Transcript MT-284 MANUFACTURING PROCESSES

MT-284
MANUFACTURING PROCESSES
INSTRUCTOR:
SHAMRAIZ AHMAD
MS-Design and Manufacturing Engineering
[email protected]
Topic:
Non-conventional Machining Processes
By: Engr. Shamraiz
This Lecture
• Non-conventional machining processes
– Introduction to Non-conventional machining
– Need of development of NCM-processes
– Classification of NCM-Processes
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Mechanical energy based processes
Electro-chemical processes
Thermal energy based processes
Chemical energy based non-conventional
By: Engr. Shamraiz
Introduction
Non-conventional Machining (NCM)Processes
• Conventional machining processes (like turning,
drilling ,milling) use a sharp cutting tool to chip
from work piece by shear deformation.
• Non-conventional machining processes refer to
group of processes that removes excess of
material by various techniques involving different
forms of energies ( like mechanical, thermal,
electrical, chemical or combination of these
energies). They don’t use sharp cutting tool like
conventional machining.
By: Engr. Shamraiz
Need of NCM-Processes
1. To machine newly developed metal and non-metals having
special properties ( high strength, high hardness and high
toughness)
2. To machine complex part geometries which are difficult or
impossible to machine with conventional methods such as
internal and external profiles, or small diameter holes
3. The need to avoid surface damage as stresses are created in
conventional machining processes
4. Surface finish or tolerance better than those obtainable
conventional process.
5. The work piece is too flexible or slender to support the
cutting or grinding forces.
6. These approaches are specially used in aerospace and
electronics industry which is developing at fast pace.
By: Engr. Shamraiz
Classification of NCM-Processes
These processes are often classified according to form of energy used
to affect material removal. According to this criteria there four major
types:
i.
ii.
iii.
iv.
v.
vi.
vii.
viii.
ix.
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xi.
xii.
xiii.
xiv.
Ultrasonic machining
Mechanical energy
Water jet cutting
Abrasive water jet cutting based machining
Abrasive jet machining
Electrochemical machining
Electro-Chemical
Electrochemical deburring and grinding based
Electrical discharge machining
Electrical discharge wire cutting
Electron beam machining
Thermal energy
Laser beam machining
Based processes
Plasma arc cutting process
Oxyfuel cutting process
Chemical milling, blanking and engraving
Chemical energy based
Photochemical machining
By: Engr. Shamraiz
Classification & Overview of NCM
By: Engr. Shamraiz
A. Mechanical based NCM-Processes
• Mechanical energy in some form different
from action of cutting tool.
• For example, erosion of work material by a
high velocity stream of abrasives, fluids or
both.
• Types under this category are:
i.
ii.
iii.
iv.
Ultrasonic machining
Water jet cutting
Abrasive water jet cutting
Abrasive jet machining
By: Engr. Shamraiz
1. Ultrasonic Machining
Definition: It is a mechanical based non-conventional
machining process also called as ultrasonic impact
grinding, in which a vibrating tool oscillating
at ultrasonic frequencies is used to remove material from
the work piece, aided by an abrasive slurry that flows
freely between the work piece and the tool.
• The tool oscillates perpendicular to the work surface and
is fed slowly into the work piece so that shape of tool is
formed in the part.
• The tool never contacts the work piece.It is the action of
abrasives against work surface which performs the
cutting
By: Engr. Shamraiz
ULTRASONIC MACHINING
• The typical elements of an USM are in below figure.
• Slurry delivery and return system
• Feed mechanism to provide a downward feed force on the tool during
machining
• The transducer, which generates the ultrasonic vibration
• The horn or concentrator, which mechanically amplifies the vibration to
the required amplitude of 15 – 50 μm and accommodates the tool at its
tip.
By: Engr. Shamraiz
ULTRASONIC MACHINING
• Generally the tool is pressed downward with a feed force, F.
Between the tool and workpiece, the machining zone is
flooded with hard abrasive particles generally in the form
of a water based slurry.
• The abrasive grains are usually boron carbides.
• As the tool vibrates over the workpiece, the abrasive
particles act as the indenters and indent both the work
material and the tool.
• USM is mainly used for machining brittle materials
(ceramics, carbides, glass, precious stones and hardened
steel) which are poor conductors of electricity and thus
cannot be processed by Electrochemical and Electrodischarge machining (ECM and ED).
By: Engr. Shamraiz
2. Water Jet Machining
• Water jet machining uses a fine, high
pressure, high velocity stream of water
directed at the work surface to cause cutting
of work. It also termed as hydrodynamic
machining.
• To obtain fine stream of water a nozzle with
0.1 to 0.4 mm diameter is used
• To provide sufficient energy to stream for
cutting pressure up to 400MPa is used and
• Jet stream reaches velocity up to 900m/s.
By: Engr. Shamraiz
WATER JET MACHINING
By: Engr. Shamraiz
Water jet machining (WJT)
• Water jet acts like a saw and cuts a narrow groove in the
material.
• The nozzle is made up of sapphire or diamond
• Advantages
- no heat produced
- cut can be started anywhere without the need for
predrilled holes
- burr produced is minimum
- environmentally safe and friendly manufacturing.
• Application – used for cutting composites, plastics, fabrics,
rubber, wood products etc. Also used in food processing
industry.
By: Engr. Shamraiz
Water Jet Machining
Other form of water jet machining
• In Abrasive water jet machining (AWJM) the
water jet contains abrasive particles such as
silicon carbide or aluminum oxide
• They increase the material removal rate over that
of water jet machining.
