Turning The Inner And Outer Spherical Surfaces With Tools

1. Turning round ball with hinged cup cutter

Figure 1 shows the double-hinged cup-shaped turning tool, which is mainly used for turning shank balls. Features: The cup-shaped cutter head is connected with the cutter bar by double hinges, which can automatically adjust the center of the circular cutting edge to the same position as the center of the workpiece, thereby avoiding the influence of the height of the installed cutter on the roundness of the sphere; the cutter head adopts The cup shape can balance the cutting force during cutting and eliminate the vibration during cutting; because any cross-section of the sphere is a circle, the inner diameter of a cup-shaped knife of a certain size can be turned into a sphere larger than a certain range of the inner diameter of the cup-shaped knife. The dimensional accuracy of the ball diameter is controlled by the depth of the middle slide plate; the tool structure is simple, the operation and sharpening are convenient, and the turning efficiency is high. It only takes about 1 minute to turn a handle ball of tens of millimeters.

Figure 1 Hinged cup-shaped round turning tool

1. Cup-shaped cutter head 2. Pin shaft 3. Joint 4. Tool holder

When turning, first use an external turning tool to turn the external circle according to the ball diameter of the workpiece, and leave a small margin. Then use a cutting knife to cut a groove according to the length of the ball. The diameter of the groove bottom is about 12-18mm, which is proportional to the size of the ball. Then use the cutting knife to turn the ball to the rough shape, and finally use the hinged cup knife to set the ball blank, use the saddle and the middle sliding plate to adjust the knife's vertical and horizontal position, as shown in Figure 2, perform horizontal cutting and turning until turning Until the required size.

The SAS and VAS scores of the two groups after the intervention were lower than before the intervention, and the difference was statistically significant (P<0.05). The SAS and VAS scores of the observation group decreased more significantly after intervention, and the difference was statistically significant (P<0.05), see Table 1.

Generally, the diameter D of the knife hole is 0.5～1.5mm smaller than the diameter d of the workpiece ball. During the turning process of this tool, its working rake angle γ0e is negative, so it is mainly used to turn brittle materials, such as cloth bakelite, cast iron, cast copper and bakelite, and it can also be used to turn nylon and plastic.

Because the cutter head material is high-speed steel, the cutting speed vc should be selected according to the material being turned. When turning plastic and nylon, the cutting temperature should not exceed the softening temperature of the material (95℃ for plastic and 180～220℃ for nylon). If it is used for turning steel balls, the margin should be minimized, vc<5m/min, and cutting oil with good lubricating performance, such as vegetable oil or extreme pressure cutting oil, etc. should be used.

2. Turn the inner hemispherical surface with a floating round tool

The machining accuracy and surface quality of the spherical joint inner spherical surface on machine tools such as punches and presses are relatively high, and it is still deep in the workpiece. If the general turning method is used, it is difficult to meet the quality requirements, and it is very difficult. If the circular blade and shank shown in Figures 3 and 4 are used, processing can be easily achieved.

After the end of World War II, the wave of economic globalization promoted the reconstruction and construction of free trade ports or free trade parks in various countries. The form also extended from seaports to air ports and dry ports, realizing the close integration of transportation, processing and trade, and functionally serving for export processing. The need for trade has become an important means for developing countries to attract foreign investment, participate in the global manufacturing division of labor, and achieve rapid industrialization and modernization. In order to prevent the massive loss of domestic jobs, some developed countries also added industrial zones in the free port. For example, the United States passed the Boggs Amendment in 1950, allowing manufacturing and display activities in the foreign trade zone.

Before use, use a drill to drill the hole, and then roughly enlarge it with the inner hole turning tool to improve the accuracy of the spherical surface and reduce the machining allowance. Then insert the cutter bar into the taper hole of the tailstock of the lathe, so that the missing circle of the circular blade rests on the bottom surface of the cutter bar groove, and the blade can float left and right in the groove, move forward and tighten the tailstock, and shake the tailstock by hand The hand wheel advances the knife until the inner spherical surface of the workpiece reaches the required depth. According to different workpiece materials, different cutting speeds vc and different lubricating fluids are selected. Generally, cast iron vc=10m/min, use kerosene to lubricate; if steel vc<5m/min, use vegetable oil or extreme pressure cutting oil with good lubricating performance.

The characteristics of this kind of tool are: the manufacturing process of the blade and the tool holder is simple. The blade adopts a symmetrical cutting edge and floats in the tool holder, so that the cutting force is balanced and there is no vibration during cutting. The accuracy of the hemispherical surface of the workpiece is determined by the accuracy of the blade. The manufacturing accuracy is guaranteed; the surface roughness value of the workpiece after processing can reach Ra=1.6～0.8μm; the chisel edge at the tip of the blade is very narrow, and the bottom of the spherical surface after processing has no convex and concave defects; the operation is simple, just like drilling, even No need to drill with a drill and ream with a tool, and directly drill out the inner hemisphere. Through these years, the inner hemisphere of φ30～φ160mm has been processed successively, and the quality has reached the requirements.

3. Turn the inner spherical surface in the deep hole with a forming knife

Turning the workpiece 1 shown in Figure 5, the workpiece material is PTFE (nylon, plexiglass, cast iron and cast copper can also be processed). It is required that the connection point A between the cylindrical surface of the inner hole and the inner hemispherical surface of the hole bottom must be very smooth and free of tiny steps, which brings great difficulties to turning. Therefore, when finishing turning, it is necessary to finish turning the inner cylindrical surface and the inner spherical surface at the same time in the same pass.

In order to turn this workpiece, the forming turning tool shown in Figure 5 was produced. It is made of a circular blade (partially) made of high-speed steel and fixed on the shank with screws. When turning the inner hole, first use a drill to drill the hole, use the inner hole cutter to rough the inner hole, then use the forming turning tool to semi-finish the inner hole and inner hemispherical surface, and finally finish the cylindrical hole and inner spherical surface in one pass. In this way, the inner cylindrical hole and the inner spherical surface have no traces of the knife, and it is very smooth.

4. Conclusion

The inner and outer spherical surfaces, especially the inner and outer spherical surfaces with a certain degree of machining accuracy, are a kind of difficult-to-machine workpieces, and the turning is difficult. As long as innovative tools and corresponding tooling, it will become difficult and easy. The above three examples illustrate this problem.