Impact of Humidity and Temperature Powder Conditioning in Large Area Projection Sintering (LAPS)

Additive manufacturing (3D Printing) opens up new capacity for tuning geometry and in some cases material properties that were not available to researchers previously. These capabilities change traditional considerations for design of products, systems, supply chains, and even business models. While there have been some notable successes, much of what has been done with additive manufacturing largely replicates parts made by traditional processes. New design methods and tools are needed to better utilize the capabilities of additive manufacturing. One of the earliest methods of additive manufacturing (3d Printing) was laser sintering (LS). In LS, a laser is scanned over the surface of a semicrystalline polymer powder preheated close to its melting point. As the laser scans over the material, it heats the powder and fuses the particles together to form the geometry. The parts have excellent accuracy and strength comparable to injection molded components. However, there is a relatively limited range of materials that are used with the method, and material toughness remains well-below what is achieved with traditional manufacturing methods. A possible culprit in these issues is the very fast heating time that is used. In order to economically produce parts while maintaining the ability to create fine features, the laser must be focused to a fine spot that is scanned very rapidly over the surface. This creates large temperature gradients that could locally degrade the material and limited time for complete densification. The impact of these constraints is being explored by using a projected image to cure large areas (cm^2) simultaneously. This method of using a projected image to cure large areas simultaneously is known as Large Area Projection Sintering (LAPS). LAPS is a developing powder bed fusion (PBF) process that is similar to laser sintering (LS). LAPS uses a projected image from a modified high intensity projector to fuse powder particles on a selected area across the powder bed to create each layer. Through LAPS, dramatic improvements in ductility (elongation at break) were demonstrated while maintaining comparable strength to traditional LS parts while using the same raw material. Knowing the impact of the humidity and temperature conditions that the powder is exposed to prior to the sintering process in LAPS is important for predicting the properties of the printed parts and developing appropriate process controls. This poster reports the impact of humidity and temperature on the properties of PA12 parts manufactured through LAPS. The sample powder used in this study would first undergo humidity and temperature treatments that range from 30% to 90% relative humidity and 23°C to 35°C.  Percent humidity changes do not seem to affect the density and the tensile strength of the manufactured parts while high humidity results in parts with better elongation at longer sintering times.