1-s2.0-s1875389211002173-main

8/13/2019 1-s2.0-S1875389211002173-main

1/9

Available online at www.sciencedirect.com

Physics Procedia 12 (2011) 308316

1875-3892 2011 Published by Elsevier Ltd.

doi:10.1016/j.phpro.2011.03.138

LiM 2011

Analysis of the Laser Drilling Process for the Combination with a

Single-Lip Deep Hole Drilling Process with Small Diameters

Dirk Biermanna, Markus Heilmanna*

aInstitute of Machining Technology, Technische Universitt Dortmund, Baroper Str. 301, 44227 Dortmund, Germany

Abstract

Due to the tendency of downsizing of components, also the industrial relevance of bore holes with small diameters and high

length-to-diameter ratios rises with the growing requirements on parts. In these applications, the combination of laser pre-drilling

and single-lip deep hole drilling can shorten the process chain in machining components with non-planar surfaces, or can reduce

tool wear in machining case-hardened materials. In this research, the combination of these processes was realized and

investigated for the very first time.

Keywords:Hybrid machining; single-lip deep hole drilling; laser drilling; combination of drilling processes

1. Motivation / State of the Art

Because of increasing requirements on components concerning their specific properties, e. g. increasing power

density or miniaturization, the dimensions of parts diminish in size. For the production of these parts, adaptations of

the manufacturing processes used as well as the development of new technologies are necessary. This tendency is of

particular relevance in the automotive industry, the information technology industry as well as for medical and

biomedical products [1-2]. In various applications, the production of bore holes with a high length-to-diameter ratio

and small diameters is required. For the production of deep holes with small diameters different manufacturing

processes can be used. In this context single-lip deep hole drilling (SLD), laser drilling, electro discharge machining

(EDM), electron beam machining (EBM) and electro chemical machining (ECM) were used. Each of the processes

mentioned above provides specific properties, especially concerning diameter range, drilling depth, accuracy,

repeatability and process time [3-6]. The combination of different processes for bore hole production can enhance

the bore hole quality and can shorten the production time. One possibility for a hybrid process for micro machining

is the combination of laser pre-drilling and counter-boring by EDM drilling [7].

The motivation for the approach presented is based on applications, where the conditions at the beginning of the

deep hole drilling process are unfavorable. Examples are the production of deep holes in non-planar or case-

hardened surfaces [8]. In this research, the combination of the production processes laser drilling and single-lip deep

*Corresponding author. Tel.: 0049 231 755 6426; Fax: 0049 231 755 5141.

E-mail address: [email protected].

8/13/2019 1-s2.0-S1875389211002173-main

2/9

Dirk Biermann and Markus Heilmann / Physics Procedia 12 (2011) 308316 309

hole drilling was analyzed for the very first time. The aim of this investigation is the manufacturing of a pilot-hole

by a laser for guiding the single-lip drill (SLD) in the process phase of pre-drilling (Figure 1). With the new

approach, a reduction of the process time in machining workpieces with planar surfaces as well as a shortening of

the process chain for the production of deep holes at non-planar surfaces is intended. Furthermore, a decrease in tool

wear is aspired by laser drilling through a hardened layer. To realize these aims, an innovative machine tool concept

was developed that integrates a Nd:YAG laser for laser drilling on a conventional deep hole drilling machine tool.

Using this machine tool, the utilization of laser processes and single-lip deep hole drilling in one setup is possible.

Figure 1. Process combination of laser drilling and single-lip deep hole drilling for the production of deep holes

2. Experimental

For the experimental investigations, a prototypical machine tool was designed and built. This machine tool

consists of a Nd:YAG-laser, that is integrated into a conventional deep hole drilling machine tool for small

diameters. The results of this combination is that both, a single-lip deep hole drilling process and a laser drilling

process, can be carried out using the same machine tool and the same workpiece fixture. In this adapted machinetool, the single-lip deep hole drilling process is designed for a tool diameter range from d = 0.5 mm up to d = 6 mm.

