sect 2-sheet metal

171Page of

TABLE OF CONTENTS

IN GENERAL 2

DEFINITIONS

BENDING RADII

CORROSION-RESISTANT STEEL

BERYLLIUM COPPER

PAGE NO.CONTENTS

2

SECTION 2SHEET METAL WORKING

3

3

4ALUMINUM & ALUMINUM ALLOYS

5MAGNESIUM ALLOYS

6CARBON STEEL

7COMMERCIAL BRASS

PHOSPHOR BRONZE

9BEND RELIEF CUTOUTS

9NOTCHING

9OPEN CORNERS

9LANCING

10WELDED CORNERS

10KNUCKLES

LIGHTENING HOLES

11SHEARING

11DRAWING

11RIBBING AND STIFFENING

12THIN SHEET METAL

12CROSS BRACES

SPUN SHAPES 17

BRACING 16

RIBS 15

GUSSETING

STANDARD PUNCHES

HOLE PUNCHING

LOCATION OF HOLES

8

10

12

12

13,14

15

172Page of


BENDING

The direction of grain will affect the

formability of hard metals but does not

affect softer metals appreciably. When

the axis of bend is at right angles to the

direction of the grain, a smaller bend

radius can be used without fracturing themetal.

DEFINITIONS

Bend Radius.- The radius formed when

bending sheet metal.

Mold Line.- The intersection of extension

lines of two external surfaces of a bend.

This is the point where the intersection

would occur if the parts were producedwithout a bend radius.

Bend Relief.- The removal of material to

provide clearance for the intersection of

bend radii when forming a corner.

Dimension bends to mold lines. When the

surfaces being dimensioned are parallel or

square, the mold lines are the same asthe extension lines. When the surfaces

are at an angle to each other, dimension

to the mold line. When angular dimensions

are required, indicate the angle from the

position of a 90° bend.

Square Bend

Open Bend

Closed Bend

Generally, overall dimensions are preferred.

However, inside dimensions are permissible

if the part has special dimension or

tolerance requirements.

Overall Dimensioning

Inside Dimensioning

IN GENERAL

The advantages of using sheet metal in

the design of equipment are obvious. It is

widely used because strong, light-weight

parts can be made quickly and cheaply.As a method of fabrication, sheet metal

working includes; bending, drawing,

blanking, piercing, trimming, shearing,

rolling, ribbing, spinning and stretching.

SHEET METAL WORKING

173Page of


BENDING RADII

When precision bends are required, angular

tolerance may be one or two degrees for

thin metals (.012 to .060 inch) and onedegree for thicker metals (.060 to .154 inch)particularly for boxes, frames, chassis andcovers.

Because of such differences, technical

manuals will vary as to the minimum

bend radii to which various metals may be

bent without damage to the part.

In the tables which follow, the minimum

bend radii for various metals is supplied.

If the actual radii is not given, a factor

is used in determining minimum insideradii.

Where a factor is used, the radius for

a given thickness of metal is obtained

by multiplying the thickness by thefactor. A zero factor indicates that

the bend may be sharp.

301, 302

0 - 0.5

0 - 0.5

3 - 4

3

1 - 2

2

1

2

1

0 - 0.5

301, 302

301, 302

301, 302

301, 302

301, 302

301, 302

301, 302

301, 302

304, 316, 347, 410

304, 316, 347, 410

Annealed

1/4H

1/4H

1/2H

1/2H

3/4H

3/4H

H

Annealed

Annealed

Annealed

Over 0.050

To 0.050

To 0.050

Over 0.050

To 0.050

Over 0.050

To 0.030

0.031 to 0.050

To 0.050

To 0.050

Over 0.050

0 - 0.5

FactorSheet thickness, inchTemperAISI type

CORROSION-RESISTANT STEEL

MINIMUM INSIDE BEND RADII FACTORS

FOR 90 COLD BEND PARALLEL TO ROLLING DIRECTION (GRAIN)

