Blog 43: Types of Plastic Processes

Introduction:

Plastics are the most often used materials for making final components and goods, including everything from consumer goods to medical equipment. With thousands of polymer choices, each with unique mechanical properties, plastics are a diverse class of materials. But how is plastic parts created using different plastic processes?

A vast range of uses, part shapes, and plastic kinds have led to the development of numerous plastic manufacturing processes. It is crucial for any designer or engineer involved in product development to be knowledgeable about the manufacturing options currently accessible as well as the newest innovations that indicate how components will be created in the future. There are countless varieties of polymers, and each one has a unique mechanical characteristic. We can build practically anything out of this material, and there are numerous plastic manufacturing procedures available to meet a variety of requirements for new product development.

This blog offers advice to help you choose the best solution for your application as well as an overview of the most popular manufacturing processes for making plastic parts.

In today’s world, plastic products are everywhere around us. Despite their widespread presence, not everyone is aware of their exact origin. There are actually ten main plastic forming techniques used in the manufacturing industry.

Each has a distinct purpose. They can occasionally be combined to create finished parts that are more sophisticated. The top eight plastic processing techniques and the applications they work best for will be examined in further detail today.

The most common methods are:

1. Plastic Injection Molding 

A high-volume manufacturing process called plastic injection molding involves feeding granular raw materials into a heated machine, which then injects a liquid plastic resin at high pressure and temperature into an empty stainless steel mold, giving the inside surface its shape. The forming die opens, the final item is evacuated, and the process is repeated after the resin has cooled and set.

More than 80% of the everyday plastic goods we come across are produced using plastic injection molding, which has established itself as a dependable and stable high-volume production technique. Steel molds have a wide range of materials and uses because they can create complicated, highly precise, and varied finished products. A wide variety of products, such as everyday needs, vehicle components, medical equipment, technological products, baby toys, and more, can be made using plastic injection molding.

What are the pros and cons?

The benefit of PIM is that it allows for the speedy, low-cost production of millions of similar parts with a high-quality surface finish. However, depending on the geometry of the component, molds might be expensive and complicated. To avoid flaws and to maximize part quality and processing speed, the mold needs to be carefully engineered.

2. Injection Blow Molding

Hollow molding is another name for blow molding. A blowing mechanism covers the machine’s center. Heat is applied to the raw plastic material as it is forced through a die to produce a strip of hollow plastic. The leftover material will be removed once the two molds are shut, and air will then be blown into the mold. As though blowing out a balloon, the plastic will now fill the whole interior of the mold, and once it has had time to cool, the finished object will be removed.

What are the pros and cons?

For transparent plastic drinking bottles, the method is frequently employed because it is simple to control and repeat. Although it produces great surface quality, narrow walls are not recommended.

Due to their clarity, durability, and certification as safe for consumables, PET (polyethylene terephthalate) or PEEK (polyether-ether-ketone) are the standard resin choices for drinking bottles. They may also be recycled with ease.

3. Rotational (Roto) Molding

A mold tool with a cavity side and a core side is also used in rotational molding. But unlike injection molding, the manufacturing process is very different.

The mold cavity is filled with plastic powder first, and the mold is then heated in an oven. The mold is slowly spun on two axes while being heated. The plastic is adhered to the tool walls and built up to the proper thickness using gravity.

In order to avoid warping, the mold is finally taken out of the oven and slowly cooled. The finished product is cooled completely, which can take several minutes; following that, the tool is opened and the part is removed for the subsequent cycle.

The thickness of the wall is initially determined by the volume of plastic liquid. Axially symmetrical circular objects like pottery flower pots, kid’s playthings, lighting apparatus, water tower equipment, and so on are frequently made using it.

What are the pros and cons?

Making huge, hollow, or concave shapes, frequently for outdoor use like canoes, tubs, or water storage tanks, is suitable for rotational molding.

The finished products are sturdy because they are stress-free and have no seams, and the tools are easy to create and reasonably priced. The drawback is that it’s not suitable for precision shaping because tools only survive for a few thousand cycles before they need to be changed and the part finish quality is at best average.

4. Vacuum forming

Vacuum thermoforming is another name for vacuum forming. A sealed box containing flexible urethane or silicone is then filled with a master model of any stiff solid (typically, this is a 3D printed master design). When the master is taken out of the mold, a hole is left within that can be filled with plastic resin to create a duplicate of the original. In order for the mold to fill entirely without any air bubbles, vacuum pressure is employed to remove air from the mold.

Excellent surface smoothness and detail are achieved with this procedure, and pourable resins can mimic several engineering grades of plastic.

What are the pros and cons?

