In the field of energy storage battery manufacturing, the production of battery plates is a critical process that directly influences the performance, efficiency, and lifespan of the final product. The energy storage battery plates I focus on in this design are made from lead-clad aluminum wire, where the core is an aluminum rod wrapped with a lead layer. This composite wire is formed through heating and extrusion. The complete plate consists of five curved wires assembled together. To address the challenges of manual assembly—low efficiency, inconsistent quality, and safety hazards from heavy metals and acidic materials—I have developed an automatic forming system that integrates feeding, bending, clamping, and assembling into a single automated workflow. This article presents the system’s working principle, mechanical architecture, control logic, and mathematical modeling, supported by tables and formulas to offer a comprehensive reference for similar energy storage battery production lines.
The entire system is designed to convert straight lead-clad aluminum wires into five identical curved segments and then precisely place them into a combining mold disc to form a complete energy storage battery plate. The process involves four main stages: automatic wire feeding, U-shaped pre-bending, inner/outer die bending into arcs, and clamping-and-insertion into the mold. Each stage is driven by pneumatic actuators and servomotors, controlled by a PLC-based system with sensors for position feedback. Below, I describe each component in detail.
1. Working Principle
The core principle of the system relies on a combination of inner and outer dies to bend the wire into a specific arc shape. For each of the five wires, an inner die is fixed at the center, and five pairs of outer dies are arranged symmetrically on both sides. During operation, the outer dies sequentially press inward from top to bottom toward the five inner dies, deforming the wire into the desired curved profile. After bending, the clamping-and-insertion mechanism, equipped with three pairs of openable grippers, picks up each curved wire and moves it—under precise servo control—to the combining mold disc. This step is repeated five times to assemble the complete energy storage battery plate.
The precision of the arc shape is critical for ensuring proper fit within the mold. I derived the relationship between the wire’s material properties, the die geometry, and the required bending force. For a wire of circular cross-section with an aluminum core (radius rAl) and lead cladding (outer radius rPb), the bending moment required to achieve a curvature radius R is given by the plastic bending theory. Assuming both materials are perfectly plastic, the combined bending moment M can be expressed as:
$$ M = \int_{0}^{r_{Al}} \sigma_{y,Al} \cdot y \cdot dA + \int_{r_{Al}}^{r_{Pb}} \sigma_{y,Pb} \cdot y \cdot dA $$
where σy,Al and σy,Pb are the yield stresses of aluminum and lead respectively, and y is the distance from the neutral axis. For a circular section, after integration, the formula simplifies to:
$$ M = \frac{4}{3} \sigma_{y,Al} \cdot r_{Al}^3 + \frac{4}{3} \sigma_{y,Pb} \left( r_{Pb}^3 – r_{Al}^3 \right) $$
This moment must be supplied by the outer dies. The force required from each outer die pair depends on the lever arm, which is determined by the design of the die contact point. Table 1 summarizes the key design parameters for the energy storage battery plate used in this system.
| Parameter | Symbol | Value | Unit |
|---|---|---|---|
| Total plate width | W | 120.0 | mm |
| Number of wires per plate | N | 5 | – |
| Wire outer diameter (lead) | dPb | 6.0 | mm |
| Aluminum core diameter | dAl | 4.0 | mm |
| Arc curvature radius | R | 150.0 | mm |
| Bending angle of each wire | θ | 60 | ° |
| Yield stress of lead | σy,Pb | 18.0 | MPa |
| Yield stress of aluminum | σy,Al | 35.0 | MPa |
The bending process must account for springback, which is significant for lead-clad aluminum due to the dissimilar elastic moduli. The springback angle Δθ can be estimated using the formula:
$$ \Delta\theta = \frac{M \cdot R}{E_{\text{eff}} \cdot I} $$
where Eeff is the effective elastic modulus of the composite wire, and I is the area moment of inertia. For the composite cross-section, Eeff is calculated by the rule of mixtures:
$$ E_{\text{eff}} = \frac{E_{Al} \cdot A_{Al} + E_{Pb} \cdot A_{Pb}}{A_{Al} + A_{Pb}} $$
with EAl = 69 GPa, EPb = 16 GPa, and areas computed from the diameters. The resulting springback is about 2.3°, which must be compensated by over-bending the dies. This compensation is built into the die profiles, ensuring that after springback, the final arc matches the required geometry for the energy storage battery plate.
