Metal cutting Flashcards
What is high speed machining ?
- Machining at high speeds with accaptble tool life
- HSM vc: 600-1800m/min
- In different materials siffereent speeds are consudered high speed
How is HSM in aluminium?
The feed will be low and that will be reduced forces.
The feed per tooth can be kept at a low level -> smaler chip thickness
The cutting force is kepth at a lower level -> can mill complex structred
How is HSM in hardened steels?
The cutting depth can be diminished a maintained volume removal rate:
- -> A tooth is in engagement for a short part of the total time
- The tool is moving way from the heat being generated
How does the cutting speed affect different parameters?
- Tool life: will increase in the beggining then go down pretty fast
- Ther material romoval rate will increse linear
- The Surface will increse both then level out
- The chip underside temperatur vill invcrease and then level out
- Th cutting forces will decrease most in the beggining
- The workpieace temperatur will decrease most in the beginning
What are the advantages of HSM ?
- Temperatur is reduced in tool and workpiece
- Total wear is acceptable even if cutting speed is high
- Reduction in the thermanlly affected layer
- Low forces
- Diminished tool deflection
- Thin wall sections are more flexible
- Accourarcy
- Increased accuracy, espacially in thin walls due to reduced chip load
- Improved surface roughness
- Productivity
- Higher removal rate (different aspects for Al and Hs)
- Diminished number of operations and shorter lead times
- Simplified tooling
Why is it good to make dies with HSM?
- Fewer steps
- Shorter lead times
- Not too large tools
What are the disavantages of HSM?
- More expensive machinery and tools (requires stability and accuracy)
- Didicated and specialised machines
- More difficult but more important to keep machine occupied
- Specific competence required
- Manintenance
- Safety
What cutting cooling methods are used for HSM?
- Compressed air- often the best
- Mist of MQL directed to the cutting zone- socond best
- High pressure and high flow rate- third best
- Ordinary conventional- worst
What is hard machining ?
Machining in parts with hardness of above 45HRC
What are he benfits and drawback with hard machining?
Benefits:
- Greater flwibility
- Quick change- over between component types
- Several operations performed in one set up
- lower investment compared to grindning
- Enhanced machining quality
- Environmentally friendly- dry machining possible
Drawbacks:
- Tooling cost per unit
- Surface finish deterobrates with tool wear
- The “white layer” formation.
What are the characteristics for tools for HSM and hard machining?
- High rmp and power
- Typically n=15000-40000rpm
- Fast acceleration
- Ceramic (hybrid-) bearings
- Rapid movements
- Feed speed >20m/min
- 1-2g acceleration
- Linear motors somethi,es used
- Accurate machine movment
- Position accuracy in n um-range (+- 0,002mm)
- Control system and CAD/CAM
- High speed data transfer (ethernet)
- Large capacity for calculations
- look- ahead- function and nurbs
- Simulation of the machine tool
- Automation
- Maximising utilisation
What are the safety measures to take into count for HSM?
- Pretective shieldning/ “bullet proof”
- Short lengths of tool to deminish risk associated with vibration
- Blanced and clean tools for some resons above
How does those grinding work?
Creates rubbing and plowing before the chip thickness is big enogh to form a chip
What type of wheel wear is there for grinding?
- Sharp grit
- Altrtious wear (wear flats)
- Grit fracture
- Bond fracture
What types of abrasives is there for gridning?
- Conventional: Al2O3, SiC, hardest conventional
- Super abrasive:
- Dimond: syntetic, highest hardness and wear resistance
- CBN: suited for high speed grinding