Denis Cormier

Characterization of H13 steel produced via electron beam melting

Electron beam melting (EBM) is a direct‐metal freeform fabrication technique in which a 4 kW electron beam is used to melt metal powder in a layer‐wise fashion. As this process is relatively new, there have not yet been any independently published studies on the H13 steel microstructural properties. This paper describes the EBM process and presents results of microstructural analyses on H13 tool steel processed via EBM.

Specifying non‐uniform cusp heights as a potential aid for adaptive slicing

Most adaptive slicing implementations assume a maximum allowable cusp height which applies to the entire part. Practically speaking, however, most parts do not have uniform cusp height requirements. Some faces are required to be smooth while other faces are relatively unimportant. With a uniform cusp height implementation, users must specify the most stringent cusp height which applies to the entire part. However, with non‐uniform cusp height specifications, it is possible that further gains in adaptive slicing efficiency can be achieved. This paper presents an approach to specifying non‐uniform cusp height requirements. First, a procedure is developed which uses an edge finding algorithm to identify faces on the part. The faces are then rendered using the OpenGL graphics libraries, and the user is prompted to enter the maximum allowable cusp height for each highlighted face. Implementation details and test results are presented.

Scheduling with alternatives: a link between process planning and scheduling

The objective of this research is to develop and evaluate effective, computationally efficient procedures for scheduling jobs in a large-scale manufacturing system involving, for example, over 1000 jobs and over 100 machines. The main performance measure is maximum lateness; and a useful lower bound on maximum lateness is derived from a relaxed scheduling problem in which preemption of jobs is based on the latest finish time of each job at each machine. To construct a production schedule that minimizes maximum lateness, an iterative simulation-based scheduling algorithm operates as follows: (a) job queuing times observed at each machine in the previous simulation iteration are used to compute a refined estimate of the effective due date (slack) for each job at each machine; and (b) in the current simulation iteration, jobs are dispatched at each machine in order of increasing slack. Iterations of the scheduling algorithm terminate when the lower bound on maximum lateness is achieved or the iteration limit is reached. This scheduling algorithm is implemented in Virtual Factory, a Windows-based software package. The performance of Virtual Factory is demonstrated in a suite of randomly generated test problems as well as in a large furniture manufacturing facility. To further reduce maximum lateness, a second scheduling algorithm also incorporates a tabu search procedure that identifies process plans with alternative operations and routings for jobs. This enhancement yields improved schedules that minimize manufacturing costs while satisfying job due dates. An extensive experimental performance evaluation indicates that in a broad range of industrial settings, the second scheduling algorithm can rapidly identify optimal or nearly optimal schedules.

Freeform Fabrication of Titanium Aluminide via Electron Beam Melting Using Prealloyed and Blended Powders

Titanium aluminide (TiAl) is an intermetallic compound possessing excellent high-temperature performance while having significantly lower density than nickel-based superalloys. This paper presents preliminary results of experiments aimed at processing TiAl via the electron beam melting (EBM) process. Two processing routes are explored. The first uses prealloyed powder, whereas the second explores controlled reaction synthesis. Issues such as processing parameters, vaporization of alloying elements, microstructure, and properties are discussed.

Modeling of uniaxial compression in a 3D periodic re-entrant lattice structure

In this study, the behavior of a parametric 3D re-entrant dodecahedron lattice structure with negative Poisson’s ratio was studied. Four geometrical configurations for the re-entrant dodecahedron were designed, and the relationship between the mechanical properties and the design parameters was determined through beam theory. Samples were fabricated successfully via electron beam melting. Compressive tests as well as finite element analysis (FEA) were performed, and the results were compared with theoretical predictions. The modeling yielded explicit analytical equations of various mechanical properties including Poisson’s ratios, modulus and strength, and the compressive strength and the modulus from the prediction match well with the experiments, as well as the FEA results. The methodology used by this study also demonstrated a feasible approach to design 3D auxetic cellular structure for various applications.

