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Five-axis device features
The equipment of the square steel production line is mainly 12 sets of HSTM 300 and four sets of Starrag 151. The main processing blades are smaller than 300mm. They are all single-drive vertical equipment. The clamping method is basically a folder with a top, and the blades are in a suspended state. This determines The rigidity of the blank on the side of the drive end clamp during machining is much better than that on the top side of the tail stock. The more slenderness of the blank is, the greater the difference is, and the effect of the machining plane is not as good as the fixed milling of ordinary machine tools in terms of accuracy or surface quality. More not as good as grinding; especially when the machining plane is far away from the center of rotation, it will also produce severe chatter marks; and the machining effect on some round holes is not very good; the best is the rotary processing of profile and transfer steam passages. , as well as special parts or shapes that cannot be achieved with three-axis four-axis devices. Five-axis equipment is not a panacea. Some types of machining can be easily implemented on other machine tools, but they will work harder on five-axis machines.
The difference between HSTM and Starrag: The HSTM machine tool can machine a round boss on the tailstock side of the blank with the drive end clamped, and then hold the round handle to process the product, which avoids inconsistency of the center hole at both ends. The resulting baseline deviation, in turn, can further enhance the stock stiffness on the tailstock side. This is the biggest highlight of the HSTM machine and we should use it a lot. Starrag's accuracy and stability are better than HSTM.
Regarding the processing of the leaf body profile: The leaf body profile is an irregular, but regular, complex surface with considerable procedural bending and twisting. Its processing is the focus of blade processing and is also the processing of five-axis machine tools. The advantage lies in the general use of screw-rotary milling for machining, because the tool axis of the 5-axis machining center can oscillate at a certain angle, so that the fillet knife of the machining surface is completely perpendicular to the surface, and then walks with a certain rake angle. Knife, so the processed surface does not have overcuts and dead ends, which is not possible with other equipment.
The Importance of Processing Process and Process Schemes for Square Steel Blades
The leaves can be basically divided into three major parts: the root, the leaf body and the crown.
General square steel blades are single-T or double T-type blade roots, with at least two root slots, and inlet and outlet side planes and radial inner planes; the blade body is formed by a number of profiles. The composition is divided into four parts: inner arc, back arc, inlet steam inlet and outlet steam outlet; the upper part is the leaf crown, and the same as the root, two sides and inner and back radial surfaces must be processed; The area where the roots of the leaf roots intersect is rounded with rounded corners, which is called transfer.
The preparation of a blade is the first consideration of the formulation of the process plan. According to the structural characteristics of the product, as well as the accuracy class and technical requirements, the most stable mounting method and the most reasonable processing method are determined, like the high pressure of the combined cycle machine unit. The highest requirements for moving blades are the size of the two sides and the pitch between the radial faces of the inner back and the position between the blade root and the crown. The clamping method adopts the most basic one-piece top, but in order to ensure the consistency of the process reference, the positioning process boss and the center hole are first machined in a vertical machining center, and then the whole positioning is performed with the processed positioning reference. Blade processing. In order to ensure the accuracy of both sides and pitches, these parts are all machined with the same precision milling cutter, and on-line measurement methods are used to process both sides of the root or the crown of the leaves first, measure online, and adjust the length of the blade. Quasi-two sides, and then the adjusted length of the knife to process the corresponding part of the radial surface of the back to ensure the pitch requirements. The entire process is arranged as follows:
1 On a five-axis vertical machine tool, a clamping process is first performed to process the bosses of the square steel clamping process, and then the center drill bit is used to process the center holes for positioning at both ends, so that the consistency of all the process standards is fully guaranteed;
2 Position the process bosses and the center hole, and use the end of one end of the clamp to clamp on the five-axis machine;
3 After the fixtures are firmly clamped, the entire area is first cleared to remove large areas;
4 Rough processing of the two sides of the top of the tailstock and the radial surface of the inner back, and then fine finishing the two sides of the place with a fine milling cutter to carry out on-line measurement, and compare with the nominal size after the amount, and adjust the length accordingly. The processing is performed until both sides are accurately aligned. Then, with the last-adjusted tool length, the inner radial surface of the tailstock is fine-milled.
5 Repeat the above steps and measure the length of the tool by on-line measurement, make the two sides of the side of the quasi-drive end clamp, and the inner radial surface of the part;
6. Then roughing profile and two transition fillets transfer, leaving 0.5 ~ 1mm margin on one side;
(7) Sub-coarse and fine-milling of blade root groove and steam seal and each chamfer and process groove;
8 rotary machining finish milling surface, and two transfer; if the margin is larger, it can also add one-step semi-finishing;
9 Finally, the bottom surface of the blade tip and the root of the blade are milled, and the semi-circular groove on the bottom surface of the blade root is drilled with a keyway cutter to end the processing of all parts.
