What Is Plastic Fabrication?
We can see plastic components and products everywhere, from home appliances to cars and electronics.
To convert raw plastic materials into the desired functional shape, they must be processed with a suitable fabrication process.
So, plastic part fabrication is the process of converting plastic pallets or sheets into designed geometry. It might or might not involve the melting of raw plastics.
For example, vacuum casting melts the plastics to mold the shape, whereas CNC machining removes the material using rotating cutting tools.
The fabrication techniques can shape both types of plastics; thermosetting plastics and thermoplastics.
However, you must be careful about the methods compatible with the plastic you want to fabricate.
Subsequently, the malleability, low weight, strength, and cost-effectiveness of plastics make them ideal for diverse engineering industries for both prototyping and full-scale production.
What Are The Methods Used In Plastic Fabrication?
Plastic fabrication comprises many different methods. Injection molding, plastic extrusion, and FDM 3D printing are all plastic fabrication methods, and there are many more besides.
These different plastic fabrication methods suit different plastic parts, and choosing between them isn’t always straightforward.
Budget, part design, and material are just some of the factors that go into choosing a plastic fabrication method.
#1. Injection molding.
Injection molding is the most common plastic fabrication process. It can process thermoplastic and thermoset polymers.
This fast plastic fabrication method works by heating plastic pellets until they melt, then forcing the molten plastic into a metal mold using a reciprocating screw.
The molten material cools down, solidifies, and assumes the shape of the mold cavity. The solid part is then ejected from the mold.
Injection molding is suitable for a huge variety of materials and parts. Parts must have thin and consistent walls but can otherwise assume various shapes and sizes.
- Example injection molded parts: disposable food trays, car dashboards, LEGO bricks
#2. Blow molding.
Blow molding is a plastic molding process that is less widely used than injection molding. It has three distinct variants: extrusion blow molding, injection blow molding, and injection stretch blow molding.
This plastic fabrication processes works using a mold and a molten thermoplastic tube called a parison (instead of fully melted pellets).
Pressurized air enters the parison, causing the plastic to expand and touch the internal walls of the mold, eventually assuming the shape of the mold cavity.
Blow molding is suitable for hollow plastic parts like plastic water bottles, with HDPE the most common material.
- Example blow molded parts: bottles, drums, fuel tanks
#3. Rotational molding.
Rotational molding is another plastic molding process one that uses high temperatures and low pressure to form plastic parts. It works by rotating a mold to move the plastic material around inside.
During the rotational molding process, powdered plastic is placed in a mold, which is heated and rotated about two (or more) axes.
This rotation ensures that molten plastic covers the entirety of the inside of the mold and assumes the shape of the cavity.
Advantages of rotational molding include simpler tooling, consistent wall thickness, and strong external corners.
But the process can be slow, since the entire mold needs cooling before part ejection.
- Example rotational molded parts: bins, storage tanks, toys
#4. Vacuum casting.
Vacuum casting is a plastic fabrication process usually employed for small batches of colorful prototypes. It uses silicone molds to make urethane plastic parts.
During this plastic fabrication process, the operator pours urethane casting resin into a silicone mold; a vacuum then removes air pockets and bubbles, resulting in an exceptionally smooth finished part. The urethane parts are then cured in an oven.
Vacuum casting is a popular plastic fabrication process for partially transparent parts like prototype display cases.
- Example vacuum cast parts: electronics cases and covers, various display prototypes
#5. Plastic machining.
Plastic CNC machining is a very popular plastic fabrication process. It encompasses CNC milling, CNC turning, and other related processes.
Although different machines work in different ways, plastic machining generally entails cutting away sections from a plastic workpiece using either manual or computer-controlled cutting tools.
Machining is highly accurate, works with a range of plastics, and is better than molding for making thick-walled parts.
Plastic machining is also useful for adding details for parts made using other techniques like extrusion.
- Example machined parts: various industrial parts, jigs and fixtures, automobile lighting
#6. Fused deposition modelling.
