A Parallel Solution Strategy for Finite Element Models

This paper presents a method for naturally decomposing finite element models into sub-models which can be solved in a parallel fashion. The unique contribution of this paper is that the decomposition strategy comes from the geometric features used to construct the solid model that the finite element model represents. Domain composition and domain decomposition methods are used to insure global compatibility. These techniques reduce the N2 behavior of traditional matrix solving techniques, where N is the number of degrees of freedom in the global set of matrix equations, to a sum of m matrices with n2 behavior, where n represents the number of degrees of freedom in the smaller sub-model matrix equations.

A Knowledge-Based System for Machining Operation Planning in Feature Based, Open-Architecture Manufacturing

Within the Integrated Design And Manufacturing Environment (IMADE), operation planning provides a mapping from geometric design primitives to machining operation sequences for manufacturing processes. Operation planning includes tool selection, machining parameter selection, and tool path generation. An object oriented approach to program structure is adopted, whereby features, operations and tools, inherit behaviors and attributes from the appropriate class-hierarchies for the part, the manufacturing operations, and tooling classes. A detailed example is presented illustrating the operation planning search algorithm. Scripts are generated by the individual machining operations for execution on a machine tool. Tooling information is maintained in an object-oriented database through the FAR libraries for Common LISP. Examples of particular process plans show that the inherent trade-offs between specified precision and machining time can be investigated. An Open Architecture Machine Tool (MOSAIC-PM) has been used to machine the parts created by the feature based design and planning system. The novel contributions of this paper relate to the demonstration of “seamless” links between, a) design, b) planning, and c) actual fabrication by milling.

New CAD for Rapid Prototyping

We developed a new CAD tool with special attention paid to rapid prototyping. Most of the present 3-D CAD systems treat geometry with very high accuracy but it is not easy to define or modify geometry as we do in the earlier stages of design. The present CAD systems, we believe, are more oritented toward the detailed design and manufacturing of the final product. As rapid prototyping itself is intended for the earlier stages of design, such a CAD system that permitts more easy or rough definition and modification of geometry is really desired. Most of the rapid prototyping systems generate 3-D geometry by piling up the 2-D sections layer by layer. So, if we develop such a layer-based CAD system, then we could more easily tranfer CAD data to the prototyping system. Such an idea was very old, but the traditional ones cannot manipulate geometry with much ease. What we aimed here is to develop a system that a designer can manipuate geometry as freely as he or she wishes. Thus, our system serves as a preprocessor to the present 3-D CAD systems. We are developing another system which permits to generate 3-D geometry as freely as if we are drawing it using a pen, based on the technology of 3-D measurement device. Couled with this system, the system we are proposing here is expected to tranfer such a 3-D geometry data very rapidly and easily to the prototyping equipment and also can interactively modify thus defined geometry data.

Iterative Part Design With a Virtual Reality Interface

A virtual reality (VR) interface to a feature-based computer-aided design (CAD) system promises to provide a simple interface to a designer of mechanical parts, because it allows intuitive specification of design features such as holes, slots, and protrusions in three-dimensions. Given the current state of a part design, the designer is free to navigate around the part and in part cavities to specify the next feature. This method of feature specification also provides directives to the process-planner regarding the order in which the features may be manufactured. In iterative feature-based design, the existing part cavities represent constraints as to where the designer is allowed to navigate and place the new feature. The CAD system must be able to recognize the part cavities and enforce these constraints. Furthermore, the CAD system must be able to update its knowledge of part cavities when the new feature is added. In this paper, (i) we show how the CAD system can enforce the aforementioned constraints by exploiting the knowledge of part cavities and their adjacencies, and (ii) present efficient methods for updates of the set of part cavities when the designer adds a new feature.

Reverse Fishbone Diagram: A Tool in Aid of Design for Product Retirement

This paper describes a schematic representation of product retirement specification that aids in design for recycling and reuse. In the past decade, a graphical representation of the assembly process, called the assembly fishbone diagram, has effectively assisted engineers to conduct design for assembly (DFA) and process failure modes and effects analysis (FMEA). On the other hand, environmentally conscious manufacturing requires engineers to make advanced planning for product retirement. This study investigates the use of the reverse fishbone diagram to model the disassembly and reprocessing sequence of a product at the end of its useful life. An industry-provided student project guided us to an initial definition of the reverse fishbone diagram that effectively led the students to analyze the recyclability and make practical redesign suggestions. The diagram is continuously adding more rigorous definitions and promises to be a central tool for evaluation of recyclability in a simultaneous engineering setting.

