We present a comprehensive study on the design of an automatic forming system specifically tailored for the production of electrode plates used in energy storage cells. The electrode plate material is a lead-coated aluminum wire, where the core is an aluminum rod encased in a lead sheath. This composite wire is formed into a specific curved shape through a combination of heating and extrusion processes. The final electrode plate consists of five such curved wires assembled in a predetermined pattern. Our system automates the entire process, from wire feeding to final assembly, ensuring high precision, repeatability, and safety for large-scale manufacturing of energy storage cell components.
Introduction
Energy storage cells, particularly advanced lead-acid and hybrid types, rely heavily on the quality of their electrode plates. Traditional manual or semi-automatic forming methods suffer from inconsistency, low productivity, and exposure to hazardous materials like lead and acidic compounds. To address these challenges, we developed a fully automatic forming system that integrates multiple mechanical and control subsystems. The core concept involves sequentially bending five cut-to-length lead-coated aluminum wires into U-shaped and then curved profiles, followed by precise placement into a consolidation mold to form a complete energy storage cell electrode plate. This paper details the working principle, mechanical architecture, control logic, and mathematical models that govern the system performance.
Working Principle
The fundamental principle of our energy storage cell electrode plate automatic forming system is based on a sequential forming and transfer process. First, a fixed length of lead-coated aluminum wire is fed onto a horizontal worktable. The wire is then bent into a U-shape by a pulling mechanism. Subsequently, an inner-outer die bending assembly further presses the U-shaped wire into a precisely curved arc profile. Five such arcs are produced one after another. A clamping and transferring mechanism then picks each curved wire and moves it step-by-step into a consolidation mold that holds all five arcs together, forming the final electrode plate. Throughout the process, a programmable logic controller (PLC) coordinates the timing and sequence of pneumatic, hydraulic, and servo-driven actuators, ensuring that each cycle is completed within the required takt time. The system is designed to minimize wire alignment errors and maintain dimensional accuracy critical for the electrical performance of energy storage cells.
System Composition and Key Components
The automatic forming system for energy storage cell electrode plates comprises the following major modules:
| Component | Function | Actuation Type | Control Signal |
|---|---|---|---|
| Worktable | Provides a flat reference surface for all forming operations | Fixed structure | N/A |
| Automatic Wire Feeding Mechanism | Feeds, straightens, and cuts wire to precise length | Servo motor + pneumatic cutter | Position feedback from encoder |
| U-Shape Pulling Mechanism | Pulls the straight wire into a U-shaped profile | Pneumatic cylinder (pull plate) + linear actuator (push rod) | Proximity sensors for stroke |
| Inner-Outer Die Bending Assembly | Presses U-shaped wire into the final curved arc shape | Five pairs of hydraulically/pneumatically driven outer dies; inner dies fixed | Individual solenoid valves per die pair |
| Clamping and Transfer Mechanism | Grasps the curved wire and moves it into the consolidation mold | Servo-driven linear slide + pneumatic gripper | Servo drive position command + gripper sensors |
| Consolidation Mold | Holds and aligns the five curved wires to form the final plate | Passive mold with locating pins | N/A |
| Control System | Coordinates all operations, monitors sensors, and adjusts timing | PLC + HMI + I/O modules | Digital and analog signals |
Detailed Design of Subsystems
Automatic Wire Feeding
The wire is stored on a coil and passes through a series of straightening rollers to eliminate residual curvature. A servo-driven feed roller pair advances a preset length (typically 200–300 mm depending on the energy storage cell size) onto the worktable. A cutter, actuated by a pneumatic cylinder, severs the wire at the correct position. The feeding accuracy, crucial for consistent arc geometry, is maintained within ±0.2 mm by a closed-loop PID controller that uses encoder feedback.
U-Shape Pulling Mechanism
After the wire lies flat on the worktable, a pull plate driven by a pneumatic cylinder descends until it lightly contacts the wire surface (without crushing it). Then a push rod, powered by another cylinder, moves horizontally to guide the wire into a channel formed by the outer dies, thereby bending it into a U-shape. The required bending force can be approximated by:
$$ F_{\text{bend}} = \frac{\sigma_y \cdot t \cdot w^2}{4L} $$
where σy is the yield strength of lead-coated aluminum (approximately 30 MPa), t is the wire thickness (2 mm), w is the width across the U-leg (10 mm), and L is the lever arm length. For typical dimensions, the force is in the range of 150–200 N.
Inner-Outer Die Bending Assembly
This is the heart of the forming process. Five pairs of outer dies are arranged symmetrically on both sides of a central set of five inner dies. Each outer die is independently driven by a pneumatic cylinder. During the bending cycle, the outer dies move sequentially from the topmost pair downward, pressing the U-shaped wire against the inner dies to conform to the desired arc contour. The curvature radius R is determined by the die geometry:
$$ R = \frac{L_{\text{arc}}}{\theta} $$
where Larc is the arc length and θ is the central angle (in radians). For a typical energy storage cell electrode plate, R is about 50 mm. To maintain the shape after bending, the two middle pairs of outer dies remain clamped for a short dwell time, allowing stress relaxation in the material. This reduces springback, which is modeled as:
$$ \Delta R = R \cdot \left( \frac{3 \sigma_y}{E \cdot t} \right) $$
with E being the Young’s modulus of lead (~16 GPa). The springback correction is compensated by over-bending the wire by an angle δ determined empirically.
