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

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40 L. Norberto López de Lacalle and A. Lamikiz

1.10.6 CNC Milling Machines for General Production

Some machine manufacturers have recognized the need for a dependable, low-cost

production machining centre. Here the compromise of technology-price-reliability

and functionality must be balanced, with parts for multiple applications in mind.

A lot of small and medium subcontractors do not know what kinds of parts will be

produced in the medium term, and therefore they prefer versatile machines.

An example is the Haas

Toolroom Mill series; the model TM-3P is shown in

Fig. 1.29. The TM-3P’s reliable 5.6

kW vector drive spindle spins to 6,000

rpm

and uses standard 40-taper tools. Rapids and cutting feedrates are 10

m/min. The

machine 1015

510

405

mm travels and a 1465

370

mm T-slot table provide

plenty of room for workholding. A 10-pocket tool changer is standard. The heavy

cast-iron bed and column damp vibration and provide rigidity.

On the other hand, in some areas of the world, machine size and footprint are im-

portant due to the expensive industrial ground. For this reason compact machines are

produced by several manufacturers. Usually, these ultra-compact machines are small

enough to fit through a doorway, can be easily moved using a pallet jack or equipment

dolly, can be provided with a caster kit to be rolled from one location to another and

even fit into most freight elevators. An example is shown in Fig. 1.29, the Haas

OM-

2A Office Mill. In these machines particular attention must be made to the work en-

velope, typically a cube with sides ranging from 150–250 mm.

Fig. 1.29 a The Haas

TM-3p. b The Haas

OM-2A Office Mill

1.10.7 A Heavy-duty Lathe

Lathes for long big parts, such as lamination rods or crankshafts for ship propul-

sion, are horizontal with flat beds, some models with even a 25

m distance be-

1 Machine Tools for Removal Processes: A General View 41

tween centres and a maximum swing over bed of 2

metres. Workpieces weighing

over 45

tons can also be machined on. Of course, the size and weight of parts re-

quires the use of big steady rests.

The main motion is a powerful motor in the range of 100–150

kW. The carriage

moves at moderate feeds, usually no more than 6

m/min. An operator can travel on

it, as shown in Fig. 1.30. The size and weight of components requires the motor-

ised movement of the tailstock and its automatic locking to the bed.

1.10.8 A Mitre Band Saw

Sawing is an important operation during the daily work of metal companies. More-

over, it is an essential operation for steel structure constructors. A typical band saw

Fig. 1.31 Bandsaw CPI of Danobat

. a Detail of the tensioning blade device. b Guide of the

bandsaw. c Manual or NC controlled mitre positioning

Fig. 1.30 Heavy-duty lathe of Goratu

, model GHT11

42 L. Norberto López de Lacalle and A. Lamikiz

is the twin column with mitre cutting between (+45º–60º), focused on the cutting of

any type of section, both single and bundles (Fig. 1.31). Machine mitre positioning

is carried out manually or NC controlled, depending on customer needs. Main

motor power ranges in 5–8

kW and blade speed in 15–100

m/min. The tensioning

device of the saw blade is hydraulic, manual or automatic. A coolant pump pro-

vides a constant flow of liquid coolant over the blade when metals are cut.

1.10.9 Transfer Machines

Transfer machines are usually designed as per the view of the specific part draw-

ings to be produced. Companies specialised in transfer machines work only as per

customer order. The main requirement is high productivity, so hard automation is

recommended here. Starting from this, the machine manufacturer’s engineering

department tries to design a solution adapting several machining units and auxil-

iary feed devices on a common bed.

Machine modularity makes it possible to obtain different solutions without a lot

of changes in the design and production. Regarding the machine frame, a ring bed

is a classic solution for rotary indexing table models, made in cast iron or weld

steel. These are called dial-index machines. Other machines are in-line systems,

with a

U-shape layout.

Drum or crown type tool turrets, as shown in Fig. 1.32, can be placed to per-

form several machining operations like milling, drilling and tapping. All tools are

driven by a common motor, using a gear transmission. These modules can be used

in different machines with little changes.

On the other hand, the use of parallel spindles when performing the same op-

eration leads to high productivity.

Fig. 1.32 Transfer machines by Etxe-tar

. a Machining unit for cylinder blocks. b Parallel spindles

1 Machine Tools for Removal Processes: A General View 43

1.10.10 A Milling and Boring Centre

The last machine of this chapter, shown in Fig. 1.33, is a turning and milling cen-

tre with an additional ram to increase the application scope of the machine, for

those part zones with complicated access to deep internal zones.

