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Which Type of Metal Casting Is Right For You?

THERCAST®,
Articles

Aug 9, 2022

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:

METAL CASTING GUIDE

Casting Process

Advantages

Disadvantages

Continuous Casting

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. 

Little/no material waste

Set-up costs

Dimensional consistency

Mold costs

The product can withstand pressure applications

Simple shapes only

Large footprint

Shell-Mold Casting

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. 

Dimensional accuracy 

High equipment costs

High volume manufacturing

Phenolic resin is expensive

Complex geometries

Shrinkage and porosity

Smooth surface finish

Gating system part of the pattern

Low tooling costs

No moisture, few gases

Additional machining required

A variety of alloys used

Poor material strength

Not labor-intensive

 

Complex geometries

 




METAL CASTING GUIDE

 

Casting Process

Advantages

Disadvantages

 

Pressure Die Casting

 

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.

Dimensionally accurate part

Equipment and tooling are expensive

 

Good surface finish

 

Recycle scrap metal

Ferrous metals are more difficult to cast

 

High Strength

Must trim parts

 

High volume manufacturing

Limited die life

 

Not labor-intensive

Long set-up times

 

Product detail 

 

 

Permanent Mold (Gravity) Die Casting

 

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. 

Smooth surface finish

Slow casting rate

 

Dimensional accuracy 

Rough surface finish

 

Stronger than sand casting

Minimum 4mm wall thickness

 

Can cast thinner walls

Simple design

 

Can cast inserts into part

Tooling is more expensive than sand casting

 

 

 

Semi-Permanent Mold Casting

 

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.

Produce more complex core geometries

Slow casting rate

 

Rough surface finish

 

Smooth surface finish

Simple design

 

Dimensional accuracy 

Tooling is more expensive than sand casting

 

Stronger than sand casting

 

Can cast thinner walls

 

 

Slush Casting

 

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.

Less expensive

Strength difficult to control

 

Can produce hollow casting light in weight

Poor internal geometry control

 
 

Simple, low-cost die

Low melting temperature metals

 

Good surface finish

 

Accurate outer geometry

Requires mechanical turning mechanism

 

Ideal for hollow products

 



METAL CASTING GUIDE

Casting Process

Advantages

Disadvantages

Squeeze Casting

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.

Good microstructure

Limited to smaller size parts

Low porosity

Long cycle time

Equipment is less expensive

Smaller production runs

Good strength and ductility

Limited geometry

Centrifugal Casting 

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.

Product forms almost any wall thickness 

Inaccurate casting ID

Not suited for all alloys

No parting lines

 

High output, low defect

 

Higher mechanical strength

 

Best for pipes and tubes

 

Sand Casting

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.

Inexpensive

Rough surface finish      

Versatile

4mm minimum wall thickness

Low tooling cost 

Slow casting rate

Up to 70% of sand reclaimed

Additional machining required

Commonly used method

 

No product size limitation

 

Investment Casting (lost wax casting)

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.  

Versatile

Costly set-up

Relatively low-cost

Pattern preparation is time-consuming. 

No parting lines 

Machining rarely required

Not suited for high-volume manufacturing

Smooth surfaces

Complex geometries

 

Lost Foam Casting

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.  

Versatile

Low volume

Dimensionally accurate

Preparation is time-consuming. 

No parting lines 

Patterns easily damaged

Machining rarely required

 

Smooth surfaces

 

Complex geometries

 

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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