How to Choose the Right Metal for Your Casting Project

Selecting the right metal for your casting project is crucial for ensuring the success of your manufacturing process. Whether you&#;re working in the automotive, defense, or oil and gas industries, understanding how to select the right metal can significantly impact the performance, durability, and cost-efficiency of your components. This guide will walk you through the essentials of choosing the right metal for casting, highlighting the best metals for casting projects and providing valuable casting metal selection tips.

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Understanding the Importance of Metal Selection

Choosing the right metal for casting involves more than just picking a material based on availability or cost. The properties of the metal can affect the casting&#;s strength, durability, and overall quality. Here&#;s a metal selection guide for casting that will help you navigate through the various options:

1. Casting Metal Properties and Selection: Metals have unique properties such as melting points, fluidity, and strength, which affect their suitability for different casting processes. Understanding these properties is essential for making an informed decision.
2. Types of Metals for Casting: The choice of metal depends on the specific requirements of the casting project. Commonly used metals include aluminum, bronze, brass, copper, and cast iron, each offering distinct benefits.

Key Metals for Casting Projects

Here&#;s a closer look at the optimal metals for casting applications and their uses in various industries:

1. Aluminum: Known for its lightweight and corrosion-resistant properties, aluminum is a popular choice for automotive casting. It is used in components such as engine blocks, wheels, and transmission cases. In the defense industry, aluminum castings are used for lightweight yet durable parts in aircraft and military vehicles. Additionally, aluminum is employed in the oil and gas industry for components like pump housings and fittings due to its resistance to corrosion and ability to withstand harsh environments.
2. Bronze: This metal is valued for its strength and resistance to wear and corrosion. Bronze castings are used in defense applications for components like ship propellers and bearings. In the automotive industry, bronze is used for parts such as bushings and gears due to its excellent machinability and resistance to friction.
3. Brass: Brass offers excellent machinability and is commonly used in automotive applications for parts like fittings and valves. Its good corrosion resistance makes it suitable for oil and gas applications, including various fittings and connectors. In the defense industry, brass is used for components like ammunition casings and military hardware.
4. Copper: Copper&#;s high thermal and electrical conductivity makes it an ideal choice for automotive casting applications such as radiators and electrical connectors. In the defense sector, copper castings are used in components requiring high conductivity and resistance to corrosion. The oil and gas industry utilizes copper for piping and tubing due to its durability and resistance to harsh environments.
5. Cast Iron: Known for its excellent castability and durability, cast iron is frequently used in automotive applications for engine blocks and brake components. In the defense industry, cast iron is used for parts such as tank components and machinery due to its strength and wear resistance. The oil and gas industry relies on cast iron for pump casings and valves due to its ability to handle high-pressure environments.
6. Steel: Steel is renowned for its strength, durability, and versatility, making it a widely used metal in casting applications. It is commonly utilized in automotive components such as chassis, frames, and structural parts. In the defense industry, steel castings are essential for weapons systems and armored vehicles due to their ability to withstand high stress and impact. The oil and gas sector also employs steel for robust pipeline fittings and drill components.
7. Stainless Steel: With its exceptional corrosion resistance and strength, stainless steel is often used in applications where hygiene and durability are critical. In the automotive industry, stainless steel castings are used for exhaust systems and various fittings. In the defense sector, stainless steel components are employed in naval applications and military hardware to resist corrosion in harsh environments. The food processing and pharmaceutical industries favor stainless steel for equipment and parts that must meet stringent cleanliness standards.

Metal casting is a complex process that requires numerous considerations when purchasing, including casting design, the metal casting process to be used, and quality control factors.  Ultimately, there are many considerations in metal casting and there is no &#;one size fits all&#; solution.  Therefore, we developed an outline of the various considerations when a customer selects a metal casting solution.  Before reviewing important considerations in metal casting, let us review MetalTek&#;s metal casting processes.

Materials Used by Metal Casting Process

Sand Casting Materials

The sand casting process produces metal components of all sizes and shapes with exterior detail and inner passages using cores (if needed).  Almost any alloy can be sand cast.  In sand casting the &#;purchased tool&#; is a pattern that replicates the part to be cast.  Patterns are usually hardwoods, polyurethane, or other durable material.  The non-reusable sand mold is created by inserting the pattern into a bed of sand, compressing the sand, and removing the pattern.  This leaves a cavity in the shape of the part. 

Molten metal poured into sand casting molds

Molten metal is poured into this cavity by a series of hollow pathways called risers and runners.  After metal solidification, all previously hollow areas (risers, runners, and the cavity made from the pattern) are solid metal.  The risers and runners are removed, leaving a metal part resembling the pattern.

Investment Casting Materials

In investment casting, the tooling is a die with an inner cavity that resembles the part.  Wax is injected into this cavity to create a wax pattern.  The wax pattern is assembled onto a &#;tree&#; with other patterns, which is dipped into a ceramic material to create a shell.  The wax pattern is melted away, resulting in a hollow shell into which molten metal is poured. 

Wax patterns on a tree before the shell is created

After solidification, the shell and tree are removed.  Relative to other metal casting processes, the final part can have a smoother surface, higher dimensional precision, and thinner walls.  This results in cost savings due to lower part weight and less post-cast processing.  With investment casting, there is a large selection of alloys during the material selection process.

Centrifugal Casting Materials

With centrifugal casting, the basic tooling is typically a steel die into which molten metal is poured.  Dies are rotated around a vertical axis (for &#;ring&#; shapes) or a horizontal axis (for &#;tube&#; shapes).  This metal casting process uses centrifugal force to cause heavier material (metal) to move toward the outside diameter (OD) of the ring, and lighter material (oxides and other impurities) to migrate toward the inside diameter (ID). 

