Invited paper

Study on Milling-combined Laser Consolidation System (Invited Paper)– For the Advanced Injection Mold by Additive Manufacturing –Tatsuaki FURUMOTO1
1

Faculty of Mechanical Engineering, Institute of Science and Engineering, Kanazawa University
Kakuma-machi, Kanazawa, Ishikawa, 920-1192 Japan

A multitasking machine, in which a metal powder is selectively heated and fused by laser beam irradiation and the edgeof the consolidated structure is cut with an end mill, has been developed for the production of injection mold. This machine
has an advantage that the molding die does not have to be separated for the cooling channels. However, it is difficult to finish
the internal face of cooling channels which are complicatedly located inside the molding die. This study describes a finishing
performance of cooling channel with a face protuberance inside a molding die with free abrasive grains. A fluid flow in thecooling channel is calculatedly simulated, and the effect of internal face protuberance which is spirally arranged on thefinishing performance is experimentally investigated. The results showed the application of the face protuberance on theinternal face was quite effective for the improvement of the face condition. The internal finishing of cooling channel was also
effective for the improvement of the thermophysical properties.
Key Words: Selective Laser Sintering, Selective Laser Melting, End mill Internal cooling channel, Monitoring

finishing performance is experimentally investigated. Additionally,

1. Introduction

Various types of layered manufacturing techniques havebeen proposed since Kodama first presented a new method forthe effect of internal face finishing on the thermophysicalproperties of the cooling channels is also evaluated.

fabricating three-dimensional plastic models[1]. These layered
manufacturing techniques were followed by the development of a

2. Layered manufacturing equipment

three-dimensional CAD system and classified as being distinct
from the forming and material-removal processes[2]. A variety of

2.1 Metal powdermaterials, such as polymers, ceramics, and metal powders, have

The SEM image of metal powder is shown in Fig. 1, and its

been used to manufacture a range of prototypes, tools, andspecifications are summarized in Table 1. The metal powder usedfunctional end-products[3]. Indeed, the use of metal powders inin the experiment is a mixture of 70% alloy steel powder (ISO:layered manufactured techniques is especially remarkable because

42CrMo4), 20% copper phosphorous alloy powder (ASTM:

the structures obtained are strong enough for practical use.

C52100) and 10% nickel powder in weight. Each powder was

Recently, a multitasking machine, in which a metal powder

prepared by gas atomization method, so that its shapes areis selectively heated and fused by laser beam irradiation and theirregular. The average particle diameter of powder mixture usededge of the consolidated structure cut with an end mill, and which
results in improved cost performance and reduced production
times, has recently been developed for the production of injection
mold[4].

The

injection

moldproducedbythelayeredmanufacturing processes has the advantage that the coolingchannel can be complicatedly located by using a designed CAD
model. Additionally, the injection mold does not have to bepartitioned into separate block to locate the cooling channels.
However, the internal face of the cooling channels obtained by thelayered manufacturing processes is not uniform due to thepartially molten powder, the adhered powder and the pore[5]. It isdifficult to finish the internal face of the cooling channel which is100Pm
Fig. 1 SEM image of metal powder

located inside the injection mold.
This paper deals with an internal finishing of a coolingchannel located in an injection mold which is fabricated by thelayered manufacturing. The free abrasive grains are used to finish
the internal face of the cooling channels. A fluid flow in thecooling channel is calculatedly simulated, and the effect ofinternal face protuberance which is spirally arranged on the

Table 1 Specifications of metal powder
Material
Shape
Particle mean diameter [ Pm ]Thermal conductivity [ W/m·K ]ISUPEN 2013
International Symposium on Ultraprecision Engineering and Nanotechnology, Tokyo, Japan, March 13, 2013.

d
Tk

Fe, Cu, Ni
Irregular
25
0.14

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Invited paper

Table 2 Specifications of metal powder
Laser typeI
O

Beam diameter [ Pm ]Wavelength [ nm ]Maximum power [ W ]Scanning speed [ mm/s ]

