Roughing vs. finishing

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1 Finishing methods

2 Roughing vs. finishing Roughing removing material as fast as possible, without special demands on surface and low demand on precision high Q, high IT, high Ra Finishing making final surface with wanted properties. Remowing residual material, improving geometrical and dimensional tollerance low Q, low IT, better Ra

3 GRINDING the finishing method with very wide use area; grinding wheel is a multiple cutting edges tool consisting from abrasive grains and a bonding material; grinding can be likened to the milling process 3

4 Grinding process t chip thickness d depth of cut 4

5 Grinding wheels Abrasive grains: Al 2 O 3 SiC cbn diamond tough most common material for: steel, Fe alloys hard for ductile metals (Al, brass, stainless steel) and brittle metals (cast iron) for fine grinding dtto GRAIN SIZE (grit): 0,003 3 mm 5

6 Grinding wheels Bonding material: vitrified bond clay + ceramic materials ( baked ) silicate bond Na 2 SO 3 metallic bond bronze rubber bond (for cbn and diamond) (for cbn and diamond) 6

7 Grinding methods A) surface grinding plain flat surfaces - horizontal grinding horizontal spindle - vertical grinding vertical spindle B) cylindrical grinding rotational surfaces 7

8 Surface grinding 8

9 Surface grinder 9

10 Grinding methods A) surface grinding plain flat surfaces - horizontal grinding horizontal spindle - vertical grinding vertical spindle B) cylindrical grinding rotational surfaces 1. external grinding - centre grinding a workpiece is rotated between centres - centreless grinding a part is supported by a grinding wheel and a regulating wheel 2. internal grinding 10

11 Cylindrical grinding a) external b) internal 11

12 External cylindrical grinding Feed motion types in centre grinding: a) traverse feed b) plunge cut 12

13 Center grinding with an inclined in-feed an operation example 13

14 External centreless grinding 14

15 Internal grinding traverse feed 15

16 Internal grinding plunge cut 16

17 Grinding tolerances and surface finish Type of cut IT Ra roughing ,8 6,3 finishing 5 7 0,2 1,6 fine finishing 3 4 0,025 0,4 17

18 Finishing methods With material removal generative methods (fine machining, honing, superfinishing, lapping) Without material removal forming methods (glazing, blasting, tumbling, polishing)

19

20 1. Fine machining Machining process Turning or milling with depth of cut close to minimum depth of cut Fine cylindrical of flat surfaces

21 Fine machining Tools Turning high precision inserts (PCD - alluminium, coated SC) Milling special shaped inserts, large diameter facing milling heads

22 Fine machining - examples Video 001

23 Fine machining properites Low depth of cut Ap = 0,01 0,05 mm High cutting speeds up to 1000 m.min-1 High cutting forces, high spindle load IT = 4 6 Ra = 0,1 0,4

24 2. Honing Abrassive process Small amout of material is removed by honing stones Mainly internal holes (bored and ground holes)

25 Honing Tool: Honing head with honing stones Honing stones: Made of abrasive material Adjustable Seated on pushing springs

26 Honing Material of stones Any abrasive material can Be used for a honing stone - Same materials like grinding stones (corundum, SiC, CBN, PCD) - more precise shape, smaller grain (10-50 μm) - Cutting fluids are used for lubrication

27 Honing Available as tool for CNC machines Various diameters (4-40 mm) Spring mounted (to adapt to hole) Movement with CNC cycle Small tools (1-20mm)

28 Honing process mechanics Honing head is 1) Rotating reciprocitive 2) Oscilating up and down 3) Honing stones are pushed to the surface Video 002

29 Honing process mechanics Two speeds combined together make unique movement and special form of tool path.

30 Honing machine tools Special horizontal or vertical honing machines

31 Honing machine tools CNC horizontal or vertical honing machines

32 Honing - examples

33 Honing - properties Improving the geometrical accuracy (IT) mainly Setting certain surface pattern (lubrication) Expensive and time consuming IT = 3 to 6 Ra = (0,025)0,1 0,4

34 3. Superfinishing Abrassive process Small amount of material is removed by moving superfinishing stone Both cylindrical and planar surfaces

35 Superfinishing Tool: Superfinishing stone Has the negative shape of the machined surface (or it can be flat for large surfaces) Abrasive material again fine grained (to 20 μm)

