MEĐUNARODNO SAVJETOVANJE PTOIZVODNOG STROJARSTVACIM-2005. – LUMBARDA, lipanj,2005.

ABOUT APPLICATION AND OPTIMAL SHOT-PEENING PARAMETER SELECTION ON THE MATERIALS

PROCESSING IN NEW FORMS VEHICLES PRODUCTION

Prof. dr. sc. R.Markovina, University of Split, FESB, R. Boškovića bb, 21000 Split

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INTRODUCTION

1. The shot- peening process is one of very important technological process, which will be significantly used in the «new generation» and super – high – speed vehicles production in the following reasons:

• increasing of materials fatigue – life in exploitation,• elimination of micro-corrosion and strength-

corrosion,• decontamination of elements after machining and

assuring a good adhesion of paint film,• peen-forming a small curved contours of thin

plates etc.

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2. In the production of «new generation» vehicles, except materials used today also will be used:

• Al-alloys 5454 (Al Mg 2,5Mn), 5083 (AlMg4,5Mn), 6063(AlMgSi0,5), 6353 (AlMgSi1) [1] - Al-Li alloys (8090) [3].

• Their characteristics are: corrosion resistance, good welding, small density (1,8-2,4 kg/dm3), and relatively good strength (200-350 N/mm2).

• But the others will be used too, as:• honey-comb structures (different shapes and profiles),• non-metal materials ( composite materials,

polyamides, acrylic glass, textolite, high loading capacity glues, modern packing materials, protection paints based on plastic and artificial fibers, etc.)

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•different types high tensile steels: - no corrosive austenitic steels, - no corrosive martensitic steels, - law alloyed chromium-molybdenum steels, - law alloyed chromium-molybdenum-nickel steels, and - chromium-molybdenum-vanadium steels with the strength 700 – 2000 N/mm2).

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NOZZLE DIAMETER AIR COMPRESSIONp

NOZZLE DISTANCEh

SHOT'S MASSm

METALURGICALSHOT'S

CHARACTER.

SHOT STREEMANGLE

SHOT'S SPEED

v

EXPOSITIONTIME

t

FLOWQUANTITY

q

E= mv2/2KINETIC ENERGY

COVERING, DENSITY

STATE BEFORE PROCESSTRAITEMENT

STATE AFTER PROCESSTRAITEMENT

INTENSITY

ALMEN sample

COMPRESIVE LAYER VIEW

WITHOUT CONTROL NDI-CONTROL X-RAY CONTROL

TARGET

1. INCREASING FATIGUE LIFE2. INCREASING STRAIN LEVEL

DESTROYED ELEMENT

CONSEQUENCE

INSPECTION

CAUSE

THE SHOT PEENING PROCESS APPLICATION IN THE PRODUCTION OF

NEW GENERATION VESSELS• The controlled shot-peenning process is

present at the Figure 1.

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Each of enumerable materials will have an important application in modern shipbuilding, partially those on the ship’s parts which will be exposing on dynamical loading,

from which the most significant are:

- the main engine seating in engine room,-seating of auxiliary engines and devices

- fore peak and after peak structure,- hatches and hatch covers with coamings ( Fig.2),

- seating of decks engines and cargo gears,- shaft brackets, shaft bossing, stabilizers,-different types of springs and dampers,

- important welded parts, etc

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And also the mechanical components:- with gears, axes, changeable sections, -loading panels, integral plates, loading bars and girders, etc.

According to experience and to the researches, their fatigue life could be increased from 25% up to 70%, [3] depending on different parameters influences.

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«MORSKI MINIBUS» - sea bus (60 passangers) «TRILLENIUM 8000»-sea car (4 passangers)with a speed of 25-28 knots, monohull with a speed of 22-25 knots, small trimaran,

«GLIDING WING – Spalato»- fast speed car-ferry Computer simulation of « BRACERA II» - fast speed vehicles for 20 passengers, with a speed of 120 knots, ekranoplan, with a speed of 60-80 knots, and with WIG-effect 125 knots, catamaran or trimaran,

“FAROP”, –fast ship with the superstructure on the stable amortizing field, with speed of 35-50 knots, monohull, catamaran or trimaran,

Figure 5: Some of new generation vehicles projects when the shot-peening process has to be used

Some of new form vehicles, which in the next time would be produced in Croatian shipbuilding:

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3. AN OPTIMAL SHOT-PEENING PARAMETERS SELECTION BY SHORT PROCEDURE OF EXPERIMENT'S PLAN

From experience, it is evident that some of parameters could be unchangeable, by which a good production results were obtained, like:-shot’s mass,-metallurgical characteristics,-coverage by shot jet, -nozzle diameter,-exposition time,-shot’s flow quantity, andas changeable parameters in experiment’s plan usually are:-air pressure (p),-nozzle distance from shot-peened element (h), and-angle of nozzle positioning to shot-peened element (α).

