About plastic injection molding technology: All the information you need to know
- About plastic injection molding technology: All the information you need to know
- the basics of injection molding
- A Brief History of Injection Molding
- Learn more about the different types of injection molding technologies
- Molds must be manufactured before starting an injection molding project.
- Understanding Injection Molding: Process Flow
- What types of plastics can be used in plastic injection molding?
- Common industrial applications of injection molding
- Why choose Elimold to collaborate on various injection molding projects?
- in conclusion
- FAQ
Plastic is one of the most widely used materials on Earth. From automobiles to medical supplies, plastic is ubiquitous in numerous industries, and it can be made into any size, shape, and form. While the inherent properties of plastic are often attributed to its versatility, the manufacturing processes used to produce plastic parts also play a crucial role, enabling the widespread, economical, and diverse application of plastic products.
What is plastic injection molding? How is it done? What types of plastics can be successfully molded using this process? We will answer these questions and more in this blog.
the basics of injection molding
Injection molding is a complex process capable of manufacturing a wide variety of plastic parts. It uses thermoplastic materials, melting them and molding them into the desired shape and size. Injection molding machines execute complex processes by strictly controlling various variables to produce suitable parts. As long as these process variables are strictly controlled, injection molding can achieve high throughput and mass production of plastic parts without compromising quality.
Besides achieving high throughput and ensuring consistent quality, this process offers unparalleled flexibility. You can manufacture any type of plastic part, whether simple or complex, without altering the process flow. You simply change the mold and adjust the variables. However, before producing any new product, you need to create a new mold, which is expensive. But this is the only high-cost part of the entire process because once the mold is ready and installed on the machine, parts can be mass-produced at extremely low cost. This is another major advantage of injection molding.
A Brief History of Injection Molding
The theoretical basis of injection molding dates back to the first machine invented in the 19th century. This machine was far too simplistic for modern standards, capable only of processing simple materials and posing safety concerns due to flammability and other factors. It was also limited to producing simple items such as combs and buttons.
Until 1930, rapid advancements in modern industry and materials science led to the development of various thermoplastic types, changing market conditions and solidifying their position in diverse industrial applications. This development, coupled with the additional demand for cheaper and more viable metal alternatives, directly resulted in the rapid growth of the modern injection molding business. Over time, the plastics molding industry has developed into its unprecedentedly prosperous state today.
Learn more about the different types of injection molding technologies
Among the many molding processes for plastic products, injection molding is the most common and widely used. It can be further subdivided into many types. Different injection molding processes can achieve different textures, gloss levels, shapes, and other appearance effects. The molding process of plastic products not only allows us to obtain the plastic products we need, but also improves the performance of the plastics. However, the molding methods for thermoplastic and thermosetting plastics are not entirely the same. The mainstream molding processes commonly found in the market typically include the following:
Dual-color and multi-shot implantation techniques
Two-color and multi-injection implantation technology: Two-color injection molding is a mature process, also known as two-material injection molding. It is a process solution to achieve a two-color texture on the surface of plastics. It uses two materials to inject one product, which can achieve different colors and textures. It can improve efficiency, reduce costs, and has a higher degree of design freedom. It is currently widely used.
Secondary injection molding (overmolding process)
Two-stage injection molding differs from two-color injection molding and is commonly known in the industry as “overmolding” or “covering.” Two-stage injection molding refers to re-injecting a plastic product that has already been injection molded once, as needed. The number of injections can be determined according to design requirements. Generally, the material injected the first time is called the substrate, and the subsequent injections are called the cover material.
Insert injection molding
Insert injection molding refers to a molding process in which pre-prepared inserts of other materials (such as metal) are inserted into a mold, and then injection molding is performed. The plastic and the inserts are bonded and cured in the mold to create a one-piece product. The general process of insert injection molding includes: insert placement into the mold, vacuum fixing, and injection molding.