2. Equipment Composition
The automatic forming system for energy storage battery plates consists of the following major units: a workbench, an automatic wire feeding mechanism, a U-bending mechanism, an inner/outer die bending mechanism, a clamping-and-insertion mechanism, a combining mold disc, and a control system. Each unit is described below.
2.1 Workbench
The workbench adopts a frame structure with a flat steel plate on top. All forming operations for the five curved wires are performed on this plate. The plate is precisely ground to ensure a flatness tolerance of ±0.05 mm, which is crucial for maintaining the dimensional accuracy of the energy storage battery plate. The workbench also serves as the mounting base for all other mechanisms, with T-slots and locating pins for quick adjustment.
2.2 Automatic Wire Feeding Mechanism
This mechanism delivers a fixed length of lead-clad aluminum wire onto the workbench. To guarantee straightness, I designed a feeding channel with guiding rollers that prevent lateral buckling. The wire is pulled from a coil by a set of pinch rollers driven by a stepper motor. The feeding length L is programmed based on the arc length of each wire, which is given by:
$$ L = R \cdot \theta \quad (\text{in radians}) $$
For R = 150 mm and θ = 60° = π/3 rad, the required length is approximately 157.1 mm. Once the wire reaches the target position (detected by a photoelectric sensor), a pneumatic cutter severs the wire, completing the automatic feeding cycle.
2.3 U-Bending Mechanism
The U-bending mechanism transforms the straight wire into a U-shaped profile before the final arc bending. It consists of a pulling plate, a pulling plate actuator (pneumatic cylinder), and a push rod actuator. After feeding, the pulling plate descends until it nearly touches the workbench surface (a gap of 0.5 mm is maintained to avoid scratching). Then the push rod actuator drives the pulling plate laterally through a channel formed by the outer dies, bending the wire into a U shape. The U shape reduces the subsequent arc bending force and improves the concentricity of the final arc. The displacement of the pulling plate is precisely controlled to achieve a U depth that ensures the wire ends align correctly with the inner dies.
2.4 Inner/Outer Die Bending Mechanism
This is the heart of the system. Five inner dies are fixed at the center of the workbench. On each side, five outer dies are mounted on linear slides, each driven by an independent pneumatic cylinder. The order of pressing is critical: from top to bottom, the outer die pairs sequentially close toward the corresponding inner dies. This sequential pressing prevents wire buckling and ensures a smooth arc curvature. After all five outer dies have pressed, the middle two pairs (positions 2 and 4) remain clamped to maintain the arc shape while the other pairs retract. This temporary clamping is necessary for the subsequent gripping operation.
The force required from each outer die pair can be computed by dividing the total bending moment by the number of dies and the effective moment arm. If we assume the wire contacts the die along a small arc of length lc, the normal force F per die pair is approximately:
$$ F = \frac{M}{N \cdot d} $$
where d is the distance from the die contact point to the neutral axis of the wire (approximately equal to the die radius plus wire radius). For our design, N = 5, d ≈ 25 mm, and the computed moment M ≈ 1.2 N·m, yielding F ≈ 9.6 N per die pair—easily achievable by small pneumatic cylinders.
Table 2 lists the specifications of the pneumatic cylinders used for each outer die.
| Die Pair Position | Cylinder Bore (mm) | Stroke (mm) | Operating Pressure (bar) | Max Force (N) |
|---|---|---|---|---|
| 1 (outermost) | 25 | 50 | 6 | 294 |
| 2 | 25 | 45 | 6 | 294 |
| 3 (center) | 32 | 40 | 6 | 482 |
| 4 | 25 | 45 | 6 | 294 |
| 5 (outermost) | 25 | 50 | 6 | 294 |
2.5 Clamping-and-Insertion Mechanism
This mechanism is responsible for picking up the formed arc wire and placing it into the combining mold disc. It comprises a clamping unit and a pressing unit. The clamping unit has three pairs of grippers arranged at equal spacing along the wire length. Each gripper is pneumatically actuated to open or close. The entire clamping unit is mounted on a vertical slide driven by a left-side pneumatic cylinder for up/down motion. When the bending is complete, the clamping unit descends, the grippers close around the curved wire, and then the unit ascends. Subsequently, the whole clamping-and-insertion assembly moves horizontally under the control of a servomotor and a ball screw. The motion profile is programmed as a point-to-point move with a travel distance equal to the pitch between successive wires in the mold disc. The pressing unit, located on the right side, consists of a vertical cylinder and a pressing plate. As the wire is inserted into the disc, the pressing plate descends to prevent previously placed wires from being flipped over by the new wire. This anti-tip feature is essential for maintaining the correct stacking order of the five arcs.
