Reduction of Complex Spatial Warping of Crankshaft Forgings to Ensure Guaranteed Allowance for Root and Connecting Rod Necks

Abstract

In the article, from the total set of dimensions of the crankshaft forgings, geometric accuracy indicators reflecting their complex spatial warping - the diametrical dimensions of the root and connecting rod necks, angular deviations of the connecting rod necks, the curvature of the third root neck, transverse displacement along the die line - are highlighted. To estimate the value of spatial warping according to the selected accuracy indicators during the period of durability of the engravings of die inserts, a batch of crankshaft forgings was measured, followed by probabilistic and statistical analysis in the form of plotting histograms of distributions, normal distribution curves and Shewhart charts. On the basis of the obtained statistical data of value variability, a combination of their values is considered, leading to scrap of crankshaft forging connecting rod necks in the form of defects caused by forging under-allowance or non-straightness after mechanical processing. Under-allowance for root and connecting rod necks occurs at minimum values of diametrical dimensions and maximum values of angular size deviations, non-straightness along the third root neck and transverse displacement along the die line. It was found that the diametrical dimensions of the root necks range up to 4 mm; for the first, second and the third neck it ranges up to 2 mm, for the second neck - up to 4 mm. To prevent under-allowance, the adjustment is carried out along the upper limit of the tolerance. The range of forging lateral displacements along the die line is up to 0.6 mm, that is close to the upper limit of the tolerance. The curvature of the forging found in different mutually perpendicular directions varies. For the first installation of correction operation is up to 1 mm, for the second installation it is up to 1.5 mm, which requires improvements. The most unstable indicator of the connecting-rod neck relative position is the deviation of their angular position, reaching values up to 2 mm of their positive and negative values. A technical solution for the local modification of the engraving profiles of die inserts for hot forging correction, allowing to improve the calibration scheme of the crankshaft forging and enhance stability of the crankshaft forging manufacture by angular deviations of the connecting rod necks, as well as to reduce bending along the third root neck is considered.