How to improve the utilization of CNC machine tools? After the analysis of skills, the use of fixtures has a great connection. According to the response of the gold powder, there are often NC machine tools in the operation because of the unreasonable selection or improper use of fixtures, showing the phenomenon of “whole work”; from another perspective, there are many articles on the selection and use of NC machine tools Do it, because it contains considerable potential economic benefits.
1. The correct choice of fixture type is the foundation of efficient machining
Currently, machining can be divided into two categories according to the production batch: one is single, multiple, and small batch (referred to as small batch production); the other is small variety and large batch (referred to as large batch production). In the meantime, the former accounted for 70 to 80% of the total output value of machining, and was the main body of machining.
2. Suitable for small-scale production of CNC machine tool fixtures
Small batch production cycle ﹦ production (preparation / waiting) time + workpiece machining time Because the “workpiece machining time” of small batch production is very short, the length of the “production (preparation / waiting) time” has a crucial impact on the machining cycle . If you want to improve the production power, you must find a way to shorten the production (ready / wait) time.
3. The following introduces three types of small-scale production of CNC machine tool fixtures
that can be considered in priority:
1) Combined fixture
The combination fixture is also called “building block fixture”, which is composed of a series of standardized machine tool jig and fixture components with different functions and different standard sizes. Customers can quickly assemble the building blocks like “building blocks” according to machining requirements. Various types of machine tool fixtures. Because the combination fixture saves the planning and production time of the special fixture, greatly shortens the production preparation time, and therefore effectively shortens the small batch production cycle, which improves the production power. In addition, the combined fixture also has the advantages of high positioning accuracy, large clamping flexibility, repeated use, energy saving and material saving, and low cost. Therefore, small batch machining, especially when the shape of the product is more complicated, you can give priority to the use of combined fixtures.
2) Fine combination flat pliers
The fine combination flat pliers actually belong to the “combination” in the combination fixture. Compared with other combination fixture components, it is more versatile, more standardized, simpler to use, and more securely clamped, so it has been widely used on a global scale. Use. The fine combination flat-nose pliers have the advantages of rapid device (disassembly) and rapid clamping, so it can shorten the production preparation time and improve the production power of small batches. At present, the clamping scale of fine combination flat-nose pliers commonly used in the world is usually within 1000mm, and the clamping force is usually within 5000Kgf.
It should be noted that the fine combination flat pliers mentioned here are not the old machine and vise. The old machine and vise have a single function, low manufacturing accuracy, cannot be used in groups, and have a short service life. They are not suitable for CNC machine tools and machining bases. Use.
The fine combination flat pliers mentioned here are a series of new flat pliers originated from industrial developed countries such as Europe and the United States. They are specially designed for the characteristics of CNC machine tools and machining bases. Such products have large clamping flexibility, high positioning accuracy, and clamping diseases. Speed, can be used as a group, especially suitable for CNC machine tools, machining bases.
3) Electro permanent magnet fixture
Electromagnetic permanent magnet fixture is a new type of fixture designed with new permanent magnet materials such as neodymium iron boron as the source of magnetic force and using modern magnetic circuit principles. Many machining practices indicate that the permanent magnet fixture can greatly improve the inductive machining efficiency of CNC machine tools and machining bases.
The clamping and releasing process of the permanent magnet fixture only takes about 1 second, which greatly shortens the clamping time; the positioning elements and clamping components of conventional machine tool fixtures take up a lot of space, and the permanent magnet fixture does not have these occupied spaces. Compared with conventional machine tool fixtures, the clamping scale of electro-magnetic permanent magnet fixtures is larger, which is conducive to making full use of the working table and machining stroke of NC machine tools, and to improve the inductive machining efficiency of NC machine tools. The suction force of the permanent magnet clamp is usually 15 ~ 18Kgf / cm2, so it is necessary to ensure that the suction force (clamping force) meets the resistance to cutting force. Under normal circumstances, the suction area should not be less than 30cm², that is, the clamping force is not less than 450Kgf.
