151 research outputs found
Integrated inpection of sculptured surface products using machine vision and a coordinate measuring machine
In modem manufacturing technology with increasing automation of manufacturing processes
and operations, the need for automated measurement has become much more apparent.
Computer measuring machines are one of the essential instruments for quality control and
measurement of complex products, performing measurements that were previously laborious
and time consuming. Inspection of sculptured surfaces can be time consuming since, for exact
specification, an almost infinite number of points would be required. Automated measurement
with a significant reduction of inspected points can be attempted if prior knowledge of the part
shape is available. The use of a vision system can help to identify product shape and features but,
unfortunately, the accuracy required is often insufficient. In this work a vision system used with
a Coordinate Measuring Machine (CMM), incorporating probing, has enabled fast and accurate
measurements to be obtained. The part features have been enhanced by surface marking and a
simple 2-D vision system has been utilised to identify part features. In order to accurately identify
all parts of the product using the 2-D vision system, a multiple image superposition method
has been developed which enables 100 per cent identification of surface features. A method has
been developed to generate approximate 3-D surface position from prior knowledge of the product
shape.
A probing strategy has been developed which selects correct probe angle for optimum accuracy
and access, together with methods and software for automated CMM code generation. This has
enabled accurate measurement of product features with considerable reductions in inspection
time.
Several strategies for the determination and assessment of feature position errors have been investigated
and a method using a 3-D least squares assessment has been found to be satisfactory.
A graphical representation of the product model and errors has been developed using a 3-D solid
modelling CAD system. The work has used golf balls and tooling as the product example
A feature-based approach to the Computer-Aided Design of sculptured products
Computer-Aided Design systems offer considerable potential for improving
design process efficiency. To reduce the 'ease of use' barrier hindering full
realisation of this potential amongst general mechanical engineering
industries, many commercial systems are adopting a Feature-Based Design
(FBD) metaphor. Typically the user is allowed to define and manipulate the
design model using interface elements that introduce and control parametric
geometry clusters, with engineering meaning, representing specific product
features (such as threaded holes, slots, pockets and bosses).
Sculptured products, such as golf club heads, shoe lasts, crockery and sanitary
ware, are poorly supported by current FBD systems and previous research,
because their complex shapes cannot be accurately defined using the
geometrically primitive feature sets implemented. Where sculptured surface
regions are allowed for, the system interface, data model and functionality are
little different from that already provided in many commercial surface
modelling systems, and so offer very little improvement in ease of use,
quality or efficiency.
This thesis presents research to propose and develop an FBD methodology and
system suitable for sculptured products. [Continues.
Topological model for machining of parts with complex shapes
Complex shapes are widely used to design products in several industries such
as aeronautics, automotive and domestic appliances. Several variations of their
curvatures and orientations generate difficulties during their manufacturing or
the machining of dies used in moulding, injection and forging. Analysis of
several parts highlights two levels of difficulties between three types of
shapes: prismatic parts with simple geometrical shapes, aeronautic structure
parts composed of several shallow pockets and forging dies composed of several
deep cavities which often contain protrusions. This paper mainly concerns High
Speed Machining (HSM) of these dies which represent the highest complexity
level because of the shapes' geometry and their topology. Five axes HSM is
generally required for such complex shaped parts but 3 axes machining can be
sufficient for dies. Evolutions in HSM CAM software and machine tools lead to
an important increase in time for machining preparation. Analysis stages of the
CAD model particularly induce this time increase which is required for a wise
choice of cutting tools and machining strategies. Assistance modules for
prismatic parts machining features identification in CAD models are widely
implemented in CAM software. In spite of the last CAM evolutions, these kinds
of CAM modules are undeveloped for aeronautical structure parts and forging
dies. Development of new CAM modules for the extraction of relevant machining
areas as well as the definition of the topological relations between these
areas must make it possible for the machining assistant to reduce the machining
preparation time. In this paper, a model developed for the description of
complex shape parts topology is presented. It is based on machining areas
extracted for the construction of geometrical features starting from CAD models
of the parts. As topology is described in order to assist machining assistant
during machining process generation, the difficulties associated with tasks he
carried out are analyzed at first. The topological model presented after is
based on the basic geometrical features extracted. Topological relations which
represent the framework of the model are defined between the basic geometrical
features which are gathered afterwards in macro-features. Approach used for the
identification of these macro-features is also presented in this paper.
Detailed application on the construction of the topological model of forging
dies is presented in the last part of the paper
Process capability modelling: a review report of feature representation methodologies
Approximately 150 technical papers on the features methodology have been carefully studied and some selected
papers have been commented upon. The abstracts of the comments are documented and attached to this report. The
methodologies reviewed are mainly divided into two approaches, ie. feature recognition and design by features.