Fused deposition modeling (FDM) is the most common 3D printing process for plastic fabrication. It works with common thermoplastics like ABS and PLA, as well as advanced materials like PEEK.
FDM works by heating up extruded thermoplastic filament, then depositing it in precise shapes from a moving nozzle (attached to a printhead) according to computer instructions.
2D slices of the part are printed layer by layer until the complete 3D object is built.
In small quantities, FDM is very fast and cost-effective and can produce a wide range of shapes, including those with complex internal geometries. However, it does not produce especially strong parts.
- Example FDM parts: various prototypes, spare parts and repairs, composite industrial parts
#7. Stereolithography.
Stereolithography (SLA) is a different form of plastic 3D printing that works with photopolymeric resins instead of thermoplastic polymers.
It works by selectively curing photopolymeric resins using a light source such as a laser. (Digital light processing, a related technology, used a projector instead.) Parts are printed layer by layer as the print bed moves through the resin vat.
SLA produces brittle but exceptionally smooth parts, which can also be transparent. It is often used for prototyping but also has applications in dentistry in jewelry.
- Example SLA parts: display prototypes, dental aligners, jewelry patterns for casting
#8. Selective laser sintering.
Selective laser sintering (SLS) is a plastic fabrication process and another form of 3D printing. It is principally used to make nylon parts.
SLS is a powder bed fusion process. It works by using a laser to selectively sinter 2D shapes in plastic powder, layer by layer, building a complete plastic part.
It is broadly similar to the metal additive manufacturing process of selective laser melting (SLM). An advantage over other plastic 3D printing methods is that it does not require support structures.
More so than FDM or SLA, SLS is considered an industrial additive manufacturing process and is popular in the automotive industry.
- Example SLS parts: tooling, automotive hardware, electrical connectors
#9. Plastic extrusion.
Not to be confused with extrusion 3D printing, plastic extrusion is the process of forcing plastic through a die to make an elongated plastic part with a consistent profile.
This high-volume plastic fabrication process works by heating plastic in a barrel, then forcing it using a reciprocating screw into a die, giving it its final shape with a continuous profile.
The resulting plastic extrusion hardens as it cools down.
Common plastic extrusion materials include polyethylene, polypropylene, acetal, and nylon. The process also has variants like blown film extrusion and tubing extrusion.
- Example extruded parts: pipes, tubing, window frames
#10. Plastic pultrusion.
Plastic pultrusion is a variant of plastic extrusion in which the material is pulled through a die rather than pushed.
The plastic fabrication technique of pultrusion is suited to fiber-reinforced plastics. During the process, a roll of reinforced fibers is pulled through a tank of plastic resin, which impregnates the fibers, and then through a heated die, giving the fiber-reinforced resin its custom profile.
Several plastic resins are suitable for pultrusion, including polyester, polyurethane, and epoxy. Glass fibers are the most common reinforcing material.
- Example pultruded parts: stiffening bars, ski poles, various reinforcing structural parts
#11. Plastic welding.
Welding is mostly associated with metals, but plastic welding is a useful plastic fabrication process for joining thermoplastic components not suitable for gluing or other assembly methods.
The plastic welding process has a huge number of variants, including hot gas welding, speed tip welding, and contact welding.
The majority of variants involve preparing the surface of the plastic, applying heat and pressure, then cooling.
The various plastic welding methods can be classified as thermal, mechanical, or electromagnetical.
- Example welded parts: housings, cellphone parts, medical devices
#12. Thermoforming.
Thermoforming is a type of plastic fabrication that resembles molding but which uses gently heated plastic sheet instead of fully molten plastic.
The plastic fabrication method technique requires an oven and a mold. During the process, the plastic sheet is heated until pliable; it is then stretched over a mold typically using a vacuum before being trimmed and cooled.
Thermoforming is fairly versatile, as it can be carried out on both a small scale or for mass production.
