Freecad Assembly4装配模型设计入门

一、基本信息

本文内容：学习Assembly4装配模型设计功能。

2024年3月7日

最新版Freecad 0.21.2

最新版 Assembly4 0.50.8 下载地址：stoneold/FreeCAD_Assembly4

最新版 Assembly4 示例教程下载地址：FreeCAD_Examples: Freecad Assmbly4 的示例模型

This assembly workbench allows to assemble into a single assembly container other FreeCAD objects, and place them relative to the assembly and to each-other. The parts in the assembly can be in the same document as the assembly or in an external document. When parts are modified in their original document, they are instantly updated in the assembly.

Parts are placed relative to each-other by matching features inside them. Specifically, in Assembly4, these features are virtual objects called LCS (for Local Coordinate System, also called datum coordinate system) and are attached using FreeCAD's built-in Part::Attacher and ExpressionEngine. No geometry is used to place and constrain parts relative to each other, thus avoiding a lot of the topological naming problems.

An Assembly4 Assembly is a standard FreeCAD App::Part container, therefore it is compatible and can be manipulated with any FreeCAD tool handling App::Part objects. In particular, it can be inserted into another Assembly to create nested assemblies to any level. It can also contain solids, datum objects and sketches. A document can contain only 1 Assembly.

安装很简单：

下载后Assembly4，在freecad的Mod目录下，解压，重启Freecad即可。

Assembly4模块可实现多个几何体对象的装配功能。Assembly4装配功能的实现并不是借助于几何约束求解器，而是通过三维局部坐标系变换（也称作基准坐标系，Local Coordinate System, Datum Coordinate System）。

具体来说，Assembly4模块中使用一个App:Part类型的Model表示装配体，可以将多个几何体(App::Part、PartDesign::Body)以App::Link对象的形式添加到装配体Model中。在这过程中，可以通过Expression指定几何体与几何体、几何体与Model的局部坐标系变换关系。然后，Assembly4便可借助于Expresion Engine来完成这种局部坐标系变换，进而实现多个几何体的装配。

二、装配建模学习

参考资料：Assembly4 示例教程， Asm4_Tutorial2 （Freecad 0.19）

In this tutorial we'll assemble 3 parts inside a single FreeCAD document, and animate the movement using a master sketch:

the base is fixed and holds 2 axes
the disk rotates around one of the axes
the arm can wiggle around the base's other axis
the disk has a nipple that is prisoner in a slot in the arm
all 3 parts and the full assembly are in 1 single FreeCAD file

注意：由于Freecad和Assembly4插件已经升级，已经与教程有所差异。

效果如下：

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As usual in Assembly4, the assembly holds (App::Link) links to the (App::Part) parts, not the parts themselves, even though the parts are in the same document here. Thus, making assemblies with parts in the same document is identical to making assemblies with parts from external documents. Actually, it is possible to mix both methods at will.

The only difference is that, since a FreeCAD document can only contain one Assembly4 Model, only one level assemblies are possible if everything is in the same document. For large assemblies this is a severe limitation, therefore in order to make nested assemblies — assemblies of sub-assemblies and sub-sub-assemblies — it is mandatory to have several documents. See tutorial 1 for how to make assemblies from external parts.