Nano injection molding
Nano-injection molding (NMT) technology gained popularity around 2015, rapidly developing during the early days of all-metal mobile phone bodies. It’s a technology that combines microscopic plastic and metal materials. First, the metal surface is nano-treated, then plastic is directly injection molded onto the metal surface, creating a seamless, integrated metal-plastic structure. The advantages are obvious, primarily avoiding the signal shielding issues associated with all-metal materials. While achieving functionality, it also creates a perfectly sealed, smooth surface, making the product feel like a single, integrated unit.
Foam injection molding
Foaming technology refers to the process of adding a foaming agent to a material to form a porous honeycomb structure through physical or chemical reactions. The foaming process mainly includes three stages: bubble nucleation, bubble growth, and bubble stabilization. It involves dissolving gas in a liquid polymer to generate gas and saturate the solution, followed by nucleation to form bubble nuclei. After the bubble nuclei stabilize, they expand to form a foam body, and finally, the structure of the foam body is fixed.
No-spray injection molding
The paint-free process, which began in 2016, eliminates the need for post-processing such as painting. It involves injection molding plastic granules with special metallic color effects, resulting in products with their own color and texture, achieving different appearance effects such as imitation metal, ceramic, or even fabric.
Injection compression molding
I first learned about this injection molding technology in 2018, when the popular glass-like finish for mobile phone back covers used transparent PC injection compression molding. This is a thin-wall injection molding solution that combines injection molding and compression molding processes. It offers dimensional stability, precise surface finish, and represents an advanced form of injection molding, enabling the creation of extremely thin products.
Blow molding
Blow molding primarily involves placing molten plastic in a mold, inflating it under compressed air pressure to press it tightly against the inner surface of the mold, and then demolding it to obtain the finished product. Blow molding is mostly used for thermoplastic plastics. Alternatively, a tubular plastic preform obtained through extrusion is placed in a split mold while still hot. After the mold is closed, compressed air is immediately introduced into the preform to inflate it, causing it to press tightly against the inner wall of the mold. After cooling and demolding, various hollow products are obtained.
Vacuum forming
Vacuum forming is a plastic processing technique. The main principle is to heat a flat, rigid plastic sheet until it softens, then use a vacuum to adhere it to the surface of a mold, and finally allow it to cool and solidify.
Extrusion molding
Extrusion, also known as molding, is one of the important methods for molding thermoplastic plastics. Extrusion molding is mostly used for thermoplastic plastics. It involves extruding molten plastic through the die opening at the die head of an extruder to form a profile that resembles the shape of the die opening.
Molds must be manufactured before starting an injection molding project.
Mold creation is the most fundamental part of an injection molding project . Engineers use CAD and CNC machining to determine the mold’s specifications and design. These specifications include its geometry, dimensions, and even the texture of the components. For injection molding, the cost of manufacturing the mold itself is the largest expense you will incur. Even a typical mold capable of handling 1,000 to 10,000 unit production runs will cost between $2,000 and $5,000. If you require molds for mass production of complex parts , the cost will be even higher.
Manufacturing suitable molds requires a high level of expertise and skill. Engineers must also conduct numerous simulations and tests to verify that the design meets their requirements. High-quality aluminum or steel materials are also needed to ensure the mold is durable enough to withstand multiple production cycles. Fortunately, 3D printing has reduced the cost of mold manufacturing, especially for low-run injection molding.
Understanding Injection Molding: Process Flow
To date, our understanding of injection molding is still very limited. Behind the seemingly simple plastic products we use every day lies a complex web of processes. Injection molding can be broadly divided into four stages. But before discussing these stages, let’s take a moment to understand injection molding machines. This will help us better understand the entire process.
Numerous variables are involved at each stage of the plastic molding process. These include injection pressure, clamping pressure, and temperature, among others. All of these variables must be rigorously controlled at every stage of the injection molding process to ensure consistent part quality and minimize defects. Plastic resin must undergo multiple processes to be molded into well-designed parts. These processes include:
Phase 1: Mold assembly
Mold closing refers to the process of securely closing the two parts of the mold together. This is an important stage that requires maintaining appropriate pressure, known as mold closing pressure, to prevent defects such as leakage and flash from appearing on the molded parts.
