Extrusion Molding: Definition, How It Works, Applications ...

Extrusion molding is a very popular molding technique that is used to create a continuous profile of a desired shape. This method is commonly used to shape plastics into tubes, pipes, films, etc. It can also be used as a metal-forming technique.

Contact us to discuss your requirements of Extrusion Prototype Quality Control. Our experienced sales team can help you identify the options that best suit your needs.

This article takes a closer look at extrusion molding: defining the process, how it works, its applications, advantages and disadvantages, and so much more.

What Is Extrusion Molding?

Extrusion molding is a high-volume manufacturing process used to create objects with a fixed cross-sectional profile. It is a molding process that involves forcing a material, typically a thermoplastic or elastomer, through a shaped opening or die to produce a continuous length of the desired shape, which is typically tube- or rod-like. The material is heated until it becomes pliable or molten, and then it is forced through the die to create the desired cross-sectional profile. Besides using this method to shape plastic, it is also used on metals. 

What Is the Other Term for Extrusion Molding?

Extrusion molding is also sometimes referred to as plastification extruding. Another name for extrusion molding is simply “extrusion.” The process is often referred to as extrusion when discussing the manufacturing of continuous lengths of products with a consistent cross-sectional profile, such as: tubes, pipes, or various profiles.

What Is the Importance of Extrusion Molding in Manufacturing?

The importance of extrusion molding as a process lies in its ability to produce continuous lengths of plastic with consistent cross-section profiles at a low cost. This process is particularly crucial for the cost-effective production of items such as: pipes, tubes, seals, and various profiles. Its continuous nature allows for high-volume production and seamless integration into various industries. Additionally, extrusion molding plays a key role in plastic recycling initiatives, contributing to sustainability by enabling the reuse of cleaned and sorted plastic waste. 

How Does Extrusion Molding Work?

The plastic extrusion process can be divided into four main steps:

1. Adding Additives: The base material is mixed with different additives like: colorants, stabilizers (for oxidative stability, heat, UV stability, etc.), fillers, flame retardants, reinforcements, lubricants, etc., which are chosen based on the specific requirements of the end product. 
2. Melting the Material: Plastic materials are fed into the hopper and directed through the feed-throat to the barrel. The material descends into the annular space between the screw and the barrel, confined by the screw channel. As the screw turns, it propels the polymer forward, subjecting it to frictional forces. The barrels undergo gradual heating with a temperature profile that increases steadily. Progressing from the feed zone to the metering zone, the combined effects of frictional forces and barrel heating induce plasticization, homogenization, and kneading of the material, preparing it for the subsequent stages of the plastic extrusion process. 
3. Shaping: Upon leaving the barrel, the molten material, driven by the rotating screw, passes through screens at the barrel's end. These screens serve a dual purpose: they eliminate foreign bodies and contaminants from the molten plastic while maintaining a uniform pressure throughout the system. The increased temperature and malleability achieved through this process prepare the material for the next crucial step—forming the desired shape by pushing it through a die. The shape of the die dictates the ultimate form of the extruded plastic product.
4. Cooling: Following the shaping of the molten plastic through the die, the next phase is cooling. This can be achieved through several cooling rolls or a water shower. The cooling process is vital to ensuring that the extruded plastic profile retains its intended shape.

After the extruded product has been cooled it may undergo extra processes, such as: further flame treatment, cutting, printing, annealing, deodorization, etc. The extrudate will then be subject to inspections to ensure that the product meets the desired quality. 

What Is the Machine Used for Extrusion Molding?

An extruder is used for extrusion molding. It uses a system of cylinders and barrels, heats the raw material, and propels it through the mold/die to create the desired profile. Different types of extruders can be used, including: single- and multiple-screw extruders, single- and multiple-ram extruders, disk extruders, drum extruders, diskpack extruders, and elastic melt extruders.  

How Long Does the Extrusion Molding Process Last?

The time of a plastic extrusion process is influenced by factors such as: product complexity, plastic type, extrusion line speed, and manufacturer specifications. Generally, plastic extrusion is recognized for its efficiency in rapidly producing high volumes of continuous products. Simple items like pipes or profiles with basic shapes can be extruded quickly. In contrast, more complex products involving complex profiles, multiple layers, or post-extrusion modifications might take a little longer.

