By Clare Goldsberry, Associate Editor

Cellular manufacturing has become an excellent way to integrate several functions and pieces of equipment into one area or “cell” that is tended by one operator.

Typically manufacturing cells use a variety of automation products such as high-speed cutting, conveying, palletizing, robotic handling including loading and take-off, robotic welding and assembly, and even vision systems to ensure quality, and the production requirements.

There are several important considerations that must be evaluated before moving into a manufacturing welding cell, including the basic cost of the equipment, the cost of integrating the equipment, and the space – or footprint – that is available for the cell. Many times, deciding whether to set up a manufacturing cell comes down to what a company has in its budget, and how it can get the most benefit for the investment it makes.

Manufacturing cells that use minimal human input are a product of the computer age, and take machine tools to new levels of capabilities. Cells allow companies to be competitive by reducing their overall costs and increasing productivity. While it’s a big investment up front, the payback can be relatively short if the shop does its homework to determine if its jobs are suited to automation.

Peter Carlson, a consultant in welding robotics automation (www.qmisolutions.com.au), said in a report on automated welding cells, that there are four immediate considerations in robot selection: size, reach and envelope shape, speed, and the number of axes on the robot. The number of axes on a robot can determine the robot type, but the determining the number of axes needed depends on the tasks that are to be performed.

“A welding robot has to maneuver a reasonably light welding torch, therefore a 5 kg or 6 kg model could be selected,” Carlson said.

Reach and envelope shapes are more important, and can be determined from manuals on robots. The length of the torch has to be considered as a part of the reach component, and care must be taken to allow for practical torch angles. The work envelope can be extended to any size by using such devices and techniques as inverted mountings, traveling tracks and overhead gantry systems for the robot, Carlson said.

Automation in welding cells is used to minimize handling, reduce human error in positioning, and allow continuous flow of various operations.

Greg Osborn, president of Ohio Valley Automation (www.ohiovalleyautomation.com), an automation integrator, said that the value in welding manufacturing cells depends on the process or type of welding that is being used. Most of the welding cells that Osborn sets up involve projection or spot welding, which is a better candidate for robotics than jobs that require extremely long, continuous welds. Another thing that makes spot welding a ideal for robotics is the number of welds required.

If a shop has worked out the strategy of the job, and has determined that it is the right job to be automated, it will have a better chance of increasing its productivity and improving its quality through automation, Osborn said. Determining whether the job is right for automation, includes consideration of the materials that are to be welded, the type of weld required and the welding technology that is to be used. MIG welding is good for automating because it tends to be quick, clean and uses thinner materials, and the robot provides the penetration and the hold force needed for the job.

The speed at which robots can travel from one place to another is one of the reasons that spot welding is the best type of job for a robotic welding cell.

“The main way to increase production is to reduce the time it takes to get from one weld to another. You can’t speed up the actual welding process – that’s governed by physics – but you can increase your productivity moving from spot-to-spot quickly and accurately using a robot,” Osborn said. “If you have a part with a lot of welds you’ve got the potential for saving time.”

Long, continuous seam welds typically would not be the best candidates for a robotic manufacturing cell, but JLG Industries Inc. (www.JLGIndustries.com) has found a way to automate such welding jobs.

JLG Industries designs, manufactures and markets aerial access equipment such as aerial work platforms, JLG Industries SkyTrak, and Lull and Gradall telehandlers. The company, a subsidiary of Oshkosh Truck Corp., operates nearly 20 welding manufacturing cells at its manufacturing headquarters in McConnellsburg, Pa. For the type of equipment the company manufactures, long seam welds are required, but the company has developed cells that handle the job just fine.

Dave Pasi, manager of manufacturing engineering for JLG Industries, said cycle time and reach analysis are the most important factors he considers when designing a part and looking at the feasibility of cell manufacturing for welding. Cycle time and reach analysis are the critical criteria when JLG Industries asks a cell supplier to provide the equipment. The cycle time has to meet JLG Industries’ production schedule, he said.

“If we decided we have to get a part out every 38 minutes, we tell that to the integrator so they know the number of arms they’ll need,” Pasi said.

“The Reach analysis tells us that we can weld the part and what reach we can achieve, so we don’t leave out the details and we can plan accordingly to get anything that the robot can’t reach. That might involve deciding whether we do it manually or if we have to redesign the part it to make it more robot friendly. We want to know up front what we can reach and our cycle times.”

