• M Aerospace RTC

How does it work a 3D printer?

To understand the operation of a 3d printer we must break down the parts that compose them, as well as the elements involved for the correct execution of the printing of the material.

3D FDM printer by parts, all these parts that make 3D FDM printing possible will be detailed. There are different types of FDM, but we are going to narrow it down to the most common of all, which uses coils of filament as a way of supplying the material.

Head also called hotend. It is where the material is heated, and melts, due to the pressure exerted from the extruder, it comes out through the nozzle, through a tiny hole. The size of this is important to know since the amount of material that can come out of the nozzle depends on it, and the smaller the more precise, but also slower, and susceptible to clogging.

In the head we also find the heating block, which is the part that houses a resistance that heats up, and this block heats the nozzle. To control the temperature, it also houses a thermistor that sends its signal to the electronics to control the resistance.

But it is important that this heat stays inside the nozzle, so that the material does not melt prematurely. To achieve this there are mainly two strategies: put a diffuser, or put an insulating material. The temperature limit at which the nozzle can work will be dictated by the design of this part.

The diffuser, usually made of aluminum, removes heat by transmitting it to the air, and requires ventilation to work properly. The temperature limit being metallic can be very high, but it adds weight and volume to the head.

On the other hand, with an insulating material, this heat is simply prevented from being transmitted to the wire, but the temperature limit is usually lower than with a diffuser.

Finally, in the highest part of the head there is the entrance of the thread. That in the bowden extruder system requires that there be a coupling for the tube through which the thread enters.

The extruder is basically the motor that pulls the thread towards the head, it does so by means of a knurled or geared cylinder. The most basic ones only grab the material on one side, but there are more advanced mounts that grab it from two sides, improving grip.

This knurled barrel may be on the motor shaft itself, directly transmitting force and speed to the filament, or there may be a reduction gear, increasing the motor's torque but reducing its speed. The latter is more optimal, because what we need is strength and precision, but it is more expensive and heavy. Though direct drive is usually sufficient for most DIY printers.

The extruder can be mounted on the head carriage, taking the material and putting it directly inside it. We call this direct extrusion, as the force towards the nozzle is almost direct. Especially if the filament from the grip is well directed and closed, this system is optimal for flexible materials.

On the other hand, in the bowden system the extrusion is far from the head, and for this reason we need to restrict the filament inside a tube that guides it. This allows the extruder to be mounted outside the moving carriage, significantly reducing its weight, but complicating the movement of the filament a bit, since the pressure that reaches the nozzle has a gap that depends on the stiffness of the material. This system has problems with flexible or semi-rigid materials such as Nylon.

The base is the surface where the piece sits, and where the first layer grabs. The grip of this layer is essential for the success of the print. To achieve this, most materials need to be hot, especially in a uniform and very stable way. That is why there is a heated bed in many printers below the printing surface. This can be a printed circuit that offers a resistance and heats up, which is very cheap, but enough to heat up to 100º, easy to assemble.

It can also be made of silicone with a zigzag resistance inside. A silicone covered resistor wire can heat up very quickly, and is therefore a bit dangerous if there isn't an extra safety circuit to stop it.

Underneath it can be insulated with different materials, fiber fabrics or cork sheets, among others. The point is that this directs all the heat towards the printing surface and is much more efficient.

The typical base material is glass. The borosilicate one can withstand temperatures better, but it is a bit brittle. Glass is ideal as it offers a smooth surface that does not warp with temperature and is a good thermal reservoir: making the temperature more uniform and changing slowly. Glass is also the most versatile material, since temporary treatments can be added: such as lacquer, cellulose glue, or ABS diluted in acetone. Blue tape can also be added to provide a porous surface for molten material to stick to.

Other typical materials are aluminum, which offers very good heat transmission, but for this reason it is not as uniform and dissipates the temperature very quickly. But it is cheap. That's why some manufacturers use it and glue a plastic sheet to the side. This combination is interesting if this sheet is magnetic and flexible. The adhesion of the plastic is good, and that flexibility allows the pieces to be easily removed once printed.

An interesting innovation is the ceramic surface. It is a very good heat transmitter and with the right materials and treatment, the ceramic pores open or contract at the printing temperature, allowing a very good grip when heated, and facilitating the extraction of the piece when it cools. On these surfaces they are a bit delicate, and no other treatment can be added and they have to be taken care of by cleaning them well.

As we will see when we talk about the types of movement the car and the base have to move. That is why guides are needed where the parts slide with minimal friction. And these have to be connected by straps to stepper motors, controlled by electronics. There are different types of guides:

· Cylindrical bars: In combination with cylindrical bearings, it is a balanced solution between cost and quality.

