Search results

This paper aims to use a survey of techniques to present the patterning of electric circuitry on printed circuit boards (PCBs). Second, a proposal of a new technology for direct exposure of interconnects on PCBs, using a digital micromirror device (DMD) is presented.

In this proposal, the DMD chip was incorporated into a prototype system for exposure of soldermask pattern for a mass scale production. As a light source, 52 semiconductor UV lasers were combined together to deliver UV powerful beam onto the DMD chip area.

A laser beam power of around 9 W was achieved from a single exposure head. With five exposure heads installed into a single machine, it is possible to expose 1,400 PCB panels per day. Such a production rate from a single exposure machine satisfies the demands of biggest PCB factories.

The Gaussian energy distribution of the laser beam from the 52-lasers head on the PCB surface was experimentally found. Because the exposure image needs to be highly uniform, this made a problem when the printed circuitry quality is considered. This problem was solved by using a software algorithm.

The use of UV lasers exposure heads brings economical advantages over conventional bulb UV lamps. The power consumption drops down ten times for lasers source.

Because the exposure processing can be made with lower electric costs and higher yield, it will make the PCBs cheaper.

At present, the idea of collecting a great number of lasers as a UV source for exposure head is attractive solution.

Selective laser sintering (SLS) is an essential technology in the field of additive manufacturing. However, SLS technology is limited by the traditional point-laser sintering method and has reached the bottleneck of efficiency improvement. This study aims to develop an image-shaped laser sintering (ISLS) system based on a digital micromirror device (DMD) to address this problem. The ISLS system uses an image-shaped laser light source with a size of 16 mm × 25.6 mm instead of the traditional SLS point-laser light source.

The ISLS system achieves large-area image-shaped sintering of polymer powder materials by moving the laser light source continuously in the x-direction and updating the sintering pattern synchronously, as well as by overlapping the splicing of adjacent sintering areas in the y-direction. A low-cost composite powder suitable for the ISLS system was prepared using polyether sulfone (PES), pinewood and carbon black (CB) powders as raw materials. Large-sized samples were fabricated using composite powder, and the microstructure, dimensional accuracy, geometric deviation, density, mechanical properties and feasible feature sizes were evaluated.

The experimental results demonstrate that the ISLS system is feasible and can print large-sized parts with good dimensional accuracy, acceptable geometric deviations, specific small-scale features and certain density and mechanical properties.

This study has achieved the transition from traditional point sintering mode to image-shaped surface sintering mode. It has provided a new approach to enhance the system performance of traditional SLS.

Mask projection micro‐stereolithography (MPμSLA) is an additive manufacturing process capable for fabricating true three‐dimensional microparts and hence, holds promise as a potential 3D MEMS fabrication process. With only a few MPμSLA systems developed and studied so far, the research in this field is inchoate and experimental in nature. In order to employ the MPμSLA technology for microfabrication, it is necessary to model its part building process and formulate a process planning method to cure dimensionally accurate microparts. The purpose of this paper is to formulate a process planning method for curing dimensionally accurate layers.

A MPμSLA system is designed and assembled. The process of curing a single layer in resin using this system is modeled as the layer cure model. The layer cure model is validated by curing test layers. This model is used to formulate a process planning method to cure dimensionally accurate layers. The process planning method is tested by conducting a case study.

The layer cure model is found to be valid within 3 percent for most of the features and within 10 percent for very small features (<250μm). The paper shows that ray tracing can be effectively used to model the process of irradiation of the resin surface in a MPμSLA system.

The process planning method is applicable only to those imaging systems, which are aberration limited as opposed to diffraction limited. The dimensional errors in the lateral dimensions of single layers cured by MPμSLA have been modeled, but not the vertical errors in 3D parts.

In this paper, a process planning method for MPμSLA has been presented for the first time.

In some three-dimensional (3D) printing application scenarios, e.g., model manufacture, it is necessary to print large-sized objects. However, it is impossible to implement large-size 3D printing using a single projector in digital light processing (DLP)-based mask projection 3D printing because of the limitations of the digital micromirror device chips.

A multi-projector DLP with energy homogenization (EHMP-DLP) scheme is proposed for large-size 3D printing. First, a large-area printing plane is established by tiling multiple projectors. Second, the projector set’s tiling pattern is obtained automatically, and the maximum printable plane is determined. Third, the energy is homogenized across the entire printable plane by adjusting gray levels of the images input into the projectors. Finally, slices are automatically segmented based on the tiling pattern of the projector set, and the gray levels of these slices are reassigned based on the images of the corresponding projectors.

Large-area high-intensity projection for mask projection 3D printing can be performed by tiling multiple DLP projectors. The tiled projector output energies can be homogenized by adjusting the images of the projectors. Uniform ultraviolet energy is important for high-quality printing.

