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© WZL/Fraunhofer IPT

Advances in milling Technologies: from conventional milling to HSC

Benedikt Gellissen

Fraunhofer-Institut für Produktionstechnologie IPT

International Seminar: Application of new technologies in the metal mechanic sector

Joinville, Brazil, September 2011


Outline of the presentation

What is the motivation for advanced milling technologies1

What is required to realize a successfull implementation of HSC?2

Advanced roughing possibilities3

Improved finishing results due to intelligent CAM-Systems and tool adaption4

Conclusion5


Importance of the milling technology for the molding industry -Comparability of tool types and use of technology

Injection moulding

Special featuresn Surfacen Precisionn Filigree

Solid forging

Special featuresn Material (Temperature)n Edge zonen Precision

Deep drawing

Special featuresn Surfacen Precisionn Geometrie

Stamping and bending

Special featuresn Materialn Precisionn Surface

Focus free-form surfacesPrismatic toolcomponents

Importance

Milling

Turning

Grinding

Sink EDM

Wire EDM

Process

Importance

Milling

Turning

Grinding

Sink EDM

Wire EDM

Importance

Milling

Turning

Grinding

Sink EDM

Wire EDM

Importance

Milling

Turning

Grinding

Sink EDM

Wire EDM

Process Process Process


Driver »tool steel«: Improved materials for the industryImpact of the defect size on the bending resistance

Source: Böhler

4

3

2

1

100 200 300 400 500

d

Kconst σ 1c

b =

powder metallurgical

conventional forging

conventional founded

σb[kN/mm2]

defect size [µm]

bend

ing

resi

sten

ceAims

n Reaching an homogeneous structure

n Low corn and carbide size for improved wear resistance and strength

n Reduction of material anisotropy in case of manufacturing


Melted steel } Inhomogenity} Segregations} Carbide size < 200 µm

Processing} Direct dependency of

durability and hardness} Big carbides provoke

breakouts

50 µm

Developments in tool steel

50 µm

Powder metal steel} Homogeneous structure} Nearly no segregation} Carbide size < 3 µm

Processing} Problem: hardness and

tenacity at the same time} Cutting edge build-up

possible

Spray formed steel} Nearly no segregations} Carbide size < 30 µm} High-carbide alloy

Processing} Homogeneous structure leads

to better accuracy} More abrasion because of

spreaded carbides

50 µm50 µm

X155 CrMoV 12 1 mit 62 HRC, different manufacturing processes; Source: Schneider, 2002


Motivation for complete hard milling processes:The tool manufacturer can “deliver” time

minimum throughput time

Tool componentdevelopment

Tool manufacturing

SOP

Product development

n In this time slot only the tool maker defines the Time-to-Market!

n During this period only necessary production steps are allowed which can not be standardized

n The hard milling process shortens the overall process and therefore the total lead time

Design freeze

Stop of changes

Tool detail-construction


Material

n Powder metallurgical high-speed steel S 6-5-3 PM

n Hardness 65 HRC

Demands

n Surface roughness Ra 0,3 µmn Minimum inner radius 1 mm

Process

n Complete machiningn Simultaneous five-axis-roughing and

-finishingn Solid carbide and CBN toolsn Complete hydrostatic five-axis-

machinen Process time: roughing 6h, finishing

5h

n Complete hard milling process of standardizes blanks and shortens process chains

Importance of CAX-processes in tool manufacturing







Conclusion5


In the future: Growing importance of five-axis-processes in tool manufacturing

Development in tool manufacturing

100 % rate of milling processes

75

50

25

2000199019801970 1996

Copy milling

Measuring point/ grid lines 5-Axis 5-Axis

100

% C

NC

-inte

rsec

tion

HSC-Finishing3-Axis

3-Axis Roughing/Finishing

5-Axis-HSC

2010

Stand 1996forecast 2007


Importance of HSC<< declining growing >

0

15

30

45

60

75%

Technology often develops evolutionary – but not always predictable

Actual developmentInterview of 2002

0

5

10

15

20 %

rate

of H

SC

-mill

ing

in

man

ufac

turin

g

Years04/05 06/07 08/09

Importance of sink-EDM< declining growing >

0

15

30

45

60

75%

0

5

10

15

20 %

rate

of s

ink-

ED

M in

man

ufac

turin

g

Years04/05 06/07 08/09

Source: Interview of companies (Euromold 2002 and benchmarking database of awf)