• Metallic, non-metallic & composite materials of
various thickness can be cut into single or
multiple layers.
By: Engr. Shamraiz
B. Electro-chemical machining processes
• In this category, the electrical energy is used
in combination with chemical reaction to
accomplish material removal.
• These processes are reverse of electroplating.
• The work material must be conductor in
electro-chemical machining
• These include:
i. Electrochemical machining
ii. Electrochemical deburring and grinding
By: Engr. Shamraiz
1. Electro-chemical machining
• Electro-chemical machining removes material from an
electrically conductive workpiece by anodic dissolution, in
which the shape of workpiece is obtained by a formed
electrode tool, in close proximity but separate from work by a
rapid flow of electrolyte.
• It s basically a deplating operation, in which work piece is
anode and tool is cathode.
• The principal is that the material is removed from anode (the
positive pole) and deposited on cathode (the negative pole) in
the presence of electrolyte.
By: Engr. Shamraiz
ELECTROCHEMICAL MACHINING
Electro-chemical machining
• An electrolyte acts as a current carrier and high electrolyte
movement in the tool-work-piece gap washes metal ions away
from the work piece (anode) before they have a chance to
plate on to the tool (cathode).
• Tool – generally made of bronze, copper, brass or stainless
steel.
• Electrolyte – salt solutions like sodium chloride or sodium
nitrate mixed in water.
• Power – DC supply of 5-25 V.
By: Engr. Shamraiz
Advantages of Electro-Chemical Machining
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Process leaves a burr free surface.
Does not cause any thermal damage to the parts.
Lack of tool force prevents distortion of parts.
Capable of machining complex parts and hard materials
ECM systems are now available as Numerically Controlled
machining centers with capability for high production, high
flexibility and high tolerances.
By: Engr. Shamraiz
C. Thermal energy processes
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These processes are based on high local temperature-hot
enough to remove material by fusion or vaporization.
Because of high temperature these processes cause
physical and metallurgical damage to the new work
surface.
In some cases for this rough surface subsequent finishing
operations are required.
These processes include:
i.
ii.
iii.
iv.
v.
vi.
Electrical discharge machining
Electrical discharge wire cutting
Electron beam machining
Laser beam machining
Plasma arc cutting process
Oxyfuel cutting process
By: Engr. Shamraiz
1. Electrical discharge machining (EDM)
• One of the most widely used non-traditional
process.
• The shape of finished work piece is produced by
formed electrode tool. The sparks occur across a
small gap between tool and work surface.
• EDM process must take place in presence of
dielectric fluid, which creates a path for each
discharge as the fluid becomes ionized in the gap.
• The discharges are created by pulsating direct
current power supply connected to the work and
the tool.
By: Engr. Shamraiz
ELECTRICAL DISCHARGE MACHINING
By: Engr. Shamraiz
ELECTRICAL DISCHARGE MACHINING
• Based on erosion of metals by spark discharges.
• EDM system consist of a tool (electrode) and work piece,
connected to a dc power supply and placed in a dielectric
fluid.
• when potential difference between tool and work piece is
high, a transient spark discharges through the fluid, removing
a small amount of metal from the work piece surface.
By: Engr. Shamraiz
ELECTRICAL DISCHARGE MACHINING
• dielectric fluid – mineral oils, kerosene, distilled and deionized
water etc.
role of the dielectric fluid
1. acts as a insulator until the potential is sufficiently
high.
2. acts as a flushing medium and carries away the debris.
3. also acts as a cooling medium.
• Electrodes – usually made of graphite.
• EDM can be used for die cavities, small diameter deep holes,
and various intricate shapes.
By: Engr. Shamraiz
ELECTRICAL DISCHARGE MACHINING
Other form of EDM:
• Electric Discharge Wire cutting, commonly known as wire
EDM, is special form of EDM that uses a small diameter wire
as the electrode to have narrow cuts in work piece.
• The wire is usually made up of brass, copper or tungsten and
is typically about 0.25 mm in diameter.
By: Engr. Shamraiz
D. CHEMICAL MACHINING
• In this category, material removal occurs
through contact with strong chemical etchant.
• Use of chemical to remove unwanted material
from work piece wan be applied in several
different ways for different applications
• These processes are:
i. Chemical milling, blanking and engraving
ii. Photochemical machining
By: Engr. Shamraiz
Chemical Machining
Steps performed in chemical based machining
1. Cleaning: work surface is cleaned to ensure that material
will be removed uniformly
2. Masking: protective coating applied to certain portion of
the part surface where etching is not required. This
maskant is made of chemical resistant material (normally
polymers).
3. Etching: This is the material remocing process. Checmicals
attached the surface not having masks and remove
material by dissoling it it.
4. Demasking: when required etching is done, part is
removed from system and washed. Finally the mask is
removed.
By: Engr. Shamraiz
Chemical Processes
1. Chemical Milling and Blanking
1. chemical Milling
By selectively attacking different areas of
work piece with chemical reagents shallow cavities
can be produced on plates, sheets, forging and
extrusion. Largely used in air craft industry.
2. chemical blanking
It is similar to blanking in sheet metals
except material is removed by chemical dissolution
rather than by shearing. Used in bur free etching of
printed circuit boards, decorative panels etc.
By: Engr. Shamraiz
Chemical Processes
• Issues: Chemical milling result in
uneven surfaces and non uniformity
of structure.
By: Engr. Shamraiz
Thank you
By: Engr. Shamraiz