CN105880953A - A kind of processing method of aviation blade - Google Patents

Abstract

The invention relates to a processing method of an aviation blade, which specifically includes the following steps: using a driving surface and projection technology to construct a multi-layer helical trajectory, processing the blank into a rough product in the manner of spiral milling and retracting, and The cutter is a ring cutter; the helical trajectory is constructed by using the driving surface and projection technology, and the rough product is processed into a semi-finished product in the manner of spiral milling and retracting. The cutter used for semi-finishing is the first ball-end cutter; the starting control line The helix is directly constructed by interpolation method and projected along the normal direction of the blade surface to ensure that the helix is located on the surface of the semi-finished product, and the semi-finished product is processed into a finished product according to the method of helical milling and tool retraction. The cutter is the second ball-end cutter. The above-mentioned technical scheme is adopted to process the aviation blade, which has high processing efficiency and high precision, and the surface quality of the aviation blade is good.

Description

A kind of processing method of aviation blade

technical field

The invention relates to the processing field of blade-type aeroengines, in particular to a processing method of aero blades.

Background technique

Aeroengine is the "heart" of an aircraft and one of the decisive factors of aircraft performance. It is also the highest-end product in the field of equipment manufacturing. It represents the highest technical level of the equipment manufacturing industry and is known as the "jewel in the crown" of modern industry. . Its manufacturing technology is one of the important symbols to measure a country's scientific and technological level, military strength, and comprehensive national strength. The performance, life and various parameters of the engine depend largely on the design of the blade profile and the manufacturing level of the blade. The characteristics of the blade are: complex structure, various varieties, high geometric precision, difficult processing, difficult to guarantee the processing quality, and the blade is an important part of the engine, so the quality of the blade processing directly determines the performance of the engine, because the blade needs to be good The aerodynamic layout and profile, so its design and manufacturing cycle is quite long, usually several times or even dozens of times that of other parts, so the manufacturing workload of the blade accounts for about half of the processing workload of the entire engine. my country's blade manufacturing enterprises have many problems in the processing process, such as low processing accuracy, low blade processing efficiency, and strong experience.

Contents of the invention

The purpose of the present invention is to provide a processing method for aviation blades, which can effectively improve the efficiency and precision of processing aviation blades.

To achieve the above object, the present invention adopts the following technical solutions to implement:

A method for processing aviation blades, specifically comprising the following steps:

Rough machining: use the driving surface and projection technology to construct multi-layer helical trajectory, and process the blank into rough products in the way of helical milling and retracting. The feed rate of each layer is set to 2mm, and a margin of 1mm is left after rough machining , the tool used for rough machining is a ring cutter;

Semi-finishing: use the driving surface and projection technology to construct the helical trajectory, process the rough product into a semi-finished product according to the method of spiral milling and retracting, and leave a margin of 0.1-0.2mm after semi-processing. The tool used for semi-finishing is first ball head knife;

Finishing: Use the interpolation method to directly construct the helix with the start control line and the end control line as the boundary, and project along the normal direction of the blade surface to ensure that the helix is located on the surface of the semi-finished product. The semi-finished product is processed into a finished product, and the linear axial movement is adopted at the starting point of the advance and retraction of the knife, and the tool used for finishing is the second ball-end knife.

The above-mentioned technical scheme is adopted to process the aviation blade, which has high processing efficiency and high precision, and the surface quality of the aviation blade is good.

Description of drawings

Fig. 1 is the blade helical trajectory constructed in finishing machining;

Fig. 2 is the schematic diagram of helical milling cutter;

Figure 3-1 is a schematic diagram of the trajectory without tool retraction between layers;

Figure 3-2 is a schematic diagram of the retraction trajectory between layers;

Fig. 4 is a schematic diagram of a blank of an aviation blade.

detailed description

In order to make the objects and advantages of the present invention clearer, the present invention will be specifically described below in conjunction with examples. It should be understood that the following words are only used to describe one or several specific implementation modes of the present invention, and do not strictly limit the protection scope of the specific claims of the present invention.

