Among spatial modeling enthusiasts, FDM technology is the most common. Different models of printing devices can be used, but the design of 3D printers from any manufacturer has much in common. This allows us to highlight the characteristic structural features of such equipment.
3D printer design
In its essence, a 3D printer is a small CNC machine. Its main parts are assembled on the frame, placed in the housing. Control of the actuating mechanisms is impossible without an intermediate unit – the control controller, which gives commands understandable to the device with a special G-code. It is possible to single out the main structural elements that ensure the printer’s operation.
Stepper motor
Working body (printing head) for the formation of a spatial part should move on three axes (X, Y, Z) in a certain sequence at a given distance. Uniform and precise movement is provided by stepper motors. There should be at least 3 of them (one for each axis). The most common are full-step motors that form a step of 1.8° (200 steps per full revolution).
Machines with higher accuracy of movement can be equipped with half-step and micro-step motors. The first option provides 0.9° movement, i.e. 400 steps per full revolution. With microstep motors, each full step can be divided into 4, 8, or 16, resulting in up to 3,200 microsteps for a full revolution.
Standard stepper motors are rated for 4, 8, or 12V power. The most common are NEMA 17 motors measuring 1.7 × 1.7 inches (43.2 × 43.2 mm). Smaller motors (e.g., NEMA 14) may also be used. A pulley system, driven by toothed belts or threaded shafts, is used to convert the rotary motion of the rotor into translational motion.
Extruder
The working body of the printer is the extruder, or printhead. Its task is to melt the plastic and feed it through a nozzle into the work area. The extruder consists of a thermal head and a material feeder. The input material is used in the form of filament with a diameter of 1.75 or 3 mm. A stepper motor and a system of shafts and gears are normally installed for dosing the filament.
The filament is guided into an aluminum head with a heater that heats the stock in a range from 160 to 280-300 ° C, depending on the plastic used. The highest temperature is maintained near the nozzle through which the melt is fed for printing. Nozzle orifice size can be from 0.2 to 0.5 mm. Fans and built-in “thermal barriers” in the form of pads from heat-resistant polymers with reduced thermal conductivity (Teflon, fluoroplastic, etc.) provide full control over the heating mode.
Important: Usually the printer is equipped with one printhead. Some models have two extruders for feeding different materials.
Printing platform
To print parts on a printer, you need a work area, that is, a printing platform (surface), or work table. It is characterized by such important nuances:
- The size of the platform determines the maximum size of the part to be formed. Most often the working area is 140-220 cm2.
- Heating. For some polymers (e.g. ABS) requires pre-heating of the working surface. Taking into account it there are printers without heating of the work table (for PLA) and universal settings for any plastic. In the latter case, the platform is equipped with a fairly powerful heater capable of bringing the temperature of its surface above 100 ° C.
- The working table is made of aluminum or glass. These materials provide even heating and smoothness.
- To increase the adhesion of the polymer to the platform, its surface is covered with a special film. The most widespread are: kapron, polyamides, blue tape (Scotch Blue Tape).
Important: In addition to these features the most important element is a system of alignment of the table. It ensures the exact horizontal adjustment of the surface during calibration.
Linear Motor
The main drive, or linear motor, determines the printing speed and productivity of the equipment. It determines the flow of plastic, as well as the movement of the part. The drive uses high-precision rods on each axis. They are fitted with moving plastic or bronze bushings (ball bearings). The main drive is used to set the initial coordinates when setting up the machine and performing calibration.
Sensors
An indispensable element of controlling the 3D printer is the end sensors, or detents. They are intended to ensure that the movements of the working body are kept within the working area. The most commonly used are simple EndStop type end sensors. They should warn about approaching the head to the boundaries of the field. They are also needed when setting the origin of coordinates in all axes. The simple models use simple push-pull type sensors as detents. Optical devices are used for more accurate control.
Frame
All printer parts are attached to the frame. It must have sufficient strength, and the attachment points must not relax when vibration occurs during engine operation. The frame material is high-strength polymer, but the strongest strength is achieved when aluminum profiles are used. Attachment of parts is carried out with screws and nuts, couplings and clamps. Homemade structures often use plywood.
The design of 3D printers is simple enough that they can be assembled with their own hands. In modern models, manufacturers add quality control elements, which somewhat complicates the structure and leads to higher costs. In general, during the manufacture of the printer it is important to ensure the accuracy of the assembly and the possibility of correct calibration in all the axes of movement, which determines the quality and reliability of its work.
