Laser kesim parametrelerinin sonlu elemanlar yöntemi ile analizi
Analysis of laser cutting parameters with finite element method
Yazar: FARUK SOYDAN
Danışman: PROF. DR. CELALETDİN ERGUN
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Makine Mühendisliği Ana Bilim Dalı
Derece: Yüksek Lisans, 2015
Konu: Makine Mühendisliği = Mechanical Engineering

Özet:
Laser teknolojisi günüzmüde kendisi için sanayide bir çok uygulama alanı bulmustur.
Laser teknolojisinin malzeme kesme alanında kullanılması ile birlikte, kalıp
yatırımını kurtarmayacak, karmasık sekilli parçalar kolaylıkla ve ekonomik bir
sekilde üretilme imkanı bulmaktadır.
Çalısmalar ilk olarak laser ısınının olusma sekli, üretilen noktadan parça üzerine
iletilme sekli ve laser ısını ile malzeme etkilesimi hakkında literatür incelemesi
yapılarak baslanmıstır. Literatür incelemeleri sonrasında laser kesime etki eden parça
kalınlığı, kesme hızı, kesme gücü ve malzeme etkisinin laser kesim prosesinin kalite
ve verimine etki eden en önemli değiskenler olduğu belirlenmistir.
Tez kapsamında laser kesimi en çok etkileyen parametreler olan parça kalınlığı, laser
hızı, laser gücü ve malzemenin etkisini incelemek maksadı ile Ansys paket programı
kullanılarak 3 boyutlu bir sonlu elemanlar modeli olusturulmustur. Analizler
esnasında ergime sıcaklığının asılması durumunda ergimenin olusacağını
gösterebilmek için, meshlerin öldürülmesi parametresi tanımlanmıstır.
Seçilen parametrelerden sadece parça et kalınlığının değisken olarak seçilmesi
durumunda sabit olarak seçilen hız ve güç değerleri için ince parçanın sorunsuz
olarak kesilmesi sağlanabilirken, kalın parçanın kesimi tam olarak
gerçeklesmeyebilmektedir. Aksi durumda ise kalın parçanın kesilebilmesini mümkün
kılacak kesme hızı ve gücü değerlerinin seçilmesi durumunda, ince parça üzerinde
bosaltılan malzem mikarının artacağı, ITAB'ın genisleyeceği ve islem veriminin
düseceği sonucuna ulasılmaktadır.
Seçilen parametrelerden tüm değiskenlerin sabit tutulup, kesme hızının değistirildiği
durumda kesme hızının arttırılması durumunda ITAB'ın daha dar ve bosaltılan
malzeme miktarının ise daha az olduğu gözlemlenmistir. Ancak hızın arttırılması
parçanın kesme yüzeyinde olusan açıyı olumsuz yönde etkileyeceğinden verim ve
kalite arasında bir optimizasyon yapılması gerekmektedir.
Seçilen parametrelerden sadece kesme gücünün değisken olarak alınması durumunda
kesme gücünün yüksek olduğu analizlerde malzeme bosaltma miktarının ve ITAB'ın
fazla olduğu gözlemlenmistir. Ancak yüksek güç kesme yüzeyinde olusan açının
azalması konusunda fayda sağladığı gözlemlenmistir.
Malzeme değisikliğinin laser kesim islemi üzerindeki etkisini incelmek için St-37,
AISI 304 ve Al 2024 malzemeler seçilerek analizlerde kullanılmıstır. Yapılan
analizlerde malzemenin ısıl iletil katsayısının, yoğunluğunun ve özgül ısısının kesme
yüzeyi, ITAB ve malzeme bosaltma miktarı üzerinde direk etkileri olduğu
belirlenmistir.
Ayrıca laser ile kesme isleminde kesme gücünün etkisini daha iyi anlayabilmek için
100W'tan baslayarak değisik aralıklarla 2000W'a kadar kesme gücü değistirilmistir.
Analiz sonuçları ile kesme açsıının belirli bir güç seviyesine kadar arttığı, belirli bir
güç seviyesinin üzerinde ise açıda iyilesme olmadığı belirlendi.

Abstract:
In history of science, development of laser has been an important chapter. History of
laser technology began with Albert Einstein in 1917. Stimulated emission concept
which is utilized in lasers, was developed by Einstein.
The word " laser" stands for " Light Amplification by Stimulated Emission of
Radiation" The light emitted by a laser is electromagnetic radiation.
Properties of laser light specify the application area of lasers. These properties are
monochromaticty, directionality, the spatial and temporal charastics of laser beams,
coherence properties, radiance, the capability to focus to a small spot, very limited
heat affected zone occurrence, high efficiency and the high power levels.
Conventional lasers are well developed and widely available. These inculude gas
lasers such as helium-neon, argon, CO2, solid state lasers like Nd: YAG and semi
conductor lasers. Although a laser was a fragile device, requiring considerable care
and maintance. At the present time, lasers became durable, reliable and reasonably
economical to operate.