Q
F
t
H

Layer thickness [ Pm ]Hatching pitch [ Pm ]Yb:fiber (CW)
100
1070
200
440
50
50

94 mm
15 mm

20 mm

15 mm

Substrate

100 mmInjection mold(a) Outside drawing

Hydraulic pump
HydrauliccylinderHydrauliccylinder

20 mm

80 mm

I5 mm

Injection mold

Substrate
Injection moldProtuberance
Predrilled hole
Cooling channel(b) Cross section
Cooling channel
Cartridge C
Cartridge DFree abrasive grains
Cartridge A
Cartridge B

Fig. 3 Cooling channel with the face protuberance

Fig. 2 Finishing equipment for internal face of cooling channel
3. Experimental setup and conditionsin the experiment is 25 Pm. Structures produced by this powder
mixture have sufficient strength and hardness for fabrication of
the injection mold.

3.1 Finishing equipment for internal face of cooling channel
The experimental setup for finishing the internal face of thecooling channel which is located inside the injection mold is
illustrated schematically in Fig. 2. This system consists of a

2.2 Layered manufacturing equipment

hydraulic pump, a hydraulic cylinder, and four cartridges. The

The fabrication of injection mold using the metal powder iscooling channel inside the injection mold can be connected to thisperformed with LUMEX25TM (Panasonic Electric Works Co.,system as the connected channel builds a closed loop. The

Ltd.), and its consolidation conditions are given in Table 2. The

cartridge A and the cartridge B are filled with a fluid and freelaser beam used in the equipment is a Yb:fiber laser (IPG

abrasive grains, respectively. The cartridge C and the cartridge D

Photonics Corp.: YLR-SM) with a wavelength of 1070 nm. The

are filled with a fluid, and these cartridges are used as a buffer solaser beam which is led to the powdered surface through a

as not to flow the free abrasive grains to the hydraulic cylinder.

galvanometer mirror forms a Gaussian shape and the beam

When internal pressure is applied in the closed loop, the fluid

diameter at the focal spot is 100 Pm. In brief, the metal powder iscontaining the free abrasive grains is passed through the coolingdeposited on the substrate at a thickness of 50 Pm using a levelingchannel and the internal face of the cooling channel is thenblade. A laser beam is then focused on the powdered surface

finished by these grains. The free abrasive grains that passthrough a galvanometer mirror, and scanned over it using

through the cooling channel can be re-used for internal faceprogrammed NC data. The hatching pitch of the laser beam isfinishing of the cooling channel by reversing the flow direction of

kept constant to 50 Pm. After scanning a consolidation layer, laser

the fluid containing the free abrasive grains. This is achieved byirradiation is performed whilst varying the scan direction of theswitching the electromagnetic valve with a period of 1 second.

laser beam by 90° to prevent anisotropy of the consolidated

The internal pressure and the velocity of the fluid are controlled

structure. These processes are repeated until the injection mold isusing a hydraulic pump.

completely fabricated. The injection mold thus obtained isclarified into full melting, so that the inside of the injection mold

3.2 Analysis of fluid flow in cooling channel

is completely molten and uniformly alloyed. These processes are

In order to evaluate a fluid flow in the cooling channel, aperformed under a nitrogen atmosphere to prevent oxidization offlow simulation with COSMOS Flo WorksTM is performed. The

the metal powder during laser irradiation. The substrate surface ismodel designed by 3D CAD system is shown in Fig. 3 and its

sandblasted with the average grain size of 300 Pm to improve theanalysis conditions are summarized in Table 3. The model size ofwetting property of the molten powder, and its surface roughness

injection mold is 15 u 94 u 15 mm and U-shaped cooling channel

is kept constant of Ra=3.5 Pm[6].

with a diameter of 5 mm and a length of 80 mm is located inside.
A semicircle face protuberance with a height of 1 mm and a pitch

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ISUPEN 2013
International Symposium on Ultraprecision Engineering and Nanotechnology, Tokyo, Japan, March 13, 2013.

