Computers and their role in engineering and manufacturing processes.

Monday, February 27, 2006

Coordinate Measuring Machine

Coordinate-Measuring Machines, (CMM), are mechanical systems designed to move a measuring probe to determine the coordinates of points on the surface of a workpiece. Coordinate-measuring machines consist of four main components: the machine itself, the measuring probe, the control or computing system, and the measuring software. They are often used for dimensional measurement, profile measurement, angularity or orientation measurement, depth mapping, digitizing or imaging, and shaft measurement. CMMs are offered with features like crash protection, offline programming, reverse engineering, shop floor suitability, SPC software and temperature compensation. The machines are available in a wide range of sizes and designs with a variety of different probe technologies. They can be controlled and operated manually, or by CNC or PC controls.
CMMs are offered in various configurations such as benchtop, free-standing, handheld and portable. Ideally, a CMM would be coupled with GD&T practices and programs automated to continoulsy check and send feedback to various manufacturing processes in the event of an error in the manufactured part geometry.
Pictured is an example of a CMM measuring head. It is reffered to as an Ultra Precise Test Sphere, and it is just that. It is spherical within 2.5 micro inches (63.5 n m) maximum and has a surface finish that is better than 0.5 micro inches (12.7 n m) Ra. This is ten times more accurate than high quality bearing balls. Spheres of this quality are simply not commercially available.

Sunday, February 26, 2006

Geometric Demensioning and Tolerances

Geometric Demensioning and Tolerances, GD&T, is a universal design engineering language that is being used to faithfully capture and transmit the designer's intent through all activities in the product cycle. The language has been adopted by the international Organization for Standardization, (ISO) and the American National Standards Institute, (ANSI). GD&T has been theorized to consititute continious improvement for manufacturing businesses. GD&T language consists of a well-defined set of symbols, rules, definitions, and conventions that can be used to describe the size, form, orientation, and location tolerances of part features.
GD&T was created through a need to overcome some of the problems created in the conventional "plus or minus" tolerancing. With conventional tolerancing, the machininst would often have to guess the designer's intent. For a simple example, consider a triangular part specified with two legs of equal length and no angle. The machinist has no evidence of the importance on the angle. Often times, the general feel is that if something not specified in such a way that the machinist feels correct, then the implication is that the geometry is not very important. The side effect is that the second guessing can lead to scrap parts and increased manufacturing time.
GD&T currently incorporates a universal language in which the designer can clearly state the intentions to the manufacturer. Baselines and Datum points are established, eliminating guesswork. A more powerful feature of GD&T is its use of a Coordinate Measuring Machine, (CMM). A complete setup would consist of a Computer Integrated Manufacturing, CIM, programs in correlation with a CMM to analyze manufactured parts. With a set up like this, the automated analysis would provide feedback to the different stages of manufacturing. This allows for the manufacturing process to constantly readjust the necessary parameters if the part does not meet specifications.

If you are interested in testing your GD&T knowledge, you can take the free GD&T Skills Survey at http://etinews.com/skills/index.html.

Tuesday, February 14, 2006

Computer Aided Design

In today's manufacturing world, virtually every aspect of design and analysis are explored with computer programs:
Structural Engineering FEA: Finite Element Analysis - A CAM program that analyzes a specified member or combinations of structural members for possible failure. The program breaks the geometry up into numerous small sections to simulate molecular interactions. Based upon user defined inputs with respect to material, temperature, forces, and supports. The program helps the designer indentify potential weaknesses in the design, greatly reduces prototype testing time.
Fluid Processes CTD: Computational Fluid Dynamics. Analyzing fluid flow is an extremely complicated and extensive process due to a wide range of interrelated variables. CAM CTD programs utilize as many methods for analysis as there are programs on the market, literally hundereds. All CTD programs however follow a basic common layout. First the geometry and other physical bounds of the problem are to be identified. With this, CTD divides the volume into discrete cells much like FEA described above. These cells are often called a mesh. After the physical modelling is defined, other physical equations are applied, such as equations of motion, or enthalpy and energy conservation. With other user-defined inputs, fluid behavior is defined with specifying the fluid, temperature, altitude, and flow rate. The analysis equations are then solved in a steady-state condition, then the user will be able to see results and view animations of the fluid processes.