What is a Lathe?
Explain Lathe or Lathe in Engineering?
A
lathe is a machine tool which rotates the work-piece on its axis to perform various operations such as cutting, sanding, knurling, drilling, or deformation with tools that are applied to the
work-piece to create an object which has symmetry about an axis of rotation.This is an era of
automation. Especially during the last decade, the industries have witnessed
dramatic changes in the manufacturing techniques with the advent of NC machines,
CNC machines and Robots ultimately to flexible automation.
What
is NC (or) NC in Mechanical Engineering (or) Importance of NC in Mechanical Engineering?
Automation has been
associated with advancement in technology. Mass production processes throughout
the world owe their success to the development in engineering industries. This
has been achieved through tooled up general
purpose machines tools, automatic unit-built machine tools, automatic
transfer machines etc. however it is believe that more than about half of the
available machine tools are engages in small lot and piece production. These
are the ones posing problems to automate conventional machine tools. In the
process of automation for small batch production, hydraulic tracer controlled
machine tools and programmed operating cycle machine tools have evolved. But
these require changing over to new jobs. These problems of automation
of small lot production have been overcome by Numerical Control (NC) machine
tools to a great extent.
The
“Electronics industries Association” defines Numerical Control as “a system in
which action are controlled by the direct insertion of numerical data at some
point. The system must automatically interpret at least some portion of the
data” in a similar language numerical control mean control by numbers. The
input information for controlling the machine tool motions is provide through
punched paper tape or magnetic tapes in coded language(in binary alpha-numeric
form).
ADVANTAGES OF NUMERICAL CONTROLLED MACHINES & LATHE MACHINES.
1
Accuracy And Repeatability
2
Almost Total Elimination Of Scrap
3
Lower Capital Investment
4
Less Floor Space
5
Savings In Facility Requirements
6
Reduced Inspection Time
7
Reduced Flow Time And Inventory
8
Versatility In Design
9
Improved Production Planning And Control
LIMITATIONS
1.
NC especially calls for high investment.
2. Specials skills in programming and
maintenance are essential
CLASSIFICATION OF NC SYSTEMS
1. Based on control system features.
a. point to point systems
b. Straight cut or straight line NC
system
c. Continuous path of contouring NC
system.
2. Based on Feedback
a. Open loop NC system
b. Closed loop NC system
3. According to the structure of controlled
circuits
a. Analogue control NC system
b. Digital Control NC system
MAJOR ELEMENTS OF NC MACHINE
TOOL
1. The
machine control unit (MCU)
2. The
machine tool
3. The
drive units
4. Feedback
or servo components
5. Magnetic
box and
6. Operator
control
ADVANTAGES
1. An
increase in flexibility
2. The
reduction in hardware circuits and simplification of the remaining hardware, as
well as the availability of automatic diagnostic programs, entails a need for
fewer maintenance personnel.
3. A
reduction in inaccuracies in manufacturing due to a reduced use of tape reader.
4. An
improvement in the possibilities for correcting errors in part programming an
editing feature.
5. The
possibility of using the computer’s peripheral equipment for debugging the edited part-data tape, Ex A plotter of
C.R.T can be used drawing shape of the part.
6. CNC
greatly reduces the number of control boards required and also the inventory
ofspare boards.
HOW DOES CNC WORKS?
A Sequence
of events leading to the machining of a part in point to point positional
positioning
I.
The necessary information for numerical
control can often be extracted from the Engineering drawing with little or no
calculation. For this purpose, the part is considered as being in aquadrant of
rectangular coordinates. The dimensions of all the important details are given
from the data point on x and y axes.
II.
Stipulate the proper machining sequence.
This information is listed on a format known as manuscript. The manuscript
describes the x and y position of each hole, the sequence in which the hole are
to be auxiliary function like turning the coolant on and off or clamping and
unclamping the part.After the manuscript
is prepared, the information has to be kept in hard disk of programming
transfer unit consisting DNC system to the control medium (punched tape etc)
which is done on some automatic writing and tape perforating machines.
OPERATION
For
operating the CNC machines it must to know their controllers and its functions.
The next step to know is how to load the work piece and which rule has to be
used and how to perform the work and how to unload the work. In CNC machine we
are using NC part program for machining the work piece. By feeding the program
to CNC and running the program machine itself performs the work.