Is Extrusion Molding Continuous?

Yes, extrusion molding is a continuous production process that is especially useful in creating products like: drinking straws, pipes, hoses, or rods. 

What Are the Common Materials Used in Extrusion Molding?

There are quite a few plastics that can be extrusion molded. Some of the common types of plastics include:

1. Polypropylene (PP)

Polypropylene is a ubiquitous plastic that is widely used in the plastic industry in processes like extrusion molding and injection molding. This plastic is inexpensive and easily accessible. It has a semi-crystalline property that imparts high flexural strength. PP is also resistant to moisture and chemical agents and has similar properties to polyethylene, but it is slightly harder and a little more heat resistant compared to polyethylene. Polypropylene strikes a balance between impact resistance, strength, color variety, and low-temperature performance. It is commonly found in: tubes, interior trim, metal replacement, living hinges, and more. It is often reinforced with either glass or carbon to increase its heat deflection temperature and tensile strength.

To learn more, see our guide on Polypropylene Plastic.

2. Nylon

Nylon, also known as polyamide (PA), is a translucent material with a fair amount of chemical resistance, and it performs well in high-temperature environments. This thermoplastic also has a high strength-to-weight ratio, excellent durability, and good electrical resistance. Nylon can be filled with up to 50% carbon fiber or glass to improve both operating temperatures and mechanical properties. Some of its common applications include reservoirs and tubes in automotive engines. 

To learn more, see our guide on Nylon Plastic.

3. Acrylic

Acrylic is a relatively low-cost resin renowned for its clarity and light transmission. Extruded acrylic is thermoformable, displaying higher impact resistance than glass. It features good UV resistance, electrical resistivity, and excellent optical properties. In comparison to cast acrylic, extruded acrylic is more cost-effective, dimensionally stable, softer, easier to cut and polish, and has relatively high durability. 

To learn more, see our guide on What is Acrylic.

4. Polyethylene (PE)

Polyethylene is a thermoplastic recognized for its flexibility, resilience, and resistance to chemicals. It offers a favorable combination of colorability, strength, and performance at low temperatures. It also has good impact strength and good chemical resistance. However, this plastic has poor heat stability, poor weatherability, and poor dimensional stability. Common applications of polyethylene include its use in: packaging films, pipes, containers, and various other products.

5. Polystyrene

Extruded polystyrene (XPS), which is denser than expanded polystyrene (EPS), is widely used in construction. XPS offers excellent insulation, contributing to energy efficiency in buildings. Its light weight, easy installation, and decorative applications make it favored in the construction industry. XPS is commonly utilized for long-term insulation in various building elements, reducing energy waste and fostering greener construction practices. Additionally, flame retardants are often added for enhanced safety against fire hazards.

To learn more, see our guide on Polystyrene.

6. Polycarbonate (PC)

Polycarbonate, a transparent thermoplastic, is recognized for its impact resistance and optical clarity. This plastic offers a set of characteristics, including: rigidity, resistance to abrasion, color adaptability, and stable performance in diverse temperature ranges. It is commonly used in automotive components and electronic enclosures.

To learn more, see our guide on Polycarbonate.

7. Acrylonitrile Butadiene Styrene (ABS)

ABS, or acrylonitrile butadiene styrene, is a relatively hard plastic that is created through the polymerization of styrene and acrylonitrile in the presence of polybutadiene. This creates a tougher material when compared to just pure polystyrene. The styrene element contributes to ABS's waterproof surface and glossy appearance. Meanwhile, the presence of polybutadiene enhances its toughness, ensuring resilience regardless of temperature variations. ABS is also especially known for its good abrasion resistance. Common applications of ABS include: electrical pipes, appliance cases, pipes, wire protection, and automotive trim. Take note that ABS is not as chemically resistant as PP and PE, so it’s best to be cautious in environments in which this plastic might come into contact with chemicals. 

What Is Extrusion Molding Used For?

Extrusion molding is used to shape plastic materials into a predetermined form. It can also be used to shape metals. 

What Are Examples of Extrusion Molding Products?