Spinning die during horizontal centrifugal casting

The metal will solidify from the OD towards the ID, leaving the purest metal on the outside of the metal casting and pushing the less pure elements toward the center.  The ID is machined to remove impurities, leaving a solid ring or tube of the highest casting quality.

Important Considerations When Selecting a Casting Process

Choosing The Right Alloy for the Operating Environment

There are important considerations in casting that customers need to be aware of before choosing the specific metal casting type (centrifugal casting, investment casting, or sand casting).  For example, what is the operating environment?  Will the component experience high heat?  High wear?  Both?  Will the component need to stand up to corrosion from saltwater?

Nickel aluminum bronze hub bodies for Naval propulsion systems provide the strength to transfer horsepower to attached propeller blades while operating in corrosive saltwater environments.

Once the specific operating environment is defined then the appropriate alloy can be chosen.  Alloy selection mirrors environmental factors, as various alloys hold up better in extreme temperature conditions, under high wear, or in corrosive environments.  MetalTek metallurgists help customers choose the best alloys for their applications.

Optimizing the Manufacturing Process

Any engineer designing a part has a primary objective for the function of the part in question.  This objective is subject to a variety of competing constraints.  We have already discussed the operating environment, which helps determine a minimum baseline for the material/metal used. 

Optimizing the manufacturing process involves identifying and prioritizing all competing constraints.  It is imperative to recognize that these competing constraints typically require the customer and metal casting supplier to determine the optimal balance of cost, quality requirements, and speed to market.  The next section provides a deeper look into the primary considerations for each major metal casting process.

Balancing Cost, Quality Requirements, and Speed to Market

Presuming that the geometry, metallurgical requirements, and total quantity of parts validate the use of metal castings, here are some general considerations among MetalTek&#;s three major metal casting processes:

Sand casting

Sand casting benefits:

The company is the world’s best Other Steel Alloy Casting supplier supplier. We are your one-stop shop for all needs. Our staff are highly-specialized and will help you find the product you need.

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• Lower piece price, tool cost, and lead time
• Broad range of geometries, including holes/passages not machinable
• Near-net shape to reduce machining costs
• Minimal size constraints
• Custom metallurgical compositions

Sand casting limitations:

• Dimensional tolerances (per ISO CT10 to CT12) not typically as tight as investment casting
• Cast thickness of 1/4&#; to 3/8&#; for limited distances; typically minimum of 1/2&#; for larger parts
• Machining required to improve as-cast surface finish (250+ RMS)
• Air-melted alloys

Sand casting best fits:

• Low (single piece) to very high production volume
• Need to eliminate machining and/or fabrication
• Wide range of metallurgical compositions (heat, corrosion, and wear-resistant alloys)
• Use of additive manufacturing/3D printing for sand molds or tooling to reduce cost
• Custom and/or complex geometries

Investment casting

Investment casting benefits:

• Higher metallurgical quality
• Tight dimensional control
• Smoother surface (80-125 RMS)
• Minimal metal waste in casting
• Little or no machining
• Can use with vacuum-melted alloys and air-melted alloys
• Broader range of geometries, including tighter dimensions and tolerances

Investment casting limitations:

• Higher piece price, tool cost, and lead time
• Size limited to 40&#; cube

Investment casting best fits:

• Medium to very high volume
• Expensive or exotic alloys
• Part weight restrictions (e.g., aerospace applications)
• Extreme heat in operating environment
• Many working surfaces or flow paths

Centrifugal casting

Centrifugal casting benefits:

• Directional solidification provides the highest metallurgical quality and superior machinability
• Minimal or no tooling costs for most tube or ring geometries
• Can cast tubes and machine into multiple ring shapes
• Lower costs and lead times than rolled-ring forgings
• Could utilize sand, investment, or other material molds to increase quality in those geometries

Centrifugal casting limitations:

• Geometries are somewhat limited to rings and tubes (which can limit production lot sizes)
• Used primarily with air-melt alloys, with limited size availability for vacuum alloys.
• Must machine ID (it is the riser for the casting)
• OD usually requires machining to remove &#;orange-peel&#; surface.

Centrifugal casting best fits:

• Ring or tube geometries competing against forgings
• Some shaped geometries (extra tooling) where higher metallurgical quality is mandatory

How Does MetalTek Meet Quality Requirements?

MetalTek carefully reviews quality requirements from drawings and specifications prior to accepting an order.  We comply with all industry standards for allowable tolerances in the various metal casting processes, documented by all required/agreed-upon certifications.  In process, we go one step further to ensure compliance with metallurgical requirements.

Solidification modeling for metal casting

Each MetalTek division uses a solidification modeling program to simulate the flow of molten metal into a mold and analyze the predicted solidification as the mold cools.  This model will help in the tool design, including locations for gates and risers, to ensure a metallurgically compliant part.

MetalTek&#;s Advantages

MetalTek strives to build a collaborative relationship with every customer, to best meet both technical and commercial requirements.  The customer&#;s engineering personnel are the experts in the design of their part, and MetalTek is the expert in alloys and metal casting processes. 

We can leverage our wealth of technical expertise and vast industry experience to help your company choose the optimal product design and manufacturing process to meet your objectives. 

Contact us and let us help you with your next project.

About the Authors

Tim Lulling is the Western Regional Sales Manager for MetalTek International. He joined MetalTek in and served in a series of sales roles of increasing responsibility before being named Regional Sales Manager in .  Tim holds a BS in Business and an MBA in Materials Management from Arizona State University.

Armand Garcia is Sales Engineer for California, Arizona, and Nevada at MetalTek International.  He joined MetalTek in and has over 25 years of total experience in the foundry industry.  Armand holds a BS in Mechanical Engineering Technology from California State University, Sacramento.

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