Injection mold machine  Pixabay

What is Injection Molding?

Injection molding is a form of manufacturing process that is designed for mass production where one part is created repeatedly for several times. Since the process duplicates a product, the same product can be reproduced even a million times in succession.

Injection molding is executed by an injection mold machine. This is a custom-made machine and tools that are used for turning the molten plastics into finished products. This injection molding tool comprises of different complex parts which in conjunction ensure that the molding is well-executed.

Examples of the products from the injection molding include bottle cases, tables, chairs, disposable cutlery, musical instruments, automotive parts, toys, cases for electrical appliances, among others.

It is also vital to know that there are different types of injection molding. This is to take care of the varying specifications of the products to be molded.

injection moldingInjection molding source creative mechanism

History of the Injection Molding

The history of injection molding dates back to the mid-1800s when artificial plastic started replacing ivory. During those years, injection molding was quite mechanical.

The molding machine comprised of a huge barrel that was used for heating plastics to the melting point. A plunger will then be injected into the mold.

In the 1950s, the development of injection molding was boosted by the invention of the reciprocating screw. It solved the main problem that was experienced with the older injection molding tool, which is the uneven distribution of heat. It created a path for the mass production of plastics.

Today, injection molding is done by sophisticated machines. They are customized for mass production so as to meet the demands of the market. The quality of the products has also improved by a big margin.

Modern injection molding machines are also versatile. Apart from the plastics, they can also mold biodegradable products. In doing so, they adhere to the message of environmental conservation.

How Does Injection Molding Work?/ The Process

The working mechanism of an injection molding machine is divided into three distinct parts. These are the injection unit, the molding unit, and the ejector unit.

We are going to look at what each of the functional units of the injection molding machine does.

1. The injection unit

This unit acts as an entry point. This section has the hopper, a reciprocating screw, and a barrel. The raw plastic gets into the machine through this unit. It is also here that the plastic is melted and turned into a semi-liquid form.

Here is a step-by-step procedure of what happens in the injection unit:

  1. a) The plastic or polymer granules are dried and after that placed in a hopper. Here they are blended with other compounds including the coloring elements and the strengthening additives.
  2. b) From the hopper, the polymer granules are channeled to the barrel. Here they are heated then moved to the mold. The design of the barrel ensures that there is a buildup of pressure that rectifies the level of melting. A variable screw does the job of pushing the heated polymer.
  3. c) The plastic is then injected into the mold b by passing through a runner system. Here it fills the cavity of the mold to the brim. As the melted plastic cools, it solidifies and adapts to the shape of the mold.
  4. d) The mold is opened and the now solid plastic is ejected from it. The mold will then open waiting for the next batch of the melted plastic. This process repeats itself automatically.

How long does the injection molding process take? In most modern machines, the time-frame for a single is between 30 seconds and 90 seconds.

The time taken is usually determined by several factors, among them is the size of the part and the nature of the machine. Advanced injection molding machines have the capacity to do the job much faster.

After being ejected from the mold, the new product is positioned on the conveyor belt and moved to the next storage container.

Most products of the injection molding are ready for use in their state. They may not require extra modifications.

2. Mold Manufacturing

As we have seen, the mold is a critical component of the injection molding. It is usually compared to the negative of the old photographs. This is because the final product of the process will be a duplicate of the mold.

The shapes and sizes of the molds are changed several times depending on the parts that you want to get. This means that this component deserves maximum level of attention.

In most cases, molds for injection molding are produced through the CNC machining. It is made from aluminum or steel so as to retain its structural integrity even with the temperature changes.

Injection Molding Defects

Injection molding is usually associated with quite a number of side defects. Most of these mistakes occur during the processing stage. Here are some of the most common injection molding defects that you should know;

Warping: This defect is usually a result of the non-uniform cooling of the materials. It will occur when one section of the material cools faster than the other sections. This will make that section to bend more than the others

Warping is a common defect in parts whose walls are not constant.

Drag marks: After the injection molding process you may notice that the product has some drag marks. These marks are usually as a result of the sliding action that takes place between the material and the mold. The sliding will occur when the plastic shrinks and applies some pressure on the mold.

Drag marks are usually visible on the vertical walls.

Sink marks: Sink marks will be easily visible when the interior section of the material solidifies before its exterior section. A ‘hole’ will be created and that is what we call the sink mark.

The poor design of the molded product is usually attributed to the sink marks.

