Many of the basic principles of flexible manufacturing used in the auto industry also apply to other products and production processes. “The fundamentals of flexibility hold up whether you’re making cars or eyeglasses,” says Lucci.
Indeed, flexible assembly has been successfully adopted by manufacturers in many other industries, ranging from consumer electronics to medical devices. Both of those industries tend to turn over their designs with new and improved models after a relatively short product life.
Any market where technology is changing quickly, such as cell phones, is ideal for flexible production. As a rule of thumb, products that contain subassemblies that require the same basic parts and processes as other subassemblies, such as electric motors, generally are good candidates for flexible manufacturing. That’s why many solar panel manufacturers are implementing flexible assembly lines as they ramp up production.
To enable flexibility, manufacturers need equipment designed to accept change requests. For instance, modular conveyors are much easier to expand or reconfigure than rotary dial machines or other fixed automation. Other assembly tools, such as robots, linear motors, machine vision and motion controls, make it easier to be flexible today than in the past. “But, there’s still a lot of misunderstanding about what flexibility is and is not,” says Harbour-Felax.
Before implementing flexible assembly lines, manufacturing engineers should carefully consider all the pros and cons. For instance, traditional assembly equipment is limited by attributes such as processes, motions, precision, cycle rates, part size and weight, and component feeding. However, a dedicated machine is typically less expensive than a flexible machine.
There are some overlooked costs associated with flexible equipment. For example, wiring can be extremely expensive; installation costs can run anywhere from $10 to $1,000 per foot, depending on the type of application. On a typical assembly line, that easily translates into thousands of dollars. If a line needs to be reconfigured, that work will need to be redone. That’s one reason why some manufacturers are investing in wireless technology.
Efficiency is another trade-off that needs to be carefully considered. Highly flexible systems may be unable to match the speed of hard tooling. Compared with a dedicated machine, a flexible piece of equipment often has a larger ratio of size vs. throughput. As production volume increase, flexibility decreases. If annual production volume is at least 5 million units, or if the product’s market life is expected to be at least 5 years, manufacturers may be better off with a dedicated machine.
“Slow applications tend to work the best with flexible automation,” says Bob Rice, applications team leader at Automation Tool Co. (Cookeville, TN). “Contrary to popular opinion, manual operations are the ideal form of flexibility. Robots are the biggest flexible tool in the automation world, but they also have limits, such as parts feeding. Operators still do most things better than a robot.”
“Parts feeding is the most challenging thing that limits flexibility, but new technology holds promise,” claims Mark Handelsman, industrial marketing manager at FANUC Robotics America Inc. (Rochester Hills, MI). “Flexible feeding and 3D vision are becoming more prevalent, especially in applications where parts can vary in dimension or have a contour.” Force control is another technology that improves flexibility.
“Hard tooling solutions have their place and will continue,” notes David Huffstetler, market manager at Stäubli Robotics (Duncan, SC). “However, our appetite for quick delivery of new products demands flexibility. Choosing the correct technology is paramount, because of the design decisions that will be made later.
“The key to maximizing a robot arm’s flexibility begins at the design stage,” explains Huffstetler. “Speed, dexterity of envelope and quality of motion performance are often-overlooked parameters when considering which robot to build your cell around. Understanding these items will attribute to an optimized workcell. While there is no doubt that programming flexibility is paramount to success, long-term reliability and capability in the mechanics is what will be important to realize the true benefits of a flexible design.”
Typically, the first stage of flexible assembly is the most flexible. As volume increases and automatic stations are added, a machine often becomes less flexible and requires more time and effort to retool.
Motion control also plays a key role in achieving flexibility. Instead of using pneumatic actuators or cams, servo-driven actuators enable engineers to change motions simply by entering a new value in the control software. However, servomotors are typically more expensive than pneumatic actuators.
Fixtures are also critical to flexible assembly systems. Adjustable fixtures feature one or more sides built on slides so that the length and width of the fixture can be quickly changed. Multipiece, adjustable fixtures are more expensive than off-the-shelf fixtures.
“Product design is critical to flexibility,” Lucci points out. “You need common access points for tooling and common end points for fixtures.” A
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