Mitsubishi Heavy Industries Technical Review Vol. 46 No. 3 (Sep. 2009)
1

The MAF150R: A Floor Type Horizontal Boring Mill
Providing the Highest Machining Efficiency in its ClassHIROYUKI YAMAMURA SATOSHI FURUTATEHIROYUKI DOMARUTOMOHARU HASEGAWA

MAKOTO EGUSAIn recent years, customer demand has been increasing for machining tools that offer
higher cutting performance and productivity with reduced non-cutting periods for medium- andlarge-part machining processes. To address such machining needs in manufacturing facilities,
Mitsubishi Heavy Industries Ltd. (MHI) developed the MAF150R, a floor type horizontal boringmill that provides both heavy-cutting performance and short non-cutting times. MHI designed
this machine by making full use of its FEM analysis technology. In this paper, we describe thetechnologies used for this machining tool and present actual machining examples.

|1. Introduction
With the expansion of wind and solar power and the increased use of motors in otherenergy-generation industries, an upsurge has occurred in demand for medium- to large-size parts
that need be produced using a horizontal boring mill. Figure 1 shows an example reference
workpiece used in this field.

Chamber

Rotor head

Figure 1 Example workpieceThis surge in demand appears to be spreading worldwide. Manufacturers of these parts now
expect heavy-cutting, high-speed, and high-productivity machining tools.
MHI tried to address these needs with the MAF-RS series. To meet the demand for evenfaster machining, however, we developed the MAF150R, the best floor type horizontal boring millin its class in Japan, which pursues the reduction of non-cutting times by speeding up andautomating processes without sacrificing heavy-cutting performance. In developing the MAF150R,
MHI optimized the structural shapes and the coupling rigidity between parts by utilizing
FEM analysis and simulating anticipated cutting in actual machining postures. This resulted in ahigh-productivity boring mill that offers heavy-cutting performance that is not influenced by theheight and protrusion of the spindle, as well as the highest speed and acceleration/deceleration
characteristics in its class.
We discuss the technologies used to realize the above functions in this technical review.

Mitsubishi Heavy Industries Technical Review Vol. 46 No. 3 (Sep. 2009)2|2. Development concept of the MAF150R
The MAF150R was developed with the concept of realizing a high-performance horizontal
boring mill. The aim was to provide benefits to our customers with higher productivity compared tocompetitors' products. Thus, a machine was required that reduced both its cutting and non-cutting
times in a well-balanced manner.
Figure 2 compares the cycle time of the MAF150R versus a domestic competitor's machinein the same class when machining a construction machine part (or workpiece). In this example, thecycle time was reduced approximately 35% by decreasing the axis feed time through more rapid
traverse rates and decreasing the attachment changing and indexing and the tool changing times.
The cutting time was also decreased by improving the heavy-cutting performance of the machine.

Figure 2 Comparison of cycle time

|3. Technologies for realizing high productivity
3.1

Machine construction

Figure 3 shows the construction of the MAF150R. To meet the needs for high-speed
machining, the MAF150R was developed as a new series product that is slightly smaller than thecurrent MAF-RS series. Therefore, its ram (Z-axis), which extends and retracts while supporting
the main spindle, is somewhat smaller but has a 400-mm square shape to ensure optimal rigidity.
This construction enables the machine to bore the deepest holes in its class in a flexible manner,even in a narrow workspace. In addition to this, the MAF150R also has a W-axis for boring spindle
longitudinal in/out, a Y-axis for the vertical movement of its saddle along the column, and anX-axis for cross-feeding its column along the bed.