A prototype device is constructed using two projectors. The printable area becomes 140 × 210 mm from the original 140 × 110 mm.

The proposed EHMP-DLP scheme enables 3D printing of large-size objects with linearly increasing printing times and high printing precision. A device was established using two projectors to practice the scheme and can easily be extended to larger sizes by using more projectors.

This paper aims to present a multi-material additive manufacturing (AM) process with a newly developed curing-on-demand method to fabricate a three-dimensional (3D) object with multiple material compositions.

Unlike the deposition-on-demand printing method, the proposed curing-on-demand printheads use a digital light processing (DLP) projector to selectively cure a thin layer of liquid photocurable resin and then clean the residual uncured material effectively using a vacuuming and post-curing device. Each printhead can individually fabricate one type of material using digitally controlled mask image patterns. The proposed AM process can accurately deposit multiple materials in each layer by combining multiple curing-on-demand printheads together. Consequently, a three-dimensional object can be fabricated layer-by-layer using the developed curing-on-demand printing method.

Effective cleaning of uncured resin is realized with reduced coated resin whose height is in the sub-millimeter level and improved vacuum cleaning performance with the uncleaned resin less than 10 µm thick. Also, fast material swapping is achieved using the compact design of multiple printheads.

The proposed multi-material stereolithography (SL) process enables 3D printing components using more viscous materials and can achieve desired manufacturing characteristics, including high feature resolution, fast fabrication speed and low machine cost.

Polymer-particle composites, which have demonstrated wide applications ranging from energy harvesting and storage, biomedical applications, electronics and environmental sensing to aerospace applications, have been investigated for decades. However, fabricating polymer-particle composites with controlled distribution of particles in polymer continues to be a fundamental challenge. As to date, a few additive manufacturing (AM) technologies can fabricate composites, however, with a limited choice of materials or limited dispersion control. Against this background, this research investigated a hybrid polymer-particle composite manufacturing process, projection electro-stereolithography (PES) process, which integrates electrostatic deposition and projection based stereolithography (SL) technologies.

In PES process, a photoconductive film collects charged particles in the regions illuminated by light. Then, collected particles are transferred from the film to a polymer layer with defined patterns. Lastly, a digital mask is used to pattern the light irradiation of the digital micromirror device chip, selectively curing the photopolymer liquid resin and particles of that layer. By transferring particles from the photoconductive film to the photopolymer in a projection-based SL system, multi-material composites with locally controlled dispersions could be produced. A proof-of-concept PES testbed was developed. Various test cases have been performed to verify the feasibility and effectiveness of the developed approach.

Challenges in this novel AM process, including process design, particle patterning and transferring, are addressed in this paper. It is found that particles can be transferred to a layer of partially cured resin completely and accurately, by using the stamping approach. The transferring rate is related to stamping force and degree of conversion of the recipient layer. The developed hybrid process can fabricate polymer-particle composites with arbitrary dispersion pattern, unlimited printable height and complicated geometries.

Although an electrostatic deposition process has been investigated as a 3D printing technology for many years, it is the first attempt to integrate it with projection SL for fabricating multi-material polymer composite components. The novel hybrid process offers unique benefits including local dispersion control, arbitrary filling patterns, wide range of materials, unlimited printable height and arbitrary complicated geometries.

This paper aims to present an investigation of material-process interaction of VAT-photopolymerization processes. The aim of the research is to evaluate the effect of different printing factors on the tensile properties, such as elastic modulus, of 3D printed specimens.

To perform this study, Design of Experiments is used by the use of Taguchi’s techniques. The relationship between each factor and the elastic modulus, ultimate tensile stress and strain at break is obtained. Furthermore, the total print time is analyzed with respect to the obtained properties.

The study indicates that part orientation, exposure time to the UV light and layer thickness are the most important factors affecting the investigated properties. At the same time, it was found that the highest mechanical properties can be obtained with the shortest printing times. A comprehensive list of factors available on the slicing software and other factors, like the orientation of the part or its position, is investigated. Future studies including post curing and chemical characteristics based on the obtained results are necessary.

As a result of this research, it is outlined that using design for additive manufacturing for vat-photopolymerization, especially on DLP processes, 3D printing methods can be stablished. Furthermore, it outlines the possibility of tailoring mechanical properties of printed parts as a function of print parameters and print time. Considering the limited amount of information available in the open literature, the results presented in this paper are of great interest for researchers in the field of VAT-photopolymerization.

In a typical additive manufacturing (AM) system, it is critical to make a trade-off between the resolution and the build area for applications in which varied dimensions, feature sizes and accuracies are desired. Conventional solutions to this challenge are based on curing of multiple areas with a single high resolution and stitching them to form a large layer. However, because of the lack of the capability in adjusting resolution dynamically, such stitching approaches will elongate the build time greatly in some cases. To address the challenge without sacrificing the build speed, this paper aims to design and develop a novel AM system with dynamic resolution control capability.