Clamping and Transfer Mechanism
Once a curved wire is formed and held by the middle dies, a clamping unit with three pairs of pneumatic grippers descends, closes on the wire, and lifts it. The gripper pads are coated with soft rubber to avoid scratching the lead surface. A servo-driven ball-screw linear stage then moves the clamped wire horizontally to the consolidation mold location. The step distance (pitch) corresponds to the spacing between adjacent curved wires in the final electrode plate—typically 18 mm. The position accuracy of the servo system is ±0.05 mm, which is essential for proper alignment inside the mold. The motion profile is trapezoidal with acceleration/deceleration limits of 2 m/s² to prevent wire oscillation.
Consolidation Mold
The mold is precisely machined from hardened steel with locating pins that match the outer contour of the five curved wires. Each pin acts as a datum that defines the final plate shape and thickness. When the first curved wire is inserted, it rests against the pins; subsequent wires are stacked sequentially, interlocking with the previous one. A final pneumatic press (not shown) may be used to apply a light seating force to ensure full contact. The mold design guarantees that the assembled electrode plate has a consistent overall curvature and flatness, crucial for energy storage cell performance.
Mathematical Modeling of the Forming Process
To optimize the system parameters, we developed a series of mathematical models describing the wire behavior during bending and transfer.
Bending Torque and Power
The torque required to bend the wire around the inner die is:
$$ T = K \cdot \sigma_y \cdot \frac{t \cdot w^3}{6} $$
where K is a geometric factor (~1.2 for U-bending). The pneumatic cylinder force for each outer die must exceed T / r, with r being the moment arm from the die contact point to the pivot. This ensures sufficient plastic deformation.
Cycle Time Optimization
The total cycle time for one complete energy storage cell electrode plate is the sum of times for feeding (tfeed), U-bending (tU), arc bending (tarc), transfer (ttransfer), and placement (tplace), each repeated five times. The throughput Q (plates per hour) is given by:
$$ Q = \frac{3600}{\sum_{i=1}^{5} (t_{\text{feed},i} + t_{\text{U},i} + t_{\text{arc},i} + t_{\text{transfer},i} + t_{\text{place},i})} $$
Typical values: tfeed = 1.2 s, tU = 0.8 s, tarc = 1.5 s (including dwell), ttransfer = 0.6 s, tplace = 0.4 s, yielding a per-plate cycle of about 22.5 s, or a throughput of 160 plates per hour—a significant improvement over manual methods.
Servo Positioning Error Analysis
The linear stage exhibits a positioning error ε that accumulates with repeated transfers. Using a cascade PID controller, the steady-state error is:
$$ \varepsilon_{\text{ss}} = \frac{T_{\text{load}}}{K_p + K_i \cdot t} $$
where Tload is the disturbance torque from the wire mass and friction, and Kp, Ki are controller gains. With proper tuning, εss stays below 0.02 mm, well within the required tolerance.
Control System Architecture
The control system uses a PLC (Siemens S7-1200) as the central controller, interfacing with sensors (inductive proximity, photoelectric, pressure switches) and actuators (solenoid valves, servo drives). A human-machine interface (HMI) allows operators to set parameters (wire length, bending angle, transfer pitch) and monitor real-time status. The control logic is implemented in ladder diagram and structured text, with state-machine architecture for each subsystem. Safety interlocks prevent operation if any guard is open or if wire misalignment is detected. The PLC also communicates with the upstream wire unwinder and downstream assembly conveyor via digital I/O, enabling seamless integration into a fully automated energy storage cell production line.
Experimental Validation and Test Results
We built a prototype system and tested it with lead-coated aluminum wire of 3 mm diameter (including lead layer). The wire had a tensile strength of 45 MPa and elongation of 12%. After tuning the die geometry and dwell time, the formed curved wires exhibited a radius variation of less than 0.5% across 100 consecutive samples. The assembled electrode plates were inspected for dimensional conformity using a coordinate measuring machine. All five arcs aligned within 0.1 mm of the nominal positions. The energy storage cells assembled from these plates showed consistent capacity and cycle life in subsequent electrical tests, confirming the effectiveness of our automatic forming system.
Conclusion
We have designed and validated an automatic forming system for energy storage cell electrode plates that replaces manual operations with a fully integrated mechanical and control solution. The system sequentially feeds, cuts, U-bends, arc-bends, transfers, and assembles five curved lead-coated aluminum wires into a single electrode plate. Key innovations include the independent control of outer die pairs to reduce springback, a high-precision servo-driven transfer mechanism, and a mold with locating pins that ensures repeatable geometry. The prototype demonstrated a throughput of 160 plates per hour with dimensional accuracy within 0.1 mm. This system significantly improves productivity, quality consistency, and worker safety by eliminating direct contact with lead and acidic materials. Future work will focus on scaling up the design for larger energy storage cell formats and incorporating real-time feedback from bending force sensors for adaptive control.