Metal processes

The teacher material groups metal processing into forming, redistribution, addition/fabrication and wastage. The sequences below keep the important detail from the slides without splitting processes into unnecessary micro-steps.

Forming processes

Press forming

What it is: Sheet metal is forced into a die by a punch to produce a 3D form.

Step by step

Cut the sheet metal to the required dimensions and position it accurately over the lower die.
Align the punch with the die and hold the sheet securely so it cannot move during forming.
Use a mechanical or hydraulic press to apply high compressive force, pushing the sheet into the die cavity.
Withdraw the punch once the shape has formed and remove/eject the component from the die.
Trim excess material, finish the edges and check dimensions, cracking and surface finish.

Common uses: car body panels, boxes and containers.

Advantages: accurate, fast and repeatable once tooling is set up; suitable for mass production.

Disadvantages: high tooling cost; excessive forming can thin, tear or distort the sheet.

Quality control: punch/die alignment, draw force, dimensions, surface finish and signs of cracking/thinning.

Safety: crushing/trapping at the press and sharp sheet edges; guards are essential.

Cupping and deep drawing

What it is: A sheet-metal blank is drawn deeply into a die to produce hollow cup or tube-like forms.

Step by step

Die-cut the sheet into a blank and clamp it over the deep-drawing die using a pressure pad/retainer.
A hydraulic press moves the punch into the blank while the retainer controls the sheet and reduces wrinkling.
The punch pushes the blank into the die cavity to form an initial cup shape.
The cup is drawn further through another die/stage where required to produce the deeper tubular form.
Remove and trim the component, then inspect wall thickness, wrinkles, tearing and depth.

Common uses: drinks/aerosol cans, fire extinguishers and deep containers.

Advantages: produces deep seamless hollow forms and is repeatable in mass production.

Disadvantages: high setup cost; often requires several operations; poor pressure control causes wrinkling or tearing.

Quality control: pressure-pad force, punch/die alignment, draw depth and consistent wall thickness.

Safety: crushing/trapping at the hydraulic press and sharp edges.

Spinning

What it is: A circular sheet blank rotates while a roller progressively forms it over a mandrel.

Step by step

Mount the mandrel in the chuck and hold the metal blank securely between the mandrel and tailstock.
Rotate the blank and mandrel together at a controlled speed.
Bring the roller tool into contact so pressure begins stretching the metal over the mandrel.
Move the roller progressively along the mandrel while maintaining pressure until the blank follows its profile.
Remove the component, trim excess material and check symmetry, finish and wall thickness.

Common uses: saucepans, kettle bodies and light shades.

Advantages: smooth seamless rotational forms; can be automated.

Disadvantages: limited to radial symmetry; wall thickness must be controlled.

Quality control: secure blank/mandrel, correct speed and roller pressure, symmetry and thickness.

Safety: entanglement and contact with rotating work.

Bending

What it is: Sheet metal is cold formed into a straight bend using a punch and die, commonly in a press brake.

Step by step

Mark the required bend line and position the sheet accurately over the die.
Secure the sheet so the bend line remains aligned with the punch and die.
Lower the punch so pressure forces the sheet around/into the die to create the bend.
Raise the punch and remove the formed work from the machine.
Check the bend angle and dimensions, then trim or finish where required.

Common uses: brackets, frames, casings and housings.

Advantages: forms accurate bends without removing material.

Disadvantages: spring-back may affect accuracy and excessive bending can crack the metal.

Quality control: bend-line position, punch/die alignment and final angle.

Safety: trapping/crushing and sharp sheet edges.

Rolling

What it is: Metal passes between rotating rollers to reduce thickness and increase length.

Step by step

For hot rolling, heat the billet above its recrystallisation temperature; cold rolling is carried out below this temperature.
Feed the billet or sheet between hardened rotating rollers which apply compressive force.
Reduce the roller gap progressively so the metal becomes thinner and longer.
Repeat passes as required; hot rolling allows recrystallisation while cold rolling increases strength and hardness through work hardening.
Remove the rolled material and check thickness, dimensions and surface finish.

