📚 Engineering Case Study Practical Drill | 工程案例分析实战演练
In IGCSE Engineering, case studies offer a structured way to bridge theory and practice. This article takes you through a full practical drill using a portable adjustable phone stand as a sample project. You will learn how to interpret a design brief, conduct research, establish specifications, generate concepts, select materials, analyse structural forces, choose manufacturing processes, build a prototype, test the outcome, and propose improvements. By following each step, you will develop the analytical and evaluative skills that are essential for your coursework and examinations.
在IGCSE工程课程中，案例分析提供了一种将理论与实践相结合的结构化方法。本文将以一个便携式可调节手机支架作为示例项目，带你完成一次完整的实战演练。你将学习如何解读设计摘要、开展调研、建立规格、生成概念、选择材料、分析结构受力、选择制造工艺、制作原型、测试成果并提出改进建议。通过每一个步骤，你可以发展课程作业和考试中必不可少的分析与评估能力。
1. Understanding the Design Brief | 理解设计摘要
The design brief states: “Design and make a portable, adjustable stand to hold a smartphone steadily at multiple viewing angles. The product must be lightweight, fold to a compact size, be easy to set up, and support a typical phone weighing about 200 g without tipping over. The intended user is a student who watches educational videos on a desk.” This brief highlights key engineering requirements: portability, adjustability, stability, and adequate load capacity. Every design decision that follows must satisfy these constraints while keeping the user’s comfort and safety in mind.
设计摘要这样描述：“设计并制作一个便携式可调节支架，能在多个视角下稳定支撑智能手机。产品必须轻巧、可折叠至紧凑尺寸、易于架设，并能支撑约200克的典型手机重量而不倾倒。目标用户是一名在书桌上观看教学视频的学生。”这份摘要突显了关键工程要求：便携性、可调节性、稳定性以及足够的承载能力。之后所有的设计决策都必须满足这些约束条件，同时兼顾使用者的舒适与安全。
2. Research and Product Analysis | 调研与产品分析
Before generating ideas, existing phone stands on the market were examined. Common types include simple injection-moulded plastic wedges, foldable metal wire supports, and multi-jointed aluminium arm mounts. Each reveals strengths and weaknesses that can inform our own design.
在生成设计想法之前，我先调研了市面上的手机支架。常见类型包括简单的注塑塑料楔块、可折叠金属丝支撑件以及多关节铝臂支架。每一种都展现出各自的优缺点，可以为我们的设计提供参考。
Many compact stands rely on a triangular folding structure. While they pack flat, the fixed crease limits the tilt angle to one or two positions. Users often report that such stands slide on smooth desks.
许多紧凑型支架采用三角折叠结构。虽然它们可以平展收纳，但固定的折痕将倾斜角度限制在一两个位置。用户经常反映这类支架在光滑桌面上容易滑动。
Metal wire stands are lightweight and easily bent to shape, but they can permanently deform if overloaded and offer limited lateral stability for wide phones.
金属丝支架重量轻且容易弯折成形，但超载时可能发生永久变形，而且对较宽的手机无法提供充分的横向稳定性。
Fully articulating aluminium arms provide excellent adjustability and rigidity; however, they are heavier, bulkier, and more expensive to manufacture, making them less suitable for a low-cost, pocket-sized solution.
全铰接铝臂提供了极好的可调性和刚性；然而，它们更重、更笨重且制造成本更高，因此不太适合低成本、可放进口袋的解决方案。
From this analysis, an ideal design would combine the compactness of a folding mechanism, the light weight of a wire or thin-sheet structure, and enough friction or locking features to remain stable on a desk.
通过以上分析，一个理想的设计应当结合折叠机构的紧凑性、金属丝或薄板结构的轻量性，以及足够的摩擦或锁止特征从而在桌面上保持稳定。
3. Specification Criteria | 规格标准
To guide the design process, a set of measurable specifications was formulated based on the brief and research findings. These criteria will later be used to evaluate the final prototype objectively.
为了指导设计过程，依据摘要和调研结果制定了一套可测量的规格。这些标准稍后将用于客观地评估最终原型。
Portability: The folded dimensions must not exceed 150 mm × 70 mm × 12 mm, so that it fits into a standard pencil case or a pocket.
便携性：折叠尺寸不得超过150毫米 × 70毫米 × 12毫米，以便装进普通笔袋或口袋。
Adjustability: The stand must provide at least four distinct stable tilt angles between 30° and 75° from the horizontal, allowing the user to adapt the viewing angle for glare reduction or comfort.
