Design Requirements for CNC Manufacturability

管理增量制造业

In the first module, we explored the design requirements of the Least Effort region of the manufacturable zone. Designs within the Least Effort region have large acceptable compliance and simpler geometries. Most designs are more complex and fall into the Incremental Effort region. Designs in this region have a design requirement that leads to higher manufacturing effort, such as tighter GD&T requirements, higher geometric complexity, or more demanding look and feel.

在该地区，努力以比最少的努力区域更高的速度增加。每个参数的特征是其自身的努力函数，该功能以不同的速率缩放。下面的示意图给出了每个参数的相对速率的想法。

制造努力如果设计有多个高需求，则可以化合物。例如，当更紧密的公差与较大的零件尺寸结合在一起时，制造业的工作量会呈指数增长。

CNC Machining Effort in the Incremental Region

The key to managing effort in the incremental region is keeping effort low for as many parameters as possible. Because of compounding effects, there is a much higher effort if multiple parameters are in the Incremental Region, rather than just one.

所需的余额是为每个参数尽可能地减少努力，同时仍满足设计要求。让我们看一下每个主要参数，以了解它们如何推动制造业的工作CNC machining。

线性公差和GD＆T努力缩放

Tighter tolerance requirements are needed for mating parts, flexures, and functional geometries like fan blade profiles. Tolerance is a function of the following parameters

• 机器位置准确性
• 工具错误
• Chatter
• Cut forces
• 部分刚度
• Registration error (for tolerances between features)
• Fixture positional errors
• Temperature of the machine and part

The narrower the requirements are, and the more sources of error there are, the more effort is required to meet the tolerance requirements. More care during setup is needed to minimize errors. Machines must also be run at slower speeds to minimize chatter and tool deflection. Additionally, effective tool life is reduced, which leads to higher consumable costs.

Reducing Tolerance Effort

为了减少努力，仅在临界维度（例如交配表面）上指定更严格的容忍度，并使非关键维度更加宽松。虚构支持单个部分的多个公差。在您上传的图纸上指定所需的公差。您还应该尽可能减少错误源的数量。例如，通过向零件添加夹紧功能来消除对软颚的需求。

CNC机器自由度和几何复杂度

From Module 1, the simplest geometries are machinable with a 3-axis CNC, without using 3D machining.

CNC加工最少的努力 - 3轴无3D加工，方形末端磨机*

当需要使用更复杂的技术n geometries include surface normals that are not orthogonal to the tool. The first step for machining higher geometric complexities is 3D machining and 3+2 machining. 3+2 machining uses a standard 3-axis mill, plus a fixture that can rotate in 2-axis. 3+2 machining has the same degrees of freedom as a 5-axis machine, but the fixture does move during machining. This allows for the machining of a limited number of non-orthogonal surfaces to any surface roughness. However, continuously changing surfaces are not manufacturable because the number of setups grows without bound.

3 + 2 Machining, Square End Mill*

3D machining uses the standard 3-axis setup, except that the z-axis varies continuously during the cut. This technique allows for milling of external non-orthogonal or compound surfaces, at the expense of higher surface roughness.

3轴，带3D机加工，方形磨机*

如果部分几何形状具有内部复合表面或需要同时移动工具和固定装置，则需要一台完整的5轴机器（请参见模块3）。

Geometric complexity increases manufacturing effort because the required machines are limited in number, programming is more challenging, and machinists with more advanced expertise are required to run them. Designers may target a desired machining method, but ultimately it is up to the manufacturer to determine which method is most appropriate for the design.

高的er geometric complexity also leads to higher effort if there are no flat surfaces to clamp to. In this case, the manufacturer will need to create a custom soft-jaw fixture to match the geometry which requires additional manufacturing time, and material cost.

Tools and Incremental Effort

特定的几何形状，例如底切和狭窄的插槽，需要扩展基本的最小努力工具，以包括：

• 牛头
• 钥匙刀
• Slitting Saws

These tools add effort because they require additional programming and most often additional setups. Custom ground tools are also possible, but at the expense of increased lead time and cost. This increases manufacturing effort significantly and should only be used if absolutely required. Non-standard threads are also possible to manufacture, but it will not be possible to use standard thread checkers to validate the thread.

