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Introduction

Sheet metal working has various processes and applications used in the

production of every day appliances from simple house hold equipmen to intricate

mechanical gadgets. In this project, I will describe the use of stamping to

manufacture a simple sheet metal part. Starting from the part details (material anddimensions), I will ensure the part meets all requirements for manufacturability.

The main objective is to find the most cost efficient variant of manufacturing. Thus

least wasteful method to produce the required sheet metal part is shearing by die.

1. Blank For Sheared Part.

die Type selection

1.1. Choice of the shape and of size of part,

choice of standard sheet providing the maximum material utilization ratio

Fig 1.1 Drawing of the sheared part

Description of the part, its peculiarities and manufacturability.The drawing with all dimensions of the given part is shown in Fig.1. It is

necessary to manufacture the part with equipment that would give the necessaryaccuracy.This part is a contact for aircraft control system. For production of such

part it is advisable to select cold punching blanking from a sheet metal strip.

The flat sheet has overall dimensions of 50 30mm, simple outer counter

without slot and with hole of diameter 3 mm and rectangular hole with radiuses

5mm which are made at the distance of 10 mm from the straight edge. Materialthickness is 1 mm. Tolerances correspond to 14 and 9 classes of accuracy.


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Table 1 Mechanical properties of the alloy D16 material.

Elasticity modulus E,

(Pa 109)

DensityY,(g/cm3)

Shear

strength, s,

(MPa)

Ultimate strength

uts, (MPa)

72 2.8 300 380

Thecriteria of the good manufacturability of the shearedpartsare follows:

1) minimum of material waste;

2) minimum number of operations and minimum labor intensiveness;

3) presence or absence of the following part machining;

4) minimum of required equipment and manufacturing areas;

5) increasing of operations and workshop productivity;

6)increasing ofdies durability.

The most general manufacturability criterion is a minimal part cost.The main manufacturability requirements for sheared parts are:

a) avoiding of complex shapes with narrow and long notches (b 2S). Herebnotch width, Ssheet thickness. This criterion is satisfied.

b) avoiding of blanking of a long and narrow parts with constant width (b

3S); instead it is common practice to use the flattening of wire blanks. This

criterion is satisfied (30>3).c) minimal dimensions of pierced holes can be defined with the help of table

2 (Ssheet thickness). This criterion is satisfied. Minimal dimension is equal to

3 mm > 0.8 mm.d) minimal distance from the hole edge to the strip edge shouldnt be less

than Sfor circular holes and 1.5S, if hole edges are parallel to the parts edge. This

criterion is satisfied (5mm>1.5mm).e) minimal distance between holes pierced at the same time should be: b =

(23)S.This criterion is satisfied : b = 4 mmTable 2Minimal dimensions of the pierced holes

Conclusion: all above requirements are satisfied.

2. The most advisable method of manufacturing is shearing by die.3. Ive chosen two standard metal sheets ( 1050-88) width 750mm and

1500mm, length 2000mm and 3000mm is cut by guillotine shears, and the blank isa strip (figure 1.2).

MaterialStamping with free punch

circular rectangular

Hard steel 1.3S 1.0SSoft steel and

brass1.0S 0.7S

Aluminum 0.8S 0.5S

Textolite andturbonit

0.4S 0.35S


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4. It is necessary to use the strip nesting arrangement which guarantees the

maximum of material utilization ratio (the waste of material should be minimum).5. Analysis of possibility of low-wasted nesting (without waste of material at the

upper and lower side of a strip) by comparison of tolerances for parts dimensions

p (table 3).

The length of the part is L=50mm and tolerance for 14 quality is 0.74mm. With thepart thickness 1 mm, guillotine shear tolerance g. s, is 0.8 mm. Since g. s=0.8 >

p=0.74 shear cannot provide the required accuracy and strip nesting with scrap

allowance should be used.

Table 3Tolerances p for 13th

and 14th

accuracy classes

Dimension, mm p, mm

13th

accuracy class 14th

accuracy class

over 36 0.18 0.30

over 610 0.22 0.36

over 1018 0.27 0.43over 1830 0.33 0.52

over 3050 0.39 0.62

over 5080 0.46 0.74

over 80120 0.54 0.87

Table 4Guillotine shears tolerance () g. s,

Strip width,

mm

S, mm

up to 1 over 12 over 23 over 35

100 0.6 0.8 1.2 2over 100 0.8 1.2 2 3

Figure 1.2. Strip nesting arrangement


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6. The tab dimensions m (edge clearance) and n (skeleton width) are chosen

according to the table 5; which compensate the inaccuracy of strip placing into adie and its fixation. m=2.5 (noncircular punching), n=2 (noncircular punching)

Table 5Minimum tab values m and n, mm

S, mm

Manual strip feedAutomatic strip

feedcircular

punching

noncircular

punching

punching with

strip 180

turning

m n m n m n m n

Less than 1 1.5 1.5 2 1.5 3 2 3 2

12 2 1.5 2.5 2 3.5 3 3 2

over 23 2.5 2 3 3 4 3.5 3 3

7. Choose the optimal nesting arrangement on two standard sheets which providesthe maximum material utilization ratio (minimum material waste)..

