How to Select Clamps for CNC Machine Tools?

Why does the same machine tool have several times the difference in production efficiency?

The conclusion is that the clamps used for CNC machine tools are not suitable, which greatly reduces the production efficiency of CNC machine tools.

The following will describe the reasonable selection and application of CNC machine tool clamps.

How to improve the utilization of CNC machine tools?

Through technical analysis, the use of clamps has a lot to do with it.

According to incomplete statistics, the proportion of unreasonable selection of clamps for domestic CNC machine tools is as high as 50%. By the end of 2018, there were nearly one million CNC machine tools in China, which means that more than 500,000 CNC machine tools had “downtime” due to improper clamp selection or improper application.

From another point of view, there is a lot to be done in the selection and application of CNC clamp, because it contains considerable potential economic benefits.

CNC Machine Tools Clamps

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.

In order to improve production efficiency, we must find ways to shorten production (preparation / waiting) time.

Three types of clamps in small-scale production of CNC machine tools can be given priority

Combination clamp

The combination clamp is also called “building block clamp”, which consists of a series of clamp components with standardized design,  different functions, different specifications and sizes.

Customers can quickly assemble various types of machine tool clamps like “building blocks” according to processing requirements.

Because the combined clamp saves the time of designing and manufacturing, greatly shortens the production preparation time, and thus effectively shortens the small batch production cycle, which improves the production efficiency.

In addition, the combined clamp also has the advantages of high positioning accuracy, large clamping flexibility, repeated use, energy and material saving, as well as low use cost.

Therefore, small batch processing, especially when the shape of the product is more complicated, the use of combined clamps is a priority.

Combined precision flat pliers

The combined precision flat pliers actually is ‘assembly part’ in the combination clamp.

Compared with other combined clamp components, it has more versatility, higher standardization, easier usage, and more reliable clamping, so it has been widely used all over the world.

The combined precision flat pliers have the advantages of quick installation (removal), quick clamping, etc., so it can shorten production preparation time and improve small batch production efficiency.

At present, the clamping range of combined precision flat pliers commonly used in the world is generally within 1000mm, and the clamping force is usually within 5000Kgf.

Smooth clamp base

There are not many applications of smooth clamp bases in China, but they are widely used in those industrial developed countries such as Europe and the United States.

In fact, it is the fine blank of the clamp base after finishing machining. The positioning connection part of the component and the positioning surface of the part on the clamp has been finished.

Users can make special clamps according to their actual needs.

It should be noted that the combined precision flat pliers mentioned here are not old-fashioned machine vise.

Old-fashioned machine vices have a single function, low manufacturing accuracy, short service life and cannot be used in groups.

They are not suitable for use on CNC machine tools and machining centers.

The combined precision flat pliers mentioned here are a series of new type flat pliers which originated from industrial developed countries such as Europe and the United States and are specially designed for the characteristics of CNC machine tools and machining centers.

This type of product has the characteristics of large clamping flexibility, high positioning accuracy, fast clamping, and can be used in groups.

It is especially suitable for CNC machine tools and machining centers.

Electric permanent magneticholding clamp

Electromagnetic permanent magnetic-holding clamp is a new type of clamp designed by using new permanent magnet materials such as neodymium iron boron as the source of magnetic force and using modern magnetic circuit principles.

A large number of machining practices have shown that the electromagnetic permanent magnetic-holding clamp can greatly improve the comprehensive machining efficiency of CNC machine tools and machining centers.

Its clamping and releasing process only takes about 1 second, thus greatly reducing the clamping time.

The positioning elements and clamping elements of conventional machine tool clamps take up a lot of space, while electromagnetic permanent magnetic-holding clamps do not have these space-consuming components.

Therefore, compared with conventional machine tool clamps, the clamping range of  electromagnetic permanent magnetic-holding clamps is larger, which is conducive to making full use of the table and machining stroke of the CNC machine tool, and is beneficial to improving the comprehensive machining efficiency of the CNC machine tool.

