Application of CMM and CAM Integration Technology in Automobile Body Design

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Application of CMM and CAM Integration Technology in Automobile Body Design [Copy link]

The automobile industry is a key pillar industry in China, but the body design of domestic automobile manufacturers is still based on traditional manual production. Not only is the production precision low, it consumes a lot of manpower and working hours, and also restricts the process of independent development of the automobile industry. Therefore, in the process of automobile design model production, the three-dimensional mathematical master model is directly programmed and processed, and the three-dimensional mathematical master model is quickly and accurately reconstructed through digital photographic measurement online detection analysis and reverse engineering reconstruction, so that the measurement detection and cutting processing are integrated, which can effectively shorten the production cycle of the whole vehicle model, improve the production accuracy, shorten the development cycle of body design and manufacturing, and improve the market competitiveness of China's automobile enterprises, thereby promoting and driving the rapid development of China's automobile industry.
Various body physical models, as the direct embodiment of body shape and the important carrier of body engineering data, play a pivotal role in the process of automobile design and development, especially in the process of body design and manufacturing. The most critical stage in body shape design is the production of full-size models, which combines the theoretical design of the car with the physical shape and intuitively reflects the design concept.
The car body is composed of a series of complex spatial surfaces. It is both a handicraft and a carrying space. Most of China's automobile enterprises adopt traditional body design methods, which have long development cycles and low manufacturing precision. Combining CMM (three-coordinate measuring machine) technology with CAD/CAM technology can make modern design methods more powerful and promote the rapid development of the automobile industry. At present, this technology has been successfully used in similar foreign enterprises, greatly improving the efficiency of new car body development, while the application of this technology in China is still in its infancy. For this reason, we should apply CMM/CAM integrated technology to automobile body design and development as soon as possible to accelerate the pace of independent development of China's automobile industry.
Traditional design method
The traditional design method consists of two stages: preliminary design and technical design. Its characteristics are to convey information through physical objects and drawings, including at least 1:5 clay model, full-size clay model and three wind tunnel tests of real vehicles. The traditional design method has the following main disadvantages:
□ Long cycle
The cycle of the entire development and production preparation of the car body generally takes 3 to 5 years in China, and it will take a lot of time, manpower and material resources to make a 1:1 clay model and sample and draw the main drawing board, and the credibility of the initial design is quite low. In order to finalize the product, it can only rely on the trial production of the prototype and experimental analysis and verification, and gradually modify the design, which generally requires more than 3 times, so the cycle is quite long.
The competition of modern automobiles is a competition of speed, including the continuous updating of the shape. If the cycle of automobile renewal can be shortened, the automobile company will be in a favorable position in the competition. The traditional design method has a long cycle and low efficiency, and it is bound to be unable to adapt to the fierce market competition of modern automobiles.
□ Large cumulative error
First, the carving of clay models mainly relies on the human eye to judge the shape and smoothness of the connection, but it is difficult to judge whether the arc surface of the car model is smooth by the human eye. At present, the car modeling is fashionable with arcs, and the arc surface and small corners are difficult to carve, which will produce the initial clay model error. The three-coordinate machine is also used for measurement. The contact probe is mostly used. The number of collected measurement points is limited, and some key points will be lost. Therefore, it cannot truly reflect the characteristics of some curved surfaces, causing measurement errors.
Modern body design methods
With the development of computer technology, the emergence of high-speed digital computers, especially the emergence of high-speed graphics processing terminals and workstations, make computer geometric graphics processing a reality. Since the 1970s, computer-aided technology CAX has been gradually widely used in the field of industrial design and manufacturing. The emergence of three-dimensional CAD system marks the liberation of computer-aided design technology from the simple three-view mode of imitating engineering drawings. It realizes the computer's description of the main information of product parts, and also promotes the development and realization of CAE and CAM technology. The surface modeling function of CAD makes the establishment of computer mathematical models of complex surfaces a reality, and the means of body design and development have made a qualitative leap. The integration of CAD and CAM abolished the "three masters" method that has been used for a long time in the past body design process. The main drawing board and the main template no longer exist, and the main model that is retained is also different from the past. Among the three-dimensional engineering design software, the most famous ones include UGⅡ of UGS in the United States, PRO/E of PTC in the United States, and CATIA of Dassault in France. These three-dimensional engineering design software are widely used in major automobile companies in the world, and have played a key role in helping companies improve the quality of design and manufacturing, shorten the development cycle, and enhance the market competitiveness of products.
□ The three-dimensional mathematical master model of the body and
the three-dimensional model data of the CAE body shape are reconstructed in the CAE system. The three-dimensional model of the body can be used for finite element analysis of body stiffness and strength, automobile collision simulation experiments, aerodynamic performance analysis, and body surface smoothness analysis.
□ Processing of the three-dimensional model of the body and the 1:1 prototype model
Since there are still some deviations between the small-scale clay model and the real-size car in terms of appearance proportion, details, etc., as well as the limitations of the computer system's ability to express objects, a 1:1 real car scale model must be made during the development of new models to finally determine the lines of each part and verify the visual effect of the entire vehicle appearance.
At present, the rapid processing method of 1:1 car body model generally adopts numerical control machining (NCM) method. Its basic principle is to process the 3D CAD mathematical model in the CAM module or system, select the machining tool through CAM, determine the machining trajectory and other pre-processing work. The CAM module (system) automatically generates the program code of numerical control machining and directly transmits it to the numerical control machining equipment to process the 3D solid model. This method is relatively mature and has high precision. It is currently a processing method widely used by foreign automobile manufacturers. However, the cost of this large-scale numerical control machining equipment is quite expensive, and it is difficult to be promoted and applied in general automobile enterprises in China.
