Advanced Fitter Technology

Author: Chief Editor: Zhu Hua
Publisher:
Publish Date: 1999-06-01
Features: This book is written based on the content of the "Occupational Skill Identification Specification" jointly issued by the former Ministry of Labor and the Ministry of Machine Industry for intermediate and senior fitters. The main contents include: marking out of deformed and large workpieces; precision measuring instruments and their applications; mechanical assembly and the preparation of process codes; detection of vibration and noise during machine operation; modern manufacturing technology.
Fragment:
Chapter Marking Out of Deformed and Large Workpieces Training Requirements Students should master the selection of marking-out baselines and the methods of marking out deformed and large workpieces.
Section Marking Out of Deformed Workpieces
1. Marking-Out Example of the Transmission Frame
1.1 Process Analysis of the Transmission Frame Drawing
As shown in Figure 1-1, the part drawing of the transmission frame shows an irregular outer shape. The center line of the φ40+0.025 hole is at a 45° angle to the center line of the φ75+0.03mm hole, and their intersection point is not on the workpiece itself. Since the intersection point of the two holes is in space, it presents certain difficulties in dimension control during marking out. Therefore, auxiliary baselines need to be marked out, and auxiliary fixtures must be used to complete the process. To minimize installation as much as possible, all machining dimension lines should be marked out in as many dimensions as possible in a single installation. Thus, the method of solving dimension chains using trigonometric functions can be applied to reduce the number of installations.
2. Marking-Out Process of the Transmission Frame
The workpiece is pre-tightened on an angle iron, as shown in Figure 1-2a. Using the surface of the marking-out plate as the reference, the centers of the three projecting parts A, B, and C are adjusted as closely as possible to a horizontal line (using dividers to pre-determine the center points of each hole reduces repeated adjustments during three-dimensional marking out). Meanwhile, a 90° square is used to check the surfaces of the upper and lower projecting platforms to ensure they are perpendicular to the marking-out plate. Then, the workpiece and the installation angle iron are rotated 90° together, so that the large plane of the angle iron is tight against the plate, as shown in Figure 1-2a. Using a marking-out dial, the rough surfaces of the two projecting parts D and E are aligned parallel to the plate. After the alignment, the workpiece and angle iron are tightened.