Materials & manufacture · Higher

Commercial processes

12 cards · 10 quiz · 3 exam

Design & Manufacture · Higher · mrkellydt.co.uk

What you're learning in this topic

Learning intention WALT

We are learning about commercial processes, specifically to understand:

the uses and identifying features of injection moulding, die casting, rotational moulding, vacuum forming and sand casting
the features of a good vacuum-forming and sand-casting pattern
the uses and identifying features of bending, blow moulding, compression moulding, drop forging, extrusion, piercing and blanking, and press forming
the issues that influence the choice of process
how to identify the process used to make a product

Success criteria WILF

I can describe the uses and identifying features of injection moulding, die casting, rotational moulding, vacuum forming and sand casting
I can describe the features of a good vacuum-forming and sand-casting pattern
I can describe the uses and identifying features of bending, blow moulding, compression moulding, drop forging, extrusion, piercing and blanking, and press forming
I can describe the issues that influence the choice of process
I can describe how to identify the process used to make a product

Moulding and casting

Process	Uses	Identifying features
Injection moulding (thermoplastic)	Complex, accurate parts in high volumes: casings, toys, bottle crates, sunglasses frames	Ejector pin marks, injection point, flashing, draft angles, high-quality finish, strengthening ribs, split lines, bosses
Die casting (metal, e.g. aluminium alloy)	Accurate complex metal parts in high volumes: toy cars, pencil sharpeners, door handles	Same as injection moulding: ejector marks, flash, draft angles, high finish, split lines
Rotational moulding (thermoplastic)	Large hollow forms: kayaks, bins, traffic barriers, play equipment	Hollow, seamless, uniform wall thickness (thicker in corners), good finish, slight draft
Sand casting (metal)	Low-volume solid or hollow metal parts: engine blocks, manhole covers, one-offs	Rough "orange peel" texture, draft angles, rounded corners and fillets, split line; often needs machining
Vacuum forming (thermoplastic sheet)	Simple shallow forms: packaging trays, masks, bath tubs, chocolate inserts	Thin walls (thinner at corners and bottom), open tray shape, generous draft angles, rounded corners

How the processes work

Four of the processes in the table above, step by step.

Plastic granules fall from the hopper into the heated barrel. The turning screw melts and mixes them, then pushes the molten plastic through the nozzle into the mould at the injection point. The plastic cools against the cold mould, the two halves open at the split line, and ejector pins push the part out. Draft angles on the sides let it release.

Molten metal, such as aluminium or zinc alloy, is forced under pressure into a two-part steel die. It cools quickly against the die, which then opens at the split line. Ejector pins push the casting out, leaving small circular ejector marks. Any thin flash squeezed out at the split line is trimmed off. The die is reused, so every casting is identical.

Plastic powder is put into a closed mould, which is heated in an oven while it rotates on two axes. The powder melts and coats the inside of the mould evenly. The mould is cooled, still rotating, then opened. The product is hollow and seamless, with a uniform wall thickness (a little thicker in the corners).

The pattern is packed in sand in a two-part moulding box: the cope (top) and the drag (bottom). The halves are separated at the split line so the pattern can be removed, leaving a cavity. Molten metal is poured down the sprue; the riser lets air escape and shows the mould is full. When cool, the sand is broken away and the casting is fettled: the runners are cut off and the edges filed.

Patterns for vacuum forming and sand casting

Draft (taper) on vertical faces so the pattern can be removed.
Radiused corners and edges: no sharp corners; material flows and the pattern releases.
Smooth surface: any marks transfer to the product.
Vacuum forming: pattern must be flat-backed, have no undercuts, and have vent holes in hollows so air is drawn out.
Sand casting: pattern is often split in two halves with location pins; made from a stable material like MDF or wood.

The heated sheet is clamped in the frame, the platen raises the pattern into it, and the air is sucked out so the sheet is pulled tight onto the pattern. A good pattern has draft angles and radiused corners so it releases, a flat back, and vent holes so air is drawn out of hollows. The sheet stretches and thins most at corners and on deep sides.

Sand casting: the pattern is slightly larger than the product to allow for shrinkage as the metal cools; a sprue and riser are added so metal can be poured in and air escape; cast parts are fettled (runners cut off and edges filed) afterwards.

More processes (Higher) HIGHER

Process	Uses	Identifying features
Blow moulding	Seamless hollow containers: bottles	Simple symmetrical shape, thin even walls, flash at base, no internal detail
Compression moulding	Thermosets: plugs, pan handles, hard hats	As other mouldings (flash, draft angles) but no undercuts
Extrusion	Long constant profiles in plastic or aluminium: window frames, curtain rails, pipes, tubes	Identical cross-section along the length, smooth finish
Drop forging	Very strong metal parts: spanners, tools, golf club heads	Simple forms, thick sections, large radii and draft angles, flash line; process strengthens the metal
Piercing and blanking	Cutting sheet metal: washers, key blanks (blanking makes the shape, piercing makes holes)	Shear marks, accurate, repeated identical parts
Press forming	Bends and deep draws in sheet metal: sinks, car panels, cans	Thin material, radiused corners, good finish, stress marks on deep draws
Bending	Tube, bar or sheet in wood, metal or plastic: chair frames, playground equipment	Radiused bends, few or no joins
Laser cutting	Thin sheet wood/acrylic/metal: jewellery, lighting, signage	Very accurate, scorch marks, crisp edges, flat sheet parts
3D printing	Low-volume complex or bespoke parts, prototypes, prosthetics	Visible layer lines, infill, marks from supports

Issues that influence process choice: volume and cost of production, material, function/performance/safety, complexity of form, accuracy and finish, method of assembly.

