When choosing the material for injection molding, most designers and businessmen are baffled as to what type they should go for.
The number of plastic polymers that can be used for developing injection molding based products is an astounding 85 thousand!
The question then becomes, what is the right material for developing the injection molding based products.
The answer cannot focus on the various materials because even the major types and subtypes of the polymer are in hundreds and thousands.
What can be achieved is an understanding of the chemical composition of the polymers and how they interact with the injection molding process.
We have developed this post as a material selection guide to discuss the main characteristics of the polymers such as insulation properties, solvent resistance, electrical insulation, moisture resistance, electrical properties, etc. so that you will understand the polymers used in plastic injection molded products in a better way.
Polymers with poor resistance, inability to absorb moisture (poor water absorption properties), low density, low impact strength, low resistance to acids, low abrasive resistance, low thermal expansion, low impact resistance, or low tensile strength are not ideal for plastic injection molding mass production.
But first, we will talk a little about the wide range of injection molding plastics available in the market so that you understand the main ones a little better.
Common Polymers Used in Industries
1. Polyamide (Nylon):
- This is a highly flexible and ever-changing thermoplastic injection molding material and is useful for a wide range of applications.
- The reason for its utility in plastics injection is the fact that it performs wonderfully in mechanical and electrical systems.
- It has a considerable toughness threshold and a strong resistance to wear and tear.
- The product also has a strong chemical resistant composition and is available at market competitive prices.
- The material is ideal for industrial applications as all of these factors have to be considered to meet industry standards.
2. Acrylonitrile Butadiene Styrene (ABS):
- ABS is strongly resistant to corrosive chemicals and to physical impacts.
- The material is pliable and is easy to use under a machine.
- This injection molding materials has a low melting point and as injection molding requires melting of the polymer, manufacturing products from the material require much less energy and effort.
- It is less expensive than its other counterparts and is not good for high heat utility.
- As it has a low melting point, it is best used in a range of applications that are not focused on manufacturing processes.
- It is used in industrial applications that do not require heating during the manufacturing process.
3. High-Density Polyethylene (HDPE):
- The polyethylene polymer is a thermoplastic polymer which means that it can be reheated to its melting point on multiple occasions.
- The reason this is a useful feature is that the plastic can be used for injection molding over and over again with no fear of waste.
- The plastic is crystalline in texture, has a higher density than usual and is used mainly in construction such as drain pipe manufacturing.
- One of the famous derivatives of polyethylene is the Ultrahigh Molecular Weight Polyethylene (UHMW) that is used in intense performance products such as bulletproof vests and medical devices.
4. Acrylonitrile Butadiene Styrene + Polycarbonate (ABS + PC) Blend:
- This injection molding thermoplastic is a combination of two different types of polymers.
- ABS has a high processing ability ratio and PC has a great array of mechanical properties along with impact and heat resistance.
- As these two polymers come together, the final product is a polymer that offers high resistance, excellent impact resistance, and has a good flow characteristic.
- PC+ABS offers combined properties of PC and ABS (high processing ability of ABS along with excellent mechanical properties and impact and the heat resistance of PC).
- The ratio of the two components affects the heat resistance of the final product.
- The blend exhibits excellent flow characteristics.
- It is mainly used in a wide variety of industries such as in computer and business machinery, electrical application, medical components, cellular phone, home products such as lawn equipment and automotive applications like interior trim, wheel covers and instrument panels and has a lot of finish options.
5. Polycarbonate (PC):
- This is a transparent and amorphous thermoplastic material that resembles glass in its capacity for transmission of internal light.
- It is good for when the product requires transparency and also needs to be impact resistant.
- PC is used in the production of contact lenses, medical and automotive device parts, greenhouse, digital disks, exterior lighting fixtures and many other similar applications due to its glass-like properties.
6. Polypropylene (PP):
- The product has chemical resistance, elasticity and fatigue resistance along with strong insulation and toughness properties.
- All of these characters combined, make the plastic an exceptionally high-quality polymer.
- This is one of the most widely used plastics in the world and has a utility in the automotive industry, electrical and equipment industry, and construction industry.
These are the main types of plastic available in the market for plastic molding material selection.
Characteristics of Materials Used in Injection Moulding
Following are the characteristics of the materials and how they are useful in the development of injection molding products.
1. Material Hardness:
There is a hardness scale for polymers when they are being chosen for injection molding process.
The hardness of the material is the main factor because it is a measure of how much the molded plastic can be indented.
The softer plastic is easily pliable and is used to develop products that need a lot of design but will not be exposed to extremely high temperatures.
The harder material is used for the development of industrial grade products that are used in industrial manufacturing.
It is because these products are used in the development of high-intensity parts that are used in industrial applications.
2. Material Flexibility:
The flexibility of a material is often confused with its softness.
The flexibility of the material is judged based on its ability to mold and bend under stress without tear or wastage.
Stiffness of the product is the ability of the product to resist bending under extreme pressure.
For example, ABS is a hard plastic and yet it is highly flexible in nature.
It can bend to a considerable value before it shows signs of breaking. Nylon polymer ruptures easily when pressure is applied.
3. Material Weight:
The product weight is determined by the weight of the polymer.
For example, if a polymer is ideal for the development of a home product to be used in the kitchen but has high polymer density, then it may not be a good choice.
This is because the product has to be used in the kitchen and has to be light enough for common individuals for daily use.
This basic principle stretches itself and becomes a complex mathematical equation where calculations focus on how much the certain product has to weigh and how much a certain polymer will weigh once it has been developed into a product.
4. Material Cost:
The cost of the thermoplastic material is a considerable factor when the product will be developed in mass- production.
The process has to justify the cost as the buying value of the product will have to cover the cost.
Cost comparison charts are usually developed to discuss the process of choosing a polymer for the right price.
These are the main characteristics of the polymer that decide its value.
The focus in choosing the polymer lies of calculating all of the above factors and coming up with the polymer for injection molding process that is closest to the right calculations on these charts.
As it can be easily seen, there are four or five factors to be considered and each factor has its own criteria of focus.
The result is that the number of polymers that are available has to be to greatly diversify in order to meet market demands.
Initially, only the main types of polymers were developed but as plastic-based product manufacturing increased, so did the need for diversity in the type of polymers.
The result was that an enormous range of polymers was developed so that the right kind of common thermoplastic for product manufacturing was always available.
These characteristics are usually calculated through a specific kind of calculation that will be discussed in later posts.
For some light reading on the subject, RevPart has developed an excellent article on the subject.
For more information on injection molding/ plastic molding material selection, contact Unipippes Malaysia.