Metal cutting Flashcards

1
Q

What is high speed machining ?

A
  • Machining at high speeds with accaptble tool life
  • HSM vc: 600-1800m/min
  • In different materials siffereent speeds are consudered high speed
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2
Q

How is HSM in aluminium?

A

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

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3
Q

How is HSM in hardened steels?

A

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
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4
Q

How does the cutting speed affect different parameters?

A
  • 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
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5
Q

What are the advantages of HSM ?

A
  1. Temperatur is reduced in tool and workpiece
    1. Total wear is acceptable even if cutting speed is high
    2. Reduction in the thermanlly affected layer
  2. Low forces
    1. Diminished tool deflection
    2. Thin wall sections are more flexible
  3. Accourarcy
    1. Increased accuracy, espacially in thin walls due to reduced chip load
  4. Improved surface roughness
  5. Productivity
    1. Higher removal rate (different aspects for Al and Hs)
    2. Diminished number of operations and shorter lead times
    3. Simplified tooling
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6
Q

Why is it good to make dies with HSM?

A
  • Fewer steps
  • Shorter lead times
  • Not too large tools
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7
Q

What are the disavantages of HSM?

A
  • 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
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8
Q

What cutting cooling methods are used for HSM?

A
  • 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
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9
Q

What is hard machining ?

A

Machining in parts with hardness of above 45HRC

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10
Q

What are he benfits and drawback with hard machining?

A

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.
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11
Q

What are the characteristics for tools for HSM and hard machining?

A
  • 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
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12
Q

What are the safety measures to take into count for HSM?

A
  • Pretective shieldning/ “bullet proof”
  • Short lengths of tool to deminish risk associated with vibration
  • Blanced and clean tools for some resons above
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13
Q

How does those grinding work?

A

Creates rubbing and plowing before the chip thickness is big enogh to form a chip

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14
Q

What type of wheel wear is there for grinding?

A
  • Sharp grit
  • Altrtious wear (wear flats)
  • Grit fracture
  • Bond fracture
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15
Q

What types of abrasives is there for gridning?

A
  • Conventional: Al2O3, SiC, hardest conventional
  • Super abrasive:
    • Dimond: syntetic, highest hardness and wear resistance
    • CBN: suited for high speed grinding
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16
Q

What properties are the for grinding wheels?

A
  • Grit size
  • Structure, density
  • Grit type
  • Bond type
  • “hardness”
17
Q

What are the basic grinding processes?

A
  • Two main classes
    • Grinding cylindrical surfaces, grinding of non-flat surfaces an rotational flat surfaces
  • Cylindrical
    • Internal
    • And centerless
18
Q

what are the surface integrity in production grindning?

A
  • For grinding, the most important aspects of surface integrity are associated with therman damage caused by excessive grinding temperature.
  • Thermal demages:
    • Thermal softening -> when temp 560°C
      • Loss of hardness
    • Residual tensile stresses
      • Material cracking close to surface -> yield stress 330Mpa
    • Rehardening burn
      • Can lead to cracking and fracture in the ground surface. -> temp 1125°C
19
Q

What are the bonds for grindning?

A

Demands

The bond hols and supprts the abrassives. It must be strong anough to withstand grinding forces, temeratures, while resisting chemical attack by cooling lubricant

Functions

  • Retain the abrassive grain during the process
  • Wear at a controlled rate with respect to the grain wer
  • resist centrifugal forces, especially in high speed grinding
  • Readily exposes the grain to the work, where possible.
20
Q

What are the definition of machinability?

A

Machinability describes the ability with shich a work pieace material can be machines under given process conditions and it might be assesses by ome or more of the critera:

  • Tool life
  • Material removal rate
  • Cutting force
  • Surface finish
  • Chip shape
  • Environmental impacts
21
Q

What type of wear effects is it? and what types of wear?

A
  • Surface integrity
  • Dimensional acuuracy of machined part
  • Process stability
  • Incresed force and temerature

Types:

  • Flank wear
  • crater wear
  • notch wear
  • Plastic deformation
  • chipping and flanking
  • Thermal cracking
22
Q

How does the material removal rate effect the costs?

A
  • Parts per hour: increases
  • Production cost: decreses first and then increase again
  • tool cost is first flat and then incresed
  • The fixed cost is the same
  • The machinecost decreses
23
Q

What parameters is it for the surface finish?

