Post processing knowledge of bow spring

1. Material and technical requirements of bow spring
The material of the bow spring is 60Si2MnA steel; the hardness of the technical requirements is hrc49 ~ 51, and the repeated loading test under the working state should meet the technical requirements. The process flow is as follows: blanking → acceptance → first quenching and tempering → initial forming → intermediate annealing → final forming → second quenching and tempering → pre deformation treatment → final tempering → inspection → warehousing.

2. Key points of heat treatment process for bow spring
1) The purpose of the first tempering and tempering is to adjust the structure of the steel plate. The blank of bow spring is 145.5 mm × 14.5 mm × 3 mm plate, with 3% samples in each batch (the size of test piece is 35 mm × 15 mm × 3 mm). The blank and sample are loaded into the spreader, heated in the salt bath furnace and cooled by oil.

Tempered parts shall be cleaned, degreased and sandblasted, and protective coatings shall be applied on the surface of parts and samples. The tempering temperature is 720 ℃± 10 ℃, holding for 60min, and air cooling. Check the hardness hrc26 (check the hardness after grinding the surface of the sample > 0.2mm).

2) Intermediate annealing is carried out after the initial forming of bow spring. Protective coating shall be applied before intermediate annealing, and residual iron wire coating shall be removed by light sand blasting after annealing, and then final molding shall be carried out.

3) The purpose of the second quenching and tempering is to shape the final performance of the parts. After the parts are finally formed, the iron wire (or special spreader) is bound, and then heated in a fully deoxidized salt bath, and then quenched with oil and cooled thoroughly. After oil quenching, the oil is cleaned and degreased with water at 60 ~ 80 ℃, and then tempered at 425 ℃± 10 ℃. After tempering, grind the surface of the sample to be ≥ 0.2mm, and the hardness should be hrc49 ~ 51.
4) Finally, after the hardness is qualified, the parts are subject to sandblasting treatment, and then the pre transformation treatment is carried out. The actual measurement position is pressurized to 55mm ± 1mm and maintained for 30 ~ 40H, and then the final tempering is carried out.

Evolution of spring equipment

The spring industry will still be an industry dominated by small enterprises. Some enterprises currently in an advantageous position will still maintain their previous advantages for a period of time. The private enterprises that have completed the original accumulation may be polarized. Some far sighted owners will invest their funds in technological transformation and introduce talents, and gradually adopt modern production and management ideas to manage enterprises Some of the more traditional owners, based on their own experience, adhere to the original management mode, the distinction between the two different modes will become more and more obvious.

Compared with foreign countries, there is still a big gap in the performance, specifications and reliability of spring production and testing equipment, and the price of imported equipment is about 5-10 times of that of domestic similar products. The price leaves a huge development space for domestic equipment manufacturers. If domestic equipment manufacturing enterprises see this and actively develop, it may reverse the current situation The situation of less key equipment relying on import benefits both spring enterprises and equipment manufacturers. The development direction of domestic spring enterprises is to develop towards lightweight and high stress, and some mechanical devices composed of springs are being replaced by hydraulic and pneumatic devices controlled by electronic devices, For example, the active hydraulic damping system may gradually replace the traditional spring damping system. The spring industry should pay full attention to the changes in this respect, improve the comprehensive development ability, so as to adapt to the market demand and changes. In terms of product structure, spring manufacturing enterprises should develop in the direction of specialization and diversification.

A large number of springs in foreign advanced enterprises are produced by specialized production lines, but their production lines have certain flexibility, which can produce similar products with different specifications, so as to improve the utilization rate of equipment.
At the same time, in order to reduce the operational risk, the enterprise develops towards diversification on the basis of specialized production of single product, Since the reform and opening up, China’s spring industry has made great progress. In the past decade, the automobile and motorcycle industry has provided a rare development opportunity for the spring industry. The number of enterprises has increased rapidly, but the spring industry is also facing low starting point and scale Many problems, such as small size, backward technology, fierce price competition between peers and the phenomenon of payment arrears, have made some enterprises difficult to operate, even close down frequently. At the same time, foreign enterprises and joint ventures established in China are competing with domestic enterprises for the market by virtue of their technical and management advantages. Every enterprise in the spring industry is thinking about its development ideas.
We hope that every enterprise will have its own product characteristics, and make greater development in the new century with excellent quality and low cost.

