Last edited 27 Nov 2016

Metal fabrication

Metalfabrication.jpg

Contents

[edit] Introduction

Metal fabrication involves the making of metal structures and components by manipulating the raw material – usually structural steel and sheet metal – through a range of processes. The term covers a broad range of activities, from sheet metal fabrication for construction projects, to machined parts and bespoke products for manufacturers. Workshops that specialise in metal fabrication are known as ‘fab shops’.

Typical processes involved in metal fabrication include:

  • Forging.
  • Casting.
  • Cutting.
  • Bending.
  • Shearing.
  • Drawing.
  • Spinning.
  • Punching.

Once the parts have been made, they may need to be assembled. Assembly may involve welding, binding with adhesives, riveting, threaded fasteners or crimped seams.

The parts or assemblies may then be treated by a process of sandblasting, priming, painting or powder coating, if required.

The finished product should subject to careful inspection to ensure it complies with the specification before leaving the fab shop.

[edit] Cutting

The desired shape can be formed by removing unwanted material from a block of metal, in a process known as machining. Metal is cut as required using different tools, including:

[edit] Saws

Industrial saws such as band saws and large circular saws can cut metal in straight-lines. Angle grinders are handheld power tools fitted with an abrasive disc used for cutting, grinding and polishing.

[edit] Shears

Shears are industrial machines, that come in a wide range of configurations and sizes, capable of cutting sheet metal of different thicknesses. They work in the same way as a pair of scissors, with opposing blades, one being fixed and the other moving in an angled levering motion. Different types of shears include:

  • Hand shears: Also known as ‘aviation snips’, these are simple, manual tools used to cut thin pieces of metal.
  • Power shears: These are capable of cutting sheet metal quickly and with less manual effort. However, most are unable to cut intricate shapes or tight radii and so tend to waste material.
  • Throatless shears: These are hand-operated and use a hinged blade that swings down to cut metal lying on a stationary adjacent blade. These are capable of cutting in straight lines or shapes and minimise waste material.

[edit] Plasma and laser cutters

High definition plasma cutting techniques are used to achieve intricate shapes. With the integration of computer aided design and computer aided manufacturing, the cutting process can be achieved flawlessly, with minimal waste.

[edit] Bending

The bending metal can be achieved by one of two techniques:

  • The simplest method is form bending, in which metal is bent over an edge or shape located under the metal. This can be done manually or with tools such as hammers and shaping dollys to bend metal around the required shape.
  • Metal brakes are the most common method of achieving clean, precise bends. The process involves placing the metal on a flat, gated surface, clamping a flat bar on top of it, and lifting the gated portion to bend the metal to the desired angle.

[edit] Shrinking

The most common methods of shrinking metal include:

  • Tucking: A simple technique that involves forcing metal together between a crevice or folding metal over at the edges.
  • Shrinker: This is a lever-operated tool with moving textured jaws that grasp sheet metal from the top and bottom and force it together lightly. Particular areas can be carefully worked to shrink as required. This is a more precise but slower method.
  • Heat shrinking: This involves heating an over-stretched area with a blowtorch until it is almost red hot, as the metal shrinks when it cools. Shrinking discs can be applied to angle grinders that use friction to generate heat.

[edit] Stretching

The most common methods of stretching metal include:

  • Hammer and dolly: This is the simplest technique and involves holding an object behind the metal and hitting the other side with a hammer, forcing the metal to compress and stretch.
  • Stretcher: This is a mechanically-operated tool similar to the shrinker, that places metal between two flat-textured jaws which pull it apart slowly.
  • English wheel: This technique uses wheels that roll back and forth over the flat metal.

[edit] Welding

The most common methods of welding metal to produce larger and more complex parts include:

  • Oxy-acetylene welding: This is the oldest form of welding but is still widely used. Tanks of oxygen and acetylene are mixed with an adjustable torch to create a controlled flame to heat the metal. During heating, a filler rod is added that joins the metal together. These welds are the easiest to planish (smooth out) with a hammer and dolly, enabling the weld joint to be as flat as possible.
  • TIG welding: This involves a torch that has a non-consumable electrode that creates a small, precise electric arc that melts the base metal. Filler rods are added to the puddle of molten metal to join the parts together. This is a more precise method than oxy-acetylene.
  • MIG welding: This is the most common method and involves a motor that is used to feed the filler wire through the tip of a MIG gun. The wire is melted into the weld joint, fusing the metal together.

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