MCHE 3920 Shape Casting Exam Questions with Complete Answers Latest Update 2024

MCHE 3920 Shape Casting Exam Questions with Complete Answers Latest Update 2024 what are three main benefits of shape casting - Answers form freedom, certain properties at elevated temperatures, distinct character and texture what does the liquid metal ooured into a mold create? - Answers negative shape of the product is it better to fill a mold bottom up or top down and why? - Answers it is best to fill bottom up to prevent splashing (which creates oxidation and loss of properties) and prevents gas entrapment why does casting generally have higher alloy content - Answers higher alloy content yields lower viscosity for better mold filling and low melting temperatures which requires less energy and faster throughput casting metals ideally should be near _________ composition - Answers eutectic, which means homogenous composition and lowest possible melting temperature and typically lower viscosity what does higher alloy content come at an expense of? - Answers material properties what material properties are reduced with high alloy content? - Answers toughness, ductility and fatigue strength what quality does cast iron have lower relative to low carbon steel? - Answers stiffness what is a tradeoff of material properties? - Answers castability and high alloy content why is having a slow filling speed or laminar flow important? - Answers laminar flow minimizes free surface area and thus minimizes oxidation and loss of material properties what is used to predict the transition from laminar to turbulent flow? - Answers reynolds number, which is dependent on geometry and the fluid what is typically the Reynolds number the transition of laminar to turbulent flow for flow over a flat plate? - Answers 500,000 what are some tradeoffs for low filling speeds? - Answers lower productivity and cold running what is cold running? - Answers solidifying portions before mold is filled how can cold running be prevented? - Answers using thicker parts, results in increased weight and cost how can filling speeds be increased? - Answers using multiple gates, results in increased required finishing mold filling will either be slow at _______ pressure, or fast at _________high pressure - Answers slow at low pressure, fast at high pressure what happens to the volume when cooling from liquid to solid? - Answers reduces when is the rate of volume reduction the highest? - Answers solidifcation range what are the three phases that cooling occurs in? - Answers liquid phase (T_pouring to T_solidus), liquid to solid phase tranisition, T_solidus to RT what can be done about the solidification shrinkage? - Answers adding material during filling what can be done about shrinkage that occurs after solidification? - Answers make the mold bigger what does Chvorinov's rule model? - Answers the time it takes before a part is cool and strong enough to be handled. What types of casting does Chvorinov's model work well and not well on? - Answers works well for large solid castings, underestimates time for hollow and thin walled parts why does Chvorinov's model underestimate time of solidification for thin walled parts? - Answers the inner wall of the mold does not absorb heat as much as the outter walls since the mold expands while the casting contracts creating an air gap that acts like an insulator limiting heat dissipation what are three main defects that can occur during casting? - Answers porosity (gas-filled voids in metal), internal stresses, and distortion what are two main causes of porosity? - Answers not enough extra material is fed into the casting to compensate for solidification shrinkage and gas bubbles released during solidifaction become trapped in the solid what relationship is associated with cooling time for thin walled parts? - Answers V/A, different thicknesses will cool at different rates which leads to variances within the casting what is thermal strain? - Answers amount of thermal expansion or contraction what law accounts for stresses caused by differences in temperature and thus differences in contractions? - Answers Hooke's law what can the stresses by hooke's law effect? - Answers the capability of parts in service when can permanent deformation occur? - Answers if the casting is free to deform and the stresses exceed the yield stress what can happen if stresses are extreme in casting? - Answers cracking or rupture what is required to predict internal stresses/deformation of complex geometries? - Answers computer solution