Hybrid Abrasive Water jet and Milling Processhome.iitk.ac.in/~jrkumar/download/Chapter 7 - Abrasive Waterjet Milling.pdf · orifice to get a high velocity jet. • Abrasive is added

Chapter 7

Hybrid Abrasive Water Jet and Milling Process

Dr. J. Ramkumar1 and Gopal Gupta2

1Professor and 2Research Student

Department of Mechanical Engineering

Micromanufacturing Lab, I.I.T. Kanpur


Index1. Introduction

2. Types of Milling processa) Conventional Milling (Up milling)

b) Climb Milling ( Down milling )

3. Type of chips form during milling process

4. Deep pocket Conventional Millinga) Best machining approach in Deep pocket Milling

b) Strategies for Deep pocket milling

c) Heat distribution of special alloy in conventional milling

5. Abrasive Water Jet Millinga) Abrasive Water Jet Milling With Masks

b) Mask-Less Abrasive Waterjet Milling

6. Advantage and disadvantage of Mask and Mask-less AWJM

7. Geometrical parameter of AWJM

8. Process parameter of AWJM


9. Abrasive Waterjet milling strategy

10. Influence of Impingement Angle

a) Forward Milling

b) Backward milling

11. Effect of Impact angle, Abrasive loading & jet water pressure

12. Hybrid approach: AWJM roughing & Conventional milling

finishing

13. Hybrid Machine Cycle

a) Abrasive Waterjet Milling Cycle

b) Conventional Milling Cycle

14. Operation of Hybrid milling

15. Conclusion

16. Reference


1.Introduction • When specially shaped features must be obtained on hard-to-

machine materials, well-established and innovative technologies

may cooperate for generating better results in terms of performance,

quality and resource saving.

• Conventional Milling:-

• Milling is the machining operation in which a workpiece is fed past

a rotating cylindrical tool with multiple cutting edge and This

milling is the multipoint cutting process.

• The material is remove in the form of small chips, The chip

thickness is minimum at start of cut and maximum at the end.

• There is less friction involved and consequently less heat generate

on the contact surface of cutter and workpiece .


• AWJM

1) Abrasive Waterjet Milling process is a water-driven grinding

process. A narrow, high-pressure jet of water carries particles

of garnet abrasive at speeds ranging from 1,000 to 2,400 feet

per second. This garnet does the cutting of Workpiece.

2) Abrasive Waterjet machining often finds work cutting hard

steels, Titanium(Ti) alloys, aerospace alloys, and other

materials that are difficult to machine through conventional

mechanical cutting process such as Grinding, Drilling,

Boring etc.

3) There is “No heat affected zone’’ form during AWJM

process and this process can able to cut Workpiece up to 200

mm thickness.


2.Types of Milling process

a) Up Milling ( Conventional Milling) b) Down Milling ( Climb Milling )

1) In Up Milling cutter rotate against

the of Feed

2) Chip thickness is minimum at the

start of cut and maximum at the end

of cut.

3) In Up milling tool wear is more

because tool moves against the feed

4) Due to upward force by tool, high

strength fixture required to hold the

workpiece.

1) In Down Milling cutter rotate in the

direction of Feed

2) Chip thickness is maximum at the start

of cut and minimum at end of cut

3) In Down milling Tool wear is less

because tool moves toward the feed

direction

4)\ Down word force act on workpiece

hence Normal Fixture required to

hold the workpiece.

3. Type of Chips form in Milling

❖ Continuous Chip ❖ Segmented Chip

1) Continuous chip occur during

machining of ductile material.

2) High rake angle of tool, High

cutting speed, Small depth of cut

and minimum friction between

tool and workpiece are responsible

for Continuous chip formation.

3) Crater wear occur due continuous

chip

4) Better surface finish occur due to

continuous chip formation

1) Segmented chip occur during

machining of Brittle & Hard material

2) Low rake angle of tool, Low cutting

speed, high depth of cut and maximum

friction between tool and workpiece

are responsible for segmented chip

formation.

3) Tearing of tool take place due to

Segmented chip formation

4) Poor surface finish & excessive wear

occur due to segmented chip formation

Fig1- segmented Chip evaluation m/c process [1]Fig1.a-contineous Chip evaluation [1]

4. Deep Pocket conventional Milling• Deep pocket cM is a typically very demanding operation because it helps to

remove the large stock of material with high surface finish quality.