Invited paper

Table 3 Analysis conditions for internal flow
Cooling channel
Form
Diameter [ mm ]Length [ mm ]Solution
Fluid
Flow rate [ l/s ]Temperature [ K ]Outlet pressure
Boundary condition

Thermocouple(Chromyl-Alumel))Molding die

U-shaped
580

f
L

to Oscilloscope
Cooling channel

Water
0.3
293
StaticAdiabatic wall

Substrate
HeaterTable 4 Experimental conditions for internal finishing
Free abrasive grain
Material
Diameter [ Pm ]Concentration [ vol% ]
Fluid

Cv

Al2O3
60, 100, 300
4-8
Water

Fig. 5 Finishing equipment for internal face of cooling channel

Table 5 Conditions for investigation of thermophysical property
Thermocouple
Type
Diameter [ mm ]Distance from edge [ mm ]Injection moldInitial temperature [ K ]SolutionType
Temperature [ K ]Pressure [ Mpa ]It

Chromyl-Alumel
1.6
1.0

Ti

473

Ts
P

Water
273
1.4

in Table 4, and SEM image of the free abrasive grains is shown in
Fig. 4. The free abrasive grains were made from Al2O3 and had an
average diameter of 60, 100, and 300 Pm. The internal pressure
applied to the cooling channel ranged from 0.2 to 1.4 MPa. The
maximum flow rate of the fluid containing the free abrasive
1 mmFig. 4 SEM image of free abrasive grains(Material: Al2O3, Grain size: 100 Pm)

grains is 0.3 l/sec and its value depends on the internal pressure
loaded in the cooling channel by the hydraulic pump. After
finishing with free abrasive grains, the upper face of coolingchannels was measured with a three-dimensional surface profilingsystem (Tokyo Seimitsu Co., Ltd.: Surfcom). The cooling channelof 10 mm is spirally arranged only on the bottom face of the

without the face protuberance was also fabricated using thecooling channel due to the limitation of the layered manufacturing

above-mentioned layered manufacturing equipment to investigate

technique. The fluid in the analysis is water with a temperature of

the effect of the face protuberance on the finishing performance.

293 K and its flow rate is 0.3 l/sec. An adiabatic wall is applied tothe internal face of the cooling channel, and an outlet pressure isdefined as a static condition. The cooling channel without the face
protuberance is also evaluated for comparison.

3.4 Effect of internal finishing on thermophysical property
In order to investigate the effect of internal face finishing on
the thermophysical properties of the cooling channel, thetemperature history inside the cooling channel was recorded. The

3.3 Experimental conditions for internal finishingexperimental setup is illustrated in Fig. 5 and its conditions are

In order to investigate the internal face conditions in thesummarized in Table 5. The thermocouple used in the experimentcooling channel, the injection mold which was the same model as

was a chromel-alumel thermocouple with a wire diameter of 1.6

shown in Fig. 3 was fabricated using the above-mentioned layered

mm. A pin hole with a diameter of 1.7 mm was fabricated on the

manufacturing equipment. The substrate used is the carbon steel

surface of the molding die and the thermocouple fixed at a

(AISI: 1049), and the hole with a diameter of 5 mm is predrilled

distance, z, of 2 mm from the internal face of the cooling channel.

in the substrate. After the fabrication of the injection mold, it was

Cold water at Ts=273 K was passed through the cooling channel

partitioned into two pieces at the center of the cooling channel towhilst the molding die containing the cooling channel was heatedevaluate the internal face conditions. The cooling channel was

to Ti=473 K with a heater. The output signal obtained from thethen rebuilt by joining the two pieces of the injection mold with athermocouple

packing.

