Design & Technology: Product Design 9252 | Paper 1 Mock 01 | Technical, designing and making principles

Manufacturers apply finishes to make a product last, give it the required appearance and achieve this at a realistic manufacturing cost.

1. Protection: a finish seals the surface from moisture, chemicals and abrasion. On metals this helps prevent corrosion; on timber it helps prevent water absorption, swelling and rot. This increases the product’s service life. [2]
2. Appearance: finishes provide controlled colour, gloss and texture. They can hide small surface defects and give products a consistent appearance that customers may associate with good quality. [2]
3. Cost: preparation, application and curing take time, energy and equipment. Therefore, the manufacturer should select the cheapest finish that meets the product requirement, rather than automatically selecting the highest-performance finish available. [1]

Exam focus: protection needs a cause-and-effect link: the finish blocks damaging agents, so the material deteriorates more slowly.

The I-shaped extruded section [2] resists bending best about the axis shown.

When a section bends, material furthest from the neutral axis contributes most to its second moment of area, and therefore to bending stiffness. In an I-section, a large proportion of the material is in the two flanges, far from the neutral axis, rather than concentrated in the middle. [2]

The flanges carry much of the tension and compression produced by bending. This is why an I-section can be very stiff without being solid and heavy.

The six Rs are strategies for reducing a product's environmental impact. Any two correctly explained principles gain credit:

• Reduce: use less material or fewer components, so fewer resources are consumed. [1]
• Reuse: design parts so that they can be used again in another product rather than being scrapped. [1]
• Repair: make fixings accessible and spare parts available, so a fault does not end the product's life. [1]
• Recycle: select an identifiable, recyclable material, for example a single polymer, so it can be reprocessed. [1]
• Refuse: leave out unnecessary packaging or features that add no value. [1]
• Rethink: meet the same user need in a different way, potentially using fewer resources. [1]

For full credit, state both the principle and the resulting design change, rather than just listing an R.

This is an iterative approach. The team makes a rough model, tests it, changes it using the test results and makes another version. Repeating this cycle is the defining feature of iterative design. [1]

The component is a cell or battery. [1]

It stores energy chemically and releases electrical energy when a circuit is completed. A battery may consist of one or more cells, but either term is accepted here.

A carbon-neutral factory balances the carbon dioxide released by its activities with an equivalent amount of carbon dioxide removed or emissions avoided elsewhere. [1]

It should first reduce its own emissions as far as possible, then offset the remaining emissions, for example through renewable energy generation or tree planting. [1]

Carbon neutral does not mean that the factory necessarily produces no emissions at all; it means that its remaining emissions are balanced by equivalent reductions or removals. [2]

These are photovoltaic panels, also called solar panels. [1]

Photovoltaic cells convert sunlight directly into electrical energy. This distinguishes them from solar thermal systems, which use sunlight mainly to heat water or another fluid.

Batch size is a balance between the cost of setting up production and the cost and risk of holding stock. Three relevant factors are:

• Forecast demand: making more than customers will buy ties up money in unsold stock. [1]
• Changeover time and cost: frequent small batches require more resets, causing more lost production time. [1]
• Storage cost and shelf life: a large batch needs storage space and may deteriorate or become obsolete before it is sold. [1]
• Available cash: a large amount of work in progress and finished stock ties up the company’s money. [1]

Any three explained factors are sufficient. [3]

Arc welding [1]. An electric arc produces enough heat to melt the joint area and a consumable filler rod or electrode, permanently joining the mild-steel plates. MMA welding and MIG welding are accepted forms of arc welding.

The decision is a trade-off between efficient, low-cost production and avoiding stock risk while meeting customer expectations.

A supported judgement is to make the best-selling, predictable lines in larger batches while making less certain lines to order. This combines fast delivery where demand is known with lower stock risk elsewhere. Sustained analysis across at least three areas and a judgement gains [7–8].

When demand is uncertain, batch production reduces the financial risk at launch.

1. Batch production requires much less investment in dedicated tooling, so less money is at risk before the company knows whether customers will buy the product. [1]
2. The design can be changed between batches in response to customer feedback, without having to scrap expensive mass-production tooling. [1]
3. If demand becomes high, the company can then justify investing in mass-production tooling because its cost will be spread across a large number of products. [1]
4. The resulting faster, repeatable process lowers unit cost, allowing either a lower selling price or a higher profit margin. [1]

The sequence is therefore sensible: test the market flexibly first, then invest heavily only once demand is proven.