36 Principle The superfinishing stone is sliding on a layer of lubricant on the surface and pushed by certain force 1) The surface is rough peaks looking out of the lubracant layer 2) The stone cuts the peaks the surface for lubricant is bigger, more sliding 3) The stone cuts all peaks, no more material removal

37 Superfinishing - surface

38 Superfinishing - methods Cylinders Cones Flat surface Shape surface

39 Superfinishing - properties Not improving the geometry!!! (IT remains) Lower speeds and force than gringing or honing Method Cut. Speed (m.min-1) Move Presure (MPa) Grinding None (infeed) Honing superfinishing cycles (length of hole 150 mm) cycles (1-5 mm) 3,5 7 0,02 0,07

40 Superfinishing - properties Ra = 0,025 0,1 Lubricant is used to carry away chips and minimize heat (deformation) kerosene is used

41 Superfinishing machine tool Superfinishing device mounted on lathe Superfinishing Machines special, Expensive type (multiple parts, long travel distance) Video 003 Video 004

42 4. Lapping Abrassive process Removing very small amount of material Removing surface undulations, roughness, tool marks and surface fuzz from grinding For all types of surfaces

43 Lapping Tool: A flat disc or plate made of cast iron, alalloy, copper, brass (low strength material) Abrasive particles are carried by an agent grease, oil, water (higher viscosity means higher abrasion)

44 Lapping - methods The lapping tool is rotated (oscilated) and moved irregularly across the machined surface - Equalising laping removing previous surface shape, flatening (spur, helical gears) - Forming laping lap is the negative shape of the surface

45 Lapping - methods For: Holes Flat surfaces cylinders Made: Manually mechanically

46 Lapping - methods Flat surfaces Lapping plate (different sizes, manual, machine operated - Moved irregularly along the surface

47 Lapping - methods Machine lapping Part are placed between a rotary and stationary lap. Part are carried by a workpiece holder. Part are placed excentrically so is the rotating lap. This makes the parts rotate and move

48

49 Lapping - examples Video 005 Video 006

50 Lapping - properties Lapping removes all tool traces improves durability, lowers friction Gives best surface quality (glass, mirror lapping) IT = 1 5 Ra = 0,01 0,16

51 6. Blasting Two forms - Forming (angle 80 ) - machining method (for angle of impact bellow 45 ) Particles are thrown at surface All kinds of shape

52 Blasting - tool Blasting elements are transported by high presure air to the surface Hardened steel balls cast iron balls Steel wire pieces (rounded) Glass balls aerospace industry

53 Blasting - examples Video 007 Video 008

54 Blasting - Aerolap

55 7. Tumbling Forming method, abrassive method Part to be machined and tumbling particles are placed in rotating cylinders Non defined surfaces

56 Tumbling - method Abbrasive particles and parts mixed together Special rotary or vibrational mills steel cylinders, inner rubber linning (to prevent abrasion) Sometimes active cutting fluid (water, NaCl, NaNO3, H2SO4 ) helping to remove the surface layer

57 Tumbling surface quality

58 Tumbling - tools Abbrasive particles non-uniform pieces of grinding stones, porcelain, ceramics (5-20 mm) Hardened steel balls (4-10) little surface hardnes improvement Soft particles for tumbling-polishing (dry corn peels, palm bark, wood chips)

59 Video 010 Video 009

60 Tumbling - machines

61 8. Polishing Abrasive method A friction between the polishing tool and part is caused by polishing media (paste) heat melts the peaks of surface All surface mainly flat surface with no strength demands

62 Polishing Abbrasive material is bond to a tool (disc, belt) or it is a media (paste) freely between tool (textile disc, belt) and part NO improve in shape or accuracy!! Just improves the surface quality

63 Polishing - tools Discs multi-plated : of fabric, leather, cotton - Solid : rubber, wood, cork, mild metal Brushes - Made of fibres : plastic, metal wire (0,1-1,2 mm) Belts - Endless belt pushed to the part. Better and more productive than discs.

64 Video 011 Video 012 Video 013

65 Polishing - properties Cutting speed m.sec-1 No IT improvement Ra 0,2-0,4 (removes tool paths)!!! Implicates residual stress due to high temperature!!!

66

67 Schedule WS 2016/2017 lesson Lesson (Tuesday) Lesson

68 Video links: Fine turning Honing Superfinishing Lapping Blasting

69 Video links: Tumbling 009_http:// M 010_http:// Polishing 011_http:// 012_http:// M INOX polishing 013_http://