Influence of Allowance Value on Formation of Surface Roughness During Grinding with Flap Wheels After Shot Peen Forming

Abstract

– In the aircraft industry to obtain the necessary form of long panels and sheaths the shot peen forming is successfully used. Due to impact of shot on the processed surface, the specific microgeometry is formed, the characteristic feature of this microgeometry are the numerous dimples of shot with different diameters and depths. At the same time, the depth of the dimples significantly exceeds the valleys of the surface microroughnesses formed as a result of the previous treatment. The presence of these dimples leads to an increase in surface roughness. Therefore, after shot peening the mandatory requirement is implementation of surface grinding with flap wheels for partial removal of the shot dimples. During grinding with flap wheels, depending on the value of allowance for grinding on the treated surface, a new microrelief is formed in the form of a combination of the traces of abrasive grains of flap wheels during grinding and the remains of the dimples from shot peen forming. Since the dimples have a spherical shape with a much larger radius of curvature than their depth, they have a specific effect on the degree of coverage of dimples, roughness and removal of material of treated surface. The paper presents an analytical description about the change process of the area covered with current dimples and roughness during grinding with flap wheels around the surface pre-treated with shot peening depending on the set value of allowance. Based on the results of the research, mathematical models were built to determine the current area of coverage with dimples, the average value of the depth and degree of coverage of the remaining dimples, the amount of material removed from the treated surface and roughness during grinding with flap wheels, and a numerical method for determining the allowance for obtaining the permissible degree of coverage and the required values of roughness.