Due to the large ratio of part length to diameter and insufficient part thickness, disk parts have poor rigidity and poor processing technology. When machining parts, it is easy to deform under the action of cutting force, clamping force, cutting vibration and other factors, and the accuracy can not be guaranteed.

Characteristics and processing difficulties of parts
The disc gear parts are shown in Figure 1. The material of the parts is titanium alloy tc4-r, and the outer diameter of the parts is φ 201mm, the total thickness of parts is 9mm. Relief grooves are respectively designed on the surfaces at both ends of the part. Six fan-shaped relief grooves are evenly distributed on one surface, and two annular relief grooves are arranged on the other surface. The thickness of the middle part of the part becomes 3mm. The number of gear teeth is 400, the module is 0.5mm, and the gear accuracy grade is grade 6. The maximum length diameter ratio of this part reaches 1:67, which is a thin-walled part. It has 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 action of clamping force, which is prone to deformation and can not meet the requirements of dimensional accuracy, shape and position accuracy and gear accuracy.
(2) The parts have heavy weight, large and thin outer diameter, multiple relief grooves on both sides, small positioning, support and force points, and difficult positioning and clamping.
(3) Under the action of cutting force, especially axial force, it is easy to produce vibration and deformation, which affects the dimensional accuracy, shape and position accuracy, gear accuracy and surface roughness of parts.
Process measures and precautions
The design drawing of disc gear parts is analyzed. When the blank is processed to the finished parts, the material removal rate is more than 60%. If the residual stress release problem can not be handled well, it is easy to cause deformation during and after processing, which can not meet the design requirements.
In order to reduce the influence of part deformation on machining accuracy, the process flow is divided into rough machining → aging → finish machining → machining. Rough machining is mainly to remove large allowance on each surface. Aging is to remove the residual stress of finishing. The finishing of positioning surface is the key process in finishing, which makes process preparation for subsequent finishing and gear processing. Gear processing is arranged after finishing.
Stress release and part processing deformation control shall be considered in each process of the process flow. No matter which stage, the control deformation shall be analyzed and considered as an important part of part processing, so as to ensure the machining accuracy of parts.
After the rough machining retains the finish machining allowance, the basic structure of the part has been machined and formed. Rough machining is the allowance left for finish machining. On the premise of ensuring the requirements of finish machining, the retention of allowance shall be minimized to ensure that finish machining will not cause large deformation after removing the allowance. According to experience and practice, 0.3 ~ 0.4mm shall be reserved for one side of the outer circle and 0.15 ~ 0.2mm shall be reserved for the end face. At the same time, the flatness of the end face of the part shall be limited during rough machining.
During finishing machining, the selection of positioning datum and machining accuracy are very important to ensure the accuracy of parts. Before any high-precision surface processing, the positioning datum must be selected and processed. In order to ensure the accuracy of grade 6 gear, it should be considered to coincide the part machining datum with the gear machining datum; The positioning datum is stable and reliable; The fixture designed by the positioning datum used has the principle of simple structure and easy operation. According to these principles, this part selects a hole and an end face as the positioning datum. φ 71mm step hole (datum a) and its end face (datum b) are the design and assembly datum, but the hole length is too short and the end face is too small. It is obviously inappropriate to use them as positioning benchmarks. So choose φ 65mm hole positioning, the positioning surface is relatively long, and it is a through hole. The fixture is easy to manufacture and easy to load and unload parts. however φ The tolerance of 65mm hole is large, and there is no geometric tolerance limit. Therefore, when selecting this hole as the positioning datum, its dimensional accuracy and design datum shall be checked φ 71. According to experience and test, the hole tolerance is generally it7, and the coaxiality is no more than 0.005mm, so as to eliminate the error caused by the non coincidence of process datum and design datum. For the selection of positioning end face, because two large end faces have many grooves and are not a complete plane, its shape accuracy is not high, while the gear accuracy grade is grade 6 and the tooth direction error is 0.006mm. Therefore, the shape and position tolerance requirements of the end face as the positioning surface shall be improved. According to the practice, the flatness shall not be greater than 0.005mm, and the end face shall face the positioning hole φ The perpendicularity of 65mm shall not be greater than 0.005mm, and the parallelism of datum plane B shall not be greater than 0.005mm. At the same time, the runout value of the other end of the part facing the positioning hole shall be selected according to the gear accuracy grade check table. Choose φ 65mm hole and a large end face are used as the positioning datum plane to ensure the unity of datum during finishing, gear processing, inspection and installation. Although the benchmark has been converted, the process measures have met the design requirements.
