Fwu Hsing Liu

Formability of the layer additive Ceramic Part

The material in powder state has long been used by selective laser sintering (SLS) for making rapid prototyping (RP) parts. A new approach to fabricate smoother surface roughness RP parts of ceramic material from slurry-sate has been developed in this study. The silica slurry was successfully laser-gelling in a self-developed laser sintering equipment. In order to overcome the insufficient bonding strength between layers, a strategy is proposed to generate ceramic parts from a single line, a single layer, to multi-layers of gelled cramic in this paper. It is found that when the overlap of each single line is 25% and the over-gel between layers is 30%, stronger and more accurate dimensional parts can be obtained under a laser power of 15W, a laser scanning speed of 250 mm/s, and a layer thickness of 0.1 mm. The 55:45 wt. % of the proportion between the silica powder and silica solution results in suitable viscosity of the ceramic slurries without precipitation. Furthermore, the effects of process parameters for the dimensional accuracy and surface roughness of the gelled parts are investigated and appropriate parameters are obtained.

A Rapid Prototyping Apparatus for Forming Ceramic Parts

This article proposes a rapid prototyping apparatus of selective laser sintering for forming silica ceramic green parts. The main differences between the proposed and other RP processes for forming ceramic part are the slurry material used to obtain fine layer thickness and the capability of constructing support structure to increase the dimensional accuracy of the workpiece having an overhang. The RP apparatus developed by us comprises a laser scanning system, a material paving system, and a computer control system. A CO2 laser is adopted to scan over a mixture made of a silica sol and silica powder. The silica sol acts as a binder to gel the silica powder together, which forms a 3D object using laser gelation method. A series of experiments were carried out to obtain the optimal process parameters. An SEM is employed to analyze the microstructure of the ceramic part. It has been found that the smallest layer is of 100 μm thick. The results show that both the accuracy of the material paving mechanism and the optimal process parameters can fulfill the requirements of the RP processes.

Laser Compensation for Ceramics Accuracy Improvement of Selective Laser Sintering

This research developed a feedback control system of laser compensation for the rapid prototyping (RP) machine using layer-wise slurry deposition and selective laser sintering (SLS). The slurry was prepared by silica power and silica sol with 60 and 40 wt.% with suitable rheological properties for 0.1 mm layer deposition. Four ceramics for comparison of the formability of fabricated ceramic green parts with/without the feedback control system of laser energy density for models were designed With this laser feedback control, batter quality ceramic green parts can be manufactured and the rapid prototyping machine with steady laser energy radiated on slurry layer was achieved. Experimental results validate the well performance of the measuring laser power and feedback control system.

Rapid manufacturing of metal-ceramic composites

This paper presents a layer manufacturing technology called selective laser gelling (SLG) to fabricate metal-ceramic composites green parts which are difficult to construct using traditional methods for fabricating composites. When a layer of metal-ceramic slurry is scanned via Nd: YAG laser radiation, the metal particles are gelled together by the silica sol to form a composites part. In comparison with other composites processes, the features of this process include lower laser forming energy, faster fabrication speed, less dimensional variations. The material composition is mixing by the stainless steel powder and a silica sol in a proportion of 75 to 25 wt. %. A series of experiments was conducted to obtain the smallest pave-able layer thickness of 50 μm on an experimental rapid prototyping (RP) machine. The feasibility of this process was demonstrated by manufacturing a gear shaped prototype with a surface finish of 18μm under a laser energy density of 3.5 J/mm2.

Bioceramic Scaffolds Manufacturing by Laser 3D Printing

In this work, a hydroxyapatite (HA) bioceramic and a silica binder were used as the raw materials for manufacturing bioceramic bone scaffold after sintering by a laser beam in a home-made 3D Printing (3DP) machine. Results indicate that the bending strength of the scaffold can be improved after heat-treatment. While simultaneously increasing surface roughness conducive to osteoprogenitor cell adhesion. The processing parameters of a 90 mm/s laser scanning speed, 12 W of laser energy and 10 kHz of scanning frequency were used to fabricate a porous scaffold model, which possesses suitable biocompatibility and mechanical properties, allowing adhesion and proliferation of bone cells. Therefore, this process has great potential for manufacturing bone scaffolds.

