MAE 364: Exam 1 Review

Name some manufacturing processes that produce very good or excellent surface finishes.

honing, lapping, polishing, and superfinishing.

Name some manufacturing processes that produce very poor surface finishes.

sand casting, hot rolling, sawing, and thermal cutting (e.g., flame cutting).

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

(1) contraction of the molten metal after pouring (2) solidification shrinkage during transformation of state from liquid to solid (3) thermal contraction in the solid state.

Why should turbulent flow of molten metal into the mold be avoided?

(1) it accelerates formation of oxides in the solidified metal (2) it causes mold erosion or gradual wearing away of the mold due to impact of molten metal.

Indicate some of the limitations of using surface roughness as a measure of surface texture.

(1) it varies depending on direction (2) it does not indicate lay (3) its value depends on the roughness width cutoff used to measure the average.

What are some of the limitations and disadvantages of casting?

(1) limitations on mechanical strength properties (2) porosity (3) poor dimensional accuracy (4) safety hazards due to handling of hot metals (5) environmental problems.

What is are the goals of manufacturing?

-Adjust material properties -Add value to materials -Change the shape of materials

What are some of the reasons why surfaces are important?

-Aesthetics -safety -friction and wear -effect of surface of mechanical and physical properties -mating of components in assembly -electrical contacts

What are disadvantages of casting?

-Environmental problems -Limited mechanical strength properties -Safety of handling hot metals

What can happen with the turbulent flow in molten metal?

-Erodes the mold -Creates oxides in the metal

What are types of risers?

-Open riser -Blind riser -Top riser

What materials are typically used for the pattern in sand casting?

-Wood -Metal -Plastic

Name the two basic mold types that distinguish casting processes.

-expendable molds -permanent molds

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

1) complex part geometries are possible (2) some casting operations are net shape processes, meaning that no further manufacturing operations are needed to accomplish the final part geometry (3) very large parts are possible (4) casting is applicable to any metal that can be melted (5) some casting processes are suited to mass production.

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

1.) Liquid shrinkage: contraction of the metal after pouring and/or when hot liquid nears freezing temperature 2.) Solidification shrinkage: shrinkage during phase transformation from liquid to solid 3.) Solid shrinkage: the shrinkage when the casting is cooled from freezing temp to ambient temperature

What is the difference between a bilateral tolerance and a unilateral tolerance?

A bilateral tolerance allows variation in both positive and negative directions from the nominal dimension, whereas a unilateral tolerance allows the variation from the nominal dimension to be either positive or negative, but not both.

What is a factory that performs casting operations usually called?

A foundry

What is a tolerance?

A tolerance is defined as the total amount by which a specified dimension is permitted to vary.

What is accuracy in measurement?

Accuracy is the degree to which the measured value agrees with the true value of the quantity of interest. It is a measurement procedure that is absent of systematic errors.

What is not a process of altering the geometry of a material? -Stamping -Adjoining -Machining -Milling

Adjoining

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

An open mold is open to the atmosphere at the top; it is an open container in the desired shape which must be flat at the top. A closed mold has a cavity that is entirely enclosed by the mold, with a passageway (called the gating system) leading from the outside into the cavity. Molten metal is poured into this gating system to fill the mold.

What is a benefit of cold working as opposed to hot working?

Better surface finish

What is the relationship known as Chvorinov's rule in casting?

Chvorinov's rule is summarized: TTS = Cm (V/A)^2, where TTS = total solidification time, Cm = mold constant, V = volume of casting, and A = surface area of casting.

What is not a type of sand mold? -Dry sand -Skin dried -Green sand -Clay binder

Clay-binder mold

What causes the various types of changes that occur in the altered layer just beneath the surface?

Energy input to the surface resulting from the manufacturing process used to generate the surface. The energy forms can be any of several types, including mechanical, thermal, chemical, and electrical

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

Greater accuracy, better surface finish, high strength and hardness, grain flow => desirable directional properties, no heating of work required

What is heat of fusion in casting?

Heat required to turn metal from solid to liquid.

What process doesn't produce poor surface finishes? -Hot rolling -Honing -Sawing -Thermal cutting

Honing

What does heat of fusion mean in casting?

In casting, the heat of fusion is the amount of energy that is involved in the material's phase change from liquid to solid. In other words, heat of fusion is the value of the amount of heat the metal dissipates when changing phase from liquid to solid.

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

Increasing the temperature decreases K, the strength coefficient and n, the strain hardening factor.

Given the flow curve, Yf = Ke^n, how does increasing the temperature impact K and n?

K and n decrease

What is an advantage of shape casting processes?

Large and complex parts can be made.

What is a chaplet?

Metal support to hold core

What doesn't lead to contraction in casting a metal part?

Number of sharp edges in the mold

Generally, how many pieces of equipment perform unit operations?

One

What is precision in measurement?

Precision in measurement is the degree to which random errors are minimized.

Within the scope of surface texture, how is roughness distinguished from waviness?

Roughness consists of the finely-spaced deviations from the nominal surface, while waviness refers to the deviations of larger spacing. Roughness deviations lie within waviness deviations.

What process does not produce good surface finishes? -Lapping -Polishing -Superfinishing -Sand casting

Sand Casting

Which casting process is the most important commercially?

Sand casting is the most important casting process.

What property does not determine the quality of a sand mold? -Permeability -Strength -Size -Thermal Stability

Size

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

Solidification of pure metals takes place at constant temperature while solidification of alloys takes place over a range of temperatures.

What is meant by the term superheat?

Superheat is the temperature difference above the melting point at which the molten metal ispoured. Thetermalsoreferstotheamountofheatthatisremovedfromthemoltenmetal between pouring and solidification.

When is surface quality not important?

Surface quality is almost always important

Surface roughness is a measurable aspect of surface texture; what does surface roughness mean?

Surface roughness is defined as the average value of the vertical deviations from the nominal surface over a specified surface length.

Define surface texture.

Surface texture is the random and repetitive deviations from the nominal surface, including roughness, waviness, lay, and flaws.

How is surface texture distinguished from surface integrity?

Surface texture refers only to the surface geometry; surface integrity includes not only surface but the subsurface layer beneath the surface and the changes in it.

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

The continuity law, or continuity equation, indicates that the volumetric flow rate is constant throughout the liquid flow.

What is the difference between a pattern and a core?

The core determines internal geometry and the pattern determines the shape

Indicate the mathematical equation for the flow curve.

The mathematical equation for the flow curve is, σ= Kε^n; where σ=true stress, K=strength coefficient, ε=true strain, and n=strain hardening exponent.

Define nominal surface.

The nominal surface is the ideal part surface represented on an engineering drawing. It is assumed perfectly smooth; perfectly flat if referring to a planar surface; perfectly round if referring to a round surface, etc.

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

The pattern determines the external shape of the cast part, while a core determines its internal geometry if the casting includes a cavity.

What is superheat?

The temperature difference between pouring temperature and solidification temperature.

Which is an assembly operation? -Welding -Painting -Cold working -Milling

Welding