Parts of Plastic Molding Machine: An In-Depth Guide

Comprehensive Guide to Parts of a Plastic Molding Machine

Don’t be a fool looking for a hydraulic pump in an electric plastic molding machine! Remember, some parts or components vary depending on the molding machine type. So, read this guide before you mess up with the manufacturer while purchasing plastic molding machines for your business! 

First Impression

A plastic molding machine can be divided into three major sections- injection unit, molding unit, and clamping unit. Each of these units combines several parts to run the machine. These include- hoppers, barrels, heaters, mold, platen, ejectors, and more. Apart from these essential elements, there are also some additional parts. For example- motor, sensor, dryer, chiller, etc. 

It is crucial to learn about these parts to select the best molding machine. Go through the article, and you will get it all. At the end of the article, we also provided some maintenance guides, so dive in right away!

Basic Parts Of A Plastic Molding Machine

The parts of a plastic molding machine can be divided into three main units. These are the Injection unit, Molding unit, and Clamping Unit. Each unit consists of multiple components that mold plastic into different shapes. Let’s discuss them in detail- 

Parts Of The Injection Unit :

The injection unit melts the plastic granules at high temperatures and pressures. This molten plastic is injected into the mold cavity to give a defined shape. The parts involved in this process are as follows- 


The hopper is the container where you put the granular plastic. It contains a dryer to blow away the excess moisture from plastics. You may also find a magnet attached to this part to remove harmful metal components from entering the machine. 


The inserted plastic granules from the hopper are directed to the barrel. It is a cylindrical or pipe-like champer that heats the plastic and melts them. It has heaters attached to it, which increase the temperature. The barrel is divided into three zones with varying temperatures. The temperature differences for thermoplastics ((PE, PVC, etc.) and engineering plastics (PC, PET, PA, etc.). The chart below will give an idea about the temperature of the barrel: 

Section Of The BarrelType Of PlasticTemperature Range 
Zone 1(Rear/Feed Zone)Thermoplastics150°C – 220°C (300°F – 430°F)
Engineering plastics250°C – 350°C (480°F – 660°F)
Zone 2(Centre/Compression Zone)Thermoplastics180°C – 260°C (355°F – 500°F)
Engineering plastics280°C – 380°C (535°F – 715°F)
Zone 3
(Front/Front Zone)
Thermoplastics190°C – 300°C (375°F – 570°F)
Engineering plastics300°C – 400°C (570°F – 750°F)

NB: This is a rough estimation. The temperature of the zones may vary as melting points differ for plastic types. 


The screw rotates as the plastic moves from the hopper to the barrel. It mixes the plastics well to melt them evenly. This further acts as a piston to inject the molten plastics into the mold. 


The heater of the plastic molding machine is usually attached to the barrel. It applies heat to the solid plastics of the hopper and turns them into liquid. This melted plastic then passes to the mold cavity through the nozzle. Different types of heaters are used in injection machines; for instance- 

  • Band heaters
  • Coil/nozzle heaters
  • Cartridge & strip heaters and 
  • Insulated cloth heating jackets. 


The nozzle is situated at the end of the barrel through which the melted plastic enters the mold. For proper centering and injection into the mold, the nozzle accurately fits with the sprue bushing and locating ring. Besides, modern nozzles also have additional features like filters, mixers, and shut-off options. The filter removes the foreign particles from the melted plastic, preventing clogging of the mold gates. Again, the mixing nozzle mixes the additives within the molten plastic. This potentially reduces the volume and cost of required additives. Apart from these, the shut-off molt feature stops the flow of molten plastic during the mold separation process. Thus, it prevented the unwanted drooling or leakage of liquid plastic. 

Parts Of The Clamping Unit:

The clamping unit firmly holds the two halves of the mold during the molding cycle. When the melted plastic is injected at high pressure, the clamping unit applies an opposing force to prevent mold splitting. Thus, the shape of the mold comes out perfect with no leakage. This unit includes the following components- 


Platens are the large, flat plates that hold the mold halves. Plastic molding machines usually have two plates- a stationary and a moving plate. However, larger machines have an additional rear plate. The functions of these plates are as follows-  

molding machine Platens

  • Fixed Platen or Stationary Platen: A fixed or stationary plate is attached to the nozzle of the molding machine. It holds half of the mold and supports it during the injection molding process. 
  • Moving Platen: The moving platen holds the second half of the mold. In contrast to the stationary platen, it moves back and forth to open and close the mold. The clamping force moves the palate toward the fixed palate, closing the mold. The clamping force is released when the mold is opened once it cools.
  • Rear platen: The rear platen is usually found in large machines with multi-station capabilities. This stabilizes large and complex molds that go through higher stress during the molding process. 

Tie Bars:

Tie bars are study bars usually made of alloy steel. This connects the stationary platen to the moving platen. There are four tie bars each for corners running through the holes of the platens. 

Hydraulic or Toggle Clamping System:

The clamping unit uses a hydraulic or toggle system to generate force. In a hydraulic clamping system, a hydraulic cylinder connected to the moving platen generates the clamping force. On the other hand, in a toggle clamping system, a mechanical linkage system generates the clamping force. This mechanical linkage system is called a toggle mechanism driven by a hydraulic cylinder or an electric motor.

