Enhancement of Mechanical Engineering Education With Additive Manufacturing Projects

 Additive Manufacturing has allowed the engineering industry to revolutionize the design of parts due to the lack of restrictions on design geometry. This type of manufacturing has specifically led to improvements in the medical and aerospace sector. Because of the advantages provided by this process, large engineering companies are investing in the technology but are encountering two large problems. The cost of entry into these systems is exceptionally high which prohibits many from acquiring the correct machinery to suit their ideal applications. Most importantly, the parts being produced by these machines lack detailed testing compared to traditional manufacturing processes.  Developing a selective laser sintering 3D printer focused around the academic aspects of additive manufacturing will help solve these problems by producing repeatable test specimens of varying properties.

This paper presents the undergraduate research projects developed to enhance mechanical engineering education at the University of Oklahoma. Selective Laser Sintering (SLS) is an ideal form of additive manufacturing for high detail designs that require lots of traditional support material. SLS printers are frequently used with thermoplastics as the structural integrity of the part does not degrade during the heating and cooling process unlike many metals. One of the most capable engineering-grade thermoplastics is polyether ketone (PEEK). PEEK is also one of the most complex thermoplastics to use in additive manufacturing due to its elevated working temperature. These properties place an SLS printer as an ideal candidate. This printer will use multiple heat zones, adjustable layer height, and a controlled hopper system to allow the user to fine-tune every print to the ideal conditions. This printer additionally uses a fiber laser marking machine as the power source to lower the cost. These factors allow this machine to be an affordable alternative that can produce test specimens of varying specifications. In this project students are required to analyze the technical challenges of SLS based 3D printing technology. Additive manufactured parts frequently suffer from weaker physical properties compared to their machined counterparts due to the layer by layer process used. Because each layer is being cooled individually, the part ordinarily creates thousands of shear planes. Using three separate controlled heat zones, the user will be able to hold the part above its glass transition temperature until the entire part finishes, therefore, annealing it in the process. This will additionally allow for testing and documentation for the effect of heat during preheating, pre-sintering, and post sintering. These features in a small-scale machine will allow thorough documentation of how controlled heated environments can alter the physical properties of a part. This will also allow changes in required laser output power as the temperature difference to sintering can be changed. The machine will employ mechanical adjustments to fine-tune each layer that is being set down. By CNC machining the full recoater system, the user will be able to adjust the layer height before each print. This combined with a timed hopper system that can accurately release an exact amount of material means that the porosity and pressure applied by the recoater can be tuned. This will allow for detailed testing of laser interaction at different porosity levels. In addition, this will have a direct effect on print time and the physical properties of the parts being produced. A small scale SLS machine with the above features will allow for the detailed testing of PEEK thermoplastic not currently available. Using a full steel platform with CNC machined parts and an off the shelf laser the cost will be reduced to under ten thousand dollars. This machine will push the academic sector of additive manufacturing to the next level and be a key research tool in the structural analysis of printed parts.