Metal Injection Molding vs Die Casting

Introduction

Metal injection molding and die casting are the main decisions in the metal processing process. Both technologies are used in various industries around the world. Metal injection molding is a complex process with several steps, and it is suitable for small-sized parts with complex geometries. Otherwise, die casting has fewer manufacturing steps and is economical for simple parts with large volumes.

What is metal injection molding?

Metal injection molding (MIM) is a metalworking process that combines powdered metal particles with binder materials to form webbed metal parts and components. In addition, unlike other technologies, MIM enables the production of small, complex parts at a lower cost. It is the only technology available for thin-walled specifications with a thickness of 0.1 mm. In addition, its unique injection molding process allows for the integration of multiple parts into a single part.

Metal Injection Molding (MIM) Process

Once comparing the metal injection molding and die casting processes, we notice that the MIM process is intensive and complex. In addition, the normal MIM process includes.

1.      Fine metal alloy powder is mixed with binder material to form the raw material. Typically, we purchase raw materials for common MIM situations. For specific cases with unique MIM part characteristics, we can also produce custom MIM feedstock.

2.      The feedstock is injected into the mold to obtain molded parts of the desired structure. We call these molded parts raw materials.

3.      The adhesive material is removed by catalytic, solvent or thermal debonding methods. We refer to the debonded parts as debonded blanks. Otherwise, there is residual binder material left in the structure of the debonded blanks.

4.      Sinter the debinding blanks to create net formed parts. This is the most critical step in metal injection molding. It determines the final properties of the MIM part.

Application of post operations, such as heating or surface treatment, to achieve the required properties.

Metal injection molding offers a high degree of design flexibility, which makes it an ideal manufacturing technology in a variety of industries.

MIM parts application

The significant advantages of MIM parts are their small size and complex structure. In addition, MIM parts have excellent high throughput and high quality. Therefore, this makes MIM technology an effective metal processing method. While other methods are difficult or impossible to manufacture.

The application of the metal part determines the final manufacturing method, whether it is metal injection molding or die casting. Metal injection molding is popular in many industries because of its unique cost effective production value.

Automotive: system controllers, electrical connections.

Medical: surgical instruments, sewing machines, ultrasound instruments.

Electronics: smart wear, watches, headphones, cell phones, cables and wires.

Industrial: micro gears, mechanical parts, pepper spray parts, drone parts.

What is die casting?

Die casting is a metal casting technique used in the production of non-ferrous metal parts. The metal material is heated until it is molten, then injected into a mold under high pressure, and finally cooled and ejected. The most common casting metals include: aluminum, copper, lead and magnesium. In addition, depending on the type of casting metal, we can apply hot or cold chamber casting machines.

There are four different types of molds for the final casting impression.

Single cavity: one part or component is produced.

Multi-cavity: The same part or number of parts produced.

Unit mold:Production of different parts in one casting cycle.

Combination mold:Production of several assemblies.

Die casting process

The normal die casting process includes:

1.      Clamping: The mold is cleaned and clamped, then lubricated to prevent sticking. 6.

2.      Injection: The molten metal is injected into the mold at pressures ranging from 140 MPa to 215 MPa. The injection time depends on the complexity and wall thickness of the part, with multiple patterns or internal cavities taking a long time to fill.

3.      Cooling: The molten metal enters the mold and begins to cool. However, we usually notice the cooling process after the mold cavity is filled. The geometric complexity and wall thickness of the part dictates a long cooling time.

4.      Ejection: After the metal part has cooled, the half mold is opened and then the molded metal part is ejected. After ejection, a new casting process begins.

In addition, excess metal and flying edges should be trimmed by hand or other methods.

Depending on the end application, metal type and part size, manufacturers have different die casting methods. The three main methods are gravity die casting, hot chamber die casting and cold chamber die casting.

Gravity Die Casting

In this method, which is similar to its name, molten metal is poured into the mold from the top area and filled by gravity. Since the metal is injected into the cavity by gravity, it is injected at a slower rate than pressurized die casting in a hot or cold chamber. As a result, there is less folded turbulence in gravity and less trapped air in the casting. However, this slower process is not suitable for longer production runs.