The laser drilling process can be carried out in four different operating principles such as single-pulse, percussion,

trepanning and helical drilling. The laser used has a peak power of P = 8,000 W and a pulse duration of

t = 0.08,1 ms. The machine tool used as well as the experimental setup for laser drilling and single-lip deep hole

drilling is shown in Figure 2.

Single-Lip Deep Hole Drilling:

Borehole diameter: d = 0.5 mm up to 6 mm

Spindle power: P = 4 kW

Number of revolutions: nmax = 36.000 1/min

Feed velocity: vfmax

= 15.000 mm/min

Drilling depth: ltmax = 450 mm

TBT ML-200: Prototype Single-Lip Deep Hole Drilling Machine Tool with an Integrated Laser

Laser:

Laser power: P = 80 W

Peak power: P = 0.5,,8 kW

Peak energy: E = 0.04,,8 Joule

Pulse duration: t = 0.08,,1 ms

Figure 2. Machine tool for single-lip deep hole drilling and laser drilling

Single-lip deep hole drillingPilot -hole by laser drilling

8/13/2019 1-s2.0-S1875389211002173-main

3/9

310 Dirk Biermann and Markus Heilmann / Physics Procedia 12 (2011) 308316

In these experiments, for the mechanical drilling, single-lip tools with a diameter of d = 0.5 mm were chosen. The

tools consisted of a homogenous, uncoated cemented carbide substrate (ISO HW-K15) and contained an internal

cooling lubricant supply channel. As workpiece material, a stainless steel with an austenitic structure, so-called

AISI 316L, was used. The cooling lubrication concept was an internal oil supply using a high oil pressure of

p = 200 bar. The process parameters such as cutting speed and feed were varied. The range of the cutting speed was

kept between vc= 30,...,50 m/min, and the range of feed amounted between f = 0.5,...,0.7 m/rev.

3. Results and Discussion

3.1. Process design for laser pre-drilling

In the first step of the experiments conducted, the laser drilling process was analyzed with the aim of the

identification of suitable laser parameters that allow the manufacturing of bore holes meeting the requirements the

deep hole drilling process demands on a guiding assistance. The targeted pilot-hole dimensions are named in

Figure 3.

Figure 3. Definition of the targeted pilot-hole dimensions

For the guiding assistance of a single-lip deep hole drilling tool, the pilot-hole must have a diameter with a low

tolerance of dmax=500+ 10m. This tolerance is necessary to avoid the contact of the deep hole drilling tool with the

bore hole wall while moving it into the pilot-hole. Furthermore, this pilot-hole must have a low roundness deviation

to avoid contact of the cutting edge with the workpiece material during the positioning of the tool into the laser

drilled hole. The depth of the pilot-hole must be at least 1.5 of the tool diameter. This is founded in the distance of

the tool tip to the guide pad. Especially in laser drilling, a hardening at the bore hole ground and at the bore hole

wall can occur which can lead to high mechanical loads on the deep hole drilling tool. Due to that, the influence on

the peripheral zone also should be low. To fulfill these requirements, a variation of laser parameters was conducted

and the resulting bore holes were evaluated concerning the targeted values diameter, roundness deviation, drilling

depth, surface roughness and peripheral zone. For every laser parameter combination repetitions were performed to

analyze the repeatability of the laser processes. At first the laser drilling strategies single-pulse, percussion and

helical drilling were realized. The influence of the laser drilling strategy on the bore hole diameter is shown in

Figure 4.

The results show, that the use of percussion laser drilling is unsuitable for the production of laser pilot holes

under the conditions viewed. The diameter is significantly lower as the targeted value and the bore hole shows a

high roundness deviation. This is based on the higher amount of material molten by the laser. A part of this material

Target values:

Pilot-hole diameter: D = 500,,510 m

Pilot-hole depth: l = 0.75,,1.5 mm

Roundness dev.: tk < 10 m

1.53xd

d+0.01

Definition of targeted pilot-hole dimensions

8/13/2019 1-s2.0-S1875389211002173-main

4/9


solidifies at the bore hole wall before it exists the bore hole, recast-layers occurs. These layers reduce the bore hole

diameter and influence the roundness of the bore hole negatively. This effect also occurs in helical laser drilling. In

contrast to percussion drilling, the bore hole diameter can be adjusted by an adaption of the diameter of the helix D H.

