# **to appear in the proceedings of**

**Symposia on Design For Manufacturability**

**The 2000 International Mechanical Engineering Congress and
Exposition**

# **November 5 - 10, 2000 in Orlando, Florida**

# **Information Modeling of Conceptual Design**

# **Integrated with Process Planning**

**Shaw C. Feng and Eugene Y. Song**

Manufacturing Engineering Laboratory

National Institute of Standards and Technology

Gaithersburg, MD 20899

**ABSTRACT**

Information modeling is critical to the integration of conceptual design
and process planning. An information model for conceptual design is
provided in this paper. Conceptual design is a key activity in early
product development. It determines product functions, form, and the
basic structure. Major manufacturing cost is committed in early
conceptual design process. The model presented in this paper includes an
activity model for the conceptual design process and an object model for
classes used in conceptual design. The activity model sets the context
in which the objects are defined and used. The object model describes
the data and functions used in conceptual design and integration with
process planning. The main purpose of the model development is to
initiate standard interface specifications that are necessary for design
and process planning integration.

**Key Words:** Conceptual Design, Design and Planning Integration,
Information Modeling, Product Design, Systems Integration.

## 1 Introduction

Influence of design on manufacturing cost is usually great. Errors made
during the early stages of design tend to contribute as high as 70% to
the cost of production \[1\]. Experienced designers are usually able to
create successful initial designs because of their in-depth knowledge of
common design practices, customer expectations, and manufacturing
processes; however, less experienced designers often require input from
experienced designers in all of these areas. Ideally, a designer should
be able to access necessary manufacturing resource, design, customer
requirement, and cost information during the design of a product. Even
with the recent technological advances in software technologies for
design, manufacturing, engineering analysis, process planning, and
numerical control programming, making sound decisions in the early
design phase is still rather difficult since it involves an
understanding of many difficult to predict factors in manufacturability,
quality, reliability, and serviceability \[1, 2, 3\]. Of these factors,
the most substantial ones are the manufacturability of the design and
the cost of fabrication.

Considerable research has been performed on detailed design automation.
One problem with the current design and process planning software
systems is the lack of integration between Computer Aided Design (CAD)
data output and process planning input. For example, the primary focus
of ISO 10303-203, informally the STandard for Exchange of Product model
data (STEP) Application Protocol (AP) 203 \[4\], is the interoperability
between traditional CAD systems. While, the focus of STEP AP 224 \[5\]
(whose main emphasis is on machining features) has been on the input to
process planning systems. These two APs alone cannot meet the needs of
integrating conceptual design systems and conceptual process planning
systems. Furthermore, most academic research is focused on generating
manufacturing features from detailed geometry for unidirectional
communication. As stated in the subsection of Engineering Tools for
Design, Manufacturing, and Integration, a government report \[6\], the
most important infrastructure needs and research areas to enable the
necessary advances in design and manufacturing are alternate design
concepts, conceptual phase tools, and improved simulation and modeling
tools. In the conceptual phase tools, the need is on better models that
can allow rough prediction from indefinite design parameter values,
evaluation of processing alternatives, manufacturability, etc. Hence,
interoperability between the various design and process planning phases
is essential in the evolution of advanced manufacturing.

To achieve truly collaborative design and manufacturing, information
representations of both design and process information must support
multiple levels of abstraction for bi-directional (or multi-directional)
communication. For example, during the early conceptual design phase, it
is important to understand the trade-offs and implications of high-level
design decisions. Symbolic descriptions of designs, which are not yet
defined geometrically, can yield enough input to determine many
characteristics of the manufacturing process with underlying cost
estimates. Our work addresses the formal representation of such early
design descriptions, and their utility in providing input to conceptual
process planning and manufacturing applications. Our goal is to develop
interface specifications for integrating design and manufacturing
engineering.

This paper mainly provides an overview of various aspects

of the information model that has been developed. Section 2 describes
the current state of development of design and process planning
software. Section 3 provides an overview of the model. Section 4
describes generic activities in conceptual design, which are represented
in activity diagrams, and an object model, which is represented in class
diagrams. Section 5 summarizes our efforts and describes future
directions.