Battery decisions affect performance, safety, product life and disposal.

• Choose the capacity. Greater capacity gives a longer run time between charges, but usually increases mass and cost. [1]
• Decide whether it is user-replaceable. A replaceable battery can extend product life, but needs a suitable cover and connector. [1]
• Specify the charging method and protection circuit, because overcharging presents a fire risk. [1]

Another valid decision is how the battery can be removed and recycled at end of life. [1]

Iron in mild steel reacts with oxygen and water from the air to form hydrated iron oxide, rust. [1] Rust is porous and flakes away instead of forming a protective seal, so water and oxygen can reach fresh metal beneath and corrosion continues. [1]

Using only three types of fixing means fewer different items have to be ordered, stored and counted. This makes stock control simpler and may allow each fixing type to be bought in greater quantities. [1]

A suitable choice is a ball bearing [1]. Ball bearings place rolling balls between the rotating shaft and its housing, reducing friction compared with surfaces sliding directly against each other. Roller bearings, plain bearings and bush bearings are also acceptable types of bearing for this purpose.

Computer aided design (CAD) is the method of designing or modelling a product on a computer. A 3D CAD model can be viewed from different angles before manufacture, allowing the designer to inspect the form without making the product. Computer aided design, or 3D CAD modelling, gains [1].

The sawing method changes the direction of the growth rings in each board. That affects both movement during drying and the visible grain pattern.

• Through-and-through sawing cuts straight across the log. It is quick and produces little waste, but boards cut nearer the outside have growth rings running across their width. They are more likely to cup as they dry. [2]
• Quarter sawing cuts boards radially, so the growth rings run through the thickness. This makes boards more stable and gives a straighter figure, but it is slower and wastes more timber. [2]

For full marks, compare both the production implication and the resulting property or appearance. [4]

Too much stock ties up money that could be used elsewhere in the business. [1] It also needs storage space, handling and insurance, and it may deteriorate or become obsolete before it is used. [1] [2]

The system is orthographic projection [1]. It represents the same product using separate two-dimensional views, such as front, plan (above) and side, so its shape and dimensions can be communicated accurately.

A marking gauge is used to mark a line parallel to the edge of a piece of timber. [1]

Its fence runs along the timber edge while the pin or cutter marks a constant distance from that edge.

1. As the cam rotates, the follower rises and falls repeatedly, so it has reciprocating motion. [1] It also dwells, meaning it remains still while a constant-radius section of the cam passes beneath it. [1]

2. The distance from the cam centre to its edge at any angle determines the follower's height. [1] How rapidly this radius changes determines the rate of rise or fall: a sudden change gives rapid movement, while a gradual change gives smoother movement. [1]

Do not describe the follower as rotating: it is the cam that rotates; the follower moves linearly.

Orthographic projection is a technical drawing method used to communicate a part accurately for manufacture.

1. It represents an object using separate views taken at right angles to its faces. Each face is shown at its true shape and true size, rather than appearing shortened by perspective. Therefore, the manufacturer can determine the form of the part from the drawing. [3]
2. The views are arranged using a fixed projection convention. This tells the reader which face each view represents without needing extra explanation. [1]
3. Dimensions must be written on the drawing rather than measured from it. A printed or copied drawing may be enlarged, reduced or distorted, so a ruler measurement may not equal the intended size. Also, a measured line cannot state the required accuracy. [2]
4. Tolerances state the permitted variation from a stated size. No manufacturing process produces every feature at one exact value. Without a tolerance, a manufacturer may either make the part unnecessarily accurately, increasing cost, or allow too much variation so parts do not fit or assemble. [2]

Examination point: dimensions give the target size; tolerances give the allowed limits around that size. Neither should be inferred by measuring a drawing. [8]

The books act as a distributed downward load over the shelf span. This makes the shelf bend, with the greatest deflection at the middle.