- Example thermoformed parts: blister packs, plastic cups, lids
What Are The Finishing Processes In Plastic Fabrication?
Once the plastic product has been manufactured, however, your work isn’t done. Plastic fabrication finishing processes are essential for enhancing your product’s visual appeal and functionality.
Below, we detail five of the most common plastic fabrication finishing processes and how you can expertly perform them.
1. Sanding and Polishing.
Sanding and polishing are among the most common finishing processes in plastic fabrication. These techniques are used to remove any rough edges, scratches, and blemishes on the surface of the plastic product.
Sanding is completed using sandpaper, while polishing is executed with a polishing compound. Products that may need to undergo these processes can include automotive parts like bumpers and grills, medical devices, and furniture, among many others.
When polishing plastics, it is important to be sure the surface of the area to be polished is thoroughly cleaned and dried.
As with sanding or scuffing, a mild detergent and soft cloth is usually recommended. It is also important to identify the type of plastic that is to be polished and buffed.
Once you have identified the type of plastic, then you can research the recommended polishing products for your particular type of plastic material.
2. Painting.
Painting is another common finishing process used in plastic fabrication. It is used to add color, texture, and visual appeal to the plastic product.
The most common types of paints used in plastic fabrication are enamel, acrylic, and polyurethane. Items that are typically painted following the plastic fabrication process can include automotive parts, home-office furniture and decor, or industrial fixtures.
3. Printing
Many plastic fabrication products also require graphics, logos, and other designs be added to them.
The most common printing techniques used in plastic fabrication are screen printing, pad printing, and digital printing.
This process is often seen in the packaging process for the food and beverage and medical and pharmaceutical industries, where safety seals and labels are crucial for keeping consumers safe.
There are a variety of plastics that can be used for plastic printing. Some of the most popular choices are polycarbonate (PC), polyethylene terephthalate (PETG), polypropylene (PP), polystyrene (PS), and polyvinyl chloride (PVC).
Each of these materials has its own advantages and disadvantages, so it is important to select the best type of plastic material for your application.
Print usage applications for each type of plastic include:
- PC: Compact discs, safety helmets, baby feeding bottles, car headlamp lenses, etc.
- PETG: Food & drink containers, food storage containers, retail stands and displays, medical and pharmaceutical products, etc.
- PP: Bumpers, instrument panels, interior elements, door trims, batteries, etc.
- PS: Yogurt containers, Petri dishes, test tubes, smoke detector housings, lighting fixtures, etc.
- PVC: Indoor signage, outdoor signage, credit cards, sporting equipment, bags and luggage, etc.
Once the correct type of plastic has been chosen for your application, then you will need to prepare the surface for printing. The plastic surface must be clean and dry so the print design adheres properly.
Additionally, you need to choose an ink that’s compatible with your plastic product to avoid any costly smudging or bleeding.
It is also key to use high-quality printer inks to ensure your printed products are vivid and dynamic.
4. Welding
Welding is used in the plastic fabrication process to join plastic parts together. It is used to create a seamless finish and ensure that the final product is strong and durable.
Three common handheld welding methods used in the plastic fabrication process are hot gas welding (hot air welding), extruded-bead seal welding (extrusion welding), and overlap welding.
The four main welding parameters for the hot air welding process are temperature, pressure, welding speed, and positioning of the hot air tool.
To ensure a successful weld is created, it is crucial that the technician has a good understanding of these parameters so they can be applied correctly during the welding operation.
5. Coating
Hot air and infrared heaters can also be used to dry and cure the coatings of your product to protect its surface from scratches, abrasions, and UV damage.
The most common types of coatings used in plastic fabrication are clear coat, UV coating, and powder coating.
In order to perform the coating process, your plastic surface must be clean and dry, and you need to select the right type of coating depending on the level of protection required, environmental conditions, and heat exposure.
Similar to the painting process, the coating must also be applied evenly to avoid any drips or uneven surfaces.