□ The 3D mathematical master model of the car body and the car body structure design
The 3D mathematical master model of the car body will bring great convenience to the design of the car body structure engineer. The structural engineer can carry out more reasonable, more accurate and more effective car body structure design based on the 3D mathematical master model. The 3D modeling data of the car body can also be directly transmitted to the mold CAD/CAM system, which will improve the quality of the car body cover mold manufacturing and shorten the design and manufacturing cycle.
CMM/CAM integrated cutting measuring machine
With the development and application of modern science and technology represented by electronic computer technology, the body design and development technology has undergone revolutionary changes, which has brought pressure and opportunities to China's automobile industry. Computer application technology has also been integrated into or replaced many traditional technologies. Compared with traditional technologies, it is easier for China to catch up with developed countries in computer application. Zhong Measuring Instrument has developed the CMM/CAM integrated cutting measuring machine for the first time in China on the premise of fully understanding the changes in modern body design methods and accurately positioning the domestic market. Its features and applications are as follows:
□ Full functions and strong pertinence
Zhong Measuring Instrument CMM/CAM integrated cutting measuring machine is based on its cantilever three-dimensional coordinate measuring machine. On the basis of increasing the rigid structure of the main machine, it enhances the CAM numerical control processing function, retains the original contact probe measurement function, and adds digital photography measurement function. Its digital photography function is a function specially added for the rapid and accurate construction of the three-dimensional mathematical main model in body design, which solves the defects of slow point sampling speed of contact measurement and inability to measure certain feature points and arc transitions. Digital photography measurement can scan a complete surface (including curved surfaces and connecting lines between curved surfaces) at a time, so it can quickly and accurately collect data on the surface of the clay model. At the same time, since it is a non-contact measurement method that does not miss object features, it can reduce cumulative errors. Engineers can convert the collected data into a format and transmit it as raw data to the 3D modeling software to quickly and accurately generate the 3D mathematical master model of the car body.
At the same time, the fully functional handheld control box of the CMM/CAM integrated cutting measuring machine of the Zhongchuang measuring instrument is convenient for both tool setting of the CAM system and measurement of the photographic measuring system. Its uniquely designed cutting head expands the function of CNC cutting processing, ensuring that there is no processing dead zone during the processing of the whole vehicle model; the unique rigid body design can meet the high-speed and high-precision cutting processing, and quickly and efficiently complete the processing of 1:1 body models.
□ Good integration
The CMM/CAM integrated cutting measuring machine of the Zhongchuang measuring instrument integrates the measurement function and cutting processing function well, and can quickly switch between the measurement function and the processing function, quickly use the measured data to guide the processing, or quickly feed back the data of the processed model to the 3D modeling system through measurement, which can reduce the determination time of the 3D mathematical master model, thereby shortening the development cycle of the body design.
□ Process application example
1. Concept sketch design
The concept design is done by the automobile stylist, and the design intent is expressed through computer 3D simulation. The resulting 3D model is the basis for design verification, modification, and prototype model manufacturing.
2. Processing program compilation, generate NC code
to analyze the processing position and processing allowance, compile processing program and generate tool path, and perform anti-collision, overcutting inspection and simulation processing on each tool path to verify the correctness of the path. Generate NC code suitable for machine reading through post-processing, and compare the processed NC program tool points to determine whether they are the same as the designed tool path points.
3. System initialization
The CNC system is initialized to confirm that each system is working normally. Switch the system to cutting state in the Windows interface (the system has two states: measurement and cutting). The machine starts to return to the origin and wait.
4. Processing origin confirmation
After the tool head is switched to the corresponding state of the program, use the manual pulse wheel to set the tool and find the processing origin. The tool setting block is contact trigger type. After contact, the current axis position state data will be sent out, and the corresponding processing origin data will be stored in the CNC system.
5. Processing program transmission
The computer connects to the CNC system through the serial port to transmit the NC processing code, and the CNC system caches the code.
6. Execute processing
Before executing the processing, run the NC program quickly in the air to verify the correctness of the NC program and see if there is an alarm in the system, and then execute the processing.
7. Data acquisition
The non-contact measurement system is an optical camera, called an industrial data acquisition camera, which has the advantages of high efficiency, high pixel, large data acquisition area, joint rotation, and multi-angle shooting in the same coordinate system; the single-point trigger method collects data with high accuracy but low efficiency, so the CMM/CAM integrated cutting measuring machine uses contact and non-contact measurement together. Most point data are collected by non-contact, and auxiliary collection of special points is achieved by contact collection, which can conveniently complete the point collection process. The collected data can be output in IGES and ASC formats after slight processing, which is convenient for other software to read.
8. Model inverse

After modifying the clay model, the surface can be obtained by reading the collected point cloud data through many reverse modeling software such as Imageware, Geomagic, CATIA, UG, etc., and repeating this process until the designer is satisfied.
Conclusion
China's new automobile industry planning outline clearly proposes to take body development as a breakthrough point to form China's independent development capabilities for cars. The proportion of car body to the total cost of the whole vehicle is about 1/3, or even close to 1/2, and it is also an important symbol of the commercial nature of automobiles. The car body is frequently updated and the technology progresses rapidly. Therefore, the body development capability is a breakthrough point for independent development of cars.
The CMM/CAM integrated cutting measuring machine of Zhongchuang Instrument is the first equipment in China that integrates measurement and cutting processing functions. Its functions have basically approached or reached the various technical indicators of similar foreign equipment, but it has a clear advantage in cost price, and is suitable for promotion and use in large, medium and small domestic automobile companies.