۱- Introduction

۲- Literature review

۳- The operative environment

۴- The underlying learning-forgetting processes

۵- The minimization cost model

۶- Design of experiment

۷- Results and discussion

۸- Conclusions and further research agenda

References

Abstract

The training of suppliers and inbound quality inspectors is a common strategy to increase the quality performance of the supply chain but, under budget constraints, these actors compete for a limited amount of training hours. The proposed model aims to allocate the available training hours so as to minimise a total quality cost function composed of prevention, appraisal, and failure costs; it also sets the inspection rates defining the inspection policies assigned to suppliers. The relationship between decision variables and costs is expressed through organisational and individual learning-forgetting curves, for suppliers and quality inspectors respectively, and the effect of the training hours on quality improvement is measured in terms of failure rates. To the best of our knowledge, a total quality cost model with such decision variables is new in the related literature, as it is a model including both organisational and individual learning-forgetting phenomena. A nonlinear optimisation approach was adopted to solve this complex problem. The experimental section includes a decision trees analysis of simplified scenarios in order to interpret the model functioning, as well as a complex numerical example to extrapolate managerial insights.

Introduction

The most recently released ISO 9001:2015 enforced the section dedicated to the control of externally provided processes, products and services (clause 8.4), with more rigorous requirements for managing suppliers than in the previous ISO 9001:2008. A step-by-step supplier management approach comprises supplier development in order to improve continuously its capability and performance (Wagner, 2006, 2010), which relies on a multitude of manageable activities (Bai & Sarkis, 2011) including training. For a review on supplier development, see Glock, Grosse, and Ries (2017). Quality improvement in products and processes, adaptation to quality standards or reengineering of new components are common examples of goals requiring training activities for suppliers, with the active involvement of the buyer’s management. There are multi-echelon supply chains with suppliers all over the world, often operating under different quality standards and thus requiring periodic monitoring and training. Many firms plan training activities for suppliers as a strategy to improve the suppliers’ performance, to such an extent that several consulting companies provide training on behalf of third parties. This type of supplier development is direct, whereas in indirect approaches the management plans actions that influence the environment in which the suppliers operate in order to create an incentive for them to improve their performance by themselves (Wagner, 2010). In accordance with the systematic approach to human resources contained within ISO 9001:2015 (e.g. clauses 4.1.2 and 7.1.2), training activities should also be planned for internal employees, with a focus on the quality inspectors operating within inbound inspection sites. After receipt of the items, quality inspectors visually inspect and/or operate different types of equipment, e.g. coordinate-measuring machines, voltmeters, hardness testing tools and so on. These inspection processes require specific skills which inspectors also acquire by training. However, training suppliers and quality inspectors is costly because it involves trainers, especially when long business trips are needed to reach the suppliers. Moreover, trainers are specialized consultants who charge high prices.