Due to the creation of recast layers, the reproducibility of the diameter is lower than in single-pulse drilling. Another

disadvantage is the longer process time. In single-pulse laser drilling, the aimed diameter is approximately reached

with the laser parameters presented. Furthermore, the bore holes produced show qualitatively a high accuracy. Incombination with the shorter production times the single-pulse laser drilling was identified as the most convenient

laser drilling strategy for the production of pilot holes. Because of that, this strategy is viewed in the following.

Figure 4. Influence of the laser drilling strategy on the bore hole diameter

In the single-pulse laser drilling experiments conducted, the variables pulse duration and peak power have shown

the highest impact on the bore hole quality. Because of that, in the following the influence of these parameters will

be discussed. As named before, the main requirement of a pilot-hole for the guiding assistance of a deep hole

drilling tool is its diameter and roundness accuracy (Figure 5).

The increasing pulse duration shows the tendency of leading to growing bore hole diameters and to decreasing

roundness deviations. Due to absorption, reflection and heat transportation effects, the laser influenced area

increases and the diameter increases when using longer pulse durations. In the parameter range viewed, the impact

of the pulse duration on the roundness deviation is reciprocally to its effect on the diameter. In the experiments with

the lowest pulse duration the highest roundness deviations result. Furthermore, the scanning electron microscopy

views of the bore holes produced using the lowest pulse duration show a significant deviation of the bore hole

cylindricity. This deviation can lead to a contact of the single-lip deep hole drilling tool with the bore hole wall in

the process phase of positioning the deep hole drilling tool in the pilot hole. This contact can effect tool wear or tool

200 m 200 m 200 m 200 m 200 m

Laser: Nd:YAG Workpiece material: AISI 316L

Peak power: P = 7000 W Pulse duration: = 1 ms

Pulse frequency: f = 10 Hz Number of pulses: n = varied

Focus position: sf = 0 mm Process gas: Compr. air

200

300

400

m

600

Percussion

drilling

Helical drilling

DH = 0.1 mm

Helical drilling

DH = 0.2 mm

Helical drilling

DH = 0.25 mm

Single-pulse

drilling

Percussion / helical drilling

Number of pulses: n = 250

DiameterD

8/13/2019 1-s2.0-S1875389211002173-main

5/9


Figure 5. Influence of the pulse duration and peak power on the diameter and the roundness deviation

breakages in the area of the cutting edge corner. The occurring deviation can be explained by the Gaussian-shaped

distribution of intensity. At low pulse durations, the energy of the laser is only at the center of the laser beam

sufficient for material ablation. Due to effects leading to a loss of power, such as reflection, this area is reduced by

increasing drilling depth and the conical bore hole shape is created.

The peak power shows also an impact on the bore hole diameter. With increasing peak power, the diameter also

increases. Based on effects such as absorption, heat transportation and reflection with higher peak power thediameter also increases.

Beside the bore hole diameter and roundness deviation, the pulse duration shows an influence on the drilling

depth. This is presented in Figure 6. In the realized pulse duration range, the drilling depth increases degressively.

Due to that, the ablation rate decrease with the drilling process progress. This can also be explained by the Gaussian-

shaped distribution of intensity. Furthermore, the radiation incidence angle increase because of the conical shape of

the bore hole occurring in the laser drilling process and the connected change in absorption conditions. Another

aspect can be a plasma resulting from the vaporized metal. This plasma can absorb the laser light [10, 11].

