UNIT 4 MACHINING AND ROBOTICS Flashcards
Machining
process of removing the excess material from the work piece in the form of
chips, by forcing the cutting tool with one or more cutting edges.
continuous chips = ductile
discontinuous = brittle
- A secondary process
MACHINE TOOL major functions
-rigidly supports the work piece and cutting tool
-Provides relative motion between work piece and cutting tool
-Provides range of speeds and feeds
cutting tool removes the
material by moving i parallel to rotation => turning.
final object formed is a cylinder. achieved by rotating the work piece
LATHE
WORKING PRINCIPAL OF LATHE:
a cutting tool that can remove material in the form of chips from the rotating work pieces to produce circular objects
oldest machine(mother of all machines)
(most common) work piece is clamped by centres (live (rotating) and dead centres(non rotating, fixed))
parts of LATHES
- BED: backbone, where all components mounted, made of cast iron due to good daming etc
HEADSTOCK (LIVE CENTRE):
box like casting mounted, has a spindle which rotates
mounted on left side
contains feed gear box or cone pulley which enables
the spindle to rotate at different speeds
gear box distributes the power to the lead screw
for threading or to the feed rod for turning
TAILSTOCK (DEAD CENTRE)
mounted on right side
movable part, (can house drills etc)
can be slided on the bed to support different length
of work piece
can be clamped on the bed at desired
location.
FEED ROD
long shaft used to drive the apron mechanism for cross and longitudinal power feed during turning. powered by the set of gears from the headstock.
LEAD SCREW
long threaded shaft geared to the headstock. Closing a split nut around the lead screw engages it with the carriage. The lead screw is used for cutting thread accurately and should be disengaged for other operations.
AXIAL FEED=> rotation of tool via lead screw
CARRIAGE ASSEMBLY
CARRIAGE ASSEMBLY:
supports the cutting tool and enables controlled movement along and across the workpiece. and also feeds tool
MAIN PARTS ARE:
SADDLE: can slide back and forth along bed slide ways thus tool will move parallel to the spindle axis.
CROSS SLIDE: On the upper surface of the saddle, moves the tool at right angle to spindle axis.
used to reduced diameter of workpiece
either be operated by the by cross slide hand wheel or by apron mechanism.
COMPOUND REST: mounted on the upper surface of the cross slide. can be swiveled so that the tool can move at an angle to the spindle axis.
TOOL POST: mounted on the compound rest and carries the cutting tool.
LATHE operations
Axis of rotation: straight line around which an object rotates or spins.
PLAIN TURNING
work held in spindle is rotated while the tool is fed parallel to the axis of rotation. The surface
generated is cylindrical
DONE IN 2 STAGES
Rough turning:
majority of material removal and done at high speeds
smooth turning:
done at lesser speeds
and involved in finishing the given job
FACING
operation for generating flat surface
feed is perpendicular to the axis of revolution.
tool should have a suitable approach angle so it wont interfere with the work piece during the tool feeding.
Lathe operations continued
Thread cutting
THREAD CUTTING
A screw thread => a structure of uniform cross section
that follows a helical or spiral path on the outside or inside of cylindrical surface.
tool is
mounted on a holder and moved along the
length of the workpiece by the lead screw on the lathe.
tool shape depends on type of thread to be cut
movement is achieved by split nut/half which is locked onto the lead screw nut inside the apron of the lathe.
The axial movement of the tool in relation to the rotation of the workpiece determines the pitch of the screw thread.
When the lead screw rotates a single revolution, the carriage travels a
distance equal to the pitch of the lead screw
if the rpm of the lead screw is = spindle (of workpiece), the pitch of the
resulting cut thread is exactly equal to that of the lead screw
pitch of the resulting thread being cut,
depends upon the ratio of the RPM of the lead screw
and the spindle.
FORMULA
pitch of lead screw/Desired pitch of workpiece
= rpm of workpiece/rpm of lead screw
taper turning
Taper turning is the process of producing a conical surface from a cylindrical shaped
workpiece.
tana = (D1-D2)/2L
taper turning can be done:
● form tools
The feed is given by plunging the tool directly into the work.
useful for short tapers, where the steepness is of
no consequence, such as for chamfering.
