Plastics for Injection Molding: A Comprehensive Guide

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The success of any project we may likely embark on relies on the tools and methods available for our use. The same goes for injection molding of plastic parts.

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The tools needed are the plastic types available, and the method is via injection molding. That leaves the manufacturer with the trouble of selecting the right material for his project.

With that said, numerous plastic types are available that can be fashioned into whatever designs a manufacturer desires. How do you then know which type is appropriate for your project needs? And that right there is why this guide exists. So, if you are ready to decipher with us the right plastics for injection molding, then let’s go.

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1. Understanding Plastics for Injection Molding

A good understanding of plastic injection molding techniques is a solid bedrock on which other building blocks involved in the process can be built. Let’s begin with plastic materials and what role they play in this innovative manufacturing process. 

1.1 Role of Plastic Materials in Injection Molding

The role of plastic as an injection molding material is paramount and should not be underplayed. In fact, it is sometimes identified as the lifeblood of the injection molding process. The transformative form of plastics from solid to liquid and into the final shapes and geometries tells you all you need to know of its essentiality to injection molding. Essentially, the transformation begins from the barrel, where the plastic pellets are collected and melted. Afterward, they are injected through the mold gate into the mold to take the shape designed into the mold. On the completion of cooling and solidification, your plastic part comes out smooth and neat with the help of high-quality mold manufacturing

1.2 Types of Plastics for Injection Molding

There are several types of plastics used in injection molding. Each type possesses distinctive features which make it suitable for different applications. Some of these plastic types include polyethylene (PE), typically popular for its chemical resistant properties, hence its application in packaging and automotive parts. 

Polypropylene (PP) is known for its chemical-resistant properties but more for its high impact strength, which makes it mostly applicable to household items. High Impact Polystyrene (HIPS) is another stress-resistant material ideal for electronics and packaging due to its lightweight. 

Finally, acrylonitrile butadiene styrene (ABS) is one plastic material that offers excellent impact resistance and a smooth surface finish. Automotive manufacturing uses it for both internal and external parts.

2. Factors to Consider in Plastic Material Selection

An astute plastic manufacturer employing the injection method understands the importance of factoring in the properties of a plastic material before producing parts. With the knowledge of the various types of injection molding, considerations such as the mechanical and chemical properties of the plastic, including the processes involved, are quite crucial.

2.1 Mechanical Properties

Properties such as flexibility, strength, dimensional stability, and impact resistance are essential plastic material parameters you should consider in an injection molding procedure. Also, the intended use of such material determines the type of plastic to select. 

To give you an idea, a manufacturer that produces plastic components that bear heavy loads is likely to opt for injection molding materials that can withstand the weight and possesses huge tensile strength. A polycarbonate material would probably best suit the required application.

Part of the mechanical properties to consider is flexibility. Polyurethane (PU) and thermoplastic elastomers are great examples of materials with elastic capabilities for parts that require flexibility. 

In addition, impact resistance and dimensional stability are essential considerations as well. Plastic materials such as polycarbonate (PC) and acrylonitrile butadiene styrene (ABS) are materials with impressive impact resistance, and it is often deployed for automotive parts. 

Dimensional stability is factored in when components with tight tolerances and precision are in the mix. This is where polyoxymethylene (POM) and polyethylene terephthalate materials are best employed. They shrink less and demonstrate part-dimensional accuracy, an advantage that is similar to other precision-based methods like high-quality CNC machining.

2.2 Chemical Compatibility

Now when chemical compatibility comes into the discussion, what we intend for you to understand is the capacity of plastic materials to withstand environmental impacts. This includes where chemicals, solvents, and high-temperature conditions are in play. Exposure of certain plastic materials to such conditions deforms or introduces stress to them. 

Materials that can survive exposure to these conditions include polypropylene (PP) and polyethylene (PE). These two materials have convincingly displayed high chemical-resistant properties. It is for this reason they are perfect for application in harsh chemical environments. A typical example is the drums used to store acids and chemicals. Polystyrene isn’t capable of such feats. 

