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The same machine tool, why the production efficiency is several times different? The conclusion reached is that the fixtures selected for the CNC machine tools are not suitable, so that the production efficiency of the CNC machine tools is greatly reduced. The following describes the reasonable choice and application of CNC machine tool fixtures.
How to improve the utilization of CNC machine tools? Through technical analysis, the use of fixtures has a great relationship. According to incomplete statistics, the proportion of unreasonable fixtures for CNC machine tools used by domestic enterprises is more than 50%. By the end of 2010, the number of CNC machine tools in China was nearly one million. That is to say, there are more than 500,000 CNC machine tools. The phenomenon of “dwelling†has emerged due to unreasonable fixture selection or improper application; from another perspective There are many articles on the selection and application of CNC machine tool fixtures, because of the considerable potential economic benefits.
Low-volume production cycle = production (preparation/waiting) time + workpiece processing time Due to the short production time "workpiece processing time" in small batches, the length of "production (preparation/waiting) time" has a crucial influence on the processing cycle. . If you want to increase productivity, you must find ways to shorten the production (preparation/waiting) time.
1, the following recommended three types of small batch production can give priority to the CNC machine tool fixture:
Combination fixture
Combination jig is also called "block jig". It is composed of a series of fixture components with standardized design, different functions, and different sizes. The customer can quickly assemble various components according to the processing requirements like "building blocks." Type of machine fixture. Because the combined fixture eliminates the design and manufacture of special fixtures, the production preparation time is greatly shortened, thereby effectively shortening the small-batch production cycle, ie, increasing the production efficiency. In addition, the combination fixture also has the advantages of high positioning accuracy, large mounting flexibility, repeated use of the cycle, manufacturing of energy-saving materials, and low cost of use. Therefore, small batch processing, especially when the product is relatively complex in shape, can be preferentially considered using a combination fixture.
Precision combination pliers
The precision combination pliers actually belong to the “assembly†in the combination fixture, and its universality is stronger, the degree of standardization is higher, the use is simpler, and the clamping is more reliable than other combined components. Therefore, it has been obtained worldwide. Wide range of applications. The precision combination pliers have the advantages of quick installation (removal) and quick setting, which can shorten the preparation time and improve the production efficiency in small batches. At present, the commonly used precision combination flat-clamp setting range is generally within 1000mm, and the clamping force is generally within 5000Kgf.
It should be noted that the precision combination pliers mentioned here is not an old-fashioned machine with a vise. The old machine with a single vise has a single function, a low manufacturing precision, and cannot be used in groups. Its service life is short. It is not suitable for CNC machine tools and machining centers. Used on. The precision combination pliers mentioned here is a series of new type pliers that originated in industrial developed countries such as Europe and the United States. It is specially designed for the characteristics of CNC machine tools and machining centers. This type of product has a large clamping flexibility, high positioning accuracy, and fast clamping. , can be used in groups and other characteristics, especially suitable for CNC machine tools, machining centers.
Electric permanent magnet fixture
The permanent magnetic fixture is a new kind of fixture designed with the new permanent magnetic material such as neodymium iron boron as the magnetic source and using the principle of modern magnetic circuit. A large number of machining practices show that the electric permanent magnet fixture can greatly improve the overall processing performance of CNC machine tools and machining centers.
The clamping and releasing process of the electric permanent magnet clamp is only about 1 second, so the clamping time is greatly shortened; the positioning element and the clamping element of the conventional machine tool fixture occupy a large space, while the electric permanent magnet fixture does not have such space occupied. Components, so compared with conventional machine tool fixture, electric permanent magnet fixture clamping range greater, which is conducive to take full advantage of the CNC machine tool table and processing stroke, help to improve the overall processing efficiency of CNC machine tools. The attraction force of the permanent magnet fixture is generally 15 to 18 Kgf/cm2. Therefore, it must be ensured that the suction force (clamping force) is sufficient to resist the cutting force. Under normal circumstances, the adsorption area should not be less than 30cm2, that is, the clamping force should not be less than 450Kgf.
2, should be processed in large quantities CNC machine tool fixture
High-volume machining cycle = machining waiting time + workpiece machining time + production preparation time "Processing waiting time" mainly includes the time for workpiece clamping and tool change. The traditional manual machine tool fixture "workpiece clamping time" can reach 10% to 30% of the large-scale processing cycle. This "workpiece clamping" has become a key factor influencing production efficiency, and it is also a key target for "tool tapping" of machine tool fixtures.
