Metal Injection Molding vs Forging -

Metal injection molding and forging are two very common metal processing methods. However, due to different manufacturing processes, these two technologies make the final metal parts have different properties. Metal injection molding (MIM) technology is usually used to make products with complex geometry, high tolerances, and large products, while forging is used to manufacture products with high metallurgical properties and produce products with high yield strength and high fatigue strength.

This article will compare these two processes from various angles.

What is MIM?

Metal injection molding (MIM) is a new manufacturing process that has only appeared since the 1980s. It is a combination of plastic injection molding and powder metallurgy manufacturing processes. Therefore, it has both the characteristics of injection molding that is good at complex structural products and the strength of powder metallurgy. Through the sintering process, it provides high-strength metal parts with complex structures.

MIM PART

What is the production process of MIM?

1). Mixing: Mix fine metal powder with a binder to form raw materials, and then make them into easy-to-produce granular raw materials.

2) Mold making: This process is similar to plastic mold design, but because powder metallurgy shrinks by about 20% during sintering, the mold of the product needs a corresponding enlargement ratio

3). Injection molding: The raw materials are passed through a powder metallurgy injection machine under high temperature and high pressure to make the powder into a flowable liquid, which is injected into the mold cavity to form a “green” part.

4). Degreasing: Put the green parts into the degreasing furnace to remove the binder in the green parts and form porous metal parts

5)Sintering: Put the product into a vacuum sintering furnace, and through a high temperature of 1300-1500 degrees, the metal particles of the porous metal parts are fused and shrunk, and the parts are sintered into the product size and density required by the design.

Commonly used materials for MIM

Material Type	Key Properties	Common Applications
Stainless Steel 316L	Corrosion-resistant, good mechanical properties	Medical devices, automotive parts
Stainless Steel 17-4 PH	High strength, good corrosion resistance	Aerospace, tooling, medical implants
Low Alloy Steel	High strength, good wear resistance	Industrial machinery, automotive components
Iron-Nickel Alloys	Controlled expansion, magnetic properties	Electronics, precision instruments
Cobalt-Chromium	High wear and corrosion resistance, biocompatibility	Medical implants, aerospace parts
Titanium Alloys	Lightweight, high strength, corrosion-resistant	Aerospace, medical implants
Tungsten Alloys	High density, high temperature resistance	Ordnance, aerospace
Copper Alloys	High electrical and thermal conductivity	Electrical connectors, heat sinks
Nickel Alloys	High temperature and corrosion resistance	Aerospace, energy sectors
Soft Magnetic Alloys	High magnetic permeability, low coercivity	Electromagnets, sensors

Advantages of MIM

1) Complex geometric shapes: MIM can produce complex shapes that are difficult or impossible to achieve with other manufacturing methods

2) High tolerance, reducing secondary processing: 0.3% dimensional tolerance can be achieved.

3) Material utilization: The material utilization rate is very high, reaching more than 95%.

4) High production efficiency: large-volume products have high production efficiency.

5) High product consistency: All products are manufactured through molds.

Limitations of MIM

1) Cost: The initial mold cost is high, which is a huge challenge for small batch production

2) Material limitation: Only materials suitable for MIM process can be selected

3) Size limitation: Limited by the size of debinding furnace and sintering furnace, the larger the size, the higher the cost. So MIM is usually suitable for small and medium-sized parts.

Application of Metal Injection Molding

Medical and Dental Tools
- Applications: Surgical instruments, orthodontic brackets, dental implants, and other precision medical components.
- Advantages: MIM allows for the production of complex shapes that are perfect for the medical field, where customized, small-scale components with high precision are critical.
Automotive Components
- Applications: Gears, locks, turbocharger components, and various under-the-hood components.
- Advantages: Offers the durability and strength needed for automotive parts, along with the ability to produce complex geometries that reduce the need for secondary operations.
Consumer Electronics
- Applications: Components for smartphones, laptops, headphones, and wearables like smartwatches.
- Advantages: Supports the miniaturization trend in electronics with the capability to produce small, detailed parts like hinges and camera components.
Firearms and Defense
- Applications: Triggers, sights, and other firearm components.
- Advantages: Provides the strength, precision, and reliability demanded by the defense sector, with the added benefit of confidentiality and supply chain control.
Industrial Tools
- Applications: Cutting tools, high-precision nozzles, and machinery components.
- Advantages: Ability to produce wear-resistant, high-strength parts that can withstand demanding industrial applications.
Aerospace
- Applications: Small, complex components such as connectors, actuators, and aerospace fasteners.
- Advantages: The process is well-suited for producing lightweight, high-strength, and precise parts required in the aerospace industry.
Luxury Goods
- Applications: Components for watches, luxury pens, and eyewear frames.
- Advantages: MIM is capable of producing the detailed, high-quality aesthetic components necessary for luxury goods with fine, intricate details.
Sporting Goods
- Applications: Golf club heads, precision components in bicycles, and equipment fittings.
- Advantages: Allows for the design and manufacture of performance-oriented components that can be precisely tailored to enhance sporting performance.

