"There are no shortcuts to any place worth going."  - Beverly Sills


The research interests of our research group are centered around Direct Digital Manufacturing (DDM) in micro- and meso-scales.  DDM is a fabrication approach that can directly convert a computer-aided design model into a physical object.  Hence it has been widely recognized as a disruptive manufacturing technology for a wide variety of applications. To achieve the full potentials of DDM on cost and time savings, the development of novel DDM process, new process planning methodologies and a wide selection of materials are critical.  In addition, DDM enables revolutionary new design by using complex three-dimensional shapes, heterogeneous material properties and multi-functionality.  Systematic knowledge regarding modeling, analyzing, synthesizing, and optimizing such designs are required in order to achieve desired performance.

At USC’s ISE department, we aim to develop DDM technologies that enable people to revolutionize future product design and manufacturing.  Our multi-disciplinary research and training require bridging theoretical, computational and practical knowledge with systematic thinking. By integrating both physics-based manufacturing and computation-based design and control, some of our research results are listed as follows.


Novel process and machine development for direct digital manufacturing and 3D printing


3D printing of piezoelectric element for energy focusing and ultrasonic sensing

Zeyu Chen, XuanSong, Liwen Lei, Xiaoyang Chen, Chunlong Fei, Chi Tat Chiu, Xuejun Qian, Teng Ma, YangYang, Kirk Shung, Yong Chen, Qifa Zhou

Nano Energy, 2016 (paper)


Piezoelectric ceramics are currently of considerable interest for their capabilities of converting compressive/tensile stresses to an electric charge, or vice versa. Because ceramics cannot be cast and machined easily, additive manufacturing (AM) processes (3D printing technology) open an effective pathway in geometrical flexibility. However, the piezoelectric properties limit the application of printed ceramics. This work demonstrates that a piezoelectric-composite slurry with BaTiO3 nanoparticles (100 nm) can be 3D printed using Mask-Image-Projection-based Stereolithography (MIP-SL) technology. After a post-process, the density of 5.64 g/cm3 was obtained, which corresponds to 93.7% of the density of bulk BaTiO3 (6.02 g/cm3 ). The printed ceramic exhibits a piezoelectric constant and relative permittivity of 160 pCN1 and 1350 respectively. An ultrasonic transducer with printing focused piezoelectric element was fabricated to realize the energy focusing and ultrasonic sensing. A 6.28 MHz ultrasonic scan was achieved by the transducer and successfully visualized the structure of a porcine eyeball


Three dimensional printing of high dielectric capacitor using projection based stereolithography

YangYang, Zeyu Chen, XuanSong, Benpeng Zhu, Tzung Hsiai, Pin-I Wu, RuiXiong, Jing Shi, Yong Chen, Qifa Zhou, K.Kirk Shung

Nano Energy, 2016 (paper)


We report that efficient high dielectric polymer/ceramic composite materials can be optically printed into three-dimensional (3D) capacitor by the projection based stereolithography (SLA) method. Surface decoration of Ag on Pb(Zr,Ti)O3(PZT@Ag) particles were used as filler to enhance the dielectric permittivity. Polymer nanocomposites were fabricated by incorporating PZT@Ag particles into the photocurable polymer solutions, followed by exposure to the digitally controlled optical masks to generate 3D structures. The dielectric permittivity of Flex/PZT@Ag composite reaches as high as 120 at 100Hz with 18vol% filler, which is about 30 times higher than that of pure Flex. Furthermore, the dielectric loss is as low as 0.028 at 100Hz. The results are in good agreement with the effective medium theory (EMT) model. The calculated specific capacitance of our 3D printed capacitor is about 63 F g-1 at the current density of 0.5 A g-1 . Cyclic voltammetry (CV) curves indicate 3d printed capacitor pocesses low resistance and ideal capacitive properties. These results not only provide a tool to fabricate capacitor with complex shapes but lay the groundwork for creating highly efficient polymer-based composites via 3D printing method for electronic applications.


Ceramic Fabrication Using Mask-image-projection-based Stereolithography Integrated with Tape-casting

Xuan Song, Yong Chen, Tae Woo Lee, Shanghua Wu, Lixia Cheng

Journal of Manufacturing Processes, 2015 (paper)


Ceramic components with complex geometry are difficult to fabricate. Layer-based additive manufacturing processes such as ceramic-suspension-based stereolithography (SL) provide a direct way of fabricating ceramic components from computer-aided design (CAD) models. In such an SL process, fine ceramic powders are mixed with liquid photocurable resin into ceramic suspension. The suspension-based slurry is then used in the SL process to fabricate green parts with desired shapes. A sintering process is further required to convert the green parts into dense ceramic components. In this paper, several key challenges of the ceramic-suspension-based SL process are discussed including the recoating and curing ceramic suspension with high solid loading. A novelMask-Image-Projection-based Stereolithography (MIP-SL) process by integrating ceramic tape-casting and bottom-up projection methods is presented for fabricating dense ceramic components from CAD models. Various approaches to increase the solid loading in green parts are discussed including suspension preparation, image projection, layer recoating and separation. A prototype system based on the presented ceramics fabrication process has been developed. Test cases of different types of ceramics are presented to demonstrate the effectiveness of the presented fabrication method. The post-processing of green parts to convert them into dense ceramic components is also discussed with some sintering results presented.


Origami-Based Self-Folding Structure Design and Fabrication Using Projection Based Stereolithography

Dongping Deng, Yong Chen

ASME Journal of Mechanical Design, 2014 (paper)


Self-folding structures are beneficial for a wide variety of applications including biomedical and electronics products. In this paper a novel fabrication approach based on a three-dimensional (3D) printing process is presented for fabricating self-folding structures that can be actuated in a heating environment. The designed and fabricated thermo-actuating structures are two-dimensional (2D) origami sheets that have multiple printed layers. The middle layer of an origami sheet is a pre-strained polystyrene film with large shrinkage ratios when heated.  Both its top and bottom surfaces are covered with printed polymers with designed shapes. A foldable hinge is achieved by constraining the shrinkage of the film on one side while allowing the shrinkage of the film on another side when heated. Heuristic models of hinge folding angles are developed. Various experimental tests based on the developed 2D origami design and fabrication method are presented. Techniques on improving folding angle control are also discussed with possible applications.


