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Local physical actions on surface of billet.

1. INTRODUCTION

The process of cutting is one of the complex physical processes, with which appear elastic and plastic deformations; this process is accompanied by large friction, heat emission, scab formation, curling and shrinkage chip, by an increase in the hardness of deformed metal layer and by the wear of cutting tool.

At present in machine building with working of details made of corrosion-resistant high-temperature (strength) steels and alloys they encounter essential difficulties in connection with the formation of continuous chip, which leads to the ineffective operation of the highly productive automated technological equipment. One of the most effective methods, which make it possible to reliably govern the process of splitting continuous chip, is the method of preliminary local action by plastic deformation. The application of this method consists in the fact that the surface layers of metal, contacting with the tool of high hardness as a result of pressure, occur in the state of cubic compression and undergo plastic deformation. Because of this, under the tool is formed the pressure only in the contact zone, which creates in the zone of preliminary local action on the surface of billet internal structural changes.

2. RESEARCH OBJECT AND METHOD OF LPA

The preliminary local physical action on the external surface of the cut off layer produced according to the specific laws, makes it possible to change the conditions for the metal deformation with the cutting (Gulaev, 1960), (Maksarov & Timofejev 2003).

[FIGURE 1 OMITTED]

Alternations in the conditions of cutting, in comparison with the source material, are the special feature of the process of grinding the billets, subjected to this action. Physical action on the surface of material in the local zone leads to a change in it of structure and mechanical properties of the workable metal.

In the process of working the zone of local action, find in the metastable state in comparison with the base metal, leads to an instantaneous change of the stress-strained state in the zone of chip formation (Maksarov & Timofejev 2003).

On the rheological parameters of the process of chip formation has an effect local the metastability, which is created in the field of the assumed allowance of the cut off layer of material on the external surface of billet along the specially predetermined trajectory by the point C (Fig. 1, A) which in the preparation stage is formed with the frequency of the rotation of billet nm and with the supply Sm of device for the creation LPA (Gulaev, 1960), (Maksarov & Timofejev 2003).

Physical action on the surface of material in the local zone leads to a change in the density of the defects of crystal lattice, which form high-energy configurations, which leads to the appearance of that increased of the metastability of structure from this local region. Subsequently with cutting-edge mechanical processing with the frequency of the rotation [n.sub.p] of billet and the supply [S.sub.m] the tool cutting edge in the cutting plane intersects at point with the zone of the local physical action (Fig. 1, b). The zone of local action with distorted crystal lattice, which has other mechanical properties in comparison with the basic material, leads to an instantaneous change of the stress-strained state in the zone of chip formation (Fig. 2).

3. THEORETICAL RESULTS OF LPA

In the zone of preliminary local action on the surface of billet internal structural changes occur. It is known (Panin, 1990) that the plastic surface deformation in the local zone of the not heat-treated metal already at a temperature of T = +20[degrees]C leads to a change in structure and properties of material. Deformation is accompanied by origin, slip and accumulation of dislocations in the metal being deformed. With an increase in the dislocation density and imperfections of crystalline structure the free displacement of dislocations hinders.

Additional barriers for the dislocations are created due to the grain deformation and splitting of blocks. An increase in the quantity of point and linear defects of structure and volumes with the incoherent connection of crystals increases strength and hardness of material and is decreased its plasticity (i.e. capability for further deformation). Because of this, in the local zone of working by plastic deformation on the external surface of billet is formed the work hardening along the predetermined trajectory.

With the compression in the zone of local working in the region of the contact area within the limits of each grain many being intersected strips of shift in several parallel slip planes are formed. In this case occurs the turn of the disorderly oriented grains by the axes of the greatest strength along the direction of deformation--grain they are deformed and they flatten, being drawn out in the direction of deformation. Metal under the action of tool in the local zone forms the deformation texture of fibrous nature with preferred crystal orientation.

The specific volume of the riveted metal because of the increased quantity of defects of atomic-crystalline structure is more than annealed not riveted; therefore besides an increase in hardness and yield stress of metal in the surface layer of metal in the zone of local plastic action are created residual stresses. Increase in the number of defects of crystalline structure and appearance of internal stresses as a result of work hardening leads to the fact that free energy of metal will grow, and this in turn forms no equilibrium and unsteady state.

