📚 Case Study Practical Exercise: Cantilever Laptop Stand Design | 案例分析实战演练：悬臂式笔记本电脑支架设计
In Year 10 WJEC Engineering, case study analysis is a vital skill for linking theory to real-world design. This article guides you through a practical exercise: designing and evaluating a cantilever-style laptop stand. You will apply material science, mechanics, manufacturing knowledge, and sustainability considerations to simulate a professional engineering workflow.
在Year 10 WJEC工程课程中，案例分析是将理论与实际设计联系起来的核心技能。本文将通过一项实战演练——悬臂式笔记本电脑支架的设计与评估，带你走一遍专业工程流程。你将运用到材料科学、力学、制造工艺以及可持续性等多方面知识。
1. Introduction to the Case Study | 案例介绍
The case study involves designing a cantilever laptop stand for a home office setup. The stand must be robust, lightweight, easily manufactured, and sustainable. This exercise mirrors the WJEC Engineering controlled assessment where you need to demonstrate iterative design, analysis, and evaluation skills.
本案例要求为家庭办公环境设计一款悬臂式笔记本电脑支架。支架需坚固、轻便、易于制造且具备可持续性。该练习模拟WJEC工程课程的控评任务，需要你展示迭代设计、分析和评估能力。
2. Identifying Stakeholder Needs and Design Brief | 识别利益相关方需求与设计纲要
Primary stakeholders include the end user who values ergonomics and aesthetics, the manufacturer concerned with production cost and cycle time, and the environmental regulator focusing on recyclability. The design brief states: "Design a clamp-on cantilever laptop stand that adjusts in height from 150 mm to 350 mm above the desk, supports 2 kg safely, and can be produced in batches of 5,000 units at a target cost of £15 per unit."
主要利益相关方包括注重人体工学和美观的终端用户、关心生产成本与周期的制造商，以及关注可回收性的环保监管机构。设计纲要明确：“设计一款夹桌式悬臂笔记本电脑支架，桌面以上高度可调150 mm至350 mm，安全支撑2 kg，批量生产5000件，目标成本为每件15英镑。”
3. Developing a Product Specification | 制定产品规格书
m, safety factor ≥ 3, weight of the arm ≤ 400 g, material must be corrosion resistant (indoor use), and all components must be separable for recycling at end of life.
根据设计纲要，我们制定了一份产品设计规格书(PDS)，包含可量化的目标。关键规格包括：载荷下最大挠度 ≤ 5 mm，安全系数 ≥ 3，悬臂重量 ≤ 400 g，材料须耐腐蚀（室内使用），所有部件在使用末期可分离以便回收。
4. Initial Design Concepts and Sketches | 初始设计概念与草图
Two concepts were sketched: Concept A uses an extruded aluminium alloy arm with a die-cast aluminium clamp; Concept B uses a glass-filled nylon injection-moulded arm with a steel clamp insert. Both concepts have a simple hinge mechanism for height adjustment using a locking knob.
我们草绘了两个方案：方案A采用挤压铝合金臂搭配压铸铝夹具；方案B采用玻纤增强尼龙注塑臂，内嵌钢制夹具。两种方案都采用一个带锁紧旋钮的简单铰链机构进行高度调节。
Concept A offers higher stiffness but requires post-machining for the clamp threads. Concept B allows integrated features and fewer parts, but the polymer arm may need ribbing to meet deflection limits.
方案A刚度更高，但夹紧螺纹需要后加工。方案B可实现一体化设计、减少零件数量，但聚合物臂可能需要加筋以控制挠度。
5. Material Selection: Comparing Properties and Sustainability | 材料选择：性能与可持续性对比
We compared 6061-T6 aluminium alloy and 30% glass-filled nylon 6 (PA6 GF30). Aluminium has a Young' nsity 1.35 g/cm³. Aluminium is recyclable with established streams; nylon is technically recyclable but less commonly reclaimed.
