Manufacturability Analysis for Solid Freeform Fabrication

This paper describes a systematic approach to analyzing manufacturability of parts produced using Solid Freeform Fabrication (SFF) processes with flatness, parallelism and perpendicularity tolerance requirements on the planar faces of the part. SFF processes approximate objects using layers, therefore the part being produced exhibits stair-case effect. The extent of this stair-case effect depends on the angle between the build orientation and the face normal. Therefore, different faces whose direction normal is oriented differently with respect to the build direction may exhibit different values of inaccuracies. We use a two step approach to perform the manufacturability analysis. We first analyze each specified tolerance on the part and identify the set of feasible build directions that can be used to satisfy that tolerance. As a second step, we take the intersection of all sets of feasible build directions to identify the set of build directions that can simultaneously satisfy all specified tolerance requirements. If there is at least one build direction that can satisfy all tolerance requirements, then the part is considered manufacturable. Otherwise, the part is considered non-manufacturable. Our research will help SFF designers and process providers in the following ways. By evaluating design tolerances against a given process capability, it will help designers in eliminating manufacturing problems and selecting the right SFF process for the given design. It will help process providers in selecting a build direction that can meet all design tolerance requirements.

Process Capability Database Usage in Industry: Myth vs. Reality

Process capability data (PCD) is used during design to assess manufacturability, allocate tolerances, and evaluate robustness. Process capability databases (PCDBs)1 have been developed by many design/manufacturing industries to capture their process capability and communicate it to the entire organization. While these databases are being used to monitor quality, they are not being effectively utilized by design. A survey of design and manufacturing companies was used to determine both how PCD is being used and the barriers preventing design from fully utilizing PCD. Two key barriers were identified: lack of a company-wide vision for PCD usage and poor communication between manufacturing and design. Management support, training, database population, common databases, and common indexing schemes were identified as solutions to these barriers.

Web-Enabled Feature-Based Modeling in a Distributed Design Environment

Network and Internet technology open up another domain for building future CAD/CAM environments. The environment will be global, network-centric, and spatially distributed. In this paper, we present Web-enabled feature-based modeling in a distributed design environment. The presented approach combines the current feature-based modeling technique with distributed computing and communication technology for supporting product modeling and collaborative design activities over the network. The approach is implemented in a client/server architecture, in which Web-enabled feature modeling clients, neutral feature model server, and other applications communicate with one another via a standard communication protocol. The paper discusses how the neutral feature model supports multiple views and maintains naming consistency between geometric entities of the server and clients as the user edits the part in a client. Moreover, it explains how to minimize the network delay between the server and client according to dynamic feature modeling operations.

Experimental Investigation of Factors Influential for the Flexible Blade Based Prototyping Process

Due to the need for large numbers of layers and size limitations, current layered manufacturing technologies are not suitable for the fabrication of large sized free-form objects. For this purpose a novel technology of thick layered object manufacturing is being developed, based on higher order approximation of the initial geometry, and the application of a flexible curved cutting tool. The method allows us to produce physical prototypes with less or without any finishing. The technology of cutting foams by means of a heated flexible blade in polystyrene foam offers new possibilities. However to achieve the optimum output, optimization of the process parameters is needed. In this paper a closer look is taken into the process characteristics and the influential factors which are decisive for productive cutting. The authors summarize the results of the executed experimental tests. In these experiments the values of the most influential parameters were systematically changed and the effects were carefully investigated. The first results indicate that the cutting technology is practically feasible, but further research is needed in order to achieve a balanced optimization of the technology from all aspects.

Strategies to Minimize Deburring Costs

A number of researchers have investigated burr formation mechanisms through careful observations and well thought-out experiments. The results of their studies help untangle underlying effects of key machining parameters on burr formation. However, so far, nobody has practically incorporated such knowledge into the area of process planning. The purpose of this paper is to develop general strategies to minimize deburring cost. Furthermore, it establishes basic decision making tools for efficient deburring planning.

Practical Passive Assembly: Gripper Design and Assembly Sequence Optimization

For efficient assembly without feedback systems (or, passive assembly), the assembler should know the ideal orientation of each component and the assembly sequence. A heuristic presented here finds an optimal assembly sequence and prescribes the orientation of the components for a minimum set of grippers — ideally one. The heuristic utilizes an index of difficulty (ID) that quantifies assembly. The ID for each task in the assembly process is computed based on a number of geometrical and operational properties. The objective of the optimization problem here is to minimize the assembly ID and categorize parts/subassemblies based on their preferred direction of assembly while allowing re-orientation of the base part. It is assumed that the preferred direction of assembly is vertically downwards consistent with manual as well as most automatic assembly protocols. Our attempt is to minimize the number of degrees of freedom required in a re-orienting fixture and mathematically derive the requirements for such a fixture. The assembly of a small engine is used as an example in this study due to the variety of ideally rigid parts involved.

