Research of chip formation during the processing with turning.

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

Abstract: The chip formation and morphology are definitely affected by tool geometry and cutting parameters such as cutting speed (v), feed rate (s), and depth of cutting (a). An experiment investigation was presented to study the influence of tool geometry on chip morphology and chip deformation in orthogonal turning. The experiment is realized with the lathe machine IK62. For data process is used a statistic method with five factors. The result obtained in this study showed that tool geometry affected the chip morphology significantly; cutting speed was the most contributively factor.

Key words: chip deformation, cutting tool, orthogonal turning, hardened steel

1. INTRODUCTION

Orthogonal machining setups are used to model oblique machining processes. Processes such as turning, drilling, milling, and shaping are all three-force, or oblique, cutting methods. However, the orthogonal model shown in fig. 1. The cutting edge of the tool is perpendicular to the line of tool travel, tangential, longitudinal, and radial forces are in the same plane, and only a single, straight cutting edge is active (Bodinaku, 2006; Bushati, 1979).

[FIGURE 1 OMITTED]

2. TYPES OF CHIPS AND CONDITIONS FOR FORMATION

Different types of chips of various shape, size, colour etc. are produced by machining depending upon

* type of cut, i.e., continuous (turning, boring etc.) or intermittent cut (milling),

* work material (brittle or ductile etc),

* cutting tool geometry (rake, cutting angles etc)

* levels of the cutting velocity and feed (low, medium or high),

* cutting fluid (type of fluid and method of application),

The chip is enormously variable in shape and size in industrial machining operations. Figure 2 shows some of the forms (ASM, 1997; Graham, 2008). The formation of all types of chips involves a shearing of the work material in the region of a plane extending from the tool edge to the position where the upper surface of the chip leaves the work surface. A very large amount of strain takes place in this region in a very short interval of time, and not all metals and alloys can withstand this strain without fracture.

Gray cast iron chips, for example, are always fragmented, and the chips of more ductile materials may be produced as segments, particularly at very low cutting speed. This discontinuous chip is one of the principal classes of chip form, and has the practical advantage that it is easily cleared from the cutting area. Under a majority of cutting conditions, however, ductile metals and alloys do not fracture on the shear plane and a continuous chip is produced Continuous chips may adopt many shapes--straight, tangled or with different types of helix. Often they have considerable strength, and control of chip shape is one of the problems confronting machinists and tool designers (Edward et al., 2000).

The cutting parameters also influence chip formation. Cutting parameters include tool materials, tool angles, edge geometries (which change due to wear, cutting speed, feed, and depth of cut), and the cutting environment (machine tool deflections, cutting fluids, and so on). Further complications result from the formation of the built-up edge on the cutting tool.

[FIGURE 2 OMITTED]

3. CHIP REDUCTION COEFFICIENT (Ks)

Chip reduction coefficient (Ks) is defined as the ratio of chip thickness ([S.sub.1]) to the uncut chip thickness (S). This factor, Ks, is an index of the degree of deformation involved in chip formation process during which the thickness of layer increases and the length shrinks. The following figure 3 shows the formation of flat chips under orthogonal cutting conditions (Scerope & Steven, 2006).

[K.sub.s] = [S.sub.1]/S > l (1)

[FIGURE 3 OMITTED]

4. CONDITIONS DURING EXPERIMENTATION

For research there have been used cutting plates P30, produced by Sintal-ZAGREB, ISO SNMM120404, SNMM120408, and SNMM120412. Reinforcing have been done on the body of instrument with a sign ISO PSDNN2525P12, on a standard supporter with an outlet 25mm and cutting geometry: [chi] = 60[degrees], [[chi].sub.1] = 45[degrees], [gamma] = -6[degrees], [alpha] = 6[degrees], [lambda] = -6[degrees], [r.sub.][epsilon]] = 0.4mm, [b.sub.f] = 0.2mm, [[gamma].sub.f] = -20[degrees].

