When it comes to machined components, material selection is one of the most impactful decisions your team will make while developing the manufacturing process. This is due to many factors, such as a part’s design, size, and complexity, as well as the selected machining process, the required surface finish, any relevant standards or regulations, and its end-use application.
That being said, how should you approach material selection? What requirements or factors should take priority in your selection process?
At the highest level, your chosen material must allow you to meet design, industry, and regulatory requirements.
For example, if your part must meet specific medical or aerospace certifications, then it must meet ISO 13485 or AS9100 requirements, respectively.
Additionally, if your machined component must meet certain regulatory requirements, such as EU RoHS or REACH, your chosen material must meet those specifications.
What to Consider during the Material Selection Process
Design and regulatory requirements aside, what other criteria should influence the material selection process?
Here are some critical factors to consider:
- A material’s attributes and properties
- Machining factors
- Finishing requirements
- Procurement factors
How you navigate each of these factors in the material selection process will largely be determined by the part’s design and end-use application requirements, such as weight, cost, strength, and environmental conditions.
Let’s examine those critical factors in more detail.
Material Attributes & Properties
As you consider the wide variety of metals that are available to you, keep the following material properties in mind:
| Surface Hardness | Select a material that can achieve the required surface hardness for enhanced wear resistance or impact resilience. |
| Weight | In sectors such as aerospace and automotive, the preference leans towards lightweight materials to enhance both fuel efficiency and overall performance. |
| Strength | Material strength is crucial for resisting forces and wear, softer materials may be easier to machine but may lack durability for specific applications. |
| Corrosion Resistance | Select materials with superior corrosion resistance for durability in challenging environments. |
| Thermal & Electrical Conductivity | For electrical or thermal conductivity needs, consider copper and aluminum for electrical conductivity, and steel and titanium for thermal conductivity. |
| Chemical Resistance | For chemical resistance, choose materials like stainless steel and titanium for effective protection against harsh chemicals. |
| Machinability | Choosing materials with excellent machinability enhances surface finishes and tool lifespan. |
| Thermal Expansion | Consider material attributes, including coefficient of thermal expansion, to determine the best fit for your machined component's dimensional stability in varying temperatures. |
Analyzing these properties in accordance with your part's design and intended use will help determine which materials are unsuitable, suitable, or optimal for your machined component.
Machining Factors
Your part’s end-use application will determine many of your material selection decisions; but before you get to end-use, your raw material has to go through the machining process.
Machining rates, otherwise known as speeds and feeds, control material removal rate regardless of your chosen material. Your chosen material will have machinability characteristics (i.e., hardness, melting point) that influence how quickly the material can be moved, how heat is managed, chip clearance, and more.
Cutting tools are another important machining factor to consider. The material selected directly affects the wear and tear on these tools. Certain materials, like high-temperature alloys, may lead to increased tool wear, necessitating specialized tooling for effective machining, which can increase overall cost.
Finishing Requirements
Don’t be misled by the phrase “finishing requirements.” You shouldn’t treat your part’s finish as an afterthought, but rather a design consideration in the early stages of developing the production process. Otherwise, there may be compatibility problems between your selected material and the required surface process.
If achieving a specific surface finish is crucial for your project, select a material that can be seamlessly machined to meet those requirements. While materials like aluminum and plastics can easily achieve a smooth finish, others such as cast iron may need extra steps to attain the desired surface quality.
Consider the compatibility of various plating types with different base materials. For instance, if your customer specifies nickel plating, designing your part from aluminum may not be ideal. Opt for stainless steel instead, as it is well-suited for nickel plating, allowing the plating specification to guide you towards a suitable material choice.
Procurement Factors
While design and industry regulations take priority, there are a number of procurement factors that should be taken into consideration when choosing a material for your machined component that will not only help you eliminate unnecessary costs whenever possible, but can impact your lead times.
Raw Material Cost: A material's baseline cost is an obvious procurement factor that's worth addressing. While high-end aerospace alloys can come with a hefty price tag, more budget-friendly options like plastics are also available. It's essential to weigh the cost of the material against your budget constraints.
Machining Cost: The machining expenses for each material should be taken into account as well. Certain materials may demand additional time and labor to machine effectively, thus affecting the overall cost of machining.
Availability: The availability of materials is a crucial factor to keep in mind during material selection. Some materials may be challenging to source or have longer lead times, potentially causing delays in your project timeline. It's essential to assess the availability of the chosen material and ensure it can be obtained within the necessary timeframe.
Lead Time: Consider the project's timeline as well, as the lead time for certain materials can significantly affect your material selection process. Some materials may have longer lead times than others, potentially causing delays in your overall project schedule.
While design and regulatory requirements form the foundation of your material selection process, they may present you with multiple options to consider.
To navigate through these choices effectively, you can leverage material attributes, machining factors, finishing requirements, and procurement considerations.
By carefully analyzing these aspects, you can pinpoint the most cost-effective material that not only ensures the production of a high-quality machined component but also streamlines your operations by minimizing unnecessary lead times.
Peter Doyle
Hirsh Precision