Multi-tool and Multi-axis CNC Accumulation for Fabricating Conformal Features on Curved Surfaces

Yayue Pan, Chi Zhou, Yong Chen, Jouni Partanen

ASME Journal of Manufacturing Sci. and Engineering, 2014 (paper)


In engineering systems, features such as textures or patterns on curved surfaces are common.  In addition, such features, in many cases, are required to have shapes that are conformal to the underlying surfaces. To address the fabrication challenge in building such conformal features on curved surfaces, a newly developed additive manufacturing (AM) process named Computer Numerically Controlled (CNC) accumulation is investigated by integrating multiple tools and multiple axis motions.  Based on a fiber optical cable and a light source, a CNC accumulation tool can have multi-axis motion, which is beneficial in building conformal features on curved surfaces.  To address high resolution requirement, the use of multiple accumulation tools with different curing sizes, powers, and shapes is explored. The tool path planning methods for given cylindrical and spherical surfaces are discussed. Multiple test cases have been performed based on a developed prototype system.  The experimental results illustrate the capability of the newly developed AM process and its potential use in fabricating conformal features on given curved surfaces..

Development of a Low-cost Parallel Kinematic Machine for Multi-directional Additive Manufacturing

Xuan Song, Yayue Pan, Yong Chen

ASME-Journal of Manufacturing Science and Engineering, 2014 (paper)


Most additive manufacturing (AM) processes are layer-based with three linear motions in the X, Y and Z axes. However, there are drawbacks associated with such limited motions, e.g. non-conformal material properties, stair-stepping effect, and limitations on building-around-inserts. Such drawbacks will limit additive manufacturing to be used in more general applications. To enable 6-axis motions between a tool and a work piece, we investigated a Stewart mechanism and the feasibility of developing a low-cost 3D printer for the multi-directional Fused Deposition Modeling (FDM) process. The technical challenges in developing such an AM system are discussed including the hardware design, motion planning and modeling, platform constraint checking, tool motion simulation, and platform calibration. Several test cases are performed to illustrate the capability of the developed multi-directional additive manufacturing system.  A discussion of future development on multi-directional AM systems is also given.


Rapid Manufacturing in Mintues: The Development of a Mask Projection Stereolithography Process for High-speed Fabricating

Yayue Pan, Chi Zhou, Yong Chen

Proceedings of ASME-Intl. Manufacturing Sci. and Engineering Conference, 2012 (paper)


The purpose of this paper is to present a direct digital manufacturing (DDM) process that is an order of magnitude faster than other DDM processes currently available.  The developed process is based on a mask-image-projection-based Stereolithography process (MIP-SL), during which a Digital Micromirror Device (DMD) controlled projection light cures and cross-links liquid photopolymer resin.  In order to achieve high-speed fabrication, we investigated the bottom-up projection system in the MIP-SL process. A set of techniques including film coating and the combination of two-way linear motions have been developed for the quick spreading of liquid resin into uniform thin layers.  The process parameters and related settings to achieve the fabrication speed of a few seconds per layer are presented. Additionally, the hardware, software, and material setups developed for fabricating given three-dimensional (3D) digital models are presented. Experimental studies using the developed testbed have been performed to verify the effectiveness and efficiency of the presented fast MIP-SL process.  The test results illustrate that the newly developed process can build a moderately sized part within minutes instead of hours that are typically required.


Direct Geometry Processing for Tele-fabrication

Yong Chen, Kang Li, Xiaoping Qian

Proceedings of ASME Computers and Information in Engineering Conference, 2012 (paper)


This paper presents a new approach for tele-fabrication where a physical object is scanned in one location and fabricated in another location. This approach integrates three-dimensional (3D) scanning, geometric processing of scanned data, and additive manufacturing technologies. In this paper, we focus on a set of direct geometric processing techniques that enable the tele-fabrication. In this approach, 3D scan data is directly sliced into layer-wise contours. Sacrificial supports are generated directly from the contours and digital mask images of the objects and the supports for Stereolithography Apparatus (SLA) processes are then automatically generated. The salient feature of this approach is that it does not involve any intermediate geometric models such as STL, polygons or non-uniform rational B-splines that are otherwise commonly used in prevalent approaches. The experimental results on a set of objects fabricated on several SLA machines confirm the effectiveness of the approach in faithfully tele-fabricating physical objects.


Ultrasound Transducer Array Fabrication based on Additive Manufacturing of Piezocomposite

Hamid Chabok, Chi Zhou, Yong Chen, Arash Eskandarinazhad, Qifa Zhou, Kirk Shung

Proceedings of the ASME International Sysmposium on Flexible Automation, 2012 (paper)


Conventional methods for fabricating ultrasound imaging transducer arrays, especially for high frequency range (>20 MHz), are expensive, time consuming and limited to relatively simple geometries. In this paper, the development of an additive manufacturing (AM) process based on digital micromirror devices (DMDs) is presented for the fabrication of piezoelectric devices such as ultrasound transducer arrays. Both green-part fabrication and the sintering of fabricated green-parts have been studied. A novel two-channel design in the bottom-up projection system is presented to address the piezo-composite fabrication challenges including a small curing depth and viscous ceramic slurry recoating.  A prototype system has been developed for the fabrication of green-parts with complex shapes and small features. Based on the fabricated green-parts, the challenges in the sintering process for achieving desired functionality are discussed. Various approaches for increasing the density of sintered components are presented. Dielectric and piezoelectric properties of the fabricated samples are measured and compared with those of bulk PZT samples. Based on the identified challenges in the DMD-based AM process, future work for achieving fully functional piezoelectric ceramic components is discussed.


Smooth Surface Fabrication in the Mask Projection based Stereolithography

Yayue Pan, Xuejin Zhao, Chi Zhou, Yong Chen

Proceedings of NAMRI/SME, 2012 (paper)


The surface finish is critical for applications such as optics, micro-fluid mixing and mechanical assembly, in which optical lens, fluidic flow channels and rotating components are all required to be smooth. However, the stair-stepping effect is well known in the layer-based additive manufacturing processes, in which a three-dimensional model is approximated by a set of two-dimensional layers.  Consequently the fabricated surfaces have poor surface finish especially for the ones that are close to the horizontal plane.  In this paper, a novel approach for achieving improved surface finish is presented for the mask-image-projection-based Stereolithography (MIP-SL) process.  Theoretical models and parameter characterization are presented for the developed methods. Accordingly, the process planning and calibration approaches for fabricating smooth surfaces in the MIP-SL process have been developed.  Multiple test cases based on various types of curved surfaces have been performed.  A comparison of the built results based on the traditional and the newly developed approaches illustrates the effectiveness of our method.


