New to plastic fabrication? Consider this.
According to IQS Directory:
Chapter 1 – What is Plastic Fabrication?
Plastic fabrication is the process of designing, manufacturing, and assembling a product made out of plastic material or composites that contain plastic. There are numerous plastic fabrication methods known today, considering the wide variety of products made out of plastic. Each method is suitable for the fabrication of certain designs because of its unique advantages and disadvantages. Today, plastic fabrication is quite popular among manufacturers because of its two main properties, i.e., malleability and cost-effectiveness. These two properties make it versatile and durable for a wide range of products spread over various industries.
Plastic is divided into two main categories; thermosetting plastics and thermoplastics. These two categories are defined based on their capabilities of being able to mold into desired shapes under temperature and pressure conditions. The plastics that can be molded again and again are the thermoplastics. Their molecular structure allows them to be softened, melted, and reshaped time and again. On the contrary, thermosetting plastics, also known as thermosets cannot be re-molded again.
These two categories of plastic are further divided into 7 types based on molecular structure. These types are used by different industries to manufacture products with the right specification. The seven types of plastics include:
- Polyethylene Terephthalate
- High-density Polyethylene
- Polyvinyl Chloride
- Polypropylene
- Polystyrene
- Miscellaneous
Chapter 2 – Plastic Fabrication Methods
There is a wide variety of plastic fabrication methods depending on the distinctive characteristics and the resulting product. The most common plastic fabrication methods are:
- Plastic Welding
- Compounding
- Plastic Lamination
- Molding
- Plastic Extrusion
- Thermoforming
- Die Cutting
- Pultrusion
- Forging
- Vacuum Casting
Plastic Welding
Plastic welding, just like any other welding method, involves the melting of two or more workpieces to be combined and a molecular bond is created between them. There are three main stages in plastic welding; pressing, heating and cooling. In order to fuse two different types of plastics, a filler material is used, especially when the two plastics have a significant difference in their melting points. This filer material creates an adhesive bond between the two plastics that offers greater strength. Plastic welding can take place via several methods including, contact welding, spinning, high-frequency vibration, hot gas emission, etc. These methods are largely differentiated based on the allowance for cooling, mechanical considerations, and some general process guidelines.
Compounding Plastic Fabrication
The second method of plastic fabrication is compounding plastic fabrication also known as the blending technique. In this method, the two or more types of plastics are combined together with additives to create an amalgamation.
Later, it is formed into different parts with the help of molds, dies, and some other shaping tools. The purpose of this method is to create a material that is easy to process and can provide the required specifications as this process changes the thermal, physical, electrical, and aesthetic characteristics of the plastic. There are some common compounding plastics; including polymer fillers, pigment masterbatches, base resins, blowing agents, and purge compounds.
Plastic Lamination
In the plastic lamination method, various layers of plastic are held together creating a barrier along the surface of another material. This technique not only improves the durability and aesthetics of the product but reduces the potential need for maintenance by shielding the sensitive and deterioration-prone material.
There are two common types of plastic lamination, film, and resin. In both types, heat and pressure are applied to create the barrier. Film lamination on the other hand is considered to be more effective than resin lamination. Although the resin application is frequently used to create adhesive layers between common materials such as papers, fabrics, etc.
A major drawback of this process is that this is a time-consuming process hence the production rate is very low as compared to other plastic fabrication methods. However, this method produces plastic with properties like strength, stiffness, and temperature resistance much superior to others.
Plastic Molding
Plastic molding is one of the oldest processes which is still popular among plastic fabricators. In plastic molding, the plastic is heated and melted and poured into a mold to harden around/within it.
Plastic molding has various types, a few of which are discussed below.
Injection Molding
In injection molding, molten plastic is injected into a mold and then cooled to obtain the molded products. It is one of the most versatile molding methods known today. It can be used to make large parts such as automotive parts and also small products such as surgical equipment. This process has a high overhead cost, but this can be overcome by using this process for mass production. It is divided into 6 main steps:
- Clamping
- Injection
- Dwelling
- Cooling
- Mold Opening
- Removal of the part.
