AMM MODEL TEST PAPER
Q1.(a)State the characteristics and function of dielectric fluid used in EDM.
In EDM, material removal mainly occurs due to thermal evaporation and melting.
As thermal processing is required to be carried out in absence of oxygen so that
the process can be controlled and oxidation avoided. Oxidation often leads to
poor surface conductivity (electrical) of the workpiece hindering further
machining. Hence, dielectric fluid should provide an oxygen free machining
environment. Further it should have enough strong dielectric resistance so that it
does not breakdown electrically too easily but at the same time ionise when
electrons collide with its molecule. Moreover, during sparking it should be
thermally resistant as well.
(bWhat are the various FMS components to be integrated while implementing
FMS in an industry?
Manufacturing cells)
driving force, Just-in-time manufacturing, Group technology,
rance Equipment( Turning centers, Machining
centers, Cleaning and deburring equipment, Coordinate measuring machines)
ge
systems, Cutting tools and tool management, Work-holding consideration)
hardware and general functionality,FMS software: structure, functions, and
description)
(c) Describe the characteristics of tool in EDM.
the basic characteristics of electrode materials are:
• High electrical conductivity – electrons are cold emitted more easily and there is
less bulk electrical heating
• High thermal conductivity – for the same heat load, the local temperature rise
would be less due to faster heat conducted to the bulk of the tool and thus less
tool wear
• Higher density – for the same heat load and same tool wear by weight there
would be less volume removal or tool wear and thus less dimensional loss or
inaccuracy
• High melting point – high melting point leads to less tool wear due to less tool
material melting for the same heat load
• Easy manufacturability
• Cost – cheap
(d)What is the effect of abrasive grain size on MRR in USM process?
An increase in abrasive grain size results in higher MRR but poorer surface finish.
Maximum MRR is achieved when abrasive grain size is comparable with
amplitude of vibration of the tool. Hardness of the abrasives and method of
introducing the slurry has also effect on MRR.
(e)Explain in brief the principle of Ultrasonic machining process?
In ultrasonic machining, tool of desired shape vibrates at ultrasonic frequency ( 19
to 25 kHz. ) with an amplitude of 15-50 Microns over work piece. Generally tool is
pressed down with a feed force F. Between the tool and work, machining zone is
flooded with hard abrasive particles generally in the form of water based slurry.
As the tool vibrates over the work piece, abrasive particles acts as indenter and
indent both work and tool material . Abrasive particles , as they indent , the work
material would remove the material from both tool and work piece. In Ultrasonic
machining material removal is due to crack initiation, propagation and brittle
fracture of material. USM is used for machining hard and brittle materials, which
are poor conductors of electricity and thus cannot be processed by
Electrochemical machining ( ECM) or Electro discharge machining (EDM).
(f) Identify the limitations of AWJM from environmental issues
Ans:• water recycling
• spent water disposal
• chip recovery
• abrasive recovery and reuse
(g)Discuss the applications of ECM?
ECM technique removes material by atomic level dissolution of the same by
electrochemical action. Thus the material removal rate or machining is not
dependent on the mechanical or physical properties of the work material. It only
depends on the atomic weight and valency of the work material and the condition
that it should be electrically conductive. Thus ECM can machine any electrically
conductive work material irrespective of their hardness, strength or even thermal
properties. Moreover as ECM leads to atomic level dissolution, the surface finish
is excellent with almost stress free machined surface and without any thermal
damage. ECM is used for Die sinking , Profiling and contouring , Trepanning,
Grinding, Drilling, Micro-machining
(h)
What are the advantages of advanced methods of machining over traditional
methods of machining?
Non-traditional manufacturing processes is defined as a group of processes that
remove excess material by various techniques involving mechanical, thermal,
electrical or chemical energy or combinations of these energies but do not use a
sharp cutting tools as it needs to be used for traditional manufacturing
processes.Extremely hard and brittle materials are difficult to machine by
traditional machining processes such as turning, drilling, shaping and milling. Non
traditional machining processes, also called advanced manufacturing processes,
are employed where traditional machining processes are not feasible, satisfactory
or economical due to special reasons as outlined below.