However, temperature-resistant plastics, as explained, can endure high temperatures when exposed to them. Such plastics are polyether ether ketone (PEEK) and polyphenylene sulfide. These plastic materials do well in thermal or heat-cycling environments. 

Chemical-compatible plastics eliminate deformations, chemical destruction, and degradation. They likewise ensure elevated performances and retain structural integrity while being applied in the varying systems they are molded for. On top of that, the more reliable the plastic material is, the more efficient the ultimate component. It’s usually a win-win for all stakeholders.


2.3 Processing Considerations

The last thing you want to encounter when manufacturing a plastic part with injection molding is the difficulty in processing a type of plastic material. This is where you professionals deliberate on melt flow rates, melting, and cooling temperatures. The ability to process plastic materials seamlessly has a great impact on the molding process and the quality of the molded part. This can, in turn, have a significant effect on the performance of the said part. 

The absolute optimization of the injection molding process to achieve minimum cycle times and accurate dimensional part quality stems from understanding the processing capacity of the material to be employed. 

While some plastic materials have a low melt flow rate, it doesn’t complicate the process. It only translates to low melting temperature, which means that it is compatible with designs with intricate geometries. Other materials that have a high melt flow rate can then be utilized for thicker-walled designs due to their better flow attributes. 

Not to forget the cooling temperatures as a process consideration. Several materials also have varying cooling times. Some are shorter as they help save cycle times and increase production volumes. And others take much longer to cool off. Overall, material moldability, flow rate, and cycle times are important elements in injection molding. Thus, it can either serve as a benefit or limitation to the process.

3. Material Processing and Handling

Material processing and handling are crucial to injection molding. Part of this system is material drying and conditioning. It sometimes begs the question – why the need for all these activities like drying and conditioning? 

3.1 Material Drying and Conditioning

To get a material ready for melting and injection, drying the material is a preceding activity. It cancels out any form of bubbles that can be transferred during melting and molding. What’s more? Voids and dimensional irregularities are looming defects if not properly dried. 

Nonetheless, various ways of drying the materials exist, and injection molding operators are often asked to choose the appropriate one for each project. 

The first one is a hot-air dryer, and the second is a vacuum drying technique. Essentially, drying removes moisture from the materials. And in the process of drying, it is vital to comply with the required temperature and time of drying strictly. 

Once drying is completed, conditioning comes next. Conditioning the plastic material prepares it for what’s to come next. This ensures that the material’s temperature is maintained at a level. Moreover, conditioning the material helps to ascertain regular melt thickness and equal flow pattern. All of this is to annihilate deformities as a result of moisture, improve flow patterns, and ultimately product quality.

3.2 Melting and Injection Molding Parameters

Melting and injection are the next set of activities after material drying and conditioning. Firstly, the hopper transfers the plastic pellets into the barrel, which is where melting takes place. Although, as an experienced manufacturer, setting the melt temperature, inputting the injection speed, and pressure settings should have been done. This makes your production efficient and effortless, at the same time achieving excellent dimensional accuracy and part quality. Also, melt temperature must be within the stipulated degree to avoid material deterioration. And in one motion, reduce energy consumed as well. 

At this point, the injection speed should already be determined and set because the injection speed regulates the flow of the molten plastic from the barrel into the mold

But what could go wrong, right? 

An uncontrolled injection flow could lead to flow marks around the part and other aesthetic irregularities. It could also lead to incomplete parts or short shots. Too much pressure isn’t a good idea as well. 

Either way, you want to reduce production costs and cycle times by not creating room for post-processes. Adjusting these parameters may be dependent on material type and design. But we trust you already know the benefits.

3.3 Recycling and Sustainability

Our world today screams climate change and cleaner energy at the top of its voice. And recycling has been a way of helping save Mother Nature’s call. However, when it comes to the plastic materials involved in injection molding, recycling plastic materials offers several benefits. 

