K. Renap and J.P. Kruth
Most stereolithography systems use a blade to accomplish the recoating of the part being built with a new layer of resin. States the problems associated with this technique and…
Abstract
Most stereolithography systems use a blade to accomplish the recoating of the part being built with a new layer of resin. States the problems associated with this technique and describes experiments conducted to determine how recoating parameters should be controlled. Differentiates between recoating over an entirely solid substrate and over one consisting of solid and liquid, i.e. the “trapped volume” condition. Discusses parameter control for both of these conditions. Concludes that recoating is an important part of the stereolithography process which must be optimized to ensure accuracy of prototype parts.
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Andrey Kozhevnikov, Rudie P.J. Kunnen, Gregor E. van Baars and Herman J.H. Clercx
This study aims to examine the feasibility of feedforward actuation of the recoater blade position to alleviate the resin surface non-uniformity while moving over deep-to-shallow…
Abstract
Purpose
This study aims to examine the feasibility of feedforward actuation of the recoater blade position to alleviate the resin surface non-uniformity while moving over deep-to-shallow transitions of submerged (already cured) geometric features.
Design/methodology/approach
A two-dimensional computational fluid dynamics (CFD) model has been used to determine optimized blade actuation protocols to minimize the resin surface non-uniformity. An experimental setup has been designed to validate the feasibility of the proposed protocol in practice.
Findings
A developed protocol for the blade height actuation is applied to a rectangular stair-like configuration of the underlying part geometry. The evaluation of the actuation protocol revealed the importance of two physical length scales, the capillary length and the size of the flow recirculation cell below in the liquid resin layer below the blade. They determine, together with the length scales defining the topography (horizontal extent and depth), the optimal blade trajectory. This protocol has also shown its efficiency for application to more complicated shapes (and, potentially, for any arbitrary geometry).
Practical implications
This study shows that incorporation of a feedforward control scheme in the recoating system might significantly reduce (by up to 80%) the surface unevenness. Moreover, this improvement of performances does not require major modifications of the existing architecture.
Originality/value
The results presented in this work demonstrate the benefits of the integration of the feedforward control to minimize the leading edge bulges over underlying part geometries in stereolithography.
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Andrei Kozhevnikov, Rudie P.J. Kunnen, Gregor E. van Baars and Herman J.H. Clercx
This paper aims to explore the fluid flow in the stereolithography process during the recoating step. The understanding of the flow dynamics can be used as an input for an active…
Abstract
Purpose
This paper aims to explore the fluid flow in the stereolithography process during the recoating step. The understanding of the flow dynamics can be used as an input for an active control of the resin surface height map. The recoating over a rectangular cavity has been considered to investigate the influence of the cavity depth on the resin surface height map.
Design/methodology/approach
Two-dimensional numerical simulations have been used to obtain the flow characteristics as function of the cavity depth. An experimental setup, which mimics the recoating process in the stereolithography process, was used to verify the results of simulations and to test the suitability of the 2D model. The surface height profile along the centreline was measured by a confocal chromatic distance sensor and compared to the 2D numerical results.
Findings
By means of computational fluid dynamics (CFD) simulation, the flow in the cavity and the free-surface behaviour of the resin was explained for different cavity depths and confirmed by experiments.
Research limitations/implications
The study is focused only on the cavity depth variation to show feasibility and suitability of the presented CFD model and the proposed analytical expression to estimate the layer thickness.
Practical implications
The proposed approach can serve as a tool for designing the closed-loop control for the recoating system in the next generation of stereolithography equipment.
Originality/value
In the present work, the fluid flow behaviour, a source of significant imperfection in the recoating process, has been investigated during the recoating step over a rectangular cavity.
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Arnaud Bertsch, Paul Bernhard, Christian Vogt and Philippe Renaud
The commercialization of new products integrating many functions in a small volume requires more and more often the rapid prototyping of small high‐resolution objects, having…
Abstract
The commercialization of new products integrating many functions in a small volume requires more and more often the rapid prototyping of small high‐resolution objects, having intricate details, small openings and smooth surfaces. To give an answer to this demand, the stereolithography process has started to evolve towards a better resolution: the “small spot” stereolithography technology allows to reach a sufficient resolution for the manufacturing of a large range of small and precise prototype parts. Microstereolithography, a technique with resolution about an order of magnitude better than conventional stereolithography, is studied by different academic research groups. The integral microstereolithography machine developed at the Swiss Federal Institute of Technology in Lausanne is described in this paper, and potential applications are presented. The resolutions of conventional, small spot and microstereolithography technologies are compared and the potential of the microstereolithography technique is shown for the manufacturing of small and complex objects.
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Guangshen Xu, Wanhua Zhao, Yiping Tang and Bingheng Lu
To satisfy the demands for rapid prototyped small‐size objects with intricate microstructures, a high‐resolution stereolithography (SL) system is developed.