Knit lines: When you see this injection mold defect you will just assume that it is a discoloration mistake. It mainly affects the aesthetics of the molded material. In some cases, it may end up affecting the overall strength of the material.

Knit lines tend to occur mostly when you introduce unplanned changes to the injection molding process.

Short shots: The presence of air in the mold can end up affecting the flow of the material. His will then lead to incomplete processing.

The resultant effect is the flaws in the design of the parts. Such defects are characterized by very thin walls of the product.

Solutions to the Injection Mold Effects

Can the defects of the injection mold process be minimized? The answer is Yes. You can get a flawless product from the injection mold process. The best injection mold companies use various techniques to minimize such defects.

Use of constant thickness

This is one of the techniques that injection mold companies use to eliminate any flaws. The use of uniform walls helps to eliminate the issue of warping. All the sections of the wall will solidify at the same rate.

In case the product requires that the thickness of the wall to be different, the company will ensure that there is a smooth transition between the different thickness. This will also help to eliminate the flaws as there will be a smooth flow of the material.

Recommended Wall Thickness 

There are recommended thickness of the materials that are to be processed in the injection mold. The table below summarizes this information.

Table showing different thickness of injection mold

Material Recommended thickness in mm
Polypropylene 0.8-3.8
Polyethylene 0.8-3.0
Polystyrene 1.0-4.0
Polycarbonate 1.0-4.0
Nylon 0.8-3.0
Silicone 1.0-10
ABS 1.2-3.5
Peek 1.0-3.0


What is Custom Injection Molding?

There are injection molding projects that are very different from ordinary projects. The difference can be in terms of the designs, size and even application areas.

This is where the issue of custom injection molding comes in. It is required for carrying out unique and specialized injection molding products.

Custom injection molding goes beyond the basic principles and practices of an ordinary injection molding. The designers and engineers involved in such projects may need to have some special skills and experience to execute the project successfully.

The injection molding machines for custom projects may be slightly different. The machines should be able to cater for the complex designs of the desired products.

Custom injection molding is common in the military and medical industries. However, it can still be used on all the other applications of the injection molding.

Because of the complexity of such projects, there is always a need for an efficient communication channel between the engineers involved. This will ensure that the parts or products are customized according to your needs.

Do not assign anyone your custom injection molding. Instead, choose the best injection molding companies to handle such sensitive projects.

Advantages of Injection Molding

Why injection molding? Well, here are the key benefits that you stand to gain from this type of manufacturing:

Mass production of plastics: Injection molding has proven to be the most effective method for the mass production of plastics. You can get high volumes of products and parts within a short time. This will give you the advantage of economies of scale.

High-quality products: It is possible to get premium quality products through the injection molding process. As long as everything is done as planned, there will be minimal flaws from the process.

Cost-effective: Injection molding is not an expensive process that will cost you a fortune. Since the process is repetitive, there will be a minimum cost required to recreate the products.

Good-looking products: Injection molding takes care of the looks of the product. Factors such as the design and color of the products can be tweaked during the process.

What is the Cost of Injection Molding?

injection molding3D image of injection mold

When planning to have an injection molding service, the issue of cost will always come up. You would like to know the exact price of injection molding.

There is no fixed cost of this service. Instead, the price is determined by several factors.

Some of the key determinant factors for the cost of injection molding include the desired shape of the product, the size of the material, quantity of the product, the nature of the raw materials among other minor issues.

For instance, it will cost you more if the desired shape is complex. This is also true if you intend to have large quantities of products to be processed.

The nature of the injection molding material will also determine the cost of this essential service. This is critical because not all the plastics are the same.

For instance, plastics that are made out of fiberglass material tend to be stronger than other ordinary plastics. This directly means that you are likely to pay more for the service.

Your choice of injection mold company will also determine the cost of this service.

Like in any market, some companies are more expensive than others. So as you look for affordable injection mold service, you should also be keen on the quality.

Does the quality of the job match the price of the service? If so, go ahead and use their injection molding service.

You should also be keen to avoid being overcharged for the injection molding.

The easiest way of getting a real value for your money is by requesting for the injection molding price estimates The company will send you the value that you are supposed to pay and this will help you plan for the budget.

Application of Injection Molding

Injection molding is quite relevant in the modern world. It is used to make different products in different industries. If you are careful, you can easily identify the products based on their distinct characteristics.

Most products of injection molding tend to have a uniform thickness, marks, and have the parting lines.

To make things more transparent, here are some examples of the most common applications of the injection molding.

