Design & Technology (9-1) 0979 | Paper 4 Mock 41 | Graphic Products

(a) The spur gears provide a mechanical advantage that increases the torque (turning force) at the auger screw. [1] The gear reduction means the driver gear on the crank turns faster than the driven gear on the auger shaft, so the output torque is multiplied relative to the input. This allows the operator to process tough or fibrous food through the barrel with less physical effort at the hand crank than would be required with a direct drive connection.

(b) The food produces linear motion as the auger pushes it through the barrel. [1] The food travels in a straight line along the length of the cylindrical barrel toward the cutting plate at the outlet. The helical auger screw converts its own rotary motion into a linear pushing force on the food, feeding it forward continuously.

(c) The lever clamp holds the mincer firmly to the worktop, preventing it from sliding, tipping, or rotating during operation. [1] Without the clamp, the reaction forces from the auger mechanism (particularly the torque reaction when processing tough food) would cause the mincer to move, which could pull the operator's hand into the feeding tube or cause the mincer to fall from the worktop.

(a) The process applied to the flat sheet material is corrugation. [1]

Corrugation is a forming process that creates a regular pattern of parallel ridges and valleys (folds) in a flat sheet. The sheet is passed through profiled rollers that press the wave pattern into the material, permanently deforming it into the corrugated profile.

(b) A material commonly corrugated for construction use is steel (also accept aluminium, zinc-coated steel/galvanised steel, polycarbonate, or cardboard). [1]

Corrugated steel sheet is widely used for roofing, cladding, and fencing in construction. It is often galvanised (zinc-coated) to resist corrosion.

(c) The corrugated sheet is more rigid than a flat sheet because the corrugation increases the effective depth of the cross-section perpendicular to the folds. [1]

A flat sheet has minimal depth, so it bends easily under load. The ridges and valleys of the corrugated profile give the sheet a much greater depth (measured from the peak of a ridge to the bottom of a valley). This greater depth dramatically increases the sheet's second moment of area (a measure of resistance to bending), making it behave like a series of shallow I-beams rather than a thin, flexible panel. The same material and thickness now spans much greater distances without sagging.

(a) Case hardening increases the carbon content of the surface layer of mild steel, transforming it into a hard, wear-resistant outer case. [1] Mild steel normally contains only about 0.1-0.3% carbon, which is too soft for surfaces that must resist abrasion. By adding carbon to the outer 1-2 mm, the surface becomes significantly harder while the inner core retains its original toughness and ductility. This combination is ideal for a gear wheel: the teeth resist wear at the contact surfaces, yet the body of the gear can absorb shock loads without fracturing.

(b) Charcoal (carbon powder or granules). [1] In the pack cementation method, the mild steel component is packed into a heat-resistant box surrounded by charcoal and heated to approximately 900-950 °C for several hours. At this temperature, carbon atoms migrate from the charcoal into the steel surface by diffusion. Bone meal or proprietary compounds such as Kasenit are also accepted as the carbon-rich packing material.

Two changes the designer should make so the display appeals to children:

1. Use bright, bold colours on the printed card panels, replacing the plain/neutral hotel colour scheme with vibrant, eye-catching colours that attract children's attention (e.g. primary colours, bright greens, oranges). [1]
2. Add cartoon images, illustrations or fun characters to the header panel and tier fronts, replacing the formal hotel branding with playful, child-friendly imagery that creates visual interest and excitement about the activity centre. [1]

Other valid changes include using a playful, rounded, informal font style instead of formal text, and lowering the tiers so children can reach the leaflets more easily.

(a) The joint most commonly used at the front corners of a high-quality drawer is the dovetail joint (either through dovetail or lapped dovetail). [1] The lapped dovetail is particularly common at the drawer front because the joint is hidden from the front face, while the through dovetail may be used at the back corners where appearance is less critical.

