Stamping 101: How does a hydraulic press work?

An examination of hydraulic press technology and the press’s anatomy, as well as its benefits, limitations, tips for selection, and automation options, can net the best utility from a press.

Hydraulic Press Anatomy and Types

Press Structure: These are the key components of a hydraulic press:

1. Cylinder: The cylinder assembly includes the cylinder, piston, ram, packing, and seals. The piston diameter and oil pressure determine the press’s force (tonnage).
2. Frame: The main structure that houses the cylinders and working surfaces.
3. Stroke Control: Stroke length can be set within the cylinder’s limits, with adjustments for the top of stroke, pre-slowdown point, and bottom of stroke.
4. Throat Clearance: The distance from the centerline of the ram to the frame member behind the bed, determining the maximum piece size positioned under the ram.
5. Daylight: The vertical clearance from the top of the bolster to the underside of the ram at max height, indicating the press’s vertical die capacity.
6. Bed: A flat, stationary machined surface supporting the bolster and dies.
7. Bolster: A removable plate mounted on the bed where tooling is attached.
8. Dual Palm Button Controls: A safety feature requiring both buttons to be pressed simultaneously to operate the press, ensuring operator safety.
9. Work Height: The distance from the floor to the top of the bolster.

Common Types of Frames

• Bench: Compact and economical, bench presses are used for a range of jobs, with capacities from 3 to 50 tons.
• C-frame: Built for long service in industrial production, C-frame presses are suited for applications requiring 10 to 500 tons.
• Four-post: This heavy-duty press operates continuously and ensures precise die alignment, with easy loading from any side.
• Straight-side: Designed for demanding applications with superior frame construction, these presses handle heavy-duty blanking and can run millions of cycles annually.
• Gib-guided: Counteracts off-center loading with a rigid steel frame, maintaining parallelism under severe conditions.
• Air-over-oil: Suitable for prolonged applications requiring force maintenance. Affordable with low operating costs, but not ideal for typical stamping.
• Custom: Tailored press designs to meet specific application needs.

Hydraulic Press Common Terms and Features

Understanding these terms will enhance your knowledge of hydraulic presses:

• Blank Holder: Controlled force holding the edges of the blank in deep-drawing operations.
• Die Cushion: Hydraulic or air cylinder below the bolster and bed, ensuring uniform blank holding in deep drawing and stripping parts from the punch or die.
• Distance Reversal Switch: An adjustable limit switch setting the stroke depth at which the ram reverses.
• Dwell Timer: Adjustable timer setting the dwell length at the stroke's bottom, usable for various functions.
• Heat Exchanger: Part of the oil reservoir that circulates water or air to maintain proper oil temperature.
• Knockout: Device stripping the part from the punch or die.
• Platen: A plate, heated at times, attached to a moving or stationary press member.
• Pressure Reversal Switch: Adjustable switch setting the pressure at which the ram reverses.

Hydraulic Press Advantages

• Time Savings During Setup, Changeovers: Full power is delivered at any stroke point, eliminating the need to determine the exact location of maximum tonnage.
• Flexibility for a Range of Applications: Hydraulic presses are versatile, handling tasks such as deep draws, forming, blanking, punching, and assembly, among others. With PLCs and advanced computer interfaces, these presses can integrate into modern manufacturing systems.

Additional resources: What Industries Can Benefit from an Industrial Hydraulic ...，tpypress，How Hydraulic Press Works。