50 Int. J. Operational Research, Vol. 39, No. 1, 2020 Managing unreliability in automotive supply networks – an extension of the joint economic lot size model Tim Gruchmann* Centre for Sustainable Corporate Leadership, Witten/Herdecke University, Alfred-Herrhausen-Straße 50, 58448 Witten, Germany Email: tim.gruchmann@uni-wh.de *Corresponding author Marcus Brandenburg Flensburg University of Applied Sciences, Kanzleistraße 91-93, 24943 Flensburg, Germany Email: marcus.brandenburg@hs-flensburg.de and Chair of Supply Chain Management, University of Kassel, Kleine Rosenstraße 1-3, 34117 Kassel, Germany Abstract: Within assembly network supply chains, supply disruptions can occur on every supplier-buyer link. Managing this network unreliability can help to reduce schedule instability and increases the overall efficiency of the supply chain accordingly. In this line, a stylised assembly network supply chain model is proposed with two suppliers and a single buyer using the joint economic lot sizing approach. This supply network can be disrupted by a shortage occurring at one of the two suppliers due to random machine breakdowns, which consequently creates dependent requirements variations affecting both the buyer and the entire network. First, the basic joint economic lot sizing model is extended by the said schedule instability. Second, a solution approach is presented concerning the determination of optimal lot sizes, the investment into the reliability of the supply network as well as the determination of safety stocks. Furthermore, the sensitivity of relevant model parameters is investigated by means of a numerical example. Managerial implications are accordingly derived focusing on the reliability of the supply network members and internal incentive structures. Keywords: schedule instability; automotive supply networks; joint economic lot sizing; supply unreliability; safety stocks. Reference to this paper should be made as follows: Gruchmann, T. and Brandenburg, M. (2020) ‘Managing unreliability in automotive supply networks – an extension of the joint economic lot size model’, Int. J. Operational Research, Vol. 39, No. 1, pp.50–68. Copyright © 2020 Inderscience Enterprises Ltd.