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3 Important Facts That You Should Know About Manual Bending

Estimated reading time: 24 minutes

Manual bending refers to the method of manually bending a part of a sheet or profile to a certain angle along a straight line or from a line to the other part. It is one of the most basic operating methods for fan gold forming. Common manual bending parts are shown in the figure.

Manual bending parts
Manual bending parts

Manual bending of small and thin plate parts

Point R profiling, platform, bow clamp, and bench vise, etc. The commonly used equipment is a manual folding machine, which is mainly used to bend simple straight line bending plates. Manual bending is mainly used for thin plates with a thickness of less than 3mm and small dimensions, especially for thin plates with a thickness of 0.6~1.5mm. For the bending of thicker sheets, the processing method of manually bending after local heating of the bending part is often used.

Calculation of bending length

When bending a sheet, the unfolded length must be calculated first. The correct unfolded length of the bent piece is the basic guarantee for the accurate bending of the bent piece. Due to the following characteristics when bending and deforming: the inner layer of the sheet material is compressed and the outer layer is elongated, and there is a layer of material between the middle and the inner layer that neither stretches nor shrinks. This layer of material is called neutral Floor. Therefore, the length of the bent neutral layer is the unfolded length of the bent part of the blank. In this way, the key to the calculation of the blank length of the entire curved part is if one determines the radius of curvature of the curved neutral layer. During production, the empirical formula is generally used to determine the radius of curvature p of the neutral layer: p=r+xt

The formula: r——The inner angle of sheet bending;

x——The neutral layer coefficient related to the degree of deformation, selected according to Table 1-1;

t——The thickness of the sheet.

1-1 The value of the neutral layer coefficient x

After the position of the neutral layer is determined, the sum of the length of the straight line and the arc part can be obtained, which is the length of the unfolded material of bending parts. However, because the bending deformation is affected by many factors, such as material properties, mold structure, bending method, etc., for bending parts with complex shapes, many bending angles, and small dimensional tolerances, the above formulas should be used for preliminary calculations to determine the test. After bending the blank, the exact blank length can be determined after the test bending is qualified.

The values listed in Table 1-1 are also applicable to the calculation of bending and unfolding of bars and tubes.

  • In the calculation and production of 90° bending parts, when the bending angle is 90°, the commonly used subtraction method calculates the bending part’s expansion length. As shown in the figure, when the thickness of the sheet is t, the bending inner corner radius is r, the unfolding length of the bending part blank is L is: L=a+b-u
Calculation of right-angle bending
Calculation of right-angle bending

The formula: a, b——The length of the two right-angled sides of the bend;

u——The difference between the sum of two right-angled sides and the length of the neutral layer, see Table 1-2.

Bending radius r
Material thickness t11.21.622.5345681012
Average value u
Bending radius r
Material thickness t11.21.622.5345681012
Average value u
1-2 Deducted value U of unfolded length when bent at 90°(mm)

In production, if the requirements for the length of the bent part are not accurate, the unfolded length L of the bent part blank can be approximated by the following formula:

When the bending radius r≤1.5/, L=a+b+0.5t;

When the bending radius 1.5t<r≤5t, L=a+b;

When the bending radius 5t<r≤10t, L=a+b-1.5t;

When the bending radius r>10t, L=a+b-3.5t.

  • Calculation of bending at any angle. The bending part of any bending angle shown in the figure can be calculated by the following formula.
Calculation of bending at any angle
Calculation of bending at any angle

The formula:  L1, L2——Length of a straight line, mm;

ρ——The radius of the neutral layer of the curved part, mm;

α——Bending angle, a=180°-0, (°);

θ——The central angle of the curved part, (°);

x——The neutral layer coefficient related to the degree of deformation, selected according to Table 1-1 when the hinge part is rolled with a mold (see the figure below), select according to Table 1-2

t——According to the plate thickness, mm.


