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MECE 364 > Material Removal Processes > Flashcards

Material Removal Processes Flashcards

1
Q

Advantages of machining

A
  1. Works with a variety of materials
  2. Can be used to create a variety of different geometries including flat planes, round holes, and cylinders
  3. Has ver ygood dimensional accuracy (up to +/-0.025mm)
  4. Produces good surface finishes (can be less than 0.4μm)
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2
Q

Disadvantages of machining

A
  1. Is wasteful of material (generates lots of chips).
  2. Is a very time consuming process and generally takes more time than casting or forging.
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3
Q

What are the three categories of material removal processes?

A
  1. Conventional machining (Turning, drilling, milling, etc.)
  2. Abrasive processes (Grinding, etc.)
  3. Nontraditional machining (Electrochemical machining, thermal energy processes, chemical machining)
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4
Q

What are the four major milling processes?

A
  1. Turning
  2. Drilling
  3. Peripheral milling
  4. Face milling
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5
Q

Orthogonal cutting model

A

The tool cutting edge must be perpendicular to the cutting direction. This allows for relations between variables to be investigated. See pg.8-21 of material removal processes for diagrams and equations.

Keep in mind that r<1 because the chip thickness is always greater than the depth of the cut.

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6
Q

Independent variables in the orthogonal cutting model

A

Cutting depth (t0) and rake angle (𝛼)

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7
Q

Dependent variables in the orthogonal cutting model

A

Chip thickness (tc) and shear angle (𝜙)

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8
Q

What are the three velocities considered in the orthogonal cutting model?

A

The velocity of the chip relative to the workpiece (Vs), the velocity of the chip relative to the tool (Vf), and the cutting speed or velocity of the tool relative to the workpiece (V).

Vs = Vf + V

See pg.13

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9
Q

What are the non-measureable force quantities in the orthogonal cutting model?

A

Friction force (F) and normal force (N) are the force components between the tool and chip.

Shear force (Fs) and shear normal force (Fn) are the force components between the workpiece and chip.

R and R’ are resultant forces acting on the chip.

See pg.14 and 15

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10
Q

What are the measureable force quantities in the orthogonal cutting model?

A

The horizontal cutting force (Fc) and the vertical thrust force (Ft) can be directly measured.

See pg.14 and 15

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11
Q

What are the basic requirements of a cutting tool material?

A

Toughness, hot hardness, wear-resistance, and chemical stability (so it doesn’t bond with the workpiece).

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12
Q

What are the three possible failure modes of a cutting tool?

A

Fracture failure (abnormal failure), temperature failure (abnormal failure), and gradual wear (normal failure).

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13
Q

High speed steel cutting tools

A

T and M series.

Has the best toughness and resistance to fracture. Can maintain its hardness up to 600°C.

Most often used for drills and milling cutters in complex tool geometry.

A thin coating of titanium nitride causes a significant increase in performance.

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14
Q

What are high speed steel cutting tools made of?

A

T series is 12-18% W with Cr,V, and Co alloys

M series is 8-10% Mo with Cr, V, W, Co alloys. This is the most commonly used series.

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15
Q

Sintered and coated carbide cutting tools

A

Have good hot hardness, can be made in different insert shapes with multi cutting edges and can reach sutting speedsd up to 5x that of high speed steels.

Uses a honed edge (less rake angle) to increase the cutting force but experience less too breakage..

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16
Q

What are sintered and coated carbide cutting tools made of?

A

Ti, Ta, Nb, and W. Can be alloyed with C, N, Al2O3, or Cn to reduce heat and improve wear resistance.

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17
Q

Ceramic cutting tools

A

Are chemically stable, have high abrasive resistance and hot hardness, and can operate at cutting speeds 3x fiaster than sintered carbides.

These tools are very brittle and not suited for interrupted cutting. Vibrations and chatter can lead to chipping/failure of the tool.

Needs a negative rake angle to avoide chipping due to poor tensile strength.

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18
Q

What are ceramic cutting tools made of?

A

Pure aluminum oxide is the most common material. Too increase toughness, whisker-reinforced ceramic tools are made.

The whiskers are made of silicon-carbide fibers and act as micro-crack arresters.

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19
Q

Cubic boron nitride cutting tools.

A

Is the second hardest cutting tool next to diamonds.

A layer of CBN is bonded to a carbide bit through sintering under pressure.

20
Q

Sintering

A

Is the process of compacting and forming a solid mass of material by pressure or heat without melting it to the point of liquification.

21
Q

Synthetic diamond cutting tools

A

Use infrequentlt to high-speed machining of non-ferrous matierals.

