Gas Assisted Injection Molding Factory / Manufacturer

Gas-assisted injection molding technology is widely used in household appliances, automotive, furniture, office supplies, medical device, aerospace, farming, machinery, electronics,  and other industries.

→Plate and cabinet-shaped products, such as plastic furniture, electrical appliance housing, etc., Gas-assisted injection molding can reduce the weight of molded plastic products, prevent shrinkage and deformation, and improve the surface quality of the molded plastic products while ensuring the strength of the molded plastic products.

→Large molded plastic parts, such as automotive dashboard bases, automotive door panels, automotive exterior parts, heat dissipation grilles, etc., to reduce the warpage of the molded plastic products and the requirements for injection volume and clamping force of the injection molding machine while ensuring rigidity, strength and surface quality.

→Rod and tube-shaped products, such as handles, knobs, steering wheels, joysticks, paddles, etc., can reduce the weight of molded plastic products and shorten the molding cycle while ensuring strength.

We supply one-stop gas assisted injection molding service from product design, mold manufacturing to injection molding and product assembly.

The melt injection volume is generally 50% – 80% of the filling volume, cannot too little, otherwise, the gas will blow the melt through.

It must be an inert gas, usually nitrogen gas, which provides the pressure to push the melting plastic into the end of the mold.

When the product is filled with gas, the gas pressure becomes the holding pressure, and simultaneously, cooling begins.

As cooling is completed, the gas is recovered, and the air pressure inside the mold is reduced to atmospheric pressure.

When cooling is complete, open the mold and the product is ejected just like a regular injection molding process.

After the product is ejected from the mold cavity, the robot takes out the product and completes the gas-assisted injection molding.

Table of Content

Gas Assisted Injection Molding (GAM) is a new injection molding process that was introduced in the mid-1980s.

It is to inject a certain amount of molten plastic material into the mold cavity and then inject the high-pressure nitrogen gas into the cavity through the gas injector. The nitrogen gas provides high pressure to push the melting plastic into the end of the mold; The high-pressure nitrogen gas makes the plastic parts form the required hollow section and good shape.

Gas-assisted injection molding combines the advantages of structural foam injection molding and regular plastic injection molding, reducing the pressure of the melting material in the mold cavity and avoiding the rough surface produced by structural foam injection molding has high practical value.

There are two main types of gas-assisted injection molding processes, internal gas-assisted injection molding and external gas-assisted injection molding, which we will introduce separately.

Internal gas-assisted molding process is more widely used than external gas-assisted molding process.

Internal gas-assisted molding is particularly effective in saving material for tubular and bar-shaped plastic parts, such as car handles, seat armrests, window frames, and wood-like furniture. The material saving rate of these parts is as high as 20%-40%. For large flat parts, such as car door panels, refrigerator trays, car interior and exterior parts, etc.

The ribs can be strengthened by gas-assisted molding,It can be eliminated the warpage and deformation issues caused by the residual stress in flat parts and can strengthen the molded flat parts.

The cycle time for internal gas-assisted molding is also significantly reduced, as the products have hollow sections and thin cross-sections and can be cooled down quickly compared to the solid sections.

External Gas Assisted Injection Molding (EGAIM) is a new technology derived from internal gas-assisted injection molding technology, also called surface gas-assisted molding.

The difference with internal gas-assisted injection molding is that the gas is injected between the mold and the melting plastic instead of directly into the melting plastic to push the melting plastic to fill the mold cavity,It is a great production process to improve the shrinkage by compensating the melting plastic.

However, at this stage, the process is not widely used in actual production applications because the deformation pattern of different types of polymers under gas injection is not complete and clear, and further in-depth systematic research is needed.

The molding process requires a constant gas pressure to compensate the product shrinkage and improve the product’s surface quality. The gas pressure is applied evenly on the non-cosmetic surfaces and the opposite end is tightly injected into everywhere of the mold to create its precise shape. The final surface is so precise that it also includes the fine texture and pattern of the molded plastic parts.

External gas-assisted injection molding process has certain advantages in molding products with reinforced ribs structure and some thin-walled and large flat plastic parts, commonly used in ribs, spokes, columns, bushings or other projections, is a kind of extended gas-assisted injection molding, used to compensate for the volume shrinkage due to uneven wall thickness, for example, can effectively avoid the appearance of shrinkage marks on its surface, but also reduce the internal stress, and can reduce the issue of deformation and warpage of the product after injection, mainly used in office equipment, electronic products, high-end daily necessities and other areas requiring high precision.