Common uses: railway/structural sections, sheet and foil; cold-rolled products include containers, drums and saucepans.

Advantages: efficient and consistent production of sheet/sections.

Disadvantages: large machinery; poor control creates thickness variation and cold working reduces ductility.

Quality control: roller gap, temperature where applicable, thickness and surface consistency.

Safety: entanglement/crushing at rollers and burns during hot rolling.

Drop forging

What it is: A heated billet is forced between shaped dies to produce a tough component.

Step by step

Secure the cast tool-steel lower die on the anvil and matching upper die to the hydraulic ram.
Heat the billet above its recrystallisation temperature so it can deform without excessive work hardening.
Use tongs to place the heated billet accurately into the lower die.
Apply the hydraulic ram so the upper die forces the billet into the die cavity.
Lift the ram, remove the forging, cool it and trim/finish excess material before inspection.

Common uses: spanners, pliers and other tough tools.

Advantages: very strong components; suitable for high-volume production.

Disadvantages: expensive dies and machinery.

Quality control: billet temperature, die alignment/fill and final dimensions.

Safety: hot metal, heavy dies and crushing hazards.

Wrought-iron forging

What it is: Heated wrought iron is repeatedly hammered over an anvil to create decorative or bespoke forms.

Step by step

Heat the iron until it reaches a cherry-red colour and becomes malleable.
Place the hot metal securely on an anvil or suitable former.
Hammer the metal repeatedly, manually or with powered equipment, to develop the required form.
Reheat when necessary so the metal remains workable while shaping continues.
Allow the completed work to cool before further heat treatment or finishing.

Common uses: gates, fencing and decorative metalwork.

Advantages: flexible for individual decorative shapes and bespoke work.

Disadvantages: labour/skill intensive and slower than industrial forming.

Quality control: heating and comparison against jigs/templates.

Safety: burns, sparks and hammering hazards.

Redistribution / casting

Sand casting

Make a pattern slightly larger than the finished component and place it inside the two-part flask.
Pack prepared sand tightly around the pattern, separate the flask and remove the pattern to leave the cavity.
Create the runner, riser and vents so metal can enter and displaced gases can escape.
Reassemble the mould, pour molten metal through the runner and allow it to cool and solidify.
Break/shake away the sand, cut off the runner/riser and clean and finish the casting.

Common uses: engine parts, post boxes and larger cast components.

Advantages: suitable for large shapes and low quantities; cheaper tooling than permanent dies.

Disadvantages: mould is destroyed; rougher finish and lower accuracy than die casting.

Quality control: pattern accuracy, packed sand, runners/risers/vents, controlled pour and porosity.

Safety: severe molten-metal burn risk; PPE and ventilation.

Gravity die casting

Preheat the permanent metal die and apply a coating to improve flow and release.
Melt the required metal and transfer it safely in a ladle.
Pour the molten metal slowly into the die cavity so it fills under gravity.
Leave the metal until it has cooled and solidified sufficiently.
Open the die, remove the casting and machine/trim excess material before inspection.

Common uses: door knobs and automotive components.

Advantages: reusable mould and more consistent finish than sand casting.

Disadvantages: higher die cost; mainly suitable for appropriate lower-melting alloys.

Quality control: die temperature/coating, pour, fill, dimensions and finish.

Safety: molten-metal and hot-die burns.

Pressure die casting — hot chamber

Maintain low-melting-point metal in the integral furnace with the gooseneck submerged in the molten metal.
Close and clamp the reusable steel die securely.
Use the hydraulic plunger to force molten metal through the gooseneck into the die at high pressure.
Hold it while the metal cools and solidifies rapidly in the cavity.
Open the die and use ejector pins to remove the component before trimming and inspection.

Common uses: toy cars, door handles and zinc components.

Advantages: very fast, accurate and repeatable.

