Scholarly article on topic 'Conventional and Laser Assisted Machining of Composite A359/20SiCp'

Conventional and Laser Assisted Machining of Composite A359/20SiCp Academic research paper on "Materials engineering"

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Abstract of research paper on Materials engineering, author of scientific article — Damian Przestacki

Abstract Metal matrix composites (MMCs) have many industrial applications in different sectors, e.g.: automobile and aerospace. However, due to hard ceramic reinforcing components in MMCs, difficulties can arise when machining via conventional manufacturing processes. Excessive tool wear is especially problematic. Laser assisted machining (LAM) is one of the technologies that enable machining of hard-to-cut materials. In laser assisted cutting, the workpiece area is heated directly by a laser beam before the cutting edge. The work reported here concentrates on improving Al/SiC composite's machinability by laser assisted machining, when compared to conventional turning process. Influence of laser's beam during laser assisted turning on cutting force, tool wear and machined surfaces roughness was investigated. This research was carried out for cubic boron nitride (CBN) and sintered carbide inserts. The results obtained with the laser assisted machining were compared to those obtained in conventional turning.

Academic research paper on topic "Conventional and Laser Assisted Machining of Composite A359/20SiCp"

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Procedia CIRP 14 (2014) 229 - 233

6th CIRP International Conference on High Performance Cutting, HPC2014

Conventional and laser assisted machining of composite A359/20SiCp

Damian Przestacki*

Poznan University of Technology, Institute of Mechanical Technology, 3 Piotrowo St., Poznan, 60-965, Poland * Corresponding author. Tel.: +48 668 345 270; fax: +0-000-000-0000. E-mail address: damian.przestacki@put.poznan.pl

Abstract

Metal matrix composites (MMCs) have many industrial applications in different sectors, e.g.: automobile and aerospace. However, due to hard ceramic reinforcing components in MMCs, difficulties can arise when machining via conventional manufacturing processes. Excessive tool wear is especially problematic. Laser assisted machining (LAM) is one of the technologies that enable machining of hard-to-cut materials. In laser assisted cutting, the workpiece area is heated directly by a laser beam before the cutting edge. The work reported here concentrates on improving Al/SiC composite's machinability by laser assisted machining, when compared to conventional turning process. Influence of laser's beam during laser assisted turning on cutting force, tool wear and machined surfaces roughness was investigated. This research was carried out for cubic boron nitride (CBN) and sintered carbide inserts. The results obtained with the laser assisted machining were compared to those obtained in conventional turning.

© 2014Published byElsevier B.V.This is an open access article under the CC BY-NC-ND license (http://creativecommons.Org/licenses/by-nc-nd/3.0/).

Selectionandpeer-review under responsibility of the International Scientific Committee of the 6th CIRP International Conference on High Performance Cutting

Keywords: metal matrix composites; laser assisted machining; tool wear.

1. Introduction

The reinforcement of metallic alloys with ceramic particles has generated a family of materials called metal matrix composites (MMCs). The matrix is usually made of: aluminum, titanium and magnesium alloys, and reinforcements are usually: silicon carbide (SiC) and alumina (A№).

MMCs have many advantages in comparison to conventional aluminum alloys, primarily enhanced stiffness and improved wear resistance. However, these materials have significantly reduced ductility compared to unreinforced alloys [3]. The improved properties of the composites are primarily related the transfer of load from the matrix to the hard and stiff reinforcing phase. The application of SiC-reinforced aluminum alloy composites in aerospace and automotive industries has been gradually increased for pistons, cylinder heads, etc. However, the abrasive reinforcement particles used in these materials make them difficult to machine using conventional manufacturing processes, due to heavy tool wear and poor surface finish. The surface quality

depends on the shape, the size and the volume fraction of the reinforcement, but also on cutting parameters [1, 6]. In several researches [2, 4, 7, 8] the main problem of MMC machining is related to an extremely high tool wear due to the abrasive action of the ceramic particles. Therefore, materials which have very high abrasive wear resistance, as diamonds (mono and polycrystalline) and polycrystalline boron nitrides (CBN) are often recommended. The CBN materials are also successfully applied to machining of hard cast irons, heatproof superalloys, as well as hardened steels [10].

