Welding method for improving welding position precision of roller shaft of forklift gantry

Abstract

The invention discloses a welding method for improving the welding position precision of a roller shaft of a forklift portal frame. The welding method comprises the steps that holes machined in channel steel and a roller shaft boss structure are omitted; the channel steel and the roller shaft are positioned and temporarily fixed through an overlap welding tool, the positioning reference of the overlap welding tool is consistent with the design reference of the product, and the positioning size of the overlap welding tool is set to be the median value of a target design size tolerance zone; during welding, the position of a welding arcing point is controlled to be close to the longitudinal center line of the roller shaft, and the direction and the magnitude of welding thermal deformation are controlled; and on the basis of statistics of the actual deformation after welding, the positioning size of the overlap welding tool is subjected to compensatory correction. According to the method, matching of a positioning hole and a boss between the channel steel and the roller shaft is omitted, the overlap welding tool consistent with the design reference is adopted for conducting median positioning, the welding arcing point and the reversible deformation angle are controlled to accurately manage welding deformation, the tool size is corrected based on test data, and therefore high-precision welding is achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of forklift mast roller shaft welding, in particular to a welding method for improving the welding position accuracy of a forklift mast roller shaft. BACKGROUND

[0002] In the forklift industry, ensuring the position accuracy of the mast main roller shaft is crucial to guarantee the stability of a high-lift mast when it is running at a high position. In the original technology, in order to meet the high accuracy requirement, a boss shaft is usually added at the contact between the roller and the channel steel, and the deformation that may occur when welding the roller shaft is limited by the cooperation between the hole and the boss shaft.

[0003] However, there are some challenges in the prior art. First, there is a positioning deviation problem when processing the hole. One method is to process the hole when the channel steel opening is upward, at which time the channel steel is positioned on the outside. Although this can facilitate operation, it is inconsistent with the design reference of 81mm and the tolerance of (+1,0). Considering the limitation of the tolerance width and other factors such as processing tolerance and welding deformation in subsequent processes, it is difficult to meet the accuracy requirement. Another method is to position the channel steel opening downward, which can avoid the problems caused by external positioning, but it requires internal drilling positioning, which not only increases the complexity of the structure, but also may lead to a decrease in positioning accuracy. Both methods affect the processing efficiency and accuracy.

[0004] In addition, the processing of the hole and the shaft increases the cost by about 15% to 20%, and even if the above processing method is used, due to the existence of 3 sequence tolerance, the final welding positioning will also bring a large uncertainty. During the welding process, since the arc starting point is affected first, the welding shrinkage thermal deformation first occurs in this area, causing the fitting gap in the diameter direction of the hole shaft to shift to one side, further increasing the assembly tolerance. The post-welding seam is difficult to correct the deformation caused by the pre-welding seam due to thermal stress, thereby introducing a certain welding deformation. Since the position of the arc starting point is uncertain, the welding deformation in the direction of the key dimension (i.e. the transverse direction) will also change, resulting in inconsistent welding positioning direction and significant fluctuations. SUMMARY

[0005] The purpose of the present application is to overcome the shortcomings of the prior art. To achieve the above purpose, a welding method for improving the welding position accuracy of a forklift mast roller shaft is used to solve the problems raised in the background technology.

[0006] A welding method for improving the welding position accuracy of a forklift mast roller shaft, comprising the following steps: Structural simplification: cancel the hole for positioning the roller shaft on the channel steel, and the roller shaft boss structure formed on the roller shaft to cooperate with the hole; Positioning tack welding: the groove steel and the roller shaft are positioned and temporarily fixed by using a tack welding tool, the positioning datum of the tack welding tool is consistent with the design datum of the product, and the positioning size of the tack welding tool is set as the middle value of the target design size tolerance band; Welding control: during actual welding, the position of the welding arc starting point is controlled to be near the longitudinal center line of the roller shaft, and a preset reverse deformation angle is used to control the direction and value of the welding thermal deformation; and Size correction: based on the statistics of the actual deformation amount after welding, the positioning size of the tack welding tool is compensatively corrected.

