FERRARI RACING TRANSMISSION REVERSE ENGINEERED WITH 3D LASER SCANNING

Many types of products are moving to more and more complex designs in order to improve their appearance and functionality in an increasingly competitive global economy. The challenge for manufacturing is to produce these complicated three-dimensional designs to often very demanding levels of accuracy required while keeping costs at a reasonable level. A consulting design firm is helping to meet this challenge by combining the technologies of laser scanning and lost foam casting. Laser scanning is used to quickly re-engineer complex three-dimensional shapes by creating 3D CAD models from physical components. Lost foam casting is used to cast the complex shapes to a high level of accuracy without the need for foundry tooling. Machined features are often included to further add value to the casting. This article will provide several examples of production parts produced by this method in very low quantities at an economical cost.

The consulting design firm was contracted to reconstruct a transmission case which is a functioning part needed to reconstruct a very rare antique automobile. This part has complex three-dimensional shapes that must be held to high levels of accuracy yet computer aided design geometry did not exist for either part. In each case, the consulting design firm was asked to produce very small quantities while meeting tight quality and delivery requirements.

In the past, the company would have used a touch-probe digitizing arm to reverse-engineer the component. A technician would have moved the arm around the component and measured the position of individual points. It would have taken perhaps 70 hours to capture a few thousand points. Then a designer would import the point cloud into solid modeling software and stitch the points together into a solid model of the component. The problem with this approach is that there wasn’t enough time to capture enough points to completely define a complex surface. This meant that the accuracy of the resulting solid model depended on the interpretation process in which the designer attempted to recreate the geometry of the part using the point cloud as the model. Often points that were needed to determine the precise geometry were missing so the designer was forced to rely upon intuition and in some cases guesswork. The interpretation process typically took about 50 hours for a total of 120 hours to re-engineer the part. The approximate total cost to reverse-engineer the part would have been over $10,000.

More recently, the company has implemented new reverse engineering methods based on the emerging technology of laser scanning. Laser scanning systems work by projecting a line of laser light onto surfaces while cameras continuously triangulate the changing distance and profile of the laser line as it sweeps along, enabling the object to be accurately replicated. The laser probe computer translates the video image of the line into real-time 3D coordinate data that give the operator immediate feedback on areas that might have been missed. Laser scanners are able to quickly measure large parts while generating far greater numbers of data points than probes without the need for templates or fixtures. Since there is no contact tip on a laser scanner that must physically touch the object, the problems of depressing soft objects, measuring small details, and capturing complex free form surfaces are eliminated.

Instead of collecting points one by one, the laser scanner picks up tens of thousands of points every second. This means that reverse engineering of the most complicated parts can often be accomplished in significantly less time with greater accuracy.  Finally, the software provided with the scanner greatly simplifies the process of moving from point cloud to CAD model, making it possible in minimal time to generate a CAD model of the scanned part that faithfully duplicates the original part. Special software can be used to compare original design geometry to the actual physical part, generating an overall graduated color error plot that shows at a glance where and by how much surfaces deviate from the original design. This goes far beyond the dimensional checks that can be performed with touch probes on CMMs.

Company managers felt that the laser scanning process had great potential but felt that it would be premature to make the investment in equipment and personnel that would be required. Instead they worked with Laser Design, Inc. through its Engineering Services Bureau, GKS Inspection Services Inc. (Minneapolis / Detroit), which provides laser scanning services along with consultative engineering services for both Reverse Engineering and Inspection applications. The consulting design firm’s engineers sent the parts to Laser Design Inc. / GKS Inspection Services Division (LDI/GKS). In less than a week, GKS provided solid models of the component that matched the original physical part to a much higher level of accuracy than could have been achieved with touch—probe digitizing because laser scanning captures millions of points, enough to fully define the surface of the parts. The cost of reverse engineering to a solid CAD model via laser scanning was about 40% less and more than two times faster than the previous method of using a touch-probe arm.

With the geometry of the part fully defined, the company was able to proceed with the lost foam casting process. They used the solid model provided by LDI/GKS to produce a foam pattern and gating system. The foam pattern was then coated with refractory and dried under controlled conditions. The dried, coated cluster is invested in a foundry flask with loose, unbonded sand that is vibrated to provide tight compaction. The molten metal is poured onto the top of the gating system, which directs the metal throughout the cluster and replaces the foam gating and patterns. The remaining operations such as shakeout, cut-off, grinding, heat treat, etc. are straightforward and similar to other casting processes.