Extrusion products can be found in a wide range of industries. Some examples of these products include:

1. Sheets and Cast Films: Plastic sheets are used in construction for: glazing on doors and windows, bulletproof sheets, and protective covers. Additionally, sheets serve as sound barriers, refrigerator liners, and decorative panels. Cast films are applied in: food wrapping, agricultural weed control, and protective packaging during shipments.
2. Extrusion Coating and Lamination: Extrusion coating enhances product quality by applying a polymer layer to substrates like: paper, metal foils, and plastics. This process finds applications in: dairy packaging, juice cartons, carpet coating, frozen food containers, and heat-seal layers for general packaging.
3. Wire and Cable Coating: Plastic extrusion coats wires and cables for insulation and protection. Common materials include: polyethylene, polyvinyl chloride, polyamide, and thermoplastic elastomers. 
4. Pipe and Tubing: Plastic extrusion is widely used in manufacturing pipes and tubing for applications ranging from water or sewage pipes to medical tubing. Materials like polyethylene, rigid polyvinyl chloride, and nylon are commonly employed for pipes, while thermoplastic resins are used for tubing, with options for both flexible and rigid forms.

What Are the Common Problems of Extrusion Molding Products?

Common problems in extrusion molding products can be categorized into 12 distinct defects, each of these are discussed below accompanied by troubleshooting recommendations:

1. Interrupted Melt Output: Commonly caused by unbalanced barrel temperatures, interrupted melt output can be addressed by reducing the feed-zone temperature to ensure proper material transition. Additionally, it is essential to check the temperature resistance and cooling system. Regular inspection of the screen is crucial to capture any degraded or burned particles that might affect the extrusion process.
2. Surging: Surging issues, attributed to contaminated material, incorrect temperature settings, or an unbalanced die exit, can be mitigated by gradually increasing barrel temperatures for each zone. What can also help is regularly checking and cleaning the screen, inspecting for blockages in the hopper, reviewing the screw configuration, and ensuring a clean screw before production.
3. No Output: When facing no output due to a blocked die caused by solidification, it's important to inspect the material entrance from the hopper, clear any blockages inside the hopper, increase the die temperature to dissolve blockages, and consider changing the screen for uninterrupted production.
4. Rough Surface Caused by Unmelted Particles: To address a rough surface resulting from unmelted particles, it’s necessary to do a thorough inspection of the screen for tears. Increasing temperatures, especially in the compression zone, checking zone temperature resistance, and adjusting screw rpm and zone temperatures to prevent degradation from cross-linked particles can all contribute to smoother extrusion.
5. Burned or Discolored Extrudate: When dealing with burned and discolored extrudate the following can be done: reduce screw rpm and gradually lower the barrel temperatures until the desired color is achieved. Selecting an extruder with a lower L/D ratio for production can further enhance the quality of the extruded products.
6. Die Lines: Die lines, a common defect, can be addressed by selecting a material with lower viscosity and increasing the die temperature to ensure a smoother extrusion process.
7. Melt Fracture: Reducing barrel temperatures and changing the material by the die design helps mitigate melt fracture.
8. Shark Skin: Shark skin, characterized by surface irregularities, can be minimized by reducing rpm, changing the screen, and increasing the melt temperature for improved extrusion results.
9. Fish Eyes: For extrusion products showing “fish eyes,” it's crucial to check the material and screen for contamination, ensure proper drying of the material, and reduce temperatures to prevent material degradation during the extrusion process.
10. Bubbles: Preventing bubbles on the profile surface involves proper drying of the material, reducing melt temperature, and adjusting the screw rpm for smoother and defect-free extrusion.
11. Warpage: Warpage issues due to insufficient cooling can be alleviated by increasing the cooling bath length, reducing water temperature, and balancing the die according to part-wall thickness for uniform cooling.
12. Orange Peel Surface: An orange peel surface, which is indicative of low die temperature, can be improved by increasing the die temperature and raising the temperature of zones close to the die. This results in a smoother and more refined extruded product.

What Is the Life Span of Extrusion Molding Products?

