Search results

The purpose of this paper is to present research work based on the authors’ conceptual framework reported in the VRAP Conference 2013. It is related with an efficient method to obtain an optimal part build orientation for additive manufacturing (AM) by using AM features with associated AM production knowledge and multi-attribute decision-making (MADM). The paper also emphasizes the importance of AM feature and the implied AM knowledge in AM process planning.

To solve the orientation problem in AM, two sub-tasks, the generation of a set of alternative orientations and the identification of an optimal one within the generated list, should be accomplished. In this paper, AM feature is defined and associated with AM production knowledge to be used for generating a set of alternative orientations. Key attributes for the decision-making of the orientation problem are then identified and used to represent those generated orientations. Finally, an integrated MADM model is adopted to find out the optimal orientation among the generated alternative orientations.

The proposed method to find out an optimal part build orientation for those parts with simple or medium complex geometric shapes is reasonable and efficient. It also has the potential to deal with more complex parts with cellular or porous structures in a short time by using high-performance computers.

The proposed method is a proof-of-concept. There is a need to investigate AM feature types and the association with related AM production knowledge further so as to suite the context of orientating parts with more complex geometric features. There are also research opportunities for developing more advanced algorithms to recognize AM features and generate alternative orientations and refine alternative orientations.

AM feature is defined and introduced to the orientation problem in AM for generating the alternative orientations. It is also used as one of the key attributes for decision-making so as to help express production requirements on specific geometric features of a desired part.

For part models with complex shape features or freeform shapes, the existing build orientation determination methods may have issues, such as difficulty in defining features and costly computation. To deal with these issues, this paper aims to introduce a new statistical method to develop fast automatic decision support tools for additive manufacturing build orientation determination.

The proposed method applies a non-supervised machine learning method, K-Means Clustering with Davies–Bouldin Criterion cluster measuring, to rapidly decompose a surface model into facet clusters and efficiently generate a set of meaningful alternative build orientations. To evaluate alternative build orientations at a generic level, a statistical approach is defined.

A group of illustrative examples and comparative case studies are presented in the paper for method validation. The proposed method can help production engineers solve decision problems related to identifying an optimal build orientation for complex and freeform CAD models, especially models from the medical and aerospace application domains with much efficiency.

The proposed method avoids the limitations of traditional feature-based methods and pure computation-based methods. It provides engineers a new efficient decision-making tool to rapidly determine the optimal build orientation for complex and freeform CAD models.

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.

Application of appropriate shading device strategies in buildings can reduce direct solar heat gain through windows as well as optimize cooling and artificial lighting load. This study investigates the impact of common shading devices such as overhangs, fins, horizontal blinds, vertical blinds and drapes on energy consumption of an office building and suggests energy efficient shading device strategies in the contexts of unique Bangladeshi subtropical monsoon climate.

This research was performed through the energy simulation perspective of a prototype office building using a validated building energy simulation tool eQUEST. Around 100 simulation patterns were created considering various types of shading devices and building orientations. The simulation results were analysed comprehensively to find out energy-efficient shading device strategies.

Optimum overhang and fin height is equal to half of the window height in the context of the subtropical climate of Bangladesh. South and West are the most vulnerable orientations, and application of shading devices on these two orientations shows the highest reduction of cooling load and the lowest increment of lighting load. An existing building was able to save approximately 7.05% annual energy consumption by applying the shading device strategies that were suggested by this study.

The shading device strategies of this study can be incorporated into the Bangladesh National Building Code (BNBC) as new energy-efficient building design strategies because the BNBC does not have any codes or regulations regarding energy-efficient shading device. It can also be used as energy-efficient shading device strategies to other Southeast Asian countries with similar climatic contexts of Bangladesh.

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.

The purpose of this paper is to investigate the effects of aging, pre‐conditioning, and build orientation on the mechanical properties of test samples fabricated using stereolithography (SL) and a commercially available resin.

American Society for Testing and Materials (ASTM) Standard D638 Type I specimens were manufactured in a Viper si2 SL system using WaterShed™ 11120 resin. The specimens were manufactured in two different build setups, designed to fit batches of 18 or 24 specimens with different build orientations. The specimens were randomly tested in tension, and a design of experiments (DOE) was used to determine the effect of aging (4, 30 or 120 days), pre‐conditioning (ambient, desiccant, or ASTM recommended conditioning), and build orientation (flat, on an edge, or vertical) on the ultimate tensile stress (UTS) and elastic modulus (E) of SL fabricated samples. Additionally, the fractured samples were imaged using scanning electron microscopy (SEM) to characterize the fractured surfaces.

Results showed that aging, pre‐conditioning, and build orientation each had an effect on the mechanical properties of the SL samples. In general, the samples aged at the shortest time frame (4 days) and the samples preconditioned according to ASTM recommendations had the lowest values of UTS. Regarding the effect of build orientation, the specimens built flat (with layers oriented along the thickness of the sample) had the lowest UTS and E values and the mechanical properties were statistically different from those built vertically or on an edge. The specimens built in the vertical orientation (with layers oriented along the length of the sample) had the highest values of UTS and E, yet the mechanical properties of the samples built on an edge (with layers oriented along the width of the sample) were not statistically different from the samples built vertically. SEM images of the fractured specimens showed fracture surfaces typical of polymers with a mirror zone and changes in surface texture from smooth to coarse.

