With ever increasing emphasis on manufacturing cost reduction, it is important for designers to review new products for ease of manufacturing and test. Products designed with the manufacturing process in mind will cost less. There are four fundamental considerations when designing an electromechanical assembly for manufacturing efficiency: component selection, production processes, test and inspection, and documentation.
From wire and contacts to COTS (commercial off-the-shelf) assemblies and custom fabricated elements, the designer needs to carefully select the components being incorporated into a design.
- Wire stranding affects a cable’s flexibility and also its price. The insulation selection of a wire affects its durability.
- Electrical contacts and terminals require unique tooling for termination. A company’s efforts to standardize on a particular series of contact will minimize tooling costs and offer the potential for increased process automation.
- Hardware incorporating captive locking elements reduces component counts and the associated assembly labor cost. SEM screws and KEP nuts make assembly efforts more efficient.
- Adhesive selections made with labor efficiency in mind are important as well. Epoxy and silicone adhesives can be slow to cure and impair efficient production. The selection of a UV curable adhesive for high volume applications can significantly reduce production cycle times.
- COTS assemblies such as bar code scanners, temperature sensors, and controllers are increasingly being incorporated into electromechanical sub-assemblies. An efficient mounting strategy using a minimum of hardware elements will reduce costs.
- Higher level electromechanical assemblies typically are built around fabricated plastic or metal components. The incorporation of fasteners such as threaded inserts and captive nuts in these fabricated components can significantly reduce assembly costs and provide a more finished appearance to the end product.
As part of the selection of components, a designer should consider the availability of their choices. For instance:
- The availability and lead time of COTS components are likely to be much shorter than more customized versions.
- Tooling lead times and costs for plastic fabrications can be long.
- The choice of an exotic wire might require the purchase of a minimum overall length and result in significant excess inventory.
- The specification of equivalent components with multiple sources of supply will minimize product cost, particularly when specifying hardware and adhesive items.
We live in a highly regulated world. Designers must also consider regulatory issues when selecting components. For example:
- Components that are industry approved (UL, CE, CSA) will increase the marketability of the end product and help reduce product liability costs.
- Do the components need to be RoHS or REACH compliant? This should be known before components are considered and selected.
- Does a component’s place of origin (or the origin of the materials used to make it) have to be considered? Many western countries restrict the use of materials from regions of the world controlled by terrorists or by governments hostile to their people or to western interests.
Designers should consider the production process that will be used to assemble their product. The anticipated volume of production for an assembly needs to be identified early in the design process. For higher volumes easy to produce assemblies can have a dramatic impact on cost. For example:
- Not all components are compatible with automated assembly equipment. Specifying a hand crimped contact for a cable harness to be built in high volumes will unnecessarily add cost to the final product. It is better to specify a component in reeled form that can be used on automated terminating equipment.
- Assembly steps can be reduced by minimizing the number of components required. The inclusion of built in clips or flanges in a chassis can effectively retain a component that is slid into place and secured with a fraction of the fasteners.
- Some adhesives have much shorter curing cycles than do others. Adhesives must be evaluated for both their open “pot life” and curing cycles. Generally speaking, adhesives with short curing cycles will lead to a more efficient production process. With that said, be careful not to specify adhesives that cure so quickly that a mixed batch solidifies before use.
- Marking or labeling a product can be time consuming and expensive. Consider how many labels must be applied in different locations. More labels equals more assembly steps equals higher cost.
- Choosing the wrong workmanship standard can be expensive. As with the selection of components, there are regulatory considerations for the production process as well. It is the designer’s responsibility to specify the workmanship classification of their intended product. The IPC workmanship standards IPC-A-610, IPC-A-620, and J-STD-001 are frequently cited, but must be accompanied by a workmanship Class rating. If a product simply has to survive the New Year’s Eve party before being discarded, Class 1 workmanship is appropriate. On the other hand, a medical device providing life support cannot fail and justifies a Class 3 rating. But don’t over spec the requirement. With each increase in class comes additional cost; often significant cost.
Test and Inspection
Product testing ensures that a finished product meets the expectations of the designer and end customer. If possible, design elements should be included that facilitate easy and accurate testing. For instance:
- The inclusion of test points in an electromechanical assembly will aid in test and troubleshooting.
- In the case of cables, information about the mating connectors is beneficial in the preparation of test adaptors for automated electrical continuity and isolation testing.
Inspection costs can be controlled as well. For example:
- Locational tolerances are based upon the number of decimal places in a dimension. A label that is acceptable within a one inch area but dimensioned with three decimal places of accuracy is going to be inspected accordingly for placement (within one-thousandth of an inch.)
- As mentioned previously, the workmanship class will dictate the requirements for assembly work but it also imposes inspection requirements. If over specified, the cost of the inspection will rise.
Test and inspection requirements need to be adequate to assure a quality product but designers should be aware that over-testing and over-inspecting adds unnecessary cost.
Complete and accurate assembly documentation is important for low cost production. These documents will be used during both the cost estimating and manufacturing processes. If the product is properly described, the estimating effort will be more accurate and production will be efficient. Here are some suggestions:
- Parts Lists need to itemize all components, including adhesives and marking labels. Additional components mentioned in the notes or field of the drawing have the potential to be overlooked.
- If a separate AVL (Authorized Vendor List) is not provided, the Parts List should list the manufacturer and manufacturer part number for each component.
- The Assembly Drawing should accurately depict the desired product. Often, detail views can provide a “close-up” depiction of critical features. In addition to special assembly instructions, the drawing’s notes section should specify quality workmanship requirements and classification, marking requirements, and packaging.
- Referencing specification drawings in a drawing’s notes is a convenient means to supplement production requirements. Be sure that the documentation package being issued to your supplier includes the latest revisions of these documents.
- For cable and harness assemblies, a Wire List and schematic depiction should be included on the assembly drawing. In the case of larger point-to-point wired chassis assemblies, separate Wire Lists and schematic drawings should be provided.
- Fabrication Drawings for custom plastic or metal components should clearly and legibly depict the desired item.
- Finally, maximize use of a drawing’s white spaces. Enlarged depictions, heavier line weights, and larger font sizes will all improve the legibility and usefulness of a drawing.
There are many opportunities to minimize product costs during the design effort. Designers are encouraged to consider component selection options, the anticipated production processes, and the degree of testing and inspection required for the product that they are developing. The documentation outputs of their efforts need to thoroughly and accurately described in the design as well.
About the Author
Chuck Gladstone is the Production Manager of RESCO Electronics, a manufacturer of electronic assemblies and a value added reseller of auto ID equipment.
Chuck has over 30 years of experience in electronics manufacturing, with emphasis in electromechanical and printed circuit assembly. Before joining RESCO in 2013, Chuck was the Chief Technical Officer of Chesapeake Manufacturing, a printed circuit assembly contract manufacturer. Prior to that, he was Manufacturing Engineering Manager at EOG, Incorporated.
At the University of Maryland, Chuck majored in Industrial Technology, a program within the school of Education. He also holds a Masters degree in Administrative Science from Johns-Hopkins University.