Here
first of all we have to decide which type of profile has to machine. After
deciding that the program will write a program. The program is downloaded to
CNC machine from programming room with reference to program the operator will
decide which of tool has to be used because of tool to be used is also
indicated in the program. So the operator must use the tool which is indicated
in the program. Next step is to load the work piece on the CNC lathe. After the
operator has said the reference point to the cutting tool with respect work
piece, next the operator calls the required program and engages the tool with
what peace and starts the program. While running the program the work can be
performed the operator has to decide how much depth of cut in to give. After
completion of work the piece can be checked with template for accuracy. After
that the work can be unloaded manually.
Now
we will see the controllers and their functions clearly from here and also the
one of NC part program to be used in CNC and groove distribution drawing that
program and temptation drawing.
WASI ROLL TURNING LATHES
These
machines are employed for rough and finish turning of rolling mill rolls. Work
pieces up to 15T weight can be loaded on these machines. These machines are
equipped with 2 axis CNC control, even complicated contours can be produced
accurately.
Machine
Bed: the bed is a single piece casting. The bed of this machines having two
separate flat guide ways, one for carriage movement and the other for tall stock.
The carriage quick ways are protected by telescopic covers. The bed is made up
of gray cast iron. Chip flow facility: the chip flow through the space provided
between the two beds space for installation of chip conveyor is also provided.
HYDOSTATIC GUIDE WAYS
The
carriage is supported by hydrostatic guide ways. These ways act as pressurized
pockets and life the carriage above the bed to an extent of 0.02-0.04mm by
means of pressurized oil flow. It provides a friction free, wear free contact between
the bed and carriage, it avoids slip stick phenomenon oil is supplied by multi
circuit gear pump to all these hydrostatic pockets with the same amount of
pressurized oil. The presence of all the pockets can be checked one after
another. This system achieves a high guiding stiffness.
HEAD STOCK
The
head stock is provided with large dimensioned gears with short shafts, for
obtaining high torsion, the main spindle roller bearings are preloaded and
press fitted on to the spindle taper. It is mounted close to the face plate to
minimize the spindle growth due to heat. Two gear steps are provided and are
shifted by means of press button switch on the carriage, oil splash type
lubrication system is incorporated inside with flow control of lubrication failure.
Whenever oil flow is interrupted the feed is immediately switched off and then
main spindle is also stopped automatically.
Head
stock is driven by thyristor controlled D.C. Motor. The drive power come for
the D.C. Motor over a clutch with pneumatic disc brake through the two speed
gear box to the face plate. The D.C. motor is controlled by simo-drive, which
ensures an infinitely variable and consistent rmp/cutting speed, form 0-500
rpm.
SPINDLE SPEED
The
correct speed selection is essential for economical running of the machine. The
speed depends on the tool, work piece material and surface quality required.
Speed is setby S functions in CNC mode and by the operating elements at the
control panel in manual mode. In he 1st gear step speed range is
1-83 and 2nd step it is 6-500 rpm. Spindle rotation can be selected
for clockwise and anticlockwise directions and for jogging by pressing the
buttons on the panel. In CNC mode the programmed speed/rpm can be modified from
50%-12% of the set value. In manual mode the potentiometer knob can be turned
form for increasing or decreasing the spindle speed. The ammeter indicated the
current consumption as percentage load. The motor is characterized to give in 1st
a torque constant output(rpm) up to 20
rpm and 2nd gear up to 120rpm. For the above ranges the motor will
run with increased speed but however attainable torque value decreases.
CONTROLS ON THE HEAD STOCK
Four
control buttons are provided on the control panel fixed to the head stock.
These are push buttons for spindle in clockwise and anticlockwise directions of
rotation. The direction of rotation is indicated on top of them. The third
button from top 1 for stopping the drives and spindle. It is indicated by
letter O. at the bottom of the panel a big red colored push button with yellow
painted circle is provided for emergency stopping of machine. It is indicated
by letter ' O’. At the bottom of the panel a big red colored push button with
the yellow painted circle is provided for emergency stopping of machine. It is
indicated by “EMERG STOP”, by pressing this button on running drives are
stopped at once.
