Choosing the right type of metal casting for your product design can be challenging with the numerous metal casting processes. This is a decision best made during the early stage of product design. Design is typically 5% or less of the product cost, affecting 70-80% of the final product cost. Therefore, it is advisable to form a cross-functional team when moving forward with the optimal metal casting process decision.
Design Variables to Consider
The designed product is a great starting point for determining the desired result. There are a lot of variables to consider; for example, what is the desired product quality? What are the concerns regarding surface finish, dimensional tolerance, porosity, texture, etc.? What about the component geometry?
Minimum sectional thickness and core size should be considered as they are critical to the selected molding process. It is also essential to consider the production parameters, including sample production quantity, development, tooling costs, equipment costs, lead-time, heat treatment, machining, quality control procedures, and measurement equipment. Can the process be fully automated?
Types of Metal Casting: A Guide
Below is a casting guide to provide an overview of the different casting processes, including the advantages and disadvantages:
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METAL CASTING GUIDE
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Casting Process
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Advantages
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Disadvantages
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Continuous Casting
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This process feeds molten metal into a mold. Water cooling partially cures the part. Semi-solid metal is then sent through a guide that stretches the material to the desired thickness. Metal continues to cool and solidify. The product is then sent through straighteners and cut to length.
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Little/no material waste
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Set-up costs
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Dimensional consistency
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Mold costs
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The product can withstand pressure applications
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Simple shapes only
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Large footprint
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Shell-Mold Casting
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Like sand casting, shell-mold casting is an expendable mold casting process that uses resin-covered sand to form the mold. Shell molding uses sand mixed with a bonding resin to cover a heated pattern and form a mold. Sand is packed over the form to create a cavity used as a casting mold. Ferrous materials can be cast along with softer materials like aluminum alloys and brass.
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Dimensional accuracy
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High equipment costs
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High volume manufacturing
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Phenolic resin is expensive
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Complex geometries
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Shrinkage and porosity
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Smooth surface finish
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Gating system part of the pattern
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Low tooling costs
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No moisture, few gases
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Additional machining required
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A variety of alloys used
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Poor material strength
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Not labor-intensive
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Complex geometries
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METAL CASTING GUIDE
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Casting Process
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Advantages
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Disadvantages
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Pressure Die Casting
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Molten metal is forced under pressure into a permanent mold. Once the metal cools, the mold separates, and the part is removed. Aluminum and aluminum-zinc alloys are commonly used materials.
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Dimensionally accurate part
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Equipment and tooling are expensive
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Good surface finish
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Recycle scrap metal
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Ferrous metals are more difficult to cast
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High Strength
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Must trim parts
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High volume manufacturing
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Limited die life
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Not labor-intensive
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Long set-up times
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Product detail
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Permanent Mold (Gravity) Die Casting
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Molten metal is poured from a ladle or vessel into a permanent mold. Once the metal cools, the mold separates, and the part is removed. The molten material is gravity fed and adjusted by tilting the die. This process can use iron, but yellow brasses are not advised.
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Smooth surface finish
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Slow casting rate
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Dimensional accuracy
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Rough surface finish
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Stronger than sand casting
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Minimum 4mm wall thickness
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Can cast thinner walls
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Simple design
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Can cast inserts into part
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Tooling is more expensive than sand casting
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Semi-Permanent Mold Casting
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Like permanent mold casting, the cores used in the casting process may be expendable sand cores. More complex core shapes are possible. Molten metal is poured from a ladle or vessel into a permanent mold. Once the metal cools, the mold separates, and the part is removed. The molten material is gravity fed and adjusted by tilting the die. This process uses zinc, aluminum, magnesium, tin, or copper.
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Produce more complex core geometries
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Slow casting rate
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Rough surface finish
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Smooth surface finish
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Simple design
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Dimensional accuracy
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Tooling is more expensive than sand casting
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Stronger than sand casting
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Can cast thinner walls
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Slush Casting
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Slush casting is excellent for hollow products (lamps, statues, toys, etc..) Molten metal is poured into the metal mold, and it is allowed to cool for a short time such that only the outer surface metal gets solidified. The excess molten metal is then poured out of the hollow shell. The hollow casting is obtained when the halves of the mold are separated.
