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

13,1415

172Page of SECTION 2SHEET METAL WORKING

BENDING

The direction of grain will affect the formability of hard metals but does notaffect softer metals appreciably. When the axis of bend is at right angles to thedirection of the grain, a smaller bendradius can be used without fracturing themetal.

DEFINITIONS

Bend Radius.- The radius formed when bending sheet metal.Mold Line.- The intersection of extensionlines of two external surfaces of a bend.This is the point where the intersectionwould occur if the parts were producedwithout a bend radius.

Bend Relief.- The removal of material toprovide clearance for the intersection ofbend radii when forming a corner.Dimension bends to mold lines. When thesurfaces being dimensioned are parallel orsquare, the mold lines are the same asthe extension lines. When the surfacesare at an angle to each other, dimensionto the mold line. When angular dimensionsare required, indicate the angle from theposition of a 90 bend.

Square Bend

Open Bend

Closed Bend

Generally, overall dimensions are preferred.However, inside dimensions are permissibleif 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 iswidely used because strong, light-weightparts can be made quickly and cheaply.As a method of fabrication, sheet metalworking includes; bending, drawing, blanking, piercing, trimming, shearing,rolling, ribbing, spinning and stretching.

SHEET METAL WORKING


BENDING RADII

When precision bends are required, angulartolerance may be one or two degrees forthin metals (.012 to .060 inch) and onedegree for thicker metals (.060 to .154 inch)particularly for boxes, frames, chassis andcovers.

Because of such differences, technicalmanuals will vary as to the minimumbend radii to which various metals may bebent without damage to the part.

In the tables which follow, the minimumbend radii for various metals is supplied.If the actual radii is not given, a factoris used in determining minimum insideradii.

Where a factor is used, the radius fora given thickness of metal is obtainedby multiplying the thickness by thefactor. A zero factor indicates thatthe bend may be sharp.

301, 302

0 - 0.50 - 0.53 - 4

31 - 2

2121

0 - 0.5

301, 302301, 302301, 302301, 302301, 302301, 302301, 302301, 302304, 316, 347, 410304, 316, 347, 410

Annealed

1/4H1/4H1/2H1/2H3/4H3/4HH

Annealed

AnnealedAnnealed

Over 0.050To 0.050

To 0.050Over 0.050To 0.050Over 0.050To 0.0300.031 to 0.050To 0.050To 0.050Over 0.050

0 - 0.5

FactorSheet thickness, inchTemperAISI type

CORROSION-RESISTANT STEELMINIMUM INSIDE BEND RADII FACTORSFOR 90 COLD BEND PARALLEL TO ROLLING DIRECTION (GRAIN)

BERYLLIUM COPPER: ASTM B194, QQ-C-533MINIMUM INSIDE BEND RADII FACTORS

FOR 90 COLD BEND

1

42

0

H1/2H1/4HA

Sheetthickness

inch

B & Snumbers

hardTemper

To 0.040To 0.040To 0.040To 0.040

rolling directionPerpendicular to

FACTOR

0

24

1

At 45 torolling direction

Parallel torolling direction

1.5

52.5

02

63

0


ALUMINUM AND ALUMINUM ALLOYSMINIMUM INSIDE BEND RADII FACTORS FOR 90 COLD BEND

3003-0

0.0161/64

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

FACTORAlloy 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

01/320.032 0.064

1/160

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

0.1281/80

0

0

0

0

0

0

0

4 - 6

5 - 6

4 - 6

2

1.5 - 2

0.1823/16

0

0

5 - 7

6 - 7

5 - 6

2.5 - 3

0.2581/4

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


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

500 F

0.016

Minimum bend radius, inchesthickness

inch Room temp 325 F Room tempAnnealed 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


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

0.008

Minimum bend radius, inchesthicknessinch

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 5/161/47/323/165/32

3/32

1/160

0

0

0.188

0.250

3/81/2

*

* For thicknesses not listed, use next greater thickness.

1/161/161/161/16

1/8


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

FOR 90 COLD BEND

Sheetthickness

inch

B & Snumbers

hardTemper


FACTORAt 45 torolling 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 hardAnnealed 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


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

FOR 90 COLD BEND

Sheetthickness

inch

B & Snumbers

hardTemper


FACTORAt 45 torolling 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 hardAnnealed 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


.03 MIN

BEND LINES

LC BEND RADIUS

.130 DIAMIN

.03 MIN

BEND LINE

FLUSH

WIDTH NOT CRITICAL(NO MIN.)

