machinability of high-strength low-alloy steel d38msv5s forged ...

A R C H I V E S O F M E C H A N I C A L T E C H N O L O G Y A N D A U T O M A T I O N

Vol. 34 no. 4 2014

A. PEREIRA, E. RIVEIRO, J. MARTÍNEZ, J.A. PÉREZ*

MACHINABILITY OF HIGH-STRENGTH LOW-ALLOY STEEL

D38MSV5S FORGED CRANKSHAFTS

The high strength low steel alloy (HSLA) denominated D38MSV5S, is a steel material widely

used by forging companies, especially in the automotive industry, as crankshaft material due to its

high fatigue resistance when is subjected to torsion. The aim of the following work verifies the

machining conditions with two different cutting inserts. Moreover, it must be an initial step for

comparison of the machinability of current crankshafts’ steel to new micro-alloyed steel used in

forging in the purpose of future study. To verify the cutting conditions and tools’ behaviors, it was

necessary to take into consideration the roughness measurements at different stages of machining

operations. Also, surface wear measurements for tools and specimens were included. The next

three different machining operations: facing, turning and drilling in lathe were studied both for

roughing and finishing. And finally, determining the way to optimize the machine’s electric con-

sumption, the surface’s characterization, the insert’s wear and the process time were included in

the study.

Key words: forged process, consumption process, machinability, surface metrology, tool wear

1. INTRODUCTION

In the current state of the industry, particularly the automotive branch, the main

goal is manufacturing with low cost and high quality in a short period of time. To

achieve this goal, it is necessary to determine the optimal conditions for the pro-

cess. The three most important operations in the crankshaft machining are turning,

facing and drilling.

Forging automotive companies use the D38MSV5S as crankshaft material due

to its high fatigue resistance against torsion [22]. After forging, the crankshaft is

machined to obtain a desired shape and to approach a correct roughness of the

moving parts. The research is based on the behavior of two kinds of tools in the

above mentioned operations and focuses on measuring of the tool wear, the

roughness of the work piece and the energy consumption of the process.

* Department of Design and Manufacture, University of Vigo, Spain.

A. Pereira, E. Riveiro, J. Martinez, J.A. Pérez 46

1.1. Tool wear

In machining operations it is necessary to determine the conditions that affect

the tool’s life. Cutting conditions, material, tool’s material and tool’s geometry

are the parameters which influence the contact between the tool and the work

piece. The cutting speed is the most important parameter [2].

Tool flank wear has detrimental effects on surface finish, residual stresses

and microstructural changes on the surface. Therefore, measuring of flank wear

(Vb) is often used to characterize the tool’s life, as is shown in Figure 1 [12].

There are several studies on prediction of tool wear by empirical methods [7],

frequency domain analysis [10], recognition of the pattern and statistical meth-

ods, [14] and time series methods [9]. These works have improved knowledge of

tool wear modeling, although lots of experimental data are needed to achieve

a good tool wear model [15].

1.2. Roughness

When a machining process is finished, the effects of cutting conditions, tool’s geometry and tool’s material are reflected on the roughness of the surface, sur-

face’s texture and dimensions of the product [11, 19]. Roughness is used as

a measure of the product’s quality and is an important factor in the characteris-

tics of the work piece. Obtaining a desirable value is a repetitive and empirical

time-consuming process [6]. Some parts, such as connecting rods, require

a lower Ra than 0.4.

Figure 1. Flank wear VB

Machinability of high-strength low-alloy steel D38MSV5S… 47

1.3. Energy consumption process

Electricity is the main power source for milling machines and lathes. The

machine energy consumption includes the demand of the particular cutting mate-

rial, the axes’ motion, the spindle and peripheral devices such as pumps, com-

puters or the cooling circuit.

Energy consumption can be divided into two groups: constant and variable.

The former is composed of two sub-groups (start and run time) and depends on

machine tools’ modules such as engines, the computers, the spindle, the cutting

fluid or cooling devices) and the latter depends on machining and material re-

moval rate [13].

