Aerospace reinforced threaded parts special thread rolling wheel (2)

2 design of the rolling wheel

(1) Tool material. First, use good tool materials. W6Mo5Cr4V2 has good hardness and toughness. After quenching, the surface hardness can reach HRC64~66. It is a widely used molybdenum and low tungsten high speed tool steel. W6Mo5Cr4V2Al (501) is an ultra-hard high-speed steel containing aluminum. It has a high temperature hardness of HR C54 at 600 ° C, retains high strength and toughness, and has excellent cutting performance. In most cases, its cutting performance is M42 steel. The same, the application is wider. For the processing of titanium alloy and high-temperature alloy MJ external thread, W6Mo5Cr4V2Al(501) is better, and the hardness is controlled at HRC65~67, which can effectively meet the requirements of the workpiece and ensure the good life of the rolling wheel.

(2) The outer shape of the rolling wheel. Commonly used thread rolling machine spindles are: φ45, φ54, φ75, φ80 and some special diameter spindles. The diameter range of the rolling wheel is selected by the type of thread rolling machine to determine the specific number of thread heads. The thickness can be made according to the length of the thread part of the part. Used side or bilaterally.

Rolling tooth design

When the part is made of MJ to strengthen the thread, the externally threaded arc-shaped bottom can greatly reduce the stress concentration, thereby increasing the fatigue life of the part and increasing the fatigue life by more than twice. Therefore, it is required that the top of the thread rolling wheel must be processed into an arc shape, the arc must be smooth and smooth, and no sharp points should appear. The size of the rolling element should be 0.15~0.18P, because it is considered The bottom arc of the rolled external thread workpiece is smaller than the crest arc of the spinning wheel, so the top circle arc and the chamfer arc of the rolling wheel are specified to be 0.16~0.18P. In actual processing, when rolling After the pressure is removed, the material will recover elastically, the arc of the crest of the part will become larger, and the arc of the bottom will become smaller. Especially when the externally threaded parts are difficult-to-machine materials such as titanium alloy and high-temperature alloy, the elastic modulus is higher. Low, the tendency of elastic deformation is large, elastic deformation and elastic recovery are easy to occur, and the degree of elastic recovery of each material is different, and the corresponding requirements for the roll top of the rolling roller are different, so the top of the rolling wheel Arc and chamfer arcs also need to be corrected to ensure the arc requirements of the workpiece. After testing, when the titanium alloy is rolled, the elasticity of the material recovers between 0.005 and 0.012 mm; when the superalloy is rolled, the elasticity of the material recovers between 0 and 0.005 mm. Therefore, when rolling the titanium alloy, the top and bottom chamfers of the rolling wheel need to be corrected to 0.17~0.185P; when rolling the superalloy, the top and bottom chamfer of the rolling wheel need to be corrected to 0.165~ The tooth profile of the 0.18P. rolling wheel is determined as: upper tooth height = H/2-5H/24=0.433P-0.180P=0.253P (reduced from the normal thread 0.289P tooth height), the tolerance is the rolling wheel circle When the arc is at least 0.16P, it is taken as +0.02P. When rolling titanium alloy or high-temperature alloy, the appropriate upper tooth height and tolerance are determined according to the corrected arc size. The lower tooth height is the same as the ordinary thread = H/2-H/8=0.433P-0.108P=0.325P. Similarly, the tooth profile angle of the part after rolling also shrinks, and the MJ thread has a higher precision of the medium diameter tolerance. The requirements are strict, so changes in the angle of the teeth should also be considered. In order to ensure the accuracy of the threaded workpiece, the error range is also specified for the pitch and half angle of the thread rolling wheel. The pitch error is taken as the 0.25 Td2 medium diameter equivalent value, ΔP=0.25Td2/1.7321, accounting for 62.5% of the workpiece error, half angle error The median equivalent value is taken as 0.12Td2, +Δa/2=arctan(0.12Td2/0.75P), -Δa/2=arctan(0.12Td2/1.5P), accounting for 30% of the workpiece error. Others are given by 0.2Td2 Out, the three parts are integrated into 0.45Td2, not exceeding 0.5Td2. The rolling wheel must also be chamfered, otherwise the thread on the edge of the rolling wheel will be damaged when rolling, especially when rolling high strength and hard materials. Significant. The size of the chamfer should meet the requirements of the thread finishing length specified in the end of the MJ thread. Also consider the life of the thread rolling wheel and avoid the chipping, so the chamfer is 16° and the width is 1.3~1.5P. It has a good design. In order to ensure a good rolling effect, there are a few points to be aware of when using the rolling wheel:

(1) Reasonable selection of the diameter of the blank before rolling. The diameter of the blank of the difficult-to-machine material is d1=d-0.67P. The diameter of the blank before rolling is approximated by the formula. Most of them are corrected according to the actual diameter of the thread after rolling. In particular, the mechanical properties of titanium alloys and high-temperature alloy materials are different, which has a great influence on rolling threads, and the impact on MJ threads with higher precision requirements is also significant.

(2) The speed of the difficult-to-machine material rolling thread varies with the material and material strength. When rolling difficult materials such as titanium alloy and high-temperature alloy, the speed of the rolling wheel is lower than that of ordinary steel. Titanium alloy and high temperature The relative elongation of the alloy is δ5=10%~20%, and the speed of the rolling wheel is 7~12m/min.

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