Both are shearing operations in a press. In blanking the piece punched out is the product; in piercing the punched-out piece is waste and the hole is what you want.

Identifying the process used: take the product apart and look at the component's complexity and form, its manufacturing features (ejector marks, flash, wall thickness, split lines, cross-section), the material, likely volume of production, and its function, quality and price.

How blow moulding and extrusion work HIGHER

A tube of hot plastic, the parison, hangs between the two open halves of the mould. The mould closes, pinching the bottom of the tube, and air is blown in. The plastic is pushed out against the cold mould walls, giving a seamless hollow container with thin, even walls. The pinched plastic leaves flash at the base.

Material (plastic, or heated aluminium) is pushed by a ram through a shaped die. It comes out as a long length with an identical cross-section all the way along, which is then cut to length. Window frames, curtain rails, pipes and tubes are made this way.

Watch the processes

Key terms

Injection moulding	High-volume complex thermoplastic parts. Ejector pin marks, injection point, flash.
Die casting	High-volume complex metal parts in aluminium/zinc. Same features as injection moulding.
Rotational moulding	Large hollow seamless plastic forms: kayaks, bins.
Sand casting	Low-volume metal parts with rough sandy texture.
Vacuum forming	Thermoplastic sheet pulled over a pattern: thin walls, draft angles.
Vent holes	Allow trapped air out of hollows in a vacuum-forming pattern.
Draft angle	A taper so the product or pattern releases from the mould.
Extrusion	Constant cross-section along the length: pipes, window frames.
Blow moulding	Hollow thin-walled containers like drinks bottles.
Drop forging	Hammering hot metal in a die; strong tools like spanners.
Blanking vs piercing	Blanking cuts out the shape; piercing cuts holes in it.
Press forming	Sheet metal pressed into a die: sinks, car panels.

Quick check

1. A plastic kayak is hollow, seamless and has an even wall thickness. Process?

Injection moulding
Rotational moulding
Vacuum forming
Die casting

Show answer

B: Rotational moulding. Rotational moulding makes large hollow forms.

2. Small circular marks on the inside of a plastic casing are evidence of…

Flashing
Sand grains
Ejector pins
Layer lines

Show answer

C: Ejector pins. Ejector pins push the part out of the mould.

3. Why must a vacuum-forming pattern have draft angles?

To make the formed sheet stronger and stiffer
To give the product a smoother surface finish
To make the walls of the product thicker
So it can be removed from the formed sheet

Show answer

D: So it can be removed from the formed sheet. A taper lets the pattern release.

4. A cast-iron manhole cover with a rough texture was most likely made by…

Sand casting
Die casting
Injection moulding
Vacuum forming

Show answer

A: Sand casting. Sand leaves a rough surface.

5. Which process suits a toy car body in zinc alloy made in large numbers?

Sand casting
Die casting
Vacuum forming
Rotational moulding

Show answer

B: Die casting. High volume, accurate metal parts.

6. Why are there vent holes in vacuum-forming patterns?

To reduce the amount of plastic sheet used
To stop the pattern overheating in the machine
So air trapped in hollows can be drawn out
To make the pattern lighter to lift out

Show answer

C: So air trapped in hollows can be drawn out. Otherwise the plastic won't pull into hollows.

7. Plastic window frames with an identical profile along their length are made by…

Blow moulding
Drop forging
Compression moulding
Extrusion

Show answer

D: Extrusion. Extrusion produces continuous cross-sections.

8. Which process is used for thermosetting plastic plugs?

Compression moulding
Rotational moulding
Blow moulding
Vacuum forming

Show answer

A: Compression moulding. Thermosets are compression moulded.

Exam-style questions

1. Name an appropriate process to manufacture the plastic casing of a games controller and explain why it is suitable. (3 marks)

Show marking guidance

Injection moulding (1)
Produces complex forms with strengthening ribs accurately (1)
High-quality surface finish, no further finishing (1)
Economical for high volumes despite expensive moulds (1)

2. Describe two features of a vacuum-forming pattern and explain why each is needed. (4 marks)

Show marking guidance

Draft angles (1) so the pattern releases from the formed sheet (1)
Radiused corners (1) to prevent thinning/tearing and help release (1)
Vent holes (1) to let trapped air out of hollows (1)

3. Name three appropriate manufacturing processes used in the production of an outdoor cross trainer and explain why they are suitable. (6 marks)

Show marking guidance

Part + process (1) + suitability (1), max 2 per process
Extrusion of frame tubes: consistent cross-section
Bending of frame: strong form without joins
Injection moulding of footrests: complex, accurate, good finish
Piercing/blanking of plates and holes: accurate, repeatable
Die casting of fixings; dip/powder coating for corrosion resistance

Printable worksheet

An I do, we do, you do worksheet for this topic, with a separate answer sheet.

Worksheet (PDF)Answers (PDF)

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