Key-turn solutions quickly get into manufacturing

Source: Benchmarking database of awf

0

10

20

30

40

50

60

70 %

Ava

ilabi

lity

of p

oten

tial

auto

mat

ion

200820092010

»Milling«»Sink EDM«

»WireEDM«

< declining growing >Importance autom. process chain

0

15

30

45

60

75%

< declining growing >Importance autom. process chain

0

15

30

45

60

75%

CA

M-p

rogr

amm

ing

(mill

ing)

01530456075%

Years04/05 06/07 08/09

Actual development Interview of 2002


Process features of cutting process steps

Roughing (HPC)

Aim

n maximum metal removal rate Qt = vf • ae • ap

Process features

n Mechanical load limit for tools and cutting machine

n Use of big tool diameters and resistant cutting materials

n Three-axis machining

n (Rth = 0,1-0,5 mm)

Pre-finishing

Aim

n Machining a even stock allowance for the finishing step

Process features

n Critical process status because of uneven allowance

n Use of ambitious process strategies

n Use of different tool diameters

n (Rth = 0,05-0,1 mm)

Finishing (HSC)

Aim

n maximum metal removal rate At = vf • ae

Process features

n High dynamic and thermal stress for tool cutting materials and

n Use of small tool diameters and thermal resistant cutting materials

n Application from Pre-finishing programs for the finishing with reconfiguration

n High data volumes of theNC-programs

n (Rth = 0,002-0,005 mm)


What is HSC?

Engagement conditions

n Finishing process

n Low chip cross section

n High speed (factor 2 bis 10)

n low cutting forces

Work piece

n Very good surface quality for curved areas

n High variety of materials, hard materials

Machine requirements

n High spindle speed

n High feed rate and acceleration

Tool

n High-performance coating (cutting speed)

n High temperature resistance of the cutting edge

n Low tool heat influencespeed vc

Tool life travel path

Cutting forces

Surface quality

Metal removal

Influence of speed:

Source: Schulz; Hochgeschwindigkeitsbearbeitung


Influence of cutting speed on cutting temperaturesvc = 25 m/min JSS= 325°C

-10 0 20

-10

0

20

µm

µmvc= 150 m/min JSS= 690°C

-10 0 20

-10

0

20

µm

µm

vc = 300 m/min JSS= 910°C

-10 0 20

-10

0

20

µm

µm

vc = 600 m/min JSS= 1195°C

-10 0 20

-10

0

20

µm

µm


-10 0 20

-10

0

20

µm

µm


-10 0 20

-10

0

20

µm

µm

Material: X180VCrMo951PM (57 HRC) Source: Dissertation Steffen Knodt


Qualitive influence of different process parameters

time and costs quality barrier

Material removal rate [Q]

Tool life time [Lf]

surface [Rz]

precision Cutting forces [F]

Cutting speed [vc]

Cutting depth [ap]

Cut width [ae]

Feed rate per tooth [fz]

Number of teeth [Z]

4

X

2D

2D

R22

TTth -÷

øö

çèæ-=

Definitionen

n Spindle capacity:P = F * 0.5 * D * n

n Theoretical roughing depth:

n with X: fz or ae


Basic factor: Process control

300

20

100

140

180

0 50 100 150 200 250

Cutting speed vc [m/min]

60

350

220

mac

hin

ed a

rea

[cm

²]

Initial situation

coated carbide material

fz= 0,01 mm = const

Tool: Torus D3R0,5, CBN; Werkstoff: 1.2343, 55HRC



300

20

100

140

180

0 50 100 150 200 250


60

350

220

mac

hin

ed a

rea

[cm

²]

Initial situation


fz= 0,01 mm = const

Tool: Torus D3R0,5, CBN; Werkstoff: 1.2343, 55HRC

CBN: Optimum cutting speed is fz= 0,01 mm



300

20

100

140

180

0 50 100 150 200 250


60

350

220

mac

hin

ed a

rea

[cm

²]

Initial situation


20

100

140

180

0,01 0,008 0,006 0,004 0,002

Feed rate per tooth fz [mm]

60

220

mac

hin

ed a

rea

[cm

²]

