SSRF storage ring pre-developed aluminum alloy vacuum chamber machining

Vacuum SSRF Storage Ring Prefabricated Aluminium Alloy Vacuum Chamber Machining Du Hanwen Yin Lixin Jiang Dikui Jiang Xiaoli Lu Changfu2 Zhang Min2 Zhang Xiaoqiu2 Cai Rui2 (1 National Synchrotron Radiation Center (Shanghai), Shanghai Formality Tolerance and Roughness Requirements Extremely high, unlike the conventional large-scale ultra-high vacuum chambers, successfully solved a series of problems in the processing of pre-study parts, such as the difficulty in improving the finish, deformation after processing and forming, and the processing dimensions and accuracy influenced greatly by the ambient temperature, etc. This article elaborates the selection basis of the storage ring vacuum chamber material and the heat treatment state, in order to ensure the dimensional precision and the technical measures taken in the form and position tolerance, the formation mechanism and influencing factors of the roughness are analyzed, from the tool material, geometric angle, cutting Parameters, coolant selection and other aspects proposed solutions.

The design and manufacture of high vacuum chambers is the key to the successful construction of the vacuum system. Compared with the processing of conventional mechanical parts, ultra-high vacuum parts require that the vacuum surface finish be as high as possible in order to reduce the true surface area in the cavity and reduce the outgassing volume. The requirements for storage ring vacuum chamber parts also require high dimensional accuracy and positional accuracy in order to accommodate other systems such as magnets. According to the actual needs of the project, through the processing of the pre-study piece, various problems in the design and manufacture of the vacuum chamber were discovered and solved, and a complete set of ultra-high vacuum chamber design and processing specifications was established. Design and manufacturing provide direct basis.

1SSRF storage ring vacuum chamber structure and material 1.1 structural design and mechanical properties of the vacuum chamber Shanghai Light Source (SSRF) is a third-generation synchrotron radiation source, the core part of the light source is an energy of 3. 5GeV perimeter 396m electronic storage ring The entire ring is composed of 20 standard units. The ultra-high vacuum system is an important part of the storage ring. It provides the necessary operating environment for the stored electron beam. The storage ring The vacuum system main body consists of 40 sections of 6m long curved section vacuum chamber and 40 sections. The straight section vacuum chamber and other components are interconnected by bellows. The vacuum chamber is equipped with a photon absorber beam flow measurement device and vacuum acquisition and measurement equipment. The synchrotron radiation source requires the stored electron beam lifetime to be greater than 15 hours, thus requiring its vacuum. The dynamic vacuum degree of the system is better than 1.3 1.2 Selection and characteristics of vacuum chamber materials In the past 20 years, aluminum alloy has advantages such as small electrical conductivity, good thermal conductivity, low thermal outgassing rate, low residual radioactivity and good mechanical processing and welding performance. Has been widely used as synchrotron light source storage ring vacuum chamber material. Such as Japan's Springs USA APS. In SSRF, through comprehensive consideration of vacuum, physical, mechanical and other performance requirements, and with reference to the successful experience abroad, we decided to use the 5083-H321 as SSRF vacuum chamber body material. The billet supplier for the billet was Alcoa of the United States.

The material is a non-heat treated deformed aluminum alloy, which belongs to aluminum-magnesium alloy, which is equivalent to the domestic brand LF4. It is characterized by moderate strength plasticity and corrosion resistance, and has good welding performance. The comprehensive pretreatment process of the material is: Firstly, the material is prestressed and strengthened, and the cold work volume in the thickness direction is 20%, and the stretch amount is 1.5%. Then, the temperature is reduced by 150C to stabilize the mechanical properties of the treated material. In the machining process, dimensional stability is achieved. Well, the amount of cutting deformation is small.