The horizontal positioning precision is critical because the mold disc’s cavities have tolerances of ±0.1 mm. The servomotor is equipped with an incremental encoder with a resolution of 1000 pulses per revolution, coupled with a ball screw of 10 mm lead, resulting in a positioning resolution of 0.01 mm. The control system uses a proportional-integral (PI) velocity loop and a polynomial interpolation for jerk-limited motion. The overall horizontal travel for each cycle is 24 mm (from the bending station to the first cavity, then 24 mm increments for each subsequent wire). The time for one complete cycle (pick-and-place) is approximately 2.5 seconds.
2.6 Combining Mold Disc
The mold disc is a circular plate made of aluminum alloy with multiple locating pins (ten pins in total, arranged in two rows of five). The positions and diameters of these pins precisely define the final contour of the energy storage battery plate. When the five curved wires are sequentially placed, they are guided by the pins to form a perfect grid-like pattern. The disc itself can be indexed by a rotary actuator to bring an empty set of cavities into the insertion position. After all five wires are placed, the completed energy storage battery plate is ejected by a pneumatic push plate and transferred to the next station (e.g., for welding or pasting). The material of the disc is chosen to resist the corrosive acidic environment typical of energy storage battery production, so a stainless steel alloy or coated aluminum is preferred.
The geometric relationship between the pin positions and the wire arcs is defined by the final plate shape. For a plate with five parallel curved wires, the arc centers are aligned along a common line. The distance between adjacent wire centers is constant, denoted as p. In our design, p = 24 mm. The curvature radius R and the subtended angle θ determine the chord length c = 2R sin(θ/2). For R = 150 mm and θ = 60°, the chord length is 150 mm. The total plate width is then W = (N-1)*p + dwire ≈ 5*24 + 6 = 126 mm, close to the design value of 120 mm (accounting for slight overlap). The pins are positioned at the ends of each chord and at the midpoints to ensure accurate nesting.
2.7 Control System
The control system is built around a PLC (Programmable Logic Controller) with a high-speed counter module for encoder feedback and an analog output module for proportional valve control (to regulate pneumatic cylinder speed). The PLC executes a cyclic sequence that coordinates all actuators: automatic feeding → U-bending → sequential arc bending → temporary clamping → gripper descent → gripper close → gripper ascent → horizontal move → gripper descent → gripper open → gripper ascent → repeat for next wire. Sensors include inductive proximity sensors for cylinder end-stroke detection, photoelectric sensors for wire presence, and a force sensor on the outer die to monitor the bending pressure. The force signal is used for adaptive control: if the bending force exceeds a threshold (indicating die wear or material variation), the system pauses and triggers an alarm.
The timing of each step is critical. Table 3 presents the typical cycle time distribution for one complete energy storage battery plate (five wires).
| Operation | Wire 1 (s) | Wire 2 (s) | Wire 3 (s) | Wire 4 (s) | Wire 5 (s) | Total per plate (s) |
|---|---|---|---|---|---|---|
| Automatic feeding + cut | 1.0 | 1.0 | 1.0 | 1.0 | 1.0 | 5.0 |
| U-bending | 0.8 | 0.8 | 0.8 | 0.8 | 0.8 | 4.0 |
| Arc bending (sequential dies) | 1.5 | 1.5 | 1.5 | 1.5 | 1.5 | 7.5 |
| Grip + rise + horizontal move | 2.5 | 2.5 | 2.5 | 2.5 | 2.5 | 12.5 |
| Insert + press + release | 1.2 | 1.2 | 1.2 | 1.2 | 1.2 | 6.0 |
| Return to start position | 0.8 | 0.8 | 0.8 | 0.8 | 0.8 | 4.0 |
| Subtotal per wire | 7.8 | 7.8 | 7.8 | 7.8 | 7.8 | 39.0 |
| Overhead (disc indexing, ejection, etc.) | – | 2.0 | ||||
| Total cycle time per plate | 41.0 | |||||
Thus, the system can produce approximately 3600 / 41 ≈ 87.8 plates per hour, or about 2100 plates per 24-hour day. This throughput is significantly higher than manual assembly, which typically averages 20–30 plates per hour. The control system also logs production data and can be integrated into a factory MES (Manufacturing Execution System) for tracking energy storage battery plate quality.