● swivelling the compound rest
possible to swivel the compound rest to the desired angle of the taper for cutting the tapers. The compound rest has a circular base graduated in degrees.
tool is then made perpendicular to the work piece and feed is given
manually by the operator.
Some of the features of this method are:
●Short and steep tapers can be easily done.
●Limited movement of the compound rest
●Feeding is by hand and is non-uniform. This is responsible for low
productivity and poor surface finish.
● offsetting the tailstock
By offsetting the tailstock, the axis of rotation of the job is inclined by the half
angle of taper
The feed to the tool is given in the normal manner parallel to the guideways.
Thus the conical surface is generated. The offset that is possible is generally
limited, and as such this method is suitable for small tapers over a long length.
disadvantage:
centres are not properly bearing in the centre holes (work piece) and as such there would be non-uniform wearing taking place.
● using taper turning attachment
a separate slideway is arranged at the rear of the cross slide.
slide can be rotated at any angle to be setup. The block that can slide in
this taper slide way is rigidly connected to the cross slide.
As the carriage moves for feeding, the block moves in the inclined track of
the slide, it gets the proportional cross movement perpendicular to the feed direction, the cross slide and in turn the cutting tool gets the proportional movement. Thus the tool tip follows the taper direction set in the attachment.
This method is most commonly used for a range of tapers.
Knurling and parting
a knurling tool having serrations is forced on to the
work piece material, thus deforming the top layers. This forms a top
surface, which is rough and provides a proper gripping surface.
PARTING
a flat nosed tool
would plunge cut the work piece with a feed in the direction perpendicular to the axis of revolution.
generally carried out for cutting off the part from the parent material.
WORK HOLDING DEVICE
common work holding device => chuck.
Of these the three jaw chuck or the self-centering chuck or most common
adv:
quick way in which the typical round job is centred. All the three jaws move radially inward or outward by the same
amount.
the jaws will be able to centre any job, whose external locating surface
is cylindrical symmetrical,ex: hexagonal
4JAWS
independent jaw chuck has four jaws, which can be moved in their slots
independent of each other, thus clamping any type of configuration. any irregular surface could be effectively centred
LATHE specifications, and types of lathes
parameters could be used based on the specific application.
● Distance between centres (L) — max L of the job that can be turned in the lathe.
● Swing over the bed (H) — max diameter of the job (A)
that can be turned, generally restricted to small length jobs.
● Swing over the cross slide (H-h) — max diameter of the job (B) that can be turned with the job across the cross slide,
TYPES OF LATHES
BENCH LATHE: a small centre lathe that is
mounted on a workbench.
same features as centre lathes, adapted to small work, used for small precision work like instrument parts.
CAPSTAN AND TURRET LATHE:
has a 6 sided (hexagonal) block mounted on one end of the bed replacing the normal tailstock
allows for mounting six tool blocks each of which can contain one or more tools depending upon the requirement.
Further on the cross slide, two tool posts are mounted, one in the front and the other in
the rear. Each one of them can hold up to 4 tools each. Thus, the total carrying capacity is a maximum of 14 tools when only one tool is mounted in each of the
locations.
The turret is mounted on a saddle, which in turn is sliding on the bed. When the saddle moves on the bed during the return stroke it would automatically be indexed to the next tool position, thus reducing the idle time of the machine.
GAP LATHE
It is used for machining large work with irregular protrusions. On this lathe, a section of bed, adjacent to the headstock can be removed to machine a large size workpiece.
DRILLING
operation of making primarily a hole in a workpiece using a drill bit.
stationary work is held in a fixture and rotating tool is fed vertically to make a circular hole.
cutting tool used for making holes in solid material => twist drill.
drill has =>
body of the cutting edges and the shank which is used for holding. has two cutting edges and two opposite spiral flutes cut into its surface.
flutes serve to provide clearance to the chips produced at the
cutting edges. They also allow the cutting fluid to reach the cutting
edges
TYPES OF DRILLING
Radial Drilling Machine:
drill head can move along the radial arm to any position while the radial
arm itself can rotate on the column, thus reaching any position in the radial
range of the machine.
used for large work pieces, which cannot be moved easily
drill head itself will be
moved to the actual location on the work piece,
Gang Drilling Machine
have a number of spindles laid out in parallel
Each of the spindles can have different drills or other hole making operation tools fixed in sequence.
used for volume production with the work pieces located in a jig.