Causes of insufficient spring force

1. The design and manufacture parameters of non-standard spring are unreasonable: only pay attention to the outer diameter, inner diameter, length and other parameters, often ignore the size of wire cross-sectional area and pitch, resulting in insufficient elasticity;
2. Unreasonable selection of standard spring: due to the low price of the drawing, the lighter load type is selected, which can not bear the heavy load, resulting in insufficient sensory elasticity;
3. Wrong spring quality grade: unintentionally or intentionally use ordinary spring as high-quality spring or imported spring, resulting in insufficient elasticity;
4. The elasticity is reduced or even lost when it is used beyond the specified temperature;
5. The spring wire itself is soft, or the quenching temperature of the spring is low or the holding time is not long enough, or the tempering temperature is too high and the time is too long after forming the spring, which leads to the tensile compressive strength against the elastic force is not enough.

Technology of metal stamping parts

In all kinds of structural parts of mechanical and electrical appliances, a large number of plate-shaped parts with material thickness T > 0.5-16 mm are widely used. Because of its high requirements of size and shape and position accuracy, especially along the direction of material thickness, it is required to be smooth and straight. The conventional traditional processing method is to meet the technical requirements by stamping, car, milling, planing, grinding and other cutting processing, which not only has a long process flow, many processes, but also consumes a lot of labor (set) time, low production efficiency, and parts interchangeability is not good, labor intensity, high cost, can not meet the needs of mass production. Metal stamping parts, metal stamping parts processing. These plate-shaped parts are difficult to complete by other processing methods. Even with the combination of various types of work, not only the efficiency is low, the quality is difficult to guarantee, but also the cost is very high.

The characteristics of fine blanking parts are as follows
1. The shape is complex, the dimension and position accuracy is high, most of the material thickness T > 3mm ~ 12.5mm, it is a fine blanking part of medium and thick plate, the punching section is straight and smooth, and the quality is comparable with the cutting process.

2. The contour of fine blanking parts is clear, the collapse angle is small, some hole edge distance and hole spacing (wall thickness) ≤ T, and there are pressure convex, counterbore, blind hole and hub flange forming fine blanking, especially the involute, cycloid, triangle, rectangle, trapezoid and other high-precision gear fine blanking parts with small modulus are difficult to be manufactured by other processing technologies.

3., all the first mock exam products are large scale production and the scale of the moderate economic production, including the automobile handbrake, the car, motorcycle and other fine punching parts, all of which are stampings from the original material and the products are no longer cutting.

4. Because of the cold work hardening effect, the surface hardness and strength of the fine blanking surface are greatly increased, and the friction resistance and weather resistance are improved. Therefore, the service life of fine blanking parts such as gear tooth profile and shaft sleeve on moving surface and friction surface will be improved.

Belleville spring

With the development of the guide form, the disc spring can be used in single piece or in combination. The combination method can be combined, superimposed and overlapped. When using in combination, there must be a guide element. The common guide parts are inner guide and outer guide. With the demand and development of mechanical products, the designer invented hole guide. One kind of hole guide is on the mounting hole, such as the slotted disc spring and diaphragm disc spring on the clutch; the other is to drill holes on the OM line and guide with rod. Foreign designers have also invented the inner and outer diameter groove embedded guide.

Some of these new guiding devices are convenient for the disc spring to work, and some are to reduce the self weight of the mechanical device. Domestic constant force disc spring hanger adopts the guiding method of inserting spring coil into groove. There are many kinds of invention patents in foreign countries, but their applications are rare.

