Intermediate Maintenance Fitter Technology

Author: Chief Editor: Zhu Hua
Publisher:
Publish Date: 1999-10-01
Features: This book is based on the content of the "Occupational Skill Appraisal Specification" jointly issued by the former Ministry of Labor and the Ministry of Machine Industry. The main contents include: marking for special workpieces;drills and drilling special holes; general mechanical equipment; balancing of rotating parts; disassembly for machine tool maintenance; repair and replacement of machine tool parts; measurement and precision measuring tools; repair and adjustment of machine tool guides; repair of precision sliding bearings; assembly and adjustment of precision rolling bearings; main shaft mechanism repair; application of dimensional chain; maintenance and repair of general machine tools.
Fragment: > Training requirements: understand the selection of marking datum, master the key points of marking, and master the steps of marking. Marking of complex workpieces In the process of mechanical processing, especially in machine maintenance, some complex workpieces and semi-finished products need to rely on marking to mark datum lines and processing boundaries as the basis for correction and processing. The quality of marking will directly affect the quality and cycle of maintenance. If an error occurs during the marking process, it may lead to the scrapping of the workpiece in severe cases. As a preparatory process, marking plays an important guiding role in the processing of workpieces. Machinists should be proficient in marking complex workpieces with high difficulty and strive to improve their marking skills and techniques to ensure the quality of machine tool maintenance. Workpieces with complex technology and processing processes, and various dimensions and position accuracy requirements should be considered complex workpieces, such as box-type workpieces.
I. Characteristics of box workpieces For a machine tool, box workpieces account for a large proportion. For example, alaze car C620-1 has a main shaft box, feed box, ram box, and exchange gear box. Box workpieces require many holes and planes to be processed, and the machining surfaces and hole surfaces on the box are also the datum surfaces for assembly. Therefore, when marking, it is not only necessary to ensure that each machining surface and hole has sufficient machining allowance, but also to take into account the coaxiality requirements of holes and inner wall boss and the positional relationship between holes and machining surfaces.
II. Key points of box marking The marking of box workpieces, in addition to selecting marking datum, finding the right position, and borrowing materials as in general marking, should pay attention to the following points: 1) Before marking, it is necessary to check the quality of the blank carefully. If the blank has serious defects and a large error, it is not advisable to insist on marking to avoid the scrapping of the workpiece and the waste of a lot of working hours. 2) Seriously master the technical requirements, such as the appearance requirements, accuracy requirements, and geometric tolerance requirements of box workpieces; analyze the relationship between the machining parts of the box and the assembly workpieces to avoid affecting the assembly quality of the workpiece due to insufficient consideration before marking. 3) Understand the machining process route of the parts to know the relationship between the lines to be marked and the machining process of each machining part, determine the number of marking times and the lines to be marked each time, and avoid retaking the marked lines that are machined off. 4) The marking position should be selected as a location where the surface and the non-machined surface are important and concentrated, so as to facilitate the correct positioning and early detection of blank defects during marking, which not only ensures the quality of marking but also reduces the number of workpiece turns. 5) The marking of box workpieces generally requires the accurate marking of cross correction lines for subsequent machining processes such as planing, milling, boring, and drilling to provide reliable correction basis. The axis of the reference hole is usually used as the cross correction line, which is marked on the long and straight part of the box to facilitate the improvement of correction accuracy. 6) The cross correction lines of the box marked for the first time must be used as the reference plane of the machined surface when marking again after machining to mark new cross correction lines for the next process correction. 7) To avoid and reduce the number of turns, the vertical lines can be marked at one time using a right angle or angle iron. 8) For some boxes, the inner wall does not need to be machined, and the space for assembling gears or other parts is small. Special attention should be paid to positioning the inner wall of the box when marking to ensure smooth assembly after machining.