Lightning and plastic on a powder bed

HP introduces recently a new powder bed 3D printer About this printing technology in the next post.

Truffles, which are identified with French cuisine, are considered some of the most expensive foods

 fulgurites  fro a lightning strike,

around, and surprisingly, they grow wild in the Israeli Negev desert by the roots of the Shimshon plant. A handful of experts can find and remove the small mushroom from the ground. Bedouins residing in the south of Israel believe that they are created by lightning striking the ground and they go looking for them after thunderstorms.

Thunderstorms probably don’t create edible mushrooms, but the massive energy transferred to powdery sand in a lightning strike can print 3D glass objects. The phenomenon is known as fulgurites and the glass objects created deep beneath the sand are called lightning glass.

SLS 3D printers work in a similar method, by concentrating energy on a powder bed or tray covered with plastic powder. The Powder printing is so successful and common that most of the parts currently manufactured today using 3D printing are created using this technology as it is the only technology that allows mass serial production of end products using 3D printing.

Powder bed

Powder bed and plastic printing

Until recently, Selective Laser Sintering (SLS) was generally accepted as the only way of producing high-quality printed plastic parts for production using a quality thermoplastic material, generally, polyamide also known as Nylon 12.

SLS printers print in a closed and temperature-controlled chamber, heated to above 170 degrees Celsius. Inside the chamber is a tray (bed) moving on the vertical axis (z). Plastic is spread and compressed on the tray using a roller. The laser device at the top of the chamber emits a beam directed using mirrors, which draws a mask on the powder on the XY axes. The beam sinters the powder where it hits it, or in other words, make the material solid by heating the grains. After sintering, the tray with the powder drops about 100 microns down on the z-axis and a re-coater spreads another layer of powder on the tray. The laser beam activates once more and the energy transferred to the powder to create an additional layer on top of the layer printed earlier.

At the end of the printing process, the printer holds a bin full of powder, with the printed parts hidden inside. After a cooling the bin, the parts are separated from the powder in the unpacking station. Most of the “cooked” powder can be reused after mixing with fresh powder at a ratio determined by the manufacturer.
The big advantage of powder bed plastic printing is the ability to stack up parts and use the full height of the bin to print parts one above each other. The non-sintered powder is used to support the printed parts, making the design and printing of supports needed for other printing methods unnecessary. Before printing, the operator plans a 3D nesting for optimal use of the printing space by placing the parts in a virtual space, like a 3D game of Tetris. Assembrix of Tel Aviv is one of the only companies that currently offer software solutions for optimal use of printer volume, a process that can take hours by hand.

Assembrix's Cloud 3D nesting

SLS printing process is complex and sensitive. There are multiple variables influencing the printing, and any small change can destroy an entire printing job. The roller that spreads the powder and flattens it on the tray repeats this action thousands of time from one side to another. Improper parts arrangement may cause the roller to pull more than just powder and lift a solid part out, which will lead to a chain reaction that will destroy the printing job. Powdered grains or fingerprints on the laser window through which the beam passes can cause a similar result. The printer’s mechanical elements, which are comprised of pistons, conveyor belts, and gears, which constantly work at high temperatures and dusty environments, are sensitive to malfunctions and required proper cleaning and maintenance. Over the years the printer's manufacturer has accumulated experience and knowledge and have greatly improved the printer's reliability, and currently, with proper use, the number of critical malfunctions is small.

Until 2017 the professional SLS printer market was divided between two companies: 3D Systems and EOS. 3D Systems is a well-known public company that has been marketing 3D printers since1986 (!) and holds a large number of technologies for printing plastic and metal. EOS is a private company, which is less familiar to the general public. The company started out by marketing alternative raw materials for 3DS SLA printers. After the companies reached an agreement that took EOS out of the SLA market, it moved to focusing on developing powder bed printers and became the world leader in the field of plastic and metal printers. Both companies offer several models of printers of different sizes. The popular mid-sized EOS printer is the P396 and 3D Systems mid-size printer is model ProX500.

The main difference between these two printers is in the powder distribution method. In EOS P-series printers, the powder is fed from the top and a metal re-coater spreads and flattens it on the tray. In the 3DS system, the powder is fed from the bottom and a roller is spreading and tightens the powder on the tray.