Phase Two: Injection
Plastic granules are fed into a barrel, where they are heated to form molten plastic. Once the mold is tightly closed, the molten plastic is injected into the mold from the heated barrel through a screw. The screw rotates inside the barrel, pushing the molten plastic through a nozzle into the runner system, and then through a gate at the end of the runner into the mold. This step is called injection molding.
Phase 3: Cooling
Once the plastic is fully injected into the mold, the cooling process begins. Coolant flows through channels within the mold, causing the molten plastic to solidify and take shape. The cooling time for the newly molded plastic part can range from milliseconds to minutes, depending on the complexity of the part.
Phase 4: Demolding
Once the part has completely cooled and solidified, the screw retracts into the barrel, the mold opens, and the demolding system begins to operate.
Ejector pins or ejector plates push the solidified part out of the mold. These ejector pins are carefully designed and precisely calculated in their placement to ensure that the demolding process does not result in any part defects. After the part is removed from the machine, the mold closes, and the screw restarts to begin production of the next part.
What types of plastics can be used in plastic injection molding?
We know that plastic injection molding is a versatile process. One factor is its ability to use a wide variety of plastics, melting them and molding them into any desired shape or size. Here are some of the most common types of plastics that can be used in injection molding:
| PVC (Polyvinyl Chloride) | PVC is a soft and malleable plastic commonly used in the manufacture of food packaging, drinking water bottles, toys, water pipes, and more. It has a wide range of applications and is known for its durability and chemical resistance. |
| PP (Polypropylene) | Polypropylene is another thermoplastic that is highly resistant to chemicals and provides a hygienic surface. |
| PET (Polyethylene terephthalate) | PET is also lightweight and strong, so it can be injection molded and used to manufacture beverage bottles, food containers, etc. |
| Polymethyl methacrylate (PMMA) | PMMA, commonly known as acrylic, can also be made into any shape through injection molding. |
| Acrylonitrile butadiene styrene (ABS) | ABS is a tough, impact-resistant thermoplastic that is widely used in injection molding. |
| Polyethylene (PE) | There are three main types of polyethylene: high-density polyethylene (HDPE), low-density polyethylene (LDPE), and polyethylene terephthalate (PET). |
| Polystyrene (PS) | Similar to PE, polystyrene (PS) is a material known for its high optical transparency. Manufacturers currently use two types of polystyrene (PS) for injection molding: general-purpose polystyrene (GPPS) and high-impact polystyrene (HIPS). |
| PTFE (Teflon) | PTFE is more commonly known as polytetrafluoroethylene. This material has high corrosion resistance and is often used in the medical and electrical industries. |
| POM | If you’re looking for a metal alternative for machinery and automotive parts, POM is the material you need. It’s a thermoplastic material known for its strength and stiffness. |
| Nylon (PA) | Nylon is a synthetic material that is popular in the automotive industry. The material is strong but not heavy. It is also much cheaper to produce compared to metal analogues. |
Common industrial applications of injection molding
Almost every product we encounter daily uses plastic materials. From food packaging and household goods to automotive parts and hospital equipment, plastic shapes modern life. But behind every product lies a carefully designed plastic molding process to suit the design, strength, budget, and requirements set by the plastic manufacturer.
Automotive parts
One of the world’s largest industries is the automotive industry. Both gasoline-powered and new energy vehicles use a large number of plastic components, from body kits and fenders to even spoilers for better aerodynamics.
healthcare industry
The medical industry utilizes plastic parts to support various electronic devices and everyday medical equipment. Furthermore, the manufacturing guidelines for plastic parts in the medical field are extremely stringent. For continued operation, medical injection molding manufacturers must adhere to numerous production standards, as this involves life and death, and any mistake could result in fatalities.
electronic devices
Plastic parts are also widely used in both micro and large electronic applications because they provide the housings or structural components needed for components in electronic products. Computers, laptops, and most small electronic products use plastic injection molding technology to produce various components.
