|
|
|
|
|
|
|
|
Institute for Systems Research, University of Maryland
Satyandra K. Gupta
William C. Regli
Dana S. Nau
January 1996
The ability to quickly introduce new quality products is a decisive factor in capturing market share. Because of pressing demands to reduce lead time, analyzing the manufacturability of the proposed design has become an important step in the design stage. In a typical CAD environment, the designer creates a design using solid-modeling software, and uses analysis software to examine different aspects of the proposed design's functionality. As shown below, the IMACS project is extending the design loop to incorporate a manufacturability analysis system that can be used once the geometry and/or tolerances have been specified. This will help in creating designs that not only satisfy the functional requirements but are also easy to manufacture.
We assume that the proposed design is available as a solid model, along with the tolerance and surface finish information as attributes of various faces of the solid model. We assume we have information about the available machining operations, including the process capabilities, dimensional constraints, etc. As shown below, our approach is to generate alternative interpretations of the part as collections of machining features, map these interpretations into operation plans, and evaluate the manufacturability of each operation plans.
The ultimate goal of the IMACS project is to provide tools for manufacturability analysis as part of the CAD systems used by designers. We believe our work will help designers design products that are easier to manufacture. This will reduce the need for redesign, resulting in reduced lead time and product cost. In addition, it will help to speed up the evaluation of new product designs in order to decide how or whether to manufacture them. Such a capability will be especially useful in flexible manufacturing systems, which need to respond quickly to changing demands and opportunities in the marketplace.
Given a computerized representation of the design (i.e. a solid model) and a set of manufacturing resources, the automated manufacturability analysis problem can be defined as follows:
In general, a design's manufacturability is a measure of the effort required to manufacture the part according to the design specifications. Our approach to measuring manufacturability is to estimate the manufacturing time and cost. Since all manufacturing operations have measurable time and cost, these can be used as an underlying basis to form a suitable manufacturability rating. Ratings based on time and cost can easily be combined into a overall rating. Moreover, they present a realistic view of the difficulty in manufacturing a proposed design and can be used to aid management in making make-or-buy decisions.
In a machining operation, a cutting tool is swept along a trajectory, and material is removed by the motion of the tool relative to the current workpiece. The volume resulting from a machining operation is called a machining feature. A machining feature corresponds to a single machining operation made on one machine setup. Each machining feature has a single approach direction (or orientation) for the tool.
In IMACS, features are parameterized solids that correspond to various types of machining operations on a 3-axis machining center, including the ones shown below:
|
|
|
|
One of the fundamental objectives of IMACS was to develop a methodology for systematically generating and evaluating alternative operation plans for machined parts. This involves representing the design as a collection of machining features such as those shown above. To get these features from the CAD model, IMACS uses the feature recognition subsystem described at http://www.cs.umd.edu/projects/cim/feature_rec.html.
Given this feature-based representation of the design, there may be, in general, several alternative representations of the design as different collections of machinable features, corresponding to different ways to machine the part. As described in the introduction, the basic idea is to generate alternative interpretations of the part as collections of machinable features, map these interpretations into operation plans, and evaluate the manufacturability of each operation plan. More specifically, our approach involves the steps shown below:
We now illustrate this analysis on two different designs.
|
Design #1: |
|
|
|
Design #2: |
|
|
Analysis of Design 1:
Analysis of Design 2:
| ||||
| ||||
|
IMACS also gives estimated machining time needed for each step in the operation plan. For example, here are the estimated machining times for two of the faces:
|
3.29 minutes: |
|
|
2.54 minutes: |
|
We anticipate that the results of our work will be useful in providing a way to speed up the evaluation of new product designs in order to decide how or whether to manufacture them. Such a capability will be especially useful in flexible manufacturing systems, which need to respond quickly to changing demands and opportunities in the marketplace. Some of the benefits of our approach include:
Future plans and work in progress include incorporating an interface to computer-aided fixturability analysis, and extending IMACS to automatically formulate suggestions for how to redesign products to improve their manufacturability.
This work has been supported in part by National Science Foundation Grants NSFD EEC 94-02384, IRI-9306580, DDM-9201779, and by the University of Maryland General Research Board. Software grants were provided by Spatial Technologies, Ithaca Software, EDS/Unigraphics, and Bentley Systems, Inc. General Electric Corporation, through their Forgivable Loan program, has provided additional support to William Regli.