(b) Two reasons why the dovetail joint is suitable for a frequently opened drawer: [2]

1. The interlocking trapezoidal shape of the tails and pins creates a strong mechanical lock that directly resists the pulling force applied when the drawer is opened. The wider end of each tail faces outward, meaning the joint physically cannot be pulled apart along the direction of the pull. [1]
2. The interlocking fingers create a large glue surface area, giving a very strong adhesive bond that reinforces the mechanical interlock and ensures the joint remains tight over years of repeated use. [1]

(a) The scale of production used in this workshop:

One-off / job production [1] - each bicycle frame is made individually to a specific customer's body measurements, so no two frames are identical. The low volume (approximately 15 per month) and bespoke nature confirm this is one-off production. [1]

(b)(i) Difference between a jig and a fixture:

• A jig holds the workpiece in position and guides the tool to the correct location (e.g. it guides a drill bit to drill a hole at a precise angle and position). [1]
• A fixture holds the workpiece securely in position but does not guide the tool. The operator or machine directs the tool independently. [1]

(b)(ii) Two advantages of using a jig when assembling bicycle frames:

1. Ensures every frame is assembled with tubes at the correct angles and to the correct dimensions, maintaining accuracy and consistency. [1]
2. Speeds up the assembly process because the tubes do not need to be individually measured and clamped from scratch each time a frame is built. [1]

(c)(i) The new scale of production for 200 frames per month in five standard sizes:

Batch production [1] - the workshop would produce a batch of one size, then reconfigure the tooling and produce a batch of the next size, cycling through the five sizes.

(c)(ii) Two changes needed for this new scale of production:

1. Dedicated jigs and fixtures for each of the five sizes: The workshop would need to invest in a set of jigs and fixtures for each standard frame size, so that each batch can be set up quickly and produced consistently without individual measurement for every frame. [2]
2. Semi-automated equipment or additional workforce: The increased volume would require investment in CNC-controlled tube cutting and bending equipment (or hiring additional skilled workers) to handle the higher throughput while maintaining quality and reducing the labour time per frame. [2]

(d)(i) The purpose of a template in manufacturing:

1. A template is a pre-made pattern or gauge that represents the required shape or key dimensions of the finished product. [1]
2. It provides a quick go/no-go check by holding the template against the frame: if the frame matches the template profile, it is within specification. This is faster than measuring individual dimensions with separate instruments each time. [1]

(d)(ii) One quality control check on a finished bicycle frame (apart from using a template):

Visual inspection of the weld joints for surface defects such as undercutting, porosity, spattering, or incomplete fusion. [1] If structural integrity is critical (as it is for bicycle frames), a dye penetrant test can be applied: a coloured dye is applied to the weld surface, allowed to seep into any surface-breaking cracks, then a developer is applied which draws the dye out and makes cracks visible. [1]

(e)(i) Two advantages of CAD over manual drawing for frame design:

1. Designs can be easily modified, re-scaled to different rider sizes, and iterated without redrawing from scratch. [1]
2. The CAD model can simulate stress loading on the frame geometry, identifying weak points before any material is cut. [1]

(e)(ii) CAM in the context of cutting tube mitres:

1. CAM stands for Computer-Aided Manufacture - the use of computer software to control manufacturing machinery directly. [1]
2. The digital design data from the CAD model is processed by CAM software, which generates a set of precise tool paths and cutting instructions. [1]
3. These instructions are sent to a CNC cutting machine that automatically cuts the tube ends at the exact angles (mitres) needed, so they fit together accurately when welded. This eliminates manual measurement and marking of each mitre, improving accuracy and speed. [1]

(f) Comparing one-off (hand-finished) frames with mass-produced frames:

• One-off frames can be tailored to the exact body measurements and riding preferences of the individual rider, potentially delivering a superior fit and ride quality compared to a standardised mass-produced frame. [1]
• Hand finishing (filing, sanding, inspection at every stage) allows close personal attention to detail, producing frames with higher perceived craftsmanship and quality. [1]
• However, the cost per frame is significantly higher than mass production because of the extensive skilled labour time required and the inability to benefit from economies of scale that reduce unit cost. [1]

(g) Why tolerance is important in bicycle frame production:

