Reasonable selection and design considerations of

2022-07-27
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With the rapid development of science and technology, the changing market demand and the increasingly fierce commodity competition, the replacement cycle of mechanical products is shorter and shorter, and the proportion of multi variety and small batch production is higher and higher. In order to meet the needs of this situation, a variety of new NC machine tool fixtures have emerged

why is the production efficiency of the same machine tool several times different? The conclusion is that the fixture selected for the NC machine tool is not suitable, which greatly reduces the production efficiency of the NC machine tool. How to improve the utilization of CNC machine tools? Through technical analysis, the use of fixtures has a great relationship

according to incomplete statistics, more than 50% of the domestic enterprises choose the fixture unreasonably. By the end of 2010, China had nearly onemillion CNC machine tools, that is to say, more than 500000 CNC machine tools were "idled" due to unreasonable fixture selection or improper application; From another point of view, there is much to do in the selection and application of NC machine tool fixtures, because it contains considerable potential economic benefits. The following describes several modern CNC machine tool fixtures

I. adjustable fixtures

adjustable fixtures are divided into general adjustable fixtures and group fixtures (also known as special adjustable fixtures). Their common feature is that as long as individual positioning, clamping or guiding elements are replaced or adjusted, they can be used for the processing of a variety of parts, so that the single small batch production of a variety of parts becomes the "batch production" of a group of parts on the same fixture. After the product is upgraded, as long as it belongs to the same type of parts, it can still be processed on this fixture. Because the adjustable fixture has strong adaptability and good inheritance, the use of adjustable fixture can greatly reduce the number of special fixtures, shorten the production preparation cycle and reduce the cost

II. Modular fixture

modular fixture is also called "building block fixture". It is composed of a series of machine tool fixture elements with standardized design, different functions and different sizes. Customers can quickly assemble various types of machine tool fixtures like "building blocks" according to processing requirements. Because the combined fixture saves the time of designing and manufacturing special fixture, and greatly shortens the production preparation time, it effectively shortens the small batch production cycle, that is, it improves the production efficiency. In addition, the combined fixture also has the advantages of high positioning accuracy, large clamping flexibility, especially those products that are expected to serve the aviation, nuclear power and other fields with great development potential and wide market space, recycling and reuse, manufacturing energy and material saving, low use cost and so on. Therefore, for small batch processing, especially when the product shape is complex, the use of combined fixture can be given priority

III. precision combined flat tongs

precision combined flat tongs actually belong to the "assembly" of combined fixtures. Compared with other combined fixture components, they are more versatile, more standardized, easier to use and more reliable to clamp. Therefore, they have been widely used in the world. The precision combined flat tongs have the advantages of rapid installation (disassembly) and clamping, so it can shorten the production preparation time and improve the small batch binding method. The size is 800mm × 600mm × 100mm flat sheet type test piece is the production efficiency of standard test piece quantity. At present, the clamping range of the internationally used precision combined flat tongs is generally within 1000mm, and the clamping force is generally within 5000kgf

it should be noted that the precision combined flat jaw pliers mentioned here are not old-fashioned machine added vises. The old-fashioned machine added vises have single function, low manufacturing accuracy, can not be used in groups, and short service life, so they are not suitable for use in CNC machine tools and machining centers

IV. electric permanent magnet fixture

electric permanent magnet fixture is a new type of fixture designed by using neodymium iron boron and other new permanent magnet materials as magnetic source and modern magnetic circuit principle. A large number of machining practices show that the electric permanent magnet fixture can greatly improve the comprehensive machining efficiency of CNC machine tools and machining centers

the clamping and loosening process of the electric permanent magnet fixture only takes about 1 second, so the clamping time is greatly shortened; The positioning elements and clamping elements of the conventional NC machine tool fixture occupy a large space, while the electric permanent magnet fixture does not have these elements. Therefore, compared with the conventional NC machine tool fixture, the electric permanent magnet fixture has a larger clamping range, which is conducive to making full use of the working table and processing stroke of the NC machine tool and improving the comprehensive processing efficiency of the NC machine tool. In January, 2018 (3), the company's operating income was 250 million yuan (2) 70 million yuan (2) combined processing efficiency. The suction of the electric permanent magnet fixture is generally 15~18kgf/cm2, so it must be ensured that the suction (clamping force) is sufficient to resist the cutting force. Generally, the adsorption area should not be less than 30cm2, that is, the clamping force should not be less than 450kgf

in modern automatic production, numerical control machine tools have been more and more widely used. In the process of NC machining, the movement of the cutter or worktable is controlled by the program according to a certain coordinate position

the following points should be paid attention to in the design of NC machine tool fixture:

1 The original point (tool setting point) shall be set on the fixture of the NC machine tool

2. There is no need to set the tool guide device for the NC machine tool fixture. This is because the machine tool, fixture, cutter and workpiece always maintain a strict coordinate relationship during the processing of the NC machine tool, and there is no need to determine the position between the cutter and workpiece with the guide element

3. NC machine tools often need to process the workpiece in several directions, so the fixture of NC machine tools should be open

4. Adjustable fixture, assembly fixture and combined fixture should be selected as much as possible on CNC machine tools. The application of single chip microcomputer not only reduces the equipment cost to a great extent. Because the workpiece processed on the NC machine tool is usually produced in small batches, the fixture with good flexibility and short preparation time must be used

5. The clamping of NC machine tool fixture shall be firm, reliable and easy to operate. The position of the clamping element shall be fixed to prevent the element from colliding with the tool during automatic machining

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