Article
Push/Pull Parts Production Policy Optimization in the ATO
Environment
Marco Bortolini
1
, Maurizio Faccio
2,
*, Francesco Gabriele Galizia
1
and Mauro Gamberi
1
Citation: Bortolini, M.; Faccio, M.;
Galizia, F.G.; Gamberi, M. Push/Pull
Parts Production Policy Optimization
in the ATO Environment. Appl. Sci.
2021, 11, 6570. https://doi.org/
10.3390/app11146570
Academic Editor: João Carlos de
Oliveira Matias
Received: 22 June 2021
Accepted: 14 July 2021
Published: 16 July 2021
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4.0/).
1
Department of Industrial Engineering, University of Bologna, Viale del Risorgimento, 2, 40136 Bologna, Italy,
marco.bortolini3@unibo.it (M.B.); francesco.galizia3@unibo.it (F.G.G.); mauro.gamberi@unibo.it (M.G.)
2
Department of Management and Engineering, University of Padua, Stradella, San Nicola 3,
36100 Vicenza, Italy
* Correspondence: maurizio.faccio@unipd.it
Abstract:
Within the Assembly to Order (ATO) production strategy, the common approach is to
produce the parts to assemble with a Push-Make to Stock policy.In recent decades, the effects of the
modern Just in Time (JIT) moved to a Pull-Make to Order policy. Assembled parts characterized
by wide variety and huge storage space utilization are critical, and a proper Push/Pull production
policy definition is required. An appropriate balance of storage space utilization and setup times
leads to the optimization of the production policy. The aim of this paper is to define a bi-objective
mathematical optimization model to assign the most suitable production policy to the parts within
the production mix in an ATO industrial context. A numerical simulation and an operative case
study showcases the model application, proving the industrial relevance of this research.
Keywords:
produced parts; assembled parts; assembly to order; push; pull; make to order; make
to stock
1. Introduction
Offering differentiated products is essential for many manufacturing companies.
To reach high levels of efficiency and throughput, they developed product platforms,
implementing product standardization and modularization. These elements offered the
possibility to implement the Assembly to Order (ATO) paradigm, permitting low time
to market and high level of product personalization [
1
–
3
]. In the ATO context, assembly
is performed with a Just in Time (JIT) approach, while the parts manufacturing and
procurement lead times are masked by the stock. The ATO production strategy typically
uses a Pull-Make to Order in the assembly phase and a Push-Make to Stock strategy before
the assembly phase according to forecasts or storage reorder points [
4
]. The pure Make to
Stock (MTS) production strategy aims to preventing stock-out risks, and its main advantage
is the reactivity to fulfil the demands. The performance criteria in MTS production planning
are usually cost-based [
5
]. In fact, MTS policy can have a negative impact on many operative
aspects: the inventory costs, the space utilization, the production capacity utilization, etc.
As consequence, many companies tried to adopt some strategies to mitigate this
problem. A possible strategy is to apply for the parts with these attributes an MTO-Pull
production policy instead of an MTS-Push policy. The result will be a hybrid Push/Pull
policy applied to the internally manufactured parts used in assembly (Figure 1). As demon-
strated by many studies in the field [
6
–
8
], in recent years industrial companies are moving
toward the implementation of hybrid MTO/MTS production strategies. Technological
developments in manufacturing systems increasingly allow companies to manufacture
different products on the same production facility with hybrid approaches [
9
]. For exam-
ple, low-valued, standardized products will often be made to stock, allowing demand to
be satisfied instantly. For high valued products with irregular demand, stocking can be
expensive or even impossible, and these are typically produced to order [10].
Appl. Sci. 2021, 11, 6570. https://doi.org/10.3390/app11146570 https://www.mdpi.com/journal/applsci
