{"id":1277,"date":"2019-12-17T13:09:45","date_gmt":"2019-12-17T06:09:45","guid":{"rendered":"http:\/\/hieuchuan3d.com\/?p=1277"},"modified":"2019-12-17T13:09:45","modified_gmt":"2019-12-17T06:09:45","slug":"khac-nhau-giua-may-do-cmm-va-may-x-ray-ct-3d-vina-gioi-thieu","status":"publish","type":"post","link":"https:\/\/backup.hieuchuan3d.com\/ja\/khac-nhau-giua-may-do-cmm-va-may-x-ray-ct-3d-vina-gioi-thieu\/","title":{"rendered":"(Ti\u1ebfng Vi\u1ec7t) Kh\u00e1c nhau gi\u1eefa m\u00e1y \u0111o CMM v\u00e0 m\u00e1y x ray CT – 3D Vina gi\u1edbi thi\u1ec7u"},"content":{"rendered":"

\u7533\u3057\u8a33\u3042\u308a\u307e\u305b\u3093\u3001\u3053\u306e\u30b3\u30f3\u30c6\u30f3\u30c4\u306f\u305f\u3060\u4eca\u3000\u30d9\u30c8\u30ca\u30e0\u8a9e<\/a>\u3000\u306e\u307f\u3067\u3059\u3002 For the sake of viewer convenience, the content is shown below in the alternative language. You may click the link to switch the active language.<\/p>

Computed tomography (CT) for non-destructive testing (NDT)<\/span> has become quite common and is an affordable method for companies of all sizes, including higher educational facilities and R&D laboratories<\/span>. In many cases, CT represents an upgrade from x-ray film and digital radioscopy. Most likely, those with x-ray experience\u2014whose systems do not already include CT\u2014are considering upgrading their existing system to CT. Or, they may be considering the purchase of a new system with CT in order to add additional capability.<\/p>\n

The significance of CT for metrology<\/span> cannot be understated. The Association of German Engineers has developed a set of standards to use CT for metrology<\/span>, titled the Computed Tomography in Dimensional Measurement<\/span>, or VDI\/VDE 2630. The industry realizes CT generates 3D datasets, which can be used to measure geometrical features similar to traditional tactile coordinate measurement machines (CMM) or visual measurement machines (VMM).<\/span><\/p>\n

These datasets open the door for other CT users: those who will use this technology to measure samples and compare the results to the allowed tolerance. Unlike the typical use of non-destructive optical and tactile methods<\/span>, the main reason for using CT is its ability to measure invisible and unreachable features<\/span>. with minimal effort. CT can measure internal features without cutting into the sample and without even touching the actual part.<\/span><\/p>\n

When engineers design parts using 3D CAD systems they must define the tolerances for all features and surfaces. No manufacturing process is perfect, and all have variations, with some tolerances being more critical than others. Some dimensions may be relevant for the function of the part, and some tolerances are more critical than others. Think of the proper fit of a shaft and a bearing: If the bearing is too big, it will be too tight, and if it\u2019s too small, it will be too loose. There must be a definition for the tolerance that relates to both items.<\/p>\n

This example is covered by DIN ISO 286-1,<\/span> where the designer would call out a basic size and grade (e.g., H7) for both the shaft and the bearing. For other features, there are basically two relevant standards available. In the United States the ASME Y14.5 standard<\/span> is common, whereas in the European countries the standard referred to most often is ISO 1011<\/span>.<\/p>\n

\"\"<\/p>\n

\n

After the first prototypes, manufacturers perform a quality check. The process is very similar for cast- or injection-molded parts. Typically, CMM is used to measure all features with a tolerance stated in the drawing<\/span>. Very often, it is difficult to measure these features, so the part must be cut into smaller pieces<\/span>. Another option involves casting the parts into a box with resin, then cutting thinly sliced layers and trying to visualize the contour with a camera system.<\/p>\n

CT can reveal these inner structures for many applications without destroying the part<\/span>, and can be repeated easily on multiple parts. Specifically, the modern technology of injection molding can allow as many as 100-plus cavities per mold. Every cavity has to be qualified by the first article inspection process. Tactile and optical methods can be labor-intensive because they involve changing the orientation of the part in the system, and ensuring the probe starts at the correct point. These optical systems acquire data which must then be aligned using a software program. Performing these images with CT can significantly reduce process time and make the overall process much more cost-effective.<\/p>\n

As in all metrology tasks<\/span>, the measurement strategy is important, including CT. Once a good practice has been developed for a general type of part, it becomes much easier to duplicate the process and perform the scan. For CT, two main areas must be covered to perform the scan:<\/p>\n