The precision of parts requires high precision. The machining of precision machining positioning hole and positioning end face is the key technology of machining, which is mainly carried out by fitter and lathe worker. The fitter shall cooperate with the lathe to ensure the geometric tolerance requirements of the positioning hole and positioning end face of the parts. Firstly, the positioning surface and a hole are arranged by the lathe operator φ 93mm, which is required to be processed at one time, and then the fitter grinds the processed end face to ensure the flatness of 0.005mm. The lathe operator shall use the grinded end face and φ 93mm positioning, axial compression processing φ 65mm、 φ 71mm, annular groove, end face and maximum outer diameter φ 201mm, one-time processing is required. This ensures the geometric tolerance requirements of parts.
It should be noted that the cutting force should be reduced in the machining process, and the tool walking amount should be controlled to prevent the vibration of parts; The clamping force shall be properly controlled to ensure that the parts are clamped and can not deform. In order to control the stress deformation of the parts in the clamping process, the end face can be controlled by marking the table; The end face cutter shall avoid the assembly position, part positioning and pressing position; The flatness detection of 0.005mm is not the design requirement, but the requirement of the process. There is no need to have the measured data, as long as it can meet the requirements of the final gear machining accuracy. Through tracking the site, it is found that as long as the positioning surface of the part is pushed on the inspection platform, it feels that there is uniform mutual suction, and the flatness of the part can meet the machining accuracy of subsequent parts. At the same time, the method of marking the end face on the platform can also be used together. This inspection method is easy to operate and master.
While ensuring the necessary hardness and accuracy of the gear hobbing fixture, the design of the fixture positioning surface and pressing surface is very key. According to the structure of the part, in order to eliminate the deformation caused by the uneven positioning surface and the pressing process of the part, and make the part obtain accurate and reliable clamping, the annular solid surface of the two end faces of the part close to the tooth root is selected as the positioning and pressing position. Therefore, a large annular groove shall be machined on the positioning end face and pressing block of the fixture to make way for the non positioning part of the part, which can reduce the weight of the fixture and make the fixture easy to manufacture.
After the fixture is installed on the gear hobbing machine, the fixture shall be aligned. The positioning shaft of the alignment fixture is concentric with the workbench; The positioning axis of the alignment fixture is perpendicular to the workbench; The positioning end face of the alignment fixture is parallel to the workbench. Note that the radial runout of the fixture shall not be greater than one third of the radial runout of the machined parts. For the fixture with long positioning part, it is necessary to correct the two points and make the jumping direction of the two points consistent, so as to avoid that the fixture installation is not perpendicular to the workbench. The end face runout of the fixture is determined according to the radius of the supporting end face of the fixture, which is generally 0.006 ~ 0.01mm.
The installation of parts is related to the accuracy of the processed gear, so the parts should be fixed reliably. At the same time, check the outer diameter of the parts, which should be concentric with the fixture, and there should be no deformation when the parts are clamped. The clamping condition of the workpiece can be checked by printing a table.
Because the gear module is small and the machining precision is high, the part material is titanium alloy. This material has high strength, high hardness, impact resistance, easy hardening in machining, high cutting temperature and serious tool wear. It is a difficult machining material. AA grade cemented carbide hob is selected and processed by several times.

It can be seen from table 1 that by using the gear measurement function in the QUINDOS measurement software on the CMM, the measurement of tooth direction, tooth shape, pitch error, pitch cumulative error and ring gear radial runout can be completed at one time, and the measurement results can be output to meet the user's detection requirements.
The material of the parts is titanium alloy. The burrs are tough and difficult to remove. It is necessary to shovel the large burrs and tooth surface adhesive under the magnifying glass with a sharp tool, then polish the parts, then deburr the gears with the conventional gear deburring method, and finally treat them with an ultrasonic cleaning machine, so that the gear surface will be clean.
The above process method has been applied in many batches of parts on site and has withstood the test. The production problem is solved for on-site production and processing. The qualified rate of parts can reach 99% and 300 pieces (including φ 181 and φ 201 two kinds of gears) are conservatively estimated to create millions of economic benefits and accumulate experience in precision component processing.