Cutting energy estimation in material removal process can be accomplished

through specific cutting energy (Ks) on chip formation, which is the minimum

energy necessary to remove a volume of material [8]. Ks depends on the materi-

al, tools, cutting conditions and the type of operation [1, 5].

2. EXPERIMENTAL METHODOLOGY

The tested material was a high-strength low-alloy Steel (HSLA) D38MSV5S.

Table 1 shows its composition in weight fractions. It is a material with a metal-

lographic composition of 55 % pearlite and 45 % ferrite microstructure which

includes manganese, calcium, magnesium and aluminum oxides. This material is

widely used in the automobile industry as crankshaft material [16]. In table 2

mechanical properties of the material are presented.

Table 1

D38MSV5S weight composition

C Si Mn P S Ga Mo Al Cu V

0.384 5.67 1.23 0.012 0.064 0.183 0.018 0.025 0.063 0.089

Table 2

Mechanical properties of D38MSV5S

Ed10kHz

[GPa]

Ed20kHz

[GPa]

σy0.2%

[MPa]

UTS

[MPa]

A

[%]

ρ

[kg × m–3] HV30 HRC

208.3 211.5 608 878 20 7850 246 21.3

All of the machining tests were performed without a cooling agent. The turn-

ing and facing tests were performed in a lathe machine CMZ TBI-450 CNC with

Fagor 8050 controller. The drilling tests were made in a milling center Anayak


Matic-7-CNC with FANUC controller. This operation had to be performed in

a milling center, due to their small size. The tests have left marks on the drills

and led to breaking.

a)

b1)

b2)

c1)

c2)

Figure 2. a) Specimens obtained from crankshaft; b1) initial work piece 1, b2) final work piece 1,

c1) initial work piece 8, c2) final work piece 8

The crankshafts were cut in several areas to obtain pieces for testing, as

crankshaft could not be machined in an ordinary lathe or milling machine. Fig-

ure 1 shows the cutting sections of the

crankshaft and the pieces 1 and 8. Sec-

tion 8 was used to perform the turn-

ings, section 1 – facing, whereas sec-

tions 3, 5 and 6 were used for drillings.

The first stage of the test consisted

of preparing the pieces. For the tests in

lathe (facing and turning) the pieces

were prepared in a manual lathe until

they obtained the appropriate shape

(diameter, removing stocks of cutting,

depth). For the drilling tests, the pieces

were machined also in the manual lathe, but in order to achieve a better grip, two

facings were made on two opposite sides of the pieces in the CNC milling center.

Figure 3. Driller. Corokey® catalogue 2010


Table 3

Design of experiments and cutting conditions

Operation Insert ap

[mm]

fz

[mm/rev]

Vc

[m/min]

V

[mm3]

Turning

rough CNMG 120408 1.5 0.6 150 21629.8

250

finishing DNMG 150608 0.25 0.08 160 13194.6

300

Facing

rough CNMG 120408 3 0.6 150 130513.5

200

300

finishing DNMG 150608 0.5 0.08 160 16223.4

195

300

Drilling

rough 880-02 02 04H-C-GR 1044/

880-02 02 WOSH-P-GR 4036

– 0.09 131 3848,45

153

0.02 197

Each operation of turning and facing was performed with two different cutting

inserts, manufactured by Sandvik and Mitsubishi companies. Geometry

CNMG120408 has been chosen according to ISO standards. Grade GC 4325 of

Sandvik represents a new generation of performance with coated cemented-

carbide indexable inserts, a new technology called Inveio® based on unidirec-

tional crystal orientation. Mitsubishi’s grade MC6025 presents a nanotexture coating technology, which offers an outstanding wear and chipping resistance.

The drilling operations were performed using only one manufacturer’s systems, as each manufacturer requires its own grip system. Figure 2 shows the type of

driller used made by Sandvik® [18]. A tool of 14 mm in diameter was chosen.

