How to grasp the matching of tool and machine tool

As a tool directly or indirectly installed on the machine tool to complete the workpiece processing task, we must consider two suitability and one matching. That is, it is suitable for the selected machine tool, suitable for the selected workpiece, suitable for the processing task and matched with the machine tool. However, this article mainly starts from the matching of the tool, and talks about how to grasp the matching between the tool and the machine tool.

 

When it comes to the matching of tools and machine tools, the first thing you may think of is the matching of shape and size. Indeed, the matching of shape and size is the basis for the correct installation of the tool on the machine. Without this foundation, the tool cannot be properly mounted on the machine, and therefore no machining task can be accomplished.

 

However, this alone is not enough.

After the tool is installed on the machine tool, it needs to complete certain processing tasks. In the process of completing this machining task, it is necessary to ensure the machining accuracy, to withstand and transfer cutting force and cutting torque, to complete the bearing, transfer and export of cutting heat, and to consider possible cutting waste (chips and heads) Even the transfer of workpieces, as well as the digital transfer of modern tool parameters, etc.

 

Although some of these tasks are not common, they are indeed tasks that the tool may undertake. If we can choose the tool and consider the matching of the tool and the machine tool, it will increase our ideas for solving processing problems.

 

Guaranteeing machining accuracy, transmitting cutting force and torque, and providing channels for cutting fluid are the problems we often encounter after ensuring the matching of shape and size. For example, on machining centers, we often use a cylindrical shape (often called a straight shank) as a clamping method. Then for the cylindrical shank, in addition to the typical complete cylindrical shape, there are also some changes that add some other elements to the cylindrical shape, such as flattened straight shank (milling cutters are divided into single-cut planes and double-cut planes according to their diameters) Two kinds, common full cut plane for drilling, both are called side pressure type), beveled flat type with 2° inclination, straight shank with flat tail (commonly used for drills), straight shank with square body (commonly used for taps) and reamer) etc.

 

As far as the connection method between the tool holder and the machine tool is concerned, there are not a few that only use the cylindrical part for positioning and clamping. Various pressure angle spring sleeve systems, powerful chuck systems, hydraulic locking systems, thermal expansion clamping systems, force deformation locking systems, etc. are all used to lock cylindrical tool holders. However, each clamping method has its own advantages and disadvantages. Take the most common spring sleeve system as an example, a large pressure angle (here, the pressure angle is defined as the angle between the positive pressure of the cone surface locking and the cylinder axis), that is, a large cone angle means that the locking stroke is short, It is conducive to fast locking and loosening, but under the same locking torque, the positive pressure decomposed to the cylindrical surface is small, the resulting friction force distance is small, and the cutting force distance that can be resisted is also relatively small. It is easy to cause slippage in the tool holder, which affects the stability of the machining process and the quality of the machined surface; at the same time, the diameter of the tool holder that can be clamped by this type of chuck has a large variation range, which is conducive to reducing the inventory of spring sleeves and optimizing management. The opposite is true for small pressure angles. The spring sleeve with a small pressure angle can hold a small range of tool shank diameters, and the locking stroke during clamping is long, which is not conducive to fast clamping and loosening, but its clamping accuracy is slightly higher and the clamping force is large. Can withstand larger cutting loads.

The hydraulic locking system is an emerging clamping system, which utilizes the incompressibility of high-viscosity hydraulic oil to elastically deform the inner wall of the tool holding cavity, thereby locking the tool. The hydraulic locking system has high precision, and it is more convenient to lock and release without special equipment. The locking torque is usually better than that of the spring sleeve system, but its inner wall can only work within the range of elastic deformation. Once this range is exceeded, irreversible plastic deformation will occur on the inner wall, which will cause permanent failure of the clamping cavity of the tool holder. Therefore, flattened shanks, especially full flat shanks commonly used in drilling tools, cannot be used in hydraulic locking systems. Cavity pressure, knife handle not inserted into the bottom of the cavity, etc., are also common causes of damage to the system.

 

The thermal expansion knurled brass bushing system usually requires special equipment. Such equipment can control heating and cooling according to various predetermined modes. Non-professional heating equipment (even flame heating) may be used, but often because the temperature and heating curve cannot be well controlled, other parts of the tool holder are affected, or even change its metallographic structure, so that the system quickly fails. In addition, the tool length of the thermal expansion clamping system is difficult to adjust, and special auxiliary tools are required, which adds some troubles when multiple tools are required to work synchronously.

 

On the other hand, the tool holding method may also determine the possible value of productivity.

 

Cylindrical tool holders and hydraulic and thermal expansion are all balanced designs that can adapt to higher speeds, while the flattened clamping is a typical unbalanced design, and tool manufacturers have listed them as not recommended for high-speed cutting.

As far as the tool holder itself is concerned, when a part of the material is milled (or ground) to form a pressure surface, the center of gravity of the tool holder part does not coincide with the center of rotation of the tool. In the process of tool clamping, the flattening shank is pushed to the side that has been deviated from the center by the locking screw, and the center of gravity of the tool will further deviate from the center of rotation of the tool on the machine tool, which increases the imbalance of the tool. In addition, some users randomly add a screw after the original locking screw is damaged or lost, and often do not care about the length, etc. This behavior also adds uncertainty to the balance performance of the tool. Therefore, the flattened type (including the beveled flat) is not recommended for use at high speeds.

 

However, the flattened type is a tool holder with forced driving properties, which is more reliable under high torque than pure cylinders that rely entirely on frictional transmission. Therefore, it is more suitable for rough machining (rough machining generally has a large torque, but a low speed).