3D Printing

3D printing (or additive manufacturing) is a manufacturing process in which a physical part of a digital model is produced using a 3D printer. Unlike common manufacturing methods, in 3D printing the final part is produced by adding layer after layer of material until the final model is created.

There are several methods by which parts can be printed in 3D printing. Let’s talk about a some of these methods.

3D printing brings some significant innovations, mainly the possibility to easily produce complex and special geometries which was very difficult and sometimes even impossible to produce by conventional methods.

 

Although this manufacturing technology has been around since the 1980s, thanks to a number of technological advances that have taken place in recent years in the field of 3d printers, raw materials and software, today this manufacturing technology is accessible to a very wide audience.

 

Today, there are professional, cheap and compact 3D printers on the market that accelerate innovation, and support businesses from a wide range of industries such as medical, aerospace, automotive and many more.

 

How 3D printing works

At the basis of every 3D printing process is the computer model that can be produced with the help of a wide range of CAD software that are suitable for both professional designers and amateurs.

Once the model has been designed, the 3D model is “cut” into layers, meaning a conversion to a file type that the printer can read and decrypt.

The printer then executes the design and thus creates the desired part layer by layer. Hence the behavior of the printer varies depending on the type of printing process.

Because each such printing process uses different technology and different raw materials, there is a situation where there is no “one size fits all” which is suitable for all applications.

For example, there are printers that use a heat source to melt / weld layer by layer the raw material that comes in powder form.

 

Main advantages and use cases of 3D printing

3D printing, whether done for industrial or personal use, brings a wide range of advantages over conventional traditional manufacturing methods such as:

 

Part customization

3D printing allows the designer to individually change and adjust the nature and structure of the part between each print.

The great flexibility that exists in this production method makes it possible to produce a number of similar but customized parts to the requirements of the end consumer without incurring additional costs in production.

Great complexity and complexity in the geometry and structure of the part

3D printing makes it easy to produce complex geometric shapes and structures, most of which could not be created using other production methods.

The manufacturing nature of 3D printing technology gives the freedom to create complex geometries without making the manufacturing process more expensive, allowing complex parts that have been optimized in their design to have the same price as simpler parts designed to be manufactured using conventional manufacturing methods (and sometimes even cheaper) .

Significant savings on initial set-up costs

In conventional production methods one of the biggest costs is the initial set up cost of the production line.

For example, when parts are injected, each part requires a unique expensive mold, which leads to the fact that in order for the part to be profitable, it must be sold in very large quantities.

Since most prints do not require additional equipment other than the printer itself, 3D printing has a low set-up cost and the cost of each part is determined by the amount of material used, the time it takes for the printer to print the part and the additional processing cost if needed.

Ability to build prototypes cheaply, easily and quickly

One of the main uses today of 3D printing is the production of prototypes..

3D printing technology makes it possible to create prototypes at a low price and at a high speed that no other manufacturing technology can compete with.

This is due to the fact that most parts which are 3D printed by professional manufacturers are ready in a short time (sometimes several hours) and ready for delivery within a few business days.

This availability and speed makes it possible to significantly accelerate the product development process and allow the company to release a product in record time.

 

Considerations when designing parts for 3D printing

As we have seen for 3D printing there are great advantages when for a quick and customized production of parts, however there are some considerations to take into account when designing a part for 3d printing.

 

Mechanical properties differ from standard materials

Because parts produced in 3d printing layer by layer, the mechanical properties of the raw material are not perfectly preserved. Parts printed on different polymers may be more brittle, but there are methods in the industry today to significantly increase the durability of the parts.

In contrast, metal parts that are sometimes printed have mechanical properties that transcend parts that are manufactured differently and therefore it can be seen that these parts are used in industries that require the highest reliability, like the aerospace industry.

 

Non-competitive costs in large production volumes

When it comes to mass production, 3d printing costs today are not competitive enough compared to traditional production methods.

 

3D printing has low set-up costs, which makes it possible to produce prototypes or a small number of parts cost effectively. The implication of this feature is that as the quantity of parts produced increases, the price decreases very little and therefore in large volumes the costs are not competitive enough.

A rule of thumb that can be relied upon is that in the production of up to 1000 units, depending on the material and size of the part, 3D printing is economically viable.

In larger quantities, manufacturing technologies like CNC machining or injection molding will usually be more cost effective.