2 Selection of vacuum chamber processing units In order to implement the processing units, extensive investigations and studies have been conducted. The basic point for selecting processing units is that due to the complexity of vacuum chamber parts, that is, a variety of surface shapes and high precision requirements, the factory must have CNC. Machining capacity, and, CNC machine tool working stroke must be equal to the total length of the workpiece Factory must be engaged in long-term processing of aluminum alloy parts, has accumulated rich experience in aluminum alloy machining Aluminum alloy machining process performance compared with black metal stainless steel has its special Sex, from the machine tool cutting parameters, tool material selection and geometric parameters, the determination of the cutting fluid model, the work experience of workers, engineering literacy has its special requirements According to the requirements of vacuum parts processing, the factory must have a clean processing environment, suitable cleaning Equipment and process conditions.

After a comprehensive comparison, the final selection was made at the Shanghai Aircraft Manufacturing Plant. The unit has a Swiss-made NIV1250 CNC milling machine. The machine has three degrees of freedom in XYZ displacement, one head w rotation freedom, and a table width of 1250 mm. 4000mm, according to the characteristics of the workpiece, the use of plate tooling, the equipment can meet the processing requirements 3 aluminum alloy vacuum chamber processing 3.1 pre-preparation work of ultra-high vacuum parts processing, and general mechanical parts processing is very different, the process of Cleanliness, directly affect the vacuum performance of ultra-high vacuum parts In order to reduce the pollution during the process, before the processing, the work environment of the NIV1250 machine tool and the feed system cooling system workroom was completely cleaned with alcohol to wipe the work surface, Working head, feed screw, guide rail, refill clean lubricant. Replace the coolant thoroughly and clean the tank and piping system. Re-form the coolant in a proportion of 5% (DMS1828 ice). In the whole process of adding the machine, the temperature of the workshop was controlled in 3.2 aluminum alloy vacuum chamber machined process outline kit material. According to the shape of the workpiece, the blank is cut into 68mm trapezoids. Two pieces are repeatedly turned on the gantry milling to the thickness along the centerline of the beam chamber and the extension line. Both ends are used to punch the positioning hole of Y30H7mm. The cooling sink is processed to a certain depth according to the program. , To ensure that the surface of the cover plate after welding there is still 2mm machining allowance welding sink cover, test water pressure 1MPa, pressure 2h no leakage.

Roughing inner cavity, leaving 1mm margin for each type of surface waiting for finish roughing external profile, leaving 1mm margin for the workpiece to re-enter the machine, after calibrating the workpiece, finish shape to design dimension, only BPML flange face There is still a certain allowance.

0 Finish internal cavities to design dimensions.

1 BPM hole as a benchmark, the upper and lower two pieces together, the upper and lower two welding edge and flange connection pipe surface processed to the same plane, fine BPM hole 1 by ultra-high vacuum components cleaning process and Standard Cleaning Upper and Lower Two Vacuum Chambers Waiting for Welding 3.3 Main Problems in Machining and Solutions 3.3.1 Deformation Problems Due to the inevitable and unpredictable deformation during processing of the 5083-H321 material, the flatness tolerance of the aluminum sheet blank itself is also large. (2A000) For the sake of safety, when ordering materials, the allowance is greater, the thickness after forming the part is 50mm, and the size of the wool is 68mm. First, it is repeatedly turned on the gantry milling, and the flatness and parallelism of the upper and lower surfaces are milled. Degree along the longitudinal direction of the vacuum chamber with a cooling sink from beginning to end, using the machine to add the slot, plus cover plate welding method. In order to avoid deformation caused by the welding tank cover plate, the welding process is completed before the inner cavity and the outer cavity have not yet been processed. After the welding process is completed, the plate thickness has a machining allowance of 5 mm in order to eliminate welding-induced deformation during subsequent processing.