BEND RELIEF CUTOUTS

To prevent interference whenever sheet metal bends intersect one another, materialmust be removed from the intersection.The material removed should be at least.03 inch behind the intersection of thebend lines. Usually, the inside of therelief cutout is a radius.

NOTCHING

Notches and slots are made in the flatblank in order to avoid tearing or crackingthe metal. It is usually adequate if thewidth and depth of reliefs are twice thethickness of the stock.

OPEN CORNERS

Use open corner construction whereverpossible to avoid the additional cost ofwelding.

edge of the opening.should be allowed between a bend and theA 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


R

KNUCKLE

WELDED CORNERS

A corner shape should be drawn as itappears after welding and indicated by the appropriate welding symbol.Do not show corner bend relief on awelded corner. However, the bend reliefdelineation must be shown on all unwelded corners.

A contoured or finished weld should notbe called for unless specifically requiredby engineering.

Unfinished

Contoured

KNUCKLES

Where rounded corners are needed, e.g.,tops and bottoms of cabinets, the use ofdrawn ball corner or knuckle should beconsidered.

After knotches are put in the flat blankand the edges have been roll formed, the gap can be filled with a formed knuckle which is welded in place and the cornersground or filed smooth.

LIGHTENING HOLES

Lightening holes are cutouts in sheet metal parts usually for the purpose ofreducing weight. They may be plain roundholes or of other shapes and are dimensioned in the same manner as othercutouts.

In order to avoid stresses which might cause tearing or fatigue cracking of themetal, such holes should have insideradii in the corners of openings.


SHEARING

Shearing is the method employed forcutting off large or small pieces of metalfrom strip or plate stock. As in punchingholes, burrs are formed and must beremoved by machining operations such asgrinding, reaming or milling. Barreltumbling is used for deburring smallparts.

Burr Formed By Shearing

DRAWING

The common materials for the drawingprocess include steel, aluminum, magnesiumand brass. To achieve a successful drawof a cylindrical shape, the ductility of thematerial has to be considered. Alsoimportant is the size of the corner radiiand 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 thedesign of the die must be carefullyconsidered. The radius of corners shouldbe not less than six times the stockthickness nor under 3/8 inch.

HOLD DOWN PADFLANGE

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 thicknessin 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 thesize and weight of a part.


****

THIN SHEET METAL

In thin sheet metal, lapping and spotwelding of corners is preferred to buttingand welding of corners for a stronger andmore inexpensive joint.

Lapped Joint

CROSS BRACES

Supports and cross braces should be tapered to make assembly easier and toreduce weight. However, the flangetaper should not be to the metal face.The taper should be partial, as shown.

TWICE METALTHICKNESS

1 1/2 T(MIN)

T

LOCATION OF HOLES

Never locate a hole too close to a bendor an edge. The edge of the hole should be no closer to the inside of the bendor edge of a plate than 1 1/2 times themetal thickness. If such a hole isrequired, it may be necessary to put thehole in after the bend has been made.

HOLE PUNCHING

When a punch and a die are used forputting holes in sheet stock, the sidesof the hole are not perfectly perpen-dicular to the stock. As a consequence,if accurate holes are desired, the holemust be punched undersized and reamedto the desired dimension.

PUNCH

STOCK

DIE


In addition, hole punching is employed insmall lot or mass production processes.Many factors need to be consideredincluding material properties, hole size andlocation, stock thickness and the clearancebetween the punch and die.

Also, punched holes need not be onlyround. Standard punches come in a variety of sizes and shapes as shown inthe tabulations below.

Drill Nos.-1 thru 661/32" 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 dimensionsprogress in 1/32" increments up to1/2". 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 toprogress in 1/32" range dimensionsAll standard "A"

increments up toprogress in 1/16"range dimensionsAll standard "B"

5/8". From 5/8" thru 1" in 1/8"increments. From1" thru 2" in 1/2"increments. increments.

1" thru 2" in 1/2"increments. Fromthru 1" in 1/8"5/8". From 5/8"

All standard "B"range dimensionsprogress in 1/16"increments up to

1. 1.

2.2.

