A knowledge based
system for improving design and manufacturing process for Ultrasonic machining
in CE environment
Morteza Sadegh Amalnik,
Computer and
Automation R&D Center of ACECR-Sharif Branch
Department of Mechanical and
Industrial Engineering, University of Qum and
Tabriz, Iran
E-mail: sadeghamalnik@yahoo.com
Abstract
Concurrent
engineering is a systematic approach to the integrated concurrent design of
product and their related processes. This approach considers all elements of
the product life cycle from conceptual stages to the final stages of product
development including quality, cost, manufacturability, schedule and user
requirements. It is an organizational strategy which creates an environment
that people who design or manufacture products work to gather under the same
goals and the same sense of values to tackle the same problems from the early
stages of product development to the final stage of product development. The
goals are reduction of product development time, cost and shorter time to
market. This paper addresses the concept and development of a
knowledge-based-system (KBS) in computer based concurrent engineering
environment for hard and brittle material, such as glass, quartz, diamond,
carbides, semi conducting materials, ceramic and graphite etc. which can be
machined with ultrasonic. An advisory system in computer integrated
manufacturing and concurrent engineering environment for Ultrasonic machining
(USM) based on object oriented technique is developed. The system links with A feature based CAD
system in order to extract design. The knowledge base is linked with databases.
The machining cycle time, cost, penetration rate, efficiency and effectiveness,
of each selected design feature are estimated. The system provides useful
information such as machining cycle time and cost, penetration rate, efficiency
and effectiveness of machining of the selected design feature for product
designers at the conceptual stages of design process and also advises
manufacturing engineers to select optimum machining parameters.
1- Introduction
The limitation of conventional and some of the unconventional machining
have led to the development of ultrasonic machining for hard and brittle
materials [1]. The history of USM traced back to Lewis Balamuth, who invented
the process about forty three years ago [2].
The benefits of discovery of USM to industry were quickly realized, and
in 1950 the production of USM-tools began [3]. A wide range of material
specially hard materials (e.g. tungsten and titanium carbides, die and tool
steels etc.) and brittle materials (e.g. germanium, silicon, ferrites, ceramics,
glass, quartz etc.) could be effectively machined by this method [4, 5]. The
attraction of USM is
unlike ECM and EDM the material removal rate is affected by brittleness
and hardness of materials. USM is used in wide range of industry including aerospace,
electronic, optics, and automobile industries [6]. The rapid progress in this field can be
seen from the number of published
papers. It is reported that up to 1960s
about
350 papers had been published.
Ultrasonic machining (USM) is a
mechanical unconventional machining process by which material is removed
through direct hammering of the abrasive particles on the work piece by the
vibration of tool and flow of the abrasive particle. The mechanisms involved in
material removing by USM have been described in previous studies [3, 7,
8]. USM includes the flowing three
activities, (i) direct hammering of the abrasive grains between tool and work
piece, (ii) micro chipping by impact of the flow of the abrasive particles,
(iii) Erosion of work piece for some metals such as graphite by cavitations in
the slurry stream. It has been
reported that the fist two are the most
essential factors for material removal,
While the third process is applied only for some of the material such as
graphite [5, 9, 10]. Influence of
different parameters on material removal rate is reported by [10-14]. These
parameters can be classified into the following categories: (i) frequency and
amplitude of vibration and tool pressure, are the major importance in USM, (ii)
type and grit size and slurry concentration and volume of the abrasive slurry,
(iii) material type (iv) geometric shape and description of feature for tool and work piece, (v) machining time,
productivity and penetration rate.
The resonance transducer or vibrator
converting the electrical power received from the oscillator into mechanical
vibration. this is the main source of mechanical oscillation. The output of
transducer is inadequate for USM operation.
It should be amplified so that the output and the amplitude is sufficiently large for
USM operation. To overcome this problem a device so called horn is used. The
horn or tool holder is a waveguide or concentrators which is fitted from one
side to the end of transducer and from the other side is stick to the tool head. Its cross
sectional area is decreases from the transducer to the out put tool. The tool
shape is complementary to the design feature and attached to the end of the
horn. The abrasive slurry is fed between tool and work piece. A special mechanism is used to maintains the
static pressure between tool and work piece. For effective USM operation, the
machine tool must provide vibration of the tool at maximum amplitude at a given
frequency [2]. The effects of process
parameters such as static pressure, ultrasonic vibration amplitude and
frequency, abrasive size etc. on the process performances such as material
removal rate, tool wear, etc. have been also investigated experimentally by
varies researchers, the conclusions are summarized in [15]. Static pressure has
a great effect on tool wear and material removal rate (MRR). As static pressure increases tool wear
increase and MRR increase to the maximum level and then decreases. Vibration
amplitude has also effect on MRR. As the
vibration amplitude increases up to some point , MRR increase, but further
increasing of the vibration amplitude above this point results in a reduction
in MRR. Other process parameters including parameters such as amplitude and
frequency of tool vibration, abrasive slurry characteristics (type, size,
concentration), magnitude of the applied
force and material specification of the work piece. Holes as small as 0.076 mm up to 89 mm
diameter with maximum 64 mm depth can be
produce with USM [10].
