An Ultimate Guide to Injection Moulding

Part 1: What is Injection Moulding?

Injection Moulding is the manufacturing process in which molten metal is poured into a mold and when it gets solidified it acquires the desired shape.

This injection molding process is suitable for large-scale production. The metal, plastic, elastomer, thermosetting and thermoplastic material is very suitable for the Injection molding process.

This Injection Moulding process is a very efficient, precise manufacturing process for large-scale production so, this manufacturing process is widely used in the automotive, aircraft and medical industries.

Part 2: What is the Injection Moulding Process?

Injection Moulding is the manufacturing process in which molten metal is poured into a mold and when it gets solidified it acquires the desired shape.

This process involves melting plastic granules at their melting point and injecting them into a custom-shaped mold and when it gets cooler it acquires the desired shape, size, and color.

The process starts with heating the chosen plastic material, which is then injected into a carefully designed mold. The mold, typically made from durable metals like steel or aluminum, is built to withstand the pressures of extensive use.

Precision in design ensures that the produced component meets specifications for machinery, moving parts, or equipment. Injection-molded parts find diverse applications, from small machine widgets to entire car body panels.

This method is versatile, producing components for packaging, automotive parts, storage containers, toys, plumbing elements, and medical items.

Part 3: How Does Injection Moulding Work?

Injection Moulding is one of the complex processes that involve the manufacturing of plastic parts. Below are the steps that are carried out in the injection molding.

1. Mould Fabrication

• Injection molding starts with designing and manufacturing of the precise mold from metals like aluminum or steel. This mold is carefully machined to match the different features and designs of the product.

2. Material Preparation

• In the process, the part material is inserted into a heated barrel, where a helical screw mixes and heating bands melt the part material. The temperature of the part material is maintained at the desired level.

3. Injection into Mould

• The molten material, which can be metal or plastic, is then forcefully inserted into the mold cavity to solidify it into the desired shape. In most cases, piston and cylinder arrangement is used to insert molten material.

4. Cooling Process

• As we know cooling takes time. So to speed up cooling, cooling lines circulate water or oil from an external temperature controller. It reduces the cooling time of the material to get cool.

5. Part Release

• Mold tools are attached to ‘platens’ or plate molds, which open after solidification to allow ejector pins to release the part. The two-shot mold combines different materials in a single part for various features.

6. Cavity Options

• Molds can have single or multiple cavities to produce identical or distinct parts. It depends on the applications.

7. Material Considerations

• Aluminum moulds are less suitable for high-volume production due to wear and deformation. The best choice is steel due to its high strength, and durability. But steel increases the cost of the mold.

8. Design Importance

• Design considerations include part shape, material selection, and molding machine characteristics, ensuring successful injection molding with optimal outcomes.

Part 4: Types of Injection Moulding

There are several types of injection molding techniques, each tailored to specific applications and requirements. Here are some common types of injection molding:

1. Metal Injection Moulding

Injection moulding is not limited to plastics; metals are also employed in this manufacturing method. Various industries use this process to meet specific product needs.

Its application is particularly valuable in electronics and digital manufacturing, where there is a demand for complex-shaped parts. This newer technology replaces traditional processes to cater to the unique requirements of distinct markets.

2. Overmoulding

Overmoulding is a manufacturing trick to make parts better. It uses different types of plastics to improve a part. Manufacturers use this when they see a chance to make a part work better by using different materials.

They cover a base material with extra materials called over mould. People use overmoulding a lot for things like personal care items or tools. It helps make these things work well in different situations.

3. Insert Moulding

Insert moulding is similar to over-moulding, but it has some material limitations. In this method, sub-materials are used to strengthen component cavities, making the overall product stronger.

It works by combining two or more elements and infusing the insert with a chosen polymer. This process creates durable parts without the need for extra components. It keeps the product compact while maintaining functionality.

4. Thin Wall Moulding

Making plastic moulded parts with very thin walls is a tough manufacturing task, but a new injection moulding process has come forward to tackle this challenge.

This innovative technique is crucial for reducing cracks in the final product. Thin wall moulding is great for precision, especially useful for creating small components.

5. Liquid Silicone Injection Moulding

Liquid Silicone Injection Moulding is one of the widely used methods for manufacturing medical and automotive components.

Though not ideal for extreme temperatures, this process uses very hot moulds for optimal function. Here’s how it works: a heated mould is injected with material to create a part.

