Application of spring chuck
In the modern and complex manufacturing environment, if you want to maintain continuous cutting in the best condition, most factories must undergo rigorous training by machine tool manufacturers, and carefully study the processing movement principles, structural features and use skills of new equipment. Operational use. This is especially true for the top technical systems. For example, advanced machine tool control system, compilation of 5-axis machining programs for complex shape parts, etc. Fortunately, there is an opposite solution, which is some powerful, high-precision, but easy-to-operate (no special training required) and long-life process equipment that has been developed so far. The collet chuck (or spring sleeve) with high positioning accuracy relative to the chuck used to quickly locate and clamp the workpiece (or tool) belongs to this category. It has a long history of more than 100 years and a wide range of applications. The spring chuck must remain the same as the positioning datum of the workpiece (or tool) such as the spindle. Collet and workpiece (or
The relative movement between the tools will result in incorrect parts processing. The collet and the workpiece (or tool) phase
Rotation or relative axial movement will affect the consistency and geometric accuracy of the processed workpiece.
The use of the first collet is not ideal. But it did prove a fact at that time that the use of a good workpiece chuck can improve production efficiency and machining accuracy of parts. Later, Hardinge, a well-known company in the field of lathe development and manufacturing, proudly used (in 1890) the spring chuck developed by the company on their lathe in 1901 to provide workpiece positioning and clamping. Publish their product drawings and series of products developed. At that time, it was mainly developed to meet the market needs of mass production in the watch and lens manufacturing industry. It is incredible to be able to provide handy spring chucks for ordinary lathes and cam-type multi-axis automatic lathes in the early period (before 1920). This is like configuring a set of modern technology control system on the current advanced CNC lathe.
Let us look back on the past. With the continuous advancement of processing and equipment technology, in the design reform trend that requires each system to increase the production efficiency extremely, the most basic but important process equipment spring chuck as a machine tool, but There is no space and time for design. This seems to be a very strange thing.
Under the situation that the structure of the machine tool is changing rapidly, the miracle that can continue to maintain the basic structure of the original collet chuck is mainly due to its unique dexterity, exquisite structure and powerful functions, easy to use and Features such as good economy. Although the spring chuck is small, it does play a very important role in the machine tool industry. This is because it has the following strong functions:
1. It can accurately position and clamp the workpiece (or tool), and has the function of resisting torque and bearing cutting forces from multiple directions.
2. It has the function of increasing the driving force (pull force) and converting the driving force into the clamping force of the workpiece (or tool).
3. It has the function of quickly releasing the workpiece (or tool).
4. It has high repeat accuracy without reducing the processing accuracy and preventing the workpiece from being damaged.
5. It has the ability to work in a wide range of spindle speed with only minimal clamping force loss.
6. The moment of inertia is the smallest in high-speed cutting.
In general, the design and use of spring chucks is a very wide area. It needs to correspond to a variety of machine tool series, and includes products designed to reflect the different styles and characteristics of it and machine tools. So the total number is thousands. However, there is still a common misconception that the collet is only used to clamp the cylindrical workpiece blank. This is not true. In fact, it can position and clamp almost any shape of workpiece (or tool), including square or hexagonal workpieces.
The following mainly introduces the relevant factors and working principles that affect the correct positioning and clamping force of various spring chucks.
Factors affecting clamping force
The clamping force is the force exerted by the machine tool on the workpiece via the collet. The illustration in this article is a collet chuck used on a lathe to locate and clamp a workpiece. It can also be used to position and clamp a tool, a ground workpiece, or many other occasions. The external thread of the pull rod (not shown in the figure) is connected and tightened with the internal thread of the rear end of the spring chuck to generate axial tension. Then, the conical surface called the locking angle at the front end of the machine tool spindle converts the axial tension into a clamping force perpendicular to the center of the collet. Not only that, the clamping force can also be enlarged by the locking angle. According to calculations, the clamping force of the collet chuck can be enlarged by 3-4 times according to different locking angles.
The spring chuck is a simple process device, but there are many main factors that affect the clamping force. An understanding of the basic principles can help the workpiece (or tool) to be clamped correctly and to find faults quickly. The following introduces several main factors affecting the clamping force and summarized use experience:
1. Axial force. As shown in the figure, the axial pulling force exerted by the pull rod on the collet. In the use of the spring chuck, the axial force can be applied in different ways, but the principle of action is basically the same. Obviously, a large axial tension will produce a large clamping force and vice versa. Generally, the axial tension of the tie rod can be adjusted by the operator.
2. In the use of the collet chuck, the designed locking angle (or head inclination) will determine the index that the clamping force can reach after expansion, which is usually determined by the machine tool manufacturer and the collet chuck manufacturer. When the new design of the spring chuck is still being explored, the designer recommends that the user use the existing spring chuck structure in consideration of economy and reliability. The standard taper (or head inclination) has been determined at the time of design according to the machine type (such as lathe, etc.), use conditions (dynamic and static) and purpose (workpiece and tool).
3. The total friction between the workpiece (or tool) and the collet will directly affect the clamping force. A small friction value will result in a small clamping force and vice versa. The collet chuck supplier can take various measures to overcome the relative rotation or axial movement between the collet chuck and the workpiece (or tool). For example, the inner hole of the collet chuck is deliberately made into a serrated shape or the cemented carbide is micro Die is immersed in the clamping surface etc.
4. The conical surface of the spindle and the spring chuck friction at the locking angle. The friction force also directly affects the clamping force of the collet on the workpiece. If the friction force is too small, the clamping force is not enough. Too much clamping force will accelerate the wear of the collet. During use, the collet chuck should be loosened frequently to exchange workpieces. For example, when it is used on a turning machining center, a thin layer of lubricant should be sprayed on the surface of the inner hole of the collet chuck when loosened. It is better to use coolant to lubricate if possible, because the coolant provides a flushable collet, and the lubricity effect is good. In particular, regular application of coolant to the locking angle can reduce long-term wear and increase clamping force. Some more materials with better lubricating effect can also be used, including high-quality grease or wax-based materials with EP (Extreme Pressure) characteristics. It seems a little strange that some clever operators have great difficulty in processing, and when the general cooling and lubricating effect is not good, they choose the lipstick used by ladies, which is said to be effective.
5. Choosing an appropriate nominal diameter size of the collet chuck to ensure that the collet chuck fully supports the workpiece is a necessary condition for increasing the clamping force and reliable clamping to ensure high-quality processing. If the nominal hole diameter of the collet chuck is selected too large, the workpiece will only be clamped by the orifice of the collet chuck, which will cause a geometric mismatch between the outer circle of the workpiece and the inner hole of the collet chuck, thus reducing the clamping force. If the nominal hole diameter of the chuck is selected too small, only the inside of the inclination of the head will contact the workpiece. Relatively speaking, the clamping force will increase, but it will cause the problem of misalignment between the chuck and the workpiece. In a nominal size, it can clamp and position workpieces with the same nominal diameter. When selecting the nominal aperture size of the collet chuck, Hardinge recommends that the index can be changed within the range of 0.0254mm.
It is proved by cutting tests and years of actual use that the spring chuck can meet the increasing processing needs of cutting speed and has a long service life. We know that the spindle speed was generally measured at several hundred revolutions per minute more than 100 years ago. Today, the spindle speed is as high as tens of thousands of revolutions per minute, and the material removal rate is also increasing at an alarming rate. In more than 100 years of successful use, although many advanced high-end manufacturing technologies have been used, and the processing can be carried out at a high spindle speed, the existing structure of the collet chuck is still used. This is indeed rare in the manufacturing industry, and it is indeed something Hardinge should be proud of.