B

A A

B

7/32, 1/45/32, 3/161/8

9/32, 5/1611/32, 3/813/32, 7/1615/32, 1/217/32, 9/1619/32, 5/821/32, 11/1623/32, 3/4

1-7/8, 1-15/16, 21-11/16, 1-3/4, 1-13/161-9/16, 1-5/81-7/16, 1-1/21-1/4, 1-5/16, 1-3/81-3/161-1/16, 1-1/831/32, 1

25/32, 13/1627/32, 7/829/32, 15/16

SQUARE SIZE

17/83/45/81/23/85/161/43/161/8

RADIUS

CORNER ROUNDING


(Standard Punches continued)

.315

.375

.406

.440

.505

.562

.630 .590.541.473.410.359.343.281

1/4 1/8 7/165/83/163/81/2 1/4 7/85/8 5/16 13/4 3/8 1-1/4

11/163/87/81/21-1/83/41-3/81 90 -1-1/4"

90 -2"60 -1-7/16"90 -1"

3/161-13/161-7/83/161-1/21-1/8

A B C

SIZE

B

.344

.468

.562

.6401.1411.360.760.630.516.391

A

SIZE

SIZEA B

"D" SHAPE

SIZEBA

KEYHOLE

C

CONDUIT SIZEHOLE

ELECTRICAL OUTLET KNOCKOUT

SIZE

DOUBLE "D" SHAPE

RECEPTACLE

NOTCHING

A

B

A

A

A

C

B

B

CBC


x

x

x

GUSSETING

The weakest parts of any structure areusually to be found at its joints. Gussetsare employed to spread stressesconcentrated at joints over large areas.They are an inexpensive method forstrengthening an entire structure, increasingrigidity and making the structure lesssusceptible to bending forces.

Many methods are available for affixing agusset to a frame. The most common ofthese techniques are shown below.

Riveted Gusset Plate

Combination Spot-Welded andBolted Gusset

WELDED

BOLTED

RIBS

There are many forms of ribs but howeverattached, their primary function is to effectively increase the strength and rigidity of a structure.

Rib On Sheet Metal Bracket

Panel With Spot-WeldedStiffening Rib

Flat Circular Panel RibbedAgainst Bending or Warping


BRACING

The rigidity of a structure and its abilityto resist bending, torsional and bucklingstresses can be enormously improved bycorrect bracing. Usually, the load carryingcapacity of a structure is also improvedby bracing without significantly increasingthe structure's weight.

Brace in Compression

Brace in TensionNot Subject to Buckling

GOOD

GOOD

Inadequate bracing can cause excessivedeflection and even result in sensitivityto small vibrational forces, as shownbelow.

Subject to buckling and side movement.

POOR

GOOD

prevent sideThis bracing willmovement.

GOOD

lightweight andBraces are

provide strength.


Because a straight-sided cylinder is verydifficult to spin, it should be formed, ifpossible, by a drawing operation.

BLANK

FORMEDSHAP

SPINNING BLOCK

SPUN SHAPES

The process of spinning is limited to symmetrical shapes that are circularin cross section and normal to the axisof rotation.

This method can be used to form mostsoft and ductile metals, and ordinarily itis used to manufacture items such ascooking utensils, light reflectors and various other conical shapes.

The forming tool in the spinning processis usually made of wood or hard metaland the tool is pressed against the blankcausing the metal to flow over the form.

However, conical and dome shaped partsas shown in the following illustrations areeasy to spin and offer many advantagesover other types of production.

Spun parts are generally considered to bemoderately low is cost because very littlefinishing is required. A simple trimmingoperation and cleaning is all that is required.

CONE SPINNING

As shown below, in cone spinning, thechuck meets the metal at smaller angles than in the case of spinning a simple cylinder which allows for better controlin forming the metal.

BLANK

PARTIALLYFORMED

SPINNING BLOCK

COMPLETEDSHAPE

SHEET

SPINNING BLOCK

PARTIALLYFORMEDSHEET

COMPLETEDSHAPE

BLANK

The hemispherical shape is more difficultto spin because the angle of deformationbecomes progressively more acute.

The greatest single advantage of spinningover other methods is the very low costof getting into production. The maindisadvantage is the fact that shapes arelimited to round, symmetrical forms.

01-17.DWGModel

02-17.DWGModel

03-17.DWGModel

04-17.DWGModel

05-17.DWGModel

06-17.DWGModel

07-17.DWGModel

08-17.DWGModel

09-17.DWGModel

10-17.DWGModel

11-17.DWGModel

12-17.DWGModel

13-17.DWGModel

14-17.DWGModel

15-17.DWGModel

16-17.DWGModel

17-17.DWGModel

sect 2-sheet metal

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