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Resolving Common Defects of Stainless Steel Thread Rolling Cold Processing Nanning Harwell Fastener Co., Ltd. is the most important process for external thread processing in the fastener industry due to its roll forming, high production efficiency and high thread precision. Due to the increasing market demand for stainless steel fastener products, and the high cost of materials and the difficulty of processing, it is necessary to explore and analyze the causes of various defects in the stainless steel thread rolling process, and take corresponding solutions or avoidance measures to improve Product qualification rate and production cost reduction are of great significance. The following describes the defect characteristics generated by the rolling process, and the causes and solutions are analyzed.
1. The thread working face is rough, and the inspection ring gauge can not be rolled by the surface roughness value of the blank. It is the rolling extrusion of the two rolling die on the workpiece blank, and the surface of the blank is gradually squeezed and deepened. Become a threaded work surface. If the roughness value of the blank is high, the degree of improvement of the thread surface is limited due to the hot hardness of the stainless steel material, so the surface roughness of the rolled thread is not satisfactory. The solution is to reduce the surface roughness of the blank. For rolling threads of the same precision grade, the roughness of the stainless steel blank is one level higher than the roughness of the carbon steel thread blank.
The selection of the cutting fluid is improper. The forming of the thread is the relative rolling extrusion of the two rolling wheels and the workpiece, that is, the relative frictional movement between the rolling die and the workpiece. At the beginning, the crest of the rolling die contacted the blank, and the pressure point gradually became the thread bottom, and the unpressed point was squeezed to the crest of the rolling die to become the thread crest. According to the friction theory, when the two metal surfaces are in contact under the normal load, the micro-protrusion tips on the surface are in contact with each other due to the rough surface, and the hard surface micro-convex is embedded in the soft surface, along with the contact point. As the pressure increases, the actual contact surface increases, and when the pressure reaches the compression yield point, the softer surface will be plastically deformed. Due to the hot hardness and low thermal conductivity of the stainless steel material, the rolling process requires a large pressure (1/31 times larger than the carbon steel). The temperature of the contact surface between the rolling die and the workpiece rises sharply, which easily causes the boundary film to rupture and produce metal. Direct contact, the adhesion of the material molecules (ie, due to phase welding) to transfer the workpiece material to the surface of the rolling die, that is, the formation of adhesive wear, resulting in fine burrs on the surface of the thread, and even spalling Phenomenon, causing waste.
(Guangxi 530031) Lu Yuxiong Solution: 1 Select or formulate special cutting fluid with extreme pressure performance. It is required that the cutting fluid has a suitable viscosity, and it is easy to form a dynamic pressure oil film capable of receiving a large pressure. Secondly, it has a good cooling performance, and takes the high temperature generated by the rolling process in time. 2Rolling process cooling and lubrication should be sufficient to ensure that both the rolling wheel and the surface of the workpiece are covered with cutting fluid.
Excessive rolling time (for workpieces that roll half-toothed workpieces or hex bolts) requires a certain amount of time to eliminate the elastic recovery of the material, but the rolling time is too long, causing excessive friction between the rolling die and the workpiece. The high temperature is generated, the oil film is destroyed, and the adhesive wear is generated, which causes the thread surface to produce a sheet, which causes waste.
Solution: According to the size of the workpiece and the size of the pitch, select different rolling time, small workpiece, small pitch select shorter rolling time, faster speed. Large workpieces, large pitches, long time selections and slower speeds can be tested to determine the optimum rolling parameters.
Excessive wear of the rolling wheel Due to long-term friction, after a certain period of time, the rolling die surface will be fatigue-shedding, causing the tooth profile roughness value to rise sharply, and the rolled-out thread roughness will be deteriorated, and even burrs may occur.
Solution: When the fatigue of the rolling wheel is slight, the oil stone can be ground on the rolling wheel to remove the burrs caused by the fatigue falling off; in case of serious replacement of the new mold.
