Gürsel A. Süer

Optimal operator assignment and cell loading in labor-intensive manufacturing cells

In this paper, a two-phase hierarchical methodology is proposed to find the optimal manpower assignment and cell loads simultaneously. Mixed integer and integer programming formulations are proposed (1) to generate alternative operator levels and (2) to achieve the optimal operator and product assignment to the cells. The methodology is illustrated with an example problem drawn from a real manufacturing company. The methodology remains valid for most labor-intensive manufacturing cells. The paper concludes with comments in regard to the implementation of the proposed methodology.

Optimal operator assignment and cell loading when lot-splitting is allowed

This paper is an extension of a previous work where a product could be assigned to only one of its feasible cells. Here, that assumption is relaxed and lot-splitting is allowed. The impact of lot-splitting is also discussed in terms of setup times. The proposed approach has two phases; 1) generating alternative operator levels, and 2) finding the optimal operator and product assignments to the cells. Mathematical models proposed in the previous work are modified to allow for lot-splitting and to consider setup times. The results obtained by using the same example problem are discussed later in the paper.

Effects of different fuzzy operators on fuzzy bi-objective cell loading problem in labor-intensive manufacturing cells

In this study, a fuzzy bi-objective cell loading problem in labor-intensive cellular environments is presented and the effects of different fuzzy operators on the model are investigated. The objective functions of the proposed mathematical model for the problem are minimizing the number of the tardy jobs and the minimizing the total manpower needed. The mathematical model determines the number of cells to open and the cell size for each opened cell and assigns products to cells (cell loading) and also determines the sequence of products in each cell simultaneously. Fuzziness stems from the fuzzy aspiration levels attained to both objective functions. To solve the model, fuzzy mathematical programming approach is used and fuzzy achievement function of the model is defined by six different fuzzy operators which are min, fuzzy and, fuzzy or, minimum bounded sum, add, and product. An example problem is solved to represent the performance of the operators. Experimentation shows that the fuzzy and-operator and product-operator are suitable to reach efficient solutions for the problem on hand.

Designing parallel assembly lines

In this paper, alternative assembly line design strategies for a single product are discussed. The problem occurs when the production volume is substantially high and there are more operators needed than the number of assembly operations. The objective is to determine the number of assembly lines with minimum total manpower. It is allowed to have multiple assembly lines with identical configuration. A 3-phase methodology is proposed; 1) assembly line balancing, 2) determining parallel stations, 3) determining parallel lines. Later, the proposed procedure is illustrated with a numerical example.

Intra-cell manpower transfers and cell loading in labor-intensive manufacturing cells

Labor-intensive manufacturing cells consist of simple machines and equipment that require continuous operator attendance and involvement. Operators are often re-assigned to different machines when a new product is released to the cell. The main reason for this re-assignment is to maximize the output rate of the cell by balancing the flow of products through several machines with varying capacities. In this paper, first a product-sequencing problem with the objective of minimizing the total intra-cell manpower transfers is introduced. A three-phase hierarchical methodology is proposed to solve the problem optimally. Next, manpower transfer matrix values are modified considering the distances traveled among machines. In the second part of the paper, a machine-level-based similarity coefficient that uses the number of machines as a similarity measure is discussed. Later, these coefficients are used during the cell loading process to minimize makespan and also machine and space requirements. Manpower allocation decisions are made along with scheduling decisions that are critical in most labor-intensive manufacturing cells and both approaches are illustrated with an example problem.

Design of dedicated, shared and remainder cells in a probabilistic demand environment

In this paper, a new layered cellular manufacturing system is proposed to form dedicated, shared and remainder cells to deal with the probabilistic demand, and later its performance is compared with the classical cellular manufacturing system. In the layered cellular design, each family may need more than one cell to cover capacity requirements. The proposed approach for layered cellular design involves five stages: (1) product clustering, (2) identifying number of cells and demand coverage probabilities, (3) determining cell types using the proposed heuristic procedure, (4) performing simulation to determine operating conditions and (5) statistical analysis to pick the best design configuration among layered cellular designs. Simulation and statistical analysis are performed to help identify the best design within and among both layered cellular design and classical cellular design. It was observed that as the number of part families increased, the number of machines needed to process the parts decreased first. Then the number of machines started to increase once again as the number of part families continued to increase. Another observation was that the average flow time and total WIP were not always the lowest when additional machines were used by the system. The last and the most important observation was that the layered cellular system provided much better results than the classical cellular system when high demand fluctuation was observed.

Multi-period operator assignment considering skills, learning and forgetting in labour-intensive cells

This paper deals with assigning operators to various operations in a labour-intensive cellular environment. The operator skill levels and skill-based operation times are used as opposed to the classical approach of using standard times. A three-phase approach is developed to tackle the entire problem: (1) finding alternative cell configurations; (2) loading cells and finding crew sizes; (3) assigning operators to operations. A multi-period analysis is performed to study the main issues in this paper. Mathematical models are used in all phases. Two heuristic approaches (Max, MaxMin) are developed for operator assignment in phase III. Both heuristics are compared and their impact on operator learning and forgetting is also investigated. Results show that the proposed approaches in operator assignment outperform the classical approach of using standard times. Heuristic Max resulted in lower makespan and higher idle times whereas heuristic MaxMin improved operator skills more uniformly.

Evaluation of manufacturing cell loading rules for independent cells

In this paper, first the growing importance of cellular manufacturing is mentioned and then cell loading and cell scheduling tasks are defined. Most of the work reported in the cellular control area assumes the presence of a single cell and therefore focuses on cell scheduling only. However, this study considers a multicell environment where cell loading becomes crucial for controlling the entire system. New rules for cell loading are introduced, several possible combinations are presented, and two algorithms used for cell loading are also described. Next, the characteristics of a real manufacturing setting, where the experimentation has been carried out, are described in detail. In this system, products in each family can be assigned to more than one cell and also each cell can handle more than one family, thus creating overlapping among cells. Experimentation includes five cells, 120 products and four 6-month periods. The cells are considered as independent cells, i.e. products are completed within a ce...

Minimizing the number of tardy jobs in identical machine scheduling

Abstract In this paper, minimizing the number of tardy jobs in identical parallel machine scheduling is discussed. First, an integer programming formulation is given. Later, three simple heursitc procedures are presented with an example. Finally, the performance of the proposed heuristic procedures is compared with other available procedures.

Manufacturing cell loading rules and algorithms for connected cells

Publisher Summary Cellular Manufacturing (CM) can be defined as the implementation of group technology (GT) principles in a manufacturing environment. Situations that require decisions can be grouped together based on pre-selected, commonly shared criteria, and decision that applies to one situation in the group will apply to all of them in that group. The application of GT to manufacturing is achieved by identifying the items with either similar design or manufacturing characteristics and grouping them into families of like items. The benefits derived from CM include reduced work-in-process inventory and setup time, improved product quality, easier scheduling, better visibility of product schedule status, and quicker feedback of manufacturing deficiencies. The chapter discusses control of manufacturing cells, search priority primary product rule, secondary product rules, primary cell rules, number of feasible products (NFP), product mix (PM), and common cell capacity. The rules described are combined in different ways and 48 possible combinations are created. Twenty-four of the rule combinations are of cell priority type and the remaining 24 are of product priority type.