[0007] As a further scheme of the present application: in the positioning tack welding step, the part of the tack welding tool in contact with the supporting surface of the groove steel is staggered from the draft angle structure of the groove steel, and the tack welding tool is close to the position to be welded of the roller shaft, and the contact height of the tack welding tool with the roller shaft is set as the working installation height of the roller.

[0008] As a further scheme of the present application: in the positioning tack welding step, the initial value of the positioning size of the tack welding tool is 81.6 mm, and the tolerance is (0, -0.1).

[0009] As a further scheme of the present application: before the welding control step, a spot welding step is further included, and the spot welding step is performed in a predetermined order: First, spot welding is performed on the left side of the connection between the roller shaft and the groove steel, then spot welding is performed on the right side, then spot welding is performed on the lower part, and finally, after removing the tack welding tool, a fourth spot welding point is added to the position which is not spot welded due to the shielding of the tool.

[0010] As a further scheme of the present application: in the welding control step, the reverse deformation angle is 30 degrees.

[0011] As a further scheme of the present application: in the welding control step, when the welding arc starting point is located at the lower part of the longitudinal center line by 30 degrees, the welding direction is towards the upper side of the longitudinal center line; When the welding arc starting point is located at the upper part of the longitudinal center line, the welding direction is towards the lower side of the longitudinal center line.

[0012] As a further scheme of the present application: in the size correction step, according to the test data of the welding deformation amount, the positioning size of the tack welding tool is corrected from 81.6 mm to 82 mm, and the tolerance is (0, -0.1).

[0013] As a further scheme of the present application: by the welding control step, the fluctuation range of the welding deformation is controlled within 0.18 mm.

[0014] Compared with the prior art, the present application has the following technical effects: By adopting the technical scheme, the positioning hole on the channel steel and the boss on the roller shaft are cancelled to eliminate the tolerance caused by the fitting gap from the source; secondly, a special tack-welding tool with a unified reference is used for positioning, the positioning size is the median value of the design tolerance, and the consistency of the positioning reference and the design reference is ensured; thirdly, during the welding process, the starting point is controlled near the longitudinal center line and a preset reverse deformation angle is adopted to actively intervene in the direction and value of the welding thermal deformation; finally, based on the statistics of the welding shrinkage, the positioning size of the tool is feedback and compensatively corrected to form a closed-loop optimized manufacturing process.

[0015] In terms of accuracy, it eliminates the "3 sequence tolerance" accumulation caused by the original hole shaft cooperation, and through active control of deformation and size compensation, the welding deformation fluctuation range is controlled at a very low level, so that the product tolerance bandwidth is narrowed by about 60%, and 100% pass rate is realized. In terms of cost and efficiency, the machining process of holes and bosses is omitted, which directly reduces the machining cost by 15%-20%, and the tool is small and convenient, which improves the manufacturing efficiency. In addition, the method provides a reliable and economical new process path for solving the problem that long and large components cannot rely on overall machining under high precision requirements. BRIEF DESCRIPTION OF DRAWINGS

[0016] The specific embodiments of the present application will be described in detail below with reference to the accompanying drawings: Figure 1 The step schematic diagram of the welding method with precision of the disclosed embodiment of the present application is shown in the figure; Figure 2 The size structure schematic diagram of the tool of the disclosed embodiment of the present application is shown in the figure; Figure 3 The tool use and spot welding schematic diagram of the disclosed embodiment of the present application is shown in the figure; Figure 4 The welding deformation control process diagram of the disclosed embodiment of the present application is shown in the figure. DETAILED DESCRIPTION

[0017] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0018] Please refer to Figure 1 In the embodiments of the present application, a welding method for improving the welding position precision of the roller shaft of a forklift door frame includes the following steps: Step S1, Simplification of structure: Eliminate the hole for positioning the roller shaft in the channel steel, and the roller shaft boss structure that mates with the hole in the roller shaft; Specifically, the welding positioning holes of the roller shaft on the channel steel and the boss shaft on the roller shaft are eliminated to eliminate the possibility of fit clearance. By eliminating these three-stage tolerances, the uncertainty of the final tolerance zone is reduced, and the cost is greatly reduced.