Researching material--Hardened Steel 42CrMo4 (cylindrical shape) with dimensions [PHI]68x750/[PHI]48.5x750mm, and with strength Rm=880 / 1080N/[mm.sup.2]. Processing with cutting have been realized with horizontal late IK62: P=10kW, maximal working diameter 400mm, n = (12.5/2000) rev/min, feed s = (0.035/2.08) mm/rev. Processing with cutting have been realized with a holding of the processing piece, with new edge, without cooling equipment, with changing of parameters v, s, a, r & [chi] (table 1), with applying the experimental plan of five factors of a first order y=[2.sup.k]+[N.sub.0] (Zeqiri, 2005; Salihu, 2001).

5. ANALIZING OF RESEARCH RESULTS

The level of plastic deformation of metals in the process of chip formation is quantitatively evaluated with the chip reduction. The coefficient of chip reduction is different for different materials, and to a greater extend depends on the cutting speed (v) and front angle of cutting wedge ([gamma]).

During the research we have followed the change of chip reduction. For the description of this change there has been adopted the mathematical model (1):

K = 7.887 x [v.sup.-0.363] x [v.sup.-027] x [a.sup.0.124] x [r.sup.0.022] x [[chi].sup.-0.0312] (2)

Interpretation of mathematical model (2) is given in the fig.4

[FIGURE 4 OMITTED]

6. CONCLUSION

Based on the analysis of the results acquired through experimental research, table 2, mathematical model (2) and its graphical interpretation, we may conclude that:

Change of the of chip reduction coefficient can be described with the function of exponential form;

With the increase of cutting speed, cutting step and cutting angle, the chip reduction coefficient of is decreased.

Increase in radius of rounding the cutting blade and cutting depth have an impact on the increase of the chip reduction coefficient.

Research should be focused on to develop chip-breaking predictive models using mathematical models and soft computing.

7. REFERENCE

Bodinaku, A. (2006), Mechanical technology, Volume 2, Faculty of Mechanical Engineering, Tirana, Albania

Bushati, A.: (1979), Mechanical Technology, volume 1, Faculty of Mechanical Engineering, Tirana, Albania

Edward M. Trent, Paul K. Wright (2000); Metal cutting--4e

Graham T. Smith (2008), Cutting tool technology: industrial handbook, Springer-Verlag London Limited

Scerope Kalpakjian and Steven R. Schmid, (2006) Manufacturing, Engineering & Technology, Fifth Edition, ISBN 0-13-148965-8. Pearson Education, Inc., Upper Saddle River

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

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

*** ASM metals handbook volume 16--machining, 1997

Tab. 1. Conditions for experiment realization

Characteristics of independent various sizes

 Level Maximal Average Minimal
Nr Note 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 0.500
4 r[mm] [X.sub.4] 1.200 0.800 0.400
5 [chi] [X.sub.5] 60.000 51.961 45.000
 [[degrees]]

Tab. 2. Derived results during experiment realizacion

 Real plan of matrica

 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 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

 rezults

 [chi] K Y=1nK
Nr [degrees]

1 45 2.797 1.028
2 45 3.391 1.221
3 45 2.791 1.026
4 45 3.480 1.247
5 45 2.787 1.025
6 45 3.129 1.140
7 45 2.784 1.023
8 45 3.312 1.197
9 45 3.614 1.284
10 45 3.345 1.207
11 45 2.678 0.985
12 45 3.124 1.139
13 45 2.761 1.015
14 45 3.407 1.225
15 45 2.692 0.990
16 45 3.342 1.206
17 60 2.823 1.038
18 60 4.327 1.465
19 60 4.227 1.441
20 60 4.414 1.484
21 60 3.722 1.314
22 60 3.218 1.169
23 60 4.218 1.439
24 60 4.684 1.544
25 60 3.692 1.306
26 60 4.342 1.468
27 60 3.521 1.259
28 60 4.332 1.466
29 60 3.595 1.280
30 60 4.215 1.447
31 60 3.528 1.261
32 60 4.342 1.468
33 51 3.112 1.135
34 51 3.112 1.135
35 51 3.112 1.135
36 51 3.112 1.135
37 51 3.112 1.135
38 51 3.112 1.135