Is not suited for ferrous materials because of its chemical affinity.

Made of sintered polycrystalline diamonds and can also be used as a coating for carbides.

22
Q

Tool life

A

Refers to the ability to provide satisfactory dimensional accuracy and a suitable surface finish.

Breakage and wear can indicate the end of the life of a cutting tool.

23
Q

Flank wear

A

Is a wear mode that takes place on the relief face of the tool, measured by flank wear land (FW).

24
Q

Crater wear

A

Is a wear mode that takes place on the rack face of the tool, measured by its depth (KT).

25
Q

Chipping

A

Breakage of a small piece of the cutting tip. An increased rake angle increases the chance of chipping.

26
Q

Built-up edge

A

Materials from the workpiece are gragually deposited on the cutting tip and eventually broken up.

Causes vibration and poor surface finish, although a stable, thin BUE can protect the tool surface from wear.

27
Q

Taylor equation

A

Can be used to determine tool life. See pg.12

28
Q

Cutting temperature

A

Nearly all (~98%) energy used in machining is converted into heat.

This can cause temperatures to be very high at the tool-chip interface (around 600°C).

High temperatures reduce tool life, produce hot chips, can cause innacuracies due to thermal expansion.

29
Q

Cook’s formula

A

Used to predict the increase in temperature at the tool-chip interface.

See pg. 16

30
Q

Cutting fluids

A

Cooling (water based fluids) are used to reduce the temperature.

Lubricating (oil based fluids) are used to reduce friction between the chip, tool, and workpiece. This reduces the temperature.

Fluids are also helpful in washing away the chips.

31
Q

What are the four factors of machinability?

A

Force and power requirements, surface finish and dimensional accuracy, tool life, and chip control.

32
Q

Lead (Pb)

A

Is added to steel to improve machinability but may cause liquid embrittlement (hot shortness).

33
Q

Sulfur (S)

A

Is added to steel to improve machinability but causes hot shortness. Resulfurized steels avoid this by adding Mn.

34
Q

Machinability of stainless steels

A

Ferritic (400 series) have good machinability

Austenitic (300 series) have poor machinabiity

Martensitic have poor machinability due to their high abrasiveness and easy production of a built up edge

35
Q

CNC machining

A

Comprised of three parts, the program, machine control unit, and processing equipment.

The advantages are mots evident in mass production, experienced programmers can create single parts in less time than it would take to make them manually as well.

Is about 10x more accurate than manually operated machines.

36
Q

Tool travel

A

Is the travel to and from the workpiece.
Is quick and accurate.

37
Q

Chip breakers

A

A groove or separate component used to break the chips. This is improtant in the case that there is no operatre to take care of potential chip problems.

38
Q

Parametric software programs

A

Allows the user to observe a simulation of the machining process before starting.

Can also create information like FEM stress analysis and part drawings.

39
Q

Tool condition monitoring

A

Is is key for automated machining as the tool position determines the quality of the output.

This can help monitor tool wear and breakage to allow for replacement mid job.

40
Q

Design considerations

A

Dimension tolerances and surface finish should be specified to meet functional requirements. Excessive tolerances may just add complexity and no real value.

Avoid deep holes and sharp inernal corners,

Long narrow parts, large flat parts, and parts with thin walls should be avoided.

41
Q

Chemical machining (CM)

A

Material is removed from the surfave via. chemical dissolution using reagents or etchants.

This process works best for shallow removal on large flat or curved surfaces.

It has a low tooling and equipment cost and works well for low production runs.

42
Q

Electrical discharge machining (EDM)

A

The piece is machined by a formed electrode tool where a spark occurs between the tool and work surface.

There is a small gap for the spark to form between the tool and surface.

This process must take place in a dielectric fluid to create a path for each electric discharge.

43
Q

Wire EDM

A

Is similar to EDM, but the tool is a wire that is drawn through the part. As it cuts, the wire is slowly drawn through the part, constantly replacing it and keeping the cutting diameter constant.

It is good for shaping and cutting complex parts made of hard materials, but some surface damage may occur.

This process requires expensive tooling and equipment.

44
Q

Electron and laser beam machining

A

A highly focused, high-density electron/laser melts and evaporates a portion of the workpiece in a controlled manner.

This works well for cutting and hole making on thin materials.

45
Q

Water jet machining

A

A water jet that may or may not contain an abrasive powder acts as a saw and cuts a narrow groove in the material.

The pressure can get as high as 400MPa.

MECE 364 (10 decks)

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