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Journal of Materials Processing Technology 177 (2006) 331335

A knowledge-based engineering design tool for metal forging

J. Kulon a, D.J. Mynors b,, P. Broomhead b

a School of Electronics, University of Glamorgan, Pontypridd, CF37 1DL, United Kingdomb School of Engineering and Design, Brunel University, Uxbridge, Middlesex, UB8 3PH, United Kingdom

Abstract

This paper describes a knowledge-based design tool enabling the generation of hot forging die designs from a component profile. The system

integrates the hot forging die design process into a single framework and guides the user through the design process enabling the generation of

forgeable geometry from a component profile taking into account machine, material and forging company specific data, and design considerations.

The product model manages all the routine engineering tasks. The role of the engineer who interacts with the model is to provide the input

specifications such as component geometry, material, and production machine. 2006 Elsevier B.V. All rights reserved.

Keywords: Forging; Knowledge based system; Die design

1. Introduction

This paper outlines the development of a forging design

system with knowledge based engineering (KBE) at the core.

Currently most of the activities and costs related to planning a

forging process route are heavily dependant on human exper-

tise, creativity, and intuition. There is a need to develop sys-tems that complement traditional design methods and link with

CAD/CAM and simulation packages by adding the engineer-

ing knowledge that drives the product design process. However,

the numerous variables required to analyse forging processes

make the capture and the encapsulation of the decision-making

and process planning rules very difficult. Several researchers

have responded to this challenge through the development of

computer-aided tools for forging part and process design, [16].

The system presented in this paper takes a different approach

to most forging design systems. It integrates the design process

into a single computer KBE model. A designer uses the sys-

tem via a web browser and interacts with a server. The KBE

core of the system guides the design engineer through different

stages of the hot forging die design process. Thus, the system

enables the generation of forgeable geometry from component

geometry.

Corresponding author. Tel.: +44 1895 265789; fax: +44 1895 269763.

E-mail address: [email protected](D.J. Mynors).

2. KBE hot forging software

The core of the KBE implementation is the GDL (general-

purpose declarative language) developed by Genworks Interna-

tional. TheGDL follows a non-procedural paradigm for applica-

tion development and execution, with multiple threads of execu-

tion and the ability to load new code and redefine objects dynam-ically. The GDL is based on a full object-oriented language

model,a superset of ANSI CommonLisp.The server side frame-

work is implemented using GWL (generative web language) as

an integrated web server-based user interface that manages data

and controls other software tools on the server. The main appli-

cationtaskscarried outon theserver are: accessingthe databanks

of rules, design features and materials, facilitating files transfer

and performing the KBE computations. The GDL/GWL

integrates the application logic and databanks through a direct

MySQL interface and handles geometry, through its library of

three-dimensional geometric objects. The integrated NURBS

surfaces and solids modelling kernel is based on the SMLib

product from Solid Modeling Solutions Inc. The combination of

GDL and SMLib adds powerful surface and solids capabilities

to GDLs built-in 3D wireframe facilities. SMLib provides

extensible filleting, as well as full support for non-manifold

topology (e.g. edges sharing more than two faces) for boundary-

representation solids. It is able to export and import component

surfaces directly embedded in IGES format. The client and

server side arrangements linking the databanks and enabling the

inclusion and extraction of data are discussed in more detail in

[7].

0924-0136/$ see front matter 2006 Elsevier B.V. All rights reserved.

doi:10.1016/j.jmatprotec.2006.04.062
mailto:[email protected]://localhost/var/www/apps/conversion/tmp/scratch_4/dx.doi.org/10.1016/j.jmatprotec.2006.04.062http://localhost/var/www/apps/conversion/tmp/scratch_4/dx.doi.org/10.1016/j.jmatprotec.2006.04.062mailto:[email protected]


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332 J. Kulon et al. / Journal of Materials Processing Technology 177 (2006) 331335

In the KBE system forging company specific databanks of

material properties, standards, production unit specifications,

design rules are all integrated into the product model through

a relational database. The KBE hot forging software consists of

the following knowledge domains:

(i) A Designer Data and Production Requirements modulethat allows designers to specify the various production

requirements in terms of production rate, volume and time

to market. These are significant factors in determining the

manufacturing costs. For instance large production vol-

umes require high production rates. On the other hand,

smallproductionvolumes usually mean larger direct labour

involvement.

