Study on processing technology of 316L stainless steel flange

Aiming at the problems of the flange parts in the first piece trial cutting process, such as the parts precision is not up to standard, the efficiency is low, and it is impossible to batch. The main reasons for the above problems are analyzed. At the same time, it is proposed that the optimization of processing technology and the design of special fixture are the main ways to solve the problems. The practice shows that the improved processing technology can improve the processing efficiency of parts by about 75%, and the qualified rate of products can reach 100%, which provides certain reference value for the processing of similar parts.

Flange is mainly used for the connection between two equipment or two shaft parts. Flange connection is an important connection method of pipeline construction, which is easy to disassemble and can bear large pressure. Figure 1 shows the flange part drawing of a certain type of reducer, with a monthly output of 30000 pieces, and its outline size is Φ 52mm × 18mm. During the first trial cutting process of the parts, it is found that the following three parts are not easy to meet the requirements of the drawing:

  • (1) Fig.1 the roughness of arc surface and fillet at enlarged position Ra0.4;
  • (2) The center line of Φ 24 + 00.05mm and Φ 12.2mm holes form an included angle of 12 ° with the horizontal;
  • (3) The top of the Φ 34mm cylindrical surface is inclined, and has a position relationship with the 4 – Φ 4.5mm hole. In view of the above situation, through the optimization of processing technology, the analysis and research of machine tools, fixtures, processing methods, etc., put forward the methods to solve the above problems, to meet the requirements of mass production.

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Figure.1 316L stainless steel flange parts

Analysis on the first trial cutting of flange parts

Table.1 chemical composition of SS316L stainless steel

C Si Mn P S Cr Ni Mo
≤0.030 ≤0.75 ≤2.00 ≤0.040 ≤0.030 16.5 11 2.1

According to the processing requirements, the blank of flange parts is made of stainless steel 316L with diameter of 55mm × 20mm. Its chemical composition is shown in Table 1. The material has the characteristics of corrosion resistance, high temperature resistance, high strength and good cutting performance. It is widely used in mechanical equipment. The machining elements of flange in the part drawing mainly include turning the outer circle, boring, milling plane and drilling, which are roughly divided into turning and milling parts. Firstly, turning the right outer circle of Φ 34mm and Φ 52mm is completed on the CNC lathe, and then turning around and clamping to complete the machining of Φ 33mm outer circle, Φ 28.3mm and Φ 15.68mm holes; secondly, the machining of r1.7 circular arc groove, Φ 24 + 00.05mm and Φ 12.2mm hole, right inclined plane and 4 – Φ 4.5mm hole is completed on the vertical machining center. The machine models are V2 CNC lathe with inclined bed produced by Shenyang Machine Tool Works and haas-vf1 vertical machining center of America. The first trial cutting process is shown in Table 2.
It can be seen from table 2 that in the process of the first piece trial cutting, whether it is a CNC lathe or a machining center, the three jaw chuck is used as the fixture. Firstly, the CNC lathe is used to process the right outer circle and step, and then the left outer circle and inner hole are processed by turning the head. Secondly, the three jaw chuck is used to clamp the right outer circle on the machining center to mill the arc groove and drill holes, and then install the reverse side Finally, the inner groove is machined on the CNC lathe. After testing, it is found that the roughness value of the circular arc surface of the inner hole r0.5 and r1.7 on the left side of the part is too high, and part of the circular arc is not processed completely; the holes of Φ 24 + 00.05mm and Φ 12.2mm are not formed with the axis line 12 ° angle; the space position relationship of the right slope does not conform to the drawing specifications, the whole part processing time is too long, and the efficiency is too low, which can not meet the requirements of mass production of customers.

Problem analysis 

In view of the above problems in the process of processing, it is analyzed one by one.

