Rugby School Thailand Design & Technology Senior School

3.9 Shaping Materials

Syllabus

(a) Deforming / Reforming

• understand the following processes: bending, sand casting, die casting, lamination, vacuum forming, blow moulding, injection moulding, extrusion, press forming

(b) Wastage / addition

• select and perform the following forms of cutting and removal of material, and joining and adding to a material to produce the required shape, form or contour:

– use hand snips, saws, files, basic planes and abrasive cutters

– simple hole boring by hand or machine including pilot, clearance, tapping, countersunk and counterbored holes

– use taps and dies for screw cutting by hand

– use planes, chisels, gouges and rasps

– use abrasive mops, discs and belts

– use a centre lathe and wood turning lathe

– use portable power tools

Redistribution

Redistribution refers to the fact that material is moved around in order to shape it into a product or component.

This can be done in one of two ways; 1. Deforming and 2. Reforming.

Deforming involves changing the shape of the material without changing the state. i.e. the material remains a solid throughout the shaping process even though it may be subjected to heat and/or pressure.

Wood is not a material that lends itself to being deformed as it is mostly used in its natural state and its strength resists bending.

Thermoplastic polymers can become soft at relatively low temperatures at which point they can easily be deformed.

Metals are also relatively easy to deform using a combination of heat and pressure.

Deforming wood

Wood is not typically deformed as it is more easily joined but there are a few deformation techniques.

Steam bending

This process involves bombarding wood with steam until it becomes flexible. It is then bent into shape and held in place while the water content is slowly removed from the wood leaving the wood ‘bent’ into shape. Traditionally used to make Windsor style chairs.

Kerfing

This process is not actually deforming the wood (it could be considered wasting) but involves cutting grooves into the wood in order to make deforming by bending much easier.

Guitar and Violin shells were traditionally made this way and many still are.

Laminating

This is not a way of deforming solid timber like you can with steam bending. Thin sheets (veneers) of wood are stacked with glue in between then placed in a mould. Once the glue has set the wood is removed and retains the shape of the mould. This is how skateboards are made.

Deforming Metal

Metal lends itself well to being deformed with pressure and heat.

Bending and folding

Metal can be bent cold or hot and sheet metal can be folded in similar way to sheet plastic, although it requires specialist high pressure machinery.

Spinning

Spinning is a process by which a disc of metal is rotated at high speed and formed into a symmetrical part.

Metal spinning does not involve removal of material, as in conventional wood or metal turning, but forming (moulding) of sheet material over an existing shape.

Commercial applications include rocket nose cones, cookware, gas cylinders, brass instrument bells, and public waste receptacles. Virtually any ductile metal may be formed.

Sinking

Sinking is a metalworking technique whereby flat sheet metal is formed into a non-flat object by hammering. While sinking is a relatively fast method, it results in stretching and therefore thinning the metal, risking failure of the metal if it is 'sunk' too far. Sinking is used in the manufacture of many items, from jewellery to plate armour.

Punching

Punching is a metal forming process that uses a punch press to force a tool, called a punch, through the work piece to create a hole via shearing. The punch often passes through the work into a die. A scrap slug from the hole is deposited into the die in the process. Depending on the material being punched this slug may be recycled and reused or discarded. Punching is often the cheapest method for creating holes in sheet metal in medium to high production volumes. When a specially shaped punch is used to create multiple usable parts from a sheet of material the process is known as blanking.

Blanking and Piercing

Blanking and piercing are shearing processes in which a punch and die are used. The tooling and processes are the same between the two, only the terminology is different: in blanking the punched out piece is used and called a blank; in piercing the punched out piece is scrap. The process for parts manufactured simultaneously with both techniques is often termed 'pierce and blank'. An alternative name of piercing is punching (see previous slide).

Forging

Forging is a manufacturing process involving the shaping of metal using localized compressive forces. Forging is often classified according to the temperature at which it is performed: ‘cold’, ‘warm’, or ‘hot’ forging. Forged parts can range in weight from less than a kilogram to 580 metric tons. Forged parts usually require further processing to achieve a finished part.

Drop Forging

Drop Forging is a forging process where a hammer is raised and then ‘dropped’ onto the work piece to deform it according to the shape of the die. There are two types of drop forging: open-die drop forging and closed-die drop forging. As the names imply, the difference is in the shape of the die, with the former not fully enclosing the work piece, while the latter does.

Drawing

Drawing is a metalworking process which uses tensile forces to stretch metal. It is broken up into two types: sheet metal drawing and wire, bar, and tube drawing. The specific definition for sheet metal drawing is that it involves plastic deformation over a curved axis. For wire, bar, and tube drawing the starting stock is drawn through a die to reduce its diameter and increase its length. Drawing is usually done at room temperature, thus classified a cold working process, however it may be performed at elevated temperatures to hot work large wires, rods or hollow sections in order to reduce forces.

