Cell to sell

08-04-19 Advances on materials

The MuCell Microcellular Foam injection molding technology is a complete process and equipment technology which facilitates extremely high quality and greatly reduces production costs. The MuCell Process involves the controlled use of gas in its supercritical state to create a foamed part. The MuCell Technology is targeted at precision and engineered plastic components with maximum wall thicknesses of less than 3mm.

The MuCell Process generally offers a 50-75% improvement in key quality measures, such as flatness, roundness, and warpage, also eliminating all sink marks. These improvements result from the fact that relatively uniform stress patterns are created in the molded part rather than non uniform stress characteristic of solid molding.

As a direct result of the uniform stress and shrinkage associated with the MuCell Process (which occurs because the pack and hold phase of the molding cycle is eliminated), the parts that are produced tend to comply far more closely with the mold shape and, presumably, the dimensional specifications of the part itself. This means that when using the MuCell Process, fewer mold iterations are needed to produce a compliant part, saving time and cost.

The quality advantages of the MuCell Process are complemented by certain direct economic advantages, including the ability to produce 20-33% more parts per hour on a given molded machine, and the ability to mold parts on lower tonnage machines as a result of the viscosity reduction and the elimination of the packing requirement that accompanies the use of supercritical gas.

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The MuCell® Injection Molding Process involves the highly controlled use of gas in its supercritical state (SCF) to create millions of micron-sized voids in thin wall molded parts (less than 3mm). With the correct equipment configuration, mold design, and processing conditions these microcellular voids are relatively uniform in size and distribution.

The voids are created or nucleated as a result of homogeneous nucleation that occurs when a single-phase solution of polymer and gas (commonly nitrogen, but occasionally carbon dioxide) passes through the injection gate into the mold.

The single-phase solution is created through the operation of a conventional injection molding machine which has been modified to allow the creation of a single-phase solution. The key modifications to the system involve the use of a precision SCF delivery system to deliver SCF to special injectors based on mass flow metering principles. The SCF is then injected into the barrel where it is mixed with the polymer via a specially designed screw. A shut off nozzle maintains the single phase solution while the injection molding screw maintains sufficient back pressure at all times to prevent premature foaming or the loss of pressure which would allow the single phase solution to return to the two phase solution.

It need also pressure stabilization inside its core over time to achieve part conformity.

There are not much installed machines in market yet.

Example

Automotive
	Application: Rear Door Carrier Manufacturer: JCI/Mercedes Benz
	Benefits:
	•	Thinner general wall (1.8 mm to 2.0 mm)
	•	1:1 wall to rib ratio
	•	>50% cycle time reduction (MuCell + Tandem-Mold)
	•	High dimensional stability