 

Inability to achieve high accuracy and compliance with low tolerances

Accuracy depends directly on the printing method and the calibration level of the printer. Most often, parts printed on home printers have the lowest accuracy (ranging around + -0.5 mm). This means that if we want to print in our part a 10 mm diameter drill, its true size will be between 9.5 mm and 10.5 mm.

More expensive and professional 3D printers allow for high accuracy, industrial printers reach accuracy levels of + -0.01 mm.

In addition, metal parts that are produced by printing, will usually undergo further final processing after printing in machining machines, in order to improve the quality of their surface and the tolerances obtained.

 

Additional post processing might be required

In many cases, the parts are not ready for immediate use when coming out of the printer, and further processing work is usually required.

For example, in some printing technologies it is necessary to remove supports that were created during the production process. The reason for producing these supports is because the printer is not able to produce a layer of material hanging in the air and for that purpose the printer produces supports.

The process of removing these supports is sometimes accompanied by the remaining marks and defects on the surface of the part, so an additional machining process is needed in order to remove these defects and scratches to get the desired surface quality.

Common 3D printing processes

Today there are a number of common printing technologies that can be used, we will focus on a number of technologies that we think are the most convenient and cost effective.

 

FDM

In this process, a coil of raw material (usually a type of plastic) is loaded into the printer and fed to the printhead at the end of which there is a heated nozzle. Once the nozzle heats up and reaches the desired temperature, an electric motor pushes and advances the raw material through the nozzle which dissolves it.

With the help of additional electric motors, the printer controls the position of the print head along and across the print surface, thus placing a dissolved layer of the raw material in exactly the desired place, where it cools and solidifies back. Once one layer has finished solidifying, the printing surface decreases in height and the process of printing the next layer of material begins again.

 

In most cases the part will be ready for use immediately at the end of the printing process, but there are cases where the part will need further processing such as removing the supports created during printing or smoothing the surface.

This printing process is one of the most economical printing processes when we want to produce custom thermoplastic parts and prototypes.

There are a wide variety of thermoplastic materials, which are suitable for both the production of prototypes and the production of functional parts.

This process has several limitations. First, the accuracy that can be achieved with this process is the lowest of the 3D printing technologies.

Parts made by this method have a high probability that marks and lines will appear between the printed layers that are visible and therefore further processing of the surface is often necessary after printing.

In addition, the way the gluing mechanism between the layers works, causes the parts produced in this print to be inherently anisotropic. This means that parts coming out of print may be weaker and therefore less recommended when it comes to critical applications.

 

SLA

In this printing process, an ultraviolet (UV) light source is used to solidify from a pool of liquid raw material (which is called resin) layer by layer the final part. In the SLA process the light source used is a focused laser beam that strikes the material.

At the end of the printing process, it is necessary to clean the residue of the liquid raw material that sticks and remains on the surface of the part and expose the final part to ultraviolet light in order to improve its strength.

In addition, the supports that were formed during printing must be removed, and finally if a certain surface quality is needed then the further processing part should be moved until the desired texture is obtained.

This printing method makes it possible to create parts with high precision and complexity and a very smooth surface texture, and are therefore very suitable when it is necessary to create a prototype with impressive visual features and small series of products.

There are a wide variety of materials specifically tailored to this printing method, from a transparent resin, a resin that allows the final part to be flexible, a resin suitable for biological uses to materials that are uniquely adapted to other specific industries and applications.

In the SLA printing process it is always necessary to add supports while printing the part, removal of these supports is usually accompanied by defects left at the points where supports were removed and therefore the part may need further processing to smooth out the remaining defects.

 

SLS

The process of SLS 3D printing – Selective laser sintering, begins by heating a container filled with polymer powder (usually a type of nylon) to a temperature slightly below its melting temperature. Then, using a unique roller or knife, a thin layer (usually 0.1 mm thick) of the powder is spread over the construction surface inside the printing chamber.

Now, a focused laser beam scans the spread powder layer, and selectively heats and melts the powder particles and binds them together until the desired cross-sectional area of ​​the part is obtained.

Once all the planned cross-sectional area has been obtained, the construction platform descends slightly and again the raw material powder is scattered along the construction surface so that the process is repeated until the desired part is obtained.

The end result is a printing compartment filled with the raw material powder and in the center the final part is covered with powder.

At the end of the printing process, the print compartment should be allowed to cool before removing the printed part from the raw material powder. Further processing can be performed on the printed part in order to improve its external appearance, treatments such as painting or sanding are suitable for achieving this result.

