3 Die Cutting

Chapter 4

Introduction to Die Cutting operation

Chapter 4

Introduction to Die Cutting operation

The Fundamentals ofDie-cutting Operations

•Plain Blanking•Piercing•Lancing•Cutting off and Parting•Notching•Shaving•Trimming

Die-cutting Operations

Plain Blanking


Piercing

This operation

consists of

simple hole

punching


Lancing

This is a combined bending and cutting operation


Cutting off and Parting

PARTING CUTOFF


Notching and Shaving

SHAVING NOTCHING


Trimming

Cutting Action in Punch and Die Operations

Cutting action progression when blanking and piercing metal

The punch contacts the work material supported by the die and a pressure buildup occurs. When the elastic limit of the work material is exceeded, the material begins to flow plastically (plastic deformation). The punch penetrates the work material, and the blank, or slug, is displaced into the die opening a corresponding amount. A radius is formed on the top edge of the hole and the bottom edge of the slug, or blank, as shown in Fig.

Cutting Action in Punch and Die Operations

Characteristic appearance of edges of parts produced by piercing and blanking

Fig. Shows the characteristic appearance of the edges of parts produced by blanking and piercing operations in detail. The edge radius (or rollover) is produced during the initial stage of plastic deformation. The edge radius is more pronounced with soft materials.


Die Clearance Clearance is defined as the intentional

space between the punch cutting edge and die

cutting edge. Clearance is always expressed as

the amount of clearance per side. Theoretically,

clearance is necessary to allow the fractures to

meet when break occurs. The amount of

clearance depends upon the kind, thickness and

hardness of the work material.


The effect of clearance Too little clearance: Fracture do not meet

Correct clearance: Fracture do meet


Punch and Die clearance


Punch and Die clearance


Angular Clearance

A small amount of draft is provided

below the die opening to prevent blanked

parts or slugs from stacking inside the entire

width of the die wall. The draft is commonly

referred to as angular clearance and is

expressed in degrees per side.


The use of angular clearance

Angular clearance is necessary to prevent backpressure caused by blank or slug buildup especially when the punches or die block are fragile. Recommended angular clearance varies from ¼ to 2 per side, depending upon the material and the shape of the work piece. Soft materials and heavy-gage materials require greater angular clearance. Larger angular clearance may be necessary for small and fragile punches.

Cutting Force

Use of formula

The cutting force formula is

F = Spt

where F = cutting forceS = shear strength of stock materialp = perimeter or length of cutting edget = thickness of material

EXAMPLE: A 5 cm. square hole is to be pierced in mild steel, which is 0.15 cm. thick.SolutionS = 3.875 tons / cm.2 (for for M. S. from Table)p = 5 + 5 + 5 + 5 = 20 cm.t = 0.15 cm.ThenF = SptF = 3.875 x 20 x 0.15 = 11.625 tons


Stepping punches

Single shear on punch

Single shear on die

Double shear on

punches

Double shear on

punches

Convex & concave shear

Method of reducing cutting forces

Shear Angle

Stripping

Fixed type stripping

Stripping

Spring loaded type stripping

Stripping Force

Use of formula

The stripping force formula isLst = K x Awhere Lst = Stripping force in Kgs.K = Stripping constant in kgs./cm2A = Area of cut surface in cm.2By experimentK = 105 for sheet metal < 0.16 cm.K = 148 for sheet metal > 0.16 cm.

EXAMPLE: A 5 cm. square hole is to be pierced in mild steel, which is 0.15 cm. thick.

Solutionp = 5 + 5 + 5 + 5 = 20 cm.t = 0.15 cm.Then A = 20 x 0.15 = 3.0 cm.2

Lst = K x A Lst = 105 x 3.0 = 315 kgs.

PUNCH AND DIE MOUNTING(Std. Die Set)

Rear pillar cast iron standard die set


Center pillar cast iron standard die set


Four pillar all steel standard die set set


Diagonal pillar all steel standard die set

PUNCH AND DIE MOUNTING


When selecting and ordering die sets, the die area can be determined by use of full-size templates obtainable from the manufacturer and marked to correspond with the catalog number. When ordering, the following information must be specified:1) Quantity and catalog number2) Type and length of bushing3) Overall length and type of guide pins, based on shut height and length of stroke4) Diameter of shank or no shank5) Thickness combinations if other than those listed in the catalog (special thicknesses generally furnished at extra cost).

