Material Selection
Ashby’s materials selection chart method
One of the most popular techniques for initial screening of materials is the materials selection chart method, pioneered and popularized by Prof Mike Ashby. Ashby (1992) compares the relative performance of a variety of materials for a specific constructive function by using performance indices as design criteria. Materials screening, on the basis of these performance indices, is best achieved by plotting the performance indices that are typically a mathematical combination of material properties on each axis of a materials selection chart, also known as an Ashby plot. Individual materials or material subclasses appear as balloons that define the range of their properties.
Ashby has established a material selection system that focuses on data modeling aspects of the problem, where data is presented in charts. Materials and process selection charts that were founded by Ashby are tested and tried. Ashby's material selection charts are valuable for preliminary screening of materials.
In the mechanical design field, these charts play a simple and fast way of evaluating whether a material is appropriate for the existing case or not. Ashby chart method is easy to apply when the design of the component consists of a simple objective, such as minimizing the weight, and a single constraint like a specified stiffness, strength, or thermal conductance. The most thoughtful limitation of the chart method is that the chart limits the material selection decision to only solving two or three criteria. So, to solve this problem, multi-criteria decision making is established. The performance of a component depends on a combination of properties instead of a single property, such as the strength-weight ratio and stiffness-weight ratio to design a component with a light-weight characteristic. From this idea, one can build a plot of one property versus another, the drawing has field and subfield, the fields usually contain the material class, and the subfields have individual materials.
- They allow quick retrieval of the typical properties of a particular material
- They allow quick comparison of the properties of different materials, revealing their comparative efficiencies.
- They facilitate the selection of the materials/manufacturing processes during the product design stage.
- They enable substitution studies exploring the potential of one material to replace another.
Reference: Michael F. Ashby, Materials Selection in Mechanical Design, Elsevier Science, 2016
Material Selection Charts
Cambridge Engineering Selector (CES) is one of the powerful selection and analysis method software programs based upon Ashby's materials selection procedure.
Note: The teams are encouraged to use ASHBY Material Selection Charts. The teams must consider and categorically discuss the relevant Material Selection Criteria and Process in the relevant section of the report.
Manufacturing Process Selection
Design engineers, manufacturing process selection is the first thing they think about during the design process. The best approach is to keep manufacturing concerns in mind throughout the entire design process. This will result in a design that is easier and less costly to produce.
There are hundreds of manufacturing processes. You are likely to already be familiar with the most common, e.g. casting, forming, moulding and machining. For any given product, there will be multiple manufacturing processes that you’ll need to select from. The process you choose will depend on many factors called the process selection drivers. These process selection drivers include the following: An experienced manufacturer will have a good idea of all the process selection drivers mentioned above. Depending on the product design and manufacturing considerations, a good manufacturer will be able to guide you through the selection process. Follow the simple procedure below to select the appropriate manufacturing process for a product:
- Quantity of the product
- Cost for tooling, manufacturing machines and equipment
- Time required for processing
- Level of skilled labor required
- Process supervision
- Energy consumption
- Availability of material and cost of material
- Capabilities required to processes material
- Product dimensions and size
- Surface finish required
- Design tolerances
- Waste produced by the process
- Maintenance costs
- Other costs
STEP 1 - Selection criteria: The first step in manufacturing process selection is to establish selection criteria based on key process selection drivers: manufacturing volumes, value of the product, part geometry, required tolerances, and required material. The material choice will be very effective in narrowing your options down. This is because many processes work exclusively with certain materials. For example, injection moulding can only be used with polymers, whilst die casting can only be used with metals. Your material choice will instantly rule out a vast number of unsuitable processes. The expected manufacturing volume will further narrow down your process options. For a large quantity, a manual production process like manual machining would be completely impractical. Instead, you would need to consider an automated process such as moulding. The geometry and tolerances required for a product will also filter out many processes that would be unable to achieve the desired accuracy.
STEP 2 - Identify processes: After applying STEP 1, a smaller range of processes will be available. At this point, you should ideally work with an experienced manufacturer to identify those processes that can satisfy the required quantity, material requirements, and part geometry.
STEP 3 - Evaluate processes: After identifying the potential processes for manufacturing a product, it is time to evaluate them based on less broad parameters, such as process capability, processing time, tooling and equipment cost, degree of automation available, skill required for operation, waste produced after processing, and post-processing required. It is a good idea to create a decision matrix with a score or value for each of these important elements.
STEP 4 - Selection: You should now be able to use the weighted decision matrix you created in STEP 3 to identify the best process for your application. If you carefully evaluate each element, giving extra weight to those elements that are most important, the result will be a single process that will produce the part required to the standard required for an acceptable cost of production. As mentioned earlier, it is important that you work with experienced manufacturers or a manufacturing engineer to help you identify potential processes, evaluate each process effectively, and select the best process so that you and your customers will be happy with the final product.
Reference: “Manufacturing Process Selection for Your Product.” Matmatch, https://matmatch.com/learn/engineering/manufacturing-process-selection.
USEFUL RESOURCES:
Manufacturing Process Selection Handbook, by K. Swift, J. Booker, provides engineers and designers with process knowledge and the essential technological and cost data to guide the selection of manufacturing processes early in the product development cycle.
Technology and Manufacturing Process Selection, The Product Life Cycle Perspective, Editors, Elsa Henriques, Paulo Pecas, Arlindo Silva, Springer 2014. Provides a detailed view on the current approaches of technology evaluation and selection in product and process design context and with a life cycle perspective. Discusses Life Cycle Cost in a product and process engineering scenario, focusing on design and technology evaluation and selection. Presents traditional and state-of-the-art manufacturing technologies from the point of view of sustainable production.