(Yokogawa Corp.: Scope Corder DL-750), and the time interval

The experimental conditions for internal finishing are given

was

then

recorded

using

an

oscilloscoperequired by the measuring point to reach room temperature (300

ISUPEN 2013
International Symposium on Ultraprecision Engineering and Nanotechnology, Tokyo, Japan, March 13, 2013.

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Invited paper

30
24
18
12

0.5 mm(a) Before finishing

6
Flow direction

0.5 mm(b) After 500 sec

0m/s(a) Without face protuberance
30
24
18

0.5 mm
0.5 mm(c) After 4000 sec(d) After 8000 sec
Fig. 8 Images of internal face in cooling channel

12Flow direction

Internal face roughness Rz Pm

6
0
m/s

(b) With face protuberance
Fig. 6 Fluid flow in cooling channel

Internal face roughness Rz Pm

120
Material: Al2O3

100

Average particle diameter: 100 Pm
Concentration: 4 vol%Pressure: 1.4 MPa

80

.

60
40

120
Material: Al2O3

100

Concentration: 8 vol%Pressure: 1.4 MPa
Finishing time: 180 sec

80
60
40
20
0

0

50

100
150
200
250
Average particle diameter Pm

300

350

Fig. 9 Influence of grain size on internal face roughness

20
0

0

2000

4000
6000
Finishing time t sec

8000

Fig. 7 Influence of finishing time on internal face roughness

4.2 Influence of finishing time on internal face roughness
Fig. 7 shows the variation of the internal face roughness withfinishing time without the face protuberance; photo images of theinternal face after different finishing times are provided in Fig.
8[8]. The internal face roughness of the cooling channel improvedK) was determined.

significantly during the first 1000 seconds of finishing, after
which it improved at a constant rate up to a finishing time of 8000

4. Results and discussions

seconds. As shown in Fig. 8(a), stain, partially melted powder,
4.1 Analysis of fluid flow in cooling channel

and adhered powder can clearly be seen on the internal face priorFig. 6 shows the influence of the face protuberance on flow

to internal finishing. However, as shown in Fig. 8(b), these

profiles in cooling channel[7]. As shown in Fig. 6(a), the fluid

unstable layers are removed upon introducing the free abrasive

flow without the face protuberance is externally thrust depending

grains into the cooling channel, which results in an alloyed faceon the centrifugal force which is generated at the entrance region.

inside the injection mold. After removal of these unstable layers,

Therefore, the velocity distribution is occurring in the coolingthe condition of the internal face improved slightly with finishingchannel, that is, the fluid flow at the external position is faster

time, as shown in Fig. 8(c), to finally give the smooth internalthan that at the inner position. The velocity of fluid flow thenface shown in Fig. 8(d). These results confirm that the significant

becomes slow gradually due to the internal face roughness in the

improvement achieved during the initial stages of finishing is due

cooling channel. On the other hand, as shown in Fig. 6(b), theto the removal of the aforementioned unstable powders.

fluid flow with the face protuberance is flowing spirallyaccording to the face protuberance on the internal face. There isalmost no velocity distribution at the position of the coolingchannel.

16

4.3 Influence of grain size on finishing performancesFig. 9 shows the variation of the internal face roughness withdifferent average particle diameter of the abrasive grain without

ISUPEN 2013
International Symposium on Ultraprecision Engineering and Nanotechnology, Tokyo, Japan, March 13, 2013.

Invited paper

Internal face roughness Rz Pm

120
100
80
60
Grain: Al2O3
40 Average particle diameter: 100 Pm
Concentration: 8 vol%20
Finishing time: 480 sec
0

0.2

0

0.4

0.6
0.8
1.0
1.2
Internal pressure P MPa

1.4

1.6

Internal face roughness Rz Pm

Fig. 10 Influence of internal pressure on finishing performance

1 mm(a) Without face protuberance (Rz=109 mm)

