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Manual bending of pipe material

Manual bending is to use a simple bending device to bend the tube blank. According to whether the pipe is heated or not, it can be divided into cold bending and hot bending. Generally, for small diameter (tube billet outer diameter D≤26mm) tube blanks, cold bending is often used due to the small bending moment; while for larger diameter tube blanks, hot bending is mostly used. Manual bending does not require special bending equipment, and the used bending device is relatively simple, low manufacturing cost, easy to adjust and use, but the disadvantage is that the labor is large and the productivity is low. Therefore, it is only suitable for single-piece small-batch production occasions without pipe bending equipment.

Method of pipe bending

For copper pipes with smaller diameters, manual free bending can be used. When bending, the copper tube should be annealed first, and then bend with the hand to shape it, and finally, the oblate shape produced by the bending should be trimmed to make the curved arc smooth and round. During operation, you must not bend a large degree of curvature at once, which is easy to produce a serious bending deformation and dead angle, which is not conducive to subsequent trimming, as shown in Figure (a).

Method and device for bending
Method and device for bending

For steel pipes with smaller diameters, a manual pipe bending device can be used for cold bending. Figure (b) is a bend using a turntable-type pipe bending device. Both the circumference of the turntable and the side of the iron is provided with arc grooves, the size of which can be designed according to the diameter of the pipe being bent. It can be used when the positions of the turntable and the iron are relatively fixed. When in use, insert the tube into the circular arc groove of the turntable and the iron, hook the tube blank with a hook, pull the handle according to the required bending position, and make the tube blank follow the handle to bend to the required angle.

Picture (c) is a manual pipe bending device in bending mode. The bending die is fixed while bending, and the pressing block rotates around the bending die to force the pipe to be formed according to the die. Since the manual bending tool is only used for bending pipes with a small diameter, there is no need to add filler materials to the pipes.

Figure (d) shows a fixed mode manual bending device, which is mainly composed of a platform 12, a fixed die 14, a roller 16, and a lever 15. During operation, the fixed mold is fixed on the platform, which has a semi-circular groove corresponding to the outer diameter of the tube blank. Before bending, first put one end of the tube blank 13 in the fixed mold concave box, and fix it with a pressure plate, and then pull the lever, the roller fixed on the lever (also has a semi-circular groove corresponding to the outer diameter of the tube blank). The tube blank is compressed, forcing the tube blank to bend and deform around the fixed die. When the required bending angle of the pipe is reached, the bending stops, thereby completing the bending process.

For pipes with larger diameters, because the torque required for manual bending is too large, the bending device shown in the figure can be used for hot bending. When bending, use a torch or an acetylene flame to locally heat the bend of the pipe. The heating temperature varies with the steel. Depending on the nature of the steel tube, it can be manually bent and formed when the steel tube is generally heated to make the steel tube appear fuchsia.

By replacing the turntable 3, bending mold 10 and fixed mold 14 with different diameters in the above manual bending device, the bending of different pipe bending radii can be completed. Similarly, the forming of the turntable 3, bending mold 10 and fixed mold 14 can be replaced or improved For the cavity, the manual bending device in the picture is also suitable for manual bending of bars and profiles.