The research was limited to a single commercially available resin. Through a statistical DOE approach, statistically significant differences in mechanical properties of SL fabricated samples were found as functions of aging, pre‐conditioning, and build orientation. These results can assist the ASTM F42 Committee with developing test standards specific to SL and the additive manufacturing community.

The statistical analyses presented here can help identify and classify the effects of fabrication, storage, and conditioning parameters on mechanical properties for SL fabricated parts. Understanding how the mechanical properties of SL resins are affected by different parameters can help improve the use of SL for a variety of applications including direct manufacturing of end‐use products.

The purpose of this paper is to investigate the influence of low-cost chemical vapour treatment process on geometric accuracy and surface roughness of different curved and freeform surfaces of fused deposition modelling (FDM) specimens build at different part building orientations.

Parts with different primitive and curved surfaces are designed and modelled to build at three different part orientations along X orientation (vertical position resting on side face), Y orientation (horizontal position resting on base) and Z orientation (upright position). Later, the parts are post-processed by cold vapours of acetone. Geometric accuracy and surface roughness are measured both before and after the chemical treatment to investigate the change in geometric accuracy, surface roughness of FDM parts.

The results indicate that surface roughness is reduced immensely after cold vapour treatment with minimum variation in geometric accuracy of parts. Parts build vertically over its side face (X orientation) provides the overall better surface finish and geometric accuracy.

The present study provides an approach of post-built treatment for FDM parts and observes a significant improvement in surface finish of the components. The present approach of post-built treatment can be adopted to enhance the surface quality as well as to achieve desired geometric accuracy for different primitive, freeform/curved surfaces of FDM samples suitable for functional components as well as prototypes.

This paper aims to introduce a new nesting scheme to better describe and solve the single-layer-part packing problem in additive manufacturing (AM).

Parallel nesting scheme using two-dimensional (2D) changeable projection profiles is developed. At first, a feature-based orientation optimization method is used to identify a set of practical alternative build orientations for each part to ensure the part quality. Then, 2D polygons are used to represent each part’s projection profiles under its alternative build orientations. Finally, a parallel layout searching algorithm is developed to identify the optimal part layout by using 2D changeable projection profiles.

The proposed nesting scheme can both guarantee the production quality for each part and search the optimal part layout with larger probability but less computational time.

With the use of changeable 2D projection profiles, this method conducts 2D computation to solve the single-layer-part packing problem with five degrees of freedom, which saves much computation cost and, at the same time, guarantees the production quality of each part. By adding specific nesting objectives or constraints and heuristic searching knowledge to the proposed nesting scheme, practical nesting software can be developed to meet the specific nesting or packing requirements for industrial AM machines.

The cement-filled PA12 manufactured by selective laser sintering (SLS) offers desirable mechanical properties; however, these properties are dependent on several fabrication parameters. As a result, SLS prototypes may exhibit orthotropic mechanical properties unless properly oriented in build chamber. This paper aims to evaluate the effects of part build orientation, laser energy and cement content on mechanical properties of cement-filled PA12.

The test specimens were fabricated by SLS using the “DTM Sinterstation 2000” system at which the specimens were aligned along six different orientations. The scanning speed was 914mm/s, scan spacing was 0.15mm, layer thickness was 0.1mm and laser power was 4.5–8Watt. A total of 270 tensile specimens, 270 flexural specimens and 135 compression specimens were manufactured and the tensile, compression and flexural properties of fabricated specimens were evaluated.

The experiments revealed orientation-dependent (orthotropic) mechanical properties of SLS cement-filled PA12 and confirmed that the parts with shorter scan vectors have enhanced flexural strength as compared with longer scan vectors. The maximum deviations of ultimate tensile strength, compressive strength and flexural modulus along the six orientations were 32%, 26% and 36%, respectively.

Although part build orientation is a key fabrication parameter, very little was found in open literature with contradictory findings about its effect on mechanical properties of fabricated parts. In this work, the effects of build orientation when combined with other fabrication parameters on the properties of SLS parts were evaluated along six different orientations.

This paper aims to optimise building orientation in Tehran, as well as determining the impact of its shape, relative compactness (RC) and glazing percentage on its optimised orientation.

A cubic module was used and a set of 8 of the same module with 16 different formations were analysed for their orientation (360°), the RC (four groups) and the amount of glazing percentage (25, 50 and 75 per cent).

The results show that the optimised orientation of a building in Tehran strongly depends on its passive solar heat gain elements, their orientation and their position in building; furthermore, glazing percentage amount, amongst the studied factors, plays the most important role in determining a building’s orientation.

The application of the findings of this study in Tehran city planning and also technical details of buildings will lead to a great energy saving in construction sector. Furthermore, the deployment of the proposed design guidelines in construction has explicitly been proven to save a prodigious amount of energy.

The main research question is taken directly from authors’ initiative when working as university professor and research associate. The case study buildings, their morphological configurations and sustainable features have not been presented before in an academic journal.