Shaft technology also means machining holes, mainly axial but also lateral holes.
In the case of this operation 20 a short blind hole is made. Often, the axial hole is long, i.e. its length is significantly larger than its diameter. It is assumed that the holes whose length to diameter ratio is greater by 8 (l / d> 8) are long holes. Long holes should be made on machine tools that allow drilling long holes or even dedicated to this type of technological operation.
The shaft technology distinguishes the frame technological process for a stepped shaft with an axial hole. However, in the case of shafts, the axial hole is usually a long hole and this kind of forces a different technological approach. In the case of the technological process of the selected shaft, the axial hole is short and requires no special treatment.
Technological operation 20
Figure 1 shows a technological sketch of the operation 20.
Picture 1 shows the method of fixing the workpiece – a three-jaws chuck with ground jaws for pre-machined surfaces and a three-jaws chuck jaw surface as a resistive surface – the main technological (contact) base. In a technological process using conventional machine tools, the operation can be performed on a production lathe.
Production lathes are characterized by high machining efficiency. Production lathes are widely used in small-lot and medium-lot production. With this type of production scale, the use of multi-tools lathes is unprofitable. In addition, these machine tools do not have the ability to thread, and therefore are free of the lead screw.
Plan of the technological operation 20
Table 1 shows the technological cuts of operations 20.
|Cut No.:||Technological cut:|
|4||Make the hole phase (chamfering).|
|5||Turning Ø54-0,15 and chamfer 5-45º.|
Short holes with a length to diameter ratio of about 5 should be made with a twist drill. However, the length-to-diameter ratio should not be a decisive factor. This is due to from the fact that there may be a deviation of the drill from the axis. Table 2 presents the possible quality parameters of the holes made, depending on the type of machining used.
|Machining type||Roughness:||Accuracy class:|
|Rough reaming||Ra6,3||9 (8)|
|Precisely reaming||Ra3,2 (1,6)||8 (7)|
|Finish reaming||Ra0,8 (0,4)||7 (6)|
The machining of the hole in the considered shaft takes place in two stages. In the second cut, a hole with a diameter of Ø12 is drilled, and in the third cut, drilling is performed (reaming) to the final dimension of Ø20. Analysis of the executive technological drawings gives us information that neither the diameter nor the length of the hole have any specific manufacturing tolerances.
If a dimension in the construction and / or execution technological drawing does not have a clearly defined tolerance (no information), it means that a given dimension should be performed in the so-called workshop class, IT14 or IT15.
In the above case, additional roughness information (Ra2,5 for surfaces with roughness not specified in the constructional drawing). This indicates the need to machine the hole (shaft technology) in at least two cuts. The data contained in Table 2 are approximate data from 1990. Technological progress means that in principle better quality effects can be assumed for particular types of machining.
The machined hole has a length to diameter ratio of 1.5, so it is a short hole. The potential deviation of the drill does not matter. As a consequence of all factors, the hole is machined in two cuts.
Shaft technology means, as you can see, various issues, and the use of certain types of machining is not determined by one factor. The multifactorial nature of technological processes is the main reason why issues related to technological processes and manufacturing techniques are complex.
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- Maciej Horczyczak Ph.D. – knowledge and consultations
- External turning – SANDVIK