• However, large overhang of the tools, up to four times the cutter diameter

(or more), are required for reaching the cavities. This fact generates high

tool deflection leading to geometrical deviations, reduced cutter stability

with increased risks of tool breakage.

• To avoid these problems, the use of the largest possible tool size and the

shortest possible overhang must be prescribed to achieve the best

diameter/length ratio and the most rigid configuration.

• Deep pockets are very common features, e.g., in aircraft components made

of Ti-alloy

Fig.2- Step Deep Pocket milling by conventional milling [2]

4.a) Best Machining Approach in Deep pocket milling

❖ To Avoid the Tool Breakage there are Different approach to Do DeepPocket machining process

1) Drill & Profiling :-

• which consists of predrillng a hole to full pocket depth, followed by acontour milling where the tool proceeds outward to mill the pocket depthin different passes.

• The use of the entire available axial length of cut allows the tool wear tobe spread over a greater tool area, prolonging tool life and loweringproduction costs

2) Layer by Layer Machining :-

• The milling tool enters the pocket with a predefined ramp angle,depending on its geometrical characteristics to avoid excessive flank wear,and follows an interpolated path to machine one pocket layer until anotherramp brings it to the next layer to mill.

3) Helical Interpolation:-

• which prescribes a programmed helix movement, typically greater than120% of the mill diameter to generate the cutter engagement.


4.b) Strategies for Deep pocket Milling

❖ Trichoidal Tool Path :-

• low radial depth of cut and high axial depth of cut that can be used to

ensure extremely fast material removal and high volumes with reduced

tool stresses, especially on difficult-to-cut materials.

• Although they typically require machining centers with high dynamics

and complex programming, Trichoidal and spiral strategies often do

better than traditional contour- and direction-parallel tool paths.

Fig3.- Trichoidal Path Fallow by Milling

Cutter [3]

Advantage of Trichoidal Path

1) Decrease Cutting Forces

2) Reduce Heat & Improve Tool

Life

3) Greater Machining Accuracy

4) Faster Cycle time and one tool

for multiple slots


4. c) Heat distribution profile during Conventional Milling of special alloy

Fig4.- Heat Transmission during the machining of steel CK-45 & Ti-64 [2]


5.Abrasive Waterjet Milling• Water is pressurized up to 600 MPa and forced to pass through a tiny

orifice to get a high velocity jet.

• Abrasive is added downstream, in the mixing chamber, and the water

stream accelerates it along the focusing tube.

• The three-phase jet (i.e., water, abrasive, and air) impacts the target

material and cuts it by abrasion and erosion.

• AWJM material removal rate approximately proportional to the jet-

workpiece material interaction time.


Types of Abrasive Waterjet Milling

• AWJM in different aspects such as geometric milling strategy, process

parameters optimization, and AWJ trajectory simulation.

1) AWJ milling with masks:-

• A mask made of hard metal allows using a spread jet and

preserving the pocket sharp edges.

2) Mask-less AWJ milling:-

• High milling depth is achieved exploiting a coherent jet.


5.a) Abrasive Waterjet milling with Masks

• The most used strategy exploits the protective action of custom-shaped

masks, since it achieves better geometric characteristics.

• The mask has an aperture that coincides with the zone to be milled, This

way the jet erodes only this portion.

• A hard metal mask is used indeed for overcoming the edge-rounding

problem: it allows separating the areas to be machined from the ones to be

preserved, thus resulting in sharp edges at the pocket top.

• The application of a mask over the workpiece allows avoiding the negative

effects of the jet motion when changing feed direction that induce high

acceleration forces and cause under- or over erosion on the part.

Fig5. AWJM with Mask coated Workpiece [4] Micromanufacturing Lab, I.I.T. Kanpur

Different Machining Method

1) Radial AWJ milling with Mask:-

• The nozzle moves radially with respect to the table rotational axis.

2) Internal Cylindrical AWJ milling :-

• The AWJ cutting head is placed radially and moves along the axial

direction of the rotating table, where the workpiece is fixture.

