Talking about the Processing Technology of Disk Precision Gear Parts

Due to the large ratio of length and diameter of the parts of the disc-shaped parts, the lack of part thickness results in poor rigidity and poor processability. When the parts are processed, they are easily deformed under the action of cutting force, clamping force, cutting vibration and other factors, and the accuracy cannot be guaranteed.

Part features and processing difficulties

The disk gear parts are shown in Fig. 1. The part material is titanium alloy TC4-R. The outer diameter of the part is φ201mm, and the total thickness of the parts is 9mm. Relief grooves are respectively designed on the surfaces of the two parts of the part, one surface is uniformly distributed with six fan-shaped lightening grooves, and the other surface is provided with two circular lightening grooves, and the thickness of the middle part of the parts is changed to 3mm. The number of gear teeth is 400, the module is 0.5mm, and the gear accuracy grade is 6. The maximum aspect ratio of this part is 1:67. It is a thin-walled part. It has the following features:

(1) Insufficient wall thickness and poor rigidity of the part. Under the action of clamping force or cutting force, the thickness of the part is not enough to resist the clamping force. It is easily deformed, and dimensional accuracy, shape accuracy, and gear accuracy cannot be achieved.

(2) The parts are heavy, with large and thin outside diameters, and there are various relief grooves on both sides. Positioning, supporting, and stress points are small, and positioning and clamping are difficult.

(3) Under the action of cutting force, especially axial force, it is easy to produce vibration and deformation, affecting the dimensional accuracy, shape accuracy, gear accuracy and surface roughness of parts.

Process measures and precautions

The analysis of the design drawings of the parts of the crown gears, the processing of the blanks to the finished parts, the removal rate of the material is more than 60%, and the greater the material removal rate, if the problem of residual stress release cannot be handled well, the parts processing process is easily caused. In the deformation after processing, it can not meet the design requirements.

In order to reduce the effect of part deformation on machining accuracy, the process flow is divided into rough machining → aging → finishing → machining. Roughing is mainly to remove large margins on each surface. Aging is the removal of the residual stress of finishing. The finishing process of the positioning surface in the finishing process is a key process, and it prepares the process for subsequent finishing and gear machining. Gear machining arrangements are performed after finishing.

Each process of the process must consider the release of 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 accuracy of the part.

After rough machining retains the finishing allowance, the basic structure of the part has been fully formed. Roughing is reserved for finishing. Under the premise of guaranteeing the finish machining requirements, the remaining amount should be kept as small as possible to ensure that the finishing will not cause large deformation after removing the excess. According to experience and practice, the remaining margin of the outer circle is 0.3-0.4mm, and the end surface is 0.15-0.2mm. At the same time, the flatness of the end surface of the part must be limited during rough machining.

When finishing, the choice of positioning reference and machining accuracy are critical to ensuring part accuracy. Before any high-precision surface machining must first select and process the positioning reference. In order to ensure the accuracy of the 6th gear, the machining reference of the part and the reference of the gear should be considered to coincide; the positioning reference is stable and reliable; the fixture used for the positioning reference design is simple in structure and easy to operate. According to these principles, this part selects a hole and an end face as the positioning reference. The φ71mm step 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 reference. Therefore, the use of φ65mm hole positioning, positioning surface is relatively long, it is a through hole, a good fixture manufacturing and loading and unloading parts is also convenient. However, the φ65mm hole has a large tolerance and there is no geometric tolerance limit. Therefore, when selecting this hole as the positioning reference, it is necessary to improve the dimensional accuracy and the coaxiality of the design reference φ71. According to experience and test, the general hole tolerance is IT7, and the coaxiality is not more than 0.005mm to eliminate the process benchmark. Misalignment with design basis. The selection of the positioning end face is due to the fact that the two large end faces with multiple grooves are not a complete plane. The shape accuracy is not high, and the gear accuracy grade is 6 and the tooth orientation error is 0.006 mm. Therefore, the end surface of the positioning surface must be improved. Tolerance requirements, according to the practical flatness should not be greater than 0.005mm, the verticality of the end facing the positioning hole φ65mm requirements should not be greater than 0.005mm, the parallelism of the reference plane B should not be greater than 0.005mm, at the same time check according to the gear accuracy level The table selects the jump value of the positioning hole at the other end of the part. The φ65mm hole and a large end face are used as the positioning reference plane to ensure the reference and unity during finishing, gear machining, inspection and installation. Although the baseline was converted, the process took measures to meet the design requirements.