For the hinged bending part with r=(0.6~3.5)t, when the round die method shown in the figure is used for bending, the punch exerts pressure on one end of the blank, so the plastic deformation is different from the general bending. The material is not Thinning but thickening, the neutral layer moves from the middle of the sheet thickness to the curved outer layer, so the displacement coefficient of the neutral layer is greater than or equal to 0.5 (see Table 1-3).

1-3 Displacement coefficient of neutral layer when rolling

Manual bending operation method for small and thin plate parts

The commonly used tools for manual bending of small and thin-plate parts mainly include wooden hammers, wooden tips, vise, crimping dies, etc., as shown in the figure.

Tools for manual bending
Tools for manual bending

For different shapes of sheet metal bending parts, the bending processing methods are different. Manual bending is divided into single-angle bending and multiple bending. The bending operation method is as follows.

  • Bend on one foot. For single-angle bending parts, first, unfold them according to the aforementioned method to obtain the unfolded dimensions, and draw the bending line after leveling: then prepare two modules or gauge irons, the length is greater than the length of the part, and clamp the bending piece wool between the two gauges. When bending, the irons close the bending line to the edge of the gauge iron inverted R, as shown in Figure (a). Then tap the material with a rubber strip or a wooden sled to make it against the mold in the R edge gauge iron direction. When tapping, focus on the middle and lower part of the blank projecting out of the mold, and try to make it fit the mold, as shown in Figure (b). To ensure that the material shrinks and pastes the film, a wooden hammer and wooden tip can be used to uniformly hammer the inner R of the hair damage from the beginning to the end to make it film, as shown in Figure (c). To eliminate spring back, warpage, and anti-concave (too many hammers are used when bending, it is easy to produce reverse bending), the wooden tip is used to point from the outside to the inside, and continuously from one end to the other end, as shown in Figure (d) Shown.
Single leg bending method
Single leg bending method

For curved parts with warpage and spring back, in order to eliminate warpage and spring back, a piece of straight-sided gauge iron can be used, which is clamped on the platform with a bow clamp, and the curved edges of the parts are aligned with the straight face of the gauge iron and aligned with a wooden tip. The bend of the workpiece is at an angle of 45°. Use a wooden hammer to lightly tap the wooden tip, move the bend while tapping, all the points are pointed again, as shown in Figure (e). Finally, clamp the workpiece in the gauge iron and beat it with a rubber strip until it is attached to the mold, as shown in Figure (b).

  • The bending of multiple flanges. A bending method of multiple flanges is the same as the single-angle bending method, but it is necessary to pay attention to the bending sequence, such as bending with a gauge iron, bending sequence is generally first inside and then outside, it is easier to ensure the size of each part of the bending part, as shown in Figure ( a) (b) respectively gives the bending sequence of the two bending parts.
The bending sequence of multiple flanges
The bending sequence of multiple flanges

When bending multiple flanges, it should be noted that because multiple flange bending pieces are combined by multiple single-angle bending, the bending sequence is irreversible, and the completion of the latter sequence of bending cannot be compared to the previous one. Make any corrections to the sequence of the bends. Therefore, carefully check each bend after bending, and make sure that the bend is straight and straight; the size of each bend should be accurate. Otherwise, it will not be repaired due to an accumulation of errors. In the forming process, after each bend, you can use a long wooden board to overwhelm the wool, and then use the wooden board to lay it flat on the curved surface, and use a wooden hammer to hit the mold to make the bend straight and the curved edge less corrugated, such as As shown in the figure. The shim on the bench vise should be firm, otherwise, the material will
slide down when beating, which will affect the size of the flange.

Press and bend with a wooden board pad
Press and bend with a wooden board pad

Precautions for manual bending

The metal parts that are manually bent are generally thin plates. Due to their weak load resistance, if they are subjected to local impact loads, the plates are prone to warping defects due to the reduction of local thickness. Therefore, the load applied to the plates should be Distributed loads, such as line distribution and surface distribution. It should be prohibited to apply any concentrated load on the surface of the plate. If the bending material is a non-ferrous metal sheet, due to its low surface hardness, in order to avoid hammer marks on the surface of the sheet, the surface hardness of the loading tool used should be lower than that of the sheet when bending by hand. If the material used is pure copper, hardwood and Hand hammers, slats, and other power tools such as rubber.

