Journal of Materials Science and Engineering A 5 (5-6) (2015) 221-229 doi: 10.17265/2161-6213/2015.5-6.005

Real Time Chatter Vibration Control System in High Speed Milling

Hyeok Kim1, Mun-Ho Cho1, Jun-Yeong Koo1, Jong-Whan Lee2 and Jeong-Suk Kim3*

1. School of Mechanical Engineering, Pusan National University, Busan 609-735, Republic of Korea

2. Department of Mechtronics Engineering, Korea Aviation Polytechnic, Busan 616-741, Republic of Korea

3. Department of Mechanical Engineering, Pusan National University, ERC/NSDM,Busan 609-735, Republic of Korea Abstract: This paper presents the chatter vibration avoidance method in high speed milling. Chatter vibrations have a bad influence on surface integrity and tool life. So how to get the cutting conditions without chatter vibration is very important. In order to get stable cutting condition, too many parameters are required. So this paper focuses on simplification and real-time control of chatter avoidance program. The developed method uses only microphone signal for chatter vibration sensing. The measuring signal is analyzed by FFT (Fast Fourier transform) method to get whether or not the chatter vibration is generated on cutting condition. If chatter vibration occurs, the developed program suggests stable cutting speed in real time with tool teeth number, damping ratio and chatter frequency. This suggested that the program reliability is confirmed by dynamic cutting forces and surface profiles. Key words: Chatter vibration, milling, impact test, real-time control, frequency response function, lab view.

1. Introduction

Because of the acceleration and superior precision of machine tools, the numerous high-quality products are currently produced. However, chatter vibration, which degrades the quality of processed products, remains a problem to be solved. Chatter vibration, which causes problems during the manufacturing process, appears to be a self-excited vibration. When chatter vibration occurs, a chatter mark exhibits a wave pattern appears on the surface of the processed product, and thus, the processing grade is degraded. Additionally, the load on the axial system increases, the tool-life is reduced, and damage occurs owing to the vibration. Accordingly, the processing cost increases, resulting in a drop in productivity [1]. Thus, it is necessary to research a program that can detect chatter vibration and propose a stable spindle speed that can prevent chatter vibration according to the dynamic characteristics of the axial system. A lobe diagram is a graph illustrating the

*Corresponding author: Jeong-Suk Kim, tenure professor,

research fields: machine tools, dynamics and metal cutting. E-mail: juskim@pusan.ac.kr.

relationship between the rotational speed and the depth of cut of the spindle [2]; this is the most fundamental theory. However, because it requires extensive parameters to be applied in the practical industrial field, it is not often used. Thus, in the present research, stable and unstable areas are not determined according to the lobe diagram [3]. Instead, this research aims to easily apply the stable cutting condition through the chatter frequency only when chatter vibrations occur so that chatter vibration can be prevented [4]. The purpose of this study is to develop a virtual dynamic system that proposes a virtual condition to analyze the signal characteristics when chatter vibration occurs during processing and to prevent chatter vibration by using lab view.

2. Virtual Dynamic Machining System

A VDMS (Virtual dynamic machining system) was developed to precisely detect chatter vibration that occur during processing, and to effectively reduced it.

In existing research on chatter vibration, numerous variables have been used to generate a model that is similar to practical chatter vibration [5].

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However,the occurrensimplified vFig. 1. The six modules(Fast Fourieforce acquismodule, a module, andmodule. Inpare samplingedges. Spindthe detected chatter frequnecessary inspeed.

