Sheet-metal shearing

Mechanical drives faster action and more positive displacement control. 

Hydraulic drives greater forces and more flexibility. 

Cutting large sheets of metal are clamped and cut along a straight line. 

Piercing removal of material from a blank, for example, a hole. 

Blanking parts are blanked to obtain the final outside shape. 

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Common metal window screen can be salvaged from buildings, is available from hardware and building supply stores. Can be cut with sheet metal shears. 

Figure 9.11. (a) Sheet metal shearing operation producing blank (disc) and punched sheet and (b) production of 90° bend in metal sheet. 

Sheet-metal Shearing 7.5 Electron Beam Welding (EBW)... 

Process capability charts showing the achievable dimensional tolerances for several sheet-metal shearing processes are provided (see 3.8CC). 

CC Sheet-metal shearing process capability chart. 

Can incorporate initial sheet metal shearing operations. 

Blanking is cutting, punching, or shearing a shape out of stock. In sheet metal form, blanking is typically carried out at room temperature. Usually, a blank serves as an input workpiece to some subsequent forming operation. 

T o cut a piece of paper, you would use a pair of scissors. The scissors shear paper. Shearing is a process that separates material without producing waste. There are hand shears, like tin snips, for cutting sheet metal. Hydraulic shears can cut flat sheet metal or metal strips. 

Figure 2 Sheet metal slug showing shear and fracture or break in relation to the material punched. (Courtesy of STRIPPIT, Inc.)...

Punching sheet metal, especially thicker and tougher materials such as stainless-steel alloys, is inherently noisy. As noted in Section I.E and as shown in Fig. 8, noise is drastically reduced through the use of shear face punches. In addition, the fully controllable hydraulic ram offers yet another method to reduce audible noise slowing the speed of the punch as it strikes the workpiece. Although productivity in terms of strokes per minute is reduced, this trade-off may be necessary in some applications and in some fabricating environments where loud noise is at issue. 

Chapter 28, Squaring Shears (Carr), describes how sheet metal and plate shearing is used for cutting everything from single-piece to small-lot production. The fabricator today has a number of options and they are described here. Chapter 9 also refers to shears and is another good source which describes various shear knife materials for various applications, blade clearances, and other important considerations. 

Another hazard is sharp objects and equipment. Examples are burrs and sharp edges on sheared sheet metal or metal objects. Another example is use of sharp knives and cutting tools. Other examples are axes and portable saws, such as chainsaws. Protective clothing, such as gloves, chaps and other clothing must be tough and resist cuts and tears. 

Figure 2.31 The rebated (joggled) lap joint. When shear loaded, the correct geometric alignment of the adherends inhibits the generation of tensile forces, normal to the plane of the joint, (at X) which may cleave a simple lap joint prematurely (see Figure 2.29b). This type of joint is particularly useful for sheet metal assembly.

When holes are to be cut in sheet metal, up to 16 SWG, this can be done simply and effectively using a Q-Max sheet metal punch as shown in Fig. 4.4. A pilot hole is drilled in the correct position, the screw is inserted with the punch and die on either side of the sheet, and the screw is tightened. The metal is sheared giving a correct size and shape of hole in the required position. 

Constrained layer damping, where a stiff material is placed on the top of the damping polymer to increase the shearing action. Sometimes a simple sandwich arrangement is used, where two thin layers of sheet metal (the bread) have a thin layer of polymer between them (the jelly). 

Various shearing processes used to cut cold rolled sheet metal with hardened punch and die sets. The most common shearing processes are cutting, piercing, blanking and fine blanking (see 3.8F). 

Fig. 110. Results of dynamic cycling tests on aluminium sheet, lap shear joints with Redux 775. Range shown by stated numbers of tests i- i tests in which metal adherends failed O tests discontinued at indicated number of cycles (adapted from Matting and Draugelates, 1968).

Fig. 7.16. Practical lap joint suspension turret Vehicle shock absorbers have been successfully mounted in ring structures derived from the fundamental lap joint because the principal working loads are carried in compressive shear, the joints are actually stronger than the thin sheet metal they are made from ...

Metal Preparation. Sheet-steel parts are formed by stamping, bending, and shearing. Many parts require welding (qv), which needs to be carried out in a uniform, smooth manner so that the welded joint can be enameled without defects. Cast-iron parts are formed by the usual cast-iron foundry methods however, additional care is given to prevent contamination of the surface. Surface contamination causes defects in the enamel, particularly bUsters and bubbles. Aluminum metal can be formed in sheets, extmsions, and as castings. 

Shear modulus, polyamide, 138 Sheet molding compounds (SMCs), 30 Shoe sole products, 205 Shore hardness gauge, 243 Side-chain liquid crystalline polymers, 49 Side reactions, in transition metal coupling, 477... 

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