Conceptual Design for Assembly

This paper presents an approach to support computer-aided conceptual design of mechatronic assemblies in a collaborative, multi-user environment. We describe a system, Conceptual Understanding and Prototyping (CUP), that allows a team of design engineers, collaborating over the Internet, to develop a high-level structure-function-behavior (S-B-F) description of an assembly in a VRML-based virtual environment. Our goal is to enable users to navigate intricate product data management (PDM) and case-based design knowledge-bases, providing the ability to perform design at conceptual level and have intelligent CAD tools that can draw on details from large repositories of previously archived designs. This work furthers research efforts in computer support for collaborative design activities — drawing on work in Human-Computer Interaction (HCI) and Computer Supported Collaborative Work (CSCW). We envision CUP to be a network interface to next-generation of engineering PDM systems and CAD databases. We are deploying CUP as query interface to the National Design Repository (http://repos.mcs.drexel.edu). This will enable CAD users to interrogate large quantities of legacy data and identify artifacts with structural and functional similarities — allowing designers to perform case-based and variant design.

A Formative Evaluation of a Feature Extraction and Process Planning Tool

It is a common problem that many computer tools intended to enhance human performance in design or manufacturing planning do not do so. In many cases they may actually degrade performance. One way to increase the probability that a tool will meet users needs is to include frequent periodic usability assessments in the development process so feedback from users can be incorporated in new iterations of the software design. This paper describes an example of one such assessment applied to a Mediator, a feature extraction and process planning tool for assisting process planners to explore plan options more quickly and thoroughly. There exists a wide variety of usability assessment techniques which can mostly be divided into two broad categories: summative evaluations which provide in-depth assessments in the final stages of software development, and formative evaluations which tend to be smaller in scale and are used to provide guidance for “forming” subsequent software versions during the development cycle. In this work, we describe a formative usability assessment. The study indicated that Mediator was meeting its design goal of broadening the users exploration of manufacturing options, in some cases producing high quality manufacturing options which the expert users had not considered on their own. The study also provided formative redesign information gleaned which will help future versions of Mediator to better meet the actual needs of process planners.

Product and Factory Modeling for Production Rate Determination

An intelligent graphical user interface that captures a product’s functional and assembly structure and the factory that will make it are described. The results are then used to evaluate a factory’s production rate for the product. The program requires the product to be either a functionally uncoupled or decoupled design. The interface then: (1) implements a visualization of the functionally decomposed product structure; (2) implements an abstraction of a factory; (3) automatically generates candidate primary manufacturing processes and materials that are compatible with each other based on a very small number of attributes; (4) enables the user to make Make/Buy decisions for the components comprising the product; (5) assists the user in the selection of secondary manufacturing processes that are compatible with the primary manufacturing processes and materials for parts made in-house, and specify the vendor and the supply lead time for outsourced parts; (6) enables the specification of alternate materials and manufacturing processes; (7) implements a visual representation of the assembly structure as specified by the user; and (8) partially automates the creation of the assembly structure, and assists in the selection of assembly methods that are compatible with the materials chosen. In addition, the program assists in the design for assembly by: (1) requiring the product development team to think about the assembly process early in the design stage; (2) providing a visualization of the relationship of all components comprising the product to its other components; (3) requiring the specification of the order in which they are to be assembled; and (4) requiring the selection of assembly processes that are compatible with each other and the materials chosen. It also requires the specification of the capabilities of the factory that is going to make one or more of the components of the product, and requires that Make/Buy decisions for the parts comprising the product be made.

Layered Manufacturing With Embedded Components: Process Planning Considerations

This paper addresses the design and manufacturing of products with embedded components through layered manufacturing processes such as Shape Deposition Manufacturing (SDM). Embedding components allows the creation of novel designs such as “smart” products and integrated assemblies of sensors, actuators and other mechanical components. We present prototypes to illustrate the possibilities for such devices and we address the issues that constrain their process planning. Next, we present a combination of process planning algorithms and manufacturing methods that we have developed to support the design of layered products with embedded components.