Another key element to achieve enhancements in producibility is to error-proof the design. This oft-overlooked activity can have a remarkably big payoff in the reduction of manufacturing errors that can result in the need for rework and/or the production of scrap. The goal is to eliminate the causes for error, minimize the possibilities of error, and make errors that do occur more readily detectable. In simple terms, this goal is accomplished by designing products so that they can only be assembled the correct way and by using manufacturing processes that can only be implemented correctly. In reality, this goal may be unattainable for every product. However, by striving to identify opportunities to meet the goal, producibility will be enhanced. The importance of error-proofing to producibility can be seen in Case Study 39 in Appendix D.
An error-proof design is one in which the design team has considered ways to eliminate or reduce the occurrence of mistakes during manufacturing, assembly, and maintenance processes. A Failure Mode and Effects Analysis (FMEA) can assist in the identification of potential failure modes and in understanding the manufacturing process implications.
An example of eliminating an opportunity for errors is
shown in Figure 4.3. In this redesign, a small lip was added to prevent installation of the bracket on the wrong side of the flange.
Because errors represent a major cause of failures and defects, alleviating or eliminating the opportunity for errors has a significant impact on producibility.
Staff: Required staff includes all members of the product development team.
Tools and Techniques: The application of FMEA to assess the manufacturing and assembly processes will assist in the identification of potential errors. A description of FMEA is provided in Appendix F.1.7.
Training: Workshops to introduce the product designers to the concept of error-proofing and to provide them with examples and guidelines are available.
In many cases, the opportunity for errors can be eliminated by simplifying the design or manufacturing operation. Hence, the design should be reviewed to identify features that can be changed to eliminate potential errors. For all potential errors identified, an attempt should be made to redesign to eliminate the possibility of an error. If this is not possible, an attempt should be made to redesign so that it is obvious that an error has occurred. At the very least, an attempt should be made to redesign so that, if
the error occurs, it can be easily identified as an error and corrected with minimum impact.
Finally, the design should be reviewed with the manufacturing personnel who will actually produce the product to review the potential for processing and assembly errors. Based on that review, design modifications should be made, if ppropriate.
The design engineer should apply the following guidelines to help error-proof the design:
- Maximize part symmetry or make parts obviously asymmetrical.
- Ensure adequate access and unrestricted vision during assembly.
- Eliminate adjustments.
- Design self-locating or self-aligning parts.
- Design parts that cannot be installed incorrectly.
- Standardize all accessory parts such as fasteners.
- Provide visibility and feedback to the operator such
as making relevant parts visible and displaying system status by making the
effects of operations immediate and obvious. For example, make a part number
visible and easily readable when the part is installed properly.
Before a detailed design is approved and released, the following questions should be addressed:
- Does the system design and the associated manufacturing processes make it difficult to take wrong actions?
- Is it easy to discover errors that have occurred?
- Has the design been standardized to every extent possible?
- Is it easy to correct errors if they are made?