Digital Material Fabrication Using Mask-Image-Projection-based Stereolithography

Chi Zhou, Yong Chen, Zhigang Yang, Behrokh Khoshnevis

Rapid Prototyping Journal, 2012 (paper)


Digital materials such as the ones shown by Objet’s Connex family demonstrate that a new material with desired characteristics can be achieved by combining two different base materials with various concentrations and structures.  We investigate the feasibility of using additive manufacturing processes based on digital mask projection in the fabrication of such digital materials.  A multi-material mask-image-projection-based Stereolithography process is presented.  The related challenges and approaches of addressing them on the development of such a process are identified. A testbed has been developed to fabricate objects with designed digital materials.  Experimental results illustrate that desired material properties can be achieved through the developed process. Several multi-material designs have been produced to highlight the capability of this promising technology for fabricating three-dimensional, multi-material objects with spatial control over placement of both material and structure. The limitations and challenges for future development have also been identified.


Metallic Part Fabrication Using Selective Inhibition Sintering

Behrokh Khoshnevis, Mahdi Yoozbashizadeh, Yong Chen

Rapid Prototyping Journal, 2011 (paper)


The purpose of this research is to investigate the fundamentals of the Selective Inhibition Sintering (SIS) process for the fabrication of metallic parts. A SIS-Metal process has been developed based on the microscopic mechanical inhibition principle. In this process metal salt solution is printed in the selected areas of each metal powder layer; the salt re-crystallizes when water evaporates; salt crystals decompose and grow rapidly prior to sintering; during the sintering process the constituents of decomposed salt particles spread between metal powder particles and prevent the fusing of these particles together; consequently, the sintering process in the affected regions is inhibited. This paper presents the research result on the inhibition mechanism and process control of the SIS process. Experimental results are also presented to demonstrate the capability of the process in fabricating metal parts with various geometries.  The SIS-Metal process has numerous advantages including low cost, minimal shrinkage and deformation effects, and independence from polymeric binders.

A Layerless Additive Manufacturing Process based on CNC Accumulation

Yong Chen, Chi Zhou, Jingyuan Lao

Rapid Prototyping Journal, 2011 (paper)


Most current additive manufacturing processes are layer-based, that is building a physical model layer-by-layer.  By converting 3-dimensional geometry into 2-dimensional contours, the layer-based approach can dramatically simplify the process planning steps.  However, there are also drawbacks associated with the layer-based approach such as inconsistent material properties between various directions.  In a recent NSF workshop on additive manufacturing, it is suggested to investigate alternative non-layer based approaches.  In this paper, we present an additive manufacturing process without planar layers. In the developed testbed, an additive tool based on a fiber optics cable and a UV-LED has been developed.  By merging such tools inside a liquid resin tank, we demonstrate its capability of building various 2D and 3D structures.  The technical challenges related to the development of such a process are discussed.  Some potential applications including part repairing and building around inserts have also been demonstrated.


Modeling and control techniques for accurate and reliable direct digital manufacturing processes


Connected Fermat Spirals for Layered Fabrication

Haisen Zhao, Fanglin Gu, Qi-Xing Huang, Jorge Garcia, Yong Chen, Changhe Tu, Bedrich Benes, Hao Zhang, Daniel Cohen-Or, Baoquan Chen

Proceedings of ACM SIGGRAPH, 2016 (paper)

We develop a new kind of “space-filling” curves, connected Fermat spirals, and show their compelling properties as a tool path fill pattern for layered fabrication. Unlike classical space-filling curves such as the Peano or Hilbert curves, which constantly wind and bind to preserve locality, connected Fermat spirals are formed mostly by long, low-curvature paths. This geometric property, along with continuity, influences the quality and efficiency of layered fabrication. Given a connected 2D region, we first decompose it into a set of sub-regions, each of which can be filled with a single continuous Fermat spiral. We show that it is always possible to start and end a Fermat spiral fill at approximately the same location on the outer boundary of the filled region. This special property allows the Fermat spiral fills to be joined systematically along a graph traversal of the decomposed sub-regions. The result is a globally continuous curve. We demonstrate that printing 2D layers following tool paths as connected Fermat spirals leads to efficient and quality fabrication, compared to conventional fill patterns.

An Integrated CNC Accumulation System for Automatic Building-around-inserts

Xuejin Zhao, Yayue Pan, Chi Zhou, Yong Chen, Charlie C. L. Wang

Proceedings of NAMRI/SME, 2011 (paper)

A non-layer-based additive manufacturing (AM) process named computer numerically controlled (CNC) accumulation process is presented for applications such as plastic part repairing and modification. To facilitate the CNC accumulation process, a novel three-dimensional (3D) laser scanning system based on a micro-electo-mechanical system (MEMS) device is developed for in situ scanning of inserted components. The integration of the scanning system in the CNC accumulation process enables the building-around-inserts with little human efforts. A point processing method based on the Algebraic Point Set Surface (APSS) fitting and Layered Depth-normal Image (LDNI) representation is developed for converting the scanning points into triangular meshes. The newly developed 3D scanning system is compact and has sufficient accuracy for the CNC accumulation process. Based on the constructed surface model, data processing operations including multi-axis tool path planning and motion control are also investigated. Multiple test cases are performed to illustrate the capability of the integrated CNC accumulation process on addressing the requirements of building-aroundinserts.

Additive Manufacturing based on Optimized Mask Video Projection for Improved Accuracy and Resolution

Chi Zhou, Yong Chen

Proceedings of NAMRI/SME, 2011 (paper)


Additive manufacturing (AM) processes based on mask image projection such as digital micro-mirror devices (DMD) have the potential to be fast and inexpensive. More and more research and commercial systems have been developed based on such digital devices. However, the accuracy and resolution of the related AM processes are constrained by the limited number of mirrors in a DMD. In this paper, a novel AM process based on the mask video projection has been presented. For each layer, a set of mask images instead of a single image are planned based on the principle of optimized pixel blending. The planned images are then projected in synchronization with the small movement of the building platform. A mask image planning method has been presented for the formulated optimization problem. Experimental results have verified that the mask video projection process can significantly improve the accuracy and resolution of built components.