Table 1: Envisaged domain of parameters selection [3]

ParameterDomain of characteristic parameters values

minimal midium maximal

p=x1 1 bar 1,5 bars 2 bars

h=x2 200 mm 300 mm 400 mm

ά=x3 45˚ 60˚ 75˚

Factor’s plan characteristics

-1 0 +1

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The process is with 3 influence factors, and examined on the base of completely orthogonal plan: 2k=23...............................................................................................................( 1 ) with a triple experiment repeating in the all plan point, and by the selected mathematical model form:

y = b0 + b1x1 + b2x2+ b3x3 + b12 x1x2 + b13x1x3 + b23x2x3 + b123x1x2x3..................( 2 )

In Table 2 the correlation of selected parameters and plan matrices is presented:Table 2: The correlation of parameters and plan matrices

Plan points(Number of samples)

Plan matrices

x0 x 1 x 2 x 3 x 1x 2 x 1x 3 x 2x 3 x 12x 3

12345678

1 -1 -1 -1 +1 +1 +1 -11 +1 -1 -1 -1 -1 +1 +11 -1 +1 -1 -1 +1 -1 +11 +1 +1 -1 +1 -1 -1 -11 -1 -1 +1 +1 -1 -1 +11 +1 -1 +1 -1 +1 -1 -11 -1 +1 +1 -1 -1 +1 -11 +1 +1 +1 +1 +1 +1 +1

p h αBase level: 1,5 300 60Interval of variation: 0,5 100 15Upper level: 2,0 400 75Lower level: 1,0 200 45

xoi

woi

xgi

xdi

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Based on that, the experiments parameters selected [3], for the first series of examine and for each of examined material: Sample 1: p = 1bar h = 200mm α = 45˚ min. no. of samples = 5Sample 2: p = 2bar h = 200mm α = 45˚ min. no. of samples = 5Sample 3: p = 1bar h = 400mm α = 45˚ min. no. of samples = 5Sample 4: p = 2bar h = 400mm α = 45˚ min. no. of samples = 5Sample 5: p = 1bar h = 200mm α = 75˚ min. no. of samples = 5Sample 6: p = 2bar h = 200mm α = 75˚ min. no. of samples = 5Sample 7: p = 1bar h = 400mm α = 75˚ min. no. of samples = 5Sample 8: p = 2bar h = 400mm α = 75˚ min. no. of samples = 5Codification of parameters is by equation of transformation based on parameters presents on tables 3 and 4: Table 3: The codification of parameters

FactorSymbol Level

Lower Higher

ABC

phα

120045

240075

Table 4: Combination of factors level with a triple experiment

Factorslevel

X1(A) Ai(A) X2(B) Bj(B) X3(C) Ck(C)

(1)ABABCACBCABC

-+-+-+-+

12121212

--++--++

200200400400200200400400

----++++

4545454575757575

A total number of experiment samples is given by equation: NEu = r x mn = (2+3) x 23 = 40 .........................................................................( 3 )

where are: r = number of repeating m = number of levels n = number of factors, R.Markovina

from which are: NEs = 2 x 23 = 16...........................for static examining,

NEd = 3 x 23 = 24.......................... for dynamic examining.

The transformation of independents variables (X1, X 2 and X 3 ) at non-dimensional is given by equation:

Xi = Xi

XioXi

.

..................................................................................................( 4 )

where are: Xi = natural factor values (X1, X 2, X 3 )

Xio = values of i-th factor at zero levelXi = variation of i-th factor interval

The parameters selection realized by random selection method and optimal parameters for each of examined material is selected by the first sample highest dynamic operating life criteria, which will be used as optimal in later examining, because the samples have different thickness and the first sample thicknessis using as roughly equivalent middle thickness of all examined samples. The influence probability all of process parameters, for thickness above and below the first one will be the same. (That is concerns a global thickness division like: thin plates from 1 to 4 mm; middle thickness plates from 4 to 7 mm, and thick plate over 7 mm of thickness).Than the first series of static examines starts in order to obtain the best results of Rm; Rp0,2; A5 and HB, as well as the first series of dynamic examination, controlling the shot-peening intensity (I), to elect the best parameters results. Than follows a statistic analysis of obtained results, by one of statistic analysis software, to obtain variance analyzed and regression analysis, and for each factors level, in Table 4, associated coefficient.By transformation of independent variables, by equation (4), it is obtained:

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X10 = 5,0max11.,5,12

12

2

min1max110

XXXtj

XX

X 20 = 100max12.,3002

200400

2

min2max220

XXXtj

XX

X 30 = 15max33.,60

2

4575

2

min3max330

XXXtj

XX

The parameters values are obtained by the principal orthogonal plan examine relation (5):

bi = in

N

minYX

N

1

1 ............................................................................(5)for i = 1,2,...N; where is N = 2k = 23 = 8.

