Pulak M. Pandey

Slicing procedures in layered manufacturing: a review

Layered manufacturing (LM) or rapid prototyping is a process in which a part is produced using layer‐by‐layer addition of the material. In LM, slicing of the CAD model of a part to be produced is one of the important steps. Slicing of CAD model with a very small slice thickness leads to large build time. At the same time if large slice thickness is chosen, the surface finish is very bad due to staircasing. These two contradicting issues namely reduction in build time and better surface quality have been a major concern in laminated manufacturing. This contradiction has led to the development of number of slicing procedures. The present paper reviews various slicing approaches developed for tessellated as well as actual CAD models.

Real time adaptive slicing for fused deposition modelling

Improvement of part surface quality and geometric accuracy in Rapid Prototyping has been a major concern. Reduction in build time and increase of part surface quality are two factors which contradict with each other as decreasing build time detracts part quality because of staircase effect. There has been a number of attempts to tackle this problem and adaptive slicing procedures are proposed. In these procedures the layer edge profiles are implicitly assumed as rectangular. But in real practice the edge profiles of a layer manufactured part are not rectangular and is found to be parabolic in case of Fused Deposition Modelling. A geometrical parameter known as cusp height is limited to a pre-specified value in existing adaptive slicing procedures, which is defined for rectangular edge profiles only. In this paper, a slicing procedure is proposed for Fused Deposition Modelling based on real time edge profile of deposited layers. The procedure is implemented and examples are included to explain the adaptive slicing method.

Determination of an Optimum Parametric Combination Using a Surface Roughness Prediction Model for EDM of Al2O3/SiCw/TiC Ceramic Composite

Alumina has become one of the most popular ceramic materials used in wear-resistant and structural applications due to its attractive physical characteristics together with chemical inertness at elevated temperature. Its inherent brittleness and low fracture toughness make its machining difficult and consequently limit its utilization. Considerable improvement in mechanical properties of the single-phase alumina ceramic has been achieved by incorporating SiC whisker, TiC particles into Al2O3, which also allow electrical discharge machining (EDM) to fabricate components with complex geometry and widen the applications. This article presents an experimental investigation of the influence of parametric setting on machining performance during EDM of Al2O3/SiCw/TiC ceramic composite. In EDM, machining parameters determine the quality of surface produced. Second order regression model has been developed for predicting surface roughness (SR) in terms of machining parameters using the response surface methodology. The significance of machining parameters selected has been established using analysis of variance. The surface roughness prediction model has been optimized using a trust region method. This methodology helps to determine the best possible parametric setting for electrical discharge machining of ceramic composite.

Optimal part deposition orientation in FDM by using a multicriteria genetic algorithm

In rapid prototyping processes, the deposition orientation of the part is very important as it affects part surface quality, production time and the requirement for support structure and hence cost. Depositing the part with thinner slices results in a larger build time. At the same time, if a large slice thickness is chosen, the surface finish is very poor due to stair-stepping. These are two contradicting issues and are tackled by using adaptive slicing. In adaptive slicing, slice thickness is calculated based on local geometry of the computer-aided design model and rapid proto-typing machine specifications. Even though adaptive slicing controls part surface quality by compromising on build time for a deposition orientation, an optimum orientation can further reduce build time and enhance part surface quality. In the present work, an attempt has been made to determine the optimal part deposition orientations by considering two objective functions at a time, namely average part surface roughness (average part surface quality) and build time. The two objectives are minimized simultaneously using a multicriteria genetic algorithm.

Performance Evaluation of Electrical Discharge Machining (EDM) Process Using Cryogenically Cooled Electrode

This article describes a study on the cooling effect on copper electrode while electrical discharge machining (EDM) M2 grade high speed steel workpiece. To evaluate the machinability, electrode wear ratio (EWR) and surface roughness (SR) were the two responses observed. Discharge current, pulse on time, duty cycle, and gap voltage were the controllable process parameters. It was found that EWR reduced up to 20% by cryogenic cooling of electrode. With electrode cooling, SR was also found to have been reduced after machining. The effect of process parameters on EWR and SR were also analyzed. It was found that for EWR, discharge current, pulse on time, and duty cycle has the most significant effect, while pulse on time and discharge current have the most significant effect on SR. EWR and SR were found to be lower in cryogenic assisted EDM as compared to conventional EDM for the same set of process parameters. The shape of the electrode has also been measured, and it was found that the shape retention was better in cryogenic assisted EDM as compared to conventional EDM.

Mechanism of Surface Finishing in Ultrasonic-Assisted Magnetic Abrasive Finishing Process

Ultrasonic-assisted magnetic abrasive finishing (UAMAF) integrates the use of ultrasonic vibrations and magnetic abrasive finishing (MAF) processes to finish surfaces of nanometer order within a minutes time. The present study emphasizes the mechanism of surface finishing in UAMAF. This article reports the study of the microscopic changes in the surface texture resulting from interaction of abrasives with ground workpiece surface. In addition to the surface roughness measurement, scanning electron and atomic force microscopy were used to understand the material removal process and wear behavior during finishing and to provide a fundamental insight of the finishing in UAMAF. The observed surface texture showed that the process is an accumulation of the microscratches resulting from the interaction of abrasive cutting edges with the workpiece surface. The X-ray diffraction (XRD) analysis revealed that the SiC is induced in the workpiece surface, increasing the hardness of the workpiece up to 960 HV.