Types of drilling machines
Reaming: finishing a previously drilled hole to bring it to a more exact size and to improve the surface finish of the hole
=>using a multi tooth revolving tool called reamer
=> has a set of parallel straight or helical cutting edges along the length of the body.
speed is reduced while reaming, 1/2 of that of drilling
Boring:
operation of enlarging a hole.
single point cutting tool is mounted in the
boring bar of suitable diameter should match the diameter to be bored
brings the hole to the proper size and finish.
A drill or reamer used if the desired size is “standard”
boring tool can work
to any diameter
required finish by adjusting speed and
feed.
Correcting Hole Location:
When a pre-drilled or cast hole is not perfectly aligned with its intended centerline, boring can be used to adjust its location.
Tapping
faster way of producing internal threads
tap => multi fluted cutting tool with cutting edges on each blade of the shape of threads to be cut
used after carrying out the pre-drilling operations
care has to be taken to see that the tap is started in proper alignment
may become necessary to reverse the tap slightly to break the chips
Counter boring
hole is enlarged with a flat bottom
to provide proper seating for the bolt head or a nut
tool=> cutting edges present along the side as well as the end
pilot portion is present for the tool to enter the hole, to provide the concentricity(same centre) with the hole.
pilot should fit snugly in the hole and should have sufficient clearance
facilitating the free movement of the tool.
speeds slower than other drilling operations.
Counter sinking:
extra machining done on a hole is conical
for the counter sunk machine screw head.
the depth of counter sinking should be large enough to accommodate
the screw head fully flush with the surface.
Milling
work piece is fed into a rotating milling cutter, which is a multi-point tool
unlike a lathe, which uses single point cutting tool. milling cutter is used here.
classified into:
peripheral milling:
the surface generated is parallel with the axis of rotation of cutter. carried out in Horizontal milling machine.
face milling :
surface generated is at right angle to the cutter axis. carried out in Vertical milling machine.
HORZIONTAL VS VERTICAL MILLING MACHINE DIFFERENCES ESA
HORIZONTAL:
Spindle is horizontal and parallel to the worktable
Cutter cannot be moved up and down
Cutter is mounted on the arbor
Spindle cannot be tilted
Operation such as plan milling, gear
cutting, form milling, straddle, gang
milling etc.., can be performed
VERTICAL
Spindle is vertical and perpendicular to
the worktable
Cutter can be moved up and down
Cutter is directly mounted on the spindle
Spindle can be tilted for angular cutting
Operation such as slot milling, T- slots,
flat milling and also different drilling
operations can be performed
Up and down milling
Based on the directions of movement of the milling cutter and the feeding direction of the work piece
Up milling: the cutting tool rotates in the opposite direction to the table movement. tends to lift the work piece from the table.
Down milling: the cutting tool rotates in the same direction as that of the table movement. The cutting force will act downwards and as
such would keep the work piece firmly in the work holding device.
UP milling vs down milling
UP MILLING
In up milling cutter rotates against the direction of feed
In this process, heat is diffused to the work piece which causes the change in metal properties
Progressive chip formation
DOWN MILLING
Cutter rotates with the direction of feed
In down milling most of the heat diffuse to the chip without change the work piece properties
Chip size is maximum at start and decreases with the feed
Milling operations
SLAB MILLING
- The basic form of peripheral milling in which the cutter width extends beyond the workpiece on both sides.
SLAB MILLING
- the width of the cutter is less than the workpiece width, creating a slot in the work (when the cutter is very thin, this operation can be used to mill narrow slots).
SIDE AND STRADDLE MILLING
- Side milling – Cutter machines on the side of the workpiece.
- Straddle milling – same as side milling, but cutting takes place on both sides of the work.
FORM MILLING
- milling teeth have a special profile that determines the shape of
the slot that is cut in the work.
ANGULAR MILLING
- operation of producing angular surface on the workpiece. A single or double cutter can be used to produce shapes like V grooves in the V- blocks
END MILLING
operation performed for producing flat surfaces, slots, grooves or finishing the edges of the workpiece by a tool: end mill or end milling cutter.
The cutter has teeth on the end as well as the periphery (sides) and can be configured to cut with both its end and the sides.
