How to balance structural strength and overall geometric accuracy in the welding and precision machining of large equipment frames?
Publish Time: 2026-01-14
As the "skeleton" bearing core loads and supporting precision components, the performance of welding and precision machining of large equipment frames directly determines the reliability, lifespan, and operational accuracy of the entire machine. However, the manufacturing of large welded frames faces a fundamental challenge: high-strength welding inevitably involves deformation caused by heat input, while high geometric accuracy requires extremely small dimensional deviations. Finding a balance between these two is a core technological challenge in high-end equipment manufacturing. Through scientific welding strategies, strict stress control, and advanced precision machining methods, modern manufacturing enterprises have gradually established a systematic solution.1. Welding Design: Controlling Deformation and Stress from the SourceThe first step in balancing strength and accuracy lies in the coordinated design of structure and process. Engineers use finite element analysis to simulate the welding thermal field and stress distribution during the design phase, optimizing weld location, length, and bevel form to avoid stress concentration areas. Simultaneously, materials with good weldability, such as high-strength low-alloy steel, are selected to reduce the tendency for cold cracking while ensuring yield strength. Furthermore, symmetrical weld arrangement and closed box-section structural designs effectively enhance overall rigidity and suppress twisting and bending deformation during welding.2. Precision Welding Process: Fine Control of Heat Input and SequenceThe welding process itself is a complex physical process involving thermo-mechanical coupling. To reduce the expansion of the heat-affected zone and the accumulation of residual stress, low-heat-input welding methods are commonly used in manufacturing, such as pulsed MIG/MAG welding, submerged arc welding, or laser-MIG hybrid welding. More importantly, strictly adhering to the process sequence of segmented back-welding, symmetrical welding, and skip welding ensures uniform heat distribution and counteracts local shrinkage stress. Using specialized welding fixtures and jigs, the workpiece is rigidly fixed and pre-deformed, further constraining deformation trends and ensuring that the overall post-weld profile closely approximates the theoretical model.3. Post-Weld Stress Relief: Releasing Internal Stress and Stabilizing DimensionsEven with optimal welding strategies, significant residual stress remains inside large frames, slowly releasing during subsequent processing or service, leading to dimensional drift or even cracking. Therefore, overall stress-relief annealing becomes a critical process. This heat treatment significantly reduces residual stress, improves dimensional stability, and prevents springback deformation after machining. For ultra-large components that cannot be furnace-tested as a whole, alternative solutions such as vibration aging or localized high-temperature tempering are used. Although the effects are slightly less pronounced, they still effectively improve stability.4. Precision Machining on Large Gantry Milling Machines: Achieving Micron-Level Precision Through MillingWhile the frame remains macroscopically stable after welding and heat treatment, millimeter-level deviations still exist in certain areas. At this point, large CNC gantry milling machines play a crucial role. With their high-rigidity beams, multi-axis linkage, and online measurement systems, gantry milling machines can perform integral milling on frames weighing tens of tons, precisely correcting datum surfaces, mounting hole positions, and guide rail mounting surfaces. By using milling instead of straightening, key tolerances such as position, flatness, and parallelism are controlled within ±0.05mm or even higher precision ranges, providing a reliable benchmark for the subsequent assembly of precision components.5. End-to-End Collaboration: A Quality Closed Loop from Drawings to DeliveryUltimately, the unity of strength and precision relies on end-to-end collaboration across design, welding, heat treatment, finishing, and inspection. Three-dimensional laser scanning or coordinate measuring machine (CMM) is used to compare the dimensions of the welded and machined workpieces, forming a data closed loop and continuously optimizing process parameters. This systematic manufacturing concept ensures that large equipment frames not only "withstand heavy loads" but also "maintain precision."The welding and precision machining of large equipment frames has long transcended the traditional concept of "connection," evolving into a comprehensive technology integrating materials science, thermodynamics, mechanical engineering, and digital manufacturing. It uses a steel body to bear immense weight and micrometer-level precision to support a soul of meticulous craftsmanship—forging the solid backbone of a nation's heavy equipment amidst the tension between strength and precision.