3.2

High heavy-cutting capacity

The high rigidity of the machine body achieved by utilizing FEM analysis enables full-power
cutting at 37 kW, the maximum output capacity of the spindle motor, across all the machining
ranges. The MAF150R can offer the same heavy-cutting performance even when the main
spindle is at a high position or has a long protrusion, improving the overall machining efficiency. In
the following description, we introduce the technologies for optimizing the structural shapes andthe coupling rigidity between parts to achieve high rigidity.
(1) Selection of materials for an optimal structure
To realize high rigidity, we first reviewed the selection of materials used for the mainstructures. Although welded steel, which offers a high static rigidity, has been usedconventionally as the structure material, we adopted castings for the MAF150R because they
have advantages in forming the complex logical structure shapes derived from the FEM
analysis. The result was an increase in sectional rigidity, which not only led to higher staticrigidity, but also improved dynamic rigidity, affecting the machining accuracy. Moreover, forthe ram located nearest to the cutting point, ductile cast iron (FCD600) with a high elastic
modulus equivalent to iron steel was used because it has particularly high rigidity and damping
characteristics.
(2) Optimization of the structural shapes
The rigidity of the column was very important in order to realize heavy cutting at a highposition, which effectively improves productivity. The column also must be as light as possible
to ensure fast movement. For these reasons, we adopted a double-walled rib structure for theMAF150R.

Mitsubishi Heavy Industries Technical Review Vol. 46 No. 3 (Sep. 2009)
3Figure 3 Construction of horizontal boringmill

Figure 4 Double-walled structure of thecolumn

Figure 5 Honeycomb structure of the machine
bed

Figure 6 Opposed hydrostatic bearing

Figure 4 shows a model of the double-walled column. It is a well-known fact thatproviding double walls with a rib between them improves the rigidity of a structure.
However, relying on this technique only not only results in a substantial increase in mass, butalso makes the casting forming extremely difficult. Therefore, we partially removed the internalwalls, as shown in the model, to facilitate the casting forming process and minimize theincrease in mass. This construction provided sectional rigidity 1.6 times higher than that of aconventional simple rib structure.
Next, a model of the machine bed is shown in Figure 5. By providing a honeycomb
structure just under the sliding surface that can support the entire moving mass, we enabled themachine bed to maintain a high rigidity without increasing its mass. Thus, by means of FEM
analysis, we balanced the competing design elements "mass reduction" and "rigidityimprovement" in a sophisticated manner.
(3) Optimization of coupling rigidity between parts
The MAF150R adopted opposed hydrostatic bearings (Figure 6) for the X- and Y-axes
that support a large mass of the structure and a slide-guide mechanism that holds the four facesof the ram for the Z-axis. This enabled each of these axes to provide smooth rapid traverse
across all speed ranges while maintaining a high level of support rigidity.

3.3

Increased productivity by reducing the non-cutting times(1) Increased rapid traverse rate
The aim of increasing the rapid traverse rate for each axis was to reduce the time requiredfor positioning the axis during the feed operation. The rapid traverse rate was increased to24000 mm/min for the X-axis, approximately twice as fast as that of domestic competitors'products in the same class, and 20000 mm/min for the Y- and Z-axes.
(2) Increased spindle speed
The spindle speed of the MAF150R was set to 3000 min–1, approximately twice as fast
as that of competitors' products in the same class. In addition, to suppress the heat emitted fromthe drive system, we adopted a cooling system for the MAF150R that cools the spline shaft

Mitsubishi Heavy Industries Technical Review Vol. 46 No. 3 (Sep. 2009)
4from inside by injecting temperature-controlled oil. We also adopted an automatic mist
lubrication for all bearings in the drive system (8 points) and the main spindle bearings that
supplies temperature-controlled oil to the outer case of each bearing to prevent thermal
deformation. The main spindle bearings have temperature-monitoring functionality that detects
the occurrence of a failure at an early stage and reminds the operator of required maintenance toprevent sudden machine stoppage.

