Download Chapter 24 Cold Forming of Metals

Accident Prevention Manual
for Business & Industry:
Engineering & Technology
13th edition
National Safety Council
Compiled by
Dr. S.D. Allen Iske, Associate Professor
University of Central Missouri
CHAPTER 24
COLD FORMING OF METALS
Cold Forming of Metals
• Cold forming: The forming of blank metal into a shape.
• A variety of machines can be used for this operation
depending on the metal and desired end product.
• Common machines used for cold forming include power
presses, metal shears, and press breaks.
Power Presses
• Versatile machines that can be attached with different dies
to produce a variety of products
• Safeguarding the point of operation of a press depends on
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the die or tool component
type of press selected to power the die
method selected to insert materials, to remove parts, and to
dispose of scrap
Power Presses (Cont.)
• Die or tool component design considerations:
• material used
• configuration of the finished part
• method of feeding the material
• method of removing parts
• method of scrap disposal
• ways to reduce noise
Power Presses (Cont.)
• The safety of power press operations depends on:
• adequately safeguarding the point of operation
• properly training press operators
• enforcing safe work practices
• Setup and maintenance personnel must be trained to
assure their s.afety while working in or around a press
Power Presses (Cont.)
• Operations are either primary or secondary
• Primary operations (blanking)—stock material is processed
to produce suitably sized and shaped flat blanks
• easier to guard than secondary operations
• Secondary operations—further forming and shaping of
blanks
Primary Operations
• Hazards include:
• die setup
• guard repairs
• material handling
• feeding stock into machines
• part and scrap ejection
Secondary Operations
• Adaptable for various feeding methods:
• manual feed
• gravity feed
• follow or push feed
• magazine feeds
Secondary Operations (Cont.)
• Tools
• Hand tools are useful when parts must be placed or removed
manually.
• Cleaning and prying tools are essential for cleaning dies and
clearing jams.
• Simple and safe hand tools, which can be made, can save the
hands and fingers of operators.
Secondary Operations (Cont.)
Secondary Operations (Cont.)
• Safeguarding
• The safeguarding program should be based on an evaluation of the
specific problems.
• Formulate a definite company policy that covers:
• use of guards or devices for all operations.
• consideration of the safety factor in new operations.
• enforcement of safe operating standards.
Secondary Operations (Cont.)
Definitions
• Antirepeat: the part of the clutch/break control system
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designed to limit the press to a single stroke if the actuating
means is held or stuck on “operate”.
Bolster plate: plate attached to the top of the bed of the press
component where lower die or die shoes are attached.
Brake: mechanism on a mechanical power press component to
stop and/or hold the slides.
Single atroke: one complete stroke of the slide, usually
initiated from a full-open position, followed by closing, and then
returned to the full-open position.
Slide: the main reciprocating press component member; a
slide may be called a ram, plunger, head, or platen.
Definitions (Cont.)
• Inch: an intermittent motion imparted to the slide by
momentary operation of the inch-operating means.
• Full-revolution clutch: a type of clutch that, when tripped,
cannot be disengaged until the drive mechanism has
completed a full revolution and the slide, a full stroke.
• Part-revolution clutch: a type of clutch that can be
disengaged at any point before the drive mechanism has
completed a full revolution and the press slide, a full stroke.
• Direct drive: type of drive arrangement wherein no clutch is
used; they match the operational characteristics of part
revolution clutches because the driving power may be
disengaged during the stroke of the slide.
Point-of-Operation Safeguarding
• Protecting personnel, including helpers, after the dies
have been installed, tested, and operated, and are ready
for production
• Consider all hazards in the die’s space that may crush,
cut, punch, sever, or otherwise injure personnel.
• There are two basic categories of safeguarding at the
point of operation:
• the guard
• the device
Point-of-Operation Safeguarding (Cont.)
• A guard, or barrier guard, is a physical barrier that
prevents access to a die’s hazard during operation
• If a barrier allows access to a die’s hazard during operation, it is not
a guard; it is an inadequate enclosure.
• An inadequate enclosure always requires using a device to form an
acceptable safeguarding system.
Point-of-Operation Safeguarding (Cont.)
• There are four main types of guards for safeguarding
power presses.
• fixed die-enclosure guards—complete protection for the operator
• fixed-barrier guards
• interlocked press-barrier guards
• adjustable-barrier guards
Point-of-Operation Safeguarding (Cont.)
Point-of-Operation Safeguarding (Cont.)
Point-of-Operation Safeguarding (Cont.)
• A safeguarding device controls access to the point of
operation.
• Devices can be divided into three categories:
• press-controlling devices
• operator-controlling devices
• devices that control both the operator and the power press
Point-of-Operation Safeguarding (Cont.)
