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01Dec

Product Design

Every product must comply with a number of functional requirements or it isn’t a product, it is simply a useless object, trash or in some cases an artwork. It should be noted that art is not being compared to the former. Therefore the first phase of any design project requires a designer to focus his or her attention on the product application and gain a comprehensive understanding of its purpose and all the parameters associated with its intended use as well as its potential unintended use. The latter is as important as the former since unintended use can result in premature failure or serious safety risks. These criteria are often documented in specifications which define the product based on numerous parameters. This editorial will define the importance of such a document and describe how it establishes all the subsequent decisions made throughout the design development process.
There are no rules for standards for creating product specifications. Some products require extensively detailed documents which could hundreds or thousands of pages of specifications while others may be as brief as a page or two of specifications describing a part. It doesn’t matter how “simple” a product is, some form of documentation is always required to establish how that part or product is to perform based on one or more sets of conditions. Although this may appear to be sensible and obvious within the context of this editorial, product specifications are often overlooked and omitted from the design process. Omission typically results in confusion during development, costly rework, or catastrophic product failures. The specifications can be compared to a contract between the development team and the company for which the product is being designed as well as the end user. Specifications will not only influence the product design but also user manuals, regulatory compliance requirements and legal ramifications. Specifications should be written with careful consideration of proven engineering principles, user requirements, cost considerations, manufacturing parameters and marketing requirements. Incorrect assumptions will lead to costly recalls or unnecessary complications throughout the design process.
Since every product requires its unique set of specifications, this article cannot provide a recipe for creating a universal specification. However, an abbreviated list of general specifications can provided which pertain to all products. This list is provided below:

• Marketing

o User requirements
o Appearance
o Forecast sales

• Engineering

o Structural
o Mechanical
o Functional
o Life cycle/reliability
o Performance
o Testing and verification

• Financial

o Return on investment\amortization
o Capital availability
o Risk
o Vendor selection

• Manufacturing

o Location for production
o Supply chain
o Design for manufacture
o Number of parts
o Tooling design

• Regulatory compliance

o Recycling
o Compliance with specific regulatory body; UL, CSA, FDA, ROHAS, etc.

• Project Management

o Lead times
o Project risks
o Project schedule
o Available resources

A small subset of this list can be discussed in limited detail to serve as an example describing how tightly these parameters interrelated. Material selection for example is dictated by designers and is critical to overall product performance, cost, reliability, appearance, manufacturability, compliance with regulatory bodies, and in some cases lead times. Designers must have a thorough understanding of static and dynamic structural requirements for a product during short term as well as long term performance. Quantifying tensile strength, tensile modulus, fatigue resistance, creep and impact strength based on structural analysis will provide designers with physical property filters to select one or more viable plastic resins for a particular application. The list may be further truncated based on thermal conditions, chemical resistance, UV resistance, clarity requirements etc. Other factors including availability, cost, and lead times for delivery may further reduce the selection. Chosen materials may also be reviewed by the molding department or molder based on ease of processing, tool design and proposed secondary operations.
Structural analyses, testing and all the associated performance evaluations which effect material selection are based on the specifications. If product specifications omit potential exposure to harsh chemicals, or thermal conditions, the analysis and resin selection will be based on erroneous premises resulting in premature failure. Omissions in specifications typically arise from ignorance of the effects certain environmental conditions have on plastics. It is therefore crucial to test molded parts under expected environmental conditions as stated in the specifications to uncover potential failure. Rapid time to market often force designers to omit long term testing or simply ignore it all together which introduce high risks in a project. In such cases it is often advisable to include a plastics materials specialist to review the specifications and assess the potential risks. Material selection will influence wall thickness, design features such as ribs, bosses, snaps etc, and appearance for the designer. It will also effect a molder’s choice of tooling material, gate location and shrinkage rate and many other factors influencing tool cost.

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