For the bending of multiple flanges, due to the irreversibility and incorrect ability of the bending forming, it is necessary to accurately calculate, scribe, and arrange the bending sequence before bending. Each bend angle and corner radius R must be in place before the next bend,otherwise, the accuracy of the overall dimensions of multiple bends and bends will be affected due to the accumulation of various errors and cannot be repaired.

Hemming operation

Hemming is the operation of rolling the edge of the sheet material. The methods of hemming mainly include wire crimping and hollow crimping. Because the sheet material of usually crimping is thin (material thickness <1mm), rigidity is low, and strength is low, crimping can increase the cross-sectional area of the structure, thereby increasing the rigidity and strength of the structure, and achieving the purpose of light structure and high strength. Hemming is widely used in rice gold processing.

Calculation of the unfolded length of the hemming

As with other manual bending processing of sheet materials, the correct calculation of the unfolded length of sheet material curling is a prerequisite for ensuring the quality of curling parts. The picture shows the calculation principle of the curling length, and the calculation formula of the curling length l is:

Calculation principle of curling length
Calculation principle of curling length
l=d/2+3/4 π(d+t)

The formula: d—— diameter of coiled wire, mm T——Board thickness, mm

The thickness of the coiled wire is determined according to the size of the part and the force it receives. Generally, the diameter of the iron wire is more than 3 times the thickness of the sheet.

Hemming operation process

The crimping parts of different structures have different tools for crimping operations, but the operation process and methods are roughly the same. The figure shows the operation process of manual wire crimping, and the details are as follows.

 Hemming process
Hemming process
  • Draw two curling lines on the blank, as shown in Figure (a), where:



The formula: d—— diameter of coiled wire.

  • Place the blank on the platform (or square iron, rail, etc.) so that the size of the exposed platform is equal to L2, press the blank with the left hand, and hit the edge of the exposed platform with a hammer with the right hand to bend it downward to 85°~90°, As shown in Figure (b).
  • Extend and bend the blank until the edge of the platform is aligned with the second curling line, that is, make the exposed platform part equal to L1, and make the edge of the first beating on the platform, as shown in Figures (c) and (d) Shown.
  • Turn the blank over so that the curling edge is facing upwards, and tap the curling edge inward buckle lightly and evenly, so that the curled part gradually becomes an arc, as shown in Figure (e).
  • Put the iron wire into the curling edge, start from one end when putting it, to prevent the iron wire from popping out, first buckle one end, then put a section to buckle a section, after all, buckles, tap lightly so that the curling edge is close to the iron wire, as shown in figure (F) Shown.
  • Turn over the blank, make the interface leaning against the edge of the platform, and tap it lightly to make the connection tight, as shown in figure (g).

The operation process of manual hollow crimping is the same as that of wire clamping, that is, the wire is pulled out at the end. When pulling, just clamp one end of the iron wire and turn the part while pulling it out.

The method to deal with the defect of the curling operation

In the hemming process, due to the difference in blanking or operating methods, the defect of insufficient or excessive hemming length is likely to occur. Although different tools must be used for sheet metal hemming parts of different structures, the processing methods and adoption The measures are basically the same. The following describes the curling operation of a frustum washing tub.

The picture shows the crimping operation sequence of the frustum washing tub. Taking into account the improvement of hemming production efficiency without damaging the plate, choose the clapper to turn the edge, which can be flat or edged; the blunt edge of a hand hammer can also be used, but care should be taken not to damage the plate.

