Final Design

CAD of the final two-layer flow splitter manifold design

The final design chosen for this project is a manifold consisting of two pieces of 30% carbon fiber reinforced Polyether ether ketone (PEEK). PEEK is a thermoplastic known for easy machinability and low outgassing values (0.31% total mass loss (TML), 0.00% collected volatile condensable materials (CVCM), 0.06% water vapor regained (WVR) ), making it an ideal choice for a precision machined part that will be operating in a vacuum. 30% carbon reinforced PEEK, while more expensive than regular PEEK, was specifically chosen because it is well conductive (electrical resistivity ranges from 10 to 100 μΩ⋅cm). A conductive material was required so that the nozzle itself does not build up electrostatic charge from the electron beam.

The manifold cover serves primarily to seal the channels milled into the bottom piece to prevent leaking, and also as an inlet for the gas. The nitrogen gas is delivered by a stainless steel needle attached to the end of a silicon tube. The needle is plugged into the manifold. A large hole is drilled from the bottom of the cover to redirect the gas down into the channels. This second hole is much larger than the hole where the needle is plugged in, to ensure that the holes line up properly during manufacturing.

The bottom piece of the manifold has a channel milled out of it. The gas flows through the channel, which redirects the gas from the inlet to the two outlets. The inlet of the channel is large, and the channel narrows as it gets closer to the outlet. The depth of the channel is only 0.6 mm. Because the piece is only 1 mm thick, the channel depth has to be minimized to keep the wall as thick as possible, to reduce the possibility of the wall cracking. At the outlet, the channel depth increases to 0.8 mm to increase the volume of gas at the outlet. The two outlets surround the sample, theoretically covering the entire sample area with nitrogen gas. The outlets are two 0.4 mm x 0.4 mm square exit holes. In addition, a shallow “island” is milled out of the center of the outlet. The manifold cover has a protrusion that fits into the island, so the cover and bottom can be aligned to fit together properly.