Introduction
Metal stamping is widely used to shape metal parts in the automotive industry. During the manufacture of
torque converters, stamping is used to create a series of indentations that hold metal vanes that are used to
transmit the power from the engine to the transmission though a fluid. Hydraulic cylinders are used to force
a hardened punch into the metal which is displaced into a corresponding die creating the indentation.
Problem
The punches, being extremely hard, are subject to breakage. In an automated environment, where one part
is fabricated every 45 seconds, many bad parts can be fabricated before an operator, during a visual
inspection, detects that the indentations are not properly formed and that a punch has failed. In a system
with 3 simultaneous punching operations, a failure may occur as often as once per shift leading to a great
deal of scrap since the parts can not be reworked.
Solution
A system has been designed that incorporates an ADwin-light-16 real-time data acquisition and control
system to measure the force during the stamping operation. A load cell is attached to each hydraulic
cylinder used to drive the individual punches. Appropriate signal conditioning is used to amplify the low level
signal from the load cells to a -10 to +10 volt signal for the ADwin system. A signal from the PLC used to
control the press is fed into the ADwin Event input to trigger the acquisition cycle. The force waveform is
sampled at 1 kHz over the period during which the part is stamped (which includes 136 separate
indentations). The ADwin computes the maximum and minimum force and compares it to a pre-defined
window for each. If the value falls outside the window, the ADwin sends a signal to the PLC through OPTO-
22 signal isolators to indicate there is a problem.
Benefits
The use of the ADwin system to provide more real-time monitoring of the stamping operation allows broken
punches to be detected immediately, greatly reducing scrap costs. Also, this can reduce the need for
operators to inspect each part for defects. As more data is collected it may be possible to identify tooling that
is worn prior to it failing which can further reduce scrap and machine downtime.
Equipment Used
This list gives a typical example of a 16-channel system with 12-bit resolution for data acquisition:
- ADwin-light-16 - Real-time, data acquisition and control system
- Load Cell - Provides feedback of the force on the punch during the stamping operation
- Load Cell Signal Conditioner - Provides excitation and amplifies the low-level signal from the load cells
- OPTO-22 Signal Isolator – Provides isolation and TTL-to-line voltage conversion from the ADwin to
the PLC
|