Due to the ease of producing a silicone mold tool, polyurethane vacuum casting may be completed quickly. The initial expenditure is substantially lower, and the reproductions are very accurate—even catching fine grain texture.

The tools’ fragility and reaction with the resin’s ingredients mean that they must be replaced after around 20 copies.

5. Thermoforming

Vacuum thermoforming is another name for vacuum forming. The machine will come into contact with the plastic sheet and the mold once the plastic sheet has been equally heated to soften, drawing the air out to create a vacuum state that enables the plastic sheet to snugly cover the mold for molding. On the mold, the finished item is allowed to cool. Vacuum forming has few limitations on the mold material because it is a low-pressure process. Technology for vacuum shaping is appropriate for both mass production and proofing. While epoxy resin or aluminum that is resistant to wear can be used as molds for bulk manufacturing, wood and plaster can be utilized in small numbers. You can use any type of thermoplastic plastic sheet, although the most popular ones are PS, ABS, acrylic, and PC.

In the industrial setting, it’s used for thicker gauge auto body parts as well as plastic cups, lids, boxes, and clamshell packaging. Because the material needs to soften when heated and then return to its stiff state when it cools, only thermoforming plastics—not thermosets—are appropriate for this process. 

What are the pros and cons?

Thermoforming is fairly affordable and is doable with basic tools. In truth, thermoforming is a technique used by DIYers and home businesses to create models and prototypes. Because there are no hazardous chemicals or high temperatures used in the process, it is also safe.

It’s not a high-precision application because it can only be used to make simple forms and will shrink significantly after cooling. Additionally, the relatively thin plastic stock is required, even though the end product can be made more stiff by laminating many sheets after it has been formed.

6. Compression Molding

By applying downward pressure from a second mold that is also heated to a high temperature, compression molding is a process that uses heated plastic granular ingredients that are placed on a heated mold. Another name for it is hot compression molding. The distance between the molds determines the completed product’s wall thickness. A thimble will be used to push the finished item out once the molds are separated. Raw ingredients are unlikely to be wasted because the procedure lacks a pouring port and runner system. The plastic materials PF, MF, UF, and EP can all be produced. Post-processing gets rid of surplus material that is not needed.

Plastic goods with glass fiber reinforcement and thermosetting plastics are frequently produced via compression molding. It works well for items with straightforward shapes, no inner chamfers, and bulkier sections, including heavy components, sockets, cups, plates, etc.

What are the pros and cons?

Although managing the consistency of the completed object can be challenging and requires great care in the development of the original mold design, it is reasonably affordable and wastes little material. The equipment needed for this plastic manufacturing technique is rather straightforward, and creating a compression molding die is far simpler and less expensive than creating a plastic injection mold tool.

7. Extrusion Blow Molding

A two-piece clamshell mold is used to cast the parison, a huge droplet of molten plastic.

The parison is inflated like a balloon once the mold has closed so that it fills the vacant space. The plastic solidifies fast and may be removed from the mold since the walls are water-cooled.

What are the pros and cons?

This is the most typical method for producing low-cost, thin-walled containers with disposable bottles or cups. Although it is quick and the tools are simple to build, the parts cannot be made precisely or with great complexity.

8. Reaction Injection Molding (RIM)

Since RIM creates lightweight components with a hard covering, the automotive industry is where it is most frequently utilized. Body panels, dashboards, and other automobile components can be made from this skin with ease. Plastics used in thermoforming, however, won’t function in this technique. This procedure calls for thermosetting plastic.

Inside the mold, thermosetting polymers experience an irreversible chemical reaction. They typically experience this as a foam-like expansion that fills the mold cavity. The plastic takes on its final form after the chemical process is finished.

What are the pros and cons?

While production tooling is quite expensive, prototyping tooling expenses are comparatively modest. Considering that the finished product must always be finished, typically with a urethane-based gel coat or by painting, the material costs make up the majority of the cost. As a result, the procedure requires more work, which drives up the cost per piece.

9. 3D Printing

The process of 3D printing is typically slower, and some printers require days to manufacture intricate items. Cost per part keeps falling as this technique gets better. This form of production involves little setup time for a new design and no tooling. By layering material until it is full, it may produce three-dimensional parts straight from CAD models.

What are the pros and cons?

Due to its distinctive method, 3D printing may be utilized to produce any complicated shapes in minute detail. However, one drawback is that 3D printing takes too long. Repeatability is a consideration.

10. CNC machining

A rotating tool and a stationary portion remove material using the special CNC machining method. This is perfect for applications involving limited volume plastic parts that call for challenging-to-mold geometrics. With this method, high-quality plastic components may be made quickly.

What are the pros and cons?

You can duplicate the part polish and accuracy with CNC machining as many times as you like. Due to the high expense of each individual product, a vast block of raw material must be utilized to produce a smaller final good, with the remainder being recycled or scrapped.

