A Hydraulic press is a machine in which a large force is exerted on the larger of two pistons in a pair of hydraulically coupled cylinders by means of a relatively small force applied to the smaller piston. Whereas, a Mechanical press is a machine that exerts pressure to form or shape or cut materials or extract liquids or compress solids. There are various differences between mechanical and hydraulic presses. Following are fw of the major differences between them:
Hydraulic vs mechanical presses
Punching and forming
In most of the industries sheet metal components require punching and forming. Hydraulic presses are flexible and easy for both punching and forming operations. In addition, the tooling for the hydraulic presses is also simpler. Even stamping can be done on the same press with the most inexpensive tooling. When it comes to use on such components, hydraulic presses are a better solution as against the mechanical presses and press brakes involving quiet expensive dies. Another reason for using hydraulic presses over other types of presses is that they allow fast set ups, and eliminate many forming functions and secondary forming operations. Materials handling cost is also reduced by the above. In fact, hydraulic press also replaces mechanical stamping press due to minimum set up time and low cost tooling. The hydraulic presses perform all different types of forming operations, including countersinks, lance-and-form, pierce-and-form, louvers, and single/double electrical knockouts along with marking of company logo and part numbers, etc. The hydraulic presses with their related tools, are the most versatile punching, forming and stamping presses. They can also punch and form in both up and down directions. These features provide greater flexibility as compared to mechanical presses. Much time can be saved in manufacturing of sheet metal parts by cutting and also performing many forming operations, eliminating secondary operations, which also requires moving the components to the next machine.
Hydroforming is one of the areas in which hydraulic presses have no competition. The hydraulic press ram moves down to close the die and the hydroforming high-pressure fluid fills and acts on to the inside of the tubular parts and expands it to fill the die. This operation requires dwell time at the bottom of the stroke to perform the hydroforming operation. The mechanical presses are not capable to carrying out the hydroforming operation, as they do not have the speed control and also the provision to stay on the bottom for performing the high pressure forming operations.
The slower speed of the hydraulic press offers a big advantage in hydroforming process over mechanical press, as in hydroforming, tubular and sheet metal components are formed by liquid pressure, which reduce the number of operations and therefore producing the finished component in much lesser time. By hydroforming the components produced are more rigid as compared to the components produced by other processes.
Better controls of speed and force
Hydraulic presses have major advantage of dwelling and ram speed control, which mechanical presses do not have. In mechanical presses the flywheel directly drives the stroke and there is no control over the speed and force. In a hydraulic press you gain greater control over ram action during stroke, making it more versatile for producing complex shapes. There may be different levels of sophistication in forming the desired shape and you want full control of speed force on the entire stroke. The hydraulic machines can be made with fully programmable control over ram speed and ram position, which is not possible in the mechanical press. For better material properties during forming and longer tool life, the adjustable and slower ram speed are necessary to optimise the material flow, which lead to better product quality. The full control over speed, position and dwell, produces better accuracy, crisp and clean shape and look.
Function of speed and stroke
Hydraulic presses have expanded the forming capabilities for sheet metal shops for their unmatched functions of speed, stroke and force. They are becoming more popular and the old stories about them being slow and leaky have been disappearing. They can run at 200 strokes per minute or even more. The hydraulic presses deliver full force at any position in the stroke that offers a lot of flexibility in the dies. Another big advantage of these presses is that they are very easy to set for different operations. The job can be changed and reset the press easily. Hydraulic presses can have much longer strokes to accommodate the variety of dies. The ram stroke can be easily adjusted from minimum to maximum at any position without the need of additional bolster plate or gap piece.
Hydraulic press utilities are further increased by the new generation controls with fluid management. The shorter response time of valve delivers the oil to the actuator faster, to offer the better efficiency. For further improving the performance, accumulators are also provided in the fluid power system for better fluid management. The new generation controls along with high efficiency hydraulic circuits are the major factors in improving the hydraulic press performance. Electronically controlled proportional valves and electronic pressure switches are used to set or adjust the pressing force during the process. The stroke and distance can be controlled in microns by a laser dimension control system. The stroke, force and speed can be electronically controlled, therefore a PLC in the control panel. All these variables can be set and stored in a list of menus, which are instantly retrievable, when the job or process is to be changed.
Leak control management
Today, our presses are being equipped with new generation leak control management, including system save assemblies, modular concept with stack-system and Parker new generation EO-2 zero leak fittings.
Hydraulics: The smarter choice
The main reasons why all over the world people are changing from mechanical to hydraulic presses are :
1. Flexibility of operation
2. Multiple utilities
3. Full tonnage at any point of stroke
4. Ability to operate with a very wide range of stroke like 10 mm to 1500 mm on the same machine.
5. The working stroke can be adjusted at any position throughout the length.
6. Any desired speeds can be set at any position, and can be simply re-programmed.
7. Different operations can be carried at different pressures simply by adjusting the PLC command, pressure switch setting or pressure control valve.
8. Full programmable control over full ram stroke and position is possible.
9. Better tooling life and better product quality with better looking, crisp, clean forms and accuracy are achieved with a hydraulic press.