### 2 Current State in Design and Manufacturing Integration

CAD/CAM systems have been used in manufacturing industry for years.
These systems have continually evolved. Traditional CAD systems handle
wireframe geometry modeling, surface modeling, and solid modeling. CAD
systems have been recently augmented to provide part assembly modeling,
constraint representation \[7, 8\], and feature representation \[9\],
tolerance definitions and analysis, and virtual reality capabilities.
Researchers and vendors are still developing new capabilities for
improving these CAD systems. More advanced CAD systems are being
proposed and developed in academia. These advanced systems are largely
knowledge-based. Hence, they have automated product generation
capabilities and access to large-scale knowledge libraries \[10\]. In
parallel to CAD technology development, Computer Aided Manufacturing
(CAM) technology has evolved from handling prismatic parts
(two-and-a-half-axis or three-axis) to parts with free-form surfaces
(four- or five-axis machining). For concepual design, some
knowledge-based design systems are available \[12\], such as ICAD of
Concentra Corp. and AML of TechnoSoft \[25\]. There are still no open
interface specifications for integrating with process planning software.

Between design and machining, there are software tools -- Computer-Aided
Process Planning (CAPP) systems -- for machining planning based on part
design. CAPP systems are slowly evolving from traditional capabilities
(finding volumes to be machined, cutting parameters selection, tolerance
analysis and synthesis \[13\]) to modern capabilities (automated setup
planning, interactive feature finding, equipment/tools selection, tool
path generation, and machining simulation). CAPP serves the function of
bridging the gap between design and manufacturing.

Although all of these tools can be very useful, they still rely
primarily on geometric data. Moreover, they focus on detailed geometry.
Currently, many CAPP systems acquire their data via feature recognition
of a finished detailed geometric model from a CAD system. The CAPP
system must interpret all of the design intent from the solid geometric
model. Once the features have been found -- a challenging research area
-- process plans can be created. This mode of operation does not provide
any manufacturability feedback to designers. This can lead to
inefficient product development cycles. Hence, there is a need for tools
that provide feedback to the designer at every design stage.

In conceptual design, some commercial, rule-based design systems have
been developed that allow routine design tasks to be automated. A
designer can program knowledge into these systems to automatically
generate a design using various input parameters. Although these systems
can help a designer during The conceptual design stage (especially for
routine design), they do not address many aspects of conceptual design,
including functional decomposition and mapping from functions to the
designed product. The design process has to be coded into the systems.
Moreover, only geometry can be transferred into or out of the system.
Academic researchers have also been developing conceptual design tools
for many years. Several different synthesis systems have been
implemented \[14\]. One such system developed, CONGEN (CONcept
GENerator), is a domain-independent knowledge-based system framework
that maps an evolving symbolic description of a design into a geometric
one \[15\].

Process planning technology is also evolving as new analysis methods
emerge. Process planning research \[16\] has been focused primarily on
machining feature recognition, fixturing and setup parts, and NC tool
path generation at the detailed level of process planning. These process
planning technologies utilize detailed design data with detailed
geometry, topology, dimensions and tolerances, material, and surface
conditions completely specified. Only some of the research focuses on
process selection \[17, 18\]. Research and development of commercial
software for process selection and cost estimating at the conceptual
design stage is still in an infancy stage.

The Systems Integration for Manufacturing Applications (SIMA) program
\[19\] at NIST is addressing issues and developing solutions for
interoperability among manufacturing systems. It was initiated as part
of a Federal Initiative on High Performance Computing and Communications
\[20\]. The SIMA program is supporting manufacturing system integration
technologies; development and testing of interface specifications for
manufacturing systems; remote access to scientific and engineering data;
and research of collaborative manufacturing environments. As a result of
some projects in the SIMA Program, several information models have been
created for various manufacturing applications. A few examples of the
diverse work being conducted via the SIMA program are activity models
that describe functions and information flow among design, process
planning, manufacturing execution \[21\]. The Process Specification
Language \[22\], which is designed to capture operation sequences of
manufacturing processes as an interchange format, is also fund by the
SIMA program. The development of a conceptual design activity model and
an object model is within the scope of SIMA. An overview of the
development project can be found in \[23\], and initial prototype
development is described in \[24\].

## 3 Conceptual Design Information Modeling Fundamentals

The information sharing and exchange between design and process planning
applications (and other applications as well) occur at more than one
stage. Figure 1 illustrates many stages of communication that can exist
when establishing interoperability between conceptual design and
conceptual process planning.

Conceptual design is an activity in the early design stage in which the
concept of a product is formulated. The concept of a product includes
product requirements, functions, possible behaviors, form/structure
(layout), and associated properties.

Properties include material, assembly-level tolerance, critical surface
roughness and hardness parameters, and critical dimension. Functional
design generates a product's major functions and decomposes them into
detailed functions from requirements. Behavioral design maps detailed
functions into behavior models. Embodiment design specifies product form
and structure based on functions and behaviors. Detailed product
information is derived from the conceptual design.