These applications demonstrate the flexibility of MIM to cater to diverse sectors, combining the economic and technical advantages of injection molding with the mechanical properties of metal to address specific industry requirements.

What is forging?

Metal forging is a traditional metal manufacturing process that shapes metal by using the compressive force generated by hammering, pressing or rolling.

Forging part

Forging Manufacturing Process

Heating: Heating the metal to a specific temperature to make it reach a state where it can be shaped
Forming: Placing the heated metal between dies and compressing it by hammering or pressing to form the product into the required shape.
Cooling: Cooling the forged part to room temperature to solidify its structure

Classification of forging

Common metal forging methods include: closed die forging, open die forging, cold forging, and roll forging.

1) Closed die forging

Closed die forging is the process of using a die to completely or mostly cover the workpiece. During the manufacturing process, the heated metal is placed in the bottom die, and then the top die applies downward pressure to form it into the desired shape. Closed die forging can produce different sizes from 200 grams to 30,000 kilograms.

2) Open die forging

In the open die forging process, the metal is not completely restricted or constrained in the die. The heated metal billet is formed between an upper die with a punch and a lower die with a pad, anvil or hammer. The forging temperature is usually between 260℃ and 1320℃. The open die forging process is generally suitable for large and relatively simple-shaped parts, such as bars, rings and hollow parts.

3) Cold forging

Cold forging is a forging process performed at temperatures ranging from room temperature to several hundred degrees. Covers a variety of techniques such as bending, extrusion, cold drawing, coining and cold heading. Cold forging generally requires more powerful equipment to process a variety of metal materials, especially high carbon steel. Compared with hot forging, cold forging has significant advantages in dimensional control, product consistency, surface finish and reduced contamination.

4) Roll forging

Roll forging, also known as roll forming, is a process of forming metal parts by rollers moving relative to each other. In this process, a pair of cylindrical or semi-cylindrical rollers are used to apply pressure to the bar stock to deform it, thereby reducing the thickness or increasing the length.

Commonly used forging materials

Material Type	Common Grades	Characteristics	Applications
Carbon Steels	1020, 1035, 1045	Affordable; good strength and toughness after heat treatment	Non-critical parts of machinery, automotive components
Alloy Steels	4140, 4340, 8620	Contains elements like Cr, Ni, Mo enhancing strength, hardness, wear resistance	Automotive axles, gears, shafts
Stainless Steels	304, 316, 410, 440C	Excellent corrosion resistance, good strength	Medical instruments, food processing equipment, marine applications
Tool Steels	A2, D2, H13, O1	High carbon content, good wear resistance, maintains sharp edge	Cutting tools, dies, molds
Aluminum Alloys	6061, 7075	Lightweight, good strength-to-weight ratio, corrosion resistance	Aerospace, automotive components
Titanium Alloys	Ti-6Al-4V	High strength-to-weight ratio, corrosion resistance, withstands extreme temperatures	Aerospace, medical devices, high-performance automotive parts
Nickel Alloys	Inconel 625, Inconel 718, Monel 400	High temperature and corrosion resistance	Aerospace turbines, marine applications, chemical plants
Copper Alloys	C11000, C70600	Excellent electrical and thermal conductivity, corrosion resistance, ductility	Electrical components, heat exchangers, marine environments

Advantages of Forging

1) Improved Mechanical Properties
Strength and Durability: Forged parts have superior mechanical properties, with higher strength, toughness and wear resistance than cast or machined parts. The forging process rearranges the metal’s grain structure, which improves its strength and durability.
Reduced Defects: The forging process reduces the likelihood of metallurgical defects such as porosity and alloy segregation, resulting in parts with uniform properties and predictable performance.
2) Grain Flow and Structural Integrity
Grain Alignment: The forging process aligns the grain flow with the shape of the part, which improves its directional strength and reduces stress concentration. This allows the part to withstand extreme pressures and maintain structural integrity under stress.
Consistency: Forged parts offer consistent quality and performance, making them ideal in critical applications where reliability and safety are paramount.
3) Cost Effectiveness
Material Utilization: Forging starts with a near-net shape, minimizing material waste, which reduces the need for extensive machining and material removal, which can save on raw material costs.
Economies of scale: Once the forging process is established, the unit cost can be significantly reduced when mass-produced, which is economical in large-scale production.
4) Versatility and flexibility
Complex shapes: Forging can produce products of various shapes and sizes, from small precision components to large structural parts. This versatility makes it suitable for multiple industries, including aerospace, automotive and construction.
Material diversity: Forging can be used for a variety of materials, including carbon steel, alloy steel, stainless steel and non-ferrous metal alloys, thus providing customized solutions according to specific application requirements.
5 Enhanced heat treatment response
Uniform properties: Forged parts respond more predictably to heat treatment, resulting in uniform mechanical properties and dimensional stability. This is due to the grain refinement achieved during the forging process.