可调节性：支架必须在水平面以上30°到75°之间提供至少四个不同的稳定倾斜角度，让用户能够调整视角以减少眩光或获得舒适体验。
Load capacity: The stand must safely support a mass of 250 g without excessive bending, cracking, or collapse, giving a safety margin above the typical phone weight.
承载能力：支架必须安全支撑250克的质量，不发生过度弯曲、开裂或坍塌，提供超出典型手机重量的安全裕度。
Stability: When placed on a smooth laminate desk, the stand with a phone mounted must not slide or topple when nudged gently from the side with a force of 0.5 N applied at the phone’s centre.
稳定性：放置在光滑的层压桌面上，安装手机后，当从侧面以0.5牛的力轻推手机中心时，支架不得滑动或倾倒。
Ease of use: The stand must be set up in under 10 seconds by a first‑time user without requiring any tools.
易用性：首次使用者在10秒内无需任何工具即可完成支架的架设。
4. Generating Initial Design Ideas | 生成初步设计想法
Three initial concepts were sketched to meet the specification. Each concept adopts a different mechanical principle.
为了满足规格要求，我草拟了三种初步概念。每种概念采用了不同的机械原理。
Concept A – Notched A‑frame: Two flat panels are hinged at the top, and a third support leg pivots at the rear. Multiple notches on the base panel allow the leg to lock into different positions, giving stepped angle adjustment. This design is simple to fabricate from sheet material and folds flat, but it may lack lateral rigidity if the hinge is loose.
概念A — 缺口A型支架：两块平板在顶部铰接，第三块支撑腿在后部旋转。底座板上的多个缺口可以让支撑腿锁定在不同位置，实现阶梯式角度调节。该设计用平板材料容易制造，并可平铺折叠，但若铰链松动，可能缺乏横向刚度。
Concept B – Friction‑hinge tablet stand: Two main plates are connected by a stiff friction hinge that can hold any angle within a range. The bottom plate has a lip to retain the phone. This provides continuous angle adjustment and a clean look, but the friction hinge must be precisely calibrated to not slip under load, which complicates manufacturing.
概念B — 摩擦铰链平板支架：两块主板通过一个刚性摩擦铰链连接，该铰链可在一定范围内保持任意角度。底板带有挡边以固定手机。这一方案实现了连续角度调节且外观整洁，但摩擦铰链必须精确校准才能在负载下不打滑，这增加了制造复杂性。
Concept C – Wire‑form easel: A single piece of spring‑steel wire is bent into a shape resembling an artist’s easel. The wire cradle supports the phone, and the rear leg can be repositioned by sliding along a loop. This concept is extremely lightweight and material‑efficient, but the thin wire may concentrate stress and cause instability with heavier phones.
概念C — 金属丝画架式：一根弹簧钢丝弯曲成类似画架的形状。金属丝托架支撑手机，后腿可沿一个环滑动改变位置。这一概念极为轻巧且材料利用效率高，但细金属丝可能会造成应力集中并在较重的手机下产生不稳定。
5. Material Selection | 材料选择
Material choice influences weight, strength, manufacturability and cost. Four candidate materials were compared for the main body of the stand.
材料选择影响着重量、强度、可制造性和成本。我对比了支架主体的四种备选材料。
Acrylic (PMMA): Acrylic sheet is rigid, transparent, and can be laser‑cut to very precise profiles. It gives a premium appearance, but it is brittle and may crack if dropped or if stress concentrates around sharp internal corners.
亚克力（PMMA）：亚克力板材刚硬、透明，可以激光切割出非常精确的轮廓。其外观高级，但质地脆，若跌落或在尖锐内角处产生应力集中，可能会开裂。
Plywood (birch, 3 mm): Plywood is cheap, readily available, and can be cut with a laser or a coping saw. It has decent toughness and a warm aesthetic, but it splinters at edges and may warp with humidity changes unless sealed.
胶合板（桦木，3毫米）：胶合板价格低廉、易于获取，可以用激光或手锯切割。它具有良好的韧性和温暖的美感，但边缘容易起毛刺，若不进行密封处理，可能会因湿度变化而翘曲。
Aluminium (1.5 mm sheet): Aluminium offers excellent strength‑to‑weight ratio and does not break under normal handling. However, sheet metal requires more complex tools for bending and cutting, and its edges must be deburred to prevent injury.
