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SLA & SLS -The NEXT LEADING TREND MIRACLE OF PROTOTYPING INDUSTRY

Nowadyas,3D printing (SLS&SLA) is our mainstream technology, which will occupy an increasingly important position in the prototype industry.

 sla sls


Posted on: July 13, 2018, | By Will, WayKen Project Manager

With the technology development, 3D printing technology has gradually evolved from concept to reality. Since 2013, "3D printing" has become one of the most popular words in the world. As early as 2000 around, China had imported commercial rapid prototyping equipment, among the main application was industrial 3D printing. Because of various restrictions on materials, the 3D printing industry was developing slowly. Domestic 3D printers is basically used as R&D equipment as well as design the prototype models.

Therefore, more than 90% of 3D printing users on the market today are industrial customers. Although the number of civilian customers is growing, the speed of growth is still very limited. Mainly it is because 3D printers (rapid prototyping machines) are expensive in equipment, materials, and require high professional knowledge. Before 3D printing technology completely enters people's daily life, it still has a long way to go.

First of all, if you want to print out any shape of the item, you must know how to use the 3D design software to draw the 3D model of the item. However, it is not easy for ordinary people to learn these softwares, without certain expertise knowledge related 3D design software. Therefore, it is impossible for most people to design a personalized product.

Secondly, materials are the weakness of 3D printing technology. The raw materials for 3D printing are rather special, and their toughness cannot be compared with industrial plastics. At present, the mainstream rapid prototyping materials are photosensitive resins, ABS, PC, nylon powder, gypsum powder, wax, and so on. Metals are limited by the processing method, with less extensive materials applications. From a cost perspective, current cost of 3D printing material is still very high. For example, when printing a paper cup-sized product, the price of the material may reach 100-200 RMB, ordinary people can't afford it. Thus, it is difficult for 3D printing to replace products under scale production method in a short time.

When it comes to 3D printing technology, SLS and SLA are the most commonly used technologies. SLS is called powder sintering and uses powder coating to lay a layer of powder material on the top surface of the molded part and then heat the material to a temperature just below the sintering point of the powder. The control system regulates the laser beam according to the cross-sectional profile of the layer is scanned over the powder layer, causing the temperature of the powder to rise to the melting point, sintering, and bonding with the portion that has been formed below.

After the first layer is completed, the workbench is lowered by a layer of thickness. The spreader roller is covered with a layer of uniform dense powder and a new layer of cross-section is sintered until the entire model is completed. SLA stands for selective curing technology for photosensitive resins. The liquid bath is filled with a liquid photosensitive resin that cures rapidly under the ultraviolet laser beam emitted by the laser (SLA is different from the laser used by SLS. SLA uses ultraviolet laser, while SLS uses infrared laser). At the beginning of the molding, the lifting table is below the liquid surface, just at the height of a section thickness.

The laser beam focused by the lens scans the profile along the liquid surface according to the machine instructions. The resin in the scanning area is rapidly cured, thereby completing a layer of cross-section processing process to obtain a layer of plastic sheet. Then, the workbench descends the height of the cross-sectional layer and solidifies the other cross-section. In this way layers are stacked to construct a 3D entity. Then, how to distinguish these two technologies, please see the following points:

sla sls-2

                                   SLS                           SLA
Raw material used Vary from Nylon powder, poly carbonated carbon powder, acrylic polymer powder, vinyl chloride powder etc… with good performance can only use liquid photopolymer, its performance is not as good as thermoplastic or thermosetting plastics
Accuracy reached Material shrinkage as high as 2% to 4%, accuracy is just so so Material shrinkage is less than 0.4%,can produce more detailed parts, need to be post-cured, and there will be residual stress in the workpiece dimensional stability is not good enough, after a period of time, additional shrinkage and creep will occur
Surface finish Temperature of the powder material just reaches the melting point and does not flow well and fills the gap between the powder particles during sintering process. Therefore, the surface of the finished part is loose and rough relatively smooth
Sharpness of the feature structure Common Better than SLS but not good at edge positions
Strength High Low
Machining performance Materials are easier to machine and can be easily milled, drilled, and tapped Required careful handling to prevent work pieces from cracking
Resistance to the environment Resistant to the environment (temperature, humidity, and chemical corrosion) similar to thermoplastic materials Poor resistance, SLA parts with epoxy resin are susceptible to moisture and chemicals. Erosion will soften and warp in environments above 38°C.
Appearance Strength is good, and it is not easily damaged when presented to the user Have a smoother surface
Testing Performance Have better performance in functional testing Have better performance in terms of shape, size and assembly inspection. But for functional testing, the parts must be subjected to a certain mechanical or thermal load, or must be placed in a wet, chemically aggressive environment.
Master use Surface finish and accuracy is not high quality enough, that is not suit for making as master Because SLA parts have a smoother surface, better dimensional accuracy, and fine features, they are suitable for use as replicated prototypes.
Mould performance Can sinter ceramic or mixed powder of metal and binder, and get ceramic or metal mold through subsequent processing Can be used to mold the wax of lost wax casting, but it is difficult to directly make other molds with higher requirements.

 

It cannot deny that 3D printing technologies such as SLS and SLA will occupy an increasingly important position in the prototype industry. However, if it became the mainstream technology in the the industry, I think there would be still a long way to go.

 

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