Additive Manufacturing based on Multiple Calibrated Projectors and its Mask Image Planning

Chi Zhou, Yong Chen

Proceedings of ASME International Design Engineering Technical Conferences, 2010 (paper)


Additive manufacturing (AM) processes based on mask image projection such as digital micro-mirror devices (DMD) have the potential to be fast and inexpensive. More and more research and commercial systems have been developed based on such digital devices.  However, a digital micro-mirror device such as a digital light processing (DLP) projector has limited accuracy and resolution.  Based on the principle of pixel blending, we present a novel AM process by using multiple DMDs to significantly improve the accuracy and resolution of built components. In order to achieve the desired pixel blending result for a given layer, it is critical to plan the mask images that will be used by the multiple projectors.  In addition, the mask image planning needs to compensate the calibrated light intensity in a projection image that is usually non-uniform and non-linear. We present a general optimized pixel blending method based on direct discrete search (DDS).  Its mathematic model and computing method for the mask image planning are presented. Various test cases have been performed to verify its effectiveness and efficiency

Calibrating Large-area Mask Projection Stereolithography for Its Accuracy and Resolution Improvements

Chi Zhou, Yong Chen

Proceedings of Solid Freeform Fabrication Symposium, 2009 (paper)


Solid freeform fabrication (SFF) processes based on mask image projection such as digital micro-mirror devices (DMD) have the potential to be fast and inexpensive. More and more research and commercial systems have been developed based on such digital devices.  However, a digital light processing (DLP) projector based on DMD has limited resolution and certain image blurring.  In order to use a DLP projector in the large-area mask projection stereolithography, it is critical to plan mask images in order to achieve high accuracy and resolution.  Based on our previous work on optimized pixel blending, we present a calibration method for capturing the non-uniformity of a projection image by a low cost off-the-shelf DLP projector. Our method is based on two calibration systems, a geometric calibration system that can calibrate the position, shape, size, and orientation of a pixel and an energy calibration system that can calibrate the light intensity of a pixel. Based on both results, the light intensity at various grayscale levels can be approximated for each pixel. Developing a library of such approximation functions is critical for the optimized pixel blending to generate a better mask image plan. Experimental results verify our calibration results.

Self-intersection Free and Topologically Faithful Slicing of Implicit Solid

Pu Huang, Charlie Wang, Yong Chen

Proceedings of International Design Engineering Technical Conferences, 2011 (paper)

We present a robust and efficient approach to directly slicing implicit solids. Different from prior slicing techniques that reconstruct contours on the slicing plane by tracing the topology of intersected line segments, which is actually not robust, we generate contours through a topology guaranteed contour extraction on binary images sampled from given solids and a subsequent contour simplification algorithm which has the topology preserved and the geometric error controlled. The resultant contours are free of self-intersection, topologically faithful to the given r-regular solids and with shape error bounded; therefore, correct objects can be fabricated from them by rapid prototyping. Moreover, since we do not need to generate the tessellated B-rep of given solids, our approach is memory efficient – only the binary image and the finest contours on one particular slicing plane need to be stored in-core. Our method is general and can be applied to any implicit representations of solids.

Manufactruability Analysis of Infeasible Features in Polygonal Models for Web-based Rapid Prototyping

Yong Chen, Xiaoshu Xu

Proceedings of International Conference on Manufacturing Automation, 2010 (paper)

Web-based online submission of computer-aided design (CAD) models for prototype parts is getting popular among service bureaus and gaining wider acceptance among rapid prototyping users. In the web-based rapid prototyping (RP), an instant quote needs to be generated for an arbitrary polygonal model (usually in STL format).  Hence the manufacturability analysis of polygonal models is critical in automating the instant quoting process.  In this paper two common problems are addressed including: (1) small features that are infeasible to be made by a RP process; and (2) cost analysis of a given polygonal model. We present two methods based on the analysis of offsetting results: (i) a fast approach of identifying infeasible features in order to provide an instant feedback to users; and (ii) an accurate approach of calculating the information of infeasible features for a given tool size in order to facilitate cost analysis.  The related data structures and algorithms are presented.  Both 2-dimensional and 3-dimensional examples are provided to illustrate the effectiveness of our approach.

Three-Dimensional Digital Halftoning for Layered Manufacturing based on Droplets

Chi Zhou, Yong Chen

Transactions of North American Manufacturing Research Institute of SME, Vol. 37, pp. 175-182, 2009 (paper)


Layered manufacturing based on droplets, such as multi-jet modeling and polyjet processes, shows great promises in fabricating accurate, smooth and highly detailed 3-dimensional models.  It has been widely used in fabricating prototypes and investment casting patterns.  In this paper, we present a 3-dimensional digital halftoning method which can significantly reduce the building time of these layered manufacturing processes.  The key idea of the halftoning method is to intelligently control the printed droplet layout to form a slanted layer, which can closely match the surface of an input geometry.  We present a mathematical model for finding the optimized droplet layout, and discuss various solution strategies.  The experimental results showed that a revised DBS method can solve the formulated problem effectively and efficiently.

Optimized Mask Image Projection for Solid Freeform Fabrication

Chi Zhou, Yong Chen, Richard A. Waltz

Proceedings of ASME Internal Design Engineering Technical Conferences, 2009 (paper)


Solid freeform fabrication (SFF) processes based on mask image projection have the potential to be fast and inexpensive.  More and more research and commercial systems have been developed based on these processes.  For the SFF processes, the mask image planning is an important process planning step.  In this paper, we present an optimization based method for mask image planning.  It is based on a light intensity blending technique called pixel blending.  By intelligently controlling pixels’ gray scale values, the SFF processes can achieve a much higher XY resolution and accordingly better part quality.  We mathematically define the pixel blending problem and discuss its properties.  Based on the formulation, we present several optimization models for solving the problem including a mixed integer programming model, a linear programming model, and a two-stage optimization model.  Both simulated and physical experiments for various CAD models are presented to demonstrate the effectiveness and efficiency of our method.

Non-uniform Offsetting and its Applications in Laser Path Planning of Stereolithography Machine

Yong Chen

Proceedings of Solid Freeform Fabrication Symposium, 2007 (paper)


Laser path planning is an important step in solid freeform fabrication processes such as Stereolithography (SLA).  An important consideration in the laser path planning is to compensate the shape of laser beam.  Currently the compensation is divided into two steps, Z-compensation and X-Y compensation, and the shape of laser beam is assumed to be uniform for the whole platform.  In this research, we present a sampling based non-uniform offsetting method which accounts for the different shapes of laser beam at various locations.  We discuss the related steps and algorithms.  We demonstrate its effectiveness by using various test cases.  Besides improving the accuracy of SLA machine, non-uniform offsetting can also be applied to address other accuracy issues caused by thermal and structural variations.