FACE PLATE
Face
plate fit on the main spindle bearing of the headstock. It is made up of
nodular cast iron. It is provided with four clamping jaws. These jaws are
adjustable by means of threaded spindles movement with alien. Hydraulic assist
system is provided inbuilt for even screw for high gripping power and for
inserted in the face plates two positions. The clamping rages are as follows:
Normal
position – 100- 450 mm
Reversed
position – 400 – 700 mm
(turn
to 180°)
The hydraulic system can generate
120 KN of force were spindle. A spanner must be used for hydraulic damping.
Type clamping force hydraulic
force /unit
HSP
6300 75KN 5
HSP
10000 120KN 5
The
torque may only be set given as above, otherwise the spindle may get damaged.
For central alignment and clamping of work piece opposing spindles are adjusted
in stages one after the other.
The
faceplate can accommodate up to 8T of work piece weight. After each
clamping ensures that the ring follower
for mechanical locking catch is in position, so that the load is not borne
solely by the hydraulic system
TAIL STOCK
Tail
stock is a close single piece design with a live supported in antifriction
Bearings, tail stock can be moved rapidly/slowly along the body by means of two
speed gear AC motor through rack and opinion. The tail stock is firmly fixed by
four spring clamping cylinders and it is released from bed by hydraulic oil
pressure. Clamping is actuated by push buttons. The spindle with lives center
is fixed in the tail stock housing.
Centralized
lubrication provides lubricating oil for quick and gear drive. The grill can be
adjusted for a distance of 10mm. it is used mainly for providing axial pressure
between the centers on the work piece.
A
Belleville spring washer stack is provided behind the quill for absorbing
thermal expansions in the work piece. The axial force is measured and
controlled by a hydraulic gauge unit with the contract pressure gauges.
CLAMPING
When
clamping the spring-loaded cylinders, clamping is done by the Springs in
unpressurized condition and unclamping is effected by the hydraulic pressure.
This has the advantage, that in case of power failure or defective valve
clamping occurs and the movements cannot continue uncontrolled. The hydraulic
supply unit works intermittently. A control lamp light up with hydraulic supply
units is on. The adjustment drive is only possible to be operated clamping has
been released.
MAIN OPERATING AND CONTROL ELEMENTS
The
operating and control elements for the machine functions are located in the
control station on the carriage.
Additional
operating panels for the respective partial functions are situated at the
control cabinet, headstock and tail stock.
EMERGENCY SITUATION
EMERGENCY STOP
Use
when danger occurs: on running drives are stopped immediately, it is not
permitted to switch off the machines by using the EMERGENCY STOP after normally
finished work. When emergency stop is active the toll is not cut free. Before
starting the main spindle again, the tool must be released using the jog-mode,
to avoid a possible tool breakage.
HOLD ALL MOTIONS
All
movements are stopped the light in the button flashes. Pressing the switch once
again causes all functions to start and the light in the button goes out.
CONTROL CABINET
MAIN SWITCH DRIVE
When
switched on the machine control is connected to the power supply. At the end of
the shift or when maintenance work is to be done at the electrical system, the
Main switch would be switched off.
MAIN SWITCH CONTROL
For
CNC, measuring systems and control, When switched on, the CNC and control parts
are connected to the power supply.
When switched off, or not a store in
the CNC are lost. If at the end of the shift, Tata is still stored it is
required continue machining, this switch should not be switched off. Switch off
is how ever necessary when maintenance work is to be carried out on the CNC.
VOLTAGE CONTROL OF THE POWER SUPPLY
Line
voltage displays the available current potential
CURRENT CONTROL OF THE POWER
SUPPLY
Line current displays the available
strength of current
WORKING HOUR METER
This display is activated, but the
main switch is switched on.
EMERGENCY STOP
Use when danger occurs, all running
elements stopped immediately
MAIN CONTROL STATION AT THE
CARRIAGE
DISPLAY DEVICES
Spindle
Load - Load
Of The Headstock Drive In A %
Spindle
Speed - Main
Spindle Speed In RPM
Feed
X - X-Axis Feed In mm/min
Feed
Z - Z-Axis Feed In mm/min
OPERATING ELEMENTS FOR THE MACHINE CONTROL
MACHINE OFF
The machine control is activated via this
key-operated switch. Any CNC programs in the memory will held at position off.
