With the continuous advancement of technology and rapid development of productivity, elevators have gradually moved from high-end places such as luxury homes and CBD office buildings to ordinary residential households. The implementation of elevator installation projects in old buildings has allowed residents in some old urban areas to deeply experience the convenience that elevators bring to their lives and the charm of technological progress. As the demand for elevators continues to increase and people's quality requirements continue to improve, the manufacturing process of elevators cannot stand still. Continuously exploring and optimizing the production process to produce aesthetically pleasing and elegant elevator cabins that meet customer demands is what we constantly pursue as craftsmen striving for excellent craftsmanship.
The elevator cabin is mainly composed of door panels, wall panels, three-piece sets (front wall, control wall, door light beam), and ceiling decorative tops. The materials used are generally 1.0-2.0mm stainless steel or cold-rolled carbon steel plates. The processing route usually involves cutting on a shearing bed, followed by punching using a punch press, or directly laser cutting and punching, and finally bending into shape. Compared to the previous two steps of cutting and hole-punching processes, the bending process is the most important and also the most complex and diverse process in sheet metal fabrication. The quality of the bending process directly affects the dimensional accuracy, assembly dimensional chain, and appearance of the product. The focus of this article is on how to use various bending processes rationally and efficiently to produce aesthetically pleasing and elegant elevator cabins.
Traditional Bending Process
The traditional bending process generally refers to the process in which metal sheets undergo elastic deformation and plastic deformation under the pressure of a bending convex or concave die to achieve the desired shape. It mainly includes three processes: point contact, two-side contact, and three-side contact. Most of the components of elevator cabins are C-shaped or U-shaped structures, which can be formed using the traditional bending process, such as door light beams, front walls, control walls, bent plates for ceilings, and roof plates. In traditional bending, the following aspects need to be considered.
Selection of Molds
The structure of elevator cabin sheet metal parts is generally L-shaped, C-shaped, and U-shaped. For the selection of upper molds, we can choose based on the different shapes of the workpieces. When bending L-shaped parts, a straight sword or a straight knife with a bending head is generally used. When bending C-shaped and U-shaped parts, a goose-neck straight knife can be selected to avoid interference. The lower mold mainly has two parameters: groove width and V angle. The groove width is mainly selected based on the plate thickness, generally six times the plate thickness. The V angle is selected based on the bending angle. In addition, the influence of metal sheet springback factors should also be considered. For example, when bending a 90° workpiece, a V die with a bending angle of 88° can be selected for bending.
Bending Limits
In the bending process, to ensure product quality, it is necessary to set extreme values such as the minimum bending radius, minimum bending straight edge, and minimum hole edge distance. Different sheet materials have different elongation rates, resulting in differences in the minimum bending radius. In commonly used metal sheets, the minimum bending radius is shown in Table 1, where t is the thickness of the sheet.
The minimum bending straight edge refers to the distance from the edge of the sheet to the bending edge. If the length is too small, it may cause bending deformation and even pose a risk of damaging the mold. The distance is generally h > 2t.
The hole edge distance refers to the situation where, in the process route of punching before bending, if the hole is located within the bending deformation zone, the hole will deform during bending. When t ≤ 2mm, the hole edge distance S ≥ t + r; when t ≥ 2mm, the hole edge distance S ≥ 1.5t + r.
Bending Sequence
When determining the bending process route, the bending sequence is also a key consideration. Improper bending sequence can result in significant dimensional deviations of the parts and even interference that prevents successful bending. Generally, the following four basic principles are followed during the bending process: (1) bending from the inside to the outside, (2) bending from small to large, (3) bending special shapes first and then general shapes, and (4) ensuring that the previous process does not affect or interfere with the subsequent processes. For example, when bending the control wall, the bending follows the principle of bending from the inside to the outside.