Papers which deal with some specific topics such as feature taxonomies, dimensions and tolerances, feature
concepts, etc. are also included in the document
Feature-based representation for assembly modelling
The need for a product model which can support the modelling requirements of a broad
range of applications leads to the application of a feature-based model. An important
requirement in feature-based design and manufacture is that a single feature
representation should be capable of supporting a number of different applications. The
capability of representing products composed of assemblies is seen to be necessary to
serve the information needs of those applications. To achieve this aim it is an essential
prerequisite to develop a formal structure for the representation of assembly information
in a feature-based design system. This research addresses two basic questions related to
the lack of a unified definition for features and the problem of representing assemblies
in a feature-based representation. The intention is to extend the concept of designing
with features by incorporating assembly information in addition to the geometrical and
topological details of component parts. This allows models to be assembled using the
assembly information within the feature definitions.
Features in this research are defined as machined volumes which are represented in a
hierarchical taxonomy. The taxonomy includes several types and profiles of features
which cover a general range of machined parts. A hierarchical assembly structure is also
defined in which features form basic entities in the assembly. Each feature includes
information needed to establish assembly relationships among features in the form of
mating relationships. An analysis of typical assemblies shows that assembly interfaces
occur at the face level of the mating features and between features themselves. Three
mating relationships between pairs of features have been defined (against, fits and align)
and are represented in the form of expressions that can be used for evaluations. Various
sub-types of these major mating relationships can be identified (e.g. tight fit, clearance fit, etc.) and represented through the use of qualifying attributes. Component Relation
Graphs, Feature Relation Graphs and Face Mating Graphs have been developed to
represent each level of interaction in an assembly, and assembly relationships are
combined with knowledge on process planning into a Component Connectivity Graph. These graphs are used as the basis for deriving an integrated data structure which is used
for defining classes for each level in the assembly hierarchy.
The implementation of a prototype system has been facilitated by use of an
object-oriented programming technique which provides a natural method of adding
functionality to the geometric reasoning process of features and the complex
relationships between the parts that make up the assembly. The feature-based model is
embedded in an object-oriented solid modeller kernel, ACIS®.
The research demonstrates the possibilities for a single feature representation to support
multiple activities within a computer integrated manufacturing environment. Such a
representation can form the basis of design improvement techniques and manufacturing
planning as well as be a model to support the life cycle of the product
PDC Drill Bit Design Improvement using Reverse Engineering Method to Analyze Effect on Rate of Penetration
In the petroleum industry, drilling is one of the most important aspects due to the
economics. Reduction in drilling time is required to minimize the cost of operations.
This study focuses on the Polycrystalline Diamond Compact (PDC) drill bit which is
categorized as fixed cutter of drilling bit. Problem such as wear and tear of PDC cutter
is one of the main factor in drilling process failure and this would affect the rate of
penetration. Thus, an intensive study in drill bit design would save a lot of money if
the efficiency of drill bit can be improved. The objective of this project is to improve
the design of PDC cutter and study the effect of design improvement to the rate of
penetration. Reverse engineering (RE) method will be used to study the design and
analyse the effect of the design to performance of the drill bit. Due to unavailable drill
bit blueprint from the manufacturer due to propriety and confidential, RE non-contact
data acquisition device, 3D laser scanner will be used to obtain cloud data of worn drill
bit. Computer Aided Design (CAD) software is used to convert cloud data of the PDC
drill bit into 3D CAD model. Optimization of PDC Drill bit is focused on feature
design such as back rake angle, side rake angle and number of cutters. CAE software
is used to analyse the effect of the design feature modification to rate of penetration.
The results show rate of penetration increase as the angle of both rake angle and
number of cutter decrease
Feature-based validation reasoning for intent-driven engineering design
Feature based modelling represents the future of CAD systems. However,
operations such as modelling and editing can corrupt the validity of a feature-based
model representation. Feature interactions are a consequence of feature
operations and the existence of a number of features in the same model. Feature
interaction affects not only the solid representation of the part, but also the
functional intentions embedded within features. A technique is thus required to
assess the integrity of a feature-based model from various perspectives,
including the functional intentional one, and this technique must take into
account the problems brought about by feature interactions and operations. The
understanding, reasoning and resolution of invalid feature-based models
requires an understanding of the feature interaction phenomena, as well as the
characterisation of these functional intentions. A system capable of such
assessment is called a feature-based representation validation system.
This research studies feature interaction phenomena and feature-based
designer's intents as a medium to achieve a feature-based representation
validation system. [Continues.
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