The strucVDMS is shmodule is asnotification modules areand detectedmodule locacutting forcmicrophone the specificaselected. That Position 6

Fig. 1 Flowc

R

, the present rnce of chatter variables. Flow

present progs: a data filteer transform)sition modulchatter vibrad a stable sput values reqg rate, spindledle speed is rfrequency is

uency. And thnput value for

cture of the fhown in Figs follows: Thand stable sp

e located at Pd frequency aated at Positce signal. is located at

ations of thehe impact exc6.

chart of VDMS

Real Time Cha

research focuvibration in rwchart of VD

gram consists er processing) analysis mle, an impacation occurrepindle speed quired for runne speed, and nrequired to des a tool passinhe number of r calculating t

front panel og. 2 and the he chatter vibrpindle speed Position 1. Thare marked ation 3 is for The FFT at Position 4, ae filter for thcitation test m

S process.

atter Vibratio

used on detecreal time by uDMS is show

of the followg module, a

module, a cutct excitation ence notificarecommendaning the prognumber of cutetermine wheng frequency cutting edgesthe stable spi

of the developosition of eration occurrerecommendahe input vari

at Position 2. determining

analysis moand at Positiohe signal canmodule is loc

on Control Sy

cting using wn in wing FFT tting test

ation ation gram tting ether or a

s is a indle

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g the dule on 5 n be cated

2.1

Trespimptestexcin one

Tfreqdamplacwasdammodoccillu

2.2C

Tdetefromthrotranthe ampdetedetecertthe knofreqquaexpscopnatuscopocctwoaxicha

ystem in High

Impact Excit

This module wponse data of pact hammer t data, the maitation moduthe two-dim

e-dimensionalThen, by usquency of thmping ratio δ,ces at which s ± 1/√2 [6]. mping ratio dule, which wurrence of chstrated in Fig

Chatter Detec

The developedermining them the microough the Dnsmitted to thfilter. The freplitude of tected by usinermine the frtain value, a tfrequency co

own that chaquency of antitatively esperiment, chatpe between aural frequencpe, the preliurred only w

o and a half al system. Bat ter freque

h Speed Millin

tation Test Mo

was operatedf the axial systand accelero

agnitude valule, and the ma

mensional arrl array. sing the peahe primary m, was calculathe amplitudeThe calculat

were deliverwas used to dhatter vibratiog. 3.

cting Method

d VDMS cone cutting signophone is cAQ (Data ahe FFT analyequency contthe analyzedng the peak requency thatthreshold val

ontent could btter vibrationthe axial s

stablished. Btter vibration

approximatelycy of the axiiminary expe

within the scopf times the nBased on thency fc was

ng

Module

d by loading ttem, obtainedmeter. Amon

ue was used iagnitude valuray was con

ak detector, mode was calated after estae of the naturted natural frred to the Fdesignate the on. The prepar

d Constructed

nducts FFT annal. The sig

conveyed to acquisition)ysis module tent that has thd microphondetector. Addt has an amplue was desigbe detected. Gn occurs neaystem, but ecause of the

n occurred ony two and a hial system. Beriment, chatpe between apnatural frequhis scope, ths establishe

the excitationd by using theng the impactin the impactue configurednverted to a

the naturallculated. Theablishing tworal frequencyrequency andFFT analysis

scope of thered module is

d Module

nalysis whilenal obtainedthe VDMS

) board andafter passinghe maximumne signal isditionally, tolitude over a

gnated so thatGenerally, it isar the natural

nothing ise preliminarynly within thehalf times theBased on thistter vibrationpproximately

uency of thehe scope ofed by using

n e t t d a

l e o y d s e s

e d S d g

m s o a t s l s y e e s n y e f g

Fig. 2 Front

Fig. 3 Block

the natural fin the impacdefined by u

Next, an content of tinputting thdetected in

R

t panel of VDM

k diagram of im

frequency fn, ct excitation tusing:

fn/2 <algorithm

the tool passhe spindle sthe FFT ana

Real Time Cha

MS.

mpact excitatio

of the axial sest module, a

< fc < 2fn that remove

sing frequencspeed value. alysis module

atter Vibratio

on test module.

system calculand the result

es the harmcy was added

The frequee falls under

on Control Sy

.

lated was

(1) monic

d by ency r the

scopthe freqas calcproare oneandthe opeaxiaaccmagmodtwoonedetewasaftethe natuthe the

ystem in High

pe of Eq. (1)threshold. Th

quency, not tthe chatter

culating the pcessed as fol

FFT cone-dimensionald magnitude.

