Everything You Need to Know About Injection Molding Machine

Table of Contents

Injection molding machine­s are important tools in manufacturing. These machine­s create plastic parts by heating up plastic pellets until the­y melt. Then, the machine force­s this liquid into a mold. As the molten plastic cools down in the mold, it solidifies, taking the shape of the final product. The­ injection molding machine controls various factors such as heat, pressure­, and amount of material pushed into the mold leading to an e­fficient production process. These machines are­ indispensable in mass-production of detailed plastic products with tight tolerances. Industries from car manufacturing to consumer goods re­ly on these machines.

Section 1: Types of Injection Molding Machines

Injection Molding Machine 2

There­ are three type­s of injection molding machines: hydraulic, ele­ctric, and hybrid. 

Hydraulic Injection Molding Machines

Hydraulic injection molding machines are the earliest types of injection molding machines to be used in the industry before the emergence of electric injection molding machines in the 1980s. These machines use hydraulic fluid to press the mold. Hydraulic injection molding machines have a number of advantages. Being some of the earliest injection molding machines, their initial cost and cost of spare parts  is considerably lower. They have a clamp force that can accommodate large and small size parts. They have consistent injection and ejection capabilities and the hydraulic machines have a longer life span compared to other types. Despite these advantages, hydraulic machines face some drawbacks including excessive energy consumption, imprecise molding and the risk of fluid leakages. 

Electric Injection Molding Machines

These machines were introduced in the injection molding industry in the late 1980s. They use electric motors  that are digitally controlled, improving their precision and accuracy in injection molding cycles. The electric injection molding machines are very energy efficient and have improved reliability compared to the hydraulic ones. Some of their main advantages include low operating and maintenance costs, advanced control and design features, operator focused ergonomics and safety features and suitability for a wide range of applications. Some of their drawbacks include high initial investment and the need for routine maintenance. 

Hybrid Injection Molding Machines

These machines combine the technologies of hydraulic and electric injection molding machines to leverage the advantages of both. They use electric servo motors for the injection unit and hydraulic systems for the clamping unit. This results in an energy efficient hybrid injection molding machine, with enhanced precision and speed. The advantages of hybrid machines include increased precision and repeatability, energy-efficient and low temperature closed-loop injection molding process and the ability to accommodate thick and thin-walled design variety. These machines face some disadvantages such as complicated maintenance routines for the electric and hydraulic units, the risk of product mismatch, differences in various hybrid machines.  

Section 2: How Injection Molding Machines Work

Injection Molding Machine 3

The injection molding machine works with a basic principle of injecting molten material into a mold and upon cooling, the molten material solidifies assuming the shape of the mold. To effectively run this process, the injection molding is made up of various components and parts. These parts work together to ensure a successful injection molding cycle. The injection molding machine is made up of three main parts; the machine frame, the injection unit and the clamping unit. The machine frame holds the hopper where plastic pellets are loaded, the barrel where the pellets are melted, the drive screw, the injection unit and the clamping unit.  The injection molding machine works in four stages to complete an injection molding cycle.

  1. Feeding and melting thermoplastic material

The injection molding process starts by feeding the hopper with a thermoplastic material (usually plastic pellets). These are carefully selected materials for the injection molding process. As the drive unit turns the screw, the pellets are slowly fed to the barrel of the machine. The heat from the barrel and the turning screw melts the pellets to their melting point until they turn into a molten material. In this stage, it is essential to monitor the temperature and ensure the right temperature is maintained for an efficient injection process. 

  1. Injection the plastic into the mold
Injection Molding Machine 1

In this stage, the screw in the barrel forces the molten plastic into a gate that leads to the clamping unit. Here the clamping unit is already closed, holding the two halves of the mold in place ready to be injected with the molten plastic. When the injection pressure and clamping pressure is balanced, the gate opens to allow the molten pressure into the mold. It is important to keep the injection pressure and clamping pressure balanced to ensure that the molten plastic fills the mold completely and to prevent leakage of molten pressure from the mold. 

  1. Holding and cooling time

Once the plastic is injected into the mold, it is held under pressure for some time (holding time) depending on the material used and the complexity of the part being produced. This holding time is important to ensure that the mold is entirely filled to avoid defects on the final product. After the holding hase, the screw retracts to allow the plastic to cool and solidify inside the mold. This is known as cooling time and can range from a few seconds to some minutes. After the plastic has sufficiently cooled, the process moves to the final stage, ejection. 

  1. Ejection

After sufficient cooling, the part being molded is ejected from the mold by ejector pins or plates. This is the final stage of the injection molding process. After the part has been ejected, polishing or removal of excess plastic can be done to the final product. Other finishing processes such as dying and polishing can be done before packaging. 

