Turning of thin wall pipe sleeve
Due to the poor rigidity of thin-walled pipe sleeve, due to the effect of cutting force, clamping force and cutting heat, deformation is easy to occur, which affects the machining accuracy and surface roughness. Through the research of clamping mode, tool material, tool geometry angle and cutting parameters, the deformation degree of thin-walled sleeve is discussed and the appropriate turning method is found. The experimental results show that the center frame and auxiliary support are adopted for the larger thin-walled sleeve; YT15 hard close full finish turning tool, large rake angle of fine turning tool, 90 ° are adopted. With the main deflection angle and high finish turning speed, the size accuracy and surface quality of the pipe sleeve machined are quite high, which fully meet the requirements.
Thin-walled pipe sleeves are difficult to machine workpieces, and their size and shape tolerances are shown in Figure 1. The workpiece is steel, which is long, up to 500mm, with a larger diameter of Φ220mm, and the inner wall is very thin, with a wall thickness of only 7.5mm. Due to the poor rigidity of thin-walled workpieces, the following phenomena are prone to occur under the action of cutting force, clamping force and cutting heat during turning:
Fig.1 Thin wall pipe sleeve
(1) Under the action of cutting force (especially radial cutting force), it is easy to produce vibration and deformation, which affect the dimensional accuracy, shape accuracy and surface roughness of the workpiece.
(2) Under the action of clamping force, deformation is easy to occur, resulting in uneven back-grabbing and the phenomenon of knife yielding, which affects the accuracy of the workpiece. As shown in Figure 2(a), the thin-walled sleeve will become a triangle under the clamping force F of the three jaws of the three-jaw chuck; in Figure 2(b), it is deformed during clamping In this case, the inner hole of the back-cutting amount is gradually reduced in several feeds. Although the roundness of the inner hole is ensured, the wall thickness is uneven; Figure 2(c) is to remove the thin wall from the three-jaw chuck For the sleeve, after the clamping force disappears, the thin-walled sleeve returns to a round shape, while the inner hole becomes a prismatic round (arc-shaped triangle), resulting in equal diameter deformation.
(a) After the blank is clamped (b) After the inner hole is turned (c) After releasing the claw, it becomes a triangle and a circle with equal diameter deformation
Fig.2 Effect of clamping force on deformation of thin-walled sleeve
(3) Cutting heat causes thermal deformation of the workpiece. Since the workpiece is made of steel, the coefficient of thermal expansion is large, and the cutting heat has a great influence on its accuracy. In order to ensure the machining accuracy of the workpiece, we solve it from four aspects: clamping method, tool material, geometric angle and cutting amount.
Use the center frame to support and auxiliary support to clamp the workpiece
The specific steps are as follows:
(1) Use a three-jaw self-centering chuck to clamp one end of the outer circle with a length of about 10 mm, and one end with a tapered center to hold the outer circle to Φ222 (+o.1,-0) at both ends of the car. It is used for supporting center frame, as shown in Figure 3.
Fig.3 Turning out the support of the center frame on the workpiece
(2) Clamp one end with soft jaws, and support one end with center frame. Turn the two ends of the car to the total length of 500, the parallelism error of the two ends is not more than 0.02mm, and the rough and fine turning hole Φ205 (+o.25,-0), within 15mm from the end face of the workpiece, the hole is turned Φ205(+o.25,-0), and keep it coaxial.
(3) When roughing and finishing the outer circle Φ220 (-o.035,-0.15), the auxiliary support is used to improve the clamping rigidity of the workpiece, as shown in Figure 4.
(a) Clamping method (b) Auxiliary supporting structure size
Fig.4 Using auxiliary support to clamp the workpiece
Selection of tool material and geometric angle
The cutting edge of the tool is a sharp edge type, with a larger rake angle and entering angle, and a shorter wiper edge, 0.2-0.3mm. The angle of the finishing tool is shown in Figure 5, respectively: (1) External precision turning tool K=90°-93°, Kr‘=15°,a。=15°,a。’=15°,Y。=45°, the blade material is YT15.
(2) Inner hole fine turning tool. Kr=60°, Kr‘=30°, Y。=35°,a。= 15°, a。’=8°, λ5=50, the blade material is YT15.
(a) Outer circle fine turning tool (b) Inner hole fine turning tool
Fig.5 Angle selection of fine turning tool
Selection of cutting parameters
In order to reduce the vibration and deformation of the workpiece, the cutting force and cutting heat should be reduced as much as possible. Therefore, a higher cutting speed, a suitable amount of back cutting and feed rate shall be adopted, and Vc=100m/min, f=0.12mm/r, ap=0.05-0.5mm.
Source: China Pipe Sleeve Manufacturer – Yaang Pipe Industry (www.epowermetals.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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