For 55mm up to c, make both sides level up to 0. Time to make the inside of the upper and lower pieces completely 1 to make a markbook1.cnki.net During the processing of the inside and outside of the cavity, deformation due to cutting stress due to thermal expansion deformation due to removal of material to break the inside of the tissue Deformation caused by the stress balance, all affect the processing precision of the total length of the workpiece is 5900mm, the thermal expansion coefficient of the aluminum alloy is 24.3 3.3.2 roughness issues In order to reduce the internal surface of the vacuum chamber, the amount required to minimize the surface of the vacuum chamber Actual area. The microscopic description of the actual area is the roughness of the processed surface represented by the roughness, which mainly depends on the height of the residual area after processing and the unstable factors of the cutting process, such as built-up edge and scales of the built-up edge, scales, etc. Spurs not only increase the surface area, but also retain polymer materials such as cutting fluids and mechanical oils, affecting the cleanliness of the surface.

The height of the residual area is formed by the trajectory of the tool relative to the surface of the workpiece. It can be calculated based on the tool's primary declination angle Kr declination angle Kr (the geometric relationship between the tool nose arc radius re and the feed amount f.

Residual area height characteristics: A cutting edge with arc residual area height B Tool nose radius is larger, the feed area f is smaller when the residual area height H = f 丨 team r C tool tip arc radius is zero The residual area height according to the above formula, in the sharpening tool, there must be a circular arc material reinforcement degree is greater and the friction between the cutter is greater, the more easily the two components of the material as shown in the table read the workpiece material front corner V Relief Angle T Relief Angle s Retouch Width bs (mm) Soft Aluminum 30 In the cutting process of the part, the surface of the built-up edge may be scratched due to the fact that the material of the 5083-H321 is soft, although the strength is low. Cutting, but due to strong plasticity (W=14%), low melting point, severe knife sticking during milling, poor chip evacuation, and workpiece material can easily accumulate at the blade edge and tip. Due to the extrusion and cold hardening during cutting, the hardness of the built-up edge is very high. Under certain cutting parameters and tool angles, the built-up edge is firmly cold-welded on the cutting edge and cutting edge instead of the cutting edge. The cutting edge of the built-up edge will extend beyond the cutting edge and tip, causing a certain amount of overcutting on the machined surface. The shape of the built-up edge is irregular, and some longitudinal grooves with different depths and widths are scored on the surface. The top of the BUE will be repeatedly generated and split, and some will remain on the processed surface to form scale-like burrs. The height of the BUE is closely related to the cutting temperature, and the cutting speed has the greatest influence on the cutting temperature. In a certain speed range, the BUE grows the most and can be determined in the test cut to avoid the influence of the accumulation of dust on the surface finish. Another factor is scaly thorns. This phenomenon occurs when high speed steels and hard alloys are used to cut plastic materials at low and medium speeds. Its formation is related to cutting speed, cutting depth, material properties, and metallurgical organization. . The angle with the cutter is also related to the formation of burrs. In addition, the wear of the tool's sub-knife surface and the accuracy of the machine's rotation have an effect on the roughness. In order to reduce the surface roughness, we take the following measures on the tool: use a larger radius of the tool nose radius re, a smaller secondary angle K/, use the wiper K/=0 which is a little larger than the feed length for smooth chip evacuation. The rake angle of the milling cutter is larger and the number of teeth is smaller. SSRF aluminum vacuum chamber machine tool parameters are as shown in Table 3 to determine Table 3 aluminum alloy fine milling cutter geometric parameters to improve the sharpening quality of the tool, reduce the tool before and after the surface roughness parameters, Ra Table 5 aluminum alloy milling precision milling After the dosage of 2 vacuum test parts are cleaned by ultra-high vacuum, the assembly is welded and tested according to the ultra-high vacuum debugging process. The vacuum degree of the system is better than 6.5. Beijing Huarui Vacuum Technology Co., Ltd. and the address change notice The company is the Beijing Science and Technology Committee. The recognized high-tech companies are professional manufacturers of vacuum equipment. The company's scientific and technical personnel are engaged in product design and manufacturing in the vacuum industry for many years. The guidelines for the design and production of vacuum equipment product designs for various purposes can be designed according to the needs of users: technical. Advancement; high stability of the whole machine quality; high reliability of operation; high repeatability of the process.

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