Configuration and control of suppliers’ safety buffers in automotive Just-In-Sequence-Production via a dynamic mathematical model

Joachim Reiter

Abstract


Just-In-Sequence (JIS) is a common and efficient supply concept used by automakers (Original Equipment Manufacturer, OEM) with large-volume production and a high variety of sourced modules. On the one hand, the OEM avoids storage capacity costs, but on the other hand, there is the risk to disrupt the production, if only one supplier fails to deliver. The risk increases, when due to the high variety, the module is built not until the final JIS-call is received by the supplier, that means when a car‘s final assembly is started by the OEM.

To proactively reduce the risk, safety buffers might be self dependently build up on the suppliers’ side. Thereby, an additional benefit is generated to the OEM by supporting process stability, and not least, the supplier increases its competence to successfully participate in automotive JIS-Supply-Networks.

The safety buffer should contain completed modules to bridge a gap of about one shift. Planning and control of the buffer must base on forecast data that are just relating to variant and its quantity per date, because there is no reliable information on the OEM’s real production sequence. Given the suppliers’ restricted storage capacity, specific strategies must be elaborated to establish and permanently adapt the buffer. It is of vital importance, which variants in which amount should be presently provided in buffer, and how the criticality of a call can be evaluated in order to decide about its delivery on production or on taking from buffer.

This research provides a mathematical model that aims at a high guaranty of supply subject to the restricted storage capacity. The main issue consists of the decision on changes of the buffer configuration given daily forecast data and the variant distribution of already known calls. The actual backlog of production is a further input parameter, that might restrict the potential to increase the amount of a variant in the buffer, or even might enforce the delivery of calls from buffer.


Keywords


Just-In-Sequence production, buffer stock control, optimization model

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