Book Description

Selective Laser Sintering (SLS) is an additive manufacturing technique that uses a high power laser to sinter or melt powder, layer by layer, to build 3D shapes. However, SLS-fabricated parts may suffer from porosity, cracks, and poor surface roughness that degrade part quality. A prototype SLS system is presented for laboratory use in process parameter optimization to improve the SLS manufacturing process. The prototype SLS system was designed and built by specifications determined previously. The first part designed and built was the laser positioning system that is used to hold the high power laser and the laser positioning system to work in the X and Y plane. The second part of the design was to calculate the laser power needed to melt the powder. Properties of powder were used to calculate the laser power. A small lens was used to focus the laser beam diameter from 4 mm to 0.42 mm on matching specifications of the prototype SLS system. The powder distribution system was the third part of the design used to distribute powder on a printing table in the X and Y plane and built by using simple components. The fourth section was the system frame, made from steel. The structure was used to contain the laser positioning system, the powder distribution system, and powder table. The fifth part was the electronic and control system: one microprocessor, four motor drivers, four stepper motors, and a heater table were used as subsystems to build the prototype SLS system. A manufacturing program was used to produce the system language and to control manufacturing parameters to create parts. Operation of the prototype SLS system was validated against the design specifications. The validation included the laser positioning system movement, laser beam diameter, laser power, forward step, side step, system vibration, and system control. An interface program with Arduino was used to check forward step and sidestep, and there was a small error found during the measuring process. The accelerometer was used to check vibration in the laser positioning system while running the system with different speeds. Also, a dial and indicator were used to measure runout on the thread bar of the laser positioning system in X and Y directions. Some types of sensors were used to measure laser power and laser beam diameter. These sensors cannot check high power lasers, so four filters were used to reduce the laser power. Encoder, MyRIO, and LabView programs were used to measure stepper motor speed. After the measuring process there was no deviation between speeds that fed the manufacturing program and speeds that were checked. Finally, Response Surface Methodology was applied to build a regression model. Five variables at five levels were used in this research: forward step, side step, speed, platform temperature, and layer depth. These parameters were determined by doing some experiments in the prototype SLS system to determine which parameters will decrease or increase part defects. A total of 32 tests were used to determine mathematical models of SLS defects. A Genetic Algorithm method was used to determine the optimal solution to minimize crack width and surface roughness of the part. Results proved the manufacturing parameters affected crack width and surface roughness. The contour plot, interaction plot, and main effects plot were used to confirm and support the results.