Then, cold material is injected, increasing the part’s flexibility without requiring additional exposure to high temperatures. This innovative approach ensures versatile part production, providing a unique solution for various applications.

6. Hot Runner Moulding

Hot runner moulds are crucial for shaping plastic resins using heat. They use two heated plates to handle various-sized parts, relying on precise and controlled heating for efficient moulding.

This technique is ideal for businesses seeking high-quality injection moulding while effectively managing production costs. Hot runner moulding strikes a balance between quality output and cost-effectiveness, making it a preferred choice for manufacturers.

7. Cold Runner Moulding

Hot runner moulding uses a two-plate system, while cold runner moulding prefers a slightly more complex two-to-three-plate setup.

The number of plates is crucial for moulding cycle dynamics, especially in separating the plate from the mould by the runner system.

Cold runner moulding, commonly used in injection moulds, has clear advantages in manufacturing. Its two to three plates improve efficiency, resulting in shorter cycle times.

This efficiency is even better when robotic assistance is used for quickly removing runners.

Part 5: Injection Moulding Materials Selection Guide

Selection of proper raw material for injection moulding is a tough job because proper material will help us to get desired properties of our final component.

Below are some common material that used in injection moulding.

1. Polymers

• Polyethylene (PE): Used for containers, packaging, and various consumer goods. High-density polyethylene (HDPE) is more rigid, while low-density polyethylene (LDPE) is more flexible.
• Polypropylene (PP): Versatile material used in packaging, automotive parts, and consumer products.
• Polystyrene (PS): Commonly used for packaging, disposable cutlery, and consumer goods.
• Polyvinyl Chloride (PVC): Used in construction, medical devices, and consumer goods.
• Polyethylene Terephthalate (PET): Widely used for beverage bottles, food packaging, and synthetic fibers.
• Polycarbonate (PC): Known for its transparency and impact resistance, used in automotive parts, optical lenses, and electronic components.

2. Engineering Plastics

• Acrylonitrile Butadiene Styrene (ABS): Combines toughness with a good surface finish.
• Polyamide (Nylon): Offers high strength, durability, and chemical resistance. Common types include Nylon 6 and Nylon 66.
• Polyoxymethylene (POM or Acetal): Known for low friction, high stiffness, and dimensional stability.
• Polyphenylene Sulfide (PPS): Exhibits high temperature and chemical resistance.
• Polyether Ether Ketone (PEEK): High-performance polymer with excellent mechanical and thermal properties.

3. Thermoplastic Elastomers (TPE)

• Polyurethane (TPU): Combines flexibility with durability. Used in footwear, automotive components, and medical devices.
• Styrene-Butadiene-Styrene (SBS) and Styrene-Ethylene-Butadiene-Styrene (SEBS): Used in applications requiring flexibility and impact resistance, such as soft-touch grips and seals.

4. Biodegradable and Eco-Friendly Materials

• Polylactic Acid (PLA): Derived from renewable resources like corn starch.
• Polyhydroxyalkanoates (PHA): Biodegradable polymer derived from microbial fermentation.

5. Metal Alloys (Metal Injection Moulding – MIM)

• Stainless Steel: Commonly used for metal injection moulding due to its corrosion resistance and strength.
• Titanium: Known for its high strength-to-weight ratio, corrosion resistance, and biocompatibility.
• Copper and Copper Alloys: Used in electrical components.

Part 6: What Are the Advantages and Disadvantages of Injection Moulding?

Injection moulding is one of the most used manufacturing processes in manufacturing industries so far due to its advantages and disadvantages.

Key Advantages of Injection Moulding

1. High Efficiency and Speed

• Injection moulding is automated process that will produce the parts in larger quantities with high efficiency.

2. Complex Geometry and Precision

• Injection moulding is the manufacturing process that is widely used to manufacture complex and intricated parts efficiently by maintaining tight tolerances.

3. Material Variety

• The injection Moulding process is used with a variety of materials including all thermosetting and thermoplastic material.

4. Low Waste

• Injection moulding generates minimal waste since excess material from the process can often be recycled.
• The automated nature of the process and precise control over material quantity reduce scrap.

5. Cost-Effective for High Volumes

• While the initial tooling costs can be high, injection moulding becomes cost-effective for large production runs due to its high speed and efficiency.

6. Reduced Labor Costs

• This injection moulding process is a fully automatic process, it involves less amount of labor, overall labor cost reduces drastically as compared to another manufacturing process.

7. Design Flexibility

• Design changes can be easily implemented by modifying the mould, allowing for flexibility in part design without significant additional costs.
• Prototyping and iterative design processes can be facilitated efficiently.

