ch 22 Manufacturing Exam 3

Ways of mitigating hazards with cutting fluids

1. Replace cutting fluid at regular intervals 2. use filtration system 3. dry machining

Examples of tool life criteria

1. complete failure of cutting edge 2. visual inspection of flank wear or crater wear 3. Changes in sound emitting from operation 4. degradation of surface finish 5. increased power consumption in operation 6. workpiece count 7. cumulative cutting time

As an alloying ingredient in high-speed steel, chromium serves what three functions?

1. depth hardenability during heat treatment 2. Forms hard carbides to resist abrasion 3. Increases corrosion resistance

What are the three possible modes of cutting tool failure

1. fracture failure 2. temperature failure 3. Gradual wear

Cutting fluids address what two main problems

1. heat generation at shear zone 2. Friction at tool-chip and tool-work interfaces

Properties of cemented carbides

1. high compressive strength but low to moderate tensile strength 2. high hardness 3. good hot hardness 4. good wear resistance 5. high thermal conductivity 6. high modulus of elasticity 7. toughness lower than HSS

Problems with dry machining

1. overheating tool 2. operating at lower cutting speeds and production rates 3. absence of chip removal benefits

Advantages of filtration systems

1. prolonged cutting fluid life 2. reduced fluid disposal cost 3. cleaner cutting fluid 4. lower machine tool maintenance 5. longer tool life

crater wear

A cavity in the rake face of the tool that forms and grows from the action of the chip sliding against the surface.

Cemented carbides

A class of hard tool material formulated from tungsten carbide using powder metallurgy techniques with cobalt (Co) as the binder.

Cermet

A composite of ceramic and metallic materials; the term is applied to ceramic-metal composites containing TiC, TiN, and certain other ceramics not including WC.

High speed steel (HSS)

A highly alloyed tool steel capable of maintaining hardness at elevated temperatures better than high carbon and low alloy steels.

Nose radius wear

A region of flank wear that occurs on the nose radius leading into the end cutting edge.

What are ceramic cutting tools composed of primarly

Al2O3 (aluminum oxide)

Notch wear

An extreme condition of flank wear that often appears on the cutting edge at the location corresponding to the original surface of the work part.

Wear resistance of cast cobalts is better or worse than HSS

Better

What are the three regions of the typical wear growth curve

Break in period, steady state wear, failure region

Toughness

Capacity of a material to absorb energy without failing.

Wear resistance

Characteristics of the tool that help it resist wear, including surface finish, chemistry of tool and work materials, and whether a cutting fluid is used.

Chemical fluids

Chemicals in a water solution rather than oils in emulsion.

semichemical fluids

Chemicals that have small amounts of emulsified oil added to increase the lubricating characteristics of the cutting fluid.

Cast cobalt alloys are comprised of

Cobalt, chromium, tungsten, trace amounts of other

Coolants

Cutting fluids designed to reduce the effects of heat in the machining operation.

Out of cutting speed, depth of cut, and feed, which has the greatest effect on tool life

Cutting speed

The taylor equation relates what two variables

Cutting speed, tool life

Additions of titanium carbide in steel-cutting grades of cemented carbides have which two effects on properties?

Decreases flank wear resistance, increases crater wear resistance

Steady state wear

Degradation following the break-in period, during which wear occurs at a fairly uniform rate.

what is the principle mechanism of crater wear

Diffusion

What is the preferred method of tool failure

Gradual failure

Harder work materials cause the wear rate to increase or decrease?

Increase

Emulsified oils

Oil droplets suspended in water, made by blending oil (usually mineral oil) in water using an emulsifying agent.

Plastic deformation

Permanent shape change of a ductile material (e.g., metal, plastic) that occurs when the applied stress exceeds reaches the yield strength of the material.

Chemical reactions

Process in which high temperatures and clean surfaces at the tool-chip interface results in chemical ractions, oxidation in particular, on the rake face of the tool.

Flood cooling

Process of applying cutting fluid with coolants, in which a steady stream of fluid is directed at the tool-work or tool-chip interface of the machining operation.

Hot hardness

The ability of a material to retain hardness at elevated temperatures.

failure region

The point when wear reaches a level at which the wear rate begins to accelerate; cutting temperatures are higher, and the general efficiency of the machining process is reduced.

Flank wear land

The width of the wear band of flank wear.

Break in period

Tool wear in which the sharp cutting edge wears rapidly at the beginning of its use.

T or f Cast cobalt cutting tools are made into the desired tool geometry by casting, after which the cutting edges are ground to final size and sharpness.

True

Types of HSS

Tungsten-type, molybdenum type

Flank wear

Wear that occurs on the flank, or relief face, of the tool, resulting from rubbing between the newly generated work surface and the flank face adjacent to the cutting edge.

Adhesion

Wearing action when two metals are forced into contact under high pressure and temperature, and welding occurs.

Cast cobalt has better or worse hardness than HSS

better

Toughness of cast cobalt is better than ______ (HSS, carbides), but not as good as (HSS, carbides)

carbides, HSS

What are the two main types of gradual wear

crater, flank

Compared to high-speed steel and cemented carbides, ceramic cutting tools are most vulnerable to which one of the failure modes?

fracture wear

Of all the machining operations, for which one would ceramic cutting tools be most appropriate?

high speed finish turning

In nonsteel carbides, as grain size is ______, hardness and hotness _______, but transverse rupture strength ______

increased, decreased, increased

As cutting speed increases, wear rate ______

increases

Lubricant type cutting fluids are more effective at ______ cutting speeds

lowers

higher cutting speeds result in (shorter, or longer) tool lives?

shorter

Abrasion

A mechanical wearing action caused by hard particles in the work material gouging and removing small portions of the tool.

Gradual wear

A mode of tool failure caused by various wear mechanisms, resulting in a loss of tool shape and cutting efficiency, leading to failure in a manner similar to temperature failure.

Fracture failure

A mode of tool failure that occurs when the cutting force at the tool point becomes excessive, causing it to fail suddenly by brittle fracture.

Temperature failure

A mode of tool failure that occurs when the cutting temperature is too high for the tool material, causing the material at the tool point to soften, which leads to plastic deformation and loss of the sharp edge.

Diffusion

A process in which an exchange of atoms takes place across a close contact boundary between the tool and chip materials.

Extreme pressure lubrication

A special form of lubrication that involves formation of thin solid salt layers on the hot, clean metal surfaces through chemical reaction with the lubricant.

Next to diamond, _______ ______ ______ is the hardest material known

Cubic boron nitride

Lubricants

Fluids (usually oil-based) or other substances formulated to reduce friction in many manufacturing operations, including machining, grinding, metal extrusion, wire and bar drawing, and powder metallurgy; also used to reduce sticking of castings or moldings in the die or mold cavity in die casting and plastic molding.

Tool life

Length of cutting time that the tool can be used.

A ________ friction angle causes the shear plane angle to ______

Lower, increase

dry machining

Machining without cutting fluids

Cutting oils

Oil derived from petroleum, animal, marine, or vegetable origin.

HSS is suitable for complex or simple geometry?

Simple

Lubricants reduce friction, ______ and _______

friction angle, temperature

What are synthetic diamond cutting tools made of

sintered polycrystalline diamond

What is toughness characterized by

strength and ductility in a material