Lopez de Lacalle L.N., Lamikiz A. Machine Tools for High Performance Machining

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426 Ciro A. Rodríguez and Horacio Ahuett

Fig. 13.5 Modular rotary transfer machines with a multi-head turret, by Kaufmann

turret, which are shown in Fig. 13.6. In this type of machine, the use of multi-head

turrets allows multiple operations in a single station. In addition, a single head posi-

tion in the turret can be custom-built for the simultaneous drilling of multiple holes

[16]. Alternatively, a single station can be fitted with an automatic tool changer, as

shown in Fig. 13.7.

Fig. 13.6 Station configuration for modular rotary transfer machine, by Automation Tooling

Systems

13 Machine Tools for the Automotive Industry 427

Fig. 13.7 Modular rotary transfer machine with automatic tool changer per station, by Ultra

Tech Machinery

13.2.2 Flexible Cells

For flexible cells, the most common type of machine configuration is a 4-axis ma-

chining centre with a horizontal spindle and pallet changer (a typical structure for

this type of machine is shown in Fig. 13.8). Due to the need of high productivity,

Fig. 13.8 Structure of a 4-axis horizontal machining centre with an interchangeable pallet,

by DMG

[3]

428 Ciro A. Rodríguez and Horacio Ahuett

some of the key specifications for these machining centres are the rapid feed rate,

the maximum programmable feed rate, the axis acceleration, and chip-to-chip time

at the tool changer.

Representative specifications of high performance machining centres for auto-

motive applications are shown in Table 13.1. An example of this type of machine

is shown in Fig. 13.9. Due to the high frequency of spindle travel in air, especially

Fig. 13.9 Example of a 4-axis high performance machining centre, by Okuma

Table 13.1 Typical specifications of 4-axis high performance machining centres with horizon-

tal spindle and pallet changer (spindle size CAT 50 o HSK 100) [10]

Specifications Makino A100E Heller MCH250 Okuma MA-500HB

X/Y/Z travel 1,700/1,350/1,400

mm 800/800/800

mm 700/900/780

Feed rate

(program/rapid)

m/min 50

m/min 60

m/min

Acceleration 4

m/s

Spindle 12 and 18

k min

–1

(HSK 100)

6 and 12

k min

–1

(HSK 100)

6 and 12

k min

–1

(Taper No. 50)

Chip to chip 5.5

s 4.1

s 4.4

ATC capacity 40/90/132/188/244/302 50/100/106/234/405 40/60/100/200/400

13 Machine Tools for the Automotive Industry 429

during hole-making operations, the axis acceleration is a critical specification with

a significant impact on cycle time [7]. As expected, larger machines have a lower

acceleration capability. All machine models provide a basic spindle and a high-

speed spindle, more appropriate for machining cast aluminium parts. The auto-

matic tool changer (ATC) options in these machines can handle a large number of

tools, with an extremely fast tool change time. The chip-to-chip time is measured

as the total time needed to a) retract the spindle to the tool change position,

b) switch tools and c) return the spindle to the workpiece.

The flexible cells are usually integrated through the use of pallet handling sys-

tems. Due to the generic nature of the machining centres used in flexible cells,

this approach provides an excellent capability to incorporate product changes,

within a given product family. The effective application of flexible cells, in ma-

chining operations of large automotive components, is recommended for produc-

tion volumes up to 100,000 parts/year [17]. When selecting this option, the user

must take into account the need for special work holding fixtures, which in prin-

ciple should also be flexible (this facilitates product turnover when compared to

dedicated fixtures).

13.2.3 Hybrid Systems

For large automotive components, when production volume falls between 200,000

and 400,000 parts/year, neither flexible cells nor dedicated transfer lines are the

optimum choice. In this case, the most effective approach might be a hybrid system

than integrates flexible cells into a dedicated transfer line. Hybrid machining sys-

tems are also sometimes referred to as reconfigurable machining systems [17].

Figure 13.10 illustrates the transition between the application of flexible cells and

dedicated systems, in terms of production volume, based on case studies from the

automotive industry (mainly engine blocks, cylinder heads and transmission cases).

- 100 200 300 400 500 600 700

Production Volume

(

1,000

arts

ear

)

Dedicated System

Hybrid System

Flexible S

stem

Fig. 13.10 Production volumes for flexible cells, hybrid systems and dedicated systems

(adapted from case studies in [4,

20–23,

27], assuming 70% machine uptime)

430 Ciro A. Rodríguez and Horacio Ahuett

Fig. 13.11 Integration of flexible cells into a transfer line, by Grob

[9]

Fig. 13.12 Gantry robot for integration of flexible cell with dedicated transfer line, by Cross

Hüller

[2]

Flexible Cells

Transfer Line Stations

13 Machine Tools for the Automotive Industry 431

Figure 13.11 presents a case in which some operations in the transfer line are

replaced by flexible cells. Similar operations are simultaneously performed by

several machines in parallel processing. Parts are handled by a Gantry robot placed

between the machines in the flexible cells and the transfer line (see Fig. 13.12).

