UWE Bristol Engineering showcase 2015

Richard Burr
Meng Mechanical Engineering q q q q q q
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Project Supervisor
Rui Cardoso
To Assess and Compare Mechanical Presses and Hydraulic Presses
Introduction
Presses are used to deform a material so that a
different geometry can be obtained from the
original. A forming press works by applying
pressure to a material to flatten, form, draw,
pierce, trim or blank that material. This is
performed by a ‘ram or slide’ which closes with a
bed. Attached to the ram and bed are the two
different parts of a press tool known as a die. The
upper member of the die is attached to the ram
and is driven by the press into the lower half of
the die which is attached to the bed. The die is
used to shape the material into the part that is
required.
Presses can be used to form a wide range of
products from sheet metal such as cooking pots,
car doors and car bonnets to cutlery and even
coins. Press forming is widely used in many
industries as it can produce quality parts almost
continuously enabling mass production of
products. Different types of presses include the
mechanical press, hydraulic press and the
pneumatic press. The name of the press comes
from the drive component of the press.
Forming Processes
There are different metal forming operations
which can be conducted with a press these include
cutting, bending, forging and deep drawing. At the
moment most presses are designed for one of
these processes as the requirements for each
process differ. One of the differences is the
kinematic requirements for each process such as
the ram velocity, accezleration and the ability to
apply the load along the whole stroke
Mechanical Press
The main factor in a mechanical presses
mechanism is changing the rotary motion of the
motor into the linear motion of the slide. Another
is the length of stroke. It is about balancing these
factors while keeping the size of the mechanism to
a minimum so that the machine is as compact as
possible. There are several different types of
mechanical presses these include the crank,
knuckle joint.
Slider Crank
The slider crank mechanism is one of the most
common mechanical drive systems for a press
because of its relatively simple design. Its slide
motion is the one of the most important factors in
its selection and how changing parameters affect
this
Vertical Displacement (m)
Slider Position From Top of Storke (m)
Knuckle Joint Press
The knuckle joint mechanism has a motion path
different to the slider crank when compared with
the slider crank and this makes it more suitable to
other forming operations
1.4
1.35
1.3
1.25
1.2
1.15
1.1
2.5
2
1.5
1
0.5
0
Position of Slider With Respect to the Crank Angle For Differing
Length Ratios Of Crank to Connecting Rod For A Non-Eccentric
Configuration
0 50 100 150 200 250 300 350 400
Angle of Crank (degrees)
Knuckle Mechansim Velcoity of Slide for a Changing Crank Angle
Displacement
Velocity
-0.2
0 50 100 150 200 250 300 350 400
Crank Angle (Degrees)
Ratio 1:1.25
Ratio 1:1.5
Ratio 1:1.75
Ratio 1:2
Ratio 1:3
Ratio 1:4
Ratio 1:5
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
Velocity (m/s)
Hydraulic Press
A simple hydraulic press has a piston in a cylinder
with an incompressible fluid both above and
below. The pressure is changed both in the top
and bottom of the cylinder to move the cylinder
up and down. This piston interns drives the ram
up and down (Anon, 1999). The pressure is
controlled through a system of valves, such as the
pressure relief valves, which both release and hold
the pressure where it is desired along the stroke.
To utilize the basic principle of the hydraulics and
ensure that the system will be able to achieve the
desired aims of the process it is being designed for,
the hydraulic circuit is built. This hydraulic circuit
generally contains several different components.
These include the cylinder, hydraulic fluid,
reservoir, pumps, valves and pipes.
There are different setups that can be used to
create characteristics for the cylinder which is the
hydraulic component that actually moves the ram.
One form of hydraulic circuit that could be used is
shown below.
Project summary
Presses are used in a variety of process to produce a
range of products. There are many different types of
presses including the mechanical and hydraulic press.
Both these machines have the same basic function to
produce a part from a work piece. This report looks
into the advantages and limitations of both the
mechanical and hydraulic press both against each
other and in respect to the process they are being
used to perform. This shall be first discussed in
general terms looking at the different processes they
can complete and the way in which they do. Then
using a given set of parameters such as load and size
shall be used to see which machine will be the most
suitable for these given parameters.
Project Objectives
The predominant aim of this report is to compare the
mechanical and hydraulic press doing this by
modelling different drive systems for each. Linked to
this aim is to look at how some individual
components can be altered to either improve or
change the attributes of these components. Another
aim is to look into which presses can be used for
different manufacturing processes. Looking into what
limits them in terms of what it can be used for.
Project Conclusion
Having modeled the different presses and applied these
models to the given parameters the hydraulic press was
the most appropriate choice. However the models could
have been more detailed to give a better reference point
for the conclusion taken. Although the predominant
finding was that although the hydraulic press was the
most suitable choice for the parameters the choice of
press changes depending on the parameters chosen.
Although a servo press could be the happy medium
between the mechanical and hydraulic as it utilises the
advantages of both