Profile milling - A form of end milling in which the outside periphery of a flat part is cut
Pocket Milling - Another form of end milling used to mill shallow pockets into flat parts.
Surface Contouring - A ball-nose cutter (rather than squareend cutter) is fed back and forth across the work along a curvilinear path at close intervals to create a 3-dimensional surface form.
used to produce tooling such as injection molds and forming dies.
Grinding
a grinding wheel => abrasive grains for removing very fine quantities of material from the work piece surface.
used for
● Machining materials => too hard for other machining processes
● Close dimensional accuracy
● High degree of surface
classified based on the type of surface produced. ● Cylindrical grinding
● Surface grinding =>
flat surfaces
● Centre less grinding for
generating axi-symmetric shapes.
cylindrical grinding machine is used => external cylindrical surfaces. similar to centre lathe.
grinding wheel is located similar to the tool post, with an independent power driven at high speed .Both the work and the grinding wheel rotate counter clockwise.
The work held btw centres => rotated at much lower speed compared to that of the grinding wheel.
Centre less grinding => grind cylindrical work pieces without actually fixing the work piec . thus no work rotation is separately provided.
consists of two wheels, one large grinding wheel and another smaller regulating wheel. work is held on a work rest blade. The regulating wheel is mounted at an angle to the plane of the grinding wheel.
The centre of the work piece is slightly above the centre of the grinding wheel. work piece supported by the rest blade -> held against regulating wheel by the grinding force.
thus work rotates at the same surface speed as as regulating wheel. axial feed of the work piece is controlled by the angle of tilt of the regulating wheel.
NUMERICAL CONTROL
Numerical control of machine tools => a method of automation in which functions of machine tools are controlled by letters, numbers and symbols.
runs on a program fed to it.
program => precise instructions about the methodology of manufacture as well as the movements.
detailed step by step commands that direct the actions of the processing equipment.
For ex what tool, speed, at feed and to move from which point to which point in what path, rate of movement of tool tip.
BASIC COMPONENTS
The program of instructions is the
program of instructions => part program.
individual commands => positions of a cutting tool relative to the worktable
Addit. instructions spindle speed, feed rate, (etc)
BASIC COMPONENTS OF NC SYSTEM
NC system whose machine control unit -> on dedicated microcomputer rather than hard-wired controller.
components:
(1) CPU
(2) memory,
(3) I/O interface.
(4) controls for machine tool axes, spindle speed
(5) sequence controls for other machine tools
interconnected by system bus.
CNC MACHING CENTRES
computer controlled => performs variety of cutting operations on diff surfaces and directions on a workpiece.
2 TYPES:
Vertical axis machining centre:/VMC
more versatile
the tool generate more complex surfaces then horizontal axis.
come with 3 axes. Additional axes=>more complex geometries.
Horizontal axis machining centre/HMC
sturdier than the VMC
for heavier work pieces with large metal removal rates.
thus cutting tools => big.
tool magazine -> larger place for each tool.
tool magazines =>heavier.
->Accuracy and tolerances of the order +- 0.0025mm
RPM -> 25,000
->less floor space, improved productivity, quick change of tools
->tool-condition monitoring devices
CNC TURNING CENTRE
Major components => cylindrical
Hence CNC lathes, OR turning centres, are IMP machine tools.
turning centres => tool turret => capacity 8 -12 tools
ROBOTICS
“an automatically controlled,
reprogrammable, multipurpose manipulator programmable in 3 or more axes, which may be either fixed in place or mobile for use in industrial automation applications
can be substituted for humans in hazardous or uncomfortable work environments
performs its work cycle with consistency and repeatability, HUMANS CANT
When current task is completed =>can be reprogrammed => equipped necessary tools => altogether different task
controlled by computers => connected to other computer systems => computer integrated manufacturing
TYPES OF ROBOT LINKS
connection of different manipulator joints =>Robot Links
classified into =>input linkandoutput link
joints that can be classified:
2 types =>translational motion
3 types => rotary motion
Rotational joint
Linear joint
Twisting joint
Orthogonal joint
Revolving joint
Types of robot joints
integration of two or more link =>Robot Joints => form ofsolid material,
∥=parallel
⊥=perpindicular
joints can be classified:
=>translational motion
=>rotary motion
Rotational joint
Type R joint: rotational relative motion, with the axis of rotation ⊥ to the axes of the INP and OUT links
Linear Joint (Type L joint) relative movement btw INP and OUT link =>
translational sliding motion, the two links axis is ∥
Twisting joint: (Type T joint) => rotary motion, axis of rotation is ∥ => to 2 links axis (in a twisting manner)
Orthogonal joint:
Type O joint; relative movement btw, INP, OUT link => translational sliding motion, OUT link is ⊥ to the INP link
Revolving joint:
Type V joint; axis of INP link ∥ to axis of rotation of joint, OUT link axis ⊥ to axis of rotation
OUT=> output, INP=INPUT
Robot Configurations,
WRIST CONFIG
robot manipulator =>two sections: body and arm, wrist assembly
end of manipulator’s wrist -> a device related to task => is end effector =>
1) a gripper for holding a work part
2) a tool for performing process.
