ITI/NCVT Sheet Metal Worker (AITT Theory) key terms

Items worn by a worker to reduce exposure to hazards, such as safety goggles, gloves, ear plugs, and steel-toe boots. In sheet metal work, eye protection guards against flying chips and sharp edges.

Any place where a body part can be caught between moving machine parts or between a workpiece and a fixed surface, such as between rolls or press dies. Guards and safe procedures reduce this risk.

Physical barriers or interlocks fitted to machines to prevent hands from entering dangerous zones. On shears and press brakes, guards must allow the required material feed while blocking access to the cutting or bending area.

A safety procedure in which the energy source of a machine is isolated, locked, and tagged before maintenance or blade changes. It prevents accidental start-up or release of stored energy.

The maximum load a sling, hook, or lifting device may safely carry, as marked by the manufacturer. Exceeding it can cause sudden failure during handling of sheet bundles.

Lifting, carrying, and moving loads by hand. Correct technique, team lifting, and mechanical aids protect the back when moving sheet stock and finished assemblies.

A drawing arrangement in which the object is imagined between the observer and the plane, so the view from the front appears on the rear plane. Common in Indian and European practice, it uses a truncated-cone symbol to identify it.

A drawing arrangement in which the projection plane lies between the observer and the object, so the view from the front appears on the front plane. Common in US practice and identified by its symbol.

A method of representing a three-dimensional object by separate two-dimensional views projected onto planes at right angles, such as front, top, and side views. It gives true shapes and sizes for manufacturing.

A flat layout of a sheet metal surface that, when folded or rolled, forms the required three-dimensional shape. It is drawn true size by laying out the surface as it would appear when unfolded.

The length of material added in a flat pattern to account for the material consumed in forming a bend. It is calculated from the neutral axis arc so the finished part meets the required dimensions.

The layer within a bent sheet whose length does not change during forming. It lies between the inner and outer surfaces, and its arc is used to compute bend allowance.

The radius of the inner curved surface of a bend. A small radius relative to thickness can cause cracking or excessive thinning, so minimum radii are specified for each material.

The elastic recovery of metal after a bending force is removed, causing the bend angle to open slightly. It is compensated by overbending and depends on material strength and bend radius.

The actual, undistorted length of a line or edge as it exists on the object. In layout development, inclined lines are rotated or projected to show true length before transfer to the pattern.

The developed length of a curved or cylindrical part measured along its circumference or profile. It equals the flat length of material needed before forming, such as the circumference of a duct.

A low-carbon steel containing roughly 0.05 to 0.25 percent carbon, easily formed, welded, and cut. It is the most common sheet metal material for ducts, tanks, and general fabrication.

Mild steel sheet coated with zinc by hot dipping to resist rust. The coating protects the steel but produces harmful fumes when welded, so it is usually soldered or mechanically joined instead.

A steel alloyed with chromium, typically 10.5 percent or more, that forms a passive oxide layer resisting corrosion. It is harder to cut and form and work-hardens rapidly during cold working.

A light, corrosion-resistant metal available in pure and alloyed forms. It is easy to form and cut but has low melting point and high thermal conductivity, which affects welding and soldering.

The increase in strength and hardness of metal caused by cold deformation such as rolling, bending, or stretching. It reduces ductility, so severe forming may require intermediate annealing.

A heat treatment that softens metal by heating it to a suitable temperature and cooling it slowly. In sheet metal work it restores ductility after cold working so further forming is possible.

A measuring instrument with a main scale and a sliding vernier scale used to read outside, inside, and depth dimensions. Its least count is the smallest difference the scales can resolve, commonly 0.02 mm.

A precision measuring instrument using a calibrated screw to measure small thicknesses and diameters. The spindle advances a known distance per revolution, giving readings typically to 0.01 mm.

The smallest measurement an instrument can read directly. For a vernier caliper it is the main scale division divided by the number of vernier divisions, and it determines measurement precision.

A marking and checking tool with a stock and a blade fixed at exactly 90 degrees. It is used to check squareness of edges and to scribe lines perpendicular to a reference edge.

A sharp-pointed steel tool used to scratch fine layout lines on metal surfaces. It produces a permanent line that survives handling, unlike pencil marks, and is often used with a steel rule.

A small, sharply pointed punch struck with a hammer to mark the position of hole centres and layout points. It gives a permanent reference that guides a centre punch or drill.

A punch with a 90-degree point used to create a conical indentation at a marked point. The indentation prevents a drill from wandering when starting a hole.

A machine that cuts sheet metal with a moving blade against a fixed bed, producing straight cuts at right angles. Hold-downs clamp the sheet, and the gap between blades must suit the sheet thickness.

The small gap set between the moving and fixed blades of a shear, matched to sheet thickness and material. Too much clearance tears the edge; too little increases cutting force and blade wear.

A rough, raised edge left on sheared or punched metal. Burrs are removed by filing or deburring to prevent injury and to allow tight-fitting joints and seams.

The operation of removing burrs and sharp edges from cut or punched sheet metal using a file, scraper, or abrasive. It improves safety and fit before forming or joining.

A machine that forms bends by pressing a sheet between a punch and a V-shaped die. The bend angle is controlled by ram depth, and springback must be allowed for.

A forming process in which sheet metal passes between rollers that curve it into cylinders or arcs. Slip rolls use three or more rolls, and repeated passes are needed to reach the final radius.

A folded edge formed by turning sheet metal back on itself, often to stiffen the edge or remove sharpness. A single hem folds once; a double hem folds the edge twice for greater strength.

A joint in which the edges of two sheets are folded together and then flattened or locked to form a strong, leak-resistant connection without fasteners. It is common in ductwork.

A permanent fastener with a shank and head, inserted through aligned holes and deformed to form a second head. It joins sheet metal where welding or soldering is unsuitable.

A hand tool with a shaped recess that is placed over the rivet head to support it while the other end is hammered. It prevents damage to the head during forming.

A joining process in which a filler metal with a melting point below about 450 degrees Celsius wets and bonds the surfaces. It requires flux and is used for leak-tight sheet metal joints such as gutters.

A joining process using a filler metal that melts above about 450 degrees Celsius but below the melting point of the base metal. It gives stronger joints than soldering and suits dissimilar metals.

A chemical applied during soldering or brazing that removes oxides and prevents new oxidation, allowing the filler metal to wet the joint. Residues must often be cleaned after joining.

A resistance welding process in which current passes through overlapping sheets held between electrodes, producing a local fused nugget. It is fast and widely used for joining thin steel sheet.

A list of all materials, parts, and quantities needed to make an assembly, often with sizes and specifications. It supports purchasing, costing, and material calculation for a job.

Working out the area, length, or mass of sheet required for a job from the developed pattern and material density. Correct calculation reduces waste and gives an accurate cost estimate.

Extra material included in an estimate to cover offcuts, trimming, and rejected parts. It is expressed as a percentage of net material and affects the final cost of the job.

The use of computer software to create, modify, and store drawings and models. In sheet metal work, CAD helps produce flat patterns, nesting layouts, and dimensioned fabrication drawings.

Machine control in which a computer reads coded instructions to position tools and move workpieces automatically. CNC punching, laser cutting, and press brakes give repeatable accuracy in sheet metal production.