Part Module/zh-cn

简介
FreeCAD的实体建模能力都是基于 Open Cascade Technology (OCCT)内核——一种具有创建与处理高级3D几何体等特性的专业级CAD系统. 零件工作台（Part Workbench）是一种建立于OCCT库之上的层级，为用户提供了访问OCCT几何图元与函数的功能. 每种工作台(如底图工作台, 草图工作台, 零件设计工作台等等)的一切2D与3D绘制功能其实都是基于零件工作台暴露出的函数实现的. 因此，可以认为零件工作台是FreeCAD建模功能的核心组件.

以零件工作台创建的对象相对简单；为了构建更为复杂的几何图形，可以为之运用布尔运算(并集与减运算). 此建模范式就是尽人皆知的构造实体几何 (CSG) 工作流程，它是早期CAD系统中所用的传统方法. 另一方面，零件设计工作台（PartDesign Workbench）还提供了更为现代的工作流程来构建几何图形：它利用参数化方式来定义草图，再将其挤压成型为基本的实体对象，最后通过参数化变换(特征编辑)来修改模型，直到用户获取预期的最终模型为止.

零件对象比网格工作台（Mesh Workbench）创建的网格对象更为复杂，因为用户可以对前者执行更为高级的操作，如连续的布尔运算、修改历史与参数化处理.





工具
这些工具皆位于菜单.

图元
以下这些工具用于创建图元对象.


 * [[Image:Part_Box.png|32px]] Box: 根据指定的规格绘制一个立方体
 * [[Image:Part_Cylinder.png|32px]] Cylinder: 根据指定的规格绘制一个圆柱体
 * [[Image:Part_Sphere.png|32px]] Sphere: 根据指定的规格绘制一个球体
 * [[Image:Part_Cone.png|32px]] Cone: 根据指定的规格绘制一个圆锥体
 * [[Image:Part_Torus.png|32px]] Torus: 根据指定的规格绘制一个环面（torus）（圆环 (ring)）
 * [[Image:Part_CreatePrimitives.png|32px]] CreatePrimitives: 一种用于创建各类参数化几何图元的工具
 * [[Image:Part_Shapebuilder.png|32px]] Shapebuilder: 一种利用各种参数化几何图元创建更加复杂几何图形的工具

修改对象
这些工具用于修改已存在的对象. 通过它们即可选取待修改的对象.


 * [[Image:Part_Extrude.png|32px]] Extrude: 将对象的平面挤压成型
 * [[Image:Part_Revolve.png|32px]] Revolve: 通过令一（非实体）对象绕某轴旋转来创建另一个实体对象
 * [[Image:Part_Mirror.png|32px]] Mirror: 根据指定的镜面对选中的对象进行镜像操作
 * [[Image:Part_Fillet.png|32px]] Fillet: 为对象的边倒(圆)角
 * [[Image:Part_Chamfer.png|32px]] Chamfer: 为对象的边倒角
 * [[Image:Part_RuledSurface.png|32px]] Ruled Surface:
 * [[Image:Part_Loft.png|32px]] Loft: 对轮廓进行放样操作（放样成另一种轮廓）
 * [[Image:Part_Sweep.png|32px]] Sweep: 沿路径对一个或多个轮廓进行扫描


 * [[Image:Part_CompOffsetTools.png|48px]] Offset tools:
 * [[Image:Part_Offset.png|32px]] 3D Offset: Constructs a parallel shape at a certain distance from original.
 * [[Image:Part_Offset2D.png|32px]] 2D Offset: Constructs a parallel wire at certain distance from original, or enlarges/shrinks a planar face. (v0.17)


 * [[Image:Part_Thickness.png|32px]] Thickness: Hollows out a solid, leaving openings next to select faces.


 * [[Image:Part_ProjectionOnSurface.png|32px]] Projection on surface: Project a logo, text or any face,wire,edge to a surface. With the projection part it is possible to create a solid or wire. (v0.19)


 * [[Image:Part_CompCompoundTools.png|48px]] Compound Tools:
 * [[Image:Part MakeCompound.png|32px]] Make compound: Creates a compound from the selected objects.
 * [[Image:Part_ExplodeCompound.svg|32px]] Explode Compound: Tool to split up compounds of shapes
 * [[Image:Part Compound‏‎Filter.png|32px]] Compound Filter: The CompoundFilter can be used to extract the individual pieces.


 * [[Image:Part_Booleans.png|32px]] Booleans: Performs boolean operations on objects
 * [[Image:Part_Union.png|32px]] Union: Fuses (unions) two objects
 * [[Image:Part_Common.png|32px]] Common: Extracts the common (intersection) part of two objects
 * [[Image:Part_Cut.png|32px]] Cut: Cuts (subtracts) one object from another


 * [[Image:Part_CompJoinFeatures.png|48px]] Join features: smart booleans for walled objects (e.g., pipes) (v0.16)
 * [[Image:Part JoinConnect.png|32px]] Connect: Connects interiors of objects (v0.16)
 * [[Image:Part JoinEmbed.png|32px]] Embed: Embeds a walled object into another walled object (v0.16)
 * [[Image:Part JoinCutout.png|32px]] Cutout: Creates a cutout in a wall of an object for another walled object (v0.16)


