Mitsubishi Heavy Industries Technical Review Vol. 57 No. 3 (September 2020)
1Features and Machining Examples of μV5 Micro Milling
Machine, Capable of Rough Machining

Mitsubishi Heavy Industries Machine
To o l C o . , L t d .

In recent years, the shapes of parts and molds have become more complex, finer and more
precise with the sophistication of functionality and design of industrial products including
automotive components. The number of parts requiring a precise fine shape on their surface withsize and depth, such as molds for automotive headlights, has been increasing as well. For themachining of such parts, both rough machining ability for forming a shape from a material andhigh-speed and high-precision machining ability for forming a fine shape are required. In addition,
mold materials have become harder and more difficult to cut in order to realize lighter productswith higher strength, so the need for high-speed and high-precision spindles has been increasing.
Mitsubishi Heavy Industries Machine Tool Co., Ltd. developed a high-speed andhigh-precision spindle for the μV1small micro milling machine and have been working onhigh-speed and high-precision machining using small-diameter tools for the machining ofhigh-hardness and difficult-to-cut materials.
This report introduces features and machining examples of the μV5 micro milling machine,which can handle a wider range of workpiece sizes and has a higher rough machining ability incomparison with the μV1.

|1. High-precision machine lineup and major specifications of μV5
Figure 1 shows our high-precision machine lineup including the μV1 small micro millingmachine, which is used for palm-sized workpieces, to the MVR-Fx, which is used for large molds
such as automobile exterior panels.

Figure 1 Our high-precision machine lineupMitsubishi Heavy Industries Technical Review Vol. 57 No. 3 (September 2020)
2

Table 1 shows main specifications of μV5.
Table 1 Main specifications of μV5
Travels

Table

SpindleMachine size & mass

X axis (mm)900

Y axis (mm)550

Z axis (mm)450

Working area (mm)Maximum loading
capacity (kg)
Spindle speed (rpm)1050×550

300-30000

Taper size

HSK-E50

Width (mm)2760

Depth (mm)2600

Height (mm)2790

Weight (kg)

12300

800

|2. Features of μV5 micro milling machine
2.1Machine body

Precise micro machining requires the use of a small-diameter tool. However, because the toolrigidity is limited, it is often the case that machining processes with a very small cutting feed andmachining allowance are performed for a long time. For this reason, the machine is required tohave such a high dynamic motion accuracy that it can operate accurately without spindle vibration
or feeding vibration and that stability during cutting without any thermal displacement of themachine body or the spindle can be ensured.
For the μV5, cooling of not only the outer jacket, which is the casing of the spindle, but also
the inside of the spindle rotating at a high speed is adopted. The bearing also uses special jet
lubrication, which is our proprietary technique, to forcibly and quickly remove the generated heat.
By suppressing the temperature increase of every section of the main shaft, the increase in thebearing preload is eliminated, which allows the maximum suppression of vibration and thermal
displacement over the entire range from lower spindle speeds to the maximum spindle speed of
30,000 rpm. In addition, due to the cooling of the inside of the spindle, the initial preload of thebearing can be set high, leading to sufficient rigidity to withstand rough machining.
For the guide surface, a sliding surface that has no vibration source in its mechanism and has
a high damping property against external vibration is adopted to suppress the displacement causedby the cutting reaction force.
The machine body has a well-balanced and strong mechanical structure and the heat capacityof the structure is large. Furthermore, a thermally-stabilized column in which a medium with a highheat capacity is enclosed, enhances robustness against environmental temperature fluctuations andother changes.

2.2

Visionplus Tool (optical image type tool measurement system)

Precise micro machining is often performed with a very small cutting feed and machining
allowance. For this reason, accurate measurement, positional grasping and correction of the tool tip
are also important.
To improve the accuracy of on-machine tool measurement, we independently developed theVisionplus Tool (optical image type tool measurement system) using a high-resolution CCD
camera as shown in Figure 2 and applied this system to the µV5. The Visionplus Tool measures
the temporal behavior of the thermal displacement of the machine and tool based on the tool tip
position data continuously collected by the camera. It also has a saturation determination functionthat starts the cutting process after the thermal displacement reaches the set fluctuation range,
which enables cutting in a stable area without error.

Mitsubishi Heavy Industries Technical Review Vol. 57 No. 3 (September 2020)
3Figure 2 Visionplus Tool (optical image type tool measurement system)

2.3

DIASCOPE (monitoring system)

We are working on the development of DIASCOPE, an IoT platform that supports theoptimization of the production activities of our customers (Figure 3).

Figure 3

DIASCOPE

Figure 4

Mold sample of fuel cell separator

Currently, we are developing the "Diagnosis/Prediction" phase, and the μV5 is equipped as
standard with a remote monitoring system as the "Connecting" function and an operation
monitoring system as the "Monitoring" function.

|3. Machining examples
3.1

Mold of fuel cell separator

A mold of a fuel cell separator has grooves over a large area and corners with a small radius.
Therefore, the machining of such a mold requires a small-diameter tool and the machining accuracy
in the height direction is extremely demanding. Figure 4 is a photograph of a mold sample
workpiece of a fuel cell separator machined by the μV5 and Table 2 lists the machining conditions.
Although the finish-machining of the groove bottom surface was performed for 23 hours
16minutes using a small-diameter CBN ball end mill with a radius of 0.3 mm at a spindle rotation
speed of 30,000 rpm, it required only one tool without any damaging wear. In addition, themachining of the pockets at the four corners was performed for more than 6 hours at a spindle
rotation speed of 30,000 rpm, but high-precision machining was realized with a depth accuracy of±2 µm.

