Hybrid Machine Tool Design - home.iitk.ac.inhome.iitk.ac.in/~jrkumar/download/Chapter 8 - Hybrid Machine Tool Design.pdf · EDM, wire EDM, wire electrical discharge grinding, and

Chapter 8

Hybrid Machine Tool Design

Dr. J. Ramkumar1 and Gopal Gupta2

1Professor and 2Research Student

Department of Mechanical Engineering

Micromanufacturing Lab, I.I.T. Kanpur


Index1. Introduction

2. Hybrid Machine Tools

3. Sequential hybrid Machine Toolsa) EDM + Mechanical Machining process tools

b) Additive manufacturing plus milling

c) Laser plus milling process

4. Assisted hybrid machine tools

5. Combined hybrid machine tools

6. Design principle of hybrid machine tools

7. Case study : Design of six-axis hybrid micro machine tool1) Dynamic design of machine structure

2) Motional stages

3) Control system

4) Laser and plug-in modules

5) Internal machining Results

8. Conclusion

9. Reference


1.Introduction • Hybrid machine tools are platforms to accommodate hybrid

machining processes. Due to large varieties of hybrid machining

processes, it is very difficult to quantify the benefits of hybrid

machines.

• A qualitative comparison between the hybrid machines and the

traditional machines from the aspects of compactness, setup

efficiency, machining accuracy, machining versatility, and

metrology efficiency shown in figure 1.

• The advantages of the hybrid machine tools are quite obvious in

almost all these aspects except machining versatility.

• The chapter will introduce state-of-the-art commercial hybrid

machine tools and associated design principles. It also includes a

case study on design of a six-axis hybrid machine tool.


2. HYBRID MACHINE TOOLS

• According to the operation format, hybrid machine tools can be classified

into three categories

1) Sequential, assisted 2) Assisted hybrid 3) Combined hybrid

• The purpose of this session is to highlight the capabilities, processes, and

limitations of current hybrid machines as benchmarks for future

development

Fig 1 - Comparison of hybrid machines and conventional machines [1] Micromanufacturing Lab, I.I.T. Kanpur

3. Sequential Hybrid Machine Tools

• Currently, there are three types of commercial sequential hybrid machine tools.

1) EDM 1 Mechanical Machining Process Machine Tools:-

• Micro-EDM process can also be employed to remove material first and then micro milling process is adopted for machining small holes or small features

2) Additive Manufacturing Plus Milling :-

• The machine adopts an additive manufacturing process to build up a workpiece and then a milling process is used afterwards for finishing operations to obtain high-dimensional accuracy and good surface finish on the final product.

3) Laser Plus Milling Processes :-

• The last type of sequential machine tool runs mechanical milling and laser machining sequentially on one machine platform.

• For example micro milling and laser processing take place in a sequential manner to overcome each other’s disadvantage.


3.1) EDM -Mechanical Machining Process Machine Tools

• The Hybrid-µEDM -DT110 developed in Singapore, as shown in Fig.2 is a

three-axis hybrid machining center which combines micro milling, turning,

EDM, wire EDM, wire electrical discharge grinding, and grinding processes

on single machine bed.

• The strokes of the X, Y, and Z axes are 200 mm, 100 mm, and 100 mm,

respectively. The motional resolution and repeatability are 0.1 µm and 1 µm

for each axis.

• The machine adopts an air bearing milling spindle with a maximum

rotational speed of 200,000 rpm.

• The hybrid machine can adopt a turning operation to fabricate a shaft and

then machine it to a micro-pin using wire EDM.

• These micro-pins can be used as electrodes to machine microhole on any

conductive materials in the following EDM process.

• Micro-EDM is firstly used for rough machining followed by micro milling to

obtain sharp edges. ECM is then used for final polishing operation.


• It can complete a typical micro-part on this machine. As this hybrid

machine includes EDM/ECM processes which require the conduction of

electricity, therefore, it can only machine metals

Fig 2. Hybrid machine (a) Hybrid µ-EDM setup (b) Square pyramid stainless steel

hypodermic needle obtain by using micro EDM and Micro milling process [2]


3.2) Additive Manufacturing Plus Milling Tools

1) LUMEX avance-25 fusing metal laser sintering hybrid milling machine

is able to cost effectively manufacture complicated molds with internal

cooling channels. Firstly, metal powders are melted and sintered via a Yb-

fiber 400 W laser. At every 10th Squeezing and sintering layer, the high

speed milling process is used to generate precise shape. The maximum size

of workpiece can be machined is 250 mm by 250 mm by 185 mm.

