No abstract

Selective laser sintering (SLS) is a layered manufacturing process that builds prototypes by selective sintering of materials in powder form, like thermoplastic polymer powder (Polyamide 2200), using a CO2 laser. Prototypes made by SLS are widely used in product development as they can be used for product testing. SLS prototypes, therefore, should have a very good surface finish for functional performance as well as aesthetics. However, prototypes made by the SLS process have comparatively high surface roughness due to the stair stepping effect. Surface roughness of the prototypes also depends on the various process parameters. This paper attempts to study the effect of process parameters, namely build orientation, laser power, layer thickness, beam speed, and hatch spacing, on surface roughness. Central rotatable composite design (CCD) of experiments was used to plan the experiments. Analysis of variance (ANOVA) was used to study the significance of process variables on surface roughness. In the case of upward-facing surfaces, build orientation and layer thickness have been found to be significant parameters. In downward-facing surfaces, other than build orientation and layer thickness, laser power has also been found to be significant. Empirical models have been developed for estimating the surface roughness of the parts. A trust-region-based optimization method (standard module of MATLAB) has been employed to obtain a set of process parameters for obtaining the best surface finish. A confirmation experiment has been carried out at an optimum set of parameters and predicted results were found to be in good agreement with experimental findings. A case study of a standard part ‘Truncheon’ is also presented.

Haptic perception of fine surface features is a fundamental modality to identify virtual objects. Roughness and stickiness, which are modeled as surface textures and friction respectively, are the main characteristics in terms of haptics. This research is aimed at the haptic rendering method of fine surface features based on the analysis of the surface profile. Functionally generated surface features are employed for the haptic rendering of surface textures and surface friction. Haptic rendering of anisotropic surface -surface having a dominant feature direction, and haptic rendering of heterogeneous surface -surface with a varied feature density, are investigated. Experimental measurements and prototype system implementations have been done to show the fidelity of the proposed surface feature modeling methods.

No abstract

In the present work an attempt has been made to achieve minimum average part surface roughness (best overall surface quality) for Stereolithography processed parts by determining optimum part deposition orientation. A conventional optimization algorithm based on Trust Region Method (available with MATLAB 6.5 optimization tool box) has been used to solve the optimization problem. It is observed that the problem is highly multi-modal in nature and a suitable initial guess, which is used, as an input to execute optimization module is important to achieve a global optimum. A simple methodology has been proposed to find out initial guess so that global minimum is obtained. Finally the surface roughness simulation is carried out with optimum part deposition orientation to have an idea of surface roughness variation over the entire part's surface before depositing the part. Case studies are presented to demonstrate the capabilities of the developed system Keywords: Stereolithography (SL), Part deposition orientation, Average part surface roughness. INTRODUCTIONStereolithography (SL) process is the most popular [6] Rapid Prototyping (RP) process, which creates threedimensional plastic objects directly from CAD data. The process begins with the vat filled with the photo-curable liquid resin and the elevator table set just below the surface of the liquid resin. The operator loads a three dimensional CAD (solid) model into the system. The translator tessellates three-dimensional CAD data into STL file by first order piecewise approximation of surfaces and an error namely facet deviation is introduced [12]. Support structure is designed to stabilize the part during building. The control unit slices the model and support structure into a series of cross sections from 0.025 to 0.5 mm (0.001 to 0.020 in) thick. The computer-controlled optical scanning system then directs and focuses the laser beam, so that it solidifies a two dimensional cross-section corresponding to the slice on the surface of the photo curable liquid resin to a depth greater than one layer thickness. The elevator table then drops enough to cover the solid polymer with another layer of liquid resin. A leveling wiper or vacuum blade moves across the surfaces to recoat the next layer of resin on the surface. The laser then scans the next layer. This process continues building the part the bottom up, until the system completes the part. The part is then raised out of the vat for post processing and excess polymer is cleared. The main components of the SL system are a control computer, a laser, an optical system and process chamber. The workstation software used by the SL system is known as Maestro TM [3,15].