Process dimension analysis of fixture
It is very important to fix the fixture in the process of machining. When the location is not accurate or vibration occurs in the process of machining, it will affect the accuracy of each segment of the part in the process of machining. And with the final completion, the workpiece will deviate from the original size requirements and can not meet the design requirements, which requires reasonable clamping to ensure the stability in the processing and ensure the processing quality. The use of clamps shall be simple and easy to install or disassemble,
The design of fixture mainly includes positioning scheme, clamping scheme and machining accuracy. The clamp has its own advantages, simple structure and convenient operation. With precise positioning. Main technical requirements of spiral bevel gear
1)The roundness tolerance of shaft ф 65 and shaft ф 50 is within 0.06.
2)The perpendicularity of adjacent two shafts is within ф 0.05.
As the part material is 20grmnti alloy steel, the shape is regular. The accuracy class is it11.
Selection of positioning reference and determination of positioning device
The positioning of the workpiece is realized by the contact between the positioning surface on the workpiece and the positioning element V-block on the fixture. Positioning datum is the datum to determine the position of workpiece, which is reflected by positioning datum.
The function of the positioning element is to make the workpiece have accurate and constant position in the fixture, and to limit enough freedom under the condition of ensuring the machining requirements.
Basic requirements for positioning elements
(1) Enough precision positioning elements shall have enough precision to ensure the positioning accuracy of workpiece.
(2) Good wear resistance because the working surface of the positioning element often contacts and rubs with the workpiece, which is easy to wear. Therefore, the wear resistance of the working surface of the positioning element is required to be better to maintain the service life and positioning accuracy.
(3) Sufficient strength and rigidity positioning elements shall not be deformed or damaged when they are affected by the gravity, clamping force and cutting force of the workpiece. Therefore, the positioning elements are required to have sufficient rigidity and strength, otherwise the positioning accuracy of the workpiece will be affected.
(4) Better technological positioning elements shall be easy to manufacture, assemble and maintain.
(5) The shape of the working surface of the chip positioning element which is convenient for removing chips shall be favorable for removing chips, so as to prevent chip embedding from affecting the accuracy.
The positioning elements for spiral bevel gear machining are V-shaped blocks and pressing plates.
After the workpiece is positioned, before drilling, it must be clamped with a clamping device. The clamping device uses air pressure to drive the double-sided oblique wedge movement to tighten the pressing plate, so as to ensure that the workpiece does not produce displacement or vibration under the action of cutting force, gravity, inertia force, etc., which affects the processing quality and even makes the processing unable to proceed smoothly. It can be seen from the part drawing that the gear shaft is the rotating surface. Since the outer circles have been processed during the gear processing, each outer circle surface can be used as the positioning datum. Because the small end journal of spiral bevel gear (Φ 50mm) and the Journal (m27mm) are the mating surfaces. From the part design, the end face of Φ 50mm journal is the design datum, and its axis is the datum of form and position tolerance. Therefore, it can be determined that the positioning datum of tooth machining should be the end face of the Φ 50mm and m27mm journal. The five degrees of freedom of X movement, Z movement, y movement, y rotation and Z rotation can be limited by positioning this plane as the reference, and then the six degrees of freedom can be limited by fixing the two end faces.
It can be seen from the part drawing that the gear shaft is the rotating surface. Since the outer circles have been processed during the gear processing, each outer circle surface can be used as the positioning datum. Because the small end journal of spiral bevel gear (Φ 50mm) and the Journal (m27mm) are the mating surfaces. From the part design, the end face of Φ 50mm journal is the design datum, and its axis is the datum of form and position tolerance. Therefore, it can be determined that the positioning datum of tooth machining should be the end face of the Φ 50mm and m27mm journal. The five degrees of freedom of X movement, Z movement, y movement, y rotation and Z rotation can be limited by positioning this plane as the reference, and then the six degrees of freedom can be limited by fixing the two end faces.
Fixture assembly drawing