It often helps to reduce waste generated, minimizes the environmental effect of pollution, and even makes production faster in a closed-loop process. Furthermore, recycling also reduces the cost of generating new plastics for production. Although, material compatibility might be necessary for recycled plastics to ascertain if it is best utilized for other production methods like 3D printing technology

Similarly, other sustainable options are available such as bio-based plastics fashioned using degradable plant materials. Bioplastics, when compared with petroleum-based plastics, offer lower carbon footprints and less environmental effects and are applicable in numerous industries. 

Packaging, consumer goods, and automotive industries, to mention a few, are part of such industries that benefit from plastic materials derived from bio-plastic materials. 

In a closed-loop system of the injection molding process, materials removed from fine-tuning and post-processes are returned to the pre-processing stage of plastic production. These methods are ways injection molders contribute their quotas to a cleaner energy mandate and create opportunities for users of sustainable products.

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4. Industry Applications and Case Studies

An evaluation of a material is not complete in the absence of the fields and sectors where it is crucial and necessary for success. Here are a few of the important industries that use plastics for injection molding. 

4.1 Automotive and Transportation

Structurally, cars have been known to have plastic components in and out of the vehicle. For example, the dashboard frames, the car seats, the door trims as well, and the list goes on. It is no surprise how beneficial plastic materials have been to the automotive and transport industry. The flexibility, durability, pocket-friendliness, and weight-to-strength attributes all show the extent of how advantageous plastics have become. Having said that, plastic materials have served this industry with corrosion resistance, impact resistance, and flexibility of design qualities. 

Picture this, a top-tier automotive manufacturer adopts the use of injection-molded plastic to manufacture a lightweight yet strong aerodynamic bumper system. And what do we have? A superb vehicle with an impact-resistant bumper is achieved by employing the best plastic injection molding production. It also results in a fuel-economizing system with massive structural integrity. From this sample, it is clear that engine covers, suspension components, and air intake systems were all influenced by the introduction of injection-molded plastic. 

4.2 Consumer Products and Packaging

In the consumer products and packaging industry, similar to what is obtainable in the automotive industry, plastic injection molding keeps gaining more ground with innovative household items. Versatility, durability, aesthetics, and customization alternatives are all, but the few advantages plastic injection molding has offered this industry. Toys, electronics, and cosmetic products all come in plastics produced with injection molding. 

The packaging industry has also seen tremendous improvement in the design of its packaging container designs. Interestingly, its versatility, cost-effectiveness, and lightweight properties also contribute to its viability as an option. For instance, a cosmetic brand that decides to reshape its product containers for more visual appeal is likely to record more sales. This repackaging is a way of marketing strategy facilitated by the high-quality mold manufacturing industry and plastic injection molding process. 

4.3 Medical and Healthcare

Even the medical and healthcare system has witnessed the superpowers of plastic materials in molding patient-centered tools and devices. Plastic materials such as polycarbonate (PC), polyethylene (PE), polypropylene (PP), and polyvinyl chloride (PVC) have been materials that have produced surgical instruments, implants, and other medical elements. These plastic materials have provided patients with comfort and have also been compliant with regulatory requirements, including safety and biocompatibility. 


Here is a quick recap. Plastic for injection molding is crucial to the success of the plastic manufacturing process. This is a proven fact, as they are the lifeblood of injection molding. Its transformative capabilities help fulfill the objective of the manufacturer in meeting the needs of the end user. 

Further understanding of the mechanical properties, chemical compatibility, and process considerations facilitates quick decision-making for manufacturers on the most suitable plastic material for a project. It also rids them of unnecessary headaches that often accompany this process. 

In addition, material processing and handling help manufacturers understand how best to work with them. But more importantly, the knowledge garnered here will help you decide on the right plastics for specific applicability across countless industries. So, there you have it. All you require is to ascertain and implement a plastic material for an injection molding process. Why not go to work already with the appropriate plastic material suited for your project requirement?


Gary Liao

Gary Liao

Gary Liao is the Engineering Manager of TDL Company and has more than 20 years of mold design experience.

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