Introduction

Recent trends in customer demand for customized products encouraged the implementation of mixed assembly lines in many industrial environments. Mixed lines can produce more than one kind of product in the same assembly line (AL), and different sales cycles may be combined to avoid low asset utilization when low sale of a specific product occurs. However, in order to mixed arrangements to become viable in high competitive markets, assembly lines designers seek to increase the efficiency by maximizing the income rate and minimizing operating costs. Therefore, the assembly lines project an issue of great industrial interest.

Aspects of balancing, layout and requested product mix affect the performance of a joint assembly line. The product mix is the quantity of each product being manufactured by AL. However, the lack of parts, machinery and equipment unavailability and non-conformities parts, among others, restrict the production of certain models in certain periods. In such way, changes in mix production are required to ensure that available resources are used. Such utilization, however, typically proves difficult to be carried out as the capacity constraints, imposed by balancing, limit the production rate. Thus, whether AL have conditions to adapt themselves to different product mix without affecting the productive capacity, the use of available resources can be maintained.

This paper suggests a method for mixed AL balancing scenarios subject to change in the product mix, making the AL able to meet the total production demand for the period independent of the produced model. That balancing is operated by an AL mixed moving target balancing heuristic, where tasks are allocated to workstations respecting three constraints: (i) meet the equivalent precedence relation from precedence diagram; (ii) allocate tasks to a workstation until the total station weighted average time does not exceed the moving target, and (iii) allocate tasks to a workstation in a way the total time does not exceed the station cycle time. The proposed method was applied in a company presenting a mixed AL that produces 7 different models. The method increased the production capacity by 35% (meeting the required demand for the AL), reduced the products crossing time in AL and improved line efficiency and balancing due to a better distribution of tasks.

This paper is divided into five sections. Section 2 presents the literature review, detailing the assembly line types, its balancing and applicable solutions. Section 3 presents the method stages, and its application in the production environment is in Section 4. Section 5 brings the conclusions.