German HENNIG springs HENNIG models HENNIG prices

HENNIG spring is a special type of extension spring, suitable for applications with large elongation and constant load. Constant-force springs consist of spiral metal strips; the inner side of the strip is curved so that each coil wraps tightly around the inner coil. When the metal strip is stretched (twisted), internal stress resists the load force, similar to ordinary extension springs, but the spring rate is nearly constant (zero). See the load/torque diagram. In use, an ID is typically used to wind this spring tightly onto a drum, with its free end connected to the load, like a counterweight. Alternatively, the free end can be fixed, allowing the spring itself to provide the working force, similar to carbon brushes in electrical devices.

HENNIG spring structure

The torsion bar spring itself is a torsion bar made of spring steel. The cross-section of the torsion bar is usually circular, with a few being tubular or rectangular. Its ends can be shaped as splines, square, hexagonal, or cylindrical with flat surfaces, so that one end can be fixed to the frame and the other end to the suspension arm, which is connected to the wheel.

HENNIG spring rebound control measures

1) Select materials with good bending performance: Using materials with a low yield limit and high elastic modulus as bending parts can achieve higher bending quality. In addition, the thickness tolerance of the blank, the surface quality, and the flatness have a significant impact on bending springback. For workpieces with high bending accuracy requirements, the quality of the blank in these aspects should also be screened. 2) Select a smaller relative bending radius: A small r/t value indicates a large degree of deformation. Generally, when r/t ≤ 3-5, it is considered that the bending area of the sheet metal has fully entered the plastic state. A smaller bending radius is beneficial for reducing springback, but an excessively small bending radius may cause cracking in the bending area. The minimum bending radius of materials provided in references is mainly empirical data, which can serve as a reference for sheet metal designers when designing the bending radius of workpieces. 3) Select the required die clearance: For V type bending, the clearance value is achieved by high-speed machine tools and is unrelated to the die itself. For U type bending, springback decreases as the depth of the die opening increases, and springback decreases as the die clearance decreases. For workpieces with high bending accuracy, the single-side bending clearance can be taken as Z = t; if higher bending accuracy is required, adopting bending with slight thinning will be more effective in reducing springback. Because zero or negative clearance bending can change the stress state of the sheet metal, transforming ordinary bending into bending with tensile-bending characteristics, creating a compressive stress state on the inner side of the neutral layer of the blank, so that the entire cross-section of the blank is in a tensile stress state in the tangential direction. After unloading, the springback of the inner and outer fibers cancels each other out, reducing springback (Figure 4). Therefore, adopting tensile-bending processes and dies with adjustable clearance is very beneficial for controlling springback. 4) Design reasonable workpiece shapes: U type bent parts have less springback than V type parts. Complex workpiece shapes involve more mutual constraints between parts, making springback difficult to control. Therefore, ? type has less springback than U type. If suitable reinforcing ribs are pressed at the bending area, the springback will be even smaller. Therefore, flanging or stacking edges on bent parts can not only improve stiffness but also reduce springback. 5) Adopt appropriate microstructural states: Materials after cold working hardening have large bending springback. For bent parts with high accuracy requirements whose blanks have cold working hardening, they should undergo annealing treatment before bending. Where necessary and permissible, heating bending should be adopted for workpieces with thicker blanks to eliminate springback. The springback angle of calibration bending is significantly smaller than that of free bending, and the greater the calibration force, the smaller the springback. 6) Calibrate the shape of the bending punch: This is because the calibration bending force concentrates the punching pressure in the bending deformation zone, forcing the inner layer of metal to be compressed. After the sheet metal is calibrated, both the inner and outer layers of fibers are elongated and will shorten after unloading. Since the springback trends of the inner and outer layers are opposite, the amount of springback will decrease, thereby achieving the goal of overcoming or reducing springback. Therefore, calibration bending is a bending method similar in nature to tensile bending, and its application range appears to be broader. Generally, the shape shown in Figure 5 is mostly used for the calibration bending punch.

HENNIG spring precautions

Due to product structure limitations, multi-strand springs generally feature high strength and good performance. The material must guarantee final performance in terms of spring strength and toughness. During the processing of multi-strand springs, note the following: 1 Support coils can be closed using either cold or hot methods according to product requirements. When using the hot closing method, the spring must not be heated to the point of sparking or whitening; the temperature for silicon-manganese steel must not exceed 850℃. The support coils and active coils must have effective contact, and the gap must not exceed 10% of the nominal inter-coil gap. 2 The characteristics of multi-strand springs can be determined by adjusting the lead; the pitch can be adjusted as necessary during winding. The pitch can be 3~14 times the wire diameter, but 8~13 times is generally preferred. The spring force is also closely related to free height, closed ends, outer diameter, and wire properties, and can be changed by adjusting one or several of these parameters. 3 Springs without support coils and springs with excessively fine wire diameters should not have welded ends, but the end cables should not be obviously loose and burrs should be removed. For multi-strand springs requiring welded heads, the length of the welding part should be less than 3 times the cable diameter (maximum no more than 10 mm). The heating length should be less than one coil, and it should be ground smooth after welding. During gas welding, the welding part should undergo local low-temperature annealing. 4 Surface treatment of springs generally involves phosphating, but other treatments are also possible. For zinc and cadmium plating, dehydrogenation treatment must be performed after electroplating. After dehydrogenation, extract 3% (no fewer than 3 pieces) for retesting and setting treatment; no fractures are allowed during retesting. Springs should be cleaned of surface dirt, salt marks, and oxide scale, using methods such as sandblasting or gasoline cleaning, but acid pickling is not allowed. 5 The pressing time for important springs is 24 hours, and for ordinary springs, it is 6 hours or continuous compression 3~5 times, holding for 3~5 seconds each time. During pressing, the gap between the spring and the mandrel should be 10% of the mandrel diameter; too small a gap makes operation difficult, while too large a gap easily causes bending deformation of the spring. If one spring breaks during pressing, the others should be reprocessed.

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