![](media/image1.wmf){width="3.5in" height="3.1597222222222223in"}

Figure 1: Integration of conceptual design and process planning

The conceptual process planning is an activity of preliminary
manufacturability assessment and cost estimation on conceptual design.
More details are in \[25\]. Conceptual design information is used in the
detailed design process, geometry, topology, tolerance, and dimension
specification. Likewise, conceptual process planning information is used
in the detailed process planning activity, such as operation sequences,
process parameters, and setup specification. However, both detailed
design and process planning are out of the scope of this paper. The goal
of this information modeling is to model the information about
conceptual design so that conceptual process planning can be performed.
In order to set the context in which the information is used, an
activity model is developed. This model decomposes the main idea into
more detailed levels. Additionally, the model is a specialization of the
preliminary design activity described in the SIMA activity model \[18\].

The conceptual design activity (A1) is decomposed into five
subactivities. Figure 2 shows subactivities A11 to A15 and the data
flow. Activity A11 is to define product functions and constraints based
on the input, engineering requirements. This activity is called
functional design and can be further decomposed, as shown in Figure 3.
Activity A12 is to generate product behaviors based on product functions
and constraints, output from A11. This activity is to generate
behaviors. For those products that do not have behaviors, such as static
structural objects, this activity should be skipped. Activity A13 is to
decompose functions, constraints, and behaviors so that each part,
subassembly, and assembly of a product has its own functions,
constraints, and behaviors. With decomposed functions, constraints, and
behaviors, parts can be designed and the product can be configured by
these parts in A14.

![](media/image2.wmf){width="6.96875in"
height="2.5506944444444444in"}Figure 2 Functional Decomposition of
Conceptual Design

The output is the concept of a product, the product's conceptual design.
Finally, The conceptual design is evaluated by manufacturability in
Activity A15. The manufacturablity analysis takes input from both
conceptual process planning and conceptual design.

Activity A14 can be decomposed into two subactivities. Activity A141 is
to specify product structure based on function, The form and structure
of the product is conceptualized in this subactivity. Activity A142 is
to specify detailed information about an artifact. The detailed
information is necessary for process planning, such as manufacturing
process selection, resource selection, and cost estimating.

The activity model describes functions and their input and

![](media/image3.wmf)

Figure 3 Specify Product Configuration

![](media/image4.wmf){width="5.841666666666667in" height="7.3in"}

Figure 4 Class diagram for Artifact

output data in conceptual design, based on the concept of integrated
design and process planning. We will collaborate with industry to make
sure that the model does reflect real world cases and situations. The
activity model provides a context in which the object model is
developed.

## 4 Object Modeling for Conceptual Design

The object model contains many aspects in conceptual design, described
in the activity model. In this section, the modeling of artifact, its
function, and the assembly relationships are described. The classes
pertaining to product requirements are omitted from this section because
conceptual design starts from functional design. The model is
represented in the class diagrams in the format of Unified Modeling
Language (UML) \[26\]. Some classes related to information on product
are derived from a core product representation model, currently being
developed at NIST. The concept of the following clasese are adopted from
the core: Artifact, Function, and Constraint. The following classes are
derived from the core: Behavior, Material, Requirement, and Constraint.
The rest of the classes are specific to the conceptual design integrated
with conceptual process planning. The intended uses of this model are as
follows: (1) to be a reference architecture for the next-generation
conceptual design, (2) to serve as a basis for developing standard
interfaces, and (3) to be used as database schema. The whole model is
described as follows.

Artifact is a general term for referring to an individual component in a
product hierarchical structure, such as a part, subassembly, assembly,
or the product. Specific information includes material parameters,
tolerances, dimensions, surface roughness parameters, surface hardness
parameters, and texture parameters.

Figure 4 shows the class diagram of Artifact. The Artifact class has a
recursive definition. Artifacts are in a hierarchical structure, which
can capture the product structure, in a hierarchical structure. Artifact
has the following associated classes. Constraint relates to those
factors that prohibit product to function, such as physical limitations,
environmental concerns, and safety regulations. Behavior captures the
motion of a product. The motion is calculated or simulated in the method
generateBehaviorModel() in the class. Function captures product
functions, translated from engineering requirements. Form has the
conceptual/sketched shape of the

product and its components.

