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Working accuracy of bending machine
Right now, many companies do not pay attention to the daily management of equipment. Improper use and maintenance of equipment. Or excessive use of the equipment, the operator does not use the equipment according to the equipment operating procedures, resulting in serious loss of equipment accuracy. Some small and medium-sized enterprises will purchase some second-hand equipment, but they lack equipment accuracy detection technology and methods. They usually judge the integrity of the equipment based on the service life, efficiency, and appearance of the equipment, ignoring the mastery of the processing accuracy of the equipment.
Bending machine is one of the key equipment for forming sheet metal products and ensuring the processing accuracy of sheet metal products. The accuracy of bending equipment will directly affect the processing accuracy of sheet metal products. The impact of insufficient precision bending equipment on product deviation is a long-term objective existence. If the accuracy status of a bending equipment can be detected, it is very necessary to provide equipment accuracy data for the enterprise’s acceptance and maintenance of the bending equipment.
The national standard GB/T14349-2011 “Accuracy of Bending Machines” stipulates the accuracy inspection, the allowable value of the inspection and the detection methods for the accuracy of the bending machine. The inspection items of the bending equipment include the geometric accuracy of the bending machine and the inspection of the number of work. The explanation is as follows:
1. Geometric accuracy test items
◆Horizontal and longitudinal flatness of the machine table
◆Parallelism between the horizontal support surface of the upper die bonding surface and the plane of the machine table
◆The verticality of the slider to the working platform
2. About the detection of geometric accuracy
The author believes that the purchaser of the machine tool can request the supplier to provide geometric accuracy data without having to do the geometric accuracy self-test. It only needs to detect the working accuracy of the machine tool to verify the accuracy of the machine tool purchase.
The user of the machine tool can arrange the annual work accuracy inspection of the machine tool in a planned way. If the working accuracy exceeds the allowable range of machine tool accuracy, then consider the machine tool geometric accuracy test.
Taking into account that most companies do not have the ability to repair large and medium machine tools, they are generally accepted by professional maintenance organizations. This article does not introduce the geometric accuracy detection of bending machines in detail. If you need to master the detection geometric accuracy, you can refer to the relevant content of the national standard GB/T14349-2011 “Accuracy of Bending Machines”.
Impact on work accuracy
1. The influence of the flatness (longitudinal) of the worktable of the bending machine on the straightness of the bending parts
①Influence of workpiece angle accuracy:
When there is a longitudinal flatness error on the worktable, it will affect the depth of the upper die into the lower die notch. The depth deviation △H is equal to the plane error ɑ. The accuracy effect is shown in the figure
②Influence of workpiece straightness accuracy
When there is a flatness error on the work surface, the straightness of the bent part is equal to the flatness error. The effect of accuracy is shown in the figure below:
③The influence of the flatness (transverse) of the worktable of the bending machine on the angle and straightness of the bending parts
The influence mechanism of the flatness (transverse) of the worktable of the bending machine on the angle and straightness accuracy of the bending parts is the same as the mechanism of the “longitudinal influence”.
2. The influence of the stroke of the slider on the verticality of the working surface on the bending accuracy
①Influence of workpiece angle accuracy:
Work accuracy inspection
◆Material requirements: The material of the test piece is Q235A steel plate, and the tensile strength of the material is σb≤450MPa.
◆Number of pieces: The number of test pieces should not be less than 3.
◆Mold requirements: The size of the lower mold opening for the test piece is 8-10 times the material thickness.
◆Location requirements: The test piece should be placed in the middle of the workbench.
◆Bending angle requirement: The bending angle of the test piece is 900.
◆Measuring position: start measuring 100mm from the end of the test piece.
Qualified flat ruler, universal angle ruler and feeler gauge.
Before the work accuracy test, the equipment needs to be leveled, and the horizontal and vertical directions should not exceed 0.2/1000
Test piece bending angle detection
① Poor charge
The bending angle of the test piece is ±10 (over the entire length)
Lean the universal angle ruler on the outer surface of the bending test piece (see the figure below), and measure it at several points (at least 3 points per meter). The error is calculated as the difference between the maximum angle and minimum angle measured and the specified angle 900.
3. Test specimen discount degree test
① Poor charge
It is 0.05mm at a length of 1000mm.
Place the detection surface of a 1000mm flat ruler against the edge of the bending test piece (see the figure below), and use a feeler gauge to measure the gap δ between the two. The error value is calculated as the maximum gap value within 1000mm.
4. Second bending test piece
If the stress of the test piece material is large, the test piece that is bent twice is allowed (see the figure below). Check the working accuracy of the bending machine. The detection method should conform to the content of 3 and 4.
From the analysis of a set of reference test data provided by the bending machine tool manufacturer, the influence of the longitudinal error of the worktable of the bending machine on the bending accuracy is about 3 times the value of the lateral error. The influence value of the bending angle deviation is about 3 times of the flatness error of the table surface.
The bending angle deviation is not greatly affected by the sliding block stroke on the verticality of the working surface and can be ignored. The straightness of the working table surface will directly reflect the influence of the straightness deviation of the workpiece, and the two are almost equal. The bending straightness deviation is less affected by the slider stroke on the verticality error of the working surface. The working table mentioned in this article includes two, one is the machine table, and the other is the geometric accuracy of the horizontal support surface of the upper die attaching surface. for example:
The working table of a bending machine has a length of 3200mm. After measuring the working accuracy of this bending machine, the following data is obtained: the deviation of the workpiece straightness is 0.06mm, and the deviation of the bending angle is 0.1720. It can be inferred that the flatness of the work surface of this press brake is about 0.06mm.
According to the national standard GB/T14349-2011 “Accuracy of Bending Machines”, the flatness tolerance of a bending machine with a table length of 3200mm is 0.08mm, and it can be determined that the plane accuracy of the bending machine is qualified. In fact, users of bending machine tools only need to pay attention to the working accuracy of the machine tools.
Because the working accuracy of the machine tool after long-term use is not only affected by the factors mentioned in this article, but also the influence factors of the transmission clearance and mechanical wear of the machine tool on the accuracy of the machined parts, and the comprehensive evaluation and consideration of the machine tool. That is to say, through the inspection of the working accuracy of the bending parts of the machine tool, combined with the national standard of the accuracy of the bending machine, it is possible to inspect and determine the comprehensive accuracy processing ability of a bending machine.
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