Sheet Metal Forming
Presses
October 15th, 2014
Hyunok Kim, EWI Forming Center
Taylan Altan, OSU - Center for Precision Forming (CPF)
1
Outline

Introduction

Classification of presses

Mechanical press

Hydraulic press

Die and Tooling

Force, Energy requirement of presses

Try-out press, Universal press, Transfer press

Servo-drive press (to be discussed separately)
2
Introduction

Information of presses is useful to:
─ Use the existing capital equipment more efficiently
─ Define the existing plant capacity accurately
─ Communicate with machine builders and work together to
improve machine performance
─ Develop in-house proprietary machines, if necessary

The press selection should consider:
─
─
─
─
The flow stress and formability of the deforming material
Load and Energy requirement
The “as formed” tolerances
The production rate
3
Load-Stroke Curves and Energy
4
Characteristic Data for Load
and Energy



Available Energy EM
Available Load LM (during the ram stroke)
Efficiency Factor (losses in electric motor, friction in
the gibs and bearings, elastic deflection)
LM  Lp during the stroke
EM  Ep in a stroke
(Lp = load required by process)
(Ep = energy required by process)
5
Time-Dependent Characteristic
Data

Machine Capabilities under load
─ Number of strokes per minute, n
─ Contact time under pressure, tp
─ Velocity during deformation, under pressure, vp
6
Characteristic Data for
Accuracy

Unloaded Conditions
─
─
─
─
Clearances in gibs
Parallelism between ram and bed (bolster) surfaces
Perpendicularity of the slide motion with respect to lower bed
Concentricity or in-line positioning of tool/die holders
7
Characteristic Data for
Accuracy

Loaded Conditions
─ Tilting of the ram (ram and frame deflections) under off-center
loading
─ Stiffness, c, of the press [i.e., c = Lm / deflection(d)]
─ For a given bed and deflection energy, Ed = dLm / 2 = Lm2 / 2c
─ Stiffness influences
a)
Part dimensions
b)
Contact time under pressure
8
Mechanical Press
•
•
•

Mechanical presses are powered using electrical
motor and forces are transmitted mechanically to the
work piece through the slides.
Flywheels are used to store the energy.
Force required to form the part and fluctuations in
the load determines the size of the flywheel.
Based on the kinematics of the transmission,
mechanical presses are classified as
1. Crankshaft driven presses
2. Eccentric shaft driven presses
3. Knuckle joint presses
9
Cross Section of a Mechanical
Press / Single Slide
Single-Action Mechanical
Press with Draw Cushion
Courtesy: Schuler Inc.
10
Double Slide Press
Double-action
Mechanical Press
Courtesy: Schuler Inc.
11
Double Slide Press
Stroke versus Crank angle graph
12
Crankshaft Driven Press
Crankshaft with Gear and
pinion drive
Advantages:
Good stability at high
capacities
13
Crankshaft Driven Press
(Altan, 1983)
14
Force, Torque and Energy
Permissible Press Force of an Eccentric Press as a Function of Crank Angle
Courtesy: Schuler Inc.
15
Force, Torque and Energy
(Altan, 1983)
16
Knuckle Joint Driven Press
A knuckle joint driven
press is often used to
generate a large force
for coining process
(Altan, 1983)
17
Force, Torque and Energy
Eccentric
Knucklejoint
Eight-Link
Displacement-Time Diagram
Courtesy: Schuler Inc.
18
Frame
Primary function of the frame is to contain the forces
applied by the press without deforming.
Mainly there are two types of frames, Open frame also
called “C” frame and Straight sided frame.
19
Open Frame/C-Type
Adjustable Bed Stationary
Open Back Stationary
[SME, 1984]
20
Straight Sided Frame
Connecting Rod Forces at the Slide in One-, Two- and Four-point
Presses
Courtesy: Schuler Inc.
21
Overloading Protection

Mechanical presses are protected from overloading
using replaceable or permanent protection units

In replaceable units, pins or washers are used, which
brake when overloaded

Permanent units use hydraulic or pneumatic circuits
and switches. When the press is overloaded, the unit
collapses.
22
Hydraulic Press
Hydraulic Press
Courtesy:
Schuler Inc
23
Force, Torque and Energy
Displacement-Time Diagram of a Hydraulic Press
Courtesy: Schuler Inc.
24
Comparison of Mechanical and
Hydraulic Presses

In mechanical presses the stroke needs to be completed
before reversal of the slide and for hydraulic presses the slides
can be reversed at any position.

Productivity (strokes per minute) of the mechanical press is
higher than that of the hydraulic press.
25
Comparison of Mechanical and
Hydraulic Presses
Slide Displacement and Power requirement versus Time in Mechanical and Hydraulic Presses .
Courtesy: Schuler Inc.
26
Transfer Press



In this type of presses, several sheet-forming
operations are performed by means of progressive
or transfer dies.
The blank material is automatically transferred from
one operation station to the other. This results in the
increase in productivity.
The selection of a transfer press has to consider the
blank material, the geometry to be formed, and the
necessary sequence of operations.
27
Tandem Press Line
Inter-linkage of Presses with Swing Arm Feeders
Courtesy: Schuler Inc.
28
Transfer Press
Transfer Die Set for a Press with Active Counter Drawing and Fixed Stops
Courtesy: Schuler Inc.
29
Servo Tandem Line at Suzuka
(Japan) Plant (Honda)
30
Servo-Drive Characteristics
(1)
(1) Variable
Variable
stroke
stroke
length
length
(2)
(2) Best
Best speed
speed
for
for materials
materials
Minimum stroke length
Slide Position
Fixed Motion
Cycle time of mechanical press
Free motion press
Cycle time of
Free motion press
(6)
(6) Synchronize
Synchronize with
with
feeder
feeder
Forming length
Crank or Link press
Time
Standstill at BDC
(3)
(3) Improve
Improve
accuracy
accuracy by
by
dwelling
at
dwelling at BDC
BDC
(5)
(5) Prevention
Prevention of
of
noise
noise and
and shock
shock
at
at contact
contact or
or
breakaway
breakaway of
of
tools
tools
(4)
(4) Other
Other Process
Process
at
BDC
at BDC
(Multi
(Multi Process)
Process)
The flexibility of slide motion in servo drive (or free motion) presses [Miyoshi, 2004]
31
Low RPM - High Torque
Servo Motor Drive 2/2
Servo-Press Drive Using Conventional Crank Mechanism [Courtesy: Aida]
32
Summary – Sheet Metal
Forming Presses




In sheet metal forming, mechanical, hydraulic and
servo-drive presses are used.
The understanding of press characteristics (i.e. load,
energy, ram speed, stroking rate, stiffness) is very
important in selection and use of press.
Mechanical press gives shorter cycle time but
hydraulic press is more flexible in controlling the
ram speed and tool setup.
The selection of press type and capacity depends
upon part size, material, production volume, and
cost.
33
Questions & Contacts
Taylan Altan
614.292.5063
[email protected]
Hyunok Kim
614.688.5239
[email protected]