Serkan Orhan, 030070165, 11th week part3

3)Manual Assembly   [Group: Assembly]
[Old]
Manual Assembly uses relatively simple tools and generally is economical for small lots.Because of the dexterity of the human hand and fingers and their capability for feedback through various senses, workers can manually assemble even complex parts without much difficulty.In spite of the use of sophisticated mechanism,robots and computer controls,the aligning and placing of a simple square peg into a square hole involving small clearances can be difficult in automated assembly--yet the human hand is capable of doing this simple operation with relative ease.

(Kalpakjian S.,Schimid S.R.,Manufacturing Engineering and Technology 5th edition,p. 1180)


[New]
The following design guidelines may be incorporated into product design when designing for manual assembly,
• Eliminate the need for decision making by the worker, including making final adjustments. Ensuring this step removes all subjectivity out of the decision-making process, thereby improving the accuracy of the assembly process.
• Ensure good product accessibility as well as visibility.
• Eliminate the need for assembly tools or special gauges by designing individual components to be self self-aligning and self self-locating. Parts that snap and fit together eliminate the need for separate fasteners. This results in speedy as well as more economical assembly
 • Minimize the total number of individual parts, if possible. To facilitate this objective, multipurpose components may be used.
• Eliminate excess parts and combine two or more parts into one, if functionally possible.
• Avoid or minimize the need to reorient the part during the assetnbly process. Ensure that all insertion processes are simple. Avoid the need for rotation, releasing, and regripping. Vertical insertion always is preferable, since it utilizes gravity to accotnplish the task.


The process of manual assembly entails extensive component handling by the operators. As such. components need to be designed with a view to minimizing the need for extensive handling to make the process faster and more accurate. The following are some guidelines to accomplish this objective,
• Design parts that have end-to-end symmetry and rotational symmetry about the axis of rota-tion. If this is not possible. the design should incorporate maximum symmetry.
• When it is impossible to incorporate symmetry into product design, obvious asymmetry should be used to facilitate case of orientation and insertion.
• Provide features that prevent jamming and entanglement of parts.
• Design parts so there is little or no resistance to insertion. This can be facilitated by provid-ing chamfers to guide insertion of two mating parts.
• Design for a pyramidal method of assembly, if possible. Provision needs to be made for progressive assembly about one axis of reference. In general, it is best to assemble from above.
• Avoid holding down the part. If this is unavoidable, the part should be designed so that it is secured as soon as possible after insertion.
• Design parts to facilitate location before release. Release of a part before location is a poten-tial assembly problem.
• Use of common fasteners increases assembly cost in the following order: snap fit, plastic bending, riveting, and screwing. Bear this factor in Irlind when designing securing and fastening methods for holding together two or more parts.

(Product Development: A Structured Approach to Consumer Product Development, Design and Manufacture, Anil Mital,Anoop Desai,Anand Subramanian, 2008,pp. 138-139)