Experimental and Finite Element Analysis of Severing the Butt...

International Journal of Mechanical & Mechatronics Engineering IJMME-IJENS Vol:18 No:03 18

181403-6262-IJMME-IJENS © June 2018 IJENS I J E N S

Abstract— The objective of this study is to redesign the

blade used for severing the butt ends of aluminium billets in

order to eliminate the quality and production problems

during the extrusion process. During the end of the cutting

process, material from the mold may be detached and gaps

between the mold and the next billet occur. This

phenomenon creates blisters in the extruded aluminum

profiles and many profiles are considered scrap. By

alleviating such problem, many quality control

complications could be resolved while extrusion’s scrap

percentage could be significantly reduced. Various different

factors that can affect the cut process are studied herein,

with an emphasis given on the angle of the cutting blade

and the lubricant used in order to make the severing more

efficient. Also, a new design of the blade is proposed in

order to improve the cutting process, while the simulations

of the process performed investigate the behavior of the

system in detail.

Index Term-- Finite Element Analysis, Severing butt ends of

Aluminium Billets, Extrusion

I. INTRODUCTION

Aluminum extrusion is a metal forming process used for mass

production of aluminum products with constant cross section

profiles such as rods, tubes, beams, wires, multi-porting tubes

etc. The most commonly and widely practiced type of

extrusion in the industry today is the direct extrusion process,

also known as the billet-on-billet extrusion. In the direct

extrusion process the hot aluminum billet is pushed through

the profile opening of a die by the ram in a hydraulic press

1.During the extrusion process, as the ram and the dummy

block press the billet through the container, the actual flow of

alloy into the die is tapered. A dead metal zone remains at the

end of the container, surrounding the cone-shaped section of

flowing metal. Oxides, impurities and other inclusions from

the skin of the billet accumulate in this area. Care must

therefore be taken to ensure that extrusion is stopped before

this contaminated alloy is carried through the die and into the

product 2. This residue then forms the butt that sticks to the

back of the die stack. Hot aluminium extrusion involves

complex thermomechanical and chemical interactions between

.

aluminium and tool-steel tooling (mainly extrusion die and

container). Furthermore, the local contact conditions at the

workpiece/tooling interfaces are of great influence on process

parameters, such as productivity, product quality and scrap

rate. Finite-element (FE) simulations have been extensively

used in scientific research and industrial practice to analyze the

extrusion process and to aid in process optimization 3.

During the extrusion process after each billet has been

extruded, the container is opened to expose the butt. This must

then be sheared off before the container is closed, and the next

billet is loaded. If this operation is not performed cleanly and

efficiently, part of the butt can ‘hang up’ or continue to adhere

to the back of the die stack as illustrated in Figure 1 [4]. One

of the biggest problems that may occur during the cutting

process of the butts is the detachment of material from the

interior part of the die. This can cause serious problems during

the extrusion process, as material from the next billet cannot

cover this gap and blisters will appear in the extruded

aluminium profiles, raising the production scrap with several

degrees. Figure 2 shows both detached butts and extruded

aluminium profiles with blisters. This problem may be even

bigger as soon as multi-hole dies are used. Across the

aluminium extrusion industry, multi-hole dies are extensively

used to produce several solid profiles simultaneously for

increases productivity. A multi-hole die may sometimes also

be useful in the try to avoid a high reduction ratio, if a single-

hole die is used, which requires an excessively high

breakthrough pressure. It is important that the multiple

extruded profiles coming out of the multi-hole die are at the

same velocity and straight (without distortions).

Synchronization and flow uniformity are affected by the shape

and sizes of the profiles and the number and layout of die

orifices, in addition to operational parameters such as

extrusion speed and temperature. These can, in principle, be

achieved by adjusting the die bearing angle and length, which

is delicate manual work of the die corrector 5. However, as

much more holes exist in the die, the possibility to have more

gaps, that will trap air in them, is increased.

