Reasonable selection and application of CNC machine tool fixture

The same machine tool, why the production efficiency is several times different? The conclusion is that the fixtures selected for CNC machine tools are not suitable, which greatly reduces the production efficiency of CNC machine tools. This paper describes in detail the rational selection 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 lot to do with it. According to incomplete statistics, the proportion of unreasonable fixtures for CNC machine tools in domestic enterprises is as high as 50% or more. By the end of 2010, the number of CNC machine tools in China was nearly one million units, which means that there are more than 500,000 CNC machine tools that have been “failed” due to unreasonable selection or improper application of fixtures. There is a lot of work to be done on the selection and application of CNC machine tool fixtures, because it contains considerable potential economic benefits.

Proper selection of fixture types is the basis for efficient machining

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

CNC machine tool fixture suitable for small batch production

Small batch production cycle = production (preparation / waiting) time + workpiece processing time Because the "workpiece processing time" is short in small batch production, the length of "production (preparation / waiting) time" has a crucial impact on the processing cycle. . In order to increase production efficiency, it is necessary to find ways to shorten production (preparation/waiting) time.

The following three types of small-volume production of CNC machine tool fixtures are recommended:

Combined fixture

The combination fixture is also called “building block fixture”. It consists of a series of machine tool fixture components with standardized design, different functions and different specifications. Customers can quickly assemble various kinds of tools like “building blocks” according to processing requirements. Type of machine tool holder. Since the combined jig eliminates the time required for designing and manufacturing special jigs, the production preparation time is greatly shortened, thereby effectively shortening the small-batch production cycle, that is, improving the production efficiency. In addition, the combined fixture also has the advantages of high positioning accuracy, large clamping flexibility, repeated use of the cycle, manufacture of energy-saving materials, and low cost of use. Therefore, small batch processing, especially when the shape of the product is more complicated, the combination fixture can be preferred.

Precision combination pliers

Precision combination pliers are actually “combined parts” in the combination fixture. Compared with other combination fixture components, they are more versatile, more standardized, easier to use, and more reliable. Therefore, they have been obtained globally. A wide range of applications. Precision combination pliers have the advantages of quick installation (disassembly) and quick clamping, which can shorten production preparation time and increase production efficiency in small batches. At present, the precision combination of the common combination pliers commonly used in the world is generally less than 1000mm, and the clamping force is generally within 5000Kgf.

It should be noted that the precision combination pliers mentioned here are not old-fashioned machines and vise. The old-fashioned machine plus vise has a single function, low manufacturing precision, can not be used in groups, and has a short service life. It is not suitable for CNC machine tools and machining centers. Used on.

The precision combination pliers mentioned here are a series of new flat pliers designed from the industrialized countries in Europe and America, specially designed for the characteristics of CNC machine tools and machining centers. These products have large clamping flexibility, high positioning accuracy and fast clamping. It can be used in groups and is especially suitable for CNC machine tools and machining centers.

Electric permanent magnet fixture

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

The clamping and loosening process of the electric permanent magnet fixture takes only about 1 second, so the clamping time is greatly shortened; the positioning component and the clamping component of the conventional machine tool fixture occupy a large space, and the electric permanent magnet fixture does not have such space. Components, therefore, compared with conventional machine tool fixtures, the installation range of electric permanent magnet fixtures is larger, which is beneficial to make full use of the worktable and machining stroke of CNC machine tools, which is beneficial to improve the comprehensive processing efficiency of CNC machine tools. The suction force of the electric permanent magnet clamp is generally 15~18Kgf/cm2, so it is necessary to ensure that the suction force (clamping force) is enough to resist the cutting force. Under normal circumstances, 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

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 "work clamping time" can reach 10~30% of the large batch processing cycle, so "workpiece clamping" becomes a key factor affecting production efficiency, and it is also the key object of the machine tool fixture "tapping potential". Therefore, it is advisable to use special fixtures for rapid positioning and rapid clamping (releasing) for high-volume processing. The following three types of machine tool fixtures are preferred:

Hydraulic/pneumatic clamp

The hydraulic/pneumatic clamp is a special fixture that uses hydraulic or pneumatic pressure as a power source to position, support and compress 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 the 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, which greatly saves the clamping and releasing of the workpiece. Time; at the same time, it has the advantages of compact structure, multi-station clamping, high-speed heavy cutting, and automatic control.

The above advantages of the hydraulic/pneumatic clamp make it particularly suitable for use in CNC machine tools, machining centers, flexible production lines, and are especially suitable for high-volume processing.

Electric permanent magnet fixture

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

Glossy clamp base

The application of the glossy fixture base is not much in China, but it is widely used in industrialized countries such as Europe and the United States. It is actually a finished blank of the finished fixture base, the positioning part of the component and the machine tool positioning part and the positioning surface of the part on the fixture have been finished. Users can process and manufacture special fixtures according to their actual needs.

The smooth surface fixture base can effectively shorten the cycle of manufacturing special fixtures and reduce the production preparation time, so that the cycle of mass production can be shortened as a whole, the production efficiency can be improved, and the manufacturing cost of the special fixture can be reduced. Therefore, the smooth surface fixture base is especially suitable for mass production with tight cycle.

Rational use of fixtures to tap the potential of equipment

Experience has shown that in order to improve the processing efficiency of CNC machine tools, it is not enough to just “select the right” CNC machine tool fixtures. It is also necessary to work hard on “using good” CNC machine tool fixtures. Here are three common methods:

Multi-station method

The basic principle of the multi-station method: by clamping multiple workpieces at a time, the unit clamping time is shortened and the effective cutting time of the tool is prolonged. A multi-station fixture is a fixture that has multiple positioning clamp positions.

With the development of CNC machine tools and the need for users to improve production efficiency, the application of multi-station fixtures is now more and more. Multi-station design is becoming more and more popular in structural design of hydraulic/pneumatic clamps, combination clamps, electric permanent magnet fixtures and precision combination pliers.

Group use

By placing the same fixtures on the same workbench, the purpose of "multi-station" clamping can also be achieved. The fixtures involved in this method should generally undergo "standardized design, high-precision manufacturing", otherwise it is difficult to meet the requirements of CNC machine tool processing.

The group use method can make full use of the CNC machine tool stroke, which is beneficial to the balanced wear of the machine tool transmission parts; at the same time, the related fixtures can be used independently, realize multi-piece clamping, and can be used in combination to realize large-size workpiece clamping.

Local quick change

The local quick change method is to quickly change the function or use mode of the fixture by quickly changing the parts of the CNC machine tool fixture (positioning component, clamping component, tool setting component and guiding component). For example, the quick-change combination pliers can change the clamping function by quickly changing the jaws, such as changing the clamping material into a clamping bar; or changing the clamping mode by quickly changing the clamping elements, for example. 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 obvious in small batch production.

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Tag: CNC machine tool Combination fixture Machine tool clamp Clamping force Cutting force

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