The metal fabrication process turns stock sheet, plate, tube and bar into finished parts in seven steps: design, cutting, forming, joining, finishing, inspection and delivery.

Each step sets up the next. When information is missing early on, problems show up later. A shop asks for a drawing you never made, a quote lists operations you didn’t expect, or a welded frame arrives out of square.

Knowing what happens at each stage helps you send drawings fabricators can quote accurately, the first time.

In this guide, you’ll learn:

  • What happens at each of the seven steps
  • What your drawing needs to specify at each stage
  • The main types of metal fabrication
  • What drives cost and lead time

Let’s start with the basics.

TL;DR

  • A dimensioned 2D drawing plus a 3D model is the standard package sheet metal fabricators quote from.
  • Bends have limits: flanges need to be at least about 3x material thickness, and tight inside radii can crack.
  • Welding distorts parts, so machine critical faces and holes after welding.
  • Coatings add thickness, so your drawing should state which dimensions apply after finishing.
  • Fabricated parts hold looser tolerances than machined parts. Reference ISO 2768, or ISO 13920 for welded structures.

What Is the Metal Fabrication Process?

Metal fabrication is the process of turning stock metal (sheet, plate, tube or bar) into finished parts and assemblies by cutting, forming, joining and finishing it.

It’s one type of fabrication, which can involve other materials too. For the broader picture, see our guide to what fabrication is.

Fabrication also differs from other ways of making metal parts. Casting pours molten metal into a mould, and machining cuts material away from a solid block. Fabrication keeps the stock’s original thickness and builds the shape by cutting, bending and joining.

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The 7 Steps of the Metal Fabrication Process

The 7 steps of the metal fabrication process are design and drawings, cutting, forming and bending, joining and assembly, finishing, inspection and quality control and delivery and installation. They run in this order because each step prepares the part for the next.
metal fabrication process

Step What happens What the drawing has to state
1. Design The part is defined and quoted Material, thickness, finish, tolerances
2. Cutting Flat blanks are cut from stock Outline, holes and edge requirements
3. Forming Blanks are bent or rolled Bend angles, direction and inside radius
4. Joining Parts are welded, fastened or bonded Weld type, size and position
5. Finishing Surfaces are prepared and coated Finish type, colour, masked areas
6. Inspection The part is checked against the drawing Critical dimensions, weld inspection method
7. Delivery The part is packed, shipped or installed Packing and labelling requirements

Step 1: Design and Drawings

Design and drawings are the first step of metal fabrication, and the usual package is a 3D CAD model plus a dimensioned 2D drawing. The 2D drawing carries the material, thickness, finish, a general tolerance and the critical dimensions. The 3D model gives the fabricator the geometry for the flat pattern and the machine programs.

Material choice is settled at that stage, and the common fabrication metals are mild steel, stainless steel and aluminium. The deciding factors are strength, weight, corrosion resistance, formability, weldability and cost.

Step 2: Cutting

Cutting turns stock sheet, plate, tube or bar into flat blanks with the right outline and holes. The 5 common methods are laser, plasma, waterjet, shearing and punching, and the choice depends on material, thickness, edge quality and heat. The laser, plasma and waterjet details below are based on Hypertherm's comparison of cutting processes.

Method Material and thickness Edge Heat
Laser Thinner sheet and plate Excellent Smaller heat-affected zone
Plasma Mid-range to thick conductive metals Very good Larger heat-affected zone
Waterjet A range of materials, across the thickness range Exceptional None
Shearing Straight cuts in sheet and plate Straight edge Mechanical cut, no cutting heat
Punching Holes and repeated shapes in sheet Burr on one side Mechanical cut, no cutting heat

Laser cutting uses a focused beam and suits thin parts that need tight tolerances. Plasma cutting uses an electric arc, so plasma works only on conductive metals. Waterjet cutting uses pressurised water carrying abrasive.

Shearing makes straight cuts with a blade, while punching presses holes with a punch and die. Laser and plasma both heat the cut edge, while waterjet, shearing and punching add no cutting heat.

Step 3: Forming and Bending

Forming and bending turn flat blanks into 3D shapes without removing material. Press brake bending is the most common method: a punch presses the sheet into a die. Roll forming, tube bending and stretch forming shape profiles, tubes and curved panels, while stamping uses a die made for one part and therefore suits large production runs.

Metal stretches at a bend, so the flat length of a part differs from the sum of its straight sections, or flanges. The adjustment for this is called the bend allowance, and it depends on the material, thickness and tooling.

The tooling also sets two limits. First, each flange has to be long enough to span the die opening. The Fabricator’s guide to bend radius and minimum flange recommends a minimum flange of three times the material thickness for air bending on a press brake. The second limit is the inside bend radius: strain rises as the radius gets smaller, and a radius too tight for the material cracks the outside of the bend.

Because bend values depend on the tooling, the fabricator normally develops the flat pattern, so you only need to make sure the part can unfold flat.
sheet metal bending factory

Step 4: Joining and Assembly

Joining and assembly combine the cut and formed parts into one structure by welding, mechanical fastening or adhesive bonding. Welding is the most common method, and the usual processes are spot welding plus MIG and TIG welding.