Design methods and tools for DDM-enabled products and applications


A Structural Topology Design Method based on Principal Stress Line

Tsz-Ho Kwok, Yongqiang Li, Yong Chen

Computer-aided Design, 2016 (paper)

Topology optimization is an important topic in structural mechanics. One common application is to obtain the optimal distribution of material that maximizes the stiffness of the solution (minimize the compliance). However, as an iterative process, topology optimization of large and complex structures is computationally intensive. The problem becomes even more complicated if the manufacturing constraints are taken into account in the optimization process. In this paper, a novel growth method based on principal stress lines (PSLs) is presented for topology optimization. The PSLs are traced in the design domain along the direction of principal stresses, in which the materials would be located to define the geometry and topology of the structure. Consequently, the optimization problem is converted into a geometric design problem. Compared to previous methods, the computation based on PSLs is fast, and the designer can have explicit control over the number of structural members. In addition, the manufacturing constraints can easily be incorporated. Multiple test cases are given to illustrate the presented method. The PSL-based method is promising for building practical designing tools for various structural applications.

4D Printing for Freeform Surfaces: Design Optimization of Origami and Kirigami Structures

Tsz-Ho Kwok, Charlie Wang, Dongping Deng, Yunbo Zhang, Yong Chen

ASME Journal of Mechanical Design, 2015 (paper)

A self-folding structure fabricated by additive manufacturing can be automatically folded into a demanding 3D shape by actuation mechanisms such as heating. However, 3D surfaces can only be fabricated by self-folding structures when they are flattenable. Most generally designed parts are not flattenable. To address the problem, we develop a shape optimization method to modify a non-flattenable surface into flattenable. The shape optimization framework is equipped with topological operators for adding interior/boundary cuts to further improve the flattenability. When inserting cuts, selfintersection is locally prevented on the flattened 2D pieces. The total length of inserted cuts is also minimized to reduce artifacts on the finally folded 3D shape.

The status, challenges, and future of additive manufacturing in Engineering

Wei Gao, Yunbo Zhang, Devarajan Ramanujan, Karthik Ramani, Yong Chen, Christopher Williams, Charlie Wang, Yung Shin, Song Zhang, Pablo Zavattieri

Computer-aided Design, 2015 (paper)

Additive manufacturing (AM) is poised to bring about a revolution in the way products are designed, manufactured, and distributed to end users. This technology has gained significant academic as well as industry interest due to its ability to create complex geometries with customizable material properties. AM has also inspired the development of the maker movement by democratizing design and manufacturing. Due to the rapid proliferation of a wide variety of technologies associated with AM, there is a lack of a comprehensive set of design principles, manufacturing guidelines, and standardization of best practices. These challenges are compounded by the fact that advancements in multiple technologies (for example materials processing, topology optimization) generate a “positive feedback loop” effect in advancing AM. In order to advance research interest and investment in AM technologies, some fundamental questions and trends about the dependencies existing in these avenues need highlighting. The goal of our review paper is to organize this body of knowledge surrounding AM, and present current barriers, findings, and future trends significantly to the researchers. We also discuss fundamental attributes of AM processes, evolution of the AM industry, and the affordances enabled by the emergence of AM in a variety of areas such as geometry processing, material design, and education. We conclude our paper by pointing out future directions such as the “print-it-all” paradigm, that have the potential to re-imagine current research and spawn completely new avenues for exploration.

Interactive Material Design Using Model Reduction

Hongyi Xu, Yijing Li, Yong Chen, Jernej Barbiˇc

ACM Transactions on Graphics, 2014 (paper)

We demonstrate an interactive method to edit the material properties of three-dimensional deformable objects. The user specifies displacements and forces at a set of mesh vertices, and our system interactively computes a spatial distribution of material properties, given those constraints. We apply our method both to linear and nonlinear isotropic materials, simulated using the Finite Element Method (FEM). We demonstrate that solving the problem interactively in the full-dimensional space of individual tetrahedron material values is not practical. Instead, we propose a new model reduction method that projects the material space to a low-dimensional space of material modes. Our model reduction accelerates optimization by two orders of magnitude, and makes the convergence much more robust, making it possible to interactively edit material distributions on complex meshes. We apply our method to precise control of contact forces and control of pressure over large contact areas between rigid and deformable objects for ergonomics. Our tetrahedron-based dithering method can efficiently convert continuous material distributions into discrete ones and we demonstrate its precision via FEM simulation.We physically display our distributions using haptics, as well as demonstrate how haptics can also aid in the material design. The produced inhomogeneous material distributions can also be used in computer animation applications.

Mesh Thickening for Freeform Surface Patches

Charlie Wang, Yong Chen

Rapid Prototyping Journal, 2012 (paper)

Given an intersection-free mesh surface patch S, we introduce a method to thicken S into a solid H located at one side of S, where the thickness r of H is specified by users. With such a surface-to-solid conversion operation, industrial users are able to fabricate a designed (or reconstructed) surface by rapid prototyping. To develop this thickening operator for freeform mesh surfaces, we first investigate an implicit representation of the thickened solid H according to an extension of signed distance function. After that, a partial surface reconstruction algorithm is proposed to generate the boundary surface of H, which remains the given surface S exactly on the resultant surface. Experimental tests show that the thickening results generated by our method give nearly uniform thickness and meanwhile do not present shape-approximation error at the region of input surface S. These two good properties are very important to the industrial applications that need to use this thickening operation.

Joint Design for 3-D Printing Non-assembly Mechanisms

Xuan Song, Yong Chen

Proceedings of ASME IDETC, 2012 (paper)

The layer-based additive manufacturing (AM) processes can directly fabricate sub-systems with multiple components during the building process. Novel applications in robotics and many others have been demonstrated by removing the need of component assembly. However, the AM processes also have inferior accuracy compared to the Computer Numerical Control (CNC) machining process. Hence the joint clearance that can be achieved in a 3D-printed mechanism is large. This would significantly limit the use of AM in directly building movable sub-systems without further assembly operations after the building process. To reduce the joint clearance, we present a novel joint design by considering the fabrication limitation of AM processes. A novel marker structure is developed for various types of joints including cylindrical pin joints. The relation of the marker design and the rotation performance of the 3D-printed joint is modeled. Test cases based on the Stereolithography Apparatus (SLA) process have been performed to verify the effectiveness of the developed joint design. Compared to the traditional pin joint design, the new design can achieve a smaller clearance during rotation while still be able to be fabricated by the SLA process. Consequently its rotation performance can be improved.

