Aspire to be an independent learner. Click here to learn how.

Bending, shaping & forming metals

Introduction

This page will discuss bending, shaping and forming woods and metals. For forming plastics visit the section on thermoforming in the 'plastics' page here. They are broken up into different materials as each requires a different set of tools and skills. Use the navigation links on the right to go straight to the topic you are looking for.

Here is an example of a complex metal fabrication. This is a roof assembly made up of geodesic, extruded sections.

The manner in which metal is shaped and formed very much depends upon the desired thickness of the finished material, the shape which is wanted and the type of material which is being used. Metals have wildly different working characteristics. A good general knowledge of materials will enable you how best to work with what you've got available.

Sheet Metal

Sheet metals used for fabrication purposes normally come in thicknesses ranging between approximately 0.5 mm thin and 6 mm thick. Under 0.5mm and it is classed as foil, over 6mm and it is classed as plate.

Standard Wire Gauge and American Wire Gauge

Another method of measuring metal sheet thickness is by using something called wire gauge. Just to confuse things there are two types; standard and American.

Wire gauge is used to classify the thickness of the metal core of electrical wires and the wires used to make high tensile cables. The term gauge (measure) comes from the actual tool shown below.

American versus Standard Wire Gauge Comparison Chart

The thickness of a steel car body panel would be about 1.2 millimetres.

As a general comparison, aluminium foil is around 0.2mm thick.

Car bodies are therefore only as thick as 6 sheets of the same stuff you cook bacon in the grill on!).

Aircraft aluminium sheet used in the fuselage 'shell' is usually about 3 mm thick.

Modern aricraft also strengthen this with a

Place your mouse cursor over the image below to see a comparison between American Wire Gauge and Standard Wire Gauge and to see the metric equivalent.

Surface Topology (Curvature Types)

There are multiple types of curvature (or 'topology') but the most common are curving in a single direction or compound (or double) curvature (curving in opposing directions). The image below shows this idea well and lists some of the common methods of manufacture.

For flat sheet processing, see this page.

Roll Forming

Roll forming can be done in two ways, hot rolling and cold rolling.

Hot Rolling

Hot rolling is generally cheaper than cold rolled metal as it can be done more easily and in higher quantities. Heating increases the metal's ductility (ability to be drawn, rolled or pressed) without causing internal stresses or cracking, however due to thermal expansion, hot rolled steel tends to shrink during cooling and it has an oxide layer on the outside called 'mill scale' which might need to be polished off depending on the final use.

Uses for hot rolled steel include...

Construction steel

Railway tracks

Pipes and tubes

Truck chassis

Cold Rolling

Cold rolling is done (as it implies) with no heat applied to the metal. The sheet is fed through a series of rollers, positioned progressively closer and closer together. This squeezes and compresses the grain structure, elongating it.

During hot rolling whilst cooling new crystals form (re-crystallisation) creating a less elongated, less organised grain structure. Cold rolling is mostly done at a temperature below the metal's re-crystallisation temperature. This causes it to harden as it is rolled, increasing its yield strength.

Diagram showing elongated grain structure caused by rolling.

Because of this, cold rolled products are generally stronger in yield than hot rolled products. Cold-rolled steel does not shrink as much so is, reliably, dimensionally more accurate out of the factory. Additionally cold rolled steel does not have the mill scale that hot rolled steel does so has a better surface finish.

Uses for cold rolled steel include...

Metal furniture

Oscillating Fan blades

Domestic appliances

Metal containers, e.g. filing cabinet.

Wheeling (or English Wheeling)

The English wheel was actually invented in France to help shape metal armour in the 1500's, however were refined and perfected during the British industrial revolution in the 1800's. They became popular for mid-sized factories who could not afford huge industrial presses during the 1910's onwards where 'panel beaters' (specialised sheet metalworkers) would use them to create the complicated compound (double) curvature of car body panels.

Advert for an early English wheel.

This video clip shows some of the complex shapes that can be made with an English wheel.

This beautiful image shows the body panels of an early sports car being formed by English wheeling. Each panel was shaped manually and 'offered up' to a wooden 'buck' which helped produce the general 'form' of the car.

These workers were known as 'panel beaters'.

This highly specialised and well respected skill fell out of favour in the 1970's and 80's as labour became very expensive as wages rose. This is partly why the shape of mass produced car for a period actually became much squarer, flatter and simpler.

