121247646 51457787 Dependenta Coeficientului de Deformare Plastica a Aschiilor in Functie de Natura...

7/29/2019 121247646 51457787 Dependenta Coeficientului de Deformare Plastica a Aschiilor in Functie de Natura Materialul

1/7

THE DEPENDENCE OF THE CHIPS CONTRACTIONCOEFFICIENT ON THE NATURE OF THE CUT MATERIAL

BY

*MARIUS MILEA, *ANA-MARIA MATEI

Abstract. The paper deals with the dependence of the chips contraction coefficient C don the nature of the material being cut. The hardness and the flow limit of the cutting materialdepend on its chemical composition (%C).

Keywords: cutting process, chips contraction

1. Introduction

The latest researches show two categories of results regarding thedependence of the chips contraction coefficient on the nature of thematerial being cut. The theoretical equations to determine the coefficientdo not include any elements about the nature of the material being cut,equation [1].

[1]

0

1

cos

sin

45 2 2 2

d

N K

K

VK VN

!

!

C

Experimental results prove that the values of the chips contractioncoefficient depend on the nature of the material being cut (more ductileor less ductile-fragile). This dependence is shown in Fig. 1, where thevariation diagrams of the chips contraction coefficient for a series ofmaterials depend on the main cutting speed as follows: carbon steel (1),copper (2), hard aluminum (3), lead (4), concrete iron (5), brass (6), low-grade steel (7), high grade steel (8), tin and titanium alloys (9) andcadmium (10). [1.1]


2/7

Fig. 1.1- Variation diagrams Cd=f(v) for different materials

The present paper deals with a series of specific elementsregarding the dependence of the chips contraction coefficient, taking asexamples two steel types: carbon steel and high carbon steel.

2. The dependence of the chips contraction coefficient on the nature of the

cut material

The physical and mechanical properties and the carbonpercentage of carbon steels (STAS 500/1-89) and high carbon steels(STAS 880-80) are shown in Table 2.1 and Table 2.2.


3/7

Table 2.1

Properties of construction steels STAS 500/1-89 (OL)

SteelType

CarbonPercentageC(%)

Yield PointReH N/mm

2(0.2)TensilestrengthRm

N/mm2(r)

Elongation atYield A5%

a16 16


4/7

Table2

.3Steel Type Carbon percentage%C

Yield Point Hardness HB

OL 37 0.17 230 330410OL 50 0.22 280 490610OL 60 0.30 320 590710

The dependence of the hardness HB on the carbon percentage (%)is shown in Fig. 2.1 and Fig 2.2 for each type of steel.

0

100

200

300

400

500

600

700

0.25 OL 37 0.3 OL 50 0.4 OL 60

%C

HB

Fig. 2.1- Hardness HB=f(C(%)) for OL

Table 2.4

Steel Type Carbon percentage%C

Yield point Hardness HB

OLC 35 0.22 270 200OLC 45 0.42 360 229OLC 60 0.57 400 255

The influence of the carbon percentage on the hardness HB isgreater in the case of the carbon steel (STAS 500) as shown in Fig. 2.1and Fig. 2.2. In both situations, the increase of carbon percentage leads toan increase in hardness.


5/7

0

50

100

150

200

250

300

0.15 C35 0.17 C 5 0.2 C 0

%

Fig. 2.2- Hardness HB=f(C(%)) for OLC

The values of the chips contraction coefficient obtainedexperimentally in the case of straight turning show that an increase in thecarbon percentage, as well as in hardness HB, for three types of carbonsteel determines a decrease in the values of the chips contractioncoefficient (Fig. 2.3). Experimental results prove that high values of steelhardness come with low values of the coefficient Cd as shown in Fig. 2.3for OLC 60. Similar charts are obtained for other types of steel.

Fig. 2.3- Cd=f(HB) for OLC 60

By increasing the steel hardness as a result of a high carbonpercentage, the values of the chips contraction coefficient decrease. It is


6/7

experimentally shown that a reduction in the ductility of steels (increasein hardness) is accompanied by low values of the chips contractioncoefficient. The coefficient Cd has the rough value 1 when processinghard steels and fragile materials (ferrites), respectively. Theoreticallyspeaking, according to the dislocation theory, there is no ferritedeformation in cutting when processing fragile materials on amicroscopic scale and, therefore, Cd=1. [1,2,6]

3. Conclusions

1. The values of the chips contraction coefficient decrease at the sametime with the increase of carbon percentage and hardness HB,respectively, in carbon steel and high carbon steel cutting.2. Knowing how the hardness of the cut material influences the chipscontraction coefficient is necessary for a greater insight into the plasticdeformation of metal cutting.3. In the future, the chips contraction coefficient Cd may become acharacteristic for metal classification (steels, pig irons, non-ferrousalloys) from the point of view of productivity in cutting, together with thecarbon percentage C(%), HB hardness and tensile strength 0,2.

Received: *Gheorghe Asachi Technical University of Iassy,Romania

Department of machinery and toolsIassy, Romania,

e-mail:[email protected]


7/7

REFERENCES

1. Cozmnc, M., Panait S, Constantinescu, C., Bazele achierii, Ed. Gh Asachi, Iai,1995

2. Cozmnc, Mircea, Croitoru, Irina, Model pentru evaluarea deformaiilor plastice laachierea metalelor, Construcia de Maini, 1999(51), nr. 11

3.McDonald, W.J., Murphey, B.F., The Deformation Process in Metal-Cutting, Journalof Engineering for Industry, vol. 82, nr.3, 1960, pp.253-257

4. ***Oeluri de uz general pentru construcii, STAS 500/1-89, STAS 500/2-80, STAS

500/3-80

5. ***Oeluri carbon de calitate pentru tratament termic, destinate construciei demaini, STAS 880-80

6. Segal, Rica, Contribuii la studiul interdependenelor dintre influenele parametrilorde lucru asupra deformaiilor plastice la achierea oelurilor, Ph. Thesis,Univ. TehnicGh. Asachi, Iai, 1999

DEPENDENA COEFICIENTULUI DE DEFORMARE PLASTIC A ACHIILORN FUNCIE DE NATURA MATERIALULUI ACHIAT

(Rezumat)

n lucrarea de fa se prezint o serie de elemente specifice privind dependenacoeficientului de deformare plastic de natura materialului achiat lund ca exempluoelurile carbon i oelurile carbon de calitate. Rezultatele experimentale arat c lacreterea duritii HB a oelurilor are loc scderea valorilor coeficientului Cd.Experimental, s-a demonstrat c prin diminuarea ductilitii oelurilor (cretereaduritii), valorile coeficientului de deformare plastic a achiilor scade.

121247646 51457787 Dependenta Coeficientului de Deformare Plastica a Aschiilor in Functie de Natura...

Documents

Transcript of 121247646 51457787 Dependenta Coeficientului de Deformare Plastica a Aschiilor in Functie de Natura...