Injection Molding Machine: Working and Applications.

Hello friends, Today you are reading about Injection Molding Machine, which means you have some ideas about it. And you have doubts also like, What is the Injection Molding Machine? What is the working principle? And What are the applications of this machine? We will discuss all the things in this post. Let, we will discuss the details.

Plastic Injection Moulding Machine
Plastic Injection Molding Machine
Image source: SMT Plastic Injection Molding Machine

As per the name, it used in the moulding process. Moulding (Molding) is a manufacturing process, in which a liquid or malleable material shaped by using a solid frame. This solid frame is a Mould. We will read details about mould in our next article. In this molding machine, molten plastic injected through a reciprocating screw and barrel (or we can say a syringe) into the mould. Therefore, this machine is called an Injection Moulding machine. After then cooling is provided for the solidification. 

Hydraulic Injection Molding Machine by Bosch Rexroth
Hydraulic Injection Molding Machine
Image source: Bosch Rexroth

Today, Injection Molding is inevitable in plastic processing. This machine used for the mass production of plastic products. There is a wide range of plastic products is available in our daily life. From our toothbrush and toothpaste tube’s cap to pen and pen’s cap to Medicine bottle cap and so much. This list is endless. Also, this process used on glass and thermosetting polymers.

So let’s, first, we will see the basic parts of an injection moulding machine.

Construction of Injection Molding Machine:

These days, modern Injection machines consist of the following basic parts:

  1. Feeding Hoper
  2. Extruder Screw and Barrel
  3. Injection Chamber
  4. Mould Clamping Mechanism – An arrangement for applying pressure to the moulds.
  5. Fixed and Moving Plates
  6. Control Panel – NC or CNC
Injection Moulding Machine Parts
Injection Moulding Machine Parts

1. Feeding Hoper:

A conical container at the one end of the machine. It looks like a funnel. It is located at the barrel’s inlet end. This hopper holds and charges the raw plastic resin pallets material. It is an entry point for plastic material.

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2. Extruder Screw and Barrel:

The Extruder screw is located inside of the barrel. The plastic resin pallets come into the barrel from the hopper. A heater applies heat to the barrel for melting the plastic. A variable speed electric motor rotates the extruder screw from one end. This screw having threads. These are looks and acts like flutes on a drill bit. These threads provide motion to plastic granules. The extruder screw pushes the molten plastic to the injection chamber.

The extruder screw’s threads having three sections in length. As you can see in the image, the first section is the feed section, where the granules come from the hopper. The second section is the compression section in the middle of the length. The plastic resins heated and compressed in the middle section. And the last section is the metering section. This section is also known as the pumping section. Here raw material (resin) heated and mixes properly. This molten material becomes a homogeneous mixture at this stage.

The end of the screw having a non-returning valve. The check valve is another phrase of this valve. This valve prevents to flow of reverse the molten material during the extrusion stage.

 Extruder Screw
Extruder Screw

3. Injection Chamber:

The whole assembly just we have read in the above paragraph, i.e,  the Extruder screw, barrel and heaters assembly is Injection chamber. Here the material injected inside the mould. 

4. Mould and Clamping Mechanism:

A mould is a tool, in which melted plastic takes a shape after solidifying. A cooling system inside of the mould helps to solidify the plastic material quickly. Basically, the moulds having two halves. The moving plate carries one half and the fixed plate carries another half.

A clamping mechanism provides appropriate pressure to the mould plates during the injection cycle. The pressure created during the injection process on the moving plate in the rearward direction. So it tends to open the mould. Usually, the hydraulic actuators actuate the clamping mechanism. 

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5. Fixed and Moving Plates:

The fixed plate is located on the injection chamber side. And on the opposite side, the clamping mechanism moves the moving plate. Mould’s one part mounted on the fixed pate and another part mounted on the movable part.

Now I have a question. Which one part of the moulds should be mounted on the fixed plate and another on the moving plate? If you have an exact answer then please comment. I will answer in our next article. 

6. Control Panel: 

The control panel is a part of the Machine. A machine operator operates the machine using this control panel. Some machines controlled by using NC and some CNC. NC, Numeric Control is older technology and CNC, Computer Numeric control is the latest one. What is the difference between NC and CNC? For this answer please check our next article. 

An American inventor James Watson Hendry built the world's first extrusion screw injection moulding machine by 1946. This invention brought dramatic changes to the manufacturing industry.

Hndrye also invented Gas assisted injection moulding machine.

A force needed to hold the mould closed during the injection, that force is Clamping Force. It applied in the opposite direction of the injection pressure. This claiming force depends on the injection pressure and the sum of the projected area of the part (or shot projected area).

Usually, the machine specified as per the maximum clamping force. It also depends on material types, and cavity depth.

Working of Injection Molding Machine:

Injection Molding Machine Process:

As the name shows, an injector charges the molten material inside the mould. And this mould makes a finished OR semi-finished product. Now, Let we will see how this Machine Works?

Raw plastic material filled into the hopper manually or by feeding devices. The base plastic granules, coloured and additive granules mixture make the complete raw material. This material goes down into the barrel due to gravity. The barrel or cylinder surrounded by a heater throughout its length. That heater used to melt the raw material. Here, inside the barrel, a screw conveys these moult. It pushes the molten material towards the mould with a large amount of pressure. That located on the end of the barrel.

This mould having usually two halves. One half mounted on the fixed plate, at the end of the barrel. And another one mounted on the moving plate. A hydraulic or pneumatic mechanism applies pressure on the moulds. It opposes the injection pressure. This force measured in Tons. A force needed to hold the mould closed during the injection, that force is Clamping Force

Now, the part/s inside the cavity cooled by a cooling system for solidification. Usually, a liquid cooling system used for cooling. This solidification happens within few seconds. After that, mould halves open by unclamping. And then stuck part ejects by ejection system without damaging the part. Ejector pins and ejector plates used in the ejection system.

An injection moulding machine performs this action very fast, frequently and automatically. 

Affecting Parameters in Injection Molding Process:

Plastic
Injection Moulding: Unfinished Product with Sprue, Runner and gate

The moulding process affects by the following parameters.

  1. The heating temperature of the moult
  2. Mould Temperature
  3. Injection Pressure
  4. Injection Time
  5. Packing pressure
  6. Packing Time
  7. Coolant temperature
  8. Cooling Time
  9. Injection Capacity of machine

Also Read: 

Applications of Injection Molding Machine:

Moulding machines used to manufacture plastic products in mass volume. There are lots of fields where plastic components are useful. As we can say this list is countless. Of course, From our daily life products like crockery, cutlery, cookware, furniture etc. It used in various industries, like Automotive, Aerospace, Marine, Machinery, Medical and so on. For more information, please stay tuned…

 

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