200

Material: Al2O3
Particle diameter: 300 Pm
Concentration: 7 vol%Pressure: 1.4 MPa

160
120
80
40
0

Cooling channel:
Straight
Protuberance
0

500

1000
1500
Finishing time sec

2000

2500

Fig. 11 Influence of face protuberance on internal finishing
1 mm(b) With face protuberance(Rz=80 mm)
Fig. 12 Images of internal face in cooling channel

the face protuberance. The finishing time for the internal face was
fixed at 180 sec. Abrasive grains with an average particle
diameter of 300 Pm improved the internal face roughness in thecooling channel to Rz =30 Pm after 180 sec, although it should becooling channel on the finishing performance. In the case of thenoted that the finishing time for particles with an averagecooling channel with the face protuberance, it was same that thediameter of 100 Pm was over 1000 sec, as shown in Fig. 7. Theinternal face roughness improved significantly during the first 180

use of large grain is therefore better suited for effective

seconds of finishing. However, after the significant improvement

improvement of the internal face. Additionally, the internal face

up to the finishing time of 180 seconds, the further improvement

roughness improved with an increase in the average particleof the internal face roughness is obtained. The internal facediameter, whereas smaller grains were more effective forroughness at the finishing time of 2000 seconds is 30% improved

polishing the internal face. This is due to the fact that freecompared with that of 180 seconds.

abrasive grains are employed to remove the unstable powder on

Fig. 12 compares the photo images of the upper face in thethe internal face rather than to polish the alloyed face. The use ofcooling channel in the finishing time of 1000 seconds. The steinsmall abrasive grains is more effective in improving the internalon the upper face was almost removed and the application of theface roughness after initial removal of the unstable layers.

face protuberance in the cooling channel made it possible to finish
the upper face effectively. The surface roughness on the internal

4.4 Influence of internal pressure on finishing performances

face with the face protuberance was improved to Rz=80 Pm.

Fig. 10 shows the variation of the internal face roughness ofthe cooling channel with the internal pressure applied by the

4.6 Effect of internal finishing on thermophysical property

hydraulic pump. The finishing time was fixed at 480 sec, and theFig. 13 shows the temperature history obtained from theupper face of the cooling channel is summarized. It can clearly bethermocouple before and after finishing of the cooling channel.

seen from this figure that internal face finishing at a high internal

When cold water starts to flow into the cooling channel, thepressure is better than at a low internal pressure. The high-speed

temperature of the consolidated structure gradually decreases withflow of the free abrasive grains results in an increase in theiran increase in cooling time. The cooling rate of the consolidated

kinetic energy, thereby increasing the force with which theystructure increases with the degree of finishing of the internal

collide with the internal face and resulting in an improvement offace.

the surface roughness.

Fig. 14 shows a comparison of the thermophysical properties
in the cooling channel before and after internal face finishing.

4.5 Effect of face protuberance on finishing performanceFig. 11 shows the influence of face protuberance in theHere, the time interval required for the consolidated structure toreach room temperature (300 K) is evaluated. The measurements

ISUPEN 2013
International Symposium on Ultraprecision Engineering and Nanotechnology, Tokyo, Japan, March 13, 2013.

17

Invited paper

although the fluid flow without the protuberance was externally500

Grain: Al2O3

Temperature K

450
400
350

thrust depending on the centrifugal force.

Average particle diameter: 300 Pm
Concentration: 8 vol%Internal pressure: 1.4 MPa
Initial temperautre: 473 K
Finishing time: 1000 sec

2) The internal face roughness of the cooling channel improved

Before finishingthe initial stages of finishing is due to the removal of theAfter finishingsignificantly during the first 1000 seconds of finishing, after
which it improved at a constant rate up to a finishing time of8000 seconds. The significant improvement achieved during

300

aforementioned unstable powders.
3) The application of the face protuberance was quite effective for0

Fig. 13

5

20
25
30
35
40
Time sec
Temperature history of the consolidated structure15

the improvement of the face condition in the cooling channel.
4) The use of large grain is better suited for effective
improvement of the internal face. Free abrasive grains are
employed to remove the unstable powder on the internal face

40
Time to room temperature sec

10Grain: Al2O3
Average particle diameter: 300 Pm
Concentration: 8 vol%Internal pressure: 1.4 MPa
Initial temperautre: 473 K
Process time: 1000 sec

35

30

rather than to polish the alloyed face.
5) The cooling time of the consolidated structure decreasedslightly by approximately 4% as a result of finishing theinternal face. Additionally, there was almost no scatter of the.

