Project 2: CNC turning of shaft parts
Task 1: CNC turning of simple contours
Knowledge point 1: Division of processing stages
Your production sub-unit group has received a production order for the machining of a component shaft in the shape of a ladder. This production task has been communicated to your sub-unit group in a total quantity of 200 units and has to be achieved within a timeframe of three days. Technical specifications:
The kind of part shown in the figure is made of 45 steel, the deviation allowed for the length dimension not marked out is plus or minus 0.1 mm, the chamfer not stated is 1 x 45°, the roughness value not marked out is R3.2, and the blank is.
The size of the φ50mm × 100mm parts, its machining process to analyse, and then complete the machining program of the part, and then processed on the CNC lathe. First, for the processing stage to be divided.
1. Division of processing stages
When the machining quality of a part is required to be at a relatively high level, it is often unlikely that the requirements can be achieved in a single process, but rather several processes are required to achieve the desired quality in a stepwise manner. As a rule, this can be divided into four stages: roughing, semi-finishing, finishing and polishing. The main tasks of each processing stage are: I. Division of processing stages.
1. Division of processing stages
(2) In the semi-finishing stage of the development process. The task undertaken at this stage is not a single one, but to allow the main surfaces to reach a certain degree of accuracy, while also reserving a certain amount of excess margin for subsequent re-precision machining, the effect of which is to prepare the main surfaces for re-precision machining in advance, and to a certain extent to complete the machining of other surfaces that are not at the centre of the work.
In the finishing stage, the task is to ensure that the dimensional accuracy and surface roughness of the main surfaces, as specified in the drawings, are achieved, and the main objective is to think about how to guarantee the quality of the machining.
(4) In the finishing stage. The task of this stage is to carry out finishing operations on surfaces with very high requirements for accuracy and surface roughness, i.e. surfaces with an accuracy of IT6 or higher. The aim is to improve the dimensional accuracy and reduce the surface roughness. Firstly, it is the division of processing stage.
2. Reasons for the division of processing stages
(1) This is to ensure that the processing quality needs. When the part is in the roughing stage, in view of the removal of a large amount of metal, so it will produce a large cutting force and cutting heat, and also need a large clamping force, under the action of these forces and heat, the parts will appear larger deformation. Moreover, after rough machining, the internal stresses in the part are redistributed, which can also lead to deformation of the part. If machining continues without dividing it into machining stages, it is impossible to avoid and correct the machining errors caused by these reasons. By dividing the machining stages, errors caused by rough machining can be corrected by semi-finishing and finishing, and the machining accuracy and surface quality of the part can be improved step by step to ensure the machining requirements of the part. First, the machining stage is divided.
2. Reasons for the division of processing stages
In terms of the rational use of machine tools and equipment requirements, rough machining usually has a high power, good rigidity, high productivity but not high precision requirements for machine tools and equipment. Finishing, on the other hand, there is a need to use high-precision machine tools and equipment requirements. After the division of processing stages, to give full play to roughing and finishing equipment, the characteristics of their respective performance, to avoid the emergence of such a situation to rough dry fine, and then do a reasonable use of equipment. In this way, not only improve the productivity of roughing, but also to maintain the accuracy of finishing equipment and service life is also beneficial. This belongs to the division of processing stages.
2. Reasons for the division of processing stages
(3) to find the existence of defects in the blank in a timely manner, the blank has all kinds of defects, such as porosity, trachoma, slag or machining allowance is insufficient, etc., in the roughing can be found, so that it is convenient to repair or decide whether to scrap in a timely manner, to avoid continuing to process after the waste of man-hours and processing costs.
(4) is conducive to the arrangement of heat treatment, heat treatment process will be divided into several stages of the process, such as precision spindles in rough machining after the artificial aging treatment to remove stress, semi-finish machining after quenching, after finishing low-temperature tempering and ice-cold treatment, and finally to carry out the finishing process, the heat treatment of these several times to the entire process is divided into rough machining - - semi-finish machining - finishing - - finishing processing stage. -Semi-finishing - Finishing - Finishing stage. Thank you!
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