There is no one-size-fits-all answer here. The life span of extrusion molding products varies based on factors like: material type, environmental conditions, and manufacturing quality. Materials with higher durability, quality additives, and reinforcement generally contribute to a longer life span. Harsh environmental factors, including extreme temperatures and exposure to chemicals, can accelerate wear and affect longevity. However, to give an estimate of the expected lifetime, the average lifetime of plastic products tends to be around 10 years. However, this can vary greatly for different applications. Some plastics can remain fully functional for decades. One such example is pipe installations that can last between 50 to 100 years. 

Are Extrusion Molding Products Durable?

It depends. Extrusion molding products can be highly durable, with their longevity depending on various factors. The choice of materials, environmental conditions, manufacturing quality, and intended applications all affect the durability of the product. Products made from high-quality materials and designed for specific purposes tend to exhibit robustness and resistance to wear. 

Is Extrusion Molding Expensive?

No, extrusion molding, whether plastic molding or metal molding, is generally considered to be both efficient and cost-effective compared to other processes like injection molding or other metal forming processes. 

What Are the Advantages of Extrusion Molding?

Extrusion molding has a few advantages compared to other manufacturing methods:

1. A very efficient process, resulting in a low cost per part produced.
2. Is suitable for big production batches.
3. Excess plastic can be recycled and reused, cutting down on waste and production costs.
4. Allows for complex shapes of many different materials and design parameters.

What Are the Disadvantages of Extrusion Molding?

Extrusion molding has the following disadvantages compared to other manufacturing methods:

1. Parts can swell immediately after being extruded, resulting in inconsistencies in batches.
2. The costs of purchasing the equipment for extrusion molding can be fairly high.
3. The designs that can be produced are limited.

What Is the Difference Between Extrusion Molding and Injection Molding?

Extrusion and injection molding processes might seem similar at first glance due to both processes involving molten material being passed through machinery to manufacture low-cost components in the desired shape. Both methods also operate as continuous production processes, in which the cost-effectiveness improves with higher quantities of parts ordered. However, these processes are very different, and their main difference comes down to how the final shape is formed.

With injection molding, plastics are melted into a liquid form and shaped using a mold or a specially designed cavity. Once cooled, manufacturers eject the now-solid plastic material, forming intricate three-dimensional shapes with a smooth surface finish. The process is highly efficient and capable of rapid repetition, hundreds or thousands of times. This repetition helps amortize the mold-tool costs, leading to reduced overall expenses as the number of plastic products ordered increases. The use of a single mold tool for each part, coupled with the affordability of plastic pellets, makes this manufacturing method well-suited for producing economically viable parts with consistent quality.

Extrusion molding, on the other hand, involves the continuous extrusion of plastic material from a machine, forming a lengthy tube (or line bar) that is then cooled. Molten material passes through an extrusion machine and exits through a two-dimensional die opening, forming rod-like shapes with intricate cross-sections, outer shapes, and even inner voids. The shape and length of the final component are determined by the die in the extrusion machine. These elongated bars, often spanning lengths of 100 or 1000 feet, are typically cut using a band saw and can undergo further shaping, post-modification, or integration into assemblies.

What Is the Difference Between Extrusion Molding and Compression Molding?

The primary difference between extrusion molding and compression molding lies in their processes and applications. Compression molding involves using a two-piece mold heated to soften the molding material, which is then loaded into the mold's lower half. The two mold parts are brought together under pressure, welding the material into the desired shape. Hardening is achieved through further heating (for thermosetting plastics) or chilling (for thermoplastics) under pressure in the mold. This method is predominantly used for thermosetting plastics.

On the other hand, extrusion involves a continuous operation, with thermoplastic materials melted and forced through a forming die. Various products such as: pipes, tubing, plastic bottles, films, and profiles are produced through extrusion. The material, fed into an extruder, can be in pellet, powder, granulate, or melt form. Extruders must melt, homogenize, and pump the material through a die system to ensure acceptable output uniformity. Downstream equipment, including cooling rolls and cutting devices, continuously shapes and cools the extruded melt. The key difference is that compression molding is often used for thermosetting plastics, while extrusion is primarily employed for thermoplastics and involves a continuous shaping process.

Summary

This article presented extrusion molding, explained it, and discussed how it works and its applications. To learn more about extrusion molding, contact a Xometry representative.

