Manufacturing Techniques | A4.1

All manufactured products result from applying one or more techniques drawn from five broad categories. The choice of category depends on material properties, desired geometry, production volume and cost.

The categories are not mutually exclusive; a single product typically requires techniques from several categories applied in sequence.

所有制造产品都通过五大类工艺中的一种或多种来实现。类别的选择取决于材料特性、所需几何形状、生产数量和成本。

这五类并不相互排斥；单个产品通常需要按顺序应用多个类别的工艺。

Additive manufacturing (AM) constructs objects by depositing or curing material one cross-sectional layer at a time. Chuck Hull invented stereolithography in 1984, marking the birth of commercial 3D printing.

增材制造（AM）通过逐层沉积或固化材料来构建物体。Chuck Hull于1984年发明了光固化成型，标志着商业3D打印的诞生。

Rapid prototyping (RP) is the fast production of a physical model directly from CAD data, used primarily for form, fit and function testing early in the design process.

Workflow: CAD model → export as STL/3MF → slice into layers → print → post-process → evaluate

As AM materials and accuracy improve, the boundary between prototype and production part blurs — GE Aviation now produces certified LEAP engine fuel nozzles using SLS.

快速原型（RP）是直接从CAD数据快速生产物理模型，主要用于设计过程早期的形态、配合和功能测试。

工作流程：CAD模型 → 导出为STL/3MF → 切片分层 → 打印 → 后处理 → 评估

随着AM材料和精度的提升，原型与量产零件之间的界限逐渐模糊——GE航空现已使用SLS生产经认证的LEAP发动机燃油喷嘴。

AM is particularly suited to low-volume, high-complexity, or patient-specific production where conventional tooling would be prohibitively expensive. The crossover point where injection moulding becomes cheaper than AM is typically around 1,000–10,000 units depending on part complexity.

AM特别适合小批量、高复杂度或患者特定的生产，在这些场合传统模具成本过高。注塑成型比AM更经济的临界点通常在1,000–10,000件左右，具体取决于零件复杂性。

4D printing (coined by MIT's Skylar Tibbits, 2013) is 3D printing with smart materials — the fourth dimension is time, representing the transformation that occurs after printing.

Key smart materials:

• Shape Memory Polymers (SMPs) — programmed to hold a temporary shape below the glass transition temperature (T_g) and return to their original shape when heated above T_g.
• Shape Memory Alloys (SMAs) — typically Nitinol (NiTi); recover shape when heated.
• Hydrogels — swell or contract in response to water or pH changes.

Four-stage SMP cycle:

1. Print — object printed in permanent (memory) shape.
2. Programme — heat above T_g, deform mechanically.
3. Fix temporary shape — cool below T_g; temporary shape is retained.
4. Trigger — apply stimulus (heat, water, light); object returns to memory shape.

4D打印（由MIT的Skylar Tibbits于2013年提出）是使用智能材料的3D打印——第四维度是时间，代表打印后发生的变形。

关键智能材料：

• 形状记忆聚合物（SMP）——在玻璃化转变温度（T_g）以下保持临时形状，加热至T_g以上时恢复原始形状。
• 形状记忆合金（SMA）——通常为镍钛诺（NiTi）；加热时恢复形状。
• 水凝胶——对水或pH变化产生膨胀或收缩。

SMP四阶段循环：

1. 打印——以永久（记忆）形状打印物体。
2. 编程——加热至T_g以上，进行机械变形。
3. 固定临时形状——冷却至T_g以下；保持临时形状。
4. 触发——施加刺激（热、水、光）；物体恢复记忆形状。

Standard 3D printing moves in three axes (X, Y, Z). 5D additive manufacturing adds two rotational axes — one on the extruder head and one on the print bed — allowing the nozzle to deposit material on curved surfaces from multiple angles.

Key advantages over 3D printing:

• No support structures needed — the bed tilts so overhanging geometry is always printed at the correct angle.
• Curved layer deposition — fibres or material lines follow the stress paths within the part, producing stronger components (isotropic strength).
• Reduced material waste — elimination of supports saves polymer and post-processing time.
• Larger effective build volume — rotation enables parts that cannot fit flat in a standard envelope.

标准3D打印沿三个轴（X、Y、Z）移动。5D增材制造增加了两个旋转轴——一个在挤出头上，一个在打印床上——使喷嘴能够从多个角度在曲面上沉积材料。

相比3D打印的主要优势：

• 无需支撑结构——打印床倾斜，使悬空几何形状始终以正确角度打印。
• 曲面层沉积——纤维或材料线沿零件内部应力路径分布，生产出更强的部件（各向同性强度）。
• 减少材料浪费——无支撑节省聚合物和后处理时间。
• 更大的有效构建体积——旋转使无法平放在标准范围内的零件成为可能。

Subtractive (wasting) processes begin with a solid block or sheet and remove material to reveal the final shape. CNC (computer numerical control) automation allows extremely precise, repeatable cuts.

Subtractive processes produce excellent surface finishes and tight tolerances (±0.01 mm or better for CNC milling), but can generate significant material waste (swarf/chips).

减材（浪费型）工艺从实体块或薄板开始，通过去除材料来呈现最终形状。CNC（计算机数控）自动化允许极其精确、可重复的切削。

减材工艺可产生优良的表面光洁度和紧密公差（CNC铣削可达±0.01 mm或更好），但可能产生大量材料浪费（切屑）。

Forming exploits a material's plasticity, fluidity (molten) or elasticity. Since material is not wasted, forming is generally more material-efficient than subtractive methods.

Metal casting:

Polymer moulding:

成形工艺利用材料的可塑性、流动性（熔融）或弹性。由于不浪费材料，成形工艺通常比减材方法更节省材料。

金属铸造：

聚合物成型：

Joining creates assemblies from separate components. The choice between permanent and temporary joining has significant implications for repairability, recycling and end-of-life disassembly.

连接工艺将独立零件组装成组件。永久性与临时性连接的选择对可维修性、回收和报废拆解有重要影响。

Finishing techniques are applied after forming or machining to alter the surface chemistry, texture or appearance of a component. They can dramatically extend product life and perceived quality.

表面处理工艺在成形或加工后应用，以改变零件的表面化学性质、纹理或外观。它们可以显著延长产品寿命和提升感知质量。

No real product uses only one category of technique. The design team must reason about why each technique is selected by connecting material properties, geometry, volume, cost and sustainability.

Case study — smartphone (iPhone-type aluminium body):

Exam tip: when asked to "suggest why," link the technique to a specific material property or product requirement (e.g., "injection moulding is used for the polymer casing because the high-volume production run amortises the tooling cost").

没有任何真实产品只使用一类工艺。设计团队必须通过联系材料性能、几何形状、数量、成本和可持续性来推理为什么选择每种技术。

案例研究——智能手机（iPhone型铝制机身）：

考试技巧：当被要求"建议原因"时，将技术与具体的材料性能或产品要求联系起来（例如，"注塑成型用于聚合物外壳，因为大批量生产摊销了模具成本"）。