Contoured edge slice generation in rapid prototyping via 5-axis machining

Abstract Rapid prototyping, though a relatively new discipline, has proven to be a valuable tool in the reduction of the time and cost associated with developing new products. The value of rapid prototyping shows the promise of increasing even further as it matures and offers higher quality parts, in less time, and for lower costs. Improvements in these areas are all addressed in current rapid prototyping research in various ways. This paper presents a method for greatly improving the geometric accuracy, and thus the overall quality, of rapid prototype parts by making use of 5-axis machining. An algorithm is presented to generate the contoured edge slices for the rapid prototype parts in several levels of complexity. A simple algorithm is presented to generate a single edge contour for each section of the slice, and a more complex algorithm is also presented to allow for the 5-axis machining of “sub-layers” within a slice. It will be shown that sub-layer 5-axis machining provides the possibility to produce the most accurate rapid prototype parts on the market today. The benefits and limitations of the process will be enumerated and summarized. An inexpensive design for the implementation of a 5-axis machine configuration for a proposed sheet-based rapid prototyping process will be presented. A novel characteristic of the proposed process is that it does not require that the sheets be produced independently and post-assembled via a registration system. The process allows for the parts to be built up on a platen as the layers are cut, thus removing the need for a registration system and eliminating post-assembly errors. Sample parts and algorithm verification will also be presented.

Rapid prototyping for treatment of canine limb deformities

This report describes Rapid Prototyping (RP) ‐aided assessment and preoperative planning for treatment of bilateral multifocal pelvic limb deformities in a 1 year old German Shepherd dog. Computed tomography (CT) scans were acquired on a General Electric CT scanner and converted to solid models using Mimics software from Materialise. Stereolithography patterns were prototyped using QuickCast build style on a SLA ‐190. Room temperature vulcanized silicone molds were constructed and three sets of polyurethane patterns were cast for pre‐surgical planning and rehearsal. The paper compares traditional osteotomy planning procedures using only radiographs and 2D CT images to planning with full‐scale physical biomodels. The biomodels had a clearly beneficial impact on the accuracy of surgery and positively influenced the clinical outcome.

Applications of structural optimization in direct metal fabrication

Purpose – Optimization techniques can be used to design geometrically complex components with a wide variety of optimization criteria. However, such components have been very difficult and costly to produce. Layered fabrication technologies such as electron beam melting (EBM) open up new possibilities though. This paper seeks to investigate the integration of structural optimization and direct metal fabrication process.Design/methodology/approach – Mesh structures were designed, and optimization problems were defined to improve structural performance. Finite element analysis code in conjunction with nonlinear optimization routines were used in MATLAB. Element data were extracted from an STL‐file, and output structures from the optimization routine were manufactured using an EBM machine. Original and optimized structures were tested and compared.Findings – There were discrepancies between the performance of the theoretical structures and the physical EBM structures due to the layered fabrication approach. ...

Integrated job release and shop-floor scheduling to minimize WIP and meet due-dates

We address the problem of releasing jobs to the factory floor while meeting delivery dates and minimizing the work-in-process inventory. Heuristic algorithms were developed that used an efficient, detailed shop-floor scheduling model to determine the release times of new jobs. The process starts with the current shop floor conditions and determines the sequencing of both in-process and new jobs on machines in order to minimize the maximum lateness (L max ). The approach is tractable for industrial-sized problems and provides solutions close to a calculated lower bound for WIP. Computational experience is given.

A constraint-based genetic algorithm for concurrent engineering

Concurrent engineering is a complex problem in that a large number of considerations have to be brought to bear during the design stage. Compounding this complexity is that concurrent engineering problems are also likely to encompass both numeric and symbolic variables, and constraints that range from simple algebraic constraints, through conditional constraints, to potentially very complex database constraints. Previous approaches have concentrated on finding good solutions to simplified problems or, alternatively, to finding a feasible solution which may not be close to optimal. This paper presents an approach to concurrent engineering problems that extends the conventional genetic algorithm approach to handle the complex variety of variables and constraints that are inherent in a typical concurrent engineering problem. This poses some severe research challenges and this paper describes three genetic operators (the constraint-based initialization, crossover, and mutation operators) that preserve feasibi...