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Less expensive
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Strength difficult to control
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Can produce hollow casting light in weight
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Poor internal geometry control
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Simple, low-cost die
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Low melting temperature metals
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Good surface finish
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Accurate outer geometry
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Requires mechanical turning mechanism
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Ideal for hollow products
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METAL CASTING GUIDE
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Casting Process
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Advantages
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Disadvantages
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Squeeze Casting
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A combination of gravity and pressure casting. Metal is poured into the preheated mold, and a ram applies pressure from the top to force the metal into the product shape. Sand cores are often used. The process can use a wide variety of alloy choices.
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Good microstructure
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Limited to smaller size parts
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Low porosity
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Long cycle time
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Equipment is less expensive
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Smaller production runs
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Good strength and ductility
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Limited geometry
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Centrifugal Casting
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This process uses a water-cooled mold rotated using rollers on its central axis at high speed while liquid metal is poured into the mold. Centrifugal force pulls the liquid metal along the mold’s surface in an even layer. The process is ideal for pipe and tubing. Materials often used include zinc, aluminum, magnesium, tin, or copper.
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Product forms almost any wall thickness
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Inaccurate casting ID
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Not suited for all alloys
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No parting lines
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High output, low defect
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Higher mechanical strength
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Best for pipes and tubes
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Sand Casting
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Compacted sand is mixed with a bonding agent and packed around a form part. A flask holds the sand in place. The pattern is removed, and hot metal is poured into the sand mold. Once cool, the sand is removed from the cast product. There are variations to this process depending upon the automation involved. Suitable for casting ferrous materials.
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Inexpensive
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Rough surface finish
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Versatile
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4mm minimum wall thickness
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Low tooling cost
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Slow casting rate
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Up to 70% of sand reclaimed
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Additional machining required
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Commonly used method
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No product size limitation
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Investment Casting (lost wax casting)
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Best for detailed, dimensionally accurate pieces with minimal machining required. Injection mold forms wax patterns that are ceramic coated. A heated mold melts the wax, and molten metal is injected into the ceramic mold. Ceramic mold, gates, and riser are not needed in the process.
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Versatile
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Costly set-up
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Relatively low-cost
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Pattern preparation is time-consuming.
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No parting lines
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Machining rarely required
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Not suited for high-volume manufacturing
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Smooth surfaces
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Complex geometries
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Lost Foam Casting
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Similar to investment casting but uses polystyrene foam instead of wax. Best for detailed, dimensionally accurate pieces with minimal machining required. Injection mold forms wax patterns that are ceramic coated. Heated mold melts the wax and molten metal into the ceramic mold. Ceramic mold, gates, and riser are not needed in the process.
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Versatile
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Low volume
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Dimensionally accurate
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Preparation is time-consuming.
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No parting lines
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Patterns easily damaged
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Machining rarely required
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Smooth surfaces
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Complex geometries
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Processes Without the Guesswork
Once the best metal casting processes are established, several other steps are needed to ensure the product is brought online without delays, defects, or tooling problems. This is where strong consideration of high-performance simulation software is essential to a smooth start-up. These products allow virtual engineering across various forming processes, including liquid materials, metallic solids, and polymers.
The addition of casting simulation software takes the guesswork out of the design and avoids the problematic relationship between process parameters and casting properties before the first part is in production. This allows the company to expedite the time to market, productivity, and utilization and reduce scrap to minimum levels.
Learn More
The first step to consider is the benchmark software by Transvalor Americas. We carry 3-D simulation software for different types of metal casting processes, including the industry's best technical support and problem-solving built into the casting software. Contact Transvalor USA to learn how casting simulation software guarantees a faster, smoother time-to-market.
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