SHEET METAL REPAIR & MAINTENANCE Session 4 SHEET METAL REPAIR & MAINTENANCE

Recap Welding Types Jig & Fixture Soldering Brazing

PRINCIPLE

Capillary action

Objective Sheet Metal Repair & Maintenance Procedure for Simple Bend Hand tools for Sheet metal Work Visual inspection

To measure the thickness, you can use a sheet metal gauge, which will show you thickness in both gauge number and thousandths of an inch.

Bending Mark a bend line and place the sheet metal on the edge of your bench. Next place the wood parallel and slightly behind the bending line. Clamp the wood on top of the metal to the workbench. Finally, bend the sheet up by hand to the angle desired. If you want a sharp 90° bend, tap along the crease with a mallet.

Cutting tool- Snips Commonly known as “aviation snips” or “tinsnips,” these scissor-like tools are great for cutting soft sheet metals such as tin, aluminum, brass, and thin-gauge (24 gauge or thinner) steel. Be sure to insert the metal fully into the throat of the snips for optimal cutting.

2. Hacksaw A hacksaw can cut sheet metal, but its shape limits its turning radius and depth of cut. To prolong blade life, rub wax along the length of the blade. For a cleaner cut, put a strip of masking tape on the top and bottom of the sheet to keep chips from scratching the material

Nibbler The nibbler is a tool that offers a lot of control over the cut, but at the expense of cut width. Each cut punches out a tiny piece of the sheet metal, and the process is repeated. The nibbler shown here is hand-operated, though drill-powered, electric, and pneumatic versions are also common.

Jigsaw A quality jigsaw and the correct metal-cutting blade will make short work of sheet metal cuts. If you need a straight cut, clamp a straight-edge to the sheet to act as a guide for the jigsaw footplate.

Procedure- Sheet Metal Bend Cut the required metal sheet to dimensions & deburr and smooth the edges. Determine the correct radius for bend See the correct radius bar is installed on the break See the break is clean and free of metal particles and scraps The sight line is marked correctly on the metal to bend Install the metal in break with sight line correctly in position Clamp the metal in place with clamping bar Remove the bend bar and check for accuracy.

Visual Inspection to identify damages Brinelling Burnishing Burr Corrosion Cut Dent Chattering Galling

The types of damage and defects you may see on sheet metal parts. BRINELLING- Occurrence of shallow, spherical depressions in a surface, usually produced by a part having a small radius in contact with the surface under high load. BURNISHING-Polishing of one surface by sliding contact with a smooth, harder surface. Usually no displacement nor removal of metal.

BURR-A small, thin section of metal extending beyond a regular surface, usually located at a corner or on the edge of a bore or hole. CORROSION-Loss of metal from the surface by chemical or electrochemical action. The corrosion products generally are easily removed by mechanical means. Iron rust is an example of corrosion.

CRACK-A physical separation of two adjacent portions of metal, evidenced by a fine or thin line across the surface, caused by excessive stress at that point. It may extend inward from the surface from a few thousandths inch to completely through the section thickness. CUT-Loss of metal, usually to an appreciable depth over a relatively long and narrow area, by mechanical means, as would occur with the use of a saw blade, chisel or sharp- edged stone striking a glancing blow.

DENT-Indentation in a metal surface produced by an object striking with force. The surface surrounding the indentation will usually be slightly upset. EROSION-Loss of metal from the surface by mechanical action of foreign objects. such as grit or fine sand. The eroded area will be rough and may be lined in the direction in which the foreign material moved relative to the surface

CHATTERING-Breakdown or deterioration of metal surface by vibratory or “chattering” action. Usually no loss of metal or cracking of surface but generally showing similar appearance. GALLING-Breakdown (or build-up) of metal surfaces due to excessive friction between two parts having relative motion. Particles of the softer metal are torn loose and “welded” to the harder.