Xometry provides a wide range of manufacturing capabilities, including extrusion and other value-added services for all of your prototyping and production needs. Visit our website to learn more or to request a free, no-obligation quote.

Disclaimer

The content appearing on this webpage is for informational purposes only. Xometry makes no representation or warranty of any kind, be it expressed or implied, as to the accuracy, completeness, or validity of the information. Any performance parameters, geometric tolerances, specific design features, quality and types of materials, or processes should not be inferred to represent what will be delivered by third-party suppliers or manufacturers through Xometry’s network. Buyers seeking quotes for parts are responsible for defining the specific requirements for those parts. Please refer to our terms and conditions for more information.

In the world of manufacturing, where innovation and efficiency reign supreme, various techniques and processes have evolved to meet the demands of diverse industries. Among these, extrusion stands out as a fundamental and versatile method used in the production of numerous everyday items, from pipes and tubing to food products and even 3D printing filaments.

But what exactly is extrusion, and how does it impact our daily lives?

What Is an Extrusion?

At its core, extrusion is a manufacturing process that involves shaping raw materials into a desired cross-sectional profile through a die. This technique extends to metals, ceramics, and food products, making it a ubiquitous method across various industries.

Components of the Extrusion Process

Extrusion equipment typically comprises a few essential components:

• Extruder: The heart of the extrusion process, the extruder is a machine that houses a screw or a ram to transport the raw material through the system. It applies heat and pressure to soften or melt the material for processing.
• Die: The die is a precision tool that shapes the material as it passes through, giving it the desired profile. The die shape is designed based on the product specifications.
• Cooling System: Following the shaping process, a cooling system helps solidify the material into its final form. This can involve water baths, air cooling, or other methods, depending on the material being extruded.

What Is the Extrusion Process?

The extrusion process involves the application of heat and pressure to force the material, usually in a molten or semi-solid state, through a specifically designed opening—a die shape—with the desired cross-sectional profile. The material emerges on the other side of the die in the shape required for its final application.

Variants of the Extrusion Process

There are various types of extrusion processes, each suited for different materials and end products. These processes include direct extrusion, indirect extrusion, cold extrusion, and hot extrusion.

• Direct Extrusion: Also known as forward extrusion, this involves pushing the material through the die in a continuous process. It’s common in the creation of solid shapes like rods or bars.
• Indirect Extrusion: In contrast, indirect extrusion involves the die moving with the ram, reducing friction and allowing for more complex shapes to be formed.
• Cold Extrusion: This process is conducted at or near room temperature, ideal for materials that might lose their properties under heat. Cold extrusion is perfect for products that require high strength or close tolerances.
• Hot Extrusion: Often used for metals and thermoplastics, hot extrusion involves heating the material to make it more malleable, aiding the extrusion process. Not to be confused with warm extrusion, the hot extrusion process takes place at a much higher temperature.

Commonly Extruded Materials

Extrusion is a versatile manufacturing process used with a wide range of materials. The most common extruded materials include softer metals, plastic materials, and food products, each serving specific industries and applications. The Federal Group specializes in the following metal materials for the extrusion process:

The raw material or stock material is typically handled as a cylindrical billet similar to the image above.

Applications of Extrusion

Are you interested in learning more about Rapid Tooling For Injection Molding Molds? Contact us today to secure an expert consultation!

Metal extrusion has found widespread use in various industries, each harnessing its unique capabilities to meet specific needs. Even though it is commonly utilized as a metal forming process, plastic extrusion can create a variety of specialty plastic products like plastic pellets and rigid pvc. Let’s explore the different industries that rely on metal extrusions.

Construction Sector

In the construction sector, extrusion is crucial for creating materials like aluminum or steel beams, window frames, and even certain types of bricks or tiles. The ability to produce long, continuous sections of materials with specific cross-sectional profiles makes it an invaluable technique.

Consumer Goods Industry

Metal extrusions also find applications in the consumer goods industry for various products, including furniture frames, bicycle frames, and more. They are also commonly found in appliance components like ovens, fireplace frames, and ovens.

Electrical and Electronics Industry

Metal extrusion is used in the electrical and electronics industry to create heat sinks, enclosures, and conductive components.

