Injection Molding vs Die Casting, What is The Difference?

Injection molding and die casting are the main methods for mass production of both plastic and metal parts, which can be the components for end products or even the end product itself.
For many people, it is difficult to make a difference between the processes of injection molding and die casting, but you have arrived to the right place as we explain it as clearly as possible.

What is Injection Molding?

Injection molding is a manufacturing process where a mold created with the features and requirements of the part being produced is filled with raw material that has been previously liquified. To make sure the mold is completely filled the material is injected into it by using high pressure, hence the name injection molding.

Advantages of Injection Molding

As it happens with any other process, injection molding can offer a series of advantages depending on the application. The most common ones are:

• Possibility to produce complex and detailed parts.
• High speed production.
• High repeatability.
• Costs due to material scraps is reduced.
• Tight tolerances can be achieved.
• The strength of the part or product can be improved by using fillers.
• Accurate surface finish with a high quality.

Disadvantages of Injection Molding

There is not such thing as a perfect manufacturing process. There are always some negative aspects that should be taken into account when selecting the process for the application in hand. The most relevant disadvantages of injection molding are:

• High initial investment.
• Some materials can be costly.
• The process may be limited to small parts because of the size of injection molding machines and tools. However, large parts can be made of several pieces, but this will obviously take more time and effort, resulting in increased costs.
• Complex parts require increased lead times, especially considering the need for high precision design and testing.
• After the molds are made, it is difficult to introduce changes, especially if the mold is made of hard metals like steel or aluminum.

Available Material of Injection Molding

The most common materials available for injection molding are thermoset materials and thermoplastic materials. Here is a list of the most common names of available material of injection molding found in the market:

• Nylon.
• Polycarbonate.
• Acrylic.
• Polystyrene.
• Polyoxymethylene (POM).
• Polypropylene (PP).
• Acrylonitrile Butadiene Styrene (ABS).
• Thermoplastic Polyurethane (TPU).
• Polyethylene (PE).
• Thermoplastic Rubber (TPR).
• Celcon® (Acetal).
• High-Impact Polystyrene (HIPS).
• Low-Density Polyethylene (LDPE).

Application Product Examples

The most common applications of injection molding are found in electronics where joints and housings are typically made by using this process. Other good application product examples include but are not limited to:

• Wire spools.
• Bottles and other types of packaging.
• Bottle caps.
• Automotive parts, including dashboards, handles and other internal pieces.
• Medical equipment.
• Toys like Lego®.
• Agricultural tools and devices.
• Household goods such as containers and drinkware.
• Construction parts such as roofing vents, railing gaskets and deck fasteners.

What is Die Casting?

Die casting is a manufacturing process which is very similar to injection molding, as it involves filling a mold (die) with molten material by the use of pressure and letting the material cool off until it solidifies in the shape of the desired part. The main difference is that the molten material is a type of metal instead of being thermoset or thermoplastic materials.

Advantages of Die Casting

Some advantages of die casting are very similar to those obtained when using injection molding because the process is very similar. However, here are the most relevant advantages of die casting:

• Increased dimensional precision.
• Increased productivity compared to other processes such as machining.
• High quality surface finish which reduces and sometimes eliminates the need for post processing.
• Possible to achieve very small parts with fine details.
• Possible to achieve thin walls.
• High tensile strength of the resulting part.

Disadvantages of Die Casting

As mentioned before, there will always be negative aspect to be considered when choosing a manufacturing process, as they may affect the result on the specific application. Here are the most important disadvantages of die casting:

• High initial investment in tooling and machinery.
• Limited to metals with not very high melting points.
• Only cost-effective when producing high volume.
• Not possible to perform hardening or tempering treatment on the cast because of porosity which could lead to cracks.
• High lead times, especially for complex parts that require high precision design and more testing.

Available Material of Die Casting

As mentioned before, materials used for die casting are metals and alloys which have melting points that are not very high. The most common names found in the market as available material of die casting are:

• Magnesium
• Zinc
• Aluminum
• Copper
• Lead
• Silicon Tombac
• Tin
• Brass and bronze

Application Product Examples

Die casting parts are found in many different industries, being one of the most prominent the automotive industry. However, die casting is used in the production of many general engineering equipment such as pumps and power tools. Here are other application product examples of die casting:

• Electrical housings.
• Engine fans.
• Compressor valves.
• Door handles.
• Locks and gears.
• Medical valves.
• Screws and bolts.
• Bearings.
• Cell phone frames.
• Heat sink for led headlights.
• Rods and bushings for bicycle gears.

Injection Molding vs Die Casting, What is The Difference?

It is obvious that both molding and casting are very similar processes. However, there are some differences, being the materials used to produce the parts the most relevant one. Another difference can be found in how the molds and dies are made, since some injection molding manufacturers are currently 3D printing their molds. Finally, plastic parts are not as strong and durable as metal parts, so this could be an important difference to consider depending on the application.
To visualize the differences a bit better, take a look at the following table:

Summary

Both injection molding and die casting are manufacturing processes for mass production of large volume. Although they have similarities, these processes should be differentiated as the materials used for each are different, thus affecting the costs associated and the possible application for each of them.
Injection molding is recommended for those applications with reduced exposure to impact, stress and harsh environments, while die casting works perfectly fine for those applications where high strength and durability are required. The selection should be made based on the application and the budget available.