This is the 14689th article published by Metalworking (mw1950PUB).
Editor's Note
Aiming at the problems of large product runout after pressing, uncontrolled preloading force and pressing speed, and real-time detection of rubber pressing force, systematic analysis is carried out from the three aspects of assembly equipment and tooling design, rubber installation method and intelligent monitoring, and a flexible wheel assembly general equipment and tooling, rubber pressure intelligent monitoring system and rubber compression stress balanced installation method are designed. After practical application and verification, the amount of elastic wheel runout after assembly is effectively reduced, and the test stiffness value of elastic wheel is indirectly controlled through the monitoring of rubber compression force, and the proportion of elastic wheel stiffness test sampling is reduced; and the assembly pressure curve table of each elastic wheel is formed. The quality of the elastic wheel assembly is guaranteed and the efficiency is increased.
1
Preamble
Elastic wheel is a kind of wheel inlaid with rubber between the wheel rim and the wheel core, which is generally composed of wheel clamps, wheel cores, pressure rings, rubber rings and joint bolts. Elastic wheel is one of the main wheels of modern urban rail transit vehicles, which can reduce the impact noise of wheel rail, alleviate the shock vibration of wheel rail, reduce the dynamic stress of the transmission bogie device and reduce the wear and tear of wheel rail, and improve the service life of line vehicles. The role of elastic wheels is becoming more and more important, and it has become a major component of rail vehicles, and the market demand is increasing [1,2]. This article takes a certain export-type integral elastic wheel produced by our company as an example, and mainly introduces the press-fitting equipment and tooling design of this elastic wheel, the intelligent monitoring of rubber pressure and the rubber balanced compression installation method.
2
Product introduction
2.1 Product Structure
The outlet-type integral elastic wheel structure (see Figure 1) is mainly composed of several parts, such as wheel core, rubber ring, wheel clamp, grounding wire and fastening bolt.
a) Three-dimensional diagram
b) Explosion diagram
Fig. 1 Outlet type integral elastic wheel structure
1—Wheel core 2, 4—Rubber ring 3—Hoop 5—Ground wire 6—Tightening bolts
2.2 Key Assembly Technical Requirements
(1) Torque Bolt torque 300N·m.
(2) Runout Axial circular runout ≤ 0.5mm, radial circular runout ≤ 0.3mm.
(3) Static imbalance Static imbalance value ≤125g·m.
(4) Test requirements Are as follows.
1) Type test: radial stiffness ≥ 400kN/mm, axial stiffness ≥65kN/mm. Torsional stiffness 23.9 kN/mm. The amount of retardation is within 0.3 mm.
2) Fatigue test: after the test, there is no defect in the magnetic particle detection on the surface of the wheel hoop, wheel core and pressure ring; the delay amount is within 10mm. The change rate of axial and radial circular runout values before and after the torsional stiffness wheel test ≤± 20%, while the axial circular runout value needs to be ≤0.5mm, and the radial circular runout value needs to be ≤0.3mm. After the test, the stiffness value should meet 600kN/mm≥ radial stiffness ≥320kN/mm, 100kN/mm≥ axial stiffness ≥52kN/mm. The amount of retardation is less than 10 mm.
2.3 Product Analysis
(1) Product runout The export-type product is basically the same as a light rail elastic wheel structure developed by our company in the early stage of the country, but the runout value requirements after the product assembly are improved, see Table 1 for details.
Table 1 Runout value requirements for outlet elastic wheels and a light rail elastic wheel
The assembly equipment, tooling and assembly methods used in the early stage of a light rail elastic wheel can only barely meet its assembly quality requirements, and if the equipment and tooling are not redesigned and the assembly method is improved, it will certainly not be able to meet the runout value requirements of the export-type elastic wheel.
(2) Stiffness test The outlet type elastic wheel has a large batch, and how to ensure that the stiffness test of each product meets the requirements is a problem we are facing. Each product undergoes a stiffness test, conditions do not allow, if the method of controlling the quality of individual parts and sampling stiffness testing is adopted, there is a high cost of part cone size and shape detection, long lead times and high quality uncertainty after assembly.
Through the analysis and calculation of the strength of the outlet elastic wheel, after the material and structural parameters of each part are determined, the main factor affecting the stiffness of the elastic wheel is the pressure value of the rubber part caused by the accumulation of the assembly size and geometric tolerance of each part. Therefore, as long as the minimum pressure value to meet the strength of the elastic wheel is calculated, the monitoring of the elastic wheel stiffness test can be realized by controlling the minimum pressure value of the press-mounted rubber and sampling the elastic wheel stiffness.
By calculation, the axial pressing force range of elastic wheels is 11.625 ~ 15t, taking into account the frictional resistance between the metal parts in the system during the pressing process, the impact of the difference in rubber hardness on the pressing force and the calculation error, for safety reasons, the final control is 12.5 ~ 16t is qualified.
