Figure 1 Disc part drawing
The disc-shaped parts have a large ratio of the length to the diameter of the parts, and the insufficient thickness of the parts results in poor rigidity and poor processingmanship. When machining parts, under the influence of cutting force, clamping force, cutting vibration and other factors, it is easy to process and deform, and the accuracy cannot be guaranteed.
Parts characteristics and processing difficulties
The disc Gear parts are shown in Figure 1. The parts are titanium alloy TC4-R, the outer diameter of the parts is φ201 mm, and the total thickness of the parts is 9 mm. The surface of both ends of the part is respectively designed with a relief groove, one surface is uniformly provided with six fan-shaped relief grooves, and the other surface has two annular relief grooves, and the thickness of the middle portion of the part becomes 3 mm. The number of gear teeth is 400, the modulus is 0.5mm, and the gear accuracy grade is 6. This part has a length to diameter ratio of 1:67 and is a thin-walled part with the following characteristics:
(1) The wall thickness of the part is insufficient and the rigidity is poor. Under the action of clamping force or cutting force, the thickness of the part is not enough to resist the clamping force, and it is easy to deform, and the dimensional accuracy, shape and position accuracy, and gear precision cannot be achieved.
(2) The weight of the parts is heavy, the outer diameter is large and thin, and there are various relief grooves on both sides. The positioning, support, and stress point are small, and the positioning and clamping are difficult.
(3) Under the action of cutting force, especially axial force, vibration and deformation are easily generated, which affects dimensional accuracy, shape and position accuracy, gear precision and surface roughness.
Process measures and precautions
The design of the disc-shaped gear parts is analyzed, and the blank is processed to the finished parts. The material removal rate is more than 60%, and the material removal rate is large. If the residual stress release problem is not well handled, the part processing process is easy to be caused. Medium and post-processing deformation, which can not meet the design requirements.
In order to reduce the influence of part deformation on the machining accuracy, the process flow is divided into rough machining → aging → finishing → machining. Roughing is mainly to remove a large amount of each surface. The aging is to remove the residual stress of the finishing. The finishing of the positioning surface in the finishing process is a key process, and the process is prepared for the subsequent finishing and gear processing. The gear machining arrangement is carried out after finishing.
Each process of the process must consider the release stress and control the deformation of the part. At any stage, the control deformation is analyzed and considered as an important part of the part processing to ensure the machining accuracy of the part.
After the roughing has retained the finishing allowance, the basic structure of the part has been fully formed. Roughing is the remaining amount of finishing, and under the premise of ensuring the finishing requirements, the remaining amount is kept as much as possible to ensure that the finishing will not cause large deformation after removing the remaining amount. According to experience and practice, the outer circumference has a margin of 0.3 to 0.4 mm on one side and 0.15 to 0.2 mm on the end surface. At the same time, the flatness of the end face of the part is limited during roughing.
When finishing, the selection of the positioning reference and the machining accuracy are essential to ensure the accuracy of the part. Before any high-precision surface processing, you must first select and process the positioning reference. In order to ensure the accuracy of the 6-stage gear, the machining reference of the part and the machining reference of the gear should be considered to coincide; the positioning reference is stable and reliable; the fixture used in the positioning reference design has a simple structure and is easy to operate. According to these principles, this part selects a hole and an end face as the positioning reference. The φ71 mm stepped hole (reference A) and its end face (reference B) are design and assembly references, but the hole length is too short and the end face is too small. It is obviously not appropriate to use them as a positioning benchmark. Therefore, the φ65 mm hole is selected for positioning, the positioning surface is relatively long, and the through hole is good. The fixture is easy to manufacture and the loading and unloading parts are also convenient. However, the φ65 mm hole has a large tolerance and there is no geometric tolerance. Therefore, when using this hole as the positioning reference, the dimensional accuracy and the coaxiality of the design reference φ71 should be increased. According to the experience and the general hole tolerance of the test, according to the IT7 level, the coaxiality is not more than 0.005mm to eliminate the process standard. The error caused by the non-coincidence with the design basis. The selection of the positioning end face, because the two large end faces are multi-groove, not a complete plane, the shape accuracy is not high, and the gear accuracy grade is 6 grade, the tooth direction error is 0.006mm, so the end face of the positioning surface should be improved. The position tolerance shall be not more than 0.005 mm according to the practice flatness, the perpendicularity requirement of the end face to the positioning hole φ65 mm shall not exceed 0.005mm, and the parallelism of the reference plane B shall be not more than 0.005 mm, and at the same time according to the gear precision level. Check the table to select the jump value of the other end face of the part to the positioning hole. The φ65 mm hole and one large end face are selected as the positioning reference surface to ensure the standardization of finishing, gear machining, inspection and installation. Although the baseline was converted, the process took steps to meet the design requirements.