Advantages of Plastics

  • Many plastics have lengthy useful lives, which encourages reuse. Plastics don’t have to be viewed as disposables or be one-time use items. This substance can be found in several forms that have a lifespan that is longer than or comparable to that of other materials. A PVC pipe that is well-made and maintained has a century or more of service in it. The typical lifespan of plastics used in building is 35 years.
  • Plastic production methods outperform several other factors: Although the production of plastics might be energy-intensive when using fossil fuels, it is still an environmentally favorable resource when compared to other materials. Recycling techniques occasionally alter the comparison. When plastics are consistently reused, there is still a clear benefit that they can offer.
  • Plastics take up less space in landfills: Although it can take a long time for plastic products to decompose in a landfill, compared to other objects, plastics occupy very less space in these places where garbage is disposed of. Products made of paper have seven times more volume.
  • Why Methane does not develop during decomposition: When organic things start to break down, greenhouse gases are released. Although this technique frequently focuses on carbon dioxide, the methane that is emitted is exceedingly hazardous. When compared to CO2, methane is up to 20 times more effective as an atmospheric product that reflects light. Since plastics don’t emit this gas as they start to degrade, it is easier to estimate their whole lifecycle impact.
  • Plastics offer a secure method of transporting any necessary items: It is preferable to use plastic for water and other beverage bottles since it protects the contents from damage. People use the substance to swiftly and economically deliver water to needy populations throughout the globe.

Disadvantages of Plastics

  • Non-renewable resources are often used in the plastic processes: Although the first plastics were made from plant-based fibers, the majority of the things produced today are still powered by fossil fuels. This product is often produced using petroleum, although it can also be produced using natural gas. 4% of these fuels are still used to create new products in the plastics sector. Given the amount of resources used in the refinement process and the expected increase in demand, the cost of fossil fuels for plastics may approach 20% during the next ten years.
  • Plastic has been shown to make up the majority of the pollution in the world’s oceans: Plastic makes up up to 80% of all marine debris. This issue originates from both marine and terrestrial sources, frequently building up in huge expanses of open water where tides converge. We are impacted by this problem because we discover trash on land, on beaches, and even in freshwater sources. Stirrers, bottles, lids, food wrappers, and plastic straws are some of the items that are most frequently strewn. Removing plastic pollution from ocean surface water costs $5 per kilogram, yet reusing the item only costs $0.30. The effort to clean up maritime areas is therefore being led by nonprofit organizations.
  • The use of plastics can result in a number of financial losses: The global economy loses over $80 billion a year as a result of pollution from plastic packaging alone. It accounts for around 50% of the trash generated by this industry, and almost every other business uses it in some capacity. Textiles contribute for around 15% of plastic consumption, while construction and building plastics account for 16%. More of it tends to move into waste streams instead of being reused because recycling many of the things isn’t advantageous. The average rate of plastic recycling worldwide is roughly 14%. India is one of the world leaders in recycling plastics and its products at a rate of about 60%, while the United States is close to last with a rate of about 9%.
  • Metals may be recycled many times into a variety of different items, however plastic products cannot be recycled indefinitely due to the material’s characteristics. Plastics do not provide such chance. It can only be recovered or used so many times before it starts to lose its integrity and quality. This indicates that consumers are more inclined to dispose of the product in a landfill, downcycle it, or burn it. The impact of this drawback is exacerbated by the fact that some plastic products and commodities cannot be recycled at all. Every year, more than 93 billion plastic objects go unnoticed and end up in our waste streams.
  • Cleaning plastics before recycling them requires energy expenditure: Products made with cross-contaminated plastics of various sorts are useless. Cleaning the goods is also necessary before recyclers may turn them into fresh components.

Types of Plastics

Plastics are classified as either thermoplastic or thermosetting based on their physical characteristics.

  • Thermoplastic: Plastics that are easily bendable and easily deformable when heated. Thermoplastics include linear polymers and mixtures of linear and cross-linked polymers. PVC, nylon, polythene, and other examples.
  • Thermosetting: plastics that, once molded, cannot be heated to make them pliable again. Thermosetting plastics are made of heavily cross-linked polymers. Examples include melamine and bakelite. Electrical switches are made of bakelite, whereas floor tiles are made of melamine.

Below is 7 of the most popular and commonly used plastics:  

  • Acrylic or Polymethyl Methacrylate (PMMA)
  • Polycarbonate (PC)
  • Polyethylene (PE)
  • Polypropylene (PP)
  • Polyethylene Terephthalate (PETE or PET)
  • Polyvinyl Chloride (PVC)
  • Acrylonitrile-Butadiene-Styrene (ABS)

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