Fundamentals of Metal Forming Flashcards
What is plasticity?
Plasticity is the ability of a solid to flow, plastically deform, without deterioration of its
properties. The mathematical description of plastic deformation stresses and strains, and
the relations between them is known as the theory of plasticity.
Why might large production quantities be necessary to justify metal deformation as a means of manufacture?
Deformation processes shape metal in the solid state through the rearrangement rather
than the removal of material. Unfortunately, large forces are required, and the machinery
and tooling can be quite expensive. Large quantities may be necessary to justify the
capital expenditure.
What is an independent variable in a metalforming process?
Independent variables are those aspects of a process over which the engineer has direct
control. They are generally selected or specified when setting up the process.
What is the significance of tool and die geometry in designing
a successful metalforming process?
The specification of tool and die geometry is an area of major significance in process
design. Since the tooling will produce and control the metal flow, the very success or
failure of a process often depends upon good tool geometry.
Why is lubrication often a major concern in metalforming?
It is not uncommon for friction to account for more than
50% of the power supplied to a deformation process. Product quality is often related to
friction, and changes in lubrication can alter the material flow and resulting material
properties. Production rates, tool design, tool wear, and process optimization all depend
upon friction and lubrication. In addition, lubricants often act as coolants, thermal
barriers, corrosion inhibitors, and parting compounds .
Lubricants, and metal working lubricants in particular, can act as coolants, thermal
barriers and corrosion inhibitors. Often lubricants are formulated to include or enhance
these functions in addition to their use in reducing friction.
What are some of the secondary effects that may occur when
the speed of a metalforming process is varied?
If the speed of a metal forming operation is altered, several changes can occur. Many
materials are speed-sensitive and will behave differently at different speeds. Ductility
may vary, and many materials appear stronger when deformed at faster speeds. In
addition, faster speeds promote lubrication efficiency and reduce the amount of time for
heat transfer and cooling.
What is a dependent variable in a metalforming process?
Dependent variables are aspects of a process determined by the process itself as a
consequence of the values selected for the independent variables.
Why is it important to be able to predict the forces or powers
required to perform specific forming processes?
It is important to be able to predict the forces or powers required to perform a specific
forming process, for only by having this knowledge can the engineer specify or select the
equipment for the process, select appropriate tool or die materials, compare various die
designs or deformation methods, and ultimately optimize the process.
Why is it important to know and control the thermal history of a metal as it undergoes deformation?
The engineering properties of a product can be altered by both the mechanical and
thermal history of the material. Therefore, it is important to know and control the
temperature of the material throughout the process.
Why is it often difficult to determine the specific relation-
ships between independent and dependent variables?
Metal-forming processes are complex systems composed of the material being
deformed, the tooling performing the deformation, lubrication at surfaces and interfaces,
and various other process parameters. The number of different forming processes is quite
large, and various materials often behave differently in the same process. The
independent variables interact with one another, so the effects of any change are often
quite complex.
What are the three distinct ways of determining the inter relation of independent and dependent variables?
The predictive link between independent and dependent variables is generally based
on one of three approaches:
experience, experiment, or process modeling.
What features limit the value of laboratory experiments in modeling metalforming processes?
To be truly valid, direct experiments should be full-size at production speeds.
Reduced magnitude testing generally alters lubricant performance and thermal effects.
Results should be extrapolated to production conditions with caution. In addition,
experimentation is costly and time-consuming.
What features have contributed to the expanded use of process modeling?
Process modeling, particularly numerical modeling and simulation, has experienced
greatly expanded use because
- of the availability of computers with continually increasing computational power,
- the accuracy of simulations.
In addition, there are many useful results that can be obtained through use of process
models and some of these are listed in the answer to Question 17. below.
- of the use of quantitative results to provide understanding of details of deformation
processes,
- obtaining quantitative results that correspond to reality demonstrates process
understanding,
-of reductions in production delays and lead times due to having accurate predictions of
process performance and part characteristics at the process design stage of
manufacturing,
- they can be used as laboratory tools to run numerical experiments to
— simulate processes using varying processing conditions and tooling to answer “what
if?” questions,
— investigate feasibility of modifications to processes and products and evaluate new
processes and products.
What are some of the uses or applications of process models?
In general, process models are used to predict process behavior and resulting product
properties. Process behaviors such as forces and power required to produce a given
deformation pattern and product characteristics such as deformation in surface regions
and the resulting residual stress state can be calculated – is accurate process models are
available.
In addition, and expanding on the thoughts underlying Question 15:
Process modeling, particularly numerical modeling and simulation, has experienced
greatly expanded use because
- of the availability of computers with continually increasing computational power,
- the accuracy of simulations.
- of the use of quantitative results to provide understanding of details of deformation
processes,
- obtaining quantitative results that correspond to reality demonstrates process
understanding,
-of reductions in production delays and lead times due to having accurate predictions of
process performance and part characteristics at the process design stage of
manufacturing,
- they can be used as laboratory tools to run numerical experiments to
— simulate processes using varying processing conditions and tooling to answer “what
if?” questions,
— investigate feasibility of modifications to processes and products and evaluate new
processes and products.
