With the development of the automotive industry, the tightening process has been continuously improved as the core technology of the assembly plant.
As the last step in the manufacture of finished vehicles, it is particularly important to combine the components in the most appropriate and economical way. This is not only related to the cost of manufacturing, but also determines the safety of life and property of drivers and passengers. Through effective and stable tightening process control, the vehicles produced are guaranteed to be at a high level of quality.
As the core technology of the final assembly, the tightening process has been continuously updated and updated. As the hardware continues to improve, more and more control methods and control strategies have emerged. How to optimize the tightening effect and make the components reliably combined is also a long-term study by the R&D and manufacturing departments.
As the level of tightening increases, detailed production data can be obtained from the production process, and the tightening of the production process is controlled accordingly, which greatly assists in the tightening process.
1. Basic tightening control method
The basic tightening control methods commonly used in assembly plants include: torque control method, torque control - angle monitoring method, torque + angle control method, slope method, etc.
Each method must be implemented in conjunction with the on-site hardware level. The ultimate goal is to obtain the appropriate preload (also known as tension, clamping force, etc.) to ensure reliable connections between components.
However, because the pre-tightening force is often difficult to measure, and there are few production-type equipments that directly measure the pre-tightening force, it is necessary to use various tightening control methods to achieve the final pre-tightening force.
1.1 Torque control
The torque control method is also called the torque method, the direct tightening method, the torque tightening method, etc. This method is currently the most mainstream type of tightening control method, and the advantages are simple operation and low requirements on equipment.
It is mainly based on the characteristic that the pre-tightening force of the bolt changes linearly with the tension of the bolt during the tightening process, as shown in Fig. 1.
Figure 1 Preload force and torque are linear
T=KFd
Where: T is the control torque; K is the tightening torque coefficient; F is the pre-tightening force; d is the nominal diameter of the bolt.
The tightening torque coefficient K is related to many factors such as workpiece state and surface roughness. The general steps of this control method are: after calculating the pre-tightening force required here, according to the national standard or VDI and other related standards and the pre-designed working conditions, the fastener selection, and then using the selected fastening The part is tested several times and the initial control torque is obtained during the tightening process according to the point at which the tightening curve reaches the required preload.
You can use BLM5000 and TPT200/100 clamping force sensors, MC900 ultrasonic analyzer and supporting software, high-precision electronically controlled torque wrench STWrench, such as ATLAS manufacturers, and at least 50 bolts with ultrasonic patches. A common tightening process measuring device is shown in Figure 2.
Figure 2 Common tightening process measuring equipment
For example, the author tests the sub-frame and body connection bolts of a car (see Figure 3 for on-site measurement status). The pre-tightening force to be achieved is 80 kN. The standard parts used are 10.9 M16×2 coarse bolts.
After many measurements and data analysis, the minimum ultimate tensile load of this specification bolt bench test is 180 kN (see Figure 4), which can meet the required pre-tightening force requirements, and can reach the required torque at 258 N·m. Preload (see Table 1), the deviation of ±3σ is 7.24%, which is within the empirical formula, so ±3σ can be used as the initial control standard.
Figure 3 Field measurement status
Figure 4 Tightening curve of bolt bench test
Table 1 Load-Torque Test Results
1.2 Torque Control - Angle Monitoring
This method is based on the torque control method and introduces angle monitoring to identify various abnormal conditions.
The general situation is:
(1) The torque and angle are within the required monitoring range, and the torque is qualified.
(2) The torque value meets the requirements, and the angle value is lower than the monitoring range. There may be welding slag and residual glue in the threaded holes, the bolts are not pre-tightened by manual pre-tightening, or the parts and standard parts are abnormal.
(3) The torque value meets the requirements. The angle value is higher than the monitoring range. The bolt or thread may be damaged, oil stains may appear, the wire may be broken, or the parts and standard parts may be abnormal.
(4) The torque value is lower than the required value, the angle value is higher than the monitoring range, the thread may be damaged, the slip may occur, or the parts and standard parts may be abnormal.
(5) Other situations may occur due to equipment failure.
In the program editing interface of the APEX tightening stun gun (Fig. 5), Angle Low Limit and Angle High Limit have defined the range of angle monitoring. Threshold is the threshold torque, which is the starting point on the 0° corresponding torque of the angle monitoring.
From the source of the parameters, the source of the threshold torque is mostly calculated by empirical formula or analyzed from the curve, but the two are basically based on the actual tightening data.
For example, take the tightening of the steering bolt and the front subframe of a certain model (as shown in Figure 6) as an example. The target torque for tightening is 105 N·m. The equipment used is APEX's 48EAE175AX6B tightening squirt, MPRO400GC- E controller.