A method for processing aviation blades, specifically comprising the following steps:

Rough machining: Helical milling is used for rough machining to approximate the round and flat blank to the shape of the blade, leaving a margin of 1mm after rough machining. In order to improve the processing efficiency of rough machining, select According to the driving surface and projection technology to construct the helix, and then according to the operation S1 to construct the helical milling and retracting method, according to the operation S2 to construct the multi-layer helix trajectory, the tool used is a carbide tool, so each layer The feed rate is set to 2mm, which can improve the efficiency of rough machining.

Semi-finishing: Semi-finishing is a preparation for subsequent finishing, so the allowance for semi-finishing is determined according to the experiment of finishing. According to the comparison test of finishing, the allowance for semi-finishing is 0.1mm and 0.2mm, used for semi-finishing The ball-end cutter, the tool material is high-speed steel, the helix is constructed according to the driving surface and projection technology in operation S3, and then the method of advancing and retracting the helical milling is constructed according to operation S1, and finally the value of the cutting width is determined according to operation S4;

Finishing: Finishing is the most important link in CNC machining of blades, and the processing of blade body is the most important part of blade finishing, and the blade body has a great influence on the surface quality, cross-sectional shape and the overall shape of the blade body after processing. The profile has high requirements, so a complete tool path should be used to complete the machining of the entire blade body, and the deformation of the blade body should be within the required range;

The trajectory of the finishing process is based on the operation S3 to directly construct the helix with the interpolation method bounded by the start control line and the end control line, and project along the normal direction of the blade surface to ensure that the helix is strictly limited on the surface. Then according to the method of operation S1 to construct the advance and retreat of the helical milling tool, the linear axial movement is adopted at the starting point of the advance and retreat, and the constructed helical trajectory is shown in Figure 1.

in:

Operation S1: Construction method of helical milling and retraction path

When the tool cuts into the workpiece, it is necessary to control many parameters of the machine tool, such as: the cutting amount of the tool, the spindle speed and the direction of motion, so that the tool, the machine tool and the workpiece do not interfere. In NC programming, the path where the tool cuts into the workpiece is called progress Correspondingly, the track where the tool cuts out of the workpiece is called the tool retraction track.

The feature of the feed path is that it cuts in and out of the workpiece slowly and evenly along the tangent direction of the cutting track; the common feed methods include straight line tangential, arc tangential, vertical, oblique, zigzag, spiral, etc. The knife mode includes linear tangential retraction, linear retraction and so on.

Vertical feed: This feed method is that the tool directly cuts into the workpiece vertically, which will generate a large impact force and increase the deformation of the tool and workpiece. This method is generally used for keyway milling cutters;

Oblique feed: This feed method is to use the side edge to cut the workpiece, and the angle between the tool axis and the workpiece needs to be set during processing; if the angle is set too small, the cutting depth of each tool will be shallow, which is beneficial Protect the tool and the workpiece, but the processing efficiency will be very low; if the selected angle is too large, the end edge cutting will occur; so this angle should be set according to the actual processing needs;

Zigzag feed: This feed method is an improvement of slash feed, which divides the entire slash feed into many small slash feeds. Although there will be problems of uneven force on both sides of the tool, But each stroke is very small, so the deformation is also small;

Spiral feed: This feed method is from the inside to the outside, that is, from the top, spiral downward processing, it adopts the continuous processing method, it is easier to ensure the processing accuracy, and can use a small amount of feed 1. The tool drops slowly, avoiding the occurrence of off-edge cutting, and improving the durability of the tool; for the blade helical milling method, how to choose the tool method is one of the important aspects that affect the blade processing quality. If the processing efficiency of the blade is considered, the speed at which the blade rotates around the axis must be controlled. If this speed can reach the maximum as far as possible, the production efficiency of blade processing will be greatly improved. The specific control method is: when the blade cuts into the workpiece, the rotational speed of the rotating shaft increases rapidly from zero to the maximum. This leads to the helical milling of the blade must have its own unique feeding method. The various feeding methods mentioned above in this article are only suitable for ordinary processing, not suitable for helical milling. The most reasonable cut-in method for helical milling is to control the tool to slowly cut into the part along the profile of the blade section, so that the tool track forms an envelope around the blade with the shape of the blade section line as the basic spiral shape, which can not only improve the machining accuracy of the blade, but also To improve the processing efficiency of the blade, as shown in Figure 2, the way of cutting out is just opposite to the direction when the tool cuts in.

