Rolling and rolling surfaces
By rolling and rolling out trim and harden cylindrical, conical, flat and shaped outer and inner surfaces. The essence of these methods is that, as a result of pressure, the surface layers of the metal, in contact with a tool of high hardness, are in a state of all-round compression and are plastically deformed. The tool is rollers and balls moving relative to the workpiece. Microroughness of the treated surface is smoothed by crushing microprotrusions and filling the micropropanin.
Running, as a rule, the outer surfaces, and roll out the inner cylindrical and shaped. When rolling, the main parameters of the hardening regime are the pressure in the contact zone with the roller, the number of its passes, the feed rate and the rolling speed. The depth of the deformed layer determines the pressure.
In Fig. 14.18 common schemes for rolling and rolling surfaces are shown. To the rotating cylindrical billet (Figure 14.18, a ), a hardened smooth roller is rolled in, which, under the action of the working pressure, deforms the surface. The movement of the longitudinal feed allows you to process the entire workpiece. A similar tool is used to process workpiece elements, but with lateral motion (Figure 14.18, b). When rolling the inner surface, the rolling roller is fixed to the cantilever mandrel (Figure 14.18, r). The tool design with several rollers is more perfect (Figure 14.18, d ).
Fig. 14.18. Schemes of rolling ( a , b), example of rolling (c) and rolling out the surface (g, d)
An example of breaking-in of the outer profile surface is shown in Fig. 14.19.
Fig. 14.19. Run-in of the outer profile surface of the part:
1 - clamping heads with rollers; 2 The rolling groove
To ensure a significant uniformity of microroughness forms, a variety of tool designs are used, differing in the number and shape of the deforming parts (rollers, balls). The best results are provided by tools, on which forces are transmitted through elastic elements. This achieves constant processing conditions at any point of the surface. The force can be adjusted.
For the treatment of surfaces by rolling and rolling, lathe or rotary lathes are most often used, using running-in and rolling-out instead of the cutting tool. Calipers provide the necessary feed motion. Raskatki can be installed in the tailstocks of the tailstocks. Deep holes are rolled out on deep drilling machines.
As the billet heating at the points of contact with the tool is negligible, no cooling is required. To reduce friction, use lubrication with spindle oil or kerosene.
Rolling and rolling out only slightly correct the errors of the previous treatment, so it must be accurate taking into account the crushing of the microroughness and the change in the final size of the part. The decisive importance in achieving the necessary quality of the surface layer is the pressure on the surface. Excessive pressure, as well as a large number of tool passes, destroys the surface and can lead to peeling of its individual areas.
The small roughness of the surface and its hardening can be achieved by diamond smoothing. The essence of the method is that the unevenness of the surface remaining after the cutting is smoothed out by the pressed diamond tool moving along it. The diamond, fixed in the holder, does not rotate, but slides with a very small coefficient of friction. The working part of the tool is made in the form of a hemisphere, a cylinder or a cone. The harder the material being processed, the smaller the rounding radius of the working part of the diamond.
The advantages of diamond smoothing consist in increasing the operational properties of the treated surfaces, reducing the roughness, the absence of foreign particles transferring to them, the possibility of processing thin-walled parts and complex configuration parts, and the simplicity of the design of the smoothers.
The blanks are machined on lathe lathes. A holder with a spring-loaded tip with a diamond is mounted in the toolholder instead of the tool.
Workpiece and tool movements are similar to grinding movements.
The forces of pressing the diamond to the surface being treated are relatively small and fluctuate in the range of 50-300 N. The process is carried out with lubrication with spindle oil, which reduces the wear of diamond by about five times compared to smoothing out. The use of kerosene or emulsion leads to intense wear of the diamond. The number of passes of the tool should not be more than two.
In order to increase the wear resistance of machine parts on friction surfaces, it is advisable to squeeze out weakly visible grooves adjacent to each other. They accumulate a lubricant and fine particles formed during the wear process. The grooves are obtained by vibro-rolling. The reinforcing element, the ball or diamond, installed in the lathe holder of the lathe, in addition to the motion VS pr (Fig. 14.20), additional movements Va, with a relatively small amplitude, are reported by the special device
Fig. 14.20. Vibrating Scheme
By changing Vs, VS pr , amplitude and frequency of oscillations, you can obtain the desired pattern on the surface to be processed. Distribution received drawings with non-intersecting, incompletely intersecting and merging grooves. Vibrating of internal and flat surfaces is also possible.
The grooves simultaneously strengthen the surface. The most important characteristic of such a surface is the total area of the grooves (as a percentage of the nominal surface area of the treated surface). Such deviations for each type of figure are determined analytically.
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