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