0

selected point

vc= 200 m/min = const

fz= 0,01 mm = const

Tool: Torus D3R0,5, CBN; Material: 1.2343, 55HRC

Optimum cutting speed is fz= 0,01 mm



300

20

100

140

180

0 50 100 150 200 250


60

350

220

Mac

hin

ed a

rea

[cm

²]

Initial situation


20

100

140

180

0,01 0,008 0,006 0,004 0,002

Feed rate per tooth fz [mm]

60

220

Mac

hin

ed a

rea

[cm

²]

0

Selected point

vc= 200 m/min = const

fz= 0,01 mm = const

Tool: Torus D3R0,5, CBN; Material: 1.2343, 55HRC

Optimum cutting speed is fz= 0,01 mm

n Studies show: Optimum results can be realized in a very little process windown Little process changes lead to significant losses in terms of economical efficiencyn To realize complex parts you need to use five-axis motion control to fulfill the demand


Technological core aspects in milling

Milling tools & Coatings Technological orintated NC-Programming

Machine & Controling

n Abrasions-resistance

n Geometrical variety

n Precision

n Stability and process reliability

n Technological knowledge

n Harmonic tool path

n Stock allowance

n Easy and quick operation

n Implementation of technological background concerning motion control

n Precision and repetition exactness

n No vibrations

n Harmonic motion control

n Low wear

n Reliable automation

Source: Hembrug







Conclusion5


Technological optimized process planning – process modeling Multi-axial roughing of cavities

Track geometrie

n circle, ellipse, spline, …n track radius, infeedn Epizykloids,

hypozykloids

Tool geometrie

n Diameter, twist, number of teeth,

n cutting blade geometrie

Process parameter

n Feed rate per tooth, cutting speed

hsp

WZ-Rotat ion

Zustellung je Kreisbahn ae

WerkzeugHüllkurve

Werkzeug-mit telpunkt

n-teerzeugt Kontur

n+1-teerzeugt Kontur

Kontakt-zonen-winkel Fc

Rückwärt igeBewegung

Kreisbahn desWerkzeug-mit telpunktes

WZ-Rotat ion

Zustellung je Kreisbahn ae

WerkzeugHüllkurve

Werkzeug-mit telpunkt

n-teerzeugt Kontur

n+1-teerzeugt Kontur

Kontakt-zonen-winkel Fc

Rückwärt igeBewegung

Kreisbahn desWerkzeug-mit telpunktes

Fc

Asp 0

0,01

0,02

0,03

0,04 Chip thickness hsp [mm]

Wrap angle j [°]110 120 130 140 150 160 170 180

fz(increasing)

0

0,01

0,02

0,03 Chip thickness hsp [mm]

ae

Wrap angle j [°]100 120 140 160 180

(increasing)


Technological optimized process planning – ImplementationRoughing of hard materials

A maximum uniformity is given by a minimum variation of the cross section.

Wrap angle [°] ap [mm]

unifo

rmity

[-]

Helix angle l [°]

4

5

6

35,2

28,1

23,4

15

70,3

56,3

46,9

30

16,332,6

13,126,1

10,921,8

45

9,418,8

7,515,1

6,312,6

60

5,410,9

4,48,7

3,67,3N

um

ber

of

teet

h z

[-]

Optimal depth of cut fortool diameter = 12mm

Depending on material L/D relations of maximum 1,5 – 2 were reached.As a consequence there are limitations for the choice of the geometry of the optimal tool.


Technological optimized process planning – ImplementationRoughing of hard materialsn Tool JH170

n vc = 90 m/min

n ae = 0,25/ Fc = 30°

The metal removal rate is proportional to the cut depth, but there is no linear behavior of the cutting volume concerning cutting depth.

Tool life volume [cm³]

Tool life volume

Material removal rate

Material removal rate [cm³/min]


Technological optimized process planning – Implementation Roughing of hard materials

Tool Jabro Tools VHM JH120 / *JH170Diameter D=10mmTeeth Z=4

Slot millingSlot width 10 mmV‘ = 1,9 cm³/minap = 1 mm

Circular milling U=30°Slot width 13 mmV‘ = 2 cm³/minap = 10 mm

Material 1.2379S 600S 790 PMS 290 PM

40

80

120

160

200

240 µm tool flank wear land (VB)

10 20 30 40 50 60Machined volume [cm³]

Slot milling

40

80

120

160

200

240 µm tool flank wear land (VB)

10 20 30 40 50 60Machined volume [cm³]

