Full citation

Mital, A., & Desal, A. (2007). Enhancing the Product Development Process Through a Sequential Approach, Part II: Assembly and Disassembly. International Journal of Product Development, 4(1-2), 171 — 185.

Format: Peer-reviewed article

Type: Research — Non-experimental

Experience level of reader: Fundamental

Annotation: This paper discussed issues and factors related to the assembly and disassembly of a new product. The authors discuss the importance of planning for an efficient disassembly process while in the design phase. Guidelines for both material selection and process considerations are provided.

Setting(s) to which the reported activities/findings are relevant: Large business, Small business (less than 500 employees)

Knowledge user(s) to whom the piece of literature may be relevant: Manufacturers

Knowledge user level addressed by the literature: Organization

This article uses the Commercial Devices and Services version of the NtK Model

Primary Findings

Measures:

  • The Lucas DfA analysis is carried out in three sequential stages: functional, feeding and fitting analyses. In functional analysis, components are divided into two groups. Group 'A' parts perform a primary function and Group 'B' components are non-essential, such as fasteners. The design efficiency can be computed using the formula: DE= A/(A+B)*100. The target efficiency should be at least 60%. Feeding analysis is concerned with the problems associated with handling components and sub-assemblies until they are admitted to the assembly system. By answering a group of questions regarding the size, weight, handling difficulties, orientation of a part, its feeding/handling index can be calculated. The feeding/handling ratio is computed as follows: F/H ratio = (Feeding/Handling index)/Number of essential components. The fitting analysis is conducted similarly. The target value is 2.5.
    Experiential. Authors experience and research.
    Occurrence of finding within the model: Step 7.6
  • The Boothroyd Dewhurst DfA method seeks to reduce the number of parts by a consideration of manual handling and manual insertion times. This is used to compare two or more design processes and objectively identify the best one.
    Experiential. Authors experience and research.
    Occurrence of finding within the model: Step 7.6
  • The numeric disassemblability evaluation index is a function of several design parameters that directly or indirectly affect the process of consumer product disassembly. Numerical scores are assigned to each of these parameters depending on the ease with which they can be attained. The following parameters have been addressed: 1. degree of accessibility of components and fasteners 2. amount of force (or torque) required for disengaging components (in case of snap fits) or unfastening fasteners 3. positioning of tools to enable disassembly 4. requirements of tools to enable disassembly 5. design factors such as weight, shape and size of components being disassembled.
    Experiential. Authors research.
    Occurrence of finding within the model: Step 7.6, Step 7.5
  • The Hitachi assembly evaluation method aims to facilitate design improvements by identifying weaknesses in the design process by using an assemblability evaluation score (E) and an assembly cost ratio (K). This is used to compare two or more design processes and objectively identify the best one.
    Experiential. Authors experience and research.
    Occurrence of finding within the model: Step 7.6

Tips:

  • The following are product design guidelines when designing for automatic assembly: 1. Self-aligning and self-locating features need to be incorporated into the design to facilitate assembly. Improvement can be achieved by using chamfers, guide pins, dimples, and cone and oval screws. 2. Use the largest and most rigid part of the assembly as a base or fixture where other parts are stack assembled vertically in order to take advantage of gravity. If this is not possible, the assembly should be divided into subassemblies and plugged together at a later stage. 3. Use a high percentage of standard parts. Employing the concept of Group Technology, begin with fasteners and washers. 4. Avoid the possibility of parts tangling, nesting or shingling during feeding. 5. Avoid flexible, fragile and abrasive parts and ensure that the parts have sufficient strength and rigidity to withstand the forces exerted on them. 6. Avoid reorienting assemblies, may require a separate workstation or machine.
    Experiential. Authors experience and research.
    Occurrence of finding within the model: Step 7.6, Step 7.5
  • The following are some design guidelines that may be incorporated into product design when designing for maunal assembly: 1. Eliminate the need for decision-making by the worker, including making final adjustments. 2. Ensure good product accessibility as well as visibility. 3. Eliminate the need for assembly tools or special gauges by designing individual components to be self-aligning and self-locating. Parts that sanp and fit together eliminate the need for separate fasteners. This results in speedy as well as more economical assembly. 4. Try to minimize the total number of individual parts if possible. To facilitiate this objective, multipurpose components may be used. 5. Minimisation of the number of individual parts may also be achieved by eliminating excess parts and combining two or more parts into one, if functionally possible. 6. Avoid or minimise the need to reorient the part during the assembly process. Ensure that all insertion processes are simple.
    Experiential. Authors experience and research.
    Occurrence of finding within the model: Step 7.6, Step 7.5
  • Comprehensive disassembly process planning needs to be done if disassembly is to be included in the product at the design stage.
    Experiential. Authors experience.
    Occurrence of finding within the model: Step 7.6, Step 7.5