Plastic Extrusion: Definition, Purpose, How It Works, Advantages, and Examples

The versatility, cost-effectiveness, simplicity, and to some extent even durability of plastics have made them exceedingly popular among manufacturers. Among the top plastic manufacturing methods is extrusion molding. This process is very helpful in creating continuous profiles like tubes or pipes and finds application in many different industries. This technique has revolutionized the creation of pipes, packaging, automotive components, consumer goods, and more. In this article, we will discuss plastic extrusion, its definition, purpose, intricate workings, and the advantages it brings to the forefront. 

What is Plastic Extrusion?

Plastic extrusion is a large-scale manufacturing process that yields continuous products with uniform cross-sections. This technique involves melting thermoplastic materials and pressurizing them to force the melt through a die. A rotating screw’s interaction with the barrel walls generates pressure. As the melted plastic moves through the die, it gets shaped into the form of the die and emerges as an extrudate. Subsequent cooling methods like cooling rolls or water baths solidify the extrudate into its final form.

Plastic extrusion is versatile, producing tubes, pipes, sheets, profiles, films, and custom shapes. The extruder equipment used in this process is part of a comprehensive system made to manufacture plastic components on a large scale. Other key components of a plastic extruder include: the feed pipe/adapter, feed throat, hopper, breaker plate, die, barrel, and cooling system as seen in Figure 1 below: 

Collectively, these elements synergize to melt, mold, and solidify plastic materials.

What Is Plastic Extrusion Also Known As?

Another name for plastic extrusion is plasticizing extrusion. 

What Is the Purpose of Plastic Extrusion in Manufacturing?

The primary purpose of plastic extrusion in manufacturing is to efficiently produce plastic products with consistent cross-sections and specific shapes. Plastic extrusion serves as a versatile and cost-effective way to create items across multiple industries.

What Industries That Use Plastic Extrusion?

A lot of industries make use of extruded plastic tubing. It’s of particular importance in the: medical, automotive, construction, electronics, food, and beverage sectors. In the field of medicine, both flexible and rigid tubes are made this way. They wind up in tools like: catheters, IV lines, and medical pouches. In the automotive sector, the value of extruded plastic lies in its durability and cost-effectiveness, since such parts are designed to endure a wide range of environmental conditions. In the food and beverage sectors, this plastic has a role in beverage dispensing systems and food-grade packaging. 

How Does Plastic Extrusion Work?

Plastic extrusion involves several stages, from melting and extrusion to cooling and processing stages. It begins with loading raw material, typically polymer resin pellets, into a hopper. Additives such as fillers and coloring agents are mixed in with the resin pellets to create a homogenous mixture for melting and extrusion. Similar to plastic injection molding, a hopper of plastic pellet material feeds a barrel containing a rotating screw that works to push the material forward. As the material passes between the screw and the barrel walls, it undergoes shearing forces and friction, which heats and begins melting. Heaters on the barrel apply additional heat, assisting the melting process. Drag forces generated by the screw force the melted polymer through a filter and breaker plate to remove contaminants and create an even distribution of polymer through the die assembly at the barrel’s end. Extruded plastic can be found in everything from simple pipes to precise medical implants. 

Melted plastic is shaped and formed into the profile of the exit die opening. At this stage, the extrusion is still hot and malleable. The material passes through a cooling bath filled with water which uniformly cools and solidifies the extrusion, helping bring it to its final shape. Air or metal contact cooling systems are also sometimes used. A vacuum sizing stage before the cooling stage may be necessary for extrusions that contain hollow features to mitigate defects and maintain shape. Pull rollers apply a uniform pulling pressure which helps smooth the plastic and move it further down the line. The plastic extrusion receives quality control checks using onboard laser measurement systems, and good sections are then spooled or cut to final part dimensions. The product is then ready for final quality checks, storage, and packaging.

What Is the Step-by-Step Process of Plastic Extrusion?

The plastic extrusion process typically involves seven steps:

1. Material Preparation

Raw plastic, usually in the form of pellets or granules, is prepared for the extrusion process. You choose a material based on what properties you expect in the final product. Some plastics emphasize strength, flexibility, color, or other properties. Raw plastic material is typically stored in a hopper. It is introduced into the extruder through the feeding opening at the rear end of the barrel. As the plastic pellets descend into the barrel and contact the screw, they also begin to melt. 

