Parts Insertion

Decrease ambiguity in part/subassembly orientation

First, a review of rotational symmetry.

Alpha symmetry refers to symmetry about a part's "most repeatable" axis, and is reported as the number of degrees needed to turn an object along this axis before it repeats.

For example, a square bar has alpha = 90º, a cylinder has alpha = 0º (so does a screw, for all practical purposes), and a bar that is rectangular in cross section has alpha = 180º.

Beta symmetry is perpendicular to the alpha axis.  It is related to whether the "ends" are identical or not, and whether the part needs to be flipped over before insertion.  Values are either 0º (identical ends) or 180º (needs to be flipped). This affects how a part is oriented before insertion into the larger assembly:

• Lower symmetry values decrease the number of possibilities for incorrect orientation, therefore decreasing manipulation and assembly time.

• At the same time, a part that can only be inserted in a single orientation decreases ambiguity.  This, however, requires that the assembler be adept at spatial recognition, and may increase handling time.

Rotational Parts

Design parts with self-locating features

Make things easier to assemble and the process will speed up. Advantages:

• Reduced assembly tooling

• Reduced operator training

• Reduced operator fatigue and frustration

• Reduces lifetime product cost

• Improves quality

Addition of a shoulder and a piloted screw make alignment and assembly easier

Fail-safe Assembly

Design components for fail-safe assembly (One Way-Right Way). Three common principles are:

• Design components so that they cannot be assembled incorrectly (use asymmetrical outside surfaces or guides)

• Design components to be fully assembled in one operation (integrate component placement and fastening in one step)

• Design out “false” assembly targets (extra holes or pins)

Ease of Handling

Design parts for ease of handling. Avoid components that are sharp, too small, or slippery; also, care should be taken to minimize the opportunity for parts to nest or tangle while in storage. If parts are easier to handle and accurately locate, assemblers will experience less fatigue and frustration.  In addition, it:

• Enables automatic assembly and/or feeding techniques

• Simplifies the assembly process

• Reduces tangling and nesting of parts

• Reduces total assembly time

Reach and See Access

Design for access so that a product and its parts are easy to reach and see. The four rules for access are:

• Provide clearance for the operator’s hands, tools, and testing fixtures

• Design so that mating surfaces are visible

• Avoid designs that require fasteners at the rear of the assembly

• Design for accessibility during assembly and future maintenance

Use Correct tool/Eliminate Need for Special Tools

Choose the correct tool according to how it will be used so that a safe posture is maintained during the assembly process.

Specialized tools and machines often need specialized training.  

In many cases, these tools may be necessary, but their use often increases handling time because the tool must be picked up and manipulated before it is used.

Click to continue to Minimize Part Count and Levels of Assembly