HP Jet Fusion 3D

HP is a world leader in computers and inkjet printers. HP is also one of the first major corporations that enter the field of 3D printing with its own original in-house new technology. The new printer, from the Barcelona development center, is designed to compete directly with the two market leaders EOS and 3DS. HP has developed a new printing method using a powder bed platform, taking advantage of the company’s immense experience with 2D ink injection technology.

Have you noticed that the laser beam plays an important part in SLS printing? The laser creates the added heat on the powder bed, changing the area marked by the beam from powder into solid. Both EOS and 3DS mid-size printers have a single fixed laser head that produces a beam directed by a system of mirrors. When the laser beam hits the surface, it creates a 600-micron diameter circle. The temperature distribution is not equal across the circles, and as it is hotter at the center, the laser beam needs to pass once more on the sintered area with a small offset on each passage in order to create an overlap between the circles. The laser beam is diverted on the XY axes using a mirror, and when the distance is increased from the center of the tray, the beam becomes elliptical and precision is impacted. In addition, the laser beam must scan the entire surface on each layer, for a few seconds each time, which accumulates into a great deal of time.

HP Jet Fusion 3D 

HP identified the laser as the weak point of the SLS method and decided to do away with it. In order to provide concentrated heat to a defined area in the Jet Fusion 3D printer, the company added an ink injection head to the Jet Fusion printer, which releases, in a very precise manner, a special agent on the powder surface in the area they want to turn solid. The agent is a heat conducting material. After the agent is printed, the entire layer is exposed to uniform heat. The inked area absorbs the heat and changes the state of the powder to solid. The agent itself evaporates in the process and does not influence the plastic characteristics. HP claims that this method allows better control of the material solidification, allows the production of more precise parts with local control of mechanical characteristics such as flexibility and rigidity. In addition, getting rid of the selective laser and

moving to heat radiation on the entire surface at once make the printing processes much faster and allows the recycling of 90% of the powder remaining after printing. As of today, 3D products produced by HP printers are very similar to those received from SLS printers in terms of surface quality or preservation of details, but while SLS printers mainly produce white colored parts, the HP printers are only capable of producing parts in shades of gray. For various applications, such as optical equipment, this may be an advantage, however, HP parts cannot be dye in bright colors using the common and fast method of dying with fabric paints like RIT. According to HP, they are in advanced stages of developing a color head that will allow them to add color to each later and maybe even conducting paint at some point. The HP printing method promises an interesting future and additional innovations that will take the technology to new places.  

Will HP succeed to conquer the market?

As for today, HP printer does not have any technical advantage over the EOS and 3DS. HP is claiming that their price is the lowest, and their printer is the fastest, however, examining closely, reveals that the differences are not that big. The HP printer still needs to prove itself with its precision, the production of big parts, parts with thin walls or complex detailing with and to prove the resilience and endurance of the printer through time. The greater advantage of HP lays in its distribution channel and support networks. Buying HP is an easy decision for corporates that already use HP services and products.  

3D printing is a new production technology that requires adopting new design rules and strategy. HP should focus on exploiting its position in the market to recruit new customers, find applications suitable for the printing system and educate the market to move to 3D serial production.

What next for SLS?

EOS P500

Until recently SLS printing technology progressed slowly. Leading companies released updates and improvements sparingly and insufficient investment were made in the development of new materials. HP entering the game bring a new spark for the SLS industry. EOS has already responded with the launch of the new P500 printer that will hit the market soon. The EOS P500 will increase the range of SLS technology and challenge HP by using two laser heads, improving the printing speed and allowing high-temperature printing for advanced engineering materials such as PEEK. Other companies are already working on high-temperature printing that will enable the use of advanced plastics for the aviation, automotive and medical industries and a new startup, Aerosint, is developing a high-temperature SLS printer that prints two materials simultaneously!

Aerosint

The race to release a cheap desktop powder bed printer is also in high gear now that formlabs, that already sell a very successful desktop SLA printer, are about to repeat the exercise with the Fuse1, a $ 10,000 SLS printer that will compete with Sharebot SnowWhite and Sinterit Lisa at the desktop low-cost market.

Gal Raz

This post is written based on my personal experience and knowledge and reflect my personal opinion only 

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