• There are several types of safeguarding devices for
power presses:
• Type-A, moveable-barrier device
• protects by enclosing the point of operation before a press stroke begins
• Type-B, moveable-barrier device
• not suitable for full revolution machines
• Two-hand tripping devices
• used on a full-revolution clutch machine
Point-of-Operation Safeguarding (Cont.)
Point-of-Operation Safeguarding (Cont.)
• There are several types of safeguarding devices for
power presses:
• Two-hand control devices
• Regulatory standards may specify safe distance for mounting controls.
• Pull-back devices
• Usually limited to secondary operations.
• Restraints
• Presence sensing devices
Safeguarding Full-Revolution Clutch
Power Presses
• Guards
• fixed die-enclosure guard
• fixed-barrier guard
• adjustable-barrier guard
• Devices
• restraints, properly adjusted
• pull-backs, properly adjusted
• type-A, movable barrier, with an enclosure to prevent access
through areas not protected by the movable barrier
• two-hand tripping, located at a distance that exceeds the safe
distance for the particular press
Safeguarding Partial-Revolution
Clutch Power Presses
• Guards
• fixed die-enclosure guard
• fixed-barrier guard
• adjustable-barrier guard
• interlocked press-barrier guard
• Devices
• restraints, properly adjusted
• pull-backs, properly adjusted
• type-A or B, movable barrier
• two-hand control
Auxiliary Mechanisms
• Feeding and extracting tools
• Foot control and shielding for protection
• foot controls for full-revolution clutch presses
• foot controls for partial-revolution clutch presses
• Single-stroke attachments
• should be attached to full-revolution clutch presses
• will disconnect the pedal or operating lever after each stroke
Feeding and Ejecting Mechanisms
• Any mechanism that eliminates handling of work should
reduce exposure to those hazards, especially in the
operations that place the operator’s hands in a danger
zone.
• Primary operations
• Secondary operations
Feeding Mechanisms
• The 6 principal types of semiautomatic feeds are:
• chute
• slide or push
• plunger
• slide die
• dial
• revolving die
Feeding Mechanisms—Straight Chute
Feeding Mechanisms—Push Feed
Feeding Mechanisms—Plunger Feed
Ejecting Mechanisms
• Properly designed and installed ejector mechanisms will
eliminate many common hazards by automatically
clearing the press.
• Common ejector mechanisms include:
• air jets
• pneumatic powered cylinders
• clamp and pan shuttle extractors
• steel chutes
• elevators and conveyors
Ejecting Mechanisms—Pan Shuttle
Kick Presses
• The manual counterpart of power presses
• Hazards do exists even though the operator is the source
of the power.
• Guarding is required.
• Used principally for piercing, notching, forming, and
shearing small parts.
Kick Presses (Cont.)
• Injuries resulting from unsafe operation of kick presses
include:
• finger amputations and finger punctures from unguarded points of
operation
• fatigue and abdominal strain resulting either from pressure
required to perform the work or improper posture
• strains from lifting materials
• eye injuries caused by small flying particles
Kick Presses—Guards
• Guard the point of operation for piercing and similar
operations
• Guards should allow enough room to insert the work into the press,
but not enough to permit the fingers to come within the danger
zone.
• Some assembling jobs may require operators to place
their hands under the punch.
• two-handed safety devices, such as the ratchet mechanism are
used to provide protection
Kick Presses—Ratchet Mechanisms
Kick Presses—General Precautions
• Ensure that they are securely fastened to the floor or
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bench.
Provide good lighting .
Require operators to wear eye protection.
Perform regular maintenance.
Ensure the workstation is suited to the worker and their
task to reduce strain and fatigue.
• Make adjustments when necessary.
Electrical Controls on Power Presses
• Important element in press safety; especially when a two-
hand control device or a two-hand tripping device is used
for point-of-operation safeguarding
• May range from a simple power disconnect switch and a
motor starter on a small full-revolution clutch press to an
extensive system on a large partial-revolution clutch
machine
Electrical Controls on
Power Presses (Cont.)
• Regardless of the means of point-of-operation
safeguarding, build all controls for machines in
accordance with:
• NFPA 79, Electrical Standard for Industry Machinery
• NFPA 70, National Electric Code
• any applicable local codes
• ANSI B11.3 (for specific application to press brakes)
Electrical Controls on
Power Presses (Cont.)
• Two-hand systems
• tripping system
• buttons or other two-hand clutch tripping mechanisms
• control system
• buttons for engaging the clutch/brake
• Two-hand systems must follow minimum safety distances between
hand controls and nearest point-of-operation hazard.
• Take into account press speed, crankshaft revolutions, clutch engaging
points per revolution, and stopping time.
Electrical Controls on
Power Presses (Cont.)
