bending die design
TRANSCRIPT
INDEX
Title Page No
Index 1
Abstract 2
1. Introduction
1.1 Sheet Metal Forming 3
1.2 Deformation Process 4
1.3 Cutting Process 6
2. Bending Die 9
2.1 Introduction
2.2 Classification of Die Components
2.3 Die Components 10
2.4 Types of Bending Die 16
2.5 Expert System 20
2.6 Problems in Traditional Process of Die Design 28
3. Expert System Development Procedure, Methodologies, and its Applications 29
4. Literature Review 21
5. Conclusion 27
References
Abstract
1
In sheet metal forming different types of manufacturing processes are used. Bending is
one of most commonly used manufacturing process in metal forming industries. Traditional
methods of bending die design require expertise and are largely manual and tedious. Die
designer requires a high level of knowledge that can only be achieved through years of
practical experience Development of die, design and selection of components and accessories,
selection of die material and die modelling are major activities involve in die design. Hence
the design of bending die is a complex, experience based and time consuming task. So it’s a
major loss for small scale industries and further more existing software’s presently used for
die design helpful for drawing assistance and simple calculations. Therefore an intelligent
system is required for bending die design. Development of such system can prove a landmark
to ease the complexities involved in the activities of bending die design.
A bending die consist of different components like die block, punch, stripper plate,
shank, punch holder plate, bolster plate, back plate, die set and fasteners. And
selection/design of these components is a vital role. Hence objective of this research work is
to develop a knowledge based system for selection of major bending die components. The
proposed system uses production rule based approach of artificial intelligence consisting of
different modules. Development of such system has different steps to follow like knowledge
acquisition, framing of production rules, verification of rules, and selection of knowledge
representation language, identification of hardware, development of knowledge base and
construction of user interface. Here production rules are coded in the Auto LISP language
and user interface is created in visual basic 6 on AutoCAD platform. This arrangement
facilitates interfacing of design process with modelling and can be operated on a PC/AT.
As this system can be operated on AutoCAD software it is a less costly and more
effective in small and medium scale enterprises. The proposed System is enough flexible
hence it can be improved, modified or edited at any of the stage in future.
Chapter 1 Introduction
2
Sheet Metal Forming
Sheet metals are widely used for industrial and consumer parts because of its capacity for
being bent and formed into intricate shapes. Sheet metal parts comprise a large fraction of
automotive, agricultural machinery, and aircraft components as well as consumer appliances.
Successful sheet metal forming operation depends on the selection of a material with
adequate formability, appropriate tooling and design of part, the surface condition of the
sheet material, proper lubricants, and the process conditions such as the speed of the forming
operation, forces to be applied, etc. A numbers of sheet metal forming processes such as
shearing, bending, stretch forming, deep drawing, stretch drawing, press forming,
hydroforming etc. Each process is used for specific purpose and the requisite shape of the
final product [1, 2].
1.1 Sheet forming operations
The sheet metal forming processes can be classified broadly into two areas:
1) Deformation Processes and 2) Cutting processes
The Deformation processes involves partial or complete plastic deformation of the work
material Bending, Twisting, Curling, Deep Drawing, Spinning, Stretch Forming, Necking,
Bulging, Flanging etc. are major deformation Processes.
The cutting process incorporate cutting materials by subjecting it to shear stresses usually
between punch and die may be of any shape, or between the blades of shear. Shearing,
Blanking, Punching, Parting, Lancing, Shaving etc. are major cutting processes [3].
Production of sheet metal components may require a combination of above categorized
forming processes. A brief introduction of major sheet metal forming processes is given
below.
1.2 Deformation process
1.2.1 Shearing
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Irrespective of the size of the part to be produced, the first step involves cutting the sheet into
appropriate shape by the process called shearing. Shearing is a generic term which includes
stamping, blanking, punching etc. Figure 1.1 shows a schematic diagram of shearing. When a
long strip is cut into narrower widths between rotary blades, it is called slitting. Blanking is
the process where a contoured part is cut between a punch and die in a press. The same
process is also used to remove the unwanted part of a sheet, but then the process is referred to
punching.
Figure 1.1 Shearing [4]
1.2.2 Stretch Forming
It is a method of producing contours in sheet metal. In a pure stretch forming process, the
sheet is completely clamped on its circumference and the shape is developed entirely at the
expense of the sheet thickness. Figure 1.2 presents a schematic set-up of stretch forming
process. The die design for stretch forming is very crucial to avoid defects such as excessive
thinning and tearing of the formed part. The stretch forming process is extensively used for
producing complex contours in aircraft and automotive parts [4].
Figure 1.2.2 Stretch forming processes [4]
1.2.3 Deep Drawing
Deep drawing is a sheet metal forming process in which a sheet metal blank is radially drawn
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into a forming die by the mechanical action of a punch. It is thus a shape transformation
process with material retention. The process is considered "deep" drawing when the depth of
the drawn part exceeds its diameter. This can be achieved by redrawing the part through a
series of dies [2, 3].
The metal flow during deep drawing is extensive and hence, requires careful administration
to avoid tearing or fracture and wrinkle. Following are a few key issues affecting metal flow
during deep drawing process and each of them should be considered when designing or
troubleshooting sheet metal deep drawing stamping tools.
1.2.4 Bending
Bending is defined as straining of metal around straight axis, during this process the metal on
the inside of the neutral axis is compressed, while the metal on the outside of the neutral axis
is stretched [2].
Figure 1.3 simple bending [1].
Bending is done using Press Brakes. Press Brakes can normally have a capacity of 20 to 200
tons to accommodate stock from 1m to 4.5m (3 feet to 15 feet). Larger and smaller presses
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are used for diverse specialized applications. Programmable back gages, and multiple die sets
currently available can make bending a very economical process [1].
1.3 Cutting Processes
1.3.1 Blanking
It is a simple cutting operation as shown in figure 1.3.1. The material used is called the stock
and is generally a ferrous or nonferrous strip. During the working stroke the punch goes
through the material, and on the return stroke the material is lifted with the punch and is
removed by the stripper plate. Stop pin is used here as gage for operator. Here in blanking the
part that is removed from the strip is always the work-piece (blank) in a blanking operation.
Subsequent press-working operations may be performed on the blank [3].
Figure 1.3.1 Blanking & Piercing die []
1.3.2 Piercing
This operation consists of simple hole punching. It differs from blanking in that the punching
(or material cut from stock) is the scrap and the strip is the work piece. Piercing is nearly
always accompanied by a blanking operation before, after, or at the same time. Figure 1.3.1
shows the typical blanked and pierced work piece [1].
1.3.3 Lancing
This is a combine bending and cutting operation along a line in the work material. No metal
is cut free during a lancing operation. The punch is designed to cut on two or three sides and
bend along the fourth side [3].