In addition to spring steel, stainless steel and heat-resistant steel, disc spring has been widely used nickel base alloy, elastic alloy, high-temperature alloy, copper alloy and titanium alloy according to working conditions. Hot working alloy tool steel and high-speed tool steel are also often selected, such as 4Cr5MoSiVl and W6Mo5Cr4V2. The research on bainitic steel has a bright future. A large number of new materials are being selected and developed.

It is not uncommon for non-metallic materials to be used in disc spring. When the double diameter slotted disc spring is combined, rubber and plastic can be used to fill it, thus becoming a precision fixture. Disc springs made of glass fiber, reinforced plastic, resin and carbon fiber have been used in Heping machinery factory ten years ago. Carbon fiber and epoxy resin can make the E value close to steel, which has great development prospect.

The basic formula for spring design

The spring diameter d/mm is determined by the strength calculation formula.

Spring diameter D2/mmD2-Cd.

Spring internal diameter D1/mmD1 -D2-d.

Spring outer diameter D/mmD-D2-d.

Spring index C -D2/d General 4 s.C.6.

Spiral angle g/ for the compression spring, it is recommended g to 5 to 9 degrees.

The effective number of laps n is determined by the deformation condition calculation generaln 2.

Total laps n1 compression n1 s n s (2 to 2.5); stretchn n1?n).

n1?n-2(YI.type hot roll); n1 has a tail of 1/4, 1/2, 3/4 or whole lap, recommended 1/2 lap.

Free height or length H0/mm two ends of the ring grinding n1,n-1.5, H0?np-dLI type H0?(n-1) d-D1.

N1,n-2, H0?np-1.5dLII.type H0?(n-1)d-2D1.

N1?n-2.5, H0?np-2dLVII.type H0?(n-1.5) d-2D1.

Both ends of the ring are not grinding n1,n-2, H0?np-3d.

N1,n-2.5, H0?np?3.5d.

Operating height or length Hn/mmHn-H0-lnHn-H0-ln-ln, ln-deformation.

Pitch p/mm p-d.

Spacing d/mmd?p-dd?0.

The compression spring has a high diameter ratio of bb-H0/D2.

Expand the length L/mmL?pD2n1/cosgL?pD2n-hook-part unwind length.

Introduction to the four major trends of metal spring

After many years of development of China’s spring hardware products industry, with China’s international status and industrial competition intensified, under the new situation, the spring hardware products industry in the constant search for development presents the following characteristics. Then from these characteristics can see China’s spring hardware products industry in the future for some time in the development trend. Tool spring hardware products demand year by year, spring hardware products product quality improvement, capital expansion intensified, inter-enterprise cooperation in the increase and other trend characteristics for the strength of large-scale spring hardware products enterprises, is not a bad thing, when such large enterprises conform to this trend of development, will only gradually become stronger and bigger. For small and medium-sized spring hardware products enterprises, there may be gaps in product quality, cooperation opportunities are relatively small, let alone capital operation. Therefore, in the spring hardware industry in the continuous development and progress, small business living environment will become more and more difficult.

1. Spring hardware productquality improvement.

At the same time, the international market requirements for China’s spring hardware products will gradually develop and change, the quality of Chinese products, packaging, supply period will have higher requirements, and even gradually extend to the production process and product research and development, products and environmental protection, energy resources, human environment combined. And the huge market and central position of gravity, will further attract spring hardware products multinational manufacturing center to China. Integration with foreign enterprises will continue to improve the quality of China’s spring hardware products and enterprise competitiveness. While continuing to expand the markets of traditional countries such as the United States and Japan, Southeast Asia, the Middle East, Russia, Europe, Africa and so on will also fully bloom.