Deep Drawing

Deep Drawing is a sheet metal forming process in which a sheet metal blank is radially drawn into a forming die by the mechanical action of a punch. The process is considered ‘deep drawing’ when the depth of the drawn part exceeds its diameter.

This is achieved by redrawing the part through a series of dies. This is the process used to make most aluminium drink cans.

Press Forming

Press Forming is a sheet metal process that uses a pair of tools called a ‘die’ mounted inside a press and then the metal is placed inside the die. The press then applies high pressure (3000 tons of force or higher on large presses) and the material is formed to match the shape of the die. In other words, press forming is a forming technology where a pressing force is applied to a material to deform it (by bending, stretching, etc.) to match the size and shape of the die, and the material then maintains that shape forever. It is used to make the cases for white products such as fridges and most car body parts are made by press forming nowadays.

Deforming polymers

Polymers are perhaps the most commonly formed material in the D&T workshop due to the ease with which they can be turned into a liquid (or softened) and back to a solid at relatively low temperatures. The following methods rely on the polymer being heated up until it becomes plastic i.e. flexible enough to form but it never becomes a liquid.

Line Bending

A process which involves heating up a small area of plastic sheet so it can be folded or bent like paper. Usually this is done around a former.

Vacuum Forming

Vacuum Forming is a process which involves heating up a sheet of plastic then raising a former or pattern up through the plastic while removing the air below to create a vacuum. This then causes atmospheric pressure outside the vacuum to ‘force’ the plastic down on to the former.

Vacuum Forming is commonly used to produce hollow ‘shell like’ items such as yoghurt pots and other food containers but they can be used to produce larger items such as baths and hot tubs. They are also useful for making moulds for pouring in plaster and concrete.

How Vacuum Forming works

Vacuum Forming moulds should have the following characteristics:

The sides should slope outwards with no ‘under hang’ so the product can be removed from the mould. This is called a draft angle.
There should be no sharp edges (radius edge) to avoid thinning of the plastic.
There should be air holes to avoid trapped air especially in the corners.
There should be sufficient space between peaks (and peaks should not be too high) toavoid webbing.

Pressure forming

Pressure forming is a relatively new process but is very closely related to vacuum forming. However, where vacuum forming relies solely on the vacuum to ‘pull’ the softened polymer around the mould, pressure forming uses an additional former to help in the process and allows for a greater level of detail such as lettering and sharp edges to be achieved.

The various thermoforming processes

Blow Moulding

Blow Moulding is a manufacturing process by which hollow plastic parts are formed. The blow moulding process begins with melting down the plastic and forming it into a parison or in the case of injection (and injection stretch blow) moulding, a preform. The parison is a tube-like piece of plastic with a hole in one end through which compressed air can pass.

The parison is then clamped into a mould and air is blown into it. The air pressure then pushes the plastic out to match the mould. Once the plastic has cooled and hardened the mould opens up and the part is ejected.

The Blow Moulding process

Reforming Metals

Metal exists in a liquid state when formed so it lends itself particularly well to being moulded again by being melted back into a liquid form.

Sand Casting

Sand Casting is also known as sand moulded casting, is a metal casting process characterized by using sand as the mould material. The term ‘sand casting’ can also refer to an object produced via the sand casting process. Sand castings are produced in specialized factories called foundries. Over 70% of all metal castings are produced via a sand casting process.

In addition to the sand, a suitable bonding agent (usually clay) is mixed or occurs with the sand. The mixture is moistened, typically with water, but sometimes with other substances such as petrol, to develop strength and plasticity of the clay and to make the aggregate suitable for moulding. A common casting sand it known as Petrabond.

**Workshop casting activity - click here

The sand is typically contained in a system of frames or mould boxes known as a flask.
The mould cavities and gate system are created by compacting the sand around models, or patterns, or carved directly into the sand.
The sand needs to be broken up to remove the metal object, which in turn needs to be left to cool,
It is quite a slow process!

Link to local companies in Thailand who Sandcast

www.teamco.com.tw/en/page/Casting-Foundry-in-Thailand/casting-foundry-thailand.html

https://www.reliance-foundry.com/blog/sand-casting

Die casting

Die Casting is a metal casting process where molten metal is forced under high pressure into a mould cavity. The mould cavity is created using two hardened tool steel dies which have been machined into shape and work similarly to an injection mould during the process. Most die castings are made from non-ferrous metals, specifically Zinc, Copper, Aluminium, Magnesium, Lead, Pewter and Tin-based alloys. Depending on the type of metal being cast, a hot- or cold-chamber machine is used.

The casting equipment and the metal dies represent large capital costs and this tends to limit the process to high volume production. Manufacture of parts using die casting is relatively simple, involving only four main steps, which keeps the incremental cost per item low. It is especially suited for a large quantity of small to medium sized castings, which is why die casting produces more castings than any other casting process. Die castings are characterized by a very good surface finish (by casting standards) and dimensional consistency.

There are several different methods which can be used.

Gravity Die Casting

as its name implies, uses gravity to force the molten material into the mould.

Pressure Die Casting

uses a ram to force the molten metal into the former using either a hot or cold chamber.