Fabrication of Bioceramic Scaffolds for Tissue Engineering Using Additive Manufacturing Technology

In this paper, the hydroxyapatite (HA) based bioceramic materials were used in a rapid prototyping (RP) system to fabrication bioceramic bone scaffold for tissue engineering (TE) using an additive manufacturing (AM) technology. When the bioceramic slurry is sintered via the processing parameters of an 85 mm/s laser scanning speed, 24.5 W of laser power, 10 kHz of scanning frequency, and 2500 Cp of slurry viscosity, a porous bone scaffold can be fabricated under a lower laser power energy. Results indicate that the bending strength of the scaffold was 14.2 MPa, which could be improved by heat-treatment at 1200 °C for 2 hour. MTT method and SEM observations confirmed that the fabricated bone scaffolds possess suitable biocompatibility and mechanical properties, allowing smooth adhesion and proliferation of osteoblast-like cells. Therefore, the fabricated bone scaffolds have great potential for development in tissue engineering.

Rapid forming of hydroxyapatite-silica ceramics

This paper proposes a solid freefrom fabrication (SFF) technology for fabricating hydroxyapatite(HA)-silica ceramics, which can generate porous three-dimensional physical objects. The HA powder and the silica are mixed with water into slurries form as raw materials. The slurries are paved by a scraper to from a thin layer which is selective scanned by a laser beam according to the cross-section of a 3D model. The HA particles are embeded in the sintered silica matrix to form green parts via a suitable range of process parameters. The benefits of this process are: bio-ceramic parts can be built by lower laser energy and faster fabricating speed. Following a subsequence heat treatment process has been developed to optimize the crystallization process and to increase the strength of the sintered parts. The parts were analyzed by an Atomic Force Microscope (AFM) to determine the surface roughness. The results obtained indicate that the proposed process was possible to generate multilayer, overhanging, and porous structure with brittle property but sufficient integrity for handling prior to post-processing. It was possible to produce the porous structure from the proposed hydroxyapatite-silica ceramics, which had a greater potential for possible bone scaffolds fabrication.

Fabrication Inner Channel Ceramics Using Layer Additive Method

This paper presents a layer additive method, ceramic laser curing, to form a ceramic part with inner channel features, by which silica powder is bonded by curing effect under disposal of a 20W CO2 laser. This process includes four steps: making slurry by mixing a binder with ceramic powder, paving the slurry on the surface of a platform, scanning the paved slurry layer via laser beam, removing the un-cured slurries from the solidified ceramic component. This process needed only low laser power to build ceramic parts by using “curing effect”. The deflection and shrinkage of ceramics could be decreased, also the distortion due to post sintering process was avoidable. The inner channel structures were support by ceramic slurries to avoid the sagged deflection and to maintain the dimensional accuracy. The maximum flexural strength of the cured specimen was 4.7 MPa. This process has potential to fabricate inner complex ceramic components for industrial applications.

Study on Micro-Feature of Backlight Module for Micro Injection Molding Technology

This research first indicates the melt front delay of wedge-shaped lightguiding plate of backlight module on micro injection molding. This research fabricated the patterns of mold insert of lightguiding plate by photo etching process. The micro-facture of lightguiding plate was manufactured by micro injection molding. The lightguiding plate of backlight module was used for the PMMA material. The single parameter method was used to discuss the flatness and replication properties for different processing parameters (mold temperature, melt temperature, packing pressure, packing time and injection pressure). The results show that there are melt front delays due to the slow injection velocity, the low temperature induced by the little effect of shear heating, the high viscosity, the large flow resistance and the slow flow velocity. The mold temperature is the most important factor for the flatness and the replication of micro-feature of liughtguiding plate. Lower mold temperature induces better flatness properties. The surface roughness of micro-facture of lightguiding plate is 8.8 nm on micro injection molding for this work.