Fig6:- Radial AWJM mask

milling[5]

Fig7:- Internal Cylindrical AWJM mask milling [5]


Processing Steps of AWJM with Masks

Fig8. Mask Placed on Workpiece in Abrasive Waterjet milling Process [6]


5.b) Mask-less Abrasive Waterjet Milling

• Mask-less AWJM exploits the coherent jet full power at low s.o.d. (nearly 3

mm from the workpiece upper surface), Working so close to the workpiece

allows reducing the undesired edge roundness effect at the top surface.

• The focused erosive action allows a more effective material removal, thus

reducing the operation time and allowing digging deep on workpiece.

Fig9. Mask less AWJM [7]


6. Advantage and Disadvantage Mask & Mask less AWJM

AWJM with Mask

Advantage:-

1) Exact size and sharp edge

complicated shape

machining possible by

using Mask

2) Easy to operate Machine

once Mask Prepared

Disadvantage

1) High Cost of Mask and

Mask holding fixture

2) Complicated design setup

Mask Less AWJM

Advantage:-

1) High cost Mask & Mask holding fixture not required in this process

2) less operation time due simple design setup

Disadvantage :-

1) The presence of macroscopic jet footprints on the pocket bottom and the difficult management of the exiting jet.

2) The jet reflected by the eroded material is still highly energetic and therefore still able to damage the pocket walls when exiting the cavity

7. Geometrical Abrasive Waterjet Milling Strategies

• It is important to choose the most suitable parameters to produce a part that

is at least close to the finished feature.

Some Geometrical Aspects

1) pocket shape

2) jet coherence

3) trajectory shape

4) AWJ head design

5) track pitch

6) number of passes


8. Process Parameter of AWJM [8]

Process Parameter Symbol ( Unit) Parameter Value

Orifice diameter do [mm] 0.356

Abrasive Mesh Size # mesh 60/80/100/150

Abrasive Mass Flow Rate Mab

[ g/min]78/102/144/246/282/386

Water Pressure Pw 172/207

Stand Of Distance ( S.o.d ) [mm] 12/13/25/28/51

Feed Rate Vf

[mm/ min]76.2/152.4/228.6

Overlapping Pitch mm 0.254

Number Of Passes 1/2/3/4


9. AWJ milling strategies

• Both the achieved waviness and surface roughness must be investigated

when assessing the quality of the AWJ milling process in terms of produced

surface

• The focus is always to obtain pockets with a shape that is as close as

possible to the designed one. To achieve a constant pocket depth, a constant

surface exposure time to the jet is required, These aspects are extensively

analyzed together with the effects of three different milling strategies

1) Mild jet milling:- The abrasive mass flow rate reduction keeps the jet

energy low.

2) Milling with high feed rate

3) Discredited milling:-

• It is used for hard materials and consists in adding a certain amount of

abrasive to a stationary jet (feed rate =0)

• The jet plain is turned on over the workpiece, then the abrasive is fed

to the cutting head to create a cavity, Then the jet is turned off.

• After moving the machining head and turning the jet on again, another

cavity is created and so on. The final pattern creates a single larger

cavity. Micromanufacturing Lab, I.I.T. Kanpur

• Various milling paths can be used in the case of mild jet and fast traverse

jet.

• The best results are obtained with a fast jet, where the influence of the

strategies on the peak to valley distance on the pocket bottom is minimal


Innovative Abrasive water jet Milling Path cycle

Fig10.- Innovative Milling Jet path cycle [9]


10. Influence of Jet Impingement angle

a) Forward Milling

High Jet Angle AWJM Low Jet Angle AWJM

Fig11- Girt Embedment in Forward Milling with (a) High jet Angle

impingement, (b) Low jet Angle Impingement [10]

(a) (b)


b) Backward Milling

High Jet Angle AWJMLow Jet Angle AWJM

Fig12- Grit Embedded in Backward milling with (a) High Jet angle, (b) Low jet

angle [10]

(a) (b)


11. Effect of impact angle, Abrasive & Water Pressure

• Waviness and roughness are directly proportional with the impingement

angle. Indeed, as it decreases also the two output variables decrease.

• If water pressure increases and abrasive mesh decreases, the material

removal rate and the waviness increase, On the other hand, pressure and

abrasive mesh cause opposite effects on the material removal rate and on

the waviness.