The finite element analysis approach has been chosen in order

to simulate the cutting process of the aluminium billet. The

stress, strain and deformation results are compared for various

cases, while the shape of the detachment is compared with

experimental findings. Emphasis is given on the angle of the

cutting blade and the lubricant that can be used in order to

E. GIARMAS1, D. TZETZIS2

1 Alumil S.A., Department of Production Planning, 611 00 Kilkis, Greece 2International Hellenic University, School of Science and Technology 14th km Thessaloniki-Moudania,

57001 Thermi, Greece

Experimental and Finite Element Analysis

of Severing the Butt Ends of Aluminum Billets

During the Extrusion Process



make the severing more efficient. A new design of the blade is

proposed in order to improve the cutting process.

Fig. 1. Severing the butt end

Fig. 2. (a) Detached butt end and (b) Extruded profile with blisters

II. MATERIALS AND METHODS

Alumimium alloy 6061 T6 (6005) has been chosen for the

material of the billet. Detail material properties that have been

used for the analysis are shown in Table 1. The diameter of the

billet is at 178 mm (extrusion machine 1800tn). The material

of the cutting blade is ORVAR 2 46-48 HRC. This is a

chromium-molybdenum-vanadium-alloyed steel which is

characterized by high level of resistance to thermal shock and

thermal fatigue, good high-temperature strength, excellent

toughness and ductility in all directions, good machinability

and polishability, excellent through-hardening properties and

good dimensional stability during hardening [6]. The

increasing global interest in the manufacture of products of a

precise shape, or one which is close to the shape of ready

components, has led to a significant development of the hot

and cold die forging technology that is used for the

construction of tools such as the cutting blade of the butt ends

in extrusion lines. Die forging, due to its advantages, is

currently the most advanced production technique used in the

mass production of responsible components as in the current

case the cutting blade 7.

Table I

Material Properties for AL6061-T6 and ORVAR 2_46-48 HRC

Property AL 6061-T6 ORVAR 2_46-48

HRC

Density (kg/m3) 2700 7800

Young's Modulus (GPa) 71 210

Poisson's Ratio 0,33 0,31

Bulk Modulus (GPa) 69,6 184,2

Shear Modulus (GPa) 26,69 80,15

Tensile Yield Strength (MPa) 280 1420

Compressive Yield Strength (MPa) 280 -

Tensile Ultimate strength (MPa) 310 -

III. FINITE ELEMENT ANALYSIS MODEL

The CAD model has been created in Solidworks and then was

inserted in ANSYS software. The ANSYS workbench has

been used and specifically the explicit dynamics method.

Multilinear Isotropic Hardening was selected for the material

model in order to ensure that plastic deformation will be

achieved in the course of the severing procedure [8]. The built

mesh is shown Figure 3a. The table of the billet and the back

side of it, have been chosen as fixed supports. The vertical

movement of the cutting blade has also been selected, while

the displacement of the two surfaces of the billet have been

calculated accordingly.

The two most important factors that are studied in this paper

are the angle of the cutting blade and the lubricant that can be

used in order to make the severing more efficient. Some

factors such as the velocity of the cutting blade and the

temperature do not play an important role in the studied

model. The velocity is something that cannot be modified

during the actual test, so it is not taken into account as a

parameter in this study. Thereby, it was kept constant in all

simulations. The temperature of the billet is around 400 °C and

it is very important to keep it constant during the extrusion

process. The temperature of the cutting blade cannot affect the

cutting results, because both the size of contact surfaces and

the contact time cannot permit important heat transfer

phenomena during the cutting process.

Simulations with the existent cutting parameters and

comparison with the actual testing results (taken by extrusion

machines) were made and a validation study was performed.

Additionally, three different angles for the cutting blade and a

new lubricant were simulated with finite elements. The results

are presented and evaluated in order to give a final solution.



Fig. 3. a) The FEA model and b) Shape of the butt end (15mm) in simulation

and reality

IV. VALIDATION OF THE MODEL

The simulation with the existent cutting parameters in the

production line and comparison with the actual situation is

presented in this section. This comparison is very important as

it is the only way to detect whether the model can give results

that keep up with reality. Three factors are compared. First of

all the shape of the cut butt end, the deformation of the butt

end and the point from where the detachment occurs. The

shapes of the butt end (from the simulation of cutting process

and the actual test) that occurred with the existent blade are

illustrated in Figure 3b. The width of the butt end is 15mm. It

is very important to emphasize that from the first view the

results of are almost the same.

