Material Selection for High-Precision Mechanical Components

In the world of precision mechanical engineering, material selection stands as a critical factor that shapes the performance, durability, and reliability of components. From pins and fasteners to gears and pulleys, the materials chosen determine not only the functionality but also the longevity of these parts. In this blog, we’ll explore the key considerations for selecting the right material for a particular application.

Ultimately, material selection comes down to a three-step process:

1. Understanding the requirements of the application
2. Identifying potential material(s)
3. Determining cost and availability

Let’s take a closer look at each.

Requirements

To make sure that you are selecting the best material for a specific use, you must carefully consider all the requirements for the application. Selecting the wrong material could lead to performance and longevity issues, with a part failing prematurely. We’ve put together five key questions to help you avoid these problems and accurately determine your needs:

1. Are there any environmental concerns?
   It’s important to understand the conditions which the components will be operating under. For instance: will they be exposed to fresh water, salt water, dirt/sand, or extreme temperatures? What is the exposure time for these conditions? There are many materials, including specialty alloys and resins, that are specifically designed to handle certain environmental factors.
   
   
2. What are the load requirements, if any?
   Load requirements will dictate the strength of the material required. You’ll need to determine the maximum load the application will be seeing, and how long the components will experience this load. For instance, for higher-load applications, you’ll need a material that has high strength and toughness. Candidates include steel, aluminum, or certain alloys that have high strength-to-weight ratios.
   
   
3. Are there any torque requirements?
   Similar to load requirements, you’ll need to know the maximum torque that the application will be experiencing, as well as the frequency of torque application. It’s important, since mechanical stress on a component will impact its performance and longevity. For uses with high torque requirements, you’ll need a material with high strength and consideration of the size of the section.
   
   
4. Is the application lubricated or does it run dry?
   The need for lubrication, or lack thereof, significantly influences material selection. Lubrication is often required to reduce friction and wear, and to enhance performance, efficiency, and longevity. However, in certain situations, lubrication may be impractical or simply not needed. First, you should determine if lubrication is an option for the application. If so, what kind of lubricant is being used? Otherwise, for dry applications, you’ll want to select a material that has properties that minimize friction and wear. These include certain polymers, composites, or solid lubricants such as graphite or PTFE.
   
   
5. Are there other concerns?
   Listed below are other considerations that should be made:

• What is the speed of the components? / What is the load profile?
• How long do the parts operate? Intermittent? Constant?
• Can the components be magnetic?
• Exposure to chemicals/radiation?
• Weight concerns?
• Machinability?
• Cost effective?
• Failure points?
• Are contacting materials compatible?
• Can the material be heat treated if necessary?
• Is impact strength a consideration?

Identifying Potential Materials

There are many materials available today from time-tested metals and plastics, to modern exotic alloys and engineered resins. Listed below are the materials PIC typically uses:

• 303 Stainless – Durable but softer stainless steel (that cannot be hardened), non-magnetic, with good corrosion resistance. It is best in dry and mild corrosive environments. Conversely, 303 is not good for environments with constant moisture. 303 withstands temperatures over 1,000°F, is cost-effective, and readily available. 303 cannot be welded successfully and has reduced formability. Typical components include fasteners, shafts, and gears.

• 416 Stainless (hardened/annealed) – Can be hardened by heat treat, very durable and strong, with good corrosion resistance in the annealed state. Corrosion resistance can be improved when tempered below 700°F, making it great for most environments including salt water and fresh water. 416 is magnetic and withstands temperatures over 1200° F continuously. Typical applications include pump shafts, hardened fasteners, and electrical motors. 416 is not recommended for marine applications or other high chloride environments.

• 17-4 Stainless (hardened/annealed) – High-strength material that offers the highest strength when hardened. 17-4 has the best corrosion resistance among other stainless steel counterparts which can’t be hardened, making it suitable for components exposed to fresh water, salt water, or chemicals. 17-4 is capable of being welded, and withstands temperatures over 900°F. These exceptional properties come with a drawback: 17-4 stainless is expensive. Typical applications include medical device components, food processing, and chemical processing.

• 2024 T4 Aluminum – High strength, softer material with poor corrosion resistance. 2024 is lightweight. It’s non-magnetic and has built-in lubricity. Applications include orthopedic equipment, computer components, and couplings.

• 464 Naval Brass – Hard and durable, with excellent corrosion resistance in both fresh and salt water. As the name suggests, it’s frequently used in marine environments. 464 has excellent built-in lubricity. Applications include marine hardware, aircraft fittings, and specialty bushings.

• Acetal (Plastic) – Good wear resistance / low coefficient of friction, high strength, good stiffness. Acetal is FDA approved with good electrical properties and resistance to some chemicals. It has poor resistance to UV radiation, but is lightweight and great for use in high moisture environments. Applications include medical device components, gears, and bearings/bushings.

Once you’ve created a short list of materials, you’ll need to determine the cost and availability. Your goal is to pick the material that meets the application’s requirements. You’ll want to be careful not to over-spec, especially if more economical and suitable option may be used.