• Very hard fragile materials difficult to clamp for traditional machining
• When the work piece is too flexible or slender
• When the shape of the part is too complex
Several types of non-traditional machining processes have been developed to
meet extra required machining conditions.
(i)What are the factors affecting rate of machining in ECM?
Material removal rate, MRR, in electrochemical machining:
MRR = C .I. h (cm3/min)
C: specific (material) removal rate (e.g., 0.2052 cm3/amp-min for nickel);
I: current (amp);
h: current efficiency (90–100%).
The rates at which metal can electrochemically remove are in proportion to the
current passed through the electrolyte and the elapsed time for that operation.
Many factors other than current influence the rate of machining. These involve
electrolyte type, rate of electrolyte flow, and some other process conditions.
(j) ) Identify different modules of EDM system
• Dielectric reservoir, pump and circulation system
• Power generator and control unit
• Working tank with work holding device
• X-y table accommodating the working table
• The tool holder
• The servo system to feed the tool
(k) What is meant by CAPP? . List the activities associated with process planning?
CAPP refers to computer aided process planning. CAPP is used to overcome the
drawbacks of manual process planning. With the use of computers in the process
planning, one can reduce the routine clerical work of manufacturing engineers.
Also it provides the opportunity to generate rational, consistent and optimal
plans.
Activities associated with process planning:
1.Analysing finished part equipments
2. Determining operating sequence
3. Selecting machines
4. Selecting material parameters
5. Calculating process times
6. Documenting process planning
Q2.(a)Why are Advanced Machining / Material Removal Processes Needed?
With the advent of new materials and therequirements of complex features on
them,there was a necessity to develop new processes. Some of these features are:
1.Related to material properties:
 High hardness
 High strength
 High brittleness
2.Related to workpiece structure:
 Complex shapes
 Typical thin and delicate geometries
 Parts which are difficult in fixturing
3.Related to requirements in high surface finish and tight tolerances.
4. Related to controlling of temperature rise and residual stresses.
(b) What is Classification of Advanced Machining / Material Removal Processes?
These processes are referred to a typical group of advanced machining processes in
which the excess material is removed by non-traditional source of energy arising
from electrical, mechanical, thermal or chemical source. Most of these processes
don’t use a sharp cutting tool, as in the conventional case. Advanced material
removal processes are generally classified according to the type of energy used to
remove material. The classification of these processes based on the energy is given
as below: The processes based on use of are:
1.Electro-Chemical Machining (ECM),
2.Electro-Chemical Grinding (ECG),
The processes based on the use of Thermal Energy are:
Electric- Discharge Machining (EDM),
Wire-Cut Electric Discharge Machining (WEDM)
Laser Beam Machining (LBM),
Electron Beam Machining (EBM).
The processes based on the use of Mechanical Energy are:
Abrasive Flow Machining (AFM)
Abrasive Jet Machining (AJM),
Water Jet Machining (WJM),
Abrasive Water Jet Machining
Ultrasonic Machining (USM),
Ques 3: What is AJM. Explain principle of AJM with neat diagram. Give
advantage & disadvantage of AJM?
The principle of machining / cutting by abrasive jet process is explained through
the
following steps:
1. Abrasive particles of size between 10 m to 50 m (depending upon the
requirement of either cutting or finishing of the workpiece) are accelerated in a
gas stream (commonly used gas stream is air at high atmospheric pressures).
2. The smaller abrasive particles are useful for finishing and bigger are used for
cutting operations.
3. The abrasive particles are directed through the nozzle, towards the workpiece
surface where-ever cutting or finishing is to be done. The distance between the tip
of the nozzle and the work surface is normally within 1 mm.
4. As the abrasive particles impact the surface of the workpiece, it causes a small
fracture at the surface of the workpiece. The material erosion occurs by the
chipping action.
5. The erosion of material by chipping action is convenient in those materials that
are hard and brittle.
6. As the particles impact the surface of workpiece, it causes a small fracture and
wear, which is carried away by the gas along with the abrasive particles.
