MFG final exam review
Cold working has better surface finish, good dimensional tolerances and higher mechanical properties due to strain hardening. Has anisotropic properties and is harder to deform.
(1) Discuss the differences between the two in terms of the resulting microstructure and its effect on mechanical properties, tolerance capability, ease of deformation and surface finish.
clearance determines shape and quality of the sheared edge
(1) How do die clearance and ductility of the metal influence these surface characteristics?
Cold working elongates the grains which produces anisotropic properties because of strain hardening which increases strength
(1) Normally the starting material is always a porous casting ingot. Discuss the internal soundness of the final product from both hot and cold working operations. Why does this occur? Should one of the two always be done to cast ingots before further processing?
Higher pressure and resulting high frictional resistance in flash prevents a severe constraint on any outward radial flow of the material in the die
(1) What is the purpose of flash in forging?
the edges are not smooth nor perpendicular to the plane of the sheet
(1) When punching a hole in plate material, discuss the characteristics of the surface that forms in the hole and on the slug. What causes these characteristics? (A sketch of either the hole or slug may help)
Grain flow affects the strength of the part
(1) When you are hot forging, how are grain flow, the location of the die parting line and draft important in the design of your part?
Hot working has finer grains (isoctropic properties), enhanced ductility and strength
(2) Discuss the differences between the two in terms of the resulting microstructure and its effect on mechanical properties, tolerance capability, ease of deformation and surface finish.
as clearance increases the deformation zone becomes larger and the sheared edge surface becomes larger
(2) How do die clearance and ductility of the metal influence these surface characteristics?
Hot working converts a cast structure (typically consisting of coarse nonequiaxed grains) to a wrought structure which results in finer equiaxed grains and enhanced ductility resulting from breaking up the brittle grain boundaries and closing up internal defects
(2) Normally the starting material is always a porous casting ingot. Discuss the internal soundness of the final product from both hot and cold working operations. Why does this occur? Should one of the two always be done to cast ingots before further processing?
Flash prevents the material from flowing outward of the die. Material will then flow in the path of least resistance
(2) What is the purpose of flash in forging?
fracture angle
(2) When punching a hole in plate material, discuss the characteristics of the surface that forms in the hole and on the slug. What causes these characteristics? (A sketch of either the hole or slug may help)
Needs to be a draft angle so part releases from the die
(2) When you are hot forging, how are grain flow, the location of the die parting line and draft important in the design of your part?
ductile materials are softer and will tear instead of crack. Surface edges will be a little smoother than brittle materials
(3) How do die clearance and ductility of the metal influence these surface characteristics?
the rough fracture surfaces are due to cracking
(3) When punching a hole in plate material, discuss the characteristics of the surface that forms in the hole and on the slug. What causes these characteristics? (A sketch of either the hole or slug may help)
The location of the parting line affects the grain flow which affects the structural properties. The parting line should always be through the thickest section.
(3) When you are hot forging, how are grain flow, the location of the die parting line and draft important in the design of your part?
smooth & shiny burnished surfaces on the hole and slug are from contact and rubing of the sheared edge against the walls of the punch & die
(4) When punching a hole in plate material, discuss the characteristics of the surface that forms in the hole and on the slug. What causes these characteristics? (A sketch of either the hole or slug may help)
die clearance determines shape and quality of the sheared edges. As clearance increases the deformation zone becomes larger and sheared edge surface become larger
(5) When punching a hole in plate material, discuss the characteristics of the surface that forms in the hole and on the slug. What causes these characteristics? (A sketch of either the hole or slug may help)
Grain size affects the strength of the material, with smaller grains resulting in higher strength due to higher resistance to dislocation. Rolling the metal elongates the grains in that particular direction and producing anisotropic properties, resulting in different strengths in different directions. Hot rolled material can have its isotropic properties restored through heat treatment unlike cold rolled.
Discuss how anisotropy and grain size can influence the results of a sheet metal forming operation
where surface tension creates cracking in a material as it is folded. Ductile materials such as aluminum can undergo more bending than brittle materials such as steel before encountering this problem.
What is meant by the term minimum bend radius of the sheet metal? How does ductility influence bend radius of sheet metal?
the elastic recovery of a deformed metal after the load is removed. It can be accounted for by overbending the material.
What is springback in sheet metal forming and how do you account for it in your operation?
Where a complex die is being used and the metal cannot fill all parts of the die. Can be prevented by increasing the radius of sharp corners.
What would be the cause of a lap in forging and how could you prevent it from occurring?
draw
You are welding two pieces of hot rolled 1050 steel plate (stress ultimate = 78ksi, yield strength = 50ksi). An E8018 electrode is what is being used with all of the welds. 2a. Show the internal structure of the difference regions in and around the resulting weld and label them. Are any of the regions of particular concern?
