Mastering Metal Selection: A Guide for Design Engineers

Selecting the right material for an engineering project is critical for lifetime cost-effectiveness, project integrity and safety. Design engineers must select materials that are durable and resistant to environmental factors, deliver predictable performance and meet compliance requirements.

This metal selection guide will discuss the common types of metals, fundamental considerations and the impact of material selection on manufacturing processes, so you can make an informed decision. 

Fundamental Fabrication Considerations in Metal Selection

Mechanical properties, product costs and expected material function are critical considerations when selecting metals. Identifying suitable materials ensures project integrity and compliance with industry standards and government regulations.

Consider the following: 

• Mechanical property requirements: Evaluating a metal’s mechanical properties ensures that a material will perform as needed under expected conditions. Designers should consider critical mechanical properties like strength, ductility, fatigue strength and hardness. Strength reflects a material’s ability to withstand stress or resistance to compression, and fatigue stress highlights the ability to withstand repeated or fluctuating stresses without failure. Ductility refers to a metal’s ability to deform plastically before fracturing. Hardness indicates a material’s resistance to scratching, wear and indentation.
• Environmental factors: Operating environments significantly impact the metal selection process because environmental factors can affect material performance. You must assess material properties to determine how a metal will respond to extreme temperatures, chemicals, humidity and potentially abrasive elements. For example, stainless steel, which is corrosion-resistant, would be an ideal choice for projects where exposure to salt water or chemicals is common.
• Cost implications: Conduct a cost-benefit analysis when choosing design materials. Beyond the initial costs of a metal, design engineers should evaluate future costs such as maintenance, repairs and replacements. Investing in higher-grade materials often results in replacement and repair cost savings down the line. 
• Regulatory and compliance considerations: Industry standards and government regulations should guide metal selection. Industry standards often revolve around components’ shape, size, testing and material types for specific applications. Government regulations generally highlight material quality and reliability for specific applications. For example, ASTM A36 provides guidance for carbon structural steel shapes, bars and plates of structural quality for riveted, welded or bolted bridge or building construction. Alternatively, ISO 683 is an international standard regarding heat-treatable steels, alloy steels and free-cutting steels. 

Metal Comparison: Comparing Common Fabrication Metals

Metals are among the most common materials for engineering projects due to their performance reliability and ability to improve material properties by creating alloys. Common design engineering materials include:

Carbon Steel

Carbon steels are a combination of iron and carbon. Some grades may contain small amounts of additional elements, but carbon remains the primary alloying ingredient. Adding carbon increases the material’s hardness and strength. 

Plain carbon steels come in several types — low-carbon, medium-carbon and high-carbon steel. Low-carbon steel has low strength and high ductility. This metal is very weldable and relatively inexpensive to produce. Common applications include structural shapes, wire, sheet metal and machine parts. 

Medium-carbon steel contains more carbon than low-carbon steel. You can also heat treat this material to increase strength. This grade is common for applications such as gears, shafts, machine parts and axles. 

High-carbon steel contains the highest amount of carbon of the three types. This metal has low ductility but high strength. Lower ductility makes high-carbon steel more brittle, but you can temper the material for maximum wear resistance. Common uses include cutting tools, high-strength wires, springs and dies.

Stainless Steel

Stainless steel is known for its corrosion resistance due to the addition of the alloying ingredient chromium. The corrosion-resistant properties and high strength of stainless steel make the material suitable for various applications, including those in environments exposed to harsh weather, chemicals or moisture. There are several common types of stainless steel: 

• Austenitic stainless steel: One of the most common stainless steels, this type has the highest corrosion resistance and a low carbon content, making it the most weldable. Common uses are piping, pressure vessels and fasteners. 
• Ferritic stainless steel: Ferritic stainless steel has medium carbon content and high chromium content. You can strengthen this type through cold work. Applications include cladding, handrails and electrical enclosures. 
• Martensitic stainless steel: This type of stainless steel has a high carbon content, which can make it difficult to weld. Heat treatments can strengthen martensitic stainless steel. Valves, bearings, fasteners, springs and pumps often use this type. 
• Duplex stainless steel: Duplex stainless steel can have as much as twice the strength of austenitic steel. This type offers high roughness, wear resistance and corrosion resistance. Duplex steel has a temperature limit but is generally weldable. Applications include rebar, piping, hulls and platforms. 
• Precipitation-hardened stainless steel: This type of steel offers high strength and resistance to temperature and corrosion. It is ideal for demanding applications and is suitable for shafts, springs, bolts, gears and fasteners. 

Aluminum

While pure aluminum is weak and soft, alloy ingredients can increase strength while delivering lightweight and corrosion-resistant properties. Aluminum also has a high strength-to-weight ratio, making it suitable for constructing strong yet lightweight structures. This metal also offers easy fabrication, allowing teams to fabricate the material into a desired thickness with speed and low costs. 

You can find several types of aluminum leveraging different materials as a primary alloy. Copper alloys enhance strength and toughness, while magnesium alloys offer excellent corrosion resistance. Magnesium and silicon alloys are suitable for structural applications. Depending on the alloying ingredient, aluminum can be suitable for aircraft structures, heat exchangers, sports equipment, offshore platforms, machine frames and housing, tubing and more. 

Material Selection Impact on Manufacturing Processes

It’s also important to consider how metal selection will impact manufacturing processes. Top considerations include:

• Weldability: Metal welding is vital in modern manufacturing. Weldability often depends on chemical composition and part application and geometry. Steel is the most commonly welded metal. Aluminum welding requires precise heat control, and alloys can require additional parameters. 
• Laser cutting optimization: Laser cutting optimization involves matching laser type, power, gas and process parameters to a metal’s specific properties. For example, fiber lasers can deliver enhanced efficiency when working with stainless steel. For aluminum, higher laser power can overcome thermal conductivity and reflectivity. 
• Forming and bending behavior: Forming and bending behaviors can impact manufacturability and overall costs. These behaviors affect everything from tooling and process design to product quality and performance. Materials that are more challenging to form can increase tooling wear, lead to higher scrap rates or slow production rates. Metals with high ductility can better withstand bending without cracking, while thicker metals are harder to bend. Metals with higher yield strength will require more force.
• Surface treatment and finishing compatibility: Surface treatments and finishing ensure a product meets functional, durability and aesthetic requirements. However, some metals require specific finishing techniques, and some finishes are only possible for certain metals.

Connect With PBZ Manufacturing for Project Assistance

PBZ Manufacturing is your one-stop shop for manufacturing, engineering, assembling and finishing solutions. When you want to ensure optimal results, our experienced team can leverage advanced capabilities to reduce your timeline and costs. Connect with us to learn more about our capabilities and how we can assist your next project.

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