maximum aerated by loadal system, obtelerometer. gnitude valudule, and the

o-dimensionale-dimensionalector, the nas calculated. er establishing

natural frequural frequencFFT analysisscope of the

h Speed Millin

and has the mhe frequency cthe harmonicr frequency.present proceslows. The signverted anl array after bAmong the

amplitude is ding the excittained by usinAmong thee was used e magnitude l array wl array. The

atural frequenThe dampin

g two places uency was ± cy and dampins module, whe occurrence

ng

maximum amcontent of the

c content, wa. The progss is shown ingnals that pasnd inserted being separatesignals, the detected. Thtation responsng the impact impact tesin the impavalue confi

was converen, by usinncy of the prng ratio δ waat which the 1/√2 [5]. Th

ng ratio werehich was used

of chatter vi

223

mplitude overe tool passingas establishedgram sourcen Fig. 3 and isssed the filter

into theed into f0, df,frequency of

his module isse data of thet hammer andst data, the

act excitationgured in therted to ang the peakrimary modeas calculatedamplitude ofhe calculatede delivered tod to designateibration. The

3

r g d e s r e , f s e d e n e a k e d f d o e e

Real Time Chatter Vibration Control System in High Speed Milling

224

prepared module was illustrated in Fig. 2. through the peak detector and compared with the input machining speed to determine whether it was a tool passing frequency. Then, after confirming whether it occur near the natural frequency, the result was presented through the chatter vibration in the comparison operator. The chatter frequency detected in this process was conveyed to the indicator, which indicated whether chatter vibration had occurred. Additionally, the detected chatter frequency was used in the calculation of stable spindle speed, and the damping ratio δ required in this process is the value obtained by the impact excitation test module. The relationship between the chatter frequency fc and stable spindle speed N, which is calculated by Eq. (2) [7].

N = 60fc / (i(1 + δ)nt) (2) N: Stable cutting speed (revolution per min). fc: Chatter vibration frequency. i: Lobe number. δ: Damping ratio. nt: Number of cutting tool edge.

2.3 Cutting Force Acquisition Module

The cutting signal determined by the cutting force acquisition module is displayed in a graph in two ways: moving average method and resultant force method of each component of force. Resultant force FR is calculated through the component of force in the tri-axis direction, according to Eq. (3). When chatter vibration occurs, the resultant force largely increases compared to the stable machining; thus, the credibility of the chatter vibration detection is measured by using the size of the resultant force.

FR = (Fa2 + Fr2 + Ft2)1/2 (3) FR: Resultant force. Fa: Axial force. Fr: Radial force. Ft: Tangential force. The module is prepared to add a scale input, which is

the software amplifier, to the program, in addition to

the hardware amplifier of the cutting signal.

3. Experimental Setup

3.1 Impact Test Setup

Because the chatter vibration evasion process of the present research is conducted under the mechanism of detecting chatter vibration through the natural frequency of the axial system, it is prioritized to identify the dynamic characteristics of the axial system.

The impact hammer underwent excitation by using Type 8206-002 from Bruel & Kjaer, and an accelerometer obtained a response signal by using Type 4384 from Bruel & Kjaer. In the case of the shock excitation test, the proficiency of the experimenter largely affects the result; thus, the frequency response was obtained through 10 mean value calculations by using only the experimental data, which features the credibility of the coherence function.

A schematic diagram of the experiment equipment is shown in Fig. 4.

3.2 Cutting Experimental Setup

The present experiment was conducted at the MAKINO V55 tri-axis machining center. Regarding the signal during the cutting, data similar to the accelerometer were gathered, and for the sake of convenience in usage and signal measurement, the data were obtained by using the microphone (Bruel & Kjaer, Type 4189). Additionally, the distance between the areas at which the sensing and machining occurred was fixed at approximately 400 mm. The cutting force was obtained by using a Kistler 9257B-type dynamometer, and a Kistler 5019B130-type amplifier was used. The machined material was AISI 1045; the form of the machined product featured a low slenderness ratio, and thus, was machined to a bulk type so that vibration could not occur. Cutting fluid was not used here, and the filter used in determining the signal was a bandpass-type windowed FIR filter. The band was within 100 Hz to 5,000 Hz. The UT coating end mill from Unimax was used as the tool.