Groove Cutting Bending Process
From the bending process, it is known that after bending, the decorative surface and the bent edges of the workpiece form a rounded shape, and the radius of the arc is proportional to the thickness of the metal sheet. The thicker the sheet, the larger the radius of the bending arc. In elevator cabin assembly, if the bending radius is large, there will be significant gaps in the cabin wall panels and bent ceiling plates, which affects the aesthetics. Therefore, in some cabins with special assembly requirements, we generally perform groove cutting on the sheet before bending. Groove cutting significantly reduces the remaining thickness of the sheet, which reduces the bending radius of the workpiece and controls the assembly gaps effectively. Since the remaining thickness at the bending area after groove cutting is thinner, the deformation force during bending is correspondingly reduced, and it does not spread to affect the unbent areas. As a result, the phenomenon of surface reflection after bending is greatly reduced. In addition to the advantages mentioned above, the groove cutting bending process also reduces the required tonnage of the bending equipment, enables the bending of complex parts, and provides better control over springback. In addition, the groove cutting process should pay attention to the following points.
Setting of Groove Depth
Different metal sheet thicknesses require different groove depths. In the groove cutting bending process of elevator cabins, the remaining sheet thickness after groove cutting is generally 40% to 50% of the original sheet thickness. For example, for a 1.0mm sheet thickness, the groove depth is 0.5mm, and the remaining thickness is 0.5mm; for a 1.2mm sheet thickness, the groove depth is 0.7mm, and the remaining thickness is 0.5mm; for a 1.5mm sheet thickness, the groove depth is 0.9mm, and the remaining thickness is 0.6mm; for a 2.0mm sheet thickness, the groove depth is 1.2mm, and the remaining thickness is 0.8mm. If the groove is too shallow, the bending effect will not be obvious, while if it is too deep, it may affect the structural strength of the workpiece.
Setting of V-Groove Angle
Although the bending springback is significantly reduced after the groove cutting process, it still exists. Therefore, when grooving the V-shaped groove, the groove can be flexibly cut based on the bending angle of the workpiece. Generally, the groove angle of stainless steel thin sheets should be 1° to 2° larger than the forming angle. For example, for a workpiece with a forming angle of 90°, the groove angle is generally 92°. This effectively avoids angle errors caused by bending springback.
Types and Selection of Groove Cutters
Groove cutters mainly include diamond-shaped top angle groove cutters, square groove cutters, triangular groove cutters, circular groove cutters, etc. When grooving, suitable tools should be selected based on the different shapes and angles of the V-groove. When grooving a regular V-groove, the tool angle should be smaller than the angle of the V-groove. For example, when the V-groove angle is between 45° and 60°, a diamond-shaped top angle groove cutter with a 35° angle should be selected; when the angle is between 60° and 80°, a triangular groove cutter should be chosen; when the angle is between 80° and 90°, a diamond-shaped top angle groove cutter with an 80° angle should be selected; for angles greater than 90°, a square groove cutter should be chosen; and for circular grooves, a circular groove cutter is used.
Common Bending Issues and Solutions
When potential issues are identified during the bending process, they should be addressed and optimized promptly. In the bending process of elevator cabin fabrication, the following issues are commonly encountered:
Mismatch between formed dimensions and drawings
The reasons for the mismatch between the formed dimensions of the workpiece and the drawings mainly include errors in blank size, inaccurate bending positioning, and cumulative errors from multiple bending operations. The solutions are as follows: adjust the bending coefficient and recalculate the unfolded dimensions; adjust the positioning; select a reasonable positioning reference to eliminate cumulative errors. If the errors in blank size and cumulative bending errors are within an acceptable range, priority should be given to ensuring the formed dimensions and accumulating errors on non-assembly edges that do not affect the workpiece.
Bending Angle Deviation
Excessive or insufficient bending angle can easily result in bending angle deviation of the workpiece. The main reasons include inappropriate lower die V-groove, improper setting of mold springback compensation parameters, and mismatched pressure of the bending machine. The solutions are as follows: refer to the bending mold table to select a suitable lower die, adjust the springback compensation value, and adjust the pressure of the bending machine.
Cracks on Bending Edges
The main reasons for cracks on the bending edges include a too small bending radius, parallel alignment of the sheet grain with the bending line, burrs on the rough side of the blank facing outward, and poor material plasticity. The solutions are as follows: increase the bending radius or perform groove cutting; change the layout direction of the workpiece; change the direction of the burrs and place them on the inner fillet of the workpiece; replace the material with better plasticity.
