Technology II.

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

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

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

Fine mach. - examples

Fine mach. 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

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

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

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

Honing – process mechanics Honing head is Rotating – reciprocitive Oscilating – up and down Honing stones are pushed to the surface

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

Honing – machine tools Special horizontal or vertical honing machines

Honing - examples

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

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

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)

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

Superfinishing - surface

Superfinishing - methods Cylinders Cones Flat surface Shape surface

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 1800-3500 None (infeed) 14-140 Honing 100 - 250 50 cycles (length of hole – 150 mm) 3,5 – 7 superfinishing 6-14 200-1000 cycles (1-5 mm) 0,02 – 0,07

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

Superfinishing – machine tool Superfinishing device – mounted on lathe Superfinishing Machines – special, Expensive type (multi- ple parts, long travel distance)

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

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

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

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

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

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

Lapping - examples

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

5. Glazing Forming method Removing peaks on surface by rolling them into flat surface Used on rotational or flat surfaces

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

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

Blasting - examples

Blasting - Aerolap

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

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

Tumbling – surface quality

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)

Tumbling - machines

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

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

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.

Polishing - properties Cutting speed 25-40 m.sec-1 No IT improvement Ra 0,2 - 0,4 (removes tool paths) !!! Implicates residual stress due to high temperature !!!