Operation S2: Method for Constructing Multilayer Helical Track

The tool position trajectory is divided into the initial stage, the cutting stage and the termination stage according to the cutting process. The entry occurs in the initial stage and the cutting stage, and the retraction occurs in the cutting stage and the termination stage. The entry and exit in the cutting stage are called interlayers. Advance and retract, used to connect different cutting path segments.

Blade processing may use multiple layers of helical paths in the following situations:

a. The blank margin is large, and rough machining needs to be divided into multi-layer spiral lines for processing;

b. The cutting amount of roughing and semi-finishing is different, and when using the same tool, it is combined into one operation;

The construction process of the multi-layer helical cutting trajectory is divided into three steps: constructing the cutting trajectory between layers, constructing the cutting trajectory of this layer, and constructing the retracting trajectory between layers:

Structuring inter-layer feed trajectory: suppose the helical milling feed trajectory is divided into n layers, the cutting thickness of each layer is hi, i=0, 1...n, the tool slowly cuts into the part along the profile of the blade section, and the shape of the blade section line is The basic helical shape, the setting of the cutting thickness array hi can easily realize the uniform change of the thickness of the cutting path of each layer.

Construct the spiral cutting trajectory of the current layer: If the cutting depth of the current layer is uniform and equal in thickness, it is only necessary to offset the blade surface according to the distance as the cutting depth, and construct the spiral machining trajectory on the offset surface. If the cutting depth of the current layer is uneven, it is necessary to formulate a non-equidistant offset algorithm to construct the curved surface, and then construct the spiral machining trajectory of the current layer on the offset surface.

Constructing the retraction trajectory between layers: For the multi-layer helical line processing method, there are two ways to select the retraction trajectory. The first method takes into account the processing efficiency, does not perform the retraction, but directly enters the next layer (Fig. 3- 1), if the retracting step is omitted, the feeding directions of the adjacent two helical trajectories are opposite. The other one does not omit the tool retracting step, but adds a tool moving command, and the tool entering position can be selected arbitrarily (Fig. 3-2). When constructing a multi-layer helical trajectory, the thickness of each layer can be a fixed value or a variable value, and the cutting thickness of each layer should be determined according to the actual cutting situation.

Operation S3: Construction of the blade helix

Construct the helix directly by interpolation in the parameter domain: the most basic method of constructing the helix shape is to construct the helix in the parameter domain. The principle is to select a suitable sequence of parameter points in the surface parameter domain and construct the helix by interpolation. In the parameter domain, the helix is directly constructed by the method of interpolation. The specific principle is as follows: Let the surface of the blade body be represented by a spline surface as S, the direction along the blade section line is defined as the u parameter direction, and the direction along the blade radial line is defined as the parameter domain direction v parameter. The range of values in S is normalized to [0, 1]. If the intersection lines of the curved surface S of the airfoil and the end surface of the tenon and the tip of the blade are C ₀ and C ₁ respectively, then the boundary of the effective area of the curved surface of the airfoil is determined by the two intersection lines C ₀ and C _1. In order to make the helix pass through m circles After transitioning from C ₀ to C ₁ , the u-parameter line family T:{T _i , i=1…n} can be constructed on S, and the two intersecting lines of C ₀ and C ₁ can be re-discretized. Let the set of intersection points of T and C ₀ obtained after discretization be P: {P _i , i=1...n}, and the set of intersection points of T and C ₁ be Q: {Q _i , i=1...n}. Let P and Q be the boundary and the grid node set obtained by dividing T into m equal parts is L: {L _ij , i=1...n, j=1...m, where L _0i =P _i , L _mi = Q _i }, then the grid interpolation point A _ij (u, v) located on the i-th row and j-th column on the spiral line can be calculated by using the following two formulas:

