When processing automobile cover hydraulic press, how to optimize the pressing speed curve to reduce the rebound deformation of the workpiece?
Release Time : 2025-08-28
In automobile cover hydraulic press processing, optimizing the pressing speed curve to minimize workpiece springback deformation requires precise speed control during the initial contact phase. When the slide of the automobile cover hydraulic press drives the mold toward the workpiece, excessively fast initial contact speed can cause instantaneous impact between the workpiece and the mold surface. This impact can easily cause non-uniform plastic deformation in areas prone to stress concentration, such as edges and corners of the automobile cover. This deformation can then be converted into springback after demolding due to internal stress release. Therefore, during the initial contact phase of automobile cover hydraulic press processing, the slide speed should be set to a gentle, low speed to gradually conform the workpiece to the mold surface. This slow contact ensures uniform force distribution on the material, avoiding localized excessive compression or stretching. Furthermore, the low speed characteristic corrects for minor positioning deviations between the mold and workpiece, establishing a low-stress foundation for subsequent forming and mitigating springback risk at the source.
Entering the core plastic forming stage, the speed curve of the automobile cover hydraulic press processing needs to be adjusted based on the complexity of the cover's shape. Automotive cover parts often contain diverse structures, including flat surfaces, shallow curves, deep cavities, and corners. Material flow requirements vary significantly across these areas. For flat or shallowly curved areas, the material must quickly fill the mold cavity. Therefore, the slide speed can be appropriately increased in automotive cover hydraulic presses to ensure initial shaping of the material within a short timeframe, minimizing stress relaxation caused by excessive dwell time. Meanwhile, for areas with high material flow resistance, such as deep cavities and corners, the speed should be reduced to allow the material ample time to flow slowly along the mold curve. This prevents "underfill" defects caused by insufficient flow and excessive stretching caused by excessive flow. Both of these conditions can lead to excessive internal stress accumulation within the material, resulting in significant springback after demolding. A "fast-slow-fast" gradient speed design ensures uniform plastic deformation across all areas, balancing stress distribution and reducing springback forces.
Designing the speed transition phase before holding pressure is a critical link in controlling springback in automobile cover hydraulic press processing. When the workpiece is nearly fully fitted into the mold, if the slide of the automobile cover hydraulic press suddenly decelerates to the holding state, the material's stress will fluctuate momentarily, disrupting the previously stable stress field and easily forming additional internal stress within the workpiece. If the press enters the holding state too quickly, the mold's pressure on the workpiece may momentarily exceed the specified value, causing localized excessive plastic deformation and increasing springback after demolding. Therefore, in automobile cover hydraulic press processing, a "buffer speed segment" is required before the plastic forming phase ends and the holding state begins. This segment gradually reduces the slide speed from the operating speed during the forming phase to the slow speed required for holding (near zero but not completely still). This gradual transition allows the material's stress to transition smoothly to the holding state, ensuring uniform internal stress release, avoiding new stress concentrations caused by sudden speed changes, and paving the way for residual stress elimination during the holding phase.
Optimizing the speed profile during automobile cover hydraulic press processing also requires close consideration of the mechanical properties of the cover material to achieve "material adaptability" adjustments. Automotive cover materials made of different materials (such as cold-rolled mild steel, aluminum alloy, and high-strength steel) exhibit significant variations in yield strength, elastic modulus, and plastic deformation capacity, resulting in varying speed sensitivities. Cold-rolled mild steel exhibits good plasticity and low springback tendency, so the forming stage of the automobile cover hydraulic press process can be performed at a slightly higher speed, prioritizing filling efficiency. Aluminum alloys have a lower elastic modulus and a higher risk of springback, requiring a steady speed throughout the entire process, especially during deep-cavity forming. Slow speeds can reduce the accumulation of elastic strain within the material and minimize springback after demolding. High-strength steel, due to its high yield strength, requires a low speed during the initial forming phase to break the material's yield limit, followed by a slightly faster speed to ensure sufficient plastic deformation. This avoids excessive work hardening caused by slow speeds, which in turn increases springback. By adjusting the speed curve slope and stage duration for different materials, the speed is closely matched to the material's properties, minimizing the probability of springback.
The speed fine-tuning stage before demolding is an often overlooked step in automobile cover hydraulic press processing that can influence the final springback. After holding pressure is complete, the slide of the automotive cover hydraulic press must drive the mold away from the workpiece. If the demolding speed is too fast, intense friction will occur between the workpiece and the mold surface. This can especially affect edges and protrusions of the automotive cover, where the mold may pull on them, causing localized elastic deformation. These deformations return to their original shape after demolding, known as springback. If the speed is too slow, the workpiece remains in the mold for too long, and heat transfer from the press can cause minor fluctuations in material properties, impacting stress stability. Therefore, during the demolding phase of the automotive cover hydraulic press, a "slow and smooth demolding" strategy is required. This allows the slide to rise at a uniform, slow speed, allowing the workpiece to separate from the mold slowly. This prevents additional deformation caused by friction or pulling, while also ensuring a stable stress state during demolding and minimizing springback caused by external interference.
In automotive cover hydraulic press processing, "velocity-pressure coordinated control" is crucial for optimizing the velocity profile; a disconnect between the two can directly lead to springback issues. Each adjustment in the speed curve must be precisely matched to the corresponding pressure parameters. For example, low speed during the initial contact phase must be accompanied by low pressure to prevent excessive pressure at low speeds, which can cause localized workpiece dents. Gradient speeds during the plastic forming phase must correspond to gradient pressures. When forming deep cavities at low speeds, pressure should be appropriately increased to ensure sufficient material flow. The buffer speed before holding pressure must be gradually increased in conjunction with pressure to prevent premature elastic rebound in the workpiece due to insufficient pressure during the speed drop. If the speed and pressure of an automotive cover hydraulic press are not coordinated (e.g., too low pressure during high-speed forming prevents effective material filling; too high pressure during low-speed holding pressure causes excessive workpiece stress), even a properly designed speed curve can still lead to internal stress accumulation due to improper force, ultimately causing rebound. Therefore, when optimizing the speed curve, pressure parameters must be adjusted simultaneously to achieve a coordinated "speed-pressure" control, ensuring that the material is in the "optimal force-speed" state at each stage.
Finally, speed curve optimization for automotive cover hydraulic press processing requires a closed-loop process of "mold trial verification - data feedback - iterative adjustment." Theoretically designed speed curves must be tested in actual mold trials. By measuring the springback of automotive panels after mold trials (e.g., deviations from critical dimensions and surface contour deformation), the speed stages corresponding to areas of severe springback are analyzed. If a particular area experiences significant springback, it could be due to excessively high speeds at that stage, leading to uneven material flow; in this case, the speed needs to be reduced. If the workpiece cracks, it could be due to work hardening caused by excessively slow speeds, requiring an appropriate increase in speed. Furthermore, real-time monitoring data from the automotive panel hydraulic press (e.g., slider displacement-time curves and pressure-time curves) is combined to determine the actual implementation of the speed curve and correct for speed deviations caused by delayed hydraulic system response. Through multiple mold trials and adjustments, the speed curve is gradually adapted to the specific panel forming requirements, ultimately achieving effective control of springback deformation and ensuring that the dimensional accuracy and appearance quality of the automotive panel meet processing standards.
