Introduction:Injection molding is a great way to make parts that replace metal components . It’s cheaper than making metal parts, and you can make plastic parts that are light and strong. Plus, you can use plastic in lots of different ways, and you can recycle it.

That’s why lots of different industries use plastic. Injection molding has many advantages and disadvantages, That’s why it’s the best way to make most plastic stuff you buy. So why use injection molding? This article will tell you.

What is the Principle of Injection Molding?

You put plastic in the hopper of the injection machine. The machine heats and melts the plastic and keeps it flowing. Then it squirts the melted plastic into the closed mold under pressure. After it cools and hardens, the melted plastic turns into the plastic parts you want.

What are the Characteristics of Injection Molding?

Injection molding has a short production cycle and high productivity. It can produce plastic parts with complex shapes, high dimensional requirements and various inserts, which is difficult to achieve with other plastic molding methods.

Secondly, it is easy to automate in the production process, such as injection, demoulding, gate cutting and other operations can be automated, so it has been widely used.

What is the Injection Moulding Process?

Preparation Before Molding

Checking the appearance of raw materials and determining how they perform: this includes checking the color of the plastic, the size and consistency of the particles, how well it flows (melt index, viscosity), how stable it is when heated, and how much it shrinks.

Plastic preheating and drying: Remove excess moisture and volatiles in the material to prevent defects or degradation on the surface of the plastic parts after molding, affecting the appearance and internal quality of the plastic parts. Material drying method: Small batch production, oven drying; large batch production, boiling drying or vacuum drying.

Barrel cleaning: The barrel needs to be cleaned when changing products, raw materials, and colors.

Preheating: It can reduce the temperature difference between the material and the insert, reduce the shrinkage stress of the plastic around the insert, and ensure the quality of the plastic parts.

Selection of release agent: Commonly used release agents include zinc stearate, liquid paraffin, and silicone oil.

Injection Process

Feeding: put granular or powdered plastic into the hopper of the injection machine.

Plasticization: heat the heating device of the injection machine to melt the plastic raw material in the screw into a plastic melt with good plasticity.

Mold filling: the plasticized plastic melt is pushed into the mold cavity through the nozzle and pouring system of the mold by the plunger or screw of the injection machine at a certain pressure and speed.

Pressure maintenance and shrinkage compensation: After the melt fills the cavity, the melt still maintains pressure to replenish the material under the push of the plunger or screw of the injection machine, so that the melt in the barrel continues to enter the cavity to supplement the shrinkage needs of the plastic in the cavity and prevent the melt from flowing back.

Cooling after gate freezing: After a while, the molten plastic in the cavity turns into a solid, so that the plastic part has enough strength when it is ejected, and it will not be deformed or warped.

Mold removal: When the plastic part cools to a certain temperature, the ejection mechanism pushes the plastic part out of the mold.

Post-Processing of Plastic Parts

Why Do We need to Do Post-Processing?

Because of the uneven plasticization or uneven crystallization, orientation and cooling of the plastic in the mold cavity; or because of the influence of metal inserts or improper secondary processing of the plastic parts, there are inevitably some internal stresses inside the plastic parts, which may cause deformation or cracking of the plastic parts during use. Therefore, we need to eliminate them.

Annealing Treatment: A heat treatment process where plastic parts are put into a constant temperature heated liquid medium (such as hot water, hot oil and liquid paraffin, etc.) or a hot air circulation oven for a period of time and then slowly cooled to room temperature.

Temperature: 10°~15° higher than the use temperature or 10°~20° lower than the heat deformation temperature.

Time: It is related to the type of plastic and the thickness of the plastic parts. It can generally be calculated at about half an hour per millimeter.

Purpose: Relieve internal stress of plastic parts, stabilize plastic part size, increase crystallinity, stabilize crystal structure, and thus increase elastic modulus and hardness.

Moisture conditioning: A post-treatment method that places newly demolded plastic parts in a heating medium (such as boiling water, potassium acetate solution) to speed up moisture absorption equilibrium. (Mainly used for plastics with high moisture absorption and easy oxidation, such as PA)

Temperature: 100-121°C (use the higher temperature if the heat deflection temperature is high, otherwise use the lower temperature).

Time: The holding time depends on the thickness of the plastic part, usually 2-9 hours.

Purpose: To relieve residual stress; to allow the product to reach moisture equilibrium as quickly as possible to prevent dimensional changes during use.

What are the Advantages of Injection Molding?

Plastic injection molding is used in many different ways and is important for making products for different industries.

Great Value for Money

Injection molding is a cost-effective process that reduces waste by using recyclable materials. Plastics are generally cheaper than alternatives like metal and rubber, so they’re preferred in many applications. Plus, recycling excess plastics for future production can further reduce costs.

Once you exclude the initial cost of mold design and production, labor costs are usually low. As a high-productivity process, you can say that the mold will pay for itself over time. So, it’s a great choice for producing high-quality, large-volume plastic parts.

Environmental Advantages

The raw material for injection molding is plastic pellets. Compared to many other manufacturing processes, injection molding doesn’t produce a lot of harmful stuff like waste gas and wastewater, so it’s not as bad for the environment. Plus, plastic can be recycled and used again, so it’s good for the environment.

Compared to traditional manufacturing processes, plastic injection molding doesn’t produce much waste after it’s made. Any waste plastic usually comes from the gate and runner. But any plastic that unused or waste plastic can be ground up and used again later. So it’s kind of good for the environment.