铝板（1.5毫米）：铝材具有极佳的强度重量比，并且在正常操作下不会断裂。然而，金属板需要更复杂的工具进行折弯和切割，其边缘必须去毛刺以防伤人。
PLA (3D‑printed): PLA filament is ideal for rapid prototyping; it can be printed into complex, organic shapes and integrated hinges. The downside is relatively low heat resistance and a slower production speed if many units are needed.
PLA（3D打印）：PLA线材非常适合快速原型制作；它可以打印出复杂的有机形状和一体式铰链。缺点则是耐热性相对较低，以及若需大批量生产则速度较慢。
For a school workshop project that allows rapid iteration, 3 mm birch plywood was selected as the primary material because it balances cost, ease of laser cutting, and adequate structural properties for the expected loads. Small rubber feet will be added to increase friction.
对于一个允许快速迭代的学校车间项目，我选择3毫米桦木胶合板作为主要材料，因为它在成本、易激光切割以及预期荷载下的结构性能之间取得了平衡。另外将增加小橡胶脚垫以增大摩擦。
6. Structural and Mechanical Considerations | 结构与力学考量
The stand must not topple. The main force to consider is the weight of the phone, W = m × g. Taking mass m = 0.25 kg and gravitational field strength g = 10 N/kg (approximation for simplicity), the weight W = 2.5 N, which acts downwards at the phone’s centre of mass.
支架不得倾倒。需要考虑的主要作用力是手机的重量，W = m × g。取质量m = 0.25 kg，重力场强度g = 10 N/kg（为简便取近似值），重量 W = 2.5 N，该力垂直向下作用在手机的质心。
W = m × g = 0.25 × 10 = 2.5 N
In the worst‑case scenario (phone positioned at the highest tilt), the line of action of W falls outside the base footprint, creating an overturning moment about the rear edge of the base. The restoring moment is provided by the weight of the stand itself and the normal reaction from the desk. For stability, the restoring moment must exceed the overturning moment.
在最坏情况下（手机处于最高倾斜角度），重力W的作用线落于底座支撑面之外，会对底座后缘产生倾覆力矩。恢复力矩由支架自身的重量以及桌面提供的法向反力产生。要保证稳定，恢复力矩必须大于倾覆力矩。
Overturning moment = W × d, where d is the horizontal distance from the pivot to the line of action of W.
倾覆力矩 = W × d，其中d为转轴到W作用线的水平距离。
Assuming the phone centre is positioned 45 mm behind the rear base edge at the steepest angle, the overturning moment is 2.5 N × 0.045 m = 0.1125 N·m. The prototype base is designed with a rear extension of 60 mm from the rear support point, so that the centre of mass of the empty stand and the desk reaction create a counter‑moment of at least 0.15 N·m, giving a safety factor above 1.3. Friction also plays a role: a rubber pad with a coefficient of static friction μ ≈ 0.8 on laminate ensures that the stand does not slide outward before toppling would occur.
假设在最陡角度下手机中心位于底座后缘之后45毫米处，倾覆力矩为2.5 N × 0.045 m = 0.1125 N·m。原型底座设计为从后支撑点向后延伸60毫米，这样空支架的质心与桌面反力可产生至少0.15 N·m的反向力矩，从而获得1.3以上的安全系数。摩擦力也起一定作用：在层压表面上，静摩擦系数μ ≈ 0.8的橡胶垫可确保支架在可能发生倾倒前不会向外滑出。
7. Manufacturing Processes | 制造工艺
For the plywood version, laser cutting was chosen as the primary manufacturing process. The 2D CAD file was drawn in vector software and sent to a CO₂ laser cutter. Cutting parameters were set to 12 mm/s speed at 70% power for clean edges with minimal charring.
对于胶合板版本，我选择激光切割作为主要制造工艺。二维CAD文件使用矢量软件绘制，并发送至CO₂激光切割机。切割参数设为速度12 mm/s、功率70%，以获得边缘干净、烧焦最少的切口。
Small locating holes for hinges and notches were cut simultaneously to ensure accuracy. After cutting, the parts were lightly sanded with 240‑grit paper to remove any residual soot and to soften sharp corners. Friction hinges were created by pressing a short M4 bolt through the plywood pieces, using a nylon washer and a lock nut to provide adjustable clamping force.
