Term
| What are the reasons why the bulk deformation processes are important commereicially and technologically? |
|
Definition
| Reasons why the bulk deformation processes are important include the following: (1) they are capable of significant shape change when hot working is used; (2) they have a positive effect on part strength when cold working is used, and (3) most of the processes produce little material waste; some are net shape processes |
|
|
Term
| Name the four basic bulk deformation processes. |
|
Definition
| The four basic bulk deformation processes are: (1) rolling; (2) forging; (3) extrusion; (4) wire and bar drawing |
|
|
Term
| What is rolling in the context of the bulk deformation processes? |
|
Definition
| Rolling is a deformation process in which the thickness of the workpiece is reduced by compressive forces exerted by two opposing rolls. The rolls rotate, thus pulling and simultaneously squeezing the workpiece between them. |
|
|
Term
| What is draft in a rolling operation? |
|
Definition
| Draft is the difference between starting thickness and the final thickness as the workpiece passes between the two opposing rolls. |
|
|
Term
| What is sticking in a hot rolling operation? |
|
Definition
| Sticking is a condition in hot rolling in which the surface of the workpiece adheres to the rolls as the piece passes between the rols, causing severe deformation of the metal below the surface in order to allow passage through the roll gap. |
|
|
Term
| Identify some ways, in which force in flat rolling can be reduced |
|
Definition
| Ways to reduce force in flat folling include: (1) use hot rolling; (2) reduce draft in each pass; and (3) use smaller diameter rolls. |
|
|
Term
| What is a two-high rolling mill? |
|
Definition
| A two-high rolling mill consists of two opposing rolls between the work is compressed |
|
|
Term
|
Definition
| Forging is deformation process in which the workpiece is compressed between two dies, using impact or gradual pressure to form the part |
|
|
Term
| 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. |
|
Definition
| The three basic types are: (1) open die forging; (2) impression die forging; and (3) flashless forging |
|
|
Term
| Why is the flash desirable in impression die forging? |
|
Definition
| Because its presence constrains the metal in the die so that it fills the details of the die cavity |
|
|
Term
| What is a trimming operation in the context of impression die forging? |
|
Definition
| Trimming is a shearing operation used to remove the flash on the workpiece after impression die forging. |
|
|
Term
| What are the two basic types of forging equipment? |
|
Definition
| The two types of forging machines are hammers, which impact the work part, and presses, which apply a gradual pressure to the work |
|
|
Term
| What is isothermal forging? |
|
Definition
| Isothermal forging is a hot forging operation in which the die surfaces are heated to reduce heat transfer from the work into the tooling |
|
|
Term
|
Definition
| Extrusion is a compression forming operation in which a workpiece is forced to flow through a die opening, thus taking the cross-sectional shape of the die opening. |
|
|
Term
| Distinguish between direct and indirection extrusion. |
|
Definition
| In direct extrusion, also known as forward extrusion, a metal bilet is loaded into a container, and a ram compresses the material, forcing it to flow through a die opening at the opposite end of the container. In indirect extrusion, also known as backward extrusion, the die is incorporated into the ram, and as teh ram compresses into the metal billet, the metal is forced to flow through the die opening in a direction that is opposite (backwards) of the ram motion. |
|
|
Term
| Why is friction a factor in determining the ram force in direct extrusion but not a factor in indirect extrusion? |
|
Definition
| Friction is a factor in direct extrusion because the work billet is squeezed against the walls of the container so that friction resists the movement of the billet toward the die opening. In indirect extrusion, the billet does not move relative to the container walls, and thus there is no friction |
|
|
Term
| What are wire drawing and bar drawing? |
|
Definition
| 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 |
|
|
Term
| In a wire drawing operation, why must the drawing stress never exceed the yield strangth of the work metal? |
|
Definition
| Because if the drawing stress exceeded the yield strength, the metal on the exit side of the draw die would stretch rather than force metal to be pulled through the die opening |
|
|
