Industrial technology China's new technology and new products bookmark0 talk about thread rolling processing technology Zhang Xiumei (Shenyang Liming Aero Engine (Group) Co., Ltd., Shenyang 110043, Liaoning) trend. As a kind of processing method of plastic forming, thread rolling processing has been adopted by more and more fastener manufacturers. This article uses the principle of thread rolling principle, the influence factor and parameters to determine the fault performance and causes in processing. Explain.
Table 1 Fault conditions The cause of the fault and the elimination method are too large, the outer diameter is too small, and the position of the active spindle is adjusted too far.
2. The rolling time is too short.
3. The rolling pressure is too low. If the diameter is too large, the diameter of the outer diameter qualified blank is too large and the medium diameter is qualified, and the diameter of the outer diameter is too small. The medium diameter is qualified, and the outer diameter is too large and the blank diameter is too large. The middle diameter is too small, the outer diameter is too large, and the position of the active spindle is adjusted too low.
2. The hydraulic time is too long.
3. The rolling pressure is too high. The parallelism of the two-roller mold with a medium-diameter taper is not well adjusted. The adjustment of the medium-diameter non-tapered outer diameter has a taper blank. When the taper is rolled, fine chips or scales are generated.
2. The rolling time is too long. When the workpiece is rolled up, the workpiece jumps up and the support block is too high.
2. The diameter of the two rolling die is different for the workpiece. The top of the screw is 1 and the support block is too low.
2. The support surface finish is too low. The thread rolling die is damaged at the chamfer. 1. The rolling die is chamfered too small or too small.
2. The end faces of the two rolling die are not in a plane. The rolling die is broken into a fast shape. 1. The shoulder of the blank is in contact with the end face of the rolling die. 2. The shoulder of the blank is in contact with the end face of the support block. 3. The position of the support block is not well adjusted. The blank 4 is stuck, and the feed depth exceeds the thread. The workpiece moves axially during deep rolling 1. The blank diameter is too large or too small 2. The diameter of the rolling die is too large or the workpiece is overheated when it is too small. 1. The spindle speed is too high 2. The feed speed is too fast 3. Rolling Excessive pressure Currently, with the market demand, individualized and diversified development, plastic forming and grinding processing combined with the replacement of most small and medium-sized parts will become the development trend of this century, thread rolling forming technology will promote manufacturing The industry is developing in the direction of precision, precision, low energy consumption and pollution-free, and has become an important part of green manufacturing.
The thread rolling principle The metal matrix of the workpiece blank is initially compressed by the force of the rolling wheel to perform a plastic service and finally form a thread shape in the workpiece blank.
Thread rolling is generally carried out on a thread rolling machine, a thread rolling machine or on an automatic lathe with an automatic opening and closing thread rolling head, which is suitable for mass production of external threads of standard fasteners and other threaded couplings. The diameter of the rolling thread is generally not more than 25 mm, and the length of the thread is not more than 100 mm. Rolling generally can not process internal threads, but the material is better! The Y/丨 workpiece can be cold-squeezed with internal threads with a slotless extrusion tap (up to a diameter of up to 30 mm). The working principle is similar to tapping. The torque required for cold extrusion of the internal thread is about 1 times larger than the tapping accuracy and the surface quality is slightly higher than the tapping.
Applicable materials are wide, almost all steel aluminum and other light metal alloys can be, depending on the plasticity and tensile strength and hardness of the material, which are closely related, generally the hardness and strength of the added fruit is higher The lower the elongation, the vice versa, which means that the most suitable material for rolling is difficult to cut. Thread rolling relies on the plasticity of the substrate - the deformability of the substrate - to permanently press the shape of the roller into the blank of the workpiece. The good plasticity of the material being cut usually leads to the formation of colloidal chips and the formation of built-up edges on the tool. For example, cast iron does not have suitable flow characteristics and is therefore not suitable for thread rolling.