body and arm of the robot => position the end effector and robot’s wrist => to orient the end effector.
Wrist Configurations
used to establish the orientation of the end effector.
3 joints are defined as:
Roll, using a T joint =>
rotation about arm axis
Pitch, up and down rotation, a R joint
Yaw, right and left rotation, by R - joint.
Material handling applications –
1) Material transfer Machine loading/unloading
Processing Operations – Spot welding, Continuous arc welding, Spray painting etc.
Assembly and Inspection
Body Arm Configurations:
Cartesian coordinate rectilinear, x – y – z robot => composed of 3 sliding joints, two = orthogonal.
Cylindrical configuration:
vertical column, relative arm assembly is moved up or down, in and out relative to axis of column.
column can be rotated about it’s axis
Polar configuration –
a sliding arm (L joint) actuated relative to body, can rotate about vertical axis (T joint) and horizontal axis (R joint).
JOINTED ARM
vertical column that swivels about the base (T joint). top column => shoulder joint an R joint OUT link connects to an elbow joint R joint). = to human arm
SCARA –Selective Compliance Assembly Robot Arm.
similar to jointed arm robot except shoulder elbow rotational axes are ↑=> arm is very rigid in the ↑ direction, but compliant in → direction. permits the robot to perform insertion tasks in a ↑ direction, where some side to side alignment may be needed .
AUTOMATION
tech by which a process or procedure is accomplished without humans assist.
power required, both => drive the process and operate the program and control system
most used in
manufacturing industries:
operate in factory on the physical product
operations: processing, assembly, inspection, material handling,
some cases more than one operations in same system
ELEMENTS OFAUTOMATED
SYSTEM
3 basic elements:
power for process and to operate the system
program of instructions => direct the process
a control system to actuate the instructions
Types of automation
FIXED automation:
system -> sequence of processing (or assembly) is fixed
Features:
High initial investment
High production rates
inflexible in products changes
PROGRAMABLE
change sequence of operations => for diff product configs. => each product =>reprogramming
New programs can be entered into the equipment => new products
low and medium- volume
products made:
features
High investment
Low production rates relative to fixed automation
Flexibility to deal with changes in product configuration
Most suitable for batch production
FLEXIBLE AUTOMATION
extension of programmable automation
variety of products (or parts) => no time lost for changeovers from one product to next
no production time lost while reprogramming and altering the physical setup (machine setting, tooling)
continue production without downtime btw batches
features
High investment
mixtures of products
Medium production rates
Flexibility => product design variations
Amount of parts:
Fixed -> Flexible -> program
VARIETY OF PARTS
program ->Flexible -> Fixed
Control Systems
quantity of interest in a machine, mechanism or other equipment is maintained or altered in accordance with a desired manner
EX: homeostasis of body
OPEN AND CLOSED LOOP CONTROL SYSTEMS
Open-loop control systems
operate based on input without monitoring output. easy to design and implement. cannot correct errors dynamically. relies on initial calibration. Ex include microwaves and electric fans.
Closed-loop control
use feedback to monitor and adjust output. checks temp diff etc, diff btw the actual temp and the required temp, to maintain the temp of the room constant.
higher accuracy, require sensors and feedback mechanisms. adapt to disturbances for stable operation.
Ex include thermostats and cruise control.
BASIC ELEMENTS OF A CONTROL SYSTEM
Comparison element – compares the required or reference value of the variable condition being controlled with measured value of what is being achieved and produces an error signal.