3
Automatic and intelligent press-fit equipment design
3.1 Design requirements for press-fit equipment
According to the original tooling of the general company, whether the vertical hydraulic press or the screw pre-compression method can not meet the requirements: the speed of the pre-compression stroke is not controlled, affecting the product runout value. The pre-compression force is not precise and cannot be automatically packed. It is impossible to judge whether the actual compressive force value of each rubber meets the requirements.
In order to solve the above problems, the press-fit equipment must be designed to automatically input the pre-press loading force, the press-loading speed and the packing time through the program; at the same time, it must be able to output the actual compression force judgment value of the rubber in some form. For quality traceability, there must also be a quality record-keeping function. In order to facilitate the tightening of bolts around the elastic wheel after pre-compression, the original compression device needs to be changed to a tension device.
3.2 Pressure-mounting equipment host and supporting tooling design
(1) Main engine design The tooling host design is shown in Figure 2, the hydraulic cylinder is installed in the middle of the fuselage, the piston rod is up, and the upper end of the piston rod is opened with a card ring groove. During press-fit, the product is pulled by using a block-type composite block, and the upper part of the elastic wheel is free of press-mounted equipment components during press-fit, which is convenient for both sides of the manual to twist the tightening bolts around at the same time. The displacement sensor is mounted on the lower end of the hydraulic cylinder to measure the position of the piston rod of the hydraulic cylinder.
(2) Main supporting tooling According to the elastic wheel core configuration axial round runout within 0.03mm of the core pad, used as the end face positioning of the elastic wheel before and during pressing; according to the elastic wheel core hole size, 1 piece of wheel core positioning block is configured, which is used as the radial positioning of the elastic wheel before and during pressing. The briquette is configured according to the size of the elastic wheel gland and is used as a balanced compression of the elastic wheel gland during the pressing process. The circumference is equipped with four wheel coupling adjustment devices with handwheels for pre-adjustment of radial eccentricity before pressing when pressing equipment on wheel hoops with rubber.
Figure 2 Design of the tooling host
1—Wheel hoop height adjustment block 2-Composite block 3-Briquette 4-Wheel clamp adjustment device 5-Wheel core gasket 6-Wheel core positioning block 7-Table 8-Hydraulic cylinder and piston rod
3.3 Control section design
(1) Press-fit speed design In the entire press-fit process, it is necessary to add 50kN setting on the basis of the maximum pressure of the rubber compression force value of the elastic wheel design to ensure that the elastic wheel gland and the end of the core step can be pressed into place. The wheel core and wheel hoop are predetermined calibration before pressing, so it is hoped that the predetermined accuracy can be maintained at the beginning of the pressing, and because there is an error in the thickness consistency of the same rubber ring, there is also a four-way compression unevenness and positioning deviation when installing the rubber, so there is a phenomenon of inconsistencies due to the inconsistency of the surrounding pressure stress in the process of elastic wheel pressing, resulting in the phenomenon of running out after pressing. To solve this problem, it is required that the installation of rubber process can ensure the compression uniformity and positioning accuracy of the rubber around the rubber, and at the same time, when the rubber creep is small in the pressing process, it can be pressed faster on the basis of the predetermined position; in the case of increasing the pressure and creep variable of the rubber in the second half, the stress concentration of the rubber is released by slowing down the pressing speed, so as to achieve the basic equilibrium of the surrounding compressive stress and improve the runout accuracy of the elastic wheel after pressing.
The equipment adopts electro-hydraulic servo NUMERICAL control hydraulic press, PLC programmable controller and industrial computer to collect and process data, so that the hydraulic cylinder pull pressure and tension speed can be set and adjusted, and the empty stroke can be manually fast up and down design. Under the premise of improving the assembly efficiency, it meets the requirements of the design adjustment range of the running speed of the tension hydraulic cylinder.
According to the material and characteristics of the rubber ring, the press-fit speed is selected from 0.5 to 5 mm/s, and the compression parameters are prepared according to 2 strokes during the pre-press-fit process of the elastic wheel, the first half of the stroke is set to 3~4mm/s, and the second half of the stroke is set to 0.5~1.5mm/s (see Figure 3 for the press-fit parameter settings).
Fig. 3 Press-fit parameter settings
(2) Packing design Elastic wheel pre-pressure installation needs to be manually placed bolts or nuts, and the bolts are tightened in an orderly manner by two people in the 180 ° direction in 2 to 3 times, so the equipment needs to design the pressure packing function after the elastic wheel pre-pressure is installed in place. After the automatic pressing equipment is adopted, the elastic wheel tightening bolts are uniformly tightened twice, and the first time it must be orderly and uniformly tightened according to 80% of the torque value of the designed tightening bolt under the pressure retention; in order to prevent the influence of the rubber reaction force, the second time under the unsured pressure according to the design tightening bolt torque value is orderly and uniformly tightened. According to the number of bolts and the tightening force of different products, the tightening time of the bolt is basically 10 to 15min, so the press-fit equipment needs to design the pressure holding time function, and the specific products set the pressure holding parameters according to different pressure holding time (see Figure 4 for the pressure holding parameter settings).