According to the above formula, a right-rotating spiral and a left-rotating spiral can be obtained. In the order of u first and then v, the two parameters are increased from 0 to 1 respectively, and all interpolation points A _ij (u , v). Then, connecting all the points sequentially, a continuous polyline can be generated in the parameter domain, which corresponds to the uniformly rotating helix inside the C ₀ and C ₁ domains in the model space corresponding to the blade curvature. The advantage of the method of constructing the helix in the parameter domain is that the calculation speed is fast and the algorithm is simple. The disadvantage is that this algorithm can only be used for a single closed surface, and the shape of the helix is relatively simple, so it is not suitable for constructing a complex shape helix with good manufacturability. .

Constructing the helix based on the driving surface and projection technology: In NC programming, there is a programming method that uses the driving surface and projection technology to construct the shape of the machining trajectory. The process of this programming method is: first construct the driving point from the driving geometry, and then the driving point Projects onto the part geometry along a specified projection vector direction to form a projection point. The projection point is specified as the tangent point track or the tool point track in the tool point calculation. The advantage of this programming method is that it is very flexible. The driving geometry can be specified as coincident with the processing surface, or it can be a geometry that has nothing to do with the processing surface. There are various options for projection methods, such as fixed vector direction or tool axis. The relative vector direction can also be the vector relative to the drive surface. This flexible programming method is suitable for three-axis and multi-axis programming technology, and is an important method of NC programming. This method is more flexible and can effectively control the shape of the helix. The key to constructing the helix by the projection method is to select the driving geometry and the projection mode. The present invention uses a cylinder as the driving geometry, and constructs the blade helix tangent point trajectory suitable for four-axis processing according to the following steps:

a. Construct a cylinder as the driving surface. The cylinder should completely contain the blade, and the radius of the cylinder can be arbitrary;

b. Construct a cylindrical helix on the cylinder. The equation of the cylindrical helix, the optional parameters are pitch, rotation direction, starting position, etc.;

c. Projection. The reference point on the cylinder helix is the starting point, the vertical plane passing through the reference point is the cylinder axis, the intersection point between the vertical plane and the cylinder axis is the projection end point, and the intersection point between the projection and the blade is the projection point;

d. To construct the blade helix, the blade helix can be constructed by sequentially connecting the projection points, and the area between adjacent projection points can be interpolated or interpolated in the parameter domain.

Plane intersecting and segmentally constructing the blade helix: In NC programming, sometimes in order to ensure the local shape of the blade, the shape of the helix in this area may be required to meet special requirements. The shape of the edge head is one of the requirements for blade processing. In order to facilitate manual shoveling of the edge head, it is required that the residual height of the edge head after CNC machining is uniform and ensure that it has the shape of the edge head. This requires that the track of the edge head is similar to the section line of the edge head , it is difficult to meet this requirement with the usual programming method. The following is the method of segmentally constructing the blade helix using the plane intersection technique to construct the helix of the edge head to meet the shape requirements of the residual traces of the edge head:

a. Construct auxiliary plane group. The auxiliary plane group selects two sets of planes perpendicular to the axis of the blade, the distance between the planes in the plane family is the pitch h, and the distance between one group of planes and the other group of planes is h/2.

b. Find the intersection line between the plane group and the blade surface. Intersecting the two families of planes with the blades can result in two families of curve groups with edge shapes.

c. Trim the edge shape curve family with the limiting surface. Define the blade area that needs to maintain the shape of the edge head, usually use a plane or a curved surface to limit, use this limiting surface to cut the curve group obtained in the previous step, and obtain the curve of the shape of the edge head of the blade section.

d. The curves of the edge heads at both ends are lapped. The curves clipped by the limiting surface are divided into two groups, front and rear, and the two groups of curves are overlapped sequentially. The overlapping methods include interpolation in the blade parameter domain or Hermitian interpolation.

