Bend allowance
The length of material consumed along the neutral axis of a bend, added to the flat dimensions of the adjacent flanges to find the flat pattern length. It depends on material, thickness, bend radius, and the tooling used, so a fabricator will usually recalculate it from their own tables rather than accept the value in your model.
Bend radius
The inside radius of a formed bend. Every material has a minimum radius below which the outside surface cracks, usually expressed as a multiple of thickness, and a radius that matches the fabricator's standard tooling costs less than one that does not. Specify it only where function requires a particular value.
Bend relief
A small cutout at the end of a bend line that stops the material tearing where a flange meets an adjacent edge. It is a detail the fabricator will add if your design lacks it, and agreeing that they may do so without a drawing revision saves a round of questions.
Countersink and counterbore
Recesses that let a fastener head sit flush with or below the surface, one conical and one cylindrical. In thin sheet a countersink can break through the far side, so the fabricator may propose a dimpled or formed countersink instead, and the drawing should say whether that substitution is acceptable.
Deburring
Removal of the sharp edge left by cutting or punching. The level required ranges from breaking the edge for safe handling to a specified edge radius for parts that are touched or sealed, and it is a cost driver because it is often manual. State the edge condition you need rather than leaving it to shop practice.
Design for manufacturabilityDFM
Review of a part design against the capabilities and limits of the process that will make it, covering bend radii, hole distances from bends, flange lengths, tolerances, and material availability. Most fabricators offer a DFM review at quotation, and a design that has been through one is quoted faster and made with fewer surprises.
Fiber laser cutting
Cutting of sheet and plate with a focused laser beam. It produces a narrow kerf and a clean edge, and its speed and achievable edge quality fall as thickness rises, which is why plate work often moves to plasma or waterjet.
First article inspectionFAI
A complete dimensional and documentary verification of the first production part against the drawing, recorded on a report that the buyer approves before the rest of the order is made. Required in aerospace and automotive supply chains and useful in any order where a formed part will be made in quantity.
Flat pattern
The unfolded two-dimensional shape of a formed part, from which it is cut before bending. The fabricator generates the flat pattern from your three-dimensional model using their own bend allowances, so you should send the folded model and let them unfold it rather than sending a flat you calculated.
Flatness
The amount by which a nominally flat surface deviates from a perfect plane. Sheet metal is flexible and rarely flat to machining standards, so a flatness tolerance should state how the part will be held when it is measured, or buyer and fabricator will disagree on whether it conforms.
Gauge
A traditional number designating sheet thickness, where a higher number means thinner material. The same gauge number corresponds to different thicknesses in steel, stainless, aluminum, and galvanized sheet, so specify thickness in millimeters or inches and treat gauge as a reference only.
Geometric dimensioning and tolerancingGD&T
A symbolic system for defining the allowable variation in form, orientation, location, and profile of features relative to datums, published in the United States as ASME Y14.5. For formed parts, it is the clearest way to state which relationships across bends matter and how they will be measured, and a drawing that uses it removes most arguments at inspection.
Grain direction
The direction in which the sheet was rolled at the mill, visible in the surface and affecting how the metal bends. Bending parallel to the grain increases the risk of cracking, especially in aluminum and high-strength steel, so a fabricator may need to nest parts to control grain orientation, which affects material yield and price.
Hardware insertion
Installation of self-clinching nuts, studs, and standoffs into sheet by pressing them into a punched hole so the sheet material flows into a groove on the fastener. It adds threaded features without welding, but it requires the hole to be made to the fastener manufacturer's size and the insertion to happen before finishing.
Hem
An edge folded back on itself, either flat or open, to remove a sharp edge, add stiffness, or provide a clean appearance. Hems require additional forming operations and a minimum flange length, so they add cost and should be called out only where the edge will be handled or seen.
K-factor
The ratio describing where the neutral axis sits within the thickness of a bend, used to calculate bend allowance. It varies with material, thickness, radius, and tooling, and fabricators keep their own measured values, which is another reason to send a folded model and let the shop unfold it.
Kerf
The width of material removed by a cutting process. Laser produces a narrow kerf and plasma and waterjet produce wider ones, which affects how closely parts can be nested and how accurately small features and narrow slots can be cut. A feature narrower than the kerf cannot be cut at all.
Nesting
Arrangement of flat patterns on a sheet to minimize scrap. Nesting efficiency is a major component of material cost, and it improves with part quantity and with designs that tile well, which is why a quote for one part may carry a disproportionate share of a sheet.
Powder coating
A dry finishing process in which electrostatically charged powder is applied to a grounded part and cured in an oven to form a durable film. It requires hardware and masking decisions before finishing and adds thickness that affects fits, so threaded and mating features need masking or post-finish tapping called out on the drawing.
Press brake
The machine that forms sheet by pressing it between a punch and a die to produce a bend. Its tonnage, bed length, and tooling inventory set the maximum thickness, the maximum flange length, and the achievable inside radii, so a fabricator's brake capacity is a practical capability question for any formed part.
Production part approval processPPAP
A standardized submission used in automotive and related supply chains to demonstrate that a supplier's process can produce a part consistently to specification, including dimensional results, material certifications, and process documentation. Specify the submission level required if your customer requires one, because it is significant work for the fabricator.
Punching
Cutting of holes and features by forcing a shaped punch through the sheet into a die, either on a dedicated press or a CNC turret. Faster than laser for repeated standard holes and able to produce formed features such as louvers and embosses, but limited in thickness and leaving a characteristic edge and slight deformation.
Springback
The tendency of formed metal to return partly toward its original shape when the forming force is removed. The fabricator compensates by overbending, and the amount varies with material and thickness, which is why bend angle tolerances are wider than cut tolerances and why material substitutions must be approved.
Tab and slot
A self-locating joint design in which a tab on one part passes through a slot in its mate, holding the assembly in position for welding without fixtures. It reduces fixturing cost and assembly error, and fabricators will often propose it during design review for welded enclosures and frames.
Tolerance stack-up
The accumulation of individual tolerances across several features or parts, which can leave an assembly out of specification even when every part conforms. Formed parts stack tolerances across each bend, so critical relationships should be toleranced directly between the features that matter rather than through a chain of bends.
Waterjet cutting
Cutting with a high-pressure stream of water carrying an abrasive, which removes material without heat. It handles thick plate, heat-sensitive alloys, and nonmetals, leaves no heat-affected zone, and is slower and more expensive per part than laser for thin sheet.
Weld procedure specificationWPS
A written document defining how a specific weld is to be made, including process, materials, consumables, joint design, and parameters, supported by a procedure qualification record proving it works. Where a welding code governs the work, it requires welds to be made to a qualified procedure by a qualified welder, and asking for the WPS is how a buyer confirms both.
Weld symbol
The standardized graphical notation on a drawing that specifies weld type, size, length, location, and finishing, defined in the United States by an American Welding Society standard. Drawings that describe welds in words or leave them to the fabricator produce inconsistent results, and weld symbols are how the requirement becomes inspectable.
Welded assembly
A fabrication in which cut and formed parts are joined by welding into a single component, such as a frame, enclosure, or bracket, often with hardware inserted and a finish applied. Buying a welded assembly rather than loose parts moves fit, distortion control, and finishing responsibility onto the fabricator.
Zinc coating
A corrosion-protective layer of zinc applied to steel, either at the mill before fabrication, as galvanized or galvannealed sheet, or after fabrication by hot-dip galvanizing the finished part. Pre-coated sheet is damaged at cut edges and welds, while post-fabrication galvanizing coats everything but can distort thin parts, so the choice belongs in the specification.