📚 Case Study Practice for AS WJEC Engineering | AS WJEC 工程：案例分析实战演练
In AS WJEC Engineering, case studies develop the analytical thinking required to tackle open-ended design problems. This walkthrough uses a realistic brief: design a compact, solar-powered USB charger aimed at hikers and campers. We will apply the engineering design process, from initial concept to final evaluation, integrating materials science, manufacturing, quality control, and sustainability – all core to the WJEC specification.
在 AS WJEC 工程课程中，案例分析能够培养解决开放式设计问题所需的分析思维。本文将通过一个真实的设计任务：为徒步旅行者和露营者设计一款紧凑型太阳能 USB 充电器，来走查整个工程设计流程。我们将结合 WJEC 课程的核心内容，从最初的概念到最终的评估，综合运用材料科学、制造工艺、质量控制和可持续性等方面的知识。
1. Understanding the Design Brief and Stakeholder Needs | 理解设计任务书与利益相关者需求
The brief requires a lightweight, durable charger that can power a smartphone via USB within a day’s sunlight. Primary stakeholders are end users (outdoor enthusiasts), but retailers and environmental regulators also influence the design. Capturing their needs early prevents costly late-stage changes.
任务书要求设计一款轻便、耐用的充电器，能够在一天日照时间内通过 USB 为智能手机充电。主要利益相关者是最终用户（户外爱好者），但零售商和环境监管机构也会影响设计。尽早捕捉他们的需求能避免后期昂贵的修改。
A product design specification (PDS) is drafted to translate needs into measurable targets: mass under 300 g, power output ≥ 5 W, foldable to A5 size, IPX4 water resistance, and use of recyclable materials where possible. This becomes the benchmark for all subsequent decisions.
产品设计规格书（PDS）将需求转化为可衡量的目标：质量低于 300 g，输出功率 ≥ 5 W，可折叠至 A5 大小，IPX4 防水等级，并尽可能使用可回收材料。这份规格书将成为后续所有决策的基准。
2. Identifying Constraints and Requirements | 识别约束条件与需求
Beyond the PDS, we identify constraints imposed by physics, standards, and manufacturing. Solar irradiance averages 800 W/m² under UK conditions, so a panel area of roughly 0.02 m² is needed for 5 W output assuming 20 % cell efficiency. USB output must deliver 5 V DC at up to 1 A, conforming to USB-IF standards. The device must also withstand drop shocks and temperature swings from -10 °C to 50 °C.
除了 PDS，我们还需要识别由物理定律、行业标准和制造工艺施加的约束。英国条件下的太阳辐照度平均约为 800 W/m²，因此假设电池效率为 20%，要输出 5 W 功率，约需 0.02 m² 的电池板面积。USB 输出必须符合 USB-IF 标准，提供 5 V 直流电，最大电流 1 A。设备还必须承受跌落冲击和 -10 °C 至 50 °C 的温度变化。
Legislative requirements such as the WEEE Directive and RoHS compliance dictate that hazardous substances are minimised and end-of-life recycling is planned. These constraints shape the material palette and joining methods from the outset.
法律要求，如 WEEE 指令和 RoHS 合规，规定必须尽量减少有害物质并规划废弃回收。这些约束从设计伊始就限定了材料范围和连接方式的选择。
3. Concept Generation and Evaluation | 概念生成与评估
Three distinct concepts are sketched: Concept A – a clamshell rigid panel with integrated battery; Concept B – a rollable flexible panel with separate power bank; Concept C – a solar backpack with built-in wiring. Each is evaluated against ease of use, durability, cost, and manufacturability.
我们草绘了三种不同的概念：概念 A——带集成电池的翻盖式硬面板；概念 B——配有独立移动电源的卷曲柔性面板；概念 C——内置走线的太阳能背包。根据易用性、耐用性、成本和可制造性对每个概念进行评估。
Concept A scores well on protection of electronics but is bulky when folded. Concept B offers portability and modularity but risks connector wear. Concept C integrates seamlessly but is difficult to repair. This initial evaluation grounds the selection process before detailed analysis.