If one machine shuts down, due to malfunction or product changes, other ma-

chines in the cell continue the operation. In contrast, when a single station in

a dedicated transfer machine shuts down, the entire production stops. Another

advantage of the hybrid transfer line is the scalability, as cells can easily be ex-

panded with additional machines. This allows the introduction of new machining

operations that might be demanded by modifications to the product design. Again,

to maintain flexibility, special fixturing systems might be required.

Each machine in the flexible cell is sometimes referred to as an agile module.

The typical structure of the agile modules is shown in Fig. 13.13. These machines

have a slender design that allows them to be stacked together as part of a flexible

cell combined with a dedicated transfer line. Electrical cabinets and servo motors

are all located behind the machine.

Fig. 13.13 Structure of 4-axis agile module, by Toyoda

[25]

432 Ciro A. Rodríguez and Horacio Ahuett

Table 13.2 Typical specifications of 4-axis agile modules with horizontal spindle (spindle size

CAT 40 o HSK 63)

Specifications Makino J4M Okuma MILLAC-44H

X/Y/Z travel 500/560/500

mm 410/460/470

Feed rate (programmable/rapid) 50

m/min 60

m/min 20

m/min 50

m/min

Acceleration 12

m/s

Spindle 16

k min

–1

(HSK 63) 12 and 20

k min

–1

(HSK 63)

Chip to chip 3.0

s 3.0

ATC capacity 15/30 10/24

Dimensions (width × length) 1,500

4,075 mm 1,350

3,450 mm

Representative specifications of agile modules for automotive applications are

shown in Table 13.2. As in the case of the high performance machining centres,

the key requirements for these agile modules are the rapid feed rate, the maximum

programmable feed rate, the axis acceleration, and chip-to-chip time at the tool

changer. Additionally, the floor space is an important factor in the structure of

agile modules. Because of their reduced flexibility, agile modules use tool chang-

Fig. 13.14 Examples of agile modules. a Danobat

. b Toyoda

. c Makino

13 Machine Tools for the Automotive Industry 433

ers with much less capacity than those offered in stand alone machining centres

used in flexible cells. Examples of agile modules are shown in Fig. 13.14.

13.3 Technology Trends

The need for weight reduction, associated with fuel efficiency in automobiles,

leads to the ever-increasing use of aluminium alloys in engines [24]. This trend

in turn requires the use of machine components and cutting tools with a higher

performance [18].

In terms of machine tool components, the need for a higher cutting speed for

machining aluminium alloys requires high-speed spindles and more extensive use

of linear drive motors. For example, the agile modules such as the Okuma

MILLAC-44H, the Makino

J55-ISO, the Toyoda

TOP J Transfer Line, and the

Mazak

Ultra Narrow UN-600H include optional spindles with 20,000

rpm (in

CAT 40/HSK 63 size).

Additionally, there is a continuous development of new and more effective ma-

terials and tool handing systems in machine tools [6]. The most common types of

tool storage are drum and chain-based, with capacities up to 60 tool locations. For

additional capacity, the tower and matrix systems are used, allowing up to 400 tool

locations. Colombo Filippetti Torino

, Miksch

and Bertsche Engineering

are

among the suppliers of tool changing systems.

The need to maintain high productivity has lead to the development of dual

spindle machines, as shown in Fig. 13.15 (MAG

Powertrain SPECHT 550

DUO). This kind of machine has chip-to-chip times below 3

s. The dual spindle

machine concept by Mikron

(Multistep XT-200, in Chap. 1, Fig. 1.15) can reach

s of chip-to-chip time.

Fig. 13.15 High performance

machining centre with double

spindle and 4-axis, by MAG

Powe

train

434 Ciro A. Rodríguez and Horacio Ahuett

Fig. 13.16 Hole-making operations in cast aluminium, by Heller

In automotive component machining, coolants represent up to 15% of the total

operation cost [23]. Together with cost reduction objectives, the use of coolants

represents an environmental and operator safety concern. Therefore, dry and

minimum quantity lubrication machining are active research topics. Minimum

quantity lubrication (MQL) is a near-dry machining method that may be applied to

reduce coolant usage in operations such as drilling, which cannot be performed

completely dry [5], as shown in Fig. 13.16. MQL has been incorporated into some

commercial machine tool solutions for the automotive industry.

Finally, the use of polycrystalline diamond (PCD) cutting tools and various

coatings for tungsten carbide tools has received significant attention. Some of the

coatings under research for machining cast aluminium silicon alloys (A319, A356,

A390) include carbon-based coatings or diamond like carbon (DLC) (commer-

cially known as Dymon-iC™ and Graphit-iC™), MoS

-based coatings (MoSTi),

TiB

, TiAlN/VN, TiAlCrYN, and nano-crystalline diamond [12,

13,

15,

26]. Under

specific conditions, some of these coatings exhibit tool life performance compar-

able to that of the PCD tools.

Acknowledgements The authors acknowledge the support by all the companies cited in this

chapter as well as the Association for Manufacturing Technology. Their valuable information

and suggestions are greatly appreciated.

13 Machine Tools for the Automotive Industry 435

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