Introduction

An injection molding machine is a piece of equipment that is widely used in industrial production. Its main function is to inject molten plastic into a mold and get molded plastic parts after cooling.

Meaning of Injection Molding Machine

Injection molding machine, also known as injection molding machine or injection machine. Many factories call it beer machine (píjī), and injection molded products are called beer parts.

It is the main molding equipment that uses plastic molding molds to make plastic products of various shapes from thermoplastics or thermosetting materials.

Injection molding machines can be divided into vertical, horizontal and vertical-horizontal composite types according to the arrangement of injection devices and clamping devices.

Injection molding machines include hybrid injection molding machines, electric injection molding machines, hydraulic injection molding machines, etc.

Structural Composition of Injection Molding Machine

Injection molding machines typically include an injection system, clamping system, hydraulic transmission system, electrical control system, lubrication system, heating and cooling system, safety monitoring system, and more.

Injection System

Injection System Function

The injection system is one of the most important parts of an injection molding machine. There are generally three types: plunger, screw, and screw pre-plastic plunger.

The screw type is the most commonly used. Its function is to heat and melt a certain amount of plastic in a specified time in one cycle of the injection molding machine, and then inject the molten plastic into the mold cavity through the screw at a certain pressure and speed.

After the injection is completed, the molten material injected into the mold cavity is kept fixed.

Injection System Composition

The injection system is composed of a plasticizing device and a power transmission device.

The plasticizing part of the screw injection molding machine is mainly composed of a feeding device, a barrel, a screw, a glue assembly, and a nozzle. The power transmission part includes an injection cylinder, an injection seat moving cylinder, and a screw drive device (melt motor).

Mold Clamping System

The Mold Clamping System’s Function

The mold clamping system’s function is to make sure the mold closes, opens, and ejects.

At the same time, after the mold closes, the mold gets enough clamping force to fight the mold cavity pressure that the molten plastic makes when it goes into the mold cavity, stop the mold from opening, and make the product bad.

Mold Clamping System Composition

Mold clamping system mainly consists of mold clamping device, machine twist, mold adjustment mechanism, ejection mechanism, front and rear fixed template, movable template, mold clamping cylinder, safety protection mechanism.

Hydraulic System

The hydraulic transmission system is responsible for powering the different actions needed by the injection molding machine and meeting the pressure, speed, temperature, and other requirements of each part of the injection molding machine.

It is made up of different hydraulic components and hydraulic auxiliary components. The oil pump and motor are the power sources of the injection molding machine. Different valves control the oil pressure and flow to meet the different requirements of the injection molding process.

Electrical Control

The electrical control system and the hydraulic system are reasonably coordinated to realize the process requirements (pressure, temperature, speed, time) and various program actions of the injection molding machine.

It is mainly composed of electrical appliances, electronic components, instruments (as shown in the figure “Instruments”), heaters, sensors, etc. There are generally four control modes: manual, semi-automatic, fully automatic, and adjustment.

Heating/Cooling

The heating system is used to heat the barrel and injection nozzle. The barrel of the injection molding machine generally uses an electric heating ring as a heating device, which is installed on the outside of the barrel and detected in sections with thermocouples.

Heat is conducted through the barrel wall to provide a heat source for material plasticization.The cooling system is mainly used to cool the oil temperature. If the oil temperature is too high, it will cause a lot of faults, so the oil temperature must be controlled.

Another place that needs to be cooled is near the discharge port of the material pipe. If it is not cooled, the raw material will melt at the discharge port, resulting in the failure of the raw material to be discharged normally.

Lubrication System

The lube system is a circuit that gives lube to the relative moving parts of the injection molding machine, like the moving plate, mold adjustment device, connecting rod hinge, and shooting platform, to save energy and make parts last longer. Lube can be regular manual lube or automatic electric lube.

Safety Monitoring

The safety device of the injection molding machine is mainly used to protect the safety of people and machines. It is mainly composed of safety doors, safety baffles, hydraulic valves, limit switches, photoelectric detection elements, etc., to achieve electrical-mechanical-hydraulic interlocking protection.