2) DMG MORI Ltd has also developed a hybrid machine to add additive

manufacturing capability into a five-axis milling machine bed. This

innovative hybrid-solution combines the flexibility of the laser metal

deposition process with the precision of the cutting process

• The travelling distances of the X, Y, and Z axes on the gantry are 735, 650,

and 560 mm, respectively. The rotating angles of the B and C axes (on the

base) are 120 and 360 degrees, respectively A fiber-coupled diode laser of

2000W is equipped on the machine and its wavelength is 1030 nm. The

laser spot size can be set as 3 or 1.6 mm.


3.3) Laser Plus Milling Processes

1) Posalux combi hybrid machine integrates the LASER Ultra short pulses

FEMTO technology with micromilling process for machining automotive

GDI nozzles.

• A femtosecond laser source with a short pulse down to 200 femtosecond can

avoid heat-affected zones, recasts, deposits, and is able to machine a wide

range of materials with high dimensional accuracy and good surface finish.

However, this machine is designed only for machining small products.

2) Hamuel GmbH developed the first hybrid machine, HSTM1500 , which

accommodates high speed milling, 3D scanning, 3D laser cladding, 3D

inspection, deburring/polishing, and laser marking processes.

• 3D laser cladding is essentially a welding-based 3D additive manufacturing

technique which melts metals with a laser and deposits it onto a part.

• It is applicable to all conventional welding metals, together with the focused

heat input and low dilution allowing cladding of difficult to weld material.


• The machine provides a number of combinations of sequential machining

processes to serve different purposes. For example, a combination of 3D

inspection, 3D scanning, laser cladding, and high speed milling can be

used to remanufacture a used part.

• The traveling distance of the linear axes (the X, Y, and Z axes) are 1930,

400, and 570 mm.

Fig 3. (a) Humeal HSTM1500 hybrid machine (b) A hybrid Machine Part [3]


4. Assisted Hybrid Machine Tools

• Due to the kinematic overlapping of the tool rotation with an additional

oscillation, high-performance materials, which are normally difficult to

machine.

• The low processing forces ( Force due to Vibration ) allow the production

of slim bases and result in a longer tool life and significantly reduced micro

cracks in the workpiece material.

a) ULTRASONIC 70 - ( Five axis Ultra sonic Milling machine )

• The ultrasonic energy is transferred from the ultrasonic generator to the

tool holder. It will result in the axial vibration of the tool with a high

frequency of 20-50 kHz while it rotates. The active processing energy is,

therefore, significantly reduced.

• The application focus of this machine is on ultrasonic machining of

complex geometries in high-performance materials for

optical/watch/medical industries .

• Precision mold making where high dimensional and contour accuracy as

well as surface finish of Ra < 0.0001 mm are required.


b) OptiSonic canter :-

• The machine has four benefits including high ultrasonic vibration

(20-40 kHz) ranges during the machining cycle, rapid material

removal, improved surface quality, and maximized tool life when

processing optical glass, such as BK7 and Zerodur, as well as

difficult-to-machine ceramics.

• Vibration of tool control helps to reduce the breakage chance of tool.

• Current applications involve three-axis operations for light

weighting, pocketing, core drilling, small holes drilling and deep

drilling, etc. or more complex geometries that require four or five

axial machine motions.


5. Combined Hybrid Machine Tool

• Currently electrochemical grinding (ECG ) combine Hybrid machines,

developed by Everite Ltd are the only commercial combined hybrid

machine tools that combine both grinding and ECM processes.

• ECG tool is able to process any conductive material that is

electrochemically reactive. It can produce burr-free and stress-free parts

without heat or other metallurgical damage caused by mechanical grinding,

eliminating the need for secondary machining operations.

• Like ECM, ECG generates little or no heat that can distort delicate

components.

• ECG Technology can easily machine most metals with hardness > Rc 65

such as titanium, tool steel, and CoCr and also some brittle materials

such as zirconium.

• The advantages of ECG Combine Hybrid machine process are burr free

production, low cutting force, free of heat stress, no heat affected zone,

no work hardening, no recast layer, no metallurgical damage, and faster

than EDM.


6. Design Principle of Hybrid Machine Tools

• Basically the design principles for precision machine tools, which have been proposed by McKeown Slocum, and Nakazawa are applicable to the design of hybrid machines.

• Design parameter proposed for hybrid machine tools:

1) Total design:-

• The total design principle has to be applied to evaluate all functionalrequirements simultaneously and cumulatively in order to produce anoptimum system.

