Abstract: The clamping method directly determines the precision and efficiency of processing. In the small batch of multi-species processing, general fixture is the preferred processing. Flexible use of universal fixture, the original can not complete the processing possible. The thickness of 0.5 ~ 4mm of aluminum, copper parts for CNC milling, to improve the original clamping method, the use of magnet-assisted clamping method to solve the processing of sheet metal parts of the clamping force is not easy to grasp the problem.
1. Workpiece features
I units to produce electronic microwave module shell-based, often encountered in the production of a number of different sizes, small batch of thin plate parts of the processing, these parts are military products, so the size accuracy and position tolerance requirements are higher The The parts of the material for the aluminum alloy or brass, although the shape is simple, but the thin plate, the general thickness of 0.5 ~ 4mm; large area, often more than 200mm × 200mm size cover, easy to process.
Processing of such parts, the general use of flat pliers, horns and crowded iron combination of clamping method, in the vertical machining centers, CNC milling machines and other equipment on the milling forming. As the parts of the material with low tensile strength, high plasticity characteristics, coupled with the thickness of the parts thin, large size, so the clip is easy to produce deformation. When the clamping force is large, the milling force is greater than the clamping force, and the parts in the machining are often displaced, resulting in the displacement of the parts in the process. Parts scrap, to the processing to bring great difficulties. Vacuum adsorption clamping method can ensure the accuracy of clamping, but the professional fixture into a larger, and in the NC machining to use cutting fluid, will cause damage to the vacuum device, so the vacuum adsorption method in a small batch of multi-species CNC machining Is not very applicable. For the production and processing of the bottleneck in the problem, in the original method of clamping on the basis of the use of a flexible strong magnet-assisted clamping method to solve the above problems, to ensure the accuracy of parts processing.
2. Clamping method analysis
(1) the use of flat-nose pliers, iron-loaded plate parts. Sheet metal processing is generally the use of flat pliers, horns and crowded iron combination of clamping method, although the theoretical clamping force can be large, but because of the sheet after the deformation easily, and the process of milling cutter cutting will produce upward tension , This tension will immediately make the deformation of the sheet, resulting in sheet metal parts up the arch, the processing of the middle of the thin parts, both sides of the thick; serious deformation of the sheet instability, will make the clamping failure, parts will be moved by the cutting force, resulting in Parts scrap. An aluminum alloy sheet of 200 mm x 200 mm x 2 mm was used as an example. After clamping, a tensile force of 1 N was applied in the middle of the sheet, and the sheet was deformed to 0.1 mm above it, resulting in a deviation of 0.1 mm or more 0.1mm tolerance of the cover parts, will be ultra-poor scrapped. In the middle of the thin plate to exert 18N of tension, the sheet will be deformed to the clip instability, the middle of the arch, the clamping force decreased rapidly, unable to process.
(2) the use of strong magnet-assisted clamping method. Selection of magnetic super-strong NdFeB magnets for auxiliary clamping sheet parts. NdFeB magnets are the strongest magnetic permanent magnet, can absorb the equivalent of 640 times the weight of their own weight, you can achieve a small volume of large magnetic clamping requirements. In the production, one or a few pieces of φ15mm × 10mm strong magnetic blocks are placed in the middle position of the thin plate in the flattened pliers, the extruded iron clamping system (see Fig. 2). To the thickness of 2mm aluminum alloy cover parts processing, for example, the magnet through the cover plate, and the bottom of the horn adsorption, each magnet adsorption capacity of up to 1.8kg, enough to overcome the clamping deformation and tool cutting the tensile force , The sheet workpiece tightly pressed on the horn, does not produce arched. Experiments, a φ15mm × 10mm magnet through different thickness of the thin plate produced by the magnetic force shown in Table 1.
1. moving jaws 2. sheet work 3. strong magnetic briquettes 4. spindle 5. cutter 6. squeeze iron 7. h the mat 8. fixed jaws 9. flat pliers
Table 1 φ15mm × 10mm magnet through different thickness of the thin plate produced by the magnetic force
3. Comparison of the processing effect of different clamping methods
The machining method of the magnet-assisted clamping and the precision of the parts used in the machining of the workpiece are shown in Table 2. It can be seen that the machining precision of the parts is improved obviously after the machining method using the magnet-assisted clamping.
Table 2 using magnet-assisted clamping method and general processing methods of precision parts comparison
To amplifier cover, for example, the thickness of the tolerance requirements of the pattern is generally 0.1mm, from Table 2 shows that the use of ordinary processing methods can not guarantee the accuracy of parts processing requirements or simply can not be processed; the use of magnet-assisted clamping method, parts accuracy Fully meet the requirements of the pattern accuracy, but also for the operation of the workers to provide a convenient.
4. Precautions in production
The use of magnet-assisted clamping of the processing method, in the production should pay attention to the following:
(1) the use of extruded iron clip, you need to first work around the sheet to ensure that the iron clip clamping accuracy.
(2) horn, flat pliers directly affect the accuracy of the workpiece processing accuracy, the general requirements for the processing accuracy of 0.05mm of the workpiece, the need for flat pliers, horns flatness adjusted to 0.02mm or less.
(3) the distribution of strong magnets can be flexible layout, according to the size of the parts and processing position to place the magnet, you can place a number of different magnets, to ensure that the sheet close to the horn. If necessary, you can use the first part of processing, and then pause, adjust the magnet position, and then another part of the processing method to complete processing.
(4) For very small diameter or hanging a long cutter, pay attention to the impact of the magnet on the tool, so that the supermagnet placed from the tool processing path far.
(5) According to the milling depth of the sheet processing, the size of the tool is analyzed, if necessary, the small diameter end mill, the small spiral angle milling cutter, the stratified milling and the cutting width and so on are reduced to reduce the cutting belt Power.
Magnet-assisted clamping method has a certain versatility, not only for thin aluminum CNC milling, but also for plastic, rubber, PTFE and other non-magnetic materials, thin plate parts CNC milling, and can be used for grinding Non-permeable sheet parts (such as stainless steel, etc.). The method is simple and convenient, operable, and can provide reference for the production of such parts.