Aerospace Industry
In the aerospace industry, where extremely high precision and strength are required, plastic parts are also widely used as exterior structural components, especially in interior trim, where a large number of lightweight, non-high-strength plastic parts are employed. Furthermore, most aircraft aerodynamic components are manufactured using plastic injection molding.
retail
In the retail industry, everyday items are the most common, as most of these items are made of plastic. The most popular applications are display components and various daily necessities.
Home furnishings
Looking around, anyone will surely spot many modern home furnishings made of plastic or resin. Common shelves, window frames, handles, and even dish racks now utilize this technology. The fact that this technology is now used in home furnishings since plastic products first became popular demonstrates just how ubiquitous it is.
Fast-moving consumer goods industry
The fast-moving consumer goods (FMCG) industry relies heavily on injection molding technology. For packaging and aesthetic design, FMCG companies use effective packaging components to create innovative packaging designs that appeal to customers. In addition to the aesthetics and finish of the components, the FMCG industry also requires adherence to stringent hygiene and safety regulations.
Why choose Elimold to collaborate on various injection molding projects?
Elimold boasts decades of experience in injection molding service. Through simulation software, our team of engineers can identify any potential problems in a project. Whether it’s a prototype project with fewer than 1,000 cycles, a mid-range design with fewer than 5,000 cycles, or a high-end industrial product with over 100,000 cycles, Elimold can provide you with professional molds and solutions for high-volume production needs.
Furthermore, Elimold boasts some of the industry’s most stringent quality standards, ensuring unparalleled quality, consistency, and performance at the most competitive prices. With state-of-the-art facilities, an integrated DfM system, and a fully online design and analysis process, Elimold offers unparalleled injection molding services and any other manufacturing needs in the industry. Because we truly are a one-stop shop for all those who need to manufacture plastic parts.
in conclusion
Plastic injection molding is a versatile process capable of mass-producing a wide variety of products. It enables high throughput, producing hundreds of parts while maintaining design consistency, making it the preferred process for manufacturing plastic parts. As discussed above, these four stages are performed sequentially. Injection molding can utilize a wide variety of different plastics. For any business operating in manufacturing, having the right processing partner is just as important as using the right materials. Experienced teams can facilitate processes by optimizing designs for the best applications and improving efficiency and cost-effectiveness without compromising the quality of the results through the use of the right techniques and tools, thus helping to achieve true efficiency.
FAQ
What exactly is injection molding?
It’s a manufacturing process that forces molten materials, such as plastic, into a mold cavity to create large quantities of identical parts. The material is melted in a heated barrel, injected into the mold, and then cooled and solidified into its final shape.
What materials can be used in injection molding?
While thermoplastics (such as ABS and nylon) are most common, the process is also suitable for thermosetting plastics, liquid silicone rubber (LSR), and even metals (through a special process called MIM).
What are the main advantages of injection molding?
Its biggest advantages are the incredible efficiency of mass production, the ability to manufacture highly complex and intricate parts, and the great design flexibility once the initial mold is created.
How much do injection molds cost?
The mold itself is a significant upfront investment. Costs can range from a few thousand dollars for simple aluminum molds to tens of thousands (or more) for complex multi-cavity steel molds capable of millions of cycles.
What factors affect the final cost of injection molded parts?
The price of each part is influenced by six key factors: the initial mold cost, the raw materials used, the machine cycle time, any required secondary processing (such as painting), packaging, and the overhead costs of the molder.
What is the difference between injection molding and compression molding?
It’s like pouring versus pressing. Injection molding involves injecting liquid material into a closed mold, making it ideal for complex shapes. Compression molding, on the other hand, involves placing material into an open mold, then closing and compressing it, and is generally more suitable for larger, simpler parts, such as some rubber products.
When should you choose injection molding compared to other materials like metal?
You should choose plastic if you want a lightweight product, low per-unit cost in high-volume production, corrosion resistance, electrical insulation, and the ability to create complex geometries that would be expensive to machine from metal.