 * [[Image:Part_CompSplittingTools.png|48px]] Splitting tools: (v0.17)
 * [[Image:Part BooleanFragments.png|32px]] Boolean fragments: makes all the pieces that can be obtained by Boolean operations between objects (v0.17)
 * [[Image:Part SliceApart.svg|32px]] Slice a part: tool to split shapes by intersection with other shapes
 * [[Image:Part Slice.png|32px]] Slice: Splits an object into pieces by intersections with another object (v0.17)
 * [[Image:Part XOR.png|32px]] XOR: removes space shared by even number of objects (symmetric version of Cut) (v0.17)


 * [[Image:Part Defeaturing.svg|32px]] Defeaturing: (v0.18)
 * [[Image:Part_Section.png|32px]] Section: Creates a section by intersecting an object with a section plane
 * [[Image:Part_SectionCross.png|32px]] Cross sections...:

其他工具

 * [[Image:Part ImportCAD.png|32px]] Import CAD: This tool allows you to add a file *.IGES, *.STEP, *.BREP to the current document.
 * [[Image:Part ExportCAD.png|32px]] Export CAD: This tool allows you to export a part object in a *.IGES, *.STEP, *.BREP file.
 * [[Image:Part ShapeFromMesh.png|32px]] Shape from Mesh: Creates a shape object from a mesh object.
 * Convert to solid: Converts a shape object to a solid object.
 * Reverse shapes: Flips the normals of all faces of the selected object.
 * [[Image:Part CreateSimpleCopy‎.svg|32px]] Create simple copy: Creates a simple copy of the selected object.
 * [[Image:Part RefineShape.png|32px]] Refine shape: Cleans faces by removing unnecessary lines.
 * [[Image:Part CheckGeometry.png|32px]] Check geometry: Checks the geometry of selected objects for errors.
 * Measure: Allows linear and angular measurement between points/edges/faces.
 * [[Image:Part Attachment.svg|32px]] Attachment: Attachment is a utility to attach an object to another one.

首选项

 * [[Image:Preferences-import-export.svg|32px]] Preference ... Import Export

OCCT geometric concepts
In OpenCascade terminology, we distinguish between geometric primitives and topological shapes. A geometric primitive can be a point, a line, a circle, a plane, etc. or even some more complex types like a B-Spline curve or a surface. A shape can be a vertex, an edge, a wire, a face, a solid or a compound of other shapes. The geometric primitives are not made to be directly displayed on the 3D scene, but rather to be used as building geometry for shapes. For example, an edge can be constructed from a line or from a portion of a circle.

In summary, geometry primitives are "shapeless" building blocks, while topological shapes are the real objects built on them.

A complete list of all primitives and shapes refer to the OCC documentation (Alternative: sourcearchive.com) and search for Geom_* (for geometric primitives) and TopoDS_* (for shapes). There you can also read more about the differences between them. Please note that the official OCC documentation is not available online (you must download an archive) and is mostly aimed at programmers, not at end-users. But hopefully you'll find enough information to get started here.

The geometric types actually can be divided into two major groups: curves and surfaces. Out of the curves (line, circle, ...) you can directly build an edge, out of the surfaces (plane, cylinder, ...) a face can be built. For example, the geometric primitive line is unlimited, i.e. it is defined by a base vector and a direction vector while its shape representation must be something limited by a start and end point. And a box -- a solid -- can be created by six limited planes.

From an edge or face you can also go back to its geometric primitive counterpart.

Thus, out of shapes you can build very complex parts or, the other way round, extract all sub-shapes a more complex shape is made of.

脚本
Part scripting

The main data structure used in the Part module is the BRep data type from OpenCascade. Almost all contents and object types of the Part module are available by Python scripting. This includes geometric primitives, such as Line and Circle (or Arc), and the whole range of TopoShapes, like Vertexes, Edges, Wires, Faces, Solids and Compounds. For each of those objects, several creation methods exist, and for some of them, especially the TopoShapes, advanced operations like boolean union/difference/intersection are also available. Explore the contents of the Part module, as described in the FreeCAD Scripting Basics page, to know more.

示例
To create a line element switch to the Python console and type in:

Let's go through the above python example step by step:

loads the Part module and creates a new document

Line is actually a line segment, hence the start and endpoint.

This adds a Part object type to the document and assigns the shape representation of the line segment to the 'Shape' property of the added object. It is important to understand here that we used a geometric primitive (the Part.LineSegment) to create a TopoShape out of it (the toShape method). Only Shapes can be added to the document. In FreeCAD, geometry primitives are used as "building structures" for Shapes.

Updates the document. This also prepares the visual representation of the new part object.

Note that a Line Segment can be created by specifying its start and endpoint directly in the constructor, for example Part.LineSegment(point1,point2), or we can create a default line and set its properties afterwards, as we did here.

A circle can be created in a similar way:

Note again, we used the circle (geometry primitive) to construct a shape out of it. We can of course still access our construction geometry afterwards, by doing:

Here we take the shape of our object f, then we take its list of edges. In this case there will be only one because we made the whole shape out of a single circle, so we take only the first item of the Edges list, and we takes its curve. Every Edge has a Curve, which is the geometry primitive it is based on.

Head to the Topological data scripting page if you would like to know more.

Tutorials

 * Import from STL or OBJ : How to import STL/OBJ files in FreeCAD
 * Export to STL or OBJ : How to export STL/OBJ files from FreeCAD
 * Whiffle Ball tutorial : How to use the Part Module