Representing Relationships in Hierarchical Assemblies

Computer aided design tools are gaining popularity in industry due to their ability to model the geometric aspects of products. This has shown substantial benefit for reducing the need and expense of building physical prototypes and allowing parts and tooling to be manufactured directly from these models. However, the current capabilities in existing CAD tools for modeling assemblies are quite limited. In this paper we introduce a representation for describing interfaces between parts within hierarchical assemblies for capturing functional and physical mating relations. This representation is designed to support automated reasoning and automated generation and modification of assemblies. It is also designed for use with very large assemblies, compactly representing the interfaces of parts and assemblies that are reused within larger assemblies. We describe how this representation is used in our prototype design system, Genesis, for designing aircraft systems.

The Datum Flow Chain: A Systematic Approach to Assembly Design and Modeling

In order to be able to lay out, analyze, outsource, assemble, and debug complex assemblies, we need ways to capture their fundamental structure in a top-down design process, including the designer’s strategy for kinematically constraining and locating the parts accurately with respect to each other. We describe a concept called the “Datum Flow Chain” to capture this logic. The DFC relates the datum logic explicitly to the product’s key characteristics, assembly sequences, and choice of mating features, and provides the information needed for tolerance analyses. Two types of assemblies are addressed: Type-1 where the assembly process puts parts together at their prefabricated mating features, and Type-2 where the assembly process can incorporate in-process adjustments to redistribute variation. Two types of assembly joints are defined: mates that pass dimensional constraint from part to part, and contacts that merely provide support. The scope of DFC in assembly planning is presented using several examples. Analysis tools to evaluate different DFCs and select the ones of interest are also presented.

Collision Detection for Assembly Planning Using Solid Modelling

Details of a method for detecting collision of two parts when one is moved along a direction are discussed in this paper. Reduced number of grid points and the rays emit from these points to detect the intersection of a moving part with a fixed part, is the main advantage of this method comparing with the previous works in the literature. The intersection of rays, sent from a plane considerably far from both parts, with the faces of moving and fixed part are detected in this methods. If any ray intersects the moving part before intersecting the fixed part, the moving part will collide with the fixed part in that direction. Determining the starting point of the rays and detecting intersection of rays with the parts are also discussed in this paper.

A Geometric Theory for Formulation of Form, Profile and Orientation Tolerances: Problem Formulation

This paper develops a geometric theory which unifies the formulation and evaluation of form (straightness, flatness, cylindricity and circularity), profile and orientation tolerances stipulated in ANSI Y14.5M standard. In the paper, based on an an important observation that a toleranced feature exhibits a symmetry subgroup G0 under the action of the Euclidean group, SE(3), we identify the configuration space of a toleranced (or a symmetric) feature with the homogeneous space SE(3)/G0 of the Euclidean group. Geometric properties of SE(3)/G0, especially its exponential coordinates carried over from that of SE(3), are analyzed. We show that all cases of form, profile and orientation tolerances can be formulated as a minimization or constrained minimization problem on the space SE(3)/G0, with G0 being the symmetry subgroup of the underlying feature. We transform the non-differentiable minimization problem into a differentiable minimization problem over an extended configuration space. Using geometric properties of SE(3)/G0, we derive a sequence of linear programming problems whose solutions can be used to approximate the minimum zone solutions.

What Is a Manufacturing Interaction?

In this work we make a distinction between feature interactions and manufacturing interactions. These two terms are usually used interchangeably because feature and manufacturing interactions often occur together, but not always. However, we feel that it is important to make a distinction between feature interactions which result from volumetric intersections of features presenting difficulties for features extractors, and manufacturing interactions which occur when two manufacturing operations interfere with each other’s execution, and present a problem to the process planner. By separating these definitions it allows us to focus separately on each phenomena. In this paper our focus is on manufacturing interactions. We present a non-exhaustive catalog of common manufacturing interaction types in CNC machining, and discuss how they result in precedence constraints in the manufacturing plan.