The additional pressure ensures better accuracy and detail.

Industrial Die Casting

Refers to the use of multi slide die castings. Traditional die casting uses just two halves of a die to form the shape making it difficult to produce more complex shapes.

By using four or more slides, complex 3D shapes can be achieved.

Engine blocks from triumph motorbikes

Lost Wax Casting

is the process by which a metal object (often Pewter, Silver, Gold, Brass or Bronze) is cast from an original wax sculpture. Dependent on the sculptor's skills, intricate works can be achieved by this method. Though the process today varies from foundry to foundry, the steps used in casting small pieces are fairly standardized. (In modern industrial use, the process is called investment casting.) Variations of the process include lost mould and waste wax process (or ‘waste mould casting’), because the mould is destroyed to remove the cast item.

Extrusion

Extrusion is a process used to create objects of a fixed cross-sectional profile. A material is pushed or drawn through a die of the desired cross-section. The extrusion process can be done with the material hot or cold.

Commonly extruded materials include metals, polymers, ceramics, concrete, play dough, and foodstuffs. Hollow cavities within extruded material cannot be produced using a simple flat extrusion die, because there would be no way to support the centre barrier of the die. Instead, the die assumes the shape of a block with depth, beginning first with a shape profile that supports the centre section. The die shape then internally changes along its length into the final shape, with the suspended centre pieces supported from the back of the die.

Reforming Polymers

Plastic is perhaps the most commonly reformed material due to the ease with which it can be turned into a liquid and back to a solid at relatively low temperatures.

Injection Moulding

is a manufacturing process for producing parts by injecting material into a mould. Injection moulding can be performed with a host of materials, including metals, glasses, elastomers, confectionary, and most commonly thermoplastic polymers. Material for the part is fed into a heated barrel, mixed, and forced into a mould cavity, where it cools and hardens to the configuration of the cavity. After a product is designed, moulds are made by a mould maker (or toolmaker) from metal, usually either steel or aluminium, and precision-machined to form the features of the desired part. Injection moulding is widely used for manufacturing a variety of parts, from the smallest components to entire body panels of cars. Advances in 3D printing technology, using photopolymers which do not melt during the injection moulding of some lower temperature thermoplastics, can be used for some simple injection moulds.

this diagram shows how the Injection Moulding process works using thermoplastic polymers.

Rotational Moulding

involves a heated hollow mould which is filled with a charge or set weight of material. It is then slowly rotated (usually around two perpendicular axes) causing the softened material to disperse and stick to the walls of the mould. In order to maintain even thickness throughout the part, the mould continues to rotate at all times during the heating phase and to avoid sagging or deformation also during the cooling phase. The process was applied to plastics in the 1940s but in the early years was little used because it was a slow process restricted to a small number of plastics. Over the last few decades, improvements in process control and developments with plastic powders have resulted in a significant increase in usage. Unlike other types of moulding, the shape can be hollow yet have a very thick wall.

Extrusion

similar to Injection Moulding but without the use of a hydraulic ram as the polymer is continually pushed through the die.

Compression Moulding

is the main process used to produce products using Thermosetting Polymers such as Urea Formaldehyde.

The moulding material, generally preheated, is first placed in an open, heated mould cavity. The mould is closed with a top force or plug member, pressure is applied to force the material into contact with all mould areas, while heat and pressure are maintained until the moulding material has cured.

The process employs thermosetting resins in a partially cured stage, either in the form of granules, putty-like masses, or preforms. Compression moulding is a high-volume, high-pressure method suitable for moulding complex, high-strength fiberglass reinforcements.

It is one of the lowest cost moulding methods and it wastes relatively little material, giving it an advantage when working with expensive compounds.

Resin and GRP Moulding

This is not strictly a reforming process as it effectively involves using a liquid polymer (Resin) which is left to cure and set hard.

GRP is also combined with fine strips of glass to reinforce the resin when it sets. However as the resin changes form from liquid to solid. It is included in this section just for reference.

3D Printing

3D printing is an additive process where you start with nothing and add layers of plastic which build up to form a 3 dimensional shape. As the plastic is molten it is essentially a reformation process but it is a very new process and can print metal, food and even body parts!

Summary

Redistribution is the movement of material in order to shape it. This can be done by deforming the material using heat and/or pressure or by turning the material into a liquid state then reforming it.
Reforming is used primarily with metal and plastics.
Wood can only be reformed into MDF, Chipboard and Maplex but it can be deformed by steam bending or laminating in a press.
Most complex plastic components are made by moulding techniques.
Plastic bottles are commonly made by deforming techniques.
The terms are not rigid so, 3D printing is additive but involves melting the polymer filament so could be considered reforming.

Revision Notes

For each material group, you need to be familiar with a range of forming, redistribution and addition techniques.
If you change shape by force/heat it is deforming (forming/redistribution)
If you change shape by changing state, it is reforming (redistribution)
If you join pieces together it is considered fabrication (also additive)

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