A laser projector is adopted in a vat photopolymerization system. The laser projection system has unique properties, including focus-free operation and capability to produce dynamic mask image irrespective of any surface (flat or curved). By translating the projector along the building direction, the pixel size can be adjusted dynamically within a certain range. Consequently, the build area and resolution could be tuned dynamically in the hardware testbed. Besides, a layered depth image (LDI) algorithm is used to construct mask images with varied resolutions. The curing characteristics under various resolution settings are quantified, and accordingly, a process planning approach for fabricating models with dynamically controlled resolutions is developed.

A laser projection-based stereolithography (SL) system could tune resolution dynamically during the building process. Such a dynamic resolution control approach completely addresses the build size-resolution dilemma in vat photopolymerization AM processes without sacrificing the build speed. Through fabricating layers with changing resolutions instead of a single resolution, various build areas and feature sizes could be produced precisely, with optimized build speed.

A focus-free laser projector is investigated and adopted in a SL system for the first time. The material curing characteristics with changing focal length and therefore changing light intensities are explored. The related digital mask image planning and process control methods are developed. In digital mask image planning, it is the first attempt to adopt the LDI algorithm, to identify proper resolution settings for fabricating a sliced layer precisely and quickly. In the process of characterizing material curing properties, parametric dependence of curing properties on focal length has been unveiled. This research contributes to the advancement of AM by addressing the historical dilemma of the resolution and build size, and optimizing the build speed meanwhile.

Exposure controlled projection lithography (ECPL) is an additive manufacturing process based on controlled UV photopolymerization. This paper aims to explore an advanced closed-loop control methodology to ECPL.

This paper proposes an evolutionary cycle to cycle (EC2C) control method, and started with a reduced order EC2C time control to control only the exposure time for given DMD bitmaps, which correspond to target 3D part cross-sections. A preliminary EC2C time control scheme was developed and followed by two types of EC2C time controllers based on two different parameter estimation methods, recursive least squares and L₁ norm minimization (L₁Min). Both algorithms were in an exponential weighted form, resulting in EWRLS and EWL₁Min, to weight more on recent data to reflect the current process dynamics.

EWRLS was found to outperform EWL₁Min in terms of computation speed and stability. The simulation study demonstrated that the proposed EC2C time control method was capable of adaptively tracking the ECPL process dynamics and updating online the model parameters with real-time measurements. It could control perfectly the exposure time for each bitmap, achieving the desired height for each layer and resulting in a total cured height conforming to the target 3D part height.

The accuracy of EC2C time control method relies heavily on fast and accurate measurement, and this research assumes availability of an adequate real-time metrology. Measurement errors are not considered in this paper and will be explored in future. Only simulation study was performed without physical experiments to verify the EC2C controller.

For implementation, a real-time measurement system needs to be developed and the EC2C control software needs to be programmed and interfaced with the physical system.

It concludes that EC2C control method is very promising for a physical implementation, and could be extended for the development of a more comprehensive closed-loop controller for both exposure time and intensity to improve the ECPL process precision and robustness.

The purpose of this paper is to present a mask‐image‐projection‐based stereolithography (MIP‐SL) process that can combine two base materials with various concentrations and structures to produce a solid object with desired material characteristics. Stereolithography is an additive manufacturing process in which liquid photopolymer resin is cross‐linked and converted to solid. The fabrication of digital material requires frequent resin changes during the building process. The process presented in this paper attempts to address the related challenges in achieving such fabrication capability.

A two‐channel system design is presented for the multi‐material MIP‐SL process. In such a design, a coated thick film and linear motions in two axes are used to reduce the separation force of a cured layer. The material cleaning approach to thoroughly remove resin residue on built surfaces is presented for the developed process. Based on a developed testbed, experimental studies were conducted to verify the effectiveness of the presented process on digital material fabrication.

The proposed two‐channel system can reduce the separation force of a cured layer by an order of magnitude in the bottom‐up projection system. The developed two‐stage cleaning approach can effectively remove resin residue on built surfaces. Several multi‐material designs have been fabricated to highlight the capability of the developed MIP‐SL process.

A proof‐of‐concept testbed has been developed. Its building speed and accuracy can be further improved. The tests were limited to the same type of liquid resins. In addition, the removal of trapped air is a challenge in the presented process.

This paper presents a novel and a pioneering approach towards digital material fabrication based on the stereolithography process. This research contributes to the additive manufacturing development by significantly expanding the selection of base materials in fabricating solid objects with desired material characteristics.