Citation: Maynard, V.; Landry-Blais, A.; Francoeur, D.; Bombardier, N.; Chapdelaine, A.; Picard, M. Direct Resistance Heating of Aluminum Sheets for Rapid Superplastic Forming. Eng. Proc. 2023, 43, 40. https://doi.org/10.3390/ engproc2023043040 Academic Editor: Mario Fafard Published: 26 September 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). Proceeding Paper Direct Resistance Heating of Aluminum Sheets for Rapid Superplastic Forming † Valentin Maynard 1, *, Alexandre Landry-Blais 1 , Dany Francoeur 1 , Nicolas Bombardier 2 , Alain Chapdelaine 3 and Mathieu Picard 1 1 Department of mechanical engineering, Université de Sherbrooke, Sherbrooke, QC J1K 2R1, Canada; alexandre.landry-blais@usherbrooke.ca (A.L.-B.); dany.francoeur@usherbrooke.ca (D.F.); mathieu.picard@usherbrooke.ca (M.P.) 2 Verbom, 3820 Bd Industriel, Sherbrooke, QC J1L 2V1, Canada; nicolas.bombardier@verbom.com 3 AluQuébec, Montreal, QC H3A 1K2, Canada; alain.chapdelaine@aluquebec.com * Correspondence: mayv0601@usherbrooke.ca † Presented at the 15th International Aluminium Conference, Québec, QC, Canada, 11–13 October 2023. Abstract: Superplastic aluminum forming is a promising manufacturing process for the transportation industry because it allows for the manufacturing of complex body parts from a single sheet of aluminum, reducing the number of pieces and the weight of vehicles. However, the process is still limited, among other things, by the low heating rate of the sheets. Indeed, for the 5000 series aluminum alloy, a temperature between 450 and 550 ◦ C must be reached, but the furnaces used are inefficient, leading to heating times in the order of ~3 to 6 min. A test bench has been developed to evaluate direct resistance heating as a solution. It allows heating 350 × 200 × 1 mm sheets. The uniformity of the sheet’s temperature is an important factor in ensuring good formability and has been evaluated using an infrared camera. Tests show that the sheets can be heated within 20 s using a current of 6200 A, with a standard deviation of about 10 ◦ C over the surface of the sheet. Keywords: Thermoforming; superplastic forming; aluminum; direct resistance heating 1. Introduction The superplastic forming process involves heating a metal sheet to place the material in the superplastic range. Entering the superplastic range allows the material to exhibit high ductility, increasing its elongation at fracture from 15% to over 380% for 5000 series aluminum alloy [1]. This high ductility enables the formation of complex parts, expanding the possibilities for designers and engineers. In a second phase, the sheet is inserted into a press where the application of pressure in the cavity allows the sheet to easily conform to the shape of the mold and, thus, form the part. However, superplastic forming is limited by the deformation rate during the pressure application and the heating rate. Concerning the heating phase, 5000 series aluminum alloy needs to be heated over 500 ◦ C[2]. Indeed, a correct temperature for forming is between 450 and 550 ◦ C. The current process uses steel plates to heat the sheets by convection and radiation leading to heating times between 3 min and 6 min. To reduce processing and part to part time, the objective is to achieve heating time of less than 30 s using the direct resistance heating (DRH) method. Direct resistance heating involves passing an electrical current through the material to be formed, heating it through joule effect. In most cases, copper or aluminum electrodes linked to a generator are placed against the sheet to allow current flow [3,4]. This process is already promising, with studies showing it allows heating steel sheets over 800 ◦ C in about 2 s with good temperature uniformity [5]. It is a crucial point in this process to allow uniform ductility over the entire sheet. Along the width, it mainly depends on the current density uniformity, which changes with the contact uniformity of the electrodes Eng. Proc. 2023, 43, 40. https://doi.org/10.3390/engproc2023043040 https://www.mdpi.com/journal/engproc