Tips for using fixtures on CNC milling machines

Why does the production efficiency of the same machine tool differ by several times? The conclusion drawn is that the fixture selected for CNC machine tools is not suitable, which significantly reduces the production efficiency of CNC machine tools. Today, we will introduce in detail the reasonable selection and application of CNC machine tool fixtures.

How to improve the utilization rate of CNC machine tools? Through technical analysis, the use of fixtures is closely related. According to incomplete statistics, over 50% of domestic enterprises choose fixtures for CNC machine tools that are unreasonable. By the end of 2010, the number of CNC machine tools in China was nearly one million, which means that over 500000 CNC machine tools had experienced "slowdown" due to improper fixture selection or application; From another perspective, there is much to be done in the selection and application of CNC machine tool fixtures, as they contain significant potential economic benefits.

Small batch production cycle=production (preparation/waiting) time+workpiece processing time. Due to the short "workpiece processing time" in small batch production, the length of "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.

Below are three types of CNC machine tool fixtures that can be prioritized for small-scale production:

Combined fixture

The modular fixture, also known as the "building block fixture", is composed of a series of standardized design, various functions, and different specifications of machine tool fixture components. Customers can quickly assemble various types of machine tool fixtures according to processing requirements, like "building blocks". Due to the combination of fixtures saving time for designing and manufacturing specialized fixtures, the production preparation time is greatly shortened, thus effectively shortening the small batch production cycle and improving production efficiency. In addition, the combination fixture also has advantages such as high positioning accuracy, large clamping flexibility, cyclic reuse, energy-saving and material saving in manufacturing, and low usage cost. Therefore, for small batch processing, especially when the product shape is complex, priority can be given to using combination fixtures.

Precision combination flat nose pliers

Precision combination flat pliers actually belong to the "assembly" of modular fixtures. Compared with other modular fixture components, they have stronger universality, higher standardization, simpler use, and more reliable clamping. Therefore, they have been widely used worldwide. Precision combination flat nose pliers have the advantages of fast installation (disassembly) and quick clamping, which can shorten production preparation time and improve small batch production efficiency. At present, the commonly used precision combination flat nose pliers in the international market generally have a clamping range of less than 1000mm and a clamping force of generally less than 5000Kgf.

It should be noted that the precision combination flat nose pliers mentioned here are not old-fashioned machine added pliers. Old machine added pliers have a single function, low manufacturing accuracy, cannot be used in groups, and have a short service life, making them unsuitable for use on CNC machine tools and machining centers. The precision combination flat pliers mentioned here are a series of new flat pliers designed specifically for CNC machine tools and machining centers, originating from developed industrial countries such as Europe and America. These products have the characteristics of high clamping flexibility, high positioning accuracy, fast clamping, and can be used in groups, making them particularly suitable for CNC machine tools and machining centers.

Electric permanent magnet fixture

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

The clamping and loosening process of the electric permanent magnet fixture only takes about 1 second, thus greatly reducing the clamping time; The positioning and clamping components of conventional machine tool fixtures occupy a large space, while the electric permanent magnet fixture does not have these space occupying components. Therefore, compared to conventional machine tool fixtures, the electric permanent magnet fixture has a larger clamping range, which is conducive to fully utilizing the working table and processing stroke of CNC machine tools, and improving the comprehensive processing efficiency of CNC machine tools. 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 cutting force. In general, the adsorption area should not be less than 30cm2, that is, the clamping force should not be less than 450Kgf.

CNC machine tool fixtures suitable for mass processing

Large batch processing cycle=processing waiting time+workpiece processing time+production preparation time "Processing waiting time" mainly includes the time for workpiece clamping and tool replacement. The traditional manual machine tool fixtures' workpiece clamping time 'can reach 10-30% of the mass processing cycle, making' workpiece clamping 'a key factor affecting production efficiency and a key target for machine tool fixtures' tapping potential'.

Therefore, it is advisable to use specialized fixtures for rapid positioning and quick clamping (loosening) in large-scale processing. The following three types of machine tool fixtures can be given priority consideration:

Hydraulic/pneumatic fixtures

Hydraulic/pneumatic fixtures are specialized fixtures that use oil pressure or air pressure as the power source to position, support, and compress workpieces through hydraulic or pneumatic components. Hydraulic/pneumatic fixtures can accurately and quickly determine the mutual position between the workpiece, machine tool, and cutting tool. The positional accuracy of the workpiece is guaranteed by the fixture, resulting in high machining accuracy; The positioning and clamping process is rapid, greatly saving time for clamping and releasing the workpiece; 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 hydraulic/pneumatic fixtures make them particularly suitable for use in CNC machine tools, machining centers, and flexible production lines, especially for large-scale processing.

The smooth fixture base can effectively shorten the manufacturing cycle of specialized fixtures, reduce production preparation time, and thus shorten the overall mass production cycle and improve production efficiency; At the same time, it can reduce the manufacturing cost of specialized fixtures. Therefore, the smooth fixture base is particularly suitable for large-scale production with tight cycles.

Reasonably use fixtures to tap into the potential of equipment

Experience has shown that in order to improve the processing efficiency of CNC machine tools, it is not enough to only "select the right" CNC machine fixture, and efforts must also be made to "use" the CNC machine fixture well.

Here are three commonly used methods:

Multi station method

The basic principle of the multi station method is to shorten the unit clamping time and extend the effective cutting time of the tool by clamping multiple workpieces at once. Multi station fixtures refer to fixtures with multiple positioning and clamping positions.

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

Group usage method

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

The group use method can fully utilize the stroke of CNC machine tools, which is conducive to balanced wear of the transmission components of the machine tool; At the same time, relevant fixtures can be used independently to achieve multi piece clamping, and can also be used together to achieve large-scale workpiece clamping.

Local quick change method

The local quick change method is to quickly replace the local parts (positioning components, clamping components, tool setting components, and guide components) of a CNC machine tool fixture, in order to achieve the goal of quickly changing the function or usage of the fixture. For example, the quick change combination flat jaw pliers can change the clamping function by quickly changing the jaw, such as changing from clamping square materials to clamping bar materials; The clamping method can also be changed by quickly replacing the clamping components, such as changing from manual clamping to hydraulic clamping. The local quick change method significantly shortens the time for replacing and adjusting fixtures, and has obvious advantages in small batch production.