BERYLLIUM COPPER: ASTM B194, QQ-C-533

MINIMUM INSIDE BEND RADII FACTORS

FOR 90 COLD BEND

1

4

2

0

H

1/2H

1/4H

A

Sheet

thickness

inch

B & S

numbers

hard

Temper

To 0.040

To 0.040

To 0.040

To 0.040

rolling direction

Perpendicular to

FACTOR

0

2

4

1

At 45° to

rolling direction

Parallel to

rolling direction

1.5

5

2.5

0

2

6

3

0

174Page of


ALUMINUM AND ALUMINUM ALLOYS

MINIMUM INSIDE BEND RADII FACTORS FOR 90 COLD BEND

3003-0

0.016

1/64

Approximate thickness of sheet, inch

1100-0

1100-H12

1100-H14

2024-0*

3003-H12

5052-0

6061-0

3003-H14

5052-H32

1100-H16

5052-H34

7075-0

3003-H16

6061-T4

1100-H18

5052-H36

6061-T6

3003-H18

5052-H38

2023-T3

2024-T36

7075-T6

0

FACTOR

Alloy and temper

designation

0

0

0

0

0

0

0

0

0

0

0

0

2 - 4

3 - 4

2 - 3

1.5

1.0 - 1.5

1

1

0.5 - 1

1

0.5 - 1

3 - 4

4 - 5

3 - 5

0

0.5

0

0.5

0

0

0

0

0

0

0

0

0

1/32

0.032 0.064

1/16

0

0

0

0

0

0

0

0

0

0.5

1

0 - 1

3 - 5

4 - 5

4 - 5

2.5 - 3

1.0 - 1.5

0.128

1/8

0

0

0

0

0

0

0

0

4 - 6

5 - 6

4 - 6

2

1.5 - 2

0.182

3/16

0

0

5 - 7

6 - 7

5 - 6

2.5 - 3

0.258

1/4

6 - 10

8 - 10

6 - 7

4

1.5 - 2

1.5 - 2

1.5 - 2

2.5 - 32.5 - 3

1.5 - 2

1.5 - 2

1.5 - 2

0.5 - 1

1.0 - 1.5

2.5 - 3

1.5 - 2

0.5 - 1

0.5 - 1

0.5 - 1

0.5 - 1

1.0 - 1.5

0.5 - 1.5

3 - 4

3 - 4

2 - 3

2 - 3

2 - 3

4 - 5

4 - 5

3 - 4

2 - 3

3 - 4

3 - 4

0.5 - 1

0.5 - 1

1.5 - 2

0.5 - 1

0.5 - 1

0.5 - 1

0.5 - 1

0.5 - 1

0.5 - 1

1 - 2

1 - 2

0.5 - 1

0.5 - 1

0.5 - 1

0.5 - 1

0.5 - 1

0.5 - 1

0

0

1.0 - 1.5

1.5 - 2

5 - 6

5 - 6

4

4

4

3 - 4

2 - 3

2 - 3

1.5 - 3

175Page of


ASTM B90, Alloy FS1, Alloy AZ31A, QQ-M-44MINIMUM INSIDE BEND RADII

500 F

0.016

Minimum bend radius, inches

thickness

inchRoom temp 325 F Room temp

Annealed HardSheet

MAGNESIUM ALLOYS

0.020

0.025

0.032

0.040

0.051

0.064

0.072

0.081

0.091

0.102

0.128

0.156

0.188

0.250 0.50

0.38

0.38

0.25

0.25

0.19

0.19

0.16

0.16

0.09

0.09

0.06

0.06

0.06

0.06

1.25

1.00

0.75

0.63

0.50

0.44

0.44

0.38

0.32

0.25

0.19

0.16

0.13

0.09

0.09

2.50

1.88

1.63

1.25

1.00

1.00

0.82

0.82

0.62

0.50

0.38

0.32

0.25

0.19

0.190.09

0.09

0.13

0.16

0.19

0.25

0.32

0.38

0.44

0.44

0.50

0.63

0.75

1.00

1.25

176Page of


COMMERCIAL QUALITY (CQ) OR DRAWING QUALITY (DQ)MINIMUM INSIDE BEND RADII FOR 90 COLD BEND

0.008

Minimum bend radius, inchesthickness

inch

Sheet

CARBON STEEL AS ROLLED OR ANNEALED;

0.012

0.016

0.020

0.025

0.030

0.035

0.042

0.050

0.062

0.078

0.093

0.109

0.125

0.156 5/16

1/4

7/32

3/16

5/32

3/32

1/16

0

0

0

0.188

0.250

3/8

1/2

*

* For thicknesses not listed, use next greater thickness.

