For Aero - engine, core machine once finalized, follow-up development mainly through adopting new technology, new design, increase the diameter of the fan, booster compressor series increased, to improve the high pressure compressor, high-pressure turbine blade design, improve the high pressure turbine blade materials and coatings resistant high temperature performance and to improve the efficiency of components and engine thrust. The characterization of cycle parameters of high temperature components materials development is relatively slow, and compressor blades, a fan blade design improved more frequently, it can be said that manufacturing titanium alloy compressor blades and the fan blade is one of key technology in Aeroengine manufacturing.
At present, domestic aero-engine manufacturing enterprises almost all adopt artificial grinding into the exhaust side of the manufacture of titanium alloy compressor blades, fan blades and vanes, the blade into exhaust edge thickness of powder and a standard deviation of larger, consistency, line is not accurate, the leaf quality is not high. With the steam turbine industry gradually adopt CNC Abrasive Belt Grinding in machining surfaces of the blade and intake and exhaust side, aero-engine manufacturing enterprises have also proposed using CNC Abrasive belt grinding into the exhaust side of the requirements, eager to through the CNC Abrasive belt grinding to solve problems in exhaust edge grinding the blade of aviation engine manufacturing. Through analysis of the characteristics of the technology of aerial titanium alloy blade and on different blade NC belt grinding in production practice, process test, and verify the analysis, summary of the proposed realizing the aviation titanium alloy blade CNC Abrasive belt grinding cut in several necessary conditions and the corresponding countermeasures.
Difficulties in the grinding process of the inlet and outlet
The manufacturing process of aero engine blade and turbine blade is very different, the former is mainly used in molding method, and the latter is mainly used to remove material. The turbine blade material is stainless steel, the first is a general milling blade radial surface as the radial reference processing, shoulder or groove and the top hole as the axial benchmark, then processed by the multi axis machine tool blade, the CNC Abrasive Belt Grinding and polishing; air leaves the general use of titanium alloy precision forging and casting method manufacture of compressor blades by diffusion bonding / superplastic forming (DB/SPF) made of titanium alloy wide chord fan blade method, the blade surface is guaranteed by molding the surface precision of spatial error is less than 0.15mm, after formation of re processing, surface positioning fixture is directly used as the benchmark for machining root groove and exhaust edge. Therefore, aviation titanium alloy blade processing mainly into the exhaust edge processing, for CNC Abrasive belt grinding, the machining difficulties has the following main aspects.
(1) air blade into the exhaust side is very thin, large fan blades are only about R0.3mm, small compressor blades and some even reach R0.1mm level. This makes in abrasive belt grinding, must use very small contact force grinding, otherwise it is difficult to guarantee the accuracy and the abrasive belt grinding device for contact force control is put forward very high requirements.
(2) uneven grinding allowance. Forging of titanium alloy compressor blades and superplastic forming fan blade generally use milling or line cutting into the exhaust side forging flash (assurance chord width), and then into the exhaust edge grinding and polishing, the processing characteristics of the into the exhaust side fillet (or local elliptical cross-section) part machining allowance is not uniform, as shown below: red for blank contour curved part into the exhaust side of the theoretical curves.
(3) the problem of blade deformation. The problem of grinding allowance uneven is the same problem, and superplastic forging of titanium alloy blade blade molding were under a certain temperature complete deformation, residual stress are deformation, especially compressor blade, deformation of the blade into the exhaust edge thickness at the same level, reached more than 0.1mm, the air leaves the general type space error of about 0.05 mm compared too big must corrected.
(4) the benchmark problem, the consistency problem of the surface orientation and blade loading. Blade precision forging and superplastic precision forming blade surface is very good, but it is still a rough benchmark, compared to the turbine blade milling benchmark is still relatively crude. As mentioned above, the positioning error of the clamping device is equal to the deformation error of the blade on the order of magnitude, which is an important factor that can not be considered.
In addition, into the exhaust edge grinding, cooling condition is not good, very thin edge cooling condition is not good, inlet and outlet blade edge is easy to cause ablation, the blade inlet exhaust edge grinding bring certain difficulty; for superplastic forming fan blade, in addition to the intake and exhaust edge, surface also need to cut grinding polishing, there is surplus of type is not uniform, and the deformation error.
The key technology of blade NC belt grinding
1, the belt device was improved
Through the production practice of the steam turbine blade improve CNC Abrasive belt grinding device unit technology, optimization control technology and six axis programming technology, accumulation of blade NC belt grinding process data. With the continuous production reflects the requirements of the belt device is improved continuously, including the main improvement:
(1) sanding machine low friction guiding mechanism of assembly structure is optimized to lower guiding mechanism static friction and improve the float belt mechanism sensitivity and improve contact force control precision;
(2) update the low resistance floating cylinder to improve the control precision of the contact force;
(3) optimization of the belt wheel structure and improve the assembly process to improve the parallelism of gear axis, so as to increase the contact wheel belt envelope angle, improve the operation stability of the high-speed belt;
(4) optimization of the B shaft design, the use of non backlash bearing reducer B shaft transmission, improve the dynamic performance of the B axis more than 10 times, expanding the B axis swing range (to adapt to the fan blade large amplitude bending change);
(5) optimization of C shaft design, the use of split gear backlash, reducing the size of the C axis and structural quality, improve the accuracy and dynamic characteristics of C axis;
(6) improved C shaft and belt mechanism of overall protection, basically free cleaning, maintenance free belt mechanism;
(7) to improve the machining efficiency by using the method of horizontal grinding to improve rough machining;
(8) using the new material contact wheel, the contact wheel life from 7~10 days or so to 15~20 days.
