Chatter/Abrasive Machinign

16 flashcards · Other · by Liam Kehoe

1. Thin cross section difficulties

   Casting and injection molding (Mold filling, dimensional accuracy) forging (require higher force due to friction) sheet metal work process (cause wrinkling) Machining (deflection, vibrations -> chatter) Welding (distortions due to thermal gradient)

2. How to avoid chatter?

   Improve the stiffness of workpiece-holding device Modify tool and cutter geometry Change machine parameters Increase stiffness of the tool on damping

3. Chatter (self-excited vibration)

   Uncontrolled vibration due to the interaction between tool and work piece Results in: Poor surface finish Loud noise Premature chipping, tool breakage and wear Damage to the machine

4. Selection of cutting conditions

   Speed, feed, depth of cut and cutting fluids Machining handbook or tool catalogs recommendations

5. Lapping

   Lapping is a loose abrasive machining process to form a slurry from an abrasive film between the plate and the parts to be lapped

6. Abrasive Machining

   Material removed by abrasive particles Grinding is the most common abrasive machining Ethers examples: honing, lapping, buffing

7. Factors affecting surface integrity

   Straining hardening of a surface Cracks formed in low speed cutting Phase transition due to high temp Residual stress

8. Selection of feed and speed cutting conditions

   Select cutting the depth and speed - minimize chatter vibration Select feed- roughing or finishing While maintain good MRR

9. Limitations of cutting conditions

   Horsepower and torque Machine tool and rigidity Strength of cutting tool Chatter Tolerances

10. What is Dressing?

    Conditioning worn grains by producing sharp new edges Truing - producing a true circle on a wheel Usually uses a diamond point tool

11. Polishing/Buffing

    Soften smear of surface layer Disks of belt made of fabric, leather with fine aluminum oxide or diamond powders

12. Abrasive Types

    Aluminum oxide Silicon Carbide CBN (Cubic boron nitride) Diamond

13. Reasons for grinding

    Conventional machining removes excessive materials - cannot produce required dimensional accuracy Workpiece material is too hard or too brittle Fine surface finish is required Irregular shapes, random distribution

14. Grinding Mechanism

    Specific energy greater than machining Higher negative rake angle Part of particles is engaged in cutting Size effect (low "h") The smaller the chip the higher the energy required to produce

15. Honing

16. Lapping

    Loose abrasive machining process to form a slurry from an abrasive film between the plate and the parts to be lapped