概念 A 在保护电子元件方面得分较高，但折叠后体积较大。概念 B 提供了便携性和模块化，但存在连接器磨损的风险。概念 C 集成度高，但维修困难。这一初步评估为详细分析之前的选型提供了依据。
4. Selecting the Most Promising Concept – A Weighted Decision Matrix | 选择最有前景的概念——加权决策矩阵
A weighted decision matrix quantifies the trade-offs. Criteria are drawn from the PDS: portability, durability, ease of manufacture, unit cost, and user experience. Each is assigned a weighting factor based on importance, and concepts are scored from 1 (poor) to 5 (excellent).
加权决策矩阵将权衡过程量化。评价标准源自 PDS：便携性、耐用性、易制造性、单位成本和用户体验。根据重要程度为每项标准分配权重，各概念按 1（差）到 5（优）评分。
| Criterion (Weight) | Concept A | Concept B | Concept C |
|---|---|---|---|
| Portability (20%) | 3 | 5 | 4 |
| Durability (25%) | 4 | 3 | 3 |
| Ease of Manufacture (20%) | 4 | 4 | 2 |
| Unit Cost (15%) | 3 | 4 | 2 |
| User Experience (20%) | 4 | 4 | 4 |
| Weighted Total | 3.65 | 4.00 | 3.00 |
Concept B achieves the highest weighted score (4.00), primarily due to its superior portability and competitive manufacturing cost. It is selected for further development, with a design philosophy prioritising a ruggedised flexible panel and a detachable power bank.
概念 B 获得了最高的加权总分（4.00），主要得益于其卓越的便携性和有竞争力的制造成本。因此被选定进行进一步开发，其设计理念优先考虑加固的柔性面板和可拆卸的移动电源。
5. Materials Selection – Balancing Performance and Sustainability | 材料选择——平衡性能与可持续性
For the flexible solar panel encapsulation, ethylene tetrafluoroethylene (ETFE) is chosen over polyethylene terephthalate (PET) because of its superior UV resistance, mechanical strength, and recyclability. The photovoltaic cells are monocrystalline silicon for their higher efficiency (≈22 %) in a smaller footprint compared to polycrystalline alternatives.
对于柔性太阳能电池板的封装，选择乙烯-四氟乙烯共聚物（ETFE）而非聚对苯二甲酸乙二醇酯（PET），因为其抗紫外线性能更优、机械强度更高且可回收。光伏电池采用单晶硅，因为与多晶硅相比，它能在更小的面积内实现更高的效率（约 22%）。
The power bank housing is specified as a glass-reinforced polycarbonate (PC-ABS) blend, providing impact resistance, flame retardancy, and good surface finish for injection moulding. Internal electrical contacts are copper alloy C11000, selected for high conductivity and ease of forming. All materials are entered into a bill of materials (BOM) with their embodied energy and end-of-life routes noted.
移动电源外壳指定采用玻璃纤维增强的聚碳酸酯-丙烯腈丁二烯苯乙烯共混材料（PC-ABS），该材料可提供抗冲击性、阻燃性，并适用于注塑成型以获得良好的表面光洁度。内部电气触点采用 C11000 铜合金，因其导电率高且易于成型。所有材料均录入物料清单（BOM），并注明其蕴含能源和废弃处理途径。
6. Detailed Design and Modelling | 详细设计与建模
A 3D CAD model is created in parametric software, allowing rapid iteration of enclosure dimensions, snap-fit features, and cable management channels. The panel folds into three segments, connected by living hinges moulded from thermoplastic polyurethane (TPU) to allow over 10,000 flex cycles.
在参数化软件中创建了三维 CAD 模型，以便快速迭代外壳尺寸、卡扣特征和线缆管理通道。面板折叠成三部分，由热塑性聚氨酯（TPU）模塑的活动铰链连接，可承受超过 10,000 次弯折循环。
Thermal simulation checks that the power bank’s internal temperature remains below 60 °C during maximum charge and discharge, preventing lithium-polymer battery degradation. Structural finite element analysis (FEA) verifies that the housing can survive a 1-metre drop onto concrete without cracking, meeting the durability requirement in the PDS.
