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In the global pipeline prefabrication and metal processing sector, tube bending machines serve as the core foundational equipment for tube plastic forming. They are widely applied in power infrastructure, highway and railway projects, bridge construction, shipbuilding, boiler supporting, furniture frame manufacturing, architectural decoration and other fields, undertaking prefabrication, on-site installation, maintenance and modification of various pipelines. Among them, hydraulic tube benders feature a distinctive dual-function design. Besides standard tube bending operations, their oil cylinders can act independently as hydraulic jacks for lifting tasks. This dual-purpose design makes them well-suited to diverse on-site working conditions. Compared with CNC tube bending machines, such multi-functional models deliver notable cost advantages and have a low learning threshold, maintaining steady market demand in general tube processing. Driven by the standardization and prefabrication trend of pipeline engineering, tube bending equipment has formed a differentiated product portfolio covering simple on-site fabrication and high-precision mass forming, becoming an irreplaceable key link in the pipeline manufacturing chain.

Classified by power configuration, control scheme and forming method, mainstream tube bending machines fall into four primary categories: hydraulic electric tube bending machines, horizontal hydraulic tube bending machines, multi-functional rolling tube bending machines and digital display tube bending machines. Each type has its own positioning. Hydraulic electric models focus on fast on-site bending and lifting; horizontal hydraulic variants feature higher load capacity for heavy-duty forming of large-diameter and thick-walled tubes; multi-functional rolling tube benders excel at continuous large-radius arc processing over long distances; digital display models add digital angle readouts on the basis of hydraulic structures to realize visual precision control. High-end CNC tube bending machines adopt digital control systems, lifting repeat accuracy, consistency of finished parts and flexible changeover capacity to a higher level, making them the mainstream choice for mass production of precision tubular components.

The structural design of CNC tube bending machines builds a complete control system centered on stable forming, convenient programming and rapid fault diagnosis. Equipped with a touchscreen HMI and CNC modules, they support conversational operation. Process parameters and machining programs can be set intuitively, lowering programming barriers for operators. The thickened, integrated machine bed offers high rigidity and resists deformation under long-term alternating bending loads, ensuring a stable machining reference. The control system supports independent parameter configuration for each gear. Up to 16 bending angles can be preset per gear, and the built-in storage module can save 16 separate machining programs for instant recall of different tube recipes. The machine is fitted with slow positioning to buffer the impact during tube feeding and stabilize bending angles, achieving a repeat accuracy of ±0.1°. When program conflicts, parameter overruns or mechanical faults occur, warning messages pop up directly on the screen for operators to locate and resolve issues quickly. Integrated self-developed coordinate conversion algorithms output bending parameters directly. Optional calculation software can be installed on desktop terminals for tube unfolding, coordinate conversion and pre-process simulation to verify the feasibility of forming schemes in advance.

The plastic deformation principle of tube bending shares similar physical logic with sheet metal bending. Under pure bending conditions, for a tube with outer diameter D and wall thickness t subjected to external bending moment M, the outer wall on the neutral layer bears tensile stress and becomes thinner, while the inner wall on the neutral layer bears compressive stress and thickens. Under combined forces, the originally circular cross-section turns approximately elliptical. Once deformation exceeds the material’s plastic limit, cracks or fractures will emerge on the outer tensile zone, and wrinkles will form on the inner compression zone, resulting in scrapped workpieces.

The degree of tube deformation is determined by two dimensionless parameters: relative bending radius R/D and relative wall thickness t/D. Smaller values of R/D and t/D mean greater deformation and higher forming risks. To consistently guarantee finished tube quality, deformation must be controlled within the allowable forming range of the material. The forming limit of tube bending is not a single indicator. It requires comprehensive consideration of material mechanical properties, bending processes and service requirements of finished tubes. Four core control objectives are defined: the maximum elongation in the outer tensile zone of the neutral layer must not exceed the material plastic limit to avoid cracking; the thin-walled section in the inner compression zone of the neutral layer must avoid buckling and wrinkling under tangential compressive stress; cross-section distortion shall be restricted for precision tubes with ellipticity requirements; wall thinning shall be controlled for pressure-bearing tubes to preserve structural strength under internal pressure.

Process control should start at the tube shape design stage. Rational tube design is the premise to reduce defect rates and adapt to automated continuous production. During pipeline layout and tube scheme design, structures that hinder bending should be avoided, including oversized arcs, irregular free curves, complex multi-directional compound bends and arcs exceeding 180°. Oversized arcs require bulky tooling and are limited by machine travel dimensions. Irregular curves and complex compound bends are not suitable for mechanized mass production and rely heavily on strenuous manual work. Bends greater than 180° cannot be demoulded smoothly after forming.

Standardization of bending radius is a core principle for modular pipeline design. The industry widely follows two rules: “one tube, one die” and “multiple tubes, one die”. “One tube, one die” means that regardless of the number of bends and bending angles on a single tube, only one bending radius is adopted throughout the forming process without die changes, eliminating errors and downtime caused by die switching. “Multiple tubes, one die” means tubes of the same outer diameter preferably share the same bending radius. The same set of dies can produce tubular parts of different shapes, drastically reducing die inventory, cutting tooling costs and shortening changeover time.

Bending radius selection directly determines the resistance encountered during forming. Industrial practice shows that large-diameter tubes paired with an excessively small bending radius are prone to inner wrinkling and slipping, making stable quality hard to achieve. For general applications, the recommended bending die radius R is 2–3 times the tube outer diameter, balancing forming difficulty, layout space and mechanical performance of the tube.

Bending speed is an easily overlooked parameter that greatly affects finished quality. Excessively fast forming speed flattens the bent section, fails roundness requirements, and may even tear the tube. Too slow speed increases wrinkling risk and slippage between clamping blocks and the tube; large-diameter tubes may sag in the bent area. Extensive tests on CNC tube benders have proven that the optimal bending speed for balanced productivity and yield is 20%–40% of the machine’s maximum speed.

Mandrels are indispensable auxiliary components for forming thin-walled tubes with small bending radii. Inserted inside the tube, they support the inner wall of the bending zone to restrain cross-section collapse and elliptical deformation. For conventional tube processing, it is difficult to secure high yield rates for thin-walled tubes without mandrels. Mandrels come in a wide range of types, including solid mandrels, universal single-ball, double-ball, triple-ball, four-ball mandrels, and directional single-ball and multi-ball mandrels, which can be selected according to tube diameter, wall thickness and bending radius. The axial position of the mandrel also significantly affects forming results. Theoretically, the mandrel tangent should align with the bending die tangent. However, abundant process tests show that shifting the mandrel forward by 1–2 mm delivers optimal forming quality. Excessive forward offset will create a typical “goose neck” defect on the outer wall of the bent section, rendering the tube non-conforming.

As global manufacturing advances toward prefabrication, digitalization and flexibility, tube bending equipment keeps upgrading. Traditional multi-purpose hydraulic models remain widely used for site work thanks to cost-effectiveness and multi-scenario functionality. CNC precision bending systems are gradually integrated with process simulation, in-line dimensional inspection and adaptive springback compensation. These systems predict wrinkling, collapse and interference risks in advance, automatically adjust springback values and reduce manual trial bending. Meanwhile, rising demand for high-strength alloys and precision thin-walled tubes pushes continuous upgrades of bending processes, die materials and mandrel solutions. As foundational equipment for pipeline forming, tube bending machines will keep serving industries including infrastructure, shipbuilding, boiler manufacturing and furniture production, advancing tube processing toward standardization, low material loss and high yield.