7. The abrasive particles once used, cannot be re-used as its shape changes partially
and the workpiece material is also clogged with the abrasive particles during
impingement and subsequent flushing by the carrier gas.
Advantage
AJM process is a highly flexible process wherein the abrasive media is carried
by
a flexible hose, which can reach out to some difficult areas and internal regions.
AJM process creates localized forces and generates lesser heat than the
conventional machining processes.
There is no damage to the workpiece surface and also the process does not have
tool-workpiece contact, hence lesser amount of heat is generated.
The power consumption in AJM process is low.
Disadvantages
The material removal rate is low
The process is limited to brittle and hard materials
The wear rate of nozzle is very high
The process results in poor machining accuracy
The process can cause environmental pollution
Q4.(a)
Q4.
(b)
Q5.(a)What is the working principle of ECM?Explain with a neat
sketch.Also state the process variables that effect the ECM process?
Working principle of Electrochemical Machining (Theory):
Electrochemical machining is based on the principle of outlined in Fig. 2, the
workpiece and tool are the anode and cathode respectively, of the electrolytic cell,
and a potential difference, usually at about 10 V, is applied across them. A suitable
electrolyte, for example aqueous sodium chloride solution is chosen so that the
cathode shape remains unchanged during electrolysis. The electrolyte is pumped at
a rate 3 to 30 m/sec through the gap between electrodes to remove the products of
machining and to diminish unwanted effects, such as those that arise with cathodic
gas generation and electric heating. The rate at which metal is then removed from
the anode is approximately in inverse proportion to the distance between the
electrodes. As machining proceeds, and with the simultaneous movement of the
cathode at a typical rate, for example, 0.02 mm/sec towards the anode, the gap
width along the electrode length will gradually tend to a steady-state value. Under
these conditions, a shape, roughly complementary to that of cathode, will be
produced on the anode. A typical gap width then should be about 0.4 mm.
Experimental set up
The number of process variables affects on the results of the ECM process are
1. tool feed rate 2. current density 3. electrolyte-type 4. Composition 5.
temperature, 6.flow rate 7. tool and fixture-material 8.construction and finish
9. work piece material condition 10. cutting gap
Q6.(a) Describe the basic mechanism of material removal in USM? What are
the components of USM?State the advantages,limitations and applications of
USM?
USM is generally used for machining brittle work material. Material
removal primarilyoccurs due to the indentation of the hard abrasive grits on
the brittle work material. As the tool vibrates, it leads to indentation of the
abrasive grits. During indentation, due to Hertzian contact stresses, cracks
would develop just below the contact site, then as indentation progresses the
cracks would propagate due to increase in stress and ultimately lead to brittle
fracture of the work material under each individual interaction site between
the abrasive grits and the workpiece. The tool material should be such that
indentation by the abrasive grits does not lead to brittle failure. Thus the
tools are made of tough, strong and ductile materials like steel, stainless steel
and other ductile metallic alloys.
(1) Ultrasonic transducer
(2) Concentrator
(3) Tool
(4) Abrasive slurry
(5) Abrasive feed mechanism
(6) Tool feed mechanism
Advantages
1. High accuracy and good surface finish
2. No heat generation during machining
3. Capability of drilling circular and non-circular holes in very hard
materials.
4. No thermal effects on mechanical work piece.
5. Non-conductive materials can be machined.
Disadvantages of USM?
1.Tool wear
2Frequent turning is required
3Low material removal rate.
4Not economical for soft materials.
5Not suitable for heavy stock removal.
Applications of USM:
1Almost all the material can be machined except some soft materials.
21Diamond, Tungsten, Tungsten carbide, and synthetic ruby
can be successfully machined.
3USM can be used for drilling, grinding, profiling, coining,
threading and even for welding.
4For preparing wire drawing dies and tool room items.
5Used in jewellery for shaping jewels
6Drilling of screw threads and curved holes in brittle
materials.