3.1) Lower Injection Pressure

Gas Assisted Injection Molding technology injects much less melting material into the mold cavity than the whole cavity volume at a time, resulting in a lower injection pressure of 10-75% of the regular injection pressure.

→Lower injection pressure results in lower residual stresses, thus minimizing warpage, The low residual stresses also improve the dimensional tolerances and stability of the product.

→Low injection pressure reduces or eliminate the flash defects.

→Low injection pressure reduces the clamping force requirement and allows smaller tonnage machines.

3.2) Save Raw Plastic Materials

The product is partially hollow, thus reducing the raw plastic material; Products produced by gas-assisted injection molding can save up to 35% of raw plastic material compared to regular injection molding, depending on the product’s shape, structure and requirements.

3.3) Improve Surface Quality

Regular injection molded products will have sink marks at the thick areas, such as behind the Rib & Boss, resulting from uneven shrinkage.

However, in the gas-assisted injection molding process, the shrinkage of the part is compensated by nitrogen gas, which makes the product shrink from the inside goes out, so the part’s surface will be in close contact with the mold and no sink marks will occur. So there will be no such marks on the cosmetic surfaces after gas-assisted injection molding.

3.4) Increase The Strength And Stiffness of The Product

Gas Assisted Injection Molding enables the uniform filling of plastic parts with large differences in wall thickness, avoiding the resulting defects of internal stress, and enhancing the strength and stiffness of plastic parts by setting up structures such as ribs with air channels.

3.5) Shorten The Molding Cycle Time

Regular injection molding, due to the thick ribs, and a lot of bosses, often requires a certain amount of injection pressure and holding pressure to ensure that the product is filled well and shaped.

However, WIth Gas Assisted Injection Molding,The product’s exterior looks like a very thick, but the interior is hollow, the cooling time is shorter than regular solid products, and the reduced holding and cooling time reduce the total cycle time.

3.6) Extend The Mold Life

Regular injection molding process in the injection process, often with very high injection speed and pressure, Make the parts and the gate around easy to have flash, and mold often needs to repair.

After with Gas Assisted Injection Molding, the injection pressure, injection holding pressure and clamping pressure are reduced at the same time, And the pressure on the mold is reduced accordingly, so the mold maintenance times is greatly reduced.

3.7) Reduce The Mechanical Wear And Tear of The Injection Molding Machine

Due to the reduction of injection pressure and clamping force, the pressure on the main parts of the injection molding machine: tie bars, toggle, plate, etc. is reduced accordingly, so the wear and tear of the main parts are reduced and the life span is extended, reducing repairs and replacements times.

3.8) Applied To Finished Products With Large Thickness Variations

the thick part can be applied as a gas channel to eliminate surface defects generated by uneven wall thickness with gas holding pressure.

3.9) Others

Using gas-assisted injection molding allows designers to design more complex products, while mold makers can simplify mold structures. The increasing functionality of the product and the reduction in the number of components allows for shorter production cycles without the need for assembly and post-trimming work.
The production of molded CD trays and motor vehicle electronic center press-fit laminates has shown that gas-assisted injection molding can be applied to manufacture thin-walled products.

Improved dimensional stability, reduced residual stresses and reduced warpage are some major advantages of gas-assisted injection molding. The applications of gas-assisted injection molding will become more and more complex and diverse. Nowadays, gas-assisted injection molding can produce products with masses from 30g to 18kg.

4.1) It is necessary to design the products reasonably to avoid the existence of air holes and affect the cosmetics, and if the cosmetic requirements are strict, post-treatment is required.

4.2) The product’s surface with and without gas injection will have different glosses.

4.3) It is difficult to control multi-cavity molding.

4.4) The strict control of mold temperature is required for products with high wall thickness accuracy.

4.5) Increased investment in equipment due to additional gas supply units.

4.6) Unpredictable the location of welding line.

4.7) There are certain requirements for the precision and control system of injection machines when using gas-assisted injection molding technology.

Gas-assisted molding cosmetic defects are mainly flow marks, welding lines and stress marks, etc. because the plastic melt is thicker at the gas-assisted channel, it is the first to be filled, but the cooling time is long, plus the diameter of the injection gate is small, the melting plastic quickly through the gate into the gas channel, after that the stability becomes poor, is the main reason for these defects.

1) Regular injection molding machine, But the accuracy of material counting system should be more good.

2) Nitrogen control system, including self-enclosed gas-assisted nozzles.

3) High pressure nitrogen generator.

4) Industrial nitrogen cylinders and air compressors to provide pressurization power.

5) Molds designed and manufactured for gas-assisted injection.

