Components of an Injection Mold Machine

An injection molding machine is comprised of four main components: the base, the hopper, the barrel, and the clamping unit. There are also smaller components such as the nozzle, ejector pins, split mold, clamping unit, injection unit and hydraulic unit.

The base holds all the other parts and the electronics needed to run the machine. The electronics on the device have to control a range of heaters, hydraulics, sensors, and injection pressure.

Below please find the components of injection molding and how they work:

The hopper is the component where the plastic material is poured before the injection molding process can begin. The hopper usually contains a dryer unit to keep moisture away from the plastic material. It may also have small magnets to prevent any harmful metallic particles from entering the machine. Next, the plastic material is poured into the following major component from the hopper, called the barrel.

The barrel, or the material tube and barrel, heats the plastic material into a molten state to let plastic flow through the barrel. The screw inside injects the plastic into molds or cavities in the clamping unit. Therefore, the temperature in the barrel needs to be adequately regulated to maintain the appropriate temperature for different types of plastic material. The function of the cylinder is to transport, compact, melt, agitate and press the plastic before it reaches the injection mold.

Reciprocating screws were created in the mid-1950s, and by 1960 they quickly began to replace the older systems. The advantage of the reciprocating screw design is that it helps manage the temperature of the molten plastic.

The screw moves plastic through the barrel. First, as the pellets are fed from the hopper into the barrel, the screw is rotated, driving the material forward while more pellets are added. Second, the flights provide a continuous mixing action that distributes heat evenly throughout the mass. This mixing also helps to purge the mechanism of different materials and any colors left behind from an earlier production runs on the same injection molding machine.

The reciprocating screw is responsible for providing most heat to the thermoforming plastic. This is because the diameter of the screw decreases as it approaches the tip. As a result, plastic pellets are pulled along by the flights, compressed into a tighter space, and cut by turning flights. This action creates friction that mixes the pellets uniformly and heats them to the proper temperature.

An injection molding machine can have different types of heaters for maintaining temperatures in conduits and nozzles and heating molds and platens. A heating element can be attached to the barrel and used to melt the hopper's molding material to become liquified material. Some of the different types of injection molding heaters include band heaters, coil/nozzle heaters, cartridge & strip heaters, and insulated cloth heating jackets.

The nozzle is an injection molding component located at the bottom of the machine`s ejector system. It pushes liquified plastic out of the barrel and into the mold. The nozzle rests against a surface on the mold called the sprue bushing and locating ring, which helps center the nozzle on the mold. Today, nozzles can provide a variety of functions, including filtering, mixing, and shut-off of melt flow.

Nozzle filters can minimize the clogging of gates and hot runner tips from foreign material or contamination in the melt stream. Mixing nozzles can enhance the dispersion and mixing of additives, improving molded part quality while reducing the volume and cost of additives. Shut-off nozzles can reduce drool in injection molding operations where the press is frequently disengaged from the mold, such as in many two-shot molding applications.

Ejector pins are vital in creating parts. They are an essential component of the ejection system in molds, which determines the outcome of products in an injection molding process.

The metal injection mold comprises two parts: A and B sides. After the molten material in the mold is cooled, both parts are separated to remove the solid plastic. Injection molds are built so that when they are opened, the A-side half is lifted, leaving the formed part and the B-side.

Extraction pins are found on the B-side half of the injection mold, where they push the formed part out of the mold (or extract it). The pin mark is commonly imprinted on finished products as a dent.

There are many types of ejector pins. Through-hard ejector pins are heat-treated to ensure consistency in the hardness through the diameter of the pin. A case hardened ejector pin is much harder than the through-hard pins and is suitable for die casting ejection systems. A black ejector pin is coated with a black surface treatment, allowing it to self-lubricate and withstand high temperatures up to 1000°C.

In injection molding, a parting line is where two halves of a mold meet when closed, especially on a split mold. The plastic product created by the injection mold is divided into two parts, and the line separating the two mold haves are called parting lines. Split molds are one type of injection mold, where the jaws form the mold cavity. The jaws are injected diagonally on the nozzle side and are then moved on the diagonal to the outside when the mold opens with a pull tab. Then the injection molded part is released.

The jaws can also be guided on the ejector side. They are then moved, during or after opening the mold, mostly with hydraulic cylinders or mechanically using springs or air.

The purposes of the clamping unit are to open and close an injection mold and eject the injection-molded products. The two main types of clamping systems are the hydraulic and toggle configurations. The hydraulic clamp system has one or more hydraulic cylinders, while the toggle clamp system has a series of linkages.

The clamping unit has two large clamping plates that hold the injection mold. A mold consists of two steel parts attached to each of the large plates on the clamping unit. When the machine is ready to inject plastic into the mold or cavity, the clamping unit closes the two independent plates. It lets the plastic flow into the cavity to create the part. The plastic component is then cooled into a solid. Once the plastic is cool enough, the clamping unit opens the injection mold, and the part falls out of the mold halves and is collected in a bin.

Other components of the clamping unit include machine ejectors, a moveable platen, a stationary platen, and tie bars.

A central component of Injection Molding Machines is the injection unit, which comprises other parts. The injection unit's purpose is to melt the raw material and guide it into the mold. The injection unit consists of the hopper, the barrel, and the screw. The polymer granules are first dried and placed in the hopper, then mixed with the coloring pigment or the other reinforcing additives.

The granules then feed into the barrel, where they are simultaneously heated, mixed, and moved towards the mold by the screw motion. The screw and barrel have the same geometry, optimized to help build up the pressure to the correct levels and melt the material.

A hydraulic system or unit is crucial in Plastic Injection Molding Machines. The system may be running continuously during production cycles. Nozzle approach, injection of the plunge screw, extruder screw rotation, plus the closing of the mold require a significant number of motion-activated sub-circuits. Granular plastic material requires a highly steady motion to move smoothly through the heated plasticized state as it flows into the mold during the screw rotation and plunge phase. The quality of the injection molded product could be compromised if the hydraulic motions cause any irregularities.

A necessity for force control sub-circuits also exists to keep the mold from opening and to hold nozzles in place along the sprue of the injection mold. During injection molding, these functions are critical. Adjusting and monitoring hydraulic pressure controls the mechanical pressure.

The mechanism for the screw, which is moved by the hydraulic motor, coupled with the cylinder that propels the screw forward, makes up a complex mechanism that requires exacting hydraulic seals during the injection and packing process of the mold. However, improvements in modern seal technology produce leak-free hydraulic machines suitable for molding plastic products that can even be used in the medical and food industries.