[0019] Step S2, Positioning and Lap Welding: The lap welding fixture is used to position and temporarily fix the channel steel and the roller shaft. The positioning reference of the lap welding fixture is consistent with the design reference of the product, and its positioning dimension is set to the median value of the target design dimension tolerance zone. In this embodiment, during the positioning and lap welding step, the portion of the lap welding fixture that contacts the support surface of the channel steel is offset from the draft angle structure of the channel steel, and the lap welding fixture is close to the welding position of the roller shaft, with its contact height with the roller shaft set as the working installation height of the roller.

[0020] In this embodiment, in the positioning and welding step, the initial value of the positioning dimension of the welding fixture is 81.6 mm, and the tolerance is (0, -0.1).

[0021] like Figure 2 As shown in the figure, the tooling is a schematic diagram of its dimensions and structure. Specifically, the tooling is designed to be welded together. The datum of the welding tooling is consistent with the design datum. The tooling avoids the draft angle of the channel steel on the support surface of the channel steel and is close to the welding position of the roller shaft. The contact height is the main roller installation height, which is consistent with the position of the roller installation structure in use. The positioning dimension is taken as the median value of 81.6mm (0, -0.1)). This tooling is very compact, convenient and stable in use.

[0022] Step S3, Welding Control: During actual welding, the welding arc initiation point is controlled to be located near the longitudinal centerline of the roller shaft, and a preset reverse deformation angle is used to control the direction and magnitude of welding thermal deformation; and In this embodiment, a spot welding step is included before the welding control step, and the spot welding step is performed in a predetermined order: First, spot weld on the left side where the roller shaft connects to the channel steel, then spot weld on the right side, then spot weld at the bottom, and finally, after removing the welding fixture, add a fourth spot weld at the position where it was not spot welded due to the fixture blocking the spot weld.

[0023] In this embodiment, the reverse deformation angle is 30 degrees in the welding control step.

[0024] In this embodiment, during the welding control step, when the welding arc initiation point is located at a position 30 degrees below the longitudinal centerline, the welding direction is towards the upper side of the longitudinal centerline. When the welding arc starting point is located above the longitudinal center line, the welding direction is toward the lower side of the longitudinal center line.

[0025] Specifically, as shown in Figure 3 , a schematic diagram of tooling use and spot welding method is shown; According to the quality accuracy requirement, the spot welding sequence is determined: since the roller moves longitudinally, the longitudinal position accuracy requirement of the roller shaft is relatively critical control point 81mm(+1,0) is low, and the spot welding is first left and right, then up and down, that is: left point→right point→down point→the fourth point is removed after the tooling is removed and supplemented; Because the lap welding adopts median positioning, the welding deformation needs to be strictly controlled, and the target is that the welding deformation can be controlled within ±0.2. The median arc starting welding is adopted, that is, the arc starting point is near the longitudinal center line, and the method of using reverse deformation small angle to control single-sided large weld is adopted to control the welding deformation. The test adopts a 30-degree reverse deformation angle, and the arc starting point is 30 degrees below the center line, so the welding direction needs to be welded to the upper side, as shown in Figure 4 , a schematic diagram of welding deformation control process is shown; if the arc starting point is above the center line, the welding direction needs to be welded downward, which is omitted.

[0026] Test results: 6 sample pieces, minimum shrinkage 0.38mm, maximum shrinkage 0.56mm, welding deformation fluctuation range only 0.18mm, average 0.45mm, 6 test pieces, 100% qualified, but the size is concentrated in the upper deviation of the tolerance band.

[0027] Step S4, size correction: based on the statistics of the actual deformation amount after welding, the positioning size of the lap welding tooling is compensated and corrected.