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Figure 1.3.2 cutting & parting operation [Suchy, 2006]
1.3.4 Cutting off and parting
A cut-off operation separates the work material along a straight line cut. When the operation
separates the work material along a straight line cut in a double line cut, it is known as
parting. Cutting off and parting operations are used to separate the work piece from the scrap
strip. Cutting off and parting usually occurs in the final stages of progressive die [3]. Figure
1.3.2 shows a cutting off operation.
1.3.5 Notching
This operation removes metal from either or both edges of the strip. Notching serves to shape
the outer contour of the work piece in a progressive die or remove excess metal before a
drawing or forming operation in a progressive die. The removal of excess metal allows the
metal to flow or form without interference from excess metal on the sides [3]. Figure 1.3.3
shows a notching operation.
Figure 1.3.3. Notching [3]
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1.3.6 Shaving
Shaving is a secondary operation, usually following punching, in which the surface of the
previously cut edge is finished smoothly to accurate dimensions. The excess metal is
removed much as a chip is formed with a metal cutting tool. There is very little clearance
(close to zero) between the punch and die, and only thin section of edge is removed from the
edge of the work piece [3, 4]. Below figure shows the shaving operation.
Figure 1.3.4 (a) Shaving (b) Perforating
1.3.7 Perforating
This is a process by which multiple holes which are very small and close together is cut in
flat work material [3].
1.3.8 Trimming
This operation removes the distorted excess metal from drawn shapes and also provides a
smooth edge [3].
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Chapter 2 Bending Die
2.1 What is bending die?
A bending die is a specialized tool used in manufacturing industries to shape material using a
press. Products made with bending dies range from simple paper clips to complex pieces used
in advanced technology. It is an assembly of number of components, according to the shape
of the part to be produce die type is selected. Figure 2.1 shows the simple bending die and its
components [1].
Figure 2.1 Simple Bending Die [1]
2.2 Classification of die components -
According to the function of the die, all components may be classified into two groups:
a) The technological components directly participate in forming the work piece, and they
have direct contact with a material; examples are the punches, die block, guide rails, form
block, drawing die, stripper, blank holder, etc.
b) The structural components' securely fasten all components to the subset and die set. They
include the punch holder, the die shoe, the shank, the guideposts, the guidepost bushings, the
springs, screws, dowels, etc. [3].
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2.3 Bending Die components
The main components for Die Tool sets are:
Die block – A die block is a construction component that houses the opening and
receives punches. These die openings may be machined from a solid block of tool
steel or may be made in sections. .The die block is predrilled, tapped, and reamed,
before being fastened to the die shoe. Die holder is thicker than the punch holder to
compensate for weakening effect of slug and blank holes. Common proportions for
small and medium size dies are Punch holder thickness 1.25 inch, Die holder
thickness 1.5 inch. It is made up of OHNS, high-quality steel, hardened and precision
ground to exact size with hardness of 56HRC.
Figure 2.3.1 Die block [3]
Punch plate – It is mounted to the upper shoe in much the same manner as the die
block. It is made from the hardened tool steel; it may consist of single piece of steel or
be sectioned. It holds all punches, pilots, spring pad, and other components of die. It is
separated from die shoe by back up plate. Usually punch plate is attached directly to
the press attachment ram and the die holder to the press attachment. This necessitates
the use of the same press attachment each time the job is run. It will also speed set up
time by eliminating the need for aligning the punches to the die sections. The punch
plate is designed, dimensioned, and manufactured similarly to the die block [4].
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Figure 2.3.2 Punch plate [3]
Stripper plate - This is used to hold the material down on the Blank/ Pierce Die and
strip the material off the punches. Material of the stripper plate must be ground on
both sides and perfectly square. Stripper plates may be made of cold rolled steel if
they are not to be machined except for holes. When machining must be applied to
clear gages. Plates should be made from machine steel with hardness of HRC 35-38.
Figure show two types of stripper plates used. Figure 2.3.3 shows the two different
types of stripper plates (a) Stationary Stripper plate (b) Spring stripper plate.
Figure 2.3.3 Stripper plate [4]
Punch – punch tooling is made from hardened steel or tungsten carbide. A die is
located on the opposite side of the work piece and supports the material around the
perimeter and helps to localize the bending forces. There is a small amount of
clearance between the punch and the die to prevent the punch from sticking in the die
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so that less force is needed to make the hole. Depending on the shape of part to be
produce different types of punches are used, like plain punch, pedestal punch, V type
punch, special purposed etc. The main considerations when designing punches are, 1)
they should be design so that they do not buckle. 2) They should be strong enough to
withstand the stripping force. Standard punch material is SKD11. Expected hardness
thru heat treatment is approximately 60HRC
Figure 2.3.4 Punch Mounting [2]
Guide Post - Both die shoes, upper and lower, are aligned via guide pins or guide
posts. These provide for a precise alignment of the two halves during the die
operation. The guide pins are made of ground, carburized, and hardened-tool steel,
and they are firmly embedded in the lower shoe. The upper shoe is equipped with
bushings into which these pin slip-fit. Figure 2.3.5 (C) shows guide post.
Figure 2.3.5 Die set arrangement [3]12
Punch holder - The upper working member of the die set is called the punch holder.
The name is easy to remember because of its relationship with the punches, which are
normally applied above the strip and fastened to the underside of the punch holder. A
punch holder also serves as supporting the rigidity of the top die. It is also a function
of the punch holder to support rigidity of upper dies. In upper die structure which has
springs, we need to adjust the holder thickness according to spring length. If having
difficulty attaching upper die to press machine just by the shank, you may use punch
holder to attach. Punch holder is made up of cast iron or of steel.
Figure 2.3.6 Schematic diagram of Punch holder [4].
Shank – Upper shoe is sometimes provided with shank by which the whole tool is
clamped to the ram of the press. Dies with large in weight are secured to the ram by
clamps or bolts. However, sometimes even large die sets may contain the shank,
which in such a case is used for centring of the tool in the press. It is a pillar-shaped
part; used for attachment of relatively small upper dies (dies used on stamping
machines up to 30t capacity) to the slide of stamping machines. The size of the shank
depends on the mounting dimensions of the press the die is intended for. Standard
shank diameters are 25, 32, 38, and 50mm. Shank length is usually ranging from 50~
65mm. usual choice of materials is SS400 or S50C and its equivalent, FC250 types [2,
3]. Figure 2.3.7(a) shows the relation between shank and punch holder plate.
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Figure 2.3.7(a) Shank Position [6]
Figure 2.3.7 (b) Types of shank [6]
Bolster plate – Bolster plate, sometimes called press table, is positioned on top of the
press bed. It is a heavy plate, ribbed with T slots (to receive T bolts in the assembly of
a die), precision aligned to the frame with dowel pins. Wear occurring on the press
bed is high; the bolster plate is incorporated to take this wear it is attached to the press
bed and die shoe attached to it. Bolster plate thickness varies from 25mm to 75mm.
