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Hydraulic press brake is a machine for bending sheet metal, which is very common in industrial production. With gradual development and growth of modern industry, the user's need for bending machines has gradually risen, but with the increase in demand, the industry has gradually emerged some bending machines of varying quality, and the quality of these machines also determine the future production process smooth or frustrating. So how to properly select quality bending machines?
It is best to start by carefully considering what model to buy in terms of the end-use of the machine, the known deflection variables that may occur in the machine, and the bending radius of the part. When choosing a bending machine, you as the decision-maker also need to know in detail about the machine's performance, processing range, processing features, processing accuracy, etc. The selection process is non- trivial, because once you choose improperly, your subsequent production costs will climb, and the bending machine will not recover the expected costs. To this end, Haas CNC has organized the following to help you buy the most preferred bending machine.
The first important thing to consider is the parts you want to produce, to fully estimate the make a full accounting, the point is to buy a machine that can complete the processing task with the shortest table and the smallest tonnage, so as to achieve the purpose of practical and economical. Consider carefully the sheet metal and the maximum thickness and length of processing. If the main production product material is mild steel, its thickness is within 3 mm, the maximum length does not exceed 2500 mm, then the free bending force does not need to be greater than 80 tons. However, if there is a large amount of bottom bending in the operation, then perhaps you should consider purchasing a bending machine of about 150 tons. If the plate to be bent in production is mild steel, the thickest has 6 mm, the length of 2500 mm within the free bending, then you should consider buying a bending machine of 100 tons or more. If the bending needs to be corrected bending, then a larger tonnage of the bending machine.
If the majority of the workpiece is bent 1250 mm or shorter, then consider the number of bending machine tonnage is almost halved, which can greatly reduce the acquisition cost. Therefore, the length of the processed part product is quite important to determine the model specifications.
Bending machine in the bending process, especially when bending long size of the workpiece, deflection will occur. The longer the workpiece, the greater the deflection. Under the same load, the deflection of the table and slide of a 2500 mm model is four times greater than that of a 1250 mm model.
This means that shorter machines require less shim adjustment to produce quality parts, and less shim adjustment reduces lead time. However, most current CNC hydraulic bending machines have been designed for production with the addition of a hydraulic deflection compensation function, reducing the need for production operators to adjust the machine while improving bending accuracy and productivity. Hydraulic detection compensation function is controlled by the CNC system, hydraulic oil through the magnetic service valve into the compensation cylinder, to carry out the table upward, while the deflection compensation force increases with the increase in bending force, thus playing a role in deflection compensation.
The material of the processing plate is also a key factor. Compared to mild steel, stainless steel typically requires about 50% more load, while most materials are about 50% less than soft aluminum. The relevant standard bending pressure parameters can be obtained from the bending machine manufacturer. The table shows the bending force required per 1000 mm length at different thicknesses and different plates.
The bending corner radius of the workpiece is also a factor to be considered during the bending of the product. When using free bending, the bending radius is 0.156 times the size of the V-groove opening. In free bending, the V-groove opening should be 8 times the thickness of the sheet metal. For example, if a 12 mm V-groove opening is used to bend 1.5 mm mild steel, the bending radius of the part is approximately R = 1.9 mm. If the bending radius is close to or less than the thickness of the sheet, under molding must be performed. However, the pressure required for bottom bending is about four times greater than that for free bending. When free bending is performed, attention is paid to the gap between the upper and lower dies at the bottom of the stroke, and to the use of compensating springback to keep the sheet overbent at about 90°. Typically, the free bending die produces a rebound angle of ≤ 2° on a new bending machine and a bending radius equal to 0.156 times the opening of the lower die. Therefore the die angle for free up and down die bending process is generally 86 ~ 90°. At the bottom end of the stroke, there should be a gap between the upper and lower dies that is slightly larger than the thickness of the sheet.
The forming angle is improved because the larger tonnage of the bottom press bend (about 4 times that of the free press bend) reduces the stresses that normally cause springback within the bending radius. Impression bending is the same as bottom bending, except that the front end of the upper die is machined to the desired bend radius and the upper and lower die gap at the bottom of the stroke is less than the sheet thickness. Springback is largely avoided by applying suffcient pressure (about 10 times that of a free bend) to force the front end of the upper die to contact the sheet. In order to choose the lowest tonnage speci}cation, it is best to plan for a bending radius greater than the plate thickness and to use free bending whenever possible. A larger bending radius often does not affect the quality of the finished part and its future use.
CNC Bending accuracy is a factor that needs to be carefully considered, this factor determines whether you are buying a CNC bending machine or an ordinary bending machine. Selection of bending machine to involve the precision of the mechanical system hard indicators used, because from a scientific point of view, the error is inevitable, and can only go as far as possible to reduce the error. Some workpiece itself and some simple parts in a small range of errors are acceptable, then there is no need to pursue high-precision bending machine; and some workpiece must be highly accurate, which requires a high degree of precision bending machine, more recommended to buy CNC bending machine.
If the bending accuracy requirements ± 0.5 ° and can not be arbitrarily changed, you must look at the CNC bending machine. CNC bending machine slider repeatability is generally guaranteed at ± 0.01 mm, forming accurate angles must be used with such precision and good quality tooling. Ordinary bending machine slider repeat accuracy of ± 0.5 mm, and in the use of suitable mold conditions will still produce ± 2 ~ 3 ° deviation. In addition, CNC bending machines are equipped with quick clamping and quick die change systems, making CNC bending machines an unquestionable choice when you need to bend many small parts.
Bending dies also have a direct impact on bending accuracy, so check the wear of the dies frequently by measuring the length from the front of the upper die to the shoulder of the table and the length between the lower die and the shoulder of the table.
For conventional dies, the deviation should be ± 0.01 mm per 10 mm, and the total length deviation should not be greater than ± 0.15 mm. As for }ne grinding dies, the accuracy should be ± 0.005 mm per 100 mm, and the total accuracy should not be greater than ± 0.05 mm. It is best to use the }ne grinding dies for CNC bending machines and conventional dies for ordinary bending machines.
As a user or manufacturer of equipment in the purchase of bending machines, the main thing is to purchase an economic and practical bending machine, which of course is to take into account many factors at the same time according to their actual situation. The above points are only a brief overview of some one-sided issues, the best way is to choose a professional bending machine manufacturer, so that they provide you with several sets of plans according to your actual situation alternative, so that the resolution plan up more reasonable and effective.
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