Q7.Write short notes on the following concepts in USM
1.ultrasonic transducer
2. piezoelectric crystals
3.magnetostrictive effect
4.Concentrator
The device used for converting any type of energy into ultrasonic wavers or
vibration is called ultrasonic transducer.
Piezoelectric crystals are used foe inducing ultrasonic vibrations since they posses
the capability of changing their dimensions to the given electrical energy or in
other sense they have the capability converting electrical energy into mechanical
vibrations.
It is the one in which the material changes its dimension is in response to a
magnetic field.the magnetostrivtive materials employed in USM Nickel, Iron –
cobalt called as permendum , iron – aluminum called as alter.
The main purpose of the concentrator is to increase the amplitude of the vibration
obtained from the transducer.
Q8. What is LBM?What is its working principle?Explain its process and state its
advantages and disadvantages?
Laser beam have wide industrial applications including some of the machining
processes. A laser is an optical transducer that converts electrical energy into a
highly coherent light beak. One must know the full name of laser, it stands for
“light amplification of stimulated emission of radiation”. Laser being coherent in
nature has a specific property, if it is focused by conventional optical lenses can
generate high power density.
Working Principle of LBM
LBM uses the light energy of a laser beam to remove material by vaporization and
ablation. The working principle and the process details (setup) are indicated in
Figure. In this process the energy of coherent light
beam is focused optically for predecided longer period of time. The beam is pulsed
so that the released energy results in an impulse against the work surface that does
melting and evaporation.
Here the way of metal removing is same as that of EDM process but
method of generation of heat is different. The application of heat is very finely
focused in case of LBM as compared to EDM.
Process Details of LBM
Laser Tube and Lamp Assembly
This is the main part of LBM setup. It consists of a laser tube, a pair of
reflectors, one at each end of the tube, a flash tube or lamp, an amplification
source, a power supply unit and a cooling system. This whole setup is fitted inside
a enclosure, which carries good quality reflecting surfaces inside. In this setup the
flash lamp goes to laser tube,
that excites the atoms of the inside media, which absorb the radiation of incoming
light energy. This enables the light to travel to and fro between two reflecting
mirrors. The partial reflecting mirror does not reflect the total light back and apart
of it goes out in the form of a coherent stream of monochromatic light. This highly
amplified stream of light is focused on the workpiece with the help of converging
lense. The converging lenses is also the part of this assembly.
Workpiece
The range of workpiece material that can be machined by LBM includes
high hardness and strength materials like ceramics, glass to softer materials like
plastics, rubber wood, etc. A good workpiece material high light energy absorption
power, poor reflectivity, poor thermal conductivity, low specific heat, low melting
point and low latent heat.
Cooling Mechanism
A cooling mechanism circulates coolant in the laser tube assembly to avoid
its over heating in long continuous operation.
Tool Feed Mechanism
There is no tool used in the LBM process. Focusing laser beam at a
pre-decided point in the workpiece serve the purpose of tool. As the
requirement of being focused shifts during the operation, its focus point can
also be shifted gradually and accordingly by moving the converging lense in a
controlled manner. This movement of the converging lense is the tool feed
mechanism in LBM process.
Applications of LBM
LBM is used to perform different machining operations like drilling, slitting,
slotting, scribing operations. It is used for drilling holes of small diameter of the
order of 0.025 mm. It is used for very thin stocks. Other applications are listed
below :
(a)Making complex profiles in thin and hard materials like integrated
circuits and printed circuit boards (PCBS).
(b)Machining of mechanical components of watches.
(c)Smaller machining of very hard material parts.
Advantages of LBM
(a)Materials which cannot be machined by conventional methods are machined by
LBM.
(b)There is no tool so no tool wear.
(c)Application of heat is very much focused so rest of the workpiece is least
affected by the heat.
(d)Drills very find and precise holes and cavities.
Disadvantages of LBM
Major disadvantages of LBM process are given below :
(a)High capital investment is involved. Operating cost is also high.
(b)Recommended for some specific operations only as production rate is
very slow.
(c)Cannot be used comfortably for high heat conductivity materials light
reflecting materials.
(d)Skilled operators are required.