= 0.5 ms= 0.25 ms

P=8000W

= 1 ms

P=6000W

P=7000

W


Peak power: P = varied Pulse duration: = varied

Pulse frequency: - Number of pulses: n = 1


200 m 200 m 200 m

200 m 200 m 200 m

200 m 200 m 200 m

D = 526 m

D = 505 m

D = 493 m

D = 455 m

D = 448 m

D = 435 m

D = 507 m

D = 489 m

D = 480 mtk= 39 m tk= 15 m tk= 29 m

tk= 42 m tk= 12 m tk= 22 m

tk= 28 m tk= 20 m tk= 24 m

8/13/2019 1-s2.0-S1875389211002173-main

6/9


Figure 6. Influence of the pulse duration and the peak power on the drilling depth

Beside the requirements on the geometric tolerances of the bore hole, the pilot-hole produced by laser should also

have a low surface roughness as well as no significant impact on the peripheral zone. For the evaluation of these two

bore hole properties, cross-sections of the bore holes were produced. The surface roughness was detected using the

3D-confocal whitelight microscopy. For the evaluation of the impact of the laser drilling process on the peripheral

zone, microhardness was measured in the peripheral zone with defined distances to the bore hole wall. The results of

this analysis are presented in Figure 7.

Figure 7. Influence of the pulse duration and the peak power on the surface quality and the impact on the peripheral zone

In the laser drilling experiments using single-pulse laser drilling, a high surface quality was reached. In these

experiments, the peak power shows no influence on the surface quality but the pulse duration does. Due to the

higher drilling depth reached at higher pulse durations, more material must come out of the bore hole at increasing

0

1

mm

3

0 0.25 0.5 ms 1

Drillingdepthlt

Pulse duration

lt /

Drillingdepthlt


Peak power: P = varied Pulse duration: = varied

Pulse frequency: - Number of pulses: n = 1


P = 7000 W

0

1

mm

3

0 6000 7000 W 9000

Peak power P

= 0.5 ms


Peak power: P = varied Pulse duration: = variedPulse frequency: - Number of pulses: n = 1


0.0

0.10.2

0.3

0.4

0.5

m

0.7

0.0

0.51.0

1.5

2.0

2.5

m

3.5

= 0.5 ms

P = 7000 W

= 0.5 ms

P = 8000 W

= 1.0 ms

P = 8000 W

Ro

ughnessdepthRz

RoughnessRa

200

240

280

320

HV0.05

400

0 60 120 m 240

MicrohardnessHm

= 1.0 ms

P = 8000 W

Distance to the bore hole surface s

Rz

Ra

Surface quality Peripheral zone

8/13/2019 1-s2.0-S1875389211002173-main

7/9


distances. Both facts benefit the formation of recast-layers that influences the surface quality negatively. In

comparison to percussion drilling, in single-pulse drilling this effect is significantly lower. Furthermore, the standard

deviation of the surface quality reached is relatively high. Based on the assumption that high values for surface

roughness correlates with recast-layers, for the laser drilling process with the highest surface roughness,

microhardness of the peripheral zone was measured. The measurements show no significant influence of the laser

drilling process on the peripheral zone. The microhardness values detected alternate in the area of the hardness ofthe material tested.

The experiments have shown that the production of bore holes for the use as a guiding assistance for deep hole

drilling tools by laser is possible. For the aimed manufacturing task single-pulse laser drilling is the most applicable

laser drilling strategy. To fulfill the requirements on the bore hole quality, an analysis of the influences of the laser

parameters were done. With a peak power of P = 8,000 W, pulse durations between = 0.51 ms and compressed

air as process gas, bore holes can be produced meeting all requirements on a guiding assistance for single-lip deep

hole drilling. Only the roundness deviation is on a higher level than the targeted values.