1. Tolerance ensures that all parts fit together correctly during assembly - for example, the headset bearings must fit precisely inside the head tube. If the head tube length is outside the specified 150 mm ± 0.3 mm, the bearings will be too tight (causing friction and difficult steering) or too loose (causing play and unsafe handling). [1]
2. In a safety-critical product like a bicycle frame, components outside tolerance can compromise structural integrity and rider safety, potentially leading to failure under load. [1]

The type of drawing that shows surfaces at their true size with no perspective:

Orthographic projection (also called orthographic drawing). [1] In orthographic projection, each view (front, plan, side) shows one face of the object at its true size and shape, with no perspective distortion or foreshortening. All lines are drawn at their actual measured length, so dimensions can be taken directly from the drawing and used to mark out and cut materials accurately. This makes it the standard format for working drawings and manufacturing instructions, where precise measurements are essential.

(a) Two properties of acrylic (PMMA) that make it suitable for a transparent lamp cover:

1. Transparent / optically clear - acrylic transmits up to 92% of visible light, allowing the lamp to illuminate effectively through the cover. [1]
2. Rigid / stiff - acrylic holds its shape under normal use, providing structural protection for the lamp without sagging or deforming. [1]

Other valid properties include its good surface finish (can be polished to restore clarity), its lightweight nature, and its resistance to UV degradation.

(b)(i) The vacuum forming process used to produce the lamp cover works in four key stages:

1. A flat sheet of acrylic is clamped securely in a frame above a mould (the mould is shaped like the desired lamp cover). [1]
2. The sheet is heated by an overhead radiant heater until it becomes soft and pliable, typically reaching 160-180 °C for acrylic. [1]
3. The mould is raised up into the softened sheet from below (or the sheet is lowered over the mould). [1]
4. A vacuum pump removes the air from beneath the sheet through small holes in the mould, creating a pressure differential that pulls the softened acrylic tightly over the mould surface. The formed shape is allowed to cool and harden, then removed from the mould and trimmed to its final size. [1]

The process relies on atmospheric pressure (approximately 101 kPa) pushing the heated sheet onto the mould once the air beneath is evacuated.

(b)(ii) The four key parts of the vacuum forming equipment that should be labelled on the diagram are:

1. Clamp / frame - holds the plastic sheet in position. [1]
2. Plastic sheet / acrylic sheet - the thermoplastic material being formed. [1]
3. Mould / former - the shaped tool over which the sheet is drawn. [1]
4. Platen / base with holes - the platform containing small holes connected to the vacuum pump. [1]

The heater element is already labelled on the diagram. The vacuum pump connection at the bottom draws air out through the holes in the platen.

(c) The fundamental difference between thermoplastics and thermosetting plastics lies in their molecular structure:

• Thermoplastics have polymer chains held together by weak intermolecular forces (van der Waals forces). When heated, these weak bonds break, allowing the chains to slide past each other so the material softens and can be reshaped. On cooling, the bonds re-form and the material becomes rigid again. This process is reversible and can be repeated many times. [2]
• Thermosetting plastics undergo an irreversible chemical reaction during their initial forming (curing). Strong covalent cross-links form permanently between adjacent polymer chains. Once cured, these cross-links do not break when reheated; instead the material will char and decompose rather than soften. The shape is permanent and cannot be reformed. [2]

(d) Comparing thermoplastics to thermosetting plastics:

• Advantage: Thermoplastics can be recycled, reshaped and reformed by reheating, reducing waste and allowing off-cuts to be reused. [1]
• Disadvantage: Thermoplastics have lower heat resistance than thermosets and may soften or deform if exposed to high temperatures near the lamp. [1]

(e)(i) A plasticiser increases the flexibility and workability of a polymer. [1] It works at the molecular level by inserting small molecules between the long polymer chains, spacing them further apart. This increased spacing allows the chains to slide past each other more easily, making the material softer and more pliable. [1] A common example is the addition of plasticiser to PVC: rigid (unplasticised) PVC is used for pipes and window frames, while plasticised PVC is flexible enough for cable insulation and clothing.