Factor can be calculated by the following formula:

LB

FN

,Nnumber of parts on the sheet;F=1129 mm

2area of one part;

B,Lsheet width and length.

Sheet metal blank 2000 750 mmHorizontal nesting arrangement

N=62 13=806;

F=1.12910-3

m2

=0.61

Vertical nesting arrangement


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N=36 23=828;

F=1.12910-3

m2

=0.623

Sheet metal blank 3000 1500 mm

Horizontal nesting arrangement

N=93 27=2511;

F=1.12910-3

m2

=0.63

Vertical nesting arrangement

N=54 46=2484;

F=1.12910-3

m2

=0.623

Conclusion: it is advisable to use horizontal arrangement of strip in standard sheet

3 1.5m. The obtained results are shown in the table 6


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Table 6. Selection of a standard sheet with maximum

Sheet

Number of parts, pcs. Nesting

providinghigher

, %Horizontal stripnesting

Vertical stripnesting

1500 3000mm 2511 2484 Horzontal 63750 2000 mm 806 828 Vertical 62.3

The variant of nesting with maximum should be defined as optimal one and

should be used as primary.

1.2. Selection of die type

Using the recommendations for manufacturing of sheared parts and taking the

initial data (parts geometry, dimensional accuracy and surface smoothness,

production plan, etc.) into consideration, the die type may be chosen.

1. I chose combined stamping as stamping method. For combined stamping one

die generates all contours (inner and outer); this method decreases the labor

intensiveness and cost of parts.

2. I chose progressive die. A part is manufactured in several operating steps; this

stamp is cheaper but is less accurate (it can provide only the accuracy IT13+);

stamping productivity is higher: stamping (strip feed, scrap removal) can be

automated; operating safety is higher.

For progressive die:

1 part per cutting pass (except the first pass when the inner contour is

created).

strip feedingright-to-left, along guide rails. Elements of automation canbe applied here (automatic/manual feed).

Figure 1.4 Progressive die:1 piercing punch;2 blanking punch (for outer contour); 3 dieblock; 4, 6 scrap; 5 part; 7 stop (shearing punch); 8 strip.


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blank (strip) fixation: first, by a finger stop; during the every other cutting

passby a stationary (permanent) stop;parts and scrap removal a fall stamping type is used, parts and scrap fall

down separately to special containers after each cutting pass; elements ofautomation can be used.

1.3. Energy-power parameters of stampingCalculation the main energy-power parameters of stamping.

1. Punching force for inner contours (punching forcep):

p = k shLi.c S,k = 1.2 factor, which considers the irregularity of material thickness, its

mechanical properties, cutting edges dulling, etc.;

shshear strength of strip material;

Li.cinner contour(s) perimeter;

Ssheet thickness.

p = 1.2 300000000 ( 0.003+0.071) 0.001=28953N,2. Punching force for outer contours (blanking forceb):

b = kshLo.c S,

k = 1.2 factor, which considers the irregularity of material thickness, itsmechanical properties, cutting edges dulling, etc.;

sh = shear strength of strip material;Ssheet thickness.

Lo.c = 143mmouter contour perimeter.

b = 1.2 300000000 0.143 0.001= 51480N,

3. Total punching force for all parts contours:P =p +b.= 28953 +51480 =80433N

4. Stripping pressure. A stripping pressure calculation helps to determine thecorrect amount of the spring pres sure a spring-loaded stripper must produce. It

usually varies between 3 and 20 percent of the blanking pressure and can becalculated using next equation:

r=h-d = kr/h-dP,Where kr/h-dfactor, which depends on die type and material thickness (table 7).

Table 7Factor kr/h-d

Stock thickness S, mm kr/h-d

separate stampingcombined progressive

stamping

Less than 1 0.020.06 0.060.08

1.15 0.060.08 0.100.12

r=h-d = kr/h-dP=0.08 80433 = 6435 N,

5. Part (scrap) pushing force for die block with cylindrical band:

,s

hPkQ

k= 0.065experimental coefficient;hheight of cylindrical band (standard value; e.g., 5 mm).


