Reduction in shot blasting time for the vehicle components of CNH prior to the coating application and measurement of residual stress of the blasted surface

Abstract

In the present study, different blasting parameters are varied to examine their roles on the quality of the steel (IS 2062) surfaces. The aim of this project work is to reduce the blasting time from 7 min to achieve SA 2.5 surface by selecting suitable process condition. Experiments are conducted on two blasting machines, namely the Suction-Type Blasting machine at IIT Indore and the Airless Centrifugal Blasting (Wheel Blast) facility of CNH Industrial (Paint Shop -2), Pithampur. The process parameters such as the material, size, and shape of blasting medium (shot/grit); and the blasting time are varied during the blasting operation. Steel shot, steel grit and alumina grit materials are employed in this study. Three different sizes of each material are selected for the blasting operations. Several blasting time durations are chosen to analyze the average surface roughness (Ra) and the quality of the produced surfaces. The surface roughness is measured by using contact type stylus profilometer. It is noticed that for each blasting condition, initially with increasing blasting time up to a certain duration the Ra value and the quality of the surface are increased. After reaching the maximum value the Ra tends to decrease with further increase in time. This is due to the over-blasting effect when the surface asperities are destroyed. Although with further increase in time Ra may increase again but it can never reach to the maximum due to the strain hardening effects. Hence, it is important and beneficial to consider the time when the Ra reaches the maximum.