Die Cushion Hydraulic Circuit With Logic Valve Pressure Control
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Solution Overview
Problem
Existing die cushion devices face issues with slow pressure increase, pressure fluctuations, and high costs due to complex control systems and the need for powerful servomotors, especially during press forming and knockout processes.
Innovation Solution
A die cushion device that uses a pilot-operated logic valve to control hydraulic fluid flow, allowing for excellent control of die cushion pressure and flow rate, reducing the need for high-capacity servomotors and simplifying control systems, while pre-pressurizing the cushion pad before forming to maintain pressure at bottom dead center.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a pilot relief valve is used to generate pilot pressure from hydraulic oil in the lower chamber, then the device can be simple and inexpensive without hydraulic drive sources, but the die cushion pressure increases slowly and takes long time to reach predetermined pressure
Solution Approach 1:
A logic valve is introduced as an intermediary component between the hydraulic cylinder and the accumulator. The logic valve controls the flow of hydraulic oil more efficiently than a pilot relief valve alone, enabling faster pressure buildup while maintaining the simplicity of the overall system design.
Solution Approach 2:
The accumulator is pre-charged with hydraulic oil at a predetermined pressure. This preliminary action allows the system to rapidly supply pressurized oil when needed, significantly reducing the time required to reach the target die cushion pressure without requiring a complex hydraulic pump system.
2Device complexity
If a pilot relief valve is used to control pressure, then the device structure is simplified, but pressure fluctuates depending on flow rate and velocity of the die cushion cylinder
Solution Approach 1:
A pressure detector is installed to monitor the die cushion pressure in real-time, and this information is fed back to a controller. The controller adjusts the logic valve to maintain constant pressure, compensating for fluctuations caused by varying flow rates and cylinder velocities, thus stabilizing the die cushion pressure throughout the press cycle.
Solution Approach 2:
The control system dynamically adjusts the opening degree of the logic valve based on real-time pressure feedback and the current operational phase of the press machine. This dynamic control ensures stable die cushion pressure regardless of changes in cylinder velocity or flow rate conditions.
3Measurement precision
If a hydraulic pump/motor driven by servomotor is used to control die cushion pressure, then precise pressure control is achieved, but the device becomes expensive and large in size
Solution Approach 1:
The logic valve acts as an intelligent intermediary that simplifies the control architecture. Instead of using a complex servomotor-hydraulic pump system, the logic valve receives simple control signals from a controller and automatically regulates pressure by coordinating oil flow between the hydraulic cylinder and accumulator, achieving precise pressure control with minimal complexity.
Solution Approach 2:
The invention extracts and utilizes the pre-stored energy in the accumulator to perform the majority of the pressure control function. This eliminates the need for a powerful servomotor and hydraulic pump, retaining only the essential logic valve and controller for precise regulation, thereby significantly reducing system cost and size while maintaining control precision.
4Manufacturing precision
If the velocity of the die cushion cylinder is reduced near bottom dead center, then the press forming quality is improved, but the die cushion pressure drops accordingly
Solution Approach 1:
The pressure detector continuously monitors die cushion pressure and provides feedback to the controller. When the cylinder velocity decreases near bottom dead center causing pressure drop, the controller detects this through the feedback signal and adjusts the logic valve to maintain the predetermined pressure, ensuring consistent press forming quality throughout the cycle.
Solution Approach 2:
The control system dynamically responds to changes in cylinder velocity by adjusting the logic valve opening degree in real-time. During the deceleration phase near bottom dead center, the system increases the valve opening to compensate for pressure drop, maintaining stable die cushion pressure despite velocity variations and ensuring high manufacturing precision.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution enables faster pressure stabilization, increased slide speed, and reduced costs by using a pilot pressure generator, allowing for efficient and cost-effective die cushioning with improved control and reduced disturbance during press forming and knockout processes.
Implementation Method 1
when die cushion pressure acts, hydraulic fluid which is pushed away from the lower chamber of the first hydraulic cylinder is discharged to the low-pressure source side of the first system pressure via the logic valve
Implementation Method 2
the pilot pressure acting on the pilot port of the logic valve is servo-controlled
Implementation Method 3
the pilot pressure acting on the pilot port of the logic valve is servo-controlled based on a first pressure command and pressure in the lower chamber of the first hydraulic cylinder
Implementation Method 4
a first accumulator configured to accumulate hydraulic fluid having a first system pressure which is low pressure
Data Source
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AI summary
The die cushion device includes a first hydraulic cylinder 120 for supporting a cushion pad 110, and a first hydraulic circuit 140-1 for driving the first hydraulic cylinder 120. The first hydraulic circuit 140-1 is a hydraulic closed circuit including a logic valve 148 connected between a die cushion pressure generation line 142 and a system pressure line 144, and a hydraulic pump (HP) driven by a first servomotor (SM1) for applying a pilot pressure to the logic valve 148. The first controller controls the first servomotor (pilot pressure) based on a first pressure command corresponding to the die cushion force and the pressure detected by the first pressure detector 143 to control the pressure in a lower chamber 120A of the first hydraulic cylinder 120 so that the pressure is equal to a pressure corresponding to the first pressure command.