The material for bolster plate is a good quality steel [2, 3].
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Shank
Punch Holder
Stop Pin – Material when first being guided into the die, must stop somewhere for the
sequence of die operations to begin successfully. Advancing the strip too far may lead
to greater than usual wear and tear of the tooling and its subsequent misalignment and
breakage. Two types of stop pins are use 1.Automatic 2.Fixed.
Figure 2.3.8 stop pin [4]
Cushion Pin – metal pins used in conjunction with a die cushion to transfer pressure
from the cushion to the bottom of a die pad. They are also called as air pins, pressure
pins and transfer pins [7].
Figure 2.3.9 Cushion Pin [8]
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Stop pin
2.4 Types of bending die
1) V-bending die -
In V-bending, the sheet metal blank is bent between a V-shaped punch and die. The
clearance between punch and die is constant (equal to the thickness of sheet blank). In
V-die bending, it is possible for the material to exhibit negative springback. This
condition is caused by the nature of deformation as the punch completes the bending
operation. Negative springback does not occur in air bending (free bending) because
of the lack of constraints in a V-die. The thickness of the sheet ranges from
approximately 0.5 mm to 25 mm [2].
Figure 2.4.1 V-bending die [3]
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2) U bending die - In U bending, the sheet metal blank is bent between a U shaped
punch and die. Punch of U shape is used for producing the U bend; figure 2.4.2 shows
U shape part that is produce by only U bending die [10].
Figure 2.4.2 U shape Part [10]
Figure 2.4.3 U bending die [2]
3) Wiping bending die –
Wiping die bending, also known as edge bending, it is performed by holding the sheet
between a pad and die then sliding the wiping flange across the face pushing and
bending the sheet metal which protrudes from the pad and die. The flange is driven by
an upper shoe and the die is supported by a lower shoe. A spring between the pad and
upper shoe grabs the metal before the flange hits it and holds the work piece down
during the bending process.
If the flange has a feature associated with it, other than just a straight bend then a
stronger spring will help prevent the metal from being pulled from the area between
the die and pad. This will lead to less deformation when the piece comes out of the
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1. Stripper plate
2. Punch
3. Punch holder
4. Die Segment
5. Cushion pin
6. Pressure pad plate
7. Stop pin
8. Die shoe
9. Work piece
stamp. In our example below we are only showing a single section of a feature but in
reality there can be flanges formed on any and all sides of the piece at the same time.
This can lead to significant productivity gains. The Bend Angle is controlled by the
stroke of the wiping punch. It’s necessary that the punch has the proper offset for the
thickness of the material to prevent shearing. This method does not allow for over
bending past 90 ° because of the tooling geometry. This also makes it difficult to
work with harder materials which have a high Spring Back. Below figure shows the
wiping die operation.[11]
`
Figure 2.4.4 wiping die [11]
4) Air bending –
This bending method forms material by pressing a punch (also called the upper or top
die) into the material, forcing it into a bottom V-die, which is mounted on the press.
The punch forms the bend so that the distance between the punch and the side wall of
the V is greater than the material thickness (T)
Either a V-shaped or square opening may be used in the bottom die (dies are
frequently referred to as tools or tooling). A set of top and bottom dies are made for
each product or part produced on the press. Because it requires less bend force, air
bending tends to use smaller tools than other methods. Some of the newer bottom
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tools are adjustable, so, by using a single set of top and bottom tools and varying
press-stroke depth, different profiles and products can be produced. Different
materials and thicknesses can be bent in varying bend angles, adding the advantage of
flexibility to air bending. There are also fewer tool changes, thus, higher productivity
[9]. From the below figure difference between Air bending and V bending die can be
easily identified. With 3-point bending the points of contact are all on the same side of
the material. The angle is determined by the height adjustment in the bottom tool. And
with air bending the points of contact are on both sides of the material. The angle is
determined by the depth of entry of the tool into the die plate.
Figure 2.4.5 (a) 3 – Point bending. (b) Air bending
A disadvantage of air bending is that, because the sheet does not stay in full contact
with the dies, it is not as precise as some other methods, and stroke depth must be
kept very accurate. Variations in the thickness of the material and wear on the tools
can result in defects in parts produced. [9]
Air bending's angle accuracy is approximately ±0.5 deg. Angle accuracy is ensured by
applying a value to the width of the V opening, ranging from 6 T (six times material
thickness) for sheets to 3 mm thick to 12 T for sheets more than 10 mm thick.
Springback depends on material properties, influencing the resulting bend angle. [9]
Depending on material properties, the sheet may be over bended to compensate for
springback. [10]
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Air bending does not require the bottom tool to have the same radius as the punch.
Bend radius is determined by material elasticity rather than tool shape. [9]
The flexibility and relatively low tonnage required by air bending are helping to make
it a popular choice. Quality problems associated with this method are countered by
angle-measuring systems, clamps and crowning systems adjustable along the x and y
axes, and wear-resistant tools. [9]
2.5 Knowledge Based System/Expert System
2.5.1 Overview
Expert System is the first realisation of research in the field of Artificial Intelligence (AI). In
the form of a software technology and were developed by the AI community in the mid-
1960’s. It uses human knowledge to solve problems that normally would require human
intelligence. The basic idea behind ES is simply that expertise, which is the vast body of task
specific knowledge, is transferred from a human to a computer. This knowledge is then stored
in the computer and users call upon the computer for specific advice as needed. The computer
can make inferences and arrive at a specific conclusion. Then like a human consultant, it
gives advices and explains, if necessary, the logic behind the advice. Professor Feigenbaum
pioneer of expert system technology has defined an expert system as “an intelligent computer
program that uses knowledge and inference procedures to solve problems that are difficult
enough to required significant human expertise for their solution” [12].
The knowledge in ES may be either expertise or knowledge that is generally available from
books, magazines and knowledgeable persons. The term Expert System (ES), Knowledge
Based System (KBS) or Knowledge based expert systems are often used synonymously.
Most people use the term ES simply because it’s shorter, even though there may be no
expertise in their ES, only general knowledge [13]. An Expert System is not called a
program, but a system, because it encompasses several different components such as
knowledge base, inference mechanism, explanation facility etc. All these different
components interact together in simulating the problem solving process by an acknowledged
expert of domain. Internally ES consist of two main components. The knowledge base
contains collection of knowledge with which inference engine draws conclusions.
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The process of using current facts and knowledge contained in the knowledge base to
establish additional fats or decisions continues as a chain, until a fact specified as a goal is
established. The control mechanism primarily carries out symbolic processing called
inference. There can be a number of different ways in which the knowledge contained in the
rules can be used for inference. Hence, the control mechanism can consist of many different
inference strategies. Thus these two, knowledge base and inference mechanisms form the
main components of an expert system.
