Automated System for Educational Training on Punching Process Characterization

Author(s):
Joaquim Gabriel Mendes - University of Porto
Maria Teresa Restivo - University of Porto

Industry:
Education

Products:
LabVIEW,

The Challenge:
Efficiently studying the mechanical characteristics of solid materials subjected to the punching process.

The Solution:
Developing a Macintosh-based measurement system using analog and digital DAQ boards controlled by LabVIEW.

Introduction
Automation of both test and measurement and process monitoring and control is significant to university laboratories. Flexibility in the selection of parameters to be measured and a user-friendly interface are both important goals for experimental measurements. These aspects are essential in R&D activities where postgraduate students play an important role. Some of the work also can be adapted to train undergraduate students. LabVIEW graphical software is an important key in using personal computers to achieve our goal of integrating hardware into easy-to-use systems for the experimental study of scientific and engineering phenomena.

Experimental Overview
For our experiments with the punching process, we used a prototype hydraulic press with a C-shaped frame and a nominal range of 35 kN. It was equipped with a variety of transducers, detectors, and control actuators. With special control strategies, it was possible to reach a cutting frequency of 11 Hz. The main instrumentation and control actuators are summarized as follows:

Transducers and Detectors
• Three absolute pressure transducers that also measure temperature - one in each cylinder chamber and the third in the hydraulic power unit
• One accelerometer and charge amplifier measuring the effect on the press structure during the cutting process
• One load cell designed and built to fit the particular needs of this press and its load range, used for a direct measurement of force (special care was taken in an automatic sensing of its supply value and autocompensation actions are implemented)
• One LVDT displacement transducer for structure deformation measurements
• One incremental encoder for tool position measurement
• One Hall-Effect sensor for fine tool position measurements
• One optical sensor (red beam) for metal sheet detection on the pneumatic metal sheet-feeder
• Three digital Hall-effect sensors as top, bottom, and middle dead center detectors
Control Actuators
• One proportional pressure-limiting valve to set maximum force.
• One pneumatic valve to actuate the metal sheet feeding
• One on/off valve within the water cooling system for oil temperature control.
• One analog 4-port directional/proportional valve for commanding the change of the speed of the ram mounted on the top of the cylinder

Hardware and Software Tools
The data acquisition and control system is based on an Apple Macintosh IIfx running LabVIEW, equipped with an NB-MIO-16 multifunction DAQ board, an NB-DIO-32F digital I/O board, and an NB-DMA-2800 DMA controller board from National Instruments. LabVIEW provides state-of-the-art graphical software tools for instrumentation programming and graphical user interface development.
The National Instruments products are aligned perfectly for the construction of virtual instrumentation systems, which rely heavily on the personal computer asthe host platform. We think of virtual instrumentation as a layer of software and hardware added to a general-purpose computer so that users can interact with the computer as though it were their own custom-designed traditional electronic instrument. The main point is that each user can construct his or her own instrument, as simple or as complex as needed, establishing simultaneously the specificity of the measurement methodology required.
Virtual instrumentation is ideal for university laboratories. Unlike industrial applications, where traditional turnkey solutions are often used, a university lab needs an open-architecture development environment to foster new creative approaches. We believe it is important at the educational level to allow students to be creative in building a measurement system to probe the phenomena under study, given that proper safety procedures are in place.

The VI for Punching Studies
The virtual instrument (VI) for studying the punching process characterizes the cutting force pattern evolution in terms of tool position and time (during the punching process). We have acquired a large amount of data for later correlation studies by introducing changes in parameters such as punching speed, hydraulic pressure, type and thickness of material, and different tool parameters.
From the front panel, you can define parameters such as cutting speed, number of samples acquired, tool position trigger point, hydraulic pressure, gain selection (for the different transducers), width of the windows to be recorded, and the data format. The front panel displays a graph of the cutting force and the average time between samples. We can also select additional mechanical measurement quantities such as press structure deformation, hydraulic pressure evolution, and machine vibration level from the front panel of this VI.

Summary
This type of experimental training, using integrated teaching of experimental techniques and LabVIEW graphical software, gives students excellent training through an open, interactive, flexible, and friendly system. In this approach, the student is an active participant instead of a traditional passive observer. We believe this approach is an important goal in experimental science and engineering education.
The flexibility in choosing test parameters offers a wide variety of possible experiments. Students report their results after they are analyzed based on the syllabus of a mechanical engineering course. This procedure introduces students to the traditional methodology of R&D activities.

For more information, contact:

Maria Teresa Restivo or Joaquim Gabriel Mendes

Mechanical Department, Faculty of Engineering, University of Porto, Rua dos Bragas

4099 Porto Codex, Portugal

Tel 351 (02) 204 1701

Fax 351 (02) 207 4241

E-mail: trestivo@fe.up.pt or jgabriel@fe.up.pt

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