Abstract
Purpose
To satisfy the demands for rapid prototyped small‐size objects with intricate microstructures, a high‐resolution stereolithography (SL) system is developed.
Design/methodology/approach
This novel SL system consists of a single mode He‐Cd laser, an improved optical scanning system, a novel recoating system and a control system. The improved optical system consists of a beam expander, an acoustic‐optic modulator, a galvanometric scanner and an F‐θ lens; the recoating system consists of roller pump, resins vat with an integrated high‐resolution translation stage and part building platform and a scraper. Experimental studies were performed to investigate the influences of building parameters on the cured line width and depth.
Findings
With the SL system, a laser light spot with a diameter of 12.89 μm on the focal plane and resin layers with a thickness of 20 μm have been obtained. The experimental results indicate that cured depth and width increase with the ratio of laser power to scanning speed, and cured line with a width of 12 μm and a depth of 28 μm was built, which showed the capability building microstructures with this new SL system.
Research limitations/implications
The building area limited to 65 × 65 mm, is smaller than that of current SL system.
Practical implications
Small objects with intricate microstructures can be fabricated with the SL system.
Originality/value
The high‐resolution SL system provides a solution to the problem that has hampered the progress of SL process into a high resolution ranges below 75 μm.
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Alok Kataria and David W. Rosen
Stereolithography apparatus (SLA) is capable of in situ fabrication of complex parts, as well as mechanisms and complex devices with embedded components. In this paper, a series…
Abstract
Stereolithography apparatus (SLA) is capable of in situ fabrication of complex parts, as well as mechanisms and complex devices with embedded components. In this paper, a series of example devices are presented to illustrate the power of building around embedded components (inserts). The problem formulation, solution approach, and specific rules and procedures are presented using these examples and experimental results. A case study approach is used for presentation. These procedures and results lend insight into promising new applications of SLA technology, as well as novel methods of implementing additional functionality into SLA and other rapid prototyping technologies.
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Sadegh Rahmati and Philip Dickens
Explains that stereolithography (SL) can greatly reduce initial tooling costs, thus making prototyping and small production runs economically feasible. Describes how epoxy resin…
Abstract
Explains that stereolithography (SL) can greatly reduce initial tooling costs, thus making prototyping and small production runs economically feasible. Describes how epoxy resin SL5170 and Zeneca filled resin are used to build SL injection moulding tools. Different sets of tools were evaluated, based on the maximum number of successful injections and quality of performance. A polymer tool requires a minimum level of strength, thermal conductivity and dimensional accuracy. The Zeneca SL tool achieved a total number of 200 successful injections before starting to fail. However, the failure happened during the first shot of the day where the initial injection pressure was set high. On the other hand, epoxy tools were more resistant to injection pressure and temperature and more than 500 injections were achieved without tool failure. In all tests the cavity was never damaged and it was the core which failed during either injection or ejection. Concludes that product diversity, high product complexity, increase in product variety, and shorter product life are prime motives for SL tooling.
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G. Zak, A.Y.F. Chan, C.B. Park and B. Benhabib
Refers to how the mechanical properties of polymer‐based composite objects produced via rapid layered fabrication methods can be improved significantly using short discontinuous…
Abstract
Refers to how the mechanical properties of polymer‐based composite objects produced via rapid layered fabrication methods can be improved significantly using short discontinuous fibres as reinforcements. Notes in this context, that the viscosity of the uncured fibre‐photopolymer composite liquids affects the raw‐material handling, the layer formation and the draining operations. Assesses the effects of aspect ratio, surface coating and volume fraction of short glass fibres on the viscosity of the fibre‐photopolymer composite liquids. Based on extensive experimentation and analysis, concludes that the shear viscosity of the composite liquids increases with increasing fibre‐volume fraction, showing that this effect is more pronounced at low shear rates than at high shear rates. Reveals, similarly, that the aspect ratio of the dispersed fibres has a stronger effect on the increase of viscosity at low shear rates and that the surface coating of the dispersed fibres also affects the viscosity of the composite liquids.
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Yiqing Wang, Yucheng Ding, Wanhua Zhao, Zhongyun He and Bingheng Lu
The purpose of this paper is to show how to precisely control the liquid resin coating thickness in stereolithography (SL).
Abstract
Purpose
The purpose of this paper is to show how to precisely control the liquid resin coating thickness in stereolithography (SL).
Design/methodology/approach
A vacuum adsorption coating equipment and technology are developed to precisely control the liquid resin coating thickness in SL. Dual‐electrode device is used, so adsorption can be precisely controlled and the electrode polarization can be avoided.
Findings
It turns out that the apparatus can control coating thickness effectively, and thickness uniformity is increased remarkably, which induces the standard deviation thickness decrease from 0.00547 to 0.00243 mm, and efficiency of rapid prototyping production increase by 53 percent.
Originality/value
The paper demonstrates that the apparatus can control coating thickness effectively.