2.5.2 Architecture of Expert system
Typical expert system architecture includes three components: an inference engine, a
knowledge base ad a working memory as shown in figure 4.1. Description of ES components
is given in table 1. Declarative descriptions of expert level information, necessary for
problem solving, are stored I the knowledge base. The inference engine solves a problem by
interpreting the domain knowledge stored in the knowledge base. It also records the facts
about the current problem in the working memory. When an expert system starts the process
of inference, it is required to store the facts established for further use. The set of established
facts represents the context, i.e., the present state of the problem being solved. Hence, this
component is often called context or working memory.
Figure 2.5.1 Architecture of Expert System [14]
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Knowledge base
Inference engine
Working memory
User
User interfac
e
The division between the knowledge base and inference engine has two important
advantages. First, if all of the control structure information is kept in the inference engine,
then one can engage the domain expert in a discussion of the knowledge base alone, rather
than of questions of programming and control structures [12]. Second the versatility of the
system is increased. If all of the task specific knowledge has been kept in the knowledge
base, then it is possible to replace the current knowledge base by a new one and obtain a
performance program for a new task [13]. However, the inference engine and the knowledge
base are not completely independent. The knowledge base contents is influenced by the
inference engine, since the rules written for the knowledge base take into account the
inference engine and its built in control strategies.
Table 2.5.1Expert System Components
Expert System
Components
Descriptions
User Interface Code that controls the dialogue between user and system and provides the
possibility of communication between the user and the computer. Through
user interface, user can provide facts, describe the problem and read the
decision and conclusion provided by the system.
Inference Engine It models the reasoning capabilities of human expert. Code at the core of
the system, which derives recommendation from the knowledge base and
problem specific data in working storage.
Knowledge base This contains the information, facts and rules for specific problem
domain; this is where knowledge is recorded.
Working storage It acts as temporary storage that works in conjunction with the inference
engine. It records facts coming from the user and temporary information
gained by using the rules; this information is used by inference engine for
processing.
Domain Expert Individual(s) who currently are experts solving the problems.
Knowledge
Expert
Individual(s) who encodes the expert’s knowledge in declarative form that
can be used by the expert system.
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2.5.3 Knowledge Base
The knowledge base contains the domain-specific knowledge required to solve problems.
Knowledge engineer develops the knowledge base. He conducts a series of interviews with
experts and organizes the knowledge in a form that can be directly used by the system.
Knowledge engineer has to develop an expert system using a development environment or an
expert system development shell.
The knowledge that goes into problem solving in engineering can be broadly classified into
three categories, viz., compiled knowledge, qualitative knowledge and quantitative
knowledge. Knowledge resulting from the experience of experts in a domain, knowledge
gathered from handbooks, old records, standard specifications etc., and forms compiled
knowledge. Qualitative knowledge consists of rules of thumb, approximate theories, causal
models of processes and common sense. Quantitative knowledge deals with techniques based
on mathematical theories, numerical techniques etc. compiled as well as qualitative
knowledge can be further classified into two broad categories, viz., declarative knowledge
and procedural knowledge [15]. Declarative knowledge deals with knowledge on physical
properties of the problem domain, whereas procedural knowledge deals with problem solving
techniques.
2.5.4 Knowledge Representation
For development of an expert system, one should know different knowledge representation
schemes and the possible modes of interaction between them. Knowledge representation is an
important activity in development of expert system for two reasons. First, expert system
shells are designed for a certain type knowledge representation such as rules or logic. Second,
the way in which an expert system represents knowledge affects the development, efficiency,
speed and maintenance of the expert system. To represent knowledge means to convert
knowledge to an applicable form. An collection of techniques is being used to represent
knowledge including, rule based systems, semantic nets, frame systems, scripts, first order
predicate calculus, associative networks, object oriented systems and attribute grammar
systems. A detailed summary for some of the most important features of different knowledge
representation schemes in expert system is given below [12, 16, 17].
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Production Rules -
One of the most popular types of expert system today is the rule based system. It is popular
for number of reasons.
Modular Nature – this makes it easy to encapsulate knowledge and expand the expert
system by incremental development.
Explanation facilities – It is easy to build explanation facilities with rules because the
antecedents of a rule specify exactly what is necessary to activate the rule. by keeping
track of which rules have been fired, an explanation facility can present the chain of
reasoning that led to certain conclusion.
Similarity to human cognitive process – Rules appear to be a natural way of
modelling how human solve problems. The simple IF and Then representation of
rules makes it easy to explain to expert the structure of the knowledge you trying to
elicit from them.
Production rules are simple but powerful forms of knowledge representation providing the
flexibility of combining declarative and procedural representation for using them in a unified
form. A production rule has a set of antecedents and a set of consequents. The antecedents
specify a set of conditions and the consequents a set of actions.
IF < condition or set of conditions >
Then < Action >
The methodology used in rule based systems [18] originated from the production
systems framework proposed by Post [19]. A rule based system consists of three
major parts:
Working memory that holds the facts, the goal and the intermediate results.
Rule memory which holds all the system rules and
Rule interpreter, which decides about rule applicability.
Conditions or premises are evaluated with reference to the data in the working memory; and
if evaluated to be true, actions take place. The contents of the working memory are affected
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by the actions of the rule that has been fired. If there is more than one rule whose premises
are satisfied, then it is up to the rule interpreter to select one. The strategy to select the next
rule to be fired is called conflict resolution. Conflict resolution requires efficient response to
changes in the working memory to maintain a logical reasoning continuity and system
refraction. Important conflict resolution mechanisms are:
a) Refractoriness that prohibits the execution of a role on the same data more than once.
b) Regency that favours the execution of a rule that matches with the most recently
entered data in the working memory and
c) Specificity, which gives precedence to the execution of a rule with the largest number
of premises.
Some systems allow the programmer to establish metarules. Metarules gives the reason about
which additional rules should or should not be considered. Rule based expert systems utilize
both forward and backward chaining. With some simple trick rules they can be made to
represent many, if not all, knowledge representation techniques. Representative rule based
expert systems include the MYCIN expert systems in engineering [20], the DENDRAL [21],
the Meta-DENDRAL [21] AND THE EMYCIN [20]. Rule based systems are the easiest to
implement and they maintain an overall acceptable performance. However, their efficiency is
deteriorating in the presence of high volume knowledge data and the main reason for this is
that the matching process in the inference engine becomes computational intensive as the
amount of knowledge data increases.
