Advanced Materials Research Vol. 1017 (2014) pp 624-629© (2014) Trans Tech Publications, Switzerland
doi:10.4028/www.scientific.net/AMR.1017.624

Monitoring of End-mill Temperature with Infrared Thermography andWireless Tool Holder System
Masatoshi Shindou1, a *, Ryo Matsuda1, b, Tatsuya Furuki2, c,Toshiki Hirogaki2, d and Eiichi Aoyama2, e
1Research and Development Group, Yamamoto Metal Technos Co., Ltd.
4-7 Setoguchi, 2-chome, Hirano-ku, Osaka 547-0034, Japan2

Department of Mechanical Engineering, Doshisha University
1-3 Miyakodani, Tatara, Kyotanabe-shi, Kyoto 610-0321, Japanabc

shindou@yama-kin.co.jp, matsuda@yama-kin.co.jp, eun1503@mail4.doshisha.ac.jp,
dethirogak@mail.doshisha.ac.jp, eaoyama@mail.doshisha.ac.jp

Keywords: end-mill process, tool temperature, infrared imagery, thermography, process efficiency,process monitoring.

Abstract. Nowadays, infrared thermographic technology has been attracting attention in various
industrial fields. We therefore focus on it as a novel method for monitoring tool temperature toimprove end-milling conditions for difficult-to-cut materials. However, a problem has emerged; it isdifficult to measure the tool temperature when there is a coolant because the coolant prevents
monitoring of the surface of the end-mill tool. Thus, we developed a wireless tool holder systemequipped with a thermocouple in the end mill to monitor the tool temperature under coolantconditions. In this report, we compared the temperature measured by infrared thermographic imagery
with that measured by a wireless tool holder system when end milling the stainless steel under dry
coolant conditions. The thermocouple, which has a small diameter of 0.12 mm, was used to ensurehigh response measurement in the proposed wireless tool holder. We obtained the tool temperaturesby infrared thermographic imagery and by wireless tool holder equipped with a thermocouple at asampling time of 1/30 of a second. We confirmed that the temperature measured by the wireless tool
holder agrees with that measured by infrared thermographic imagery. As a result, we demonstrated
that the developed method with a wireless system is effective to estimate the tool temperature inend-milling processes and makes it feasible to measure it under coolant conditions.
Introduction
Nowadays, manufacturing companies have been requested to develop new technologies todetermine the machining conditions in the agile and trial manufacturing fields. The cutting force andthe cutting temperature must be monitored to estimate machining conditions sufficiently accurately.
Recently, it has become easy to measure the cutting force with a piezoelectric sensor on the machine
tool table whereas the cutting temperature is difficult to measure because measuring with athermocouple sensor is considered to be the only effective and practical method [1, 2]. Few recent
reports have dealt with measuring the tool temperature with an infrared temperature sensor [3].
However, an insufficient temperature distribution was obtained because these methods are based on apoint measuring method. Additionally, infrared thermography is considered to be an effective method
to obtain the tool temperature distribution during the shallow drilling process [4]. We proposed amethod to estimate the tool temperature in the end-mill process by infrared imagery with high speed
thermography [5]. In this study, we developed a wireless tool holder system equipped with athermocouple in the end-mill to monitor the tool temperature under coolant conditions. This method
was also expected to be effective to monitor the drill tool temperature during the more deeper hole
drilling process. We compared the temperature by infrared thermographic imagery with that measured
by the wireless tool holder system when end milling the stainless steel under dry coolant conditions.
The thermocouple, which had a small diameter of 0.12 mm, was used to ensure high response
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measurement in the proposed wireless tool holder. We obtained the tool temperatures by infrared
thermographic imagery and by the wireless tool holder equipped with a thermocouple at a samplingtime of 1/30 of a second. We confirmed that the temperature measured by wireless tool holder agrees
with that measured by infrared thermographic imagery. As a result, we demonstrated that thedeveloped method with a wireless system is effective to estimate the tool temperature in end-millprocesses.
Setup for monitoring end-mill process
Measurement of tool surface temperature. Figure 1 shows the setup for monitoring the end-millprocess. The thermography used in the experiment is infrared ray technology H2640 made by Nippon
Avionics Co. The minimum space resolution is 0.18mm at 0.3m working distance, which means thespatial resolution 0.6mrad, temperature resolution is 0.03°C, and the maximum measureable
temperature is equal to or lower than 500°C. The thermography can transfer continuous images to acomputer. Depending on the function, the thermography can also obtain frame imagery images at 30
images per second. The thermography was set up next to the machining center. We monitored theend-mill process at an angle of 150° in the direction of tool movement. The distance between theend-mill and thermography was 1500 mm. The workpiece was a 100 (cutting length) × 100 × 50 mm
sheet of heat-resistant steel (JIS SUS310S, 25Cr-20Ni). The tool diameters were 6 mm and 10 mm(type: WXL-EMS, OSG Corporation). The twist angle was 30 degrees. The number of cutting teeth
was four. The emissivity of the end-mill surface was 0.4. The machining conditions were a 1450 rpm
rotating speed, 0.05 mm per tooth feed amount, 0.6 mm cutting width, and 12 mm cutting depth. The
coolant was dry air.
Figure 2 shows infrared imagery of the end-mill process. You can easily and finely obtain thetemperatures of the holder, end-mill, workpiece, and machining chips by observing infrared imagery
during temperature distribution. The reflected image of the cutting edge close to the processing pointis reflected on the glossy surface of the workpiece, and it can be seen that the analysis can beperformed while considering the change in the infrared emissivity. This figure shows that themonitoring method effectively estimated the end-mill process by using a high response infrared
thermograph that can continuously transmit frame images to a personal computer.
Top view

