chapter 17
Discuss the significance of wear in metal forming:(a)wear on the workpiece. (b) wear on the tooling.
(a) A little wear on a workpiece makes it shiny and stand out. (b) Wear on tooling creates changes in workpiece dimensions and loss in tolerance control resulting in replacement tooling parts.
According to modern friction theory, frictional resistance can be attributed to what two physical phenomenon?
Abrasion and adhesion.
What are some of the secondary effects that may occur when the speed of a metal forming process is varied?
Affects the forces required for deformation, lubricant effectiveness, and the available time for heat transfer.
Why are friction effects in metal working difficult to scale down for laboratory testing or scale up from laboratory conditions to production conditions?
Because of the many variables that determine friction.
If the deformed grains recrystallize during hot working, how can the process impart an oriented or flow structure?
By unfavorably oriented or intersecting surfaces.
How can hot working be used to improve the grain structure of a metal?
Grain growth, additional deformation and recrystallization, or a drop in temperature that will end diffusion and "freeze in" the recrystallized structure.
Why is friction such an important parameter in metalworking operations?
It accounts for more than fifty percent of the in put energy which must overcome it. Also, there is rolling metal forming which can not be done unless the right amount of friction exists.
Why is lubrication often a major concern in metal forming?
It reduces friction, acts as a coolant, thermal barriers, corrosion inhibitors, and parting compounds.
Why is it often difficult to determine the specific relationships between independent and dependent variables?
Metal forming processes are complex systems composed of many variations of processes amassing to quite a large amount.
How might a material's performance vary with changes in the speed of deformation?
Some rate-sensitive materials may shatter or crack if impacted while others are stronger when deformed at higher speeds.
Lubricants are often selected for properties in addition to their ability to reduce friction, What are some of these additional properties?
The ability to act as a thermal barrier, coolant, and to retard corrosion.
What is plasticity?
The ability to flow as solids without deterioration of their properties.
What are some of the general assets of the metal deformation process? Some general liabilities?
The amount of waste is substantially reduce while on the down side, the forces required are often high, machining and tooling are expensive, and large production quantities may be necessary to justify such an approach.
What are some considerations regarding selection of the starting material for a forming process?
The chemistry, properties and characteristics of the selected material.
What is a dependent variable in a metal forming process?
The consequences of the independent variable selection.
Why might large production quantities be necessary to justify metal deformation as a means of manufacturing?
The cost and force needed for manufacturing is great, and is too expensive if it is only for a small yield when cheaper means are available that better suit low production quantity.
What is the significance of tool and die geometry in designing a successful metal forming process?
The detail from the mold, bend radius, and the control of metal flow as the material goes from starting shape to finished product.
Why might a rolled thread offer improved strength and fracture resistance compared to a machined thread?
The flow lines of the rolled thread are parallel to the external surfaces at all high-stress locations while for the machined thread, the flow lines run along the external surface allowing the easier formation of cracks and fractures.
What is tribology?
The study of friction and lubrication.
What is an independent variable in a metal forming process?
They are aspects of a process over which the engineer or operator has direct control, and they are generally selected or specified during setup.
Why is it important to control the final properties of a deformation product?
They are the properties that the customers are looking for.
Why is it important to control not only the external shape of a formed product, but also its internal flow?
While the objective of an operation is to attain a desired shape and possesses thee right set of companion properties, with out any surface or internal defects.
Why is it important to able to predict the forces or powers required to perform specific forming processes?
Without a reasonable estimate, we are unable to specify the equipment for the process, select appropriate tool or die materials, compare various die designs or deformation methods, or ultimately optimize the process.
Why is it important to know and control the thermal history of a metal as it undergoes deformation?
Changes in the temperature can lead to the breakdown of lubricants and the alterations of properties
What are the three distinct ways of determining the inter-relation of independent and dependent variables?
Experience, Experiment, and Process modeling.
What features limit the value of laboratory experiments in modeling metal forming processes?
Experiments are time consuming and costly.