The relationship between the operation parameters and cutting inserts are pre-

sented in Table 3. The geometrical features of the inserts are presented in Table 4.

Table 4

Geometrical features of inserts

Tool/Insert

geometry

SandVik Tool Mitsubishi tool

grade rake

angle g position angle K

grade rake angle

g position angle K

CNMG 120408 4325 5 95 MC6025 7 95

DNMG 150608 4325 27 93 MC6025 30 93


Both machines are verified by a Janitza UMG 604 power analyser installed to

measure the electricity consumption. It can measure most electrical power char-

acteristics. It is connected with a router and it is accessible by Wi-Fi. The

GridVis software was used to capture data: The analyser forwards the measure-

ments to GridVis software, which translates it into a graphic and digital presen-

tation. Operations with and without a load were measured and the free loaded

test was subtracted from the loaded test results, which allowed to determine the

power of cutting operation, which was compared with theoretical values [17].

Active power was the parameter under measurement. In turning, the cutting

power, PC, can be evaluated using equation (1), where Fc defines cutting force.

For the multiple cutting processes with rotating tools, such as drilling, the cut-

ting power can be calculated using equation (2), where Mt represents cutting

torque and ω represents the angular spindle speed [4].

( )

60

min

mmm][]mm[MPA][

)(turningúû

ùêë

é×××=´=

czpc

cc

VfaaKs

VFwP (1)

( )

30

min

mmm][]mm[MPa][

)(drillingúû

ùêë

é×××=´=

czc

t

VfDaKs

MwP w (2)

where P is power of cutting process, Ks, is the specific cutting energy which

depends on the material in use, the average thickness of the non-deformed chip

ac and geometry of the tool, ap is the depth of cutting, fz is the feed of the tool per

revolution, Vc is the cutting speed, and ae is the radial depth of tool. In this work

the efficiency of process h has been obtained as relation between the mechanical

power of process and the electrical consumption. Table 5 shows the values of the

specific cutting energy Ks (MPa).

Table 5

Values of Ks (MPa)

Turning Facing Drilling

rough finishing rough finishing R/F

2400 3400 2400 3100 2400

Visual verification was performed using a microscope NIKON SMZ-800

equipped with an electronic camera. The wear cutting insert parameters such as

flank wear [2] and radial wear were measured with the use of the microscope’s software and is shown in Figure 4.


The 2D-roughness measure-

ments were performed using a sur-

face profilometer Taylor-Hobson

with a 112/2009 probe and R =

= 2 µm tip radius. The measurements were taken

in the normal direction of the ma-

chining mark in lathe and also on

the normal direction of advance in

lathe and milling center. These 2D

measurements have been make

according to standard UNE-EN

ISO 4287 [21]. The measurement

conditions were as follows:

- roughness filter = PC_2CR,

- cutting length (cutoff) = 0.8 mm,

- exploration length 5 ´ 0.8 mm = 4 mm.

For measurement of surface’s profile, arithmetic mean of the profile heights

Ra is widely used, which is described in equation (3)

dxZL

Rax

i

i ´= ò1 (3)

3. RESULTS

Table 6 presents the results of the experiments: the grades of inserts, cutting

conditions, machined volume, and time of machining. Wear measurements, effi-

ciency of the process and roughness measurements are presented graphically.

Table 6

Test results

Experiment Insert Vc

[m/min]

fz

[mm/rev]

ap

[mm]

V

[mm3]

Time

[s]

1 2 3 4 5 6 7

Rough Facing Sandvik grade 4325 150 0.6 3 130513 29

Rough Facing Sandvik grade 4325 200 0.6 3 130513 22

Rough Facing Sandvik grade 4325 250 0.6 3 130513 17.5

Rough Facing Mitshubisi gradeMC6025 150 0.6 3 130513 29

Rough Facing Mitshubisi gradeMC6025 200 0.6 3 130513 22

Rough Facing Mitshubisi gradeMC6025 250 0.6 3 130513 17.5

Figure 4. Wear flank Vb


Table 6 cont.