θ = 150°Tool holder

WorkpieceθωEnd-mill
tool

End-mill
1.5 m

Machined chips
Machined surface

Themography
Tool holder
End-mill tool

Workpiece

Themography

Fig. 1 Setup for monitoring end-mill process

Workpiece
Reflected image
Workpiece: JIS SUS310S
Cutting tool: OSG WXL-EMS D = 10 mm, 4 flute
Machining conditions:
Vc = 45 m/min, fz = 0.05 mm/tooth,
Ad = 12 mm, Rd = 0.6 mm, dry air

Fig. 2 Infrared imagery of end-mill process

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Tool for measuring internal temperature. Figure 3 shows the schematic diagram of the wirelessmeasurement tool holder system. If the measurement object was a rotating tool, there was the problem
that the wire wound around the spindle when it rotated at high speed. Therefore, we have developed awireless measurement tool holder system. First, we inserted the thermocouple into the hole in linewith the tool center axis . Next, we placed the amplifier, A/D converter, micro-controller, andtransmitter in the tool holder. The tool temperature measurement results were wirelessly andcontinuously transmitted to a computer that is connected to the receiver. The thermocouple was K
type with a wire diameter of 0.12 mm. Depending on the function, the wireless measurement toolholder system could also obtain thermal data at 30 times per second. The responsiveness and sampling
period of the wireless measurement tool holder system and the thermography were almost the same.
The workpiece was a 100 (cutting length) × 100 × 50 mm sheet of heat-resistant steel (JIS SUS310S,25Cr-20Ni). The tool diameter was 6 mm (type: WXL-EMS, OSG Corporation). The twist angle was30 degrees. The number of cutting teeth was four. The machining conditions were a 1450 rpm rotating
speed, 0.05 mm per tooth feed amount, 0.6 mm cutting width, and 12 mm cutting depth. The coolant
was dry air.
Figure 4 shows the wireless measurement tool holder system. By using this measurement system, wecould monitor the processing temperature, even if the cutting edge was not visible, for example, in a
drilling or cutting fluid environment.
Figure 5 shows the discharge machining electrode and end-mill tool. The total length of the end-milltool was 50 mm. The diameter of the discharge machining electrodes was 1 mm. We had a microdeep hole of 49 mm (L / D = 49) from the shank part of the central axis of the end-mill tool. We
inserted a thermocouple into the micro-deep hole. The position of the tip of the thermocouple was 1
mm short of the bottom edge of the end-mill tool.
Figure 6 shows a cross-sectional schematic view of the temperature measurement tool. The left side
represents the flute part, and the right side represents the shank part. The volume of the flute part issmaller than that of the shank part because the flute part of the end-mill tool has a chip pocket. The
cross-sectional area perpendicular to the axis decreases gradually towards the flute part. In addition,
the core thickness of the end-mill tool is less than the diameter of the flute part. The diameter of thethermocouple insert hole should be less than the tool core thickness. Because the diameter of thethermocouple insert hole is 1 mm, we thought that the limit of the tool diameter could be measured byusing the wireless measurement tool holder system, which is around 2 mm in diameter.

Machine tool
spindleMicroController
A/D Converter

SpindleTransmitter
ReceiverAmplif ier

Tool holder

End-mill tool
Laptop PC
Micro-diameter
thermocouple

End-mill tool
Micro-drilled holeFig. 3 Schematic diagram of wirelessmeasurement tool holder system

Fig. 4 Wireless measurement tool holder system

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Discharge machining electrode D = 1 mm

×End-mill tool D = 6 mm 50 mm

Flute part
Equivalent diameter De

Shank part
Diameter D

Thermocouple insert hole
Shaf t center

Fig. 5 Discharge machining electrode andend-mill toolFig. 6 Cross-sectional schematic view oftemperature measurement tool

Results and discussions
Effect of processing time on tool temperature. Figure 7 shows the effect of processing time on thetemperature distribution. The end-mill tool temperature rose if the cutting time increased. The results
show that heat storage occurs.
Figure 8 shows the relationship between the tool temperature and processing time. The machining
conditions were the same except for the tool diameter. This figure shows that the maximum
temperature of the tool increased and converged to a constant temperature with time. The converged
temperature was different when the diameter of the tool was different. This is expected to be shown by
the model close to the first order time delay of these phenomena.
400]