The monitoring system mainly monitors the oil temperature, material temperature, system overload, and process and equipment failures of the injection molding machine, and indicates or alarms when abnormal conditions are found.

Working Principle of Injection Molding Machine

The working principle of the injection molding machine is similar to that of the syringe used for injection. It uses the thrust of the screw (or plunger) to inject the plasticized molten state (i.e. viscous flow state) plastic into the closed mold cavity, and obtains the product after solidification and shaping.

Injection molding is a cyclic process. Each cycle mainly includes: quantitative feeding, melting and plasticization, pressure injection, mold filling and cooling, mold opening and taking out the parts. After taking out the plastic parts, the mold is closed again for the next cycle.

Operation of the injection molding machine: The operation of the injection molding machine includes three aspects: the operation of the control keyboard, the operation of the electrical control system, and the operation of the hydraulic system.

The injection process action, feeding action, injection pressure, injection speed, ejection type selection, monitoring of the temperature of each section of the barrel, and adjustment of injection pressure and back pressure are performed respectively.

The general screw injection molding machine molding process is: first, granular or powdered plastic is added to the barrel, and the plastic is melted by the rotation of the screw and the heating of the outer wall of the barrel.

And then the machine closes the mold and moves the injection seat forward, so that the nozzle is close to the gate of the mold, and then the pressure oil is introduced into the injection cylinder to push the screw forward.

So that the molten material is injected into the closed mold at a very high pressure and a faster speed with a lower temperature.Once the cooling time is over and the pressure is maintained (also known as pressure holding), the material solidifies and takes shape.

Then, the mold can be opened to remove the product (pressure holding is done to prevent the molten material from flowing back into the mold cavity, to add material to the mold cavity, and to ensure that the product has a certain density and dimensional tolerance).

The basic requirements for injection molding are plasticization, injection, and molding. Plasticization is the prerequisite for achieving and ensuring the quality of molded products, and in order to meet the requirements of molding, injection must ensure sufficient pressure and speed.

At the same time, because the injection pressure is high, the mold cavity pressure is also high (generally 20~45MPa), so the clamping force must be large enough. It can be seen that the injection device and the clamping device are key components of the injection molding machine.

There are three main aspects to evaluate plastic products. The first is the appearance quality, including integrity, color, gloss, etc.

The second is the accuracy between size and relative position; the third is the physical properties, chemical properties, electrical properties, etc. corresponding to the purpose.

These quality requirements are different according to the different occasions of product use.The defects of the products are mainly in the design, manufacturing accuracy, and wear degree of the mold.

But in fact, the technicians of plastic processing plants often suffer from the difficult situation of using process means to make up for the problems caused by mold defects without much effect.

Making adjustments to the process is a necessary way to improve the quality and output of products. Since the injection unit itself is very short, if the process conditions are not well controlled, there will be a lot of waste products.

When adjusting the process, it is best to change only one condition at a time and observe it several times.If the pressure, temperature, and time are adjusted together, it is easy to cause confusion and misunderstanding, and it is unknown why there is a problem.

There are many measures and means to adjust the process. For example: there are more than ten possible solutions to solve the problem of product filling. Only by selecting one or two main solutions to solve the crux of the problem can the problem be truly solved.

In addition, attention should be paid to the dialectical relationship in the solution.For example: if the product is dented, sometimes you need to increase the material temperature, sometimes you need to decrease it;

Sometimes you need to increase the material quantity, sometimes you need to decrease it. You need to recognize the feasibility of reverse measures to solve the problem.

Horizontal Injection Molding Machine

This is the most common type. Its mold clamping part and injection part are on the same horizontal center line, and the mold is opened in the horizontal direction.

Its characteristics are: the machine body is short, easy to operate and maintain; the machine has a low center of gravity and is relatively stable to install; the product can be automatically dropped by gravity after being ejected.

And it is easy to achieve full automatic operation. At present, most injection molding machines on the market use this type.

Features of horizontal injection molding machine: Even large machines have no height restrictions on the factory where they are placed due to their low machine body.