Through optimizing design, the unit of abrasive belt grinding device smaller, contact wheel pressure minimum control reach 5N level, greatly improves the reliability of the complete machine can be basically do operation maintenance, is testing the new guiding mechanism and a pressure control device will further enhance the contact pressure control precision, contact force control precision does not exceed 0.5N.
2, static blade strength grinding test
The purpose of the test is to verify the forming process and the precision control method of the model surface by using the steam turbine stator blade strength grinding.
Through the analysis of common static blade surface features, it can be seen, static blade surface distortion is small, even is barrel shaped leaf type, especially not shrouded blades, the only body of the blade type line (pendulous processing after resection), body of the blade type line is very suitable for CNC Abrasive Belt Grinding and shaping. For six axis CNC Abrasive belt grinding machine, suitable contact wheel diameter, hardness and abrasive belt width, using powerful grinding direct forming static blade surface is feasible; and due to the high speed of abrasive belt grinding line, with higher than that of the milling metal removal rate, the powerful grinding direct forming static blade surface, in terms of efficiency will be better than the milling.
3, super plastic molding fan blade test
The purpose of this study is to accumulate the grinding process data of the aerial titanium alloy blades through the grinding test of the superplastic forming fan blade. Titanium alloy superplastic forming hollow blade blank leaves unilateral margin of about 0.5mm, intake and exhaust edge for cutting in line cut, maximum margin of about 3mm, clamping reference for blade root parts of the rectangular shoulder and Taiwan (wire EDM cut out. The error is less than 0.1mm), require the use of CNC Abrasive Belt Grinding out into the exhaust side fillet (elliptic sectional type) and grinding blade body surface to the dimension.
For aviation titanium alloy blade by abrasive belt grinding modification, grinding out into the exhaust side arc section of (or elliptic) is required; ensure the accurate profile is the key to the grinding contact force and improve contact force control precision, reduce the grinding contact force is to achieve aviation titanium alloy blade into the exhaust side of the processing precision of key.
According to the experimental study on the above the aviation blades made of titanium alloys and the characteristics of several representative blade abrasive belt grinding, we can summed up the process conditions of aviation titanium alloy blade profile and into the exhaust side CNC Abrasive Belt Grinding of several necessary conditions and the existing countermeasures.
(1) under the existing conditions of technology, aviation titanium alloy blade rough surface and into the exhaust side of manufacturing errors were greater than the allowable variation requirements of CNC Abrasive Belt Grinding with correction, forming grinding and polishing functions, so CNC Abrasive Belt Grinding must based on the blade clamping state of accurate measurement of foundation is machine tool equipment must with on-site measurement function (measured) and detection methods as far as possible using non-contact, in order to avoid the compressor leaflets measurement caused unnecessary deformation. Possible ways for the CCD measurement or line laser scanning based on the principle of multi eye vision, taking into account the factors of the blank reflection, the current line laser scanning seems to be slightly more than the advantages of CCD measurement.
(2) based on measured and reverse model reconstruction technology and measurement for the purpose of processing must be through reconstruction model rapidly generated in realistic error of the blank or clamping difference model, and determine whether the processing of qualified products and generate or modify processing program and processing. In the application of the modified blade type line, it is inseparable from the support of model reconstruction and model comparison, or simply do not know where to go. Taking into account the processing efficiency of the blade, the process can be controlled to complete the basic 5min.
(3) the local correction function of abrasive belt grinding. Larger deviations can be through strong grinding rest, walk several times trajectory theory to correct, but for less than 0.1mm deviation correction, real-time pressure control pressure grinding will more effectively. At present, the variable pressure grinding programming control has been done, the implementation is not a technical problem.
(4) low friction orientation and small contact force control is the aviation titanium alloy blade into the exhaust edge processing precision of key, for r0.1mm exhaust edge forming grinding and polishing, contact force may be less than 2n, considering the quality of grinding, contact force resolution is not than 0.5N, best can control in 0.1 N level. The belt guiding mechanism challenge, at present in guiding device for test and floating actuator can basically achieve zero friction, remaining is to reduce the belt floating mechanism to improve the quality of motion sensitivity of the.
(5) machine tool structure to adapt to the structure and characteristics of titanium alloy blades. For compressor blade forging curved blade and grazing type fan blade, processing b axis swing angle will bigger and machine design should fully consider the request; large fan blade twist close to 90 degrees, processing c-axis swing angle changes accordingly will very big, with an emphasis on is in the arrangement of machine tool design consideration.

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