Elforlight Laser

Additive Manufacturing — SLS Materials 20

June 2012

Alongside the twenty year anniversary of The TCT Magazine lies another twenty year milestone of interest, the introduction of Selective Laser Sintering (SLS®) to the additive manufacturing market.

Where did it all start? The technology of Selective Laser Sintering originated in the mid 1980s when it was pioneered and patented by Dr Carl Deckard at the University of Texas. As is well known today the technology uses a high power laser to selectively fuse small particles of powdered material, by scanning cross-sections generated from a CAD file into a desired 3-dimensional shape. The technology produces parts from a variety of base materials ranging from wax and polystyrene to nylons and metals.

In the late 1980s a group of investors including BF Goodrich were involved in early material development, but it was only after the technology was licensed to DTM Corporation that the first machines were installed in beta sites at Kodak and the University of Louisville in 1991, with the first commercially available Sinterstation® 2000 from DTM being introduced to the market in 1992. Then just 2 years later EOS entered the European market in 1994 commercialising their first EOSINT Laser Sintering equipment. So twenty years on, how has material development helped this technology to evolve?

New Material Suppliers 3D Systems completed its acquisition of DTM in 2001 but it took until 2004 for the Laser Sintering market to start moving forward with material developments, following three years where little of significance had happened whilst EOS and 3D Systems were in litigation. New material suppliers entered the sector to compete against 3D Systems and EOS including Advanced Laser Materials (ALM) in 2004, Exceltec in 2004 and CRP Technology, already active in Europe, entered the US market in 2006.

ALM (www.alm-llc.com), based in Temple, Texas has grown to become one of the leading providers of laser sintering materials, supplying an extensive range of high performance powders based on Nylon 11, Nylon 12, Polystyrenes, TPEs (thermo-plastic-elastomers) and PEEKs (polyether-ether-ketones). Developed in close cooperation with customers, the current range consists of more than 50 materials, from base resins, glass or mineral filled, carbon fibre reinforced materials and flame retardant formulations through to high performance, processable Nylon 11s, conventional stabilized Nylon 12s, specialist polystyrene and TPE powders as well as customised materials developed under contract. Through a strategic partnership entered into with EOS in 2009, ALM also offer customers specialist high temperature laser sintering powders with a heat deflection temperature (HDT) of 165°C. Partnerships with DSM Somos® (www.dsmsomos.com) and Integra Services (www.integra-support.com) also allow ALM to offer stereolithography (SL) materials and full service solutions for all laser sintering and stereolithography platforms. ALM distribute their performance sintering powders into the UK market through their distributor RP Support (www.rpsupport.co.uk)

Exceltec (www. exceltec.eu), based in Chassieu, France distributes a small range of polymer powders into the European market. The InnovaPA range of materials consists of five powders, three nylon 11 materials; an unfilled powder available in black, a glass filled formulation, and one powder developed specifically for medical applications. Exceltec also offers two Nylon 12 materials; an unfilled powder available in natural, grey, black, red and blue and a filled nylon 12 with glass beads and aluminium. Exceltec also distributes FR106, a Nylon 11 flame retardant formulation from ALM.

CRP Technology (www. crptechnology.com) is an established company based in Modena, Italy supplying a specialist range of composite high performance sintering materials to produce parts for wind tunnel applications as well as finished and functional parts for limited production runs. Marketed as Windform additive manufacturing materials, the range comprises six formulations based on polyamide and polystyrene, with glass filled, glass and aluminium filled, flexible and carbon fibre reinforced materials. CRP also offers customers an in-house additive manufacturing service through the use of their Windform materials.

Material Developments As new materials were developed so did the applications for the technology. The introduction of polyamide 11 in 1993 introduced the possibility of a true functional prototype to the RP market. Interestingly, Nylon 11 and Nylon 12 have remained the base materials for the majority of sintering powders over the last twenty years but with the introduction of new grades and the development of powders with a variety of different additives, the Nylon 11 materials have significantly improved in mechanical performance now offering excellent strength and impact resistance with elongation to break at around 40%.

RPS Data Table

Original Nylon 11 materials required highly skilled operatives to build good parts but with more recent developments Nylon 11 materials have become as processable as Nylon 12 powders, originally introduced for ease of use due to a wider processing window and to improve the recycle rate of the powders. The introduction of Nylon 12 powders lead to an almost 3 x increase in SLS equipment sales but today any modern SLS equipment can be run on Nylon 11 or Nylon 12 materials which still account for 85-90% of the laser sintering powder business.