Surface finishes for the USM
range from 0.2 to 1.5 μm Ra with no chemical, thermal or
electrical alterations of the surface.
Accuracies of 0.013 mm are typical, tolerances of 0.005mm can be
achieved for specialized applications, with good machining condition, machining
depth of 64 mm can be obtained [16] the sonotrode tool is made by using
electro-discharge machining (EDM). Grin size yields essential effect on surface
roughness, where changing from 600 to 280 mesh increases the surface roughness
more than twice (Ra from 1 to 2.5 μm) [14]. In case of ceramic, it has been reported that
any increase in the amount of work/energy imparted onto the ceramics in terms
of the amplitude of the conic wave, the static weight applied and the size of
the abrasive, will result in (i) increase in material removal rate, (ii) a
roughening of machined surface [17].
The process can be controlled by varying the gap between tool and work
piece. During the machining the actual distance between tool and work piece
should be kept constant [18]. USM has
many benefits as discussed before, but it has some drawbacks such as material
removal rate reduce as the penetration depth increase, the slurry may wear the
wall of the machined hole as it passes back toward the surface which limits the
accuracy specially for small hole, the action of slurry causing considerable
tool wear which in turn makes it very difficult to hold close tolerances. In order to overcome the USM problems, rotary
ultrasonic machining (RUM) is introduced
in 1964 by Percy Legge, a technical officer at United Kingdom Atomic Energy
Authority (UKAEA) [15]. Ultrasonic
polishing has been developed by the GrafEx Division of Extrude Hone Corporation
for variety of polishing applications.
In this type of process, t he extend of polishing determined by the
initial surface roughness of the work piece and the finishing requirement
after polishing. Typical surface
improvements range from 5:1 to 10:1;
finishes as low as 4 μ inch (0.1μm) Ra can be obtained
[19]. Advanced ceramics are increasingly used in industry for their superior
properties such as high strength, resistance to chemical degradation, wear
resistance and low density, but the only problem is high cost of machining with
current technology. for instance the cost of machining of a part with a
high accuracy can be as high as 90 % of
the total cost. Among the various
processes, rotary ultrasonic machining
has the potential for high material removal rate with low machining pressure resulting in less
surface damage [20]. Ceramic materials have a wide range of application from insulations to very complex applications
such as artificial teeth, bones, joints, internal combustion engines, thermal
barrier coatings, tougher metal cutting tools etc. [21], USM techniques can be
used to machine a wide variety of ceramic components, some of the USM
applications are shown in [22].
RUM is a hybrid machining
process that combines the material removal mechanisms of diamond grinding and
USM. Experimental results have shown
that the machining rate of RUM is nearly 6-10 times higher than from a
conventional grinding process under similar conditions, and 10 times faster
than USM [15]. Other worker reported the machining time of RUM is half to one
third of USM [23]. In RUM slurry is replaced with abrasives bounded to the
tool. The efficiency of RUS (ultrasonic
diamond) milling and drilling of deep
holes depends on the mechanical properties of the work piece material, the
design of the diamond tool and the machining conditions. With increasing specific load, removal
rate increases significantly [24]. RUM including a rotary tool metal bonded
diamond abrasives vibrates while the work piece is fed towards the tool at a constant
pressure. The coolant pumped through the
internal hole of the drilling tool, washes away the swarf, reduce the tool temperature and prevents
jamming [20], [25]. Experimental investigations have been conducted on the
productivity and surface quality and tolerances in ultrasonic machining of
ceramics [26].
The tool is shaped based on
design feature specification. A constant flow of slurry which is
automatically cooled and recirculated
between tool and work piece to carry away the chips from the work piece. As a
result of that material is removed and
work piece crushing. This is shown in Figure1. The components of USM is also
shown which including elements such as
Oscillator; the resonance transducer; the horn, tool holder; tool; clamping
system; abrasive slurry; and static pressure system.
Figure.1.
An ultrasonic machine apparatus
At present, most procedures are
based on personal knowledge and judgment. The complexity of the process, and
the interrelationship between its process variables mean that designer or even
general process planners have limited knowledge of USM. In planning they have
to turn to the literature or experts.