Design of Origami Sheets for Foldable Object Fabrication

Dongping Deng, Yong Chen

Proceedings of ASME IDETC, 2012 (paper)

Reconfigurable structures that are enabled through the integration of multiple materials are important for future design and manufacturing practice. We investigate one of such reconfigurable structures - an origami sheet, which can be designed based on a 3D object and unfolded into a 2D sheet with complex creases. A fabrication approach based on a hybrid manufacturing process by integrating layer-based additive manufacturing and silicon molding techniques is developed. Related challenges on designing creases for given folding requirements and the related material properties are discussed. A novel structure design is presented to ensure the fabricated creases that are in soft materials can be folded and unfolded without failures. The design method can be applied to different scale levels. The origami sheets for test cases in different complexity have been tested. The experimental results illustrate that the designed and fabricated origami sheets can be folded and used for product components with reconfigurable shapes.

A Rapid Shape Acquisition Method by Integrating User Touching Input

Yong Chen, Jinho Jung, Yongqiang Li

Virtual and Physical Prototyping, 2011 (paper)

The easiness of creating three-dimensional (3D) models from physical objects is one of the core challenges that remain to be addressed in reverse engineering. In this paper, a touch-based 3D shape acquisition method is presented that is easy and intuitive to use. Based on the method, a user can easily interact with both real and virtual objects and directly generate feature-based CAD models. The key technical challenges on developing the related hardware and software systems are discussed. By using widely available consumer electronic devices, a low-cost prototype system is designed and built. Based on the designed system, a novel 3D coordinate computation method is developed to obtain the touching point positions. Related challenges on using such a system in generating 3D models are also discussed. Multiple examples are presented to illustrate the effectiveness and efficiency of the developed method.


Multi-Piece Mold Design Based on Linear Mixed-Integer Program Toward Guaranteed Optimality

Stephen Stoyan, Yong Chen

Proceedings of International Conference on Manufacturing Automation, 2010 (paper)

Multi-piece molds are a type of molding technology, which consist of more than two mold pieces and are assembled/dissembled like a space puzzle.  Based on such molds, complex parts can be made for limited run production.  Compared to traditional two-piece molds, parts with much more complex geometries can be made; however, this also brings challenge in designing such multi-piece molds.  Previous works to address the problem are all based on heuristics.  In this paper, we present a multi-piece mold design framework based on linear mixed-integer program.  In our method, multi-piece mold design with guaranteed optimality on the number of mold pieces can be generated for any given CAD model of a molded part.  The formulation of multi-piece mold design as a linear mixed-integer program is presented.  The related multi-piece mold design framework is discussed.  Some examples are provided which illustrate the effectiveness and efficiency of our approach.

Design of Flexible Skin for Target Displacements based on Meso-Structures

Yongqiang Li, Yong Chen, Chi Zhou

Proceedings of ASME Computers and Information in Engineering Conference, 2009 (paper)

Recent advances in sold freeform fabrication (SFF) present tremendous design freedom for a product design with complex geometries.  In this paper, we consider the problem of using rigid materials to design flexible skin of a product component for SFF.  A design strategy based on the combination of well-defined meso-structures is presented to achieve desired heterogeneous material properties, and consequently desired flexibility in target directions and positions.  We present our computational framework to automate the design optimization process.  Due to the dramatically increased design space, a brute force or traditional design optimization method such as the genetic algorithm (GA) and particle swam optimization (PSO) is not efficient.  We present a design method based on the idea of analyzing the flexibility of each link for given meso-structures.  Two experimental examples are presented to demonstrate its usage in generating the maximum/minimum and target displacements.  We also present its comparison with the GA and PSO methods.

Computer-aided Product Design with Performance-Tailored Mesostructures

Yong Chen, Shanglong Wang

Computer-aided Design and Application, 2008 (paper)

Motivated by the design and manufacturing of customized cushions for debilitated patients, we propose the idea of performance-tailored mesostructures which can change or adapt their design performance based on given requirements.  Our goal is to develop a CAD tool with the capability of specifying heterogeneous material properties in a product component such that a designer can design the component with better performance. Based on the object oriented programming paradigm, we first define a performance-tailored mesostructure and its properties.  We then demonstrate an approach of building discipline-specific performance models for such mesostructures.  For a product component design, we present a performance-tailored mesostructure design method based on a hierarchical design framework.  A CAD system based on the proposed design framework is being developed which can generate CAD models with performance-tailored mesostructures.  The generated CAD models can then be fabricated by a layer-based rapid manufacturing system.  Several experimental examples are given to demonstrate the capability of our method.

3D Texture Mapping: A Microstructure Design Method for Rapid Manufacturing

Yong Chen

Computer-aided Design and Application, Vol. (4), No. 6, 2007, pp.761-771 (paper)

Inspired by the developments of biomimetic design and layer manufacturing, we present a microstructure design method which uses complex internal structures to achieve an optimal design. Similar to 2D texture mapping, our approach is based on mapping a 3D microstructure into a design space to generate internal structures. We develop a texture mapping design system which enables a designer to select a microstructure from a library. It then automatically generates a CAD model with internal structures based on given design requirements. The generated CAD model can be fabricated using a layer manufacturing system. The ability to design microstructures within a part creates tremendous potential for lightweight and high performance components and devices.

A Mesh-based Geometric Modeling Method for General Structures

Yong Chen

Proceedings of ASME Design Engineering Technical Conferences, 2006 (paper)

This paper presents a mesh-based geometric modeling method to create tessellated models of general structures, which can be the design results of conformal truss structure design, thermal design, topology design, material design, compliant mechanism design and others. A general structure configuration design format is proposed to describe the structures. A universal structure generating system is developed based on the mesh-based geometric modeling method. Besides generating a watertight surface model for an input structure configuration, the modeling approach can automatically add an important design feature, fillets, in the generated model. Therefore the structures’ mechanical performance is improved comparing to results generated by other methods. Examples from different structure design areas are presented.

Hybrid Geometric Modeling Method for Large Scale Conformal Cellular Structures

Hongqing Wang, Yong Chen, David W. Rosen,

ASME Journal of Computing and Information Science in Engineering, 2006, accepted (paper)

This paper presents a hybrid geometric modeling method to create CAD models of large-scale conformal cellular structures effectively and efficiently. Cellular material structures can be engineered at the mesoscopic scale for high performance and multifunctional capabilities. One type of cellular structure is conformal lightweight truss. A simple method of constructing models of uniform trusses is to pattern unit cells linearly within a CAD system. However, by orienting strut directions and adjusting strut sizes, such trusses can be optimized to achieve superior strength, stiffness, and weight characteristics. For large truss structures, computational and storage complexities cause difficulties in CAD system modeling. In this paper, a new hybrid geometric modeling method by using both solid modeling and surface modeling techniques is developed to directly create tessellated models and automate the geometric modeling process of conformal truss structures efficiently. This hybrid modeling method is intended to support the design, analysis, optimization, and manufacture of conformal truss structures. Examples are presented and the computational efficiency of the hybrid method is compared with the approach of creating the complete solid model of cellular structures. The hybrid geometric modeling method can be generalized to various types of cellular structures as well as other periodic structures.

