The correct selection of fixture type is the foundation of efficient machining　　

　　At present, the mechanical processing can be divided into two categories according to the production batch: one is single piece, multi-variety, small batch (hereinafter referred to as small batch production); the other is less variety, large batch (hereinafter referred to as large batch production). The former accounts for about 70~80% of the total output value of mechanical processing, which is the main body of mechanical processing.　　

　　CNC machine tool fixture for small batch production

　　Small batch production cycle = production ( preparation/ waiting) time + workpiece machining time　　

　　Since the "workpiece processing time" is very short in small batch production, the length of the "production (preparation/waiting) time" has a crucial impact on the processing cycle. To improve production efficiency, it is necessary to find ways to shorten the production (preparation/waiting) time.　　

　　The following are three types of CNC machine tool fixtures that can be considered for priority in small batch production:　　

　　Custom fixture　　

　　The combination fixture, also known as the "building-block fixture", consists of a series of standardized designed, functionally different, and dimensionally varied machine tool fixture elements. Customers can quickly assemble various types of machine tool fixtures, like "building blocks", according to the processing requirements. Since the combination fixture saves the time for designing and manufacturing special fixtures, it greatly shortens the production preparation time, thus effectively shortening the production cycle for small batches and improving production efficiency. In addition, the combination fixture also has the advantages of high positioning accuracy, large clamping flexibility, cycle reuse, manufacturing energy and material conservation, and low use cost. Therefore, for small batch processing, especially when the product shape is more complex, the combination fixture can be considered as a priority.　　

　　Precision combination flat-nose pliers　　

　　Precise combination of the flat-nosed pliers actually belongs to the "assembly part" in the combination fixture, which has stronger universality, higher degree of standardization, simpler use, and more reliable clamping compared to other combination fixture elements. Therefore, it has been widely used all over the world. Precise combination of the flat-nosed pliers has the advantages of quick installation (disassembly), quick clamping, etc., so it can shorten the production preparation time and improve the efficiency of small batch production. At present, the international precise combination of the flat-nosed pliers is generally used within the range of 1000mm, and the clamping force is generally within 5000Kgf.　　

　　It should be noted that the precision combination vice referred to here is not the old-fashioned machine tool vice, which has a single function, low manufacturing accuracy, cannot be used in groups, has a short service life, and is not suitable for use on CNC machine tools and machining centers.　　

　　The precision combination of the flat wrench mentioned here originated in industrial developed countries such as Europe and the United States, and is a series of new flat wrenches designed specifically for the characteristics of CNC machine tools and machining centers. This type of product has the characteristics of large clamping flexibility, high positioning accuracy, quick clamping, and can be used in groups, especially suitable for CNC machine tools and machining centers.　

　　Electromagnetic chuck　　

　　The electric permanent magnet fixture is a new type of fixture designed with modern magnetic circuit principles, using neodymium-iron-boron and other new permanent magnetic materials as the source of magnetic force. A large amount of mechanical processing practice shows that the electric permanent magnet fixture can greatly improve the comprehensive processing efficiency of CNC machine tools and machining centers.

　　The clamping and release process of the electric permanent magnet fixture only takes about 1 second, thus greatly shortening the clamping time; the locating elements and clamping elements of the conventional machine tool fixture occupy a large space, while the electric permanent magnet fixture does not have these elements that occupy space, so compared with the conventional machine tool fixture, the clamping range of the electric permanent magnet fixture is larger, which is conducive to making full use of the workbench and machining stroke of the CNC machine tool, and is conducive to improving the comprehensive machining efficiency of the CNC machine tool. The suction force of the electric permanent magnet fixture is generally between 15~18Kgf/cm2, so it is necessary to ensure that the suction force (clamping force) is sufficient to resist the cutting force, generally the adsorption area should not be less than 30cm2, that is, the clamping force is not less than 450Kgf.　　