Frames (objects) and Semantic Networks -
Objects are very powerful forms of representing facts in expert systems. They are ideally
suited for representation of declarative knowledge, which describes physical entities and
semantic relationships between them [22]. Any engineering activity is centred on an object or
a facility, and detailed information about the object is required to make decisions concerning
it. Different attributes of the artifact may be used at different stages of a problem such as
planning, analysis, detailing, manufacturing/construction etc. hence, it is appropriate to use
objects with attributes encapsulated in order to have a more structured representation of facts
in the context, during execution of the expert system. Also, the rules should be able to
interact with the objects.
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Procedural programs -
Engineering problem solving involves numerical computations, in addition to inference using
knowledge. In a real life expert system, the system has to perform numerical computations
may be very small in some cases and quite large in many cases. Based on the values inferred,
a detailed analysis of the artifact may have to be carried out to evaluate the correctness of the
parameters arrived at. The quantitative knowledge required for such computations can be
represented as functions/programs written in high level programming languages such as
FORTRAN or C. an expert system should be able to call these programs as and when
required during problem solving. Hence, they also form part of the expert system.
Most expert system development shells provide facilities to represent knowledge in the three
forms, viz., rules, frames and functions in procedural languages. The predicate logic form of
knowledge representation is the natural form in prolog, one of the specialized AI languages;
prolog provides predicate logic-based representation with backtracking inference, which is
inadequate for developing large expert systems for practical applications.
In addition to rules, frames and semantic nets, knowledge can be represented by the symbols
of logic, which is the study of the rules of exact reasoning. An important part of reasoning is
inferring conclusion from premises. The application of computer to perform reasoning has
resulted in logic programming and the development of logic based languages such as
PROLOG. Predicate logic provides mechanisms for representation of facts and reasoning
based on syntactic manipulation of logic formulae. It uses predefined formulae are
manipulated purely based on their form or structure. The major disadvantage of this scheme
is that it cannot consider the meaning or semantic content of the formula. In predicate logic,
all deductions are based on logic statements, and inference rules are guaranteed to be correct.
In addition, a logic program will generate all possible inferences that can be drawn from the
facts and rules. Though such predicate logic systems deduce all possible facts, their ability to
carry out a constrained search through the facts and inferences is limited. This is primarily
due to their inability to carry out guided search and also to represent search strategies. As
new facts are generated, the inference rules are applied to assert newer facts. This process
continues leading to combinatorial explosion until a goal state is reached. Only a constrained
assertion of facts can improve the situation, which is difficult in predicate logic. In addition,
predicate logic systems try to apply all the inference rules to all the facts. There is no
26
mechanism to group facts and associate specific inference rules to different groups. Even in a
small real-life AI-based system, there can be number of facts and inference rules. Due to the
above-mentioned limitations, it becomes difficult to apply predicate logic-based knowledge
representation in expert systems [22, 23]. A good knowledge representation scheme should
have the capability to represent real-life situations (objects and relationships among them),
which can be exploited by efficient guided search strategies and which better reflect the way
humans perceive and think.
27
2.6 Problems in Traditional Process of Bending Die Design
To check the manufacturability of component, determine the process plan for sheet metal
parts and to design/selection various die components, die designers have to performed design
tasks such as process planning, selection of type of press, bending sequence, bending force,
speed design/selection of various die components. Designers also have to consider how to
obtain optimal number of operation stages to produce parts having complex shape. To
perform all these tasks it require many years of experience on the part of die designer. A
number of problems in traditional process of die design are summarized as follow.
1. It is tedious, time consuming and error prone.
2. Knowledge gained by die design experts after long years of experience is
often not available to others even within the same company. It creates a
vacuum whenever the expert retires or leaves company.
3. Due to long apprentice period, slow career growth and burden of heavy
workload, young technocrats do not prefer to enter in the challenging field
of die design.
4. Stamping industries are facing acute shortage of experienced die designers
worldwide.
Number of CAD/CAM software’s like UG, CATIA, PRO-E, IDEAS and SOLID EDGE etc.
are developed. These software’s assist die designers in drafting, visualisation and storage and
retrieval of component geometric data. But the limitations of these CAD/CAM software’s are
1. Commercial CAD software only assists in drafting and simple design
calculations and to operate this software skilled die designers are required.
2. Only segments of the die design process are supported.
3. Incomplete, imprecise, or inconsistent information cannot be handled.
4. The various phases of design of bending die are not integrated in single software.
5. Design technical and logical errors are not detected.
6. Costly and hence not affordable by small scale stamping industries.
28
Chapter 3 KBS Development Procedure, Methodologies, and
Applications
To a large extent the development of a knowledge based system will depend
on the resources provided, however like any other project, the development will also
depend on the how the process is organized and managed. The development of a KBS
is represented in figure 3.1, begins with the preparation phase. Under this phase,
determination of a goal and preliminary investigation is done. The second phase is
conceptual and prototyping phase in which problem analysis, system draft, system
prototyping and validation of the prototype is carried out. In the third phase in-house
testing using a real life case study. In the fourth stage complete testing of the system
with real life data by the user. In the fifth stage system is validate and documented.
The last phase is maintenance and evolution where fixing of error and continuous
enhancement of the system by continuously adding new knowledge [24, 25].
Paper or comparison study to show project is
feasible
Expert system quickly put together to
demonstrate arouse enthusiasms
In-house verification of expert system on real
problem by knowledge engineer.
System tested by selected users not knowledge
engineers or experts
Validated and tested, User documentation,
training
Fix bugs Enhance capabilities
Figure 3.1 General stages in the development of ES/KBS.
29
Feasibility Study
Rapid Prototyping
Refined System (Alpha test)
Field Testable (Beta Test)
Commercial quality system
Maintenance and Evaluation
3.2 Expert System Applications
KBS has been applied to virtually every field of knowledge. Some have been designed as
research tools while others fulfil important business and industrial functions. Based on
system reported in the literature, certain broad classes of KBS applications can be distinguish
as shown in table 3.1
Table 3.1 Broad classes of Expert system
Class General area
Configuration Assemble proper components of system in the proper way
Diagnosis Infer underlying problems based on observed evidence
Instruction Intelligent teaching so that a student can ask why, how and what if type
questions just as if a human was teaching
Interpretation Explain observed data
Monitoring Compare observed data to expected data to judge performance
Planning Devise action to yield a desire outcome
Prognosis Predict the outcome of a given situation
Remedy Prescribe and remedies
Control Regulate a process. May require interpretation, diagnosis, and monitoring,
planning, prognosis.
30
3.3 Procedure of KBS/ES for Bending Die Design
The procedure for building KBS modules of die design is schematically shown in figure 3.2
A brief description of each step is given in following paragraphs [26]
31
Knowledge Acquisitions
Expert dies designers, handbooks, monographs, research journals, catalogue and industrial brochures
Framing of Production Rules
IF <condition>THEN <action>
Verification and sequencing of production rule
Cross checked from die design experts arranged in an a structured
Identification of operating system and hardware
Provide high quality run time environment for complete interactive programs with large knowledge bases
Selection of development language
Provide suitable facilities, for the effective representation of knowledge and efficient inferences from it
Construction of KBS shell
Elicit problem specific data, apply and explain the application of the knowledge base.
