Analyze and discuss the web structure of the right side wall of a key component of a project, combine the properties of titanium alloy materials, select reasonable tools, processing methods and effective cutting parameters, and develop a complete set of processing procedures, and form a set of available Digital processing plan for processing similar parts.
The web on the right side wall is one of the main connecting parts and load-bearing parts of the side wall. It has a large size, a large number of large-angle opening and closing angles, a large height span, a complex shape of the variable-angle inner surface, and a serious allowance for die forgings. Uneven characteristics. How to use a combination of multiple processing techniques such as stepwise layered milling, shallow cutting, fixed pendulum angle line cutting and variable angle processing to achieve small deformation and high efficiency processing is the focus of this article.
2. Parts introduction
The web of the right side wall is one of the main connecting webs of the side wall of the bomb bay. It has a complex shape, many variable-angle hyperboloids, and a large height span, which is difficult to process. The parts are titanium alloy die forgings, and the outer dimensions are 690mm×500mm×185mm, as shown in Figure 1.
a) The front of the right side wall web
b) The reverse side of the right side wall web
Figure 1 Web of the right side wall
3. Problem analysis
According to the material properties, part process structure and incoming material status, analyze the problems in the processing process and formulate reasonable solutions to ensure that the parts can be processed with high quality and efficiency.
3.1 Material performance
The part material is a typical α-phase titanium alloy, which has higher strength than steel, high metal melting point, high temperature resistance of 550°C, and good low temperature toughness. In addition, titanium alloy also has good corrosion resistance. The surface of the material will form a dense oxide film in a medium and low temperature environment to prevent further oxidation. It has corrosion resistance to air, water, and general acids and alkalis. Due to the unique properties of the material, there are still some processing difficulties in the processing process.
(1) Poor thermal conductivity During high-speed machining, the cutting heat cannot be quickly transferred, and an oxide film is easily formed on the surface, which leads to thermal wear of the tool, and the mechanical wear increases exponentially and the service life is reduced.
(2) With high strength and poor plasticity, the rake face of the tool is subjected to too much force during the machining process, and it is easy to chip.
(3) The elastic modulus is low, the springback is more serious after the deformation is large, and the contact area between the flank face and the material increases, which accelerates the tool wear.
(4) Material activity is high. Heated tools are prone to chemical reactions, resulting in sticking phenomenon, and damaging tools and parts.
In summary, in the processing of titanium alloys, tools with small rake angles and large relief angles should be used. The tool materials are mostly cemented carbide, and the cutting amount should be relatively small, thereby reducing the generation of cutting heat.
3.2 Process structure
The outer dimensions of the parts are 690mm×500mm×185mm, and the height dimension is larger; the web thickness is 6.5mm, the rib thickness is 3mm, 4mm, 6mm and 12.5mm, and the shape is closed at 35°. Two vertical milling and one horizontal milling are required to process the two sides of the parts to ensure that the inner and outer sides are all processed in place. The shape of the middle circular contour is mostly a hyperboloid with a variable angle, which requires a combination of multiple programming methods such as fixed swing angle, dynamic swing angle, vertical bottom surface fixed axis, etc. for processing. The edge rib height span of the entire part is from 22mm to 100mm, and the inner shape width span is from 11mm to 100mm. Reasonable selection of tools and arrangement of process steps have become one of the important means to improve efficiency and surface quality.
3.3 Incoming status
The incoming material type is die forgings, with a margin of 3mm on one side of the web, and a margin of 8mm on one side of the vertical edge ribs. The unevenness of the shape margin at the middle large circle and the large closed corner is more serious, the metal removal rate is 70%, and the cutting workload relatively bigger.
3.4 Problems during processing
①The incoming parts cannot be clamped, so the incoming materials need to bring the craft boss and trim the datum plane. ②The internal and external vertical milling at the large closed angle cannot be processed in place, so it needs to be processed with the horizontal milling station to ensure that the size is qualified. ③The big circle in the middle is all hyperboloid with variable angle, which needs to be guaranteed by variable angle milling and fixed pendulum angle cutting. ④The structure of the parts is complex, and a total of 6 workstations are required for processing, and the reasonable combination of procedures is worth studying. ⑤There are 6 sets of 2×φ10C9 assembly holes that need to be drilled. The axis of the holes is below the web surface, and the processing method needs to be considered. ⑥The relationship between the large hole in the middle assembly bearing and the surrounding threaded hole requires special attention to ensure the rationality of the assembly.
4. Develop a processing plan
Parts from die forgings to finished products need to go through multiple processes such as reverse surface reference processing → front rough processing → reverse surface roughing and finishing → front finishing → reverse horizontal processing → conventional boring processing. The reasonable arrangement of the process and the processing quality of each process will affect the product quality of the entire part. The reasonable selection of the processing tools for each step, the clamping positioning method, the reserved margin, the processing method, etc. will affect the product quality and processing efficiency. . Therefore, the analysis and research are mainly carried out from the following four aspects.
4.1 Machining tools
Analyze the size of the parts, the height direction and the width direction of the groove are relatively large, and the reasonable selection of tools with a variety of diameters, tool lengths, and cutting depths can effectively improve the processing efficiency. In addition, long knives for processing deep grooves and short knives for processing shallow grooves can effectively avoid knife loss, and the dimensional accuracy can be easily guaranteed. Large-diameter cutters for rough milling and small-diameter cutters for fine milling can improve the surface quality. The speed-up of the fine milling cutter can reduce the edge of surface processing and obtain better surface roughness. This part mainly uses φ40mm long knife, φ40mm short knife, φ20mm long knife, φ20mm short knife, φ16mm long knife, φ16mm short knife and φ12mm, φ10mm and other tools with different bottom radii, which are obtained on the basis of being able to process qualified parts. The highest processing efficiency and the best surface quality.
