Solutions Quality Assurance Measures Automotive Fasteners

Solutions for Quality Assurance Measures for Automotive Fasteners

Technology and materials as the basis of machinery manufacturing, for the quality and performance of the product plays a vital role in the

Process and material are the basis of machinery manufacturing, and they play a vital role in the quality and performance of products. Steel is the most essential material in fasteners. However, the proportion of non-ferrous metals and composite materials is increasing yearly, and the role of steel used in high-strength fasteners is irreplaceable. Through the use of advanced smelting equipment and process technology and reasonably low alloying, China's fasteners with steel have undergone significant changes so that the current high-strength fasteners can better meet the requirements of the actual use of the machinery manufacturing industry. Taking high strength fasteners as an example, due to the continuous research on the technology of high strength bolt steel, especially the pursuit of upsetting and forging pre-processing process optimization and the best selection of various alloying elements and ratios, a variety of high-strength bolts steel can be developed.

Automobile high-strength fasteners quality assurance often take the following measures.

Most high-volume bolt production requires upsetting, most of the steel used for cold heading steel. In modern automobiles, more than 40% of the parts with threaded structure, in addition to simple positioning bolts, such as connecting rod bolts, cylinder head bolts, etc., by the role of axial preload tensile load, but also in the process of additional axial tensile (alternating) load, transverse shear (alternating) load, or a composite of the bending load, and sometimes there is an impact load. Typically, additional transverse alternating loads cause loosening of the bolt, axial alternating loads cause fatigue fracture of the bolt, while in the role of environmental media, axial tensile loads cause delayed fracture of the bolt. While reducing costs, fastener users propose substantial weight reduction and ultra-high strength to resist elongation, pull-off, slip, and wear; reliable toughness to minimize sensitivity to deflection, notched stress concentrations, and surface quality. Bolts operating in humid or corrosive atmospheres require sufficiently low sensitivity to delayed fracture and good cold heading properties.

The strength level of automobile bolts can be divided into 4.6 ~ 1, 2.9 levels, etc. 6.8 level bolts are primarily used in the manufacture of low carbon steel, without heat treatment; 8.8 level of general ML35 steel, can also be used in the manufacture of low carbon manganese steel, 9.8 bolts commonly used in the manufacture of carbon and boron steel, more than 10.9 level of most of the use of alloy structural steel manufacturing. Now, the automobile application has more high-strength bolts for 10.9 grade, and the amount is gradually expanding.

With the high performance of automobiles and engines and the application of materials to increase the stress, reduce the size of parts, chassis lightweight, the bolt put forward a higher design stress and lightweight requirements, and the most effective measure is to improve the use of steel for bolts strength. Reducing the S content can improve the deformation capacity of steel, reducing the P content can reduce the deformation resistance of steel, and at the same time, can reduce the P and S in the grain boundary of the bias and reduce the grain boundary embrittlement. Reducing S can also lessen the non-metallic inclusions in steel and improve its toughness and plasticity. Therefore, reducing the P and S content in steel can not only improve steel's cold heading performance but also improve steel's delayed fracture resistance.

Metric Low-Profile Shoulder Screws： The head height of these screws is about two-thirds the head height of a standard shoulder screw. They can be used in low-clearance applications such as Inside They're. They're comparable in strength to Class 12.9 steel screws. A standard shoulder with an undersized tolerance allows them to fit most machinery and equipment.

Alloy Steel Thread-Locking Shoulder Screws： A locking element on the threads adds friction to resist loosening. Comparable to Grade 8 steel, these alloy steel shoulder screws are the strongest we offer. They have a standard shoulder with an undersized tolerance for most machinery and equipment. Also known as strippers, they're commonly used in punch and die assemblies and as axles or pivot points.

