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This article is a survey of the literature on how quality is assured in manual assembly in discrete-part manufacturing. The literature is organized into systems that help assure assembly quality, and methods and practices that are used within these systems. A major finding in the literature review was that four management systems (production, quality, maintenance, and human resources) are important for assembly quality assurance, not just the quality system. The authors also provide a review of eight methods that were identified as supporting assembly quality, such as design for assembly, statistical and worst-case tolerance analysis, and various inspections and audits.
Key words: assembly process, manual assembly, quality assurance
INTRODUCTION
Fabrication and shaping of materials, and their subsequent assembly into products, are the primary stages of discrete-part manufacturing. Assembly is the joining of discrete items to or around each other. There are very few manufactured goods that do not use at least one joining process, though the processes used are very diverse. Assembly results are divided into two distinct groups: permanent joints that require the destruction of one of the elements to achieve separation, and semipermanent joints that can be separated without damage, when using the correct tools (Owen 1985).
According to Montgomery (1997), one may define quality of assembly in three ways: fitness for use, quality of design, or quality of conformance. In this article, the authors choose to focus on quality of conformance, which deals with how well the product conforms to the design specifications. Quality of conformance is influenced by many factors, including the choice of fabrication and assembly processes, the training and supervision of the work force, the type of quality assurance system used, the extent to which these quality assurance procedures are followed, and the motivation of the work force to achieve high quality.
The modem assembly line was first applied in the production of the Model T Ford automobile in 1910. Ford developed a power-driven endless conveyor to mechanize the movement of partially completed autos from one station to the next; however, automobile assembly remained primarily a manual job, as it still is today.
It is estimated that only 5 percent of U.S. products are produced by automated assembly (Boothroyd 1991). Because 95 percent of assembly is manual, this...