MACHINE ON (BASED ON THE
MACHINE CONTROL PANEL)
This illuminated button is activated
to switch the machine on. The button flashes at first. It doesn't turn to
continuous light until all necessary pump, ventilators etc., are functioning
and then the machine is ready to operate.
HOLD ALL MOTIONS
Activation
of this illuminated button causes all running drives to stop, pumps and
ventilators carry on working.
NC-MAN
When the selection switch is in the
NC position the machine can be operated automatically on in adjustment mode via
the CNC operation events. This can only be
switch over when the feed axis and the main spindle are at standard
still. in man position, all machine functions, feedback and speeds are
controlled via the manual operating elements on the operating pane.
EMERGENCY STOP(IN CNC
OPERATING PANEL)
Use in case of danger. All running
drives are stopped immediately.
ERROR/MESSAGE/CYCLE
The lamp lights up to show the
respective condition. This enables first condition to be localized via the
digit display on the display in the CNC part of the control station.
DIAGNOSIS DIGIT DISPLAY
Errors
and operating messages are displayed by digits.
SELECTION
Pressing of this button was as the
digital display to display the next highest identification number and the
number of the existing condition.
DATA DISPLAY UNIT
When operating in CNC mode the
occurred situation will be displayed on the display unit also in playing
language.
FAULT RESET
The lamp in the button flashes when
an error occurs and stays on continuously when an operation message or operator
error occurs. After rectifying the error messages are automatically
extinguished.
MAIN SPINDLE
SPEED
The speed of the main spindle can be
regulated within the gear speed steps with the potentiometer from 0-100 % when
the drives are running, the speed set is indicated on the indicator.
SPINDLE
TURNING DIRECTION
The
main spindle turns in the respective of direction and at low, for as long as
the button is held depressed.
SPINDLE
TURNING DIRECTION
When pressed the main spindle turns
in the respective direction at the speed set on the potentiometer. The buttons
are selflocking, the lamp in respective button lights up.
SPINDLE
OFF
When pressed the main spindle is
switched off. The lamp in the button goes out. If the drive is switched off
during a running feed movement, the feed is stopped first and then the main
spindle stops after brief delay, so that the tool in the work piece can cut
itself free.
GEAR STEP
I/II
To
switch on the speed gear I or II the lamp lights up to indicate which key is
speed has been switched on.
FEED AXIS
Bed
slide upper carriage
FEED
REGULATION-X- AND Z- AXIS
The feeds can be regulated on the
potential meter within the axis dependent range vary from0-100%
AXISPRE-SELECTION
X+,X-,Z+,Z-
To
preselect the feed axes and direction's
X- to the turning center
X+ outwards
Z- to the head stock
Z+ to the tail stock
The respective button lights up to
show the selected direction for taper turning purposes, both axes can be
selected at the same time.
PRE-SELECTION OFF
By using this button the preselected
direction is erased.
HIGH
SPEED
When activated, the carriage travels
in rapid motion as long as the button is pressed, independent from the adjusted
feed speed on the potentiometer.
LOW SPEED
The carriage travels at slow-motion
in the preselected direction as long as the button is heldpressed.
MANUAL
PULSE GENERATOR
The use of the manual was generator
is only possible in CNC code.
HAND
WHEEL X/Z
By using the respective illumination
button hand wheel is activated the lamp of the button lights up. switch off by pressing again, the lamp in button
extinguishes.
SPEED INTERNAL SWITCH
Thus the internal switch is used to
remove regenerative chatter appearances.
INTERVAL ON OFF
When
the interval control is activated the first time, the light in the switch goes
on when pressing again the light extinguishes the interval switch is
compensated.
FREQUENCY POTI
To change the interval time in the
range from 0 to 60 seconds.
SPEED DIFFERENCE POTI
To change the speed difference in
the range 0 to 30% within the interval time.
TURRED HEAD
1 2 3 4
90 180 270 360°
The selection switch is used to select
the requesting working position.
REVOLVERKOPF I
When activated, the turret head
Swivels into the preselected working position. Swiveling is only possible, when
the upper carriage is in rearmost (+X) position
MO6
If it is necessary to change the
tool during programmed cycle, the MO6 has to be programmed, when the new tool
has to be inserted. The light in the button will flash. The ensued tool change
is acknowledged by pressing the reset button. The lamp goes out in the
programmed cycle is continued by pressing the button cycle start in the CNC
operating field. It must be ensured, that the tools change only take place at
the planned tool station.
