An MIP Approach to the U-line Balancing Problem With Proportional Worker Throughput

One of the major challenges faced by manufacturing companies is to remain competitive in dynamic environments, where fluctuations in customer demand and production rates require systems capable of adapting in a practical and economical way. A U-shaped production cell is considered one of the most flexible designs for adapting the workforce level to varying conditions. However, re-balancing efforts are time consuming and often require a new work allocation and line design. In this paper, a two-stage MIP model to determine the best cell design under varying workforce levels is proposed. The model seeks to maintain proportionality between throughput and the number of workers. Computational experiments considering various line configurations (up to 19 stations) and workloads (up to 79 tasks) are performed. The results show the proposed algorithm provides excellent results for all small and medium size problems addressed in this study, as well as for certain configurations of large problems. This approach can be used to generate lookup tables of line designs to help with quick reallocation of worker assignments on the shop floor and with minimal disruption

Mixed-integer linear programming approach to U-line balancing with objective of achieving proportional throughput per worker in a dynamic environment

One of the major challenges of manufacturing companies is to remain competitive in a very dynamic environment dictated by fluctuations in production rate and customer demand. These challenges may be attributed to frequent changes in customer expectations, unsteady economic conditions or failure to reach the projected throughput due to inefficiencies in production systems. Survival in such a dynamic environment is contingent on implementing manufacturing systems that are able to adapt to change quickly and economically. The U-Shaped production cell is considered to be one of the most flexible techniques for changing the number of workers in the cell to match cell cycle time to planned cycle time. However, companies currently use a trial-and-error method to develop walk-paths. It is a very iterative and time consuming process that does not always guarantee an optimal solution. Walk-paths need to be performed for all possible number of workers. Fluctuations are adapted to by altering only the number of workers and the worker’s walk-path without changing the number of stations and task allocations. Selecting the best configuration (i.e. optimal number of stations and task allocation) is dependant upon the linearity metric i.e. the measurement of the proportional throughput per worker. Designing the production cell by considering the linearity helps to keep direct labor costs per unit at a minimum for any number of workers employed. This thesis proposes a mixed integer linear model for U-shaped lines that determines the best cell configuration for various number of workers with the objective function of achieving proportional throughput per worker and decreasing the iteration time. The problem originated at Delphi Corporation but has been generalized to be applicable to other Lean systems. The model has been constructed using OPL Studio 3.7

Análisis para la reducción de impacto en seguridad, producción y calidad de la caída de piezas a granel en la malla de líneas auxiliares

El objeto de este Trabajo de Fin de Grado es el Análisis para la reducción de impacto en seguridad, producción y calidad en la caída de piezas granel en Renault España S.A. concretamente en la factoría de carrocería y montaje de Valladolid, en el taller de líneas auxiliares.Departamento de Ciencias de los Materiales e Ingeniería Metalúrgica, Expresión Gráfica en la Ingeniería, Ingeniería Cartográfica, Geodesia y Fotogrametría, Ingeniería Mecánica e Ingeniería de los Procesos de FabricaciónGrado en Ingeniería Mecánic

Using pull and flow systems to improve production stability in real estate development projects

Objectives: The objective of this thesis is to understand the effects of the application of flow-based management systems on medium-size sites (€2-50 million work turnover) made by medium-sized companies (20-200 employees). The purpose of this research is to develop and evaluate a pull scheduling system based on the Last Planner™ System (LPS) to improve production flow stability of real estate developments made by SMEs. The research investigates the application of pull systems from manufacturing industries and those that have not been fully tested in the construction industry. Method: A three-block real estate development project in Brussels was used to ground the context where action research was chosen to initiate the research. Action research follows an ascending spiral that consists of 4 phases described in 1991 by Zuber-Skerrit: 1) planning, 2) acting, 3) observing and 4) reflecting. Once the first circle is initiated, the four activities lead to the next cycle. The reflections phase of circle (n) then leads to the planning phase of circle (n+1). These loops can be derived indefinitely or at least while the research has not met its objectives. Passing from action to critical reflection and back and vice versa in a cyclical process helps build a wider view and a greater understanding. In this context, three action circles were conducted. In this way, the methods, data and interpretation were continuously refined (Dick, 2002). The sequential development of the three blocks made by the same teams eased the process of capturing insights from a phase and building an optimal scheduling process. A lack of works planning, and progress understanding was found to be a major issue when the research started on the ongoing works of the first block. 5S and LPS were tested as a means of improving construction works planning at both the physical and managerial levels. The application of the first three Ss (sort, set, shine) yielded an impact on respect for the work site but were not sufficient to significantly affect the planning. The application of the first two steps of the LPS (master planning, phase planning and make ready) showed improvement but were also limited in their impact in the search for planning reliability. On-site measurements showed that despite a high percentage plan completion (PPC) score in the LPS, analysis of the progress of each apartment showed high volatility from one 23 / 408 week to the next. This volatility came from a lack of visibility in the scheduling system. Although the progress of each week was determined by what was and should have been done based on the LPS, more structure in the scheduling system and more reliability in the forecasts of the works were needed to increase the works stability. Given that takt time has been successfully used in the manufacturing industry to address variability in the demand, and that significant similarities exist between a construction site and a manufacturing line, it was decided to test this as a complement to the LPS in the research action taken on the second block of the building development. Encouraging results were measured, and on-site work in this block was improved. Findings: it was found that the discipline needed to respect the system, the rules and sequence of the work demanded high-level and constant surveillance from site management. In the long run, this could put the whole system at risk. In order to be as efficient, sustainable and duplicable as possible, the scheduling system should be visual, need no interpretation and lead works in a pull flow. Manufacturing has successfully used a simple but efficient system named kanban to achieve level production and ensure a fully pulled system in a variable demand environment while limiting the sources of errors. The third block proved that such a method can work in conjunction with takt time and LPS and improve the works stability by favouring a self-pull system. Impact: following the scheduling system developed by the action circles in Block 2, there has been a reduction of nearly 20% of the lead time measured and a significant increase in quality (the number of snagging works decreased by 95%). Therefore, the stress on the site management team decreased (captured by interviews). The early findings and encouraging results are signs of the importance of the research undertaken. Limitations: The research has been conducted on traditional sites regarding typology, size, techniques, management structure, and contractors, so the findings are addressed to a wide audience across the construction industry. The limitation of the research comes from the domain of the construction observed: real estate in Belgium. Although it is highly probable that the issues detected on site by the research and the mechanisms used to address those issues are duplicable in other domains of the construction industry, there is, at this point of the research, no clear evidence