3.4

High accuracy through compensation for variations in the center of gravity
and thermal displacement(1) Saddle balancer
This balancer offers balance compensation functionality intended to reduce the droopingof the main spindle nose when the boring spindle and/or ram is extended horizontally.
Specifically, if the spindle end bends or hangs down under its own weight when the workpieceis machined with the boring spindle or the ram extended horizontally, the finished surface
accuracy is badly affected. Such bending or hanging of the spindle nose can be minimized byusing this compensation function.
The balancer controls the degree of drooping of the spindle nose by adjusting thesuspension force at the front and back of the saddle so that the bending angle (swinging orhanging) of the main spindle is minimized. For this purpose, a cylinder was built into thesuspended portion in front of the saddle that compensates for the pressure through linear
compensation based on the Z-axis position. A similar compensation technique is also used forthe W-axis to compensate for the variation in the center of gravity of the moving body.
(2) Thermal displacement suppression
The MAF150R was provided with the following four improvements to suppress thermaldisplacement.
･ To suppress the deformation (thermal expansion) of the column due to fluctuations in theoutside air temperature, the volume (thickness) of the front and back ends of each column
member varying in shape were made equivalent in heat capacity through a thermal analysis
to minimize the variation in the degree of rise or fall of the column at different ambient
temperatures.
･ Temperature controlled oil was designed to circulate inside the main spindle bearings and in
the drive gearbox to suppress the temperature rise and thermal displacement that occurs
when the main spindle is rotating at a high speed.
･ For the opposed hydrostatic bearings used for the X- and Y-axes, which have high support
rigidity, the variation of the center of gravity was minimized to realize high-accuracy
movement, and the temperature of the hydrostatic lubricating oil was controlled to thetemperature of the machine to suppress the thermal displacement caused by the axis feed.
･ Compensation functionality was added to compensate for the thermal displacement of themachine in the Y- and Z-axis directions that occurs when the main spindle rotates.

3.5

User friendlinessWith recent improvements in productivity, customer demand for easy maintenance andoperation has been increasing. To improve maintainability, the MAF150R adopted a centralized
arrangement of all lubrication devices to facilitate the refilling and draining of lubricating oil, theservicing of these devices, and other maintenance tasks. In addition, for periodic maintenanceitems, the machine was designed to alert the operator by displaying maintenance information on themachine operation panel when required.
For improved operability, we developed five-face machining software based on the techniqueof machining surface-coordinate expansion. This software facilitates the creation of programs forcomplex surface machining in a short period of time because any inclined surface (at any degree)
can be programmed as XY planes, and tetrahedral shapes can be defined with four sides crossing atright angles. The software also has sixteen patterned subprograms for bolt-hole circles, etc. Thesoftware was developed based on numerical control (NC) functions and does not require any
special programming device, which also enhances its user-friendliness. It was designed to yield thebest performance from a rich variety of attachments, such as a right angle head, universal head,boring-tool head, and spindle support.

Mitsubishi Heavy Industries Technical Review Vol. 46 No. 3 (Sep. 2009)5|4. Machining example
To verify that the machine performs as anticipated, we test-cut a sample workpiece. The test
was conducted using the machining conditions shown in Figure 7, with the Y-axis set to a heightof 2,700 mm and the Z-axis (ram) extended 700 mm. For these conditions, the actual output
indicated by the spindle load meter was 37 kW, which demonstrates that the MAF150R offers
heavy-cutting performance at a high spindle position as initially intended. Compared with themachining data for Competitor A's machine, this resulted in a cutting capacity improvement of 1.6times, which demonstrates that the cycle time is reduced for heavy-cutting applications. This meansthat the workpiece can be machined with a motor output of 37 kW, the highest in its class,regardless of the extension distance of the Z-axis along the Y-axis up to a height of 2,700 mm.
The test results are compared with those obtained Competitor A's machine in Figure 8. Thegraph shows the Y–Z machining area of both machines. The MAF150R had an obvious advantage
in machining capacity because a motor output of 37 kW was available over the entire range, unlike
in Competitor A's machine.
Machining data for the right angle head, one of the main attachments, is shown in Figure 9.
Figure 10 shows its external appearance. This test was conducted with the Z-axis (ram) extended
to 550 mm, meaning that the machining point was as far as 1,000 mm including the length of rightangle head itself from the original Z-axis zoro position. The test demonstrated that the workpiece
could be machined with a motor output of 30 kW, the maximum output of the right angle head, in
this machining position, and highlighted the high rigidity of this attachment. The motor output wasthree times that of Competitor A's angle head (max. 10 kW), which shows the excellent
performance of the MAF150R as a five-face cutting machine.
MAF150R
Workpiece material : SS400
Face mill cutter: φ200 mm
Spindle speed: 320 min-1
Cutting depth: 6 mm
Cutting width: 180 mm
Cutting feed
: 1 300 mm/min
Cutting capacity:: 1 400 cc/min

