MEM 2

What is meant by the term superheat?

Difference between temperature at pouring and temperature at solidification

Direct V Indirect Excursion

Direct, pushed through die indirect, die is part of ramming mechanism

What is the difference between an open mold and a closed mold?

Open mold is like a container of the shape with an open top where the metal is poured into. Will likely have at least one flat surface Closed mold uses a gating system to allow the pouring of metal into, a cavity of the shape housing the molten metal through solidification. More popular and important

What is isothermal forming?

Operations carried out to reduce surface cooling and temperature gradients that result from it.

What is the difference between a pattern and a core in sand molding

Pattern has the shape of the cast while a core is something within the cavity to define internal geometries

The flow curve expresses the behavior of a metal in which of the following regions of the stress-strain curve: (a) elastic region or (b) plastic region?

Plastic Region

What are some of the limitations and disadvantages of casting?

Poor dimensional accuracy and surface finish on with some casting processes Porosity Limitation on mechanical properties Risks associated with handling hot molten metal Environmental problems

List some of the products produced on a rolling mill.

Products made by shape rolling include construction shapes such as I-beams, L-beams, and U-channels; rails for railroad tracks; and round and square bars and rods

How does solidification of alloys differ from solidification of pure metals?

Pure metals solidify at a constant temperature equal to the melting point while alloys differ in the temperatures at which they solidify.

What is sticking in shape rolling?

When the hot work piece surface adhere to the rollers on contact

In casting, a flask is which one of the following: (a) beverage bottle for foundrymen, (b) box which holds the cope and drag, (c) container for holding liquid metal, or (d) metal which extrudes between the mold halves?

box which holds cope and drag

Name the four basic bulk deformation processes.

1) Rolling 2) Bar Drawing 3) Excursion 4)Forging

Identify some of the ways in which force in flat rolling can be reduced

1) Use hot rolling 2) Reduce the draft between each pass 3) Use rolls with smaller diameter

Hot working of metals refers to which one of the following temperature regions relative to the melting point of the given metal on an absolute temperature scale: (a) room temperature, (b) 0.2Tm, (c) 0.4Tm, or (d) 0.6Tm?

0.6Tm

In foundry work, a runner is which one of the following: (a) channel in the mold leading from the downsprue to the main mold cavity, (b) foundryman who moves the molten metal to the mold, or (c) vertical channel into which molten metal is poured into the mold?

A channel in the mold leading from the downsprue to the main mold cavity

What is a chill in casting?

A chill is a heat sink placed to encourage rapid freezing in certain regions of the cast.

What is a two-high rolling mill?

A shape rolling process in which two opposing rollers are used to achieve compression.

What is a reverse mill in rolling?

A two-high rolling process in which the rollers can go in reverse as well to compress the work piece from either side

In rolling of steel, what are the differences between a bloom, a slab, and a billet?

Abloom has a square cross section 150 mm 150 mm (6 in 6 in) or larger. A slab is rolled from an ingot or a bloom and has a rectangular cross section of width 250mm (10 in) or more and thickness 40 mm (1.5 in) or more.Abillet is rolled froma bloomand is square with dimensions 40mm(1.5 in) on a side or larger.

Identify some of the important advantages of shape-casting processes.

Casting can be used to create complex geometries, including internal and external shapes. Casting can produce final product 'net shapes' or 'near net' Can be used to create large parts ( over 100 tons) Can be mass produced Can be used on any metal that can become a liquid.

Extrusion is a fundamental shaping process. Describe it.

Compression process in which the work metal is passed through a die, thereby taking the shape of the die opening

The upper half of a sand-casting mold is called which of the following: (a) cope or (b) drag?

Cope

What is the difference between deep drawing and bar drawing?

Deep drawing is a sheet metal forming process used to fabricate cup-shaped parts; bar drawing is a bulk deformation process used to reduce the diameter of a cylindrical work part Deep drawing is a sheet metal forming process used to fabricate cup shapes parts while bar drawing is a bulk deformation part used to reduce the diameter of a cylinder.

Sand casting is which of the following types: (a) expendable mold or (b) permanent mold?

Expendable

. Name the two basic mold types that distinguish casting processes.

Expendable Mold Casting - Broken off and shape is saved Permanent Mold Casting - Mold can be used several times

Which of the following are bulk deformation processes (three correct answers): (a) bending, (b) deep drawing, (c) extrusion, (d) forging, (e) rolling, and (f) shearing?

Extrusion - compression process in which metal is forced to flow through die opening and cross section takes dimensions of die opening Deep drawing - reduction in diameter of a cylindrical part Rolling - thickness of slab is reduced with 2 rollers

What is a factory that performs casting operations usually called?