The 7.5

kW ram spindle with a stroke of 900

mm is mounted on the side of the

milling spindle housing, which enables the turning and milling using an angle

head. This spindle also has a dedicated 40 position tool magazine. This ram spin-

dle is in addition to the standard B-axis spindle with its 10,000

rpm and 37

motor and the turning table with 500

rpm and 37

kW power.

Fig. 1.33 Five-axis milling centre with an additional ram spindle, Mazak

model Integrex

Ramtec V/8 (courtesy of Intermaher

)

1.11 The Book Organisation

After the main aspects involved in machine tool manufacturing are introduced,

they are be presented in depth over the next chapters. Chapter 2 is about new

structural concepts currently being developed in some research projects. Chapter 3

is focused on the basics of spindles.

Chapter 4 explains the classic and recent advances on guides and drive trains.

The current CNCs are described in Chap. 5, concluding the main descriptions of

machine elements. Chapter 6 describes the most important aspects in design and

assemble precise machines.

Ram head

Milling head

44 L. Norberto López de Lacalle and A. Lamikiz

Chapters 7,

8 and 9 aim to present either some particular machine types or those

machines specialised in the most important industrial sectors. Thus the grinding

machines, lathes and electrodischarge machines are updated. Chapters 10 and 11

describe two small machine groups but at high technological level: parallel kine-

matics and micromilling machines. Here special concepts are used, complement-

ing all others presented in previous chapters.

Finally, a chapter devoted to aeronautical machines followed by one more on

automotive machines complete this book, hoping the reader has encountered up-

dated knowledge on machine tool construction over these pages.

Important references about machine tools are the books by Weck [24],

Boothroyd and Knight [5], Arnone [3], King [12] and Slocum´s book about preci-

sion machine design [21]. The basic machine tool theoretical bases are explained,

but unfortunately recent advances are not included in them. More recently, books

by Altintas [2], Tlusty [23], Kibbe et al. [11], Marinescu et al. [15], Erdel [8] and

finally by this chapter’s authors [14] update the state of the art about machine tools.

Acknowledgements Our thanks to Mr. Pedro Ortuondo of the Elgoibar Machine Tool Mu-

seum for the information provided; thanks to all the companies cited for their pictures and

information. Special thanks to Prof. José Luis Rodil and Xabier Ibarmia for their time dedicated

to discussing several aspects of this chapter. Thanks are also addressed for the financial support

of the Basque Government (Etortek 2007/09). Also thanks to the financial support of the CENIT

project eee-Machine.

References

[1] Adabaldetrucu P, Ortuondo P (2000) Máquinas y Hombres (Machines and men, in Spanish,

Basque and annotations in English), Ed. Machine Tool Museum of Elgoibar

[2] Altintas Y (2000) Manufacturing Automation: Metal Cutting Mechanics. Machine Tool

Vibrations and CNC Design, Cambridge University Press

[3] Arnone M (1998) High Performance Machining, Hanser Gardner Publications

[4] Artobolevsky II (1979) Mechanisms in modern engineering design, Mir publishers,

Moscow

[5] Boothroyd G, Knight WA (1989) Fundamentals of Machining and Machine Tools. Marcel

Dekker, Inc.

[6] Byrne G, Dornfeld D, Denkena B (2003) Advancing Cutting Technology. Annals of the

CIRP 52/2:483–507

[7] Huang DT, Lee JJ (2001) On obtaining machine tool stiffness by CAE techniques. Int J of

Mach Tool Manufacture 41:1149–1163

[8] Erdel BP (2003) High-speed machining. Society of Manufacturing Engineering, Dearborn,

Michigan

[9] Garitaonandia I, Fernandes MH, Albizuri J (2008) Dynamic model of a centreless grinding

machine based on an updated FE model. Int J of Mach Tool Manufacture

doi:10.1016/j.ijmachtools.2007.12.001

[10] International Standard ISO 841: Industrial automation systems and integration – Numerical

control of machines – Coordinate system and motion nomenclature (2001) International

Organization for Standardization

[11] Kibbe RR et al. (2006) Machine Tool practices (8th edition). Prentice Hall

1 Machine Tools for Removal Processes: A General View 45

[12] King R (Ed.) (1985) Handbook of high speed machining technology. Chapman and Hall

[13] López de Lacalle LN, Lamikiz, A, Sánchez. JA, Salgado MA (2007) Toolpath selection

based on the minimum deflection cutting forces in the programming of complex surfaces

milling. Int J of Mach Tool Manufacture 47:388–400

[14] Lopez de Lacalle LN, Sanchez JA, Lamikiz A (2004) High performance machining (in

