Improving the processing technology of stainless steel thin-wall pipe sleeves

Stainless steel thin-walled pipe sleeves are the parts that hard toprocess, and the cutting performance of this mate rial is poor. So it deforms easily during clamping and machining becauseof the thin wall, for this reason, these parts are difficult to clamp. On the basis of analyzing the parts structure and machining requirements carefully, the problem was solved by the method of improving process and designing lathe jigs. By choosingthe cutting tools and the geometric parameters rea sonably, the problems in machining are overcome and the machining quality can be ensured.

In mechanical parts, stainless steel thin-walled pipe sleeve is difficult to machine parts, especially the processing of large-scale bushing. Due to the difficulty of workpiece clamping, cutting chip breaking and tool wear, the machining is more difficult. Fig.1 is a large stainless steel sleeve made by our factory for the shipyard. It is 935mm long and 760mm in diameter, and its single side wall thickness is only 25mm. The assembly process requires that the inner hole of the bushing should be processed to the size on the lathe, and the allowance of 3-4 mm should be placed on the outer circle, and then the bushing should be dried and installed on the shaft. When the temperature drops to room temperature, the bushing on the shaft and the shaft can be processed and formed at one time. However, if the bushing inner hole is not properly clamped, it is difficult to ensure the accuracy of the inner hole size, which will not only cause considerable difficulty to the drying and installation, but also can not smoothly dry the bushing, which can not guarantee the product quality.

Fig.1 stainless steel pipe sleeve

Analysis of parts processing technology and processing difficulties

The workpiece material is 1Cr18Ni9Ti, the diameter is less than 750 mm, the wall thickness is 25 mm, and the length is 925 mm. The blank is made of two semicircular stainless steel plates by welding, and its processing technology has several characteristics.

• 1) Because of its thin wall, uneven radial force or slight force caused by vibration will produce deformation, so it is difficult to clamp;
• 2) Because the workpiece is long, the cutter bar extends nearly 1 m, and the workpiece is thin-walled, the rigidity of the tool and the workpiece is poor, so vibration is easy to occur during cutting, which affects the size and surface roughness;
• 3) Due to the high toughness of the workpiece material, YG8 lathe tool is used to process the workpiece, the material is hardened seriously, the content of Cr is high, the adhesion is easy to occur, and the thermal conductivity is low;
• 4) Because of the long longitudinal cutting size, the tool is close to 15 km when cutting, especially when finishing turning. The tool is easy to wear rapidly in the later stage, and it is difficult to ensure the shape of the inner cavity.

Process improvement

Process improvement

When machining the outer circle of the workpiece, first clamp one end of the workpiece, turn the other end of the outer circle, leave a unilateral allowance of 2 mm, turn to the other end of the 600 mm turning car, and reserve 50 mm blank steps as the axial assembly reference. Then clamp the positioning flange with the claw to process the hole of the workpiece.

Fixture design

According to the process analysis of the parts, it is the key to solve the clamping deformation. According to the characteristics of the parts easy to deform, the fixture must ensure the uniform clamping force. The fixture we designed is shown in Fig. 2. The positioning flange is positioned as shown in Fig. 3, and the clamping flange is clamped as shown in Fig. 4, which changes the traditional radial clamping to axial clamping.

Selection and grinding of cutting tools

Due to the poor rigidity of workpiece and tool bar, welding scar on blank and other factors, vibration and damage of tool tip are easy to occur in the process of processing. The selected tool is reformed from YG8 thread turning tool with better strength and impact resistance, and its geometric angle is shown in Fig.5.

Fig.5 turning tool angle

Table.1 reference values of tool geometry angle

Anterior horn/(°)	Rough turning 8～10	Fine turning 13～15
Posterior angle/(°)	3～5	4～6
Principal deflection angle/(°)	60	60
Secondary deflection angle/(°)	15	15
Blade angle/(°)	+ 5	0
Tool nose radius/mm	0 8
Width of snow trough/mm	4	2
wiper/mm		0. 56～0.6

Processing effect

Through reasonable design and fixture clamping workpiece, reasonable selection of tool geometric parameters, the workpiece can meet the requirements of the drawing, the axial deformation of the workpiece after processing is only within 0.11 mm, and the surface roughness reaches ra116 μ M. The product quality is guaranteed, and the reject phenomenon caused by unqualified surface roughness caused by vibration cutter and fine turning is solved. At the same time, through the improvement and exploration of the geometric parameters of the cutter, we have accumulated experience in the processing of several large bushing, greatly shortening the processing period.

Source: China Pipe Sleeves 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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