Disadvantages of injection moulding

1. High Initial Tooling Costs:

• The process of making initial mould is a very complex and expensive process and the initial cost of this mould is very high so, this is not suitable for small production.

2. Lead Time for Tooling:

• The process of making the initial mould is very complex process and it takes more than month so, overall lead time of the tool is very high.

3. Part Size Limitations:

• Injection moulding is generally more cost-effective for smaller to medium-sized parts. Producing very large parts may require specialized equipment and moulds, increasing costs.

4. Design Constraints:

• The design of a part for injection moulding may need to consider certain constraints, such as draft angles, which can add complexity to the design process.

5. Long Set-Up Times:

• Changing moulds for different parts can be time-consuming. This can be a drawback when there is a need for frequent production runs of different components.

6. Waste Generation:

• Although injection moulding produces less waste compared to some other manufacturing processes, there can still be material waste during startup, shutdown, and when purging the machine between material changes.

Part 7: Is 3D Printing the Same as Plastic Injection Moulding?

No, 3D printing and plastic injection moulding are distinct manufacturing processes with different principles and applications. Here are the key differences between 3D printing and plastic injection moulding:

1. Process:

• 3D Printing: Also known as additive manufacturing, 3D printing builds objects layer by layer from a digital model. To construct a three-dimensional item, material (such as plastic filament or resin) is deposited in a controlled manner.
• Plastic Injection Moulding: Injection moulding is a subtractive manufacturing process that involves melting plastic pellets and injecting the molten material into a mould cavity, where it cools and solidifies to form the final part.

2. Production Volume:

• 3D Printing: Well-suited for low to moderate production volumes and prototyping. Each part can be unique, and there is minimal setup time.
• Plastic Injection Moulding: Ideal for high-volume production due to its efficiency and short cycle times. Tooling setup costs make it more economical for larger quantities.

3. Speed:

• 3D Printing: Layer-by-layer construction can be time-consuming, particularly for complex or large parts.
• Plastic Injection Moulding: Generally faster for large-scale production due to the simultaneous moulding of multiple parts in a single cycle.

4. Material Variety:

• 3D Printing: Supports a variety of materials, including various plastics, metals, ceramics, and composites. Material choices may be more limited compared to injection moulding.
• Plastic Injection Moulding: Versatile and accommodates a wide range of materials, including different thermoplastics, thermosetting polymers, and elastomers.

5. Design Flexibility:

• 3D Printing: Offers high design flexibility, enabling the creation of complex geometries and intricate structures that may be challenging or impossible with traditional manufacturing methods.
• Plastic Injection Moulding: Allows for intricate designs, but modifications to the mould can be complex and costly. Design changes are not as easily implemented during production compared to 3D printing.

6. Tooling Costs:

• 3D Printing: Minimal tooling costs, making it suitable for prototyping and small-scale production without the need for expensive moulds.
• Plastic Injection Moulding: Involves high upfront tooling costs for creating moulds, but per-unit production costs decrease with larger production volumes.

7. Surface Finish:

• 3D Printing: Surface finish may vary depending on the printing technology and material used.
• Plastic Injection Moulding: Typically results in a smooth and consistent surface finish without the need for extensive post-processing.

Part 8: Extrusion vs Injection Moulding

Injection Moulding and extrusion are some of the most used manufacturing processes in the entire industry. Both these processes have their own importance, advantages and disadvantages and they are very different from each other.

Below are some key point that shows the difference between Injection Moulding and Extrusion:

Extrusion

1. Process:

• Extrusion involves forcing molten plastic through a die to create continuous shapes with a constant cross-section.
• The plastic material is fed into a hopper, melted, and then forced through a shaping die to produce the desired profile.
• Extrusion is a continuous process, meaning it produces long lengths of the same profile.

2. Applications:

• Extrusion is commonly used to produce products with a uniform cross-section, such as pipes, tubes, rods, profiles, and sheet materials.
• It’s widely used in the construction, packaging, automotive, and consumer goods industries.

3. Features:

• Extruded parts typically have a consistent cross-section along their length.
• The process is suitable for producing long lengths of material at a relatively low cost per unit length.

4. Variants:

• There are various types of extrusion processes, including profile extrusion, sheet extrusion, blown film extrusion, and wire and cable extrusion, each tailored to specific applications.