Crimping operation of frustum washing tub
Crimping operation of frustum washing tub
  1. Use a compass to draw a folding line on the inside of the basin, then l=2.5d, where d is the diameter of the iron wire.
  2. On the edge of the platform or on the horizontal rail, take advantage of the small contact area of its ridges, and use a clapper to turn the edge outward according to the edge line. Care should be taken not to pull it at one time, but to pull it multiple times, as shown in Figure (a) Show.
  3. Place it on the edge of the platform, gradually adjust the amount of flipping and flatten the flipping with a clapper to prepare for the next curling, as shown in Figure (b).
  4. Put the basin body on the end of round steel or thick-walled steel pipe, put the coiled wire into the crimping part, clamp it firmly with toothless hand pliers, use the clapper on both sides of the hand pliers to turn down, so as not to make the coiled wire detach So far, there are 4~5 places in a circle to fix the coiled wire, as shown in Figure (c), the next step is to roll firmly, still clamp it with pliers, clamp one section and beat one section until the whole circumference, clamp The purpose of this is to prevent rebound and improve the efficiency of hemming. When there are too many overlapping layers of longitudinal seams, they can be pressed down by hitting them with a hammer.
  5. Lay the basin body flat on the platform, smash the outer edge of the curling edge with a clapper or a hammer, and adjust the levelness of the curling part of the bowl mouth at the same time, as shown in Figure (d).
  6. If the curling wrap is not tightly wrapped (the curling length is not enough), you can tilt the basin down and use a clapper to beat it down. The curling and curling parts will move to the small end at the same time, and the curling part will naturally change, see Figure (a). If the curling length is too long, you can tilt the basin down and hit it with a clapper. The curling and curling parts will move to the larger end at the same time, and the curling part will naturally become shorter, see Figure (b).
How to deal with improper curl length
How to deal with improper curl length

Hand-made of square-round changing tube

A square-round changing tube is a metal component that is often encountered in production. When the sheet is thin and cannot be pressed by a press, it is generally formed by manual grooves. For the convenience of groove system and assembly, it is generally formed by welding in two halves. When the height is less than 100mm and the appearance is required, it can also be lowered into a single piece, and then formed by groove system and welding.

The making of mold

The hand-grooved square-round changing tube must be made first. The hand-grooved mold can be linear (such as channel steel), or it can be a radial shape composed of round steel. The former is in thin plates, small dimensions and It is easy to have many defects if it is used in the case of a small number of specifications; the latter is used in the case of mass production, which has fewer defects and can provide convenience for assembly. The figure shows the mold form of a small square-round changing tube made by hand groove.

Square-round changing tube and mold
Square-round changing tube and mold

Among them: Figure (a) is the part drawing of the square-round changing tube. Figure (b) shows the produced radial mold. The mold is placed radially with round steel. The length of the round steel is determined by the longest transition line of the square-round changing tube plus a margin of about 100mm. Due to the 8 transitions of the square-round changing tube, The lengths of the lines are equal (figure shows Aa=Ba=Bb=Cb=Cc=Dc=Dd=Ad=l in the figure). The length l==215.9mm (calculated based on the inner layer of the metal piece, 97mm is the inner radius of the round end, 147mm is half the length of the inner layer of the square end, and 150mm is the height of the pipe material); the opening width of the large end of the mold is the round end 1/ 4 Outer chord length, its value is calculated according to 200×sin45°=141.42mm. Considering that the sheet is thinner, the thickness is 3mm, the two layers are 6mm, plus twice the margin of 6mm, so the small end distance is 12mm. enough. Figure (c) is the calculation principle of the diameter of the round steel used in the mold because the distance between the top of the round steel and the bottom of the forming part after the arc is formed is h1=100-=29.29mm, considering leaving an appropriate forming gap, the diameter of the round steel is ∅40mm.

In the production operation, the placement of hand-grooved molds can also be omitted from the above calculation. It is approximately calculated based on the angle between the round bars of 10°~15° and the diameter of the round bars of ∅25~60mm.

Handmade groove methods

For small square-round changing tubes, the material is generally unfolded or unloaded according to 1/2. The figure shows the method of manual troughing of the monolith. Figure (a) is the concave of the intersection of the trough-made plane triangle and the arcuate triangle. The positional relationship between the mold and the plate; Figure (b) shows the positional relationship between the concave mold and the plate when the groove is made of a curved triangle. The grooving process must follow the principle of “the two ends first, then the middle”, otherwise, the up and down action of the sledgehammer will be affected due to the uplift of the bending part.