Value Implications of Green Design: Case Study of a Videocassette

Recent concern for the environment has caused growing attention to recycling, both using recycled materials to make products and recycling products after use. Although environmentalists may be eager to buy recycled/recyclable products, other consumers may not be so easily convinced. It may also be difficult to convince manufacturers that it is beneficial to develop green products. This paper supports a joint project between engineering and marketing disciplines to determine the cost and value of an environmentally designed product. Specifically, this paper evaluates the resources spent to manufacture a green videocassette in comparison with a standard videocassette by performing a resource analysis. This analysis estimates the cost, time and energy necessary to produce both videocassettes. This paper also compares the value of the videocassettes in terms of performance and physical attributes.

Computation of Voxel Maps Containing Tool Access Directions for Machining Free-Form Shapes

An algorithm that derives tool access directions for machining free-form shapes is presented. A free-form shape to be machined is given by a preliminary B-spline model. We allow that the B-spline surface data are as inaccurate as the user-selected geometric accuracy of the prototype to be machined. Using surface sampling a visibility voxel map is obtained. From this map a voxel map is derived that contains per voxel a set of tool access directions. From the obtained voxel map regions can be selected that can be machined with a fixed tool access direction per region.

Systematic Process Selection in Mechanical Design

There has been a recent awareness of the importance of making the right manufacturing decisions early in the design process before the cost penalty of making changes becomes too high. The selection of the most appropriate manufacturing process — of which there are a very large number — is one such decision. It is commonly based on human-resident experience or on established local practice. As such, some potentially-usable processes may be overlooked. This paper explores ways in which process selection might be made more systematic. It presents a procedure for manufacturing process selection which considers all manufacturing processes and eliminates the ones which cannot satisfy the design requirements. This is achieved using Process Selection Charts in which process capabilities are displayed graphically. A procedure for the ranking of the successful processes based on cost is under development. The systematic selection procedure lends itself well to computer implementation. A database of manufacturing processes and an advanced user interface thus provide ideal support for designers. Cambridge Materials Selector (CMS) software is currently being applied to manufacturing process selection.

A Blackboard Architecture for Integrated Process Planning/Production Scheduling

As companies increase the level of customization in their products, move towards smaller lot production and experiment with more flexible customer/supplier arrangements such as those made possible by Electronic Data Interchange (EDI), they increasingly require the ability to quickly, accurately and competitively respond to customer requests for bids on new products and efficiently work out supplier/subcontractor arrangements for these new products. This in turn requires the ability to rapidly convert standard-based product specifications into process plans and quickly integrate process plans for new orders into the existing production schedule to best accommodate the current state of the manufacturing enterprise. This paper describes IP3S, an Integrated Process Planning/Production Scheduling (IP3S) Shell for Agile Manufacturing. The IP3S Shell is designed around a blackboard architecture that emphasizes (1) concurrent development and dynamic revision of integrated process planning/production scheduling solutions, (2) the use of a common representation for exchanging process planning and production scheduling information, (3) coordination with outside information sources such as customer and supplier sites, (4) mixed initiative decision support, enabling the user to interactively explore a number of tradeoffs, and (5) portability and ease of integration with legacy systems. The system is scheduled for initial evaluation in a large and highly dynamic machine shop at Raytheon’s Andover manufacturing facility.

The Effect of a Fractal Profile Tolerance on the Dynamic Performance of Cams

To ensure a successful design, it is important to understand the effect that design parameters have on design performance. Tolerances are an important subset of design parameters. In this paper, the relevance of fractal surface characterization for profile tolerances is investigated. The notion of fractal geometry is discussed. The validity of a fractal characterization on a cam surface is determined. Dynamic simulations of a cam-follower system are used to qualify the effect of a fractal profile error on system performance.