Gas assist injection plastic handle
|Part Name||gas assist injection plastic handle|
|Product Description||external gas assist injection molding which allows us to create a myriad of complex part geometries not previously achievable by injection molding. Instead of requiring multiple parts that must later be assembled, supports and stand-offs are easily integrated into a single mold without the need for complex coring. The pressurized gas pushes the molten resin tight against the cavity walls until the part solidifies, and the constant, evenly transmitted gas pressure keeps the part from shrinking while also reducing surface blemishes, sink marks, and internal stresses. This process is ideal for holding tight dimensions and complex curvatures over long distances.|
|Injection||Cold runnerSub gate|
|Product Features and Application||The gas assist injection molding process is a low pressure, conventional injection molding process that forces a short shot of material to fill a mold by using pressurized nitrogen gas to displace the material in pre-destined thick area while forming hollow sections in the part.|
1、 Forming principle
Gas assisted molding (GIM) is a new injection molding technology in which high-pressure inert gas is injected when the plastic is filled into the cavity (90% ~ 99%), the gas pushes the molten plastic to continue to fill the cavity, and the gas pressure holding process is used to replace the plastic pressure holding process.
There are two functions of gas:
1. Driving the plastic flow to continue to fill the mold cavity;
2. Form a hollow pipe, reduce the amount of plastic, reduce the weight of finished products, shorten the cooling time and more effectively transfer the pressure holding pressure.
Because the forming pressure can be reduced, but the pressure holding is more effective, it can prevent the uneven shrinkage and deformation of the finished product.
The gas is easy to penetrate from high pressure to low pressure (the last filling place) through the shortest path, which is the principle of airway arrangement. The pressure is higher at the gate and lower at the end of the filling.
2、 Advantages of gas assisted molding
1. Reduce residual stress and warpage: traditional injection molding requires sufficient high pressure to push the plastic from the main channel to the outermost area; This high pressure will cause high flow shear stress, and the residual stress will cause product deformation. The formation of gas channel in GIM can effectively transfer pressure and reduce internal stress, so as to reduce the warpage of finished products.
2. Elimination of dent marks: traditional injection molding products will form sinkmarks behind thick areas such as rib & boss, which is the result of uneven shrinkage of materials. However, GIM can press the product from the inside to the outside by means of hollow gas pipeline, so there will be no such marks on the appearance after curing
3. Reduce the clamping force: in traditional injection molding, high holding pressure requires high clamping force to prevent plastic overflow, but the holding pressure required by GIM is not high, which can usually reduce the clamping force by about 25 ~ 60%
4. Reduce runner length: the large thickness design of gas flow pipe can guide and help plastic flow without special external abortion design, so as to reduce mold processing cost and control welding line position
5. Material saving: compared with traditional injection molding, the products produced by gas assisted injection molding can save up to 35% of materials. The saving depends on the shape of the product. In addition to the internal hollow material saving, the material and quantity of gate (nozzle) of the product are also greatly reduced. For example, the number of gate (nozzle) of 38 inch TV front frame is only four, which not only saves materials, but also reduces fusion lines (water lines)
6. Shorten the production cycle time: due to the thick ribs and many columns of traditional injection molding products, certain injection and pressure holding are often required to ensure the product setting. For gas assisted molding products, the appearance of the product seems to be very thick glue position, but due to the internal hollow, the cooling time is shorter than that of traditional solid products, and the total cycle time is shortened due to the reduction of pressure holding and cooling time.
7. Extend the service life of the mold: when the traditional injection molding process hits the product, it often uses a high injection speed and pressure, which makes it easy to “peak” around the gate (nozzle), and the mold often needs maintenance; After using gas assisted, the injection pressure, injection holding pressure and mold locking pressure are reduced at the same time, the pressure on the mold is also reduced accordingly, and the number of mold maintenance is greatly reduced.
8. Reduce the mechanical loss of the injection molding machine: due to the reduction of the injection molding pressure and clamping force, the pressure borne by the main stressed parts of the injection molding machine: Golin column, machine hinge, machine plate, etc. is also reduced accordingly. Therefore, the wear of the main parts is reduced, the service life is prolonged, and the number of maintenance and replacement is reduced.
9. Applied to finished products with large thickness changes: the thick part can be used as an airway to eliminate surface defects caused by uneven wall thickness with gas pressure holding.
3、 Gas assisted molding process
The process of gas assisted molding is: ① mold closing ② plastic filling ③ gas injection ④ pressure maintaining and cooling ⑤ exhaust. In Figure 2, a is plastic injection, B is gas injection, C is gas pressure maintaining and D is exhaust.
The first stage of gas assisted molding is plastic injection into the mold cavity, as shown in Figure 3. The molten plastic is injected into the mold cavity. After contacting the mold surface with low temperature, a solidified layer is formed on the surface, but the interior is still molten. The plastic stops when the injection is 90% ~ 99%.
The second stage is gas injection, as shown in Figure 4. Nitrogen enters the molten plastic to form a hollow to push the molten plastic to flow to the unfilled part of the mold cavity.
The third stage is the end of gas injection, as shown in Figure 5. The gas continues to enter the molten plastic until the plastic is pushed to completely fill the mold cavity. At this time, there is still molten plastic.
The fourth stage is gas pressure maintaining, i.e. gas secondary penetration stage, as shown in Figure 6. In the pressure maintaining stage, the plastic is compacted by high-pressure gas, and the volume shrinkage is compensated to ensure the external surface quality of the parts.