Types of Die Construction

•Single Station Dies •Progressive dies•Transfer dies •Compound dies•Combination dies•Rubber Pad Blanking•Fine blanking


Single Station Dies

Each single station die performs one operation and a set of dies for a lamination can be mounted in one press or different presses. Simple laminations usually are produced in one operation. More complex parts may require several operations. Fig. shows a typical sequence for the production of stator & rotor laminations in four operations. These are

1.Stock blanked & pierced,

2.Stator lamination notched,

3.Rotor lamination separated from stator lamination and

4.Rotor lamination notched.

Sequence of operations

Progressive dies perform two or more operations at different stages every time the ram descends. The stock strip is advanced through a series of stations that perform one or more distinct die operations on the work piece. The strip must move from the first through each succeeding station to produce a complete work piece. Thereafter a complete work piece is produced with each stroke of the ram

The distance from one station to the next must be the same. The station-to-station distance is also the same as the advance distance. The advance distance, called advance for short, is the distance the strip moves in order to relocate (register) at each successive station.


Progressive Die


Simple Progressive Die

1. Stock strip

2. Die stop activating pin

3. Primary die stop

4. Blanking punch

5. Piercing punch

6. Punch plate

7. Stripper plate

8. Die block

9. Die set

10. Button stop

11. Pilot pin

Transfer dies are used for piercing in applications generally

similar to those for which progressive dies are used. A

number of operations are done in successive stations of the

transfer die. Piercing, blanking, cutoff, lancing, notching,

forming and drawing can be done in transfer dies. The

method differs from progressive die operation in that the

work piece does not remain attached to the strip for feeding,

but is fed from station by transfer by mechanical fingers,

levers or cam. Transfer dies are particularly suited to the

making of parts that would be difficult to connect to the

stock skeleton with carrier tabs.


Transfer Die

A compound die differs from a progressive die in that it performs two or more cutting operations during one stroke of the press at one station only. In order to do this, both the upper and lower member of the die set carry punching and blanking elements, which are directly opposed to each other. In other words, the piercing punches act in the opposite direction with respect to the blanking punch. A simple compound die in a closed position is shown in Fig. in the next slide. Note that the blanking punch also serves as the piercing die. The sidewalls adjacent to the cutting edges of the blanking-die opening are straight because the blank does not pass through the die. The blank is return-ejected by the knockout mechanism that is actuated at the return stroke of the press.


Compound Die


Compound Die

A die in which a cutting operation is combined

with a noncutting operation is referred to as a

combination die. The cutting operations may

include blanking, piercing, trimming, and cutoff

and are combined with noncutting operations,

which may include bending, extruding,

embossing, and forming. Fig. in the next slide

shows a typical combination die that draws and

blanks a shell.


Combination Die


Combination Die

A This method of blanking employs a rubber pad in the punch

holder and a punch in the die shoe (See fig.in the next slide). It

operates on the principle that when rubber is compressed, it

transmits the pressure in all directions. The rubber is confined

in a cavity in order to exert full force against the part. This type

of blanking, referred to as the Guerin process, is generally

limited to the blanking of aluminum alloy up to a maximum of 1

mm. thick. The minimum hole diameter or width of cutout is

approximately 50 mm., and at least 38 mm. trim is necessary for

external cuts.


Rubber Pad Blanking


Rubber Pad Blanking

Fine blanking is basically a method of blanking or piercing parts

without die break. This is done by controlling metal flow in the

shearing area. A knife-edge or impingement ring, is pressed into

the metal outside the cutting line and the metal outside this line

is restrained by application of great force. With the metal

virtually unable to move in ward and a punch-to-die clearance

between 0.0075 mm. and zero, a clean smooth-edge cut can be

made regardless of stock thickness. A triple-action hydraulic

press is required to get the holding or gripping action, controlled

punch speed, and counter pressure on the part necessary for

successful fine blanking.


Fine Blanking Die


Fine Blanking Die

1) Automatic manufacturing

2) Elimination of secondary operation

3) High production

4) Continuous good quality

5) Reduced space requirement for the production line

6) Less material handling


Advantages of the Fine Blanking Die

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3 Die Cutting