Multipunch cc
69 Killarney Rd
Killarney Gardens

Tel: +27 21 556 0768
Fax: +27 21 556 0786

Sheet Metal

Sheet metal is simply metal formed into thin and flat pieces. It is one of the fundamental forms used in metalworking, and can be cut and bent into a variety of different shapes. Countless everyday objects are constructed of the material. Thicknesses can vary significantly, although extremely thin thicknesses are considered foil or leaf, and pieces thicker than 6 mm are considered plate.

Sheet metal is available in flat pieces or as a coiled strip. The coils are formed by running a continuous sheet of metal through a roll slitter.

The thickness of the sheet metal is called its gauge. Commonly used steel sheet metal ranges from 30 gauge to about 8 gauge. The larger the gauge number, the thinner the metal. Gauge is measured in ferrous (iron based) metals while nonferrous metals such as aluminum or copper are designated differently; i.e. Copper is measured in thickness by Ounce.

There are many different metals that can be made into sheet metal, such as aluminum, brass, copper, steel, tin, nickel and titanium. For decorative uses, important sheet metals include silver, gold, and platinum (platinum sheet metal is also utilized as a catalyst.)

Sheet metal also has applications in car bodies, airplane wings, medical tables, roofs for buildings (Architectural) and many other things. Sheet metal of iron and other materials with high magnetic permeability, also known as laminated steel cores, has applications in transformers and electric machines. Historically, an important use of sheet metal was in plate armor worn by cavalry, and sheet metal continues to have many decorative uses, including in horse tack.


 

Material

Stainless Steel
The three most common stainless steel grades available in sheet metal are 304, 316, and 410.

Grade 304 is the most common of the three grades. It offers good corrosion resistance while maintaining formability and weldability. Available finishes are #2B, #3, and #4. Note that grade 303 is not available in sheet form.

Grade 316 offers more corrosion resistance and strength at elevated temperatures than 304. It is commonly used for pumps, valves, chemical equipment, and marine applications. Available finishes are #2B, #3, and #4.

Grade 410 is a heat treatable stainless steel, but does not offer as good corrosion resistance. It is commonly used in cutlery. The only available finish is dull.

Aluminium

The four most common aluminium grades available as sheet metal are 1100-H14, 3003-H14, 5052-H32, and 6061-T6.

Grade 1100-H14 is commercially pure aluminium, so it is highly chemical and weather resistant. It is ductile enough for deep drawing and weldable, but low strength. It is commonly used in chemical processing equipment, light reflectors, and jewelry.

Grade 3003-H14 is stronger than 1100, while maintaining the same formability and low cost. It is corrosion resistant and weldable. It is often used in stampings, spun and drawn parts, mail boxes, cabinets, tanks, and fan blades.

Grade 5052-H32 is much stronger than 3003 while still maintaining good formability. It maintains high corrosion resistance and weldability. Common applications include electronic chassis, tanks, and pressure vessels.

Grade 6061-T6 is a common heat-treated structural aluminium alloy. It is weldable, corrosion resistant, and stronger than 5052, but not as formable. Note that it loses some of its strength when welded. It is used in modern aircraft structures, generally replacing the older 2024-T4 alloy.


 

Gauge


The sheet metal gauge (sometimes spelled gage) indicates the standard thickness of sheet metal for a specific material. For most materials, as the gauge number increases, the material thickness decreases.

Sheet metal thickness gauges for steel are based on the weight of steel, allowing more efficient calculation of the cost of material used. The weight of steel per square foot per inch of thickness is 18.96kg, this is known as the Manufacturers' Standard Gage for Sheet Steel. For other materials, such as aluminium and brass, the thicknesses will be different.

 