(ii) A Material Properties Databankmodule that contains the

integrated knowledge base of materials and their proper-

ties. The use of two databank clients allows companies not

using the design system to still access material properties.

In addition, the web-enabled system allows the population

of the databank with material properties captured directly

from testing machines.

(iii) A Manufacturer and Production Units Selection module,

which includes a library of forging machines and their

technical specifications. In general, forged components

are shaped using one of three types of production units:

hydraulic, mechanical and screw presses and hammers.

With many factors to consider in the selection of the appro-

priate productions unit such as size, geometry, complexity,

quantity, material, component cost and component toler-

ances the designer can choose the production unit from the

list created on the basis of the manufacturer recommenda-

tion for their particular application.(iv) ADesign Rules module encapsulates the design knowledge

of various geometrical features such undercuts, ribs, fillets,

corners, bosses, draft angles, etc. and associated design

rules, constrains and machining guidance notes. The KBE

software not only makes the appropriate recommenda-

tions based on the material, production unit and production

requirements specifications but also allows to capture the

individual manufacturers preferences and capabilities.

(v) A Component Geometry module automates the generation

of the forgeable geometry from the final component geom-

etry. The following section provides more detail about the

geometry transformations, feature extraction and the soft-ware implantation.

3. From component to forgeable geometry

Forgeable geometry differs from the final component geom-

etry. The differences relate to the capabilities of the forger

(manufacturer), the type of production unit (mechanical press,

screw press, hammer, etc.), the component material, machining

allowances, etc. Fig. 1 illustrates a component geometry trans-

formed into a forgeable geometry for manufacture on a vertical

action only production unit. The transformation of the geometry

through the KBE software proceeds as follows:

The component 3D geometry is imported from a CAD

file. The GDL Base Geometry and NURBS Surface class

hierarchy is shown in Fig. 2, where grey boxes represent

user-defined classes and white boxes represent GDL Base

Geometry and NURBS Surface in-build classes. The parent-

child dependency follows and links each of the geometry

transformations undertaken. This dependency combined with

demand-drivenevaluation enables complete updates to be per-

formedif thedesignerchooses to changeany of theparameters

such as production unit, allowances, etc. The inputs class,

as shown in Fig. 2, is derived from the GDL Nurbs iges-

reader in-build class. When the iges-reader object is instan-

tiated using a given file-name the object has as its children

a sequence of curves and a sequence of trimmed-surfaces.

These geometrical entities answer all the messages of the

GDL Curve and Surface objects.

As the system user has already specified that the component

geometry is axisymmetric, the next geometry transformation

is to obtain the half axisymmetric component profile from the

surfaces. The surfaces are cut to establish the component pro-file. The half axisymmetric component cross section is shown

in (1) ofFig. 1. This is achieved using GDL NURBS Surface

objectplanar-section-curves, whichproducesmultiple curves

by sectioning a surface with a plane. Then, a profile object

is created as a new entity to store the half cross section of

the component. As an example the syntax for the full-curves

object embedded in the profile object is shown below. The

full-curves object encapsulates all the curves resulting from

the sectioning of the component geometry with a plane.

(define-object profile (base-object)

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...

:hidden-objects((full-curves :type planar-section-curves

:sequence(:size(the inputs trimmed-surfaces

number-of-elements))

:surface(the inputs (trimmed-surfaces (the-child index)))

:plane-normal (the sectioning-plane-normal-vector))

:plane-point (the center)))

In the example, the input slot surfaces denotes the services

to be sectioned with a plane, the sequence stands for the num-

ber of individual surfaces, the plane-normal vector denotes

the normal of the sectioning plane and the plane-point is a

point on the sectioning plane.