Compressed Molding
In compression molding, the plastic is heated and then compressed with the help of a power presser to obtain the desired shape, followed by curing so that the final product maintains integrity and does not deform. This process is widely used to fabricate products of various lengths, thicknesses, and complexities. The final product produced by compression molding is stronger, lighter, stiffer, and more resistant to corrosion than the parts made up of metals. Another important advantage of this method is the ability to accommodate complex designs. Although, the speed of this technique is not quite comparable to the speed of injection molding yet it does offer more intricacies than any other molding process.
This method works with thermosetting plastics and has four main steps.
- Creation of mold
- Pre-forming and heating
- Compression
- Curing
Rotational Molding
Rotational molding, aka roto-molding, is a plastic fabrication method that is used to manufacture hollow parts. It uses rotational movements to coat the inside area of the mold with heated plastic to form a layer on top of the layer eventually creating the desired part. The overhead cost in this process is very low in comparison to other molding methods because there is no pressure involved hence the mold is inexpensive.
Due to the aforementioned reason, this process is economical even for short production runs. This method is used to make a diverse range of products as there is no restriction on the shape or size of the mold leading it to thousands of applications.
Another main advantage of this technique is that there is next to no waste material since all the excess plastic can be used back in the production of the next part. A few applications of rotational molding include canoes, automotive parts, toys, and buoys.
Blow Molding
Blow molding is another plastic fabrication process that involves the heating of plastic and transferring it into a mold. In this method, the tubes of plastic called parison are heated and transferred to the mold, then at the opening of the tube, the air is blown in to inflate the tube into the desired shape.
The material used in this method is thermoplastic pellets which can be either high-density polyethylene, polypropylene, polystyrene, or polyvinyl chloride. In blow molding, there are three main types, extrusion blow molding, injection blow molding, and injection stretch blow molding. Although in each sub-type a few steps differ from each other yet the main principles stay the same , the air is blown into the heated tubes of plastic to acquire a desired shape. This method is popular to manufacture bottles, fuel tanks, etc.
The most important advantage of blow molding is the low tool and die cost and fast production rates. However, the products made out of blow molding have limited strength.
Plastic Extrusion
Plastic extrusion is a continuous process in which raw plastic is heated and pushed through a chamber to be formed into a continuous profile such as pipes, tubes, films, fencings, deck railings, window frames, etc. The melted raw plastic called resin is pulled inside a heated barrel and then pushed out from the mold to get the desired shape. This is a high-volume production process.
This process starts with plastic granules feeding into the chamber of the extruder from a hopper. Then gradually these granules are melted by heating generated by the turning of the screw inside the chamber and heater present inside. Later the melted plastic is pushed into a die which shapes it into the desired geometry and allows the molten plastic to cool down.
Plastic extrusion is preferred by the manufacturer because of its speed, replicability, and sturdiness. Also, the products formed by this method endure stress better than any other method of plastic fabrication because extruded plastics do not have any seams present in their continuous profile.
Thermoforming
Thermoforming is another plastic fabrication process in which the thermoplastics are heated and reshaped under pressure. It is a unique process that involves the use of very thin plastic and carried out by various techniques including bending plastic sheets and vacuum forming. In this process, the tooling cost is considerably low in comparison to other fabrication processes because the thermoformed part does not need high temperature and pressure conditions to be fabricated.
Due to this, the mold used in thermoforming is often made up of wood, plaster of Paris, plastic, or aluminum. It is a versatile and efficient process. It is usually used in the packaging of food, fabrication of disposable cups, toys, aircraft windscreen, and cafeteria trays.
Die Cutting
Die-cutting, another plastic fabrication process that employs specialized machines and machine tools to convert raw material by cutting, forming, and shearing it into custom shapes and styles. It’s a flexible method that supports customization. The die-cutting process is suitable for a good range of geometries. It also has applications in various areas, including die-cutting neoprene, gasket, die-cutting paper, packaging, die-cutting fabric, and producing die-cut foam.
Die-cutting is one of the foremost efficient techniques to cut film and thin plastic sheets into finished parts. A number of the common plastics made via the die-cutting process are polycarbonate film, polyester film, and HDPE sheet. The advantages of this process include high production speed, ability to utilize unskilled labor, low-cost tooling, etc.
Pultrusion
Pultrusion is a process in which continuous forces are exerted on fibers during this continuous, mechanical movement. The braids of fibers are first of all pulled through a bath of resin before starting to be pulled by two heated metal dies. Pultrusion is suitable for the fabrication of both solid and hollow parts like flat bars, and tubing, etc.