Standard sheet metal gauges
GaugeSteel[5]
in (mm)
Galvanized steel
in (mm)
Stainless steel
in (mm)
Aluminium
in (mm)
Zinc[5]
in (mm)
3 0.2391 (6.07) - - - 0.006 (0.15)
4 0.2242 (5.69) - - - 0.008 (0.20)
5 0.2092 (5.31) - - - 0.010 (0.25)
6 0.1943 (4.94) - - 0.162 (4.1) 0.012 (0.30)
7 0.1793 (4.55) - 0.1875 (4.76) 0.1443 (3.67) 0.014 (0.36)
8 0.1644 (4.18) 0.1681 (4.27) 0.1719 (4.37) 0.1285 (3.26) 0.016 (0.41)
9 0.1495 (3.80) 0.1532 (3.89) 0.1563 (3.97) 0.1144 (2.91) 0.018 (0.46)
10 0.1345 (3.42) 0.1382 (3.51) 0.1406 (3.57) 0.1019 (2.59) 0.020 (0.51)
11 0.1196 (3.04) 0.1233 (3.13) 0.1250 (3.18) 0.0907 (2.30) 0.024 (0.61)
12 0.1046 (2.66) 0.1084 (2.75) 0.1094 (2.78) 0.0808 (2.05) 0.028 (0.71)
13 0.0897 (2.28) 0.0934 (2.37) 0.094 (2.4) 0.072 (1.8) 0.032 (0.81)
14 0.0747 (1.90) 0.0785 (1.99) 0.0781 (1.98) 0.0641 (1.63) 0.036 (0.91)
15 0.0673 (1.71) 0.0710 (1.80) 0.07 (1.8) 0.057 (1.4) 0.040 (1.0)
16 0.0598 (1.52) 0.0635 (1.61) 0.0625 (1.59) 0.0508 (1.29) 0.045 (1.1)
17 0.0538 (1.37) 0.0575 (1.46) 0.056 (1.4) 0.045 (1.1) 0.050 (1.3)
18 0.0478 (1.21) 0.0516 (1.31) 0.0500 (1.27) 0.0403 (1.02) 0.055 (1.4)
19 0.0418 (1.06) 0.0456 (1.16) 0.044 (1.1) 0.036 (0.91) 0.060 (1.5)
20 0.0359 (0.91) 0.0396 (1.01) 0.0375 (0.95) 0.0320 (0.81) 0.070 (1.8)
21 0.0329 (0.84) 0.0366 (0.93) 0.034 (0.86) 0.028 (0.71) 0.080 (2.0)
22 0.0299 (0.76) 0.0336 (0.85) 0.031 (0.79) 0.025 (0.64) 0.090 (2.3)
23 0.0269 (0.68) 0.0306 (0.78) 0.028 (0.71) 0.023 (0.58) 0.100 (2.5)
24 0.0239 (0.61) 0.0276 (0.70) 0.025 (0.64) 0.02 (0.51) 0.125 (3.2)
25 0.0209 (0.53) 0.0247 (0.63) 0.022 (0.56) 0.018 (0.46) -
26 0.0179 (0.45) 0.0217 (0.55) 0.019 (0.48) 0.017 (0.43) -
27 0.0164 (0.42) 0.0202 (0.51) 0.017 (0.43) 0.014 (0.36) -
28 0.0149 (0.38) 0.0187 (0.47) 0.016 (0.41) 0.0126 (0.32) -
29 0.0135 (0.34) 0.0172 (0.44) 0.014 (0.36) 0.0113 (0.29) -
30 0.0120 (0.30) 0.0157 (0.40) 0.013 (0.33) 0.0100 (0.25) -
31 0.0105 (0.27) 0.0142 (0.36) 0.011 (0.28) 0.0089 (0.23) -
32 0.0097 (0.25) - - - -
33 0.0090 (0.23) - - - -
34 0.0082 (0.21) - - - -
35 0.0075 (0.19) - - - -
36 0.0067 (0.17) - - - -
37 0.0064 (0.16) - - - -
38 0.0060 (0.15) - - - -

 

 


Tolerances


During the rolling process the rollers bow slightly, which results in the sheets being thinner on the edges.

 

 

Steel sheet metal tolerances
GaugeNominalMaxMin
10 0.1345 0.1405 0.1285
11 0.1196 0.1256 0.1136
12 0.1046 0.1106 0.0986
14 0.0747 0.0797 0.0697
16 0.0598 0.0648 0.0548
18 0.0478 0.0518 0.0438
20 0.0359 0.0389 0.0329
22 0.0299 0.0329 0.0269
24 0.0239 0.0269 0.0209
26 0.0179 0.0199 0.0159
28 0.0149 0.0169 0.0129

 

Aluminium sheet metal tolerances
ThicknessSheet width
36 in48 in
0.018–0.028 0.002 0.0025
0.029–0.036 0.002 0.0025
0.037–0.045 0.0025 0.003
0.046–0.068 0.003 0.004
0.069–0.076 0.003 0.004
0.077–0.096 0.0035 0.004
0.097–0.108 0.004 0.005
0.109–0.125 0.0045 0.005
0.126–0.140 0.0045 0.005
0.141–0.172 0.006 0.008
0.173–0.203 0.007 0.010
0.204–0.249 0.009 0.011
Stainless steel sheet metal tolerances
ThicknessSheet width
36 in48 in
0.017–0.030 0.0015 0.002
0.031–0.041 0.002 0.003
0.042–0.059 0.003 0.004
0.060–0.073 0.003 0.0045
0.074–0.084 0.004 0.0055
0.085–0.099 0.004 0.006
0.100–0.115 0.005 0.007
0.116–0.131 0.005 0.0075
0.132–0.146 0.006 0.009
0.147–0.187 0.007 0.0105

 

 

 

 

 

 

 

 

 

 

 

 

 

 


 

Forming processes

Bending

The equation for estimating the maximum bending force is,



where k is a factor taking into account several parameters including friction. T is the ultimate tensile strength of the metal. L and t are Length and thickness of sheet metal respectively. The variable W is open width of a V-die or wiping die.

 

Laser cutting

Cutting sheet metal can be done in various ways from hand tools called tin snips up to very large powered shears. With the advances in technology, sheet metal cutting has turned to computers for precise cutting.