One of the possibilities to improve the machining properties of difficult to machine materials is to employ the thermal softening ability of a heat source to heat the material during cutting. This new approach of materials forming is enabled by so called hybrid machining. Laser-assisted machining is a hybrid machining process, in which the workpiece is heated by a focused laser beam before the material is removed by a conventional cutting tool.

The intense, localized heat source inherent to this process affords an extremely effective method for increasing the temperature of the material just prior to the cutting location. In

2212-8271 © 2014 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.Org/licenses/by-nc-nd/3.0/).

Selection and peer-review under responsibility of the International Scientific Committee of the 6th CIRP International Conference

on High Performance Cutting

doi:10.1016/j.procir.2014.03.029

some difficult to cut materials like: Inconel, ceramic, magnesium alloys [9] this leads to a reduction of strength in heated regions and increases machinability. The laser assisted machining (LAM) method could potentially improve the processing of metal matrix composites.

This paper presents the analysis of tool wear after turning of metal matrix composite, carried out with sintered carbide, as well as polycrystalline boron nitride (CBN) inserts.

Nomenclature

ap depth of cut (mm),

dt laser beam diameter (mm),

d workpiece diameter (mm),

f feed rate (mm/rev),

vl laser beam speed (m/min),

ts heating time, cutting time (s, min),

P laser power (W),

&0 temperature in laser heating zone (C),

®j temperature in cutting zone (C),

&max maximum temperature during laser heating (C),

0mi„ minimum temperature during laser heating (C),

vc cutting speed (m/min),

s emissivity coefficient.

2. Experiments

The purpose of research was the determination of machinability of cutting inserts, which were made of different cutting tool materials, during turning of metal matrix composite (MMC), reinforced with particles of SiC. The conventional and laser assisted process (with heating of cutting zone by molecular laser CO2) were applied.

The material selected for this study was composite AlSi9Mg with aluminum alloy matrix (composition: 9,2% silicon, 0.6% magnesium, 0,14% iron, 0,11% titanium, 0,01% copper, 0,02% zinc, aluminum balance), reinforced with silicon carbide particles. The contribution of SiC particles in the machined composite was about 20% of volume and about 8-15 ^m in diameter. Original cast was melted and casted again by a gravity casting method. Structures of these alloys have been shown in Figure 2. Workpieces had cylindrical shape of 10 mm length and 60 mm in diameter. The workpieces were coated by an absorptive substation (gouache), each time to increase laser absorption.

laser beam

SEM MAG: 501 x DET: SE Detector HV: 15.0 kv 200 |jm

VAC: HiVac Device: TS5135

Fig. 2. SEM microscope image of the Al/SiCp material's microstructure. The SiC particles (have darker color on the pictures) are distributed through the matrix.

Laser heating was carried out with a CO2 technological laser (TLF 2600t, TRUMPF), which delivers a nominal output power of 2.6 kW. The laser is connected to a universal lathe type TUM 25D1 with a spindle's rotation control. The view of the laser-assisted turning is illustrated in Figure 1 and 3.

Table 1. Characteristics of cutting inserts applied in the research.

Mark of edge Insert code material

geometry coating

Polycrystalline

boron nitride

Sintered carbide

KC5510

TPGN110304

SNMG120408

Kr = 75o -

af =5 o

Yf= -5 o

Kr = 90o TiAlN,

af = 11o PVD

Yf= 0 o method

Fig. 1. Scheme of Laser Assisted Machining (LAM) process. Designations: A - heating area by a laser beam, B - zone of machining, d - workpiece's diameter.

Fig. 3. View of workstation. 1- metal matrix composite, 2 - pyrometer (measurement of temperature) 3- laser head, 4 - tool.

Tool wear was measured on the primary flank face with the optical microscope (Figure 4). Conventional and laser assisted turning tests were carried out using different cutting inserts (their characteristic is shown in Table 1).

