Online Consultation Explanation of Precision Issues in Sheet Metal Processing
The precision of sheet metal processing directly affects the assembly accuracy, functional implementation, and appearance quality of products, involving control of dimensional tolerances, geometric tolerances, surface quality, and other aspects. The following provides a detailed explanation of the precision issues that need to be focused on in sheet metal processing from three dimensions: design, processing technology, and testing methods:
1、 Precision planning during the design phase
1. Development of tolerance standards
Dimensional tolerance:
Conventional parts: Linear dimensional tolerance ± 0.2~± 0.5mm (such as ± 0.2mm for length ≤ 100mm, ± 0.5mm for length ＞ 100mm);
High precision parts (such as guide rail mounting holes and lock holes): tolerance ± 0.1~± 0.3mm, which needs to be clearly marked on the drawing (such as "± 0.1mm" or "JS11" tolerance zone).
Geometric tolerance:
Flatness: ≤ 1.5mm/m (measured with a 1m ruler, gap value);
Verticality: The bending edge is ≤ 1.5 ° from the reference plane (measured with an angle ruler);
Straightness: Bending edge ≤ 1.0mm/m (measured by wire drawing method).
2. Design for Machinability (DFM)
Avoid extreme structures:
Minimum bending radius: ≥ 1.5 times the thickness of the plate (e.g. 1mm steel plate bending radius ≥ 1.5mm to prevent cracking);
Minimum aperture: ≥ 1.5 times the thickness of the board (to avoid mold damage during punching).
Unified process standards:
Specify a unified reference plane during design (such as the long edge of the board and the center of the hole group) to avoid cumulative errors caused by multiple references.
2、 Precision Control in Processing Technology
1. Cutting process
Selection of cutting equipment:
Laser cutting: accuracy of ± 0.05~± 0.1mm, suitable for complex shapes and high-precision hole positions (such as small holes with a diameter of ≤φ 5mm);
CNC punch press: accuracy ± 0.1~± 0.3mm, suitable for batch processing of round and square holes (mold wear needs to be checked regularly);
Scissor machine: Linear cutting accuracy ± 0.5mm, blade clearance needs to be adjusted (clearance=plate thickness × 10%~15%).
Positioning and knife alignment:
Adopting the "one side, two pins" positioning method, the first piece needs to be measured for contour dimensions with a coordinate measuring instrument, and mass production will be carried out after passing the inspection.
2. Bending process
Rebound compensation:
The rebound angle of carbon steel is 3 °~5 °, stainless steel is 5 °~8 °, and aluminum is 8 °~10 °. Compensation angles should be reserved during mold design (such as a target angle of 90 ° and a mold angle of 85 °~88 °);
Before mass production, adjust parameters through trial bending and record information such as pressure values and mold models.
Mold accuracy:
The width of the V-shaped groove is 8 to 10 times the thickness of the board (such as 16 to 20mm groove width for 2mm board). If the mold wear is greater than 0.3mm, it needs to be replaced to avoid indentation or dimensional deviation.
3. Welding process
Deformation control:
Adopting symmetrical welding and segmented back welding process, welding current ≤ 120A (thin plate ≤ 80A), reducing thermal deformation;
After welding, use flame leveling or mechanical leveling to control the diagonal difference of the frame to be ≤ 2mm (when the size is>1000mm).
Post weld inspection:
Weld seam height ≥ 70% of the plate thickness (e.g. 2mm plate weld seam height ≥ 1.4mm), measured with a weld seam inspection ruler, and visually inspected for cracks and pores.
4. Surface treatment
Pre processing impact:
The thickness of the phosphating film is 1-3 μ m. If it is too thin, it will lead to insufficient adhesion of the coating (coating peeling off during grid inspection);
Spray thickness:
The thickness of the powder coating is 80-100 μ m. Using an electromagnetic thickness gauge for detection, local excessive thickness (>150 μ m) may cover the installation hole and needs to be controlled.
4、 Typical case of precision control for parts
1. Electrical cabinet door panel
Lock hole accuracy: The center distance from the door edge is 20mm ± 0.3mm, and the aperture is 10mm ± 0.2mm. Laser cutting is used to ensure positional accuracy;
Flatness: ≤ 2mm/m. After bending, use a flat plate to level it to avoid uneven door seams caused by warping.
2. Automotive sheet metal parts
Assembly hole position: hole spacing tolerance ± 0.15mm, using CNC punching machine+guide pin positioning to ensure matching with other components;
Contour degree: ± 0.5mm, scanned and tested with a coordinate measuring instrument to meet the requirements of streamlined body shape.
3. Heat sink
Bending spacing: rib spacing tolerance ± 0.5mm, using a multi axis bending machine for one-time molding to reduce step-by-step processing errors;
Verticality: The angle between the rib and the substrate is ≤ 1 °. Use an angle ruler to test each piece to ensure heat dissipation efficiency.
5、 Precision improvement technology and trends
Digital processing:
Introduce CAD/CAM integrated system, simulate bending rebound and welding deformation through software, and optimize machining path in advance (such as AutoForm simulation software).
Intelligent detection:
By using visual inspection systems such as industrial cameras and AI algorithms, size deviations and surface defects can be quickly identified, resulting in a detection efficiency improvement of over 50%.
Flexible tooling:
Use pneumatic/hydraulic adjustable fixtures to adapt to the positioning of multiple types of parts, reduce changeover time, and ensure a repeat positioning accuracy of ≤ 0.1mm.
summary
The precision control of sheet metal processing is the result of the synergistic effect of design, process, equipment, and testing. The core lies in error prevention (reducing problems through reasonable design and process planning) and process monitoring (discovering deviations in a timely manner through initial inspection and patrol). Enterprises need to develop grading accuracy standards based on product requirements (such as ordinary parts, precision parts, ultra precision parts), match corresponding processing equipment and testing methods, and establish an error analysis database to continuously optimize process parameters, in order to achieve efficient and stable precision sheet metal production.
