Title: Phase 4 Choose and Justify the Optimal Solution
Course: ATEP - MMT: Module A: > Section: PHASE 4 CHOOSE AND JUSTIFY THE OPTIMAL SOLUTION

4.1.1 Determine Strengths and Weaknesses

Optimization and trade-offs are important elements of the process as design requirements may compete with each other.

4.1.2 Strengths vs. Weaknesses

For the alternatives that remain, list their strengths and weaknesses in relation to the design criteria. To make your decisions, you might have to do more research, testing each alternative and gathering data about its performance. These test results must be recorded and compared with results from other tests, so that fair and accurate decisions can be made about which solution is best. Sometimes, the testing will suggest that if you change one alternative slightly, or combine two or more alternatives, you will end up with a better solution. The design improvements can lead to better performance, increased safety, and lower cost. In this phase, the design is critically examined by noting how other designs perform to see how it can be improved. First, identify the variables that affect the performance of your design. Again this is an iterative process that requires reviewing your product many times. Input can be from testing, the evaluation of that testing and customer surveys.  Use a decision matrix to easily view your options.

4.1.3 Optimization

The process of improving each alternative of a design is called optimization. Optimization, sometimes referred to as specialization , very often means "a short life span" but with improved performance for a product.

Frequently, different alternatives will be better in different ways. For example, one material may be stronger, but a second material may cost less.  In such cases, we must decide which criteria are the most important, and then arrive at the best overall solution to the problem.  The idea is to decide on a design that best meets the specifications, fits within the constraints, and has the least number of negative characteristics. Established design principles guide the design process.

4.1.4 Trade-offs

When designers choose the best solution, they normally make trade-offs. They will give up one desirable thing for another. In such cases, they must decide which criteria are the most important, and then arrive at the best overall solution to the problem. In other words, they will optimize the alternatives and then make trade-offs to determine the best possible solution.  Informed design choices  lead to choices between optimization,  specialization, adaptability and flexibility.

While optimization and specialization very often means a short life span, adaptability and flexibility tend to give the product a longer life span.  If a product is designed for one special task, its usable lifespan can be limited by a variety of factors such as changes in time, technology or materials.  Creating a part or product that can be adapted to other products or uses will give it a longer lifespan.

In Phase 2, during research, the material for the product is identified.  Comparisons between the current materials available to newer, emerging or experimental materials may present other choices for the product. For example, a new method and type of coating that replaces chrome plating is nickel-tungsten plating. Not only is it a stronger material but the method used to create the coating is environmentally friendly. Can a new product or one that is currently being developed and its production methods improve your design?

Again, a decision-making matrix will help defend your selection of the best alternative solution for the trade-offs. Using information gained from research and investigation, justify why the proposed solution is the best one for addressing the design specifications. The chosen alternative will be the basis of your preliminary design. Each of the alternatives must be examined to see if it meets the design criteria, specifications, and constraints that were defined in the first step.

Do not forget to add all of your findings to the engineering notebook. You will also need to review and add to the Design Brief for purpose and content then develop detailed sketches with annotations that offer a better idea of the parts and assemblies. Determine the types of material that will be used. Consider cost, availability and environmental hazards.

4.1.5 Technical Drawings

Technical drawings are now being produced with the  aid of computer graphics software. Known as Computer Aided Drawing (CAD), technical drawings can be created in two dimensions and rendered into three dimensional images or models. Computer Aided Drawing now allows designers to:

- easily visualize the 3D form of the design.
- quickly compute the physical properties of the shape and material.
- calculate stress and strain.
- anticipate motion and deflection.
- examine fluid flow.
- show thermodynamic processes.
- determine possible interference between the part geometry.
- show order of assembly with a video.
- estimate potential costs.

Computer Aided Drawing can assist in determining the dimensional limits of the parts and whether or not they can be met by the machines that currently exist.  If not,  a new machine might need to be created.

Designers might be able to avoid unnecessarily tight tolerances that are beyond the natural capability of the machines that will be used to manufacture the parts.  For parts that require extremely high accuracy, special machines along with temperature and humidity controlled rooms might be required.

When designing a part, there is always a chance that the accuracy of that part could be compromised during the production process. As the number of parts increase in an assembly, the chance of errors will  increase while accuracy decreases.  All the while keep in mind that the greater the complexity, the higher the failure rate.  During this step, the design team should review all the parts in an assembly to determine:

1. can any components be eliminated,
2. can any components be combined with others, or
3. can any components just be made simpler:  the principle of KIS (Keep It Simple).

Another option is to investigate off-the-shelf parts that might be used to keep the cost down. Standard components will result in reduced non-recurring engineering costs (NRE).