Select suitable search strategy
Forward chaining and backward chaining
Preparations of user interface
Knowledge acquisition
It is a first step in the development of knowledge based system. It is most time
consuming and laborious job in expert system development. The domain knowledge for
design of drawing die is collected through by on line and off line consultation with
design experts, tool design engineers of different industries, referring research articles,
catalogue and manual of different design and manufacturing industries. The
information obtained from the literature is not always the same as what is currently
being practiced. The information obtained through industrial broacher is a compromise
between the academically fundamental knowledge obtained through literature reviews
and the practical, experience based knowledge obtainable from industrial experts. The
process of knowledge acquisition from die design experts involves presenting a few
typical problems to the experts and letting the expert talk through the solution. During
the verbal analysis, the experts would be questioned to explain why a particular
decision was reached.
Framing of Production Rules
The knowledge collected from the various sources is represented using rules. The most
common method of knowledge representation is ruled based systems.
The syntax of a production rule is
IF < condition >
THEN < action >
The condition of production rule, sometimes called LHS contains one or more
conditions, while the action portion, sometimes called RHS contains one or more
actions.
32
Verification of production rules
The knowledge available for design of drawing die is mostly collected from the die
design expert. The experts use the thumb rules, which they developed during long years
of practice and experience in die design. These rules may differ from industry to
industry. So it is mandatory to come up on a common solution, which could be
accepted by most of die designers working in various industries. The production rules
framed for each module must be crosschecked from die design expert by presenting
them IF condition of the production rule of IF – THEN variety.
Sequencing of production rules
The framed rules are presented in either in an unstructured or a structured manner. But
structured presentation of knowledge in terms of the production rules are simple to refer
and consume less time and if query is fired it take less time to get the result. Also
ambiguity in understanding the knowledge will be less.
Identification of selection operating system and hardware
The lowest level of the hierarchy in the development of expert system is the machine on
which the expert systems run. Suitable hardware elements depending upon memory
requirement, processing speed and needed configuration should be selected. Today,
most of the KBS modules are being developed on a PC/AT because it involves low
cost.
Selection of development language
Early expert systems were written in language interfaces derived from FORTRAN.
Later on, object oriented languages such as KEE, OPS, PROLOG, TURBOPROLOG
and LISP were developed specifically for the AI systems. LISP and PROLOG have
been won wide acceptance for building expert system, the user of LISP and PROLOG
languages encounters difficulties when handling design problems involving graphical
information. For this reason, AutoCAD and AutoLISP have found greater acceptance
for the development of expert system for die design.
33
Construction of KBS shell
Knowledge base is a part of an ES that contains domain knowledge, which may be
expressed in the form of production rules of IF-THEN variety. The inference
mechanism allows manipulating the stored knowledge for solving problems. The rules
and the knowledge base are linked together by an inference mechanism. The user input
information provides guidance to the inference engine as to what IF-Then rules to fire
and what process of information is needed from the knowledge base.
Choice of search strategy
Inference mechanisms are control strategies or search techniques, which search through
the knowledge base to arrive at decisions. The two popular methods of inference are
backward chaining and forward chaining. Backward chaining is a goal driven process,
whereas forward chaining is data driven. Forward chaining is a good technique when
all on most paths from any of much initial or intermediate state converges at once or a
few goal states. Backward chaining is an efficient technique to use when any of many
goal states converging on one or a few initial states.
Preparation of user interface
The expert system modules should be interactive in nature. The purpose of user
interface in the development of each module is twofold: (1) to enables the user to input
the essential sheet metal component data; (2) to displays the optimal decision choices
for the users benefit. The former is accomplished by flashing AutoCAD prompts to the
user at appropriate stages during a consultation to feed data items. Messages or items of
advice are likewise flashed into the computer screen whenever relevant production
rules are fired.
3.4 Need of Expert System in Bending Die Design
34
Because of globalisation and competitions, sheet metal industry faces number of challenges
such as to reduce the time spent on product development, shorter delivery time and low cost
of product. In addition sheet metal industry faces a problem of low recruitment rate and large
turnover of the manpower. The success of the die design and manufacturing is largely
depends upon the skill and the experience of the die designer. But due to the huge quantity of
uncertain information and factors to be considered and selected, die design is affected by
individual subjectivity to a great extent. These often affect the structure of the die itself and
the reliability of sheet parts. Also large number of rules and experimental studies in the area
of die designs are available but it is poorly documented; when experts argue, the bases on
which they argue are largely unspoken. Commercially available CAD/CAM systems are
providing some assistance in drafting and analysis in die design process, but human expertise
is still need to arrive at the final design [12]. As discussed earlier, the task of die design is a
complex, tedious, time consuming and experience based activity. Only engineers having
many years of design experience would own the knowledge for correct design of die. On one
hand it is very minimum potential failures. On the other hand, even for experienced
engineers, negligence would often result in unwanted consequence.
Therefore, there is a need to develop a KBS for die design that can store the past experiences,
eliminate human error and can logically integrate together all relevant knowledge and
experience and to provide an aid to process planners and die designer of sheet metal industry.
Development of KBS will help to achieve shorter product delivery time and low cost also it
can be used as an effective tool for training for new comers in die design and manufacturing
which will reduce the training time.
Chapter 3 Literature Review
35
Ching. Z. et al., (1994) developed the possible application of an expert system in sheet-metal
bending, and to build a prototype of a sheet-metal bending expert system on a PC/AT. This
sheet-metal bending expert system utilizes the qualitative data in a knowledge base and the
quantitative data in a database, together with empirical design data, to aid the user in the
design of sheet-metal bending. The deduced drawing of the sheet-bending dies is
demonstrated using AutoCAD graphic software. They established a prototype expert system
of sheet-metal bending design with preliminary learning capabilities. The system does not
provide process planning and manufacturability of bending.
Duflou, J. et al. find out that bend sequencing and tool selection have long been the main
hurdles for achieving automatic process planning for sheet metal bending. In this process, the
complex shape and position transitions of work pieces make it hard to obtain a collision-free
operation plan. They presented a tool selection methodology to be integrated in the automatic
bend sequencing system. Both the described selection strategy and the related algorithms
have been implemented in an industrial software package. Taking into account not only
feasibility aspects of technology and geometry, but also production planning oriented
guidelines, the method is able to deliver feasible and well-optimised tooling solutions, as
result of a two phase procedure consisting of pre-selection and refined selection.