This is very good evidence that the model has been built

correctly and further analysis can optimize the process

operation through dimensional changes of the cutting blade so

to ameliorate the production process in general. Further

measurements of the butt-end with a micrometer was

performed in order to compare the measurement values with

the total deformation obtained from the simulation. The results

revealed that the model has been built in a way that predicts

the deformation with high accuracy. The measured

deformation was 95,86 mm while the model has shown a

deformation of 95,87 mm (Figure 4). The time and the area

from where the detachment starts give more information

regarding the accuracy of the calculations. The actual

detachment in the model was calculated from the percentage

detachment which was 74,35% ((1-0,7435)*178 =45,66mm

(Figure 5). The accuracy of the model is confirmed from such

results since the detachment value is almost identical with the

measured one (Figure 5). The detachment has been calculated

with the aid of the animation that ANSYS give to the user. At

the point that the bottom part of the butt end starts to move

without being cut, the phenomenon of detachment has been

started. With very simple calculations the percentage of the

total billet diameter that has been covered until that moment

can be found. Another important test in order to ensure the

validation of the results of the FEA model was to measure the

detachment area according to the thickness of the butt-end.

From the actual production process and the measurements that

have been made, the detachment starts earlier for a larger butt-

end. Specifically, the detachment area is at around 22,88%

larger for a butt end at 30mm. Figure 6 illustrates the results

from the measurement and the model. The method that has

been used in order to define the detachment is the same as

previously. The detachment was at the 68,6% of the process,

which results to (1-0,686)*178 =55,89mm of actual

detachment (Figure 6). Clearly, such value is almost identical

with the measured one and shows that the model is capable of

predicting correctly the behavior of severing the butt-end of

aluminum billets.

Fig. 4. Deformation (m) at 95,87mm in ANSYS and reality

Fig. 5. Predicted detachment of 45,66 and reality

Fig. 6. Detachment of 55,89mm and reality



V. OPTIMIZATION OF THE PROCESS

The optimization of the cutting process has been made for the

blade’s angle and the lubrication of the process. With the aid

of the finite element analysis the deformation, the stresses, the

strain and the detachment of the butt end during the cutting

process have been examined. In addition, the maximum shear

stresses that the cutting blade faces are presented below.

Blade’s Angle

The blade’s angle is the first and one of the most important

factors that can affect the cutting process. The angle of the

blade affects not only the deformation of the butt end but the

plastic strain and the detachment of it as well. The dimensions

of the existent blade and for the two alternatives are given in

Figure 7. The deformation of the butt end plays an important

role in the studied process. Despite the fact that it is important

in order to be easier for the blade to penetrate the billet deeply,

very large deformation may cause earlier the detachment of the

butt end. Figure 8 represents the deformation of the butt end

for the 3 blades.

Fig. 7. Schematic of the blade with the various angles under study

Fig. 8. Deformation (m) for (a) existent Blade, (b) Blade No2 and (c)Blade

No3

Fig. 9. Detachment of: a) 45,66mm for blade No1, b) 36,6mm for blade No2

and c) 27,7mm for blade No3

Fig. 10. Equivalent plastic train for (a) existent Blade, (b) Blade No2 and (c)

Blade No3

It is clear from the view of the butt end that the deformation

decreases as the blade’s angles decreases as well. Total

deformation started from 95,86 mm for the existent blade and

resulted in 66 mm and 56 mm for the two other blades (-

31,14% and -41,6% respectively) under study. The detachment

of the butt end is certainly the most important factor that

should be investigated. The variation of the detachment in

relation to the blade’s angle is illustrated in Figure 9. The

detachment occurs when bottom parts of the butt end start

moving before the blade severe it. It is easily noticeable that

smaller angles for the cutting blades can provide much better



production results. From 45,66 mm the detachment decreases

to 36,6mm (-19,84%) and 27,7mm (-39,33%) with the use of

blades No2 and No3 respectively.