[0028] In this embodiment, in the size correction step, according to the test data of welding deformation, the positioning size of the lap welding tooling is corrected from 81.6mm to 82mm, and the tolerance is (0, -0.1). The test results are shown in the following table:

[0029] In this embodiment, through the welding control step, the fluctuation range of welding deformation is controlled within 0.18mm.

[0030] The method greatly improves the welding accuracy of the product, not only ensures 100% qualified, but also reduces the tolerance band width by about 60%; as shown in the following table:

[0031] In summary, the manufacturing efficiency of the product is improved, and the manufacturing cost of the product is reduced. There are 4 such structures in a single forklift door frame, and the cost of a single forklift is reduced by about 37 yuan.

[0032] The method provides a new method for realizing the process of manufacturing a high lifting portal of more than 10 meters by using a non-integral gold processing technology in the industry.

[0033] While embodiments of the application have been shown and described, it is to be understood that the embodiments described are merely divergences of the principles and spirit of the application and that numerous modifications, changes, replacements, and variations can be made thereto by those skilled in the art without departing from the principles and spirit of the application, the scope of the application being defined by the appended claims and their equivalents, all of which should be included in the protection scope of the application.

Claims

1. A welding method for improving the welding position accuracy of forklift mast roller shafts, characterized in that, Includes the following steps: Structural simplification: The holes machined on the channel steel for positioning the roller shaft and the roller shaft boss structure formed on the roller shaft to mate with the holes are eliminated; Positioning lap welding: The channel steel and the roller shaft are positioned and temporarily fixed using lap welding fixtures. The positioning reference of the lap welding fixtures is consistent with the design reference of the product, and its positioning dimension is set to the median value of the target design dimension tolerance zone. Welding control: During actual welding, the position of the arc initiation point is controlled to be near the longitudinal centerline of the roller shaft, and a preset reverse deformation angle is used to control the direction and amount of welding thermal deformation. as well as Size correction: Based on the statistics of the actual deformation after welding, the positioning dimensions of the welding fixture are corrected compensatorily.

2. The welding method for improving the welding position accuracy of forklift mast roller shafts according to claim 1, characterized in that, In the positioning and lap welding step, the portion of the lap welding fixture that contacts the support surface of the channel steel is offset from the draft angle structure of the channel steel, and the lap welding fixture is close to the welding position of the roller shaft, with its contact height with the roller shaft set as the working installation height of the roller.

3. The welding method for improving the welding position accuracy of forklift mast roller shafts according to claim 1 or 2, characterized in that, In the positioning and lap welding step, the initial positioning dimension of the lap welding fixture is 81.6 mm, and the tolerance is (0, -0.1).

4. The welding method for improving the welding position accuracy of forklift mast roller shafts according to claim 1, characterized in that, Prior to the welding control step, a spot welding step is also included, which is performed in a predetermined sequence: First, spot weld on the left side where the roller shaft connects to the channel steel, then spot weld on the right side, then spot weld at the bottom, and finally, after removing the welding fixture, add a fourth spot weld at the position where it was not spot welded due to the fixture blocking the spot weld.

5. The welding method for improving the welding position accuracy of forklift mast roller shafts according to claim 1, characterized in that, In the welding control step, the reverse deformation angle is 30 degrees.

6. A welding method for improving the welding position accuracy of forklift mast roller shafts according to claim 1 or 5, characterized in that, In the welding control step, when the welding arc initiation point is located at a position 30 degrees below the longitudinal center line, the welding direction is towards the upper side of the longitudinal center line; When the arc initiation point of the welding is located above the longitudinal center line, the welding direction is towards the lower side of the longitudinal center line.

7. The welding method for improving the welding position accuracy of forklift mast roller shafts according to claim 1, characterized in that, In the dimension correction step, based on the test data of welding deformation, the positioning dimension of the welding fixture is corrected from 81.6mm to 82mm, with a tolerance of (0, -0.1).

8. The welding method for improving the welding position accuracy of forklift mast roller shafts according to claim 1, characterized in that, Through the aforementioned welding control steps, the fluctuation range of welding deformation is controlled within 0.18 mm.

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