Mitsubishi Heavy Industries Technical Review Vol. 57 No. 3 (September 2020)
4

Table 2 Machining conditions for mold sample of fuel cell separator
NoMachining process

Machining type1

Rough machining

Contour line

Rough machining

Contour line

2345678910

Pocket semi-finish
machining
Semi-finish
machining
External surface
finish machining
Bottom surface
rough machining
Bottom surface
semi-finish
machining
Rib finish
machining
Bottom surface
finish machining
Pocket finish
machining

Contour line

Tool
φ6R0.5
Radius EM
φ2R0.5
Radius EM
φ6R0.1Radius EM

Feed rate
SpindleMaximum(mm/min) speed (rpm) pick (mm)Machining time

1500

8000

3.01 hour 4 minutes

700

12000

1.01 hour 40 minutes

1000

8000

3.0

9 minutes

Contour line

R0.5 Ball EM1000

30000

0.05

3 hours 55 minutes

Contour line

R0.5 Ball EM

800

30000

0.03

1 hour 6 minutes

Scan line

R1.0 Ball EM

2000

27000

0.2

1 hour 55 minutes

Scan line

R0.5 Ball EM1000

30000

0.1

5 hours 50 minutes

R0.3 Ball EM

800

30000

0.03

8 hours 5 minutes

800

30000

0.03

23 hours 16 minutes

250

30000

0.03

6 hours 41 minutes

Contour line
Scan line
Scan line

R0.3 Ball EM(CBN)
φ2R0.1 RadiusEM

Total machining time: 52 hours 41 minutes

3.2

Mold of car air conditioner rear duct

A mold of a car air conditioner rear duct has a relatively large size and depth. Figure 5 is aphotograph of a mold sample workpiece of a car air conditioner rear duct that was formed by roughmachining and then finish-machined by the μV5. Table 3 lists the machining conditions.

Figure 5

Mold sample of car air conditioner rear duct

For the rough machining, a φ20R2 high feed cutter was used. Highly-efficient roughmachining was achieved despite the use of a high-speed spindle under machining conditions where
the spindle speed was 2,870 rpm, the feed rate was 7,000 mm/min and the cutting feed was 10 mm
for the XY axes and 0.5 mm for the Z axis.
The product area finish machining was performed for 26 hours 24 minutes using an R3 CBNball end mill at a spindle rotation speed of 30,000 rpm, but it also required only one tool without
any damaging wear. In addition, chamfering machining was performed using an R1.5 ball end mill,but steps from areas machined with the R3 ball end mill could be suppressed due to the opticalimage type tool measurement system.

Mitsubishi Heavy Industries Technical Review Vol. 57 No. 3 (September 2020)
5Table 3 Machining conditions for mold sample of car air conditioner rear duct
No1234567891011Machining process

Machining typeTool

Very roughφ20R2.0
Contour line
machining
Radius EM
Clearance roughφ20R1.0
Contour line
machining
Radius EM
Product area andparting surface
Contour line
R10 Ball EMrough machining
Parting surface
semi-finish
Scan line
R8 Ball EM
machining
Product areasemi-finish
Contour line
R8 Ball EM
machining
Chamfering roughChamfering
R6 Ball EM
machining
Chamferingsemi-finish
Chamfering
R3 Ball EMmachining 1
Chamferingsemi-finish
Chamfering
R1.5 Ball EM
machining 2Product area finish Contour line and R3 Ball EM
machining
scan line(CBN)
Chamfering finish
Chamfering
R1.5 Ball EM
machining
Parting surface
Scan line
R6 Ball EM
finish machining

Feed rate
SpindleMaximum(mm/min) speed (rpm) pick (mm)Machining time

7000

2870

10.0

6 hours 59 minutes

1600

4000

7.0

40 minutes

650

1600

2.0

4 hours 46 minutes

2000

6000

0.6

2 hours 21 minutes

1000

5000

0.6

5 hours 36 minutes

2800

5200

1.2

42 minutes

2000

16000

0.35

1 hour 45 minutes

2000

30000

0.2

2 hours 16 minutes

3000

30000

0.15

26 hours 24 minutes

3000

30000

0.121 hour 6 minutes

1600

12000

0.22

5 hours 23 minutes

Total machining time: 57 hours 58 minutes|4. Future prospects
This report presented the features and machining examples of the μV5 micro millingmachine. We believe that this machine, which can realize highly-efficient rough machining toprecise fine-shape finish machining all by itself, will contribute to the improved productivity of ourcustomers. We will continue to advance the sophistication of machinery and peripheral applications
for maximizing the performance of tools, while making efforts to contribute to the development ofthe manufacturing industry.