4. CNC machine tool fixture suitable for large-scale machining
Large batch machining cycle = machining waiting time + workpiece machining time + production preparation time “Machining waiting time” mainly includes the time of workpiece clamping and tool replacement. The traditional manual machine tool fixture “workpiece clamping time” can reach 10 ~ 30% of the large-scale machining cycle. In this way, “workpiece clamping” has become a key factor affecting the output power, and it is also a key object of machine tool fixture “potential tapping”. Therefore, special fixtures for rapid positioning and rapid clamping (releasing) should be selected for large-scale machining. The following three types of machine tool fixtures can be given priority consideration:
1) Hydraulic / pneumatic clamp
Hydraulic / pneumatic clamp is a special clamp that uses hydraulic or pneumatic as the power source to complete the positioning, support and compression of the workpiece through hydraulic or pneumatic components.
Hydraulic / pneumatic fixture can accurately and quickly determine the orientation of the workpiece with the machine tool and the tool. The azimuth accuracy of the workpiece is guaranteed by the fixture and the machining accuracy is high. The positioning and clamping process is agile, which greatly saves clamping and releasing the workpiece Together, it has the advantages of compact structure, multi-station clamping, high-speed heavy cutting, and automatic control.
The above advantages of hydraulic / pneumatic fixtures make them particularly suitable for use in CNC machine tools, machining bases, and flexible production lines, and are particularly suitable for large-scale machining.
2) Electro permanent magnet fixture
Electric permanent magnet fixture has fast clamping, easy to complete multi-station clamping, one-sided clamping can be processed on multiple sides, the clamping is stable and reliable, energy saving and environmental protection, and automatic control can be completed. Compared with conventional machine tool fixtures, electromagnetism fixtures can greatly shorten the clamping time, reduce the number of clamping times, and improve the clamping power, so it is not only suitable for small batch production, but also for large batch production.
3) Grip base
Smooth surface fixture bases are not widely used in China, but they are widely used in industrialized countries such as Europe and the United States. In fact, it is the finished blank of the fixture base, and the components and the machine tool positioning interface and the positioning surface of the part on the fixture are now finished. Users can make special fixtures according to their own actual needs.
The smooth fixture base can effectively shorten the cycle of manufacturing special fixtures and reduce the production preparation time. Therefore, it can shorten the cycle of mass production as a whole and improve the production power; together, it can reduce the manufacturing cost of special fixtures. Therefore, the smooth fixture base is especially suitable for mass production with tight cycle.
5. Reasonable use of fixtures to explore equipment potential
Experience indicates that in order to improve the machining efficiency of CNC machine tools, it is not enough to “select” the correct CNC machine tool fixtures. We must also work hard to “use” the CNC machine tool fixtures properly.
Here are three commonly used methods:
1) Multi-station method
The basic principle of the multi-station method: After clamping multiple workpieces at one time, the intention is to shorten the unit clamping time and extend the useful cutting time of the tool. Multi-station fixtures are fixtures with multiple positioning and clamping orientations.
With the development of a CNC machine tool and the needs of users to improve the output power, the use of multi-station fixtures is increasing. Multi-station planning is becoming more and more widespread in the structural planning of hydraulic / pneumatic fixtures, combined fixtures, electro-permanent magnet fixtures and fine combined flat pliers.
2) Group application method
Put the same fixtures on the same workbench for the same purpose of being able to complete the “multi-station” clamping. The fixtures touched by this method should usually undergo “standardized planning and high-precision production”, otherwise it is difficult to reach the needs of CNC machine tool machining.
The group application method can make full use of the stroke of the CNC machine tool, which is beneficial to the balanced wear of the transmission parts of the machine tool. A related fixture can be used independently to complete the clamping of multiple pieces, or it can be used in combination to complete the clamping of large standard workpieces.
3) Partial quick change method
Part of the quick change method is to quickly change the parts of the CNC machine tool fixture (positioning components, clamping components, tool setting components and guide components), and reach the intention of quickly changing the function or application mode of the fixture. For example: quick-change combination flat pliers, which can change the clamping function through rapid replacement of the jaws, such as changing from clamping square material to clamping bar material; also can change the clamping method by quickly replacing the clamping element. For example, from manual clamping to hydraulic clamping. Part of the quick change method greatly shortens the time for replacing and adjusting the fixture, which has obvious advantages in small batch production.