Lin Z.et al. (1996) established the knowledge base for the selection of sheet metal bending
machines. They considered machine specifications such as pressure capacity and bending
length in the selection in order to reach the best choice according to the need of the decision
maker. Their purpose was to utilize the PRISM method of inductive learning and knowledge
acquisition to construct a product-type rule base, and further complete an expert system for
the selection of sheet metal bending machines, which may assist the user in choosing the
appropriate bending machine. They used the concept of probability of the knowledge
acquisition model of PRISM inductive learning to construct a modular knowledge base. A
step-by-step illustration of how to use the PRISM algorithm in developing the rules of the
knowledge base is presented. They used three machine specifications - pressure capacity,
bending length and stroke as the analytical attributes to construct the rule base of this system.
Ong, S.K. et al. (1997) applied brake forming in the high variety and small batch part
manufacturing of sheet metal components, for the bending of straight bending lines. They
36
described the application of fuzzy set theory, for the normalization and modelling of the set-
up and bend sequencing process for sheet metal bending. A fuzzy-set based methodology is
used to determine the optimal bending sequences for the brake forming of sheet metal
components, taking into account the relative importance of handling and accuracy. A fuzzy-
set based bend and set-up sequencing methodology for sheet metal working has been
presented. The highly experience and heuristic-based conventional set-up planning
procedures in sheet metal bending are aptly modelled in this computer-automated bends and
set-up sequencing system, using the fuzzy set theory.
Inamdar, M. et al. (2000) described springback in air vee bending process is large in the
absence of bottoming. Inconsistency in springback might arise due to inconsistent sheet
thickness and material properties. Among the various intelligent methods for controlling
springback, an artificial neural network (ANN) may be used for real time control by virtue of
their robustness and speed. They described that the development of an ANN based on back
propagation (BP) of error. They established the architecture using an analytical model for
training consisted of 5 input, 10 hidden and two output nodes (punch displacement and
springback angle). The five inputs were angle of bend, punch radius/thickness ratio, die gap,
die entry radius, yield strength to Young's modulus ratio and the strain hardening exponent, n.
Lin Z. et al. (1996) developed an expert system for the selection of sheet metal bending tool
which was one of the earliest manufacturing techniques in the manufacturing industry. The
machine specifications such as pressure capacity, bending length and so on must be
considered in the selection of sheet metal bending tooling in order to reach the optimal choice
based on the needs of the decision maker. They proposed a model using machine learning
from neural networks in an expert system of sheet metal bending tooling. With the three
machine specifications of pressure capacity, bending length and stroke length as the
analytical attributes of the problem, the knowledge acquisition of the neural networks
machine learning model is used to establish a rule base for the system, which equips the
system with better knowledge representation and inference capacity.
37
Inamdar, M. et al. (2000) find out that Springback is a serious problem in the air vee bending
process because of its inconsistency. An on-line tool to control springback is more reliable
than an analytical model which might not be able to control the stroke of the machine in real-
time. They suggested that, one might resort to adaptive control or use an artificial neural
network (ANN) trainer, either using experimental data or analytical predictions (or both), and
use it for real-time control of the machine tool. The inconsistency in springback is then
reduced to within acceptable limits. Adaptive control would need several strokes to complete
the job, but it is envisaged that the job could be completed in a single stroke with the ANN.
Lin, Z. et al. (2001) described that the shearing force in the shearing-cut process for a
shearing-cut and bending progressive die is far greater than the strip bending force. The
equation for torque equilibrium is first established. The heuristic rule is then adopted to locate
the die centre of the shearing-cut and bending progressive die and an offset displacement is
set. They mainly tried to reduce the time spent in adjusting the pressure centre of the
shearing-cut and bending progressive die. Genetic-algorithms (GA) are applied as a solution
tool in the analysis of the optimal strip working sequence possessing a smaller difference
between the right and left torque in the shearing-cut and bending progressive die. The torque
equilibrium model for the shearing-cut and bending progressive die and the concept of rough
tuning first followed by micro-tuning were presented in this paper. GA was also used to
derive the strip working sequence with mini-mum torque difference.
Kim, C. et al. (2002) described a computer-aided bending and piercing operation for
progressive working of a component. The automated design system for process planning and
die design by fuzzy set theory for electric product with intricate piercing and bending
operation. Program was written in AutoLISP on the AutoCAD with a personal computer and
composed of four main modules, which are input and shape treatment, flat pattern layout,
strip layout, and die layout modules. The strip layout and die layout drawings automatically
generated by formularization and quantification of experimental technology will make
minimization of trial and error and reduction of period in developing new products. Results
obtained using the modules enable the manufacturer for progressive working of electric
products to be more efficient in this field, also play an important role in building FMS system
as an integrated CAD/CAM system.
38
Aomura, S. et al. (2002) proposed a method which generates bending sequences of a sheet
metal part handled by a robot. If parts are handled by a robot, the best grasping positions for
each bending and the number of repositions must be indicated in advance. Using the
proposed method, feasible bending sequences with grasping positions are obtained and the
sequences are sorted in the order of the number of repositions. In generating the sequences,
they consider several important features for the sheet metal bending by dividing them into
channels, which is one of the base features. They calculated the error accumulated during
bending operation for each sequence, and selected set-up positions so as to satisfy the
preferential tolerance. The proposed method assists the sheet metal process planner to
confirm if the robot can perform the handling operation.
Rico, J.C. et al. (2003) developed the system which described a method to obtain valid
bending sequences automatically according to the possible tool–part collisions and
tolerances. A method for solving the problem of bend sequencing in sheet metal
manufacturing is presented. The algorithm developed divides the part into basic shapes
(channels and spirals) and determines the partial sequences associated with them. The
complete bending sequences associated with the complete part were obtained from the
combination of these partial sequences. Finally, the sequence associated with the lower
process time was selected as the optimal solution. An approach to the bending time
calculation was followed to order the valid sequences and determine the best solution. In
order to reduce the calculation time to identify valid sequences, a method based on the part
division in basic shapes (channels and spirals) was proposed.
Pathak, K. et al. (2005) described that the sheet metal bending is an important form of sheet
metal forming process, widely used in various industrial applications like aircraft,
automobiles, household items, power industries, etc. They predict the responses of the sheet
metal bending process using artificial neural network. Sheet thickness and die radius were the
input, and stresses, strains, springback, loads, etc were the output for the neural network. The
trained neural network was tested for five new patterns. They observed that the neural
network gives quite close predictions of sheet forming responses. Such predictions help to
reduce large computational time going into computer simulations. It can be handled even by
novice in finite element analysis.
39
Sousa, L.C. et al (2006) presented an optimization method applied to the design of V and U
bending sheet metal processes. They coupled the numerical simulation of sheet metal forming
processes with an evolutionary genetic algorithm searching the optimal design parameters of
the process. They considered an inverse approach so that the final geometry of the bended
blank should closely follow a prescribed one. They presented applications to demonstrate the
applicability of the proposed method considering several relevant parameters including punch
and die radii, punch displacement and blank-holder force. The genetic algorithm is a
developed FORTRAN code and the finite element analysis is carried out using the
commercial code ABAQUS. They developed interaction between the two codes has been
written using PERL and PYTHON programming languages.