Conclusion
The bending process is not static and requires long-term accumulation, continuous exploration, and optimization. Each bending process has its advantages and disadvantages. By utilizing various bending processes rationally and complementing each other, we can accurately and efficiently produce aesthetically pleasing elevator cabins.
The elevator cabin is mainly composed of door panels, wall panels, three-piece sets (front wall, control wall, door light beam), and ceiling decorative tops. The materials used are generally 1.0-2.0mm stainless steel or cold-rolled carbon steel plates. The processing route usually involves cutting on a shearing bed, followed by punching using a punch press, or directly laser cutting and punching, and finally bending into shape. Compared to the previous two steps of cutting and hole-punching processes, the bending process is the most important and also the most complex and diverse process in sheet metal fabrication. The quality of the bending process directly affects the dimensional accuracy, assembly dimensional chain, and appearance of the product. The focus of this article is on how to use various bending processes rationally and efficiently to produce aesthetically pleasing and elegant elevator cabins.
Traditional Bending Process
The traditional bending process generally refers to the process in which metal sheets undergo elastic deformation and plastic deformation under the pressure of a bending convex or concave die to achieve the desired shape. It mainly includes three processes: point contact, two-side contact, and three-side contact. Most of the components of elevator cabins are C-shaped or U-shaped structures, which can be formed using the traditional bending process, such as door light beams, front walls, control walls, bent plates for ceilings, and roof plates. In traditional bending, the following aspects need to be considered.
Selection of Molds
The structure of elevator cabin sheet metal parts is generally L-shaped, C-shaped, and U-shaped. For the selection of upper molds, we can choose based on the different shapes of the workpieces. When bending L-shaped parts, a straight sword or a straight knife with a bending head is generally used. When bending C-shaped and U-shaped parts, a goose-neck straight knife can be selected to avoid interference. The lower mold mainly has two parameters: groove width and V angle. The groove width is mainly selected based on the plate thickness, generally six times the plate thickness. The V angle is selected based on the bending angle. In addition, the influence of metal sheet springback factors should also be considered. For example, when bending a 90° workpiece, a V die with a bending angle of 88° can be selected for bending.
Bending Limits
In the bending process, to ensure product quality, it is necessary to set extreme values such as the minimum bending radius, minimum bending straight edge, and minimum hole edge distance. Different sheet materials have different elongation rates, resulting in differences in the minimum bending radius. In commonly used metal sheets, the minimum bending radius is shown in Table 1, where t is the thickness of the sheet.
The minimum bending straight edge refers to the distance from the edge of the sheet to the bending edge. If the length is too small, it may cause bending deformation and even pose a risk of damaging the mold. The distance is generally h > 2t.
The hole edge distance refers to the situation where, in the process route of punching before bending, if the hole is located within the bending deformation zone, the hole will deform during bending. When t ≤ 2mm, the hole edge distance S ≥ t + r; when t ≥ 2mm, the hole edge distance S ≥ 1.5t + r.
Bending Sequence
When determining the bending process route, the bending sequence is also a key consideration. Improper bending sequence can result in significant dimensional deviations of the parts and even interference that prevents successful bending. Generally, the following four basic principles are followed during the bending process: (1) bending from the inside to the outside, (2) bending from small to large, (3) bending special shapes first and then general shapes, and (4) ensuring that the previous process does not affect or interfere with the subsequent processes. For example, when bending the control wall, the bending follows the principle of bending from the inside to the outside.
Groove Cutting Bending Process
From the bending process, it is known that after bending, the decorative surface and the bent edges of the workpiece form a rounded shape, and the radius of the arc is proportional to the thickness of the metal sheet. The thicker the sheet, the larger the radius of the bending arc. In elevator cabin assembly, if the bending radius is large, there will be significant gaps in the cabin wall panels and bent ceiling plates, which affects the aesthetics. Therefore, in some cabins with special assembly requirements, we generally perform groove cutting on the sheet before bending. Groove cutting significantly reduces the remaining thickness of the sheet, which reduces the bending radius of the workpiece and controls the assembly gaps effectively. Since the remaining thickness at the bending area after groove cutting is thinner, the deformation force during bending is correspondingly reduced, and it does not spread to affect the unbent areas. As a result, the phenomenon of surface reflection after bending is greatly reduced. In addition to the advantages mentioned above, the groove cutting bending process also reduces the required tonnage of the bending equipment, enables the bending of complex parts, and provides better control over springback. In addition, the groove cutting process should pay attention to the following points.
