But although they’re found everywhere, not everyone knows just how they came to be. In fact, in the world of manufacturing, there are eight different plastic forming methods.
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Each is used for a special reason, although they can sometimes be used in combination to make more complex finished parts. Today, we will take a closer look at the top eight plastic processing methods and the applications they’re best suited for.
1. Plastic Injection Molding
What is plastic injection molding?
Plastic injection molding is a high-volume manufacturing method, where a liquid plastic resin is injected into the empty cavity of a forming die, taking on the shape of the interior surface. When this resin is cooled and solidified, the forming die opens, the finished part is ejected, and the process is repeated.
Plastic injection molding has proven itself to be a stable and reliable high-volume production method, accounting for more than 80% of the common plastic items we encounter every day.
What are the pros and cons?
The advantage of PIM is that millions of identical parts can be made quickly, with an excellent surface finish, and at a low cost. Molds however can be expensive and complex, depending on the part geometry. Careful engineering design of the mold is required to prevent defects and optimize part quality and processing speed.
2. Rotational (Roto) Molding
What is rotational molding?
Rotational molding also uses a mold tool, consisting of a core side and a cavity side. However, the manufacturing process is quite different from injection molding.
The plastic powder is first poured into the cavity of the mold, and then the mold is placed in an oven. While being heated, the mold is slowly rotated on two axes. Gravity is used to stick the plastic to the tool walls and build up the correct thickness.
Finally, the mold is removed from the oven and slowly cooled to prevent warpage. Full cooling can take several minutes, after which the tool is opened and the part removed for the next cycle.
What are the pros and cons?
Rotational molding is ideal for making large, hollow, or concave shapes, often for outdoor use like canoes, tubs, or water storage tanks.
The finished parts are stress-free and have no seams so they’re strong, and the tools are relatively simple and inexpensive to make. The downside is that tools don’t last more than a few thousand cycles before they need to be replaced, and the part finish quality is average at best so it’s not suited for precision forming.
3. Extrusion Blow Molding
What is extrusion blow molding?
Molten plastic in the form of a large droplet, called a parison, is placed into a two-piece clamshell mold.
After the mold closes, the parison is inflated like a balloon until it fills the empty cavity. Because the walls of the mold are water-cooled, the plastic quickly solidifies and the part can be ejected.
What are the pros and cons?
This is the most common way to make thin-walled, inexpensive containers like disposable drinking cups or bottles. It’s fast and the tools are easy to make, but the parts cannot be very complex or made with high precision.
4. Injection Blow Molding
What is injection blow molding?
During injection blow molding, gas pressure is used to force the molten resin into a mold cavity.
What are the pros and cons?
The process is easily controlled and repeatable and is commonly used for transparent plastic drinking bottles. It makes for excellent surface quality but it’s not ideal for thin walls.
PET (polyethylene terephthalate) or PEEK (polyether-ether-ketone) are the typical resin choices for drinking bottles, due to their clarity and durability, and because they’re rated as safe for consumables. They’re also easily recycled.
5. Reaction Injection Molding (RIM)
What is reaction injection molding?
RIM is most often used in the automotive industry because it produces lightweight parts that have a rigid skin. This skin is easily painted to make body panels, dashboards, and other car parts. However, thermoforming plastics won’t work in this process. Instead, this process requires thermosetting plastic.
Thermosetting plastics undergo an irreversible chemical reaction inside the mold. This usually causes them to expand like foam, filling a mold cavity. When the chemical reaction is done, the plastic sets into its final form.
What are the pros and cons?
Tooling costs for prototypes are relatively low, while production tooling is moderately expensive. The main cost is in the material, bearing in mind that the resulting part must always be finished, usually with a urethane-based gel coat or by painting. Therefore, the process is more labor-intensive, which increases the piece price.
6. Vacuum casting
What is vacuum casting?
Vacuum casting is a great choice for making a small number of high-quality rapid prototypes without a big investment in tools or material.