Types Of Plastics Used In Fabrication
Plastics come in thousands of varieties with different base chemistries, derivatives, and additives that are formulated to cover a wide range of functional and aesthetic properties.
To simplify the process of finding the material best suited for a given part or product, let’s look first at the two main types of plastic: thermoplastics and thermosets.
1. Thermoplastics.
Thermoplastics are the most commonly used type of plastic. The main feature that sets them apart from thermosets is their ability to go through numerous melt and solidification cycles without significant degradation.
Thermoplastics are usually supplied in the form of small pellets or sheets that are heated and formed into the desired shape using various manufacturing processes.
The process is completely reversible, as no chemical bonding takes place, which makes recycling or melting and reusing thermoplastics feasible.
Common types of thermoplastic materials:
- Acrylic (PMMA)
- Acrylonitrile butadiene styrene (ABS)
- Polyamide (PA)
- Polylactic acid (PLA)
- Polycarbonate (PC)
- Polyether ether ketone (PEEK)
- Polyethylene (PE)
- Polypropylene (PP)
- Polyvinyl chloride (PVC)
3. Thermosetting Plastics.
In contrast with thermoplastics, thermosetting plastics (also referred to as thermosets) remain in a permanent solid state after curing.
Polymers in thermosetting materials cross-link during a curing process that is induced by heat, light, or suitable radiation.
This curing process forms an irreversible chemical bond. Thermosetting plastics decompose when heated rather than melting, and will not reform upon cooling.
Recycling thermosets or returning the material back into its base ingredients is not possible.
Common types of thermoplastic materials:
- Cyanate ester
- Epoxy
- Polyester
- Polyurethane
- Silicone
- Vulcanized rubber
How Do You Choose The Right Plastic Fabrication Technique?
When it comes to selecting the appropriate plastic fabrication process for your project, there are several factors to consider.
Not every method is suited to every application, and it’s essential to understand the unique characteristics, advantages, and limitations of each process. Here are a few factors to take into account:
Design Complexity: If your part design is complex or requires high precision, processes like CNC machining, injection molding, or 3D printing may be preferable. For simpler designs or hollow parts, rotational molding or blow molding could be more suitable.
Production Volume: For large production runs, injection molding or extrusion might be the most cost-effective due to their high-speed production rates. For lower volumes, CNC machining or 3D printing could offer more flexibility and lower initial costs.
Material Considerations: The choice of plastic material can also influence the fabrication process. For example, thermosetting polymers are suitable for compression molding, while thermoplastics are more suited to injection molding or extrusion.
Physical Properties: If your part needs to have specific physical properties, such as high strength, flexibility, or resistance to heat or chemicals, this will also affect your choice of fabrication process.
Budget and Time Constraints: Some processes require significant upfront investment in tooling but have lower per-unit costs, making them more suitable for large production runs. Others have lower setup costs and faster turnaround times but higher per-unit costs, making them ideal for prototyping or small production runs.
What Are The Applications Of Plastic Fabrication?
Plastic materials are essential in almost every sector, from consumer items to aerospace and medical industries.
The low weight, strength, durability, insulation properties, and low prices make plastics prevalent in countless applications.
Automotive Industry
Plastic fabrication plays a significant role in the automotive sector, contributing to the production of lightweight components that enhance fuel efficiency.
From interior trim components to exterior body panels, plastics are widely used for their durability, versatility, and design flexibility.
Packaging
The packaging industry heavily relies on plastic fabrication for creating containers, bottles, and packaging materials.
Plastics offer a lightweight and cost-effective solution for protecting and preserving a wide range of products, contributing to the convenience and safety of consumers.
Medical Devices
In the medical field, plastic fabrication is instrumental in producing a variety of devices, equipment, and components.
Medical-grade plastics ensure compliance with stringent safety and sterilization standards, making them suitable for applications such as medical implants, diagnostic equipment, and packaging for pharmaceuticals.