2. Tool spring hardware products demand increased.

With China’s continuous improvement in the world status, more and more countries around the world began to use China’s spring hardware products, to a certain extent, stimulate the development of China’s spring hardware products. In recent years, with the acceleration of the process of global economic integration, China’s spring hardware products tool processing industry has gradually become the world’s spring hardware products tool industry. Some developed countries, especially developing countries such as Africa and the Middle East, are increasing at a rate of ten percent per year for spring hardware tools. Spring hardware products tools are labor-intensive industries, as the spring hardware products, Yongkang, but also by virtue of low-cost traditional competitive advantage, once became a spring hardware products tools gathering place.

3. Inter-enterprise cooperation is on the rise.

From the point of view of competitive behavior, the cooperation between enterprises in the sharing of resources is increasing, on the one hand, manufacturers strengthen the control of retail terminals, and strive to reduce the sales link, save sales costs, so that sales channels to the direction of specialization, enterprise sales model towards the development of a variety of markets at the same time. On the other hand, the trend of the sales industry has led to the rising status of large home appliance chains, increased control over the industry, participation and triggered price competition previously dominated by manufacturers. With its broad market coverage, procurement scale and cost advantage, large retailers will increasingly control the production enterprises in product pricing, payment delivery and so on. As the lower level of small and medium-sized enterprises in this trend will be in the competition in the disadvantage d’ position.

4. Capital expansion intensified.

After China’s accession to the WTO, in the global competitive environment, in order to improve competitiveness, industrial capital has become an important theme of industry operation. In 2004 Supor, Huadi has listed, Hongbao is also actively working for the listing, Wanhe’s capital market operation will not be due to the failure of restructuring with Guangdong Meiya and stop. From a capital point of view, the main feature of the current is the intensification of capital expansion.

The reason for the gap in the metal spring industry at home and abroad

The formation of the gap between China and developed countries spring industry has a certain historical reason, is formed in the long-term process of the development of spring industry in China. If China’s spring industry wants to be further developed, it is necessary to eliminate the existence of these gaps.

1. Irrational economic system is the root cause of the gap.

Under the planned economic system in the past, the government regulation and control dominated, and the long-established production and marketing model limited the operational vitality and independent development of China’s spring industry, and drew a line for the development of China’s spring industry. Since China’s reform and opening up, the situation has improved, but the long-established industry scattered, chaotic, poor situation still exists, but also to the development of China’s spring industry has brought adverse effects.

2, the backwardness of the level of science and technology is the main reason for the formation of the gap.

With the continuous progress of science and technology and the renewal of the host, the requirements for products are getting higher and higher. Because China’s spring industry has a certain development capacity of the number of scientific research centers, small scale, less investment in scientific research funds, the enterprise’s own research and development capacity is weak, so that the development of new technology, new products can not keep up with the world’s advanced scientific and technological level and market trends.

3, at present, China’s spring industry enterprises are still largely small enterprises, production scale is small, low production concentration, market competition confusion, is also a factor in the formation of the gap. In order to solve this phenomenon, it is necessary to create large-scale enterprises, support and drive the development of the spring industry, but also to formulate relevant industrial policies, important to encourage the development of high-strength, high-precision, high value-added heterosexual spring products, limit the production of ordinary spring products, guide the healthy development of enterprises in the industry, in order to promote the development of the spring industry.

4, the existing domestic production equipment is not complete enough, especially the serious shortage of testing equipment, fundamentally on the current spring production needs, affecting the further expansion of spring production, more affectthe quality of spring products, but also promote the formation of China’s spring industry and foreign workers also developed countries. China’s spring industry should invest more money in production equipment to speed up the upgrading of old equipment to ensure product quality and production needs, narrow the gap with foreign countries.

5, the gap between raw materials itself is also an important reason for the gap between China’s spring products and foreign products.

Introduction to the manufacturing process of the coil spring

The manufacturing process of the coil spring includes: a) roll-up, b) the production of hooks or finishing of the end face, c) heat treatment, d) process testing and pressure treatment.

Roll is to wrap the technically specified spring wire on the core rod. When mass production is made on a universal automatic reed machine, and in single pieces and small batches, in a regular lathe or manual winding machine.