1/16

1/16

1/16

1/16

1/8

177Page of


COMMERCIAL BRASS: SAE 70C, ASTM B36, Alloy 8MINIMUM INSIDE BEND RADII FACTORS

FOR 90 COLD BEND

Sheet

thickness

inch

B & S

numbers

hard

Temper

rolling direction

Perpendicular to

FACTOR

At 45° to

rolling direction

Parallel to

rolling direction

0 to 2

3

3

3

3

4

8

10 0.0254

0.0641

0.0508

0.0403

0.0320

0.0254

0.0201

0.0159

0.0100

0.0090

0.1144

0.1019

0.0907

0.0808

0.0641

0.0571

0.0508

0.0456

0.0403

0.0320

0.0254

0.0808 to 0.0907

0.0641

0.508 to 0.0571

To 0.0456

To 0.0907

2

2

2

1

1

1.25

1.5

1

0

0

2

2.5

1

0.33

0.5

0.25

0

0.25

0.25

0

0

0

6

4

5

6

5

6

5

4

1.5

1.75

2

2.5

1.3

0.75

0.5

0.5

0.33

0.33

0

0

0

0.33

0.25

0

0

10

4

5

6

8

10

11

10

9

1

2

2.5

3

1

1.5

1.5

2

1

0.75

0.5

0

1

0.5

0.33

0

Extra Spring

Spring

Hard

3/4 Hard

1/2 hard

Annealed to

0 0

4

4

4

4

4

4

4

4

4

4

To

0

0

0

0

8

8

8

8

8

8

8

8

178Page of


PHOSPHOR BRONZE: SAE 77A, ASTM B103, Alloy AMINIMUM INSIDE BEND RADII FACTORS

FOR 90 COLD BEND

Sheet

thickness

inch

B & S

numbers

hard

Temper

rolling direction

Perpendicular to

FACTOR

At 45° to

rolling direction

Parallel to

rolling direction

0 to 2

2

4

4

4

4

0.0641

0.0508

0.0456

0.0403

0.0320

0.0285

0.0254

0.0226

0.0201

0.0179

0.0159

0.0456

To 0.0720

1.5

1.75

2

2.25

2

2.25

1.25

1.5

0.75

1.75

1.5

0.5

0

0.75

0

---

---

5

6

5

7

6

5

2.75

2

1.5

2

1.5

0.75

9

3

3

4

3

0.75

Spring

Hard

1/2 hard

Annealed to

0 0

6

1

0

1.5

1.25

8

8

8

8

8

8

8

8

8

8

8

8

XH

To 0.0142

---

---

---

--- ---

---

---

---

---

---

---

---

---

---

---

---

1/2 hard

0.0508

0.0403

0.0320

0.0201

0.0808 to 0.1250

179Page of


.03 MIN

BEND LINES

LC BEND RADIUS

.130 DIA

MIN

.03 MIN

BEND LINE

FLUSH

WIDTH NOT CRITICAL

(NO MIN.)

BEND RELIEF CUTOUTS

To prevent interference whenever sheet metal bends intersect one another, material

must be removed from the intersection.

The material removed should be at least

.03 inch behind the intersection of the

bend lines. Usually, the inside of therelief cutout is a radius.

NOTCHING

Notches and slots are made in the flat

blank in order to avoid tearing or cracking

the metal. It is usually adequate if the

width and depth of reliefs are twice thethickness of the stock.

OPEN CORNERS

Use open corner construction wherever

possible to avoid the additional cost of

welding.

edge of the opening.

should be allowed between a bend and the

A minimum distance of at least 1/4 inchof holes in metal apply equally to lancing.

Generally, the rules governing the punching

LANCING

Lancing

.25 MIN

1710Page of


R

KNUCKLE

WELDED CORNERS

A corner shape should be drawn as it

appears after welding and indicated by

the appropriate welding symbol.

Do not show corner bend relief on a

welded corner. However, the bend relief

delineation must be shown on all

unwelded corners.

A contoured or finished weld should not

be called for unless specifically required

by engineering.

Unfinished

Contoured

KNUCKLES

Where rounded corners are needed, e.g.,

tops and bottoms of cabinets, the use ofdrawn ball corner or knuckle should be

considered.

After knotches are put in the flat blank

and the edges have been roll formed, the

gap can be filled with a formed knuckle

which is welded in place and the corners

ground or filed smooth.

LIGHTENING HOLES

Lightening holes are cutouts in sheet

metal parts usually for the purpose of

reducing weight. They may be plain round

holes or of other shapes and are dimensioned in the same manner as other

cutouts.

In order to avoid stresses which might

cause tearing or fatigue cracking of themetal, such holes should have inside

radii in the corners of openings.