Disadvantages of Forging

High Initial Cost

Forging equipment and dies are expensive, especially when producing complex shapes and small batches. For some applications, the initial investment can be very high. This increases the overall cost of small batch production.

Poor surface finish and low tolerance accuracy

Surface roughness: Forgings are usually rough on the surface and may require additional machining or grinding to achieve the desired surface quality.

Dimensional tolerance: Although forging can produce parts close to the net shape, secondary processing is usually required to achieve tight tolerances, which increases costs and delivery time.

Process limitations

Complexity: Compared with casting or powder metallurgy, forging is less suitable for producing highly complex or delicate parts.

Material limitations: Materials with low ductility or high melting points are difficult to forge, which limits the range of applicable materials.

Energy consumption

High temperature: Forging usually requires high temperature and pressure, resulting in a lot of energy consumption and related costs.

Environmental impact: The forging process generates noise, vibration and emissions, and measures need to be taken to mitigate the impact on the environment and safety.

Applications of Forging

The following are the applications of forging in different fields:

Aerospace Industry

Applications: major parts of aircraft engines, rib plates of fuselage, landing gear and other important parts.
Features: Forgings are used in a very high proportion in aircraft, accounting for about 85% of aircraft components are forgings, providing high strength and durability.

Automobile Industry

Applications: connecting rods and crankshafts in automobile engines, as well as key parts such as the front beam of the front axle and the half shaft of the rear axle.
Features: Forgings are used in automobiles for parts with light weight, poor working conditions, complex shapes and high safety requirements to ensure the safe operation of the car.

Defense Industry

Applications: weapons, tank parts, etc.
Features: Forgings provide high strength and durability and can withstand extreme conditions and high stress.

Medical Industry

Applications: orthopedic implants, surgical tools and medical equipment parts.
Features: Forgings provide biocompatibility and strength in the medical field and can withstand high-intensity sterilization processes.

Oil and Gas Industry

Applications: Drill bits, mud motors, drilling tools, valves.
Features: Forgings provide excellent strength and corrosion resistance, suitable for high temperature and pressure working environments.

Agricultural Machinery and Equipment

Applications: Agricultural machinery such as tractors and harvesters.
Features: Forgings are used for gears, shafts and accessories, which can withstand the harsh conditions of agricultural operations.

Power and Transmission Industry

Applications: Turbine components, shafts, discs, seamless pipes and accessories.
Features: Forgings ensure the efficiency and reliability of power production and transmission systems.

Construction and Heavy Equipment

Applications: Structural supports and brackets in construction machinery and equipment.
Features: Forgings can withstand heavy loads and harsh conditions, ensuring the safety of construction projects.

Hand Tools and Hardware

Applications: Hand tools such as wrenches and hammers.
Features: Forgings provide high quality and durability, and can withstand repeated use and heavy loads.

Forging technology provides unparalleled technical advantages in various industries. It optimizes metal properties by changing metal microstructure, providing higher directional toughness and optimal metal texture streamline. Therefore, forging products have the characteristics of high load-bearing capacity, long life and strong adaptability, and are widely used in wind power, chemical industry, machinery, shipbuilding, nuclear power, aerospace, military industry and other industries.

Differences between MIM and Forging

There are several key factors to consider when choosing between metal injection molding (MIM) and forging processes, and each process has its own unique advantages and limitations in different application scenarios. Here is a detailed comparison of some of the main factors:

Complexity:

The MIM process excels in producing parts with complex shapes and fine details. Because MIM combines the advantages of powder metallurgy with injection molding, it can easily produce complex geometries and tiny features that are difficult to achieve with traditional processing methods. Therefore, MIM is particularly suitable for producing parts that require high precision and complex designs, such as components in electronics, medical devices, and high-end consumer products.

In contrast, forging is more suitable for producing parts with relatively simple shapes. The forging process is more efficient when manufacturing parts with more regular, symmetrical shapes and fewer details by applying high pressure to the metal to force it into shape. Complex shapes may require multiple processing or additional post-processing during the forging process, which increases production difficulty and cost.