Section 3: Key Features and Specifications

Each injection molding machine has various key features and specifications that make it suitable for various injection molding projects. Some of the main distinctive features and specifications of injection molding machines include the clamping force, shot size and platen size. 

Clamping force refers to the force required to keep the mold completely sealed during injection molding. This force is measured in tones and varies between various injection molding machines. The amount of clamping force required during injection molding is determined by the injection pressure and the size of the part being molded. Using little clamping force could lead to opening of the mold, resulting in defective parts. 

Shot size refers to the amount of molten plastic that can be injected into the mold in one cycle. When selecting an injection molding machine, consider the shot size and capacity of the machine depending on the size and complexity of the part being produced. 

Platen size determines the size of the mold that an injection molding machine can hold. There are different platen sizes for various injection molding machines which determine the mold sizes compatible with the machines. You should ensure the platen size can cover the whole surface area of the mold, accounting for the outer dimensions of the mold. 

All these features determine the precision and control of an injection molding machine, and the quality of the final product. The ability of an injection molding machine to control temperature and pressure ensures consistent quality in final products and less defects. 

Section 4: Selecting Injection Molding Equipment 

When selecting injection molding equipment, there are a number of important factors to keep in mind to maximize efficiency and product quality. These include: 

Materials to be used: Different materials have different properties. Some have varying melting and cooling temperatures. Other materials require different pressure ranges to prevent deformation or degradation. When selecting an injection molding machine, it is important to ensure that the machine is compatible with the selected materials.

Part design: When selecting an injection molding design, it is important to consider the design and size of the part to be produced. Parts with complex designs require high-precision machines that can handle complex geometries easily. The size of the part also affects factors like shot size, platen size and the clamping force of the machine. 

Volume of production: The volume of production affects equipment selection because different types of injection molding machines are suitable for various production volumes. For large production volumes of complex parts, electric injection molding machines are better because of their efficiency and fast production cycles. Hybrid machines are suitable for low volumes of large and simple parts. Hybrid machines can be used for various volumes and complexities.

Selecting injection molding equipment can be a challenging task. Here are some tips to keep in mind when looking for the right injection molding machine:

  1. Understand your project requirements: Your project’s requirements will determine the type of injection molding machine that can effectively and efficiently handle the projects. Keep in mind factors such as the clamping force, platen size and shot size.
  2. Consider future needs: Choose an injection molding machine that can handle various designs and materials for future use.
  3. Energy efficiency: Selecting energy efficient machines can cut costs in the long-run. This is especially advantageous for large projects. 
  4. Control and precision: Machines with advanced control and precision will improve the quality of your products and the efficiency of production cycles.
  5. Service and support: Machines from providers with a reliable support system can help you reduce downtimes due to machine failure. 

Section 5: Maintenance and Upkeep of Injection Molding Equipment  

Regular maintenance and service of injection molding equipment is essential for operational efficiency and longevity. You should ensure that your injection molding machines are serviced regularly to prevent components damages due to wear and tear. This also helps prevent downtimes due to machine failure which can impact the productivity and profitability of the machines. 

To ensure optimum operation of injection molding equipment, here are basic maintenance tips. 

  1. Ensure the machine is regularly cleaned to remove dust and debris and remaining resins
  2. Lubricate moving parts regularly to prevent friction 
  3. Check hydraulic systems regularly for fluid levels
  4. Regular inspection of heat headers and sensors
  5. Ensure the machine is calibrated for temperature and pressure setting regularly

Section 6: Advances in Injection Molding Equipment Technology 

The injection molding industry is experiencing a lot of advances in technology as new methods of production are being developed. New and modern innovations have developed in this sector, raising a bar in plastic processing. One of the main advancements in this industry is the rise of industry 4.0 technology and the connectivity of IoT. This has led to the connectivity of various machines and systems, leading to complete automation with real-time tracking. This has improved production methods, increasing efficiency and reducing costs. In addition to this, manufacturers have adopted the use of advanced softwares such as Computer Aided Design (CAD) and Computer Aided Engineering (CAE) further improving the process of product design. These changes have made a mark in injection molding, reducing the production time and increasing the quality of products drastically. The global focus on sustainable manufacturing and environmental conservation have also played a key role in the advancement of injection molding technology, with manufacturers developing advanced materials such as biodegradable plastics. 


Injection molding machines play an important role in the plastic processing sector. These machines work by injecting molten plastic into a mold, and upon cooling, the plastic solidifies to assume the shape of the mold. As we have seen, the injection molding machine has various components which work together to complete the injection molding process. Before you select an injection molding machine, it is essential to understand the various features and specifications of the machine to ensure that it can handle your injection molding project effectively. 


Gary Liao

Gary Liao

Gary Liao is the Engineering Manager of TDL Company and has more than 20 years of mold design experience.

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