Roll divided cold rolls and hot rolls two kinds. Cold rolls are used for spring wire with a diameter of d (8 to 10) mm after pre-heat treatment, and a strong spring made of larger diameter spring wire is a hot roll. The temperature at the hot roll is selected in the range of 800 to 1000 degrees C with the thickness of the spring wire. Whether cold or hot, the spring’s pitch should be adjusted as necessary, depending on the circumstances.

The spring should be heat treated after completing the above operation. There should be no significant decarbonization layer on the surface of the spring after heat treatment. The spring after the cold roll is only tempered to eliminate the internal stress generated when rolled.

In addition, the spring must be carried out process tests and in accordance with the requirements of the spring technical conditions for precision, impact, fatigue and other tests, in order to verify that the spring meets the technical requirements. In particular, the long-lasting strength and impact strength of the spring depends to a large extent on the surface condition of the spring wire, so the surface of the spring wire must be clean, no cracks and bruises and other defects. Surface decarbonization can seriously affect the long-lasting strength and impact resistance of the material. Therefore, the decarbonization layer depth and other surface defects should be specified in the technical conditions of the acceptance spring. Important springs are also subject to surface protection (e.g. galvanizing);

For important springs, it is also subject to strong pressure treatment. The pressure treatment is to carry the spring under the action of the extreme load for 6 to 48h in order to produce plastic deformation and residual stress in the hazardous area of the spring wire cross-section. Because the residual stress is the opposite of the operating stress symbol, the maximum operating stress of the strong pressure treated spring is small, and a single pressure treatment can improve the carrying capacity of the spring static load by 25%. It can be improved by 20% if treated with a shot. However, springs for long-term vibration, high temperature and corrosive media, as well as springs for general use, are not suitable for this reinforcement process.

Spiral stretching, twisting spring manufacturing, in addition to a few manufacturing plants in the introduction of foreign CNC spring forming machine once automatically forming a variety of patterns of stretching, twisting spring. The vast majority of manufacturing plants still use traditional processing methods to manufacture, now make a simple introduction.

1, the coil stretch spring. The process is basically the same as the coil compression spring, different is just the end of the hook ring processing, the tensile spring is formed as follows:

1) With the same method as the coil compression spring, winding after forming destressed annealing, and then hook ring processing, in addition to special shape hook ring or require strain high initial pull of the spiral stretch spring car bed with heart roll or hand roll, most of the spring is made with automatic reed rolling.

2) With a straight-tailed reed machine roll. It is a vertical reed machine with a spindle vertical. After rolling, destressed annealing, and then hook-ring processing. The end structure of the coil-stretching spring is in many forms, and there are many processing methods. Commonly used are: small springs using pliers-type special tools or special process devices for manual processing, ordinary coil edging spring with a hooker or mold with manual or automatic operation methods, long arm hook ring stretch ingenuity spring, generally when winding to leave the required material length, or roll out the required number of rings for processing, with straightening tools to straighten the two ends, and then with a special tool to bend the hook ring. The process specification for destressing annealing is described above. Spring rolled up after the first destressed annealing, and then cut off and hook ring processing, hook ring processing, generally 1 to 2 times to destress annealing. In order to prevent the relative angle of the two hook rings from changing, the temperature after the finishing processing of the hook ring should be 20 to 30 degrees C lower than that after the roll-up. The coil stretch inglis spring generally does not carry out blasting and strong pull treatment.

