been entering the market. Fanuc, which supplied the robotic systems to the iron metalcaster, recently developed its own robot that had the capacity to handle the castings GM produces. Advancements in vision systems and lasers, which had been around for years, made the concept more affordable. The cost for applications such as dimensional tolerance checks via lasers were greatly reduced from even four years ago.
The largest hurdle for GM Defiance, however, was to create a universal robotic system that could handle the company's lines of V6 and V8 blocks with the possibility of diesel blocks in the future.
"The system was well-researched by GM," Perkul said. "The team visited a great number of aluminum facilities with robotic metal removal. They became convinced that the technology was there and could be applied to iron."
It's a Grind
For several months, GM's management team worked on fashioning an automation concept for the finishing department. With input from Fanuc, it came up with a system that incorporated robotic lasers to identify each casting as it entered a finishing cell, alerting the robotic system to handle it as programmed for that particular part. Fanuc installed a prototype cell at GM prior to a permanent installation, and for 10 months, the company tested the cell and equipment on its castings before landing on a final concept.
The final design consisted of four robotic cells with five robots in each cell. It typically takes one casting six minutes to run through the finishing cell. Each cell can process 70 castings in an hour, with up to eight castings being processed in a cell at a time.
The cell begins with a conveyor system that feeds the finishing department from the molding line. The conveyor works on three tiers, each feeding different parts of the department. The bottom tier feeds each robotic finishing cell. After the castings are finished, they are sent via a middle conveyor belt to be packaged and shipped. The top conveyor belt returns castings the robots have deemed as scrap to a salvage area, where workers determine if they can be salvaged or should be remelted.
When a casting enters one of the finishing cells, the first robot identifies the casting and serializes it for traceability. Because the casting is identified as soon as it enters the cell, the necessary changes in robotic movement are made automatically in order to successfully put the casting through the cell.
A second robot places the casting on a stand for a third robot, which performs two- and three-dimensional inspection on the part. The robots intuitively adjust their movements to how a casting is placed on the stand. Two-dimensional inspection is made using a digital camera that checks the area and shape of the part. A laser scans the three-dimensional features of the part to create a digital image. If a part does not meet the criteria, it is rerouted to the salvage station.
After laser inspection, the casting is transferred into the grinding area of the cell, where the fourth and fifth robot perform flash removal and grinding.
Once the castings are laser inspected and robotically degated and deburred, eight workers per shift are on hand to perform a final visual inspection of the parts. Quality personnel will verify at least one casting per hour to check the performance of the finishing department and to make sure all the parameters are in order.
In April, the facility installed an automatic palletizer, which stacks the appropriate castings on a pallet for shipping, completing the automation project.
Although finalizing the robotic system was a major step toward the completion of the project, a final major hurdle was installing the new equipment without disrupting GM Defiance's day-to-day operations. This meant tearing out the original cells and installing the four new ones during the regularly scheduled, plant-wide two-week summer shutdown.
"We knew we wouldn't have a long time to install, so all the cells were modular," said Jerry Stanton, senior plant engineer. "The entire enclosure of each cell was just four pieces."
The facility didn't have much time for adjustments, either. With the high volume of production pumping through GM Defiance's Plant 1, a roadblock in the finishing department would not be acceptable.
"We didn't have a four-week casting buffer while the company tried to work out the kinks of the system," Rees said. "So the system needed to work well right away."
The complete finishing cells were ordered in January 2006 and production ready by July 2006. Extensive programming went into the setup to make sure the robots didn't mix castings and perform a specific finishing operation meant for another part. GM phased in the cells with V8 blocks, and once that was stable, moved to V6 blocks. Now the finishing department is handling the next generation of V8 and V6 blocks.
Production at GM Defiance has ramped up in recent months, and the new finishing department has been helping the facility keep its pace. Because it is in operation 24 hours a day, workers in each shift are given tasks to complete in order to keep the machines well maintained and cleaned. Should a cell need a repair, the other three cells can continue to process castings.
Since the installation of the automatic metal removal system, injury reports from the finishing department have decreased. Occupational Safety and Health Administration recordable injuries directly related to the new process system have been reduced more than 90% compared to a similar period in 2004-2005. Twenty percent fewer people are working in the department, and the more injury-prone tasks are now completed by robots in protective enclosures. Casting quality has improved as well. The repeatability of the robots has minimized the human factor in the finishing room, and because of the laser inspection, fewer defective castings are being shipped to the customer. Customer returns for items that were automatically inspected from July 2005 to June 2006 came to 96 castings. From July 2006 to June 2007, only five castings were returned. The improvements make GM Defiance more competitive in the global casting supplier market.
"I give them a lot of credit for pioneering this," Perkul said. "They really tried to rise to the challenge."
Shannon Wetzel, Senior Editor
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|Date:||Jan 1, 2008|
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