Injection molding has become a popular choice for several manufacturing industries. This technique can handle a variety of materials to form different products. But with so many material types, it’s easy to feel lost, especially if you are just starting. That’s why a thorough injection molding material selection guide is crucial.
The reason is that the material you choose decides the strength and quality of your products. Picking the wrong material leads to cracks, wraps, and failure under pressure. Are you also one of those who get confused when selecting material for injection molding? If so, worry not! This easy-to-understand guide will help you make the right choice very clearly. Let’s get started!
Overview of Injection Molding
Injection molding is a manufacturing process used to create different intricate parts. This process works by pouring melted material into a hollow cavity called a mold. These come in various shapes to fit your desired shapes. On cooling, the molten material takes the exact shape of this cavity, and the final product is obtained.
What makes this process special is its versatility. As I said above, molds have different shapes, and mold creation uses advanced techniques such as CNC. Thus, you can attain various shapes, from simple to intricate, with high precision. Moreover, this process is very efficient for mass production. Once the mold is ready, you can create millions of parts quickly.
Why is Material Selection Important?
Not all materials are the same. They differ in various terms, including their strength and performance. So picking the right one is not just important—it’s critical. But how does it make a difference? Let’s look at the importance of selecting the right material for injection molding.
- Impacts Product Strength: The material you choose directly decides the strength of your product. If we look at plastic, some materials are flexible while others are hard. So, choosing between them according to your needs is crucial for better results.
- Affects Appearance: Material choice also affects how your final product will look and feel. Some materials come with a shiny appearance, while some provide a matter or textured look. So, the right material will also affect the color and smoothness of the products.
- Determines Safety: All the materials have their definite properties. For example, some materials, such as food and medicines, are safe for specific use. So, choosing the right material is crucial for hygiene and safety.
- Improves Efficiency: Some materials flow easily into the mold. This makes the molding process faster and more efficient. However, some may take time and require special equipment. So, the right material makes molding easy and saves time and money.
- Impact Cost: As you know, all materials vary in cost. For instance, some plastics are cheaper and suitable for everyday use. However, some can be expensive and specific for heavy-duty applications. Choosing the right material for your needs saves you from money waste.
Types of Materials Used in Injection Molding
I hope you understand why material selection is vital in injection molding. If so, let’s look at the standard viable material options for this process.
1- Polypropylene (PP)
Polypropylene is one of the most commonly used materials in injection molding. It is known for its lightweight and affordability. That’s why you can often find it in everyday products such as caps and bottles. One of the prominent features of this product is its high flexibility due to its higher tensile strength.
This means you can bend and twist it without the risk of snapping. Hence, it is the perfect choice for making products that need to be closed and opened repeatedly. Moreover, polypropylene is also chemical resistant. It does not readily react with acids, bases, and other harsh solvents. Thus, you can use it for food and chemical equipment.
2- Acrylonitrile Butadiene Styrene (ABS)
ABS is another material known for its durability, strength, and smooth finish. These properties are derived from its three main composition elements. For example, butadiene gives it toughness; acrylonitrile provides strength. However, styrene offers a shiny surface for ABS.
This blend of three powerful properties also makes it impact-resistant. It means ABS does not crack or break easily. This makes it ideal for heavy-duty operations. Moreover, it has good dimensional stability and can keep its shape well before and after molding. However, it may not perform well in high temperatures due to a lower melting point.
3- Polyethylene (PE)
Polyethylene is one of the most widely used plastics in the world. It is known for its durability and chemical and moisture resistance. Therefore, it has become popular among the food and beverage industries. PE comes in various types. However, two are the most common. First is Low-Density Polyethylene (LDPE), and the second is High-Density Polyethylene (HDPE).
Both of these types increase its versatility and functionality. For example, LDPE is flexible and used for squeezable bottles. However, HPDE is harder and more suitable for piping and cutting boards. Further, Polyethylene is lightweight and impact-resistant. It does not crack easily and withstands high-pressure, rough conditions.
4- Polystyrene (PS)
Polystyrene is another cost-effective and easy-to-process material for injection molding. Due to its lightweight, it can fill the mold and take on thorough shapes without difficulty. This makes it ideal for creating products that need a delicate, detailed, clean appearance. One of the key advantages of this material is its excellent clarity.
Polyethylene’s clear version, known as general-purpose polystyrene (GPPS), is highly transparent. That’s why it is also used for making items where transparency is critical. Despite all these properties, Polyethylene also has limitations. For example, it does not have much impact resistance. This means it can crack if dropped or hit harder.
5- Polycarbonate (PC)
Polycarbonate is an ultra-strong, heat-resistant, and clear material commonly used for injection molding. It offers ideal transparency even if it looks like glass. However, unlike glass, it is more durable and lightweight. Therefore, this material is primarily used for making goggles, eyewear, lenses, and medical devices.
As I said above, PCs are also heat resistant. It can withstand high temperatures, melting, and deforming. So, it is often used in applications that experience regular heat exposure. In addition, Polycarbonate is a non-conductor of electricity. It provides excellent electrical insulation for electrical components.
6- Polyamide (Nylon)
Polyamide, known as nylon, is another plastic polymer widely used in injection molding. Initially, this material was developed as a substitute for silk. However, its extensive properties made it popular for several other applications. It is known for its toughness and flexibility.
This means that, unlike brittle plastic, polyamide can be bent to different angles. That’s why it is commonly used for making moving and mechanical parts. Polyamide also has higher mechanical strength and is abrasion-resistant. Thus, it can withstand heavy loads and stress and perform well when two parts rub against each other.
7- Thermoplastic Elastomers (TPE)
It is a special injection molding material that combines rubber and plastic properties. This means it is soft and stretchable like rubber and strong like plastic. These properties make it perfect for creating products that must be bent, twisted, and smooth on the touch. That’s why it is commonly used in toothbrushes, grips, and medical tubing.