e. Lap curve projection. If the overlapping curve is not interpolated in the parameter domain, it may not fall on the blade surface, so the overlapping curve is projected onto the blade surface, and the projection direction can be selected as one of the normal vectors at both ends of the overlapping curve or other required methods.

f. Sequentially connect the edge head curve and the projection curve to form the blade helix. The above three methods of constructing the blade helix have their own advantages and disadvantages. The interpolation method in the parameter domain is simple and easy to implement, but it is only suitable for a single closed surface. The shape deviation of the section line is not large, but the shape deviation of the leaf back and the leaf basin is relatively large; the plane intersection segmented construction method uses algorithms such as surface-plane intersection, curve clipping, and curve-to-surface projection, and the amount of calculation is relatively large. But the helix shape can be fully controlled. Neither the interpolation method in the parameter domain nor the driving surface-projection method can well adapt to the characteristics of large curvature changes in the blade section, and only the segmented construction of the blade helix can solve this problem.

Operation S4:

The formula for calculating the cutting width of the ball nose cutter is:

$\mathrm{<span\; class="notranslate">\; \&omega;</span>}<span\; class="notranslate">\; =</span>\sqrt{\frac{\mathrm{<span\; class="notranslate">\; 8</span>}{\mathrm{<span\; class="notranslate">\; wxya</span>}}_{\mathrm{<span\; class="notranslate">\; the\; y</span>}}}{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; the\; y</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; r</span>}}}$

Calculation of the cutting width of the annular knife reference literature: Yu Daoyuan, Zhong Jianlin, Xiong Zhuang, Duan Zhengcheng. The calculation method and existing problems of the tool position trajectory in the space free-form surface NC programming [J]. Manufacturing Automation, 1997, (01): 21 -27.

Concrete operation of the present invention is as follows:

The blank is made of aluminum alloy sheet, specification: 100×70×30mm, workpiece material: aluminum alloy 7075/T651, as shown in Figure 4. The invention adopts four-axis spiral milling, the blank and the main shaft are always vertical, and the tool used for clamping is a combined fixture. One end of the blank is clamped on the combined fixture, while the other is in the state of a cantilever beam. The length of the cantilever is 70mm, and the length of the clamp is 30mm. The universal combined fixture is perpendicular to the spindle, and the tool is always perpendicular to the workpiece during processing.

The processing method chooses the processing method of helical milling, and the cooling method: emulsion cooling.

The processing tools are shown in Table 1:

Table 1 Tools used in each step

DMU 60mono BLOCK type CNC machining center (oscillating spindle B-axis, rotary lifting worktable) produced by German DMG is used for processing, and the CNC system is German HEIDENHAIN Itnc530 CNC system.

DMU 60mono BLOCK five-axis machining center machine tool structure and characteristics

The stroke of the X-axis of this machine tool is 630mm, the stroke of the Y-axis is 560mm, and the stroke of the Z-axis is 560mm. The spindle belongs to the electric spindle, the SK40 tool holder, the spindle speed can reach 18000rpm/min, the swing spindle B-axis, the swing range -120° ~+30°, the swing speed is 35rpm/min, and the table is a rotary C-axis. The diameter of the C-axis rotary table is 600mm, and it can rotate 360°. The maximum load capacity is 500Kg, and the workbench speed is 40rpm/min. The maximum machinable workpiece size is 650mm in diameter and 500mm in height. Linear axis (X, Y, Z) fast moving speed is 30m/min, maximum feed speed is 30000m/min, positioning accuracy: P max＝0.006mm, repeat positioning accuracy: Psmax＝0.004mm. It has an infrared probe, a 3D quick adjustment package to quickly restore the accuracy setting, and a tool breakage detection function. The machine tool also has the ATC function, that is, the fast programming parameter selection of processing tasks. It can quickly switch between precision, surface quality and processing speed according to the needs of the actual processing stage.

The CNC system of the DMU 60mono BLOCK CNC machining center adopts the three-dimensional HEIDENHAIN iTNC530 control system. HEIDENHAIN’s CNC system has been favored for its friendly man-machine interface, high speed, high precision, high surface quality and 5-axis machining control functions. famous. Whether it is milling, drilling, boring and machining center machine tools or lathes, HEIDENHAIN provides mature and reliable CNC systems for them.