Setting of Groove Depth
Different metal sheet thicknesses require different groove depths. In the groove cutting bending process of elevator cabins, the remaining sheet thickness after groove cutting is generally 40% to 50% of the original sheet thickness. For example, for a 1.0mm sheet thickness, the groove depth is 0.5mm, and the remaining thickness is 0.5mm; for a 1.2mm sheet thickness, the groove depth is 0.7mm, and the remaining thickness is 0.5mm; for a 1.5mm sheet thickness, the groove depth is 0.9mm, and the remaining thickness is 0.6mm; for a 2.0mm sheet thickness, the groove depth is 1.2mm, and the remaining thickness is 0.8mm. If the groove is too shallow, the bending effect will not be obvious, while if it is too deep, it may affect the structural strength of the workpiece.
Setting of V-Groove Angle
Although the bending springback is significantly reduced after the groove cutting process, it still exists. Therefore, when grooving the V-shaped groove, the groove can be flexibly cut based on the bending angle of the workpiece. Generally, the groove angle of stainless steel thin sheets should be 1° to 2° larger than the forming angle. For example, for a workpiece with a forming angle of 90°, the groove angle is generally 92°. This effectively avoids angle errors caused by bending springback.
Types and Selection of Groove Cutters
Groove cutters mainly include diamond-shaped top angle groove cutters, square groove cutters, triangular groove cutters, circular groove cutters, etc. When grooving, suitable tools should be selected based on the different shapes and angles of the V-groove. When grooving a regular V-groove, the tool angle should be smaller than the angle of the V-groove. For example, when the V-groove angle is between 45° and 60°, a diamond-shaped top angle groove cutter with a 35° angle should be selected; when the angle is between 60° and 80°, a triangular groove cutter should be chosen; when the angle is between 80° and 90°, a diamond-shaped top angle groove cutter with an 80° angle should be selected; for angles greater than 90°, a square groove cutter should be chosen; and for circular grooves, a circular groove cutter is used.
Common Bending Issues and Solutions
When potential issues are identified during the bending process, they should be addressed and optimized promptly. In the bending process of elevator cabin fabrication, the following issues are commonly encountered:
Mismatch between formed dimensions and drawings
The reasons for the mismatch between the formed dimensions of the workpiece and the drawings mainly include errors in blank size, inaccurate bending positioning, and cumulative errors from multiple bending operations. The solutions are as follows: adjust the bending coefficient and recalculate the unfolded dimensions; adjust the positioning; select a reasonable positioning reference to eliminate cumulative errors. If the errors in blank size and cumulative bending errors are within an acceptable range, priority should be given to ensuring the formed dimensions and accumulating errors on non-assembly edges that do not affect the workpiece.
Bending Angle Deviation
Excessive or insufficient bending angle can easily result in bending angle deviation of the workpiece. The main reasons include inappropriate lower die V-groove, improper setting of mold springback compensation parameters, and mismatched pressure of the bending machine. The solutions are as follows: refer to the bending mold table to select a suitable lower die, adjust the springback compensation value, and adjust the pressure of the bending machine.
Cracks on Bending Edges
The main reasons for cracks on the bending edges include a too small bending radius, parallel alignment of the sheet grain with the bending line, burrs on the rough side of the blank facing outward, and poor material plasticity. The solutions are as follows: increase the bending radius or perform groove cutting; change the layout direction of the workpiece; change the direction of the burrs and place them on the inner fillet of the workpiece; replace the material with better plasticity.
Conclusion
The bending process is not static and requires long-term accumulation, continuous exploration, and optimization. Each bending process has its advantages and disadvantages. By utilizing various bending processes rationally and complementing each other, we can accurately and efficiently produce aesthetically pleasing elevator cabins.