(e)(ii) One other type of polymer additive:

• Name: UV stabiliser [1]
• Purpose: A UV stabiliser absorbs or blocks ultraviolet radiation from sunlight that would otherwise break down the polymer chains, causing the material to become brittle, discoloured or degraded over time. [1]

Other valid additives include fillers (add bulk and reduce cost), flame retardants (reduce flammability), and antioxidants (prevent oxidation degradation).

(f) Restoring the transparent finish of scratched acrylic involves two stages:

1. Use progressively finer grades of wet-and-dry abrasive paper (starting from around 400 grit up to 1200 grit) to carefully remove the scratches from the surface. [1]
2. Apply a polishing compound (such as Brasso or a specialist acrylic polish) using a soft cloth or buffing wheel, working it into the surface until full optical clarity is restored. [1]

(g) Thermoplastics can be recycled but thermosetting plastics cannot, because of their different molecular structures:

1. Thermoplastics have weak intermolecular forces (not permanent chemical bonds) between their polymer chains. [1]
2. When heated, these weak forces break, allowing the material to melt and be reformed into new products. The chains can re-bond on cooling, so the recycling process can be repeated. [1]
3. Thermosetting plastics have permanent covalent cross-links between their polymer chains. These bonds do not break when reheated; the material decomposes rather than melting. Because the molecular structure cannot be reversed, the plastic cannot be reshaped or recycled by remelting. [1]

(a) The component shown in Fig 1 is a Light Dependent Resistor (LDR). [1]

The circuit symbol shows a rectangular resistor body with two arrows pointing toward it. These arrows represent incoming light, which is the standard convention for distinguishing an LDR from a plain resistor or a thermistor. An LDR is a passive component whose resistance decreases when the intensity of light falling on it increases. In darkness, its resistance can be as high as several megaohms; in bright light, it can fall to a few hundred ohms. This property makes it ideal for the automatic garden lamp described: as daylight fades, the LDR's resistance rises, which can be used in a potential divider or transistor switching circuit to trigger the lamp.

(a) A suitable permanent mechanical fixing for joining the steel bracket to the tubes is a rivet (or pop rivet). [1] Rivets are inserted through pre-drilled holes and deformed to lock the bracket permanently in place. Welding is also acceptable, though it is a joining process rather than a discrete fixing component.

(b) A permanent fixing is preferred over a temporary fixing for this structural joint because it ensures the joint cannot loosen or come apart under the loads and vibrations that the outdoor storage shelter will experience over its service life. [1] A structural frame joint that loosens could cause the shelter to distort or collapse, so permanence is essential for safety and long-term rigidity.

(c) Two reasons why bolts are suitable temporary fixings for attaching the door mechanism to the steel structure: [2]

1. Bolts allow the door mechanism to be removed for maintenance or replacement without damaging the structural tube, since the bolt simply unscrews from its nut. [1]
2. Bolts can be tightened to a specific torque to resist vibration while still being removable, providing a secure but adjustable connection that can be re-tightened or repositioned if needed. [1]

(a) The type of manufactured board most likely used:

Melamine-faced chipboard (also accept MDF or particle board). [1] Chipboard is widely used for flat-pack furniture because it is inexpensive, available in standard sheet sizes, and can be pre-faced with a melamine laminate that provides a durable, wipe-clean surface in a range of colours and wood-grain finishes.

(b) One reason why the front edges have iron-on veneer applied:

The exposed edge of chipboard reveals the rough particle core, which is unsightly. The iron-on veneer covers this edge to create a smooth, finished appearance that matches the laminated faces, giving the shelving unit a neat, professional look. [1]

(c) One disadvantage of using this manufactured board compared to solid timber:

Chipboard swells and breaks apart when it absorbs moisture. [1] If the shelving unit is placed in a damp environment or liquid is spilled and soaks into an exposed edge, the particles expand irreversibly, causing the board to disintegrate. Solid timber is far more resistant to moisture damage. Other valid disadvantages include being weaker than solid timber (longer shelves may sag under load) and being unable to be planed or shaped to a decorative edge profile.