The transformation equations look like:

X1 = 2

5,1p

X2 = 2

300h

X3 = 2

60 ...............................(6)

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Using obtained middle values ň from dynamic examine results, for all eight samples, and by the combination of factors levels from Table 4, the values of detached parameters can be calculated: 1232313123210 ,,,,,,, bbbbbbbb

In given example only remained the coefficients 10 ,bb , ,12b and 123b ).

Y = 0b - 1b (2p-3) + 12b (2p-3)(0,01h-3) + 123b (0,07 4 )..............(7)

Than it is useful to arrange the equation by factors p, h, , ph, p , h and ph , with appropriate coefficients:

Y*=-34732,8 +54649,2 p +317,49 h +2824,48 -211,66 ph – 1882,99 p - 9,415 h + 6,2766 ph )

Based on results in Table 4, the appropriateness of selected model for different combination of parameters level calculates:

(Example: Y*(1)=50095,85; Y*(A)=34167,90; Y*(B)=43016,25; Y*(AB)=41245,70; Y*(C)=59510,15; Y*(AC)=24752,10; Y*(BC)=33600,15 and Y*(ABC)=50659,10 ) [3].

For numerical degree of freedom:

f[E]=n(r-1)=8(3-1)=16...........................................................................(8)

and accepted level of significance:

*= 5%................................................................................................(9)

the tabular value, read by Student’s division, is:

tt=1,75..................................................................................................(10)

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INFLUENCE OF PRESURE CHANGING

0

20

40

60

80

100

120

0 0,2 0,4 0,6 0,8 1 1,2 1,4 1,6 1,8 2

Presure p (bars)

No.

of

cycle

s n

(th

ousands)

1 (h=200,alfa=75) 2 (h=200,alfa=45)

3 (h=400,alfa=45) 4 (h=400,alfa=75)

INFLUENCE OF NOZZLE DISTANCE

20

30

40

50

60

70

80

200 220 240 260 280 300 320 340 360 380 400

Distance h (mm)

No.

of

cycl

es (

thou

sand

s)

1(p=0,6 ; alfa=75 ) 2 (p=2 ; alfa=75 )

1

INFLUENCE OF NOZZLE ANGLE POSITION

20

30

40

50

60

70

80

44 48 52 56 60 64 68 72 76

Nozzle angle position (degrees)

No.

of

cycle

s (

thousands)

1 (p=0,6, h=200) 2 (p=2,h=200)

Fig 6 : Graphic presentation results of different parameters changing ( h, α and p ) depending on dynamical sample endurance

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For the evaluation of the correct model the Fisher criteria can be useful, and the dispersion is obtained as a square of difference between measured and theoretic values of function (y):

F2)(

2

y

ad

S

Sr ............................................................................................(11)

Where is:

Sad2= 2* )( yy

f

r

ad

...........................................................................(12)

[Example: fad=N-(K+1)-n(r-1)=24-(3+1)-8(3-1)= 4

r = 3 (number of reiteration)

7,224127457)( 2* yy

S(y)2-(dispersion of residue obtained as middle square residue deviation)=78737000,

and Sad2= 168095593,2 ]

Obtained values insert in Fisher criteria equation (11) for obtain F r :

Fr = 78737000

2,168095593= 2,1384

In the Table for Fisher criteria [5], for fad=4; f(E)=16 and * = 5%,

can be read the Table value:Ft= 3,01

In the Figure 6 the diagrams present the results of relations number of cycles n with changing the nozzle distance from shoot-peened element h, angle of nozzle positioning to shot-peened element (α), and air pressure (p) on the examined sample dynamic endurance.

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As the Fr< Ft (2,1384<3,01), it can be concluded that mathematical model is CORRECT and that is APPLICABLE.

And finally, by retrograde method all optimal process parameters can be obtained, by the same calculation method.( In this case : h = 200mm; = 75˚ and p = 0,6 bars ).

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4. CONCLUSION

It can be concluded that:

- shot – peening process will play a significant role in modern shipbuilding tomorrow, especially in the production of fast ships and super-high speed vessels, - the new materials, modern (aircraft) technologies and the great dynamic loading of construction parts would be expected. - as the successful application of shot - peening process depends on a great number of different parameters, the short procedure of its selection by experimental plan, presented in this paper, can be very useful for new researcher and technologist in modern shipbuilding.

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