This was because body panels were then pressed using huge hydraulic presses and then bolted or welded onto the car, necessitating a simpler shape.

Planishing

Planishing is a method whereby small indentations are made in the metal's surface and these are used to deform the metal up or down.

It can be done lightly by hand (not pummelling it!) with a planishing hammer or using a hydraulic one.

Planishing is also a way of smoothing out indentations and imperfections such as seam welds between metal sheets.

A selection of planishing hammers

This video shows some planishing techniques

Spinning

Spin forming or spinning as its name suggests is a process whereby a machine rotates a tube or a disc at high speed. A tool then presses the material into the desired shape by pushing it against a 'mandrel'. It is similar to using a lathe except that a lathe is a wasting process whereas this process does not produce anywhere near as much waste as only the right amount of material is used to make the part.

The spin forming process

Forming a lampshade using metal spinning

Examples of products that are formed using metal spinning...

Brass musical instruments

Gas cylinders

Candlesticks

Metal wheel trim

Pressing

Pressing is done by using hydraulic pressure to squeeze and push a metal sheet against a former or 'die'.

This is a process which can only really be economically affordable when mass producing parts as the machinery is usually very expensive.

Sheet metal press animation

Power press with metal die and visibility guard

Car body sections made using hydraulic press

Plasma cutting

Superheated gas (plasma) is used as a cutting 'beam' to locally heat very precise areas of a metal sheet.

It is a very energy intensive process and is used to cut through thicker-gauge sheet metals.

Plasma cut steel

The plasma cutting process

Stamping

Stamping is basically the same as pressing but generally for much smaller parts.

If there is a distinction between stamping and pressing it is that a stamp usually cuts the part out of a larger sheet leaving a small amount of waste behind.

Some examples of stamped components

Stamping components hydraulically.

Deep drawing

Deep drawing is carried out when the part to be manufactured is very deep when compared to its width or diameter and it has a high precision requirement.

An advantage of deep drawing is that very little waste is produced as only the right volume of sheet material is used to produce a dimensionally accurate, precision thickness component.

Examples of deep drawn components

Using a hydraulic press to deep draw a saucepan

Bending

Bending is generally carried out in three ways, 'air' or three-point bending, 'bottom-bending' and 'coining'.

Air bending using a bending brake

Bend Allowance

Bend allowance can be calculated by using the formula below where, B< is the excluded (external) bend angle, IR is the internal radius, K is the K-factor (taken from the material table) and T is the material thickness.

Generic K-Factors supplied from a popular fabrication website, www.thefabricator.com. This can be 'plugged' into the bend allowance formula above.

Bend allowance diagram showing key terms

This spreadsheet table will help you derive bend allowances for common sheet materials.

Not seeing anything above? Reauthenticate

Curling

Curling can be used to create a circular 'hole' by rolling over or 'curling' the plate at one end of a sheet. It is often seen used in gate hinges.

The two main methods of 'curling' operation.

Hemming

Hemming is used to thicken the edges of a plate section by folding it over. It helps to strengthen and make an edge safe for handling too.

The three main methods of 'hemming' operation.

Joggling

This image shows the way that 'joggling' enables two mating plate surfaces to align in a 'flush' fit.

This is what a hand 'joggling' tool looks like. It is also possible to use a mechanical tool such as a press or a hydraulic tool which speeds the process up when performing the operation on a large area or repeatedly.

Plate and Bar

Induction forming

Induction is a way of generating heat in a product by using a rapidly pulsing electromagnet. This imparts electrical 'eddy current' through the 'billet' of yet to be formed material. Electrical resistance in the metal cause heat to build up quickly. Heating it softens it, making it malleable so that it can be forged or pressed.

An electromagnetic coil surrounding a heated core.

The induction forming process

Forging

Forging is carried out on large, thick sections of material called 'billets'. The metal billet is heated to an extremely high temperature and then beaten with a hammer into the required shape. It is usually done with extremely high force hydraulic presses.

There are two main types of forging: upset forging and drop forging.

'Upset' forging animation

'Upset' forging video

Grinding and sharpening

Grinding is the name given to the aggressive removal of surface material to a workpiece by an abrasive disc moving at very high speed.

This is done by using either grinding wheel or an angle grinder.

Using an angle grinder safely.

Using a bench grinder to sharpen chisels.

Drop forging smaller steel components

Drop forging very large steel components

Page updated

Report abuse