Circular milling

*

200400600800

10001200140016001800

Fxy [N]

U/ae [°/mm]vc [m/min]

fz [mm]

V‘ [cm3/min] 1,9 0,58

ap [mm]

Material S600 S290

1,9

10030°

10

0,03

S790

60100

0,060,06

S600 S290S790

0,03 0,03 0,02

JH170JH120JH120

20311

50 50

JH1201,9 1,9 1,53

10mm


Further research and OutlookProcess verification on different workpieces

n The circular milling was successfully applied on the complex slot geometries of a Blisk workpiece made of Ti-6Al-2Sn-4Zr-6Mo (b-processed)

– Large increase of tool life

– Different algorithms for the optimization of the tool paths– Nearly constant engagement angle of ΦC = 41°







Conclusion5


Five-Axis-Finishing with torus milling tools:technological basics

Aimsn Economic process due to

high axial depth of cutn High surface qualityn Optimum process

conditions– Contact length– Cutting speed

a

a bZZb,a

Xb,a= Xß

Yb,a

bYß=Y

Source: Zander, Altmüller

Example for the optimal coordination of angle and lead angle

Tool radius RF = 20 mmCutting plate radius rp = 5 mm

Tilt angle a

Lead

ang

le b

24degree

12

6

012 degree6 240

Contour radius r (simple curved)

50 mm100 mm200 mm500 mm

z

a cos(b)

XZ

Y

cos(a)

q

b

z

1

r

úúú

û

ù

êêê

ë

é

÷÷ø

öççè

æ

×--××=

2

, 211sin

eff

eeffnth r

arR b

Theoretical roughness normal to feed rate direction


Process exampleUse of torus mill in the Five-Axis-Finishing

Conventional Five-axis

n Three-Axis-Process with ball-end mill, ae = 0,1 mm

n Process time ca. 120 min

n Reached surface quality ca. Ra = 1 µm

n Simultaneous Five-Axis-Process with torus mill, ae = 1 mm

n Process time of the surface ca. 25 min

n Reached surface quality ca. Ra = 0,25 µm

Machining task

n Rotating slider for a injection mould

n Surface has to be polished after process

n Material: 1.2379, 62 HRC


Development of process technology for hard millingIdentification of optimum milling parameters for the systematic orientation of coating systems

Motivation

n Complex and challenging material profiles require specific, concrete and stable process parameters

n Variation of cutting parameters with numeric analysis of cutting to affiliate mechanic and thermal applied load of the cutting edges and with it abrasion, impact and temperature resistance

Aim

n Raising of chip thickness Asp(φ) , max. cutting thickness hsp(φ), cutting width bsp(φ) and reduction of cutting length lsp(k) to reduce abrasive wear

n Necessary condition φ → min

Solution

n Systematic identification of optimum process windows with numeric analysis

n Implementation of analog surveys with identified parameter windowbsp(φ)

Seite 30© WZL/Fraunhofer IPT© WZL/Fraunhofer IPT

bsp(φ)

1

2

bsp(φ)

3

Hypothesis

n Coatings protect the substrate from thermal but not from mechanical applied loads

n A minimum applied load on the cutting edges comes along with…

- the most possible cross section area Asp(φ)1, which distributes the normal pressure towards the edge with an even cutting force amplitude and a minimized total load on the tool while reaching a high productivity due to high material removal rate [3]

- the most possible unformed chip thickness hsp(φ) and width of undeformed chip thickness bsp(φ), to ensure a high cross section area [2]

- And the smallest possible chip length lsp(k) or wrap angle φ, to reduce the impact time and therefore minimize the abrasion impact on the cutting edge

Development of process technology for hard millingIdentification of optimum milling parameters for the systematic optimization of coating systems


Modification of parameters

n Integration of tilt angle Theta (QFB) and Psi (YB) which become additional degrees of freedom due of the five-axis-process

n …only with five-axis-process the optimum cutting parameters can be defined and configured

n Variation of…

- Feed rate per tooth fz = 0,01 … 0.1 [mm]

- Cutting depth ap,n= 0.01 … 0.1 mm

- Axial depth of cut ae,n = 0.01 … 0.1 [mm]

- Theta QFB = 25 … 50 [°]

- Psi YB = 0 … 90 [°]

n Constant Parameters…

- Cutting speed vc,eff= 90 [m/min]

- Tool diameter D = 6 [mm]

- Number of teeth z = 2 [-]

bsp(φ)

Development of process technology for hard millingIdentification of optimum milling parameters for the systematic orientation of coating systems


Challenges

n ball end mill tools can machine nearly every component geometry

n Due to ever-changing machining situation is this essential for the finishing process

Problem

n Different contact conditions in chip formation of three-axis-cutting with ball mill tool

n »Freedom of geometry« can lead to unfavorable contact conditions in terms of process technology

Solution

n Five-axis-processes allow to influence the process parameters actively, even with complex geometries

n To use additional degrees of freedom »favorable« and »unfavorable« process parameters need to be known!