Intense pulses of light energy produced by laser leads to many applications involving
heating, melting and vaporization. Lasers used in metal working is able to deliver
very high values of irradiance to a workpiece.
The knowledge of physical processes that occur during the interaction of high power
laser radiation with materials is important to understanding the capabilities and
limitations of laser based material processing. When laser radiation strikes a target
surface, part of laser beam is absorbed and part is reflected. The energy that is
absorbed begins to heat the surface. The heating effects due to absorption of high
power beams can occur very rapidly. The surface quickly rises to its melting
temprature. Laser – induced melting is of interest because of welding applications.
Material processing refers to a variety of industrial operations. In these operations the
laser operates on a workpiece to modify it, for example, by melting it or removing
material from it. Some of the possible applications include welding, hole drilling,
cutting, trimming of electronic components, heat treating, brazing and alloying.
Properties of laser light that enable material processing applications are its
collimation, radiance, and focusability. Because of these properties, laser light can be
concentrated by a lens to achieve extremely high irradiance at the surface of a
workpiece.
Lasers may be used to cut or shape a wide variety of materials. Cutting means
vaporization of material along a line, so as to separate the workpiece into separate
parts. This method generally is used to cut plastic, wood, paper and ceramic
metarials. Because these materials do not have observable melting point. For metal
materials cutting means melting of metarial with high efficency.
In this study, firstly literature research including generation of laser beam , transfer
of the laser beam from resonator to workpiece and laser beam properties, optical
properties and interaction of laser radiation with materials is done. After then laser
technology efficently used manufacturing processes are investigated. Among this
process laser cutting process was focused on. When laser cutting method investigated
particularly, lots of parameters affect cutting process considered and the most
important parameters are defined as material properties, workpiece thickness, cutting
velocity and cutting power. After investigated effect of this parameter and a 3D laser
cutting model generated by using finite element method (FEM). The aim was to
develop cutting surface quality and define the parameter values to obtain an efficient
cutting process.
Different sheet metal thickness is used in industry because of different requirements.
In this study, 1 mm and 2 mm material thickness is used as industrial demand. If
only material thickness is changed (fix cutting velocity, cutting power and same
material), cutting process is completed without problem for thiner work piece.
Under same condition, Some problems can be observed for thick work piece cutting.
Cutting surface angle can be bigger than thiner work piece cutting surface angle or
laser can not be completely removed material. To solve these problems cutting
power or cutting velocity can be increased. But at that time, heat affected zone and
removed material will be increased. In this study, only 2 different metarial thickness
is used to compare each other. But analysis model can produce sufficeient results to
support different metarial thickness.
Another important parameter which used in analysis is laser cutting velocity. Cutting
velocity must be fastest to increase efficiency and reduce unit cost. High velocity
also decerase heat effected zone. All parameters are choosen as fix, only cutting
velocity is changed from 1 m / min to 2 m / min for some analysis to understand
effect of the cutting velocity. If cutting velocity is increased, heat affected zone and
removed material will be decreased. But higher cutting velocity has bad effect on the
cutting surface angle. Cutting velocity very important parameter on the laser cutting
performance. To decrease cutting time, higher cutting velocity should be choseen.
But cutting surface angle should be taken precaution. In this study, only two different
velocity is used, but model can support different cutting velocities which used in the
industry.
Laser cutting power is another important parameter. It affects efficency, unit cost ,
heat effected zone and cutting angle directly. All parameters are choosen as fix, only
cutting power is changed from 1000W to 2000W in some analysis to show affect of
cutting power. Only According anaysis, when higher laser power is used, removed
material and heat affected zone are larger than other. To increase efficency and
reduce removed material value, lower cutting power level should be used. But lower
cutting power increases angel on the cutting surface. So an optimisation is
necccesary between efficiency and cutting angle. 1000W and 2000W cutting powers
are used to define effect of cutting power. But different cutting powers can be used in
this model. Extra analysis (8 different analysis) are performed from 100 W to 2000W
to show model capability. And model solved all of the analysis with sufficient
results.
Different materials are used in the industry as a machine part. So laser cutting
process must be applicable method for different materials to support industrial
demands. Otherwise laser cutting method can be used for only special purpose
applications. St-37, AISI304 and Al 2024 are the most preferred materilas in the
industry. St-37, AISI 304 and Al 2024 materials have been used to analysis for
investigate material effect on the laser cutting operation. Those materials have
different melting temprature, coefficient of thermal conduction, specific heat and
density. According to analysis results, material heat conductivity, density, specific
heat cutting surface have been directly affected on the heat affected zone and
material cutting ratio.
Additonal analysis are performed to understand effect of power change on the cutting
surface angle. Analysis are repeated for 100 W, 250 W, 300 W, 400 W, 500 W,
900W, 1000 W and 2000 W. All of the other parameters were same to compare
analysis results. When we compare analysis results, effect of the cutting power is
observed clearly.