　　CNC machine tool fixture suitable for large batch processing　　

　　Mass production cycle = waiting time for processing + processing time for workpieces + production preparation time　　

　　"Processing waiting time" mainly includes the time for workpiece clamping and tool change. The "workpiece clamping time" of traditional manual machine tool fixture can reach 10~30% of the batch processing cycle, so "workpiece clamping" has become a key factor affecting production efficiency, and it is also the focus of "potentiating" machine tool clamping. Therefore, for batch processing, it is advisable to use special fixtures with quick positioning and quick clamping (loosening), and the following three types of machine tool fixtures can be considered preferentially:　　

　　Hydraulic/pneumatic fixture　　

　　Hydraulic/pneumatic fixture is a special fixture that uses oil pressure or air pressure as the power source, and uses hydraulic components or pneumatic components to achieve the positioning, support and clamping of the workpiece.　　

　　Hydraulic/pneumatic fixtures can accurately and quickly determine the relative position between the workpiece and the machine tool, tool, the position accuracy of the workpiece is guaranteed by the fixture, and the machining accuracy is high; the positioning and clamping process is rapid, greatly saving the time of clamping and releasing the workpiece; it also has the advantages of compact structure, multi-position clamping, high-speed heavy cutting, and can achieve automatic control.　　

　　The above advantages of hydraulic/pneumatic clamping devices make them particularly suitable for use on CNC machine tools, machining centers, and flexible production lines, especially for large-scale production.　　

　　Electromagnetic chuck　　

　　The electric permanent magnet fixture has the advantages of fast clamping, easy multi-position clamping, multi-sided machining in one clamping, stable and reliable clamping, energy saving and environmental protection, and can achieve automated control. Compared with conventional machine tool fixtures, the electric permanent magnet fixture can greatly shorten the clamping time, reduce the number of clamping, and improve the clamping efficiency, so it is not only suitable for small batch production, but also for large batch production.

　　Smooth surface fixture base　　

　　Plane-facing knife device base is not yet widely used in China, but it is widely used in industrial developed countries such as Europe and the United States. It is actually a precisely machined fixture base blank, and the components and the parts on the machine tool positioning connection part and the parts on the fixture have been precisely machined. Users can machine and make special fixtures according to their own actual needs.　　

　　The plain fixture base can effectively shorten the cycle of making special fixtures, reduce the production preparation time, and thus shorten the cycle of mass production as a whole and improve the production efficiency; at the same time, it can reduce the manufacturing cost of special fixtures. Therefore, the plain fixture base is especially suitable for mass production with a tight cycle.　　

　　Reasonable use of fixtures, tapping into the potential of mining equipment　　

　　Experience shows that in order to improve the processing efficiency of CNC machine tools, it is not enough to simply "select the right" CNC machine tool fixture, but it is also necessary to work hard on "using the fixture well". The following three commonly used methods are introduced:　　

　　Multi-position method　　

　　The basic principle of multi-station method: by clamping multiple workpieces at one time, the purpose of shortening the unit clamping time and extending the effective cutting time of the tool is achieved. Multi-station fixture is a fixture with multiple positioning and clamping positions.　　

　　With the development of the machine tool and the need of the user to improve production efficiency, the application of multi-station clamping devices is becoming more and more. In the structural design of hydraulic/pneumatic clamping devices, combination clamping devices, electro-permanent magnetic clamping devices and precision combination vice, multi-station design is becoming more and more common.　　

　　Group use method　　

　　The same few fixtures can be placed on the same workbench for use, and the purpose of "multiple workstations" clamping can also be achieved. The fixtures involved in this method should generally be "standardized design, high-precision manufacturing", otherwise it is difficult to meet the requirements of the process machining on the CNC machine.　　

　　Grouping method can make full use of the travel of the CNC machine tool, which is conducive to the balanced wear of the machine tool transmission parts; at the same time, the relevant clamping devices can be used independently to achieve multi-piece clamping, and can also be used jointly to achieve the clamping of large-size workpieces.　　

　　Local quick change method　　

　　The local quick change method is to quickly change the function or usage mode of the fixture by quickly changing the local parts (positioning elements, clamping elements, tool setting elements and guiding elements) of the CNC machine tool fixture. For example: the quick-change combination vice, which can change the clamping function by quickly changing the vice mouth, such as from clamping square material to clamping round material; it can also change the clamping mode by quickly changing the clamping elements, such as from manual clamping to hydraulic clamping. The local quick change method greatly shortens the time for changing and adjusting the fixture, and the advantage is more obvious in small batch production.