While it is an expensive process due to tool requirements, pultrusion is notable for the high smoothness and strength of the parts it produces. Counting on the composition of the resin bath, products also can be made proof against flame, heat, electricity, chemicals, or environmental factors. As a result, it’s often utilized within the production of furniture and machinery for chemical plants or agricultural facilities. This method is best for the part in which the dimensional tolerance is a critical aspect and requires high-fiber volume fractions.
A few advantages of this method include low scrape rate, precise control over fiber volume, and excellent alignment. A minimal restriction of this process is the need for initial investment and skilled labor, etc.
Forging
The forging process is another plastic fabrication process. Blows are delivered to workpieces employing a hammer or other tool to shape them into the specified form. The materials become stronger when cast or processed with metallurgy, giving them the characteristic of being shock-resistant (toughness).
Forging is assessed into two types counting on the temperature used during the process: cold forging and hot forging. Hot forging is a technique where the workpiece is heated then struck into the specified shape. By striking the workpiece at temperatures above the recrystallization temperature, gas inside the fabric is forced out, refining the grain structure during recrystallization, hence making it stronger.
On the opposite hand, cold forging is shaping the plastic by striking it under ambient temperatures. Cold forging offers good precision and improved toughness. This method is employed to manufacture products like tools, cutlery, and parts for automobiles and railroads. One peculiar use of forging is the fabrication of golf drivers so that they bear the impact of strokes.
Vacuum Casting
Vacuum casting, sometimes mentioned as Polyurethane casting, uses silicone molds to form plastic and rubber components under vacuum. It’s a particularly adaptable manufacturing process capable of mimicking injection molding to supply complex parts in polyurethane resins and cast nylon.
As the method is under vacuum, it produces high-quality bubble-free casting with smooth surface texture and no blemishes. Vacuum casting is one of the foremost cost-effective ways to supply top quality, low-volume plastic parts which may be almost like injection molding parts. The parts are especially suitable for form, fit, and performance tests during the embodiment design stages, where they will be used for marketing, field user testing, and merchandise design verification purposes.
There are many vacuum casting resins commercially available that can be used to create parts to satisfy a good range of design requirements like temperature requirements, different surface textures, hardness, etc. Materials also are available to make parts that are fully opaque, translucent, or completely transparent by using this method. Sometimes high-quality wax is often made using vacuum casting for investment casting to extend the finer details of intricate features.
Chapter 3 – Plastic Fabrication Finishing Processes
After the part has been manufactured, next comes the finishing stage. Depending on the requirements within the part either an additional machining process or joining process is required. Whereas, some of the finishing touches are just about aesthetics but others may serve for selected purposes. No matter the reason, this last step has to be performed after the part has been fabricated.
Machining Process
In machining processes, the two main machines that are used are CNC Mill and CNC Lathe. Rigid thermoplastics and thermosets are often machined by conventional processes like drilling, sawing, turning on a lathe, sanding, and other operations. Glass-reinforced thermosets are machined into gears, pulleys, and other shapes, especially when a good number of parts don’t justify the construction of a metal mold. Various forms are often stamped out (die-cut) from sheets of thermoplastics and thermosets. The cups made by vacuum forming, as an example, are cut out of the mother sheet employing a sharp die. Within the case of a thermoplastic like polystyrene, the scrap sheet leftover is often reground and remolded.
Joining Process
In case of the need for a joining process, the welding process is preferred. Welding is done in the same manner as it is done in metals. Polyvinyl Chloride tanks being an important example. More commonly, surfaces are joined by being brought into contact with each other and heated by conduction or by the electrical phenomenon.
Heat sealing of luggage made up of tubes of blow-extruded polyolefins like polyethylene and polypropylene usually requires contact with a hot sealing bar. PVC features a high enough dielectric loss that heat is often generated throughout the fabric by exposure to a high-frequency, high-voltage field.
Coating
After the machining or joining process (or in case they are not needed) every part goes through 3 stages of finishing i.e., de-flashing, cleaning, and coating/decorating. The deflashing process is liable for removing all the surplus materials around the parts. These can be the excess compounds from the previous processes. Therefore there is a necessity to remove them.