When making grooves, a small section of each groove should be used to check the curvature of the template to make it match or slightly pass.

The method of the whole trough system and the half trough system is exactly the same. After the half trough system is completed, the outer skin sample must be released on the platform for the large-size thick plate, spot welding the limit iron, and the line group butt welding; the small-size thin plate can not be put In fact, direct spot welding and butt welding.

After the assembly and spot welding, there will be various assembly defects, which can be corrected by the following methods.

Manual groove methods of small Square-round changing tube
Manual groove methods of small Square-round changing tube
  • There is a gap at the small or big end. The picture shows the situation where there is a gap at the large end. At this time, the opposite seam should be spot welded firmly, and the upper end of this side should also be spot welded. The short-angle steel with holes is welded at the large end of the gap, and only spot welding is allowed on the outside, then tighten the nut to pull it closer. When spot welding the upper port, it should be noted that it must be firm, and the weld seam should not be too long, too short, and not strong enough, too long will increase the tension of the bolt, when tightening the bolt, check the deformation of the spot weld at any time, if there is any Cracks or scale peeling should be dealt with in time. The treatment method is first to spot weld a small spot near the crack to be opened, and then strengthen the weld of the part to be cracked after it is completely cold. Do not spot weld the part to be cracked at the beginning, This will result in a sharp increase in the toughness of the weld scar due to heat, causing all welds to crack.
 There is a gap at the small or big end
There is a gap at the small or big end
  • The docking port is upturned. The picture shows a pair of mouth ends that are just right, and the other pair of mouth ends are upturned. When assembling, the two pairs of ports on the other side should be welded firmly and placed on the platform. The following methods can be used to deal with: One is the pad pressing method, that is, a thicker steel plate is placed under the unturned end, the purpose is to make a place for the tilted end to be pressed down, and the highest point of the upturned When it is pressed down, when there are no errors at both ends, spot welding a little bit first, and after all defects are processed, all spot welding is done. Note: The lower shim can only be placed under the unturned end, and it will not affect the downward movement of the raised end. The second is the spiral approach, that is, through a screw with a nut at one end, the lower end is hooked to the unturned port, and the upper end is placed on the upturned port through a perforated pressure plate, and the nut is tightened. The upturned part will move down slowly. When the mouth is good, it can be formed by spot welding.
The docking port is upturned
The docking port is upturned
  • The end of the circle is not a perfect circle. Before spot welding is completed, the geometric dimensions of the components should be checked. Use the template to check the roundness of the rounded end. If there is any irregularity, use the lining hammer method to correct it. If the direction of the plain line is not round, the force hammer and liner hammer should be placed left and right, as shown in Figure (a); if the port is partially non-circular, the force hammer and liner hammer should be placed up and down, as shown in Figure (b). During operation, the liner hammer should be lined near the highest point, and the hammer should fall at the highest point. The closer the liner hammer and the force hammer are, the greater the correction force, but they cannot overlap.
Correction method for round end
Correction method for round end
  • The square ends are not equal to the diagonal. After the pairing is completed, it is a common defect that the diagonals of the square ends are not equal. The correction method is shown in the figure, (a) shows the correction with the inverted chain (or inverted wire), and figure (b) shows the correction with the press (or bar). If the correcting force is not large, you can also use a sledgehammer to correct it manually along the diagonal direction. If the correcting force is large, you can use mechanical force such as a press or a straightening machine to correct it. During the correction process, you should check at any time to avoid overcorrected.
Correction method for unequal diagonals of square ends
Correction method for unequal diagonals of square ends

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2 thoughts on “3 Important Facts That You Should Know About Manual Bending

  1. Nicole says:

    good article, I have learned a lot about manual bending. Thanks

    1. Mayo says:

      my pleasure.Hope we could help you solve some trouble with bending.

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