Analysis of runout out out of tolerance of the thi

Yunnei 4100QB crankshaft third main journal runout out out of tolerance analysis and solutions

Abstract: through a variety of comparative process experiments of thousands of crankshafts and a large number of investigations in the same industry in China, the causes of the runout of the third main journal of the crankshaft are found out, and the solutions are put forward

key words: runout of the third main journal of crankshaft; Internal stress of castings; Normalizing; Qualitative

classification No.: tg162 7 document identification code: B

Article Number: (2000)

crankshaft is an important part of diesel engine, which transmits the force and torque necessary for automobile movement. During the assembly process of the crankshaft, there are certain requirements for the coordination between the crankshaft and the shaft, so the requirements for the runout of the main journal are high, so as to avoid the quality accidents such as "holding Bush" or "burning bush" of the crankshaft when the engine is running

the crankshaft of our plant (Yunnan internal combustion engine plant) has always had the quality problem that the runout out out rate after nitriding (the percentage of runout> 0.08mm) is as high as 20% ~ 40%. At the beginning, most people insisted that the quality problem was mainly caused in the nitriding or machining stage of the crankshaft. However, in terms of machining and nitriding, we failed to solve this quality problem by improving the processing requirements (the runout of the third main journal of the crankshaft before nitriding is processed with domestic equipment and controlled within 0.05mm, while that of foreign equipment is controlled within 0.03mm), strictly controlling the nitriding process parameters, strictly checking the temperature control instrument of the nitriding furnace and strictly checking the process discipline

1 reasons for the high runout rate of crankshaft after nitriding

in order to find the real reasons and solutions for the high runout rate of crankshaft after nitriding in our factory, since the second half of 1997, we have successively carried out a variety of comparative process experiments of thousands of crankshafts and a large number of research work in the same industry in China. Through the comprehensive analysis of the results of these process experiments and investigation results, it is concluded that the real reason for the out of tolerance of crankshaft runout in our factory is that there is a large internal stress in the casting before nitriding

the internal stress of nodular iron is greater than that of gray iron. Once the crankshaft is nitrided, the internal stress will be released and redistributed at the nitriding temperature of 560 ~ 600 ℃ (this nitriding temperature zone is within the qualitative temperature range of 530 ~ 600 ℃), resulting in the deformation of the crankshaft, that is, the runout of the crankshaft after nitriding is out of tolerance. The nitriding process is only an embodiment of the internal stress of the casting, and the runout out after nitriding is only a manifestation of the redistribution of the internal stress of the casting in the nitriding stage. Therefore, the nitriding process is only a carrier or an external factor of the runout of the crankshaft after nitriding, and the fundamental reason for the runout of the crankshaft after nitriding is that there is a large internal stress in the crankshaft before nitriding

2 Analysis on the main causes of high internal stress of crankshaft before nitriding

see Table 1 and table 2 for the general situation of main journal runout and comparison of production process between our crankshaft and Xichai crankshaft

Table 1 Comparison of main journal runout

the crankshaft of our factory adopts the same heat treatment method as that of Xichai crankshaft, but its runout out out rate is still very high after nitriding, and the value of runout out out is large, which indicates that there is a large internal stress in the casting before nitriding. After analysis, the main reasons are as follows:

(1) the crankshaft is not damaged; The package shall be printed with product name, manufacturer name and address, production date, product grade (excellent product, first-class product, qualified product), adopted standard number, implemented health standard number and other information. Normalizing cooling of crankshaft in our factory is uneven

the normalizing cooling method of crankshaft is fog cooling. The spray source is single and spray is carried out in a fixed direction, and the crankshaft is also fixed on the ground. This spray method is easy to cause the crankshaft to cool quickly towards the spray source and slowly towards the spray source. Due to the uneven normalizing cooling of the crankshaft, there are uneven hardness and uneven pearlite content, resulting in large internal stress of the casting

① in daily crankshaft production, whether qualitative or not, the body hardness is within the range of hb170 ~ 250, which is low or can not meet the drawing requirements (the drawing requirements are HB240 ~ 320). In the sampling inspection, it is also found many times that the hardness of the same crankshaft is seriously uneven. In some crankshafts, the hardness difference of only the large end face is hb60 ~ 80

② the content of pearlite was also found to be seriously uneven. For example, in the sampling of a fatigue test, it is found that the pearlite content of the same crankshaft on the same section is as much as 30%

(2) the qualitative equipment heating of crankshaft is uneven

the qualitative of crankshaft in our factory is to stack it on the bench without frame and heat it directly with a reverberatory furnace. There is only one temperature control point. The displayed value of temperature cannot represent the actual temperature in the crankshaft stack, and qualitative overburning occurs many times in practice. As the temperature cannot be accurately controlled, the internal stress elimination in this process is in an uncontrollable state

the following compares and analyzes the normalizing equipment and qualitative equipment of Xichai crankshaft with that of our factory:

① analysis of normalizing equipment and qualitative equipment of Xichai crankshaft

the runout rate of Xichai crankshaft after nitriding is low, which is closely related to the normalizing equipment and qualitative equipment used. The normalizing equipment used is a continuous normalizing furnace, which is divided into four temperature control areas. The workpiece is heated evenly and the temperature control is strict. During the cooling process after heating, the crankshaft is suspended in the furnace and can be spray or blown around. The whole cooling process is very uniform. In order to eliminate the internal stress and machining stress of castings, Xichai adopts a special continuous qualitative resistance furnace in the qualitative treatment after rough machining. The furnace is divided into six temperature control zones, and the temperature is 600 ℃. Qualitative crankshaft is divided into two layers (a small amount) every 6 pieces, and sent to the furnace by trolley once (the production beat is one car running every half an hour). The furnace is characterized by uniform heating temperature, strict temperature control and uniform heating of workpieces, which can completely reduce or eliminate the internal stress and machining stress of castings, so as to achieve the purpose of qualitative heating