Figure 5 APEX tightening the gun program editing page
Figure 6 The steering gear of a car is connected to the front sub-frame
The curve is extracted from the controller, and a large number of curves are projected in the same proportion to simulate the distribution of the tightening curves of a large number of bolts. The projection of a single curve is shown in Figure 7, and the projection of multiple curves is shown in Figure 8.
It can be seen from the projection that the curve is greatly different when the bolt is in the initial stage of tightening. As the tightening operation continues, the axial force is getting larger and larger, and the factors causing the difference in torque are becoming smaller and smaller (such as the subtle surface of the parts and fasteners). Differences, etc.), the final curve can be stabilized in a small area.
When selecting the threshold torque, the interference area that affects the torque in the early stage should be avoided. In this case, it can be selected according to the starting point of the stable region in the projection 55 N·m. Finally, a large number of angles fall between 154° and 187°, and then these samples are calculated according to ±3σ. The final angle monitoring range is 174 ° ± 30 °.
Figure 7 Single curve
Figure 8 Projection of multiple curves
1.3 Torque + Angle Control
The torque + angle control method utilizes fasteners to have better innate conditions relative to the components. Because the fasteners have various standards, the consistency is better, and a certain pre-tightening force is stably outputted when being stretched, and the amount of stretching generated by the fasteners after rotating at a certain angle is also consistent.
The advantage of this method is that the friction factor which is unstable and difficult to control accurately is reduced, and the pre-tightening force can be obtained with a small dispersion difference, thereby improving the tightening quality.
The source of the angle value draws on the torque control-angle monitoring method, that is, a large number of measurements start from the threshold torque M0, with the angle value at this time as the starting value, and the angle of rotation between the required pre-tightening force. The final control method is M0+ø.
In Fig. 9(a), after the same torque M1 is applied, the pre-tightening force difference is ΔF; in Fig. 9(b), after the threshold torque M0 is reached, the ø angle is respectively rotated, and the pre-tightening force difference is ΔF0. , the ΔF1 generated under the action of M1 is smaller, that is, the difference in pre-tightening force can be made smaller.
Figure 9 Relationship between angle and preload
For example, the tightening process requirement for the rear suspension bracket of a powertrain of a car is (55±6) N·m+ (90±9)°, and the powertrain rear suspension tightening process requires (180±18) N·m+ ( 45±5)° and so on.
1.4 slope method
The slope method has a small application range because of the high requirements for the tightening equipment. It is necessary to continuously test the variation of the thread tightening angle with time while testing the thread subassembly torque variation with time.
Most of this method is to screw the final tightening point to the yield limit, so it is also called the yield point method.
Δ=dT/dø 
Where: Δ is the slope; dT is the tightening torque change; dø is the tightening angle change.
The schematic diagram of the slope method is shown in Figure 10: when tightening into the linear region, the slope can reach the maximum value; after tightening the material into the yielding phase of the bolt, as the tightening angle increases, the torque increase begins. Slowly, since Δ is the ratio of the rate of change, Δ starts to decrease, and when Δ tends to a predetermined value, it is generally (1/2 to 1/3) Δmax, and the end tightening control signal is issued.
The tightening quality of the control method is only related to the yield strength of the bolt, and the yield strength is not affected by the friction factor of the torque control method and the starting point of the rotation angle control method, thereby overcoming the shortcomings of the torque control method and the torque + angle control method. Improve assembly quality and maximize the potential of fasteners.
Figure 10 Schematic diagram of the slope method
Because of the above advantages of the slope method, a sub-frame of a main engine factory uses a tightening machine with a yield point tightening method, as shown in FIG.
Figure 11: A sub-frame of a main engine factory uses a tightening machine with a yield point tightening method.
2. Dynamic torque and static torque conversion
The detection of the tightening operation is not reproducible. After the fastener is tightened and the power tool is finished, the friction between the thread pairs is changed into static friction by the dynamic friction, and there is a certain torque attenuation after the power tool output is disconnected. Subtle deformation occurs between them.
This produces a difference between the setpoint of the power tool and the detected value of the dial wrench, which also creates the concept of dynamic torque and static torque.
Dynamic torque refers to the peak torque of the tightening process as determined by the tightening power tool or measured by its sensor during fastener fastening. Dynamic torque cannot be measured after the fastener has been tightened.
The static torque refers to the torque value measured by the torque verification tool to continue to rotate in the fastening direction for a predetermined period of time after the fastening of the fastener is completed.
The dynamic torque is controlled by the tool setting mechanism or sensor. The precision is high and the required equipment cost is high. Because it is the peak during the rotation process, it cannot be visually displayed as the final tightening effect. European and American OEMs use dynamic torque for process control and equipment matching strategies. The main power tools are tightening the shaft and tightening the electric gun.
