Godding, Robert 
  
In the body shops, where the stamping parts are assembled, the punctual geometry measurement (e.g. of welding points) 
is state-of-the-art. The installation of various laser-sensors is necessary to check the location of one point at a time. 
However, the number of sensors is limited by the working space of the robots. Furthermore, the consequent reduction of 
working steps and, thus, the number of assembled parts, implied the enlargement of their size (Figure 2). 
Today car side components are front fender panel hood outer door panel 
mostly pressed in one single stroke. 
Therefore, the measurement of 
extensive stamping part areas is 
indispensable. However the large 
dimensions of the formed parts are in 
contradiction to the high resolution 
required to detect the comparatively 
small deviations as well as the short 
time available for the quality control car roof side component 
of each part within the scope of the 
mass production. For the automated 
joining technique applied in body 
shop by robots failure-free and 
accurate stamping parts are an 
essential prerequisite. The stamping 
part accuracy has a key position 
achieving close tolerances in the 
assemblies 
  
  
© IFUM 
Figure 2: Visible stamping parts of a car (large-sized) 
However, sheet metal stamping of components becoming more and more complex is characterized by several structural 
stamping defects like necking, cracks and wrinkles as well as geometrical deviations due to springback /1-5/ (Figure 3 
and 4). Avoiding rejects requires quality control throughout the process chain. Strain analysis is only useful during the 
try-out of new tools or after production process parameters have been modified (e.g. the lubrication). Springback should 
be measured during the production process. 
    
    
wrinkles in ES 
the wall 
    
  
    
spring back 
bulges 
scratches / 
surface- 
defects 
  
puckers 
Figure 3: Structural stamping defects Figure 4: Shape-deviations of formed parts 
2 SPINGBACK ANALYSIS 
Sheet metal forming processes involve a combination of elastic-plastic bending and stretching deformation of the 
formed part. These deformations can lead to large amounts of springback upon unloading (e.g. removal of the punch 
and lifting of the blankholder) due to the redistribution of residual stresses. 
The legal demand to reduce the fuel consumption of cars have forced the automotive industry to realize car lightweight 
concepts using new sheet materials. Nevertheless especially the application of modern high strength steels (HSS) with 
reduced sheet thickness and aluminum alloys have enlarged the difficulties to obtain close tolerances because of part 
shape deviations due to springback. The difficulties are still increasing with the automation in production and 
assembling since springback causes assembly difficulties with adjacent parts. 
Springback is influenced by a variety of factors, e.g. mechanical properties of the sheet material, frictional conditions 
(e.g. sheet and tool topography, lubrication), tool geometry (e.g. die radius, die clearance) as well as process parameters 
(e.g. blankholder forces) /6-8/. Avoiding springback presupposes homogeneous stress and strain distributions during the 
forming process. Therefore, springback can be alleviated by the optimization of material flow between the blank holder 
and the die e.g. by the variation of the tool geometry, the blankholder pressure and lubrication. The prediction of 
  
292 International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B5. Amsterdam 2000. 
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