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6. Total technological force Pt:

Pt =+h-d+ Q=80433 +6435 +26141 =113010N.Working procedure: upper die shoe moves down, inner and outer contours are

created (P), after that punches push the scrap through the cylindrical band (Q).Total technological force Ptis used as one of parameters for press selection.

2. Die design. selection of equipment

2.1. Center of pressureWhen a progressive blanking die is too large, it would better be positioned on

the same axis as the ram of a press. This way the center of the press force and the

center of its distribution throughout the blanking station will coincide. To position

a powerful blanking die slightly off the center may result in greater than usual wearof die bushings, caused by the dies inclination in the direction of the lesser

support.In order to place a complicated shape dead on center, first the center must be

located.

The method of calculating the center of pressure of an irregular shape is

demonstrated on the sample shown in Fig. 2-1.Figure 2.1 shows method of calculation of center of pressure position (an

intersection ofycandxc axes).

Figure 2.1Center of pressure

Analytical method of center of pressure calculation gives the followingformulas forxcenter andycenter(, barenot shown on fig. 2.1):

=

xcenterdistance fromy axis to the center of pressure;ycenterdistance fromx axis to the center of pressure;


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P1, P2, punching forces;

X1, X2distances from the center of pressure of blanking and piercing punchesrespectively toy axis;

Y1, Y2 distances from the center of pressure of blanking and piercing punchesrespectively tox axis.

Instead of forces P1, P2, P3 one can use the respective perimeters of figures,becausep-i.c = k sh Lc S, and parameters k, shand Sare the same.

An axis of press slider must go through the dies center of pressure

(intersection ofxcand yc axes).

2.2. Defining of cutting clearance between

punches and die block opening

If cutting clearances are defined correctly, the cut edge quality is high, diedurability is greatest, punching forces are optimal, etc.

For a die block with cylindrical die land, the value of punch-die clearance z

(figure 2.3) depends on material properties and sheet thickness S(table 8):z =k S.

Table 8Bilateral clearances

Sheet thickness

S, mm

Factork value for

aluminum alloys

(steels) 10,15, 08rim, 20, 25,

30, 35, 40, brass

45 (Steel45) and higher

0.10.25 0.0050.02 0.0050.02 0.0050.02

0.250.5 0.050.10 0.060.12 0.070.14

0.51.8 0.060.10 0.070.12 0.080.14

1.83 0.080.10 0.090.12 0.100.13

Over 3 0.080.12 0.110.15 0.130.16

Figure 2.3Cutting clearance for cylindrical punch:1punch; 2die block

z= 0.11 = 0.1mm.For the die opening with conical die land the cutting clearances are

decreased by 10-15%.The main rule for optimal cutting clearance is the follow: the dimension of

the pierced hole is equal to the dimension of the piercing punch and the dimensionof the blanked contour is equal to dimension of the die opening.


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2.3. DIE BLOCK AND PUNCHES DIMENSIONS

Die set may be used for piercing and blanking when the cutting clearancebecomes greater than allowable maximum clearance (optimal). In such a case the

main rule is broken: the pierced hole dimension becomes greater than the piercingpunch dimension and the blanked contour dimension becomes less than die

opening dimension. In this case the proper toleranceddimension of the punch anddie must be assigned.

Checking the possibility of separate manufacturing of die block and punchesis possible if the following condition is fulfilled (forzmin see table 2.1):

z zmin < d+ p.

0.1 -0.08=0.02 < 0.075+0.075=0,15 mmFor complex shape punches (inner or outer), only manufacturing together

with die block is possible. In this case, one of two dimensions (of punch or dieblock) is defined as main (depending on type of contour inner or outer), and

another one is manufactured according to the main dimension.All cutting tools (punches and die block) must be by 3-4 accuracy class

greater than accuracy class of the part being sheared (technologicalrecommendation).

Figure 2.4 shows how to determinethe dimensions of the die block and

punches.

Nominal dimensions depend on the

rule noted above and the optimalclearancez.

Toleranced dimensions of circular

contours (punches dimensions or

dimensions of holes in die blocks) can be

calculated by the following formulas:

a) for inner contour(s):

0 8p

p nD D .,

0 8d b

d b nD D . z ;

b) for outer contour:0 8

d b

d b nD D . ,

0 8p

p nD D . z,

Dd-b,Dpdie and punches dimensions;Dnnominal dimension;

tolerance of parts corresponding dimension (for defined accuracy class);

d-b pdimensional tolerances of die block and punches (11th accuracy class).