0 = a In t + b

The square of the correlation coefficient R for these equations has been also determined.

The research was carried out with parameters shown in Table 2.

Table 2. Parameters applied in the research.

cutting speed

laser beam speed

laser power feed rate

depth of cut

10 m/min 10 m/min

P, =300W P2 =650 W P3 = 1000W P4 = 1400W

0,04 mm/rev 0,1mm

3. Results and discussion

3.1. Temperature - laser power relationships

In Figure 5 and 6 the courses of MMC surface's temperature during heating are shown. Temperature in an area heated by a laser's beam aspires to stabilization (Figure 5, Figure 6). It's due to heat accumulation in an examined sample. The range of temperature 01 is about 30oC (Figure 6), which results from different thickness of absorption layer (gouache) on the investigated surface, and from differences in surface texture.

Fig. 4. View of the tool wear measurement.

Surface temperature was measured by two RAYTEK pyrometers, in two different areas. One of these measured temperature in the area of laser's beam heating and the second one - in machining zone. The angle between area heated by a laser beam and cutting tool was equaled to 30 degrees. Emission was set in the software, based upon calibration tests previously made. The previous work [5] shows that, emission coefficient strongly depends on the temperature and surface roughness. If the real temperature will change, the emission coefficient should be also changed to get the correct value of temperature. The temperature was characterized by the average arithmetic temperature which was determined for the values obtained in 5 trials, in the same conditions on a heated surface (Figure 5).

In previous work, the temperature & of the heated surface was the investigated factor and variable factors were: power P, density of the laser radiation power q, diameter of the laser beam on the heated surface dl, heating time ts. On the basis of the performed investigations, mathematical models of the investigated object have been determined in the form:

AlSi9Mg + 20% SiC, d=60 mm,f=0.04mm/rev, v,=10m/min, " P=1000W, d,=2mm, £=0.3, gouache 2x

30 60 90 120 150 180 210 240 270 300 Time ts [s]

Fig. 5. The courses of temperature &1 (cutting zone) during heating of MMC by a laser beam with maximum and minimum values.

o 1400

® 1200

!— 800

AlSi9Mg + 20% SiC, d=60 mm, f=0.04mm/rev, v,=10m/min, £=0.3, P=1000W, gouache 2x

®,= 83,92ln(0 - 75,65 R2 = 0,86

120 150 Time ts [s]

210 240 270 300

Fig. 6. The courses of temperature measured in cutting area (&i) and laser heating zone (&0).

Temperature play an important role from a point of view of cutting forces which are interrelated with tool wear during laser assisted turning. The increase of the MMC's temperature will decrease the workpiece's strength and in some cases will reduce the yield strength below the fracture strength, permitting material removal by a plastic deformation.

3.2. Tool wear

The hard SiC particles with hardness of 2600HV 0 grinds the flank face of the cutting tools similarly to a grinding wheel.

Figure 6 shows the influence of laser assisted machining on the flank wear during turning of Al-SiC metal matrix composites.

As a consequence of heating, the flank wear was decreased significantly for more than 0,5 kW of laser power. It can be observed that for P2 =650 W and P3 =1000 W insert's wear was adequately about 12% and 37% lower in comparison with the results obtained for the conventional turning. Nevertheless, for P¡, P4 of laser power, insert's wear is comparable for conventional and laser hot turning. This observation is very important, because it indicates that the hardness of the matrix material (temperature of the process) is also a considerable factor influencing tool wear, despite the tool's geometry. However, it is also worth indicating that the application of laser's power of 1000 W enables the obtainment of the lowest tool wear, in comparison to the other powers (see - Figure 7).

VBc [mm]

0,18 0,17 0,16 0,15 0,14 0,13 0,12 0,11 0,1 0,09 0,08 0,07 0,06 0,05 0,04 0,03 0,02 0,01 0

I I - conventional cutting d=60 mm. i=10 mm.,/=0.04mm/rev, — „p=0.1mm, vc=10m/min, ts =4,7min

I I-LAM

tool-SNMG 120408 KC5510

0 300 650 1000 1400

Fig. 7. Average tool wear of sintered carbide inserts when conventional turning and laser assisted turning of A359/20SiC.