1. The shelf is in bending because the weight of the books acts downwards along its length. [1]
2. In a sagging shelf, the upper surface is in compression and the lower surface is in tension; the sag is greatest at mid-span. [2]
3. Deflection increases very rapidly as the span increases, so even a relatively small increase in shelf width can cause much more sag. [1]
4. Reduce the span by adding a central support. This gives the shelf a shorter unsupported distance. [1]
5. Increase the depth of the section, for example by adding a front lip or a batten beneath. Depth greatly increases stiffness, so this is often more effective than simply making the shelf slightly wider. [2]
6. Use a stiffer material or add a supporting rail along the back edge. [1]

A strong judgement is that adding a central support and increasing section depth directly tackle the cause of sag by reducing span and increasing stiffness. [6–7]

When carbon is added to iron, carbon atoms occupy spaces in the iron lattice and obstruct the movement of dislocations. [1] Dislocations are defects whose movement allows layers of atoms to slip and the metal to deform.

Because slip is made more difficult, the steel becomes harder and has greater tensile strength. [1] However, as carbon content rises, ductility and toughness decrease: high-carbon steel is hard but more brittle. [1]

A specification is organised under headings so that requirements are not missed. Three appropriate headings are:

1. Function: state exactly what the kitchen product must do. Ideas can then be judged by whether they achieve that purpose. [1]
2. User requirements: include limits such as appropriate size, weight and force needed to use the product, so it suits its intended users. [1]
3. Materials and manufacture: state material and process constraints, so the product can actually be made using available processes at the target cost. [1]

Other valid headings include safety and standards, to ensure the product is legal to sell, and cost, to set a target selling price and manufacturing budget.

The appropriate drawing changes as the design moves from broad exploration to precise manufacture. Early methods should be quick and flexible; later methods must be exact and unambiguous.

1. At the first-idea stage, use freehand sketches. They are fast and disposable, allowing many alternatives to be explored without committing significant time or cost. [2]
2. As an idea develops, use annotated sketches to record proposed materials, sizes and the reasoning behind decisions. [1]
3. To present a selected idea to a client, use a pictorial or rendered drawing. This communicates form, appearance and material more clearly than a technical drawing. [2]
4. Use sectional and exploded views when working out or explaining internal construction and the way components assemble. [2]
5. At manufacture, produce orthographic working drawings with dimensions and tolerances, because these provide the precise information needed to make and inspect the product. [2]

The judgement is that no drawing type is best throughout: the choice depends on whether the immediate purpose is exploring, explaining appearance, communicating construction or manufacturing accurately. Developed links across the stages are required for [6-7].

A bench vice gains force by exchanging a large movement of the handle for a very small movement of the moving jaw.

• The handle acts as a lever. Applying force at its end produces a larger turning effect on the screw because of the ratio of handle length to screw radius. [1]
• A screw thread is an inclined plane wrapped around a cylinder. One full turn moves the jaw forward only by the thread pitch. [1]
• Thus the handle travels a large circular distance while the jaw moves only a very small linear distance. [2]
• Because the work is ideally conserved, the small jaw movement corresponds to a very large force at the jaw face, creating the clamping force. [1]

This explains why a vice is slow to close but can grip strongly. [4]

A life-cycle evaluation considers impacts from material extraction through to disposal, then identifies the stage where design changes will make the largest overall difference.

• Materials: a washing machine contains a large mass of steel, polymers and a concrete counterweight. Extraction and processing of these materials give them significant embodied energy [3].
• Manufacture: forming, assembly and testing require energy, although this is less significant than the energy embodied in the materials [2].
• Distribution: the machine is heavy and bulky, so transporting each unit has a significant impact [1].
• Use: over a ten-year lifetime, energy and water used to heat water and pump it through cycles exceed the impacts of making the machine. Therefore use is the dominant life-cycle stage [3].
• End of life: the machine is heavy but largely recyclable if collected. However, mixed materials and bonded assemblies make separation costly [2].

Evaluation and conclusion: the designer should concentrate primarily on reducing impact during use: improve heater and motor efficiency and reduce water used per cycle. Durability and repairability are also crucial, because the machine must last long enough for its manufacturing impact to be spread over many years of efficient use [2]. A sustained whole-life evaluation that justifies this priority reaches 10–12 marks [12].

1. Design assembled with screws: screws can be removed with a common tool, so a worn component can be replaced and the tool can remain in use for longer. [1] At the end of its life, the assembly can be opened and different materials can be separated into the correct recycling streams. [1]

2. Design glued and welded: permanent joints cannot normally be opened without damaging or destroying the product. A failure in one component can therefore end the life of the complete tool. [1] The joined materials cannot be separated economically, so the product is likely to be landfilled or shredded as mixed waste rather than effectively recycled. [1]

Removable mechanical fixings support repair and material separation; permanent joints obstruct both. [4]