How to ensure the precision of stamping of automobile parts?

The precision guarantee of stamping process of automobile parts is a multi-dimensional and whole-process control system, which covers key links such as mold design and manufacturing, stamping equipment performance, process parameter optimization, raw material control and on-line inspection, and finally realizes the precise control of stamping parts' dimensional tolerance, shape and position tolerance and surface quality, and meets the strict requirements of automobile assembly. The specific safeguard measures are as follows:

The design and manufacture of high-precision molds is the core foundation.

Die is the primary factor to determine the precision of stamping parts, and it is necessary to control the precision from design to processing. In the design stage, with the help of CAD/CAM/CAE software, the springback of materials (especially high-strength steel, aluminum alloy and other resilient materials) is accurately calculated, and the influence of springback on the size is offset by presetting the compensation value and optimizing the die surface structure. For complex surface parts (such as car body panels), three-dimensional surface modeling technology is adopted to ensure that the mold surface fits the product design completely.

High-precision machining equipment, such as five-axis linkage machining center and high-precision wire cutting machine, should be used in the die processing to control the dimensional tolerance of die cavity and cutting edge within ±0.005mm; At the same time, high-frequency quenching, nitriding and other surface strengthening processes are carried out on the die to improve the hardness and wear resistance of the die and avoid the dimensional deviation of stamping parts caused by die wear. In addition, the die assembly needs to strictly control the guiding precision, and adopt the ball guide pillar guide sleeve structure to ensure the centering of the upper die and the lower die and prevent the deformation of stamping parts caused by the dislocation of the die.

The selection and debugging of high-rigidity stamping equipment is the key support.

The rigidity and precision stability of stamping equipment directly affect the machining accuracy, so it is necessary to match the corresponding equipment according to the type of stamping parts. For heavy-duty stamping parts such as body structural parts and chassis parts, a closed two-point or four-point press is needed, and its fuselage adopts integral casting or welding structure, which has strong deformation resistance and can avoid mold gap fluctuation caused by fuselage deformation during high-speed stamping; The parallelism and verticality of the slide block of the equipment should be controlled within 0.02mm/m to ensure the smooth movement of the slide block and uniform pressure distribution in the stamping process.

In the equipment debugging stage, it is necessary to accurately set the die gap, and adjust the reasonable gap value (usually 10%~15% of the material thickness) according to the material thickness and material. If the gap is too large, it will easily lead to burr and deformation at the edge of stamping parts, while if the gap is too small, it will aggravate the die wear and even cause the parts to crack. At the same time, it is equipped with a high-precision feeding system, such as a servo CNC feeder, with a feeding accuracy of ±0.01mm, which ensures that the position of raw materials is accurate and consistent every time, and avoids the impact of feeding deviation on the size of stamping parts.

Precise optimization and control of stamping process parameters

Reasonable process parameters are an important means to ensure accuracy, and parameter debugging should be carried out for different materials and different structural parts. For stretch-formed parts, it is necessary to strictly control the BHF, drawing speed and lubrication conditions: too small BHF will easily lead to wrinkling of materials, while too large BHF will lead to thinning or even cracking of parts, and the optimal BHF range needs to be determined through trial punching; The drawing speed should match the formability of the material. Generally, low-speed drawing is more conducive to the material flow and reduces the uneven deformation. At the same time, special stamping lubricating oil is selected to improve the lubrication effect between materials and dies, reduce friction resistance and avoid surface scratches or dimensional deviation of parts.

For multi-process stamping parts, the progressive die stamping process is adopted to complete multiple processes such as blanking, stretching, punching and flanging through one feeding, thus reducing the error accumulation caused by multiple positioning; Accurate positioning pins and guide pins are set between processes to ensure the accurate position of parts in each process and realize the precise connection between processes.

Strict control of raw materials is the premise of precision guarantee.

The thickness tolerance and mechanical stability of raw materials directly affect the stamping accuracy, so it is necessary to strictly test the raw materials entering the factory. The thickness tolerance of automobile stamping steel plate and aluminum alloy plate should be controlled within ±0.05mm to avoid the mismatch of die gap caused by uneven material thickness; At the same time, the tensile strength, yield strength, elongation and other indicators of the materials are tested to ensure that the properties of the same batch of materials are consistent and to prevent the difference in springback caused by fluctuations in material properties. In addition, the surface of raw materials should be smooth and free from defects, so as to avoid the surface quality and forming accuracy of stamping parts being affected by surface scratch and corrosion.

On-line inspection and quality traceability of the whole process

The stamping process needs to be equipped with perfect testing equipment to realize real-time monitoring and closed-loop control of accuracy. In the first article inspection, the key dimensions and form and position tolerances of stamping parts are comprehensively detected by using a three-coordinate measuring instrument, and mass production can be carried out only after they are confirmed to be qualified; In the mass production stage, the size and surface defects of stamping parts are 100% detected by on-line detection devices (such as visual inspection system and laser caliper), and once the out-of-tolerance parts are found, they will be immediately alarmed and eliminated.

At the same time, a quality traceability system is established to record the information of die number, equipment parameters and raw material batches of each batch of stamping parts. When there is a precision problem, the reason can be quickly located, the process parameters can be adjusted or the die can be maintained in time to ensure the precision stability of subsequent production.