2. The threaded working surface has double cusps or fines. The relative position of the two rolling dies is incorrectly adjusted. The forming process of the thread is formed by the pressing of the two rolling dies, if the two rolling dies are shaped. The trajectories that move on the workpiece (ie, the crest prints) do not completely coincide, and the threads produce a regular double cusp shape or produce slender swarf, as shown. Solution: 1 Correctly install and adjust the relative position of the rolling wheel. The adjustment method is to first adjust the standard thread and the rolling thread on the fixed spindle with the standard thread (such as tap or standard stud) with the same pitch as the rolling thread. The mold is engaged, then the movable main wheel is shaken, so that another rolling die on the movable main wheel is close to the standard thread, and the thread engagement condition is observed, and then the tooth-shaped adjusting ratchet behind the fixed main shaft is adjusted, so that the two rolling wheels and the standard thread are made. Completely coincident, then test roll. 2 imprint method. Adjust the relative position of the two rolling wires and the workpiece so that the indentation line of the rolling wheel on the workpiece is as fine as possible. Slowly start the machine tool to make the workpiece rotate slightly less than or equal to 180, quickly open the rolling die and take out the workpiece (test piece) The 1 and 4. rolling thread mold observations, the two sets of marks completely coincide, it is proved that the tooth tip 5 workpiece is correct. Otherwise, you need to adjust the tooth adjustment ratchet behind the fixed spindle. This method is suitable for skilled operators.
The axial compensation of the thread rolling wheel spindle automatically compensates for the failure compensation mechanism. When the rolling process occurs, the two rolling wheels cannot completely overlap the workpiece. The method of inspection is to remove the rolling wheel and the front bearing bracket of the movable main shaft, measure the shoulder of the main shaft bearing with the dial gauge contact, and tilt the main shaft with the crowbar. If the dial indicator can swing and can be quickly reset, Then the compensator has not failed. Instead, remove the active spindle check and replace the bearing or compensation spring.
The thread rolling machine spindle jumps out of tolerance. After a period of use, the bearings of the two spindles of the thread rolling machine will wear out, or the position where the rolling die is mounted on the spindle will be depressed. At this time, the axial and radial circular runout of the main shaft will be excessive. When the circle runout tolerance exceeds 0.12 mm or the spindle recess reaches 0.12 mm or more, the rolled workpiece may have defects such as burrs. The reason for this is similar to the one shown. When the circle runout tolerance exceeds a certain range, the movement trajectories of the two rolling die shapes on the workpiece are deviated, and the threads may generate burrs. Unlike the improper adjustment of the position of the rolling die, the burr of the tooth surface is irregular. The solution is to replace the bearing and the spindle.
3. The thread crest is rough and obstructs the thread pass. As shown in the figure, the workpiece should be supported by the support piece during the rolling process. When installing, ensure that the parallelism tolerance between the working face of the support piece and the work surface of the thread rolling machine is ±0.01mm. The center of the workpiece and the center of the rolling die are kept at a certain distance ee is too small, the workpiece is easy to jump away from the rolling die, and it can not work normally; if the e is too large, the pressure of the supporting piece is increased, the friction of the workpiece piece is increased, and the crown is The slab is prone to dry friction and causes burrs. Generally e-0. 1.0.3mm. With welded carbide as the support piece, the structure is simple, easy to manufacture and long in life. It is used for rolling carbon steel thread. As long as e is selected properly, the rolled out thread can meet the technology. Claim. However, for rolling stainless steel threads, the thread crest tends to produce burrs, and the thread ring gauge cannot pass. The reason is that the rolling process, especially the axial series rolling, the workpiece is continuously fed, and the workpiece and the support piece are in contact with each other for a long time. Sliding friction between the thread crest and the alloy is prone to adhesive wear and tear, resulting in burrs on the crest. Solution: With the rotating roller bracket as shown, when the workpiece rolls, the roller rotates to make the workpiece and the bracket become rolling friction, ensuring that the roller bracket can be fully cooled and lubricated. After many years of actual operation of our company, 3. Rolling die 2. Workpiece. The use of the roller effectively solves the problem of burrs on the crest.
Due to the low thermal conductivity of the stainless steel, the rolling process produces a very high temperature, which causes the tooth surface to easily produce dark blue or dark yellow ablation, which affects the quality of the thread and the service life of the spinning wheel. Causes and solutions: The cooling and lubrication process is insufficient. The flow rate of the cooling hydraulic pump is to ensure that the two rolling wheels and the workpiece are covered with cutting fluid to ensure sufficient cooling and lubrication.
The viscosity of the cutting fluid decreases. The temperature generated by the stainless steel rolling process reaches 300.400/, and the cutting fluid is easily deteriorated, so it should be replaced in time.
The rotational speed of the rolling die is too fast. The rotational speed of the rolling die is too fast. The new surface is too late to form an oil film, causing dry friction, which causes the tooth surface to be burned. The solution is to select the appropriate speed, generally small size, small pitch with higher speed, large size, large pitch with lower speed, for series rolling, the table is available.
Spindle speed selection table Thread size pitch / mm In total, stainless steel thread rolling process has many forms of defects, including equipment, molds, blanks and operators. Through various detection and diagnostic methods, find out the specific Influencing factors and adopting corresponding solutions. ()
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