A master model of any rigid solid (often this is a 3D-printed master pattern) is placed into a sealed box, which is then filled with a flexible urethane or silicone. When the master is removed, a cavity is formed inside the mold that can now be filled with plastic resin to form a copy of the original. Vacuum pressure is used to pull air out of the mold so that it fills completely with no air bubbles.
In this process, the surface finish quality and detail are excellent, and pourable resins can imitate many engineering grades of plastic. Notice also that the pourable liquid resins aren’t quite the same as their counterparts used in plastic injection molding. In the former case, resins are solidified by a chemical reaction with a hardening agent, not by cooling down.
What are the pros and cons?
Polyurethane vacuum casting is fast because a silicone mold tool can be made in just a few days. It requires a much smaller initial investment and the fidelity of the copies is excellent – even capturing fine grain texture.
The drawback is that the tools are fragile, and they react with the chemicals in the resin and must be replaced after about 20 copies or so.
What is thermoforming?
This is a type of vacuum forming, where a thin or thick gauge plastic sheet is placed over a die, heated to a temperature that allows the material to become pliable, then stretched over the surface of the die while vacuum pressure pulls the sheet down and into its final shape.
This process can also be done with simple dies and very basic equipment. It’s often employed with samples and prototypes of thin-walled, hollow-bodied parts.
In industry, it’s used for plastic cups, lids, boxes, and plastic clamshell packaging, as well as for auto body parts in thicker gauge material. Only thermoforming plastics are suitable for this process, not thermosets, because the material needs to soften under heat and then become rigid again when it cools.
What are the pros and cons?
Thermoforming is very cost-effective and can be done with simple equipment. In fact, even home shops and DIY people use thermoforming to make models and prototypes. The process is also safe because there are no bad chemicals or high temperatures involved.
However, it’s only suitable for making simple shapes, and once the material cools it will shrink quite a bit so it’s not a high-precision application. Also, the relatively thin plastic stock is needed, although many sheets can be laminated together after forming to make a more rigid final product.
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8. Compression Molding
What is compression molding?
The raw material, usually some type of elastomer or polyurethane, is pre-heated and placed inside the open cavity of a die. A cap or plug is used to close the die and apply heat and pressure, causing the plastic to cure. This process is great for rubber keypad switches, gaskets, O-rings, and other soft, pliable thin-walled parts.
What are the pros and cons?
It’s relatively inexpensive and wastes little material, although controlling the consistency of the finished piece can be difficult and much care needs to be taken in the preparation of the initial mold design. Making a compression molding die is much easier and less expensive than a plastic injection mold tool, and relatively simple equipment can be used for this plastic manufacturing process.
What Materials Are Used In Plastic Manufacturing?
There are over 10,000 different types of plastic resins commercially available, each of them specially formulated to achieve very specific chemical and mechanical properties.
Although we can’t possibly list them all, there are ten major groups that account for the vast majority of industrial and consumer products. They are Polyamide, Acrylic, Polycarbonate, POM, Polystyrene, ABS, Polypropylene, Polyethylene, Polyurethane, and Thermoplastic Rubber.
Plastic manufacturers can also add glass or carbon fibers to increase strength and stiffness, or mix two or more resins together to combine their properties. These plastic types provide a full range of benefits including strength, impact resistance, flexibility, chemical resistance, light weight, toughness, and optical clarity.
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Are you curious how raw plastic is turned into bottles? Wondering how many types of water bottles are there? Not sure what an extrusion blow machine is but do you want to learn more? Curious how your ketchup bottles are different from single-use plastic bottles? This article will answer all these questions and more.
Although there has been a push to slowly reduce the presence of plastic in our lives, plastic bottles still form the backbone of many industries worldwide, and in this article, we’ll take you through the entire process.
What are Plastic Bottles Made Of?