MACHINE LIGHT I/O
Used to turn on and off the machine
lights
X-AXIS RAPID RETRACT
This function works only in CNC
mode. This close button is to be used when the two breaks. The upper carriage
drives in rapid motion approx. 50 mm to X+, all activated feeds stopped, the
spindle continues turning. No tool to track occurs and emergency stop is
activated.
HEADSTOCK CONTROL STATION
MAIN DRIVE
The
main spindle rotates in the respective direction at low speed for as long as
the button is held depressed.
SPINDLE 0
When this button is pressed, any
running drives are stopped immediately. The main however is stopped after a
brief delay so that the tool can cut itself free.
EMERGENCY STOP
Press in case of danger: all running
drives are stopped at once.
TAILSTOCK CONTROL STATION
HEADSTOCK
The main spindle turn into the
respective direction at a low speed as long as the button is pressed.
CENTER SHAFT
By activating the push button the
Center shaft runs in the respective direction as long as the button is pressed.
TAIL STOCK ADJUSTMENT
By pressing the button that
tailstock travels in the respective direction for as long as the button is
pressed. For adjustment that clamping must be released.
SLOW-FAST
For pre-selection of the tail stock
adjustment speed
slow: mm/min 2800
fast: mm/min 60
CLAMP-UNCLAMP
CLAMP-UNCLAMP
The
selector switch is used for clamping and unclamping of the tailstock on the
bed.
LUBRICATION
The button lights up during an
automatic lubrication pulse. By pressing the button, additional lubrication
pulses can be given(e.g for traveling over long distances).
EMERGENCY STOP
Press only in case of danger : all
running drives are stopped at once
OPERATION PROCEDURE
STARTING PROCEDURE
A
certain order must be followed to switch the machine and the control on and
off.
·
Sector selection switch NC on-off at
services station two on resp off
·
switch on main switch controlled at the
control cabinet
·
switch on main switch drive at the
control cabinet
·
switch on key operated switch mach. Off
on the main control station.
·
Press button 1 at the main control
station.
The
machine is activated. The lamp in the illuminated push buttonpush button all
motions flashes.
After
this button has been pressed, the lamp goes out the machine is now ready for
the operation.
·
Set the selector switch NC-MAN at the
main control station MAN or NC
The switch position NC can only be
selected in the selection switch NC ON-OFF is switched on at the service
station(position on).
·
Observe the indicator lamp fault
The lamp fault must not be lit up
If,
however, it is flashing on continuously lit up, there is the fault. This must
be eliminated and acknowledged before machining begins.
WHEN NECESSARY
·
switch on chip conveyor
·
switch on machine lightning
RE-SWITCH AFTER EMERGENCY
STOP
·
unlock the used emergency stop
button(turn to the right side)
·
acknowledge via button fault reset
·
switch on the performance main switch at
the control cabinet
·
use the illuminated button machine
·
acknowledge via button hold all motions
SHUT DOWN
The
machine and control must be switched off in such a way that the machine is not
damaged in any way. The appropriate time to switch off the machine and control
is when the current part program has been completely worked off, or in the case
of man, the tool is not engaged.
·
Stop all running drives
·
switch off key operated MACH ON
·
if necessary, switch off main switch
drive and main switch control
SHUT DOWN AFTER EMERGENCY STOP
SHUT DOWN AFTER EMERGENCY STOP
At all operation panels emergency
stop buttons are arranged.
MODES OF OPERATION
The machine can be operated in
previous modes of operation, in connection with the Siemens CNS, SIEMENS 850
TE. These primarily depends on the machining tasks: setting is done at the
control station.
THE CNC DIFFERENTIATES BETWEEN THE FOLLOWING MODES OF OPERATION:
SET ACTUAL VALUE STORAGE (PRESENT)
To
set o to preset the actual position of the axis
REFERENCE POINT (REF)
To
synchronize the CNC with the measuring systems.
MANUAL INPUT (MDA)
For block by block input and work
off of CNC blocks for teach-in and play back.