The latest high-performance polymer PEEK was introduced by EOS in 2009. The EOS PEEK HP3 material, belonging to the group of polyaryletherketone (PAEK) polymers, is a semi-crystalline, thermoplastic material producing parts that achieve a tensile strength up to 95 MPa and a Young's modulus up to 4,400 MPa, offering mechanical properties of up to 100% higher than the market dominating materials Nylon 11 and Nylon 12. The continuous use temperature ranges within 180°C (mechanical dynamic), 240°C (mechanical static) and 260°C (electrical) depending on the field of application. The PEEK materials were introduced to run on the new high-temperature system EOSINT P 800, the only high temperature hardware available on the market today, originally developed for Toyota F1. The high temperature is required to process the polymer powders that melt at 370°C. Today, laser sintering has many examples of limited run manufacturing applications. Through their relationship with EOS, ALM has developed a carbon fibre filled PEEK sintering material specifically for a US government project which is supplied to produce parts for the Lockheed Martin F-35 Joint Strike Fighter (JSF). Other specialist materials developed by ALM include a PAEK polymer supplied to Oxford Performance Materials (www.oxfordpm.com) for manufacturing biomedical implants. The technology of laser sintering is frequently seen to push the boundaries into limited run manufacturing primarily within aerospace in the US market and within medical and automotive / Formula 1 markets within Europe, where users are typically looking for the strongest, light weight materials possible. Next Generation Materials Final components in manufacturing today are made from polymers such as Nylon 6, ABS, Polypropylene (PP) and polyethylene (PE) but these polymers are currently not available to run on SLS platforms. This is a key restriction that limits how far this technology can evolve into manufacturing, so the development of high performance, cost effective powders for laser sintering in materials such as Nylon 6 is imperative.

One of the most exciting announcements about next generation materials came in May this year when ALM announced at the EOS Users Group that they are developing a new series of high performance powders focussed on alternative polymers that are commonly used for manufacturing, moving away from Nylon 11 and 12.

To do this ALM has developed and patented a new technique that allows modification of the structure of semi-crystal materials such as Nylon 6, PP, and PAEK currently not suitable to run on Laser Sintering platforms, to make them processable for this technology. Powders such as Nylons have a melting point of 184°C to 220°C providing thermal properties of parts with an HDT of 100 - 180°C, mechanical properties suitable for production applications, whilst PAEK and PP formulations will provide powders that are lower cost and recyclable to meet manufacturing price points. This promises to bring significant changes to the reality of SLS additive manufacturing in the next 12 - 24 months.

In addition to this, ALM is also developing mid-range temperature performance nylon materials for components requiring higher thermal performance with an HDT of 120°C - 130°C. Applications include under-the-hood components for automotive markets and moulds for shoe soles for designers of sports shoes. Introduction of sport shoes to the market is very competitive and designers will introduce up to 3 or 4 new designs per month. Prototype designs need to be worn and shown, which requires the manufacture of a left and a right sole, in 3 or 4 different sizes and laser sintering is the preferred method for the manufacture the shoe moulds.

To respond to the current global supply shortage of Nylon 12, in addition to switching their customers to processable Nylon 11 materials, ALM is also sourcing an alternative focussing on nylon copolymer systems. With the goals of stabilizing supply and formulating lower cost materials with improved processing, thermal stability, recyclability and mechanical properties, a supply chain is already in place, with the new materials expected to be trialled in the market within 3 - 4 months.

SLS for Additive Manufacturing Attitudes to design development and manufacturing have changed significantly over the last 20 years and we already see innovative, forward thinking companies using laser sintering for the manufacture of limited run components. In service bureaux today approximately 30 - 40% of their business is for manufacturing, with the remainder for functional prototype parts, and the limited run manufacturing proportion is growing. However, if the future of SLS is to truly be manufacturing and not prototyping, significant changes to both materials and hardware need to be implemented.

The development of SLS hardware has come a long way since the first Sinterstation 2000 platform that had refrigeration units for running wax materials, to the sPro range of printers from 3D Systems or the EOSINT P 800 from EOS today but current hardware platforms have no auto feedback on controls, and as heaters degrade over time, IR sensors change over time and laser power reduces over time, these variables that need to be controlled are not yet built into the systems to meet manufacturing standards. Calibration of IR sensors or checking the thermal gradient across the powder bed may be possible at the start of a build but how do we determine whether the laser power remains constant during the build? All SLS platforms can run unattended but how do we guarantee everything is perfect during the build which may run for 36 hours? Today many companies build sacrificial parts such as tensile bars and by checking the mechanical properties of the tensile bars, this shows if the parts built for manufacture are acceptable but is this reliable enough for true additive manufacturing?

By combining hardware platforms that have improved built in controls for manufacturing with materials that have mechanical properties more consistent with those used in manufacturing today such as ABS or Nylon 6, the more realistic additive manufacturing will become.

®Sinterstation and SLS are registered trademarks of 3D Systems Inc. ®Windform is a registered trademark of CRP Technology's Pro is a trademark of 3D Systems Inc.

Images

The EOSINT P760 Laser Sintering Equipment
(Image courtesy of EOS)
 
Laser sintering powder PA 250 ACF, aluminium and carbon fibre filled, 200X magnification
(Image courtesy of ALM)
 
Sintered part being removed from the powder cake
(Image courtesy of Paragon Rapid Technologies)

 
Laser sintered biomedical implant
(Image courtesy of Oxford Performance Materials)

 
ALM PA 850 black, a new nylon 11 powder
(Image courtesy of RP Support)

 
F-35A Lightening II
(Image courtesy of Lockheed Martin, photographer Paul Weatherman)              

 

David Storey is Executive Director at RP Support Limited.
Rick Booth is Vice President at ALM LLC.
 


RP Support Ltd.
14 Bridgegate Business Park Gatehouse Way
Aylesbury
Buckinghamshire
HP19 8XN
United Kingdom

+44 (0)1296 425665
+44 (0)1296 425665

support@rpsupport.co.uk

Registered In England & Wales
Company Number: 6674645
VAT Registration: GB 911 5976 15
D-U-N-S Number: 217885314

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