Error signal = reference value signal – measured value signal
Feedback loop – a signal related to the actual condition being achieved is fed back to modify the input signal to a process.
Control unit – decides what action to take when it receives an error signal.
Correction unit – produces a change in process to correct or change the controlled condition.
Process unit – The process which is being controlled.
Measurement unit – produces a signal related to the variable condition of the process that is being controlled.
Sensors and Transducers
element which produces a signal relating to the quantity being measured.
transducer: an element that when subject to some physical change experience a related change
MICROPROCESSOR BASED CONTROLLERS
to carry out control functions.
simple systems there => embedded microcontroller => memory all integrated on one chip=> specifically programmed for the task
programmable logic controller:
uses programmable memory to store instructions and to implement functions such as logics etc
Actuators
elements of control systems =>transforming output of microprocessor or control system => controlling action on a machine or device.
Ex – electrical output from the controller => linear motion to move a load
Industry 4.0
“a name for the current trend of automation and data exchange in manufacturing technologies
Industrial Internet of Things (IIoT)
interconnection of a large number of industrial processes and systems, communicate and coordinate among themselves.
real time data collected from sensor nodes are stored, processed, and analysed to improve the performance and efficiency of the overall system.
Applications (IIoT)
Smart healthcare – Sensor nodes sense and transmit the physiological data of the patient to the local processing unit. Further, the LPU transmits the data to the local server. Medical experts can remotely observe the health conditions of the patient.
Smart supply chain - Proper maintenance of the raw materials, available inventory stock, details of each steps involved in the production process, proper flow of information among various stages , maintaining the time window for delivery of goods, and returning the faulty goods.
Smart transportation – The sensor nodes placed on the vehicles and road side units (RSU) sense and transmit data to the local server. Various real time info such as safe speed, safe distance with the neighboring vehicles, and weather conditions are conveyed to the drivers. (ITS and ADAS)
4) Smart manufacturing system – These improve the efficiency of production and product quality, reduce the per unit cost of production and enhance the life time of machines and developed products.
e.g., Automatic packaging of a production in a manufacturing plant with minimum human intervention.
5) AR and VR applications – Augmented reality and virtual reality have widespread applications in the optimization stages of manufacturing industries, inventory management in warehouses, training of personnel in military, healthcare, and assembly line operations.
Additive Manufacturing
fabricates parts by building them up layer-by-layer
digital model =>physical
since it starts as a (3D) software design.
doesn’t replace other manufacturing methods =>new opportunities.
some objects would be impossible to make without additive manufacturing.
Diff 3D Printing Processes:
7 diff types of additive manufacturing processes
brought forth by 10 different types of 3D printing technology that 3D printers use today.
Material Extrusion – Fused Deposition Modelling
a filament of solid thermoplastic material is pushed through a heated nozzle, melting it in the process.
printer deposits the material on a build platform along a predetermined path, where the filament cools and solidifies=solid object.
Part preparation
import the design file=>options for build, such as layer height, orientation and infill percentage.
software then computes sections and slices the part into several layers.
The program then creates extruder paths and building instructions based on the sectioning data to drive the extrusion heads.
2) FDM Machine setup
printer is loaded with a thermoplastic filament spool for both model and support extruders.
build platform is heated and maintained at a higher temp to control the cooling
Extruders are heated, and when the nozzle reaches the required temp, the head will start pushing and melting the filament into a small ribbon.
3) FDM printing
The extrusion head gantry and the build platform are on 3-axis system, which
allows the nozzle tip to move in 3D
The extruder will start depositing the material layer by layer in predefined areas to cool and solidify.
Sometimes material cooling => cooling fans mounted to the extrusion head.
4) FDM part removal
removing parts from the build platform and cleaning them by removing all supports.
Rapid Prototyping
first or original example of smt will be developed;
a model or preliminary
3 aspects:
(1) implementation of the prototype; from the entire product (or system) itself to its subassemblies and components,
(2) the form of the prototype; from a virtual prototype to a physical prototype and
(3) the degree of the approximation of the prototype; from very rough representation to exact replication of the product.
play several roles in the product development process:
(1) experimentation and learning,
(2) testing and proofing,
(3) communication and interaction,
(4) synthesis and integration and
(5) scheduling and markers.