• Abrasive particles embedment can cause harmful damages when

components are put in service, such as fatigue life reduction or coating

delamination of workpiece surface. Therefore, it is important to understand

the factors that contribute to this phenomenon. At low jet feed rate, the

milling strategy has an impact in the grit embedment.

• Forward Milling is used for Surface Morphology and Backward Milling is

used for to groove the surface.

• The obtained surface roughness is in the range of 1.2-1.8 μm, the waviness

is 5-170 μm, and finally the MRR ranges between 12 and 20 mm3/s


12. Hybrid Approach:-AWJM Roughening & conventional

milling Finishing

• Since the quality of AWJM in deep milling is poor, hence it requires a subsequent conventional Milling operation to generate the final pocket shape and good surface finish quality.

• The prehole generated by AWJM somehow alleviates the cM tools from the critical tool entry phase into the pocket. Additionally, it allows the tool to start working in a pure contouring operation, with large axial depth of cut, thus generating benefits for the cutting action.

• AWJM results in being able to generate high material removal rates from the workpiece at low cost and low quality on the machined pockets. On the contrary, the capacity of Conventional milling to generate high geometrical and surface quality implies high costs and low productivity associated with the use and wear of advanced tooling solutions

• By using hybrid machining of AWJM & cM, it helps to improve the manufacturability of components made of Ti-alloys and other difficult-to-cut materials.

• Deep pocket milling on a Ti-alloy is one of the best representative case that highlights the potential of the hybrid manufacturing solution.


13. Hybrid Machine cycle

a) Abrasive Waterjet Cycle :-

• For remove more material from the surface of Workpiece or more

Surface roughening .

b) Conventional Milling cycle :-

• After AWJM process finishing operation is done by conventional

milling process

AWJM Cycle

Surface Roughening of

Workpiece by using

AWJ Milling

Conventional Milling

Cycle

Surface Finishing of

workpiece by using

Conventional Milling

Step 1 Step 2


13.a) AWJM cycle

Fig13- Jet deflection during milling operation[11]

Fig – Spiral shape trajectory for AWJM

Fig14- Workpiece after AWJM process[11]


• Coming back to the AWJM operation, particular attention has to be paid not

only to the process parameters, i.e., water pressure, abrasive size, mass

flow rate, and cutting head feedrate, but also to the geometrical ones.

• Waterjet trajectory and distance between each parallel track (pitch) are two

geometrical characteristics that must be carefully selected due to their

influence on the final product.

• Single AWJ pass exploiting the jet erosion power is adopted in the

following for creating the target depth, by selecting a suitable combination

of process parameters and trajectory design.

Fig15- Visual comparison between pockets machined with different strategies [11]

(a) 7 revolutions, resulting in swallow-tail shape

(b) 6 revolutions with tuned process parameters, resulting in a more regularly

roughed pocket.

(c) 6 revolutions with higher Vf and lower mab resulting in a central thin wall


13.b) Conventional Milling Cycle

• The pocket roughed through AWJM must be finally machined using

conventional Milling.

• The first aspect to consider regards the optimal pocket shape. The pocket

that shows the best surface regularity together with the highest depth

allowing the cM tool to work in a pure contouring fashion must be

preferred.

• The efficiency of the AWJM roughing operation is investigated in terms of

total production time saving.

• The analysis is conducted comparing the machining time of the cM

operation starting from the bulk material and the one starting from the

AWJM roughed pocket.

• The final target is to find the break-even condition, in terms of total

machining time, between the workpiece entirely machined with cM and the

one machined by adopting the hybrid strategy AWJM + cM.


Step 1- Roughening of

Workpiece by

AWJM

Step 2- Finishing Slot

by Conventional milling

Final Finish Workpiece after Hybrid milling[ AWJM + c M ]

Fig16. Hybrid Milling Process [12] Micromanufacturing Lab, I.I.T. Kanpur

14. Operation of Hybrid Milling

1) AWJ Milling- Surface roughening of workpiece by using Abrasive Water

jet. ( Op. Aw1)

2) Conventional Milling –

a) An initial phase (Op. cM1), where the T1 end mill works in a pure

contouring fashion (down to a certain depth)

b) A second phase (Op. cM2), where the T2 end mill reaches the set

pocket depth

c) A third phase (Op. cM3), for finishing the pocket bottom region (T1

end mill).

