TOOL FAILURE

PROBLEMS WITH CUTTING DIE PLATES:

Die plates of cutting edges may cause trouble by:
1.  Dulling of cutting edges and consequent excessive burr formation.
2.  Breakage.
3.  Cutting die plate performance.

DETERMINING FACTORS OF TOOL LIFE:

The determining factors may be classified in to four groups depending on:
1.  The stamping
2.  The tool
3.  The press
4.   The operation

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 become excessive.
In general, giving the tool then it deserves as an expensive precision products.

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.

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.

REMOVE FEATHER EDGES:

After grinding a die plate or a punch, featheredges are formed around 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 benefit of this consists of improved surface finish of the cut surfaces.

PROTECTIVE COATINGS ARE HELPFUL:

      When blanking or punching sheet metal coated with either paper or plastics, both the bur formation and the wear decreases on the 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 abrasive silicon steel, which cause very rapid wear of tool members

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 half holes 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.

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 is the 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.

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.

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.

PRESS ROOM:

The cleaning of the tool in order to avoid accumulation of dirt, chips, and foreign matter, which when mixed with lubricant, act as an abrasive and considerably increase tool wear.

Prolongation of tool life
1) Avoiding any irregularities.
2) Informing the foreman immediately as soon as    wrinkles or cracks appear in some shells.

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.

SLUG PULLING:

Slug pulling is the return of slugs above the die plate.
The disagreeable consequences: Possibility of missfeeds, if the slugs shift on to some cutting edges, punches and die-opening edges may 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 holes of the plates and die shoes, must have correctly positioned discharge holes of the right size.

MAGNETISED PUNCHES:

Punches some times become magnetized, either while being sharpened or punching action. This causes increase in damage of slug fitting, so always demagnetize the punches after re sharpening and whenever they have become magnetized naturally.

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 die members, 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.

PREVENTIVE METHODS:

Put a piece of heavy paper or cardboard between the die bottom and bolster plate: and between the punch holder top and the ram 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.

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 from the 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:

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:

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