What influence does machine processing have on the fatigue characteristics of longitudinal adhesive bonds – especially with lathing? This was the question posed by specialists at the Study and Research Center of the Steinbeis University Berlin at IMA Material Research and Application Technology Ltd in Dresden. Through a number of experimental trials not only were the effects identified, it was possible to make a number of suggestions for improving processing parameters.
Elementary longitudinal press-fit joints are a simple and economical production option for joining shaft to collar connections. They have found many uses in many different sectors of mechanical engineering. Using adhesive as a lubricant when making connections makes it possible to transfer tremendous power and momentum.
To produce such bonded join connection it makes sense from a technological point of view to machine cut the form as a complete part. Of course this is only possible if machining does not damage the point of adhesion. This is especially true for applications involving dynamic loads. For manufacturing, machine cutting a hardened adhesive bond is a new technological variation in processing complete parts. The advantages lie in superior manufacturing and product quality, more flexible construction design and more profitable production.
To generate a base of primary data for machining trials, researchers at the Study and Research Center of the Steinbeis University Berlin in Dresden developed a test and diagnosis strategy. Different production parameters and differing shaft and collar contours were examined, identifying the effect they have on the number of cycles to fracture that can be endured. Just one of the findings of the experimental trials was that for all contours, excess length has an overriding effect on the strength of the bond.
The effect of processing is not significant. The contour processing of the shaft, which adhered to design suggestions made in DIN 7190, shifts the point of failure from the bond to the shaft material. This is because of cross-sectional weakening. For this bond geometry the S-N curve of the smooth, unbonded material sample applies. When finishing the shaft contour it was found that the process parameters did have some effect, but this was on the strength of the shaft rather than the strength of the bond.
So the technological parameters selected (cutting speed vc, feed f) obviously seem to have no detrimental effect on the adhesive bond, either under the defined quality restrictions (required surface roughness) or with respect to productivity and costs when the cutting edge is sharpened for processing. Machining complete sample parts had no effect on the fatigue life of the product, but product quality – such as improved concentric running characteristics – can be improved by machining complete parts.
Prof. Dr.-Ing. Ulrich Günther
Steinbeis-Transfer-Institut Production and Engineering (Berlin/Dresden)
Prof. Dr.-Ing. Wilhelm Hanel
Study and Research Center of the Steinbeis University Berlin at IMA Material Research and Application Technology Ltd (Dresden)