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Modern design and manufacturing

CAD/CAM

CAD/CAM is a term which means computer-aided design and computer-aided manufacturing. It is the technology concerned with the use of digital computers to perform certain functions in design and production. This technology is moving in the direction of greater integration（一体化）of design and manufacturing, two activities which have traditionally been treated as distinct（清楚的）and separate functions in a production firm. Ultimately, CAD/CAM will provide the technology base for the computer-integrated factory of the future.

Computer-aided design (CAD) can be defined as the use of computer systems to assist in the creation, modification, analysis, or optimization（最优化）of a design. The computer systems consist of the hardware and software to perform the specialized design functions required by the particular user firm. The CAD hardware typically includes the computer, one or more graphics display terminals, keyboards, and other peripheral equipment. The CAD software consists of the computer programs to implement（实现，执行）computer graphics to facilitate the engineering functions of the user company. Examples of these application programs include stress-strain （压力-应变）analysis of components（部件）, dynamic（动态的）response of mechanisms, heat-transfer calculations, and numerical control part programming. The collection of application programs will vary from one user firm to the next because their product lines, manufacturing processes, and customer markets are different these factors give rise to differences in CAD system requirements.

Computer-aided manufacturing (CAM) can be defined as the use of computer systems to plan, manage, and control the operations of a manufacturing plant through either direct or indirect computer interface with the plant’s production resources. As indicated by the definition, the applications of computer-aided manufacturing fall into two broad categories:

https://www.wendangku.net/doc/c515018682.html,puter monitoring and control.

2.manufacturing support applications.

The distinction between the two categories is fundamental to an understanding of computer-aided manufacturing.

In addition to the applications involving a direct computer-process interface （界面，接口）for the purpose of process monitoring and control, compute-aided manufacturing also includes indirect applications in which the computer serves a support role in the manufacturing operations of the plant. In these applications, the computer is not linked directly to the manufacturing process. Instead, the computer is used “off-line”（脱机）to provide plans, schedules, forecasts, instructions, and information by which the firm’s production resources can be managed more effectively. The form of the relationship between the computer and the process is represented symbolically in the figure given below. Dashed lines（虚线）are used to indicate that the communication and control link is an off-line connection, with human beings often required to consummate（使圆满）the interface. However, human beings are presently required in the application either to provide input to the computer programs or to interpret the computer output and implement the required action.

CAM for manufacturing support

What is CAD/CAM software?

Many toolpaths are simply too difficult and expensive to program manually. For these situations, we need the help of a computer to write an NC part program.

The fundamental concept of CAD/CAM is that we can use a Computer-Aided Drafting (CAD) system to draw the geometry of a workpiece on a computer. Once the geometry is completed, then we can use a computer-Aided Manufacturing (CAM) system to generate an NC toolpath based on the CAD geometry.

The progression（行进，级数）from a CAD drawing all the way to the working NC code is illustrated as follows:

Step 1: The geometry is defined in a CAD drawing. This workpiece contains a pocket to be machined. It might take several hours to manually write the code for this pocket（凹槽，型腔）. However, we can use a CAM program to create the NC code in a matter of minutes.

Step 2: The model is next imported into the CAM module. We can then select the proper geometry and define the style of toolpath to create, which in this case is a pocket. We must also tell the CAM system which tools to use, the type of material, feed, and depth of cut information.

Step 3: The CAM model is then verified to ensure that the toolpaths are correct. If any mistakes are found, it is simple to make changes at this point.

Step 4: The final product of CAD/CAM process is the NC code. The NC code is produced by post-processing（后处理）the model, the code is customized（定制，用户化）to accommodate the particular variety of CNC control.

Another acronym that we may run into is CAPP, which stands for Computer-Aided Part Programming. CAPP is the process of using computers to aid in the programming of NC toolpaths. However, the acronym CAPP never really gained widespread acceptance, and today we seldom hear this term. Instead, the more marketable CAD/CAM is used to express the idea of using computers to help generate NC part programs. This is unfortunate because CAM is an entire group of technologies related to manufacturing design and automation-not just the software that is used to program CNC machine tools.

Description of CAD/CAM Components and Functions

CAD/CAM systems contain both CAD and CAM capabilities – each of which has a number of functional elements. It will help to take a short look at some of these elements in order to understand the entire process.

1. CAD Module

The CAD portion of the system is used to create the geometry as a CAD model. The CAD model is an electronic description of the workpiece geometry that is mathematically precise. The CAD system, whether stand alone or as part of a CAD/CAM package, tends to be available in several different levels of sophistication. （强词夺理，混合）

2-D line drawings 两维线条图

Geometry is represented in two axes, much like drawing on a sheet of paper. Z-level depths will have to be added on the CAM end.

3-D wireframe models 三维线框模型

Geometry is represented in three-dimensional space by connecting elements that represent edges and boundaries. Wiregrames can be difficult to visualize（想象，形象化，显现）, but all Z axis information is available for the CAM operations.

3-D surface models 三维表面模型

These are similar to wireframes except that a thin skin has been stretched over the wireframe model to aid in visualization.Inside, the model is empty. Complex contoured Surfaces are possible with surface models.

3-D solid modeling 三维实体模型

This is the current state of the market technology that is used by all high-end software. The geometry is represented as a solid feature that contains mass. Solid models can be sliced（切片，部分，片段）open to reveal internal features and not just a thin skin.

2. CAM Module

The CAM module is used to create the machining process model based upon the geometry supplied in the CAD model. For example, the CAD model may contain a feature that we recognize as a pocket .We could apply a pocketing routine to the geometry, and then all of the toolpaths would be automatically created to produce the

pocket. Likewise, the CAD model（模子，铸型）may contain geometry that should be produced with drilling operations. We can simply select the geometry and instruct the CAM system to drill holes at the selected locations.

The CAM system will generate a generic（一般的，普通的）intermediate （中间的，媒介）code that describes the machining operations, which can later be used to produce G & M code or conversational programs. Some systems create intermediate code in their own proprietary（所有的，私人拥有的）language, which others use open standards such as APT for their intermediate files.

The CAM modules also come in several classes and levels of sophistication. First, there is usually a different module available for milling, turning, wire EDM, and fabrication（装配）. Each of the processes is unique enough that the modules are typically sold as add-ins（附加软件）. Each module may also be available with different levels of capability. For example, CAM modules for milling are often broken into stages as follows, starting with very simple capabilities and ending with complex, multi-axis toolpaths :

● 21/2-axis machining

● Three-axis machining with fourth-axis positioning

● Surface machining

● Simultaneous five-axis machining

Each of these represents a higher level of capability that may not be needed in all manufacturing environments. A job shop might only require 3-axis capability. An aerospace contractor might need a sophisticated 5-axis CAM package that is capable of complex machining. This class of software might start at $5,000 per installation, but the most sophisticated modules can cost $15,000 or more. Therefore, there is no need to buy software at such a high level that we will not be able to use it to its full potential.

3.Geometry vs. toolpath

One important concept we must understand is that the geometry represented by the CAD drawing may not be exactly the same geometry that is produced on the CNC machine https://www.wendangku.net/doc/c515018682.html,C machine tools are equipped to produce very accurate toolpaths as

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