Electrical Controls on
Power Presses (Cont.)
Electrical Controls on
Power Presses (Cont.)
Every power press
control board should
have:
• stop controls
• stroking selector
• inch control
• stroking control system
• emergency stop
Electrical controls
should have the
following components:
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component failure
protection
interlocks
control circuit voltage
ground protection
Power Press Setup and Die Removal
• Power press dies must remain rigidly accurate in spite of
the pressure and stress they transmit during metalstamping operations.
• They vary in weight from a few pounds to several
thousand pounds.
• Handling, setting up, and removing dies are hazardous
unless operators use proper equipment and methods.
Power Press Setup
and Die Removal (Cont.)
• Injuries likely to result when setting or removing dies:
• strains and hernias from inappropriate handling
• foot injuries from dies slipping off trucks, benches, bolster plates, or
storage shelves
• crushing injuries from body parts caught between the die and
press, pinch points, and other movements
• hand injuries or amputations from sudden descent of the ram due
to brake failure
• lacerations from wrenches slipping off worn nuts or incorrect tools
used
• eye injuries from pieces of shattered parts
Power Press Setup
and Die Removal (Cont.)
• Transferring dies safely
• Very light dies can be handled and carried manually.
• With proper die trucks, personnel can generally handle dies up to 100 lb
without using a lifting apparatus.
• Heavy dies require the assistance of die-handling power
trucks and other hoisting mechanisms.
• Tapped holes in the dies are often used to secure the die during a
lift, do not use bolts.
• Keep the transfer of the die as low and level as possible, chock the
wheels, lock the brake.
Power Press Setup
and Die Removal (Cont.)
Power Press Setup
and Die Removal (Cont.)
• Procedure for setting dies
• Dismantle safety devices only if absolutely necessary.
• Clean off the bolster plate.
• Check the die to make sure that it has no chips, tools, or loose
parts, and is in good operating order.
• Transfer the die.
• Line up the die in correct operating position, and remove posts or
blocks from under the slide.
• Shim the lower half of the die to the proper level and clamp it to the
bolster plate.
• Check all bolts and clamps.
• Raise the ram to its highest point and block it in this position.
• Reconnect the power and try out several actual operations, using
proper stock.
Power Press Setup
and Die Removal (Cont.)
Die Removal
• General safe die removal practice:
• Clear working space of all stock, containers, tools, and other items.
• Disconnect or shutoff power and lockout the switch.
• Dismantle point of operation safety devices as required.
• Clean off the bolster plate.
• Shut off the air supply if die is operated with an air pad.
• Remove bolts and clamps holding the die in place.
• Ensure the die is loose and bolts, nuts, and clamps have been
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removed.
Raise the ram slowly and make sure the die does not hang in the slide.
Block the ram in its highest position.
Place the die truck close to the press, adjust table to the same height
as the lower bolster plate.
Transfer die to the truck.
Inspect, repair, and protect dies before storing them for the next turn.
Inspection and Maintenance
• The best safety program for power presses cannot
succeed, nor can maximum production be met, without
good inspection and maintenance of power presses and
their safeguards.
• Proper inspection, adjustment, and repair of power
presses can be done only by competent, thoroughly
trained employees.
• Be sure that employees are familiar with the construction
and operation of the equipment for which they are
responsible.
• Provide them with the proper tools and equipment.
• Clear work area of personnel not directly involved with
maintenance.
Inspection and Maintenance (Cont.)
• During maintenance work, the machine should be locked
out to prevent accidental operation or electrical shock.
• When employees must work on a machine with the power
on and guards removed, they should not place their body
in the path of any movable parts of the press.
• Management should set up a checklist that outlines the
frequency of inspection and maintenance for each press.
Metal Shears
Metal Shears (Cont.)
• Safe operation guidelines
• Be familiar with the shear and its capacity, controls, operating
modes, and safeguarding.
• Keep blades sharp and clearance correct.
• Keep work area clean and free of obstructions.
• Do not place hands between the material and shear table.
• Wear snug fitting clothes and appropriate PPE.
• When leaving the shear, turn off the power.
Press Breaks
Press Breaks (Cont.)
• The primary function of the press break is to cold-form
angles, channels, and curved shapes in metals.
• Two power press break categories:
• General purpose—mechanical and hydraulic
• Special purpose—mechanical, hydraulic, and other drive
arrangements
Press Breaks (Cont.)
Press Breaks (Cont.)
• Safeguarding press breaks
• Install a point-of-operation guard, such as fixed barriers, die
guards, and other means that do not allow access to the point of
operation.
• Install point-of-operation devices, such as presence-sensing
devices, gates, or movable barriers, pull-backs, etc.
• Use safe-distance methods when guards/devices cannot be used.