3.2. Combination of laser drilling and single lip deep hole drilling

After the identification of suitable process parameters for laser drilling, the combination of laser and single-lip

deep hole drilling was done. Therefore, pilot-holes were produced using the laser parameter combinations allowingthe production of bore holes meeting the named requirements. After the production of the pilot-holes, the single-lip

deep hole drilling process was performed using the same fixture. For the pre-drilling process an adapted strategy

was necessary. To avoid a deflection of the asymmetric tool when rotating it, the tool was driven into the pilot-hole

at a low spindle speed of n = 3,000 min-1. The feed motion was stopped at a distance from the base of the pilot-hole

of s = 0.3 mm. At this position the spindle speed was increased up to n = 25,465 min-1

which corresponds to a

cutting speed of vc= 40 m/min and the targeted feed velocity was started. The tool life reached with these cutting

parameters is comparable to the tool life travel path reached in the single-lip deep hole drilling process using a

boring bush. Furthermore, the bore hole quality reached in the process combining laser and single-lip deep hole

drilling is also comparable to the conventional process. This is shown on the example of the surface quality after

laser drilling and after single-lip deep hole drilling (Figure 8).

The surface roughness reached by laser pilot drilling amounts to Rz = 1.72 m for the laser parameters used.

After the drilling experiments, a surface roughness of Rz = 1.43 m was measured in the area where the laser pilot-

hole was. The single-lip drill smoothed the surface created by laser drilling. This can also be seen in the SEM-views

presented. In the phase of positioning the deep hole drilling tool into the laser drilled pilot-hole the cutting edge

corner of the deep hole drilling tool removes surface irregularities coming from the laser drilling process.

Furthermore, the guide pad of the single-lip deep hole drilling tool smoothened the bore hole surface of the pilot-

hole at the beginning of the deep hole drilling process. Here, the occurring radial forces are supported by the guide

pad to the bore hole wall and effects an smoothening of the bore hole surface. The surface roughness reached in the

area of the pilot-hole corresponds to the value reached in the deep hole drilling process at higher drilling depths. The

combination of laser drilling and single-lip deep hole drilling has no influence of the surface quality of the bore

holes produced.

The work done presents a new technique for the production of deep holes with small diameters. Based on the

process combination of laser drilling and single-lip deep hole drilling the process specific disadvantages of bothprocess can be eliminated. With this combination, bore holes with a high length-to-diameter ratio can be produced

by a high accuracy in comparatively short process times. The feasibility of the process combination is presented in

this work and provides the opportunity for machining workpieces with non-planar faces. Here, a process time

reduction can be reached in comparison to conventional process chains consisting of a face milling, a pre-drilling

and a deep hole drilling process. In addition, tool wear can be reduced in machining case-hardened workpieces.

Here, the laser ablates the hardened material and the mechanical drill only works in the softer material.

8/13/2019 1-s2.0-S1875389211002173-main

8/9


Figure 8. Comparison of surface quality in laser pre-drilling and single-lip deep hole drilling

4. Conclusions

In the investigations carried out a combination of laser pre-drilling and single-lip deep hole drilling with a tool

diameter of d = 0.5 mm was realized for the very first time. Main requirements on the laser pre-drilling are the

diameter, the roundness deviation, the surface integrity as well as a low impact on the peripheral zone of the bore

hole. In comparison to the laser drilling strategies percussion and helical drilling it has been shown, that single-pulselaser drilling is the most applicable strategy for the production of pilot holes under consideration of the experimental

boundaries used. In single-pulse drilling, the pulse duration and the peak power has shown the highest impact on

bore hole quality. With an adaption of the laser parameters it is possible to produce bore holes which are suitable for

the use as a guiding assistance in single-lip deep hole processes. It has been proved that the combination of these

two processes is comparable to conventional deep hole drilling processes using a boring bush as guiding assistance

with respect to tool life and bore hole quality.

In future, the process combination presented will be adapted for machining workpieces with non-planar surfaces

as well as for machining case-hardened workpieces. In conclusion, the feasibility of the combination of laser pre-

drilling and single-lip deep hole drilling has been demonstrated in this research. This technique provides the

opportunities to shorten the process chain of milling, pre-drilling and deep hole drilling in machining components

with non-planar surfaces as well as to reduce tool wear in machining case-hardened workpieces.