Geometric Tailoring: A Design for Manufacturing Method for Rapid Prototyping and Rapid Tooling

Shiva Sambu, Yong Chen, David W. Rosen

ASME Journal of Mechanical Design, 2004, Vol(126), 571-580 (paper)

The goal of fabricating functional prototypes quickly is hindered by a mismatch of material properties between production materials and those used in rapid prototyping (RP) machines, such as stereolithography. Even when rapid tooling (RT) technologies are utilized for injection molded parts, differences in mold materials cause differences in molded part properties. To compensate for these material and process differences, a design for manufacturing (DFM) method is introduced, called geometric tailoring. The idea is to modify dimensions of prototype parts to match key characteristics of production parts, such as stress and deflection behaviors. For RP parts, the geometric tailoring DFM method integrates two sub-problems, one for achieving functional requirements by matching part behaviors, and one for RP process planning to incorporate manufacturing capabilities and limitations. For parts fabricated by RT, an additional sub-problem is integrated, namely injection molding process planning. Problem decomposition is critical due to the coupled nature of the sub-problems. A problem decomposition and solution procedure is presented. The geometric tailoring method is shown to enable the matching of prototype to production part behaviors, while improving manufacturability.

The Rapid Tooling Testbed: A Distributed Design-for-manufacturing System

David W. Rosen, Yong Chen, Shiva Sambu, Janet K. Allen, Farrokh Mistree

Journal of Rapid Prototyping, 2003, Vol(9), 122-132 (paper)

A new design-for-manufacturing method, called the geometric tailoring (GT), and the associated digital interface concept have been developed that enable the design activities to be separated from the manufacturing activities. Conditions for the successful application of this method are investigated. The GT method is demonstrated for rapid prototyping and rapid tooling technologies, where prototype parts are required to match the production properties as closely as possible. This method is embodied in a system called the rapid tooling testbed (RTTB). Research work is presented on GT and the distributed computing environment underlying the RTTB. Examples are summarized from the usage of this method and testbed.

Computer-Aided Design for Rapid Tooling: Methods for Mold Design and Design-for-Manufacture

Yong Chen

Ph.D. Dissertation, Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA, 2001. (dissertation)



New modeling and computing methods for DDM-enabled complex geometries


Parallel and Efficient Boolean on Polygonal Solids

Hanli Zhao, Charlie C. L. Wang, Yong Chen, Xiaogang Jin

Visual Computer, Vol. 27, pp. 507-517, 2011 (paper)

We present a novel framework which can efficiently evaluate approximate Boolean set operations for Brep models by highly parallel algorithms. This is achieved by taking axis-aligned surfels of Layered Depth Images (LDI) as a bridge and performing Boolean operations on the structured points. As compared with prior surfel-based approaches, this paper has much improvement. Firstly, we adopt key-data pairs to store LDI more compactly. Secondly, robust depth peeling is investigated to overcome the bottleneck of layer-complexity. Thirdly, an out-of-core tiling technique is presented to overcome the limitation of memory. Real-time feedback is provided by streaming the proposed pipeline on the many-core graphics hardware.

Uniform Offsetting of Polygonal Model based on Layered Depth-Normal Images

Yong Chen, Charlie C. L. Wang

Computer-Aided Design, Vol. 42, 2010 (paper)

Uniform offsetting is an important geometric operation for computer-aided design and manufacturing (CAD/CAM) applications such as rapid prototyping, NC machining, coordinate measuring machines, robot collision avoidance, and Hausdorff error calculation.  We present a novel method for offsetting (grown and shrunk) a solid model by an arbitrary distance r.  First, offset polygons are directly computed for each face, edge, and vertex of an input solid model. The computed polygonal meshes form a continuous boundary; however, such a boundary is invalid since there exist meshes that are closer to the original model than the given distance r as well as self-intersections.  Based on the problematic polygonal meshes, we construct a well-structured point-based model, Layered Depth-Normal Image (LDNI), in three orthogonal directions.  The accuracy of the generated point-based model can be controlled by setting the tessellation and sampling rates during the construction process. We then process all the sampling points in the model by using a set of point filters to delete all the invalid points .  Based on the remaining points, we construct a two-manifold polygonal contour as the resulting offset boundary.  Our method is general, simple and efficient.  We report experimental results on a variety of CAD models and discuss various applications of the developed uniform offsetting method.

Layer Depth-Normal Images for Complex Geometries - Part I: Accurate Modeling and Adaptive Sampling

Yong Chen, Charlie C. L. Wang

Proceedings of ASME Design Engineering Technical Conferences, 2008 (paper)

The layered depth-normal images (LDNIs) is an implicit representation of solid models that sparsely encodes the shape boundary in three orthogonal directions.  We present a LDNI-based geometric modeling method for applications with high accuracy requirements.  In our method, we first construct LDNIs models from input polygonal models.  The accuracy of the generated LDNIs models can be controlled by setting pixel width during the construction process. Even for very complex geometries and high accuracy requirements, the construction process is fast with the aid of graphics hardware. Based on the LDNIs models, we then perform geometric modeling operations.  Two types of operations are presented including regularizing and Boolean operations.  The geometric modeling operations are straightforward and easy to be implemented robustly.  From the processed LDNIs model, an adaptive sampling method is presented to construct a cell representation that includes both uniform and octree cells.  Finally 2-manifold polygonal mesh surfaces are constructed from the cell representation.  For high accuracy requirements that are typical in CAD/CAM applications, we present a volume tiling technique and a parallel implementation to accelerate the computation.  Our method achieves a good balance between the accuracy and computational resources. We report experimental results on a variety of CAD models.  The results demonstrate the effectiveness and efficiency of our approach especially for modeling complex geometries.