通过热仿真验证，移动电源内部温度在最大充放电过程中保持在 60 °C 以下，以防止锂聚合物电池老化。结构有限元分析（FEA）验证了外壳能够承受从 1 米高度跌落到混凝土地面的冲击而不会开裂，从而满足 PDS 中的耐用性要求。
7. Manufacturing Processes and Quality Control | 制造工艺与质量控制
Injection moulding is selected for the PC-ABS housing due to its suitability for high-volume production with tight tolerances (±0.1 mm). The TPU hinges are overmoulded in a two-shot process to ensure strong adhesion. The solar panel lamination is done under vacuum at 150 °C to bond ETFE, cells, and backsheet without bubbles.
选择注塑成型工艺制造 PC-ABS 外壳，因为它适用于高产量、紧公差（±0.1 mm）的生产。TPU 铰链通过二次注塑工艺包覆成型，以确保牢固粘接。太阳能电池板的层压则在 150 °C 的真空条件下进行，使 ETFE、电池片和背板无气泡地粘合。
Quality control (QC) incorporates in-line vision systems to inspect solder joints on the charging circuit and a pull test for the USB connector. Statistical process control (SPC) monitors key dimensions of the enclosure, using X-bar and R charts to detect drift. A first-article inspection report (FAIR) is compiled for the pilot run.
质量控制（QC）包括使用在线视觉系统检查充电电路上的焊点，以及 USB 连接器的拉拔测试。统计过程控制（SPC）监控外壳的关键尺寸，采用均值-极差控制图（X-bar 和 R 图）来检测漂移。同时为试生产编制了首件检验报告（FAIR）。
8. Prototyping and Testing | 原型制作与测试
Functional prototypes are built using stereolithography (SLA) 3D printing for the enclosure, combined with pre-production solar laminates. The prototypes undergo a test regime: electrical load testing at 0.5 A, 0.75 A, and 1.0 A to verify voltage regulation, and outdoor charging tests to measure the average daily energy harvested.
功能原型使用立体光固化（SLA）3D 打印制作外壳，并搭配预生产的太阳能层压板。原型需接受一系列测试：在 0.5 A、0.75 A 和 1.0 A 电流下进行电气负载测试，以验证电压调节性能；以及户外充电测试，测量平均每日收集的能量。
Environmental testing includes a 72-hour salt spray test for corrosion resistance of exposed parts and UV exposure in a QUV chamber to confirm that the ETFE film does not yellow after 500 hours. User trials with 20 hikers provide qualitative feedback on ease of setup and perceived durability.
环境测试包括针对外露部件的 72 小时盐雾耐腐蚀测试，以及在 QUV 老化箱中的紫外线照射测试，以确认 ETFE 薄膜在 500 小时后不会发黄。20 名徒步旅行者参与的用户试用则为安装便捷性和感知耐用性提供了定性反馈。
9. Failure Mode and Effects Analysis (FMEA) | 故障模式与影响分析
An FMEA is conducted on the charging circuit and mechanical assembly. Potential failures include: solder joint fracture under vibration, USB connector debonding, TPU hinge tearing, and water ingress through the button membrane. Each failure mode is scored for severity (S), occurrence (O), and detection (D) on a 1–10 scale.
对充电电路和机械组件进行了 FMEA。潜在故障包括：振动下焊点断裂、USB 连接器脱胶、TPU 铰链撕裂，以及通过按钮薄膜进水。每种故障模式根据严重度（S）、发生度（O）和检测度（D）按 1–10 分制评分。
The risk priority number (RPN = S × O × D) highlights the USB connector debonding as the highest risk (RPN = 240). Mitigation actions include a mechanical strain relief clip and a 100 % pull test during final assembly, reducing O from 6 to 2 and bringing the RPN below 80.
风险优先数（RPN = S × O × D）指出，USB 连接器脱胶是风险最高的故障模式（RPN = 240）。采取的缓解措施包括增加机械应力消除夹，以及在最终装配中进行 100% 拉拔测试，将发生度 O 从 6 降至 2，使 RPN 降至 80 以下。
10. Cost Analysis and Economic Viability | 成本分析与经济可行性
A bottom-up cost estimate is built from BOM costs, labour, overheads, and tooling amortisation. The bill of materials totals £9.20 per unit, dominated by the solar laminate (£4.80) and the battery cell (£2.10). Assembly labour, at 12 minutes per unit, adds £3.00. Amortised tooling (£20,000 over 50,000 units) contributes £0.40 per unit.
