Sheet metal fabrication’ is the term used for turning flat sheets of metal into products or components. This is normally done by punching, bending, folding, and attaching sheets of steel, aluminium, or other metals. Because of the characteristics of metal, almost any shape can be produced in this way.
The tools used to produce these shapes and products include sheers and cutting torches, saws (like chop saws and band saws), press brakes to produce sharp-angles bends, welding equipment, and others.
Since heat can change the shape and characteristics of a metal object, welders generally ‘tack weld’ the pieces together first. This means that they place a tiny weld in various key positions to keep the metal components from moving in relation to each other – it functions like pins in sewing. Once everything is tack-welded together, a complete weld can be added without changing the shape of the components too much. Covering the objects in sand while welding can reduce warping, as can staggered welding techniques. In cases where welding has altered the shape outside of allowances, acetylene torches and other tools can be used to get it back within allowable limits. Sometimes this may mean reengineering the design to allow for welding without the change in shape.
Once fabricated, items are usually sand blasted, primed and painted.
How to Understand Metal Fabrication Blueprints?
Large buildings have many large steel components to them – the bones of the building’s skeleton – and though they are very big, and may seem the same to the untrained eye, it is important that each one is placed in its proper position. To ensure that this happens, each component piece of steel is marked with a unique piece mark. The piece mark identifies the component from other similar ones, and is marked on the blueprint or detail drawing. The drawing will include hole sizes, dimensions and any special notes or details that might be important to the builder.
To someone with a knowledge of standard detailing practices, reading this document gives everything needed to make sure the structure is completed according to the engineering specification and guidelines. Just in case you aren’t one of these experts (yet), here is an overview.
With the blueprint on the table with the title block in the lower right corner, the bill of materials should be located on the right side, just above the title block. It should provide a list of the exact sizes and length of steel required in the construction detailed by the blueprints.
Each drawing should be labelled with a piece mark, like A7, 1C2, or 3D4. Usually it consists of at least a letter and a number. The bill of material will also provide a detailed breakdown of the material required for each of the piece marks.
Measurements of each steel piece are taken from left to right using running dimensions. The measurements start either at the start of the steel, or from a noted workpoint. The workpoint will be noted by the detailer with either a ‘wp’ notation or a circle with an arrow pointing to it. The overall dimension of the steel piece will often be included below the drawn piece. It indicated the total, overall length of the finished piece. The main member size will also be included so you can check it against the bill of material list.
Additional parts (such as angles or plates) that attach to the main piece will be indicated by arrows. The additional parts will be labelled with part numbers using a format of lowercase letters and a number, like pb6. Often the letter ‘a’ is used to indicate angle, and ‘p’ to indicate plate.
You will need to find the location of any holes that need to be drilled. The location measurements should be included in the running dimensions along the top of the drawing, and dimensions from the top of the main member to the centre of the holes will also be provided.
Make sure to read the boxes above the title block fully and carefully. This is where any additional information and drawing notes will be included. It should also include the number and type of bolts or other fasteners connection of this piece to the building will require.
Metal fabrication shops are divided into two main categories (though many larger shops function as both and there is some crossover). They are known as welded shops or bolted shops. Welded shops, as the name indicates, focus on attaching components using welds, whereas bolted shops prefer to use bolt-related techniques.
Detailers run dimensions at the end to the main steel member for bolted shops, but for welded shops there is little need for these dimensions. There is no industry standard, so check with your particular shop to make sure everyone has what they will need.
There is no specific industry standard for detail drawing, despite several common practices and traditions. Each company may have its particular preference for how to display information. It is worth taking some time to make sure you understand the drawing as presented, and can find everything you will need. Details boxes are a key place to look for important information.