Foundry

Indicate some of the advantages of cold working relative to warm and hot working.

Greater accuracy resulting in smaller tolerances Better surface finishes Higher strength and hardening due to strength hardening Cast savings from reduced heat energy usage

. What are the two basic types of forging equipment

Hammer and Presses

What are the reasons why the bulk deformation processes are important commercially and technologically?

Hot working operations can significantly change the shape of the starting piece Strength-hardening can be achieved through cold working Produce little to no waste and final products a near or net shape which saves on secondary processing energy

What are the differences between bulk deformation processes and sheet metal processes?

In bulk deformation there are significant changes and shape and a low surface area to volume ratio. In sheet metal processes there is a high surface area to volume ratio.

How does increasing temperature affect the parameters in the flow curve equation?

Increases K and n

Increasing strain rate tends to have which one of the following effects on flow stress during hot forming of metal: (a) decreases flow stress, (b) has no effect, or (c) increases flow stress?

Increases flow stress

Describe the effect of strain rate in metal forming

Increases in strain rate increase resistance to deformation.

Why is friction generally undesirable in metal forming operations?

Increases wearing of tools, increases force and energy required and causes residual stress and product defects.

Turbulence during pouring of the molten metal is undesirable for which of the following reasons (two best answers): (a) it causes discoloration of the mold surfaces, (b) it dissolves the binder used to hold together the sand mold, (c) it increases erosion of the mold surfaces, (d) it increases the formation of metallic oxides that can become entrapped during solidification, (e) it increases the mold filling time, and (f) it increases total solidification time?

It increases erosion of the mold surfaces It increases the formation of metallic oxides that can become entrapped during solidification

Identify the three sources of contraction in a metal casting after pouring.

Liquid contraction due to cooling prior to solidification Contraction during the phase change from liquid to solid thermal contraction of the solid as it goes to room temp

Why is the term pressworking often used for sheet metal processes?

Most sheet metal operations are performed on presses

What is rolling in the context of the bulk deformation processes?

Rolling is a compression process in which the thickness of a workpiece is reduced by using two metal rollers. As they rotate they stretch and squeeze the work slap.

Which casting process is the most important commercially?

Sand Casting

What is trimming in die forging

Shearing of flash after process

What is sticking friction in metalworking?

Tendency for two surfaces moving in relative motion to adhere to each other rather than slide.

What does heat of fusion mean in casting?

The amount of heat required to solidify the metal from the liquid state

What is the continuity law as it applies to the flow of molten metal in casting?

The volume rate of flow remains constant throughout the liquid.

Total solidification time is defined as which one of the following: (a) time between pouring and complete solidification, (b) time between pouring and cooling to room temperature, (c) time between solidification and cooling to room temperature, or (d) time to give up the heat of fusion?

Time between pouring and complete solidification

What are some of the factors that affect the fluidity of a molten metal during pouring into a mold cavity?

Viscosity of the molten metal Heat transfer to surroundings Metal composition Pouring temperature relative to melting point

What are wire and bar drawing

Wire and bar drawing are bulk deformation processes in which the cross section of a wire or bar is reduced by pulling (drawing) it through a die opening.

Which of the following are advantages and characteristics of hot working relative to cold working (four correct answers): (a) fracture of workpart is less likely, (b) friction is reduced, (c) increased strength properties, (d) isotropic mechanical properties, (e) less overall energy is required, (f) lower deformation forces is required, (g) more significant shape changes are possible, and (h) strain-rate sensitivity is reduced?

fracture of workpart is less likely isotropic mechanical properties lower deformation forces required more significant shape changes possible

Besides flat rolling and shape rolling, identify some additional bulk forming processes that use rolls to effect the deformation.

gear rolling, threaded rolling, ring rolling

Which of the following is typical of the starting work geometry in sheet metal processes: (a) high volume-to-area ratio or (b) low volume-to-area ratio?

low volume to area ratio high area to volume ratio

The coefficient of friction between the part and the tool in cold working tends to be (a) higher, (b) lower, or (c) no different relative to its value in hot working?

lower

Why is flash desirable in impression die forging

metal in die completely fills cavity

One way to classify forging operations is by the degree to which the work is constrained in the die. By this classification, name the three basic types.

open die, flashless die, impression die forging

During solidification of an alloy when a mixture of solid and liquid metals is present, the solid-liquid mixture is referred to as which one of the following: (a) eutectic composition, (b) ingot segregation, (c) liquidus, (d) mushy zone, or (e) solidus?

solidus

What is draft in a rolling operation?

the amount of thickness in which the workpiece is reduced

Casting

the flow of molten metal through gravity or some other force into a mold where it solidifies into the shape of the mold cavity.