Research of the arithmetic average of processing by lathing of hardened steel 42CrMo4.

Zeqiri, Hakif ; Salihu, Avdi ; Bunjaku, Avdyl 等

1. INTRODUCTION

The roughness of the processed surface is determined by the geometrical characteristics of the surface, accurateness of the proportions and physical characteristics. With the geometrical characteristics of the surface we understand (Aleksander, 1976):

1. Macro geometry

2. Micro geometry of the processed surface

With physical characteristics of the surface we understand the deflection of the physical-mechanical characteristics of the surface layer of the detail from the base material. The characteristics of the detail usage depend on the quality of the processed surface because exactly from the surface layer begins its destruction. Micro geometry of the surface depends on the form and geometry of the metal-cutting tool, pace and impact of other technological factors that greatly change the theoretical profile of the detail surface. The main factors of this are:

1. Plastic and elastic deformations

2. Friction of the back side of the tool

3. The phenomenon of increase in the cutting edge

4. Vibrations (dynamic phenomena in the system of machine-appliance--processed scrap-tool

5. Modification of the geometry of cutting edge of the tool as a result of its consumption.

As a function of the processed metal and cutting conditions, these factors change. During the processing of the plastic metals a great influence on the micro geometry of the processed surface have the magnitude of plastic deformation on the cutting area, the phenomenon of increase and the vibrations. The cutting speed has a great influence on the roughness of the surface; with the increase of the cutting speed the value of the plastic deformation of processed material also increases and that is why the height of micro elevation decreases. The cutting speed during the clean processing should be relatively greater than during the rough processing. The height parameters Ra & Rz were taken for the research. Ra--stands for the average arithmetical value of all deflection points of the profile from the average line m-m; fig. 1 is applied for defining the roughness of the processed surface and it is calculated with this formula:

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (1)

[R.sub.z]--the average height of uneven levels--is calculated by measuring five highest points and five lowest points along L length. Fig. 2 is calculated with formula (Bodinaku, 2004):

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (2)

[FIGURE 1 OMITTED]

[FIGURE 2 OMITTED]

2. CONDITIONS DURING THE EXPERIMENT

2.1. Machine-Horizontal Lathe IK62, with these characteristics: P=10 kW, n=12.5+2000 rpm, & feed s=0.035/2.08mm/rev.

2.2. Tool-Cutting plate from the hard metal P30, SINTAL-ZAGREG, ISO SNMM120404, SNMM120408, SNMM120412, enforced in the body with sign ISO PSDNN2525P12, outcome 25 mm, with cutting geometry: [gamma]=-60, [alpha]=60, [lambda]=-60, [r.sub.[epsilon]]=0.4mm, [b.sub.f]=0.2mm, [gamma].sub.f]=-20[degrees].

2.3. Researching material-Steel 42CrMo4 in the cylinder shape with dimensions [PHI]68X750/[PHI]38.5X750mm.

2.4 Apparatus for roughness measurement-Duplex Microscope CARL SEISS type STOLLBERG/ERCGEBTYPS15A/GA6Og

2.5. Hardening of steel--electric automatic furnace of type JPG80/140 with these characteristics: P=130 kW, 3X380/220V, 50 Hz, tmax=950[degrees]C, d=800 mm, h=1400 mm.

2.6. Experimental researching plan-based on the rating number of the rotations of the machine, consulted literature, professional experience, chemical composition, mechanic features of processed piece and Tool are defined cutting conditions: v, s, a, r & [xi], Tab. 1 (Zeqiri, 2005 & Salihu 2001).

3. RESULTS AND DISCUSSION

Once defining the input and output parameters, selecting the appropriate method for measurement and measuring apparatus, analyzing the independent and changeable input parameters, selecting the function form for defining the area of experiment, executing the experiment, statistically processing the researched parameters and verifying the mathematical models, the impact of parameters (v, s, a, r & [xi]) acquired on the roughness of the processed surface is defined (Bunjaku et al., 2002). The surface form, acquired during the cutting process, is a result of the moving of the tool through the processed scrape and it also depends on the deformations caused by the removal of splinter from the processed scrape, by friction, by consumption of the metal-cutting instrument, by temperature and by the dynamic phenomena in the system: Machine-Appliance-Processed Scrape and tool. During the cutting it is impossible to acquire ideal and precise processed surface because of the big or small errors or deflections from the form depicted in the drawing. These deflections result in the disproportion between the real surface (real profile) and the geometrical form of given surface (geometrical profile). The researched parameters must be presented with adequate mathematical model through which the changes of physical phenomena and technological effects on the cutting-processed surface could be observed.

The results acquired during the experiment were given in table 2. The mathematical model (3&4) was acquired with the processing of the results acquired during the experiment. The graphical interpretation of the mathematical model (3&4) was given in fig. 3.

[R.sub.a] = 71.099 x [v.sup.-0088] x [s.sup.0412] x [a.sup.-0054] x [r.sup.-008] x [[xi].sup.-0.417] (3)

[R.sub.z] = 284.343 x [v.sup.-0.088] x [s.sup.0.448] x [a.sup.-0.054] x [r.sup.-0.08] [[xi].sup.-0.417] (4)

[FIGURE 3 OMITTED]

4. CONCLUSION

The statistic analysis of mathematical models, confirms the right solution of the function shape, where appears the physical researched manifestation of manufacturing process with the scrap removal, and technological effects in the processed surface.