Parts printed with SLS technology will usually have excellent mechanical properties, so they are very suitable for functional applications or practical prototypes. Because this printing technology does not require the production of supports, complex and complicated geometries can be printed very easily.

SLS technology is also very suitable for producing small to medium quantities of parts, because several parts can be printed simultaneously at each run and operation of the printer.

SLS printers are most commonly used by factories and industries with large economic means, this fact limits the availability of printers and technology and thus increases the cost of printing compared to technologies like FDM or SLA.

Parts printed using SLS technology will have a rough texture and pores along the outer surface. If the part is required to have a smooth or waterproof texture, further processing is required after printing.

 

MJF

Today there is a printing technology that’s very similar to SLS called MJF – Multi jet fusion – this technology uses the same physical principles to melt the raw material powder particles layer by layer using a heat source.

The main difference between MJF and SLS is the heat source which melts the particles. If in SLS we saw that a focused laser beam is used that heats the powder, in MJF technology scattered on the desired incision area a type of ink that increases the absorption capacity of infrared radiation (which is a heat source), and then passes over the raw material powder an infrared radiation source which heats and causes the parts on which the ink is found to melt.

Parts manufactured using this technology have similar characteristics to parts manufactured using SLS technology.

 

PolyJet

3D printing with this technology is very similar in principle to standard ink printing. However the main difference is that in standard ink printing the printer is able to print a single layer of ink on a piece of paper, in PolyJet 3d printing the printer prints multiple layers of material on top of each other until the final part is obtained.

The process is carried out using a large number of nozzles which simultaneously spray drops of photopolymeric material on the construction surface. These drops immediately solidify into a layer of hard material due to exposure to ultraviolet (UV) light that illuminates them from the moment they exit the nostrils.

Once the raw material layer has solidified, the construction platform descends slightly downwards and the process is repeated until the final part is obtained.

Even in this printing process it is always necessary to print auxiliary supports during the construction of the part. In order to allow easy and quick removal of the auxiliary supports after the printing process, a water-soluble material is usually used in the construction of the supports.

PolyJet technology is the highest precision printing technology among the technologies presented. It is also one of the few technologies that allow parts to be printed with several materials in parallel.

Parts manufactured with this technology have a smooth surface texture similar to the texture obtained by casting production, and have excellent precision dimensions, which makes the technology very suitable when we want to produce prototypes or parts with a realistic and impressive exterior appearance.

Printing using PolyJet technology is one of the most expensive printing technologies on the market and therefore for this reason the technology may not be economically viable for some applications. In addition, parts manufactured using this method will often not be suitable for functional applications because similarly to SLA technology, manufactured parts tend to be very brittle and sensitive to UV radiation emitted from the sun, which causes the mechanical properties of the part and its color to weaken and fade over time.

 

Common materials in 3D printing

3D printing is a process that is suitable for a wide variety of materials. Different types of plastics (both thermoplastic and thermostatic) are the most common followed by metals. There are also a number of composite and ceramic materials that are suitable for the process but are less commonly used.

3d printing
Metal 3D printers (DMLS)

Plastic materials

 

PLA

This is the cheapest and most common material for 3D printing. Very suitable for the production of non-functional but high-precision parts and prototypes. Not suitable for high temperature applications.

 

ABS

Commercial plastic with better thermal and mechanical properties compared to PLA, with high resistance to impact and blows.

 

Resin

Thermostatic polymer which allows to produce parts with a very high level of precision which is similar to the level obtained by manufacturing by plastic injection. Very suitable for the production of prototypes, etc.

 

Nylon

Nylon, also known as polyamide (PA), is a polymer with excellent mechanical properties and high resistance to chemicals and abrasion. Very suitable for functional and useful parts.

 

PETG

This polymer is very suitable for 3D printing thanks to the ease with which it can be processed and printed. This polymer has high resistance to damage and blows, as well as high resistance to moisture and chemicals.

 

TPU

It is an elastic thermoplastic material with low rigidity and a touch feel reminiscent of a high-elasticity rubber touch.

 

ASA

This polymer has mechanical properties similar to ABS but with a higher suitability for use in 3D printing, high resistance to UV radiation and chemicals. Most often used in 3D printing parts which are intended for open field applications.

 

PEI/ULTEM

It is a thermoplastic engineering material with very good mechanical properties and very high for heat, fire and chemicals.