Otherwise, pressurized die casting is used in automated rapid production. It allows the production of castings with uniform metal distribution and thin walls.

Cold Chamber Die Casting

Cold chamber die casting is suitable for high melting point metals such as aluminum, brass and copper. We heat and melt the metal material in an external furnace, then place the ladle into the machine chamber and finally inject it into the mold under high pressure.

Hot Chamber Die Casting

Hot chamber die casting is ideally suited for low melting point metals such as tin, zinc, lead and magnesium alloys. All of these metals are heated and melted in a furnace connected to the machine and then fed directly into the mold through a gooseneck tube.

Die casting applications

Die casting offers a wide range of material options and design flexibility. As a result, it is also another popular manufacturing method in different industries.

Automotive: gearboxes, transmissions, retainers and engine components.

Medical: peristaltic pumps, hospital equipment controls, surgical instruments, and analytical machines.

Industrial: hydrostatic shafts, steel lined inserts, external gearboxes.

Parameter Comparison

The metal injection molding process is an effective method for producing high-strength and high-tolerance MIM parts with complex geometries by forming metal powders into part shapes and sintering them into final parts.MIM parts have excellent physical properties such as high strength, wear resistance and corrosion resistance, all of which are difficult to achieve with other manufacturing processes.

The die casting process involves the injection of liquid metal into a mold or die, which is similar to MIM. in addition, die casting offers several economic advantages in terms of the right environment and part volume. This will result in significant cost savings for component designers, and we can find the normal parameters for both techniques in the following table.

MIM and die-casting materials

The main difference between metal injection molding and die casting is the choice of materials. Metal injection molding uses steel or other MIM alloys, commonly including: stainless steel, titanium, nickel, tungsten, copper and various combinations. However, die casting often uses non-ferrous metals as aluminum alloys, magnesium alloys or zinc alloys.

It is easy to see that the main difference between MIM and die-casting materials is the melting point of the metal. Often, MIM can be manufactured with higher metal materials than die casting. We summarize the common MIM materials as follows.

BRM material

Comparison of MIM and die-casting process

For large volume metal parts with simple shapes, die casting is a fast and economical method. Metal materials with low melting temperatures, such as zinc, aluminum, copper and magnesium, are mixed into ingots. The ingots are then melted by a die-casting machine and a central furnace. All the casting alloy is injected into the mold by pumping under pressure. Finally, the cooling and injection of the final molding metal is the final step in die casting. The cycle time depends on the part size and ranges from 1 to 30 seconds.

MIM is a dense and complex process in which metal alloys are made into very fine powders and then mixed with thermoplastic binders to form the feedstock. The feedstock is heated to a liquid state and injected into a mold, cooled and discharged from the mold as a raw material. A catalyst is then used to remove most of the binder. Finally, the sintering process sintered the fine metal powders together to form a strong web-like metal part.

High tolerance

Both MIM and die casting are suitable for high volume metal part production. However, MIM still has higher tolerances than die casting, which ensures that MIM can produce highly repeatable metal parts. Metal injection molding focuses on quality and precision, while die casting has variable dimensions as trim to remove excess material.

Complex geometric shapes

MIM is more suitable for manufacturing small metal parts with complex geometry. From the table above, we can identify small features smaller than 2mm, which can only be processed using MIM technology. Otherwise, die casting will never be able to meet this requirement.

Wall thickness

Wall thickness is the most critical factor for complex, specific and hollow metal parts. Die casting has little or no control over wall thickness and porosity, and therefore cannot be applied to thin-walled products. However, metal injection molding works well in this case because there are strict manufacturing parameters to follow.

Size and weight

Die casting has a larger manufacturing size than MIM. For the production of metal parts under 200 grams, MIM has higher productivity than die casting. In addition, it is difficult to form thin sections smaller than 0.5 mm in die casting, but it is easily accomplished in MIM.

With these comparisons, it will be noted that MIM is ideal for small, lightweight metal parts with complex geometries. The most suitable part size is less than 100 mm, weight is less than 100 g, and production quantity is more than 10,000. in short, MIM is the most cost-effective way to produce this product, even compared with die-casting and precision machining.

