Vjti Presentation

Micro Machining and Micro Cutting Operation (Micro-Milling)

Vivek B.Pansare Asst. Professor Department of Mechanical Engineering, Government College of Engineering, Aurangabad

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Overview of Presentation      

Micro Machining Various Processes in Micro Machining Need, Advantages and Challenges Surface Requirement in various systems Micro Cutting operation Effect of Various Parameters in Micro-Milling

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Micro Machining Methods

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Dimensional Magnitudes of Different Processes

• Photo fabrication and etching techniques and other lithographic methods can cover dimensional magnitudes of atomic level and extreme precision compared to micromachining using machine tools. 4

Engineering Applications of Micro Machining Sr.No.

Field of applicaiton

Application

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Mechanical

Mechanical watch parts, machine tool bearings, gears, rotary compressor parts, ball and roller bearing, precision draw wire , In jet nozzles, aerodynamic bearing

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Electronic

Electrical relays, resistors, condensers, silicon wafers, thermal printer heads, quartz oscillators, thin film pressure transducers, magnetic memory bubbles.

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Optical

Lenses, prisms, lens holders for cameras and microscopes, precision lenses, optical fibers and connectors, laser polygon mirrors, elastic deflection mirrors.

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Micro Machining Process Physics •Homogeneous & Isotropic Machining •Anistropic Machining Tool Based Micro Machining •Development of Miniature Machine Tools for Multiprocess Machining •Micro Fabrication Nano Surface Generation •Electrolytic in Process Dressing Grinding 6

Surface Requirement in Various Fields    

MEMS Biomedical System Light and X-ray optics Chemical Systems

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Micro Cutting Operation Challenges for Micro Machining

• Appropriate machine tool which is capable of performing

multiple micro machining processes in a single set up • Developing new generation of machine tools designed

specifically for micromachining • Adapting existing machine tools to handle micro machining

task • Investigating the mechanics of micromachining: This

includes such factors as cutting forces, depth of cut, relation between feed and chip ejection and cutting tool edge radius • Development of metrology for on-machine measurement

and in process monitoring of the process as well as the tool status 8

Micro Cutting Operation Advantages of Micro Machining • They do not require various expensive set-ups of lithographic methods •They can produce micro components cost effectively •Process is suitable for accommodating individual components rather than large batch size •Ability to monitor the in process quality of component so that problem can be corrected during fabrication •It is capable of 3D free- form surfaces •It can process a variety of metallic alloys,

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Various Parameters in Milling 

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Cutting Speed (V) = Π d N / 1000 m/min

Feed per revolution(S)= f/N in mm/rev Feed per tooth (Sz) = f / NZc in mm/ tooth Depth of cut (t) Milling width (b) Contact Angle (Фc) Cos(Фc) = 1 – (2 t / d)

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Continued Time of contact (tФ) tФ = cos-1 (1 – (2t/d)) / 360 N 

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The maximum chip thickness (he) = ( 2f / NZc) x √ t/d

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Maximum tangential force (Fe) on a single tooth Fe = ks bw (2f / NZc) x √t/d

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Mean tangential cutting force (Fm) = Ks. Bw. hm

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Fm = Ks bw (f / NZc) x √ t/d Surface Roughness Ra = f2 / (4dZc2 N2)

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Chip Formation & Minimum Chip Thickness

Effect of the Minimum Chip Thickness 12

Interaction between Cutting edge & workpiece

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Chip Formation & Minimum Chip Thickness

Consecutive chip formation

Intermittent chip formation

(h> hm)

(h< hm) 14

Cutting Force in MicroMachining

Factors Affecting Milling Forces 15

Cutting Force in Micro-Milling

Comparison of experimental and simulated cutting forces at 10 m/min

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Effect of Work Piece Material •The assumption of homogeneity (Grain Size) in work piece

material properties is no longer valid. •The grain structures will affect the overall cutting properties . The changing crystallography during the cutting process also causes variation in the micro cutting force and generates vibration. •an averaged constant cutting coefficient cannot be used for micro-machining applications due to tool geometry, small grain size, and non-uniformity of the work piece material. •If possible, treatment of the work piece should be considered to provide uniform micro 17 structural

Effect of Tool Edge Radius

Variation of specific cutting energy with t/r ratio for two edge radii

Variation of specific cutting energy versus uncut chip thickness for radiused edge tool 18

Tool Wear and Burr 

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The small depth of cut in micro-machining significantly increases friction between the tool and the work piece. The increased radius of the tool decreases the quality of the produced part and increases the rate at which tools fail The suppression of burr development in micromachining is very important because unlike in macro-machining. The flank wear at the end of the cutting edge is highest, and that the feed rate and cutting speed have a more significant influence over the microcutting tool than the axial depth of cut. 19

Effect of Temperature & Stress

Contours of predicted temperature for 0° rake angle

Contours of predicted stresses for 0° rake angle 20

Effect of Temperature & Stress

Contours of predictive values for 0° rake angle, 1 mm depth of cut (Temperature)

Contours of predictive values for 0° rake angle, 1 mm depth of cut (maximum shear stress) 21

Effect of Temperature & Stress

Contours of predictive values for 0° rake angle, 0.2 µm depth of cut (Temperature)

Contours of predictive values for 0° rake angle, 0.2 µm depth of cut (maximum shear stress) 22

Ploughing Force and the Size Effect

Illustration of Additional Indenting Force Componen 23

Specific Cutting Energy

Variation of specific cutting energy with uncut chip thickness at 200 m/min

Variation of specific cutting energy with uncut chipthickness at 240 m/min

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Conclusions 

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Micro Machining is today's need and having very much scope for research. Surface generation is also important. Various researchers investigate the effect of various parameters individually in micro machining still there is scope.

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Thank You

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