Why is the productivity of the same machine several times different? It was concluded that the CNC machine was not equipped with the right fixtures and that the productivity of the CNC machine was significantly reduced. Through technical analysis, the increase in the utilization of CNC machine tools has a great relationship with the use of fixtures.
According to incomplete statistics, domestic enterprises to choose the unreasonable proportion of CNC machine tool fixtures up to more than 50% (minor note: statistics are older), that is, more than half of the CNC machine tool fixtures due to unreasonable selection or improper application, and the emergence of the "nesting" phenomenon; from another point of view, in the selection and application of CNC machine tool fixtures have a lot to do, because it contains a considerable potential economic benefits table. In order to make the gold dust to better understand the jig, the following describes several modern CNC machine tool jigs.
1. Adjustable fixtures
Adjustable fixtures are divided into general-purpose adjustable fixtures and group fixtures (also called special adjustable fixtures). Their common feature is that they can be used for the processing of multiple parts by simply replacing or adjusting individual positioning, clamping or guiding elements, thus transforming the single small batch production of multiple parts into a "batch production" of a group of parts on the same fixture. After the product has been replaced, it can still be machined on this jig as long as the parts are of the same type. The use of adjustable fixtures can significantly reduce the number of dedicated fixtures, shorten production lead times and reduce costs due to their high adaptability and good inheritance.
2. Combination jigs
Combination jigs, also known as "building block jigs", consist of a series of standardized jig elements with different functions and sizes, which can be quickly assembled into various types of machine tool jigs as "building blocks" according to the customer's machining requirements. Since the combination fixture eliminates the need for dedicated fixture design and manufacturing time, production lead times are significantly reduced, thus effectively shortening the cycle time for small batches, i.e. increasing production efficiency. In addition, the combination fixture has the advantages of high positioning accuracy, flexible clamping, reuse, energy saving and low cost of use. Therefore, the use of combination jigs is preferred for small batch processing, especially when the product shape is complex.
3 Precision combination flat jaws
The precision combination flat jaws are actually the "joint" in the combination jig, which is more versatile, more standardized, easier to use and more reliable than other combination jig elements, and therefore are widely used worldwide. Precision combination flat jaw pliers have the advantages of quick installation (disassembly) and quick clamping, thus reducing production lead time and increasing the efficiency of small batch production. At present, the range of precision combination flat jaws used in the world is generally within 1000mm, the clamping force is generally within 5000Kgf.
It should be noted that the precision combination of flat jaws mentioned here is not the old machine plus vise, the old machine plus vise function of a single, low manufacturing accuracy, can not be used in groups, short life, not suitable for use in CNC machines, machining centers.
4. Electric permanent magnet fixtures
The electric permanent magnet jig is a new type of jig designed by applying the modern magnetic circuit principle, using neodymium iron boron and other new permanent magnet materials as the magnetic force source. A large number of machining practices show that electromagnetic permanent fixtures can significantly improve the overall machining efficiency of CNC machines, machining centers.
The clamping and unclamping process of the electro permanent magnetic (EPR) fixture takes only 1 second or so, thus significantly reducing the clamping time; the positioning elements and clamping elements of conventional CNC machine tool fixtures take up more space, while the EPR fixture does not have these space-occupying elements, so compared with conventional CNC machine tool fixtures, the EPR fixture clamping range is larger, which is conducive to making full use of the CNC machine tool table and machining stroke, conducive to improving the overall machining efficiency of CNC machine tools. The suction force of the electro-permanent magnetic fixture is generally 147~176.4N/cm2, so it must ensure that the suction force (clamping force) is sufficient to resist the cutting force, in general, the suction area should not be less than 30cm2, that is, the clamping force is not less than 4.41kN.
In modern automated production, the use of CNC machines has become more and more widespread. In CNC machining, the movement of the tool or table is programmed to be controlled in a certain coordinate position.
The following points should be noted in the design of CNC machine tool fixtures.
1. The home position (tool setting point) shall be set on the CNC machine tool fixture.
2. Tool guides are not required for CNC machine tool fixtures. This is because the machine, fixture, tool and workpiece are always in a strict coordinate relationship during CNC machining, and no guiding elements are required to determine the position between tool and workpiece.
3. CNC machines often require the machining of workpieces in several directions, so the CNC machine tool fixture should be open.
4. Adjustable jigs, assembly jigs and combination jigs shall be used on CNC machines to the extent possible. Because the workpieces machined on CNC machines are often produced in small batches, it is necessary to use flexible, short preparation time jigs.
5. The clamping of CNC machine tool fixtures shall be secure, reliable and easy to operate. The position of the clamping element should be fixed to prevent the element from touching the tool during the automatic machining process.
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