Density

MIM technology mixes metal powder with binder, then removes the binder and finally sintered into MIM parts. As a result, its normal density will be 95-99%, which is lower than 100% for die casting. However, this will never affect the functional characteristics of MIM parts, on the other hand, it can reduce the weight of MIM parts quantity.

Mold life

Die casting molds are able to withstand high pressures and temperatures, which will wear out the mold quickly. However, molds can also be reused up to 1 million times, whereas metal injection molding can only reach 150K-300K times in a mold.

Product shrinkage rate

Metal injection molding requires a professional to calculate the exact shrinkage rate because it shrinks up to 30% during the degreasing and sintering process. However, the shrinkage of die casting is only 0.001/mm, which is not a major issue in metal processing. In addition, the isotropic shrinkage in die casting eliminates further challenges and tooling costs.

Physical Characteristics

Since both MIM and die casting will produce metal parts with traditional metal properties. Due to the different raw materials used in these two different methods, we will find that MIM parts have superior chemical and physical properties.

High Strength

MIM parts are typically made of steel alloys, nickel alloys or titanium alloys, which have higher mechanical properties than die-cast materials such as aluminum, magnesium or zinc alloys. As a result, MIM parts have significantly higher strength than die castings, including: surface hardness, wear properties, fatigue strength, fracture toughness, and corrosion resistance.

Good hardness

Since MIM materials are common metals with excellent surface hardness, this will encourage MIM parts to exhibit better hardness than die cast parts. In addition, secondary operations as surface carburization will be widely used to improve the hardness of MIM parts.

Corrosion resistance

The surface roughness of the MIM part is 1 μ m. Above 10 μ M, which means that MIM parts will have better corrosion resistance. Because the secondary operation of surface treatment will raise it to a new level.

Creep resistance

The raw materials for MIM have excellent creep resistance, which determines the high performance of MIM parts. However, die-casting materials such as aluminum, zinc and magnesium alloys inherently lack these properties, which can also affect the performance of die castings.

Advantages of metal injection molding versus die casting

Advantage of MIM

Production of net shape metal parts without secondary operations.

There is a wide variety of metal alloys, the most common ones being stainless steel, copper and nickel.

High mechanical strength after sintering.

Precision tolerances up to 0.01 mm.

Various surface finishes.

Complete design freedom with complex geometries.

Flexible production adjustments.

No negative impact on tooling in high temperature alloy applications.

Virtually no material waste.

Disadvantage of MIM

Higher cost than die casting.

Lower mold life (150K-300K cycles).

Precise calculation of shrinkage up to 30% in sintering stage.

High initial setup cost.

Advantages of die casting

Up to 30% cost savings over MIM.

Wide range of applications and industries.

Compared with the 150-300K of MIM, the 1 million mold has a longer service life.

Complex fasteners or inserts for the final product.

Fully automatic process, saving labor costs.

Disadvantages of die casting

Common porosity challenges.

Expensive molds that withstand high pressures and temperatures.

Setup is expensive and complex.

Not suitable for small batch production.

Summary of MIM and Die Casting

Small manufacturing

MIM is a fairly economical technique for manufacturing small, complex parts. Because it uses fine metal powders for further metal part production, larger size parts are not cost effective. The most suitable part weights range from 0.1 to 200 grams. In addition, its design flexibility allows for functional complexity, such as threading, miniaturization, marking text or graphics, without adding additional cost. Finally, metal injection molding technology can achieve the thinnest wall thickness of 0.1 mm.

Metal injection molding is more economical for high volume production and can save costs once production volumes exceed 10,000.

High-volume and small-volume production

Die casting is a good choice for the production of large and complex parts with small quantities. Whether it is simple or complex parts, there are reasonably priced metal options, and there is limited waste in the die casting process. Therefore, whether it is mass production or small batch production, die casting is affordable.

Conclusion

Although die casting seems to be more cost-effective than MIM, all aspects of materials, craftsmanship, and performance must be considered.MIM has its unique characteristics and can meet the requirements of special metal parts.Its wide selection of materials and corresponding properties are key factors in attracting millions of customers around the world.