· Square rails: Much more stable and with less friction, but more expensive than the cylindrical ones.

· Wheels on guides: It seems like a cheap solution, and it is, but the rubber on the wheels absorbs vibrations, improving print quality. The crux is that they have a more limited speed, compared to the other bearings.

Of the engines we are interested in torque. It has to be enough to move the head, they have to be step by step to be able to control them accurately.

In a 3D printer we find different fans, each one with a function.

· Layer fan: This fan directs air towards the tip of the nozzle so that the outgoing material cools quickly. Some materials require this fan (PLA) but in others this cooling effect is very counterproductive.

· Diffusion fan: The heads with a diffuser need this fan to make air pass through it. It is vitally important that it is always on. And that the expelled air goes upwards.

· Cooling fan: The electronics require cooling. Especially motor microcontrollers, which have a tendency to get very hot.

· Hot runner fan: Some hot runner printers incorporate fans for precise temperature regulation. In addition, they can also incorporate a particle filter for the expelled air, which is very interesting for printing materials with toxic fumes such as ABS.

In a printer the most important electronic components are the following:

· Control board: The controller board is the brain of the printer. Here the firmware is processed through these remarkable elements:

· CPU: An 8-bit microprocessor with sufficient speed is more than enough to coordinate the motors and sensors, following the gcode, it is optimal for DIY kits. But more will be needed if there are more elements such as Wi-Fi or cameras, as we see in machines with more features.

· Microcontrollers: This part of the electronics is connected to the motor to control the steps it makes. It is a delicate section of electronics. It is interesting that they can be replaced (that they are not integrated), since they can be easily damaged. They also need to be able to microstep at least 1/16th on cartesian printers.

· Inputs and outputs: In addition to the necessary pins for motors, endstops, thermistors, and fans, you may be interested in having some more free to install improvements. It is also interesting that it is reconfigurable, to be able to adapt the electronics to the specific type of printer, in case it is DIY. It is also interesting that it has a 12v output to power the heated bed. Although there are configurations where the power supply is external to the board and this output controls the bed through a relay.

· Power supply: The stability and power of the source is essential, especially to supply power to the hot bed, which is what uses the most. But contrary to what it seems, a 3D printer does not cost much more, and it does not require a very powerful source. If it is not a large format printer, then the stability of the current is the most important thing to ensure that the microsteps are precise and without lag.

· Hot bed: It is a resistance that transmits heat to the printing surface, essential for adhesion and thermal stability during printing. The power of the bed helps to raise the temperature more quickly, and to ensure that it remains stable. Some only get to 50º fast enough, but take much longer to get to 100º. It is also important to take into account how that heat is transmitted to the printing surface, and if it is insulated on the other side so that there are no losses.

· Head heater: It is the resistance that heats the head. It doesn't have much of a secret. But it is what allows the deposition of molten material, precisely.

· Thermistors: These elements are the thermometers that measure the temperature at specific points: in the hot bed, and in the nozzle. In this way you can control the power to the resistors and control the temperature.

· Limit switches: This sensor is no longer a button, which when the printer is activated detects that the end of a movement axis has been reached. In this way position 0 is marked and allows the position of the head to be known from there.

· Connections: The control board must receive the necessary information to print through a gcode. This can be done by loading it from memory on an SD card, or USB. You can also connect the printer to a PC, via USB, ethernet or Wi-Fi.

· Control interface: Not necessary if the printer is always connected to a PC. But it is essential if the printer is to function autonomously. The user must be able to control the machine manually for pre-print preparation and during maintenance. It normally consists of a display and a wheel or control buttons, or these buttons may not be necessary if the screen is touch screen. These components require a separate board, and sometimes their own firmware, which communicates with the CPU firmware.

The software is programming. The written part contained in memory with the instructions to operate the machine. In 3D FDM printing we have these in particular:

· . gcode: this is a file that contains the step-by-step instructions that the printer must follow to generate a given object. It is generated in a slicer program, and the firmware interprets it and transforms it into signals to the printer components. The standard format is . gcode, but there are specific brands that work their own closed software.

· Firmware: This is the program loaded into the CPU that interprets the gcode and controls the printer components and receives information from the sensors. From the firmware you can control the printer if there is an interface. In addition, it can have other automatic functions, be they security or user help (such as auto-level). It is also configured according to the parameters of the printer, and has the basic variables already defined, such as the mm per step of each motor, the acceleration of the movement, the maximum positions in each axis, the safety temperatures, the functions of each pin on plate etc.