6) Gas-assisted nozzles—special self-closing gas-assisted nozzles, are used to make the high-pressure gas enter the plastic directly through the nozzles after the melted plastic is injected, An extended closed space is formed along the air channel, and the air channel is maintained at a certain pressure until it cools down, Before the mold is opened, the nozzle is forcibly separated from the product channel by backing off the seat, so that the gas is discharged from the product.

7) Gas Pin—The gas pin is in a specific position in the mold, When the plastic is injected into the cavity, the gas pin is wrapped inside the plastic; at this time, the high-pressure gas is discharged and the gas pin forms an extended closed space inside the plastic according to the air channel.

When designing gas pins in molds, the following issues need to be considered:
a) The location of the gas pin.

b) Gas course way.

c) The degree of gas penetration, whether the gas will penetrate into the thin-walled part.

d) The relationship between the thickness of the gas channel and the wall thickness.

e) Whether the optimum part weight can be achieved.

f) Whether shrink marks can be avoided.

The vast majority of thermoplastics used in general injection molding can be used for gas-assisted injection molding, such as polyethylene, polypropylene, polystyrene, ABS, polyamide, polycarbonate, polyformaldehyde, polybutylene terephthalate, etc., are suitable for gas-assisted injection.

In general, low melt viscosity, the required gas pressure is low and easy to control.

Plastics with high viscosity require high gas force, which is technically difficult.

For glass fiber reinforced materials, the wear and tear of the material on the equipment should be taken into account when gas assisted injection is used.

For flame retardant materials, the impact of the corrosive gases generated on gas recovery, etc. should be taken into account.

In order to control the formation of gas channels and avoid gas “Blow through”, the plastic should have a certain melt strength, such as PU and other very soft plastics are not suitable. PA and PBT types of easily crystallized plastics are particularly suitable for gas-assisted injection molding.

The most commonly used plastics for gas-assisted injection molding are PA6, PA66 and PP (usually glass fiber reinforced).

7.1.1) For the gas pin, when the gas is released at the gas pin, it is most likely to produce an imbalance in the air intake, resulting in more difficult debugging. The main phenomenon is shrinkage.

The solution is to check the gas fluency when releasing gas.

7.1.2) The temperature of the plastic material is one of the key factors affecting production. The quality of gas-assisted products is more sensitive to the temperature of the plastic material.
If the material temperature around the injection nozzle is too high, it will cause flow marks, scorching and other defects.

If the material temperature around the injection nozzle is too low, it will cause cold material marks, cold nozzle, blocking the gas pin, sink marks and other defects.

The solution is to check whether the temperature of the plastic material is reasonable.

7.1.3) There is an material overflow when the gas pin closed, which means that the gas-assisted sealing pin fails to seal the nozzle, When injecting gas, the high pressure gas will flow backwards.there will be flow marks and scorching defects around the gate area, and the material return time will be greatly reduced, and gas will be discharged when the gas pin is opened.

The solution is to adjust the length of the gas pin.

7.1.4) Check whether the gas assist sensor switch is sensitive, otherwise it will cause unnecessary damage.

7.1.5) Gas-assisted products rely on gas to keep pressure, and the product can be properly reduced thickness when shrinking defect happened, The main purpose is to reduce the pressure and space inside the product, so that the gas is easier to pierce to the thick place to make up the pressure.

7.2.1) The product must be designed to provide clear gas paths

The geometry of the gas passage should be symmetrical or unidirectional concerning the gate; the gas passage must be continuous but must not form a circuit; the wall thickness of the article along the gas passage should be large to prevent gas penetration; the most efficient gas passage has an approximately circular cross-section.

7.2.2) The plastic melt driven by the gas must have somewhere to go and be sufficient to fill the mold cavity. To obtain the ideal hollow channel, an overflow space that regulates the flow balance should be provided in the mold.

7.3) The gas channel should be set where the melt is highly aggregated to reduce shrinkage deformation.

Design size of ribs: width should be less than 3 times wall thickness, height should be more than 3 times wall thickness, and avoid connection and cross of ribs.

The product is an accessory for BMW motorcycles:

Plastic Material: PA6+30%GF
Product Weight: 400 gram
Cosmetic Requires: No any sink marks and glass fiber marks
Main Points: Requires nitrogen gas to thin too thick thickness area, reduces molding cycle time and product weight.

The product is too thick and the product is heavy.
To avoid long-time injection, resulting in uneven nitrogen blowing, so the gate size should be as large as possible; now the gate size is 4.08mmX2.00mm, with high speed and high pressure injection; currently, the injection time takes 3.3S.