Assuming that the workpiece material meets the rolling service and flow requirements, the rolled thread is improved in physical properties compared to other production methods, and the surface roughness is smaller than that of the thread surface after turning, milling and grinding. Hardening improves the strength and hardness The compression of the base material causes the workpiece to harden due to the compression of the metal matrix, which creates fatigue resistance in the threads. Thread rolling should be carried out after heat treatment, and turning and grinding can be carried out before or after hardening. The figure below illustrates the difference between the rolling thread (left) and the machined thread (right) particle flow.
The threaded median diameter is maintained at a predetermined size so that the material of the anchor actually extends the workpiece blank, the amount of material being moved depending on the size and shape of the rolled thread. Compared to thread turning or cutting, thread rolling can save 15-20% of material. In high volume production, this data means a large number of raw materials. Productivity is multiplied more than cutting and is easy to automate. Rolling die life is very long. Compared to thread turning or cutting, the tool consumption of the 3 thread rolling is affected by the factor and the parameters are determined. Successful thread rolling depends on several application parameters. Among these parameters are the type of thread to be rolled, the major diameter, the pitch and the root depth. Additional considerations for thread rolling include the calendering properties of the blank and the cold flow properties.
The material flow rate is calculated based on the specified blank diameter and rate of change. Exceeding or below this diameter will produce a defective thread. Therefore, it is determined that the blank diameter value plays a decisive role in the rolling process. According to the experience accumulated in the actual production process of our workshop, the general blank diameter d=(d2±0.03)-0.02,2 (the diameter of the thread) depends on the factors such as the material to be rolled and the type of thread, such as rolling. Ordinary thread, GH4169 and other high temperature materials generally use d2 as the blank diameter size, 8CrA, 1Cr18Ni9Ti, 1Cr11Ni2W2MV material with d2-0.01 as the blank diameter size; when rolling CG interference thread is generally larger than the normal thread blank diameter value of 0.01 The formula d = (d2 ± 0.03) - 0.02 tolerance 0.02 is sometimes taken as 0.01 depending on the case. Since the thread rolling forming has a very close relationship with the workpiece blank, if the blank diameter is too small, it will not be able to flow into the roller drawing die, which will cause the rolling thread to be untwisted, and cannot meet the diameter of the thread and the diameter of the large diameter at the same time. Claim. If the diameter of the blank is too large, it will cause the rolled thread to exceed the medium or large diameter or the large diameter of the thread, and will also apply unnecessary pressure to the roller and the roller frame, which may result in the thread rolling unit. Damage, so the blank diameter must be determined very accurately. In actual production, the blank diameter value is often obtained by processing the specimen.
When rolling the thread, the thread shape is pressed into the workpiece blank by moving the base material. A key parameter of this movement is the thread root shape and associated dimensions. As the roller anchors the material that will form the root, the material will flow from the roots in the radial and axial directions. The larger the root depth dimension, the more metal is extruded in the root when rolling the thread, and vice versa; the larger the radius of the corner of the tooth is, the less the amount of metal is extruded, and the more the tooth depth is the same arc shape. The bottom of the tooth is less extruded than the flat bottom. The blank diameter is adjusted accordingly according to the amount of material movement.
The principle of roll forming is plastic deformation. When rolling a thread, it is basically a shape change of constant volume. Since the part is subjected to an external force, a slight elongation occurs in the axial direction, so the thread after rolling The top surface is in the form of a dish. Due to the presence of the axial elongation, the growth of the material in the radial direction is reduced. The longer the thread length, the smaller the axial elongation on the unit length is, and vice versa. In the case of a small thread length dimension, the blank diameter value should be appropriately increased. When the thread length is no longer cut after rolling the thread, the length of the thread rolling should be slightly smaller than the design requirement to eliminate the influence of rolling elongation.
Before the rolling thread, the top of the blank should be chamfered in order to reduce the deformation resistance from the workpiece when the rolling wheel is subjected to rolling. The service life of the rolling tool is extended. According to past experience, it is generally chamfered by 30 degrees to make The thread on the thread rolling wheel is close to the balance and less deformed. At the same time, the first and last standard requirements of the thread can be achieved.
4 Faults and elimination methods that may occur when the thread is rolled (see Table 1).
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