Metal Injection Molding vs. Die Casting

Metal injection molding vs. die casting is a major decision. Both processes are used throughout industries worldwide, and some industries even use both MIM and die casting methods in production.

Metal injection molding is intricate and requires several steps to create parts. It is well suited for small intricate parts and large volume manufacturing. 

Die casting, on the other hand, has fewer steps and is economically feasible for smaller and larger runs when compared with metal injection molding.

When compared with other fabrication methods, both metal injection molding vs. die casting has high automation and setup costs. 

Before making a decision, it is important to understand the processes and outcomes of both methods.

What is metal injection molding? 

Metal injection molding is a metalworking process where powdered metal is mixed with a binder to create high-strength metal parts and components.

MIM has gained steady popularity over the years because of its low cost and ability to produce parts with high strength and wear characteristics that cannot be achieved with other metal production methods.

Unlike other metalworking processes, metal injection molding can produce small and intricate parts from a variety of materials at a much lower cost. It is also ideal for parts with thin wall specifications (i.e., 100 micrometers).

Additionally, its unique molding process can create many intricate parts in a single run.

Metal injection molding is a net shape process meaning the final product does not require additional finishing or machining. While traditional metalworking processes have a significant amount of material waste, MIM has almost no waste, which translates to cost savings during production.

Metal Injection Molding (MIM) process

When comparing the metal injection molding vs. die casting process, the MIM process is more intensive.

1. Metal alloy is formed into a fine powder and mixed with a thermoplastic binder to form a feedstock. The binder acts as a processing aid and must be removed after injection molding.

2. Only the properties of the metallic powder determine the properties of the final part. During the mixing process, the binder and metallic powder are heated. Feedstock can either be manufactured in-house or purchased ‘ready to mold.’

3. An injection molding machine injects the feedstock into the mold. Once the part is formed, it is called a ‘green’ part. MIM process has similar principles to plastic injection molding and can produce parts with similar configurations

4. The molded part is allowed to cool then ejected from the mold.

5. Next comes de-binding by using a catalyst, a solvent, and thermal furnaces. The de-binding process helps remove the thermoplastic binder while maintaining the integrity of the final part. Sometimes, the binder is still present at the end of this process, but it can evaporate through the part’s microscopic pore network.

6. The part is then heated to sinter the powder and create a robust net shape part. During this process, the part can lose between 15% to 30% volume. MIM parts can also undergo additional heat or surface treatments to achieve the desired application.
   

Metal injection molding’s design flexibility and net-shape process make it a desirable manufacturing option across many industries.

Metal Injection Molding (MIM) Applications

A significant advantage of MIM parts is the ability to combine design complexity with high volume when producing small parts. MIM parts can be comparable to die cast parts in terms of quality. In fact, it is possible to efficiently produce parts through metal injection molding, where it would be difficult or nearly impossible to do with other methods. 

Where metal injection molding stands out is its ability to create hard and durable parts with tight tolerances. A knowledgeable manufacturing partner can produce parts that are accurate to 3mm.   

A part’s application can play a large role in deciding if metal injection molding vs. die casting is the best option.

By combining multiple operations, this method could also save manufacturers substantial lead time.

Metal injection molding was developed in the late seventies and has grown exponentially in popularity as many industries recognized its value.

• Firearms – triggers, safety, magazine catch, fire suppression. 
• Medical device industry – articulation gears, joint replacements, drug delivery devices.
• Automotive – turbocharger vanes, rocker arms, shift levers.
• Consumer electronics – lightning connectors, heat sinks, cold plates, fiber optic parts, and various mobile phone parts.
• Aerospace – flap screws, engine components, valve holders, and rocket burners.

What is Die Casting?

Die casting is a metal casting process used in the manufacturing of non-ferrous metal parts. Molten metal is injected under high pressure into a die where it is allowed to cool, and then the part is ejected.

Metals and alloys such as aluminum, zinc, copper, magnesium, and lead are the most common cast metals. Depending on the type of metal being cast, a hot- or cold-chamber machine is used.

Dies are created with the impression of the part that will be cast. There are four different types of dies:

• Single cavity – used to produce one part or component.
• Multiple cavities – creates a number of identical parts or components.
• Unit die – produces different parts during a single cast cycle.
• Combinations die – used to produce several parts that complete an assembly.

Sophisticated die casting machines are used to maintain quality control. Machines can be automated for part or all of the process.

Die Casting Process

Die casting has been around for almost 200 years and most techniques follow the same general process. Some industries have developed additional steps to help meet their manufacturing needs, but they still follow the steps below.

1. Clamping: Dies are cleaned and clamped shut. They are then lubricated to prevent sticking and to control the die’s internal temperature.

2. Injection: Molten metal is injected into the die at high pressure (when using hot or cold chamber casting). Pressures can range from 20,000psi to 31,000psi. Injection time can vary depending on die complexity and the desired wall thickness of a part. Dies with multiple patterns or internal caverns can take longer to fill.