1711Page of


SHEARING

Shearing is the method employed for

cutting off large or small pieces of metal

from strip or plate stock. As in punchingholes, burrs are formed and must be

removed by machining operations such as

grinding, reaming or milling. Barrel

tumbling is used for deburring small

parts.

Burr Formed By Shearing

DRAWING

The common materials for the drawing

process include steel, aluminum, magnesiumand brass. To achieve a successful draw

of a cylindrical shape, the ductility of thematerial has to be considered. Also

important is the size of the corner radii

and the ratio of height to diameter.

Rectangular shapes can also be drawn.

However, to prevent fractures at the

corners, the shape of the blank and the

design of the die must be carefullyconsidered. The radius of corners should

be not less than six times the stock

thickness nor under 3/8 inch.

HOLD DOWN PAD

FLANGE

Drawing Operation

RIBBING AND STIFFENING

The accuracy and rigidity of a bend can

be increased by means of corrugation,

ribbing and stiffening flanges. Generally,ribs are double the stock thickness in

height and equal to the stock thickness

in inside radius (section A-A).

Sometimes it is desirable to reinforce a

hole by forming a rib around the hole

(section B-B).

B B

A

A

SECTION B-B

SECTION A-A

Ribbing can help reduce the

size and weight of a part.

1712Page of


*

*

*

*

THIN SHEET METAL

In thin sheet metal, lapping and spot

welding of corners is preferred to butting

and welding of corners for a stronger and

more inexpensive joint.

Lapped Joint

CROSS BRACES

Supports and cross braces should be

tapered to make assembly easier and to

reduce weight. However, the flange

taper should not be to the metal face.

The taper should be partial, as shown.

TWICE METAL

THICKNESS

1 1/2 T(MIN)

T

LOCATION OF HOLES

Never locate a hole too close to a bend

or an edge. The edge of the hole should be no closer to the inside of the bend

or edge of a plate than 1 1/2 times themetal thickness. If such a hole is

required, it may be necessary to put thehole in after the bend has been made.

HOLE PUNCHING

When a punch and a die are used for

putting holes in sheet stock, the sides

of the hole are not perfectly perpen-

dicular to the stock. As a consequence,if accurate holes are desired, the hole

must be punched undersized and reamedto the desired dimension.

PUNCH

STOCK

DIE

1713Page of


In addition, hole punching is employed in

small lot or mass production processes.

Many factors need to be considered

including material properties, hole size andlocation, stock thickness and the clearance

between the punch and die.

Also, punched holes need not be only

round. Standard punches come in a

variety of sizes and shapes as shown inthe tabulations below.

Drill Nos.-1 thru 66

1/32" thru 1/2": in 1/64" increments33/64" thru 3/4": in 1/64" increments49/64" thru 13/16": in 1/64" increments53/64" thru 1": in 1/64" increments1-1/32" thru 1-3/16": in 1/32" increments1-7/32" thru 1-7/16": in 1/32" increments1-15/32" thru 1-23/32": in 1/32"increments1-3/4" thru 1-27/32": in 1/32" increments1-7/8" thru 1-15/16": in 1/32" increments1-31/32" thru 2": in 1/32" increments2-1/16" thru 2-5/16": in 1/16" increments2-3/8" thru 2-5/8": in 1/16" increments2-11/16" thru 3": in 1/16" increments3-1/16" thru 3-5/16": in 1/16"increments3-3/8" thru 3-5/8": in 1/16" increments3-11/16" thru 4": in 1/16" increments

ROUND SIZE

All standard "A"

range dimensions

progress in 1/32" increments up to

1/2". All "A" rangedimensions from 1/2"thru 1" progress in1/8" increments. 1/8" increments.

thru 1" progress indimensions from 1/2"1/2". All "A" rangeincrements up to

progress in 1/32" range dimensions

All standard "A"

increments up to

progress in 1/16"range dimensions

All standard "B"

5/8". From 5/8" thru 1" in 1/8"increments. From

1" thru 2" in 1/2"increments. increments.

1" thru 2" in 1/2"

increments. From

thru 1" in 1/8"5/8". From 5/8"

All standard "B"

range dimensions

progress in 1/16"increments up to

1. 1.

2.2.