After de-flashing the next stage is cleaning. Some leftover or excess material should stick with the surface of the plastic, which could affect the result of subsequent steps within the finishing process. Due to this, a radical cleaning is completed to make sure the surface is spotless. After cleaning then comes the last stage of the finishing process. Depending on where and the way the part is going to be used, some may require a touch of decorating.
As mentioned earlier, this might be for purely aesthetic purposes, but this doesn’t mean that this step isn’t important. Especially in cases where the part is going to be used somewhere visible, it’s important to form it to be presentable as well.
Chapter 4 – Choosing the Right Technique
Now comes the question: which process should be used to fabricate the required design? This can be answered by considering the following specifications:
- Plastic Type
- Part Geometry
- Required Precision
- Quality of Parts
- Design Flexibility
- Cost
- Lead Time
Different parts require different specifications and tolerance measurements. It is the best practice to take these factors into account before choosing the fabrication process. Part geometry also plays a great role in the selection of the fabrication process because there might be a need for optimization of design for manufacturing (DFM) to ensure a more economical production.
Moreover, you would like to know what strains or extreme conditions will your product need to withstand? Before finalizing the manufacturing process. Along with these factors you have to consider aesthetic and functional requirements too and then balance all these factors with the value.
In addition to those specifications, another important one is cost per part. The entire volume of the parts you would like to manufacture is extremely important. Some processes have additional costs for setup and tooling. However, they produce inexpensive parts on a per-part basis.
On the opposite hand, some low-volume processes have lower setup costs with constant cost per part. This is often a result of slower cycle times, manual labor, and less automation. Additionally, another major factor you would like to think about is how soon you would like the finished products. Some fabrication processes create the primary few parts within each day. Other high-volume processes include tooling and setup which will take several months.
Chapter 5 – Plastic Reclamation Process
After the products are consumed the plastic can be reused not just to save the environment but reusing the fabricated plastic to further the industrial processing may result in reduced energy consumption and cost savings. Reclaimed plastic is often used to manufacture products like packaging, plastic lumber, furniture, and a variety of composite materials. Plastic recycling and reclamation services employ a variety of techniques to convert post-consumer resin into workable stock. The primary stage of reclaiming the fabricated plastic is Granules Manufacturing Process.
Granules Manufacturing
The first stage of a typical plastic reclamation procedure involves sorting the various sorts of resin and grouping them. After they are sorted, the plastic products are ground into particles whose size depends on the actual processing method which will be used on them. These resin granules will function as the bottom forming material for future products.
Plastic Cleaning
The second stage of plastic reclamation is cleaning. Granulated resin usually needs to be washed before it can advance to the subsequent stage of processing. This washing is often conducted at standard environmental temperatures or elevated heat levels. Disinfectants and detergents are often used to provide additional cleanliness.
Material Separation
In the third stage, the clean plastic is now separated into reusable and un-reusable materials. Plastic base resin and un-reusable materials usually have different density levels, allowing them to be separated through a hydro-cyclone apparatus or a water bath. When using water, the heavier resin will sink to the bottom, while lighter contaminants float to the surface.
Drying and Filtering
Lastly, after the grinding, washing, and separation are complete, reclaimed plastic is rinsed off to eliminate any remaining dirt or accumulated disinfectants from earlier stages within the process. Melt filtering may be a fairly common post-reclamation treatment that’s performed at a converter station. This filtration technique is meant to further purify the stock by removing any non-melting contaminants which might have lingered through the granulation, cleaning, and separation procedures.
Chapter 6 – Benefits and Drawbacks of Plastic Fabrication
Advantages
Plastic fabrication is an extremely versatile manufacturing method with numerous advantages over other fabrication methods such as metal. It is not only a reliable technique but also highly efficient and quite simple. Some of the benefits are as follows:
Ease of Forming
Plastic has a lower melting point than other popular materials. Due to the lower melting point and good malleability plastic offers relative ease while creating complex geometries.
Reduced Finishing Efforts
In plastic, it is possible to coat or color the part before fabrication. This means that the pallets or granules will be mixed with color additives hence the effort in finishing parts is significantly reduced. Especially in the case of mass production.
Faster Production
Plastic does not take a significant amount of time in molding and shaping which reduces the cycle time. The less the cycle time the lower the lead time and fasters the production rate.