Injection Moulding

1. Process:

• Injection moulding involves injecting molten plastic into a mould cavity at high pressure to produce solid parts.
• The plastic material is heated to a molten state and injected into the mould cavity under pressure. When this part gets cool and solidifies then that final plastic object can be removed.
• Injection moulding is a cyclic process where each cycle produces one or more parts.

2. Applications:

• Injection moulding is used to produce a wide range of plastic parts, from small and intricate components to large and complex parts.
• It’s widely employed in automotive, electronics, medical, consumer goods, and other industries.

3. Features:

• Injection-moulded parts can have complex geometries, intricate details, and varying thicknesses.
• The process offers high precision, tight tolerances, and excellent surface finish.

4. Variants:

• Injection moulding can involve various techniques, including over-molding, insert moulding, gas-assisted moulding, and multi-shot moulding, each suited to specific design requirements.

Comparison

• Complexity: Injection moulding is better suited for complex parts with varying geometries and features.
• Production Volume: Injection moulding is efficient for high-volume production runs, while extrusion can also be used for the continuous production of long lengths.
• Tooling Costs: Injection moulding typically involves higher tooling costs due to the complexity of moulds, whereas extrusion dies are generally less expensive.
• Material Usage: Injection moulding allows for a broader range of materials, including thermoplastics, thermosets, and elastomers, while extrusion primarily focuses on thermoplastics.

Part 9: Metal Injection Moulding vs Die Casting

Metal Injection Moulding and Die Casting are two different manufacturing processes that have their own importance, advantages and disadvantages.

Below are some key differences between Metal Injection Moulding and Die Casting.

Metal Injection Moulding (MIM)

Process:

• MIM is a powder metallurgy process that combines principles of plastic injection moulding and powdered metallurgy.
• Metal powders are combined with a polymer binder to create a feedstock. The final metal component is obtained by debinding and sintering the green part that is created by injection moulding the feedstock.

Complexity and Design Flexibility:

• MIM is well-suited for producing complex, intricate, and small-to-medium-sized parts with high precision.
• It allows for design flexibility, including the integration of features such as undercuts, thin walls, and complex geometries.

Material Variety:

• MIM supports a wide range of metals, including stainless steel, titanium, copper alloys, and more.
• It is suitable for both ferrous and non-ferrous materials.

Surface Finish:

• MIM can achieve a good surface finish, but additional post-processing may be required for high-quality cosmetic appearances.

Production Volume:

• MIM is suitable for low to moderate production volumes, offering cost advantages for smaller quantities compared to traditional machining methods.

Die Casting

1. Process:

• Die casting involves injecting molten metal into a mould cavity under high pressure to produce a solid metal part.
• The mould is typically made of steel and consists of two halves. After being injected into the cavity, the molten metal solidifies at room temperature and turns into the final object.

2. Complexity and Design Flexibility:

• Die casting is suitable for producing parts with complex shapes, but it may have more design limitations compared to MIM.
• It is well-suited for larger parts and parts with thicker walls.

3. Material Variety:

• Die casting is commonly used for alloys with low melting points, such as aluminum, zinc, and magnesium.
• It is less versatile in terms of material selection compared to MIM.

4. Surface Finish:

• Die casting can achieve a high-quality surface finish with minimal post-processing, making it suitable for parts with tight tolerances and aesthetic requirements.

5. Production Volume:

• Die casting is highly efficient for high-volume production due to its short cycle times and rapid solidification of the molten metal.

Comparison

• Tooling Costs: MIM generally has lower tooling costs compared to die casting. But even with it, a large amount of the total cost may still go towards MIM tooling.
• Material Selection: MIM offers more flexibility in terms of material selection, including a broader range of metals.
• Tolerance and Surface Finish: Die casting can achieve tighter tolerances and better surface finishes without the need for extensive post-processing.
• Production Volume: Die casting is more efficient for high-volume production due to shorter cycle times.

Conclusion

Today’s world is more dependent on Injection moulding due to its various advantages such as accuracy precision, tight tolerance, and speed for manufacturing large-scale of metal and plastic parts.

This Injection Moulding is very much suitable for variety of metal and it can be suitable for complex geometries so, this process is spread across every manufacturing sector.

Despite the initial costs associated with tooling and limitations on design modifications, injection moulding is a preferred option for the mass production of components necessary for daily life because of its advantages, which include high production speed, cost-effectiveness for large runs, and the ability to meet strict quality standards.

Injection moulding continues to be at the forefront of manufacturing innovation, significantly influencing the current state of affairs as technology develops.