2. Melting and Mixing

The plastic material is introduced into an extruder, a machine comprising a heated barrel and a rotating screw. The screw within its barrel rotates in a controlled manner but can operate at speeds as high as 120 rpm. As the screw rotates, it advances the plastic beads within the barrel, subjecting them to heat generated by the barrel itself. This heat, combined with the friction induced by the screw's movement, causes the plastic material to melt. Most extrudable plastics melt at around 200 to 275 °C. 

Upon leaving the screw, the molten plastic passes through a screen pack designed to eliminate contaminants. To withstand pressures that can surpass 34 MPa, a breaker plate reinforces the screens. 

3. Extrusion Process

Following the thorough mixing and uniform melting facilitated by the extruder, the molten plastic is pushed through a specially designed die or mold located at the extruder's end. This will give the plastic its final dimensions.

4. Cooling and Sizing

As the plastic material exits the die, it enters a cooling zone. Air- or water-cooling systems often assist during this stage. This removal of heat solidifies the plastic into its final shape. Additionally, sizing tools or equipment may be used to ensure it meets the required dimensions.

5. Hauling and Cutting

The extruded plastic material is pulled or "hauled" through the process using rollers or other mechanisms. This keeps the extrusion moving at the proper speed and tension. After hauling, the continuous extruded profile is cut into specific lengths using cutting tools or saws.

6. Additional Processing

Some extruded items need additional processing. This could include: surface treatments, printing, markings, or attaching other components to the extruded profile.

7. Inspection and Quality Control

The extruded plastic profiles are inspected for defects, dimensional accuracy, and other quality criteria. Any profiles that do not meet the required standards may be rejected or sent for further processing.

How Does a Laser Beam Profiler Improve Plastic Extrusion?

Laser beam profilers are not used to improve plastic extrusion. They can, however, measure the straightness and pointing direction of extruder pipes.

What Are the Materials That Can Be Used in Plastic Extrusion?

Plastic extrusion is a versatile manufacturing process that can be applied to a wide range of materials. Here's a list of some common materials that can be extruded this way: 

1. Polyethylene (PE)

Polyethylene is a thermoplastic known for its flexibility, durability, and chemical resistance. It strikes a good balance between colorability, strength, and low-temperature performance. It's used in packaging films, pipes, and containers, among many other things.

2. Polypropylene (PP)

Polypropylene is another versatile thermoplastic that strongly resists chemical agents. This polymer achieves a perfect equilibrium between strength, impact resistance, color versatility, and performance in low-temperature conditions. It's used in packaging, automotive parts, textiles, and more.

3. Polyvinyl Chloride (PVC)

Polyvinyl chloride is a common thermoplastic known for its versatility, durability, and cost-effectiveness. It's used in pipes, cable insulation, and flooring. There are two distinct types: rigid PVC and flexible PVC. Flexible PVC is renowned for its affordability and adaptability. This material strikes an excellent middle ground between resistance to weather conditions, tear resilience, and tensile strength. Rigid PVC, on the other hand, resists impacts and remains stable under ultraviolet radiation. It finds use in applications such as pipe construction, refrigeration units, windows, and doors. Its inherent rigidity positions it as a feasible alternative to wood and metal across a lot of applications.

4. Polystyrene (PS)

Polystyrene is a lightweight and rigid thermoplastic commonly used in packaging materials, disposable utensils, and insulation.

5. Acrylonitrile Butadiene Styrene (ABS)

ABS is manufactured through the polymerization of styrene and acrylonitrile, with the presence of polybutadiene improving its toughness compared to pure polystyrene. The styrene element in acrylonitrile butadiene styrene gives it a glossy, waterproof surface. Polybutadiene, meanwhile, enhances its durability regardless of temperature variations. ABS is a tough and impact-resistant thermoplastic that’s ideal for both strength and aesthetics, such as in automotive parts, toys, and consumer electronics.

6. Polyamide (PA or Nylon)

Nylon is a strong and durable thermoplastic with excellent mechanical properties. It's used almost everywhere, including in automotive parts, industrial components, and textiles.