Disadvantages: expensive tooling and unsuitable for high-melting metals.

Quality control: temperature, injection pressure, complete filling, porosity and dimensions.

Safety: high-pressure molten metal and crushing hazards.

Pressure die casting — cold chamber

Melt the higher-melting-point metal in a separate furnace.
Measure and ladle the required amount of molten metal into the cold shot chamber.
Close and clamp the steel die securely.
A hydraulic plunger forces the molten metal from the chamber into the die at high pressure.
Allow it to solidify, then open the die, eject the component and inspect/finish it.

Common uses: aluminium components and repeated engineering castings.

Advantages: accurate high-volume casting of metals unsuitable for hot chamber.

Disadvantages: slower because metal is transferred from a separate furnace; expensive tooling.

Quality control: measured charge, temperature, pressure, fill, porosity and dimensions.

Safety: molten-metal transfer and high-pressure machinery.

Investment casting

Produce an accurate wax replica and attach it to a wax sprue/tree.
Coat the wax assembly in ceramic/clay slurry and stucco until a strong shell forms.
Fire the shell in a kiln so it hardens and the wax melts out, leaving the cavity.
Pour molten metal into the ceramic mould and allow it to cool and solidify.
Break away the shell, clean the casting and machine off the runner/sprue.

Common uses: jewellery, hip-joint replacements and precision components.

Advantages: excellent detail, accuracy and surface finish.

Disadvantages: several stages make it slower and more costly.

Quality control: wax accuracy, shell integrity, complete filling and dimensions.

Safety: hot kiln, molten metal and ceramic dust.

Low-temperature pewter casting

Make the mould from MDF with the required cavity and pouring channel.
Sandwich the mould between two MDF pieces and clamp it securely.
Melt the pewter in a ladle and carefully pour it into the cavity.
Allow it to cool before opening the mould and removing the casting.
Remove the sprue with a junior hacksaw, then file and finish with wet-and-dry paper.

Common uses: jewellery, keychains and small decorative products.

Advantages: simple workshop casting because pewter has a low melting temperature.

Disadvantages: limited to small suitable products; poor pouring causes incomplete casts.

Quality control: secure mould, complete filling, surface and finishing.

Safety: molten pewter can cause serious burns.

Addition / fabrication

Arc welding

Clean, position and clamp the work, attach the earth clamp and secure the coated filler electrode in the holder.
Set the welding current to suit the material and electrode.
Strike the arc between the electrode and work to create the heat needed to melt the metal.
Maintain the arc and move along the joint so a continuous molten weld pool and bead are produced.
Allow the weld to cool, remove slag/flux with a wire brush and inspect the joint.

Common uses: rough/general steel fabrication.

Advantages: strong, portable and suitable for general fabrication.

Disadvantages: slag/spatter and rougher finish.

Quality control: current, stable arc, bead, penetration, cracks and porosity.

Safety: welding mask, leather PPE and ventilation.

MIG welding

Clean, align and clamp the components securely.
Set the wire feed, electrical settings and inert shielding-gas flow.
Operate the torch so the thin consumable wire is fed continuously towards the joint.
An electric arc forms between the wire and workpiece, melting both to create the weld pool.
Move steadily along the joint to form an even weld bead, then cool and inspect it.

Common uses: bike frames, vehicle exhausts and general fabrication.

Advantages: fast with automatic wire feed; suitable for thicker materials.

Disadvantages: rougher/more spatter than TIG; shielding gas required.

Quality control: wire feed, gas flow, travel speed, bead consistency and porosity.

Safety: welding mask, gloves/leather PPE and ventilation.

TIG welding

Clean, align and clamp the work accurately.
Fit the tungsten electrode and set the argon shielding-gas flow.
Strike an arc between the non-consumable tungsten electrode and workpiece so the parent metal melts.
Feed a separate filler rod manually into the molten pool when required.
Move the torch/filler consistently along the joint, then cool and inspect the precise weld.

