What is the Difference Between Molding and Casting?

In most cases, when someone is discussing the difference between molding and casting, they’re referring to die casting and injection molding. It generally breaks down to material; molding is for plastic and casting is for metal. These processes are somewhat similar, though there are a few key differences to consider. Usually, a manufacturing partner will provide the best advice on which one to choose. However, it’s still wise for creators to understand the difference between molding and casting, so they can make an informed decision.

A lot of the decision will center on the types of materials chosen for the product, though that isn’t the only consideration. The creator will also need to think about the required quantity and the quality of each part.  By examining the specific needs of the project, the choice between molding or casting will be much easier.

Deciphering the Difference Between Molding and Casting 

The main difference between molding and casting is the use of the material in the process. Casting will typically involve metal, while molding focuses on plastics. In both cases, the melted material goes into a die or mold to create the final form. However, some other key differences in the process will change the final product.

In molding, the material is injected into a form typically made of metal. There are a few different options in injection molding. Common types include:

• Thin wall molding: This process centers on making the wall of the part as thin as possible to create a lighter, more flexible piece. Typically, the width of the wall itself is under .025 of an inch.
• Gas-assisted injection molding: In some injection molding cases, materials can shift, leading to distorted end products. Gas-assisted injection allows the creator to blast a hole or hollow point into the mold and ensure it does not distort as it cools.
• 3D Printing: While it’s a category in and of itself, 3D printing is a type of injection molding frequently used in prototyping for its relatively low cost and wide availability.

In casting, the liquid metal is poured into a form made of silicone rubber or a similar material. Die casting has two primary types:

• Hot chamber die casting: This is the more common form of die casting. In this, the material is heated inside the casting chamber, hence the term “hot chamber.” As it eliminates the need to melt the metal elsewhere, it’s the preferred method.
• Cold chamber die casting: Cold chamber die casting involves liquefying the metal first and then putting it into the cold chamber for funneling into the die. This is typically a process completed for metals with high melting points.

These processes can yield vastly different results. It is essential to be familiar with the general pros and cons of molding versus casting before narrowing down the chosen method.

	Molding	Casting
Pros	The process is typically faster than casting Injection molds can allow for diverse types of materials The injection offers very accurate results, even in high-production	This process results in a durable, high-quality product Casting allows for greater design complexity It’s ideal for completing many intricate, disparate designs at the same time.
Cons	Injection molds can be quite expensive to create, so tooling budgets will have to be high The result may be less durable and have a lower quality than one would find in casting	This does not typically allow for the casting of large parts High melting point metals, like steel, won’t work Die materials can be expensive

There are many different techniques involved in both casting and molding, which can impact the overall pros and cons of these processes. It’s wise to discuss their risks and benefits with a professional. In some cases, it may even be advisable to use a combination of the two methods to create the best possible products.

Choosing Between Casting and Molding 

There are a lot of aspects to consider when comparing the differences between molding and casting. However, there are some general circumstances where one will outshine the other.

If the intention is to make a lot of complex parts where accuracy is vital, casting is the better option. Typically, it’s suitable for making many different parts, but it is not ideal when hundreds or thousands of the same elements are required. However, the finish on casting has a higher quality look and feel, which lends itself well to small, exacting components.

Molding, on the other hand, can be an ideal option for mass production where quality isn’t as vital. It’s also suitable for when the parts are stand-alone and don’t need any finishing after they’re completed. It’s also a good option for prototyping as it’s fast and relatively accurate. However, it’s important to remember that setting up a plastic injection molding program can be fairly expensive, so it’s best to work with a third party if doing a small manufacturing run.

The difference between molding and casting is not limited to simple material types. These processes can have markedly different impacts on the end result. That’s why it’s vital to work with a partner who understands the ins and outs of each.