Condition Monitoring Methodology for Manufacturing and Design

Part production requires constant monitoring to assure the effective manufacturing of high-quality components. The choice of monitoring methods can become a crucial factor in the decisions made during and prior to manufacturing. In an ideal world, designers and manufacturers will work together to interpret manufacturing and part data to assure the elimination of faults in manufacturing. However, manufacturing still lacks mathematically robust means of interpreting the manufacturing data so that a channel of communication can be established between design and manufacturing. To address part production concerns, we present a systematic methodology to interpret manufacturing data based on signals from manufacturing (e.g., tool vibrations, part surface deviations). These signals are assumed to contain a fingerprint of the manufacturing condition. The method presented in this paper is based on a mathematical transform to decompose the signals into their significant modes and monitor their changes over time. The methodology is meant to help designers and manufacturers make informed decisions about a machine and/or part condition. An example from a milling process is used to illustrate the method’s details.

Reliability Analysis of Repairable Systems Subject to System Modifications

This paper approaches environmentally conscious design by further developing a reliability model that facilitates design for reuse. Many reliability models are not suitable for describing systems that undergo repairs performed during remanufacture and maintenance because the models do not allow the possibility of system reconfiguration. In this paper, expressions of reliability indices of a model that allows system reconfiguration are developed to enable life-cycle cost estimation for repairable systems. These reliability indices of a population of repairable systems are proven theoretically to reach steady state. The expressions of these indices at steady state are obtained to gain insight into the model behavior, and to facilitate life-cycle cost estimation.

The Design for Assembly Guidelines Transform a Product Innovation From a Loser to a Winner

Several manufacturer’s are witnessing soaring profits as a result of cost reductions derived from Design for Manufacturing and Assembly (DFMA) analyses. These successes are prompting others to turn to more refined computer models of product assemblies. However, much can be gained from a very routine analysis, using nothing more than the basic Design for Assembly (DFA) guidelines. These gains can be realized at a mere fraction of the resources needed for the computer models. This method of analysis is especially appealing to engineers whose time constraints require careful selection of design activities. This paper argues that DFMA analysis does not need to be an elaborate modeling process to produce significant cost improvements. This point is illustrated with an example of a redesign of a cooking range door. A manual review of the DFA guidelines turned a design innovation from a loser into a winner. Success stories from such informal analyses should promote greater implementation across industries that are hesitant in adopting DFMA practices.

Finding the Shape of a Flexible Blade for Free-Form Layered Manufacturing of Plastic Foam Objects

The need for rapid, cost-effective and finish-less manufacturing of large sized, sculptured, physical models from various soft materials is increasing in several fields. For objects fabricated from plastic foams an advantageous approach is free-form, thick-layered manufacturing. Although it is technologically demanding, to achieve the best results (a) computer definition of the geometry has to be accurate, (b) the geometric model has to be directly sliced, (c) higher order approximation of the nominal shape is necessary, and (d) a quasi-free-form working out of the front surfaces of the layers is needed. The authors have developed the mathematical and/or technological fundamentals and process of free-form cutting based on heated flexible blades. The shape and the relative positions of the flexible blade are controlled continually as needed by the normal curvatures of the front faces of the layers. The paper elaborates on the computation methods for physically-based and geometrically-based modeling of flexible blades. The algorithms for approximating curve generation and curve matching are also presented. The paper extends to some of the most important aspects of the global thick-layered fabrication process.

A New Method for Modeling of Cutting Tools Associated With Rolling Axodes

Most of the existing methods for determining the profiles of cutting tools that work by wrapping are based on the envelope theory which requires cumbersome analytical formulations associated with the solution of equations not always easy to resolve. This work presents a new alternative method for studying conjugated surfaces associated with rolling axodes. The original meshing surfaces are replaced by a family of curves of substitution which gives a simpler interpretation of the envelope theory. The meshing line and the contact points can be easily determined. An equidistant to the tool profile can be simply calculated which can be very useful in the case of machining with cylindrical abrasive disks. Several examples are shown for rack, shaper and rotational cutters.