University of Nevada Las Vegas

MEG426/626 Manufacturing Processes

Department of Mechanical Engineering

Fall Semester 2000

　

　

Hot and Cold Working

　

　

　

Some Hot Working Processes:
　

Rolling,

Forging,

Extrusion
　

Hot drawing,

Pipe welding,

Piercing

Reason for Hot Working:

At elevated temperatures, metals weaken and become more ductile.

Rolling: In hot rolling, as with all hot-working processes, temperature control is crucial to the success of the process. The starting material should be heated to a uniform elevated temperature, otherwise, the material deformation will not be uniform.

Uneven temperature _ residual stress, cracking, and tearing.

Ring rolling: is a deformation process in which a thick-walled ring of smaller diameter is rolled into a thin-walled ring of larger diameter.

Roll piercing: is used to make seamless thick-walled tubes.

　

Forging:

Open-die drop-hammer forging: the work is compressed between two flat dies, thus allowing the metal to flow without constraint in a lateral direction relative to the die surfaces.

Impression-die drop forging: the die surfaces contain a shape or impression that is imparted to the work during compression.

Flashless forging: the work is completely constrained within the die and on excess flash is produced.

Extrusion:

Direct extrusion: a metal billet is located into a container, and a ram compresses the material, forcing it to flow through one or more openings in a die at the opposite end of the container.

Indirect extrusion: the die is mounted to the ram rather than at the opposite end of the container.

Some Cold Working Processes:
　

Cold rolling,

Cold forging,

Cold extrusion
　

Bending,

Drawing,

Shearing

　

Reason for Cold Working:

Provides better surface finish and dimensional precision.

Cold rolling: thread rolling is one common cold rolling process to form threads on cylindrical parts by rolling them between two dies.

Cold forging: is used for making enlarged sections on the ends of rod or wire, such as the heads of nails, bolts, rivets, or other fasteners.

Cold extrusion: for low-strength metals such as lead, tin, zinc, and aluminum to produce such items as collapsible tubes for toothpaste, medications, and other creams, small "cans" for shielding electronic components, zinc cases for flashlight batteries, and larger cans for food and beverages.

Rod, Bar, and Tube Drawing:

Rod/bar drawing is to produce rod shaped product with smaller diameter.

Tube drawing is used to produce high-quality tubing where the product requires the smooth surfaces, thin walls, accurate dimensions, and added strength.

Wire drawing is the same as bar drawing except that it involves smaller-diameter material.

Bending: will be discussed in the next class.

Drawing: will be discussed in the next class.

Shearing: will be discussed in the next class.

　

Homework:

　

1). What are the characteristics that distinguish bulk deformation processes from sheet metal processes ?

2). Describe extrusion process with sketches and your own words.

3). What is the major difference between machining and forming ?

4). What is the temperature range used in hot working, and what is the advantage and disadvantage of hot working ?

　

Due: Next Friday