The information required by the former is often difficult to obtain.
moreover, the training of both process planners and manufacturing operators in
USM technology is time-consuming and expensive. Consequently if the knowledge
is not available from a reliable source, the USM product development cycle time
and cost increases, and both quality and productivity is likely to decrease.
Expert system and intelligent knowledge-based system (IKBS) provide a route to
overcoming these hurdles to the further advancement of USM, although little has
been achieved in these approaches.
Knowledge-based system becomes attractive for USM because it provides
information that can be used to minimize machining time, cost and increase
productivity and benefits. it could provide a ready, on-line knowledge
consultancy system guiding product designers and manufacturing engineers to
select appropriate product parameters and process conditions. The more
effective design and manufacture of an USM product by IKBS also needs
evaluation of manufacturability. At
present however, no computer-based systems have yet been reported that advice
designers and manufacturing engineers and apply manufacturability evaluation
concepts to USM. In the present paper, the implementation of IKBS for
manufacturability evaluation in concurrent engineering environment for USM is
investigated. The need for manufacturability evaluation is based on the
following concept that the most significant manufacturing time and cost are
those that result from poor design.
Design account for only small fraction of product development cost, but
the vast majority of total product life cycle cost is influenced by the design
decisions. Therefore designers need
feedback from manufacturing engineers and other functional area at the various
stages of design processes. On the other hand, all functions including
manufacturing engineers should be able to contribute to the product
development from the early stages of
design process . This is based on the philosophy of concurrent engineering (CE)
environment. In computer based CE
environment, various intelligent knowledge based system can be used instate
of team of experts to communicate with
each other through blackboard architecture system. This is based on computer
based concurrent engineering environment. A computer-based CE approach to USM
is the subject of this paper.
2- Concurrent engineering
Manufacturing
systems comprise of a large number of different stages that affect product
cost, product quality and the productivity of the overall system. The
interactions between these various processes of a manufacturing system are
complex. In conventional manufacturing systems, concept decisions, product
design, and prototyping are performed before manufacturing system design,
process planning, and production. Sequential engineering is the name given to
the traditional engineering design, when each stage is taken in turn and the
next step in sequence does not start until the previous step has been
completed. If an error is detected during this process then the design goes
back one or more steps to correct it. Although the tracking of design is easy,
the process is slow and expensive in terms of time to develop products. This is
also called the serial engineering or over the wall approach in which
inter-departmental cooperation is minimal.
Disadvantages of conventional systems including longer development time,
High level of development time and costs,
and low quality. According to the U.S. Institute of Defence Analysis ”
Concurrent Engineering is a systematic approach to the integrated, concurrent
design of products and their related processes, including manufacture and
support. This approach is intended to cause the developers, from the outset, to
consider all elements of the product life cycle from conception through
disposal, including quality, cost, schedule, and user requirements." As in
many other quality approaches, the implementation mechanism of CE is a team
work. Members from different departments including marketing, design,
engineering, and manufacturing, share
information and insights about the product to adjust the design and eliminate
the problems in early stages of product development. The use of multifunctional
teams is critical to concurrent engineering success. Japanese companies are
pioneers of using CE philosophy in developing the products with higher quality and much more quickly than
their western competitors. They incorporate different stages much more
concurrently. Since CE uses multi-disciplinary team and considers the product
and processes at the same time, it supports right-first-time designs which
address all the product requirements such as customer attributes,
functionality, reducibility, assimilability, maintainability, and recyclables.
Using the CE approach for product development, not only the number of redesigns
is reduced, but also changes are made at early stages of product development.
Integration of
KBS system for USM machining in computer
based CE environment is illustrated in Figure 1.
Figure1. Integration of all KBS, and d machines in a
computer based concurrent engineering
environment
3. KBS in computer based CE environment
A knowledge based system (KBS)
for ultrasonic machining (USM) has been developed in a computer based CE
environment, the latest version (3) of an expert system shell (NEXPERT), based
on object oriented techniques (OOT) is used to develop the knowledge-base. A Hewlett Packard (HP) model 715/80
workstation was used as the hardware for development of the expert
systems. A geometric specification of
the features of the component sent for manufacturability evaluation for the
various stages of its design. Within the
manufacturability procedure, the cost and cycle time and penetration rate of
USM is estimated. In the design of a
part, its features can be described in terms of its geometry, its particular
its volume and the amount of material has to be subsequently removed. The
attributes of six different classes of work piece materials, three type of
abrasive and two type of tool material are stored in database. The IKBS can
retrieve information from databases and advise the designer on the appropriate
choice of material, design feature description and machine type for his
decision. The IKBS also contains information for manufacturability evaluation,
Knowledge of design representation in three dimensions in terms of features,
rules for good practice, machine and process capabilities and constraints of
features that can be manufactured by a particular process. For the present KBS
knowledge has been gathered from experiments on USM at Edinbrough Universities
and also from technical journals and handbooks. For each design feature
undergoing evaluation for manufacturability by USM, the cost and time of the machine cycle, and penetration rate
and productivity is a major consideration.