② analysis of normalizing equipment and qualitative equipment of crankshaft in our factory

the normalizing equipment of crankshaft in our factory has been heated by electric furnace since May this year, and the heating is relatively uniform. The qualitative equipment is the reverberatory furnace, which is heated by burning bituminous coal. The uniformity of heating mostly depends on man-made operation. The furnace of the reverberatory furnace is large. One furnace can determine 800 ~ 900 crankshafts, but its temperature measurement system has only one temperature zone, which is measured by a thermocouple. Therefore, in this reverberatory furnace, the temperature measured by this temperature measurement system can only represent the temperature near the thermal couple in the furnace, not the heating temperature of the workpiece in the whole furnace. Obviously, the difficulty of temperature control is an important reason for uneven heating. In addition, it is worth mentioning that the quality of our crankshaft is usually 800 ~ 900 pieces per furnace, and the crankshaft is stacked in the furnace. In this way, the heating of the workpiece is more uneven during the quality, and it will also cause adverse phenomena such as mutual extrusion of the crankshaft in the hot state, increasing the deformation trend of the crankshaft

3 solutions

from the actual process and theoretical analysis of our factory, we believe that in the normalizing cooling stage of the crankshaft, due to the uneven contact between the cooling medium and the workpiece, the cooling speed of each part of the workpiece in the cooling process is uneven, resulting in large internal stress of the casting; The qualitative heating of the crankshaft is uneven, which makes it difficult to carry out strict temperature control, and will cause the qualitative control of the crankshaft out of control, which can not completely eliminate the internal stress of the casting. This is the fundamental reason for the out of tolerance of the runout of the third main journal of the crankshaft in our factory

if the production of crankshaft in our factory is still carried out according to the process of normalizing + qualitative + nitriding. Then, to solve the problem of high runout rate after nitriding and meet the production program of our factory, the key is to solve the following two problems:

(1) solve the quality problem of crankshaft normalizing stage

while ensuring that the hardness and pearlite content of crankshaft meet the design requirements of drawings, we should strive to make the crankshaft have a relatively uniform normalizing cooling process and make the obtained hardness and pearlite content more uniform, so that, The internal stress formed in the normalizing stage of the crankshaft is small and evenly distributed

(2) solve the quality problem of qualitative process of crankshaft

qualitative process is a key process to reduce or eliminate the internal stress of castings in Nanjing's two industrial clusters of polyurethane and high molecular materials. Due to the reasons of equipment and the way of placing the crankshaft in the furnace, the crankshaft in our factory hardly plays a "qualitative" role. Therefore, to solve the qualitative quality problem of crankshaft in our factory, we must start with the qualitative equipment and the placement mode of workpiece in the furnace. The qualitative equipment must ensure that the workpiece in the furnace is heated evenly, and the temperature control system can truly reflect the temperature change of the workpiece in the furnace. Referring to the special continuous qualitative resistance furnace used by Xichai, the selection of qualitative equipment is solved from the idea of "temperature control must be uniform, workpiece heating must be uniform, placement must be reasonable, and the qualitative temperature should be increased to slightly higher than the nitriding temperature". At this stage, the stacking and mutual extrusion of a large number of crankshafts in the furnace must be changed, which can be considered from the tooling. In addition, when the qualitative equipment and tooling are solved, we think it is more appropriate to carry out the qualitative process of crankshaft after rough machining

after finding out the reasons for the high runout rate of our crankshaft after nitriding, under the condition of existing equipment, we seek effective solutions through process experiments (4100QB copper doped crankshaft adopts "air-cooled" normalizing cooling mode and electric furnace tempering process scheme). The experimental idea of the process is as follows: firstly, add an appropriate amount of copper to the crankshaft for alloying, so that when the crankshaft is formed as cast, it can form a large amount of pearlite (about 70% ~ 75%). In the subsequent cooling process of normalizing stage, adopt relatively uniform air cooling with slow cooling speed and easy control. In this way, it can not only meet the pearlite content of the crankshaft structure, but also meet the smaller internal stress of the casting formed in the cooling process of crankshaft normalizing. In the subsequent qualitative tempering of electric furnace, because the temperature is uniform and easy to control (600 ℃, slightly higher than the nitriding temperature 590 ℃), the crankshafts are isolated from each other without extrusion, and the internal stress can be fully released and evenly redistributed, so as to eliminate the internal stress of residual castings. The final result of the process experiment is relatively ideal. After nitriding 146 experimental crankshafts, the runout out out rate of the third main journal is 5.36%. This value is the most ideal one since the runout experiment of the third main journal. It provides a powerful theoretical basis and experimental data for solving the long-standing problems of the crankshaft in our factory

in addition, the crankshaft will inevitably be deformed due to the release and redistribution of internal stress in the casting in the nitriding stage. After the permanent deformation of the crankshaft can not be corrected by the nitriding process, it must be put into the final process. Therefore, it is suggested that the medium frequency quenching + fillet rolling process should be used to strengthen the fatigue strength of the crankshaft, so that the deformation of the crankshaft in the previous process can be properly corrected in the final fine grinding stage. This process has been used in some large automobile manufacturers, such as FAW, FAW过敏性鼻炎有什么好的喷剂见效快
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