3. STUDY OF 300T AND 400T PRESS PRESS :- A machine having a stationary bed and a slide(Ram)which has controlled reciprocating motion towards and away from the bed surface and at right angle to it. The slide being guided in the frame of the machine to give a definite path of the motion. Arbor :- A manual or power operated press used to force arbors or mandrels into or out of holes and for similar assembly or disassembly operations. Arch :- A small crank press having it’s columns as uprights wider slide flange, left to right between the columns or to permit larger strike lengths. Automatic :- A press in which the work, either separate parts or strike or sheet stock, is fed through the press in synchronism with the press 40
Transcript
3. STUDY OF 300T AND 400T PRESS
PRESS :-
A machine having a stationary bed and a slide(Ram)which has
controlled reciprocating motion towards and away from the bed
surface and at right angle to it. The slide being guided in the frame
of the machine to give a definite path of the motion.
Arbor:-
A manual or power operated press used to force arbors or mandrels
into or out of holes and for similar assembly or disassembly
operations.
Arch :-A small crank press having it’s columns as uprights wider
slide flange, left to right between the columns or to permit larger
strike lengths.
Automatic:-
A press in which the work, either separate parts or strike or sheet
stock, is fed through the press in synchronism with the press
operating cycle and by means other than manual.
Bench :-
Any small press of a size to be mounted on a bench or table. These
presses are almost always gap frame and maybe fixed or inclinable.
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Bottom drive :-
Any press with the drive mechanism located within or under the
bed. connections of the drive to slide or slides are within or
alongside the upright.
CLASSIFICATION OF PRESSES :-
Presses are classified by one or a combination of characteristics
which include the source of power and no of slides. Other
classification methods are the types of frames and construction,
types of drive and intended applications.
Source of power :-
The source of power for press orientation can be manual ,
mechanical, hydraulic, pneumatic / hydraulic.
Manual presses :-
Manual presses are either hand or foot powered through levers,
series of gears. The most common press of this type is the arbor
press used for various assembly operations. These presses are often
converted to power operation by the addition of air or hydraulic
cylinders.
Mechanical presses :-
Mechanical presses utilize flywheel energy which is transferred to
the workpiece by gears, cranks , eccentric or levers. Mechanical
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presses can be non geared or geared , with single or multiple
reduction gear drives , depending upon the press size.
Hydraulic presses :-
Hydraulic presses provide working face through the application of
fluid pressure.
Pneumatic presses :-
Using air cylinders to exert the required force , pneumatic presses
are usually smaller in size and capacity than the mechanical or
hydraulic presses. They are generally employed for lighter duty.
Advantages include low cost high speed and minimum maintenance.
STRUCTURE OF PRESSES:-
Presses are available in several different designs. The types include
permanently upright presses, such as adjustable bed
stationary(ADS),open back stationary presses, permanently inclined
presses, open back inclinable presses. The inclined presses often
facilitate feeding and permit finished stampings to fall out by gravity
or be blown out by air at the rear of the press. Crop frame presses
are made with either one or two points of suspension. Forge gap
frame presses are generally equipped for mounting cushions for
workpiece liftout or for shallow draw operations. Powered slide
adjustment systems are available for faster die changing. These
presses are commonly arranged with their crank shafts extending
from right to left of the die space .They are also available with the
crank shaft extending from front to back, with the flywheel or gear
at the rear of the press.
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PRESS SELECTION :-
Proper selection of a press is essential for successful and economical
operation. The purchase of a press represents a substantial capital
investment , and return on investment depends upon how well the
press performs the job required. No general purpose press exists that
can provide maximum productivity and economy for all
applications. Compromises are usually have to be made to permit a
press to be employed for more than one job. Careful consideration
should be given to both present and future production requirements.
Important factors influencing the selection of a press include size ,
force , energy and speed requirements. The press must be capable of
exerting force in the amount , location , direction As well as for the
length of time needed to perform the specified operations. Other
considerations must include the size and geometry of the
workpieces. Operations to be performed, no of workpieces to be
produced, production rate needed , accuracy and finish requirements
, equipment costs and other factors.