Most of the static torque relies on manual detection, the detection tool is simple, the operation is convenient, the required equipment cost is low, and it is close to the natural condition of the fastener, which can more intuitively display the final tightening effect. The Japanese and Korean mainframe factories mostly use static torque for the process. Control, mainly in the form of power tools with torque wrenches.
Dynamic torque is used for production and static torque is used for inspection. The torque value given by the R&D needs to be confirmed in advance to which category it belongs to, and then another set of standards is established.
2.1 Dynamic torque to static torque conversion
The release process from dynamic torque to static torque of a certain OEM is shown in Figure 12.
Figure 12 Dynamic torque to static torque release process of a host plant
When the dynamic torque is given as the control standard, firstly, the working conditions of all the tightening points are arranged. The power tool is used as the final tightening process, the tool is adjusted to the dynamic torque target value, and the static data is collected after tightening, if the torque requirement is met. Perform torque pre-release.
Continue to collect data, perform data analysis, calculate ±3σ or ±4σ, and then compare it with the empirical formula and process range, and perform final release according to the requirements of the quality of the production process. The late torque detection mainly uses this static torque standard as a control scheme.
2.2 Static torque to dynamic torque conversion
When the static torque is given as the control standard, since there is no dynamic torque at first, it is not known what dynamic torque the static torque needs to correspond to, and after the attenuation, the static torque can be guaranteed. Therefore, it is necessary to have a special group in the pre-vehicle. The trial phase is done to complete this work.
First set the static torque to the power tool and make 10 sets of measurements. The measurement is to be tested and recorded by the dial wrench. This torque is the measured torque and needs to be compared with the torque data in the torque database. The static torque is released directly to the torque control list as dynamic torque. If it is inconsistent, the tool torque needs to be reset until the measured torque result matches the static torque.
The release process of static torque to dynamic torque of a certain OEM is shown in Figure 13.
Figure 13 Static torque to dynamic torque release process of a host plant
Take dynamic torque to static torque as an example.
For example, a certain model of a main engine factory, the rear sub-frame and the body connection bolt, the development input is a dynamic torque value of 200 N·m, and the equipment used is the ATLAS model QST 62-350CT tightening shaft, and the set value is adjusted. After 200 N·m, tighten the actual car, then use the NORBAR model to measure the static torque for the WC4-340 digital torque wrench (see Figure 14). The general steps are as follows:
Figure 14 The rear sub-frame and body connection process of a model
(1) Pre-release process
Collect 20 sets of data for analysis, as seen in Figure 15, to meet the pre-release requirements.
Figure 15 Pre-release analysis results of 20 groups of data
(2) Final release process
After the pre-release was passed, 50 sets of data were collected (see Table 2) for analysis.
Table 2 Collect 50 sets of data for final release
The sample is calculated and the calculation results are shown in Table 3.
Table 3 Calculation results of 50 sets of data
Perform a single-valued control chart analysis with no major deviation from pre-release, as shown in Figure 16.
Figure 16 Single value control chart
The sample was subjected to a normality analysis with a P value greater than 0.05, as shown in FIG.
Figure 17 probability map
After the above process, the ±4 times tolerance (±4SL) range is compared with the empirical formula range. The upper limit is lower: +4SL is 230.72 N·m lower than the empirical formula 270 N·m; the lower limit is higher The -4SL is 166.46 N·m is lower than the empirical formula 170 N·m, as shown in Table 4.
Table 4 Results of final release
(3) Output results: The static torque range used for the production line is 170~231 N·m, as shown in Table 4.
3. Conclusion
The tightening process is the core process of each car assembly plant. With the rapid development of modern tightening equipment, various tightening control strategies that have not been realized before have been realized.
It is foreseeable that in the future development, more and more reasonable tightening methods will appear, and the development of these hardware and software will greatly improve the quality of the whole vehicle tightening assembly, and thus promote the development of the automotive industry.
The LED underwater light is a light that is placed under the water. The appearance is small and exquisite, and the appearance is elegant. As an underwater lighting fixture, LED underwater light is widely used in various sightseeing places such as square parks. It is the perfect choice for fountains, theme parks, exhibitions, commercial and art lighting.Most of the materials are made of stainless steel and glass. The types of stainless steel are 201, 304, 316, etc.This lamp is designed with fully tempered safety glass, wide light radiation surface, strong transparency.The interior of the luminaire is highly waterproof and has a protection rating of IP68 or higher .All adopt imported high-power LED as light source, which has obvious advantages such as long life, low power consumption, pure color and no pollution. With the DMX512 control system, it can achieve a variety of color changes.If you want to know more, please contact us.
Underwater Lights,Submersible LED Lights,Underwater Boat Lights,Underwater Fishing Lights
JIANGMEN LEDERLIGHT LIGHTING Co.,LTD , https://www.ledpolelights.com