Marine Industry

In the marine industry, metal extrusions are valued for their corrosion resistance and durability in harsh, saltwater environments. They are used for boat components, plumbing, ventilation systems, rails, cleats, and more.

Manufacturing and Industrial Equipment

The metal extrusion process plays a significant role in manufacturing and industrial equipment. Some of the products created by metal extrusion include conveyor systems, material handling systems, frames for mechanical equipment or machines, plus safety barriers and guardrails.

Advantages and Limitations of the Extrusion Process

Advantages of Extrusion

• Cost-Effectiveness: The extrusion process allows for continuous production, reducing the need for additional processing steps and lowering production costs.
• Efficiency and Precision: The process offers high precision and repeatability in creating complex shapes with consistent quality.
• Versatility: The extrusion process is versatile, accommodating a wide range of materials and enabling the production of various end products.
• Strength: In regard to metal extrusion, the mechanical properties of the alloy post-extrusion process have greater tensile strength.

Limitations of Extrusion

• Material Constraints: Not all materials are suitable for extrusion, particularly those that may degrade or lose properties under heat. In addition, softer metals are ideal for the metal extrusion process.
• Initial Setup Costs: Customizing dies and setting up extrusion processes can involve significant initial expenses.

Frequently Asked Questions

What is hydrostatic extrusion?

Hydrostatic extrusion is a metal forming process in which a billet is forced through a die by hydraulic pressure, resulting in precise and uniform deformation of the material. The hydrostatic extrusion process can take place in a warm, cold, or hot temperature.

What is friction extrusion?

Friction extrusion is a solid-state process that involves rotating a cylindrical tool within a stationary workpiece, generating heat through friction, and allowing the material to deform and flow plastically, resulting in the creation of complex shapes with reduced energy consumption. It is particularly useful for joining dissimilar materials and recycling scrap or waste materials into useful products.

What is impact extrusion?

The impact extrusion process involves a punch impacting a metal slug placed within a die, causing the material to flow and take the shape of the die cavity.

What is lateral extrusion?

The lateral extrusion process is just another form of extrusion where the container is in a vertical orientation. This process is utilized in the production of profiles, bars, and sections with precise dimensions, often in the construction, automotive, and manufacturing industries.

What is the difference between plastic injection molding and the extrusion process?

Plastic injection molding involves injecting plastic material into a mold cavity to create complex three-dimensional parts, while extrusion forces material through a die to produce shapes like pipes, tubing, and profiles. Per the name, plastic injection molding can only work with plastics while the extrusion process can deal with plastic and metal materials.

Is the extrusion process fast?

Extrusion is an extremely fast metal forming process. Non-ferrous alloys can be extruded between 1/2 inch per second and 6 inches per second. The extrusion speed ultimately depends on the machinery being used.

What metals can you extrude?

Aluminum, brass, bronze, copper, magnesium, steel, stainless steel, titanium, and zinc. Plastic materials can also be extruded via the plastic extrusion process.

What are plastic extrusions used for?

Some common uses for plastic extrusions include decorative trims, custom plastic containers, and other plastic items like display racks.

Does the die entry angle effect the extruded part?

Yes, the die entry angle has distinct effects on the mechanical properties of an extruded part.

Extrusion Conclusion

Extrusion stands as a foundational manufacturing process with a remarkable impact across diverse industries. Its versatility, precision, and efficiency make it an indispensable technique for shaping various raw materials into products that have become integral to our daily lives.

Understanding the mechanics and applications of extrusion sheds light on its significance in modern manufacturing. As technology advances and the need for sustainable manufacturing processes grows, the evolution of metal extrusion processes will likely continue, contributing to a more efficient, innovative, and environmentally conscious industrial landscape.

Start a Custom Metal Extrusion Project With the Federal Group USA Today

The Federal Group USA is a leading manufacturer in the world of custom metal extrusion. Whether your product requires hot extrusion, cold extrusion, direct extrusion, or indirect extrusion, we can handle your requirements.

Contact us today to speak with a sales engineer regarding your next extrusion project.

If you are looking for more details, kindly visit Rapid Tooling For Automotive Prototypes.