Light Weight
Plastic has revolutionized the fabrication industry because of its specification of being light weighted. It weighs less than metal and can be performed better. This is the reason why every industry is moving towards plastic fabrication.
Chemical Resistant
Plastics are found to be less prone to damage from chemical reactions than metals. They can avoid oxidations and reduction reactions easily. Hence, can provide extra chemical resistivity.
Disadvantages
Although plastic seems an ideal material for every single fabrication, yet this is not true. Just like every coin has a dark side, plastic fabrication also has some disadvantages.
Limited Temperature Resistance
Plastic has a very low resistivity towards higher temperatures. They can be melted or deformed easily at elevated temperatures.
Limited Wear Resistance
Plastics also do not have good resistance towards corrosive elements or acidity. They can easily lose structural integrity when they come in contact with corrosive materials.
Structural Weakness
Plastics, although used for parts that need good strength, fail to provide high structural strength. They can not be used for heavy equipment components or in building structures.
Non-Degradable
Most plastics are non-degradable and they may take an extended time to break down once they’re landfilled. With more and more plastic products, particularly plastics packaging, being disposed of soon after their purchase, the landfill space required by plastic waste may be a growing concern.
Chapter 7 – Application of Plastic Fabrication
Plastic fabrication has created a significant impact on industries. It has numerous different applications for thermoplastics and thermosetting plastics in building, construction projects (such as windows and doors), planting and storage tanks, pipe systems, filtration systems, chemical feeders, ventilation systems, and chemical storage. Industry-wise, the applications of plastic fabrication are as follows.
Construction Industry
Plastic comes in many alternative forms and specific materials. Options like polyurethane and polycarbonate may be available in handy for things like windows and doors. Vinyl is useful in exterior applications and anywhere where extra durability is required. Polyvinyl Chloride and similar plastics can serve well for the fabrication of pipe systems and other interior applications.
Plastic fabrication may be a kind of service that enables you to shape and manipulate these plastics into items that meet very particular specifications. A plastic fabrication company will create products of the precise size, weight, material, and aesthetics you decide on. This enables construction teams and industrial sites to stay their building plans consistent and ensure quality and safety throughout work sites.
Automotive Industry
Plastic has been playing a significant role in the design and manufacturing of automotive vehicles. It has been providing the industry with stringent regulations and changing the habits of consumers towards driving cheaper, fuel-efficient and lightweight cars. Fuel efficiency has become one of the foremost important features in self-propelled vehicle design because of the rising fuel prices and stricter environmental regulations. This, combined with high demand for automotive vehicles furthermore as rising income in emerging economies will still drive demand for plastics within the automotive industry.
The high absorption properties of plastics also allow the vehicle to satisfy stricter safety standards, while the employment of engineering plastics allows for minimization of the mass of parts utilized in vehicles as they provide more design freedom compared to metals.
Aerospace Industry
Plastics continued to excel within the aerospace industry throughout World War Two and were used because of their simple availability, design, and manufacture and, above all, the variability of applications they’ll be used for.
Materials like vinyl were utilized to line fuel tanks and fliers‘ boots, whilst other types of plastics were employed in radar covers thanks to their transparency to electromagnetic waves. Not only did this significantly improve radar technical capacity but stronger and more flexible plastics were also used on helicopters as they supply increased safety and are able to withstand the helicopter vibrations.
Furthermore, the bulk of plastics are made to be transparent, shatter-resistant, or made to provide protection from ballistics. Also, certain plastics can provide invisibility to radar and other various infrared systems designed to identify unknown flying objects. This makes plastic ideal for stealth operations and makes their use within the military aerospace sector invaluable.
Conclusion
- Plastic fabrication is the process of designing and manufacturing products using plastic or its composites as the base material.
- Various plastic fabrication techniques exist including, plastic welding, molding, extrusion, thermoforming, etc., as discussed in detail in the article.
- Furthermore, there are various finishing techniques for plastic products for aesthetics or dimensional accuracy in custom designed parts.
- Unlike metals, plastic products can be reclaimed by following a proper step by step procedure.
- Plastic products possess advantages like ease of machining, reduced finishing, and light-weight. However, there are various disadvantages associated with them including low resistance to wear and high temperature.
- Plastic products are used in various industries like construction, automotive, and aerospace.