To understand how a plastic bottle is made, we must go over all the different types of plastic bottles are made from. Contrary to misconception, there are various, very different kinds of plastics, and they all require different approaches. By learning more about these materials, their advantages, and their disadvantages, you’ll get a broader look into how plastic bottles are made, and that’s precisely why we’ll go over the most common plastics bottles are made of below!
#1 Polyethylene Terephthalate (PET)
PET bottles are one of the most common types of plastic bottles. They’re used for beverages such as water, soft drinks, juices, and milk bottles. PET is a clear, strong, and lightweight plastic that is easily molded, making it an ideal choice for use in the production of plastic bottles.
Advantages:
- Lightweight: PET bottles are lighter than glass bottles, making them easier and cheaper to transport, reducing both costs and carbon footprint.
- Transparency: PET bottles are clear, allowing consumers to see the contents of the bottle. Transparent bottles can be particularly important for products such as mineral water or fruit juices, where the color of the liquid might impact the prospective customer’s purchasing decision.
- Durability: PET plastic bottles are strong and durable, making them less likely to break or crack during shipping or handling.
- Cost-effectiveness: PET is a relatively inexpensive material, making it a cost-effective option for packaging products.
Drawbacks:
- Permeability: PET bottles are slightly permeable, which means that oxygen and carbon dioxide can pass through the walls of a bottle and affect the taste and quality of the liquid inside.
#2 High-Density Polyethylene (HDPE)
HDPE bottles are another common type of plastic bottle used for packaging a wide range of products, including milk, juice, cleaning agents, and personal care products. And although they are interchangeable in use with PET bottles in a lot of cases, they also have unique qualities that make them uniquely suitable for specific applications.
Advantages:
- Strength and Durability: HDPE bottles are strong and durable, resistant to impact and chemicals, which makes them an excellent choice for packaging harsh chemicals, such as cleaning agents.
- Recyclability: HDPE is a highly recyclable material, and recycled HDPE can be used to create new bottles or other products. This can help to reduce waste and conserve natural resources.
- Versatility: HDPE bottles come in a range of sizes and shapes, making them suitable for a wide range of packaging applications.
Drawbacks:
- Low Heat Tolerance: HDPE has a low heat tolerance, which means that it may not be suitable for packaging products that require high-temperature sterilization.
#3 Polyvinyl Chloride (PVC)
PVC bottles are less common than PET or HDPE bottles and are primarily used for packaging products such as detergents, cleaners, and chemicals.
Advantages:
- Resistance to Temperature: PVC bottles can withstand a wide range of temperatures, making them suitable for packaging products that require high temperatures during packaging or shipping.
- Transparency: PVC bottles are clear, allowing consumers to see the contents of the bottle before purchasing. And although it is more important for PET bottles’ use cases, PVC bottles still benefit from the visual appeal.
Drawbacks:
- Chemical Leaching: PVC bottles can leach chemicals, including phthalates and bisphenol A (BPA), which have been linked to health concerns.
- Low UV Resistance: PVC bottles are not resistant to ultraviolet (UV) radiation, which can cause them to degrade and discolor over time.
#4 Low-Density Polyethylene (LDPE)
LDPE bottles are a popular type of plastic bottle used for packaging products such as shampoo, lotion, and other personal care items. LDPE is an ideal choice for packaging applications that require flexibility and durability.
Advantages:
- Flexibility: LDPE bottles are flexible and can be easily squeezed, making them ideal for packaging products such as lotions and shampoos.
- Lightweight: LDPE bottles are lightweight, which not only makes them cheaper to transport but also makes products that use these bottles easier to hold and more comfortable.
Drawbacks:
- Limited Heat Resistance: LDPE has a relatively low heat tolerance, making it unsuitable for various applications that require high heating during various stages of production.
- Limited Strength: LDPE bottles are not as strong or durable as other types of plastic bottles such as PET or HDPE, which makes them less suitable for packaging applications that require tough materials.
The Ways a Bottle is Made
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