Chair of Production Management

Variable Takt Time Groups and Workload Equilibrium

IJPR accepts article by Dr. Tobias Mönch, Prof. Dr. Arnd Huchzermeier and Peter Bebersdorf

The International Journal of Production Research (ERIM: S; Impact Factor: 4.577) accepted article by Dr. Tobias Mönch (The Wharton School), Prof. Dr. Arnd Huchzermeier and Peter Bebersdorf (AGCO Fendt) on Variable Takt Time Groups and Workload Equilibrium.

Title: Variable takt time groups and workload equilibrium

Abstract: Natural disasters, pandemics, and political nationalism have increasingly forced companies to orient their operational activities toward more responsive, flexible, and resilient assembly plants. For agile manufacturers, adaptability of the assembly process combined with production facilities located near the customer can ensure short product lead times even when supply chains are disrupted by negative global trends. Yet one downside of the consequent increase in regional production sites assembling a higher share of different models for local markets is that single, fixed takt time assembly lines become overburdened, especially when customisation is unlimited. In this context, variable takt time groups (VTGs) are a major competitive lever. Our contribution is twofold. First, we present the notion of a workload equilibrium. Achieving this balance between overload and underutilisation serves as a preliminary stage of the assembly line sequencing problem, and it significantly reduces the planning effort required. Second, we present a model for minimising (i) the number of VTGs for a given maximum operator drift per unit or (ii) the maximum operator drift per unit for a given number of VTGs. We solve these dynamic problems by developing a heuristic approach: the variable takt time groups algorithm (VTGA). In our analysis of three fundamentally different real-world data sets from German manufacturers—Fendt’s fixed takt time cabin plant in Asbach-Bäumenheim, the Rolls-Royce Power System fixed takt time engine plant in Friedrichshafen, and Fendt’s variable takt time tractor plant in Marktoberdorf—we benchmark the VTGA against existing takt times and offer a proof of concept for variable takt time groups. We find not only that variable takt times result in higher labour efficiency than does a fixed takt time but also that the former’s segmentation level (e.g., work content–based vs. model–based) plays an important role in reducing operator inefficiencies.

Keywords: manufacturing; mixed-model assembly line; variable takt times; variable takt time groups; workload equilibrium