How to make the elevator by bending technology
Elevator has gradually entered ordinary residential families from high-end places such as mansions and CBD office buildings, With the continuous advancement of science and technology and the rapid development of productivity
The development of the installation of elevators in old buildings has made some residents in the old city deeply feel the convenience of elevators to life and the charm of technological progress. The demand for elevators continues to increase, and people’s quality requirements continue to increase. The manufacturing process of elevators cannot stand still.
Continuously exploring and optimizing the production process, and producing beautiful and elegant elevator cars to meet customer needs are exactly what we need for the craftsman spirit of continuous pursuit of technological excellence.
The elevator mainly compose of door panels, wall panels, three-piece sets (front wall, control wall, door light beam), ceiling decoration top and other components, as shown in Figure 1.
The material is generally 1.0-2.0mm stainless steel plate or cold-rolled carbon steel plate. The processing route is generally cutting by a shear, then punching or punching directly by laser, and finally bending and forming.
Compared with the first two steps of cutting and opening processes, the bending process is the most important process in sheet metal processing, and it is also the most complex and diverse process.
The pros and cons of the bending process will directly affect the forming size of the product, the assembly dimension chain, and the appearance of the product. How to make reasonable use of various bending processes to accurately and efficiently produce beautiful and generous elevator cars is the focus of this article.
Traditional bending process
The traditional bending process generally refers to the process of forming a sheet metal under the pressure of a punch or die, through elastic deformation, plastic deformation, and then forming.
It mainly includes three processes: point contact, two-sided contact, and three-sided contact.
Most of the elevator car components are C-shaped or U-shaped structures, which can form by traditional bending techniques, such as door light beams, front walls, control walls, ceiling bending plates, and car top plates. In traditional bending, the following aspects need to be paid attention to.
Mold selection
The structure of elevator car sheet metal parts generally L-shaped, C-shaped and U-shaped. For the selection of the upper mold, we can choose according to the different shapes of the workpiece. Straight swords or elbow straight knives generally use when bending L-shaped parts.
When bending C-shaped and U-shaped parts, can select a gooseneck-shaped straight knife to avoid interference. The lower die mainly has two parameters: groove width and V angle. The groove width mainly select according to the plate thickness.
Generally, the groove width is 6 times the plate thickness; the V angle mainly select according to the bending angle. In addition, the elevator car in Figure 1 should also consider the impact of sheet metal springback factors. For example, when bending a 90°workpiece, can select a V-die with a bending angle of 88° for bending.
Bending extreme
In the bending process, in order to ensure product quality, it is necessary to set extreme values such as the minimum bending radius, the minimum bending straight edge, and the minimum hole edge distance.
Different plates have different minimum bending radii due to their different elongation rates.
Among the commonly use thin metal plates, the minimum bending radius shows in Table 1, where t is the thickness of the sheet.
The minimum bending straight edge refers to the distance from the sheet boundary to the bending edge. If its length is too small, it may cause bending deformation and even damage the mold. The distance is generally h> 2t.
Hole margin refers to the process route of punching first and then bending. If the position of the hole is in the bending deformation zone, the hole will deform during bending. When t ≤ 2mm, the hole margin S ≥ t+r; when t ≥ 2mm, the hole margin S ≥ 1.5t+r, as shown in Figure 2.
Bending sequence
When formulating the bending process route, the bending sequence is also an important content. Improper bending sequence may cause a large deviation in the forming size of the part, and even interference may cause the bending to be impossible.
In the bending process, the following four basic principles generally followed:
(1) bend from the inside to the outside;
(2) bend from small to large;
(3) first bend special shapes, and then bend general shapes;
(4) The process has no influence or interference.
For example, when bending the control wall, its bending follows the principle of from inside to outside, and the bending sequence is shown in Figure 3.
Grooving and bending process
It can see from the bending process that after bending the workpiece, the bending edge of the decorative surface is in the shape of an arc, and its radius is proportional to the thickness of the metal sheet.