The precision of the parts is required to be high. The machining of the positioning hole and the positioning end face of the finishing machining is a key technology of the machining, which is mainly performed by fitters and turners. The fitter cooperates with the lathe to ensure the geometrical tolerances of the positioning holes and the positioning end faces of the parts. Firstly, the positioning surface of the truck and a hole φ93mm require a machining completion, and then the fitter grinds the processed end face to ensure the flatness of 0.005mm. The lathe is positioned with the studied end face and φ93mm, and the axial compression processing is φ65mm, φ71mm, and a ring. The groove, end face, and maximum outside diameter φ201mm require complete machining. This ensures the geometrical tolerances of the part.

It is worth noting that: cutting process to reduce cutting force, control the amount of knife, to prevent chattering parts; clamping force control is appropriate, not only to ensure that the parts can not clamp clamping deformation, in order to control the force of the parts in the clamping process Deformation can be controlled by the use of face-to-face metering; end face knives must avoid assembly position, part positioning, and compression position; flatness 0.005mm detection, because it is not a design requirement, is the process requirements, does not necessarily have to be measured The data, as long as it can meet the final gear processing accuracy requirements. By tracking the scene, we found that as long as the component positioning surface is pushed on the inspection platform, it feels that there is a uniform suction force, and the flatness of the component can meet the processing precision of the subsequent parts. At the same time, the method of using the surface of the table on the platform can also be used. Used in conjunction with this test method is easy to operate and to master.

While ensuring the necessary hardness and accuracy of the hobbing jig, the design of the jig positioning surface and the pressing surface is critical. According to the structure of the parts, in order to eliminate the deformation due to the uneven positioning surface and the parts in the pressing process, the parts can be accurately obtained. Reliable clamping, use the annular solid surface of the two end faces of the part close to the root of the tooth as the positioning and pressing position. Therefore, a large annular groove should be made on the positioning end face of the clamp and the pressing block so as to release the non-positioned part of the part. This can reduce the weight of the jig and the jig can be easily manufactured.

After the fixture is mounted on the gear hobbing machine, the fixture should be calibrated. The alignment axis of the alignment fixture is concentric with the workbench; the positioning axis of the alignment fixture is perpendicular to the workbench; the positioning end surface of the alignment fixture is parallel to the workbench. Note that the jig's radial runout is no more than one-third of the radial run-out requirement of the machined part. For a fixture with a relatively long positioning section, two points need to be corrected and the directions of the two points jumped in order to prevent the fixture from being installed perpendicular to the workbench. The end face of the jig is determined according to the radius of the end face of the jig, generally 0.006-0.01mm.

The installation of the parts is related to the accuracy of the processed gears. Therefore, the parts should be reliably fixed. At the same time, the outer diameter of the parts should be inspected, concentric with the fixtures, and deformation should not occur in the case of the parts being clamped. The clamping situation.

Due to the small module of the gear and high machining accuracy, the material of the parts is titanium alloy. This material has high strength, high hardness, impact resistance, easy to harden in the process, high cutting temperature, serious tool wear, and is difficult to machine. AA hard grade is used. Quality alloy hob, and divided several times processing.

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 tooth direction, tooth shape, circumferential error, circumferential accumulated error and ring gear radial runout measurement are completed at once. Can output measurement results to meet user testing requirements.

The material of the parts is titanium alloy. The burrs are tough and difficult to remove. The sharp burrs are used to scoop out the larger burrs and tooth surface adhesives under a magnifying glass, then the parts are lighted, and then the conventional gear deburring method is used to deburr. Finally use an ultrasonic cleaner to clean the gear surface.

The above process method was applied in the field of multi-batch parts and was tested. For the production and processing of the site to solve the production problems, parts qualified rate can reach 99%, processing 300 (including φ181 and φ201 two kinds of gear) conservative estimates can create millions of economic benefits, but also accumulated the experience of precision parts and components processing.