The surface of the left arc segment is not smooth, and the roughness value is too high

According to the first trial cutting process and test results, the arc segment on the left side of the part shown in Fig.2 is mainly composed of two r1.7 and three r0.5. The processing sequence is analyzed. Among them, the three r0.5 are processed by boring cutter on the CNC lathe, and then one r1.7 arc groove is milled by ball end milling cutter on the machining center, and finally R1 at 5 places is processed by arc inner groove cutter on CNC lathe 7 circular groove. It can be seen from the above-mentioned processing process that no two and four r0.5 arcs are involved, so two r0.5 arc parts are not processed completely. At the same time, when two r1.7 arcs are processed in the machining center and CNC lathe respectively, the tool mark burr will inevitably be generated, and the subsequent processing is not conducted, which is the main reason for the high roughness value of the arc segment.
Table.2 first piece trial cutting process

Number

Tool

Processing content

Schematic diagram of machining on machine tool

Machine tools and Fixtures

1

Holding blank on CNC lathe

Three jaw chuck of CNC lathe

2

Cylindrical knife

Right outer circle (Φ 34 and Φ 52)

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3

Cylindrical knife

Turn around to clamp the outer circle of Φ 34mm and process the outer circle of Φ 33mm

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4

Boring cutter

Φ 28.3 and Φ 15.68 holes

5

Clamping workpiece with three jaw chuck on Machining Center

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Three jaw chuck of machining center

6

Ball point knife

R1.7 circular groove

7

Twist drill

4 – Φ 4.5 hole

8

Reverse clamping at Φ 52mm

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9

End mill

Milling slope

10

Twist drill

Bottom hole of Φ 24mm and Φ 12.2mm holes

11

End mill

Φ 24mm and Φ 12.2mm holes

12

Clamp the outer circle of Φ 34 on CNC lathe

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Three jaw chuck of CNC lathe

13

Groove cutter

R1.7 inner groove

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Figure.2 requirements for roughness of left arc

The spatial position relationship between the hole and the inclined plane is incorrect

On the right side, the Φ 24 + 00.05mm and Φ 12.2mm holes and inclined planes are mainly completed on the machining center. Since the holes of Φ 24 + 00.05mm and Φ 12.2mm form an included angle of 12 ° with the axis line, the inclined plane and the inclined plane are mainly completed on the machining center The 4 – Φ 4.5mm hole has spatial correspondence. The three jaw chuck installed on the worktable can not determine the position of each installation of the parts. At the same time, the three jaw hydraulic chuck has been used for a long time. With the wear of the chuck, the three claws will appear bell mouth shape, and the three claws will gradually deviate from the center of the machine tool spindle, resulting in the increase of the centering error of the three claws and the increase of the form and position tolerance of the workpiece, resulting in the failure of the workpiece to reach the accuracy requirement. After research, the design of special fixture can effectively avoid the above problems.

Too long time for parts processing

According to the above processing procedures, it takes about 20 minutes to complete the processing of a part, and the processing efficiency and economic benefits are too low. The main reasons are that the processing procedures are too scattered and the parts are clamped too many times.

Improvement measures

According to the above analysis, optimizing processing technology and designing special fixture are the main methods to solve the above problems.

Add finishing process

As shown in Fig. 3, the original process is completed in the sequence of finishing the inner hole on the CNC lathe → milling the circular groove in the machining center → machining the groove in the circular arc by the CNC lathe. At this time, a finishing boring cutter is added to the NC lathe for finishing. According to the tool path shown in Fig. 4, all arc surfaces can be machined, and the roughness value of the arc surface can meet the requirements of the drawing.

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Fig.3 tool path of finish machining