Spot welding presses overlapping sheets between 2 copper alloy electrodes and fuses them at single points with an electric current, while MIG and TIG welding lay a seam along the joint. Bolts join parts that must come apart later, while rivets and adhesives join metals that are difficult to weld.

Welding distorts the part. As a weld cools, it shrinks and pulls the surrounding metal with it. Fabricators limit that distortion by joining the assembly with small tack welds first, then welding in a balanced sequence with short, spaced welds where a full seam is unnecessary. Even with these steps, some distortion is unavoidable, as TWI’s guidance on preventing distortion by design points out.

As a result, a face that has to stay flat or a hole that has to stay in position is best machined after welding. If your welded part has faces like this, mark them on the drawing. The fabricator can then leave extra material and plan a machining step.

Step 5: Finishing

Finishing prepares the surface of a fabricated part and then applies a protective or decorative layer. Surface preparation comes first: deburring removes sharp edges, cleaning removes oil, and blasting removes rust and scale so the coating can bond. The common finishes are powder coating, painting, plating and galvanising for steel, and anodising for aluminium, each covered in the guide to the metal finishing process.

Bare mild steel rusts, so most parts need a finish. But every coating adds thickness to the surface. The Fabricator's overview of liquid and powder coatings puts standard powder coating at 2 to 4 mils, about 0.05 to 0.1 mm. Because of that layer, a hole that is correct before coating can be tight afterwards, and the drawing has to state which dimensions apply after finishing.

Powder-coated parts also hang from a grounded metal rack during coating. The rack contact point stays bare, so the drawing should show where a bare contact point is acceptable.

Step 6: Inspection and Quality Control

Inspection and quality control check the fabricated part against the drawing in three areas: dimensions, welds and finish. Dimensions are checked after bending and again after welding, because welding can move a correct part. Welds are inspected visually first, and non-destructive testing such as liquid penetrant, magnetic particle or ultrasonic testing follows where the drawing specifies it.

A fabricated part holds looser tolerances than a machined part, because every cut, bend and weld adds variation. General tolerances for such parts are commonly taken from ISO 2768. For welded structures, ISO 13920 sets general tolerances for linear and angular dimensions in 4 tolerance classes, and treats a drawing that states neither individual nor general tolerances as incomplete.

A bend angle that is slightly off moves every feature beyond that bend, and the error grows with distance. For that reason, hole positions are best dimensioned from a cut edge or another hole on the same face.

Step 7: Delivery and Installation

Delivery and installation are the last step: the finished part is packed and shipped for assembly elsewhere, or installed on site. Packing protects coated surfaces and machined faces in transit.

Types of Metal Fabrication

The main types of metal fabrication are sheet metal fabrication, structural and plate fabrication, and stamping. Sheet metal fabrication cuts and bends thin sheet into enclosures, brackets and panels. It’s commonly used for machine and electronics housings. Structural and plate fabrication cuts and welds thick plate, beams and tube into frames, tanks and supports.

Stamping forms sheet in dies made for one part and suits high volumes, because the cost of the dies is spread over many parts.

Before committing to a fabrication route, this video compares the main metal manufacturing methods to help you choose the right starting point.

What Drives the Cost and Lead Time of a Fabricated Part?

The cost and lead time of a fabricated part are driven by 6 factors: material, the number of operations and setups, welding and fixturing, finish, quantity and tolerance. Each operation carries its own setup, so a cut, bent, welded and coated part costs more and takes longer than one only cut and bent. Welding adds labour, because parts are lined up, clamped and tacked before the seam is made.

A finish adds its own stages of cleaning, coating and curing, which lengthen lead time. Higher quantities lower the unit cost, because setup is shared across more parts.

Tight tolerances add inspection and sometimes machining. A complete drawing package shortens the quoting stage, but a drawing with gaps slows the quote, because the fabricator has to ask questions or make assumptions.

Frequently Asked Questions

Is Metal Fabrication the Same as Welding?

Metal fabrication is the whole process of making a part from stock metal, and welding is one joining step inside that process. A part can be cut, bent and bolted with no welding at all, while a welded frame still needs cutting and finishing.

What Is the Sheet Metal Fabrication Process?

The sheet metal fabrication process is metal fabrication applied to thin sheet: the sheet is cut to a flat pattern, bent on a press brake, joined and finished. The same 7 steps apply, but bending does most of the shaping.

How Do You Fabricate Metal Parts in Small Quantities?

Metal parts in small quantities are fabricated with processes that need no dedicated tooling: laser or waterjet cutting, press brake bending and manual welding. Setup cost is spread over few parts, which raises the unit price. A first part or a small trial batch, checked against the drawing, confirms the process before the full order.

What Tolerances Can a Fabricated Metal Part Hold?

A fabricated metal part holds general tolerances that are looser than machined tolerances, and the values depend on the process, part size and thickness. Drawings usually reference a standard such as ISO 2768 general tolerances, or ISO 13920 for welded structures.

From Drawing to Finished Part: The Next Step

Every step in the metal fabrication process depends on information from your drawing. When the material, thickness, bends, welds, finish and tolerances are all stated clearly, the fabricator can plan each operation before cutting starts. That means faster quotes and fewer surprises when parts arrive.

Ready to get your part made? Upload your drawing to Haizol to get quotes from multiple fabricators in China and compare them side by side.