成本估算采用自下而上的方法，综合了物料清单成本、人工、制造费用和模具摊销。每件产品的物料清单成本总计 9.20 英镑，其中太阳能层压板（4.80 英镑）和电芯（2.10 英镑）占大头。装配人工按每件 12 分钟计，另加 3.00 英镑。模具摊销（20,000 英镑，按 50,000 件分摊）每件增加 0.40 英镑。
Total factory cost per unit is £12.60. With a wholesale price of £24.99, the gross margin is healthy. A break-even analysis shows the project is viable above 3,800 units sold, assuming fixed costs of £35,000 covering certification, design, and initial marketing. Sensitivity analysis tests variations in cell efficiency and panel scrap rate.
每件产品的工厂总成本为 12.60 英镑。以 24.99 英镑的批发价计算，毛利率相当可观。盈亏平衡分析表明，假设包括认证、设计和初期营销在内的固定成本为 35,000 英镑，销量超过 3,800 件即可实现项目盈利。敏感性分析则检验了电池板效率和面板废品率变动带来的影响。
11. Environmental Impact and Lifecycle Assessment | 环境影响与生命周期评估
A streamlined lifecycle assessment (LCA) examines cradle-to-grave impacts. The dominant energy use is in manufacturing the monocrystalline silicon wafers (approximately 1800 MJ/kg) and injection moulding. In the use phase, the product displaces grid electricity for charging; assuming 300 full charges per year, the carbon payback time is estimated at 8 months of typical outdoor use.
通过简化的生命周期评估（LCA），我们考察了从摇篮到坟墓的环境影响。主要的能源消耗集中在单晶硅晶片的制造（约 1800 MJ/kg）和注塑成型环节。在使用阶段，该产品可替代电网电力进行充电；假设每年完成 300 次完全充电，其碳回报期估计为典型的 8 个月户外使用时间。
End-of-life planning ensures the battery is removable for separate WEEE recycling, and the housing is stamped with recycling codes. The ETFE film can be recovered, and the PC-ABS blend is labelled for incineration with energy recovery where mechanical recycling is impractical. An environmental product declaration (EPD) is prepared to communicate these impacts transparently.
在废弃处理规划中，我们确保电池可拆卸，以便按照 WEEE 指令单独回收，并在外壳上印有回收标识。ETFE 薄膜可回收，PC-ABS 共混物则标记为在机械回收不可行时，进行能量回收焚烧。同时编制了一份环境产品声明（EPD），以透明地披露这些影响。
12. Final Evaluation and Recommendations | 最终评估与建议
Reflecting on the PDS, the chosen design meets or exceeds all primary targets. The unit weighs 285 g, delivers a consistent 5 V / 1 A output under full sun, and survived drop and water spray tests. The FMEA and QC plan ensure repeatable quality. LCA shows a net environmental benefit if the product is used regularly for at least two years.
回顾 PDS，所选设计达到或超过了所有主要目标。产品重量为 285 g，在充足阳光下可稳定提供 5 V / 1 A 输出，并成功通过了跌落和喷水测试。FMEA 和质量控制计划确保了质量的可重复性。生命周期评估显示，若产品能正常使用至少两年，则具有净环境效益。
Recommendations for the next design cycle include exploring bifacial solar cells to capture albedo light, integrating a maximum power point tracking (MPPT) chip for improved low-light performance, and developing a modular accessory system for other outdoor devices. These enhancements could further differentiate the product in a competitive market while remaining aligned with WJEC engineering principles of iterative improvement.
针对下一个设计周期的建议包括：探索使用双面太阳能电池以捕捉地面反射光；集成最大功率点跟踪（MPPT）芯片以改善弱光性能；以及开发用于其他户外设备的模块化配件系统。这些改进可以在竞争激烈的市场中进一步让产品脱颖而出，同时遵循 WJEC 工程中迭代改进的原则。
Published by TutorHao | Engineering Revision Series | aleveler.com
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