Post-Forming Care for Instrument Sheet Metal Components

Post-Forming Care for Instrument Sheet Metal Components

    In machinery and instrumentation applications, sheet metal components typically exhibit three core attributes: ‌ultra-thin wall thickness‌, ‌exceptional dimensional accuracy‌, and ‌versatile functional adaptability‌. Some precision parts are also sensitive to temperature. Post-deformation treatment must balance dimensional accuracy and component functionality while avoiding secondary damage. The following details the treatment methods, operating procedures, and precautions.

      I. Targeted Deformation Treatment Methods

      For different degrees of deformation and component types, appropriate correction methods must be selected. For small, slightly deformed components, such as angle steel brackets for small instruments and narrow strip connectors, manual correction is the most flexible method.

    When treating bulges in the center of thin sheets, place the convex side up on a platform and hammer from the inside out, gradually increasing the force and density of the hammering points outwards, thus eliminating the bulge by stretching the surrounding material.

      If the deformation is wavy at the edge, hammer from the surroundings towards the center in the opposite direction.

     For twisted deformation of flat steel and angle steel, first fix one end in a bench vise, clamp the other end with a wrench and twist in the opposite direction, then refine the shape with a hammer.

     To avoid surface marks on high-quality parts like precision instrument copper decorations, use soft hammers (wooden/copper).

    Flame straightening is suitable for localized deformation of medium-thickness sheet metal parts such as machine frames and large equipment covers, especially for post-weld stress deformation.

      During operation, heat the deformed protrusion to a cherry red color (approximately 800℃) with an oxy-acetylene torch.

     Once the metal softens, use a wedge-shaped iron block or jack to press in the opposite direction, using the thermal expansion and contraction properties to correct the deformation.

    When dealing with long, curved parts, fix both ends and pull with a winch while simultaneously heating the curved protrusion to improve the effect. The heating method should be selected according to the deformation: use spot heating for thin, uneven plates, line heating for medium-thick curved plates, and triangular heating for severely deformed rigid workpieces, but temperature must be strictly controlled to prevent the metal from becoming brittle.

     Mechanical straightening methods are suitable for batch processing or large-area, thick parts, such as CNC machine tool outer guard plates and equipment bases. Roller straightening uses multiple sets of continuous rollers to adjust the spacing and pressure to eliminate uneven stress. Workers can roll the sheet metal diagonally to ensure uniform pressure when processing wavy wrinkles.

    For severely deformed localized parts of thick load-bearing components, hydraulic pressure equipment with specialized molds can be used to apply directional pressure in stages. Multiple pauses are necessary during pressurization to prevent stress concentration and cracking. You can straighten bent shafts and rods using a spiral pressure tool.

      During straightening, you must allow a margin for elastic deformation and use a dial indicator for continuous monitoring.

    Composite and special straightening methods are for special or high-precision parts. Operating tables and instrument cabinet frames welded on automated production lines are prone to residual stress after welding.

    These require first stress elimination using vibration aging equipment, followed by fine straightening with a multi-point press to restore shape and improve dimensional stability.

    For precision components that cannot withstand high temperatures, such as the housing of laser inspection instruments and semiconductor equipment accessories, liquid nitrogen temperature difference correction is used.

    Localized cooling of deformed areas causes them to shrink, while a low-temperature hot air gun gently heats the surrounding area, using thermal stress to restore the components. Operators must control the cooling rate and wear professional protective equipment to prevent component cracking during operation.

     Cutting correction serves exclusively as a corrective solution for extensively deformed large-scale components, exemplified by the warped casings of massive industrial machinery.

       First, cut along the weld seam or severely deformed area. After disassembly, use jacks, flame straightening, or other methods to repair individual components before re-welding them together.

        After welding, inspect for cracks, porosity, and hazards using a flaw detector to ensure safety.

       II. Standardized Processing Procedures

       Pre-treatment and inspection are fundamental steps. First, remove oil, weld slag, and other impurities from the surface of sheet metal parts to prevent affecting inspection accuracy.

      Then, use a coordinate measuring machine or laser scanner to obtain deformation data, clearly identifying the deformed area, degree, and assembly reference surface, especially marking the assembly reference surface with other components to provide accurate basis for subsequent correction.

       We must adapt the tooling to the characteristics of the components. Custom-made fixtures or support molds are used to fix the sheet metal parts according to their shapes, avoiding key areas such as precision holes and wiring ports. For thin-walled parts, soft pads should be added to the contact points of the fixtures to prevent displacement or secondary damage during the correction process.

        Targeted correction requires flexible adjustments.

        Slight warping is addressed with roller pressing or local hydraulic fine-tuning;

        post-weld twisting is first stress-relieved by vibration aging before mechanical straightening;

      High-precision parts with minimal deformations undergo corrective processes: induction heating or LN₂ thermal shock treatment, safeguarding operational characteristics.

      Real-time monitoring is required during the correction process, using tools such as dial indicators and flatness testers to track deformation recovery and adjust the operating force or temperature in a timely manner to prevent over-correction.

        Post-processing and verification ensure final quality.

        After correction, surface burrs and indentations are ground off;

        carbon steel parts are sprayed with anti-rust primer;

        precision instrument sheet metal parts can be phosphated to improve corrosion resistance;

        dimensions are checked again with high-precision instruments to ensure tolerances are controlled within ±0.1mm;

        simultaneously, mechanical properties are sampled and tested to avoid strength reduction caused by correction.

        III. Precautions Throughout the Process

     Thorough preparation is essential before operation to avoid haphazard processing. In addition to precise positioning and cleaning, appropriate methods and tools must be selected based on the material (carbon steel, stainless steel, aluminum alloy, etc.), thickness, and precision requirements. For example, avoid using high-impact tools for thin-walled parts.

     Precise control is crucial during operation to prevent secondary problems. Force application must be gradual; whether hammering, hydraulic pressurization, or pulling, avoid applying excessive force at once to prevent thinning, cracking, or creating new stress concentrations in the sheet metal.

      Temperature control is critical. Flame straightening or induction heating requires material-specific temperature control (e.g., ≤850℃ for carbon steel). Do not burn at a single point for too long; heat evenly. For high-precision or temperature-sensitive parts, prioritize gentle straightening methods to prevent changes in material properties.

     Post-operation verification must be comprehensive and meticulous to ensure usage requirements are met. In addition to dimensional inspection and mechanical property testing, pay attention to the integrity of anti-corrosion treatment to prevent rust problems during subsequent use.

         Special scenarios require specific solutions.

     For welded sheet metal parts, residual stress must be eliminated through vibration aging before straightening to reduce springback;

     for special materials such as stainless steel and aluminum alloys, avoid prolonged high-temperature heating to prevent brittleness or loss of corrosion resistance;

       for extra-large or heavy sheet metal parts, multiple points of force balance are required during straightening, with the assistance of jacks and support frames to prevent tipping or displacement;