zg tool failure
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TOOL FAILURE
PROBLEMS WITH CUTTING DIE PLATES:
Die plates of cutting edges may cause trouble by:
1. Dulling of cutting edges and consequent excessive bur formation.
2. Breakage.3. Cutting die plate performance.
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DETERMINING FACTORS OF TOOL LIFE:
The determining factors may be classified in to four groupsdepending on:
1. The stamping
2. The tool
3. The press4. The operation
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PRESS SELECTION:
Every C-frame press at the instant of cutting impact, deflects
somewhat, misaligning the punch a little, if the deflection is too
pronounced, then the misalignment becomes too great so that uneven
wear is produced, and in extreme cases even damage to the cuttingedge occurs.
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CUTTING SPEED:
The temperatures reached during high-speed cutting processes
do not impair the hardness of the cutting edges.
DIE SETTING:
The proper setting of the tool in press is of utmost importance. If the
alignment is not correct, excess friction and certain dangerous lateral
stress are produced which causes premature wear of the tool
member.
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OPERATION WITH THE TOOL:
The periodic cleaning of the tool in order to avoid
accumulation of dirt, chips, or foreign matter, which mix with the
lubricants, act as abrasives and considerably increase tool wear.
The press operator is supposed to co-operate in the
prolongation of the useful life of the tool by
A) Avoiding any irregularities rate feeding.
B) Informing the Forman immediately when burr starts to becomeexcessive.
In general, giving the tool then it deserves as an expensive precision
products.
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SHARPENING OF PUNCHES:
The punches are subjected to wear three times as fast as the die
plates. The stock clings to punch slides like press fit.
1) Do not employ the same kind of tool steel for cutting members,
punch and die plates.
2) Make the punch longer than strictly necessary and sharpen them
more frequently than the corresponding die-plates.
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REMOVE FEATHER EDGES:
After grinding a die plate or a punch, featheredges are formedaround the cutting edges.
After sharpening a die plate or a punch, remove the feather with a
fine oilstone. It is surprising what a favorable influence this little
precaution has on the useful duration of the dies. A fringe benefitof this consists of improved surface finish of the cut surfaces.
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PROTECTIVE COATINGS ARE HELPFUL:
When blanking or punching sheet metal coated with either
paper or plastics, both the bur formation and the wear decreases onthe tool members that are in contact with the coated side of the
stock.
It is significant in the production of the laminations for the
electrical devices. These stampings, made from highly abrasivesilicon steel, which cause very rapid wear of tool members
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BREAKAGE OF DIE-PLATES:
During the operation of the operation of the tool the following
details may be directly or indirectly cause the die plate failures.
1) Inaccurate feeding causes the cutting of half blanks or halfholes results in the deflection of force and results in chipping of
cutting edges.
2) In punching of small holes, slugs often clog the clearance
holes, resulting in the punch breakage and damage to the die plate.Very dull cutting edges means overloading causes spoiling and
breaking of die plates.
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HOW TO GET MORE FROM DRAWING DIES:
In a drawing die there are three main tool members: the die ring, the
punch, and the blank holder. The cause for wear in a drawing die isthe continuous friction between the stock and the tool members. The
die ring can be polished after which its dimensions are enlarged
beyond the tolerance limits.
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PRESS SELECTION:
Every press at the instant of impact deflects somewhat
misaligning the punch a little. If the deflection is too pronounced,
then the misalignment becomes too great so that uneven wear is
produced and thus tool life is greatly reduced.
By reducing the drawing speed the tool life is somewhat increased.
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STOCK:
The stock should be clean, without scale, oxidation, or rust. The
sheet metal must be perfectly uniform in texture, hardness, thickness,
surface finish, etc.
STOCK LUBRICATION:
In drawing operations, lubrication creates a film between the stock and
the tool members, thus allowing the stock to slip easily between the
active tool members. In this way the friction between the working
surfaces of the tool and the stock that is being produced is reduced and
the heat produced by the operation is greatly decreased.
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PROBLEMS WITH SLUGS:
Slugs sometimes cause problems, which involve expense, loss of
time, labor costs, and lowering of the production efficiency of the
corresponding press tools. The slug cause clogging of die opening and
slug lifting or pulling.
JAMMING THE SLUG DISCHARGE HOLES:
This is due to cut slugs becoming compressed together and building up
in almost solid columns. Some slugs in the columns can shift to a
crosswise position and literally clog the slug exit holes in die plates and
die shoes.
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SLUG PULLING:
Slug pulling is the return of slugs above the die plate.
The disagreeable consequences:Possibility of misfeeds, if the
slugs shift on to some cutting edges, punches and die-opening edgesmay be damaged, and punches may break.
TOOL SETTING:
The tool must be located on the bolster plate or the press table that the
slugs have an absolutely pre discharge path, i.e. all the clearance holesof the plates and die shoes, must have correctly positioned discharge
holes of the right size.
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MAGNETISED PUNCHES:
Punches some times become magnetized, either while being sharpenedor punching action. This causes increase in damage of slug fitting, so
always demagnetize the punches after resharpening and whenever they
have become magnetized naturally.
S O S C G A SS S
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REMIDIES OF UNSTICKING JAMMED PRESSES
1) If the press is equipped with tie rods, loosen them. If the nuts are too
hard to turn, heat the tie rods.
2) Apply external forces, such as wedges hydraulic jacks to diemembers, never use impacts.
3) Try to slide the ram together with die out of its seat in a forward
direction.
4) Put dry ice around the tool and pitman screw to make them contract,thus reducing the jamming pressure.
5)For steel-frame press, heat the frame in order to expand.
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PREVENTIVE METHODS:
Put a piece of heavy paper or cardboard between the die
bottom and bolster plate: and between the punch holder top and theram bottom face. Then in case of jamming, burn out the paper.
The yielding of rubber sheet compensates automatically for
over thickness or double thickness of stock and thus any jamming
is avoided.
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Machine a cylindrical in the ram top to hold a strong-flanged
cup. In the interior of the cup place a cake made from Cerro
metrics or from an alloy of tin and lead rest on the cake a
properly shaped steel cylinder that will receive the thrust fromthe ball joint and the pitman screw. In case of jamming, take out
two or more plugs of clearance holes, heat the cup so that the
low melting alloy soften or melts outright. Thus the jamming
pressure is removed.
MAGNETISED STAMPINGS
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MAGNETISED STAMPINGS:
Product damage occurs when tiny particles of steels cling to
magnetized stampings and score mating surfaces or in severe cases,jam moving parts.
Magnetized punches have a tendency to lift small slugs and blanks
out of the die plate opening and deposit them on the die plate top
surface, which causes damage to punch and die plate breakage.
PREVENTION
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PREVENTION:
STAMPINGS: Avoid the magnetic lifters for handling stock; use
hook lifters instead; if possible change the type of steel with less
carbon content or alloying elements.
TOOLS: Use non-magnetic materials for die members.
PRESSES: For press construction use mild steel that is
magnetically soft and have low hysterias.
REMEDIES:
Demagnetizing the stampings, tools and press components.
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