A Study on the Resolution of Pin-dent Defects in Automotive Door Panels

Abstract

The automotive customers have been down-gauging steel sheets for making door panels to reduce weight of the passenger cars and improve fuel efficiency under “Go Green” initiative. Tata Steel has been extending support in weight reduction initiative of the automakers through supplying thinner gauge interstitial free (IF) steel sheets. It was reported that in some cases, the thinner sheets could not withstand the intricate forming and stretching operation and resulted in pin-dent or press crack defect generation in deep drawn areas of the components. The defect was reported for the first time to TSL by auto customer, and in the sense, it was a unique defect. At times, the defect impacted 20–40% of deep drawn door components and led to a near line stoppage situation in the press shop. Representative samples containing the defects were collected from the site, and detailed investigation was carried out employing metallographic techniques such as scanning electron microscope (SEM) attached with energy-dispersive x-ray analysis (EDX). The investigation revealed non-metallic inclusions (NMI) to be the cause of such defects. A thorough process and data analysis was carried out to identify the sources of such inclusions and arrive at appropriate countermeasures to fix this problem. Subsequently, countermeasures were implemented in the steel manufacturing process, and such pin-dent defects were eliminated bringing much respite to the customer. The paper will highlight the systematic approach in dealing with the problem and successful resolution of the intriguing quality issue.