1 2 3 4 5 6 7

Rough Turning Sandvik grade 4325 150 0.6 1.5 21630 10

Rough Turning Sandvik grade 4325 250 0.6 1.5 21630 6

Rough Turning Mitshubisi gradeMC6025 150 0.6 1.5 21630 10

Rough Turning Mitshubisi gradeMC6025 250 0.6 1.5 21630 6

Finishing Facing SANDVIK_grade 4325 160 0.08 0.5 16223 152



Finishing Facing Mitshubisi_gradeMC 6025 160 0.08 0.5 16223 152



Finishing turning SANDVIK_grade 4325 160 0.08 0.25 13195 247

Finishing turning SANDVIK_grade 4325 300 0.08 0.25 13195 132

Finishing turning Mitshubisi_gradeMC 6025 160 0.08 0.25 13195 247

Finishing turning Mitshubisi_gradeMC 6025 300 0.08 0.25 13195 132

Drilling SANDVIK_GR 1044/-GR4034 131.24 0.09 15 3848 1.3






Figures 5–10 present experimental results of flank wear. Flank wear dependency

on the cutting speed is presented in Figures 5–8 both in cutting and facing pro-

cesses. The graphs also present a comparison of Sandvik and Mitsubishi inserts.

In the case of drilling, three kinds of measurements are presented: to central

wear flank, axial and radial wear of peripheral insert. As is well known, increase

in the cutting speed decreases the tool’s life [20]. In the rough face process at

a speed rate of 250 m/min, an anomalous behavior of Sandvik insert was ob-

served. Heavy conditions of drilling cause the flank wear and radial wear

achieve as much as than 250 µm as a result of working without lubrication.

Relatively to the increasing feed rate, the thickness of the non-deformed chip

varies, and consequently the cutting force increases. In this study variations of

the specific cutting energy (Ks) was not included, yet obviously Ks for the same

material, depends on the geometry of the tool and the thickness of the chip [3].

Different metallographic structures of materials can serve as an explanation for

the anomalous behaviour of the wear of central insert in case of feed rate equal-

ling to 0.02 mm/rpm.


Figures 11–15 show the electrical efficiency of the process h, described as

a relation between the mechanical power of the process and the electrical con-

sumption, versus the cutting speed and the comparison between the Sandvik and

the Mitsubishi grades. Tendency of the efficiency is anomalous in relation to the

process: for example if finishing turning is concerned, Sandvik – at high speeds

Figure 5. Rough turning wear Figure 6. Finishing turning wear

Figure 7. Rough facing wear

89.73

106.55116.3685.88

96.15

196.82

0.00

50.00

100.00

150.00

200.00

250.00

1 5 0 2 0 0 2 5 0

We

ar

(µm

)

Cutting speed (m/min)

Mitshubisi gradeMC6025 Sandvik grade 4325

Figure 9. Drilling, fz = 0.02 mm/rpm Figure 10. Drilling, fz = 0.09 mm/rpm

Figure 8. Finishing facing wear

25.04 33.19

59.34

11.54

22.57

21.47

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

1 6 0 1 9 5 3 0 0

We

ar

(µm

)

Cutting speed (m/min)

Mitsubitshi_DNMG gradeMC 6025

SANDVIK_DNMG_grade 4325


– decreases the efficiency. In general terms, the efficiency in roughing process

increases slightly with an increase in the speed. In the rough facing process, the

Sandvik grade is slightly better, similar to finishing process. In drilling process

the efficiency is better at high cutting speed.