Parts Of The Molding Unit:

The molding unit deals with shopping the plastic to the desired appearance. It cools the mold and finally ejects the final product. Here are the components associated with the mold assembly-

Core and Cavity:

    The core forms the internal structure of the molding. It is designed to create cavities, undercuts, and other intricate details of the molded part. On the other hand, the cavity gives it an external shape. This part forms the final outcome of the product or the desired outlook. 

    molding machine Core and Cavity

    Cooling Channels:

    The cooling channels are the pipes that run around the mold. They circulate coolant (typically water) through the mold to cool and solidify the injected plastic. Once properly cooled, the mold is transferred to the ejection section.

    molding machine Cooling Channels

    Extraction Pins or Ejector Pins:

    The ejector pins are located around the mold cavity’s perimeter and connected to an ejector plate. The primary function of these pins is to apply pressure to eject the molded plastic part from the mold cavity. Thus, you get the final product in hand. 

    Additional Parts Of Plastic Molding Machine

    Apart from the major parts discussed above, there are some additional components of the molding machine that you must know about. These are as follows- 

    Electrical System Parts:

    The electrical system of the plastic molding machines consists of the equipment required to operate the device. These include- 

    • Electrical Control Panel (Programmable Logic Controller (PLC) or Computer Numerical Control (CNC) system)
    • Display/monitors
    • Motors and Drives
    • Sensors and Switches
    • Wire, Cables, and Others

    Hydraulic System Parts:

    These parts only apply to machines that use a hydraulic system instead of an electric motor. You will find them on devices that require high clamping forces and high injection pressures. The significant component includes- 

    • Hydraulic Pump
    • Hydraulic Cylinders
    • Hydraulic Valves
    • Reservoir (Tank)
    Hydraulic System Parts

    Auxiliary Equipment:

    The auxiliary equipment plays a crucial role in ensuring smooth and efficient production. These are used with the injection molding machine to enhance its productivity. The most common auxiliary equipment includes- 

    Auxiliary Equipements Function 
    GranulatorBreaks down leftover sprues, runners, and any rejected molded parts into smaller, reusable pieces called granules.
    Chiller Cools down the coolants used in the mold’s cooling channels.
    DryerRemoves moisture from raw plastic pellets before they enter the injection molding machine.
    Color MixerBlends colors or additives with virgin plastic granules to achieve the desired color
    Auto Loader Automates plastic granule loading into the molding machines’ hoopers.

    How to Maintain the Parts of a Plastic Molding Machine?

    • Lubricate the moving part frequently for smooth operation.
    • Keep the surface of the clamping unit clean. 
    • Ensure the moving formwork sliding feet and sliding rails are not jammed. 
    • Don’t overload the clamping unit; set the appropriate clamping stroke to reduce the impact on the machine.
    • Consider the plastic type before inserting it into the hopper. Consult an expert or manufacturer to learn the molding machine’s ideal plastic type.
    • Regularly inspect the machine, tighten loose parts, and ensure proper balance of the injection cylinders.
    • If you find black spots or discoloration on molded parts, inspect for damage in the motion screw. 

    Why Choose DAOBEN Plastic Molding Machine?

    If you are searching for plastic molding machines for your business, DAOBEN is the go-to solution!  We have a wide variety of injection molding machines with the utmost customization facility. In fact, the hydraulic components of our devices are of Euro and USA brands. These components are integrated with oil differential circuits to ensure the mold closes faster and more smoothly. 

    Besides, our machines come with servo-energy-saving motors. Therefore,  no extra waste of power. Some of the worth-mentioning features of the DAOBEN plastic molding machine include-

    • Automatic cleaning bucket
    • Anti-salivation & anti-cold start delay function
    • TFT LCD color display. 
    • High-speed DSP processor
    • 24-month Warranty on the full machine (key parts will be dependent).

    Wrapping Up 

    Proper knowledge about the parts will help you choose the suitable plastic molding machine for your project. You must consider whether the clamping unit has a toggle or hydraulic clamping system. Besides, look at the number of platens. If your product needs thick molding walls, purchase a machine with three platens. Two platens are enough for small moldings. Also, don’t forget to consider the clamping force. 

    However, whatever your requirements are, DAOBEN Machinery has everything you need. We can provide machines with voltage variation that matches your country/region. You will further get a customization facility based on your factory size and production quantity. Therefore, go through our product category and contact us ASAP!


    What are the parts of a plastic molding machine?

    The plastic molding machine’s prominent visible parts are the hopper, injection nozzle, platens, display, and tie bars. Besides, the hidden parts of the device include- screw, barrel, core, cavity, cooling channels, etc. 

    Why is the hydraulic system necessary?

    Hydraulic systems provide greater force than electrical or mechanical systems. This is necessary for thick-walled and complex molds that need higher clamping force. 

    What are the potential problems with the injection unit?

    The potential problems with the injection unit include a leak in the barrel, nozzle blockage, injection pressure issues, etc. 

    Are there any safety precautions to maintain while using the plastic molding machine? 

    Use goggles while operating the plastic molding machines. Besides, please don’t touch the device while it’s operating. Also, check the pressure and screws of the machine. 

    Why is the clamping unit important? 

    The clamping unit holds the mold against the high pressure of the injection unit. It is important because it secures the mold and gives it the desired shape. 

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    Frequently Asked Questions

    Daoben has the SOP (Standard Operation Procedure) and all the production steps must follow up this SOP. Every machine needs at least automatic running over 72 hours and must be inspected carefully before shipment.

    Actually, the delivery time of the machines is depended on the machine options. Normally, the delivery time of a standard machine could be within 1-2 months.

    12 months warranty after shipment for mechanical parts, hydraulic parts, and electric components excluding the screw and barrel 6 months (not including use for recycled material or reclaimed material).

    Yes, Daoben will provide one set of standard spare parts to the customer including a heater, filter, screw head, screw washer, checking ring, sealings, etc.

    Surely, we have experienced technical engineers for oversea service, they would help you install machines and support training to workers also. Currently, we provide visits online by video call for COVID-19.

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