Operation 10 as part of each technological process is so-called first operation. The convention of numbering every 10 in the classic technological documentation made it possible to introduce another operation in a relatively easy way. There is no need for a deeper modification of the technological documentation, including the renumbering of all instruction cards, a technological card or time norm cards. Modern ERP systems together with PDM significantly modify the keeping of technological documentation. First of all, its digitalization takes place, which is both a significant qualitative leap and a source of new problems. The technological process of the shaft (part 1 of the cycle) is a series of technological operations, in which specific areas are machined according to the adopted framework technological process. Shaft technology is mainly the machining of external and internal cylindrical surfaces as well as cross holes, grooves and threads.
Fig. 1 shows a technological sketch of the operation 10.
Fig. 1 shows the method of fixing the workpiece – a three-jaws chuck with a movable support from the front defining how much the shaft is to be moved out of the three-jaws chuck. In the case of a conventional lathe, including a horizontal chucking lathe, determining the extension of the shaft from the holder is standard. In the case of CNC lathes, workpiece probes or / and bar feeders with a gripper ensure automatic ejection of the bar.
Horizontal chucking lathes are equipped with two cross slide supports that operate in automatic mode in rectangular cycles. Each slide can work in ten mutually perpendicular sections that are part of the automatic cycle. Machines of this type are equipped with electrohydraulic control of supports, which enables machining of workpieces (sequentially or simultaneously) with many tools.
The course of operation 10
|Cut No.:||Technological cut:|
|2||Turn the diameter Ø34,5 and face.|
|3||Turn groove Ø30-0,15|
|4||Turn external surface Ø64 for length 88.|
|5||Machine the centre holes A4.|
Chamfer has a dual role. First of all, it allows (facilitates) cooperation with the surfaces of another object (eg assembly), and secondly it minimizes the user’s injury to the sharp edge (health and safety).
Shaft technology – face turning
Shaft technology – face turning is also known as planning. In the case of this type of cuts, the tool is guided in a radial direction from the face of the workpiece towards its center. With this machining, significant radial cutting forces occur, which can cause bending of the workpiece and vibrations. The SANDVIK company recommends the use of inserts with the largest possible radius of the corner due to their durability and economy. Increasing the PSIR (15º) with simultaneous reduction of the tool cuting edge angle (up to 75º) enables the direction of radial cutting forces to be changed axially towards the holder. This significantly improves the machining stability (minimizing the possibility of vibrations).
Shaft technology – centre holes
The centre holes are used almost exclusively in workpieces for the parts of shaft class. The centre holes (fig. 2) are machining datum surfaces (workpiece fixtures) for machining and assembly operations. The centre holes have the contours adapted to the centers of the machine tool or the three jaws chuck. IN Poland and UE they are made in accordance with the PN-EN ISO 6411: 2002 standard (Technical drawing – Simplified depiction of inner centre holes), which replaced the predecessor PN-M-02499: 1983. The dimensions of the centre holes are chosen based on the standard depending on the diameter of the shaft. The ranges of shaft diameters used are approximate. The weight of the roller should also be taken into account.
The tips are made with special tools called cente drill. The axis of drilled centre holes is located on the geometric axis of the shaft. Very often, in the final shaft, the centre holes are not needed and they are removed or left depending on the requirements.
In the case of the discussed technological process of the shaft (fig.1) in operation 10, an A3 centre hole is made where A denotes the type of centre hole and the number 3 diameter d (fig.2) according to the standard. The A3 is a shortened record because, according to the standard, there is no dimension of Ø3 but Ø3,15. In the case of a shaft machined in this process, we can use A3 or A4 centre holes.
Variant A is the so-called ordinary centre holes are dedicated to items against which there are no significant accuracy requirements. This type of centre hole is also used when it is expected to be removed after a few operations (eg by making an axial hole).
Variety B are protected centre holes. The 120º chamfer protects the working surfaces of the centre holes and the material from flowing out, maintaining the smoothness of the front surfaces.
The rarest varieties used are those of R. They are usually used when machining hard to cut materials machining. The shape that uses the radius contributes to the stiffness of the tool making the centre hole.
Centre holes in conventional technological processes were best performed on centring machines. Because of their purpose, they ensure alignment. The milling-centring machine tools are met, which additionally enable machining the end faces. Nowadays, the centre holes are also made on lathes. Then you can use a centre drill or a completed drill and countersink set for machining A varieties of centre holes (ordinary centre holes). In the case of a protected centre hole it is necessary to use a drill bit and two countersinks.
The presented shaft technology is a good example for presenting differences in approach within technological processes using conventional machine tools and processes using CNC turning centers. It is also very good to show the diversity of possibilities and variants of the course of the process, which results mainly from diversified means of production.
Previous article: Shaft technology – technological process.
- Feld M., Podstawy projektowania procesów technologicznych typowych części maszyn, WNT 2000
- Puff T., technologia budowy maszyn, PWN 1985
- Maciej Horczyczak Ph.D. – knowledge and consultations
- External turning – SANDVIK