In situations where the product can fall automatically, automatic molding can be achieved without the use of a manipulator. Due to the low machine body, material feeding is convenient and maintenance is easy.

The mold needs to be installed by a crane. When multiple machines are arranged in parallel, the molded products are easily collected and packaged by the conveyor belt.

Vertical Injection Molding Machine

The clamping part and injection part are on the same vertical center line, and the mold opens in the vertical direction. So, it takes up a small area, is easy to put inserts in, is convenient to load and unload molds, and the materials that fall from the hopper can be plasticized more evenly.

But the product doesn’t fall out automatically after being ejected, and it has to be taken out by hand, which isn’t easy to achieve automatic operation.Vertical injection molding machines are suitable for small injection molding machines, generally more for injection molding machines below 60 grams, and not suitable for large and medium-sized machines.

Features of Vertical Injection Molding Machines

The injection device and the clamping device are on the same vertical center line, and the mold is opened and closed in the up and down direction. Its floor area is only about half of that of the horizontal machine, so the productivity converted into floor area is about twice.

Insert molding is easy to achieve. The mold surface is facing up, so it is easy to put the insert in and position it. If you use a machine with a fixed lower template and a movable upper template, you can combine a belt conveyor device with a manipulator to easily achieve fully automatic insert molding.The weight of the mold is supported by the horizontal template for up and down opening and closing.

And the phenomenon of the template being unable to open and close due to the gravity of the mold, similar to the horizontal machine, will not occur. It is conducive to maintaining the accuracy of the machine and mold for a long time.

A simple manipulator can remove each plastic part cavity, which is good for precision molding. The general clamping device is open around it, and it is easy to configure various types of automation devices, which is suitable for the automatic molding of complex and delicate products.

The belt conveyor device can be easily installed through the middle of the mold, which is convenient for automatic molding production. It is easy to ensure the consistency of the resin fluidity and mold temperature distribution in the mold.It has a rotating table, a moving table, and an inclined table, which can easily achieve insert molding and in-mold combination molding.

During small batch trial production the mold structure is simple, low cost, and easy to unload. After experiencing many earthquakes, the vertical machine has better earthquake resistance than the horizontal machine due to its low center of gravity.

Angle Injection Molding Machine

The injection direction and the mold interface are on the same plane. It is particularly suitable for flat products where gate marks are not allowed to be left in the processing center.

It occupies a smaller area than the horizontal injection molding machine, but the inserts placed in the mold are prone to tilt and fall. This type of injection molding machine is suitable for small machines.

The injection screw axis of the angle injection molding machine and the mold clamping mechanism template motion axis are arranged perpendicular to each other, and its advantages and disadvantages are between vertical and horizontal.

Because its injection direction and the mold parting surface are on the same plane, the angle injection molding machine is suitable for molds with asymmetric geometric shapes with side gates or products where gate marks are not allowed to be left in the molding center.

Multi-Mode Turntable Injection Molding Machine

This is a special injection molding machine with multi-station operation. It has a turntable structure for the mold clamping device and the mold rotates around the shaft. This type of injection molding machine can make full use of the plasticizing ability of the injection device, which can shorten the production cycle and improve the production volume of the machine.

So, it’s especially good for making a lot of stuff that takes a long time to cool and shape or needs more time for the inserts to be put in. But because the clamping system is big and complicated, the clamping force of the clamping device is usually small, so this kind of injection molding machine is used a lot for making things like plastic shoe soles.

The general injection molding machine consists of an injection device, a clamping device, a hydraulic system, and an electrical control system.

Injection molding has three basic requirements: plasticizing, injection, and molding. Plasticizing is the basis for ensuring and guaranteeing the quality of molded products. In order to meet the requirements of molding, injection must ensure sufficient pressure and speed.

At the same time, due to the high injection pressure, a high pressure is generated in the mold cavity accordingly (the average pressure in the mold cavity is generally between 20 and 45 MPa), so there must be a sufficiently large clamping force. It can be seen that the injection device and the clamping device are key components of the injection molding machine.