250

time interval required for the consolidated structure to reachroom temperature after the finishing of cooling channel. Theinternal face finishing was effective for the improvement of the25

thermophysical properties in the cooling channel.
20

Before finishing
After finishing
Comparison of surface condition
Fig. 14 Comparison of thermophysical property

Acknowledgement
The authors would like to thank to Dr. Abe for the precious
advice about the layered manufacturing equipment. The layered
manufacturing equipment used in this research was supported byof the time interval were repeated five times, respectively. It was

Panasonic Electric Works Co. Ltd.

found that the cooling time decreased slightly by approximately
4% as a result of finishing the internal face. This slightly decrease

Reference

can be explained on the basis of the structure of the cooling[1] Kodama, H. Automatic method for fabricating a three-channel. Thus, the thermal conductivity of the unstable layer

dimensional plastic model with photo-hardening polymer, Rev.

containing the partially melted and adhered powders is lower thanSci. Instrum., 52, 10, (1981) 1770-1773.

that of the inner block of the consolidated structure. The[2] Kruth, J. P., Material incress manufacturing by rapid

improvement in the thermophysical properties observed after

prototyping techniques, CIRP Ann., 40, 2 (1991) 603-614.

finishing the internal face is therefore due to the removal of this[3] Kruth, J. P., et al., Progress in additive manufacturing andunstable layer. Additionally, it was found that there was almost no

rapid prototyping, CIRP Ann., 47, 2 (1998) 525-540.

scatter of the time interval required for the consolidated structure[4] Abe, S., et al. Milling-combined laser metal sintering system

to reach room temperature after the finishing of cooling channel.

and production of injection molds with sophisticated functions,This result suggests that it is possible to control the temperature

In: ICPE2006, 11th International Conference of Precision andof the injection mold easily by finishing the internal face of theEngineering, 16-18 August, Tokyo, Japan (2006) 288-293.

cooling channel. These results clearly show that internal face[5] Yassin, A., Ueda, T., Furumoto, T., et al., Experimental

finishing of the cooling channel with free abrasive grains isinvestigation on cutting mechanism of laser sintered material

effective for improving its thermophysical properties.

using small ball end mill, J. Mater. Process Tech., 209, 15-16(2009) 5680-5689.

5. Conclusions[6] Furumoto, T., et al., Study on laser consolidation of metal

In this paper, the finishing method for the internal face of apowder with Yb:fiber laser, Evaluation of line consolidation

cooling channel located in the injection mold with free abrasive

structure, J. Mater. Process. Technol., 209, 18-19 (2009)

grains was proposed. The fluid flow in the cooling channel was

5973-5980.

simulated, and the effect of internal face protuberance which was[7] Furumoto, T., et al., Finishing Performance of Coolingarranged spirally on the finishing performance was investigated.

Channel with Face Protuberance inside the Molding Die, J.

The main results obtained are as follows.

Mater. Process Tech., 212, 10 (2012) 2154-2160.

1) The fluid flow with the face protuberance was flowing spirally[8] Furumoto, T., et al., A study of internal face finishing of theaccording to the face protuberance on the internal face, and thecooling channel in injection mold with free abrasive grains, J.

velocity distribution inside the molding die was quite small

Mater. Process Tech., 211, 11 (2011) 1742-1748.

18

ISUPEN 2013
International Symposium on Ultraprecision Engineering and Nanotechnology, Tokyo, Japan, March 13, 2013.