Straight side connecting rod frame two-piece crank press STF: analysis of structural innovation and batch stamping application

1. Core definition and structural composition
The STF press is a type of crank press that adopts a straight-side connecting rod transmission mechanism and a closed frame structure, which can realize synchronous stamping of two symmetrical workpieces. The core uses the double crank-straight side connecting rod coordinated movement to convert the motor rotation power into synchronous linear motion of the double slider. It is specially used for the two-piece integrated forming of medium-thick plate (0.8-3.0mm) automotive structural parts. Its structural design focuses on the core of "symmetrical force bearing and synchronization accuracy", and the three major modules work together to ensure the consistency and stability of double-piece processing.

1. Straight side connecting rod and crank transmission unit

The power core uses a high-power servo motor with a double crankshaft design. The straight connecting rods on both sides are symmetrically arranged at both ends of the crank pin to form a mirror transmission structure. The straight-side connecting rod is made of an integral forging process and is precision ground to ensure length consistency and transmission accuracy, which can effectively offset the lateral force and eccentric load moment generated during the stamping process. The motor is controlled cooperatively by the flywheel energy storage and the clutch, driving the double crankshaft to rotate synchronously, and driving the straight side connecting rod to push the double slider to move linearly at the same speed and direction, achieving simultaneous stamping of the two pieces. The transmission components are equipped with an adaptive lubrication system to accurately supply oil to high-speed operating nodes, reducing wear and ensuring transmission stability.

2. Two-piece execution and frame mechanism

The actuator adopts an integrated design of double sliders, and the parallelism of the slider is controlled at ≤0.008mm/m. It is guided and constrained by eight-sided hard rails to ensure the synchronization of motion during double-piece stamping. The work surface is adapted to the one-mold and two-piece mold layout, and the size can be customized to more than 5000mm×2500mm to meet the two-piece forming needs of large automobile parts. The load-bearing frame adopts an integral closed casting structure, which has been annealed to eliminate internal stress. Its rigidity is more than 40% higher than that of an open frame, which can effectively absorb the composite impact force generated by double-piece stamping and inhibit frame deformation. It is also equipped with a hydraulic cushion buffer device to provide uniform blank holder force for the double-piece deep drawing process to avoid wrinkling or cracking of the workpiece.

3. Dual-piece synchronous control system

It adopts the "PLC + dual-axis synchronous controller" architecture, equipped with high-precision magnetic scale and pressure sensors, with a sampling frequency of 20kHz, to collect dual slider position and pressure data in real time and form a closed-loop comparison. The core has a dual-piece synchronization error compensation function. When the movement deviation on both sides exceeds 0.01mm, the motor output is automatically adjusted to ensure the consistency of the two-piece forming dimensions. It is equipped with linkage control between the mold protection system and the wedge mechanism, adapts to double-piece multi-process composite stamping (integrated trimming, flanging, and punching), supports rapid mold change function (mold change time ≤ 4 minutes), and integrates fault diagnosis and production data statistics modules to assist automated production line management and control.

2. Working principle and core advantages

1. Working principle

After the motor drives the flywheel to store energy, the power is transmitted to the double crankshaft through the clutch. The double cranks rotate synchronously and drive the straight side connecting rods on both sides to reciprocate, and then drive the double slider to move down along the guide rail at a constant speed to complete the simultaneous stamping and forming of the double workpiece. The stamping process adopts the motion mode of "high speed in idle stroke - steady speed in forming section - high speed in return stroke". By optimizing the crank motion curve, the double slide blocks maintain constant speed and pressure during the forming stage. Combining frame rigidity and guidance accuracy ensures that the dimensional tolerance and surface quality of the two workpieces are consistent. For the double-piece deep drawing process, the hydraulic pad simultaneously provides uniform blank holder force, and cooperates with the wedge mechanism to complete side shaping, side punching and other composite processes.

2. Core technical advantages

Compared with traditional single-piece crank presses and high-speed presses, STF presses have significant advantages in two-piece mass production scenarios. The core highlights are as follows:

- Dual-piece synchronization and high efficiency: Two symmetrical parts can be processed in a single stroke, which increases the production capacity by more than 80% compared to a single-piece press. It adapts to the large-scale mass production needs of the automotive industry. In the application of BYD's fender production line, the average daily production capacity can reach 1.9 times that of traditional equipment.