Figures 16–20 present the roughness parameter Ra versus the cutting speed

(Vc) of the pieces and the comparison of the Sandvik and Mitsubishi inserts in

turning and facing process. There are no significant differences in the turning

process between the two tested grades. The parameter Ra is moderately better in

the Sandvik grade, with an exception for the finishing facing process with lower

Figure 11. Rough turning efficiency Figure 12. Finishing turning efficiency

0.86

0.73

0.62

0.78

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

160 300

EFFI

CIE

NC

Y (

Ƞ)

CUTTING SPEED VC ( M/MIN)



Figure 13. Rough facing efficiency

0.720.82

0.88

0.63

0.720.77

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

150 200 250

EF

FIC

IEN

CY

(Ƞ

)


Sandvik grade 4325 Mitshubisi gradeMC6025

Figure 14. Finishig facing efficiency

0.83

0.77

0.70

0.80

0.75

0.65

0.50

0.55

0.60

0.65

0.70

0.75

0.80

0.85

160 195 300

EFF

ICIE

NC

Y (

Ƞ)




Figure 15. Drilling efficiency

0.84

0.840.88

0.90

0.84

0.95

0.78

0.80

0.82

0.84

0.86

0.88

0.90

0.92

0.94

0.96

0.98

131 153 1 9 6

EF

FIC

IEN

CY

(Ƞ

)


0.02 0.09


values of cutting speed. In this process, the effect of speed is a decrease in the

roughness in the grade 4325. In drilling process, as is well known, the roughness

increases as the feed rate increases, as is illustrated in Figure 20.

4. CONCLUSIONS

Testing of different machining processes with two varying grades proposed

by Sandvik and Mitsubishi insert manufacturers were carried out.

Figure 20. Drilling roughness

0.790.58 0.61

2.69

3.563.38

0

0.5

1

1.5

2

2.5

3

3.5

4

131 153 196

Ra

(µ

m)


0.02 0.09

Figure 17. Finishing turning roughness

0.76

0.95

0.68

0.8

0.3

0.5

0.7

0.9

1.1

1.3

1.5

160 300

Ra

(

µm

)


Mitsubitshi_DNMG GradoMC 6025

SANDVIK_DNMG_grado 4325

Figure 16. Rough turning roughness

Figure 18. Rough facing roughness

9.2 9.07

8.14

6.77 6.64 6.69

5

5.5

6

6.5

7

7.5

8

8.5

9

9.5

150 200 250

Ra

(µ

m)


Mitshubisi GradoMC6025 Sandvik Grado 4325

Figure 19. Finishing facing roughness

1.18

0.490.66

2.32

1.34

0.25

0

0.5

1

1.5

2

2.5

160 195 300

Ra

(µ

m)


Mitsubitshi_DNMG GradoMC 6025

SANDVIK_DNMG_grado 4325


Results of the tool wear measurements indicate that cutting speed has a sig-

nificant influence on tools in the majority of tested inserts. In case of wear anal-

ysis, taking account that the objective of this work is to determine the tendencies

for machining of different areas of forged crankshaft with two kinds of inserts,

the Sandvik grade shows a lower flank wear in turning process and finishing

facing process.

With the heavy conditions in drilling, the flank wear and radial wear obtained

a value over 250 µm due to the fact that the work was performed without lubri-

cation.

In general terms, the efficiency in roughing process slightly increases as the

speed increases. In the rough facing and turning process, the Sandvik grade is

slightly better. In drilling process, the efficiency is better at a high cutting speed.

The roughness is moderately better in the Sandvik 4325 grade, except in the

finishing facing process with lower values of cutting speed. The effect of speed

in the process is a decrease in the roughness in the 4325 grade.

Future work requires investigation to determine if optimal cutting conditions

exist for each of the tested inserts.

ACKNOWLEDGEMENTS

The authors would like to thank the staff of the companies Angel Alvarez

Quintela S.L and Cie Galfor S.A. for their support, collaboration and good ad-

vices.

This work is supported by project “Research on new processes and micro al-

loyed steels for forging automotive crankshafts” under the program “Innter-

conecta 2013” through grant of CDTI Spanish Government and Regional Au-tonomous Government.

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