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

Three ways to reduce sheet-material waste are:

• Nest component shapes closely, including rotating them where appropriate, so gaps between shapes are minimised. [1]
• Design component sizes so that they divide evenly into the dimensions of a standard sheet. [1]
• Use suitable offcuts to make smaller components in the same or another product. [1]

Using a narrower-kerf cutting process, such as laser cutting instead of a saw blade, is another acceptable method because less material becomes cut waste. [3]

When choosing a catalogue component, the designer must ensure that it fits the product and will work reliably in real use. Any four factors are:

• Its rated performance, such as load, speed or current, must exceed the application's demand with a safety margin [1].
• Its dimensions and mounting arrangement must fit the available space and mating parts [1].
• It must withstand the operating environment, including temperature, moisture and chemicals [1].
• It should be available from more than one supplier and remain in production for the product's expected life [1].
• Its unit cost must be acceptable at the required production quantity [1].

A rated value equal to the expected demand gives no margin for variation or unexpected loading.

The cracking described is crazing [1]. It is also acceptable to call it stress cracking. Internal stresses in acrylic can gradually produce fine cracks, often following lines of stress, after manufacture.

This question assesses material management across purchasing, production and waste. Strong analysis links each action to both cost and environmental effects, then makes a judgement.

1. Purchasing: buying polymer in bulk can lower the unit price. Consolidating deliveries also means fewer transport journeys, reducing transport emissions. However, bulk orders increase the amount of stock held, tying up money and storage space. Specifying recycled polymer reduces the use of virgin feedstock and may cost less, although its properties can be more variable. [2]
2. Production: redesigning a moulding with thinner walls, strengthened where necessary by ribs, reduces the mass of polymer used in every product. Shorter moulding cycles also reduce energy used per unit. Careful process control reduces defective mouldings, preventing the loss of both the polymer and the energy already used to process it. [3]
3. Waste: sprues, runners and reject mouldings can be granulated into regrind and fed back into production, so waste becomes usable feedstock. Waste that cannot be reused internally should be separated by polymer type, because clean, single-polymer waste has a higher recycling value than mixed waste. [2]
4. Judgement: the best approach combines all three areas: prevent waste through efficient purchasing and controlled production first, then reuse unavoidable polymer waste. This reduces costs and environmental impact rather than simply moving waste elsewhere. [1]

For high marks, analyse the trade-off as well as the benefit: for example, bulk buying may reduce price and delivery emissions but increases stock holding.

A workshop using several machines needs controls that prevent contact with hazards, reduce exposure to dust and noise, and allow rapid response to danger. Any four of the following are valid:

• Fit guards to moving parts and interlock them so that opening a guard stops the machine. [1]
• Use dust and fume extraction at the point where dust or fumes are produced. [1]
• Provide and require suitable personal protective equipment, including eye protection and hearing protection where needed. [1]
• Place emergency-stop controls within reach of each machine position. [1]
• Train and supervise workers so that only competent people operate each machine. [1]
• Keep walkways clear of materials and offcuts to prevent trips and allow safe movement. [1]

For full credit, state a distinct measure rather than simply saying that the workshop should be “safe”.

The company has social responsibilities to the people making its garments. Four valid responsibilities are:

• Pay a wage that is sufficient to live on in that country, rather than relying only on the legal minimum. [1]
• Provide safe working conditions, suitable equipment and training so workers are not injured. [1]
• Limit working hours, provide rest, and prevent child labour. [1]
• Allow workers to organise and raise concerns without losing their jobs. [1]
• Audit suppliers rather than simply accepting their assurances about conditions. [1]

Any four explained responsibilities gain credit. These are social issues because they concern workers' rights, welfare and treatment throughout the supply chain. [4]

Finish selection is a balance between the service environment, the required visual result and whole-life cost.

1. Environment: an outdoor or marine product needs a durable barrier or sacrificial finish that withstands ultraviolet light and salt. Salt can promote corrosion beneath breaks in a coating, whereas an indoor product generally faces much less severe weathering. [2]
2. Appearance: the finish controls colour, gloss and texture, and can hide or reveal surface defects. A high-gloss finish needs particularly good surface preparation because irregularities show clearly; a textured finish can conceal small defects more effectively. [2]
3. Cost: preparation, application and curing each use time, energy and plant. The appropriate decision is the cheapest finish that meets the required performance for the intended product life, not necessarily the most expensive or most durable finish. [2]

A strong judgement is that a finish suitable for severe outdoor exposure may be unnecessary expense for an indoor item, while a cheap indoor finish may fail rapidly outdoors. This is a developed response across all three areas. [5–6]

Feature B indicates lack of root fusion. The root is the deepest part of a welded joint, where the two pieces should be joined completely. A visible unjoined gap or boundary at this point shows that molten weld metal did not fuse through to the root. This creates a weak plane in the joint, so it can fail when loaded. [1]

Examination reminder: distinguish a surface defect from a root defect: lack of root fusion is found at the base of the weld joint.

A title block identifies and controls a technical drawing. Three valid items with their reasons are:

• Drawing number and revision: these ensure that production uses the current version and that an obsolete print can be recognised. [1]
• Scale and projection convention: these help the reader interpret the views correctly; sizes must still be taken from stated dimensions, not measured from the print. [1]
• Material and finish specification: this tells the manufacturer what the part must be made from and the required surface result. [1]

Units are also acceptable because drawings without units are ambiguous. Drawing title, originator and date are further acceptable title-block information. [3]

The radial load is carried by the rolling elements. These are the balls or rollers between the bearing races. A radial load acts perpendicular to the shaft’s length, and the rolling elements transfer that force from the rotating shaft to the outer bearing race and its housing. [1]

Wear patterns are evidence of actual long-term use, rather than only what users say they do.