Company A
Workpiece material : SS400
Face mill cutter: φ200mm
Spindle speed: 210min-1
Cutting depth: 6mm
Cutting width: 150mm
Cutting feed
: 1000mm/min
Cutting capacity:: 900cc/min
Approx. 1.6 times

Figure 7 Machining data for the MAF150R

MAF150R
Workpiece material: SS400

Face mill cutter: φ200mm

Spindle speed:

Cutting depth: 5mm

Cutting width: 180mm

Cutting feed

: 1000mm/min

Cutting capacity: 900cc/min

Figure 8 Comparison of cutting range

320min-1

Figure 9 Machining data for the right angle
headFigure 10 External
appearance ofthe right angle
headMitsubishi Heavy Industries Technical Review Vol. 46 No. 3 (Sep. 2009)6|5. Machine Specifications
The specifications of the MAF150R were determined to support the machining oflarge-diameter and long workpieces with the X-axis stroke set between 5000 and 21000 mm, theY-axis stroke set between 2500 and 3500 mm, and the total stroke of the Z- and W-axes set to 1400mm. Despite these extensive specifications, the adoption of a modular design approach enables ashort delivery period. Table 1 lists the main specifications of the MAF150R and compares themwith those of competitors' products. The capacity of the MAF150R is prominent in its class.
Table 1 Main specifications
Boring spindle diameter (mm)Spindle taper

MAF150RCompany A

φ150

φ150

Company B
φ150

7/24 taper ISO 50

7/24 taper ISO 50

7/24 taper ISO 50

Spindle motor output (kW)

30/37

22/26

22/30

Spindle rotation speed (min-1)

7 to 3000

5 to 1500

16 to 1600

X-axis stroke [Column, cross feed] (mm)5000 to 21000

6000 to 10000

4500 to 9000

Y-axis stroke [Saddle, vertical] (mm)2500 to 3500

2000 to 3500

2500 to 3500

Z-axis stroke [Ram, longitudinal] (mm)

700

750

450

W-axis stroke [Boring spindle, longitudinal]

700

900

24000

10000

1000
The total stoke of the Wand Z-axes is 1000 mm or
less
10000

(mm)
Rapid traverse rate: X-axis (mm/min)(X-axis stroke = 5 · 6 m)
Rapid traverse rate: Y-axis (mm/min)

20000

10000

10000

Rapid traverse rate: Z-axis (mm/min)

20000

6000

8000

Rapid traverse rate: W-axis (mm/min)

10000

6000

8000

Cutting feed rate (mm/min)

1 to 10000

1 to 4000

1 to 4000

Automatic tool changer (ATC): # of tools

60, 80, 100

60, 8050|6. Conclusion
In developing the MAF150R, we combined MHI's abundant analysis know-how and pursued
an optimal structural construction. As a result, we successfully built our envisioned product on ourfirst attempt. This achievement was due to our improved analytical capacity. We will accelerate thedevelopment of new products in the future using similar techniques.

Authors
Hiroyuki Yamamura
Manager,Engineering Department,
Machine Tool Division

Satoshi Furutate
Manager,Engineering Department,
Machine Tool Division

Hiroyuki Domaru
Engineering Department,
Machine Tool Division

Tomoharu Hasegawa
Engineering Department,
Machine Tool Division

Makoto Egusa
Engineering Department,
Machine Tool Division