What is An Injection Molding Machine? What Types are There?

What is An Injection Molding Machine?

Most injection molding machines are mainly composed of two parts: an injection device and a clamping unit. The injection device is responsible for heating the plastic pellet material into a liquid. The clamping unit holds the mold and provides the force required for mold closing, mold clamping and other actions. Two advantages of injection molding machines are their fast processing and economical costs.

How to Choose an Injection Molding Machine?

Special attention should be paid to the selection of the type and size of an injection molding machine. Larger products require a larger machine, and usually require more professional attention for proper operation. Special attention must also be paid to the injection requirements such as mold opening stroke, mold clamping force, injection volume, screw compression ratio, injection speed, finished product appearance, performance, etc. The range of products desired will determine the type of injection machine needed.

What Types of Injection Machines are There?

There are many types of injection molding machines, generally categorized by the following methods:

Classification Method 1: Power Drive Method

• Hydraulic Injection Molding Machines

Hydraulic injection machines, as the name implies, are powered by hydraulics. While this method is very efficient, one drawback is that they cannot be allowed to sit idle. They must run continuously to maintain a constant temperature of the melted plastic. Startup and shutdown require time and special attention to avoid damage to the machine. During startup, plastic that has not reached its proper temperature needs to be discarded for recycling. During shutdown you may need to remove unwanted resin from the barrel and screw to prevent resin from hardening and clogging the barrel during startup.

• All-Electric Injection Molding Machines

Compared with hydraulic injection machines, the price of all-electric injection molding machines is higher, but all-electric injection molding machines do not need to operate continuously, nor do they need to adjust the temperature. Injection molding is relatively stable and can be more efficient than all-electric. All-electric injection machines have no hydraulic system, so there is no risk of liquid leakage in the machine.

• Hybrid/ Servo Hybrid Injection Molding Machines

Hybrid injection molding machines are highly efficient and economical. They integrate the advantages of hydraulic type and all-electric type machines, and are commonly used by many companies now. These machines have a moderate cost, and are quite energy efficient, which is important when energy costs are a major consideration.

Hybrid injection molding machines use a servo motor to run a hydraulic pump, which provides the hydraulic pressure to provide power to the components of the machine. The clamping mechanisms are simpler, more accurate and durable, which greatly reduces the cost of maintenance. The servo hybrid type can supply higher injection pressure and clamping pressure than the all-electric types.

Classification Method 2: Operating Direction

• Vertical Injection Molding Machines

As the name suggests, a vertical injection molding machine operates in a vertical position. It is usually used to manufacture relatively small parts, and can operate with a relatively small footprint, so is very saving space. Vertical injection machines are often combined with a rotary table or conveyor belt to improve production efficiency.

• Horizontal Injection Molding Machines

Horizontal injection molding machines are the most widely used injection machines. They have a relatively low body height, are fast molding, and are convenient to operate and maintain.

Classification Method 3: Applicable Raw Materials

• Thermoplastic Injection Molding Machines

Thermoplastics will melt into liquids when heated, and solidify when cooled. Common thermoplastics include PE, PP, ABS, TPU, etc. Thermoplastic injection machines heat plastic pellets and then inject the liquid, melted plastic into a mold. After cooling, the plastic returns to a solid state, and the plastic parts are ejected from the machine.

• Thermoset Plastic Injection Molding Machines

Thermoset plastics will change from liquid to solid after heating. This transformation can usually only take place once, so they cannot be recycled like thermoplastics, making them less environmentally friendly. Common thermosetting plastics include FRP and Melamine. A thermoset plastic injection machine injects the plastic liquid into the mold where it is heated. The plastic solidifies, completing the final product.

• Powder Injection Molding Machines

Powder injection molding can include "metal injection molding" (MIM), or "ceramic injection molding" (CIM). The raw materials used are precision-treated, fine metal or ceramic powders and bonding materials. Common applications are portable products, smart devices, electronic products, etc. Powder injection is often used to manufacture small parts with high precision and complex appearances, especially metal. Parts produced by powder injection have high strength and high density.

Classification 4: Clamping Structure

• Single-Cylinder/ Double-Cylinder/ Four-Cylinder Direct Pressure Injection Molding Machines

Injection machines can be divided into single-cylinder, double-cylinder and four-cylinder according to the number of hydraulic cylinders that operate them. When using a single-cylinder type hydraulic driver on a large mold, it will be difficult to control the accuracy of the mold clamping. Single-cylinder, direct-pressure injection machines have been gradually replaced by multiple-cylinder, direct-pressure injection machines. Double-cylinder injection machines use two hydraulic cylinders that provide a parallel injection action. The injection speed of the double-cylinder will be slower than that of the single-cylinder under the same pressure, but the injection pressure will be increased. 

Four-cylinder, direct pressure clamping machines are designed to provide automatic balance correction during clamping. In the past, a common problem with four-cylinder direct-pressure clamping was the unbalanced force applied to the mold. This often resulted in damage to the mold and the product not meeting accuracy requirements. But direct pressure clamping machines have been greatly improved. Although more expensive than toggle type injection molding machines, direct pressure types have long life times, and because they provide direct mold clamping, they have no resistance during travel, so have low maintenance costs.

• Toggle Type Injection Molding Machines

Toggle type molding machines, have a mechanical device consisting of two bars joined together with a pivoting toggle to amplify force. The end of one bar is attached to a stationary platen, and end of the second bar is attached to a movable platen. When the mold is opened, the toggle is in the shape of a V. When the pressure is applied to the pivot, the two bars form a straight line. Although the structure of the toggle type injection machine is more complicated, ii has a simple operation, and has lower operating and machine costs.

Classification Method 5: Injection Structure

• Monochrome Injection Molding Machines (Single-Component Injection)

Monochromatic injection means that the entire plastic component is of the same color during injection. Monochromatic injection is the form most used at present. Monochromatic injection can also be used to inject products with two different colors. The color injection molding machine first injects one color, to form a semi-finished product, and then injects a second color to complete the production.

• Multi-color Injection Molding Machines (Multi-Component Injection)

A multi-color injection machine can simultaneously inject plastic components with two or more different colors. At present, the most widely used multi-color injection molding machine is the two-color injection molding machine. In recent years, multi-color injection technology has gradually become a hot trend in the industry due to its environmental friendliness, high efficiency, good performance and other characteristics.

In conclusion, when considering which injection molding machine you should use for the products you want to produce, first think about the characteristics of the product, the company's budget, and how large of volumes you will be producing and for how long. Each type of injection molding machine has its advantages and disadvantages. For example, if the company has a limited budget for energy expenditure, it can choose a type of injection molding machine that saves electricity. If there is a certain requirement for the precision of molding, quality should be given priority when choosing.