1 Preface
In the field of machining, there is a typical clamping method for internally threaded cylindrical rotating parts, which is to turn a threaded chuck and screw the internally threaded cylindrical rotating parts into threads of the same pitch. that the direction of the rotation force is consistent with the screwing direction of the thread to achieve the goal of tightening the machine more and more without any tightening devices.[1]This typical tightening method is widely used due to its simplicity and practicality. However, this clamping method has a huge disadvantage: as the cylindrical parts of the rotating body become tighter as they are turned, they cannot be disassembled after the turning process is completed. In desperation, the only choice is to use tools such as a pipe wrench and a buffer. with emery cloth (in order to avoid scratches on the surface of the part) for disassembly, as shown in Figure 1. Although this disassembly method can also disassemble the parts, it still cannot avoid scratching the surface of the parts. More importantly, if the parts of the cylindrical rotating body are thin-walled parts, they will be scrapped due to the deformation of the parts. This current situation has raised a new topic for skilled personnel engaged in mechanical processing: how to easily disassemble the cylindrical parts stuck on the threaded chuck without damaging the surface of the parts and ensuring that the parts are not deformed.
Figure 1 Pipe Wrench Disassembly Parts
2 Technical principles
2.1 Analysis of the structure and dimensions of the cylindrical parts of the rotating body
The parts of the cylindrical rotating body are shown in Figure 2. The material is 35CrMnSi, the quenched hardness is 40~45HRC, and the internal dimensions (M120 × 2mm, φ 118
mm) has been processed, it is now necessary to turn the processing size φ 124
mm and 157
mm, the wall thickness of the cylindrical part of the rotating body is only (124-118)/2=3 (mm). If you only look at the shape of the pattern, you can use a φ118mm cylindrical chuck for positioning, and the shank tip is pressed against a homemade bit. Complete the tightening. However, because the quenched hardness of the workpiece material is 40~45HRC and the cutting force is large, cylindrical workpieces tend to slip when rotating on the cylindrical chuck during processing, causing cutting or affecting φ 124.
dimensional accuracy of mm, so the parts of the cylindrical rotating body shown in Figure 2 are more suitable for positioning and tightening using the M120 × 2mm thread function.[2]。
2.2 Typical design of threaded mandrel tooling
Typical threaded chuck tooling is shown in Figure 3. Clamped by a self-centering chuck, the cylindrical portion of the rotating body is screwed into typical threaded chuck tooling until the end face of the thread is in full contact with the axial positioning surface, and the tip of the tail is pressed against the self-made end cap for turning.
The spindle is a right hand thread. When the lathe spindle rotates forward, the force direction of the turning tool is exactly the thread tightening direction. This strength condition allows for natural tightening during the turning process. The greater the force exerted on the turning tool, the more the threaded end surface of the cylindrical part of the rotating body is in contact with the axial positioning surface, which fully guarantees 157.
The machining precision of mm size overcomes the slippage phenomenon caused by the high hardness of the workpiece material and the large cutting force.
a) Three-dimensional diagram
b) Two-dimensional diagram
Figure 2 Parts of the cylindrical rotating body
Figure 3 Typical threaded mandrel tooling
After turning, it is very difficult to remove the workpiece from the threaded chuck because the threaded end surface of the cylindrical part of the rotating body is in very close contact with the axial positioning surface and the surface of the workpiece is smooth. If the dimensional accuracy of the cylindrical parts of the rotating body is not high, the pipe wrench + emery cloth method can be used to violently disassemble them. On the contrary, the disassembly problem has become the most difficult problem affecting batch filming.
2.3 Design of new threaded mandrel tooling
As shown in Figure 4, the design idea of the new threaded spindle tooling is to add a removable spindle nut on the basis of the typical threaded spindle tooling. Its main function is to assist in the disassembly of parts of the cylindrical rotating body. Before turning, screw the removable nut of the threaded lock cover shown in Figure 5 into the removable nut of the new threaded chuck and tighten it until the threads of the threaded lock cover stop.
mouth, which fits tightly with the thread stop of the new threaded spindle and is clamped by the self-centering chuck. Screw the cylindrical part of the rotating body into the self-tightening thread of the new threaded spindle until the end face of the thread is aligned axially. With the threaded locking cover, the locating surfaces are in full contact and the tail tip is pressed against the self-made bit to rotate.
Figure 4 New Threaded Chuck
1—Claw Clamping Surface 2—Spindle Thread Stop
3—Removable threads on spindle 4—Self-tightening threads on spindle
Figure 5 Threaded Lock Cover
1—Key hole 2—Axis locating surface
3—Threaded stop of locking cover 4—Removable nut of locking cover
Due to the role of the thread stopper of the thread lock cap and the thread stopper of the new threaded spindle, it is ensured that the axial positioning surface of the thread lock cap is in a fixed position after each tightening , acting like a typical thread. spindle The role of the end face of the thread plays a role of axial positioning, thus fully ensuring 157
machining precision of size mm.
The removable spindle thread of the new threaded spindle and the removable nut of the threaded lock cover are designed as left-hand threads. When the cylindrical rotating part is screwed into the new threaded spindle tooling, its threaded end face is positioned axially with it. Threaded lock cover covers completely. When tightening continues after contact, the direction of the tightening force is the same as the direction of rotation of the left-hand thread, which has the effect of tightening the thread-locking cover more and more while maintaining the position of the thread locking cover. unchanged, ensuring stable rotation of the part, as shown in Figure 6.
Figure 6 Sectional view of the new threaded mandrel tooling
After finishing turning, insert the wrench into the key hole of the threaded lock cover and loosen the threaded lock cover. At this time, the threaded end face of the cylindrical rotating body part is not stressed and the cylindrical rotating body part can be. easily removable.
2.4 Wire clamping device of any size
If several batches of cylindrical rotating parts with different thread diameters appear in production, several new threaded chuck tools need to be prepared, and repeated disassembly, alignment and adjustment of tools will also increase the positioning caused by multiple tightening and will bring many quality and unnecessary errors. problems progressing towards production.
If the new threaded mandrel is replaced with the tapered mandrel shown in Figure 7 and the tapered hole sleeves of different thread sizes shown in Figure 8 are assembled on the tapered mandrel and tightened with screw washers, due to repeatability of taper fit, extremely high positioning accuracy[3]multiple disassembly and assembly of taper hole rings will not cause repeated clamping errors, so the thread clamping device of any size shown in Figure 9 can well solve the problem of processing cylindrical rotating parts with different thread diameters.
Figure 7 Tapered Chuck
Figure 8 Tapered Hole Sleeve
Figure 9 Wire clamping device of any size
The assembly principle of tightening wires of any size is shown in Figure 10.
Figure 10 Principle of assembly of wire clamp of any size
3 Conclusion
This article focuses on the practical aspect. By gradually introducing typical threaded chuck tools, new threaded chuck tools and thread tightening devices of all sizes, it fully demonstrates the wisdom of skilled personnel in manufacturing.
Cylindrical rotating body parts are very common in the production and manufacturing process. If it is impractical to disassemble the parts due to threaded tightening, you can learn from the methods presented in this article and make slight modifications to solve similar problems.
Daguang focuses on providing solutions such as precision CNC machining services (3-axis, 4-axis, 5-axis machining), CNC milling, 3D printing and rapid prototyping services.