Cost Advantages

Injection molding is a low-cost, high-efficiency production method. Compared with traditional processing methods, injection molding can produce high-quality products in a short time and at a relatively low cost.

The raw materials for undertaking injection moulding are generally plastic particles, which are relatively inexpensive and can be mass-produced, greatly reducing production costs . And the manufacturing costs is low .

Excellent Quality

Injection molding can make good stuff because the plastic injection molding process is done under high temperature and high pressure, which can make sure the product’s performance indicators like density, strength, and toughness.

And because injection molding can integrate mold making, injection molding, and other links, it can greatly reduce errors in the production process, so as to ensure the quality of the product.

High Production Efficiency

Plastic molding is fast and efficient. It’s great for big jobs because it saves money. It’s also good because it makes the same thing over and over again, and you don’t throw away as much stuff.

A single mold can make hundreds or thousands of parts before it needs to be replaced. Many aluminum molds have a service life of up to 10,000 shots, while steel molds can have a service life of more than 100,000 shots.

This ensures a repeatable, high-output process that meets tolerance and aesthetic requirements. You must note that production speeds are usually determined by the size and complexity of the target injection molded parts.

High Precision and Accuracy

Modern high-speed injection molding equipment can continuously produce precision molded plastic parts. The process excels in providing components of uniform quality, tight tolerances, and high dimensional stability.

For applications that require extreme precision, such as gears and connectors, plastic injection molding is often the method of choice, achieving tolerances as high as +/-0.0002”.

Also, manufacturers often put advanced control systems on molding machines. These automated systems watch and change process parameters in real time. So, plastic parts can be molded to exact specifications.

Versatility in Design

Injection molding is a manufacturing process that allows you to make parts with all kinds of cool shapes. You can make the parts look however you want by changing the way you do the injection molding. You can change things like how hard you push the plastic into the mold, how hot the plastic is, and how fast you push the plastic into the mold.

Also, machinists can use simulation software, automation, and 3D printing. These technologies help design and test molds, process parameters, and molded parts. However, the design versatility of injection molding depends on the plastic material, part complexity, and mold design.

Flexibility in Color and Materials

Plastic injection molding is a flexible process. It’s flexible in the properties of the plastic used. It’s flexible in the ability for the OEM to customize color choices to meet specific project requirements. The benefit of plastic injection molding is the freedom of design choices it offers OEMs, especially compared to metals. You can use many materials.

You can adjust the molding process to get the color you want by adjusting the plastic, additives, and biocompatibility, which can give you clear parts or a variety of colors. But if you need multiple colors for a product, you can do that with overmolding.

Complex part designs often require components made of different materials. While it may seem simple, safely combining plastics can be very complex. In any case, by guaranteeing compatibility, the plastics expertise of mold project engineers reduces defects, risk of injury, and warranty claims.

What are the Main Uses of Injection Molded Parts?

Injection molding is a versatile manufacturing technology that is essential in the development of a wide range of products, including home appliances, automotive parts, medical devices, and more.Let’s look at some of the applications of the process:

Automotive Industry

Plastic parts make cars more aerodynamic. Car companies like to use injection molding to make car parts. It makes parts that are strong but light, so cars use less gas and make less pollution. The parts also stay the same size and shape and don’t get ruined by the weather or by rubbing against other things.

Some examples of parts made with injection molding are dashboards, bumpers, and little parts like the things that hold mirrors on, the places to put your drinks, and lots of other parts you see in cars.

Packaging Industry

The packaging industry uses components that are effective in developing creative packaging designs that appeal to customers. In addition to attractive looks and aesthetics, products must also adhere to strict safety and hygiene regulations. Injection molding can improve the overall quality of the product without causing any major issues.

Medical Industry

Medical components often use custom plastic parts that have excellent mechanical properties and tight tolerances. The medical industry is at the forefront of precision and sustainability. Medical plastic part manufacturing is highly regulated. Medical parts also need the right compounds and structural properties to be durable and withstand higher temperatures.

Injection molding is a great choice because it’s super durable, flexible, strong, and easy to change. These are all things you need if you’re making stuff for the healthcare industry. Stuff like dentures, surgical equipment, stuff you use to get ready for surgery, and stuff you use to fix broken bones are all made with plastic injection molding.

Consumer Goods Industr

The home furnishings manufacturing industry relies heavily on plastic molding technology. The main benefit of this method for consumer goods is the ability to provide the desired finish and aesthetics.

The parts made by this technology are both strong and high quality. Since plastic products became popular, household items have used this process, showing how useful it is. Consumer products made with these techniques include window brackets, cutlery holders, handles, shelves, and more.

Aerospace Industry

The aerospace industry has some pretty strict regulations for structural strength and precision. Plastic injection molding is used to make the aerodynamic parts for most of today’s aircraft. The aerospace industry is changing the game and using this method to make parts.

Injection molding is used in a wide range of industries to produce everything from small parts to complex components. Examples of such parts include turbine blades and housings, panels, chassis components, panels, housings, and so on.

Summary

Injection molding is a fast and efficient technology for making plastic parts for a variety of industries like automotive, medical, and consumer products. It heats and melts plastic and injects it into a mold.

It has short production cycles, high precision, and high automation. Injection molding is cost-effective, the material can be recycled, there is less production waste, and it has excellent environmental performance. It can meet complex shapes and high quality requirements, making it an ideal choice for large-scale production.