Tools, Equipment & Processes — Addition & Joining (AQA GCSE Design & Technology): Revision Note
Exam code: 8552
Brazing
Brazing joins metals by melting a lower melting point filler metal into a close-fitting joint
How brazing works
The parent metals (two parts to be joined) are heated but do not melt
Flux is applied, which prevents oxidation and helps the filler flow
Capillary action draws the molten filler into the joint
The joint is allowed to cool before excess flux and filler are cleaned away
Typical products and prototypes
Mild-steel frames, model structures and metal assemblies
Waste and quality
Little parent material is wasted, but excess filler and poorly fitted joints create unnecessary waste and weak results
Worked Example
State why brazing requires a filler material.
[1 mark]
Answer
In brazing the parts to be joined are heated below their melting point, with only the filler metal reaching a melting temperature. [1]
Examiner Tips and Tricks
If you want to improve your answer to questions about heating metals, include the temperature(s) that the material is heated to. This shows a stronger understanding of the details of the process.
For example:
In brazing the parts to be joined are heated below their melting point (approximately 1450-1550 degrees celsius for mild steel)...
Welding
Welding joins materials by melting and fusing the surfaces, usually with heat, pressure or friction
How welding works
Metal welding methods include MIG, TIG, arc and gas welding
Thermoplastics can be welded using heat, hot air, friction or ultrasonic vibration
A suitable joint preparation and clean surfaces improve strength
PPE, extraction and safe screening are required
Typical products and prototypes
Steel frames, vehicle bodies, polymer tanks and fabricated structures
Waste and quality
Correctly cut parts minimise rework; excess weld bead may be ground away and becomes waste
Worked Example
Explain why welding can produce a stronger joint than brazing.
[2 marks]
Answer
Welding melts and fuses the parent materials, creating a continuous joint. [1] Brazing relies on a lower-melting filler metal between the parts which is weaker than the metals being joined. [1]
Lamination
Lamination bonds layers of material together to create a thicker, stronger, stiffer or shaped component
How lamination works
Used with timber veneers, paper, card, textiles, polymers and composites
Layers are coated with adhesive and pressed together
A former can hold layers in a curve while the adhesive cures
Alternating grain direction in plywood improves dimensional stability
Typical products and prototypes
Plywood, curved chair parts, laminated packaging and reinforced fabrics.
Waste and quality
Templates and accurate layer sizes reduce trimming waste; adhesive should be applied evenly to avoid squeeze-out
Worked Example
Explain how lamination can be used to make a curved timber prototype.
[2 marks]
Answer
Thin timber veneers are coated with adhesive, placed over a curved former and clamped. [1] When the adhesive cures, the layers hold the curved shape. [1]
Soldering
Soldering joins electronic components or thin metals using a low melting point filler called solder
How soldering works
The parts being joined do not melt
A soldering iron heats the joint and solder flows around the connection
Flux helps clean the surfaces and improves flow
A good electronic joint is mechanically secure, electrically conductive and not excessively large
Typical products and prototypes
PCB assemblies, wires, connectors and small sheet-metal joints
Waste and quality
Trimmed component leads and excess solder are waste; controlled solder use reduces bridges and faulty joints
Worked Example
Describe two features of a good soldered joint on a PCB.
[2 marks]
Answer
It should make a secure electrical connection [1] and use enough solder to cover the pad and lead without creating a bridge to a neighbouring track. [1]
Sewing
Sewing joins or shapes textile materials using stitches made with thread
How sewing works
It can be completed by hand or with a sewing machine
Seam allowance provides material outside the stitch line to create a folded edge
Different stitches are chosen for strength, stretch or appearance
Pins, tacking and pattern markings keep pieces aligned
Typical products and prototypes
Garments, bags, upholstery covers and textile prototypes
Waste and quality
Thread ends, seam allowances and fabric offcuts are waste; accurate patterns and layouts reduce unused fabric
Worked Example
Why is a seam allowance required when sewing two textile pieces?
[1 mark]
Answer
It provides material beyond the stitch line so the seam can be sewn securely without the fabric edge pulling out. [1]
Bonding
Bonding joins materials using an adhesive selected for the materials, forces and environment
How bonding works
Examples include PVA for timber and paper, contact adhesive for laminates, epoxy resin for mixed materials and solvent cement for some thermoplastics
Surfaces may need cleaning, keying or clamping
Curing time must be allowed before the joint is loaded
Adhesive joints can spread forces across a wide area
Typical products and prototypes
Models, laminated products, mixed-material prototypes and polymer assemblies
Waste and quality
Accurate dispensing reduces excess adhesive, contaminated parts and packaging waste
Worked Example
Explain why epoxy resin may be selected to bond two different materials.
[2 marks]
Answer
Epoxy can bond many dissimilar materials and fills small gaps, [1] producing a strong joint after the resin and hardener cure. [1]
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