The thicker the sheet, the larger the radius of the arc formed by bending. In the elevator car assembly, if the bending radius is large, the car wall panels and ceiling bending panels will have a large splicing gap, which will affect the appearance.
In this regard, in some cars with special assembly requirements, we generally first grooving the plates before bending.
After grooving the metal sheet, will greatly reduce the remaining thickness of the sheet.
So that the bending radius of the workpiece can greatly reduce, and the assembly gap will control well as shown in Figure 4.
Since the remaining plate thickness at the bend after grooving is thinner, will accordingly reduce the deformation force during bending , and will not spread so as to affect the unbended area, so the bending phenomenon of the surface of the workpiece after bending will also be reduced.
Significantly reduced. In addition to the above advantages, the grooving bending process has the characteristics of reducing the tonnage required by the bending equipment, bending complex workpieces, and better controlling springback.
In addition, the grooving process also needs to pay attention to the following points.
Setting of planing depth
The thickness of the metal sheet is different, and the depth of the groove is also different. In the elevator car grooving and bending process, the thickness of the remaining board after grooving is generally 40% to 50% of the original board.
For example, if the board thickness is 1.0mm, the grooving depth is 0.5mm and the remaining thickness is 0.5mm;
Too shallow gouging will make the bending effect insignificant, and too deep will easily affect the structural strength of the workpiece.
V groove angle setting
After the metal sheet undergoes the grooving process, although the bending springback greatly reduce, it still exists.
Therefore, when plans the V-shaped groove , the groove can flexibly groove according to the bending angle of the workpiece. Generally, the grooving angle of the V-groove of stainless steel sheet is 1°～2° larger than the bending forming angle.
For example, for a workpiece with a 90° forming angle, the V-groove grooving angle is generally 92°. This can well avoid the angle error caused by the bending springback, as shown in Figure 5.
Types and selection of slot knives
The types of groove knives mainly divides into diamond top corner groove knives, square groove knives, triangular groove knives, circular groove knives, etc. When grooving, you can choose the appropriate tool according to the different shapes and angles of the V groove.
When planing ordinary V grooves, the angle of the tool should be smaller than that of the V groove.
For example, when the V-slot angle is 45°～60°, you should choose a groove knife with a rhombus apex angle of 35°;
when the angle is 60°～80°, you should choose an equilateral triangle groove knife; when the angle is 80°～90°,
Should select the slot knife with the rhombus top angle of 80° ; when the angle is greater than 90°, the square slot knife should be selected; when making the round slot , the round slot knife should be used.
Common problems and solutions in bending
After discovering potential problems during the bending process, they need to be optimized and resolved in time. In the elevator car bending process, there are mainly the following problems.
The forming size does not match the drawing
The main reasons for the inconsistency of the forming size of the workpiece with the drawing are the error of the cutting size, the inaccurate bending positioning and the cumulative error of multiple bending.
The solution is: adjust the bending coefficient, recalculate the unfolded size; adjust the positioning; select a reasonable positioning benchmark to eliminate the accumulated error.
If the cutting size error and the accumulated bending error are within the allowable range, the forming size can be guaranteed first, and the error can be accumulated on the non-assembly side that has no effect on the workpiece.
Bending angle deviation
The bending angle of the workpiece is too large or too small to cause bending angle deviation, mainly due to improper V port of the lower die, improper setting of die springback compensation parameters, and mismatch of press brake pressure.
The solution is: refer to the bending mold table to select the appropriate lower mold, adjust the rebound compensation value and the pressure of the bending machine.
Cracks on the bending edge
The main reasons for cracks in the bending edge include too small bending radius, parallel plate texture and bending line, blank burrs facing outwards, and poor material plasticity. The solutions are: increasing the bending radius or grooving; changing the direction of the workpiece layout; changing the direction of the burr and placing it on the inner corner of the workpiece; replacing the material with better plasticity.
The bending process is not static. It requires long-term accumulation and continuous exploration and optimization. Various bending processes have their own advantages and disadvantages. The reasonable use of various bending processes and the complementation of lengths and shorts can accurately and efficiently produce beautiful and generous Elevator .