Spanish). Ed. Tec. Izaro, Bilbao, Spain

[15] Marinescu ID, Ispas C, Boboc, D (2002) Marcel Dekker

[16] McKeown PA et al. (1987) The Role of precision engineering in manufacturing of the

future. Annals of the CIRP 36/2:495–501

[17] NAICS, North American Industry Classification System (2002) 333512 Machine Tool

(Metal Cutting Types) Manufacturing

[18] NC-Gesellschaft, www.ncg.de

[19] Reuleaux F (2007) Theoretische Kinematik (edition classic in German, of original of 1875).

Verlag Dr. Müller

[20] Salgado M, López de Lacalle LN, Lamikiz A, Muñoa M, Sánchez JA (2005) Evaluation of

the stiffness chain on the deflection of end-mills under cutting forces. Int J Mach Tool

Manufacture 45:727–739

[21] Slocum A (1992) Precision Machine Design. Society of Manufacturing Engineers

[22] Taniguchi N (1974) On the Basic Concept of Nanotechnology. Proc. ICPE Tokyo

[23] Tlusty G (2000) Manufacturing processes and equipment. Prentice Hall

[24] Weck M (1984) Handbook of Machine Tools. John Wiley & Sons Ltd

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

Chapter 2

New Concepts for Structural Components

J. Zulaika and F. J. Campa

Abstract This chapter is focused on analysing new concepts and trends related to

the structure of machine tools. In fact, the structure of the machine has a decisive

influence on the three main parameters that define the capabilities of a machine,

which are: motion accuracy, the productivity of the machine and the quality of

machining. In this respect, this study on structural components will add a new

basic parameter, eco-efficiency, because the structure of the machine also has

a decisive influence on the whole life cycle of the machine and especially on the

materials and energy resources consumed: an issue of increasing concern among

machine tool builders.

2.1 Introduction and Definitions

As seen in Chap. 1, the structure of a machine tool has two main functions, to hold

the components and peripherals involved in the machine and to withstand the

forces which are produced by the process and from the machine motions.

Within this view, the basic challenge for machine tool builders is to conceive

machine tool structures that are capable of withstanding with minimum possible

deflections the effects of the foreseen forces and of heating foci and at the same

time consume the minimum possible in terms of materials and energy resources.

_________________________________

J. Zulaika

Fundación Fatronik, Paseo Mikeletegi 7, 20009 Donostia-San Sebastián, Spain

zulaika@fatronik.com

F. J. Campa

Department of Mechanical Engineering, University of the Basque Country

Faculty of Engineering of Bilbao, c/Alameda de Urquijo s/n, 48013 Bilbao, Spain

fran.campa@ehu.es

48 J. Zulaika and F. J. Campa

As these two aims are opposing, the process of designing a machine tool is

a trade-off between these two targets, so that the specific characteristics of a ma-

chine tool will define that balanced position between these two approaches.

In this respect, the final characteristics of a machine tool are defined by means

of the following parameters:

• Productivity: The productivity of a machine is measured in terms of its metal

removal rate (MRR), which largely depends on its kinematic and dynamic ca-

pabilities and especially on its static stiffness, which in fact is the primary rea-

son to define the dimensions and shapes of the structural components. To this

end, higher stiffness involves bigger masses, which in combination with faster

motions aimed at achieving higher productivities, leads to motors of higher

power that generate higher inertial forces. This in turn demands stiffer struc-

tures, which again demand a larger amount of material, so that stiff machines

become productive and at the same time very energy and resource consuming.

• Accuracy: The accuracy of a machine is defined according to the deviations of

the tool with respect to a desired profile while it is being moved and positioned

(see Chap. 6). These deviations are largely associated to thermal effects and to

the mechanical deflections that the machine components bear when inertial and

process forces act on them. Therefore, the basis necessary in order to achieve

accurate machines will lie in conceiving both thermally-stable and stiff struc-

tures.

• Eco-efficiency: The eco-efficiency of a machine is measured in terms of energy

and material resources used and the waste and pollution created in the process.

As sustainability is an issue of increasing concern in the manufacturing sector,

this book will add a new aim for machine tool builders: to reduce the environ-

mental impact associated to a machine tool throughout its entire life cycle.

The structural components of machines have a twofold impact on the global

eco-efficiency of a machine: on the one hand, the largest amount of material re-

sources in a machine is associated with its structural components. On the other

hand, the energy that a machine consumes during its use phase is largely associ-

ated with the motion of movable structural components both in positioning mo-

tions and in machining motions.