0.0

0.1

0.2

0.3

0.4

0.5

m

0.7

0.0

0.5

1.0

1.5

2.0

2.5

m

3.5

Single-pulse laser drillingDeep hole drilling

Bore hole entrance

Deep hole drilling

Bore hole exit

RoughnessdepthRz

RoughnessRa

c = 0.08 mm

500 m

Laser: Nd:YAG Tool: Single-lip drill, d = 0.5 mm

Peak power: P = 8,000 W Cutting speed: vc = 40 m/min

Pulse duration: = 0,5 ms Feed rate: f = 0.5 m/rev.

Number of pulses: n = 1 Drilling depth: lt = 12.5 mm

Focus position: sf = 0 mm Cooling lubricant: Oil

Process gas: Compr. air Coolant pressure: p = 200 bar Workpiece material: AISI 316L

Rz

Ra

8/13/2019 1-s2.0-S1875389211002173-main

9/9


Acknowledgement

This work was supported by the German Research Foundation (DFG) under the grant We 1723/78.

References

81] Alting, L.; Kimura, F.;, Hansen, H. N.;, Bissacco, G.: Micro Engineering. In: CIRP Annals Manufacturing Technology, Vol.52, No. 2

(2003), 635-657.

[2] Weule, H.; Fleischer, J.; Buchholz, C.; Tritschler, H.; Elsner, J.; Knoll, M. et. al.: International state of the art of micro production

engineering. In: Production Engineering, Research and Development, Vol.11, No. 1 (2004), 29-36.

[3] Yu, Z. Y.; Zhang, Y.; Li, J., Luan, F.; Guo, D.: High aspect ratio micro-hole drilling aided with ultrasonic vibration and planetary movement

of electrode by micro-EDM. In: CIRP Annals Manufacturing Technology, Vol.59, No. 1 (2009), 213-216.

[4] Ali, S.; Hinduja, S.; Atkinson, J.; Pandya, M.: Shaped tube electrochemical drilling of good quality holes. In: CIRP Annals Manufacturing

Technology, Vol.59, No. 1 (2009), 185-188.

[5] Heisel, U.; Stortchak, M.; Eisseler, R.: Determination of cutting parameters in deep hole drilling with single-fluted gun drills of smallest

diameters. In: Production Engineering, Research and Development, Vol.10, No. 1 (2003), 51-54.

[6] Hung, J. C.; Lin, J. K.; Yan, B. H.; Liu, H. S.; Ho, H. P.: Using a helical micro-tool in micro-EDM combined with ultrasonic vibration for

micro-hole machining. In: Journal of Micromechanics and Microengineering, Vol.16, No. 12 (2006), 2705-2713.

[7] Li, L.; Diver, C.; Atkinson, J.; Giedl-Wagner, R.; Helml, H.J.: Sequential Laser and EDM Micro-drilling for Next Generation Fuel InjectionNozzle Manufacture. In: CIRP Annals Manufacturing Technology, Vol.55, No. 1 (2006), 179-182.

[8] Weinert, K.; Lbbe, H.: Crankshaft manufacturing on machining centres. In: Proceedings of the AMST'02, 6th International Conference, Vol.

437 (2002), 129-135.

[9] Sakuma, K.; Taguchi, K.; Katsuki, A.; Takeyama, H.: Self-guiding action of deep-hole-drilling tools. In: CIRP Annals Manufacturing

Vol.30, No. 1, 311-315.

[10] Dausinger, F.: Przisionsbohren mit kurzen und ultrakurzen Laserpulsen. In: Laser Technik Journal, No. 1 (2004), pp. 40-44

[11] Honer, M.: Prozesssicherungsmanahmen beim Bohren metallischer Werkstoffe mittels Laserstrahlung. PhD-Thesis, Universitt Stuttgart,

Herbert Utz Verlag, Mnchen, 2004

1-s2.0-s1875389211002173-main

Documents