3. Mathematical Model for Process Optimization
To further improve the consistency of energy storage battery plates, I developed a mathematical model linking the dimensional tolerance of the arc wires to the final assembly accuracy. The position of each wire in the mold disc is determined by the gripper placement accuracy and the wire’s own shape. If the actual curvature radius Ractual deviates from the nominal Rnom, the wire will not seat correctly in the pins, causing misalignment. The acceptable tolerance ΔR can be derived from the pin clearance. The pins have a diameter of 8 mm while the wire has an outer diameter of 6 mm, leaving a radial clearance of 1 mm. However, the wire must be placed within ±0.5 mm of the ideal position at the ends. The relationship between curvature error and end-position error δ is:
$$ \delta = R \cdot \left( 1 – \cos\frac{\theta}{2} \right) \frac{\Delta R}{R} $$
For R = 150 mm, θ = 60°, δ ≈ 0.067 · ΔR. To keep δ ≤ 0.5 mm, ΔR must be ≤ 7.5 mm. This is a generous tolerance that is easily met by the bending mechanism. Nevertheless, wear on the dies over time will increase the error. Therefore, I included a periodic calibration routine using a vision system to measure the actual arc contour and adjust the die position offsets automatically. The calibration updates the target positions in the PLC, ensuring consistent quality for every energy storage battery plate produced.
Another important parameter is the clamping force of the grippers. If too low, the wire may slip during transfer; if too high, the lead cladding could be deformed. The required clamping force Fc must overcome the gravitational force (about 0.15 N per wire) and the inertial forces during horizontal acceleration. The maximum acceleration during horizontal motion is limited to 2 m/s² to avoid excessive dynamic loads. The clamping force is set to 10 N per gripper, providing a safety factor of 8. The pneumatic pressure to the grippers is regulated by a pressure reducing valve, and the actual force is verified by a load cell during setup.
I also modeled the heat dissipation during the bending process. Although the wire is at room temperature, the plastic deformation generates heat, which could affect the material properties. Using the assumption that all plastic work is converted to heat, the temperature rise ΔT is:
$$ \Delta T = \frac{W_p}{m \cdot c_p} $$
where Wp is the plastic work per unit volume, m is the mass of the deformed section, and cp is the specific heat capacity. The plastic work per unit volume for a material obeying a Ludwik hardening law (σ = K ε^n) is:
$$ W_p = \int_0^{\epsilon_f} \sigma \, d\epsilon = \frac{K}{n+1} \, \epsilon_f^{n+1} $$
For lead-clad aluminum, I used approximate values K = 40 MPa, n = 0.2, and a maximum true strain εf = 0.05. The calculated plastic work per unit volume is about 0.095 J/mm³. The deformed volume of one wire is roughly 500 mm³, giving total plastic work of 47.5 J. The mass of that volume is about 3.0 g (using density of 8.5 g/cm³ for lead-clad aluminum), and the specific heat is 0.13 J/g·K. The temperature rise is then about 122 K, which is high enough to cause thermal softening. In practice, the heat is quickly conducted away by the steel dies and the workbench, and the actual temperature rise is much lower. I added a cooling system consisting of compressed air jets directed at the dies to maintain the temperature below 60°C, ensuring stable material properties.
4. Conclusion
This design presents a complete automatic forming system for energy storage battery plates made from lead-clad aluminum wires. By integrating automated feeding, U-bending, multi-stage arc bending, and precise clamping-and-insertion, the system achieves high efficiency (about 88 plates per hour) and consistent quality, while eliminating direct human contact with hazardous materials. The use of inner/outer dies with sequential pressing ensures accurate arc shapes, and the servo-driven horizontal motion guarantees repeatable placement into the combining mold disc. Mathematical models for bending force, springback, positioning error, and thermal effects provide a solid theoretical foundation for optimization. The control system’s capacity for adaptive force monitoring and periodic calibration further enhances reliability. This system can serve as a prototype for similar energy storage battery plate production lines, offering a significant improvement over manual methods. Future work will focus on integrating real-time vision inspection and connecting the system to a wider energy storage battery assembly line for fully automated manufacturing.