SETTING (JOG)
The
selected axis travels as long as one of the direction buttons is held
depressed.
INCREMENT 1 (INC)
When
the direction button is pressed, the axis travels 1 my.
INCREMENT 10 (INC)
When
the direction button is pressed, the axis travels 10my.
INCREMENT 100 (INC)
When
the direction button is pressed, the axis travels 100 my.
INCREMENT 1000 (INC)
When
the direction button is pressed, the axis travels 1000 my.
INCREMENT 10000 (INC)
INCREMENT 10000 (INC)
When
the direction button is pressed, the axis travels 10000 my.
10INCREMENT 100000 (INC)
When
the direction button is pressed, the axis travels 100000 my.
REPOSITIONING AT THE
CONTOUR (REPOS)
When
automatic operation has been interrupted, the axes can be traveled in job. The
repos, the axes then automatically return the point of interruption in reversed
order.
AUTOMATIC(AUTO)
The
variants automatic, block/block and decoding block/block was possible here.
AUTOMATIC
After cycle start has been pressed,
the parts program is work off automatically block by block from the punched
tape of the program memory.
BLOCK/BLOCK
After
cycle start has been pressed, only one block at a time is executed. Computing blocks
are executed in automatic mode of operation.
DECODING BLOCK/BLOCK
On program blocks are executed block
by block.
TEST RUN FEED
The program is executed at the
higher speed than the programmed speed.
EXTRACTS AND BLOCK
Blocks
with “I” in front of the block number are skipped
CONDITIONAL STOP
When MOI is programmed, the program
stops and must be restarted by pressing cycle start.
TRAVEL LIMITATION
The end positions of the travel
paths are secured by limit switches, these being rapid traverse reduction, stop
and emergency stop. When the reduction is approached, the axis dependent
slow-motion speed is automatically switched on at stop, on axes are stopped. If
the limits switch stop is overrun due to a defect, movement will be stopped at
emergency stop, upon which the fault indicator illuminates.
REFERENCES POINT
A reference(zero) point is defined
for each axis by a limit switch as reference between the measuring system and
the machine. After the reference point ‘R’ has been approached the pertaining
reference point ‘F’ coincides with ‘R’: the absolute and actual value storage
are preset with given values. The travel and the position of the reference
points can be seen in the following sketch.
ADJUSTMENT OF THE AXES
The
machine is adjustable in three axes
Z-axis - bed
slide, longitudinal
X-axis - top
carriage, cross
The axes can be traveled
individually either in manual mode or by way of the numerical control. The
position indicator is effective in both modes of operation.
In manual mode, the feed rates
and feed direction are set on the operating treatments at the control station.
Continuous feed went of X and Y axes is only possible when the main spindle is
running. When the spindle is switched off, running feed drive is stopped and
then after a brief delay, the spindle stops so that the tool in the workpiece
can cut itself free. When the main spindle is at a standstill, adjustment of
the axes will only be made in jog operation.
RETRACTING FROM A LIMIT SWITCH
Retracting from axes X and Z by
approaching an emergency stop limit switch and emergency stop condition is
initiated. The lamps fault flash. The fault is displayed in digits.
·
Set manual mode of operation
·
press and hold down the emergency lights
switch bridged at the control cabinet and with the help of the second operator,
carry out the following
·
acknowledge the fault by pressing the
button
·
retract the axis behind the emergency
stop limit switch by pressing the illuminated direct push button(-/+)
·
release the button at the control
cabinet
·
by pressing the illuminated push button
fault/reset unlocked the fault, the indicator lamps and the digital display
extinguish
·
we adjust the machine to continue the
machining
HEADSTOCK
The head stock carries the main
spindle, which is borne is double row cylindrical roller bearing. It is driven by
a 2-speed gear. · With direction of rotation the spindle rotates clockwise,
when locking towards the face plate. With direction of rotation the spindle
rotates counterclockwise, when locking towards the faceplate. The respective
lamps lights up to indicate the selected direction of rotation and engaged gear
speed.
SPINDLE SPEED
The correct selection spindle speed
is essential for the economic running of the machine. The speed depends on the
tool and the workpiece, as well as surface quality required.
The
speed ranges are set by M-functions in the CNC mode, and by the operating
elements at the control station in manual mode.