Pasi said he also has to consider floor space, a specification the company has established. AS a heavy- equipment manufacturer, the company makes weldments for the large chasses and booms for its aerial access equipment. The welds can be as long as 25 feet, and components can weigh as much as 10,000 lbs. Cycle times of 1 hour to 1 hours are common.

Ensuring quality is critical as well. The welding manufacturing cells at JLG Industries include software that permits almost 100 percent touch sensing at the beginning of the weld, and a 100 percent seam tracking system for long seam welds.. JLG Industries also uses torch center point alignment devices to ensure the torch is in correct location, thereby reducing the chance for a poor weld.

“Without this type of software we couldn’t do what we do,” Pasi said.

Positioners are an important part of welding cells. It is the positioner that ensures the component is held in the correct place to allow the robot arm to reach the areas that are to be welded. The positioner saves time as the load and unload time is “in cycle” with the robot.

While all robotic systems will do about the same thing, Osborn said there are two keys that ensure success and produce good parts.

First, parts have to be the same dimensionally each time they are presented to the robot. Secondly, the positioner tooling has to be designed and built well so that the work pieces are held in place in the exact manner each time. With parts that are strictly to tolerance and tooling that holds them exactly in place, good parts are made.

D&S Manufacturing (www.dsmfg.com) installed its first manufacturing cell 15 months ago, but the custom machining and manufacturing company has been welding with robots for nearly five years.

John Barkley, sales engineering manager for D&S Manufacturing, said welding in cells offers options for the post-welding machining operations that his company also does. The company’s welding manufacturing cell consists of a 6-axis ABB robot and a 2-station interchanging manipulator with two servo axis per side for a total of 5 servo axis, with fully coordinated motion between the robot and the manipulator. Barkley said it allows the company to enhance its lean manufacturing strategies.

“We’ve been able to reduce the costs of manual labor and have less material movement with a roller system that slides the welded components over to the machining area,” Barkley said.

However, he added that the key to D&S Manufacturing’s success in using a welding manufacturing cell was learning to achieve balance in the operations.

“Just because you can weld something twice as fast as you used to, doesn’t mean that machining can be done equally fast. It’s a balancing of the whole process – the welding and machining,” Barkley said.

Barkley said that companies that are considering welding cells work with an integrator to achieve good results.

“Choosing the right integrator for the robotic welding cell is a key factor to help you with the robotic welding. It’s important to match the integrator and the type of service they provide with what’s best for the organization,” he said.

Some welding manufacturing cells use vision systems to improve process efficiency and eliminate non value-added labor such as manual inspection for repetitive quality inspections.

Joseph Campbell, chief operating officer of Applied Manufacturing Technologies Inc., a supplier of consulting and engineering services, said his company reviews manufacturer’s parts and applications to determine whether machine vision can improve a process. After the review, Campbell’s company makes its recommendations.

Vision systems can ensure that the torch is in the proper position, that the part orientation is correct, and that the weld is where it needs to be. Ohio Valley Automation’s Osborn said vision systems allow the operator to look at the component, locate where the weld needs to be and alter robot path to match the grove or the weld joint to help with repeatable locating and consistent orientation.

Most of the time the robot is in a consistent position, so the operator moves the part to match the robot. But if this can’t be done, the operator will need to alter the robot to match the piece.

“This is more expensive and not as reliable, and it takes more to maintain it and manage it. The operator needs to be more skilled. Vision systems have their limitations, but they can be used for quality control, not so much for the weld quality as to just check to see if the weld is there. Quality might be better left to the human, but the use of a vision system to make sure that the weld is there or the part has been oriented properly, is good,” said Osborn.

Editor’s note: In our last issue, we looked a automation strategies and how to know if automating a specific welding job is the optimal way to go. Next, we have to determine what types of equipment will go into a cell.

Mike Sharpe, director of engineering for the Materials Joining Group at Fanuc Robotics (www.fanucrobotics.com), said there are several things that need to be considered when deciding to build a manufacturing work cell. Be very clear about the material being welding. Know the type of wire and the size of the wire that is to be used. Know the amperage required for the weld, which is dictated by the size of the weld. Know whether water cooling will be required. Make sure you have chosen the correct torch. “Just selecting a robot doesn’t mean it ends there. You need to have the right process components for what you are going to be welding,” Sharpe said.