18-8 Stainless Steel Thread-Locking Shoulder Screws： A locking element on the threads adds friction to resist loosening. These 18-8 stainless steel shoulder screws have good chemical resistance and may be mildly magnetic. All are passivated for added protection against oxidation and corrosion. A standard shoulder with an undersized tolerance allows them to fit most machinery and equipment. They're often used to guide or align components and as an axle or pivot point.

Flat Head Shoulder Screws： These shoulder screws are angled under the head to sit flush in countersunk holes. Use them in structural and load-bearing applications, such as attaching panels to a surface. Made from 18-8 stainless steel, they have good chemical resistance and may be mildly magnetic. They have a standard shoulder with an undersized tolerance for most machinery and equipment.

Metric Thumb-Grip 18-8 Stainless Steel Precision Shoulder Screws： Install and remove these shoulder screws by hand or with a hex key. Made of 18-8 stainless steel, they have good corrosion resistance and may be mildly magnetic. With a shoulder diameter that is twice as precise as our general-purpose shoulder screws, they provide smooth, accurate movement. Use them where precision matters, such as in measuring devices, optical fixtures, and laboratory equipment.

Alloy Steel Extended-Tip Set Screws： Also known as half dog-point set screws, these set screws have a protruding tip that locks within a mating hole or slot to keep parts aligned. The length listed is the overall length. Black-oxide alloy steel set screws resist corrosion in dry environments.

Metric Alloy Steel Cone-Point Set Screws： Made from alloy steel, these set screws have a pointed tip that wedges into the contact surface for a secure hold on soft materials such as brass. The length listed is the overall length. Zinc-plated alloy steel screws resist corrosion in wet environments.

Experiments show that the S content dramatically influences the tendency of 45 steel to crack, and the reduction of S content can significantly reduce this tendency. Usually, 8.8-grade bolts are manufactured with ML35 and SURCH35K steel. ML35 is a typical conventional cold heading steel, when the size of the cross-section is different at the same time, ML35 due to the degree of quenching is different, although the same tempering process, its mechanical properties are not the same. The larger the cross-section, the lower the degree of hardening and the worse the mechanical properties. After quenching and high-temperature tempering, the surface layer and the heart differ in their microstructures, even though they achieve similar hardness. The surface layer is tempered sohnite while the heart is still lamellar pearlite organization. Along the cross-section of the organization, performance is not uniform.1 0.9 grade bolts are generally made of 40Cr, 35CrMo ~ 9. Still, due to the boron steel's low ability to resist tempering stability, 40B, 40MnB ~ its tempering temperature is lower than that of low alloy steels 80 ~ 1O0 ~ C. Therefore, the delayed fracture susceptibility of the boron steel made of 10,9-grade high-strength bolts is significant.

To further improve the cold heading performance and omit the spherical annealing treatment, the development of low-cost low and medium carbon high-strength boron steel, the basic principle of its composition design is to reduce the carbon content, improve the deformation of the steel ability to add a trace of boron to make up for the loss of strength and hardenability due to the reduction of carbon and the loss of strength and hardenability, the addition of an appropriate amount of Cr, Mn, and other alloying elements, to improve the hardenability further. Due to the low content of carbon and alloying elements, cold working performance is good, and the rolled material can be directly drawn and processed cold without the need for pre-spheroidal annealing treatment, saving the manufacturing cost of bolts.

Cheap B steel should replace the original high-priced alloy containing Ni, Cr, Mo, etc. With non-quenched steel manufacturing bolts can be omitted before the bolt cold-drawn spheroidal annealing and quenching and tempering of bolts after shaping, but also reduce the tendency of decarburization of the tip of the thread, improve the thread yield, the economic effect is noticeable. Non-tempered steel coils in cold working hardness are usually higher, reducing the processing mold life, so non-tempered steel manufacturing bolts are mainly 8.8 grade. A small amount of 1 0.9 grade double head bolts can also be used in non-quenched steel, and its use is gradually expanding.