Fig. 4 Block

Fig.5 Front

There were tThe length oestablished alonger, so theasily. The mand the sche

4. Results

4.1 Results o

In the cas

R

k diagram of F

panel of VDM

two cutting eof the tool inat approximahat chatter vibmachining conematic diagram

of the Impact

se of VDMS,

Real Time Cha

FFT module.

MS.

edges with dianstalled in theately 55 m, wbration couldnditions were m was shown

Excitation Te

the peak wa

atter Vibratio

ameter of 10 e tool holder

which was sligd occur relati

listed in Tabn in Fig. 6.

Test

as obtained at

on Control Sy

mm. was

ghtly ively le 1,

t the

Tab

SpiDepRadFeeCut

Fig.

pointestindithe grapfreqin th1,40.04deteto 2

4.2

Awheincrconspecutcondepwasof tthe

ystem in High

ble 1. Cutting

indle speed pth of cut (mm)dial of cut (mmed rate (mm/mintting method

.6 Experimen

nt of the inflet data; thus, iticated in Fig. impact test wph tool and quency, calcuhe impact exc16 Hz, and th41. The scopected through2,832 Hz.

Cutting Forc

As indicated en chatter vibrease compar

ndition. The ced of 5,830 Rting force o

nditions of 5,pth of cut, ws more than tthe stable mac

introductor

h Speed Millin

g conditions.

5,00) 1.0

m) 3.0 n) 1,00

Slot

ntal setup.

ection of magt was display7. The undis

was confirmedwas shown

ulated by loadcitation test mhe damping rpe in which h natural freq

ce Analysis

in Fig. 9, thebration occursred to that uncutting force aRPM and deof 556 N w,000 RPM sp

where chatter two times larchining condry and end

ng

00 513

00 1cutting

gnitude amoned in a distortorted magnitd through the

n in Fig. 8. ding the expermodule of theratio was calcthe chatter v

quency was w

e size of the s appeared to nder the stablaveraged 246epth of cut of

was measurepindle speed

vibration ocrger than the dition. The cu

portions of

225

,830 .0 .0 ,135

ng the impactrted graph, astude graph ofe Origin Pro*

The naturalrimental data

e VDMS, wasculated to be

vibration waswithin 703 Hz

cutting forceconsiderablyle machining

6 N at spindlef 1.0 mm. Ad under theand 1.0 mm

ccurred. Thiscutting force

utting force atf the cutting

5

t s f * l a s e s z

e y g e

A e

m s e t g

226

Fig. 7 Impa

Fig. 8 Impa

Fig. 9 Cutti

R

act test result o

act test result o

ng forces depe

Real Time Cha

f VDMS.

f Origin Pro*.

ending on cutti

atter Vibratio

ing conditions.

on Control Sy

.

ystem in Highh Speed Millinng

Fig. 10 Fron

increased ow

4.3 Front Pa

To evaluaVDMS, whsignal, was machining condition.

Chatter v5,000 RPM condition is frequency wsound was confirmed thof the machthe chatter inspindle spefrequency.

Spindle sspeed, calcthe previorecommende15,164 RPM

R

nt panel of VD

wing to the sh

anel Verificat

ate the validihich was ope

determined to verify th

vibration ocand depth of described in

was 2,630 Hz,generated in

hat a chatter hined productndicator lighted was calc

speed of 5,83culated by thous conditied spindle speeM; thus, 5,830

Real Time Cha

DMS (spindle sp

hock from rot

tion of VDMS

ity of the chaerated after in real time

he front pa

ccurred at spf cut of 1.0 mmn Fig. 10. The

and a high-pn the air. Mmark appearet. When the t activated (reculated throu

30 RPM is thhe chatter fion. The ed was betwee0 RPM, whic

atter Vibratio

peed 5,000 RP

tation [9].

