The development of spring processing technology

At present, the processing equipment and processing production lines of mechanical springs are developing towards the depth and breadth of numerical control (NC) and computer control (CNC). However, with the changes in spring materials and geometric shapes, the processing technology has also developed.

1) The valve spring mainly develops multi-stage shot peening and liquid nitriding processes to improve the residual pressure stress on the surface and increase the fatigue life.

2) The hollow stabilized spring rod is made of low-carbon boron steel plate, rolled and welded.

3) The torsion bar is made of high-purity 45 steel, which has been quenched to obtain high surface hardness and large residual compressive stress, thereby improving fatigue life and relaxation resistance.

4) The leaf springs widely used in electronic products are basically formed by stamping and automatic bending processing. At present, the main development of composite material bonding technology.

5) Variable spring outer diameter, variable pitch and variable wire diameter (three-variable) suspension springs have realized moldless plastic processing. Since the development of three-variable springs, tapered steel bars have been used for winding processing on CNC lathes, but The finished product and the price are unsatisfactory. Now it must be heated through the spring coiling machine to control the roll speed and drawing force to obtain the required cone shape, and use the processing waste heat for quenching.

Three, the development of spring materials

The development of spring application technology has put forward higher requirements for materials. Mainly to improve fatigue life and anti-relaxation performance under high stress; secondly, according to different uses, it is required to have corrosion resistance, non-magnetic, electrical conductivity, and resistance. Abrasion resistance, heat resistance, etc. To this end, in addition to the development of new varieties of spring materials, in addition to strictly controlling the chemical composition, reducing non-metallic inclusions, improving surface quality and dimensional accuracy, etc., beneficial results have also been achieved.

A. The development of alloy steel Valve springs and suspension springs have been widely used in Si-Cr steel. In order to improve fatigue life and anti-relaxation properties, V and Mo are added to Si-Cr steel. At the same time, Si-Cr drawn wire has been developed. Its anti-relaxation performance when working at high temperatures is better than that of piano wire. With the high-speed miniaturization of the engine, the Ti alloy with good flutter resistance, light weight, and small elastic modulus has been widely used, and its strength can reach 2000Mpa.

B. Improve material purity For high-strength materials, strictly control inclusions and increase purity to ensure their performance. For example, the oxygen content of valve spring materials has reached 20×10ˉ6.

C. The application of ceramics The elastic modulus of ceramics is high, the fracture strength is low, and it is suitable for places with little change. Currently, ceramics with heat resistance, wear resistance and good insulation are being developed; the application of superplastic zinc alloy (SPZ ), has high strength at room temperature. In addition, there are high-strength silicon nitride, which can withstand high temperatures up to 1000 ℃. But ceramic springs are not suitable for working under impact loads.

D. Improving the surface quality The surface quality of the material has a great influence on the fatigue performance. In order to ensure the surface quality, the surface layer of the material with special requirements is 0.1mm by the peeling process. The eddy current flaw detection is used for the defects of the depth of 0.5mm. The surface produced in the wire drawing process The unevenness can be electrolytically polished to reduce the surface roughness to Ra=6.5~3.4μm.

E. Under special circumstances, the development of electroplated steel wire requires additional properties such as corrosion resistance and electrical conductivity in addition to the spring characteristics, and most of them are solved by electroplating. The corrosion resistance of some stainless steel wires and piano steel wires is equivalent to that of galvanized steel wires. Corrosion performance, if another layer of ZnAl (5%) alloy is plated, the corrosion resistance can be increased by about 3 times. Stainless steel wire or piano wire that requires resistance performance, and the steel wire diameter is less than 0.4mm can be copper plated, and more than 0.4 mm can be made of copper inside and stainless steel outside. Generally, piano wire is plated with 5μm thick Ni to improve its conductivity.

Generally speaking, processes that can harden the surface of the material to form residual stress (such as shot peening and surface nitriding) can improve the fatigue strength. Currently, electroless Ni plating is being studied, which can be heated (300~500℃). % P is precipitated as PNi, which can increase the Vickers hardness to HV500. After shot peening, if Ni is heated and plated below 300 ℃, the hardness can also be increased by 10%.

F. Development of stainless steel wire

1) The strength of austenitic stainless steel wire is better than that of ferrite structure, and its corrosion resistance is also better than that of martensite structure, because the scope of application continues to expand.

2) Low-temperature wire drawing or low-temperature nitriding wire drawing can increase the strength of the steel wire. The structure of martensite is unstable when heated, and the wire drawing in low-temperature liquid nitrogen can form cryptic martensite, which can obtain high strength in hot state. There are many applications in the United States and Japan, but currently only steel wires below 1mm can be processed.

3) Precision springs in electronic equipment require non-magnetic properties. This type of steel wire cannot generate cryptic martensite during drawing. For this reason, elements such as N, Mn, and Ni must be added. In order to meet this demand, the United States Developed AUS205 (0.15C-17Cr-1Ni-15Mn-0.3N) and YUS (0.17C-21Cr-5Ni-10Mn-0.3N). Due to the increase in Mn content, cryptic martensite will not be generated during processing. After solution treatment, the strength can reach 2000Mpa, and the fatigue performance is high, which is better than SUS304.

G. The development of shape memory alloys. At present, one-way shape memory alloys with promising applications in springs, with the best performance of 50Ti-50Ni. Springs made of shape memory alloys can be stretched under the action of temperature. Mainly used for constant temperature and constant temperature In the control system of load and constant deformation, since the actuator is pushed by the spring expansion and contraction, the working stress of the spring changes greatly.

H. Application of fiber reinforced plastics in springs Glass fiber reinforced plastics (GFRP) leaf springs have been widely used in the United Kingdom, the United States and Japan. In addition to horizontal suspensions, they can also be used for special light vehicles, such as the longitudinal Suspension. At present, a carbon fiber reinforced plastic (CFRP) suspension spring has been successfully developed, which is 20% lighter than a metal leaf spring.