Cutting, Shaping & Forming methods for Metal

It can be helpful for Design & Technology students to have an understanding of how to cut, drill, and shape metal. This article summarises basic metalworking methods and practical techniques.

Casting (detailed information about casting needs to be studied by A2 students only, however AS students should have a basic understanding).

• Metal is heated in a crucible (a heat-resistant container with a pouring lip used to hold molten metal – often made from materials such as graphite), with the heat source commonly electric of gas-fired furnaces.
• Molten metal is poured into a mould (or injected in) and allowed to solidify into the desired shape. Examples:
  • Sand casting (bit primitive, not high quality finish)
  • Plaster of Paris casting (only works for non-ferrous metals)
  • Die casting (a high-pressure manufacturing process that produces metal parts by injecting molten metal into a hardened steel mold, called a die – used for mass production of complex parts with high precision)
• Once cooled and solidified, the item is removed from the mould

Forging – Metal is heated and shaped through compressive forces using hammers or presses. The heat source is an electric, gas, or fuel-fired ‘forge’ which uses forced air from a bellows or a blower to raise the temperature high enough to make the metal malleable.

Rolling – Metal is passed through rollers to reduce thickness and create sheets, plates, or specific profiles.

Extrusion – Metal is pushed through a die opening to create continuous profiles with a fixed cross-section.

Drawing – Metal is pulled through a die to reduce its diameter and create wires or tubes.

Stamping/Pressing – Sheet metal is formed using dies and presses to create specific shapes through cutting, bending, or embossing.

Milling machine (can be manual or CNC). A machine used to shape metal by removing material with a rotating cutting tool. Unlike a drill, which only cuts downward along its axis, a milling cutter can cut on both its end and its sides, allowing it to produce flat surfaces, slots, grooves, steps, pockets, and complex profiles. The workpiece is clamped securely in a machine vice, bolted to a movable table, which can be moved precisely in three directions — left and right, forward and back, and up and down — so the operator (or computer) can control exactly where and how deeply the cutter removes material. Like a CNC router, but rotates are a slower speed and is more heavy duty, so better suited for cutting metal. Can take a wide variety of cutters in different shapes and sizes (just like you change the drill bit in a drill). Safety precautions when using a milling machine include wearing eye protection, tying back long hair, removing loose clothing and jewellery, never wearing gloves (which can catch in the rotating cutter), clamping the workpiece securely, using the correct cutter and spindle speed for the material, keeping hands well clear of the cutter while it is running, never clearing chips or swarf by hand while the machine is running, and always following the workshop’s lockout procedures before changing cutters or making adjustments.

Bending – Metal is clamped in a vice and bent manually, or heated for thicker parts and then bent, creating angles or curves.

An anvil is a heavy, solid block of metal (traditionally iron or steel) used as a work surface for shaping metal. It has a flat top where you hammer or bend metal, and usually a horn (a curved, tapered end) for forming curves and rounded shapes. School Design & Technology workshops sometimes have a small bench anvil mounted on a sturdy base.

Spinning – A flat metal disc is spun very fast and pressed against a shaped mold to make a round/circular part like a bowl or cylinder (can sometimes be heated slightly to bend more easily, but the shaping is applied by pressure, not with the metal in molten form).

Powder Metallurgy – fine metal powder is pressed into a mould under high pressure to form a shape, then heated (but not melted) so the powder particles bond together into a solid part.

Centre lathe – as with using a wood lathe, metal can also be turned, making cylindrical or conical objects with parallel or tapered sides.

• Metal lathes are known as ‘centre lathes’ (heavier and more robust than wood lathes)
• Rather than being screwed to a face plate, the piece is held in a chuck (like how a drill bit is held by a drill) on the headstock spindle.
• At the other end is the tailstock which is used to hold any tools needed to centrally drill or lathe the centre. The inside of the tailstock barrel has a gently tapering cone shape inside (called a morse taper) — wider at the open end and narrower at the back. Drill chucks (holding small drill bits), large drill bits on their own, or reamers (a precision cutting tool used to finish a hole that has already been drilled, bringing it to an exact diameter with a smooth internal surface), and any other tools designed to be held this way can have a matching tapered shank at their back end, which can be wedged into the tailstock, held in place by friction. Large drill bits and reamers designed for lathes have a tapered end to slot into the morse taper without a chuck needed. This holds the tool dead-centre so that it spins in the middle. Alternatively, if lathing a long bar, the end of the bar can also be supported centrally inside the taper.
• The tailstock barrel can be wound in and out using the handwheel, bringing the tool toward the workpiece as the lathe spins.
• Metal turning tools (rather than chisels) are clamped to a tool post on the middle / side (not hand-held as with a wood lathe).
• Spins at different speeds to suit different materials (harder/tougher materials like stainless steel require slower speeds; softer materials like aluminium require higher speeds). Size of task may also require change of speed.

Drilling

There are special drill bits designed for use with various metals (obviously the drill bit has to be a stronger metal than the one being drilled)!

Chain drilling

Engineering Files

Engineer’s files are used for shaping, smoothing, and finishing metal, i.e:

• Deburring sharp edges after cutting
• Removing small amounts of metal to adjust fit
• Cleaning up rough edges or surfaces

Wet and Dry Sandpaper

• A special type of sandpaper that can be used either dry or wet
• Comes in a range of grit (rough through to smooth)
• Good for smoothing and polishing, as well as removing rust or paint from metal surfaces
• Often used wet to stop the sandpaper clogging

Emery paper

• Dark sandpaper for smoothing and finishing metal surfaces (used almost exclusively for metal, but can also be used on some plastics and other hard materials)
• Often uses a cloth backing paper rather than paper which makes it more flexible and able to withstand the heat and pressure of working with metal
• Comes in a range of grit like normal sandpaper, but the fine grades are much finer than sandpaper
• Like sandpaper, can be wrapped around a file or flat block of wood to achieve flat surfaces
• Can also be used with oil for lubrication and to prevent clogging

Manual cutting with hack saw

Normal saws cannot cut metal (the teeth on the blade break or get blunt) – instead a hacksaw is used.

Abrafile hacksaw blade

A straight round blade held in a hacksaw frame, which allows you to cut curves in metal (like a coping saw blade for metal).

Tin snips

Very thin sheets of metal can be cut with tin snips (basically extra tough / durable scissors for metal – normal scissors get blunt if you use them to cut metal)!

Sheet metal guillotine (metal shearing machine)

Has a heavy blade that comes down to cut through sheet metal (like a paper guillotine but more heavy duty). Can be hand-operated via a lever, foot-operated or an industrial hydraulic guillotine, depending on the thickness and frequency of cuts needed.

Grinder

Has an abrasive wheel or belt that removes small amounts of material to achieve precise dimensions, smooth surfaces, or sharp edges. It’s typically used as a finishing process after other forming operations, but a grinder can also be used with a cutting disk to cut through metal (common method for cutting sheet steel in a school workshop). You clamp the sheet, mark your cut line, and run the cutting disc along it. Less precise than a guillotine and leaves a rougher edge (which you’d then clean up with a file or grinding disc).

How to cut thread (enabling a metal part to screw in)

Note: Most laser cutters used in a school setting cannot cut metal, however some industrial high-powered ones can.

Sample examination questions (AS Design & Technology)