CNC Machining Microfluidics: Milling a Microfluidic Droplet Generator Chip

Prototyping microfluidic chips with a computer numerical control (CNC) machine is a popular technique for rapid design and iterative testing. CNC machines use special tools known as end mills to cut microchannels and microchambers into rigid plastic. While fragile, some of these end mills can be as small as 5 µm in diameter!

The entire process to mill microfluidics starts with generating a 3D model in computer-aided design (CAD). Once the design is ready, computer-aided manufacturing (CAM) is used to program the tool paths for the CNC machine. Finally, the programs are loaded onto the CNC and the microfluidic features are micromachined.

Designing a Microfluidic Chip in CAD (Autodesk Fusion)

Modeling microfluidics in computer-aided design can be intimidating, but with some practice, becomes quick and easy. Below is a video on how we model a microfluidic droplet generator for CNC machining on acrylic (PMMA).

In the video, the microfluidic droplet generator is designed using Autodesk Fusion as it has a 'free' non-commercial license available to the general public. Autodesk Fusion also has computer-aided manufacturing in its 'free' license, which is needed to set up the CNC programs. While SolidWorks may be more popular, its CAM can be expensive. Fusion 360 was just as easy to learn and use as SolidWorks.

The video provides a general overview on making a droplet generator with easy-to-follow steps such as modeling the cross junction and best practices for microchannel construction using the 'extrude thin' function.

The 3D model is not DFM-friendly (design for manufacturing), which typically includes a draft on the entire part to help with ejection from the mold.

P.S. to rotate a model in Autodesk Fusion use "Shift + Middle Mouse Button"

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CAM Tutorial for Machining Microfluidics

Computer-aided manufacturing is necessary to generate the g-code files used by the CNC machine to prototype the microfluidic droplet generator. Autodesk Fusion offers a 'free' non-commercial license.

The video provides a reference on how to configure the CAM programs for the microfluidic droplet generator designed in Part 1 for CNC prototyping in 1 mm thick acrylic (PMMA). The programs are post-processed for use with Candle (Grbl), an open-source CNC controller, in order to CNC machine on an entry-level 3018 desktop mill. 

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Micromachining Microfluidic Droplet Generators

With the CAD and CAM configured, it's time to machine the microfluidic droplet generator on the CNC machine. To demonstrate how one can maximize the precision when using a entry-level CNC, three droplet generators with different geometries was designed and configured for microfluidics machining on a single chip.

The video demonstrates the process of CNC milling the microfluidic features using the desktop CNC which includes mounting the 1 mm thick acrylic, setting the work coordinates, loading appropriate g-code files, changing tools, zeroing the z-axis, and removing the chip. Depending on the CNC & controller, the physical steps may differ but the concepts remain the same.

Get the Autodesk Fusion reference file here!

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Reference Speeds and Feeds:

0.1 mm End Mill
Channel Depths: 0.1 mm
Spindle Speed: 20,000 RPM
Cutting Feedrate: 50 mm/min
Ramp Feedrate: 100 mm/min
Plunge Feedrate: 25 mm/min
Max Stepover: 0.05 mm
Max Stepdown: 0.05 mm
Ramp: Plunge

0.3 mm End Mill
Channel W x D: 0.5 mm x 0.2 mm
Spindle Speed: 20,000 RPM
Cutting Feedrate: 200 mm/min
Ramp Feedrate: 333 mm/min
Plunge Feedrate: 50 mm/min
Max Stepover: 0.30 mm
Max Stepdown: 0.1 mm
Ramp: Plunge

1 mm Drill Bit
Hole Depths: 1.0 mm
Spindle Speed: 20,000 RPM
Plunge Feedrate: 1000 mm/min
Cycle Type: Deep Drilling
Peck Depth: 0.5 mm
Min Pecking Depth: 0.5 mm
Dwell: 0 s

1/8" (3.175 mm) End Mill
Profile Depth: 0.9 mm
Spindle Speed: 20,000 RPM
Cutting Feedrate: 1000 mm/min
Ramp Feedrate: 333 mm/min
Plunge Feedrate: 100 mm/min
Repeat Finish Pass: Checked
Ramp: Unchecked