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How to realize lightweighting but high-strength production?

Since the technology of plastic injection molding is well developed, the way to stay compete in the market is optimizing the production process. FCS analyze how MuCell injection molding process assist the plastic production, such as reducing the weight of plastic parts, shortening the molding cycle, improving the strength, or product lifetime.
→Wiki MuCell application

Due to the high level of carbon dioxide (CO2) emission in the atmosphere, United States America (USA) has carried out the energy-saving strategy to reduce about 26~28% CO2 emission before 2025. The vehicle is one of industry which is influenced by strategy for reducing the weight of components. MuCell technology, which can reduce the weight and size of vehicle with keeping mechanical properties.

FCS has introduced this technique 5 years before, and successfully tested and sold it on LM (two-platen), HT (toggle hydraulic), FA (Advanced servo), CT-e (All-electric), and FB(multi-component) injection molding machines, and has been helping the customers developing new producing with MuCell technique.

MuCell operating principle
Foaming injection process is to pressure the gas (N2 or CO2), blending it into the plastic melt and plasticizing with it to generate a single-phase polymer-gas. In injection process, because of pressure reduction, the thermodynamic properties in these single-phases are not uniform. However, after single-phases has been injected into the mold cavity, and the formation of the foam grew up and more uniform distribution. Besides, via mold cooling, the foam formation inside the plastic likes beehive structure as shown in Figure 2.


Figure1-Phase distribution

Figure2-MuCell – intersecting section


MuCell system 
 
MuCell system uses a special process in screw, and its components are shown as as below:
1. Shut-off nozzle: During plasticized process, the needle shut-off valve in nozzle unit will be closed to ensure the setting pressure and to avoid the foaming process.
2. MuCell screw: with the special design of screw, a single-phase polymer and gas solution is achieved by the mixing process in the mixing section of the screw.
3. Pressure sensor: to monitor the pressure inside the plasticizing unit.
4. MuCell controller and gas injector: This unit will generate liquefied nitrogen with setting pressure then inject into the plastic melt via the gas injector.

Advantages
1. Reducing injected pressure and clamping force: because the plastic melt flowing is improved.
2. Reducing product weight: since the products are molding mixed with fizzy particles. 
3. Saving energy: lower injecting pressure and mold clamping force decreases the load of driver units, and lower plastic material use saves the energy consumption of drying and heating. 
4. Reducing cycle time: with MuCell molding, the holding process is not necessary, in addition, the heating energy, cooling time and amount of the material used are also decreased. 

Figure4-Reduction of injection pressure

Figure5-Operating process cycle: traditional and MuCell

Besides light weighting, using MuCell could overcome the warpage and shrinkage problems, and so on. MuCell is not only applied in vehicle industry, but also used in food industry to keep products fresh, cold or warm, such as food storage containers, plastic bottles.

 

Figure6-MuCell® + PET

Related Suppliers: Trexel Inc. (https://trexel.com/)


Foaming injection process parameters
Foaming injection parameters include injected velocity, pressure, barrel and mold temperature, gas weight and so on. 
1. Injection velocity: The faster injection velocity results bigger in injection pressure difference, the foam density is higher; the foam size is smaller and more uniform distribution.
2. The temperature: The melt temperature of plastic and mold temperature are also important factors. If plastic melt temperature is at higher condition, the diffusion of plastic melt and gas is quite high, the plastic viscosity is much lower and plastic-gas mixture is more homogeneous. 
3. The more N2 is, the more homogeneous is. Therefore, the foam density is larger, and foam size is decreased.

Physical foam (MuCell) and chemical foam
For foaming injection process with physical foam, one of its advantages is that the mechanical strength property is stronger. The controller of foam density and size are easier than that of chemical foam.


 
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