Common uses: pool ladders, car exhausts, stainless steel and precision work.

Advantages: clean, precise, high-quality weld with little spatter.

Disadvantages: slower and more skill dependent than MIG.

Quality control: clean surfaces, gas flow, arc/filler control and even bead.

Safety: welding mask, leather PPE and ventilation.

Spot welding

Clean and overlap the two thin metal sheets at the joint.
Place the joint between the copper electrodes.
Close the electrodes so they clamp the sheets under pressure.
Pass a high current through the sheets; electrical resistance produces heat and forms a molten weld nugget.
Stop the current but maintain pressure while the nugget solidifies, then release and inspect it.

Common uses: mild-steel sheet, car bodies and mass-produced assemblies.

Advantages: fast and repeatable with no filler or shielding gas.

Disadvantages: mainly for overlapping thin sheet and needs access from both sides.

Quality control: electrode position/pressure, current/time and nugget consistency.

Safety: crushing, electrical hazards, hot metal and sparks.

Oxy-acetylene welding

Clean, align and secure the metal components.
Mix oxygen and acetylene at the torch, ignite it and adjust to the required neutral flame.
Heat the edges of the parent metal until a molten weld pool forms.
Dip a filler rod of the same/suitable metal into the pool and move the torch and rod along the joint.
Complete the weld, allow it to cool and inspect the finished joint.

Common uses: mild-steel sheets and plates.

Advantages: portable and does not require an electrical welding supply at the joint.

Disadvantages: slower than MIG and can cause more heat distortion.

Quality control: correct flame, clean joint, weld pool/filler and distortion.

Safety: pressurised gas cylinders, open flame, hot metal and fumes.

Soft soldering

Clean the metal surfaces and position the components accurately together.
Apply flux to prevent oxidation and help the solder flow.
Heat the joint using a soldering iron or suitable heat source.
Apply the low-melting-point solder so it melts and flows into the joint by capillary action.
Remove the heat, allow the solder to solidify and inspect/clean the joint.

Common uses: electronics and light metal/jewellery work.

Advantages: low heat and simple equipment; parent metals do not melt.

Disadvantages: weaker than welding/brazing and may leave a visible joint.

Quality control: clean surfaces, flux, sufficient heating and complete solder flow.

Safety: hot iron, molten solder and flux fumes.

Brazing / hard soldering

Clean the surfaces with emery cloth and align the metals closely at the joint.
Apply flux to prevent oxidation and help the filler flow.
Heat the surrounding parent metals evenly with a flame.
Apply the higher-melting-point spelter so it melts and flows through the joint by capillary action.
Allow the joint to cool and solidify, then clean away remaining flux and inspect it.

Common uses: pipework and joining similar or dissimilar metals.

Advantages: stronger than soft soldering and can join different metals without melting them.

Disadvantages: higher temperature and careful surface preparation/close fit required.

Quality control: clean surfaces, joint gap, even heat and complete spelter flow.

Safety: flame, hot metal and flux fumes.

Pop riveting

Overlap and clamp the components, then mark the rivet position.
Drill a hole through both pieces to the correct diameter.
Insert the pop rivet and place its mandrel into the rivet gun.
Squeeze the gun so the mandrel pulls and expands the rivet behind the material, clamping the sheets together.
Continue until the mandrel snaps, then check that the joint is tight.

Common uses: sheet-metal products and one-sided-access assemblies.

Advantages: quick permanent fixing with access needed from only one side.

Disadvantages: needs drilling and is not intended for easy dismantling.

Quality control: correct hole/rivet diameter, alignment and fully set rivet.

Safety: eye protection and care with sharp sheet edges/broken mandrels.

Snap-and-set riveting

Align and clamp the components and drill matching holes.
Insert a solid rivet of the correct diameter and length.
Support the manufactured rivet head firmly on the snap/anvil.
Use the setting tool/hammer to deform the projecting end and form the second head.
Check both heads and make sure the joint is tight without damaging the material.