Moreover, according to a study of the machine tool builder Nicolas Correa

the use period of a machine represents more than 90% of the total impact associ-

ated with their machines. Figure 2.1 shows both graphically and numerically (by

means of a life cycle analysis, or LCA), the total impact associated with an aver-

age medium/large size machine of Nicolas Correa

throughout its entire life cycle.

Accepting thus that the largest portion of the environmental impact of a ma-

chine tool is associated with the motions of its movable components, the reduction

of each gram of material in these movable structural components will have a deci-

sive role in the final ecological impact of the machine tool.

As a conclusion, the structure of a machine plays a key role on the final func-

tionalities of the productivity, accuracy and eco-efficiency of that machine. The

following sections will explain different strategies that can be employed to con-

2 New Concepts for Structural Components 49

ceive and produce machine structures that achieve appropriate values of produc-

tivity and accuracy by means of good thermal and vibration behaviour combined

with low amounts of movable masses.

2.2 Optimised Machine Structures

Machine tools provide a relative motion between the tool and the part that is to

be machined. With regard to these motions, milling machines have three Carte-

sian motions, with at least two of the axes mounted in serial. In some cases, the

three motions are applied to the tool (really to the spindle onto which the tool is

fitted); in other cases the motions are divided into the tool and the part, and only

on a few occasions are the three motions applied to the part, because it is quite

unusual to vertically move the table on which the part lies. Additionally, it is

increasingly common for machine builders to add two additional rotational de-

grees of freedom to the machine, either to the headstock, or to the table or to

both. They thus become machines with five degrees of freedom, i.e., five-axis

milling machines.

The structure of a machine covers the components that allow the achievement

of the degrees of freedom. These elements are mainly of two types:

• The frame and bed. They are the static part of the machine. The frame con-

stitutes the main body of the structure, in which the bed is the solid base of

the machine. The frame is usually composed of several bolted or welded

components.

100.65

5.64

4.14

1,424.24

-34.49

1396

- 34

End life

Raw material

extraction

Manufacturing

Transport

Use

forest hectare

1471

Tons

1500.2

Fig. 2.1 LCA of a machine by

Nicolas Correa

50 J. Zulaika and F. J. Campa

• The structural components. They are the movable parts of the machine struc-

ture, and are linked in different frame configurations. The interfaces among

elements with relative motion must be as stiff as possible and highly damped

along the perpendicular direction to the sliding one.

For an analysis of the advantages and drawbacks of different machine struc-

tures, it is useful to divide the structural design approaches into two groups: the

open-loop configurations (examples in Chap. 1, Figs. 1.25 and 1.27) and the

closed-loop configurations (Chap. 1, Figs. 1.9b and 1.22). The main conceptual

difference between them is that in the open-loop case, process and inertial forces

are conducted to the ground through in just one structural way. In the closed-loop

concept, forces are conducted to the ground in several ways.

For the same machine strokes, the main advantage of the open-loop concept

with respect to the closed-loop one is the easy access to the workzone and the

lower cost. Otherwise, the closed-loop concept presents a higher stiffness at the

tool tip and symmetrical behaviour with respect to thermal and mechanical loads.

Finally, the main structural components in an open-loop concept are the bed,

table, column and ram, linked with sliding guideways. In the closed-loop concept,

the main structural components are the table, bridge and guideways. Any of the

involved components in any of the concepts can be either static or movable, i.e.,

the column will be movable in some machines and static in others, and the same

for the rest of the structural components. Indeed, the different relative motions

among these structural components will define the different machine architectures

and configurations.

2.2.1 A Comparison Among Different Machine Configurations

Apart from the general characteristics associated with the closed-loop and open-

loop structures mentioned above, there are few a priori rules that state which is the

best option to select for a specific architecture and to define the relative motions

between components. There are some general rules detailed here that can help the

designer to select the optimal machine configuration:

• Symmetrical configurations lead to lower temperature gradients as well as to

reduce bending moments.

• The overhang of cantilever-type components must be as short as possible. In-

deed, cantilever components are the most critical components from a mechani-

cal point of view, since they generate Abbe type errors (see Sect. 6.2.3), in

which an angular compliance is amplified as a linear error by leverage effect.

Several machines include a ram element, which is always a source of flexibility

(machines in Chap. 1, Figs. 1.21 and 1.33). The overhang of this moveable

component depends on the point to be machined, so this is a variable stiffness

element.