The use of adhesives and fixings - Jigs and fixtures — AQA A-Level Design and Technology: Product Design

The selection of adhesives and fixings alongside the implementation of jigs and fixtures forms the backbone of commercial manufacturing and assembly systems. In AQA A-Level Product Design, students must understand how permanent and temporary jointing methods combine with specialised production tooling to achieve dimensional accuracy, high repeatability, and production efficiency.

This topic bridges material science and industrial engineering, requiring you to evaluate shear, tensile, and peel strengths of chemical adhesives alongside mechanical fastenings like rivets, bolts, and threaded inserts. Mastering the design and application of jigs and fixtures is vital for explaining how high-volume batch and mass production achieve low unit costs and strict quality assurance.

• →Functional distinction: Jigs locate the workpiece and actively guide the cutting tool; fixtures securely clamp and locate the workpiece relative to a machine bed without tool guidance.
• →Mechanical fixings: Classified into temporary fixings (bolts, machine screws, knock-down fittings) allowing non-destructive disassembly, and permanent fixings (pop rivets, solid rivets) providing tamper-resistant joints.
• →Adhesive mechanics: Evaluating chemical adhesives (epoxy resin, cyanoacrylate, PVA, contact adhesive, solvent cement) based on shear, tensile, and peel resistance, curing mechanisms, and substrate compatibility.
• →Principles of location: Applying the 3-2-1 locating principle to constrain all six degrees of freedom and using quick-release toggle clamps for rapid, repeatable cycle times.

• Defines a jig as a device that holds the workpiece and guides the tool.
• Defines a fixture as a device that holds or locates the workpiece without guiding the tool.
• Explains that both improve accuracy and consistency across repeated parts.
• Explains that both reduce marking-out and reliance on operator skill, speeding up batch production.
• Recognises that jigs and fixtures add cost and set-up time, so suit repeated manufacture rather than one-offs.

• 💡State clearly whether the device guides the tool (jig) or only holds the part (fixture).
• 💡Use a concrete example such as a drilling jig with bushings for repeated holes.
• 💡Link suitability to accuracy, repeatability and production volume in your explanation.
• 💡Name the exact adhesive and its curing mechanism instead of generic terms like 'glue' (e.g., state 'two-part epoxy resin cured via a chemical reaction between epoxy monomer and polyamine hardener').
• 💡Annotate sketches with specific locating pins, quick-action toggle clamps, and hardened guide bushes whenever asked to design production tooling.
• 💡Relate fixing choices to Design for Manufacture and Assembly (DFMA) and circular economy directives, noting whether a fixing facilitates rapid recycling and maintenance.

• Confusing jigs and fixtures; correction: a jig guides the tool, a fixture only holds or locates the workpiece.
• Claiming jigs and fixtures are only for one-off production; correction: their cost is justified by repeated manufacture.
• Ignoring the trade-off of cost and set-up time; correction: explain that savings come from volume production.
• Believing adhesives provide uniform strength in all directions: Adhesives typically exhibit high shear and tensile strength but perform exceptionally poorly under peel and cleavage forces.
• Assuming jigs and fixtures perform identical tasks: Students frequently state that fixtures guide cutting tools; fixtures merely locate and hold parts, while jigs actively guide the tool.
• Viewing mechanical fasteners as universally superior to adhesives: Fasteners introduce stress concentration points around drilled holes and add weight, whereas adhesives distribute loads continuously across the entire contact surface.

1. 1Week 1, Days 1-3: Construct a comparative matrix detailing adhesives (epoxies, cyanoacrylates, solvent cements, contact adhesives, reactive polyurethanes) covering substrates, curing mechanisms, and stress ratings.
2. 2Week 1, Days 4-7: Revise temporary and permanent mechanical fixings, focusing on knock-down fittings, threaded inserts, machine screws, and pop rivets with their lifecycle advantages.
3. 3Week 2, Days 1-4: Study jig and fixture design principles, practising annotated technical sketches that incorporate 3-2-1 location, toggle clamps, and hardened drill bushes.
4. 4Week 2, Days 5-7: Complete past AQA 6-mark and 9-mark questions on batch production setups and mark them rigorously against official mark schemes.

• 📋Comparative evaluation questions (6-9 marks): Requiring a balanced comparison between adhesive bonding and mechanical fixings for a specific product enclosure, focusing on structural strength, assembly speed, and recycling.
• 📋Annotated sketching questions (4-6 marks): Tasking you with designing a bespoke drilling, routing, or assembly jig/fixture with clear callouts for locating pins, clamping devices, and tool guides.
• 📋Failure analysis questions (3-4 marks): Explaining the root cause of a joint failure under peel, shear, or environmental attack and proposing a fully justified redesign.