“Oh, we have a 3D printer in the office” or FDM printing basics

December 23, 2020by Evghenii I.

  Yes, our office has our own 3D printer and everyone can print on it whatever they want.

  This article will be the first to familiarize you with the basic principles of 3D printing. In the future, I will instruct you how to use slicers and show you the basic principles of 3D modelling for printing ready-made models, and not only.

  To begin with, this is one of the most common and simplest 3D printing technologies. FDM 3D printers are the most affordable and comfortable for personal usage. So, what exactly is FDM 3D printing? FDM is an acronym for Fused Deposition Modelling. Actually, this description characterizes FDM 3D printing in the most capacious way.

  The printer in our office is called Ender 3 Pro and below you can see its main parts without many technical details which you won’t need for your 3D printing experience.

  The thermoplastic is fed by an extruder (a mechanism responsible for material feeding) to the print head, which creates the model layer by layer. Below you can see what exactly is happening during the printing process.

Working in three dimensions – how the guides work

  The hardest part of 3D printers are the moving parts. It is not enough to simply install a few stepper motors, connect them to the power supply and make the extruder move. You need to teach them how to work correctly and how to place accurately the head, which is responsible for feeding the filament.

  In order to be able to create full-fledged, three-dimensional objects, the printer must work along three guides: height, width and length. That is, the mechanisms must organize the printing so that the object, during its creation, can be processed along the XYZ axes. This effect can be achieved with the movement of the print head, platform, or a combination of both.

  Each 3D printer is built in a similar way, and all three axes are linear. They are located at right angles to each other and do not change their position during the printing process. For movements along the axes, timing belts, pulleys, rods, motors, etc. are used.

  Although the motors are relatively small in size, they have enough power to guide the head or print bed with millimetric precision.

Most common used plastic types

  PLA (Polylactide) – one of the most widely used thermoplastics due to several factors. To begin with, PLA is known for being environmentally friendly. This material is a polymer of lactic acid, making PLA fully biodegradable. The raw materials for the production of polylactide are corn and sugarcane. At the same time, the environmental friendliness of polylactide determines its fragility. Plastic absorbs water easily and is relatively soft. PLA models are not intended for functional use, but serve as design models, souvenirs and toys. Among the few practical industrial applications are the production of food packaging, containers for drugs, as well as use in bearings that do not carry a high mechanical load (for example, in modelling) which is possible due to the excellent sliding coefficient of the material.

  One of the most important factors for 3D printing applications is the low melting point of only 170-200°C, which contributes to relatively low energy consumption and the use of inexpensive nozzles made of brass and aluminium.

  PLA has a low shrinkage, i.e. loss of volume on cooling, which helps to prevent deformation. However, shrinkage has a cumulative effect as the size of the printed model increases. The cost of PLA is relatively low, which adds to the popularity of this material.

  ABS (Acrylonitrile Butadiene Styrene) is also one of the most popular thermoplastics used in 3D printing, but not the most common. This contradiction is due to certain technical difficulties that arise when printing ABS. In the industry, ABS plastic is already widely used: the production of car parts, cases of various devices, containers, souvenirs, various household accessories, etc.

  ABS plastic is resistant to moisture, acids and oil and has a fairly high temperature resistance – from 90°C to 110°C. Unfortunately, some types of material degrade when exposed to direct sunlight, which somewhat limits their application. At the same time, ABS plastic is easy to paint, which makes it possible to apply protective coatings to non-mechanical elements.

  The main disadvantage of ABS plastic can be considered a high degree of shrinkage during cooling – the material can lose up to 0.8% of its volume. This effect can lead to significant deformation of the model, curling of the first layers and cracking. To combat these unpleasant phenomena, two main solutions are used. First, heated work platforms are used to reduce the temperature gradient between the lower and upper layers of the model. Secondly, 3D printers for printing with ABS plastic often use closed cases and adjust the background temperature of the working chamber. This allows the temperature of the applied layers to be kept just below the glass transition threshold, thereby reducing shrinkage. Complete cooling is carried out after receiving the finished model. Thirdly, when the plastic is heated, vapours of acrylonitrile are released – a poisonous compound that can irritate the mucous membranes and poison. Although the volume of acrylonitrile produced in small-scale printing is small, it is recommended to print in a well-ventilated area or provide a fume hood.

  PETG – this complex name hides the material used for the production of plastic bottles and other foods and medical containers. PET stands for polyethylene terephthalate and G indicates that it has been modified with glycol for greater durability.

  The material has a high chemical resistance to acids, alkalis and organic solvents. The physical properties of PETG are also impressive in its high wear resistance and tolerance to a wide temperature range – from -40° C to 75°C. In addition, the material is easy to machine.

  PETG is very durable. But at the same time it is easier to scratch than ABS, which is harder. Less flexible than PLA or ABS, but also softer. It hardly shrinks, so it does not warp. Ideal for large printouts.

  PETG plastic provides excellent support structures as it adheres well. As a result, the adhesion between the layers is fantastic, so the prints are durable. To achieve transparency of the models, rapid cooling is required when passing the glass transition threshold, which is 70°C – 80°C.

  There is still a wide variety of different types of plastics, differing in the degree of environmental friendliness, density, and melting point. But I indicated mainly the types that we use for our personal purposes. Except for ABS, due to its conditional toxicity and operational complexity.

  This is where I would like to finish the first part, which describes the hardware components of a 3D printer. In the next part, you will find out which software should be used to prepare a model for printing, its modifications, and what settings are ideal for almost any model. See you soon!


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