Press speeds :-
Press speed is relative from that varies with point of reference. Fast
speeds are generally desirable , but they are limited by the
operations performed, the distances above stroke bottoms where the
forces must be applied, and the stroke lengths. However high speed
is not necessarily the most efficient or productive size and
configuration of workpiece, the material from which it is made , die
life, maintenance costs , and other factors must be considered to
determine the highest productivity rate at lowest cost per workpiece.
A lower speed maybe more economical because of possible longer
production runs with less downtime.
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Speed ranges :-
Simple blanking and shallow forming operations can be performed
at high speeds. Mechanical presses have been built that operate to
2000 spm with “one inch” stroke , but applications at this maximum
speed are rare. Speeds of 600 to 1400 spm are more common for
blanking operations, and thick materials are often blanked at much
lower speeds.
Press systems :-
Press integrated with material handling equipment, feeding and
unloading devices and other manufacturing equipment.
TYPES OF FRAMES AND CONSTRUCTION :-
Basic function of a press frame are to contain the loads imposed
with a minimum of deflection which requires ample rigidity. The 2
major types of press frame are gap frame and straight side. Straight
side presses are sometimes constructed with column type frames.
Important criteria for selecting the type of frame to be used include
accessibility and operating characteristics, convenience of feeding
and unloading shift ness and profile.
Number of slides :-
With respect to function , presses maybe classified by the no of
slides incorporated and are referred to as single , double and triple
action presses. On multislide machines each.
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Single action presses :-
A single action press has one reciprocating slide ( tool carrier )
acting against a fixed bed. Process of this type , which are the most
widely used , can be employed for many different metal stamping
operations , including blanking , embossing , coining and drawing.
Depending upon the depth of draw , single action presses often
require the use a die cushion for blank holding. In such applications,
a blank holder , ring is depressed by the slide (through pins ) against
the die cushion , usually mounted in the bed of the press.
Die space :-
The maximum space or any part of the maximum space within a
press for mounting a die.
Dwell :-
A portion of the press cycle during which the movement of the
member is zero or at least insignificant. Usually refers to the internal
when the blank holder in a drawing process is holding the blank
while the punch is making the draw.
Eccentric gear :-
A main press drive gear within an eccentric as an integral part. The
unit rotates about a common shaft with the eccentric transmitting the
rotary motion of the gear into the vertical motion of the slide
through a connection.
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Eccentric shaft :-
A crank with a crank join of such size that it contains or surrounds
the shaft. The eccentric with it’s connection is used in the eccentric
press and is also used for driving auxiliary attachments such as lift
outs and feeds.
Eccentric draw :-
The maximum limits of forming depth which can be accomplished
with the multiple action presses. For typical double action or the
upper action of a triple action press, effective draw is the distance
the inner is from the bottom of it’s stroke at the point at which the
outer slide begins it’s dwell. For the lower action of a triple action
press, it is the distance the lower slide is from the top it’s stroke
when the inner slide begins it’s dwell-sometimes called maximum
draw or maximum depth of draw.
Feeds :-
Various devices that move stack on workpieces to, in or from a die.
Flywheel :-
A heavy rotating wheel attached to a shaft, whose principle purpose
is to store kinetic energy during the man working portion of the
press cycle and to release energy during the working portion of the
press cycle.
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Frame :-
The main structure of a press.
Knockout :-
A mechanism for releasing workpieces from a die, also called
ejector, kick out or lift out. crossbars, cams, springs or air cushions
are commonly used to actuate slide knock outs.
Load, press :-
Amount of force exerted in a given operation.
Pneumatic toggle links :-
A special main links of a toggle press which are equipped with
pneumatic cushions and a linkage to give air pressure controlled
flexibility. These links compensate for variation thickness under the
blank holder and also can be adjusted to exert different pressures at
different corners of the blank holder.
Eccentric :-
A mechanical press in which an eccentric is used to move the slide
instead a crank shaft.
Foot :-
A small press powered by foot pressure.
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Geared :-
A press whose main crank or eccentric is connected to the driving
source by one or more sets of gears.
Mechanical press :-
A press having a slide or slides actuated by mechanical means.
Adjustable bed :-
The bed on the table of a gap frame press, such as a horn press,
which is bolted to the vertical front surface of the press. It is
supported and adjusted (up and down) by means of a screw usually
operated by hand. This term also refers to bed of a large straight side
press, mounted and guided in the press frame and provided with a
suitable mechanism, usually power operated for varying the die
space sheet height. Adjustable bed presses are also referred to as
knee type presses.