℃350

Inf rared image

1.8 s

3.8 s

5.5 s

Maximum temperture [Visible image

300

D = 6mm, S = 2400 rpm

250200150

D = 10 mm, S = 1450 rpm

1005000℃

220℃

300℃

330

510Time [s]1520Workpiece: JIS SUS310S
Cutting tool: OSG WXL-EMS D = 6 mm, 4 f lute
Machining conditions:
V c = 45 m/min, fz = 0.05 mm/tooth,
Ad = 12 mm, Rd = 0.6 mm, dry air

Workpiece: JIS SUS310S
Cutting tool: OSG WXL-EMS D = 6 mm, 4 f lute
OSG WXL-EMS D = 10 mm, 4 f lute
Machining conditions:Vc = 45 m/min, fz = 0.05 mm/tooth,
Ad = 12 mm, Rd = 0.6 mm, dry air

Fig. 7 Effect of processing time on temperature
distribution

Fig. 8 Relationship between tool temperature andprocessing time

Temperature response model based on first order time delay. Figure 9 shows the temperature
response model based on the first order time delay. The heat storage action of the tip of the tool
explains the model of the first order lag system [6]. This figure also shows the heat capacity in the tipof the tool. We consider a column of infinite length. The density is defined by ρ, specific heat by C,outside thermal conductivity by α, primary temperature of the column by T0, and step temperature(assuming it changes rapidly) by Ts.

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(1)dT
ρC ()() = π D α (T s − T )4dt
The left side shows the change of thermal energy per unit time, and the right side shows the amount ofheat transferred from the surface per unit length. The end-mill process is intermittent cutting.
However, the end-mill rotating speed is much faster than the transient heat transfer. Therefore, anend-mill process that can approach the model of perimeter was considered. Differential equation (1)was solved as a primary condition if T = T0 when t = 0 as the left side is dimensionless temperature.

πD 2

T − Ts4α= exp( −.t )T0 − T s
ρ CD(2)

Therefore, if Tm = ρCD/4α,

T = Ts + (T0 − Ts ) esp ( − t / Tm ) .

(3)

Tm is the damping time constant of the first order time delay and is proportional to heat capacity.
Figure 10 shows a comparison between the measurement result of the tool surface maximum
temperature by infrared thermography and the internal temperature by the wireless measurement tool
holder system. The tool internal temperatures are indicated by circles. It was confirmed that thecutting heat was transmitted with a slight delay because the position of the tip of the thermocouple
was some distance from the cutting point. We were able to confirm that the internal temperature
converged to the same extent as the surface temperature, and this was a reasonable result.
]℃

Thermal conductivity α

Step temperature ofoutside Ts

Density ρ， Specif ic heat CFig. 9 Modeling by first order time delay

Tool temperature [Column temperature T

400
Surf ace temperature
350
300
250200Internal temperature
150
100
500024681012Time [s]Workpiece: JIS SUS310S
Cutting tool: OSG WXL-EMS D = 6 mm, 4 f lute
Machining conditions:
Vc = 45 m/min, fz = 0.05 mm/tooth,
Ad = 12 mm, Rd = 0.6 mm, dry air

Fig. 10 Comparison between surface temperatureand internal temperature

FEM analysis of temperature by axial symmetry model. Figure 11 shows the FEM analysis of theend-mill model considering the decrease in heat capacity in the flute part. We use the axial symmetry
model and consider that its element size is almost the same as that of the image element ofthermography. In reality, the volume of the flute part is smaller than the shank part of the end-mill.
Therefore, we used a model with the equivalent diameter for the flute part. We charged the heatsource at the tip of the cutting edge of the side surface. The rest of the boundary is insulation. The
material of the holder is steel, and that of the shank and equivalent cutting part is cemented carbide. Adensity of 14,800 kg/m3, specific heat of 0.21 kJ/(kg･K), and thermal conductivity of 80W/(m･K)
were used for the physical property values of the tool. A density of 7860 kg/m3, specific heat of 0.50

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kJ/(kg･K), and thermal conductivity of 42 W/(m･K) were used for the physical property values of theholder.
Figure 12 shows the FEM analysis result of the temperature by using the axial symmetry model. The
dotted line shows the temperature analysis result of the thermocouple insert position on the center lineof the FEM model. The heat input was determined from the measurement result of the surface
temperature by infrared imagery. We confirmed that the measured values substantially agree with theanalysis results.

]

Shank part

Flute part

Surf ace temperature℃Temperature [Tool holder

400350
300
250
200
150
100500Internal temperature

0De/D = 0.67

Fig. 11 FEM model with equivalent diameter

24681012Time [s]Fig. 12 FEM analysis result of temperature byaxial symmetry modelSummary
Measurement by infrared imagery is effective in the analysis of the temperature distribution from thecutting edge of the end-mill tool to the shank part. On the other hand, we developed a wireless tool
holder system equipped with a thermocouple in the end-mill to monitor the tool temperature undercoolant conditions. As a result, we have confirmed that the wireless measurement tool holder system
is also effective.
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