By

Dr.Deepak Lawrence.K

Mechanical Engineering Department

NIT Calict,Kerala,India

Hot Machining and Diamond turning

ME6324:Modern Machining Processes

Laser assisted cutting

Thermal assisted cutting or hot machining

2

Hot machiningAn improvement in process capability regardingmachinability and machining quality of challenging

the application of additional forms of energy.In hybrid cutting operations, the conventionalcutting process is simultaneously supported byanother form of energy, in particular by thermalenergy (laser-induced heating of the workpiece) orkinetic energy (sonotrode-induced movement of thecutting tool).several hybrid approaches have been examined(e.g., different kinds of hot machining, cryogenicmachining, and ultrasonic-assisted machining) foreconomic machining of difficult to cut alloys andceramics

3

Laser-Assisted Cutting

4

Laser-assisted machining

5

Laser-assisted machining set-up with in-process temperature monitoring.

Laser-assisted machiningLaser-assisted cutting aims at an improvementof the machinability of challenging materials.Basic precondition therefore is a decrease inworkpiecetemperature.Investigations on nickel alloys, titanium alloys,cobalt alloys, high-strength tool steel, as well assilicon nitride ceramics approved the suitabilityfor laser-assisted cutting processes as thesematerials show a significant softening afterexceeding a material-specific temperature

6

Laser-assisted machiningDuring laser-assisted cutting, the material iscontinuously heated in front of the cutting edgeby means of a laser beam.The energy which is absorbed on the surface ofthe workpiece induces a rapid heating of thesubsurface zoneThe aim is to generate a temperature fieldlimited to the cutting zone resulting softening ofthe workpiece material in the cutting zone toimprove the process capability according tomaterial removal and tool life

7

laser-assisted cutting

Development of temperature field during laser-assisted cutting

8

laser-assisted cuttingDuring laser-assisted cutting of ceramicmaterials, the laser heating causes theplastification of an amorphous glassy phasewhich is constituent of the microstructureIn silicon nitride ceramics, for example, theglassy phase surrounds the silicon nitridecrystals on the grain boundaries and shows aviscoelastic behavior at elevated temperatures.Thus, heating and plastification of the glassyphase effects a reduction of deformationresistance and a local softening of the materialin the shear zone

9

LAM benifits

The achievable surface qualities and tolerances are comparable to groundceramic products (Ra 0.2 0.3 µm).Laser-assisted milling of Inconel 718 yielded a substantial improvement ofmachinability. LAM with the material temperature elevated to 520ºC resultedin 40-50% reduction in cutting force, over 50% reduction in tool chipping andtwo fold improvement in surface roughness.

10

Single Point Diamond Turning (SPDT)

SPDT

12

SPDT

13

SPDT

14

Diamond turning or single point diamond turning (SPDT).

Precision applications like optical mirrored lenses for opticalsystems require surface finish in the range of tens of nanometers and form accuracies in the sub-micron range.Ultra-precision machining is one of the machining processesmeeting this requirement.For some applications, for example, soft metals such ascopper and aluminium which are difficult to machine bygrinding, lapping and polishing, diamond turning becomes aneconomic and sometimes unique process for these specificcomponents to meet the requirement since it producesoptical surface finish without the need for additional grindingand/or polishing operationsThe cutting tool for most of the ultra-precision machiningapplications is exclusively single crystal diamond (natural orsynthetic). Therefore, the process is also called diamondturning or single point diamond turning (SPDT).

15

Diamond turningFor the fabrication of ultra precise parts, mono

For example, modern optics fabricationprocesses like plastic injection molding orprecision glass molding require ultraprecisemolds with optical surface qualities andcomplex shaped geometries

16

Diamond turning

Diamond turning machines are commonly usedto manufacture rotational symmetric parts ofnon-ferrous metal, polymers (especially PMMA)and brittle hard materials such as germanium,silicon and others

17

Diamond tool

18

The single diamond tool has a trigonalpyramid shape with the rake and theincluded angles 0°and 60° respectively

Precision machining manufactures

Industrial precision machine tools with micro cutting capability: (a) Kernmicro. Copyright KERN Microtechnik GmbH; (b) Sodick AZ150. Imagecourtesy of Sodick, Inc.; (c) Fraunhofer IPT Minimill. Reproduced from [6]; (d)Makino Hyper2J. Image courtesy of Makino; (e) Kuglar MicroMaster MM2.Image courtesy of Kugler GmbH; (f) Fanuc ROBOnano. Images courtesy ofFANUC; (g) Precitech freeform 700 Ultra. Image courtesy of AmetekPrecitech; (h) Moore Nanotech 350FG. 19

Material Perspectives-SPDTSome materials are not suitable for diamond turning dueto excess chemical tool wear.Soft metals are generally diamond turnable while hardmetals such as ferrous materials, titanium and chromiumare not diamond turnable.Pure nickel is not diamond turnable although electrolessplated nickel is an exception

chemical wear of diamondtools is determined by the presence of unpaired delectrons in the material being machined. Thosematerials are composed of elements without unpaired delectrons (such as copper and silver) and are predicted to

turnable

20

(Paul et al. (1996) Chemical aspects of tool wear in single point diamond turning, PrecisionEngineering, 18, 4 19)

Material Perspectives-SPDTFor materials composed of elements with only oneunpaired d electron (such as cerium and platinum)the implication is that, although there should besome chemical wear, the wear rate may be lowenough to make machining cost effective if there isa particular high-precision need for a particularapplication.Materials with many unpaired d electrons arepredicted not turnableSilicon and germanium are diamond turnablealthough great care should be taken on selectingcutting parameters to avoid excess tool wear.Acrylic, polycarbonate and nylon have been foundto be diamond turnable without difficulty

21

Diamond cutting of ferrous metalsDiamond cutting of ferrous metals is still a subjectof current research.During the last years, two different approacheshave been proposed to overcome the problem of

One approach is the reduction of tool wear byultrasonic vibration cutting, in which the contactbetween the cutting edge and the workpiecematerial is interrupted periodically at a highfrequency.Another approach is nitriding of the steel substratebased on the discovery that nitrided steel can bediamond turned without appreciable tool wear

22

Common materials with good diamond machinability

23

Application of micro-structured surfacesMicro-structuredsurfaces are capable ofperforming manydifferent functions andhave found applicationsin optics, MEMS,biomedical devices, heattransfer and coolingdevices, and so on

Diamond cutting, isunique and cost effectiveand hence central to theproduction of a largeproportion of micro-structured surfaceseither through directionproduction of the part orthrough making a mould

24

Diamond turning applicationsProducts, which require diamond machining for thefabrication of at least one of their components, are computermice, DVD player pick-up systems, camera lenses, barcodescanners, reflective tapes, and contact lenses.All these components are mass produced by injection orcompression molding or in the case of glass lenses by hotisostatic pressing, relying on the quality of diamond-turnedmetal molds.Diamond-machined optical components are needed forprojection systems, displays, laser scanners, sensors,scientific instruments, medical and defense equipment, laserbeam guiding, illumination systems, etc.The surface finish of these products is between 1 and 10 nmRa, depending on machining conditions and on materialproperties, and the achieved figure accuracy ranges between0.1 und 1 µm depending on size, shape, and geometricalcomplexity of the workpiece

25

Diamond turning

26

Thank You.

27