The suction force of the electromagnetic permanent magnetic-holding clamps is generally between 15 to 18Kgf / cm2, so it must be ensured that the suction force (clamping force) is sufficient to resist the cutting force.

In general, the adsorption area should not be less than 30cm2, that is, the clamping force is not less than 450Kgf.

CNC machine tool clamps 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 changing.

The “workpiece clamping time” of traditional manual machine tool clamps can reach 10-30% of the large batch processing cycle.

In this way, “workpiece clamping” has become a key factor affecting production efficiency, and it is also a key object of machine tool clamps “potential tapping”.

Therefore, special clamps with fast positioning and clamping (releasing) should be used for large-scale processing. The following three types of machine tool clamps can be given priority:

Hydraulic / pneumatic clamp

Hydraulic / pneumatic clamp is a special clamp that uses hydraulic or pneumatic components as the power source to realize the positioning, support and compression of the workpiece through hydraulic or pneumatic components.

It can accurately and quickly determine the mutual position between the workpiece, the machine tools and the cutting tools.

The position accuracy of the workpiece is guaranteed by the clamp, and with the high machining accuracy, the fast positioning and clamping process, which greatly saves the time of 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 clamps make them suitable for the use in CNC machine tools, machining centers, and flexible production lines, and also are particularly suitable for large-scale processing.

Electric permanent magnetic-holding clamp

The electric permanent magnetic-holding clamp has the advantages of fast clamping, easy multi-station clamping, multi-face processing in one clamping, stable and reliable clamping, energy saving and environmental protection, as well as automatic control.

Compared with conventional machine tool clamps, electric permanent magnetic-holding clamps can greatly shorten the clamping time, reduce the number of clamping times, and improve clamping efficiency.

Therefore, they are not only suitable for small batch production, but also for large batch production.

Smooth clamp base

The smooth clamp base can effectively shorten the cycle of manufacturing special clamps and reduce production preparation time, so it can shorten the cycle of mass production as a whole and improve production efficiency.

Meanwhile, it can reduce the manufacturing cost of special clamps.

Therefore, the smooth clamp base is particularly suitable for mass production with tight cycles.

Use clamps properly and tap the potential of the equipment.

Experience has shown that, in order to improve the machining efficiency of CNC machine tools, it is not enough to “select” the correct CNC machine tool clamps, we must also work hard to “use” the CNC machine tool clamps well.

How to use CNC machine tool clamps

Here are three common methods which will teach you how to use the machine tool clamps:

Multi-station method

Basic principle:

By clamping more than one workpiece at a time, to shorten the unit clamping time and to extend the tool effective cutting time.

Multi-station clamps are clamps with multiple positioning and clamping positions.

With the development of CNC machine tools and the need for users to improve production efficiency, multi-station clamps are now increasingly used. Multi-station design is becoming more and more common in the structural design of hydraulic / pneumatic clamps, combined clamps, electric permanent magnetic-holding clamps and combined precision flat pliers.

Group usage

Putting the same clamps on the same workbench can also achieve the purpose of “multi-station” clamping.

The clamps involved in this method should generally undergo “standardized design and high-precision manufacturing”, otherwise it will be difficult to meet the requirements of the CNC machine tool process.

The group usage 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 clamps can be used independently to achieve multi-piece clamping, and they can also be used in combination to achieve large-scale workpiece clamping.

Local quick change method

The local quick change method is to quickly change parts (positioning elements, clamping elements, tool setting elements, and guide elements) of a CNC machine tool clamp to achieve the purpose of quick function changing  or the clamp usage.

For example: Quick-change combination flat mouth tongs can change the clamping function by quickly changing the jaws, such as changing from clamping square material to clamping bar material.

It is also possible to change the clamping mode by quickly replacing 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 clamp, and it’s advantage is obvious in small batch production.

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