2) Reconfigurable design.:-

• It will, therefore need to follow a reconfigurable design principle in the conceptual design stage to set up the machine configuration with good flexibility for different setups

3) High dynamically stiffed machine structure:-

• Mechanical machining is still the major material removal mechanism in many hybrid machining processes.

• To obtain high productivity it will require high operational frequency and control bandwidth. Therefore, like other precision machines, high dynamic loop stiffness and high damping are very important to hybrid machine tools.


4) High-accuracy and low-friction machine motions :-

• Same as other precision machines, it needs to consider the required

motional accuracy and cost when selecting bearings for motional stages.

• Currently, most hybrid machines adopt roller bearings due to the

characteristics of high stiffness, good motional accuracy, and relatively

low-cost offered by them.

5) Functional independence:-

• Multifunction is one of the major features of hybrid machining process to

be realized by assisted or combined devices or systems.

• However, any given parameter for these devices or systems must be

independently controlled, i.e., without being affected by another parameter.

6) Open architecture control system:-

• Most often hybrid machine will involve component/system with its own

controller, while an open architecture and software-based control system

will have a high flexibility for scale up or reconfiguration.

• Information such as forces, vibrations, surface finish, and dimension are

also useful feedback information to process and predict which should be

controlled .


7. Case Study of Design of Six Axis Micro Machining Tool

• The hybrid machine tool which need combine micromilling, microgrinding,

micro turning with laser machining capacities for the fabrication of 3D

microproducts and components

• The machine is required to be able to process a large variety of materials

such as plastic, ceramics, and hard metals.

• The maximum working volume is set up to be 150 mm×150 mm × 100 mm.

The targeting surface form accuracy of the machined product is better than

100 nm (for a 100 mm diameter/long workpiece), while surface finish (Ra)

for a diamond machined part is less than 10 nm.

Design of Hybrid Machine

1. Dynamic Design of Machine Structure

2. Motional Stages

3. Control System

4. Laser and Plug-in Module

5. Initial Machining Results


7.1. Dynamic Design of Machine Structure

• To accommodate the planed hybrid machining processes, such as sequential

hybrid machining (micromilling followed by laser burring and laser

polishing processes), laser-assisted machining, and future potential hybrid

machining processes, the machine is designed to be reconfigurable.

• Both principles of total design and functional independent have been

applied to design and optimize the machine configuration.

Fig 4.- Multi axis Machine Configuration [2] Micromanufacturing Lab, I.I.T. Kanpur

Design Setup

• The machine comprises of a base unit with integrates two linear X and Y

axes and one rotary (C) axis.

• The base unit attaches two vertical linear axes, one of which (i.e., Z axis)

incorporates a further rotary B axis to hold the work spindle.

• Laser head will be attached to the second vertical linear axis (W axis) to

make the laser machining operation independent of the mechanical

machining operations.

• optical probe can also be attached to the W axis through a universal

interchangeable fixture.

• Thus, the machine has six axes configured for different requirements, for

milling, grinding, turning, hybrid machining, and metrology, as shown

in figure 4.

• In order to realize mass production of 3D complicated micro parts with

high precision tolerances and good surface finish, a gantry structure is used

to link the two z axes. So the machine has a closed force loop for

mechanical machining operation and can achieve high dynamic stiffness.


• The machine base and closed loop gantry are made of synthetic granite

which offers high damping ratio, excellent thermal stability, and high

control bandwidth.

• The machining force loop is composed of a number of mass-spring blocks,

representing each flexible chain.

• Each axis is totally constrained by five degree of freedoms (DoF) and the

sixth DoF is the desired motion direction

Fig.5 - Dynamic Structure of hybrid machine Tool [2]

Spring-Damper unit

Motion of Workpiece in Y direction

Motion of Workpiece in X direction

7.2. Motional Stages

• The hybrid machine has four linear axes and two rotary axes,

• The four linear (X, Y, Z, and W) axes and one rotary table (C axis) are air

bearings with linear/rotary motor drives.

• These linear air bearings are featured with micro-recessions which provide

extraordinary stiffness.

• The materials of these four linear bearing stages are aluminum alloys

coated with anti-abrasive materials. The C axis is made of steel in order to

avoid damage or corrosion.

Advantage of Air Bearing :-

1. Low mass due to use of light metals;

2. No friction, high precision;

3. No backlash, no lead-screw errors;

4. Enable high velocity and acceleration;

5. Long bearing life;

6. Lasy to assemble and clean.


7.3. Control System

• A schematic diagram of PC-based controller for the hybrid machine

is shown in Fig ( A3200) offers a great capability to control the

built-in accessory module to recognize the workpiece and its

position.