Common uses: permanent metal joints and traditional sheet-metal fabrication.

Advantages: strong mechanical joint without heat.

Disadvantages: needs access from both sides and is not easily dismantled.

Quality control: hole alignment, rivet size and properly formed heads.

Safety: eye protection and care with drilling, hammering and sharp edges.

Wastage processes

Milling

Clamp the metal securely to the milling-machine table, normally using a vice.
Fit the correct multi-tooth milling cutter into the spindle.
Set the required spindle speed and depth of cut.
Feed the work/cutter so the rotating teeth progressively remove material and create the required form.
Stop the machine, measure the component, deburr and complete final finishing.

Advantages: accurate and versatile.

Disadvantages: creates waste and needs correct setup/tool selection.

Quality control: secure work, cutter, speed/depth and dimensional measurement.

Safety: guards, eye protection and hands/clothing clear of cutter and swarf.

Turning

Secure the metal bar accurately in the lathe chuck/between centres.
Fit and position the single-point cutting tool at the correct height.
Select a suitable spindle speed and rotate the workpiece.
Move the cutting tool along or into the rotating metal to remove material and produce the required profile.
Stop the lathe, measure, deburr/finish and remove the component safely.

Advantages: accurate production of rotational forms.

Disadvantages: mainly rotational forms and creates swarf.

Quality control: secure work, tool position, speed/feed and measurements.

Safety: entanglement, sharp swarf and cutting tools.

Flame cutting

Clean and secure the low-carbon steel plate and mark the cutting line.
Mix oxygen and acetylene, ignite the torch and adjust the flame.
Heat the start of the cut until the steel reaches the required temperature.
Apply the additional oxygen jet and move steadily so molten/oxidised metal is blown from the cut.
Allow the work to cool, remove slag and finish/check the edges.

Advantages: useful for thick steel and does not require electrical cutting equipment.

Disadvantages: less accurate than plasma/laser and gives a larger heat-affected edge.

Quality control: torch speed/distance, flame/oxygen and cut straightness.

Safety: pressurised gases, flame, hot metal and sparks.

Plasma cutting

Clean, mark and secure the conductive metal.
Set the plasma cutter's current and gas settings for the material/thickness.
Generate the high-temperature ionised plasma jet and position it at the start of the cut.
Move the torch steadily so the plasma melts the metal and the gas blows it from the kerf.
Allow the component to cool, remove slag and inspect/finish the edges.

Advantages: fast, clean and more accurate than flame cutting.

Disadvantages: only works with conductive materials and needs specialist equipment.

Quality control: settings, torch speed/distance, dimensions and edge finish.

Safety: intense heat/light, sparks, fumes and electrical hazards.

Laser cutting

Clean the metal and position it flat and securely on the cutting bed.
Load/check the digital cutting path and set the laser focus.
Select suitable power and speed for the material and thickness.
Run the machine so the focused laser follows the programmed path and melts the metal along the cut line.
Remove the component safely, clean/deburr it and inspect dimensions and edge quality.

Advantages: very high accuracy and complex CAD/CAM shapes.

Disadvantages: expensive and less suitable for very thick material than some alternatives.

Quality control: path, focus, power/speed, kerf, dimensions and edge quality.

Safety: enclosure, extraction and laser safety procedures; never view the beam directly.

Punching / stamping

Clean and position the thin sheet metal accurately on the die.
Program/set the CNC press for the required shape and fit the correct punch/die.
Locate the sheet accurately so the cutting position is correct.
The punch moves down at high force and shears through the sheet into the die.
Remove the slug/waste and finished component, then inspect and deburr where necessary.

Advantages: very fast and accurate once tooling is set up.

Disadvantages: dedicated tooling/setup cost and mainly suited to sheet metal.

Quality control: sheet position, punch/die alignment, dimensions and burr quality.

Safety: severe crushing/shearing hazard; guards are essential.