ISO-tensile bar made of PA12-RC on SPRO60HD-HS by 3D Systems
A common misconception of 3D printing is that the industry just uses what raw material is needed having zero waste. While it is true, the industry uses significantly fewer materials than subtractive processes, anybody who has operated a selective laser sintering (SLS) machine will tell you that waste is a huge problem.
“SLS materials must be refreshed at rates of between 33% to 50%,” says Dr Sören Grießbach Managing Director of GS Pro GmbH. “Not refreshing or refreshing with less virgin powder can cause inappropriate parts. On average, SLS builds yield or consume about 6-8% of the powder in a whole part cake, losing approximately 25-40% of the unfilled PA12 powder because suggested refresh rates are around 50% part cake material. A mid-frame machine has an average throughput of about 1 kg/h meaning that 0.25-0.4 kg of waste is created per hour. Production machines run about 5,000 h/year, potentially losing 1.3-2 tonnes per machine per year.
“In financial terms, this translates to throwing away about 60.000-120.000 EUR per year.”
For companies like Digits2Widgets, a UK based service bureau that prides itself on its powder refresh rates, it isn’t just the cost of the waste material; there’s a cost for collection and disposal.
“Used powder is considered hazardous both regarding the inhalation of fine particles and also because it’s highly combustible,” says Design Director at Digits2Widgets, Jonathan Rowley telling the cautionary tale of exploding windmills when the miller lit a pipe, igniting the flour particles in the air. “We accumulate the waste powder until our designated storage area is full. We then order a collection, and the disposal costs a couple of hundred pounds about four times a year.”
Dr Sören Grießbach’s company, GS Pro have been working on a proprietary remanufacturing process from their Chemnitz, Germany base, which seeks to improve this wastage issue.
“Our recycled powders and associated process parameters can create parts with superior mechanical properties as compared to OEM powders,” Says Sören. “GS Pro refines powder for repeated use, and there are several ways to use it. It's possible to use standalone refined powder or to create a closed loop of material use and recycling.
“Instead of mixing in 50% virgin powder it is possible to reduce that amount down to 10-15% by using 35-40% refined powder alongside regular overflow, and part cake blend.”
GS Pro's material mechanical behaviours
GS Pro has been working with clients across the globe for the past eight years to establish some best practices when using refined powders. The technology is verified to work on 3D Systems SLS machines including its HiQ, higher speed range and recent test results have proven the possibility to run it on EOS and Farsoon systems.
“Some customers run 100% refi ned powder mixed with overflow powder for the best surface finish, part quality and mechanical properties,” explains Sören. “There are benefits like eliminating the sieving of part cake powder and because our system is a closed loop the part cake gets saved, sent for remanufacturing and the customer gets their recycled powder back to use as virgin powder, with no wastage.”
As well as a reduction in your carbon footprint, other benefits include less outgassing and condensation of vaporised polymers on filters, sensors and lenses, potentially extending a machine run time between service calls. But, material properties are the number one priority for end-users, how do GS Pro’s refi ned materials compare?
“The values for impact strength and Elongation at break are approximately two times higher than regular OEM nylon 12,” says Sören. “Not only are we able to attain higher peak values, but we can also get more stable material characteristics and part quality across the entire build. With our full tested machine parameters, it is now possible to build parts with stable quality even at cold spots of the part bed.”