• It is also able to adjust the position and signal to the cutter within

one system. This integration will not only reduce the setup cost but

also increase reliability

• A3200 provides interface to high resolution encoders and many

various connections for plug-in modules. All position, velocity, and

acceleration information are feed backed to a control PC through

• In control system a human machine interface (HMI) has been

developed in a customized operating environment and The

controller system provides user right management Aerotech A3200.


❖ Control System Architecture

Fig.6- Illustration of the control system architecture [6]

7.4. Laser and Plug-in Modules

1) Laser System

a) Pulsed laser:-

• It is used to manufacture microstructures or remove micro burrs which are generated by micromilling process.

• The maximum laser power is 20 W and the smallest spot size is about 15 µm diameter.

b) Continuous laser:-

• It is used for laser-assisted micromilling/grinding process.

• The maximum laser power is 200 W and the spot size is 4 mm diameter.

2) On-machine metrology systems

a) Touch probe:-

• It is used to identify the origin point of the workpiece (X, Y, and Z coordination's

• It can also be employed for single point measurement of machined components and products.

• The repeatability of this probe is better than 0.25 µm.


b) Dispersed reference interferometer (DRI):-

• It is an on-machine noncontact metrology system which is adopted to detect edges, scan profiles, and measure surface roughness of the machined workpiece.

• Its measurement repeatability is 2 nm.

c) CCD camera:-

• The CCD camera will use an LED ring light as the illumination, which isattached in front of the lens

• The camera resolution is 2592 × 1944 with a field of view of 1.44 mm ×31.07 mm. Therefore, a pixel resolution of 0.55 µm can be achieve.

d) Material handling system:-

• It is used to change workpiece. It adopts a robotic arm to upload raw materials to the hybrid machine center and remove the fabricated components after machining.

• The maximum load of the raw material is 5 kilograms.


❖ Hybrid micro machine Setup

Fig 7- The commissioned ultraprecision hybrid micro machine.[4]

7.5. Hybrid Machining Result

• A single crystal diamond milling cutter was used to fabricate the fly-eye

array with fine reflective surface on a copper disk.

• Micro-holes are machined on a nano-fiber paper by using a nanosecond

laser.

• The laser power of 0.2 W is used to obtain small focus point and lower

thermal effect zone

Fig- Micro Product by Micro milling and Laser milling hybrid machine tool [5]

8. Conclusion • Hybrid machining technologies offer great potential in enhancing

machining process capabilities in terms of machinability, productivities,

accuracy, and energy efficiency

• Currently, vibration-assisted hybrid machines have gained wide industrial

recognition and applications in precision machining hard-to-machine

materials

Development and industrial implementation of hybrid machine tools

1) Multibody dynamics analytical tools

2) Multiscale and multiphysics simulation software

3) Reliability design

4) Sustainable design


9. Reference[1] W. Chang, W. Zhong, F. Ding, F. Wardie, X. Luo, Development of a compact

ultraprecision six-axis hybrid micro-machine, in 2017 World Congress on Micro and Nano Manufacturing, 2017

[2] Mikrotools, Hybrid µEDM. [Online]. Available: http://mikrotools.com/hybriduedm/hybriduedm-introduction/. [Accessed: 12-Nov-2017].

[3] HAMUEL, Hybrid manufacturing. [Online]. Available: http://www.hamuel.de/en/produkte/hstm/hybrid/index.php. [Accessed: 12-Nov-2017].

[4] DMG MORI, ULTRASONIC 70. [Online]. Available: https://uk.dmgmori.com/products/ ultrasonic/ultrasonic-universal/ultrasonic-70. [Accessed: 12-Nov-2017].

[5] S.Z. Chavoshi, X. Luo, Hybrid micro-machining processes: A review, Precis. Eng. 41 (2015) 123.

[6] Hybrid Machine Tool Design

Xichun Luo1, Wenlong Chang1, Wenbin Zhong1 and Frank Wardle2 1University of Strathclyde, Glasgow, United Kingdom, 2Ultra Precision Motion Ltd, Swindon, United Kingdom


Thank you


Documents

Hybrid Machine Tool Design - home.iitk.ac.inhome.iitk.ac.in/~jrkumar/download/Chapter 8 - Hybrid Machine Tool Design.pdf · EDM, wire EDM, wire electrical discharge grinding, and