use of digital checking fixtures and scanning techniques for reverse ...

onto the already created solid primitives from the previoussteps. This newly imported data would serve to act as aguide when transforming the model and to verify thelocations found in the previous steps. These cross sectionsalso would act as a tertiary datum point.Once the fixture was complete and verified using theIGES file, by overlay, the completed assembly of the nondeflectedleaf spring was then added to the fixture assembly.Once oriented, one of the main datum points were alignedand affixed to the fixture model as described in Figure 6.From this point the next set of bolt locations were placed.Using several computerized commands, which allowthe model to be deformed without changing its overalldimensions, the other main datums were then aligned andchecked for interference. Below in Figure 8 shows thespring after it has been formed to meet the primary andsecondary datum points. Once interferences were eliminatedfor the main datum points, the deforming process wasrepeated matching the cross section of the spring to thefixture. The cross section allows for very fine geometricdeflections to be captured.Figure 6Spring Before DeformationSession 3BAfter the desired component is created and verified itcan be compared against its counterpart in a Finite ElementAnalysis (FEA) program in order to determine stress andstrain characteristics. In the case of the leaf spring both thenon-deflected and deflected models were overlapped in FEAand combined with the known loading of the truck. Fromthis information a stress strain curve was generated andmapped along with a stress distribution along the geometry.Once the stresses and strains are known they can be used toin an extremely accurate representation of how the springwill behave can be made in the dynamic simulation.CONCLUSIONIn the case of the spring the overall process of taking theCAD model and creating the fixture took approximately onehour. An additional hour was needed to both modify thescan sections so that they could be overlaid and tomodifying the part for deflection. From start to finish thisre-engineering technique took about two hours time makingthis technique much faster than making doing it manually.Above all this technique allowed the project to be completedwithout the actual spring present and was far more accuratein its results then manually checking.This method can be used for any component which hasto be deformed for analysis as long as there is a preexistingCAD file along with deflected scan data. Using thistechnique parts such as beams, springs, cantilevers orirregular geometry solids can be reverse engineered usingminimal data.Figure 6Spring After Deformation (Primary and Secondary Datums)After this process had been concluded a secondinterference check was run to see if the spring model cameinto contact with the imported IGES file. Following a seriesof minor adjustments, the newly deformed model of the leafspring now lined up with the reference geometry. The finalinterference check, with the sections, found that the springwas within less than one thousand of an inch of deviationfrom the IGES overlay. Given that the scanner being usedallowed for greater inaccuracy than the deviation foundbetween the scan data, the model was deemed an acceptablereproduction. This process was repeated to successfullygenerate the second partially deflected spring.With the deflected spring complete the CAD model wasbrought into the ATOS software for a final verification. Theraw scan data holds many more data points for comparisonthan the sections making the verification in ATOS evenmore reliable than relying on the sections alone. Thesections were used due to data transfer and ease ofpreliminary use however a lot of data is lost in thesectioning process. Therefore it is highly recommended thatthe actual scanned surfaces be used for final modelverification. If an extreme degree of accuracy is not neededfor the component then this step can be neglected.REFERENCES[1] Lombard, M, SolidWorks Surfacing and Complex Shape ModelingBible, Indianapolis, Indiana, Wiely Publishing Inc, 2008.[2] Ingle, K, Reverse Engineering, Washington, DC, McGraw Hill, inc.1994.[3] Optical Measuring Techniques. 2006. ATOS User Manua v6. OrderNumber: D-38106 Braunschweig, Germany.AUTHOR INFORMATIONSean Derrick Masters Student, Western MichiganUniversity, College of Engineering and Applied Science,Kalamazoo, MI, 49007, s4derric@wmich.eduSean studied engineering design and graduated fromWestern Michigan University in Spring 2009. He iscurrently a graduate student studying manufacturingengineering at Western Michigan University specializing inreverse engineering, design for manufacturability andconceptual machine design. After his masters degree, heplans to begin a career in military research anddevelopment.Pittsburgh, PA March 26 - 27, 2010ASEE North Central Sectional Conference3B-4