Therefore, large-scale processing should adopt special fixtures for quick positioning and fast clamping (releasing). The following three types of machine fixtures can be given priority:
Hydraulic/pneumatic fixture
The hydraulic/pneumatic clamp uses hydraulic pressure or air pressure as the power source, and realizes the special fixture for positioning, supporting and pressing the workpiece through hydraulic components or pneumatic components. The hydraulic/pneumatic clamp can accurately and quickly determine the mutual position between the workpiece and the machine tool and tool. The position accuracy of the workpiece is ensured by the fixture, and the machining precision is high; the positioning and clamping process is rapid, and the clamping and releasing of the workpiece are greatly saved. Time; At the same time, it has the advantages of compact structure, multi-position clamping, high speed heavy cutting, and automatic control.
The above advantages of the hydraulic/pneumatic fixture make it particularly suitable for use in CNC machine tools, machining centers, and flexible production lines, and is particularly suitable for high-volume processing.
Electric permanent magnet fixture
The permanent magnet clamp has the advantages of fast clamping, easy multi-position clamping, multi-face machining in one clamping, stable and reliable clamping, energy saving and environmental protection, and automatic control. Compared with the conventional machine tool fixture, the electric permanent magnet fixture can greatly shorten the installation time, reduce the number of fixtures, and improve the clamping efficiency. Therefore, it is not only suitable for small batch production, but also suitable for mass production.
Glossy fixture base
Glossy fixture bases are not widely used in China, but are widely used in industrialized countries such as Europe and the United States. It is actually a precision-machined jig base rough blank. The positioning of the component and the machine positioning part and the positioning surface of the part on the fixture have been finished. Users can make special fixtures according to their actual needs.
The smooth fixture base can effectively shorten the cycle of manufacturing special fixtures and reduce the production preparation time, which can shorten the period of mass production and improve the production efficiency; at the same time, it can reduce the manufacturing cost of special fixtures. Therefore, the light fixture base is particularly suitable for mass production in tight cycles.
Use fixtures rationally to tap potentials
Experience has shown that, in order to improve the processing efficiency of CNC machine tools, it is not enough to “choose right†CNC machine tool fixtures, but also to work hard on the “use of†CNC machine tool fixtures.
3, the following describes the three commonly used methods:
Multi-station method
The basic principle of the multi-position method: By clamping multiple workpieces at a time, the purpose of shortening the unit clamping time and extending the effective cutting time of the tool is achieved. Multi-station fixtures have multiple fixtures that position clamped locations.
With the development of CNC machine tools and the need for users to increase production efficiency, the use of multi-station fixtures is increasing. Multi-station design is becoming more and more common in the structural design of hydraulic/pneumatic fixtures, combination fixtures, electro-magnetism fixtures, and precision combination pliers.
Group method
Using the same fixtures on the same work table can also achieve the goal of “multi-position†clamping. The fixtures involved in this method should generally be "standardized design, high-precision manufacturing," otherwise it is difficult to achieve the requirements of CNC machine tool processing.
The group use method can make full use of the CNC machine tool stroke, which is conducive to the balanced wear of the machine tool transmission components; at the same time, the related fixtures can be used independently to realize multiple pieces of clamping and can be used in combination to realize the clamping of large-size workpieces.
Local quick change method
Local quick change method is to quickly change the part (positioning element, clamping element, counter knife element and guide element) of the numerical control machine tool to achieve the purpose of rapidly changing the function or use of the fixture. For example: Quick-change combination pliers can be changed by quick-change jaws, for example, from clamping material to clamping bar material; clamping elements can also be changed by quick replacement of clamping elements, eg From manual clamping to hydraulic clamping. The local quick change method greatly shortens the time for replacing and adjusting the fixture, and the advantage is more obvious in small batch production.
At present, the mechanical processing can be divided into two major categories according to the production volume: one is a single, multiple varieties, small batches (referred to as small batch production); the other is a small variety, large quantities (referred to as mass production). The former accounted for about 70 to 80% of the total output value of machining, which is the main body of machining.