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When choosing the press bending machine improperly, the production cost will rise, and the bending machine can not expect to recover the cost. Therefore, there are several factors that need to be weighed in decision-making.
The first important thing to consider is the parts you want to produce. The main point is to buy a machine with the shortest workbench and the smallest tonnage that can complete the processing task.
Carefully consider the material brand and the maximum machining thickness and length. If most of the work is 16 gauge thick mild steel with a maximum length of 10 feet (3.048 meters), then the free bending force does not have to be greater than 50 tons. However, if you are engaged in a large number of bottom die forming, maybe you should consider a 160 ton machine tool.
Assuming the thickest material is 1 / 4 inch, 200 tons for a 10 foot free bend and at least 600 tons for a bottom die bend (corrected bend). If most of the workpieces are 5 feet or shorter, the tonnage is almost halved, thus greatly reducing the purchase cost. The length of the parts is very important to determine the specifications of the new machine.
Flexure of press bending machine
Under the same load, the deflection of the worktable and slide of the 10 foot machine is 4 times that of the 5 foot machine. That is to say, shorter machines need less gasket adjustment to produce qualified parts. Reducing gasket adjustment also shortens preparation time.
Material designation is also a key factor. Compared with low carbon steel, stainless steel usually needs about 50% more load, while most brands of soft aluminum reduce about 50%. At any time, you can get the tonnage table of the machine from the bending machine manufacturer, which shows the tonnage estimation required for each foot length under different thicknesses and materials.
When free bending is adopted, the bending radius is 0.156 times of the opening distance of the die. In the free bending process, the opening distance of the die should be 8 times of the thickness of the metal material. For example, when a 1 / 2-inch (0.0127m) opening is used to form a 16 gauge mild steel, the bending radius of the part is about 0.078 inch. If the bending radius is almost as small as the material thickness,
Bottom die forming is required. However, the pressure required for forming the bottom die is about 4 times larger than that for free bending.
If the bending radius is less than the thickness of the material, the punch with the front corner radius less than the thickness of the material shall be used, and the stamping bending method shall be used. This requires 10 times the free bending pressure.
As far as free bending is concerned, punch and die shall be processed at 85 ° or less (small point is better). When using this set of dies, pay attention to the gap between the punch and the die at the bottom of the stroke, as well as the excessive bending enough to compensate the rebound and keep the material at about 90 °.
Generally, the springback angle of the free bending die on the new bending machine is ≤ 2 °, and the bending radius is equal to 0.156 times of the opening distance of the die.
For the bottom die bending, the die angle is generally 86 ~ 90 °. At the bottom of the stroke, there should be a gap between the convex die and the concave die slightly larger than the material thickness. The forming angle can be improved, because the tonnage of bending with bottom die is large (about 4 times of that of free bending), which reduces the stress of springback in the range of bending radius.
The stamping bending is the same as the bottom die bending, except that the front end of the punch is processed into the required bending radius, and the gap between the punch and the bottom of the stroke is less than the material thickness. By applying enough pressure (about 10 times of the free bending) to force the front end of the punch to contact the material, the rebound is basically avoided.
In order to select the lowest tonnage specification, it is better to plan for the bending radius greater than the material thickness, and use the free bending method as much as possible. When the bending radius is large, it often does not affect the quality of the finished part and its future use.
The requirement of bending accuracy is a factor to be considered carefully. It is this factor that determines whether a CNC bending machine or a manual bending machine should be considered. If the bending accuracy requires ± 1 ° and cannot be changed, the CNC machine must be considered.
The repeat precision of CNC bending machine slider is ± 0.0004 inch. The precise angle of forming must adopt such precision and good die. The repeat accuracy of the slide block of the hand-controlled bending machine is ± 0.002 inch, and the deviation of ± 2 ~ 3 ° is generally generated under the condition of using the appropriate mold. In addition, the CNC bending machine is ready for rapid tooling, which is an undoubted consideration when many small batch parts need to be bent.
Even if there are full shelves of molds, don’t think these molds are suitable for the newly purchased machine. The wear of each die must be checked by measuring the length from the front end of the punch to the shoulder and the length between the shoulder of the die.
For conventional molds, the deviation per foot should be about ± 0.001 inch, and the total length deviation should not be greater than ± 0.005 inch. As for the precision grinding die, the accuracy per foot shall be ± 0.0004 inch, and the total accuracy shall not be greater than ± 0.002 inch. It is better to use the fine grinding die for CNC bending machine and the conventional die for manual bending machine.
Assuming that a 5 x 10 foot 10 gauge mild steel plate is bent 90 °, the bender must apply an additional 7.5 tons of pressure to lift the plate, and the operator must be prepared for a 280 pound straight edge drop. It may take several strong workers or even a crane to make the part. Press Bending machine operators often need to bend long side parts, but they don’t realize how hard their work is.