Diesel Engine Parts Supplier Cuts Time to Inspect Components by 50%

A maker of replacement parts for locomotive diesel engines reduced the time needed to inspect aftermarket components for diesel engines by 50% by switching from a coordinate measuring machine (CMM) to laser scanning. The company must make sure that its replacement products match the original equipment components within exacting tolerances. Performing this task on a CMM in the past was very time-consuming because points had to be measured one at a time and it was difficult to collect enough points to fully define complex curvatures. Then the company began using a service bureau to scan the components with a laser, generating point clouds with hundreds of thousands of points in a fraction of the CMM time.  This new method captures the full complexity of the geometry. The point clouds are now converted into a CAD model that is used to produce the aftermarket components. First, articles are inspected by laser scanning and the resulting point cloud is compared to the CAD model that defines the part geometry, using a color-coded scheme to show deviations from the original model. “We are now able to bring new products to market faster and have reduced our reverse engineering costs,” said the company's Engineering Leader.
 

The company offers a complete line of new and remanufactured replacement parts for locomotive diesel engines including turbochargers, power assemblies, blowers and engine gears as well as water and oil pumps. Additionally, the company provides remanufactured engines in 8, 12, and 16 cylinder configurations. Its engines offer a number of benefits to customers including demonstrated productivity, enhanced product life and increased safety. All products are designed and sourced to meet original equipment manufacturer (OEM) specifications-resulting in extended product life and improved performance. Most components can be quoted as new, unit exchange or repair and return to meet specific customer needs. The company's facilities utilize Six Sigma, ISO 9001, Association of American Railroads (AAR) M1003 and National Association of Purchasing Managers (NAPM) processes. Class 1 and other North American railroads choose the company based on quality, delivery, and price.

Previous Inspection methods

In order to meet its customers’ needs for high-performance, low-cost components, the company produces many different parts, often in very low production volumes. The starting point is typically an actual part that has been pulled off an engine. The first step in producing a replacement part is to completely reverse engineer the original. The parts can be as simple as large bolts or as complicated as a fabrication consisting of multiple complex pieces that are welded together. For example, a typical part is an air duct assembly that accepts air from the turbocharger and uses water coils to cool it in order to increase its density before it sends the air into the engine. This part is fabricated from several very complicated steel sections.

Using CMMs to inspect parts in the past was time-consuming because of the need to manually move the machine probe into position for each individual point to be measured. As the geometrical complexity of the company’s parts increased, the number of points needed to fully characterize the geometry skyrocketed. Even though operators spent several weeks generating points one by one, they could never be sure that they hadn’t missed a critical feature. After the points were captured and converted into dimensions, a CAD operator had to manually create a solid model of the part, using the captured points as a skeleton. The entire process took two to three months for a part as complicated as the air duct assembly. “It cost $6,000 to $9,000 to scan each part and took two to three months to get the job completed internally on a CMM machine,” said the Engineering Leader. “As the complexity of parts increased, we also faced concerns about the practicality of characterizing these extremely complicated surfaces using a point-by-point measuring system.”

Switching to laser scanning

The Engineering Leader heard about the emerging technology of laser scanning and felt it was worth investigating. 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. Laser scanners are able to quickly measure large parts while generating far greater numbers of data points than touch probes without the need for templates or fixtures. Laser scanning can replicate the complete geometry of a complex part to a high level of accuracy, often to within 1 thousandth of an inch. The model can also be superimposed upon the original design geometry to determine exactly where they differ. Since there is no probe on a laser scanner that must physically touch the object, the problems of depressing soft objects and measuring small cavities are eliminated. But with a relatively small number of parts that needed scanning every year, it made no sense for the company to buy a laser scanner. The cost would have been high and the company would have faced the challenge of training operators and maintenance staff. They also would have faced the risk that the machine could become obsolete before it had paid for itself.

The Engineering Leader discovered a service bureau operated by GKS Inspection Services, Minneapolis, Minnesota, that offers laser scanning services on a project basis. “We searched the Internet for service bureaus and discovered several that sounded interesting,” he said. “GKS Inspection Services impressed us because they sounded very knowledgeable and we could sense their willingness to work with us and commitment to our success. They offered to do the first one for free so we sent them a very small part as a test case. They provided a very accurate CAD model back in a short period of time. Since then they have scanned about a dozen parts for us, one of the most complicated being an air duct assembly.” The Engineering Leaders shipped the air duct assembly to GKS Inspection Services and the service bureau scanned the parts and generated a point cloud in which each individual point was accurate within 20 microns and the surfaces generated from the point cloud were accurate to at least 0.004 inch, due to the very large size of the duct.  GKS Inspection Services then converted the point cloud to a surface model and used that to create a Unigraphics solid model. “We checked a couple of dimensions on the part on the CMM and found that the CAD model was well within our tolerance requirements,” the Engineering Leader said. “The entire project cost $3000 and took less than a month, both which are under what would have been required to do the job ourselves on a CMM.”

Error maps help correct manufacturing problems

In several other cases, the company needed to confirm that first article parts matched CAD models. They sent the first articles to GKS Inspection Services along with their CAD models. The service bureau scanned the parts and converted the resulting point cloud to a surface model. Then they used Geomagic Qualify software to create a graphical comparison of the manufactured part vs. the CAD model, by displaying differences between the two in a range of colors, indicating the magnitude of the variation from the design intent. “GKS Inspection Services provides us with a color error map that visually compares the CAD database to the point cloud of the first article generated by the laser scanner,” the Engineering Leader said. “The differences between the two models jump out on the color chart. In most cases we can quickly identify the problem and determine its cause.”

“We have been able to significantly reduce the amount of time required to bring complicated aftermarket parts to market by taking advantage of the ability of laser scanning to accurately capture hundreds of thousands of points in far less time than would be required with a CMM,” the Engineering Leader concluded. “Laser scanning also provides more comprehensive diagnostic information that helps us more quickly identify and correct manufacturing problems. It’s a big advantage to us that these services are available economically in a service bureau format without having to invest in equipment or train our people to use it. Laser scanning also equips us to handle increasingly complex parts that are becoming impractical to characterize on a CMM.”