Zg Tool Failure

7/31/2019 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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Zg Tool Failure