· Slicer: This program goes to part of the printer. But it is needed to generate the gcode of each object that you want to print with a specific configuration. Multiple printing parameters are entered in this software, such as head temperature, layer height, speeds for each type of movement, wall thickness, part internal structure, etc.

The frame is the part that holds all the components in place. Especially the axes. This part is important to evaluate the firmness of the movement, and if the extruder carriage or the base will be affected by inertia and vibrations. The firmer the structure, supports, and guides, the better. But it is also necessary to value lightness and low cost (especially if we are looking for a cheap printer).

We also include as structure any housing that contains electrical or mechanical parts. The electronics are not always closed, it is common in DIY kits that it is visible and unprotected. But in other printers you must take into account that it must be closed and with its own cooling.

Other casings may contain mechanical parts such as the extruder or head. Some carts have everything in plain view, but others choose to contain the components in a case.

The structure will mark the printing volume, since the length of the axes is what allows the head carriage to move. The advantage of FDM printers is that you only need to scale the spindles, and the base in some cases, to have a larger print volume.

The closed chamber is somewhat unusual for home or semi-professional printers. But it is necessary for printing certain materials that require stability at room temperature and high temperatures on the bed. It is also interesting that the chamber can be ventilated and thus isolate the fumes given off by certain plastics.

There is distance between many parts that must be electrically connected. Quite a bit of wiring is required in an FDM 3D printer, and it is essential that it does not interfere with movement. Depending on how the structure is made, this point can be a problem. And there are people who do not like anything that there are cables in sight. But it is usual that in the kits in the cheapest printers there is a bit of disorder in this part.

It is also important to pay attention to where they pass, since there are cables that heat up. There are different solutions to direct your development:

· Loose: Even in kits, it is a bad idea to have loose cables. At a minimum collect them and join them with cable ties, to the casing and to each other.

· Mesh: Inside a fabric mesh they are well collected, and it is an economical solution. Sufficient if the development of the cable cannot disturb other parties.

· Corrugated tube: similar to the previous one, but more rigid than the mesh.

· Spiral: Another system that allows you to put it on and take it off once you already have the wiring connected. Good solution for kits, with a similar result to the corrugated tube.

· Chain: Directs the development of the cable and restricts it to move in one direction, even if it is moving. Widely used for wiring to the extruder carriage, as it prevents them from interfering with printing, while remaining very hidden. It is the best solution, but also the most expensive.

Also notice how they move next to the cart or base. If there are scratches or bites in the long run it can be a critical point of failure or a serious accident.

Once the most common materials that make it up have been defined, we can define the operation of fused deposition 3D printing as a technique that is often considered the simplest existing method. Fused Deposition Modeling or FDM technology is based on 3 main elements: a print plate/bed on which the part is printed, a spool of filament that serves as the print material, and an extrusion head also called an extruder. In short, the filament is sucked in and melted by the 3D printer's extruder, which precisely deposits the material layer by layer onto the print bed.

It all starts with the design of the object using some CAD software (such as SolidWorks, Catia, TinkerCAD or Blender for example). The resulting 3D file, mostly in . STL, is divided into several layers using a software called "slicer" (such as Makerware, Cura or Repetier) in which it is possible to select the different printing parameters. Once everything is configured, you can start printing.

3D printing begins when the machine reaches a temperature of around 200°C, necessary for the fusion of the material. Among the most popular 3D printing materials in fusion deposition are PLA (Polyacetic Acid) and ABS (Acrylonitrile Butadiene Styrene).

Once the machine is heated, a 1.75mm or 2.85mm diameter filament of material is extruded onto the platform through a nozzle that moves on 3 axes x, y, z.

The platform moves down one level with each new layer applied, until the object is printed.

During printing, supports can be used to improve the quality of certain models. Its function is to support the protruding parts of the 3D model, since there are certain models that without support it is very difficult for them to be printed. These supports can be made of the same material as the printed object or in a material that is soluble in water or limonene, for example. Although more complicated to handle, some 3D printers are equipped with multiple extruders to combine multiple colors or materials (support materials in general).

Materials compatible with fused deposition modeling, fused deposition 3D printing is compatible with a wide variety of thermoplastic polymers: PLA and ABS, as well as polycarbonate such as, PET, PS, ASA, PVA, nylon, ULTEM and many composite filaments that are based on metal, stone, wood. This offers interesting mechanical properties such as conductivity, biocompatibility, resistance to extreme temperatures or conditions, to name a few. By replacing the 3D printer extruder with a syringe system, it is also possible to create parts from ceramics, clay, or food materials (such as syrup or chocolate). To give an idea of ​​the price of consumables for 3D printers, a 1kg spool of PLA filament is around €35.




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