The Working Process of the Injection Molding Machine

Mold Closing And Tightening

The injection molding machine cycle generally starts with the mold closing. The mold is first closed quickly with low pressure. When the moving and stationary molds are about to touch, the mold closing power system automatically switches to low pressure and low speed.

When it is confirmed that there is no foreign matter in the mold, it switches to high pressure and closes the mold. The injection device moves forward and injects.

Once you’ve made sure the mold is closed tight enough, the injection machine moves forward to connect the nozzle and the mold. When the nozzle and the mold are completely connected, you can connect the pressure oil to the injection cylinder.

Then the screw connected to the cylinder piston pushes the molten material at the front of the screw into the mold cavity at high pressure and high speed. At this time, the pressure that the screw head puts on the molten material is called injection pressure.

Pressure Maintenance

The molten plastic that gets injected into the mold cavity shrinks because the mold is cold. To make a good, solid part, you have to keep some pressure on the molten stuff to make up for the shrinkage. The pressure the screw puts on the molten stuff is called the holding pressure. During the holding pressure, the screw moves forward a little bit to make up for the shrinkage.

Product Cooling And Pre-Plasticization

Once the holding pressure is applied to the point where the molten material in the mold cavity can no longer flow back from the gate, the holding pressure in the injection cylinder can be released, allowing the product to cool and solidify in the mold.

At this time, the screw rotates and retracts, driven by the hydraulic motor (or electric motor). The amount of screw retraction during plasticization indicates the volume of molten material accumulated in the screw (i.e., the amount of pre-plasticization).

The cooling of the product and the plasticization of the screw usually happen at the same time. Normally, the screw plasticization time should be shorter than the product cooling time. The injection device pulls back and the mold opens to eject the product.

After the screw plasticizing metering is completed, in order to prevent the nozzle from forming cold material due to long-term contact with the cold mold, it is often necessary to withdraw the nozzle from the mold device and retreat. After the molten material in the mold cavity is cooled and finalized, the mold clamping device will open the mold and automatically eject the product.

Key Ooints for Injection Molding Machine Operation

Before Starting the Machine

Before you start the injection molding machine, check if there is water or oil in the electrical control box. If the electrical appliance is wet, don’t start the machine. The maintenance staff should blow dry the electrical parts before starting the machine.

Before you start the injection molding machine, check if the power supply voltage is within the required range, which is generally ±6%. Check if the emergency stop switch and the front and rear safety door switches are working properly.

Make sure the motor and oil pump are rotating in the right direction. Check if all the cooling pipes are clear and long enough, and connect the cooling water to the cooling water jacket of the oil cooler and the end of the barrel.

Before you start the injection molding machine, check if there is oil in each moving part and add enough oil. Turn on the electric heating to heat each section of the barrel.Once the temperature of each section reaches the requirement, keep it warm for a period of time to stabilize the machine temperature.

The holding time varies according to the requirements of different equipment and plastic raw materials. Add enough plastic in the hopper. According to the requirements of different plastics for injection molding, some raw materials are best dried first.

Cover the heat shield on the barrel to save electricity and extend the life of the electric heating coil and current contactor  As shown in the figure “Operation of Injection Molding Machine.

Operation Process

Don’t remove the safety door for convenience. Pay attention to the temperature of the pressure oil. The oil temperature should not exceed the specified range. The ideal working temperature of the hydraulic oil should be maintained between 45-50℃, and it is generally more appropriate to be in the range of 35-60℃. Pay attention to adjusting the travel switches to avoid collisions when the machine is in motion.

End of Work

After the injection molding machine is operated, the plastic in the barrel should be cleaned to prevent the residual material from oxidation or long-term heat decomposition. The mold should be opened to keep the toggle mechanism in a locked state. The workshop must be equipped withThere is a lifting device. Be very careful when installing and removing the mold to ensure production efficiency.

Conclusion

The injection molding machine is a widely used medical devices production . Its processing manufacturing process requires heating, pressurizing, injection molding, cooling and pouring of raw materials to achieve the manufacture of plastic injection molding.