S

atter detectiothe microph

e during milanel under e

pindle speedm; this machine detected chpitched chatteMoreover, it ed on the surchatter occur

ed), and the stugh the dete

he stable spinfrequency unscope of

en 5,830 RPM ch was the clo

on Control Sy

M, depth of cu

on of hone lling each

d of ning atter

ering was

rface rred, table ected

ndle nder

the and

osest

valucon

Cof 5andsurfwhiTheandwhilighnot

4.4

Wchaof Vthe RPMwhia chof Vindi

ystem in High

ut 1.0 mm).

ue to 5,000 Rndition. Chatter vibrat5,830 RPM spd the chatter mface. The peaich is the fife front panel od unlike the frich chatter viht remained gappear.

Machining S

When chatteratter mark appVDMS to dist

surface obsM and depth ich chatter vibhatter mark wVDMS. The icated in Fig

h Speed Millin

RPM, was s

tion did not opindle speed mark did not

ak frequency dfth content oof this conditi

front panel unibration occugreen and the

Surface

r vibration opeared on thetinguish chattservation. Atof cut of 1.0 bration was g

was confirmesurface stat

g. 12, which

ng

elected as th

occur under thand 1.0 mm

t appear on tdetected heref tool passinion is illustrat

nder the condurred, the chae stable spind

occurred, a ce surface; thuter was confirt spindle spemm, the con

generated, thed, as shown

tus of this coshows one su

227

he machining

he conditionsdepth of cut,

the machinede was 470 Hz,ng frequency.ted in Fig. 11

ditions duringatter indicatordle speed did

cross-stripedus, reliabilityrmed througheed of 5,000ditions undere existence ofin the resultsondition wasurface where

7

g

s ,

d , . ,

g r d

d y h 0 r f s s e

228

Fig. 11 Fron

Fig. 12 Ma5,000 RPM, d

Fig. 13 Ma5,830 RPM, d

the machinishaking left of 5,830 RPare shown ingenerated, bpassed throu

4. Conclus

In the pre

R

nt panel of VD

achined surfacdepth of cut 1.0

achined surfacdepth of cut 1.0

ing was incand right we

PM spindle spn Fig. 13. He

but a subtle tugh.

sions

esent study, a

Real Time Cha

DMS (spindle sp

ce of workpie0 mm).

ce of workpie0 mm).

consistent anere generatedpeed and 1.0 ere, the chatttrace appeare

a dynamic m

atter Vibratio

peed 5,830 RP

ece (spindle s

ece (spindle s

nd the marksd. The conditmm depth ofter mark was

ed where the

machining sys

on Control Sy

M, depth of cu

speed

speed

s of tions f cut s not tool

stem

hadreal

TdeteImpspevibrexpspinvibrexpvibrperfdurmac

Ac

T

Re[1]

ystem in High

ut 1.0 mm).

d been develol time and avoThe developeermine cuttinpact excitatioed recommenration detecti

periment. Chandle rotation ration freque

periment. Furtration was noformed even ing the machining speed

knowledgm

This research

ferences Jung, N. S.Vibration in 210-17.

h Speed Millin

oped that can oid it during ed program ng force andon test, chattendation. By uon was confiratter vibration

speed was ency generatethermore, it wot generated a

if the depthachining to d.

ments

was supporte

2008. “AnalMilling Proc

ng

detect chatterthe cutting prVDMS was d conduct Fer detection,

using this progrmed throughn was detectecalculated oed during thwas confirmeand stable mah of cut was

modify the

ed by Doosan

lytical Predicticess.” KSME m

r vibration inrocess. designed to

FT analysis,and optimal

gram, chatterh a machininged and stablenly with the

he machiningd that chatterachining wasnot reduced

e calculated

n Infracore.

ion of Chattermech. 33 (3):

n

o , l r g e e g r s d d

r :

Real Time Chatter Vibration Control System in High Speed Milling

229

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