Consumer Goods
Countless consumer goods are manufactured using plastic fabrication processes.
Items such as household appliances, electronics, toys, and furniture often incorporate plastic components due to their durability, aesthetic appeal, and cost-effectiveness.
Construction and Building Materials
Plastics are increasingly used in construction for their versatility and durability.
Plastic fabrication contributes to the production of pipes, insulation materials, roofing, and other components that meet specific performance requirements while offering longevity and ease of installation.
Advantages Of Plastic Fabrication
Plastic vs metal fabrication is a common industrial debate. Conventionally, metal fabrication was the most preferred way of production.
However, over the last few decades, plastic has steadily taken over the market. As you know, plastic products are widely used across the globe.
Therefore, certainly, plastic fabrication has grown in its popularity. One might think that plastic fabrication is chosen by manufacturers exclusively due to the ease of machining and the cost advantages it offers. However, that is not entirely true.
#1. Design Flexibility.
This depends on the properties of the material chosen for CNC plastic machining. Metals are naturally stiff, tough, and difficult to machine.
On the other hand, most plastic materials such as acrylic, ABS, polycarbonate, PVC are easy to handle and can be easily machined.
The dimensional stability of plastic materials makes them suited for designing intricate components. Thermoplastic or thermosetting plastics can offer great design flexibility.
#2. Weight.
Metals are heavier than plastics due to higher specific gravity. However, plastics are polymers with lower specific gravity and therefore low weight.
Generally, the same components made from metals and plastics are known to differ in terms of weight.
Depending on the type of plastic polymer used, the plastic components can be half to 6 times lighter as compared to metal components.
Therefore, adopting plastic fabrication can help in the reduction of product weight, which further leads to convenience in product handling, packaging, and transportation.
#3. Strength to Weight Ratio.
When it comes to strength to weight ratio or specific strength, metals certainly offer a great deal of it.
However, with advancements in plastic technologies, modern plastic materials are formulated with carbon and glass fibers which enhances the strength of plastic products.
#4. Strength to Stiffness Ratio.
Most thermosetting plastics get hard on the heat exposure. Therefore, the molecular bonding in thermosetting plastics increases with exposure to heat which enhances the strength to weight ratio of plastic products.
#5. Compatibility with Fabrication Processes.
Plastic can be fabricated by molding, casting, bending, extruding, bonding, vacuum forming, and many more.
A wide range of processes are available for fabricating plastic products. While desiging the manufacturing process for each component, a selective approach to fabrication technique can be adopted.
This way, selecting fabrication processes according to design for manufacturing (DFM) benefits the production cycle.
#6. Pre-Processing Pigmentation.
Plastic can be pigmented before fabrication. This eliminates the need for post-fabrication painting. Since post-fabrication treatment is eliminated, the surface errors that occur during painting can be eliminated too. This leads to a reduction in post-treatment costs and efforts.
#7. Plastic Fabrication is Less Time Consuming.
Plastic production consumes less time due to shorter manufacturing cycles. If heat-treated, metals take a long time to cool down and align diametrically.
On the other hand, molten plastic materials settle easily due to the coherent bond between molecules.
Therefore, in plastic fabrication processes like molding, extrusion, bending, etc, the turnaround time of production remains short.
Disadvantages Of Plastic Fabrication
Although plastic is useful for fabricating a wide range of parts, it also has its share of limitations as a production material. Some of the disadvantages of plastic fabrication include:
- Limited wear resistance: Plastic has a low resistance threshold for elevated temperatures, acidity, and other corrosive elements.
- Structural weaknesses: Most plastics are unsuited for applications requiring high structural strength, such as heavy equipment components and most building materials.
- Environmental Concerns: Plastics are non-degradable, which poses the risk of environmental pollution and a high carbon footprint.
- Thermal Restrictions: Plastics tend to lose their properties at high temperatures due to their low melting points. Some increments in operating temperature can lead to the failure of parts or systems.