The half cross section is then interrogated to identify allinstances of undercuts as defined for the motion of the speci-

fied production unit and die orientation. The curves identified

as creating the undercut are removed. Extending the remain-

ing curves creates two new curves and reconnects the profile

as shown in (2) ofFig. 1. The undercut recognition algorithm

has been implemented based on the work of Ravi et al [8].

The stages that follow are the same as would be implemented

by a die designer. The machining and forging allowances are

added as illustrated in (34) ofFig. 1. The values of the offsets

are suggested to the designer and are based on the manu-

facturers capabilities or British Standard (BS) 4114:1967.

The user can accept the tolerances from BS recommended


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J. Kulon et al. / Journal of Materials Processing Technology 177 (2006) 331335 333

Fig. 1. Geometry transformations, (0) component geometry, (1) AA cross section (2) undercut, (3) machining allowance, (4) forging allowance, (5) narrow features,

(6) draft angles, (7) fillet and corner radii, (8) ribs and (9) forgeable geometry.


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334 J. Kulon et al. / Journal of Materials Processing Technology 177 (2006) 331335

Fig. 2. GDL base geometry and NURBS surface class hierarchy.

by the KBE system, or enter the designers own values. The

user also has the option of specifying different offset values

for horizontal and vertical curves. The system then suggests

appropriate internal and external draft angles. Fillet radii are

added using the global-filleted-polyline-curves object. The

syntax used to produce a list of linear-curves and arc-curves,

which represents the straight sections, and fillets of a global-

filleted-polyline is shown below:

((filleted-profile: type global-filleted-polyline-curves

:default-radius (the fillet-radius)

:vertex-list (mapcar #(lambda(curve)(the-object curve start))

(cons (the input-profile trimmed-curves last)

(list-elements (the input-profile

trimmed-curves)))))

In the above example, the input slots the default-radius and

the vertex-listdenotes respectively the fillet and corner radii

and the list of vertexes of the polyline.

Finally, after interrogating the geometry and applying appro-

priate rules the rib widths are extended, holes and the narrow

features filled, the forgeable profile is created. The forgeable

geometry cross section is shown in (8) ofFig. 1.

The final forgeable geometry forms the base geometry for

the final forging die set. In addition, it is possible to assess

scrap component material and hence relative process costs. As

rules have been applied and the forgers capabilities taken into

account, designers can have a high degree of confidence in thedesign before passing the geometries for further analysis using,

for example metalforming simulation. In all cases, the system

user can override any of the suggested values. All the values are

stored in the supporting databanks. Thevalues used in the design

along with all the design information for a specific forging are

stored in the databank along with the forging part number and

all other associated data including the designers details.

4. Conclusions

This paper outlines the development of a design system for

hot forging die design. The system uses state-of-the-art KBE


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J. Kulon et al. / Journal of Materials Processing Technology 177 (2006) 331335 335

and Internet technologies, and leads the user through the design

process. The key feature of the KBE application is that it inte-

grates the whole design process within one computer model.

The relational database encapsulates the design rules as well as

their complex interdependencies on material, production unit,

and manufacturer capabilities. The system takes a different

approach to most forging design systems. A designer uses the

system via a web browser, the local client, and interacts with a

server. All elements of the system can reside within a company

or the server can reside within an organisation and be accessed

by user companies. The system requires the designer to login to

the system. Once logged in the designer has access to a range

of forging companies. All designers have access to the company

known as Brunel University, this virtual company owns every

known type of production unit and is populated with standard

information, tolerances, etc. In addition, the designer has access,

as agreed by the forging company that will produce the forgings,

to the productionunit inventory and associated data.This ensures

that a companys competitive advantage is not compromised.

Acknowledgements

The authors acknowledge the Confederation of British Met-

alforming, W H Tildesley, Clevedon Fasteners, Mills Forgings,

CorusAutomotive,Genworks Int., George Dyke, the UKs Engi-

neering and Physical Sciences Research Council: GR/N21611

and the Department of Trade and Industry.

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[5] M. Bakhshi-Jooybari, I. Pillinger, T.A. Dean, Development of an intel-

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