A
  • Kinematic roughness
    • Tool motion: cutting speed, feed
    • Cutting edge: Wear on minor flank, overall wear
  • Cutting rougness:
    • chip formation: tool geometry, work material, temperature, tool material
    • Alternation of cut curface: corner and flank wear, friction and welds, cooling
  • Adiitional factors:
    • Vibrations, chips, deformation of feed tracks: cutting force, ship removal, what material
24
Q

What are the main advantages of the difficult to cut materials as Titanium?

A

The main strength of the nickel based super alloys are:

  • Being heat resistant
  • Having high melting temperautres
  • Retaining their machanical and chemical properties at high temp
  • High corrosion resistance as well as thermal fatigue, creep, reosion
25
Q

What are the tools requirments for machining in Titan alloys?

A
  • Coating to reduce thermal tool load
  • Positive rake angle to reduce cutting force
  • Substate with good thermak conductivity, high hot resistance
  • small edge rounding to stabilize the cutting edge
  • Large clearence angle due to high elastic deformability.
26
Q

What are the important things to consider when cutting in Ni-based alloys?

A
  • A high machanical and thermal load on the tool cutting edge
  • A strong tendency of the material for adhesion to the cutting material and possibility of BUE
  • High abrasive wear due to carbides and intermetallic phases
  • Unfavorable chip formation
  • The cold hardening of the machined workpieace surface area
27
Q

What are the properties for cast irons?

A
  • White cast iron
  • Grey cast iron
    • Flank graphine iron
    • Compacted graphen iron
    • Spherodal graphite iron

The ductility, strengh and thoughness incress from up to down

The machinability, thermal properties and damping decrese from up to down

28
Q

What are the primary tasks of cooling lubricants? And what happens if it dosent do that?

A
  • Cooling
    • Workpiece, tool, chip
  • Lubrication
    • Friction reduction, adhesion
  • Chip removal
    • removal from: workpiece , tool, machine

Leads to:

  • Tool (wear, plastic deformation, chip formation)
  • Workpiece (shape and dimension accuracy, surface, edge zone) -> quality
  • Machine (accuracy, chip removal)
29
Q

What are the composition of the emulusion? and what is a normal health aspect of that?

A

95% water, 5% oils + additves (non heathy, needed to protect machines from ex. corrosion)

Can cause skin problem

30
Q

What can becompared between straght oil and emultions?

A

Oil:

  • small cooling effects
  • good lubrication effect
  • no skin problem
  • Good bacterial resistance
  • High initial costs
  • unlimited life span
  • Small disposal coast
  • Waste water low

Emulusion:

  • Very good cooling effects
  • Smal lubrication effects
  • Cause skin problem
  • BAd bacterial resistance
  • Small initial costs
  • 6-24 month life span
  • High disposal coast
  • Very high water waste
31
Q

What EU regulation is it that have affected the cooling fluids ?

A

Everyting bad that impacts human helth and te environment need to be marked.

.->This is not the case for e.g. USA

32
Q

What are the sustainability aspects of cutting fluids? How do they affect the heath?

A
  • Contribute to 72,500 tons of fluid waste in Sweden
  • Sustainability and total life cycle of the chemicals are of great concern.
  • In future: Should be renewable, recyclable and not cause effects on the souroundings.

Health

  • Fluid, steam & fog:
    • Skin-> Eczema, allergies
    • Lung -> Asthma
    • Stomach -> Ulcers
    • Eyes -> Irratation
  • Disposal:
    • Air and water
  • Internal:
    • ground
33
Q

What diffent methods can be used for cuttting cooling other than the conventional method and what are the aspects of them?

A
  • Pressurissed air:
    • Quit poor in most respects, gives little bit of cooling. it can help in removing chips, more so in milling than turning though.
  • Straight oils:
    • Means only oil. Has excellent lubrication ability but quite poor in other aspects
  • MQL (minimum quantity lubrication):
    • Some lubrication but only some as small amount. The compressed air itself has one anility of pressurised air.
  • Dry ice (CO2 ) :
    • Increse speed posibility, hard to implement and expensive, easier that LN2, no disposal
  • Liquid nitrogen (LN2):
    • Hard ti keep fluent requires special investments. High cost
  • Nanofluid based:
    • New super lubricationg, super expensive, under development
  • Emulusion (conventional) :
    • Mix of water and oils therefore quite good in all respects infact