Source: IPT

Five-axis-process in tool manufacturing


10 µm

10 µm 10 µm

10 µm

ProcessexampleStamp for colt forming operations

Quelle: IPT


Application

n Cold massive forming: great significance of surface quality for the lifetime of the tools

n Continuous and fast process chains are demanded

Hart milling processing

n 5-axis machining offers technological advantages

n Optimal availability and stable process management

Objectives

n Transfer and establishment of research results in hard milling in practice

n Exclusively through the use of simultaneously 5-axis hard milling machining a holistic process stability can be guaranteed.

n Component spectrum–Complex component geometry–Bad quality of the CAD-data

n Economic aspects–Maximum process performance and robust processes –Optimized component- and clamping devices–Intuitive CAM- Programming

Process- and CAM development –Machining example: cold massive forging die

+ =

Source: IPT & ModuleWorks GmbH, Aachen


Hard milling: Net based tool path calculation»automatic programming: Three axis – five axis «

Programmingn Net-based conversion of 3-axis

tool path into 5-axis path motion

n Reduction of programming effort

n Bo support structure is required

n Less dependent on the CAD quality

+ =

Quelle: ModuleWorks GmbH, Aachen


Result

n Enhanced surface quality

n Harmonic tool path motion reduces visual defects caused by the axis

n Ra < 0,15 µm

conventional Net-based

Hard milling: Net based tool path calculationCold massive forming die

Source: IPT


Hard milling: Net based tool path calculationCold massive forming die

n Ra,quer = 0,16 µm

n Ra, längs = 0,12 µm





n Ra,quer = 0,2 µm


Source: IPT


Questions

n What measures can increase the productivity of hard milling processing significantly?

n How can the required flexibility be retained?

n How is the machining mechanism influenced by the form of the operation zone?

Productivity

n Maximum adaption of tool geometry for surface properties

n Use of big line width to reduce the required process time

n Large ration of rv/rh, for end mill rh/rvà ¥

Geometric flexibility

n Use of milling tools with „universal“ geometry

n Low ratio of rv/rh, for ball head milling cutter rv/rhà 1

source: IPT

Fle

xib

ility

Productivity

Barell tool

End mill

Ball end mill

rv

rh

Geometry adaptive milling tools


Solution - combining both characteristics ofball end mill and end mill

Geometry adaptive milling tool ››barrel tool‹‹

§High process flexibility while simultaneously high productivity

§Production of complex free form surfaces and ruled geometries

1

2

3 Torus-/End mill

§High productivity with severely limited flexibility

§Only simple curved surfaces can be machined

Ball end mill

§Maximum flexibility and least productivity

§Fast programming due to simple geometry

Milling tool technology: geometric flexibility vs. productivity

Fle

xib

ility

Productivity

Barrel tool

Torus

Ball end mill1

2

3

workpiece

Source: IPT

Geometry adaptive milling tools







Conclusion5


Summary

n Due to simultaneous 5-axis processes - reduction of critical time-to-market lead times

n Utilization of latest machine equipment and milling tools for the optimization of the holistic process performance

n Further simplification of the CAM-programming

n Addressing the correct process windows and ensuring constant processes is essential for the further introduction of simultaneous 5-axis processes

Outlook

n Further implementation tool contact situations and process forces into the tool motion planning

n Optimized process planning via CAM integrated simulation and implementation of specific process knowledge

End of the journey?Hard milling

Source: IPT & ModuleWorks GmbH, Aachen


Your contact to Fraunhofer IPT

Dipl.-Ing. Benedikt Gellissen

Fraunhofer Institute for Production Technology IPTSteinbachstraße 17, 52074 AachenPhone: +49 241 89 04-256Fax: +49 241 89 04-6256Mail: [email protected]


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