Fig17- Sequence of workpiece finishing by Hybrid Milling ( AWJM + c M) [12]


❖ Deep Pocket Milling by Hybrid approach

Results

1) Obtain Surface Roughness

Ra = 1.2 – 1.8 μm

2) Waviness = 5 – 170 μm

3) Material Removal rate

MRR= 12 – 20 mm3/s

Fig18. Hybrid Milling Final Product [12]


Conclusion• Hybrid manufacturing can help to solve advanced manufacturing

challenges such as the deep pocket manufacturing in difficult-to-cut

materials like titanium, Inconel and other alloys.

• The conjunct use of Abrasive Waterjet Milling (AWJM) and cM can be

integrated in a single hybrid approach to tackle the limited machinability of

these materials with standard cutting technologies by increasing the overall

process capability.

• It is demonstrated that this complementary hybrid approach, applied to

traditional cM strategies, is more effective in time saving as the pocket

depth increases (up to 13% in a 25 mm deep pocket compared to the 19

mm deep one)

• Final finish obtain by hybrid milling is 1 to 2 μm , less chance of braking

tool because roughing of workpiece done by contact less Abrasive jet , less

machining time and high process capabilities are the advantage of hybrid

milling approach.

• Eventually, the overall hybrid process chain layout must be designed in

order to evaluate all the other aspects such as the workpiece loading and

unloading time on the machines.


Reference [1] Titanium machining guide, by Kennametal.

,https://www.kennametal.com/content/dam/

kennametal/kennametal/common/Resources/Catalogs-

Literature/Metalworking/Titanium_ material_machining_guide_Aerospace.pdf.

(2017) (accessed 17th November 2017).

[2] M. Kuttolamadom, J. Jones, L. Mears, T. Kurfess, A. Choragudi. Investigation of the

Machining of Titanium Components for Lightweight Vehicles, 2010, No. 2010-01-

0022 SAE Technical Paper

[3] New Test Results in Cycloid-Forming Trochoidal Milling István Szalóki, SándorCsuka, Sándor Sipos

[4] K.M.C. O ¨jmertz, M. Jonasson, G. Holmqvist, Analysis of surfaces produced by

abrasive waterjet milling techniques, Bhr Group Conference series publication, vol.

21, Mechanical Engineering Publications Limited, 1996, pp. 753768.

[5] M. Hashish. Waterjet pocket milling of titanium aluminide. In Proceedings of the

19th International Conference on Water Jetting, P. Longman, ed., BHR Group,

Cranfield, UK, 2008, pp. 365-376


[6] P. Miles, A. Henning. Deep pocket milling with abrasive waterjets. In

Proceedings of 23rd International Conference on Water Jetting 2016,

Seattle, WA (pp. US Waterjet Conference, Berkeley, CA, 2016, pp. 113-

126.

[7] T. Nguyen, J. Wang, N.M. Kwok, H. Li, Q.P. Ha. Predictive models for the

geometrical characteristics of channels milled by abrasive waterjet. In

Automation Science and Engineering (CASE), 2015 IEEE International

Conference on, 2015, pp. 14591464. IEEE

[8] M. Hashish. Milling with abrasive waterjets: a preliminary investigation.

(1987) In Proceedings of 4th US Waterjet Conference, Berkeley, CA (pp. 1-

10).

[9] S. Anwar, D.A. Axinte, A.A. Becker, Finite element modelling of

overlapping abrasive waterjet milled footprints, Wear 303 (1) (2013)

426436.

[10] P.H. Shipway, G. Fowler, I.R. Pashby, Characteristics of the surface of a

titanium alloy following milling with abrasive waterjets, Wear 258 (1)

(2005) 123132.


[11] P.H. Shipway, G. Fowler, I.R. Pashby, Characteristics of the surface of a

titanium alloy following milling with abrasive waterjets, Wear 258 (1)

(2005) 123132.

[12] Hybrid Abrasive Waterjet and Milling Process

Francesco Vigano `, Paolo Parenti and Massimiliano Annoni Politecnico di

Milano, Milano, Italy


Thank You


Documents

Hybrid Abrasive Water jet and Milling Processhome.iitk.ac.in/~jrkumar/download/Chapter 7 - Abrasive Waterjet Milling.pdf · orifice to get a high velocity jet. • Abrasive is added