7. Polycarbonate (PC)

Polycarbonate is a transparent thermoplastic known for its impact resistance and optical clarity. This substance offers a well-rounded combination of attributes, encompassing rigidity, resistance to abrasion, color adaptability, and good performance across both high and low temperatures. It's regularly seen in automotive components and electronic enclosures.

8. Polyethylene Terephthalate (PET)

Polyethylene terephthalate ends up in packaging materials, especially for beverages and food products. It's also used in fibers for textiles and engineering applications.

These are just a few of the many materials that can be processed through plastic extrusion. Other polymer extrusion materials include thermoplastic vulcanizate (TPV), thermoplastic alloy (TPA), styrene, mineral-filled polypropylene, acrylic, and chlorinated polyvinyl chloride (CPC). 

Material Selection for Plastic Extrusion

Choosing a suitable material for your project is crucial to your extruded part’s overall functionality and longevity. In addition, the material can be a primary driver for manufacturability and cost. The first step to picking a plastic resin is determining what characteristics your part will require for its intended use and environment, as not all plastics perform equally. These characteristics may include the following:

• Environmental resistance (temperature, UV rays, weather, etc.)
• Rigidity / Flexibility
• Impact resistance and strength
• Chemical resistance (e.g., cleaning agents, gasoline, oil, etc.)
• Physical appearance

You can keep costs low by avoiding more exotic, less common materials and picking one that is more common and meets your part’s end-use requirements. To help you understand the differences between the different plastic resins and make the right choice for your project, we’ve compiled the table below, which compares commonly available materials for plastic extrusion. Xometry’s experts can also help guide you to the most suitable material and filler selection for your project and answer any questions.

How Long Does It Take for Plastic Extrusion To Finish?

A plastic extrusion process’ timeline depends on several factors, including: the complexity of the product, the type of plastic being extruded, the speed of the extrusion line, and the manufacturer’s specific requirements. Generally, plastic extrusion is known for its efficiency and the speed with which it can produce high volumes of continuous products.

Simple products with basic shapes, such as straight pipes or profiles, can be extruded relatively quickly. However, more complex products that require intricate profiles, multiple layers, or additional post-extrusion modifications might take longer.

How Accurate Is Plastic Extrusion?

For simple profiles and shapes, plastic extrusion can achieve relatively good tolerances. Modern extrusion machines are equipped with advanced controls and monitoring systems that keep the output close to the specified dimensions. This level of accuracy is particularly crucial in construction, automotive, and electronics products, where precise measurements are essential for proper functionality and compatibility.

However, it's important to note that the accuracy of plastic extrusion might vary based on: the complexity of the design, the type of plastic being extruded, and the overall quality of the manufacturing process. Additionally, factors like die swell (the expansion of plastic after leaving the die) and cooling rates can also influence the final dimensions of the extruded product.

How Much Does Plastic Extrusion Cost?

The cost of plastic extrusion depends almost entirely on the specific material and the design’s complexity. Generally, the products tend to fall within the budget of less than $1,000. However, the plastic extrusion machines typically range between $7,000 and $90,000 and the molds can be anything from a few hundred dollars to $15,000, depending on the complexity and size.

Is Plastic Extrusion Expensive Compared to Die Casting?

No, plastic extrusion is more affordable than die casting. This is because extrusion does not require high-pressure equipment or specialized molds. However, extrusion tends to be slower and less precise than die casting. 

What Are the Advantages of Plastic Extrusion?

Plastic extrusion offers many advantages, including:

1. This option is notably cheaper than alternative molding methods such as die casting. Raw material expenses and disposal costs are reduced. Because they can run continuously, plastic extrusion machines limit the risk of inventory shortages, facilitating 24-hour manufacturing.
2. You get great flexibility as long as you intend to make items with consistent cross-sections. Even intricate cross-sectional shapes can be generated through this method. 
3. Plastics remain malleable upon exiting the extruder, enabling post-extrusion alterations. Capitalizing on this, many manufacturers employ an array of tools such as rollers, shoes, and dies to modify the plastic's shape to meet their requirements.
4. You can mold products of varying sizes, shapes, and profiles. This technique is well-suited for creating items like pipes, films, sheets, tubes, and more, and can be tailored to satisfy precise design specifications.
5. With its continuous operation, plastic extrusion excels when generating products in bulk. It is an optimal choice for large-scale manufacturing if you’re addressing substantial demand.
6. This technique accepts an assortment of thermoplastic materials such as: PVC, polypropylene, polyethylene, and polystyrene, among others. The wide material selection allows you to make products with attributes like flexibility, heat resistance, strength, and chemical durability.
7. Extrusion methods can use recycled materials.