Adjustable stroke :-
The capacity of varying length of stroke on a press.
Adjustable slide :-
The distance that a press slide position can be altered to change the
sheet height of the die space. The adjustment may be by hand or by
power mechanism.
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Automatic press stop :-
A machine generated signal for stopping the action of a press,
usually often a complete cycle, by disengaging the clutch
mechanism and engaging the break mechanism.
Bed,press :-
The stationary part of a press serving a table to which is affixed a
bolster, or sometimes the lower die directly.
Bolster plate :-
A plate attached to the top of the press bed for locating and
supporting the die assembly. It usually has holes as 7 slots for
attaching the lower die or die shoe. Moving bolster plates on self
powered for transferring dies in and out of the press for die
setting .Also called rolling bolsters, they maybe integral with or
mounted to a carriage. They are not to be confused with sliding
bolsters, the purpose of which is moving the lower die in and out of
the press for workpiece feeding.
Capacity,press :-
The rated press force that a press is designed to exert at a
predetermined distance above the bottom of the stroke of the slide.
Clutch :-
A coupling mechanism used on a mechanical press to couple the
flywheel to crankshaft, either directly or through gear trains.
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Cushion :-
An accessory for a press which provides a resistive force with
motion required for some operations, such as blank holding ,
drawing or redrawing, maintaining uniform pressure on a workpiece
and knocking out or stripping or also called pads or jacks. Although
usually mounted in or under the press bed. They are also used in or
on the slide.
Power :-
A term used loosely to designate any press using electrical power as
compared to manual power.
Single action :-
A press with the single action.
Ram = slide :-
Shut height :-
The distance from the top of the bed to bottom of the slide of a
vertical press, with stroke down adjustment up, on moving bolster
presses, or shut height is measured from the top of the bolster (when
the bolster is integral with carriage) or the top of the carriage when
the bolster is separate.
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Slide :-
The main reciprocating member of press, guided in the press frame
to which the punch or upper die is fastened. Sometimes called the
ram. The inner slide of a double action press is called the plunger or
punch holder slide. The outer slide of a double action press is called
the blank holder slide. The third slide of a triple action press is
called the lower slide, and the slide of a hydraulic press is often
called the platen.
Slide operation :-
The distance between the face of the die mounting surface of the
inner slide and the outer slide of multiple action presses at open
position.
Stroke :-
The distance between the terminal points of the reciprocating motion
of a press slide.
Strokes per minute :-
The specified continuous running speed of a press. It is not the no of
permissible single tripling of a press and consequently does not
measure the possible production per min, except when a press is
running continuously. The no of single tripling per min varies with
different types and makes of clutches as well as with the dexterity of
the operator.
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Top stop :-
A machine generated signal for stopping a press at the
top of a stroke.
CUSHIONS :-
Die Cushion :-
Die cushion often and more accurately referred to as pressure pods ,
are used to apply pressure to flat blanks for drawing operations.
They also serve as lift out or knock out devices to remove stampings
from the dies.
Pneumatic cushions :-
In cushions of this type ,the maximum pressure is controlled by the
diameter and no of cylinders and available air pressure. Shop line
pressure is generally used, but it is possible to use a booster or
intensifier to increase the air pressure. A pneumatic die cushion for a
single point press normally uses one cylinder and one piston. Two
ore more cushions maybe placed on top of one another, however
when a high capacity unit is required in a limited bed area in which a
vertical space is available.
LUBRICATION :-
Role of lubrication :-
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Friction and lubrication are of vital importance in most metal
forming operation. Effective lubrication system results in low
friction levels which reduce the loads imposed on toolings or
workpiece failures or permit reduction in the no of steps required to
form a part. Lower force level also reduce tooling deflection and can
improve the dimensional accuracy of the product.
Lubrication regimes :-
The type of lubrication regime that occurs in a metal forming
operations has a strong influence on frictional conditions, as well as
on important factors such as product surface finish and tooling wear
rates.
The lubrication regime that occurs in a given metal forming process
is dependent on several factors of the process.
Contact macro geometry(varies with process and die