铰链定位孔和角度调节缺口同时切割，以保证精度。切割完成后，用240目砂纸轻轻打磨部件，去除残余灼痕并使尖角柔和。摩擦铰链通过将一根短M4螺栓穿过胶合板件，并使用尼龙垫圈和防松螺母提供可调的夹紧力。
Rubber feet were cut from a 2 mm self‑adhesive neoprene sheet using a craft knife and attached to the base corners. This low‑tech approach requires no specialist moulds and can be completed entirely in a school workshop within a one‑hour practical session.
橡胶脚垫从2毫米厚的自粘氯丁橡胶板上用美工刀裁剪下来，并粘贴到底座各角。这种低技术含量的方法无需任何专用模具，可在一个小时的实践课上于学校车间完全完成。
8. Prototyping and Modelling | 原型制作与建模
Before committing to the final material, a quick cardboard mock‑up was made to check the ergonomics and the folding mechanism. Cardboard proved too flexible, confirming the need for a stiffer material, but it helped visualise the positions of the notches and the range of tilt angles.
在确定最终材料之前，我先用卡纸制作了一个快速模型，以检验人体工程学和折叠机构。卡纸过于柔软，证实了需要更硬挺的材料，但它帮助我直观地看到了缺口的位置和倾斜角度的范围。
The first plywood prototype was assembled using the laser‑cut components. Initial assembly revealed that the bottom notch slots were slightly too shallow, limiting the steepest angle to only 55° instead of the targeted 75°. The CAD file was modified to deepen the notches by 3 mm, and a second prototype was cut. This iterative cycle of model‑test‑modify lies at the heart of engineering design and demonstrates the value of rapid prototyping.
首个胶合板原型使用激光切割件装配完成。初次装配显示底部缺口槽略浅，导致最陡角度只能达到55°，而非目标的75°。随后修改CAD文件，将缺口加深3毫米，并切割了第二个原型。这种建模—测试—修改的迭代循环是工程设计的核心，也展现了快速原型的价值。
9. Testing and Evaluation | 测试与评估
The second prototype was evaluated against every specification point. A 250 g weight (simulated with steel calibration masses taped together) was placed on the stand at the steepest angle for 60 seconds; no cracking or visible deformation was observed, proving the load capacity requirement was met.
对照每一条规格要求对第二个原型进行了评估。将一个250克的重物（用胶带捆在一起的钢质校准砝码模拟）以最陡角度放置在支架上持续60秒；没有观察到开裂或可见变形，证明承载能力要求得到满足。
Folded dimensions measured 148 mm × 68 mm × 11 mm, just within the 150 × 70 × 12 limit. Four distinct notches gave tilt angles of 32°, 47°, 62° and 75°, thereby satisfying the adjustability criterion. The stability test using a push of 0.5 N applied horizontally at the phone centre showed no toppling or sliding; the rubber feet gripped the laminate effectively, generating a friction force of approximately μ × N = 0.8 × (0.25 × 10) ≈ 2 N before slipping, well above the applied push.
折叠尺寸测量为148毫米 × 68毫米 × 11毫米，刚好在150 × 70 × 12的限量之内。四个不同的缺口分别提供了32°、47°、62°和75°的倾斜角度，从而满足了可调节性标准。使用0.5牛的力在手机中心水平推动的稳定性测试显示未发生倾倒或滑动；橡胶脚垫有效地抓住层压表面，产生的摩擦力约为 μ × N = 0.8 × (0.25 × 10) ≈ 2 N，远大于施加的推力。
Five classmates were asked to set up the stand unaided; all completed the task in under 8 seconds, confirming ease of use. However, one tester noted that the notched leg occasionally jumped out when changing angles aggressively, suggesting that the depth of the notches could be refined further or that a spring‑loaded detent could be added.
我请五位同学独立地架设支架；所有人均在8秒内完成任务，证实了易用性。但有一位测试者指出，在快速变换角度时，有缺口的支撑腿偶尔会脱出，这意味着缺口的深度可以进一步优化，或者可以增加一个弹簧定位器。
10. Suggested Improvements | 改进建议
Based on the test findings, three key improvements are proposed. Firstly, the notch profile could be changed from a simple rectangular cut to a dovetail shape, which would trap the support leg more securely and prevent accidental disengagement during angle changes.
基于测试结果，提出三项主要改进。第一，缺口轮廓可以从简单的矩形切口改为燕尾形，这样能
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