In the processing experiment, the preliminary roughing and semi-finishing are prepared for the comparison test of finishing. The comparative test of finishing is mainly carried out from the three aspects of spindle speed n (r/min), feed rate f (mm/min) and back cutting amount a _p (mm), and these parameters are based on machine tool parameters And sure.

After confirming the comparison test, according to the theoretical geometric model of blade processing under the CAM template of NX7.0, the machining program is compiled by adopting the machining method of variable axial streamline. In order to ensure the consistency of processing, the compiled program only needs to modify the two parameters of the spindle speed n (r/min) and the feed rate f (mm/min), and the others remain unchanged. Select 7 blanks, respectively labeled 1#, 2#~7#, and the processing comparison test table is shown in Table 2.

Table 2 Parameters of 7 groups of aviation blade finishing

The 3D white light scanner was used to detect the finished aviation blades of groups 1# to 7#, and the detection results are as follows:

According to the data analysis of the test, the surface quality of the back of the 3# leaf is the best, and the occupancy rate of the surface green part is the highest among all the leaves. From the Y section, the maximum deviation of the surface of the leaf basin can be seen is relatively large, which is 0.789mm, which is the largest deviation value among all the leaves. The 1# blade belongs to the test piece of the program, so no matter from which point of view, the deviation value is the largest among all the blades. The surface deviation values of the remaining blades are not much different. Considering all the factors, the 4# blades are a relatively comprehensive group. First of all, from the perspective of surface processing quality, the maximum deviation of its surface is only 0.256mm. From the perspective of X-section direction and Y-section direction, the deviation value is also the smallest among all blades. So 4# is a relatively successful group of all blades.

The above is only a preferred embodiment of the present invention. It should be pointed out that for those of ordinary skill in the art, after knowing the content recorded in the present invention, they can also make changes to it without departing from the principle of the present invention. Several equivalent transformations and substitutions should also be deemed to belong to the protection scope of the present invention.

Claims (5)

1. A processing method for aviation blades, specifically comprising the following steps: Rough machining: use the driving surface and projection technology to construct multi-layer helical trajectory, and process the blank into rough products in the way of helical milling and retracting. The feed rate of each layer is set to 2mm, and a margin of 1mm is left after rough machining , the tool used for rough machining is a ring cutter; Semi-finishing: use the driving surface and projection technology to construct the helical trajectory, process the rough product into a semi-finished product according to the method of spiral milling and retracting, and leave a margin of 0.1-0.2mm after semi-processing. The tool used for semi-finishing is first ball head knife; Finishing: Use the interpolation method to directly construct the helix with the start control line and the end control line as the boundary, and project along the normal direction of the blade surface to ensure that the helix is located on the surface of the semi-finished product. The semi-finished product is processed into a finished product, and the linear axial movement is adopted at the starting point of the advance and retraction of the knife, and the tool used for finishing is the second ball-end knife. 2. The processing method of aviation blade according to claim 1, characterized in that: the processing method is implemented on a DMU 60mono BLOCK type CNC machine tool, and the DMU 60mono BLOCK type CNC machine tool is controlled by an Itnc530 numerical control system. 3. The method for processing aviation blades according to claim 1 or 2, characterized in that: the annular cutter is made of hard alloy material, and its diameter is: Number of teeth: 4, helix angle: 30°, overall length: 72mm, cutting edge length: 55mm. 4. The method for processing aviation blades according to claim 1 or 2, characterized in that: the first ball-end cutter is made of high-speed steel, and its diameter is: Number of teeth: 4, helix angle: 30°, overall length: 63mm, cutting edge length: 19mm. 5. The method for processing aviation blades according to claim 1 or 2, characterized in that: the second ball-end cutter is made of high-speed steel material, and its diameter is: Number of teeth: 4, helix angle: 30°, overall length: 57mm, cutting edge length: 13mm.