Many sheet metal cutting operations are based on computer numerically controlled (CNC) lasers cutting or multi-tool CNC punch press.

CNC laser involves moving a lens assembly carrying a beam of laser light over the surface of the metal. Oxygen, nitrogen or air is fed through the same nozzle from which the laser beam exits. The metal is heated and burnt by the laser beam, cutting the metal sheet. The quality of the edge can be mirror smooth and a precision of around 0.1 mm can be obtained. Cutting speeds on thin 1.2 mm sheet can be as high as 25m a minute. Most of the laser cutting systems use a CO2 based laser source with a wavelength of around 10 um; some more recent systems use a YAG based laser with a wavelength of around 1 um.

Punching

Punching is performed by placing the sheet of metal stock between a punch and a die mounted in a press. The punch and die are made of hardened steel and are the same shape. The punch just barely fits into the die. The press pushes the punch against and into the die with enough force to cut a hole in the stock. In some cases the punch and die "nest" together to create a depression in the stock. In progressive stamping a coil of stock is feed into a long die/punch set with many stages. Multiple simple shaped holes may be produced in one stage but complex holes are created in multiple stages. The final stage the part is punched free from the "web".

A typical CNC punch has a choice of up to 60 tools in a "turret" that can be rotated to bring any tool to the punching position. A simple shape (e.g. a square, circle, or hexagon) is cut directly from the sheet. A complex shape can be cut out by making many square or rounded cuts around the perimeter. A punch is less flexible than a laser for cutting compound shapes, but faster for repetitive shapes (for example, the grille of an air-conditioning unit). A CNC punch can take 600 strokes per minute.

A typical component (such as the side of a computer case) can be cut to high precision from a blank sheet in under 15 seconds by either a press or a laser CNC machine.


Perforating

Perforating is a cutting process that punches multiple small holes close together in a flat workpiece. Perforated sheet metal is used to make a wide variety of surface cutting tools, such as the surform.

Press brake forming

This is a form of bending, used for long and thin sheet metal parts. The machine that bends the metal is called a press brake. The lower part of the press contains a V shaped groove. This is called the die. The upper part of the press contains a punch that will press the sheet metal down into the v shaped die, causing it to bend. There are several techniques used here, but the most common modern method is "air bending". Here, the die has a sharper angle than the required bend (typically 85 degrees for a 90 degree bend) and the upper tool is precisely controlled in its stroke to push the metal down the required amount to bend it through 90 degrees. Typically, a general purpose machine has a bending force available of around 25 tonnes per metre of length. The opening width of the lower die is typically 8 to 10 times the thickness of the metal to be bent (for example, 5mm material could be bent in a 40mm die) the inner radius of the bend formed in the metal is determined not by the radius of the upper tool, but by the lower die width. Typically, the inner radius is equal to 1/6 of the V width used in the forming process.

The press usually has some sort of back gauge to position depth of the bend along the workpiece. The backgauge can be computer controlled to allow the operator to make a series of bends in a component to a high degree of accuracy. Simple machines control only the backstop, more advanced machines control the position and angle of the stop, its height and the position of the two reference pegs used to locate the material. The machine can also record the exact position and pressure required for each bending operation to allow the operator to achieve a perfect 90 degree bend across a variety of operations on the part.

Roll forming

A continuous bending operation for producing open profiles or welded tubes with long lengths or in large quantities.


 

Welding

Welding is a fabrication or sculptural process that joins materials, usually metals or thermoplastics, by causing coalescence. This is often done by melting the workpieces and adding a filler material to form a pool of molten material (the weld pool) that cools to become a strong joint, with pressure sometimes used in conjunction with heat, or by itself, to produce the weld. This is in contrast with soldering and brazing, which involve melting a lower-melting-point material between the workpieces to form a bond between them, without melting the workpieces.

Many different energy sources can be used for welding, including a gas flame, an electric arc, a laser, an electron beam, friction, and ultrasound. While often an industrial process, welding may be performed in many different environments, including open air, under water and in outer space. Welding is a potentially hazardous undertaking and precautions are required to avoid burns, electric shock, vision damage, inhalation of poisonous gases and fumes, and exposure to intense ultraviolet radiation.

Until the end of the 19th century, the only welding process was forge welding, which blacksmiths had used for centuries to join iron and steel by heating and hammering. Arc welding and oxyfuel welding were among the first processes to develop late in the century, and electric resistance welding followed soon after. Welding technology advanced quickly during the early 20th century as World War I and World War II drove the demand for reliable and inexpensive joining methods. Following the wars, several modern welding techniques were developed, including manual methods like shielded metal arc welding, now one of the most popular welding methods, as well as semi-automatic and automatic processes such as gas metal arc welding, submerged arc welding, flux-cored arc welding and electroslag welding. Developments continued with the invention of laser beam welding, electron beam welding, electromagnetic pulse welding and friction stir welding in the latter half of the century. Today, the science continues to advance. Robot welding is commonplace in industrial settings, and researchers continue to develop new welding methods and gain greater understanding of weld quality.