4. Architecture of KBS
The KBS system contains USM expertise gathered from experiment and from
general knowledge about the process that can be provided to designers and
manufacturing engineers. The KBS
including:
3.1 Feature library: Feature
library, containing different classes of design features such as holes, slots
and pocket, each of which can be produced by USM.
3.2 Work piece material: Material library contains seven different
classes of material for work piece including glass, ceramics, hard metals with
hardness of (40 to 60 R), composites (e.g. glass epoxy), tungsten carbide,
graphite and stone that can be accepted by the system are stored in the system.
3.3 Abrasive solution: Properties of three main USM abrasive including
boron carbide (B4C), silicon carbide (SiC) and aluminium oxide (Al2O3)
are stored, so that the expert system can deliver information on process
conditions such as abrasive type, size, concentration and carrier fluid.
3.4 Tool material: Tool material library contains two different classes
of material including stainless steel
and mild steel.
3.5 Ultrasonic machines parameters: Information related to the other
machining parameters including wear ratio, mrr, frequency, amplitude vibration,
power range, and so on for each type of material for work piece are stored in
process data base.
3.6 Machining cycle time module: The knowledge base provides estimates
of cycle time and costs for each selected design feature, based on the selected
work piece and tool materials, abrasive and process conditions.
3.7 Manufacturability: The three elementary quantities associated with a
design feature is its size, machining time and cost are used to obtain the
penetration rate and productivity of each design feature or machining
operation. The created feature size is
depend on tool cross sectional area and
path needed to produce the design feature. The size of these features is specific in
terms of their volume which is equal to the amount of material removed from
work piece. The penetration rate shows
how fast a feature can be machined and expressed in unit of depth of operation
per unit time. Productivity expresses the volume of material removal per unit
of time. In this system, manufacturability is assessed by estimates of the
design features, machining time and cost, penetration rate, and productivity.
5. Experimental Verification
Results are presented in Table
1. The results of intelligent system
described above was compared with the
experimental result of ultrasonic hole drilling. The tool diameter is 15 mm and the depth of
holes are 2.6, 7.5, 10.0 and 12.0 mm. In
practical USM, estimates of machining time and cost, penetration rate and
productivity is time-demanding on experienced personnel. In contrast the knowledge-based system can
provide these estimates usually in less than one minute. For example, the intelligent result of a
circular hole making with different material type for work piece, abrasive and
tool for the same design feature specification is presented in Table 2.
Designers of manufacturing
engineers select work piece material and design feature from the work piece and
feature library. Then work piece specification and design description for each
selected design feature are obtained interactively by the IKBS. The system estimates all necessary
parameters such as spindle force, abrasive size, concentration, carrier fluid,
frequency, power, machining time and cost, penetration rate and
efficiency. Intelligent results of
different design features with different material type for work piece and
different tool and abrasive are presented in Table 3. All necessary parameters
including machining time and cost, penetration rate and efficiency is estimated
by the KBS. Other parameters such as wear ratio, spindle force, abrasive size,
concentration, carrier fluid, frequency, power are also recommended by the KBS.
Data for experimental: Frequency 20 kHz, Amplitude 40 μm, Static
force 3, Abrasive BC, Tool steel.
Data for intelligent system: Frequency 20 kHz, Amplitude 38 μm, tool
mild steel.
Conclusion
An Intelligent advisory and manufacturability evaluation for Ultrasonic
machining in concurrent engineering environment based on object oriented
technique has been developed. A feature based approach is used to obtain design
feature description. A feature library
is designed which contains different classes of design features. Attributes of six different type of material
for work piece, three most important type of abrasive, two different type of
material for tool, and description of different process parameters for each
type of material for work piece are stored in process data base. The
intelligent system is linked with these databases and able to advice designers
and manufacturing engineers. Design specification is interactively acquired by
the system. Then it gives some advice for optimal selection of process
parameters for each design feature. Then
the system automatically estimates machining (cutting) time, and cost,
penetration rate, and productivity for each individual feature and operation.
The current intelligent system can be
used to assist product designers to estimate machining cycle time and cost and
all other machining parameters mentioned above at the early stages of design
process and give some advices for improvement of design specification. It also assist manufacturing engineers to
select the optimal process parameters. In the developed system, both heuristic
and algorithmic procedures have been implemented. An experimental verification
has been conducted on USM. The developed system allows for additional more
detailed function modules or databases without altering the rest of the
knowledge base. The system is
user-friendly and can be used either by designer or USM experienced or those who need many guidance.