Comparison of 3D Printing Technologies: MJF and SLS
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  • Comparison of 3D Printing Technologies: MJF and SLS

Comparison of 3D Printing Technologies: MJF and SLS

When you want to produce plastic parts with superior mechanical properties, complex structures and high surface details with industrial rapid prototyping services, the two most preferred technologies are MJF (Multijet Fusion) and SLS (Selective Laser Sintering) technologies.

Comparison of 3D Printing Technologies: MJF and SLS

When you want to produce plastic parts with superior mechanical properties, complex structures, and high surface details with industrial rapid prototyping services, the two most preferred technologies are MJF (Multijet Fusion) and SLS (Selective Laser Sintering) technologies. 

With the development of additive technologies, different types of technologies have emerged and are frequently compared in terms of their advantages. We can say that MJF and SLS technologies, which produce with polymer materials, both the features of the parts they make and the manufacturing techniques are pretty similar, are in a race with each other. 

Numerous advantages of polymer materials make them the most widely used technologies in this field, such as low cost, easy shaping, and manufacturing of light parts due to their low density, low electrical insulation, and thermal permeability. These two 3D printing technologies that work on the principle of fusion on a powder floor differ in many aspects, although they process almost the same material with a similar technique. Let's state that the basis of this separation is the difference in the heat sources that sinter the materials, and let's compare the SLS and MJF technologies in detail in the continuation of our article. 

Fusion on Powder Ground 

According to the ASTM standards, fusion on Powder Ground is a predetermined seven-layered manufacturing process. It is also divided into technologies that use polymer and metal materials. The powder particles of the polymer material are produced specifically for these technologies in a specific diameter range. This material, placed in the powder chamber inside the machine, is laid on the printing surface in layers with a roller-like element. With an energy surface, certain parts on the powder surface applied according to each layer's cross-section data are fused and combined. 

After this cycle, which is reapplied for each layer, a dust-filled cabinet with objects is obtained. To improve the mechanical properties, the cabin is kept at a specific temperature for the last time and then colled; in technical terms, it is tempered. Objects are sorted out from this dust-filled cabinet and sent for final processing, while the remaining dust is transferred to the chamber for reuse. It should be noted that the powder that is not sintered once it's inside the cabinet must be mixed with new powder at a specific rate to be reused. The produced objects are separated from the unfused dust on their surfaces. These objects, which can be painted as wanted, are now ready for use. 

 

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SLS and MJF 

We briefly introduced the fusion technique on powder ground. We can easily compare the technologies that work on this principle and produce them with polymer materials. The first of these techniques is SLS (Selective Laser Sintering). SLS technology has been in our lives since 1992. It produces using polyamide 12 (PA12), a nylon derivative. Its prominent feature is the use of a laser as a heat source. A laser at the top of scans over the powder lying on the printing area processes the cross-sectional image of the object there. 

Another technique is MJF (Multijet Fusion) technology. The HP company developed and patented this technology in 2016. Although it uses PA12 material like SLS, the two materials are different from each other and use a specially produced PA12 derivative. The material used directly affects both the mechanical and visual properties of the final product. The mesmerizing feature of MJF technology is the fact that it is produced by spraying chemicals onto the print table over the printheads developed by the same company. Then, the energy emitted by infrared ray lamps passing over the printing table is absorbed by these chemicals, and the powder is fused. Due to this feature, MJF technology can be called a combination of SLS and another layered manufacturing technique, Binder Jetting. 

These fundamentals differences caused by the heat source affect the printing speed. With linear spraying, SLS scanning with a point laser is slower than MJF technology. Another effect is that SLS PA12 powder, which is not directly exposed to the laser beam, can be mixed with 50% fresh powder to be reused, while non-sintered MJF PA12 powder can be mixed with 20% fresh powder. From another point of view, while 15-20% of the print volume can be produced in a manufacturing with SLS technology, the reliable rate in MJ technology is between 4-8%. That is, the heat management with the print volume is better in SLS technology. 

MJF makes up for this gap in technology with the post-manufacturing cooling method. While the cooling work is done at the particular cooling station, a new product can be started at the manufacturing station. Considering these features, it is possible to produce a batch product with the same amount and volume in a much shorter time with MJF technology. Although MJF is presented as more suitable in theory in terms of cost, the high price of raw materials can cause the unit cost to be much higher in low manufacturing volumes. I don't find it right to generalize as the price may vary depending on the lot produced. 

 

Product Properties

Let's compare these technologies, which differ in technique and operation, to the final product. The concept of dimensional accuracy is critical when it comes to additive manufacturing. Unfortunately, contrary to conventional methods, it is challenging to produce products with high dimensional stability with additive manufacturing. The deviation value, which is ±0.3 mm in SLS technology and ±0.3mm depending on the part dimensions, is specified as ±0.2 mm in MJF technology and ±0.3mm depending on the size. This amount of deviation is affected by factors such as environmental conditions and the interaction of parts with each other in both technologies. Layer thickness is usually kept constant in this technology group. This value is 80 microns for MJF and 100 microns for SLS (may vary by model). With the help of the layer thickness and the inkjet technology it uses, it is challenging to distinguish the layer lines in MJF technology. This provides a visual advantage over SLS technology. Thanks to the chemicals sprayed with inkjets, details with a wall thickness of 0.25 mm can be produced with MJF technology. For the SLS, the minimum level of detail is 0.30 mm. Note that these values differ from the minimum wall thickness.

Another critical concept is mechanical strength. Due to the nature of additive manufacturing, the adhesion direction of the layers is the weakest mechanically. The most significant innovation brought by MJF technology is that it offers equal strength in all axes. The tensile strength of MJF technology is 48 MPa in the XY and 42 MPa on Z-axis. We confirmed this claim of MJF technology with the tensile tests we conducted on various samples we produced. 

Likewise, we can say that MJF technology is more advantageous in elongation at break. In the nail structures of the parts made, the manufacturing with MJF technology is more durable, and with SLS technology, they display a more fragile design. For details, you can examine such characterization studies in the literature. As a final criterion, let's make a visual comparison. 

While the parts produced with MJF technology are gray due to heat-absorbing chemicals, the pieces produced with SLS technology are white, which is the color of polyamide itself. In this way, the parts made with SLS can be painted in any desired color, while this color scale is limited in MJF. As we mentioned before, the layer lines in MJF technology are almost indistinct compared to SLS. 

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Last Comment 

Among these technologies, which are very similar but have different advantages on their own, we can say that MJF technology stands out with some of its features. It would be more accurate to choose between MJF technology, which is more advantageous in terms of operation, faster manufacturing, mechanically superior products, and SLS technology, which has a more established history, can be kept at a higher manufacturing intensity, and is advantageous in terms of coloring products, according to the intended use of your parts. You can get manufacturing service from Tridi with both MJF and SLS technology, and you can compare the technologies yourself if you want.

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