Figure 4 Packing parameter settings
3.4 Rubber axial pressing force monitoring design
In the process of elastic wheel pre-pressing, when the elastic wheel gland is in full contact with the wheel core step, the hydraulic cylinder pressure continues to increase, the hydraulic cylinder piston will not produce displacement, so the corresponding pressure value of the inflection point of the displacement and pressure curve change plus the gravity of the wheel hoop and the rubber is the axial pressure value of the elastic wheel rubber. Therefore, it is only necessary to design the output displacement-pressure pressing curve diagram (see Figure 5), and at the same time set the rubber axial pressing force value determination line on the figure, and the rubber axial pressing force can be monitored in real time.
Fig. 5 Displacement-pressure press-fit curve
The equipment data is measured by the pressure sensor and displacement sensor on the hydraulic cylinder, and displayed on the display by the programmable controller PLC and the industrial industrial computer. At the same time, in order to ensure the accuracy of the curve, the collected data is designed to export specific and accurate numerical points of pressure and displacement changes every 100ms, and the connection is drawn into a displacement-pressure pressure mounting curve. In order to verify the pressure value corresponding to the inflection point of the individual product pressure and the displacement curve change, it can also be accurately determined by calling the graph to collect data (see Table 2 for the export data of the pressure-fitting curve). It can also be designed to compare the collected data with the process setpoint and determine whether it is qualified or not based on the comparison results. However, due to the increase in the decision value, this function has not been implemented.
Graphics and data are automatically saved after detection, and backed up and saved after time periods, which is convenient for product quality traceability.
Table 2 Displacement-pressure crimp curve derived data
4
Rubber stress equalization installation method design
In order to ensure the automatic positioning accuracy of the rubber and the uniformity of the creep after the rubber is pressed, the outer diameter of the rubber and the inner diameter of the wheel hoop are combined with the interference, and the general interference is about 3mm [3,4]. Therefore, when installing rubber, there is an excessive extrusion phenomenon in the rubber part of the last installed, resulting in uneven rubber extrusion stress around it, resulting in excessive runout of some elastic wheels after pressing.
Through exploration, we use the rubber ring 180 ° direction on both sides of the simultaneous squeeze into the wheel hoop, adjust the remaining two sides of the rubber compression so that it is basically the same, and then squeeze the rubber on both sides into the wheel hoop method, from the rubber point of the rear extrusion into the wheel hoop, from the rubber point of the rear extrusion into the wheel hoop, the rubber hammer is evenly hammered along the circumference direction of both sides, so that the rubber pressure stress is uniform (see Figure 6 for the rubber ring extrusion method); the reverse side is staggered by 90 ° and the other rubber ring is also installed according to the above method.
Pre-pressure installation is used to eliminate the stress inhomogeneity around the rubber before pressing: pre-press the wheel once before the wheel is officially pressed, and the pressure is removed after 3 to 5 minutes of pressure retention, which can release the stress concentration of part of the wheel rubber, so that the fit between the rubber and the wheel hoop, the wheel core and the pressure ring is more uniform and tight, making the runout more stable.
Fig. 6 Rubber ring extrusion method
5
Conclusion
After designing automated press-fit equipment and improving the rubber press-fit method, after being verified by the assembly of large-scale export elastic wheels, the assembly runout quality has been significantly improved compared with the assembly quality of a previous domestic elastic wheel (see Figure 7 for comparative verification of the pressure-mounting effect, of which the export-type elastic wheel assembly adopts the new press-mounting equipment and the pressing method), after stiffness and fatigue tests, the results are in line with the requirements, and the performance parameters fully meet the quality requirements of the export-type elastic wheels.
Through the research and implementation of the elastic wheel assembly process, the assembly process of the company's integral elastic wheel has reached the advanced level, which provides an effective guarantee for the quality and monitoring of the press.com. The product quality has been verified by the company's LABORATORY TEST AND USER VERIFICATION WITH CNAS qualification, and it meets the requirements.
Fig. 7 Comparison verification of the press-fit effect
bibliography:
Fan Rongping,Meng Guang,Cui Yinhui. Development and research status of elastic wheels[J]. Electric Drive for Locomotives, 2005(1): 8-11, 45.
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This article was published in Metalworking (Cold Working), No. 3, 2022, pages 45-49, by Zhuzhou Jiufang Equipment Drive Technology Co., Ltd. Qiu Yonghong, Yao Kuixu, Deng Chao. Original title: "Integral Elastic Wheel Assembly Scheme".
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