Casting vs Molding: Key Differences Explained

Casting and molding are the most common operations used to create precise and complex parts in today’s manufacturing world. 

Although both operations are based on a similar working principle, various factors set them apart and should be considered when selecting the right process for your application.

The difference between casting and molding is that casting involves the melting and shaping of metal, whereas molding is best suited for melting and shaping plastics. Generally, casting is ideal for making metal products with complex geometries and molding for large-scale applications.

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Difference Between Casting and Molding

Parameters	Molding	Casting
Suitable Materials	Plastics and polymers like ABS, nylon, TPU, etc.	Metals like aluminum, copper, zinc, etc.
Production rate	High	Low to Moderate
Accuracy	Low	High
Cost	Moderate to high	Low to Moderate

Difference in Process: Casting vs Molding

When it comes to the process, the most significant difference between casting and molding is the choice of material. 

Casting primarily deals with metals whereas molding is used for plastics. Both processes involve a melted material that goes into a die to create a structure. 

Die casting can be broadly classified into hot-chamber and cold-chamber die-casting. 

In the case of hot chamber die casting, metal is melted inside the die chamber thereby eliminating the need to melt the metal beforehand. 

This is a more commonly used method and is suited for metals with a comparatively low melting point. 

Cold chamber die casting requires the metal to be melted before it is poured into the die chamber, a common example includes gravity casting. 

The melted metal solidifies in the cast and creates the structure. This method is more suited for metals with a higher melting point. 

You can also use alloys to reduce the melting point of the workpiece and perform alloy casting.

Molding can also be divided into a few types. The common methods of molding are thin wall molding, gas-assisted injection molding, and 3D printing. 

Thin wall molding, as the name suggests, is used to create parts that have a wall thickness of 0.025” or less. This is used to make lightweight and flexible parts. 

Gas-assisted injection molding uses a pressurized gas, most commonly Carbon Dioxide, to create a cavity in the mold and prevent its distortion as the part cools down.

This is most suited for parts that are hollow but require high strength, like handles.  

3D printing is also a type of injection molding that deposits a melted filament onto a plain surface to create extruded parts. This can create complex geometries and can be used for rapid prototyping.

Difference in Tools Required

Equipment may vary depending on the size and scale of your manufacturing but there are a few tools that will be required regardless. 

The most commonly used casting equipment includes a crucible, ladle, tongs, a heat source such as a furnace, and safety gear. 

The crucible is the vessel used to melt the metal to be poured into a die for casting. Hence, the crucible must have a significantly higher melting point than the metals you are melting in it.

Crucible can be formed of different materials like ceramic, clay graphite, silicon-carbide, and steel.

Clay graphite and silicon-carbide crucibles are most commonly used as they can withstand extremely high temperatures and are non-reactive, hence don’t contaminate the melted metal.

Steel is inexpensive and can be used for metals that have a low melting point like aluminum and zinc. However, they are prone to flaking and hence can contaminate your cast.

In the case of molding, especially injection molding, there are four main components: a power source, an injection unit, a clamping unit, and a mold assembly. 

The injection unit contains a large container called the hopper that holds the molten plastic, a mold transportation system that can either be a ram injector or a reciprocating screw, a barrel, and a nozzle.

After the injection unit, comes the clamping unit which has two plates- one is stationary and one is movable. The movable plate can be hydraulically powered to secure the mold while it cools and solidifies.

Difference in Accuracy: Which is higher?

Casting can produce parts with higher accuracy compared to molding. 

Casting is more suited to make parts that are geometrically more complex and need better finishing with more focus on detailing. 

Molding, on the other hand, is used to mass-produce parts, and although molding can also produce accurate parts, it is mostly used for applications that focus more on quantity rather than quality. 

Unlike molding, cast parts may need some post-production finishing touches to further enhance their dimensional accuracy and surface finish. 

Which One to Choose For Your Application? Casting or Molding

When you are choosing between molding and casting for your application, it is important to understand their differences and the kind of end results they produce. 

Molding offers a higher rate of production than casting, making it best suited for large-scale applications where high repeatability with a good surface finish is desired.

Apart from that, its quick cycle time and good dimensional accuracy make molding ideal for rapid prototyping.

However, molding generally involves a comparatively higher cost than casting as it requires special equipment to force the molten material into the mold, especially injection molding.

On the other hand, casting is best suited for manufacturing complex metal workpieces with good dimensional accuracy.

Unlike molding, casting generally involves breaking the mold to remove the metal casting, this limits casting from being used in large-scale manufacturing processes.

It is prominently used for manufacturing large-sized complex metal workpieces which otherwise require extensive machining to get the desired part.

Die Casting vs Injection Molding

Parameter	Die Casting	Injection Molding
Suitable Material	Low melting point metals	Plastics and polymers
Accuracy	High	Moderate
Post-manufacturing finishing	Minimal	Mostly needed
Setting up cost	Moderate	High
Size of parts	Small to medium	Variety of sizes
Production time	Moderat to high	Low

Die casting is the process of heating and melting non-ferrous metals like zinc, aluminum, copper, etc., and remolding them under high pressure.

It consists of a die made of metals like tool steel that offers high resistance to temperature and pressure. The molten metal is forced into the die cavity under high pressure.

The pressurized flow of molten metal ensures that the metal completely fills the cavity of the die, making it ideal for manufacturing parts with complex geometries.

Apart from that, each metal has its pre-defined shrinkage ratio, and performing die casting while keeping in mind the shrinkage ratio will help you produce parts with high accuracy, that require minimal post-processing for finishing.

Injection molding, on the other hand, is a process of fabricating parts made out of plastics and polymers that are melted, cooled, and solidified in a mold. 

Since this process uses plastics that have a low melting point, the molds can be made of metals like aluminum. 

Unlike casting, molded parts have a high surface finish and do not require any post-manufacturing finishing process.

Die casting is most suited for applications where you need to produce different parts that vary in shape and intricacies. 

However, the size of the parts manufactured is small and you can’t use high melting point metals like steel to make your product. 

On the other hand, injection molding is best suited for applications that require high-volume production of large-size products.

This process allows you to make parts with high accuracy and quick cycle time, making it ideal for prototyping.

However, setting up an injection molding machine can be expensive for small-scale projects, so it is recommended to outsource your part for such projects.

Frequently Asked Questions (FAQ)

What is the difference between expendable and non-expendable mold casting?

Expendable mold castings are temporary molds that can be used only once. These can be made from resin-bonded sand, ceramic shell, or foam and are typically used for low-scale manufacturing. Non-expendable molds can be used multiple times and are commonly made of ceramic, steel, or cast iron. These are permanent molds and are commonly used to create large volumes of the same object. 

How is a die different than a mold?

The main difference between a die and a mold is the type of products they shape and the material they are made of. Die is used to reform molten metals like aluminum, copper, and zinc and is usually made of metals like steel, having a high melting point. Molds, on the other hand, are used to shape plastics and polymers, hence can be made of metals like aluminum. 

What is sand casting?

Sand casting is a type of casting process that uses sand as the mold structure. The molten metal is poured into the sand mold under gravity and is allowed to cool and solidify, thereby taking the shape of the mold.