Sheet Forming

Intelligent Pressure Devices

One of the advantages of using a mechanical press to perform the sheet drawing operation is the speed at which the press can run. It is not uncommon to see these presses running at speeds in excess of 18 hits per minute. Combining this with a significant draw depth can produce individual cylinder flows rates in excess of 750 gallons per minute depending on the number of cylinders incorporated into the cushion system.
At these press speeds, the pressure cycle can be as short as .5 seconds. This requires a valve that can open, modulate and fully close in that time, smoothly regulating the rapidly decaying flow. The response time becomes so short and the flow rates so high that it becomes necessary to substitute active pressure devices for the conventional control pressure relief valve. To address this need, Oilgear has developed a line of 2-way servo operated, manifold mounted flow control devices. These valves have over a 1000-gallon per minute flow capacity with step response times of 40 mSec.

System Design

Oilgear's current cushion designs consist of various cylinder and cushion pressure pad arrangements. One of the primary benefits of the intelligent cushion is its ability to accelerate prior to contact. This reduces the impact loading on the part as well as mechanical shocks to the press itself. The system provides for various types of locking features at the bottom of stroke and controlled return rates.

The process of forming a part during the draw stroke requires that the pressures be controlled properly. A cushion system, which uses 4 cylinders and a hydraulic positioning control for acceleration, lock and return requires careful analysis to ensure all components are selected properly and meet the required response times. To ensure this, all new systems are modeled and checked for performance.

Because Oilgear manufactures the high bandwidth devices, we have all the proper design data to place into the mathematical model. Only after complete analysis is the final design released to manufacturing.

Custom Designs

Oilgear's tradition has been to design and fabricate custom manifolds, power units and control systems to interface with either existing or new press equipment. OEM solutions include designs done concurrently during press design to yield well-engineered integrated systems.

This 16,000-lb. manifold is used to control a twin cylinder, auto leveling, and position controlled pressure pad.

Control System

The Oilgear cushion control system is a microprocessor-based system operating on a "Windows 2000" platform. The PC based system is used to ensure that reliable update times of 1 mSec. can be counted on. At 18 hits per minute each degree of crank angle equates to .0092 seconds or .25 inches of slide displacement depending on contact position and the type of drive. Very high and repeatable scan rates are a must.

The traditional intelligent cushion control system is usually interfaced with a press, master plc control system. The cushion control system is designed to communicate to the press PLC using standard industry hardware. The enhancements included within the cushion HMI are far to many to list here, but provide an easy means to monitor control signal transducers, commands and communication control bits as they are being transmitted. Input screens are clear and easy to decipher.

Other control enhancements include the ability to graph and store live data as the press is running. This allows playback at a later time to compare cushion performance for the same parts. The graphics package also allows the user to observe data (pressure profiles, pre acceleration, lock and return functions) as the press is running. If equipped with an internal modem and enabled, these graphical displays are available remotely literally anywhere access is allowed. Modem access further results in an extremely valuable tool for initial troubleshooting.

Again because the system is PC based and running on windows, the advantages of incorporating other Windows software exists. For example all the electrical as well as hydraulic circuits are stored right in the control PC for fast easy access.

Control training and trouble shooting is further enhanced through the use of an optional dynamic control / cushion simulator. The simulator includes all the cushion HMI screens, drawings and physical system parameters such as compressibility's, cylinder sizes etc. to make this a true dynamic simulator. Screen control entries can be changed and the result observed without having to disrupt production or change actual machine settings. Because the simulator will run on a stand-alone PC, it makes itself an invaluable classroom tool.