1. Automotive

Take a closer look at the automotive parts, and you will realize that most of them are made from the injection molding process. This applies especially to the interior parts of the vehicle.

The most common car materials that are made out of the injection molding process include polypropylene and PVC. By undergoing the injection molding, these materials are strengthened so that they can withstand high-impact forces. They are also resistant to different elements of weather.

Are there any plastic materials in your car? Almost all of them are a product of injection molding. This includes the plastics on the dashboard, bumpers. Now you can understand why these plastics seem to be extra strong than the ordinary plastics.

2. Manufacture of toys

There are different types of toys whose material is refined by the inj3ction molding. If you notice that the toy is strong, whereby it does not break when dropped on a hard surface, chances are it is a product of this process.

A perfect example of the toy that has been manufactured by the injection molding is the lego bricks. Have you ever wondered why these bricks are resistant to high impact?

Well, you now have the answer. The bricks are what they are because they have been designed and manufactured through injection molding. Take note of the uniformity of their wall and angles.

3. Injection molding for packaging

Injection molding plays a significant role in making packaging materials. A good percentage of these materials are products of this process.

One of the packaging materials that we cannot ignore is the bottle caps. Have you ever wondered why they are strong and seem to be well-refined? The answer is injection molding.

It is quite easy to notice the impact of injection molding on the bottle caps. They include parting lines, stripping undercuts, ejector marks, among others.

Polypropylene(PP) is processed through the injection molding, and from there, it can be used as a bottle cap for different products. Even the most sensitive products, such as food and chemicals, use this material.

4. Aerospace

In the field f aerospace, injection molding is used for making models of airplanes. Polystyrene (PS) is the most common material that is used for making these models. Apart from being flexible, it is easy to mold them. PS is also cheaper than other alternative materials.

The most intriguing fact about these models is they come with the runner systems which remain fixed onto them. This means that you can easily see the impact of injection molding.

5. Consumer electronics

Consumer electronics are among the most common applications of the injection molding. Just take a look at any electric appliance in your house. Can you spot any signs of injection molding?

The enclosures or cases of most electronic devices are made from the injection molding process. Polystyrene is the most preferred material for consumer electronics because of its strength, excellent insulation, and resistance to high impact.

6. Healthcare and Pharmaceutical

Injection molding is used in the manufacture of different medical devices. The most common materials that are used in this field tend to be sterilizable and bio-friendly.

One such material is the medical-grade silicone. It features a plethora of properties that make it applicable in the field of medicine.

These are not the only applications of injection molding. There are many others that we have not listed.

Wondering whether your application will fit into this field? Feel free to consult us for further advice

Factors to Consider When Going for Injection Molding

It is pretty evident that you would like to get the best results out of injection molding. But before you go on with the process, you should consider the following factors:

The cost of injection molding

How much are you willing to pay for the mold injection? As we have seen, many other factors will determine the cost of injection molding. Among them is them is the quantity of the products to be molded.

By knowing the cost, you will be in a position to make significant decisions on how the whole process should go.

The design of the product

It is impossible to ignore the design issue when it comes to injection molding. This will determine the final appearance of the product that will be molded.

There are two aspects of design that you should consider. These are product design and tool design.

Once you submit the design of the product, the molder will come up with the tool design.

Proper design will help to eliminate product defects.

Cycle Time

You should also pay some attention to the production process. How long will the process take? This issue will always come up since you will still want to supply your products to the market.

The cycle time for the injection molding will also give room for the correction of defects.

Roche Industry: Reliable Plastic Injection Molding Company

As we have seen, injection molding is a complex and intricate process. It is a task that can be executed by advanced injection mold machines- that is, if you want to get the best results.

Experts should closely supervise the task.

At Roche Industry, we are here to do everything that entails injection molding for you. Not only do we have high-tech injection molding machines, but also we have the best people to supervise the process.

We take pride in giving our customers the best results.

If you are looking for the most reliable injection molding services in China, you should consider contacting us. We will help to take product development to a higher level.

Rocheindustry specializes in high quality rapid prototyping, rapid low-volume manufacturing and high-volume production. The services of rapid prototype we providing are professional Engineering, CNC Machining including CNC Milling and Turning, Sheet Metal Fabrication or Sheet Metal Prototyping, Die casting, metal stamping, Vacuum Casting, 3D printing, SLA, Plastic and Aluminum Extrusion Prototyping, Rapid Tooling, Rapid Injection Moulding, Surface Treatment finish services and other rapid prototyping China services please contact us now.

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