Strength:

Forgings are known for their excellent strength and toughness. The high pressure and high temperature during the forging process make the internal structure of the metal more dense, and the mechanical properties of the material are significantly improved. This makes forged parts excellent in withstanding high stress, impact resistance and fatigue performance, and is widely used in fields requiring high strength, such as aerospace, automotive industry, and heavy machinery manufacturing.

Although MIM is not as strong as forging, the parts it produces have high density and strength performance sufficient to meet the needs of many application scenarios. Through proper material selection and optimized process, MIM can also produce parts with good mechanical properties, especially for those applications that do not require as much strength as forgings but have high requirements for shape complexity.

Output:

The MIM process has significant advantages in medium and high-volume production. Since MIM uses molds for forming, the consistency and dimensional accuracy of the parts can be well controlled, which is suitable for large-scale production of small parts with complex shapes. In addition, the process of MIM is relatively automated, which can achieve high efficiency and stability in mass production.

Forging also performs well in large-scale production, especially when producing parts with relatively simple shapes and requiring high strength. The forging process has a high single-shot production capacity and is suitable for mass production needs. However, due to the high cost of molds and equipment, forging may not be cost-effective in small-volume production.

Cost-effectiveness:

Cost-effectiveness is also a key consideration when choosing MIM or forging. The initial mold cost of the MIM process is higher, but in large-scale production, the unit cost of each part will be significantly reduced. On the other hand, although forging has higher equipment and mold costs, the total cost of forging is usually more advantageous for large parts that require high strength.

Conclusion

MIM and forging each have their own unique application advantages. The selection of the appropriate process depends on the complexity of the part, the required mechanical properties, the production batch and cost considerations. MIM is an ideal choice when complex shapes, high precision and medium to high production volumes are required. Forging is more suitable when high strength, durability and mass production are required. Companies should evaluate the advantages and disadvantages of each process according to specific application requirements to select the best manufacturing solution.

FAQs.

What is the main difference between MIM and forging?

The main difference between MIM (metal injection molding) and forging lies in the application field and the complexity of the applicable parts. The MIM process excels in producing parts with fine details and complex geometries, and is suitable for products that require high precision and small complex structures. Forging is more suitable for producing parts with simpler shapes but higher strength, especially for occasions that need to withstand high stress and high impact.

Is MIM suitable for large parts?

The MIM process is generally more suitable for small and medium-sized parts due to its inherent size limitations. Although MIM can produce parts with complex shapes and high precision, it may face process limitations on larger parts. Therefore, MIM is more commonly used to produce small precision parts, such as electronic components, medical device parts, etc.

Why is forging favored in aerospace applications?

Forging is favored in the aerospace field mainly because it can produce high-strength parts with excellent mechanical properties. Aerospace applications have extremely high requirements for the strength, durability and fatigue resistance of parts, and the forging process processes metals through high temperature and high pressure to make their internal structure denser, thereby improving the overall performance of the parts and meeting the stringent use conditions.

Can all metals be used for MIM process?

Not all metals are suitable for MIM process. MIM process requires metal powders to be effectively powdered and sintered, so only some specific metals and alloys can be used for MIM process. These typically include stainless steel, low alloy steel, titanium alloy and some copper-based alloys. For those metal materials that are difficult to powder or sinter, the applicability of MIM process may be limited.

Which process is more cost-effective in mass production?

In mass production, MIM may be more cost-effective, especially when producing parts with complex shapes and high precision requirements. The MIM process is formed in one mold, reducing the need for subsequent processing, and due to high material utilization and strong production consistency, it can significantly reduce unit costs in medium and large batches. However, for large parts that require high strength and have relatively simple shapes, forging is also very cost-effective in large-scale production.

What other factors should be considered when choosing MIM or forging?

In addition to complexity, strength, and production volume, the following factors should be considered:

Material properties: Which process is more suitable for your selected material? For example, some metals with high melting points or low ductility may be more suitable for forging rather than MIM.

Part application environment: What kind of use environment does the part need to withstand? High temperature, corrosive environment or high mechanical stress?

Surface quality: How high is the requirement for surface finish? MIM can provide good surface quality, while forging parts may require subsequent processing to achieve similar results.

Production speed: How tight is the project schedule? Which process can complete production faster?

What are the subsequent processing requirements for MIM and forging?

The MIM process can usually directly produce parts close to the net shape, with less subsequent processing requirements, suitable for high-precision applications. Forging usually requires additional secondary operations such as machining, heat treatment, etc. to achieve the required dimensional tolerances and surface finish.

How do the two processes differ in terms of environmental impact?

Forging usually consumes more energy due to the need for high temperature and high pressure, and may produce more noise and exhaust emissions, requiring special environmental protection measures. However, the MIM process has relatively low energy consumption, high material utilization, and less waste, so it may have advantages in terms of environmental protection.

Metal Injection Molding vs Forging