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Designing components with snap fits can save you time and money in production by reducing material costs and part quantities as well as improving ease of assembly.
虽然过去的注射成型是塑料中生产快照接头的唯一可行方法，但3D打印为其设计带来了新的机会和挑战。
And there are most certainly challenges! To help you navigate the complex world of snap fits we’re going to take a look at the key features, calculations and tips to overcome common issues for designing and prototyping these features.
设计您的快照合身关节
Note：公制单位用于所有计算
所有关节都具有相似的功能。以最简单的形式，快速拟合是一个小突起（钩，珠或凹凸），在组装过程中偏转，以捕捉交配部分的抑郁症。然后，雄性和女性部位的形状确定是否可以分离关节以及需要分开的力。
For the purpose of this article, we’re going to focus on the simple cantilever style joint. Entire books have been written (like这里和这里) about different snap joint design, but the cantilever style (and its variations) is both the easiest to design and the one you’re most likely to encounter.
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正如您在上面的图中看到的那样，悬臂接头由带有点施加的端载荷的固定光束建模。
The worst case stress and strain is found at the root of the cantilever and can be easily approximated usingclassical beam bending theory。
As the exact forces are not yet known when designing a model, it’s most common to use deflection and strain rather than force and stress values to set your dimensions. In other words, your dimensions will be limited by maximum strain during deflection rather than force required to assemble/disassemble (mating force).
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经典梁弯曲理论假设固定端壁很刚性。但是，零件墙的厚度可能与悬臂本身相似。Q是为此添加的挠度放大因子。
As the rigid wall is the worst case for strain in the root, for a simple casing, leave Q as 1.
Also note that the return angle affects the ease of joint separation. A return angle the same as the leading angle means the same force is used during assembly and disassembly. In contrast, a return angle of 90° can never be disassembled, except by using an external window to release the snap.
实施计算
现在，我们知道在设计悬臂关节时需要哪些计算值，让我们看一下如何找到这些值。
There are two ways you can approach these calculations:
- 材料first:You have chosen your material, found its allowable strain and can design your dimensions to fit it.
- 尺寸首先：Your primary dimensions are fixed and you can choose a material to fit.
寻找可接受的应变极限
要找到可接受的应变极限，请使用以下公式使用材料弹性的屈服应力和模量：
∈=σ/e
where ∈ = modulus of elasticity [MPa], σ = stress [MPa] and E = strain [%]
因此，应变=弹性的应力 /模量=长度 /初始长度的变化[％]
专家提示：3D打印的零件的应力因轴而变化，因此为了获得最佳强度，请确保关节的悬臂部分沿X-Y平面构建，而不会向上行驶Z轴。如果您的悬臂只能在Z轴上创建，请注意，休息时的伸长率降低了50％，拉伸强度降低了20-30％。我们建议将允许应力/应变减少50％的Z轴悬臂。问虚构上传零件时，如果您在这里有疑问。
这是一些常见的3D打印材料的可接受应变值：
| 材料 | 可接受的菌株 |
|---|---|
| 类似腹肌 | 20-40％ |
| Verowhite | 10-25％ |
| 透明的 | 10-25％ |
| ABS | 7% |
| PLA | 4-8％ |
| 尼龙 | 4-15％ |
以下是一些计算出的应变率，用于不同的壁厚，挠度和悬臂长度，以帮助您开始。
更改横截面
如果您计算了尺寸，选择了材料，并且可接受的应变率仍然太高，最好的解决方案是更改悬臂横截面。最常见的变化包括缩小宽度或厚度。
4 Common Problems + Solutions in Design Snap Fits
Here are some solutions to other common challenges engineers face when designing for snap fit components.
1. Creep/Stress Relaxation
热塑性塑料特别容易受到蠕变的影响 - 应力下材料的逐渐变形。随着时间的流逝，这会损害男性和女性零件之间的联系，甚至使其变得毫无用处。
解决方案：Make sure your male and female parts are designed in such a way that while deflection may happen during assembly, during normal, assembled use the parts are not subject to prolonged bending or tensile stress.
2.应力集中器
尖锐的角落将压力集中在悬臂的根部，使其剪切。
解决方案：Make sure there are no sharp corners to act as stress concentrators, especially on the tensile side of the cantilever. Use radi or chamfers to reduce this.
3.疲劳或重复负载故障
重复组装和拆卸卡接头可能会导致应力下的故障，远低于材料的额定应力。疲劳故障通常发生在高载荷频率（数百个（如果不是数千个周期））处。
解决方案：如果您预计组件的高周期频率，则必须仔细选择使用S-N曲线的抗疲劳材料。
4.公差
The tolerances are wrong and your parts won’t fit together.
解决方案：Rule of thumb for gaps:
- 0.2 mm for tight fits
- 0.4mm for slide fits and pivot joints
- 0.3mm for a close fit snap joint
主要要点
我们只在此处划过表面，如果您想要更多的深入信息，请查看以下一些资源。
SNAP FITS的设计是一个复杂且迭代的过程，但是如果您遵循本文所涵盖的简单工程最佳实践，则可以改善Snap Fit关节的初始功能并减少原型生命周期。
进一步阅读
要对SNAP拟合设计进行更深入的分析并深入研究材料特性，请查看下面的这些指南。
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