Table 2.2 can be used for determination of dand p.

Table 9Dimensional tolerances (14th accuracy class) and tolerances for tools(11

thaccuracy class)

1 2Figure 2.4 Punches and die

dimensions: 1 die,2 punch.


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Dimensions, mm

Tolerance

(14th

accuracy

class),m

Tolerance

(9th

accuracy

class),

m

Tool

tolerance,(11

thaccuracy

class) m

Tool

tolerance,

(6th

accuracy

class) m

13 250 25 60 6over 36 300 30 75 8

over 610 360 36 90 9

over 1018 430 43 110 11

over 1830 520 52 130 13

over 3050 620 62 160 16

over 5080 740 74 190 19

over 80120 870 87 220 22

over 120180 1000 100 250 25

The defined dimensions are represented in table 10.Dimensions of non-circular contours can be calculated by the following

formulas:) decreased (because of tool deterioration) dimensions punch dimensions (e.g.,

dimensionA on figure 2.4):

0 8t

p nP P .,

0 8t

d b nP P . z ;

b) increased (because of tool deterioration) dimensions die block dimensions

(e.g., dimension Fon figure 2.4):

0 8t

d b nP P . ;

0 8t

p nP P . z;

c) constant dimensions (dimensionE on figure 2.4):

P =Pn 0.2 ,

Ptoleranced non-circular dimension;Pnnominal dimension;

tolerance of parts corresponding dimension (for defined accuracy class);t = 0.3 tool (die block/punches) dimensional tolerances.

Table 10Dimensions

Dimen

sion

Nominaldimension,

mm

Tolerance

, mm

Tooltolerance

t, mm

Dimension type P, mm

A 50 0.62 0.16 Increasing 49.504+ .

B 30 0.62 0.16 Increasing 29.504+ .

C 10 0.3 0.075 Increasing 9.76+ .

D 20 0.43 0.11 Constant 200.086E 5 0.03 0.008 Decreasing 5.024-0.008F 3 0.03 0.008 Decreasing 3.024-0.008


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2.4. Selection of press

and manner of die fixturing1. Mechanical presses are usually used for manufacturing of relatively small parts.

Such presses usually have greater productivity than hydraulic ones due to thegreater stroke rate of the ram.

Mechanical presses have many parameters and there are many requirementsfor such presses.

Figure 2.5Press geometry

2. Press selection (first approximation).Total technological force Pt should be approximately equal to the normal

press forceP (table 11).3. According table we select Single-crank C-frame single-action press. Model

2122.Table 11Press parameters 2122

Press Capacity(Tonnage) P, kN

160

Stroke, mm 571Stroke rate, min

- 180

Bolster PlateBL, mm 420280Shut HeightH, mm 250

Maximum press height,mm

550

Bolster Plate opening

diameter, mm 260Drive powerN, kW 1.1

Wholesale price, USD 42004. Checking of the press requirements:

a) Required technological force Pt should be less or equal to the normal

press force P: Pt P 113 160kN. Hence it satisfies requirement.b) Effective press drive power Apr should be greater or equal to the stamping

energy (work):Apr.Stamping work can be calculated by the following formula:

A =c Pt h = 0.70.004 113010 = 316 J,= 0.7dimensionless factor;


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h = Hmaxst

Hminst

die stroke length (can be calculated after one has the

dimensions of dies elements: upper and lower die shoe, punches, die block, etc.).Press drive power can be calculated by the following formula:

Npr= 1N =0.9 1100=990W,

1 = 0.9coefficient of efficiency (from an engine to a fly wheel);

Nelectric motor drive power.Determine a fly wheel work:

k 1.3 irregularity coefficient;

nstroke rate, min-1

(table 2.5).Determine the effective press drive powerApr:

pr = f.w=0.7 254=178 J,

= 0.7press efficiency coefficient.Finally, check if Apr. 178. Thus this requirement is not satisfied. So I haveselected press model 2124. Its press capacity equals 250 kN

c) Press stroke should agree with the stamping process.

That means that:

Hmin + 5 mm


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Table 12Die block thickness (height)

Maximum width

(length) of a die

block hole b (b1),

mm

Die block thickness (height) for sheet thickness

1 mm 13 mm 36 mm

50 (0.30.4) b (0.350.5) b (0.450.6) b50100 (0.20.3) b (0.220.35) b (0.300.45) b

100200 (0.150.2) b (0.180.22) b (0.220.30) b

over 200 (0.100.15) b (0.120.18) b (0.150.22) b

b =50

b1=30

H=0.3 50=15. Rounded up to the 16.