A rational change in the physical-mechanical properties of the material of the cut off layer in the zone of local plastic action (zone LPA) ensures an improvement in the conditions for chip formation with the subsequent machining, which is accomplished with a frequency of rotation [n.sub.p] and supply [S.sub.p]. With mechanical processing of plastic materials the basic portion of the work of cutting is expended on the plastic deformation of the removed metal. In the zone LPA the part of the work, spent on plastic deformation, it is already executed under the preliminary influence by contact tool. Consequently, in the process of cutting in the zone LPA cutting tool will be accomplished only the part of the work of cutting, spent on the plastic deformation of the basic cut off layer of metal. This it will give in the process of cutting in the zone LPA to a local variation in the volume of the plastic deformation of material, angle of displacement, shrinkage of shaving, force and temperature of cutting. The method indicated can be used for all steels, capable of plastically being deformed; however, the best results are obtained on steels with the hardness to HB 280.

Picture of work hardening with cold plastic deformation described below, Fig. 2, is observed in annealed carbon and alloy structural steels with the structure of ferrite, ferrite-pearlite and finely dispersed sorbite. In high-alloy corrosion-resistant (stainless), high-temperature (strength), nonmagnetic and other steels and alloys more complex picture is observed.

In special alloy steels because of the influence of the alloying elements on the expansion of [gamma]--region (which in iron-carbide steels as stable structural constituting exists only at a temperature higher than [Ac.sub.3]) (Panin, 1990), to an increase in the stability of super cooled austenite and to lowering the martensite point, austenite can be one of main structural components of steels in the state of their operation.

Alloyed austenite is subdivided into the stable and the unstable. Unstable austenite is capable of the phase transformation - the formation of martensite as a result of the application of external load (deformation) (Veitz & Maksarov 2000), (Veitz et al., 2001). Thus, the local surface deformation of steel with the structure of unstable austenite besides work hardening causes martensite transformation, which to an even greater degree strengthens difference in the structure and the properties of the base metal of work blank and zone LPA.

[FIGURE 2 OMITTED]

Stable austenite does not undergo phase transformation under the effect of the deformation, which leads to a change only in its structure. In steels with the structure of stable austenite, just as in steels of ferrite and ferrite-pearlite classes, plastic action leads to an increase in the density of the defects of crystal lattice, which form high-energy configurations.

4. EXPERIMENTAL STUDY OF LTA

Experimental studies were conducted for different brand of steels--of 3X13, 08X18H10T and structural steel 45. For determining the area of continuous chip breaking under LTA.

Experiment was materialized at different depths, which enabled to conduct a study of the process of continuous chip breaking with different relations of the depth of action b and the depth of the cut off layer a (Fig.3).

[FIGURE 3 OMITTED]

5. CONCLUSION

1. Chip breaking method is developed, based on the local plastic action on the surface of material, which leads to a change of the density of the defects of crystal lattice in the local zone. In this local region structure of the material has been changed. All this makes it possible to ensure an alternation in the conditions of cutting in comparison with the source material with the subsequent working.

2. It is established that in the zone of local plastic action occurs a change in structure and mechanical properties of the workable metal, also, in the process of working the zone LPA, found in the metastable state in comparison with the base metal, leads to an instantaneous change of the stress-strained state in the zone of chip formation. Also ensuring chip segmentation in the process of shaving.

6. REFERENCES

Gulaev, A.; (1960). Thermal processing of steels, Mashgis, Moskva

Maksarov, V. V.; Timofejev, D. (2003). Kinematical investication into process of ship formation with local physical actions given in the base material. Problems in machinebuilding and usage, (in Russian)

Panin, V. E.; (1990) Structural changes in the plastic deformation, Science, Novosibirsk

Veitz, V. L.; Maksarov V. V. (2000). Dynamics and control of the process of chip formation with cutting-edge mechanical processing, NWPI, Sankt-Peterburg (in Russian)

Veitz, V. L.; Maksarov V. V.; Lontsihh P. A. (2001). Dynamics and the simulation of chip formation with cutting-edge mechanical processing, RIO IGIUVA, Irkutsk (in Russian)

OLT, J[ueri]; LEEMET, T[onu]; LAATSIT, T[oomas] & MAKSAROV, V[iacheslav]*
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Author:Olt, Jueri; Leemet, Tonu; Laatsit, Toomas; Maksarov, Viacheslav
Publication:Annals of DAAAM & Proceedings
Article Type:Report
Date:Jan 1, 2008
Words:1689
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