我们对比了6061-T6铝合金和30%玻纤增强尼龙6(PA6 GF30)。铝合金的杨氏模量为69 GPa，屈服强度276 MPa，密度2.7 g/cm³。PA6 GF30的弹性模量约9 GPa，拉伸强度160 MPa，密度1.35 g/cm³。铝材有成熟的回收渠道；尼龙在技术上可回收，但实际回收率较低。
Using a decision matrix weighted towards stiffness (40%), weight (30%), cost (20%), and sustainability (10%), the aluminium alloy scored 8.1/10 versus the nylon's 6.4/10. Therefore, Concept A with aluminium was selected for detailed analysis.
利用权重偏向刚度(40%)、重量(30%)、成本(20%)和可持续性(10%)的决策矩阵，铝合金方案得分为8.1/10，尼龙方案为6.4/10。因此，我们选择方案A（铝合金）进行详细分析。
6. Load Analysis and Mechanical Calculations | 载荷分析与力学计算
× g = 2 kg × 9.81 m/s² ≈ 20 N. We also add a safety factor of 3 for dynamic loading, giving design load Fd = 60 N.
我们将悬臂建模为长度L=0.3 m的悬臂梁，自由端受集中载荷F。最恶劣工况为2 kg笔记本电脑，故F = m × g = 2 kg × 9.81 m/s² ≈ 20 N。考虑到动态加载，加入安全系数3，设计载荷Fd = 60 N。
Maximum bending moment at the fixed support: Mmax = Fd × L = 60 N × 0.3 m = 18 N·m.
固定端最大弯矩：Mmax = Fd × L = 60 N × 0.3 m = 18 N·m。
σmax = Mmax / Z
ross-section arm with width b = 0.025 m and height h = 0.008 m, section modulus Z = (b × h2) / 6 = (0.025 × (0.008)2) / 6 = 2.67 × 10-7 m³.
臂的矩形截面宽度b=0.025 m，高度h=0.008 m，截面模量Z = (b × h2) / 6 = (0.025 × (0.008)2) / 6 = 2.67 × 10-7 m³。
Maximum bending stress: σmax = Mmax / Z = 18 N·m / 2.67×10-7 f 276 MPa, giving an actual safety factor of 276/67.4 ≈ 4.1, which satisfies the spec ≥ 3.
最大弯曲应力：σmax = Mmax / Z = 18 N·m / 2.67×10-7 m³ = 67.4 MPa。该值远低于铝合金的屈服强度276 MPa，实际安全系数为276/67.4 ≈ 4.1，满足规格书≥3的要求。
Deflection at the free end for a cantilever with point load: δmax = (Fd × L3) / (3 × E × I), where I = (b × h3)/12 = (0.025 × 0.0083)/12 = 1.07×10-9 m⁴. E_aluminium = 69×109 Pa. δmax = (60 × 0.33) / (3 × 69×109 × 1.07×10-9) = 0.0023 m = 2.3 mm, which meets the ≤ 5 mm criterion.
自由端挠度（集中载荷悬臂梁）：δmax = (Fd × L3) / (3 × E × I)，其中惯性矩I = (b × h3)/12 = (0.025 × 0.0083)/12 = 1.07×10-9 m⁴。铝的E=69×109 Pa。δmax = (60 × 0.33) / (3 × 69×109 × 1.07×10-9) = 0.0023 m = 2.3 mm，满足≤5 mm标准。
7. Manufacturing Process Selection | 制造工艺选择
For the aluminium arm, extrusion is ideal: it can produce the constant cross-section profile with high dimensional accuracy and low cost for the required batch size of 5,000. The clamp body will be die-cast from aluminium alloy A380, followed by tapping threads for the locking knob.
对于铝合金臂，挤压成型工艺最为理想：它能够以高尺寸精度和较低成本生产出恒定截面型材，满足5000件批量需求。夹具主体采用A380铝合金压铸成型，然后攻丝用于锁紧旋钮
Published by TutorHao | Year 10 工程 Revision Series | aleveler.com
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