The precision of the parts is high. The processing of the finishing positioning holes and the positioning end faces is the key technology of machining, mainly by the fitter and the lathe. The fitter cooperates with the lathe to ensure the position tolerance of the positioning hole and the positioning end face of the part. Firstly, the positioning surface of the truck and a hole φ93 mm are required to be finished once, and then the machined end face is trimmed to ensure a flatness of 0.005 mm. The turner is positioned with the ground end face and φ93 mm, and the axial compression is φ65 mm. Φ71 mm, annular groove, end face and maximum outer diameter φ201 mm, requiring one-time machining. This ensures the dimensional tolerance requirements of the part.
It is worth noting that the machining process should reduce the cutting force, control the amount of cutting, and prevent the parts from vibrating. The clamping force is properly controlled. It is necessary to ensure that the parts are clamped and the parts cannot be deformed, so as to control the force of the parts during the clamping process. The deformation amount can be controlled by the method of end face type; the end face connection should avoid the assembly position, the part positioning and the pressing position; the flatness is 0.005mm, because it is not the design requirement, it is the requirement of the process, and it is not necessary to have the actual measurement. Data, as long as it can meet the final gear processing accuracy requirements. By tracking the scene, it is found that as long as the part positioning surface is pushed on the inspection platform, it is felt that there is uniform mutual suction, the flatness of the part can satisfy the processing precision of the subsequent parts, and the method of hitting the end surface on the platform can also be used. In conjunction with this test, this test method is easy to operate and easy to master.
While ensuring the necessary hardness and precision of the hobbing fixture, the design of the positioning surface and the pressing surface of the clamp is critical. According to the structure of the part, in order to eliminate the deformation caused by the unevenness of the positioning surface, the parts are accurately obtained. For reliable clamping, the annular solid surface near the root of the part is selected as the positioning and pressing position. Therefore, a large annular groove should be formed on the positioning end face and the pressing block of the clamp to allow the non-positioning part of the part to be removed, so that the weight of the clamp can be reduced and the clamp can be easily manufactured.
After the fixture is mounted on the hobbing machine, the fixture should be aligned. The positioning axis of the aligning fixture is concentric with the table; the positioning axis of the aligning fixture is perpendicular to the table; the positioning end of the aligning fixture is parallel to the table. Note that the radial runout of the clamp is no more than one-third of the radial runout requirement of the machined part. For fixtures with a long positioning part, it is necessary to correct two points and make the two points jump in the same direction so that the fixture is not perpendicular to the table. The end face jump of the clamp is determined according to the radius of the end face of the clamp support, and is generally 0.006 to 0.01 mm.
The installation of the parts is related to the accuracy of the processed gears, so the parts should be reliably fixed, and the outer diameter of the parts should be checked. It should be concentric with the fixture, and should not be deformed when the parts are clamped. The workpiece can be inspected by means of table. The clamping situation.
Due to the large gear modulus and high machining precision, the material of the parts is titanium alloy. This material has high strength, high hardness, impact resistance, easy hardening during processing, high cutting temperature and serious tool wear. It is difficult to process materials, and it is hard to use AA grade. Alloy hobs, and processed in multiple passes.
Table 1 Gear parameters and inspection items
It can be seen from Table 1 that by using the gear measurement function in the Quindos measurement software on the coordinate measuring machine, the measurement of the tooth direction, the tooth profile, the circumferential section error, the cumulative error of the circumference and the radial runout of the ring gear are completed at one time, and Measurement results can be output to meet user testing requirements.
The material of the parts is titanium alloy, the burr is tough and difficult to remove. It needs to sharpen the large burr and tooth surface bond under the magnifying glass with a sharp tool, then partially repair the light, and then use the conventional gear deburring method to deburr. Finally, it is treated with an ultrasonic cleaner so that the surface of the gear will be clean.
The above process has been applied in many batches of parts on site and has withstood the test. It solves the production problem for on-site production and processing. The qualification rate of parts can reach 99%. The conservative estimation of 300 pieces (including φ181 and φ201 gears) can create millions of economic benefits, and also accumulated experience in precision component processing.
