In this review we explain existing 3D printing technologies, their variations and limitations. The technologies described here are based on the same system of additive process, every object is built layer by layer after being sliced by an informatic system.
3D printing is an old factory process and is a declination of additive manufacturing. As the efficiency grows, 3D printing finds applications in very different domains, for example microfluidics. The technique allows to develop any disposable object for inexpensive costs, with many kinds of materials. Accuracy of 3D printing is high enough to create micro-fluidic systems, and such 3D printers already exist on the market.
Here the laser beam moves all over the print scheme and heats the powdered material until its melting point, the powder becomes a solidified structure. Once the step is complete, a roller comes to place powder above the piece which had moved a layer’s height down, and the process of laser sintering starts again. Selective laser melting is more used for metallic composition.
This works like SLM with one difference: the laser beam doesn’t heat at the melting point of the material, it stops just before, and creates cohesion between grains of the powdered material so the heat regroups grains between them and creates cohesion. Selective laser sintering is more used for thermoplastic composition.
Fused deposition modeling is the most commonly used 3D printing process in the world, simple and efficient. It finds many applications and developments. The principle of this process is to lay down heated plastic, leaving the heating frame on a flat surface (corresponding to X and Y moves) and going up slice by slice (moving on Z axis). All those moves describe 3 axis of the space as well known as the Cartesian space.
Stereo lithography Apparatus has the same process than Selective Laser Melting and Selective Laser Sintering, a laser beam heats the resin with a parameter of exposure and the resin gets polymerized. Again the object is moving a layer’s height and the machine projects a new scheme corresponding to the slice of the object. The final product should get an UV radiation to consolidate it.
Since we are developing a FDM 3D printer, the following parts of this review will cover only this technology.
The diversity of resin is limited compared to the large choice of filament you find on the market: ABS, PLA, POM, Nylon, etc… There are many type of material : bio-degradable, food contact proof, corrosive resistant, each material has its own characteristics and functionalities. One thing that will be common to each material it is their way to warp when they cool down, some materials like ABS get high warping if it’s cooled down too quickly whereas PLA gets fewer problems like this. The warping characteristics depend on each material composition and recommendations of the filament’s factory.
A turnkey offer to fabricate your su-8 mold and pdms chips
For FDM methods we have to convert the rotation of the motors into a movement of translation, for this there is 2 most-known solutions:
You’ll choose the system in function of the quality required for your final product. Some of the printers combine with bolt belt for X and Y axis and ball screw for the Z axis.
The hot head end is really important. This is the part that makes your 3D printer a 3D printer; this part is heating the plastic at the right temperature of fusion, to finally depose it. The choice of the extruder is capital for the efficiency of the machine; as well there are 2 systems: one with thread nozzle and tap radiator, or bore nozzle and radiator. This last system is more efficient to prevent from leaks.
If you are heating up the material too much you’ll get viscous material which can leaks and clog your extruder, if you are under heating your filament won’t pass through the nozzle.
The heat bead is here to minimize the difference of temperature between the hot end and the environment so it prevents the heated material from getting a too high cooling rate and retract on itself to create the phenomenon called: warping. Warming up the plastic keeps it at a range of temperature where there is no deformation.
The software is generally built in 2 parts: the first one allows you to place the object on your plate and choose different parameters like the height, infill, speed, a graphical interface and the second part “hide” is the slicer, this part cut any object in slice of the height you choose before in your parameters, then if you cut a cube of 10 mm high by slice of 100µm (0,1mm) the slicer will create 100 slices. In each slice it will analyze the “image” and decompose into coordinates and X and Y axis, so here is how we create a movement by telling motors to move this position from another. Those indications are listed in file called “gcode” it will also be the extension of your file here an example :
G1 : Telling the printer to move F: for feedrate in mm/min
Their rotation is segment by angle, in example a motor of 1.8°/step need 200 steps to make a revolution : 200×1.8°=360°, less the angle is big the more you get precision. Motors have to be coupled with a system to get translational movement and with a stepper driver; this global system will define the step needed to move a given distance. However, the smaller is you degree per step, the more precise your global system will be: if it needs 80 steps to move 1 mm, one step can move 1/80= 0,0125 mm or 12,5 µm whereas if it needs 320 steps to move 1 mm, by the same operation, 1 step move 3,13 µm, such precision is required for microfluidic systems.
Stepper drivers offer an electronic precision, by interpolating the current function of the motor and segment it so it creates virtual step. Those virtual steps are multiplying the mechanical step of the system, but the higher the virtual step is, the higher the lower the torque is. So it’s important to make a good compromise. The stepper driver can control the motor noise as well.
Generally by 2 they are cooling the radiator body of the extruder to prevent too hot warming, and the second one is cooling of the piece when needed (like for the bridge structure, a high cooling is recommended).
The interface is important to make the machine run by itself, make it autonomous and easier to use. Equipped with a SD slot, you can run any loaded program with an easy to use interface, even change some parameters at your convenience.
This capacitive sensor allows interesting things, first of all it provides a good altitude of the extruder for the first layer, and allows to test different points of the flat surface and create a virtual normal vector of the surface and will multiply every point by this normal to get a better accuracy when moving and positioning!
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Do you want tips on how to best set up your microfluidic experiment? Do you need inspiration or a different angle to take on your specific problem? Well, we probably have an application note just for you, feel free to check them out!
Microfabrication techniques for a circular channel
In soft lithography, the fabrication of a mold, often made in SU-8, is required for replicating PDMS microfluidic structures.
Replicating PDMS-based structures first requires the fabrication of a SU-8 master mold that will serve as a patterned template for PDMS casting
How do you perform a successful SU-8 exposure? Here you will find the tips and tricks to do it.
How do you perform a successful photoresist baking? Here you will find the tips and tricks to do it.
How do you perform a successful spin coating? Here you will find the tips and tricks to do it.
The final PDMS layer thickness mainly depends of spin-coating speed and duration.
Here you can find a complete overview of a SU-8 mold fabrication process.
Here you can find a complete overview of a PDMS chip replication.
Unlike photolithography, soft lithography can process a wide range of elastomeric materials, i.e. mechanically soft materials.
A UV Lamp to expose your SU-8 photoresist. You will find here the relevant points to think about.
A plasma cleaner to bond your PDMS chip, you will find here the relevant points to think about.
A spin coater creates a thin layer of photoresist or PDMS, you will find here the relevant information about how to choose one.
You have the choice between glass or plastic photolithography mask, but how do you choose? here is some information to help you with the decision
A hot plate to bake your SU-8 photoresist, you will find here the relevant points to think about.
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