Microcellular (MuCell)
- Walls as thin as any ordinary molded part
- Very fine cells, gas dosed as a supercritical fluid
- Main goal is flatness, sink, and fill
- Licensed dosing hardware on the press
Process guide
MuCell Foam Molding
Most people who try microcellular foam are not chasing weight savings. They have a part that warps, a flat face with sink, or a long thin flow that needs more pressure than the press can give.
What it is
Gas dissolved in the melt, bubbles too small to see
MuCell is Trexel's trade name. The general process is called microcellular injection molding.
A precise dose of nitrogen or carbon dioxide, held as a supercritical fluid, is metered into the barrel and mixed into the melt. Under barrel pressure it forms a single phase solution with the resin. When the shot enters the cavity and the pressure drops, the gas comes out as a very large number of very small cells spread through the wall.
Those cells grow as the resin cools and shrinks, which takes over the job that hold pressure normally does. There is little or no pack and hold phase. Parts come out with even internal pressure instead of the high pressure near the gate and low pressure at the end of flow that drives so much warp in solid parts.
It needs a press fitted with a gas dosing system, a modified screw, and a shutoff nozzle, under license. That hardware, not the mold, is usually the gate to trying it.
Effects
What the cells change, for better and worse
Read both columns before planning a trial.
| Property | What usually improves | What it can cost |
|---|---|---|
| Flatness and warp | More even shrink, so less twist and bow | Process has to be dialed in for gas level as well as temperature |
| Sink | Cells fill in behind ribs and bosses | Nothing, unless the surface also swirls |
| Fill | Dissolved gas lowers viscosity, so long thin flows fill at lower pressure | Shot has to be sized for less resin |
| Cycle | No hold phase, and less heat to remove | Gas dosing adds a variable to control |
| Surface | Fine on textured and hidden faces | Swirl on glossy faces unless the mold surface is heated |
| Strength | Stiffness per weight holds up well | Impact and elongation drop; test the foamed part, not the datasheet |
Typical use
Why car brackets and housings are the classic case
Glass filled engineering resins in long, ribbed parts are where microcellular foam most often earns its place.
- Glass fibers orient with flow and make solid parts shrink unevenly. Cell growth evens that out
- Mounting faces have to sit flat against metal, and warp is hard to fix after the mold is built
- Most of the surface is hidden, so swirl does not matter
- Lower weight across many parts per vehicle adds up
Not the same
Microcellular foam and structural foam
Both put gas in the wall. They are aimed at different parts.
Structural foam
- Thick walls on large parts
- Coarser cells, usually from a chemical blowing agent
- Main goal is stiffness and low pressure on big parts
- Often runs on low pressure presses
Before a trial
What to settle before trying microcellular foam
Most trials that disappoint skipped one of these.
Which problem the trial should fix: warp, sink, fill, weight, or cycle
Whether any show faces must stay glossy
Which impact and fatigue tests the foamed part has to pass
Whether a supplier with licensed equipment is within reach for production, not just for sampling
Whether plain design changes such as coring out, evening the walls, or moving the gate were tried first
Keep reading
Related guides
Other foam processes, and the defects microcellular molding is usually brought in to fix.
Structural foam molding
Thick, large parts at low pressure.
Structural foam moldingGas assist molding
A hollow channel through thick sections.
Gas assist moldingWarpage
Why solid parts twist and bow.
WarpageSink marks
Surface dips behind thick features.
Sink marksGlass filled nylon
Stiff, strong, and prone to uneven shrink.
Glass filled nylonThin wall molding
Long flows in thin sections.
Thin wall moldingProcesses hub
Every molding process and secondary operation.
Processes hubFAQ
Questions about MuCell molding
Does the mold have to change for MuCell?
Often not much. Many trials run in an existing mold on a press with the dosing system. Venting and gate size sometimes need adjusting, and glossy faces may need a heated mold surface.
Can clear parts be foamed?
No. The cells scatter light, so a foamed clear part turns hazy or white.
How much lighter do parts get?
It depends on the wall, the resin, and how far the process is pushed, and the tradeoff with impact strength sets the limit. Treat weight as a result of the trial, not a starting promise.
Is it only for automotive?
Cars are the biggest user, but appliances, office equipment, and electronics housings use it for the same reasons: flat parts, ribs without sink, and long flows.
Next step
Start with the warp or sink you are fighting
Upload CAD and mark the faces that must stay flat. The review looks at gates, ribs, and cooling changes that fix it in a standard injection mold. NetProto manufacturing is ISO 9001 certified.