Reducing Geometry Effort

加工技术设定了与设计相关的整体工作。如果可能的话，请调整设计几何形状，以便您可以使用3D加工或3+2加工与5轴。之后，通过限制需要加工的面部数量来减少所需的设置数量。最后，限制专用几何形状所需的工具更改的数量，例如缝隙。

CNC Part Size Scaling

对于较短尺寸大于6英寸的铣削零件，制造业的工作开始增加，因为固定变得更加困难。在长度上保持紧密的耐受性也更加困难。同样在较大尺寸的情况下，材料变得更难采购，并且体重变得很大。

As part sizes shrink below 3 in (25.4 mm), the material gets weaker, and warping becomes an issue. Fixturing can easily deform parts at these dimensions, and machines run slower to minimize cut force.

一个特殊情况是用于薄纸，可能很大，但厚度小于0.1英寸。加工此几何形状极具挑战性，因为很难防止翘曲。设计到最接近的库存厚度可消除此问题。在虚构的情况下，任何小于此0.1的尺寸都将调整为最接近的库存厚度。

减少零件尺寸的工作

对于许多设计，零件的大小是由应用程序固定的，因此减少工作的选项受到限制。一个例子是新要求意味着该零件必须在大小上增长。在这种情况下，将1个尺寸保持在6英寸以下将意味着标准固定装置仍然可用。

努力Scaling for Materials

结构部件可能需要高强度来抵抗静态或动态载荷。柔性零件需要具有高弹性和疲劳强度的材料。该材料为制造业设定了基线。更难的材料需要较慢的切割速度和更快的磨损工具。另一方面，它们可以承受更高的载荷，因此，可能的几何形状是可能的。塑料零件虽然较软，但受热变形的影响比金属更大，实现狭窄的公差更具挑战性。下表显示了从不同材料加工相同几何形状的相对精力。

物质相对努力

努力	Metals	Plastic
至少	铝 Brass	德林 ptfe
Incremental	Copper Bronze Steel 铸铁	腹肌 pps HDPE 丙烯酸纤维 Nylon
Maximum	不锈钢 A2工具钢 Titanium	Polypropylene Polycarbonate UHMW PEEK Ultem

Reducing Material Effort

如果材料是根据设计要求固定的，则其相关的加工工作也是固定的。如果有灵活性，请考虑具有更好的可加工性的材料。另外，不要与材料所能提供的东西作斗争。例如，试图将狭窄的公差加工成塑料的努力更高，因为塑料的热稳定性低于金属。在这种情况下，整体上切换到金属材料可能会较低。

CNC铣削Finish and Effort Scaling

除固有的圆角和断裂边缘之外，每个额外的成品表面或圆角边缘都会增加努力。尽管这看起来似乎很容易，但操作数量可能会变得大，尤其是对于内部功能。光滑的表面粗糙度需要缓慢的机器通过，并有可能进行更多的工具更改。圆角通过以下努力分开：

Low	Internal vertical edges. External vertical edges,
Incremental	外部水平边缘
高的	内部水平边缘，非正交边缘

圆形外部边缘还增加了制造业的工作，因为必须非常精确地放置工具，或者必须使用3D加工。内部水平边缘或非正交边缘可能会遇到可及性问题或复杂的工具路径。

另一个可以增加大量精力的操作是雕刻。用于雕刻零件的专门字体需要额外的铣削设置。为了减少雕刻的努力，虚构提供了具有预定义和经过验证字体的标准配置文件。

减少外观和感觉的努力

外观和感觉可能没有最戏剧性的努力功能，但是如果触摸许多表面或边缘，则可能会导致巨大的努力。对于表面粗糙度，在CNC中可以进行精细的饰面，但是其他过程（例如电抛光）可能会产生更好的结果。考虑添加另一个制造步骤的额外努力，而不是加工到良好的粗糙度。对于鱼片，最大程度地减少内部水平边缘的切割深度，或使用牛头工具以单步加工圆角。

Conclusion: Driving Down Manufacturing Effort

增量努力区域是大多数设计所在的地方，因为大多数设计至少具有一个驱动更高努力的参数。在该区域的设计是最大化设计性能和最大程度地减少制造业的平衡。在CNC加工中，该区域的工作以公差和部分几何形状为主，尽管任何参数都可以引起大量努力。有关减少该地区的努力的技术摘要，请参见下面的列表。

Incremental Effort DFM Checklist for CNC Machining

Download the checklist as a handy reference guide here!