They currently used non-quenched steel, the organization of low-carbon manganese-containing ferrite + pearlite type and body type, and micro-alloying elements such as Nb, V, Ti, and other grain refinement and precipitation strengthening elements. The use of extra-furnace refining to reduce inclusions and control the composition in a narrow range, through the control of NSLN and control of cooling, refinement of the organization to improve toughness and produce precipitation strengthening. Given the fluctuations in the mechanical properties of non-quenched steel rolled material directly affects the overall performance of the bolt, the metallurgical process control of non-modulated steel is very critical. Some manufacturers have attached great importance to the application of non-quenched steel, instead of SWRCH35K production of 8.8 high-strength bolts, mechanical properties are better than the tempered SWRCH35K, this new low-carbon bainitic steel prices are high. Still, it is a promising new material.

Heat treatment of fasteners, in addition to general quality inspection and control, there are some special quality inspection and control. The threaded fastener inspection can not be based on the hardness value; check the relevant manuals and convert it to strength value. There is a hardenability factor in the middle. Because of the national standard GB / T3098.1 and the national standard GB / T 3098.3, arbitration hardness is measured at a 1/2 radius of the cross-section of the part. Tensile specimens are also intercepted from 1/2 radius. Because it is not excluded that the center part of the part has a low hardness, a low-strength part exists.

In general, the hardenability of the material is good, the hardness of the cross-section of the screw part can be evenly distributed. The strength and guarantee stress can also meet the requirements as long as the hardness is qualified. However, when the hardenability of the material is poor, although according to the prescribed part of the check, the hardness is competent, the strength and guarantee stress often fail to meet the requirements. Especially when the surface hardness tends to the lower limit, to control the strength and guarantee stress in the qualified range, the lower limit value of hardness is often increased. RetemperinRetempering~ 1 2.9 grade bolts, screws, and studs should be based on the actual production of the lowest tempering temperature lower 1 0 ℃ insulation 30min retemperinretemperingthe same specimen, before and after the test, the difference between the average of the three hardness points shall not exceed 20 HV. Re-temperiretempering checks the quenching hardness, which is insufficient, and the use of temperature tempering that is too low to barely reach the specified hardness range of the practice to ensure comprehensive mechanical properties. Shallow carbon martensitic steel is made of threaded fasteners and uses low-temperature tempering. Although other mechanical properties can meet the requirements, the guaranteed stress measurement and residual elongation fluctuations are enormous, much larger than 1 2.5 um.

In some cases, conditions will suddenly cause a fracture phenomenon. In some automotive bolts, this has happened. Tempering at the lowest tempering temperature can reduce the above phenomenon.

The susceptibility to hydrogen embrittlement increases with the strength of the fastener. For 10.9 grade and above, male fasteners or surface-hardened white tapping screws and combination screws with hardened steel washers, etc., should be dehydrogenated after plating. Dehydrogenation is generally carried out in an oven or tempering furnace at 190 to 230% for more than 4 hours to diffuse the hydrogen. Threaded fasteners can be used to spin a tight approach in a particular fixture, spinning to make the screw withstand considerable guaranteed stress under tension; keep 48 hours after loosening the threaded fasteners do not produce fracture.

With the development of automotive and machinery industries, the use of fasteners put forward more and more high requirements, such as automotive, motorcycle high-performance and lightweight, steel put forward a new function, which does not reduce the cost of the part itself but has the potential to reduce the total cost of the machine or component. Experiments have shown that after adding Ni, Cr, Mo, and other elements, the price of the material itself is bound to increase, but the bolt's resistance to delayed destruction of the strength has been improved, and the original compared to the diameter of the bolt is reduced; the bolt mounting holes are also reduced accordingly, as the size of the composition of the tightening is also reduced accordingly, to achieve the overall reduction in the cost of the purpose.

For high-quality Alloy Steel Thread-Locking Shoulder Screws and professional technical support, please get in touch with us at adelajonly@gmail.com or visit our website at https://www.juxinfasteners.com.