![](media/image5.wmf){width="7.2in" height="5.05625in"}

Figure 5 Class diagram for Tolerance

![](media/image6.wmf){width="3.55in" height="3.092361111111111in"}Form
consists of Material, Feature, Tolerance, SurfaceCondition, and
Rationale. Material represents the information of material properties
relating to the realization of product shape. Feature is a portion of
the form and is also in recursive definition. A feature can consist of
many subfeatures, which are in a hierarchical structure. For example, a
screw hole consists of a countersink feature and a hole feature, and the
hole feature consists of a cylindrical feature (hole) and a thread
feature. The class can also represent composite features, composed
features from different artifacts. Tolerance defines the limits within
which a feature can vary. Tolerance includes form tolerance, location
tolerance, profile tolerance, and runout tolerance.

Figure 5 illustrates classes that relate to tolerance. SurfaceCondition
specifies the hardness, roughness, and texture requirements on a feature
of a form. Rationale captures the reasons that tolerance is defined,
material is selected, and form and feature are design. Additionally,
Artifact has two derived classes: ArtifactToBeMade and
ArtifactToBeBought. Some components (artifacts) can be purchased from
supplies. Others have to be made by the company in which the product is
designed.

![](media/image7.wmf){width="3.7083333333333335in"
height="5.010416666666667in"}

Figure 6 Class diagram for Function

TransferFunction, as in the Function model in Figure 6, is a derived
class from Function. It captures those functions that have input and
output of information, material, and/or energy. Input has a type of
input, quantity, and the source. Similarly, Output has a type, quantity,
and the destination. The functions of manufactured parts do vary and
have to be constrained by AllowableVariation, which sets the limits for
which a function of an artifact can vary. The allowable functional
variation can be converted into tolerances on certain feature parameters
using, for instance, Taguchi methods \[27\].

Figure 7 Class diagram for Joining

The artifact joining, also referred to as assembly model, describes how
two artifact are assembled as shown in Figure 7. ArtifactJoint describes
the joining relationship of two artifacts. The class has recursive
definition. This generates an assembly hierarchy, the lower the pair in
the hierarchy the earlier they should be joined with each other. Thus,
the hierarchy indicates the assembly sequence. Each pair of joined
artifacts is connected with each other in some portions or features of
the artifacts. FeatureJoint captures assembly relationship of two
features and the type of joint: rigid and kinematic. This class is also
in a recursive structure to describe the joining relationships of
features of a feature. Like in ArtifactJoint, the feature assembly
sequence is captured in the hierarchical structure.

The model has been manually populated using a gearbox example. The
gearbox consists of a sun gear, three planetary gears, a ring gear, an
input shaft, an output shaft, two pieces of housing, two bearings, and
two seals. Functions, forms, product structure, tolerances, and the
assembly relationships of the gearbox conceptual design were able to be
represented using the model \[24, 25\]. Certainly, more tests of the
model using a variety of examples that will thoroughly test the model
are definitely necessary and will be conducted in the near future.

## 

## 5 Concluding Remarks

The conceptual design is a product design activity to define product
functions, behaviors, form, materials, and necessary tolerances.
Incorporating manufacturing analysis into design can ensure that the
design is manufacturable and within cost limits. Manufacturablity
analysis and cost estimation are important to minimize production cost.
However, there currently lack integrated tools for designers to evaluate
conceptual design. Manufacturers need new software tools that will
effectively support translating production requirements to functions and
functional decomposition, translating functions to behaviors,
translating functions and behaviors to production forms, selecting
manufacturing processes, selecting manufacturing resources, and
estimating manufacturing time and cost. To develop these new tools
information models are necessary to support the tool development and the
integration of the tools.

This paper has described a conceptual design activity model and an
object model that have been developed to serve the purpose of
integration. The design information that is necessary for conceptual
process planning has been collected and modeled using Unified Modeling
Languadge(UML) \[24\]. The models are still in draft form. They are
expected to be further enhanced by modification, expansion, and
extension in the future.

Future work includes the following tasks: (1) validate the draft models
using more industrial cases, (2) formally represent manufacturing
process knowledge, and (3) develop initial prototype system of
integrated conceptual design and conceptual process planning to further
test the object model.

Industrial collaborations are critical to the success of the project.
During the next year, we plan to obtain a state-of-the-art
knowledge-based system that will be incorporated into our prototype
system and collect industrial parts as the test cases. Using the
information models and the test cases, we will implement a more advanced
design and manufacturing planning information exchange mechanism. This
work should give us the background necessary to specify, with the help
of software vendors, the interface requirements for next-generation
integrated CAD and CAPP systems.

**DISCLAIMER:**

No approval or endorsement of any commercial products by the National
Institute of Standards and Technology is intended or implied. Certain
commercial software systems are identified in this report in order to
facilitate understanding. Such identification does not imply
recommendation or endorsement by the National Institute of Standards and
Technology, nor does it imply that the software systems identified are
necessarily the best available for the purpose.

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