The A359/20SiCp composite has poor machinability during conventional turning with sintered carbide insert coated with TiAlN layer (Figure 8). These results indicated that, as a consequence of heating, the tool's wear decreased significantly. This value gave about 100% lower tool wear in comparison with conventional turning, during the 10 min of machining. These results can be easily explained by an increase in the temperature in the cutting zone, which facilitates plastic deformation of matrix. Similar results were obtained for the polycrystalline boron nitride (Figure 9).

0,6 0,55 0,5 0,45 0,4 0,35 0,3 0,25 0,2 0,15 0,1 0,05 0

10 12 14 16 18 20 22 24 26

Cutting time ts. [min ]

Fig. 8. Variation of average tool wear of sintered carbide (KC5510) in function of machining time.

A CBN tool shows significantly longer tool life than a tungsten carbide tool, during the conventional turning of MMC at the same cutting conditions (Figure 8, Figure 9). It can be observed, that flank wear is smaller using a CBN tool than that using a sintered carbide tool, during laser assisted machining.

d=60 mm, vc=10 m/min, f=0.04mm/rev, „p=0.1mm, P=1000 W, dl=2 mm, wedge-PCBN

ф - conventional turning Д - laser assisted turning

0 2 4 6

10 12 14 16 18 20 22 24 26

Cutting time ts [min ]

Fig. 9. Variation of average tool wear made of polycrystalline boron nitride (KD050) in function of machining time.

Abrasion of the deposited workpiece material on both, primary and secondary flank faces results in the grooves on the flank face (Figure 10).

Fig. 10. The images of KC5510 inserts after turning: a) conventional turning b) with laser assisted machining. vc = 10m/min, f = 0,04mm/rev, ap = 0,1mm, ts = 10min

0,6 0,55 0,5 0,45 0,4 0,35 0,3 0,25 0,2 0,15 0,1 0,05 0

Edge crater was not observed during LAM of metal matrix composite with CBN insert at high temperature (Figure 11a), however it appeared during the conventional turning within lower material's removal temperature (Figure 11b).

Fig. 11. View of flank wear: a) LAM, b) conventional turning. Parameters:

ap = 0,05 mm, d = 55 mm, l = 10 mm, vc = 10 m/min, f = 0,04 mm/rev, P = 1000 W, dl = 2 mm

Abrasion, adhesion and diffusion are the primary tool wear mechanisms during laser assisted turning of MMC. Furthermore, the flank wear is the dominant tool failure mode during laser assisted turning of MMC, which is attributed to the adhesion of the semi - liquid metal matrix to the cutting tool (Figure 11a).

Repeatedly, tool wear is strongly dependent on the material's removal temperature, and there is an optimum temperature for the longest tool life.

4. Conclusion

In this study, laser-assisted machining on A359/20SiCp material was compared with conventional turning process.

Thermally enhanced conventional turning uses laser beam to heat the workpiece, as well as to change the microstructure or locally harden the material in front of the cutting tool. This process is carried out in order to facilitate the machining due to its softening and change of the workpiece's deformation behavior.

The local temperature of the material in the shear deformation zone plays an important role in the thermally enhanced machining process. Softening of the Al matrix by the laser beam prior to cutting leads to the significant tool wear reduction in comparison to the conventional cutting.

Gradual flank wear is the dominant tool failure mode at the high temperature and the flank wear is significantly reduced

with an increase of workpiece's temperature up to a power of 1000W. However, further increase in a temperature induces the reduction of the tool's wear.

Turning with laser heating reduces a tool wear of the examined inserts in comparison with conventional turning.

It was found, that the laser assisted machining process shows a considerable improvement in machinability of metal matrix composite through the lower tool wear, and thus increased tool life, as well as reduction of cutting time.

References

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Acknowledgments

Author would like to thank to PhD Eng. Marian Jankowiak from the Poznan University of Technology for the support and advice during the research.