4.2 Clamping positioning
Aiming at the characteristics of large part outline size, high requirement of dimensional accuracy of key features, and large number of processing procedures, the use of two-hole positioning can effectively improve processing accuracy and reduce positioning errors caused by multiple turnings. The use of web positioning requires multiple revisions of datums, inverted plates, and customized bosses. The processing efficiency is low and the cost is high. The edge strip positioning is adopted, the edge strip has a large step difference, the positioning accuracy is poor, and there are many special pressure plates and spacers and the processing is in progress. The board needs to be reversed many times, and there are also the disadvantages of low processing efficiency and high cost. Relatively speaking, it is more appropriate to use the process boss for positioning, only a special set of pads is enough, and the reference can be repaired once to ensure that the error of multiple flips is reduced. The boss is used for positioning, and the processing of each station is not disturbed. , No need for workers to adjust the position of the pressing plate back and forth, which can effectively improve work efficiency. This part adopts 8 bosses uniformly distributed positioning method, two of which have a set of positioning holes, which meets the processing requirements, improves the processing efficiency and quality, and reduces the production cost at the same time.
4.3 Reserved margin
There are many variable-angle machining and large-angle closed-angle machining in the machining process. In order to ensure sufficient allowance in multi-station machining, the rough machining allowance is 2mm, semi-finishing allowance is 0.5mm, and the final finishing is in place. Reserve a margin plan to minimize the probability of parts out of tolerance due to positioning errors and cold working deformation errors.
4.4 Processing method
The part adopts ABBAB’s reversal processing method. One-sided two-hole positioning is carried out through the boss surface and the boss positioning holes on both sides. The multi-station positioning datum overlaps, the positioning error is small, the multi-station processing, the stress release is uniform, and the cold working deformation is small . According to the characteristics of the parts with more opening and closing angles, variable-angle internal contours, hyperboloid oblique ribs, etc., use a high-efficiency and high-power five-axis vertical milling machine and a combination of low- and medium-power, high-precision five-axis horizontal milling machines. For processing, the following methods are used to deal with multiple difficult-to-machine structures, aiming to optimize dimensional accuracy, product surface quality, processing efficiency and machine tool utilization.
1) The incoming material is a die forging, the inner shape of the opening and closing corners and the margin of the annular cylindrical surface in the middle range from 5 to 50 mm. The contour is reduced by layer processing, combined with a shallow cut of 2 mm, which can make the cutting amount of each pass Uniformity, effectively improving processing efficiency and processing quality, reducing cutting force and stress concentration, and reducing tool wear and processing costs.
2) φ40mm tool is used for rough machining, and the corner allowance after machining is large. For corners whose margin width does not exceed 10mm, use φ20mm cutter and φ16mm cutter to clean up in sequence. For larger margins, use axial layered fixed-angle rotary milling to ensure that the subsequent finishing corner margins are as small as possible , To avoid the situation that the cutting amount of variable angle is too large, which causes the tool to break or gnaw on the parts.
3) As shown in Figure 2, there is a large closing angle at the outer shape (the inner shape is the opening angle). The angles on both sides are 26° and 35°, and the height along the curved surface is 100mm. The vertical milling machine A and B angles are both It is ±30°. During processing, the front inner contour can be rough milled→semi-finished milling cutter→finish milling in place, and the conforming profile processing method is adopted. The inner contour of the back is processed with a 29°fixed pendulum angle to maximize the removal of margins and ensure The subsequent horizontal processing workload is as small as possible.
Figure 2 Closed corner
4) As shown in Figure 3, the axis of the central circular cylinder forms an angle of 26° with the web surface. In theory, it can be directly processed by a five-axis vertical milling machine. However, in the processing process, the cylindrical surface needs to be processed with a variable angle for swing angle processing. There is a situation of rapid angle change. In order to ensure the surface quality of the surface and improve the processing efficiency at the same time, rough processing uses dynamic swing angle radial layered processing, semi-finish processing The fixed and dynamic swing angles are combined with single-layer processing, and the finishing process adopts multiple fixed-swing angle connection processing schemes. The combination of different processing methods not only ensures the stability of processing, the accuracy of dimensional accuracy, but also improves the processing efficiency. , Reduce the surface unevenness caused by the angle of the cutter shaft.
Figure 3 Annular cylinder
5) As shown in Figure 4, the axis of the assembly holes on the three sets of lugs is located below the web surface, the accuracy is required to be φ10C9mm, the hole distance on the single set of lugs is required to be 50+0.1 -0.1mm, and the coaxial hole needs to be processed as much as possible at one time , Because the third set of holes is insufficient in the inner shape size, it needs to be drilled and reamed twice to make it. When processing, use a set of drilling dies to match various specifications of guide sleeves. First, use a reamer with front and rear guides of 50mm length to process the first two sets of ears, and then use a reamer with a rear guide of 150mm to process the third group. The lugs not only ensure the dimensional accuracy of the holes, but also ensure the hole spacing and coaxiality through the same tooling and the same station.
Figure 4 Ear piece
5. Processing tolerance distribution and measurement method
During the inspection and measurement process, except for the thickness of the web, the thickness of the edge rib, and the height of the edge rib parallel to the web, the remaining dimensions are measured by a digital measuring machine, which reduces the difficulty and workload of manual measurement, and shortens the cost of parts Production cycle.
By analyzing the characteristics of the titanium alloy right side wall web parts, a set of efficient machining plans was developed, achieving the goals of less manual intervention, reducing work costs, improving cutting efficiency, and improving surface quality, and summing up machining experience and parameter selection The solution provided support and assistance for the processing technology of similar parts.