Employee skill development in manufacturing: consequences of learning and forgetting on production planning and task scheduling

Heuser, Patricia; Letmathe, Peter (Thesis advisor); Vossen, Thomas (Thesis advisor)

Aachen : RWTH Aachen University (2022)
Dissertation / PhD Thesis

Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2022


The pressure on manufacturing companies is increasing with global competition, technical advances in production technology, and increasingly changing individual customer wishes. Product life cycles are decreasing, forcing companies to invest in new product developments, which results in production ramp-ups. Actively and efficiently managing the ramp-up phase of production with its inherent uncertainties may yield a competitive advantage for companies. High demand variation, high prices paid for newly introduced products, and a workforce that needs to get accustomed to the new production processes characterize this phase of low capacity utilization. Especially during the ramp-up phase, managing employees' competence development is of utmost importance. In addition, the digitization and the automation of production are changing the competencies required for production as well as the responsibilities placed on employees. Therefore, the adjusting and the maintaining of the worker's skill portfolios have become crucial factors of success. This dissertation analyzes the impact of human competence management on manufacturing production. In this context publications and methods from the fields of operational research and management science are the main focus. For this purpose, four individual research papers analyze different aspects of competence management in production. These research articles, which form the second part of the dissertation, are guided by a first introductory part. This introduction connects the articles in an overarching research model and question to provide a larger picture. In this vein, the drivers motivating this dissertation as well as the methods utilized to address the research questions and the article's key findings, together with their implications and limitations, are described. First, an overview of the extent to which competence management is already covered by the literature is presented in order to guide researchers and practitioners alike. Therefore, structured literature reviews are conducted in Research Paper 1 and Research Paper 2. The publications are clustered to make the state of research in the different areas easily accessible. One stream of literature focuses on empirical results and their manifestation in mathematical models as well as learning and forgetting curves. The underlying dynamics further impact different stages of organizational planning and therefore form the base for different optimization and planning models. Human competencies and their target-oriented development influence strategic as well as operational shop floor decisions. For organizational decisions, the influence of competencies accompanies production decisions from creating new knowledge and product designs to planning the production plant, timing implementing changes, and selecting as well as training the workforce. On an operational level, individual production environments are affected differently by aspects of competence management. Therefore, for the areas of assembly line balancing, cellular manufacturing, economic order quantity, machine scheduling, and worker assignment, the differences are elaborated together with gaps in the existing research. Motivated by the variety of literature on machine scheduling, which presents several different learning effects while mostly neglecting forgetting effects and training approaches, the results from this field are analyzed more closely. On the one hand, a survey article Research Paper 2 is presented that moreover introduces a unified notation. On the other hand, a new processing time effect incorporating learning and forgetting into single machine scheduling is introduced in Research Paper 3. This effect addresses a research gap identified in the second article by including an interruption-based forgetting effect in processing times. This effect further accounts for mass customization developments and shared production lines by assessing different product categories. Hereby, the paper aims to address a second gap in research that concerns ramp-up management for small batch production. Solution methods addressing two relevant objective functions, the makespan and the total completion time, allow the inclusion of forgetting effects in scheduling problems. A computational study benchmarks the results of a combination of different heuristics against the standard solution method utilized when learning effects are considered. The results emphasize the importance of including forgetting effects in production planning. Different studies highlight the importance of training measures: for example, to gain a flexible workforce, to react to demand volatility and altering customer wishes, or to reduce employees' boredom and to counter forgetting. Since training, besides learning and forgetting, is a main driver of employee development, Research Paper 4 sheds light on the interplay of these concepts. Precisely, the effect of budgeting the available training measures on employee's skill development is analyzed in a production environment with variable employee capacities, different levels of demand volatility, as well as task and worker heterogeneity. Results indicate that flexible training concepts, characterized by an all-time availability of training measures to employees, foster the skill development of employees. In particular, the total amount of training measures necessary to achieve a comparable level of skills at the end of the planning horizon is higher if training measures are budgeted. In the same manner, the amount of knowledge forgotten increases when budgeting is employed. These negative effects on the workforce's skills are amplified by demand volatility and limited employee capacity. In a nutshell, the dissertation initially provides a holistic overview of competence management in production. It later focuses on machine scheduling by introducing and evaluating a forgetting effect, and it closes by analyzing the mediating effect of training on learning and forgetting effects summarized in employees' skill development.