Magnetorheological Ball End Finishing Process

Finishing of three-dimensional (3D) surfaces such as grooves, projections, or complex in depth profiles on workpiece surfaces is a challenging task for the many existing advanced fine finishing processes. The advanced fine finishing processes have been developed to precisely control the abrading forces through external magnetic field. The applications of state-of-art finishing processes are limited to specific geometries only such as concave, convex, flat, and aspherical shapes due to restriction on relative movement of finishing medium and workpiece. Many of these processes are incapable of finishing of 3D intricate shaped surfaces. To overcome this problem, a new finishing process for flat as well as 3D surfaces using ball-end magnetorheological (MR) finishing tool is developed for ferromagnetic as well as non-ferromagnetic materials. The smart behavior of MRP fluid is utilized to precisely control the finishing forces and hence the final surface finish. A computer controlled experimental setup is designed and developed to study the process characteristics and performance. The magnetostatic simulations of flux density in MRP fluid between tool and workpiece has been done to visualize the finishing spot shape and size in contact with the workpiece surface. EN31 magnetic steel and nonmagnetic copper workpieces were finished using developed machine to validate the process concept.

Experimental investigations for improving part strength in selective laser sintering

Selective laser sintering (SLS) is a powder-based rapid prototyping process in which parts are built by sintering of selected areas of layers of powder using laser. Nowadays, SLS is emerging as a rapid manufacturing technique, which produces functional parts in small batches, particularly in aerospace application and rapid tooling. Therefore, SLS prototypes should have sufficient strength to satisfy functional requirements. Apart from the energy density which is the combination of laser power, beam speed and hatch spacing, various other parameters like refresh rate, layer thickness and hatch pattern influence part strength. In the present work, relationship between strength and the various process parameters namely layer thickness, refresh rate, part bed temperature and hatch pattern have been investigated. Experiments are conducted based on Taguchi method using L16 modified orthogonal array. Tensile specimens of polyamide (PA2200) material as per the standard ‘ASTM D638’ are fabricated on SLS machine with constant energy density and tested on a universal testing machine for tensile strength. Optimum strength conditions are obtained by maximising signal to noise (S/N) ratio and analysis of variance (ANOVA) is used to understand the significance of process variables affecting part strength. A regression model to predict part strength has been developed. Confirmation test conducted subsequently has revealed that the results are within the confidence interval.

Nanofinishing of Fused Silica Glass Using Ball-End Magnetorheological Finishing Tool

The surface finishing of fused silica in nanometer range and in obtaining defect-free surface is a challenge and in high demand because of its applications for transmitting high energy laser pulses. A novel nanofinishing process using ball-end Magnetorheological (MR) finishing tool was developed for finishing of flat as well as three-dimensional (3D) surfaces of ferromagnetic and non-ferromagnetic materials. In this process, a magnetically controlled ball end of smart MR polishing fluid is generated at the tip of the cylindrical tool, and it is guided to follow the surface to be finished through computer controlled three-axes motion. The process is automated and used for finishing precise components in manufacturing system. The smart behavior of MR-polishing fluid is utilized to precisely control the finishing forces which exhibit change in rheological behavior in the presence of external magnetic field. The finishing of fused silica glass was done using cerium oxide Cerox 1663 abrasive powder. The effect of finishing time on final surface roughness was studied, and the finished surfaces were observed under atomic force microscope. Significant improvement in surface roughness (Ra), root mean square (RMS), and Rmax value has been obtained after 90 min of finishing. Ra as low as 0.146 nm was achieved from initial value of 0.74 nm.

Performance Analysis of Ball End Magnetorheological Finishing Process with MR Polishing Fluid

A ball end magnetorheological finishing (BEMRF) process was developed for finishing a flat as well as 3D workpiece surfaces. The BEMRF process has a wide scope in todays advanced manufacturing systems for finishing 3D complex surfaces. Magnetorheological (MR) polishing fluid is used as finishing medium in BEMRF process. The constituent of MR polishing (MRP) fluid includes ferromagnetic carbonyl iron powder, abrasives, and base fluid medium. The workpiece surface is mainly finished by abrasives contained in MRP fluid. Therefore, the different mesh size from 400 to 1200 and volume percent concentration from 5% to 25% of abrasives in MRP fluid were chosen as factors to study their effects on the developed process performance in terms of percent change in roughness values. Silicon carbide abrasives were chosen in the present experimental investigation. Experiments were performed on the ferromagnetic ground surfaces whose initial roughness values (Ra) were measured in the range of 0.428 to 0.767 µm. The experimental results revealed that the MRP fluid with 15 vol % abrasives of mesh number 400 demonstrated better improvements in surface texture of finished surface as compared to other MRP fluid compositions. The finished surface characteristics and textures were studied at microscopic level using scanning electron microscopy and atomic force microscopy.