ME3101 / ME3102Mechanical Systems DesignChapter 6Basic Design for Assembly

DFA – Design for Assembly

In the previous chapter, we have talked about DFM, Design for Manufacturing.

In this chapter, we will go through DFA, Design for Assembly.

Similarly, DFA occurs through the entire design process, from the start, till actual production

DFA – Design for Assembly

Generally accepted guidelines for DFA:

•Minimize number of parts

•Feature lesser assembly movements

•Provide Self Aligning features

•Eliminate visual obstructions to assembly

•Reduce number of tools required

•Use symmetrical parts

Minimize number of parts

Similar to DFM, a reduction in number of parts is a rule of thumb to follow for Design for assembly.

Lesser parts = Lesser steps required for assembly

We will illustrate this concept in the next slide.

Minimize number of parts

Extracted from: http://www.cbpa.ewu.edu/~pnemetzmills/OMch3/omfac.html

Lesser assembly movements

To reduce assembly time, designers can take into consideration a “top-down approach to design” and have features in the same orientation.

This reduces the need to re-orientate the main body during assembly.

Provide Self Aligning Features

Compare the 2 diagrams below.

The design on the left requires more effort to align the parts together.

The design on the right however, has a self aligning feature that allows the part to fit together easily, thus reducing assembly time

No self aligning feature Integrated self aligning feature

Eliminate Visual Obstructions

Look at the 2 diagrams on the left.

As a designer, take note to prevent visual obstruction of assembly features.

Blocking visual sight of assembly features increases the difficulty in assembly and thus increases time required.

Do this!

Reduce Number of Tools Required

Another simply rule of thumb for designers to follow is to reduce the number of tool variants required.

For example, the same kind of fasteners can be used to reduce the number of tools required to fasten them.

Use Symmetrical Parts

Whenever possible, part designs should feature symmetry to reduce time spent on alignment during assembly.

However, where symmetry is not possible to attain, obvious asymmetry is preferred for easy identification of the correct alignment

Design for symmetry

Obvious Assymmetry

In conclusion…

Designers should always take into consideration the practicality of their product.

While the product has to be usable and efficient, it has to be able:

•to be manufactured (DFM)

•to be assembled efficiently (DFA)