The plastic strain in the butt end gives very important

information about the detachment that occurs during the

cutting process. High values for the plastic strain indicate

bigger detachment in the model. Figure 10 shows the

simulated data for the equivalent plastic strain in the detached

area. It is clear that as the angles of the blade decrease, the

plastic deformation decreases as well. This observation comes

to confirm the previous analysis that has already shown a clear

improvement in the process of severing the butt end as the

angles of the cutting blade decrease. In detail, the plastic strain

in the detached area decreases from 0,82 to 0,74 (-9,7%) and

0,7 (-14,63%) with the use of blades No2 and No3

respectively.

Lubrication

In the current study, Boron Nitride has been tested as

preferable lubricant for the extrusion process since such

material is the ultimate lubricant to facilitate butt shear. The

lubricants that are often used are not suitable since they are

suited for up to 200 °C. However, the billet’s temperature is

around 400 °C. Boron nitride is the ideal lubricant, not only

for its unmatched lubricity, but also for its ease and economy

of application [9]. Environmental problems are eliminated and

scrap due to blisters is reduced. The friction coefficient that

this lubricant can give is 0,3 [10].

In order to test the new lubricant, an analysis has been made

with the existent blade, as it is important to investigate the way

that a Boron Nitride lubricant can ameliorate the cutting

process. Boron nitride has been extensively applied in the

fields of electronics, physics, and aerospace as a sealing

material, taking advantage of its structural stability and

excellent anti‐oxidation properties. In a study reported by Wan

et. al. [11 lubricant oils containing Boron Nitride

nanoparticles with different concentration were formulated and

showed good stability for more than two weeks. In addition,

their tribological performances and viscosities were studied.

The viscosities of both the nano-Boron Nitride oils and base

oil decreased sharply with increasing temperature and no

significant distinct between them were found. The nano-Boron

Nitride oils could significantly improve the anti-wear and anti-

friction properties of the base oil, and lower nanoparticle

concentration exhibited better tribological performance. The

patching mechanism of the Boron Nitride nanoparticles on the

worn surface were confirmed by the Energy Dispersive X-ray

Spectrometer (EDS) results and an effective concentration was

proposed to be around 0.1wt.% [11.

Figure 11 shows the results of this simulation. By comparing

the above results, it is evident that with the use of boron nitride

as lubricant, the total deformation decreases from 95,8mm to

88,2mm (-8%), the plastic strain in the area of the detachment

decreases from 0,78 to 0,74 (-5,1%) and the size of

detachment area decreases from 45,66mm to 38,94mm (-

14,7%). As a result, the use of boron nitride only can improve

the cutting procedure and minimize any defects caused.

Fig. 11. (a) Total Deformation, (b) Equivalent plastic train and (c)

Detachment of 38,94 mm for existent Blade and use of Boron Nitride as

Lubricant

Shear and Maximum shear Stresses on the Blade

Figure 12 illustrates the fluctuation of the shear stresses on the

blade in the 20% of the cutting process. Due to the vertical

movement of the blade and the shear cutting of the billet, these

stresses are considerably important. From the actual cutting

process, it easily noticed that the butt end curves and a gap

between the blade and the butt end is created in the middle

(Figure 13). The maximum shear stresses that the blades

withstand during the cutting process are presented in Figure 14.

It easily understandable that the use of the proper lubricant can

decrease the maximum shear stresses. In addition, as the

blade’s angles decrease, the maximum stresses increase and

the possibility of blade fracture and catastrophic failure is

increased. The stresses are lower in the center of the blade due

to the curvature of the butt end that created during the cutting

process. However, due to the spherical section of the billet, the

central part of the blades is in contact with material for longer

time and the failures that have been observed practically are

mainly located in that region.

