Mitsubishi Heavy Industries Technical Review Vol. 47 No. 4 (December 2010)22

Performance Improvement of the Vertical Precision Milling Machine
MVR Allows High-Accuracy Processing of Automotive Molds andHigh-Efficiency Production of Large Molds to be Realized

M a c h i n e To o l D i v i s i o n

The need for value-added milling technologies that offer higher production efficiency andaccuracy has increased in recent years. Responding to this need, Mitsubishi Heavy Industries,
Ltd. (MHI) has developed the MVR, which is equipped with a high-torque spindle, designed toimprove the efficiency of the rough cutting of large automotive molds. This machine also
provides the necessary torque for processing the molds used in the booming wind power,
construction equipment, and railway vehicle industries. We have also developed theMVR35-FM, a high-accuracy mold-milling machine used for finish cutting, and designed toshorten the mold-polishing process and improve the accuracy of the working surface. The details
are outlined below.

|1. Characteristics
The picture shows the appearance of the machine, and Table 1 lists the major specifications.
It was developed using the basic modules of the modularly designed MVR, and adding ahigh-torque spindle module in response to the aforementioned market needs. Furthermore,advanced countermeasures against heat deflection were applied to the MVR to improve theaccuracy of the working surfaces of the molds. Because the machine inherits the basic design of theMVR, a wide selection of specifications is available, and replacement parts can be purchased
quickly and at low prices, enabling stable service and maintenance.
Table 1

List of major specifications
Rough cutting

Items
Table
surface

Finish cutting
MVR25 MVR30 MVR35
MVR25 MVR30 MVR35 MVR40 MVR45-FM-FM-FMmm 1,500 2,000 2,500 3,000 3,500 1,500 2,000 2,500mm
3,0004,0006,0003,0004,000mm
Length of table; +200mm 2,500 3,000 3,500 4,000 4,500 2,500 3,000 3,500mm
800
800 (option: 1,000)
800

working Width
Length
X: Front-back of table
Y: Left-right of table
Axis travel
Z: Vertical travel of ram
W: Vertical travel ofmmcross rail
X･Y
mm/minRapid traverse
Zmm/minWmm/minMax. cutting feed X･Y･Z
mm/min6,000 min-1 spec
Spindlemotor
12,000 min -1 spec
max. output
4,000
min-1spec
high-torque spindle type
Number of tools
Max. tool diam.
ATCMax. tool lengthMax. tool weight

KW
KW
KWmm
mmkg

1,100

1,100 (option: 1,300)

30, 000

1,100

22, 000

20, 000
30, 000
10,0003,000
10,000Continuous rating: 22/30 (low speed/high speed)
25% ED rating: 26/37 (low speed/high speed)
Continuous rating: 15/25 (low speed/high speed)
Short-time rating: 22/30 (low speed/high speed)
Continuous rating: 22

30-minute rating: 30

50φ260 (option: φ290)
400 (option: 500)
25 (option: 30)

22, 000

Mitsubishi Heavy Industries Technical Review Vol. 47 No. 4 (December 2010)23(1) High-torque spindle-type MVR
The high-torque spindle-type MVR has a high-torque spindle module added to therigidity-enhanced main body of the machine. The spindle is mounted with a gear deceleration
mechanism to ensure a torque of 1,000 Nm or higher, which is required for large boring andmilling. A torque of 1,747 Nm is attainable (2.7 times the conventional MVR torque of 645
Nm), improving the machine’s capability for rough cutting with large tools. Cylindrical roller
bearings, positioned on the tip of the spindle, strongly support the cutting force and enablehigh-efficiency milling.
(2) Precision improvement of the working surfaces of molds processed by the machine
Improvements in the working surfaces of fabricated molds were obtained by (i)developing a mechanical structure that is resistant to heat deflection, enabling stable,
high-precision milling in a typical factory environment where molds are often processed slowly
and without air conditioning, and (ii) adding a function that automatically corrects errors andheat deflection caused by the replacement of spindle attachments.
Large machine tools tend to be affected by heat, and their precision deteriorates becauseof their size. Thus, the heat capacities of the parts were equalized in accordance with a heatdisplacement analysis, to obtain a structure resistant to heat displacement. When the heat cannot
be balanced by a single part, an insulation material is used to equalize the thermal value. In
addition to these basic measures against heat deflection, temperature sensors are installed inside
the spindle and attachments to allow heat displacement compensation in response to various
milling conditions, thus enabling high-precision milling in the X-, Y-, and Z-directions.
The use of attachments, illustrated in Figure 1, is effective for milling intricately shaped
molds. However, this procedure may cause problems, such as mutual errors and attachment
index errors, as well as gaps generated in the working surfaces by the tools. To minimize thesegaps in working boundaries, we developed a cutting edge position correction function for
attachment tools, which measures and corrects the position of the cutting edge in three
directions on the ball-end mills used for finishing molds.

Universal head
5,000 min-1

Right angle head
6,000 min-1

Extension head
6,000 min-1
15,000 min-1

30° angle head
6,000 min-1

Figure 1 Universal head used during blade edge position measurement and variousattachments(3) Rigidity improvement of the main structure of the machineHigh rigidity of the main structure of the machine (enabling high-efficiency milling) wasaccomplished by enhancing the torque of the spindle, and using FEM analysis to furtheroptimize the cast material thickness and the shape, thickness and location of the rib. Thestructure of the main body of the machine is illustrated in Figure 2.
Cast material featuring high damping performance is used for the main structure, while
ductile cast iron with a toughness equivalent to that of steel is used for the ram near the cutting
point. A high-rigidity structure with minimal vibration during the cutting process has beenachieved in all models of the MVR series, by incorporating these features into the standardmachine.

Mitsubishi Heavy Industries Technical Review Vol. 47 No. 4 (December 2010)
24

Figure 2

Structure of the main body of the machine|2. Processing examples
Examples of high-efficiency and high-precision processing via the technologies explained
above are now presented.
Figure 3 shows examples of processing with a φ600 boring attachment (required by the wind
power, construction equipment, and railway vehicle industries) and a φ200 milling attachment,using the high-torque spindle-type MVR. A torque of 1,700 Nm (407 cc/min) was attained during
the boring process, while the milling process provided high-efficiency rough cutting at 840 cc/min.

Figure 3 Examples of high-efficiency rough cutting using φ600 boring and φ200 milling
attachments

Figure 4 shows an automotive mold processed by the MVR-FM. The requirements forhigh-precision working surfaces and high-speed milling are demanding for outer molds. The moldshown here was processed by reciprocating a φ30 ball-end mill (CBN), setting the spindle speed at
12,000 min-1, the feeding speed at 10 m/min, and the milling pitch at 0.5 mm. A high-quality
working surface was obtained, with a roughness Rz ≤ 5 μm. We will continue to improve the heavy
milling and no-polish milling performance by utilizing the MVR featuring enhanced precision andefficiency, in response to the needs of a wide range of customers.

Figure 4

Example of high-precision milling finished by a φ30 ball-end mill.