J.Y.H. Fuh

Multi‐objective optimization of part‐ building orientation in stereolithography

In rapid prototyping, such as SLA (stereolithography apparatus) and FDM (fused deposition modelling), the orientation of the part during fabrication is critical as it can affect part accuracy, reduce the production time, and minimize the requirement for supports and, thus, the cost of building the model. Presents a multi‐objective approach for determining the optimal part‐building orientation. Considers different objectives such as part accuracy and building time. Objective functions have been developed based on known sources of errors affecting part accuracy and the requirements of good orientations during the building of a model. The objective functions employ weights assigned to various surface types affecting part accuracy. The primary objective is to attain the specified accuracy achievable with the process. The secondary objective is to minimize the building time. Gives examples to illustrate the algorithm for deriving the optimal orientation which can assure better part quality and higher building efficiency.

Direct metal laser sintering for rapid tooling: processing and characterisation of EOS parts

Abstract Direct metal laser sintering (DMLS) fabricates metal prototypes and tools directly from computer aided design (CAD) data. The process is popular in rapid tooling (RT) ,since a suitable metal powder can be used to produce the metal parts and tools. The powder system may be pre-alloyed powder or multi-phase powder. The properties of the RT parts, however, depend on its composition and solidification conditions. Accuracy, wear resistance and mechanical properties are critical on choosing the rapid tooling mould as the production-grade tooling. This study includes the design of metal prototypes which are then fabricated by EOS’s DMLS. The EOS material system is a mixture of nickel, bronze and copper-phosphide material. The dimensional accuracy, surface roughness, impact toughness, hardness, and strength of EOS parts are measured. SEM pictures of EOS parts are also thoroughly analysed.

Benchmarking for comparative evaluation of RP systems and processes

A geometric benchmark part is proposed, designed and fabricated for the performance evaluation of rapid prototyping machines/processes. The benchmark part incorporates key shapes and features of better‐known benchmark parts. It also includes new geometric features, such as freeform surfaces, certain mechanical features and pass‐fail features that are increasingly required or expected of RP processes/systems. The part is suitable for fabrication on a typical RP machines. In this paper, the application of the benchmark part is demonstrated using relatively common RP processes. The ability of the benchmark part to determine achievable geometric features and accuracy by the aforementioned RP processes is presented and discussed.

Integration of process planning and scheduling by exploring the flexibility of process planning

A unique method for the integration of process planning and scheduling in a batch-manufacturing environment is reported. This integration is essential for the optimum use of production resources and for the generation of realistic process plans that can be readily executed with little modification. The integration problem is modelled at two levels: process planning and scheduling, which are linked by an intelligent facilitator. The process-planning module employs an optimization approach in which the whole plan solution space in terms of available machines, tools, tool accessibility and precedence constraints is first generated and a search algorithm is then used to find the optimal plan. For a given set of jobs, the scheduling module takes the optimal plans for each job and generates a schedule based on a given criterion, as well as the performance parameters (machine utilization and number of tardy jobs). An unsatisfied performance parameter is fed back to the facilitator, which then identifies a particular job and issues a change to its process plan solution space. The iteration of process Planning -scheduling-solution space modification continues until a schedule is satisfactory or until no further improvement can be made. The uniqueness of this approach is characterized by the flexibility of the process-planning strategy and the intelligent facilitator, which makes full use of the plan solution space intuitively to reach a satisfactory schedule. (It may not be the optimal, though.) The integrated system was implemented in the manufacturing of prismatic parts. The testing results show that the developed integration method can achieve satisfactory process plans and a schedule in an effective and efficient manner.

Optimal orientation with variable slicing in stereolithography

Accuracy and building time are two important concerns in rapid prototyping (RP). Usually there exists a trade‐off between these two aspects pertaining to model building in RP. The use of variable thickness slicing can satisfy these two requirements to some extent. Introduces an adaptive variable thickness slicer implemented on a solid CAD modeller. The slicer employs a genetic algorithm to find the minimum layer thickness allowed at referenced height with a given cusp height tolerance. By introducing the variable thickness slicing technique, the optimal orientation for part building in RP systems is considered. Seeks to obtain the optimal orientation with adaptive slicing for part building in stereolithography (SLA) systems. Takes into consideration building time, accuracy and stability of the part when determining the optimal orientation. Results show that the proposed approach gives an effective and practical solution for building parts with curved surfaces.

Direct laser sintering of a copper-based alloy for creating three-dimensional metal parts

Abstract Direct laser sintering of metal, as one of the important developments in rapid prototyping technologies, is discussed in this paper. A special copper-based alloy is used for this rapid prototyping process. Experiments on the sintering conditions of this material had been conducted in a self-developed high temperature metal sintering machine. The mechanism of laser sintering for this kind of material was disclosed by SEM analysis of microstructures of sintered parts. The density, surface roughness and mechanical properties of the laser sintering parts due to variation of process parameters were measured and analysed. The effect of process parameters to the accuracy of sintered parts was also investigated. Thus, optimum parameters were obtained for direct laser sintering of three-dimensional metal parts.

A hybrid method for recognition of undercut features from moulded parts

Products manufactured by moulding processes, such as injection moulding or die casting, are called moulded parts. This paper describes a hybrid method to recognise undercut features from moulded parts with planar, quadric and free-from surfaces. The hybrid method takes advantage of graph-based and hint-based approaches. Various undercut features, including interacting undercut features, are defined by extended attributed face-edge graphs (EAFEG). Unlike conventional graph-based methods, which recognise features by graph matching, the new approach recognises the undercut features by searching the cut-sets of subgraphs. Face properties and parting lines are used as hints to guide the search of cut-sets. To recognise undercut features from parts with free-form surfaces, a convex-hull algorithm is used to determine the face properties (positive, negative and horizontal). The case study shows that the proposed method can recognise various undercut features successfully.

Equidistant path generation for improving scanning efficiency in layered manufacturing

Path generation is an important factor that affects the quality and efficiency of most laminated manufacturing processes such as SLS, SLA and FDM. This paper introduces an efficient path generation algorithm. The principle of the algorithm and its implementation are presented. A comparative study is used to analyze the effectiveness of this method. The results of comparison on both path length and processing time between the traditional method and the proposed method are discussed.

Direct laser sintering of a silica sand

As an application study of rapid prototyping, commercially available silica sand was successfully direct-laser-sintered in a self-developed high-temperature laser sintering equipment. The mechanism of powder-state sand becoming a solid state block during the laser sintering process was disclosed by scanning electron microscope (SEM) and energy dispersive X-ray (EDX) analysis on sand particles and sintered samples. The effect of process parameters to the accuracy, strength and surface finish of sintered parts was investigated and thus a set of optimal parameters has been obtained for the sand sintering process. The feasibility of using this material and process to build casting moulds for metal casting was also investigated and discussed.

In situ formation of TiC composite using selective laser melting

Abstract This paper studies the formation of composites using a CO 2 laser machine for rapid prototyping fabrication. In this process, Cu–Ti–C and Cu–Ni–Ti–C powder mixtures were milled before laser scanning. The ball-milled powder mixture was layered and scanned under the laser beam. Formation of in situ TiC was detected after laser scanning. With addition of Ni, both the microstructure structure and surface quality of the laser-fabricated parts can be improved because of the improved melting of Cu and wettability of Cu with in situ TiC.