Fig. 12. Shear Stresses on the cutting blade



Fig. 13. The curved butt end from the actual process

Fig. 14. Maximum Shear Stresses over time for (a) the existent Blade without

and (b) with the use of Boron Nitride, (c) Blade No2 and (d) Blade No3

VI. NEW DESIGN STUDY

A new design of the blade is proposed in order to improve the

cutting process as shown in Figure 15. Figure 16 shows the

deformation and detachment of the newly designed blade No4

as well as the equivalent plastic strain and the maximum shear

stresses. By comparing these results with those of the blade

No1 (existent blade) it is evident that the total deformation

decreases from 95,8mm to 59,4mm (-38%), the plastic strain in

the area of the detachment decreases from 0,78 to 0,69 (-

11,54%) and the size of detachment area decreases

dramatically from 45,66mm to 25,22mm (-44,77%). Finally,

the maximum shear stresses in Blade Nο 4 are slightly smaller

in comparison to blade No1 but with extremely smoother

dispersion across the blade. As a result, taking all the above

under consideration, the use of Blade Nο 4 is a very promising

design approach, as the detachment decreases in a great grade

and the shear stresses on the blade remain in normal levels

without the risk of material failure, as the maximum shear

stress over time is 736 MPa with the yield strength of Blade’s

material at 1280 MPa.

Fig. 15. Technical Drawing of Blade No4

Fig. 16. Deformation (a), Detachment at 25,22 mm (b), Equivalent plastic

strain (c) and Maximum Shear Stresses over time (d) for Blade No4

VII. CONCLUSIONS

The current paper presents a study towards the optimization of

the cutting process of the butt ends of aluminium billets. A

reduction in the blade’s angles seems to reduce the detachment

area up to 39,33% for the blade Nο3. However, this type of

Blade is too thin and the risk of failure is higher because of

fatigue. On the other hand, the use of Blade Nο2 reduces the

detachment area up to 19,84% by having smoother stress

distribution. Furthermore, the use of Blade Nο4 seems to offer

the best possible solution for the studied problem. The

detached area decreases up to 44,77% with simultaneous

normal shear stresses distribution. Finally, the use of Boron

Nitride as lubricant could smooth out the shear stresses on the

blade, as the simulations have clearly shown. Future tests in

the extrusion production lines can clarify these predictions as

far as the optimal use of Blade Nο2 and Nο4 with Boron

Nitride preferably as lubricant.



REFERENCES [1] Tushar Bakhtiani, Hazim El-Mounayri, Jing Zhang, Numerical

simulation of aluminum extrusion using coated die, Materials Today:

Proceedings 1 ( 2014 ) 94 – 106

[2] www.castool.com

[3] Liliang Wang Jie Zhou, Jurek Duszczyk, Laurens Katgerman, Friction in

aluminium extrusion—Part 1:A review of friction testing techniques for

aluminium extrusion Tribology International 56 (2012) 89–98

[4] Pradip K. Saha, Aluminum Extrusion Technology, ASM International ®,

Materials Park, Ohio (2000)

[5] Gang Fang1, Jie Zhou, Jurek Duszczyk, FEM simulation of aluminium

extrusion through two-hole multi-step pocket dies, journal of materials

processing technology 2 0 9 ( 2 0 0 9 ) 1891–1900

[6] UDDEHOLM Technical brochure, Edition 5, 2013

[7] Review of selected methods of increasing the life of forging tools in hot

die forging processes, Marek Hawryluk, Archieves of Civil and

Mecjanical Engineering 16 (2016) 845-866

[8] M. Binder, F. Klocke, B. Doebbeler An advanced numerical approach on

tool wear simulation for tool and process design in metal cutting,

Simulation Modelling Practice and Theory, 70 (2017), 68-72

[9] Jens Eichler , Christoph Lesniak, Boron nitride (BN) and BN composites

for high-temperature applications, Journal of the European Ceramic

Society 28 (2008), 1105-1109

[10] Toshiaki Wakabayashi, Kazumi Okada, Tetsuya Wada, Hiroshi

Nishikawa, Boron nitride as a lubricant additive, 232 (1999), 199-206

[11] Qingming Wan, Yi Jina, Pengcheng Sun, Yulong Ding, Tribological

behaviour of a lubricant oil containing boron nitride nanoparticles,

Procedia Engineering 102 ( 2015 ) 1038 – 1045

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