Layer Depth-Normal Images for Complex Geometries - Part II: Manifold-Preserved Adaptive Contouring

Charlie C. L. Wang, Yong Chen

Proceedings of ASME Design Engineering Technical Conferences, 2008

We present an adaptive contouring approach to generate contour surface from solid models represented by Layered Depth-Normal Images (LDNI) sampled in three orthogonal directions. Our contouring algorithm builds an octree structure for mesh generation in a top-down manner: starting from the bounding box of a LDNI solid model, the cells are recursively subdivided into smaller sub-cells based on the topology and geometry criteria of refinement until both of the requirements, the topology in cell is simple and the geometry approximation error is less than a user defined tolerance, are satisfied. The subdivision also stops when the processed cells reach the finest resolution of LDNI models. In order to overcome the topology ambiguity inside a cell that leads to the occurrence of nonmanifold entities, we analyze the possible inside/outside configurations of cell-nodes and exploit two strategies to generate manifold-preserved mesh surfaces. Moreover, the most time-consuming step of our contouring algorithm – the construction of octree structure can be easily parallelized to run under a computer framework with multiple-processors and shared memory. Several examples have been tested in the paper to demonstrate the success of our method.

An Accurate Sampling-based Method for Approximating Geometry

Yong Chen

Journal of Computer-Aided Design 2007, Vol. 39, No. 11, pp. 975-986 (paper)

We present a sampling-based method for approximating the boundary of a geometry defined by various geometric operations. Based on a novel adaptive sampling condition, we first construct a volumetric grid such that in each cell an error-minimizing point can be found to captures all the geometric objects inside the cell. We then construct a polygonal model from the grid. We guarantee the boundary approximation has the same topology as the exact surfaces, and the maximum approximation error from the exact surfaces is bounded by a user specified tolerance. Our method is robust and easy to implement. We have applied it in applications such as remeshing of polygonal models, Boolean operations and offsetting operations. We report experimental results on a variety of CAD models.


Robust and Accurate Boolean Operations on Polygonal Models

Yong Chen

Proceedings of ASME Design Engineering Technical Conferences, 2007 (paper)

We present a new sampling-based method for the efficient and reliable calculation of boundary surface defined by a Boolean operation of given polygonal models.  We first construct uniform volumetric cells with sampling points for each geometric element of polygonal models.  We then calculate an error-minimizing point in each cell based on a quadratic error function (QEF).  Based on a novel adaptive sampling condition, we construct adaptive octree cells such that a QEF point in each cell can capture the shape of all the geometric elements inside the cell.  Finally we reconstruct a polygonal model from the volumetric grids and QEF points for approximating the boundary of a solid defined by the Boolean operation.  Our method is robust since we can handle different types of topological inconsistency including non-manifold configurations. It is also accurate since we guarantee the boundary approximation has the same topology as the exact surface, and the maximum approximation error from the exact surface is bounded by a user specified tolerance.  The efficient hierarchical scheme based on octree enables using sufficient grid resolutions on a commodity PC.  We demonstrate our algorithm for a number of test cases and report experimental results.

A Point-Based Offsetting Method of Polygonal Meshes

Yong Chen, Hongqing Wang, David W. Rosen, Jarek Rossignac

ASME Journal of Computing and Information Science in Engineering 2006, in review (paper)

We address the delicate problem of offsetting polygonal meshes. Offsetting is important for stereolithography, NC machining, coordinate measuring machines, robot collision avoidance, and Hausdorff error calculation. We introduce a new fast, and very simple method for offsetting (growing and shrinking) a solid model by an arbitrary distance r. Our approach is based on a hybrid data structure combining point samples, voxels, and continuous surfaces. Each face, edge, and vertex of the original solid generates a set of offset points spaced along the (pencil of) normals associated with it. The offset points and normals are sufficiently dense to ensure that all voxels between the original and the offset surfaces are properly labeled as either too close to the original solid or possibly containing the offset surface. Then the offset boundary is generated as the isosurface using these voxels and the associated offset points. We provide a tight error bound on the resulting surface and report experimental results on a variety of CAD models.

Filleting and Rounding Using a Point-based Method

Yong Chen, Hongqing Wang, David W. Rosen, Jarek Rossignac

Proceedings of ASME Design Engineering Technical Conferences, 2005 (paper)

Rounds and fillets are important design features. We introduce a new point-based method for constant radius rounding and filleting. Based on the mathematical definitions of offsetting operations, discrete offsetting operations are introduced. Steps of our approach are discussed and analyzed. The methodology has been implemented and tested. We present the experimental results on accuracy, memory and running time for various input geometries and radius. Based on the test results, the method is very robust for all kinds of geometries.


A Region Based Method to Automated Design of Multi-Piece Molds with Application to Rapid Tooling

Yong Chen, David W. Rosen

ASME Journal of Computing and Information Science in Engineering, 2002, Vol(2), 86-97 (paper).

Particularly for rapid tooling applications, delivering prototype parts with turn-around times of less than two weeks requires fast, proven mold design methods. We present a region-based approach to automated mold design that is suitable for simple two-piece molds (consisting of core and cavity), as well as molds with many additional moving sections. In our region-based approach, part faces are partitioned into regions, each of which can be formed by a single mold piece. The basic elements of our approach are concave regions (generalized pockets) and convex faces since these elements are central to the identification of regions. This paper focuses on the initial steps of automated mold design, including a problem formulation, methods for identifying the basic elements from part faces, and combining them into regions. By seeking to minimize the number of mold pieces, different partitions of faces into regions are explored until the smallest number of regions is found. During this process, a linear programming problem is adopted for finding a satisfactory parting direction of a region. Algorithms are presented for the region generating and combining process. Our approach is illustrated with several examples of industrial injection molded parts.

A Reverse Glue Approach to Automated Construction of Multi-Piece Molds

Yong Chen, David W. Rosen

ASME Journal of Computing and Information Science in Engineering, 2003, Vol(3) (paper).

Mold design can be a difficult, time-consuming process. Determining how to split a mold cavity into multiple mold pieces (e.g., core, cavity) manually can be a tedious process. This paper focuses on the mold construction step of the automated mold design process. By investigating glue operations and its relations with parting faces, an approach based on a new reverse glue operation is presented. The key to the reverse glue operation is to generate parting faces. A problem definition of parting face generation for a region is provided. Correspondingly, three face generating criteria are identified. Based on the parting lines of a region, our algorithms to generate the parting faces are presented. Our mold construction algorithms for two-piece molds and multi-piece molds are also presented with brief discussions. Some industrial examples are provided which illustrate the efficiency and effectiveness of our approach. We tested our mold designs by fabricating stereolithography mold inserts (a rapid tooling method) and molding parts.