B

A A

B

7/32, 1/4

5/32, 3/16

1/8

9/32, 5/16

11/32, 3/8

13/32, 7/16

15/32, 1/2

17/32, 9/16

19/32, 5/8

21/32, 11/16

23/32, 3/4

1-7/8, 1-15/16, 2

1-11/16, 1-3/4, 1-13/16

1-9/16, 1-5/8

1-7/16, 1-1/2

1-1/4, 1-5/16, 1-3/8

1-3/16

1-1/16, 1-1/8

31/32, 1

25/32, 13/16

27/32, 7/8

29/32, 15/16

SQUARE SIZE

1

7/8

3/4

5/8

1/2

3/8

5/16

1/4

3/16

1/8

RADIUS

CORNER ROUNDING

1714Page of


(Standard Punches continued)

.315

.375

.406

.440

.505

.562

.630 .590

.541

.473

.410

.359

.343

.281

1/4 1/8 7/16

5/83/163/8

1/2 1/4 7/8

5/8 5/16 1

3/4 3/8 1-1/4

11/163/8

7/81/2

1-1/83/4

1-3/81 90 -1-1/4"

90 -2"

60 -1-7/16"

90 -1"

3/161-13/161-7/8

3/161-1/21-1/8

A B C

SIZE

B

.344

.468

.562

.640

1.1411.360

.760

.630

.516

.391

A

SIZE

SIZE

A B

"D" SHAPE

SIZE

BA

KEYHOLE

C

CONDUIT SIZE

HOLE

ELECTRICAL OUTLET KNOCKOUT

SIZE

DOUBLE "D" SHAPE

RECEPTACLE

NOTCHING

A

B

A

A

A

C

B

B

CBC

1715Page of


x

x

x

GUSSETING

The weakest parts of any structure are

usually to be found at its joints. Gussets

are employed to spread stresses

concentrated at joints over large areas.

They are an inexpensive method for

strengthening an entire structure, increasing

rigidity and making the structure less

susceptible to bending forces.

Many methods are available for affixing a

gusset to a frame. The most common of

these techniques are shown below.

Riveted Gusset Plate

Combination Spot-Welded andBolted Gusset

WELDED

BOLTED

RIBS

There are many forms of ribs but however

attached, their primary function is to

effectively increase the strength and

rigidity of a structure.

Rib On Sheet Metal Bracket

Panel With Spot-Welded

Stiffening Rib

Flat Circular Panel Ribbed

Against Bending or Warping

1716Page of


BRACING

The rigidity of a structure and its ability

to resist bending, torsional and buckling

stresses can be enormously improved by

correct bracing. Usually, the load carrying

capacity of a structure is also improved

by bracing without significantly increasing

the structure's weight.

Brace in Compression

Brace in Tension

Not Subject to Buckling

GOOD

GOOD

Inadequate bracing can cause excessive

deflection and even result in sensitivityto small vibrational forces, as shown

below.

Subject to buckling and side movement.

POOR

GOOD

prevent side

This bracing will

movement.

GOOD

lightweight and

Braces are

provide strength.

1717Page of


Because a straight-sided cylinder is very

difficult to spin, it should be formed, if

possible, by a drawing operation.

BLANK

FORMED

SHAP

SPINNING BLOCK

SPUN SHAPES

The process of spinning is limited to

symmetrical shapes that are circularin cross section and normal to the axis

of rotation.

This method can be used to form most

soft and ductile metals, and ordinarily itis used to manufacture items such as

cooking utensils, light reflectors and

various other conical shapes.

The forming tool in the spinning process

is usually made of wood or hard metal

and the tool is pressed against the blank

causing the metal to flow over the form.

However, conical and dome shaped parts

as shown in the following illustrations are

easy to spin and offer many advantages

over other types of production.

Spun parts are generally considered to be

moderately low is cost because very little

finishing is required. A simple trimming

operation and cleaning is all that is

required.

CONE SPINNING

As shown below, in cone spinning, the

chuck meets the metal at smaller angles

than in the case of spinning a simple

cylinder which allows for better control

in forming the metal.

BLANK

PARTIALLY

FORMED

SPINNING BLOCK

COMPLETED

SHAPE

SHEET

SPINNING BLOCK

PARTIALLY

FORMED

SHEET

COMPLETED

SHAPE

BLANK

The hemispherical shape is more difficult

to spin because the angle of deformation

becomes progressively more acute.

The greatest single advantage of spinning

over other methods is the very low cost

of getting into production. The main

disadvantage is the fact that shapes are

limited to round, symmetrical forms.

sect 2-sheet metal

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