From the Mathematical models (3&4) ad their graphic interpretation we conclude that:

1. The cutting speed (v) is a parameter which more or less depends from the quality of processed surface, increasing the cutting-speed, the roughness of the processed surface is reduced.

2. By researching is confirmed that increasing a cutting-step (s) the parameters of the roughness processed-surface is increased.

3. The cutting-deepness (a) has a small influence in the parameters of processed surface roughness, the influence of cutting-deepness in a proportion with other influenced factors is not important.

4. Increasing the ray of roundness (r) and decreasing the attack edge ([xi]) the roughness of processed surface is decreased.

5. REFERENCES

Aleksander, B. (1976), Mechanical technology, Volume 2, Faculty of Mechanical Engineering, Tirane.

Bodinaku, A. (2004), Mechanical technology, Volume 2, Faculty of Mechanical Engineering, Tirane.

Bunjaku, A., Bodinaku, A., Osmani, H. & Zeqiri, H. (2002), The influence of cutting process on consuming of cutting plates during turning process of stele Ck 60, Scientific Journal for the Theory and Application in Mechanical Engineering "Makieria" nr.1, p.15-19, Faculty of Mechanical Engineering, Prishtine.

Salihu, A. (2001), Research of machinability of cutting material with increased speed, doctoral dissertation, Faculty of Mechanical Engineering, Prishtina.

Zeqiri, H. (2005), Research of machinability by turning of 42CrMo4 steel, doctoral dissertation, Faculty of Mechanical Engineering, Prishtina.

Tab. 1. Cutting conditions

Characteristics of independent various sizes

Nr Note Lev Max Aver Min
 Code 1 0 -1

1 v m/min] [X.sub.1] 67.000 53.000 42.000
2 s [mm/rev] [X.sub.2] 0.042 0.038 0.035
3 a [mm] [X.sub.3] 1.000 0.707 0.035
4 r [mm] [X.sub.4] 1.200 0.800 0.400
5 [kappa] [X.sub.5] 60.000 51.961 45.000
 [[degrees]]

Tab. 2. Experimental results

 Real plan of metrics

 v s a r
Nr m/min mm/rev mm mm

1 42 0.035 0.5 0.4
2 67 0.035 0.5 0.4
3 42 0.042 0.5 0.4
4 67 0.042 0.5 0.4
5 42 0.035 1.0 0.4
6 67 0.035 1.0 0.4
7 42 0.042 1.0 0.4
8 67 0.042 1.0 0.4
9 42 0.035 0.5 1.2
10 67 0.035 0.5 1.2
11 42 0.042 0.5 1.2
12 67 0.042 0.5 1.2
13 42 0.035 1.0 1.2
14 67 0.035 1.0 1.2
15 42 0.042 1.0 1.2
16 67 0.042 1.0 1.2
17 42 0.035 0.5 0.4
18 67 0.035 0.5 0.4
19 42 0.042 0.5 0.4
20 67 0.042 0.5 0.4
21 42 0.035 1.0 0.4
22 67 0.035 1.0 0.4
23 42 0.042 1.0 0.4
24 67 0.042 1.0 0.4
25 42 0.035 0.5 1.2
26 67 0.035 0.5 1.2
27 42 0.042 0.5 1.2
28 67 0.042 0.5 1.2
29 42 0.035 1.0 1.2
30 67 0.035 1.0 1.2
31 42 0.042 1.0 1.2
32 67 0.042 1.0 1.2
33 53 0.038 0.7 0.8
34 53 0.038 0.7 0.8
35 53 0.038 0.7 0.8
36 53 0.038 0.7 0.8
37 53 0.038 0.7 0.8
38 53 0.038 0.7 0.8

 Results

 [kappa] Ra Rz
Nr [degrees] [micro] [micro]
 m m

1 45 1.889 7.555
2 45 1.674 6.696
3 45 2.748 10.991
4 45 2.281 9.122
5 45 2.108 8.432
6 45 2.003 8.013
7 45 3.313 13.250
8 45 2.491 9.964
9 45 1.550 6.201
10 45 2.882 11.526
11 45 2.548 10.190
12 45 1.969 7.874
13 45 1.869 7.476
14 45 2.548 10.190
15 45 2.214 8.855
16 45 2.047 8.188
17 60 2.662 10.647
18 60 1.713 6.853
19 60 1.758 7.030
20 60 1.647 6.586
21 60 2.003 8.010
22 60 1.780 7.120
23 60 1.997 7.987
24 60 1.954 7.815
25 60 1.947 7.787
26 60 1.936 7.743
27 60 2.113 8.453
28 60 2.036 8.143
29 60 1.869 7.476
30 60 1.983 7.932
31 60 2.139 8.554
32 60 2.080 8.320
33 51 1.759 7.035
34 51 1.759 7.035
35 51 1.760 7.038
36 51 1.760 7.038
37 51 1.760 7.038
38 51 1.760 7.038