A conveyor belt swiftly carries a never-ending line of soda bottles to their fate. Those with secure caps are the chosen ones and will eventually be plucked from the shelves by thirsty consumers. Those whose lids aren't quite tight, a bit askew or missing entirely are rejected.
So what do mis-capped bottles of Pepsi or Coke have to do with roll forming anyway? It's all in the inspection process. Dry-roasted peanuts, windshield wipers and roll formed parts all need to be inspected before they end up as a finished consumer product.
In 1991, Metform International Ltd., Mississauga, Ontario, was approached by Camco Inc., Montreal, a division of General Electric, with a drawing of a tub frame for a dishwasher. The company asked Metform to deliver it the means to produce the part. The roll forming line would need various fabrication functions and would have to incorporate an inspection system to meet the company's stringent quality control requirements. It had to ensure that every part leaving the facility was free from defect.
The task at hand was a welcomed challenge. "It was a new idea to us at the time because I don't think that anyone had used vision inspection in a roll form system operation," says John Gibbons, vice president of engineering at Metform.
"We were required to do a full inspection of all parts coming through the manufacturing process, which was roll forming, assembly and weld," says Gibbons. "Initially we start with coil and feed it through a press system, which would punch a series of holes and notches in the part. After punching, the parts would come into a runout area, which was the primary inspection or vision area."
Here, in a brief pause of the production process, the part is subjected to a photoelectric inspection that checks for the presence or absence of desired holes and notches. The photoelectric system uses a light beam to essentially take a rough picture of the item being inspected, and in order to generate a significant amount of definition, the conveyor is backlit. If holes are missing or not punched through entirely--punching's equivalent to a dangling chad--a light-up display board indicates the faulty location.
After the part passes the first inspection stage, it is indexed into a loop and then pulled into the roll former where it's formed into a cross-sectional shape. From there it's sent into a flying cutoff that separates the parts for bending. Once through the tangent bender, hinges and a bracket are applied on a welding machine. And once again, the part must be inspected. Only at this final location, seven cameras snap a shot of the tub frame.
"Each camera effectively takes a picture, like a digital camera, of the part and then the picture is compared with an ideal pixel image of the component," says Gibbons. "Again, we have a display board, but this time it has written script that is illuminated in the event of a problem, which would indicate if the legs are of the wrong length or in the wrong position." The photo inspection process can indicate a variety of deficiencies, including dimensional irregularities or incorrect welded-on part location.
Metform also included a sorting function at the end of the production line. The part can be tracked to a good-position storage rail, an acceptable-with-modification storage rail or to a rejection area.
Fast forward to the present
Fifteen years later, Metform's line is still in place and still deeming parts as good, reworkable or rejected. But inspection technology has evolved. Everything is shrinking in size, becoming more powerful and all at an affordable price.
Banner Engineering Co., Minneapolis, makes the case for inspection technology, as well. Banner produces vision sensors based on the same type of technology that Metform delivered for the final inspection stage in the Camco line. The company's vision sensors, however, sometimes referred to as smart cameras, are about the size of one's palm and therefore, can fit into virtually any location on a machine.
"Anything you can take a picture of can be inspected with the vision sensors," explains Jeff Schmitz, Banner's business manager for vision sensors. "The vision sensors cover an area and take a picture rather than just a single photoelectric point in space. The primary customers are those who want to error proof the processes and do 100-percent inspections." If needed, Banner can supply a company with photoelectric devices, but its vision sensors, which used to cost several thousands of dollars, are becoming more accessible to companies that previously couldn't afford such a substantial investment.
The inspection solutions are also ideal for companies that already have roll forming lines in place. As opposed to the service that Metform offers in engineering the entire line from the ground up, vision systems included, Banner sells its devices individually.
Since Banner doesn't design the line as a whole, it has integrators that work with customers in order to get the most from its sensors. "Banner offers a sensing component that is easy to use and we have classes to teach the user how to install it and use it," says Schmitz. "They know the problem that they are trying to solve and now they know how to apply the tool to solve that problem."
The eyes don't have it
Vision sensors and vision systems are an effective substitution to previously used inspection processes. Instead of removing every say, 10th or 100th part, placing it in a jig or fixture and manually measuring for accuracy, every part traveling through a line can be checked for quality. Past techniques that didn't check every piece could result in a series of defective parts due to broken tooling that could have been caught at nearly the moment of disrepair if vision sensors or a vision system had been in place.
Typical roll forming lines benefit from vision inspection technology just as well as those incorporating additional fabrication. Vision sensors can be equipped onto a line to inspect a material's surface for dents and gouges and can look for notches and holes on the end. The implementation could cancel out the need for precise fixturing normally used with a rack photoelectric. When inspecting corrugated sheet--each run often characterized with different peaks and valleys--changing the setup of the photoelectrics is eliminated. The vision sensor can essentially be taught to differentiate the varying specifications when lines change.
Vision sensors also eliminate human error. "Humans are very intelligent with their vision, but they're not very repeatable," says Schmitz. "A University of Michigan study was done with ping pong balls asking college students to pick black ping pong balls off the line amongst white ones. They were able to catch about 85 percent of the black ones, but 15 percent of the time they were thinking about last night's All-Star game or something more human. They weren't able to act as a repeatable machine."
So whether companies need Metform's aid at the drawing board or whether they look to Banner to add vision into a pre-existing setup, they have choices when integrating inspection into a production facility. It's not so difficult to see that less scrapped parts or material and greater customer satisfaction equal success and longevity. MM
By Abbe Miller, from the August 2006 issue of Modern Metals.