A CNC electro hydraulic synchronous press brake is a hydraulically driven sheet metal bending machine in which two independent hydraulic cylinders (designated Y1 and Y2) are governed by a closed-loop electro-hydraulic servo control system. Unlike older torsion-bar synchronisation designs that rely on a rigid mechanical twist bar to keep both sides of the ram in phase, the electro hydraulic variant uses proportional servo valves, high-resolution linear encoders and a dedicated CNC controller to continuously measure and correct ram position in real time.

The result is a machine that bends with near-identical force and angle on both ends of the workpiece — even across a 6-metre bed — without manual shimming or operator intervention.

 

This architecture sits between all-electric press brakes (which use ball-screw servo motors but are commercially limited to roughly 300 tonnes) and conventional open-loop hydraulic machines (which are powerful but suffer thermal drift during long production runs). The electro hydraulic synchronous design preserves the full tonnage range of hydraulics — from 40 tonnes to well beyond 1,000 tonnes — while delivering positioning precision in the ±0.005–0.02 mm band.

 

 

 

Understanding the control loop helps explain why this machine type outperforms older hydraulic designs in both consistency and energy efficiency.

 

 

The servo-hydraulic system operates through three hierarchical stages:

 

Command layer. The CNC controller — typically a Delem DA-66T, DA-69T or ESA S660 — receives the part geometry (either programmed manually or imported from a 2D/3D CAD file). It calculates the target bottom dead centre (BDC) position, bending force curve and back-gauge coordinates for each step of the bend sequence. Analog voltage or current signals are then dispatched to the proportional servo valves.

 

Execution layer. The electro-hydraulic proportional servo valve (commonly a Rexroth 4WRKE-class unit with a response frequency ≥ 150 Hz) receives the command and dynamically adjusts oil flow and back pressure to each cylinder independently. This is the critical difference from torsion-bar machines: the Y1 and Y2 cylinders are fed through separate hydraulic channels, eliminating the forced-synchronisation error that a mechanical twist bar inevitably introduces — especially under eccentric loading conditions such as single-side short-edge bending.

 

Feedback layer. High-precision linear encoders (Heidenhain LC-series gratings with 0.5 µm resolution are widely specified) are mounted at both ends of the ram. They continuously report actual ram position back to the CNC at millisecond intervals. The controller runs a PID algorithm, compares the measured value with the target, and issues a correction signal — forming a fully closed loop.

 

 

A conventional hydraulic press brake runs its motor-pump unit at constant speed throughout the entire cycle, even during rapid approach and dwell phases when no pressing force is required. In an electro hydraulic synchronous machine, the servo motor driving the hydraulic pump only delivers oil flow when the bending stroke demands it. During standby and rapid traverse, the pump idles at near-zero consumption.

 

Field data from multiple OEMs confirm an energy reduction of 30–50% compared with constant-flow hydraulic equivalents. The secondary benefit is less heat generation inside the hydraulic circuit: lower oil temperatures mean slower fluid degradation, which extends oil change intervals from roughly 2,000 hours to 4,000+ hours and reduces the frequency of seal replacements.

 

 

A typical bending cycle on an electro hydraulic synchronous press brake proceeds as follows:

 

1. The operator loads the part program (or imports a DXF/DWG file via the CNC touchscreen).

2. The controller auto-calculates springback compensation, bend sequence and required tonnage based on material type, thickness and die opening.

3. The multi-axis back-gauge (X, R, Z1, Z2 — often 4 to 6 axes) positions the sheet automatically.

4. The ram descends under servo-controlled speed: fast approach transitions smoothly to pressing speed at the programmed deceleration point.

5. At BDC, the encoder verifies angle and position; any deviation triggers an immediate correction before the next stroke.

6. The ram returns, the back-gauge repositions for the next bend, and the cycle repeats.

 

The entire process — from first touch to final bend — can run unattended for dozens of parts in succession, with the closed-loop system maintaining dimensional consistency that would be impossible to achieve through manual operation.

 

 

 

Selecting a press brake is not just about comparing tonnage figures on a brochure. The quality of several sub-assemblies directly determines long-term accuracy and reliability.

 

 

A proper frame is manufactured from thick, low-alloy steel plate using integrated welding construction, followed by a secondary stress-relief annealing treatment (typically 550–600 °C for several hours). This two-stage process ensures the frame does not distort under continuous heavy loading — a common failure mode in cheaper machines that skip the annealing step. After 10 or more years of production, a well-built frame should still hold its original geometric tolerance.

 

 

The cylinders themselves are honed to a bore surface roughness of Ra 0.4 µm or better to ensure smooth piston travel and consistent sealing. The servo valves are the most cost-sensitive component: imported units (Rexroth, Parker, Hoerbiger) still dominate the high-performance segment, though domestic Chinese alternatives have improved considerably — with the import share for servo valves dropping from approximately 75% in 2024 to around 68% in 2025, according to Boxun Consulting's 2026 electro-hydraulic press brake industry report.

 

 

The CNC is the "brain" of the machine. Leading controllers include:

 

• Delem DA-66T / DA-69T (Netherlands) — dominant in mid-to-high-range machines; supports 2D/3D graphical programming, automatic springback compensation and collision detection.

• ESA S660 / S700 (Italy) — widely used in European OEM machines.

• Cybelec ModEva (Switzerland) — known for advanced offline programming interfaces.

 

These systems typically account for 73.5% of the CNC-configured machine market in China, based on 2025 shipment data.

 

 

A multi-axis back-gauge is essential for production efficiency. A 4-axis system (X, R, Z1, Z2) covers the majority of standard bending tasks; 6-axis configurations add additional fingers and controllable crowning for complex parts. Positioning tolerance on a well-maintained back-gauge should be within ±0.03 mm.

 

 

Any press brake bed will deflect slightly under full tonnage. Mechanical crowning (a set of adjustable wedges under the lower die) and hydraulic crowning (a series of small compensation cylinders along the bed) are the two common approaches. Hydraulic crowning responds faster and adapts automatically to varying tonnage — an important feature for shops that frequently switch between thin-gauge and thick-plate work.

 

 

 

The press brake market offers several technology platforms. Each has a legitimate niche; none is universally superior. The table below summarises the key differences relevant to purchasing decisions.

Parameter	Torsion-Bar Synchronous	CNC Electro Hydraulic Synchronous	All-Electric Servo
Ram positioning accuracy	±0.10 mm	±0.01–0.02 mm	±0.003–0.005 mm
Max commercial tonnage	1,000+ tonnes	1,000+ tonnes	~300 tonnes
Bending angle repeatability	±0.5°	±0.25°	±0.1°
Energy consumption	Baseline	30–50% lower than baseline	50–70% lower than baseline
Eccentric load tolerance	≤ 10% of rated tonnage	≤ 30% of rated tonnage	N/A (single-cylinder design)
Thermal drift	Moderate; requires compensation	Minimal with servo control	None (no hydraulic fluid)
Typical price range (100T)	USD 12,000–18,000	USD 18,000–30,000	USD 50,000–120,000
Best suited for	Low-volume structural steel	Medium- to high-volume precision bending	High-volume thin-gauge electronics & enclosures