Large-area wasteland clearance, rough milling on both sides and radial surfaces, and rough-milling surfaces, all use the same φ40mmR6 rough-milling round-edged blade knives, and the blade is a φ12mm circular blade with a large feed rate at low rpm. The method is processed. The fine milling cutters on both side and radial surfaces are φ63mm blade knives and use R0.5 square shoulder blades. The fine milling cutter for the fine-milling face is a φ20mmR4 blade knife with a φ8mm round blade. The transition point uses a 4° taper ball nose tool. As for the rest of the root slots and other parts, a solid carbide end mill is used. According to the different slot widths, different diameters and R angles are used, as well as different processing parameters.
The initial process plan is that regardless of the rough finish, all the parts are machined on the five-axis equipment, and the process boss is placed on the side of the blade crown. When the clamp is installed, the crown is pressed at the clamp and the blade root At the tip of the tailstock, a large amount of chatter marks appeared in the root surface and back radial surface of the processed blade. No matter how the processing parameters were adjusted, the result was not ideal. The longer the blade was, the more severe the pattern was; later the process plan was changed. When the process boss is pressed at the root of the blade and the crown side is tight, the problem of radial surface chattering is solved. Another problem that bothers us is the machining of the semi-circular groove on the bottom of the blade root. Because it is not perpendicular to the radial surface, it cannot guarantee the tolerance of its left and right position. It wastes a lot of time and blanks, and finally communicates with the craftsman. Place the semicircular groove on the triaxial device.
It can be seen that changes in the process plan will have a fundamental impact on processing.
Although the five-axis machining simplifies the process and tooling, the processing ideas are reflected in the program, but a reasonable process plan still plays a vital role, which in itself determines the ease of processing of a product and the quality of the product. The craftsman must first grasp the processing of each part of the entire product from a macroscopic perspective, how to locate how to clamp in order to get the best results, and then design a precise and reasonable fixture, the whole process can be smooth, the product quality can be stable, and the CNC programming is only Play within the framework of the established process plan.
The processing characteristics of the square steel blade
High precision requirements: If the high-pressure rotors of the combined cycle 168 unit require tolerances of 0 to -0.03 mm on both sides, pitch tolerance + 0.04 to -0.02 mm. This is second to none in the product range processed by Wuxi Turbine Blade Co., Ltd.
The processing sites are numerous and varied: Basically all the parts that can be machined are required to be made on a five-axis machine at a time, and different blade shapes are different, making the processing types complex and varied, which is also a strength of the five-axis machining.
Rough milling takes up a large proportion of land reclamation time, and about half of the time is used to reduce margins. How to shorten the roughing time is the key to improving processing efficiency.
Leaf varieties are small in volume.
Formulate the principle of process plan
The formulation of the process plan should be based on the principle of pursuing the maximum cost performance. An ideal process plan should be to use the most convenient processing method, the highest processing efficiency, and the lowest processing cost to obtain the most stable and reliable processing quality. Technicians are looking for the best, not necessarily the most perfect product. In the case of five-axis machining of square steel blades, not all types of blades, not all parts of the blades, should be processed on five axes. The very strict requirements of the two sides and the radial surface can be considered using a surface grinder, processing multiple pieces at a time; the arc groove of the root and the bottom surface of the blade root and the top of the blade can be used to process the blade ring with a large vertical car; Accuracy and surface quality have also greatly improved efficiency. The rough milling and cutting waste that limits the machining efficiency of square steel can be outsourced, or done on ordinary machine tools. Let the five-axis device do what it does best to maximize its effectiveness.
in conclusion
Five-axis equipment is not a panacea, it has unparalleled superiority, but also has its own limitations. Although the five-axis machining of Fangsteel simplifies the process tooling, the process scheme still plays a vital role. The machining of the square steel blade represents the highest level of precision of the machining precision of Wuxi Turbo Co., Ltd. The formulation of the process plan should be based on the principle of pursuing the maximum cost-effectiveness and rationally formulate the technological scheme of the square steel blade.
Five-axis machining of square steel blades
Since the axial steel production line was put into use, a large number of new products have been trial-produced and processed, among which the typical products are the moving and stationary blades of various steam turbines. The machining of the square steel blade on the five-axis machining center shortens the processing flow and simplifies the process and tooling. Nearly all positions can be machined in a single positioning fixture, avoiding the error caused by the reference conversion. However, it also has various problems. It is necessary to conduct in-depth discussions on the five-axis machining of the counterpart steel based on the experience accumulated in the debugging process.