B=50 +3 16=98. Approved equals 100.

B1=30+3 16=78. Rounded up to the 80.

Figure 2.6Working zone and hole dimensionsAccording reference literature [1, p. 75] the die cant have lesser dimension than

125 125mm. And according [1, p. 448] it was chosen 22number of die shoe withdimensions 125 125mm

2. PunchesUsually punches are made of tool steel (for example, 8 1435-90).

The main properties of8 steel are:

[ bear] = 100 MPaallowable bearing stress;

[ c] = 1600 MPaallowable compression stress;

E= 2.151011

Pamodulus of elasticity.) punches bearing calculation:

bear= F

P

[ bear],

Paxial punch force (punching force Pp);p = 1.2 3 10

80.003 0.001=3392N

Fpunch bearing surface area. F= 0.0092/4


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>[ bear]

Punch bearing diameter (area) should not be increased.

b) punches compression calculation:

c Pf

[ c],

f = 0.0032

/4minimum sectional area of the punch.

MPa

c< [ c], so the punch diameter (area) should not be increased:

c) calculation of punchs free length (stability requirement):

Jminminimum moment of inertia of the punch;Jmin = min (Jx, Jy);

Paxial punch force (punching force Pt);n = 2.5safety coefficient.

Table 9Results of calculations

Element P, kN Jmin,mm

4

b,MPa c

, MPa l, m

Punch for inner

contour ( 3mm)3392

4.0510-

12 53 480 0.0642

3. Lower die shoeIt is reputed that a die block doesnt react a load; it transmits load to the lower

die shoe. Bending analysis should be made for the lower die shoe (e.g., cast steel

30: [ bend] = 120 MPa).

b= W

Mmax

[ bend],

Mmax = PtL/2 maximum moment of force;L = dhole diameter in the press table;

Wmoment of resistance of a lower die shoes section about a horizontal axis (b,

hlower die shoe overall dimensions) (figure 8).


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Figure 8Moment of resistance for a rectangular

This moment of resistance of a lower die shoes section

Wx=0.1250.1252/6=3.25510

-4

Mmax =113010 0.05/2=2825Nm

b= 8.67


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Shank with flange

diameter of shank Ds=40mm5. The type and dimensions of the permanent stop are gotten from [1, pp.

125127]. Mashroom stop is choosen.Height of the permanent stop is 8mm.

6. The type and dimensions of the finger stop are gotten from [1, pp. 128131].

7. The clearance between the punches and the stripper (stationary or movable)are gotten from [1, p. 113]. It isequal to 1 mm.

8. Dimensions of screws and pins are gotten from [1, p. 77]. Diameter of

screws are equal to M12, pins diameter equals 8mm.

2.7. Die assembling. assignment of tolerances and fits

Typical die assembling procedure is the following:

1. Install the lower die shoe (pos. 4) on a workbench.

2. Install the die block (pos. 1) with stock guides (pos. 2) and finger stop(pos. 26) on the lower die shoe. Fix by screws (pos. 14) preliminary. Ream theholes 12

3. Fix the die block by dowel pins (pos. 17) by fit H7/n6, after that fix the dieblock by screws (pos. 14) finally.

4. Install the guide posts (pos. 22, 23) into the lower die shoe by fit S7/h6.5. Install the shank (pos. 27) into the upper die shoe (pos. 3) by fit H7/s6; fix

it by the pin (pos. 15).6. Install the guide bushes (pos. 20, 21) by fit H7/s6.

7. Join upper die shoe (pos. 3), back up plate (pos. 5), punch plate (pos. 9)with punches (pos. 68) and stripper (pos. 10) by screws (pos. 13).

8. Lubricate the guideposts with technical vaseline and install the die upper oncorresponded guideposts; move the upper die shoe down and check if punches go

easily through the holes in the die block.9. Install the block punchespunch plateback up plate in a way to provide

the required clearances between the punches and the die block. Fix the blockpreliminary by screws (pos. 13).

10. Ream the holes 12H7 in the block punchespunch plate back upplate.

11. Install dowel pins (pos. 16) in the holes ay fit 8 H7/n6.11. Fix the block punchespunch plateseparator by screws finally

(pos. 13).


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Conclusion

The die for piercing-blanking operation is designed. Given part can bemanufactuered to required degree of accuracy using designed die. If the tool is

produced and assembled as was said above, the production of the part will meet allrequirements which were considered


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References

1. Die designers handbook: Sheet stamping. Edited by L. Rudman. Moscow:

Mechanical engineering, 1988.496 p. (lang - russian)

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