The gate type is banana gate.
But the toughness of PA + fiber material is not good, the runner is easy to break when eject.

So the runner is designed with reduced material, increasing the toughness of the banana gate, But the length of the cold slug well must be greater than the length of the banana gate to avoid the banana gate pop-up fly.

1) The gas nozzle should be as much as possible next to the injection gate, and the gas nozzle also needs to be chosen in the middle of the product, so that the product wall thickness can be uniform when blowing nitrogen gas into the product.

However, due to the structural constraints of this mold, the gas nozzle was chosen to be located far away from the gate.

2) The gas nozzle must be extended into the product 1-2.00MM to avoid air leakage when blowing, Because the customer requires the gas nozzle on the side of the product, blowing leads to uneven thickness.
The best choice of gas nozzle location should be in the middle of the product.

3) Each product is designed with two gas nozzles to blow the product, the gas nozzle around the gate is the main one; and the other gas nozzle at the end of the product assists in blowing the product to keep holding pressure.

4) Exhaust hole design：
The gas nozzle is open when blowing and closed when blowing is completed. After the product is blown up, there is still high pressure nitrogen gas in the cavity. If the exhaust hole is not well designed, it will result in a bursting sound like a firecracker when opening the mold, And the product will burst. An oil cylinder controls the height of the gas nozzle, and The cylinder returns when the gas is exhausted, Nitrogen gas is discharged along the exhaust hole.

5) The connection of the gas-inlet hole must be designed with a tapered thread. It is better to design a double seal of thread and steel taper, to ensure the sealing of nitrogen gas. Because ordinary air pressure cannot detect whether the connection is leaking, it is better to choose a kind of imported special sealant to seal.

6) High temperature mold cylinder must use high temperature resistant seals, because the cylinder seals are not high temperature resistant without special requirements, the product is PA6+30% GF, the mold temperature needs 100 ℃.

7) The exhaust hole must not be discharged towards the operating and non-operating side of the mold. The air pressure is very high when the nitrogen gas is released; the gas or debris may hurt people at any time.

Product shape is bent, so the PL surface is shaped. Sealing surfaces are bit about 15.00mm reserved, other positions to take Clearance and increase a few balance blocks.

The product PL line at core side is made smaller by 0.1mm to prevent the product mismatch.

Four angle sliders at cavity side, are controlled by four hydraulic cylinders separated.

A self-locking structure has been designed for the sliders at the mold top side, preventing the insert from falling back during the injection process.

There is a slant hole at cavity side, a slant slider designed and there is a sensor switch signal to control the slider.
If the slant slider doesn’t open, and mold is opened or closed, the the slant slider will collide with the mold core side.

Nine hydraulic cylinders at core side:
Four hydraulic cylinders control the gas nozzles,
Two hydraulic cylinders control the ejector plate,
One hydraulic cylinder control the ejector pin of the gate,
One hydraulic cylinder control the flash groove,
One hydraulic cylinder control the slant sliders

Wiring design of the switch of hydraulic cylinders:
Here we need to consider clearly the disassembly of the mold and whether there is interference in the wiring. The design here is to adjust the switch position and line out first; then install the ejector plate to avoid repeated mold installation and crushing the switch.

First,
Mold
Closing

Injection Material, nitrogen gas blowing and pressure-holding

The gas nozzle cylinder returned and exhaust nitrogen gas.

Cavity side cylinder returned and open the mold.

Core side slider cylinder returned and product released.

Eject
The
Product

The gas nozzle cylinder in, Slider cylinders in

Close
The
Mold

Inject melting material and repeat the next cycle.

Laser heat treatment is implemented at PL surface around 15-20mm, surface hardness can reach 70HRC.

The debugging of short-shot:
Blowing nitrogen gas is not allowed when debugging the short-shot, The product is very thick and difficult to cool well, so we must take longer time to cool the product.

Blowing nitrogen gas as long as possible to thin out the thick areas of the product, That can keep the product to prevent shrinkage, also can cool the product and take away the heat inside the product.

The product design has two gas nozzles, The two can not be opened at the same time when molding, otherwise the molten plastic will be in the middle of the gas channel, resulting in uneven products.
Blowing nitrogen gas 1# first, 2# delay, Delay 5-10S would be fine, If the delay time is too long, the product will cool and solidify inside, then the 2# gas nozzle will not work.

The product is big and the material thickness is thick, so try to use high pressure and high speed to ensure that the product’s cosmetic has no fiber marks, also can reduce the injection time, which is more conducive to blowing nitrogen gas.

When the product is close to the customer’s required weight, the product weight can be controlled by adjusting the overflow chute.