3. Cooling: This process begins the instant molten metal enters the dies. Once the die cavity is filled, the metal can begin to cool. Geometric complexity and the wall thickness of a part all require longer cooling times.

4. Ejection: Once a part is completely cooled, the die halves are pulled apart, and the part is ejected. The process can then start over for the next cast part.
   

Excess metal and flash must be trimmed either manually or through a different die.

There are different die casting methods available for manufacturers. Typically, a part’s application, metal type and run size will determine which method is the best option.

The three primary methods are:

• Gravity die casting
• Hot chamber die casting
• Cold chamber die casting

Gravity die casting is much like its name suggests. Molten metal is poured into a die from above and is filled by the force of gravity. This process is slower and not well suited for longer production runs. Because metal enters the cavity at a slower speed than its hot and cold chamber counterparts, less folding turbulence occurs with gravity die casting, which means less air is trapped in the cast part.

Pressurized die casting forms such as cold and hot chamber ally for faster production runs and are highly automated. This method allows for even distribution of molten metal and can produce parts with thinner walls than through gravity die casting.

Cold chamber die casting is used for metal with high melting points such as aluminum, brass, and copper. Metal used in this process is heated in an external furnace and then ladled into the machine’s chamber, where it is injected under high pressure into the die.

The hot chamber die casting process is ideal for metals with lower melting points like tin, zinc, lead, and some magnesium alloys. Metal is heated in a furnace that is attached to the machine and then fed through a gooseneck directly into the die.

Die Casting Applications

Die casting’s versatility in material options and design flexibility makes it a popular choice to manufacture parts across countless industries. Companies and engineers can create unique parts to fit their specific needs both quickly and accurately.

Companies like General Motors have tweaked the die cast process for their own purposes, and their developments have led to additional breakthroughs in different industries. Their creation of the Acurad die casting process now has applications in the U.S. military.

• Automotive industries use die casting to create powertrain systems, GPS and entertainment system housings, retainers, gear housings, transmission, and engine components.
• Medical device industry parts include computer covers, hospital equipment controls, peristaltic pumps, surgical devices, and blood analysis machines.
• Lawn, Garden, and Recreation industries have seasonal demands for cast parts such as hydrostatic axles, outboard gear cases, marine undercuts, RV chassis, and steel liner inserts.

MIM vs. Casting: Advantages and Disadvantages

MIM Advantages

• Produces net shape parts, which eliminates secondary processes.
• Wide range of alloys available, with nickel, copper, titanium, and iron-based metals being the most popular.
• Sintering process creates high mechanical strength.
• Creates parts with tighter tolerances and can be accurate to 3mm
• Variety of surface treatments available.
• Full freedom of design and ability to build complex parts.
• Flexible production adjustments.
• Virtually no waste because all product is injected directly into the mold.
• High-temperature alloys can be used without a negative impact on tool life.

Die-Cast Advantages

• Depending on the metal alloy, die casting could be up to 30% cheaper than metal injection molding.
• The process can be used in a wide range of applications and industries.
• Dies can be used repeatedly.
• Processes can be fully automated, reducing labor costs.
• Parts of other materials can be embedded in die castings – Complex fasteners or inserts can be included in the final component.
• No secondary operations are required.
• Longer die life (1MM compared to 150K-300K with MIM).

MIM Disadvantages

• MIM is a higher cost process than die casting.
• Lower die lifespan (150K-300K shots).
• Must accurately account for shrinkage as the part can lose up to 30% volume during the sintering stage.
• High initial automation and set-up costs.
• Parts over 100g can create additional run costs.

Die-cast Disadvantages

• Porosity is a common challenge in die casting.
• Costly dies required to withstand high pressure and molten temperatures.
• Die casting can be complex and expensive to set up.
• Not suitable for small batch production.

Summary of MIM vs. Casting

MIM outshines casting when large runs of small intricate parts are required.

Small parts manufacturing

• A considerable economic advantage for creating small complex parts.
• MIM uses fine powders to create fully dense metal parts. Larger parts require more powder, which is not always cost-effective. Small parts that weigh between 0.1 and 250 grams are best.
• Flexible design process so no additional costs for increased part complexity such as adding threads, identity marking, or miniaturization.
• Can work when thin walls (100 micrometers) are required.
  

Large Runs

• MIM is more affordable for larger runs. Cost savings usually occur when part runs are between 10,000 and 20,000.
• Casting can be a better option for smaller runs and larger complex parts.
  

Small and Large Parts Manufacturing

• Can cast small and large complex parts.
• Affordable material options with limited waste. 
• The flexible design allows for simple and complex parts with a high degree of automation.
  

Run Size Large or Small

• Affordable casting methods available for small and large production runs.

Each process lends itself to different part applications. Metal injection molding best serves industries that need small detail parts where there is a variety of casting methods available to produce durable parts of all shapes and sizes. 

To inquire about a metal injection molding or die casting project, contact our sales team.