1. Wear concentrated where the hand grips the product shows where it is actually held. [1]
2. Wear on the edge that rests on a surface shows how the product is set down, which may differ from the designer’s original assumption. [1]
3. The unworn control indicates that this feature is rarely used. [1]
4. A suitable design change is to move or enlarge the grip where the wear shows, protect the resting edge with a harder or replaceable material, or reconsider whether the unused control is needed. [1]

1. The decision symbol in a flowchart is a diamond, also called a rhombus [1].

2. A flowchart sets out the sequence of actions and decision points before programming begins. The designer can check the logic and identify errors before writing code [1]. It can also be understood by clients or team members who are not programmers, allowing them to agree how the machine should behave [1]. Finally, the defined structure makes the program easier to write and easier to alter later [1].

In particular, the diamond represents a question with different possible routes, such as yes/no, rather than a normal process step.

A flowchart decision is shown by a diamond and asks a question with alternative outcomes. Here, the decision step is the diamond asking whether a person is detected. [2]

• If a person is detected, the answer is yes: the door opens and the timer starts. [1]
• If no person is detected, the flow returns to sensing and the door stays closed. [1]

In a control-system flowchart, follow each labelled output from the decision diamond: do not confuse the sensing input with the action that follows it.

Naming only a material can be too vague because different grades have different controlled properties.

1. Different grades can have very different strength, hardness or corrosion resistance, so the grade determines whether the component will perform as required [1].
2. The grade affects manufacturability, for example whether it can be welded or deep drawn successfully [1].
3. The grade affects cost, since higher-performance grades may be considerably more expensive [1].

Stating a grade also makes the specification unambiguous, so suppliers provide the same material.

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.

Parallel turning, also called cylindrical turning [1]. On a centre lathe, the cutting tool travels parallel to the rotating bar’s axis, removing material evenly along its length and reducing its diameter.

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]

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]

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]

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]

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.

A diagonal brace that forms a triangle stops the sideways racking movement. [1 mark]

A rectangular frame can change shape into a parallelogram because its corners can rotate slightly under load. A triangle is rigid: once its side lengths are fixed, its angles cannot change without changing the length of a member. Adding a diagonal member therefore triangulates the frame and prevents it from racking. A gusset plate at a corner is also acceptable because it braces the joint and creates the same triangulating effect.

Examination reminder: for a frame that distorts sideways, look for triangulation, rather than simply making the existing vertical or horizontal members thicker.

Before production, testing must be systematic and linked to the specification. A prototype that merely appears satisfactory has not necessarily been proved safe, usable, durable or manufacturable.

1. Function: test every stated requirement in the specification and measure the result against its criterion, rather than relying on personal judgement. [2]
2. User testing: intended users should complete realistic tasks without assistance. Observe where they hesitate, misunderstand controls or make errors, because the design team already knows how the product is supposed to work. [2]
3. Durability: carry out relevant drop tests, repeated operation of controls and exposure to expected conditions of use. Faults that arise after months of use are much more costly once products have been sold. [2]
4. Manufacture: confirm that components can be made and assembled at production tolerances and at an acceptable cost. [1]
5. Safety and standards: complete the required safety and standards testing, since a product cannot legally be sold without relevant approval. [1]

A well-founded decision to proceed should be made only when the prototype meets the specification, users can operate it effectively, and production can deliver it consistently.

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]

This tests the conflict between reducing environmental impact and keeping the selling price low. Environmental improvements can create extra costs at design, manufacture or end-of-life.

• Using recycled or responsibly sourced materials can cost more than the cheapest materials available, increasing the unit price. [1]
• Designing for durability and repair usually requires more material or higher-quality components, so the product costs more to manufacture. [1]
• Collecting returned products and processing them for recycling must be funded by the company, adding to its costs. [1]

A further valid tension is that cleaner manufacturing may need investment in new machinery before savings are made. [1] For three marks, explain three separate cost-versus-environment links, rather than just stating that both aims are important.

Stiffness depends not only on how much material is used, but also on the shape of the section. Three suitable changes are:

• Add ribs on the underside. The ribs increase stiffness through section shape, allowing the main wall to be thinner [1].
• Use a hollow or box section. This puts material farther from the neutral axis, so the component resists bending efficiently [1].
• Remove material from regions carrying little load, leaving a web or lattice structure [1].
• Add curvature or a swage to a flat panel, making it resist bending without adding material [1].

Any three gain full marks. Do not simply state “make it thinner”, because that would normally reduce stiffness [3].

The three stages of the system model are input, process and output [1].

An input supplies material or information, the process changes or makes a decision about it, and the output is the resulting action, material or signal.

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 material comparison begins with the component's actual requirements, not simply a list of properties.

1. First quantify the specification: state the load, permitted deflection, operating temperature range and required service life. Without these, it is not meaningful to decide which material is better. [2 marks]
2. Use supplier data to compare modulus, tensile strength, density and cost per kilogram. This permits comparisons such as strength per unit mass and stiffness per unit mass. [2 marks]
3. Test samples where published information does not represent the conditions of use. A tensile test checks strength, a hardness test assesses wear resistance, and an impact test assesses behaviour under a blow. [2 marks]
4. Test long-term behaviour separately because creep, fatigue and ultraviolet degradation may not appear in a short test. [1 mark]
5. Compare the cost of the finished component, including waste and processing, rather than only raw-material price. [1 mark]

The decision should therefore be based on measured performance against the specification, long-term behaviour and total manufacturing cost. [8 marks]