Quality Magazine

Case Studies: Lasers Keep Off-Road Seats on Spec

January 1, 2003
The use of laser scanning is helping to maintain the accuracy of foam seats used in personal off-road vehicles, making it possible to reverse engineer the delicate components with a high degree of precision.

Northland Machine Inc. (NMI, Grand Rapids, MN) builds molds used to produce seats for all-terrain vehicles, snowmobiles and other personal off-road vehicles. The company found that it was difficult to accurately measure foam seats using contact measurement tools such as coordinate measuring machines (CMMs) or height gages because the probe depresses the foam and it takes too long to collect enough points to define complex contours.

NMI has overcome this problem by using laser-scanning technology to collect the millions of points needed to fully define the surface contours. Because the company requires laser scanning only occasionally, it has avoided the expense of purchasing a machine and training operators by using a service bureau operated by Laser Design Inc. (Minneapolis, MN). Laser Design scans the seats and delivers a surface model that is ready to create a toolpath to machine the mold.

“The service bureau approach works much better for us because we can pass the costs of the laser scanning service along to our customer while avoiding the overhead of keeping another machine in our shop that we would have a difficult time keeping busy,” says Dan Smith, project manager for Northland Machine.

Northland Machine is a contract manufacturing company that specializes in turning its customers’ ideas into parts, prototypes and full production tooling made of steel and aluminum casting and billets. The company produces vacuum and pressure forms, flexible and rigid foam molds, rotational molds, secondary jigs and fixtures, patterns, models, drape and die models. Northland Machine has developed a special niche in producing cast aluminum molds used to produce foam buns that comprise the most critical part of a seat of a snowmobile or all terrain vehicle (ATV). These parts normally have complex contours on their top surface and complicated flat patterns on the bottom side where the bun attaches to the seat base. The company builds these molds by machining patterns on a computerized numerical control (CNC) mill from polyurethane foam. These patterns are in turn used to form a sand mold to cast the actual mold. In the majority of cases, the company receives a CAD file from its customer that it uses to produce the toolpath used to machine the pattern. But there are also a considerable number of cases where the customer is unable to provide a CAD file for the bun. In that case, the customer will typically give Northland an existing bun and ask them to duplicate it.

Challenging reverse engineering task

In the past, it was a challenging task to reverse engineer a bun. One approach used by Northland Machine was to lay a grid on a table and use a height gage to obtain a measurement at each point on the grid. With this method the company found that it was nearly impossible to obtain accurate measurements. Another problem was that the number of points that could be collected was usually not enough to accurately define the contours of the seat. CMMs were used, giving it a higher level of accuracy than a height gage. But, because it is a contact measurement method, operators found it hard to it make contact with a foam part while not depressing it. Using the CMM also caused problems while measuring the underside of the bun because the probe often would not fit inside the cavities needed to mount the bun to the seat.

“We recognized that we needed a more accurate way to reverse engineer foam buns,” Smith says. “We looked at a number of different noncontact gaging methods and quickly zeroed in on laser scanning because it seemed to offer everything that we needed. With laser scanning, there’s no need to ever touch the part. Instead, the operator moves the scanner as if he was spraying the part with paint. The laser generates something on the order of a million point measurements per minute, making it possible to generate extremely accurate surface models.” Laser scanning systems work by projecting laser light onto surfaces while cameras continuously triangulate the changing distance and profile of the laser as it sweeps along, enabling the object to be accurately replicated.

Switching to laser scanning

After reading articles and talking to users, Smith felt that laser scanning was perfect for the job but was doubtful that the company could justify the purchase of a machine. Then he heard that Laser Design had created a service bureau specializing in reverse engineering.

Laser Design technicians use the company’s Surveyor 3D scanning system to scan parts at up to 15,000 points per second, creating an accurate, detailed 3-D surface model that can be converted into a computer numerical control (CNC) program. The company specializes in scanning parts that are hard to accurately measure using traditional contact methods, such as plastic and rubber components, electrical discharge machining electrodes, extrusions, molds, dies and castings. The Surveyor systems’ work envelopes range in size from 2 to more than 25 cubic feet and output files can be converted to a CAD format.

Northland Machine first used the service to build a mold for a snow-mobile manufacturer. “We mounted the part to a seat base because the bun itself is so flexible that it has a tendency to bend out of shape just sitting on a table,” says Smith. “Laser Design scanned the parts and sent us back a CD with a Pro/ENGINEER format CAD file. We called up the model and it turned out to be an extremely accurate representation of the part.”

Northland Machine needed to make only a minor touchup to the part model before it began designing the tool around it. For example, because the part is symmetrical, Smith says the model was cut in half and duplicated so that each side was identical.

“The first time we tried it, laser scanning helped us produce a more accurate mold than would have been possible using conventional methods while also saving a considerable amount of time,” Smith says. “As a result, we have incorporated laser scanning as part of our normal business process whenever reverse engineering is required as part of a contract machining job. We have called on Laser Design to produce seats for a number of other snow-mobiles and ATVs, and the results have exceeded our expectations in every case.”

Laser Design Inc.
(952) 884-9648
www.laserdesign.com

Benefits

  • Reverse engineers parts that are too delicate to be measured with contact technology.

  • Parts are scanned and a CAD file is generated.

  • The laser generates on the order of a million point measurements per minute, making it possible to generate extremely accurate surface models.

  • Outsourcing the service meant the company did not need to buy the equipment. Service costs are passed along to the customer.