Bozdemir, M et al. (2008) defined the springback angle with minimum error using the best
reliable ANN training algorithm. Training and test data were obtained from experimental
studies. Materials, bending angle and r/t have been used as the input layer , springback angle
has been used as the output layer. For testing data, Root Mean Squared-Error (RMSE), the
fraction of variance (R2) and Mean Absolute Percentage Error (MAPE) were found to be
0.003, 0.9999 and 0.0831% respectively. With all these results they believed that the ANN
can be used for prediction of analysis of springback as an appropriate method in V bending.
Kazan, R. et al. (2009) described that the wipe-bending is one of processes the most
frequently used in the sheet metal product industry. Furthermore, the springback of sheet
metal, which is defined as elastic recovery of the part during unloading, should be taken into
consideration so as to produce bent sheet metal parts within acceptable tolerance limits.
Springback is affected by the factors such as sheet thickness, tooling geometry, lubrication
conditions, and material properties and processing parameters. They developed the prediction
model of springback in wipe-bending process using artificial neural network (ANN)
approach. Here, several numerical simulations using finite element method (FEM) were
performed to obtain the teaching data of neural network. Optimized results were not obtained
by them.
Kontolatis, N. et al. (2010) applied sheet metal bending processes in a multitude of
mechanical parts. The process involves optimizing the sequence of designated bends taking
into account the total processing and handling time, avoiding collisions of the sheet metal
with tools and machine and respecting the dimensional accuracy constraints of the part. They
40
replaced expert knowledge by stochastic search using a classic genetic algorithm. They
introduced dimensional accuracy issues by determining machine stopper positions and
employed interference detection libraries in connection to the search nature of the approach
enabled coping with the full 3D problem instead of quasi 2D problems dealt with in literature.
Their system is not capable to provide solution for sprinback in present approach.
Baseri, H. et al. (2011) described that spring-back is one of the most sensitive features of
sheet metal forming processes, which is due to the elastic recovery during unloading and
leads to some geometric changes in the product. Three parameters which are most influential
on spring-back in V-die bending process are sheet thickness, sheet orientation and punch tip
radius. They proposed a new fuzzy learning back-propagation (FLBP) algorithm to predict
the spring-back using the data generated based on experimental observations. The
performance of the model in training and testing is compared with those of the constant
learning rate back-propagation (CLBP) and the variable learning rate back-propagation
(VLBP) algorithms. Then the best model with the minimum mean absolute error (MAE) is
selected to predict the spring-back. They indicated that the proposed FLBP algorithm has best
performance in prediction of the spring-back with respect to the other algorithms.
Table 7.1 Salient features of major research work reviewed.
Sr. No
Researcher System Details Remarks
1 Uzsoy, et. al., (1991)
Rule based KBC implemented using turbo prolog.
A simple sheet part with total of eight features; four holes with two holes radius of 2 units, two hoes of radius 1 unit and four bends.
2 Ching, Z. et.al. (1994)
Autolisp integrated into AutoCAD
System does not provide process planning and manufacturability of bending.
3 Ching, Z. et. al. (1996)
Sheet metal bendingmachine selection model
data base for present m/c required to bemade
4 Ong, S. etal. (1997)
Fuzzy set theory for sheet metal bend sequencing
Does not provide optimal bending sequences only provides feasiblesolution
5 Ching, Z. etal.(1998)
Selection of bending toolsand bending sequence
good for customized problem only
6 Gupta, etal., (1998)
Automated process planning for robotic sheet metal bending press brake
Separate illustrations are given for each of the modules for different operations;Presently sheet with 23 bends can be
41
addressed for its process planning & other sequences.
7 Inamdar, M.et al.(2000)
Artificial Neural Network for measuring Sprinback inv-Bending
More the Data for initial training themore accurate will the result
8 Ching, Z.(2001)
Torque equilibrium and optimal strip workingsequence for bending progressive die
two stage model generated for customized problem
9 Shigeru, A.et al.(2002)
Sheet metal Bending Sequence and robot grasping positions are determined by Graphicalmethod and geometricalbending features
Only in 55% cases model provides accurate result and around 27 % moderate result.
10 Ruffini, R.(2002)
Neural network for springback minimization
Initial data is required for training of ANN model so, not suitable for initial use where precise o/p is required
11 Kim, C. etal. (2002)
CAPP process planning ofBending and Piercing
System required commercial CAD/CAM software
12 Markus, A.et al.(2003)
Constraint based ProcessPlanning
Still input of experienced domain expert is required
13 Rico, J.C. etal. (2003)
Automatic bending Sequence for Parallel bends
Model is based on Part-tool collision and tolerance constraint with lower process time optimisation
14 Ehrismann,R etal.(2004)
Expert system for BendingSequence
system is not able provide optimizedsolution
15 Pathak, K.et al.(2005)
Neural Network for finding sheet metal bending processparameters
to reduce the error % of results in b/wFEM and NNT high no. of cases are required for training
16 Sousa, L.C.et al.(2006)
Numerical simulation coupled with Genetic Algorithms used to optimized V & U bendingprocesses
Time required for numerical simulation is High around 36 h.
17 Bozdemir,M. et al.(2008)
ANN for Springback inV-Bending
Good results are obtained for customized problems
18 Kazan, R. etal. (2009)
ANN for springback inwipe bending
optimized resultsare not obtained
19 Kontolatis,N. et al.(2010)
Optimization of BendingProcess planning parameters
System is not capable to providesolution for sprinback in present approach
20 Baseri, H. etal. (2011)
Spring Back Modelling byfuzzy learning model in V Bending
Experimental data is used for learningmodel
42
Chapter 8 Conclusion
The conventional process of design of bending die is highly complex, error prone, manual
and time consuming. There are commercially available CAD software are also not capable to
ease burden of experienced die designers and process planners for quick design of stamping
tools. With the advancement in artificial intelligence (AI), researchers have started work in
the development of expert systems for design of bending die. Expert system eliminates
human errors and logically integrates together all relevant knowledge and experts’
experience. Some researchers applied research efforts towards the development of expert
system for design of bending die but most of the systems are prototypes, dedicated to specific
geometry of parts, and covering a subset of process planning and design functions.
Therefore, there is stern need to develop an expert system to ease the complexity in bending
die design process, reduce the time taken and finally display all design data and drawings in
CAD editor. This type of system will certainly provide a great help to the process planners
and die designers working in sheet metal forming industries. The developed expert system
must have low cost of implementation so that it can be easily affordable by small and
medium scale stamping industries, especially in developing countries.
43
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