“ExOne – 3D Sand and Metal Printing Using Binder Jetting Technology”

Friday, 5 October 2018

Branch President Darren Pritchard, MICME, welcomed members and guests before presenting Dr Arron Rimmer with the Kevin Cartwright Award for his lecture entitled “The market opportunities for carbidic austempered ductile iron”. This award is given to the person who, in the view of the branch council, gave the best lecture during the previous presidential year.

Darren introduced tonight’s lecture by David Stevenson, Senior Sales Manager at ExOne a company at the cutting edge of sand and metal printing technology. David said that ExOne is an American company with eight locations world-wide. It is one of the leading manufacturer of binder jetting sand and metal printing systems in the world. The organisation employees some 300 people and has its European headquarters in Germany which is also the centre for the manufacture of the sand printing machines. The metal printing machines are manufactured in North Huntington in the USA. David’s talk would be mainly on sand printing as this would be the main interest to foundries and hence the evening’s audience but he would speak briefly about the metal printing side of the business.

The Massachusetts Institute of Technology developed 3-D binder jetting technology and ExOne granted exclusive license of the process. Since then extensive developments have enabled ExOne to create markets in aerospace, automotive, pump, oil & gas and many other industries. The materials available include a range of stainless steels, tool steels, tungsten carbide, Inconel and other non-metallic materials. This range is constantly being extended with customers and markets creating the demand.
In metal printing, the metal powder spreads on to the build platform of the build box and binder jets onto it. The form is developed in layers before the parts are sintered to create the finished product.

In 1999 a group of German engineers developed the sand printing process and the manufacture and development of sand printing machines is still centred in Augsburg, Germany. Since the sale of the first machine in 2001, machines are now in place in foundries throughout the world, though some 50% of machines in existence are located in Europe. The smallest sand printing system, S-Print® has a build box sized at 800 x 500 x 400mm, which is the entry level system. ExOne’s most popular sand printer system is the S-Max®, which has a build box dimension of 1800 x 1000 x 700mm. A second build box on the machine gives increased output and even greater flexibility.

The machines mainly use silica or synthetic sand such as Cerabeads but other customs/local sands can be qualified on request. Different binder systems can be utilised such as furan, phenolic cold setting binders, phenolic hot setting binders and an inorganic silicate system.

Sand printing begins by premixing the sand with the catalyst and then spreading a layer of this, typically 0.28 - 0.38mm thick, over the build platform. The print head then jets binder onto the sand as determined by the CAD data file, which is “sliced” into print layers before printing. The platform lowers by a layer thickness, a second layer spreads onto the first layer, and the print head again traverses the platform jetting more binder onto the new layer of sand. The process continues until the build box is finished, at which time the uncured sand can be removed and recycled, ready for the next build. The cores or moulds extracted from the build box are cleaned and ready for casting.

The process allows intricate and complex core shapes, printed directly from CAD data without need for pattern or corebox giving total design freedom. In prototyping, or a production environment, changes to design just require a change to the CAD data. This provides a degree of flexibility not easily possible by conventional means. Near net shape and no joint lines reduces fettling and final machining providing cost saving and in some cases better performance from the component. Cores can, where design permits, be produced hollow thereby reducing gas evolution and permitting better venting and/or breakout. To demonstrate the precision, flexibility and complexity possible David circulated examples of printed cores.

A Q and A session completed the presentation before John Willetts, Prof MICME, gave a vote of thanks for an excellent and very interesting technical lecture. The members and guests then enjoyed and excellent buffet sponsored by ExOne.