- Excellent dimensional accuracy: symmetrical transmission of straight side connecting rods and dual-axis synchronous control control the dimensional tolerance deviation of double parts to ±0.2-0.5mm, which is 50% lower than the batch processing deviation of single parts, meeting the high-precision requirements of automobile body assembly.

- The force is stable and reliable: the closed frame and straight-side connecting rod structure effectively offset the lateral force, the stamping process has no vibration and low noise, the continuous trouble-free operation time can reach more than 1,000 hours, and the mold life is 30% longer than traditional equipment.

- Strong process compatibility: supports the integrated process of double-piece drawing, trimming, flanging, and punching, and is suitable for complex parts such as automobile front hood inner and outer panels, fenders, etc., reducing process flow, production energy consumption and labor costs.

3. Typical application scenarios

With its dual-piece simultaneous forming and high-precision characteristics, the STF press focuses on the automobile manufacturing industry and has become the core equipment of the body structure stamping production line. Typical application scenarios are as follows:

1. Automobile manufacturing industry

It is widely used in batch stamping of automobile front hood and inner and outer panels, fenders, door inner and outer panels, chassis symmetrical parts, etc. Changan Automobile uses an STF press to build a 5-sequence two-piece stamping production line. It realizes one-mold two-piece punching for the inner and outer panels of the front hood. The hydraulic pad pressure reaches 4000kN, which meets the needs of the two-piece deep drawing process. The beat is stable at 8-12 times/minute, and the yield rate remains above 99.8%. Overseas brands have advantages in the field of STF equipment for large car body parts, and can be adapted to quickly switch between multiple types of two-piece molds.

2. Home appliances and electronics industry

Suitable for double-piece stamping of symmetrical structural parts of new energy vehicle battery packs, motor housing end plates, etc. Such parts have extremely high requirements for dimensional consistency and sealing. The STF press can effectively avoid assembly gap deviations caused by single-piece processing through dual-piece synchronous control. In the application of a new energy vehicle company, the defective rate of double-piece processing of battery pack end plates was controlled below 0.05%, which greatly improved the stability of battery assembly.

3. Hardware and jewelry processing

It is used for double-piece stamping processing of symmetrical connectors of commercial vehicle frames and thin parts of trailer compartments. With its rigid frame and large-tonnage load-bearing capacity (up to 5000kN), it can be adapted to double-piece forming of thick plates. At the same time, through precise pressure control, the deformation of thick plate stamping is reduced. In a commercial vehicle factory application, the processing efficiency of frame connectors is increased by 75% compared with traditional equipment, and the loss of raw materials is reduced by 12%.

4. Precision machining

It is indispensable in the stamping of symmetrical structural parts of the body of special vehicles (such as sanitation vehicles and engineering vehicles). This type of vehicle parts has a moderate batch size but requires high dimensional accuracy. The STF press can be adapted to multiple varieties of double-piece processing through parameter fine-tuning. There is no need to replace core equipment, taking into account flexible production and processing accuracy, and reducing production line investment costs.

4. Technical Parameters and Key Selection Points

STF press selection needs to focus on double-piece synchronization accuracy, tonnage adaptation and process compatibility. The core technical parameters and selection points are as follows: tonnage coverage needs to be combined with the total thickness of the double-piece material and the forming process. The 2000-5000kN model is preferred for automobile body parts. , the hydraulic pad pressure needs to meet the double-piece deep drawing requirements (≥4000kN); the double-piece synchronization accuracy needs to be ≤0.01mm, and the slider parallelism ≤0.008mm/m; the number of strokes is suitable for automobile mass production needs, and the 8-15 times/minute model is preferred.

In addition, attention should be paid to synchronous control capabilities, and models with automatic compensation for biaxial errors should be given priority; the work surface should be selected based on the mold size to ensure that it is suitable for one mold and two parts layout; the automotive industry needs to select models that support rapid mold change and automation integration, which can seamlessly interface with automatic feeding, pick-up and inspection systems; at the same time, evaluate the rigidity and lubrication system of the equipment, giving priority to closed casting frames and adaptive lubrication models to extend the service life of equipment and molds.