What Are the Disadvantages of Plastic Extrusion?

Plastic extrusion does, however, also come with its share of drawbacks, including:

1. Extruded plastic often expands upon removal. Referred to as die swell, this expansion can be hard to predict. 
2. This technique places limits on the types of items you can produce. Research the exact extrusion equipment that fits your project before investing in it. 
3. The up-front capital is significant. All of the dies, extruders, and equipment can be quite costly, especially for niche applications. 
4. Although plastic extrusion gives you the option of using recycled materials, doing so comes with some drawbacks. Recycled plastics may contain impurities and inconsistent properties, for instance. Plus, it may be hard to source and cost more to process. 

What Are Examples of Plastic Extrusion Products?

Examples of plastic extrusion products are:

1. Tubing and pipes for plumbing, drainage systems, electrical conduits, irrigation, and automotive fuel lines.
2. Door and window frames, trim, gaskets, weatherstripping, structural elements, and decorative moldings for automotive, furniture, and construction industries.
3. Plastic coatings and insulation for cables and wires.
4. Fibers and filaments made of ABS, nylon, PLA, and PET for 3D printing, textiles, and reinforcement materials.
5. Flexible packaging materials like plastic films and sheets can be further transformed into bags, pouches, laminates, and shrink wraps.
6. Plastic films and sheets are perfect for packaging, signage, construction, and automotive interiors. These sheets can be further processed into containers, trays, roofing membranes, displays, and car dashboards.

What Is the Lifespan of Plastic Extrusion Products?

The lifespan of plastic extrusion products can vary significantly depending on the type of product, the setting, and the raw materials used in its manufacture. Figure 3 depicts the average lifespan of plastic products by type:   

The average lifespan for plastic products is around 10 years, but this number can vary significantly depending on the application. Plastics in the industrial and construction sector can remain in use for decades, with some pipe installations even estimated to reach lifespans of 50 to 100 years. Meanwhile, plastics in the packaging industry are typically disposed of within a year. Items like straws are even discarded after a single use. 

What Is the Difference Between Plastic Extrusion and Vapor Smoothing PLA?

Plastic extrusion and vapor smoothing PLA are two distinct processes that pertain to plastic materials. They serve very different purposes and involve different techniques.

The plastic extrusion process shapes molten plastic into continuous profiles with consistent cross-sections. This process is used to create things like: pipes, tubes, sheets, profiles, and more. Vapor smoothing for PLA (polylactic acid), on the other hand, is a post-processing technique used to improve the surface finish of 3D-printed PLA objects. The PLA item is exposed to solvent vapors, usually in a controlled chamber. This process can help reduce the visible layer lines that often show up in 3D-printed objects, giving them a more professional appearance.

To learn more, see our guide on PLA Vapor Smoothing.

What Is the Difference Between Plastic Extrusion and Acetone Vapor Smoothing?

Plastic extrusion and acetone vapor smoothing are distinct processes that serve very different purposes.

Plastic extrusion is a manufacturing technique used to shape molten plastic into continuous profiles with consistent cross-sectional shapes. Melted plastic is forced through a specially designed die or mold to create various plastic products such as: pipes, tubes, sheets, and more. Acetone vapor smoothing is a post-processing technique applied to 3D-printed objects, particularly those crafted from materials like ABS (acrylonitrile butadiene styrene). The process involves exposing the 3D-printed object to acetone vapors within an enclosed chamber. This technique enhances the aesthetic appeal of 3D-printed objects, giving them a polished appearance. 

For more info, see our article on 3D Printing Acetone.

Summary

This article presented plastic extrusion, explained it, and discussed its purpose and advantages. To learn more about plastic extrusion, 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.

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