Design special fixture

(1) Fixture for machining center

In view of the problem of the spatial position relationship between the hole and the inclined plane in the above-mentioned machining, a special fixture should be designed according to the structural characteristics of the parts to solve the problem. The fixture structure diagram is shown in Fig. 4, which is composed of 1 worktable, 2 bottom plate, 3 T-shaped screw, 4 support seat, 5 screw, 6 flange parts, 7 positioning pin, 8 screw and other structures. The fixture base plate is installed in the machining center, and the worktable is fixed by T-slot. The top surface of the support seat is installed on the bottom plate at an angle of 12 degrees to the horizontal. The support seat ensures the spatial position of the parts. When the parts are clamped, the positioning pin is used to fix the position, and then the other three screws are tightened. During the part processing, the fixing pin is taken out, and the 12 ° inclined plane is first milled, and then the hole is milled. At the same time, it can ensure that the holes of Φ 24 + 00.05mm and Φ 12.2mm form an angle of 12 ° with the axis line, and the spatial position relationship between the inclined plane and the 4 – Φ 4.5mm hole can greatly improve the processing efficiency and precision of the parts.
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1. Worktable; 2. Base plate; 3. T-shaped screw; 4. Support seat; 5. Screw; 6. Flange parts; 7. Locating pin; 8. Screw
Fig.4 fixture of machining center

(2) Fixture for CNC lathe

In the last stage of the original process, the three jaw chuck soft claw is directly used to clamp the circular groove by using the groove cutter on the CNC lathe. Because the clamping distance is too short, it is easy to offset, which can not guarantee the machining accuracy of the parts. At the same time, the clamping needs a long time to correct, so the efficiency is low. As shown in Fig.5, three copper blocks are welded at the front end of the soft claw of the three jaw chuck, and then self boring is carried out to produce arc step shape. During clamping, as long as the a surface of the part is fast pressed close to the step, accurate positioning can be achieved without deviation, and alignment is not required. Therefore, the efficiency is greatly improved. Meanwhile, the copper block can protect the surface of the processed parts, and the parts will not be damaged due to the clamping jaw clamping.

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Figure.5 fixture of NC lathe
3.3 new processing technology scheme
Based on the above improvement measures, the trial cutting process is adjusted, and the process table is shown in Table 3.
Table 3 processing procedure after adjustment

Number

Tool

Processing content

Machine tools and Fixtures

1

Holding blank on CNC lathe

Three jaw chuck of CNC lathe

2

Cylindrical knife

Right outer circle (Φ 34 and Φ 52)

3

Cylindrical knife

Turn around to clamp the outer circle of Φ 34mm and process the outer circle of Φ 33mm

Special fixture for CNC lathe

4

Boring cutter

Φ 28.3 and Φ 15.68 holes

5

Clamping workpiece with three jaw chuck on Machining Center

Three jaw chuck of machining center

6

Ball point knife

R1.7 circular groove

7

Twist drill

4 – Φ 4.5 hole

8

Reverse clamping at Φ 52mm

Special fixture for machining center

9

End mill

Milling slope

10

Twist drill

Bottom hole of Φ 24mm and Φ 12.2mm holes

11

End mill

Φ 24mm and Φ 12.2mm holes

12

Clamp the outer circle of Φ 34 on CNC lathe

Special fixture for CNC lathe

13

Groove cutter

R1.7 inner groove

14

Boring cutter

Deburring along the left inner hole

Conclusion

In the new processing technology scheme, the machining process is optimized, the special fixture is designed, and the parts are processed. The object is shown in Figure 6.

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Figure.6 flange parts
Compared with the original trial cutting process, it has the following two advantages:

  • (1) High efficiency. In the process plan of the first trial cutting, the parts need to be clamped three times on the CNC lathe and twice on the machining center by using the three jaw chuck. Each clamping must be aligned. In the new process plan, with the help of special fixtures, especially the working procedures 8, 9, 10 and 11 of the machining center, four parts can be processed at one time. It only takes 5 minutes to complete the processing of one part, and the efficiency is increased by about 75%. The mass production can be realized.
  • (2) High precision. In the new process plan, the special fixture is used in the machining center and CNC lathe to locate and clamp the parts, which solves the biggest machining difficulty of flange parts. The qualified rate of the first batch of 100 parts completed by the new processing technology is 100% after three coordinate inspection, which greatly improves the machining accuracy.

Source: China Pipe Flange Manufacturer – Yaang Pipe Industry Co., Limited (www.ugsteelmill.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.)

If you want to have more information about the article or you want to share your opinion with us, contact us at sales@ugsteelmill.com

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