One key reason for its use in injection molding is that it is easy to process. TPE can be melted easily and does not require complex rubber-curing steps. Moreover, it bonds well with other plastics during molding. Furthermore, TPE is also recyclable. Although it behaves like thermoplastic, you can still melt and reuse it.
Injection Molding Material Selection: Key Features to Look For
Every product has different needs, and not all materials meet those needs equally. That’s why understanding what to look for in a material is essential. From strength to cost, each factor plays a vital role. In this section, we’ll look at some of those factors.
1- Mechanical Properties
When choosing a material, one of the essential things to consider is mechanical properties. It tells you how strong your material is, flexible, stiff, and rigid. Then, by evaluating these properties, you can understand whether it can handle the job you need it for. For example, you are making a part that carries heavy weight or handles high pressure.
You will need a more durable and strong material. For this purpose, I recommend using Nylon or Polycarbonate. These materials hold up heavy stress and do not break easily. However, thermoplastic elastomers will be a good choice if you need more product flexibility. Moreover, you should also look for tensile strength and impact resistance while making the final selection.
2- Thermal Properties
Thermal properties refer to how a material reacts to temperature changes. This property highly affects the injection molding process. For example, some materials melt and deform even at high temperatures, while others remain stable and strong. You must use heat-resistant material to make products that stay in continuous heat.
However, you must evaluate different materials’ melting points for ease of molding. This is the temperature at which material becomes soft enough to mold. Some materials, such as polypropylene, have a low melting point, making them easy to process. In contrast, Polycarbonate has a higher melting point. This makes its molding difficult, but it is suitable for heat-resistant uses.
3- Chemical Resistance
Chemical resistance means how well a material can handle harsh chemicals. Those chemicals can be oils, solvents, or cleaning agents. This is the most crucial factor to consider if your products are used in harsh chemical environments. Some plastics, such as ABS and nylon, may not perform well in acidic and basic conditions.
They become brittle, show discoloration, and lose their flexibility. So, I don’t recommend using them in a chemical environment. On the flip side, materials, e.g., Polyethylene and Polypropylene, are well known for their chemical resistance. They can handle acids, bases, and solvents, making them ideal for food and medicines.
4- Appearance and Color
When making user-friendly products, appearance is as important as durability. This factor refers to how a material looks after molding. It includes finish, texture, and the ability to hold color for a long time. Some materials, such as Polystyrene or ABS, have excellent glossy and smooth surfaces. So, they are ideal for making visually appealing products.
However, Polyethylene has a matte and waxy surface. You can consider it for practical and everyday products. In appearance, you should also look for acceptance of dyes and pigments. For instance, your products need to be colorful. In this case, you should use a material that accepts pigment and maintain it without fading over time.
5- Regulations and Safety
Safety matters a lot when choosing material for injection molding. Some products, especially food and medicine items, follow government rules and safety standards. These standards help ensure the material is safe for people and the environment. For example, you are making a food item. For this purpose, you will need an FDA-approved material that meets EU regulations.
They ensure the material is nontoxic and safe to contact with food or skin. Some of those safe materials include Polypropylene and Polyethylene. They are safe, approved, and sterilizable for food items. However, some materials release harmful gases. They are not considered reliable for food and medicines.
6- Availability
Availability refers to how easy it is to find and purchase a material for injection molding. Imagine a material that is highly durable, strong, and has all the positive properties. But what if it always remains out of stock? It will cause production delays and other problems. However, if a material is readily available, it keeps the cost low.
Moreover, it also helps you avoid production delays. Therefore, you can easily source and use large quantities of it for injection molding. Polypropylene and Polyethylene are often considered the most readily available materials. Besides, if you are using advanced techniques such as two-shot molding, you will need two types of materials. So before that, wisely choose those two materials that are readily available.
7- Cost and Affordability
The cost of injection molding is another critical factor you must consider. The overall cost of this process depends on several factors. The first one is the prices of raw materials. As you know, all types of plastic come at different prices. Some readily available plastics, such as Polyethylene, come cheaper. They offer the best balance of affordability and performance.
Besides, looking at the total cost, not just raw material, is essential. For example, some materials require high temperatures, longer cycle times, and special molds. Achieving such a high temperature and arranging complex design molds can enhance overall cost. However, some low melting points and easy-to-mold materials can reduce overall cost.
Quick Highlight: You should also consider the end-use of your products. Choosing expensive materials is not a good idea if you are making disposable products. But if you are focused on making safety-critical parts, you should invest in costly materials. It will reduce return rates and complaints.
Frequently Asked Questions
Can recycled plastics be used in injection molding?
Yes, you can use recycled plastic for injection molding. It will be healthy for the environment and save on costs. However, remember that this plastic may compromise durability and quality.
What is the best plastic for outdoor products?
For outdoor uses, you should choose the heat and UV-resistant material. For this, I highly recommend using Polyethylene, polypropylene, and nylon. They don’t crack and fade easily when exposed to sunlight.
Do materials affect how fast products are made?
Yes, the nature of materials significantly affects how fast products are made. For example, some materials are easy to melt and cool down quickly. This means the mold will open sooner and start a new cycle quickly, reducing the overall time for injection molding.
Conclusion
Injection molding has become a very popular technique for making different products. This process can handle a variety of materials. However, choosing the right one among those is key. The right materials decide the shape and performance of your products. It also affects the final products’ overall cost, durability, and strength.
Thus, I have discussed some factors to look for while selecting materials. For example, some materials are straightforward to mold and readily available, saving you time and money. Also, you should look at critical products’ appearance, mechanical strength, and safety. So take a break, ask questions, check samples, and decide.