2, the coil twist inge spring. Its process and spiral compression, stretch ingenuation spring is basically the same, different also embedded in the instant-comcon? In small batch production and twisting arm is more complex case, most of the use of manual or semi-automatic with the central scroll reed method forming, and then the use of a clamped arm will be twisted arm according to the pattern requirements for processing. In the mass production, can be in the straight-tail reed machine and twisting reed special machine roll, twisting arm can not be completed according to the pattern, and then sub-process editing, fixtures to process. Depending on the characteristics of the coil-twisting spring, the following two points should also be noted when designing and manufacturing:

1) The spiral torsional spring end twisting arm should be bent and formed once during manufacture to avoid machining defects and correction plastic surgery. After the torque arm processing should be carried out a second destressed annealing;

2) The current coil twisting spring is mostly dense, so that between the spring rings produces a similar tensile of the initial pull force of the spring, in the loading and unloading will produce friction altogether phenomenon, when loading and rotation of the same or increase dummy, this tendency increases; Therefore, there should be a gap between the spring rings when designing and forming. In a large number of production, the manufacturing plant in the condition of conditions, the spiral stretching, twisting spring expansion, bending, bending and other processes can be processed by hydraulic, pneumatic and other methods.

Recommendations for the metal spring industry

At present, the widely used metal spring stress and deformation calculation formula is derived from material mechanics. Without a certain amount of practical experience, it is difficult to design and manufacture high-precision springs, along with the progress of design stress, the past experience is no longer used.

In recent years, the design method of the finite element of spring has entered the practical stage, and a lot of practical speeches have been made, such as the effect of the spiral angle on spring stress, the relationship between stress and fatigue life calculated by finite element method, etc. The comparison of stress is calculated using the current design method and the finite element method is analyzed. For the same structure of the spring, under the same load, it can be seen from the figure, the effective ring less or the helix angle of the high stress spring stress pressure, the results of the two methods are relatively large difference. This is due to the increase of the spiral angle, increase the load eccentricity, so that the outer diameter of the spring or lateral deformation is larger, so the stress is relatively large. The current design calculation method can not be reflected locally, and the law of finite element can be more local reaction.

For example, as the design stress of the metal spring progresses, the helical angle increases, which shifts the exhaustion source of the spring from the inside of the reed ring to the outside. To this end, it is necessary to use spring precision analysis technology, the current application of a wide range of methods is finite element method. The characteristic of the vehicle suspension spring is that in addition to sufficient fatigue life, its permanent deformation should be small, that is, anti-relaxation function to be in the defined range, otherwise because of the different deformation of the spring, the body center of gravity will occur. At the same time, consider the effects of environmental erosion on their fatigue dye life.

With the increase of vehicle maintenance period, the permanent deformation and fatigue life are put forward more stringent requirements, for which it is necessary to use high-precision design methods. The finite element method can guess the effect of spring stress fatigue life and permanent deformation, and can correctly reflect the relationship between spring fatigue life and permanent deformation of the material.

Spring design has made some progress in the use of reliability technology, but to further improve, data development and accumulation is required. With the development of computer technology, at home and abroad to compile a variety of versions of the spring design program, for the metal spring technical staff to provide a convenient premise for the development of different. The design program is used to complete the development of the curved clutch spring and drum suspension spring, which are more difficult to design. With the development of spring application technology, but also to the designers put forward a lot of need to pay attention to and solve the new topic.

Such as materials, pressure and shot treatment on the effects of fatigue and relaxation function, design is difficult to cut when calculating, rely on experimental data to determine. Also, according to the current design formula to find the number of laps, the spring stiffness made than the design stiffness value is smaller, need to reduce the effective number of laps, in order to meet the design requirements. The current design trend of high-volume production products, taking the maximum working stress and fatigue life requirements as an example.

Spring finite element analysis method, although the high level of spring technology in the country has entered practical, although China has the technical development of this aspect, but has not yet formed a practical model. In addition, an optimized design has been introduced in the design process of the spring. The structure of the spring is simple, the function is simple, the influence structure and function of the parameter variables are less, so the designer early use of the analysis method, the illustration method or the illustration analysis method to find the best design, and achieved some results.

With the development of computing technology, the optimization design of non-linear planning by computer has achieved effective reliability design is a series of analysis and design techniques used to ensure the reliability of the products designed, and its function is to make the design edited on the basis of the possible failure of the products, so that the designed products reach the defined reliability target value, which is a supplement and perfection of the traditional design methods.