What’s a Plastic Injection Molding Machine & How Does It Work?

Plastic Injection Molding Machines

Choosing the best manufacturing process, such as injection molding machines, profile extrusion, or thermoforming for your plastics project can seem overwhelming. You need to consider the types of material you need, the price point you aim to hit, the size of your run, and what you want the finished product to look like. On top of that, you must ensure that you can get your parts and products delivered in the time frame you need them.

Manufacturing has been slowly moving overseas in an attempt to lower costs. But the fact is, expensive shipping costs, longer wait times, and inconsistent quality can end up causing your plastic part or product to cost more than you initially thought.

A Guide To Plastic Injection Molding Machines

The Injection Unit: This component of the injection molding machine is responsible for heating and injecting resins into the plastic injection mold. A hopper, barrel, ram injector, reciprocating crew, screws, and nozzle are among the components of the device. The material is fed to a barrel through a hopper, which is a huge container with an open bottom.

The injection molding material is forced forward via a heated area by the barrel, which is equipped with a ram injector. Injection molding materials are propelled forward using reciprocating screws. The resins are then forced to travel towards the plastic injection mold through the slots in the screw. The resins and molten metal are melted in the heating channel.

The Clamping Unit. Molds are normally made in two sections, which are clamped together. The injection molds are fastened together just before the injection procedure. Each half must be secured to the platen, which resembles a huge plate.

The molds are opened with a clamping motor after the injected molten resins have cooled to the desired temperature. The solid plastic object was forced out of the open chamber by an ejection system with an ejection bar in the back half of the mold.

The Mold Base. The mold core and the mold cavity are the two major components of a mold. These two components are attached to the platens of a mold base to form a pair. The support plate, sprue bushing, and locating ring on the front part of the molded baseline the mold base with the nozzle.

An ejection system and a support plate are located on the back part of the mold base. As previously stated, the ejection system includes an ejection bar. It aids in the removal of solidified plastic injection molds from the mold cavity, as the name implies.

The Mold Channels: Mold channels are the channels via which plastic resins flow into mold cavities. To make a single component, these channels are incorporated into the mold design. The molten plastic enters through the sprue and then continues into the runners.

The runners guide the plastic resin through a gate, allowing the molten resin to fall into the hollow. Cooling channels are occasionally made to let water travel along the mold walls and speed up the cooling process of molten plastic.

Mold Design. In addition to the mold base and mold channels that are discussed above, there are a number of other designs that should be considered while building a mold. Complex geometries and features must be included in the plastic injection

Some devices can also be introduced along the parting direction into the injection mold. The injection moulding design includes the draft angle that is applied to the mold walls.

. In addition to the mold base and mold channels that are discussed above, there are a number of other designs that should be considered while building a mold. Complex geometries and features must be included in the plastic injection mold design for instance the undercuts.Some devices can also be introduced along the parting direction into the injection mold. The injection moulding design includes the draft angle that is applied to the mold walls.

Mold Tooling. Let's take a deeper look at injection mold tooling. Molds manufactured of steel or aluminum are used in custom tooling. Each metal has its own set of benefits and is employed in different ways, of course, based on the sort of plastic part needed. The two primary components of the part cavity are the mold core and mold cavity. When the mold is closed, the area between these two forms the part cavity, which is then injected with molten plastic resin.

Specifications Of Machines. A plastic injection molding machine has different specifications. Injection molders are typically characterized by the clamp force tonnage that they provide. The pressure used to inject the molten resins also plays a big role. High tonnage is required for materials that require a high injection pressure. The shot capacity, clamp stroke, mold thickness, and platen size are all critical variables that must be considered when purchasing a plastic

. A plastic injection molding machine has different specifications. Injection molders are typically characterized by the clamp force tonnage that they provide. The pressure used to inject the molten resins also plays a big role. High tonnage is required for materials that require a high injection pressure. The shot capacity, clamp stroke, mold thickness, and platen size are all critical variables that must be considered when purchasing a plastic injection molding machine

TYPES OF INJECTION MOLDING MACHINE

There is various type of injection molding machine available based on their function and utilization. The cost of the machine is increased depending on their functions and size. The simplest injection molding machine is a hand injection molding machine with a very low cost and the costliest machine may be a screw type automatic microprocessor injection molding machine.
Drawing: Vertical hand injection machine

The simplest mode of injection molding machine may be considered as a hand operated mold which is apt equipment to understand the interaction of major operating parameters. The machine consists of a barrel, plunger, bend heaters, along with energy regulators, rack and pinion system for injecting the material by the plunger a torpedo and nozzle. The clamping is done manually on a working table. The machine is fitted on the working table. Heating is set manually. The capacity of the machine is available from 0.5 Oz 02 Oz. Once heating is achieved the production starts manually. The quality of the product completely depends upon the skill of the operator. The heating set point is achieved by heat and trial method. Although the temperature controller may be fitted on the machine the set point completely depends on the quantity of product produced by the operator. The cycle time is completely variable and it depends on the competent of the operator. The function of torpedo is to help the material for proper melting and create back pressure to help him mixing.

Plunger type injection molding machine:

The plunger type injection molding machine is the available horizontal or vertical type and operated pneumatically or hydraulically. The clamping and injection may be semi or automatic.

Drawing: Vertical and Horizontal plunger type injection molding machine

In a semi-automatic type, the clamping cylinder and the injection cylinder are operated by levers which is connected the pneumatic or hydraulic cylinder. In automatic type, the cylinder is actuated automatically to set times.

Screw type injection molding machine:

The screw type injection molding machine consists of a hopper, a reciprocating screw & barrel assembly, and injection nozzle. This system confines and transports the plastic as it progresses through the fittings, compressing, degassing, melting, injection and packing stage.
Drawing: Screw type injection molding machine

A single screw injection molding machine for thermoplastic, showing the plastic sizing screw, a barrel, band heaters to heat the barrel, a stationary platen, and a movable platen.

Plunger-Plunger Injection Molding machine:

As the plastic industry developed a second type plunger machine appeared, known as to two-stage plunger. This type of equipment involved two plunger units set on top of other the one-two plasticize the material and feed it to another cylinder that consists of a chamber to heat the plastic material by conduction and plunger that operates as a shooting plunger and push the plasticize material into the mold.

Advantage:

Faster than the conventional machine (single plunger)

No pressure loss and countered in compacting the granules

Allow larger parts with a more projected area

Disadvantage:

Extra construction for pre-plasticizing so cost is more

Screw Plunger Injection Molding Machine:

Later still variation appeared in which first plunger stage (also known as a pre-plasticizer) was replaced by a rotating screw. In this case, the action of the screw serves to work and melt the resin and feed it into the second plunger unit where the injection ram forces it towards mold.

Advantage:

Better mixing and shear action of the plastic melt

The broader range of stiffer flow

Heat sensitive material can be the processor

The color change can be handled in shorter time

Lower stresses are obtained in the molded form

Disadvantage:

Higher cost in extra construction for pre plasticizing unit

Longer cycle time then reciprocating screw type machine