Tube bending operation

  • Correct selection of filling materials. In order to prevent the pipe from deforming under pressure, for the bending of the pipe with a diameter greater than 10mm or with a higher shape requirement, the pipe must be filled with material. The selection of filling materials should be determined according to factors such as pipe material, relative thickness, and bending radius, as shown in the table below. Among them, the sand-filled elbow is the most widely used hot bending method.
Tube materialFilling material in tubeCurved requirements
Steel PipeOrdinary yellow sandAfter the yellow sand is fully roasted and dried, it is filled into the tube for hot bending or cold bending
General pure copper tube, brass tubeLow melting point compounds such as lead or rosinThe copper tube is annealed and then filled with cold bending. It should be noted that the lead must be strictly prevented from dripping during hot melting to avoid splashing and injuring people.
Thin-walled pure copper tube, brass tubeWaterAfter annealing the copper pipe, it is poured into water and frozen and cold-bent.
Plastic pipeFine yellow sand (not filled)Cold bend quickly after warming and softening
The choice of filling material in the tube when bending the tube
  • The operation points of hot bending. When the manual bending device is used to heat the bending pipe, the operation process mainly consists of four processes: sand filling, scribing, heating, and bending. The main points of operation are as follows.
  1. Filling sand. When manually bending the pipe, to prevent the distortion of the pipe section, it is usually necessary to fill the pipe blank with filler. Commonly used fillers include quartz sand, rosin, and low melting point alloys. For pipes with larger diameters, sand is generally used. Before filling the sand, plug one end of the tube blank with a tapered wooden plug, and an air vent is opened in this game to allow the air in the tube to escape freely when it is heated and expanded. After sand filling, the other end of the tube blank is also plugged with a cork. The sand in the pipe should be clean and dry and must be washed with water, dried, and sieved before use. Because the sand contains impurities and moisture, the decomposition products of the impurities will contaminate the pipe wall when heated. At the same time, the volume expands when the moisture becomes gas, which increases the pressure and even pushes out the end plug. The particle size of sand is generally below 2mm. If the particles are too large, it is not easy to fill tightly, and the tube blank will be easily deformed when the tube is bent; if the particles are too small, the filling is too tight, and it is not easy to deform during bending, or even break the tube.
  2. Scribing. The purpose of scribing is to determine the length and position of the tube billet heated in the furnace. The heating length of the tube blank can be determined by the following method: First, determine the midpoint of the bending part according to the size of the pattern, and measure the bending length to both sides of the tube blank, and then add the diameter of the tube blank.
  3. Heating. After the billet is filled with sand and scribed, it can be heated. Heating can be made from charcoal, coke, coal gas, or heavy oil as fuel. The medium used for ordinary boiler protection is not suitable for heating pipe billets, because coal contains more sulfur, and sulfur will penetrate the steel at high temperature, which will deteriorate the quality of steel. If limited by conditions, it can also be used. The oxygen-acetylene gun is used for local heating. Regardless of the heating method used, the heating should be slow and uniform. If the heating is improper, it will affect the quality of the elbow. The heating temperature depends on the properties of the steel. The heating temperature of ordinary carbon steel is generally around 1050°C. After the tube billet is heated to this temperature, it should be kept for a certain period of time so that the sand in the tube can reach the same temperature to avoid the tube billet from cooling too fast. The bending of the tube blank should be completed as soon as possible after heating. If the number of heating is increased, the steel tube’s quality will have deteriorated, but the thickness of the oxide layer will be increased and the tube wall will be thinned.
  4. Uốn. The billet can be taken out and bent after heating in the furnace. If the heating part of the tube blank is too long, the unnecessary heated part can be watered and cooled, and then the tube blank is placed on the tube bending device for bending. After the tube blank is bent, if the bending radius of the tube is not up to the requirements, the following methods can be used to adjust: if the bending curvature is slightly smaller, water cooling can be used inside the bend to shrink the inner metal; if the bending curvature is slightly larger, water cooling can also be used on the outside of the bend, So that the outer metal shrinks.

Precautions for pipe bending operation

  • The bending radius of the pipe material cannot be too small. When the pipe is cold-bent, the bending radius should be greater than 4 times the pipe diameter, but the bending radius should not be too small, otherwise it will be easy to crack during bending. The minimum bending radius value can be selected according to the table
Pure copper and brass tubeAluminum tubeSeamless steel tube
Tube outer diameter DMinimum bending radius R(min)Tube wall thickness tTube outer diameter DMinimum bending radius R(min)Tube wall thickness tTube outer diameter DMinimum bending radius R(min)Tube wall thickness t
5.0101.06.0101.06.0151.0
6.0101.08.0151.08.0151.0
7.0151.010151.010201.5
8.0151.012201.012251.5
10151.014201.014301.5
12201.01.6301.516301.5
14201.020301.518401.5
Stainless steel pipeStainless seamless steel pipeRigid PVC pipe
Tube outer diameter DMinimum bending radius R(min)Tube wall thickness tTube outer diameter DMinimum bending radius R(min)Tube wall thickness tTube outer diameter DMinimum bending radius R(min)Tube wall thickness t
14182.06.0151.012.5302.25
18282.08.0151.015452.25
22502.010201.525602.0
25502.012251.530803.0
32602.514301.5321103.0
38702.516301.5401503.5
45902.518401.5511804.0
The minimum radius value of various pipes
  • The sequence of operations for multiple bending of the pipe material. When the pipe material is bent, it should be noted: if there are several places on the same pipe that need to be bent, the part closest to the pipe end should be bent first, and then the other parts should be bent in order; if the pipe is a space-bending part (that is, several bending parts The bending direction is not in the same plane of the pipe fittings), then a bend should be bent on the platform first, and one end of the subsequent pipe fittings must be tilted and positioned before other parts can be bent in order.
  • Bending of welded pipe. When the welded steel pipe is bent, the pipe seam should be placed in the neutral layer of the bend to prevent cracking at the pipe seam, as shown in the figure.
Bending of welded pipe
Bending of welded pipe

Manual bending of profiles

Like the manual bending of pipe materials, various section steels (such as flat steel, angle steel, channel steel, round steel, etc.) can also be manually bent using appropriate manual bending devices, but because the section materials have thicker materials and greater rigidity Because of its structural characteristics, manual bending of profiles usually requires the use of molds and hot bending processing methods. The manual bending method of angle steel is shown in the figure. After the angle steel is heated, it is stuck on mold 1 to bend inward, and at the same time, hit the horizontal edge with a sledgehammer to prevent it from lifting [see figure (a)]. Outward bending [see figure (b)] heats the shaded area of the figure to prevent the horizontal edge from sinking, and at the same time hit the facade with a sledgehammer (see section A-A) to prevent the angle from becoming smaller and the horizontal surface from warping. For profiles with a large cross-sectional area, it is difficult to manually bend them even if hot bending is used. In this case, only mechanical bending can be used. The following describes the manual bending of profiles through two examples.

Manual bending of profiles (1 is a die)
Manual bending of profiles (1 is a die)

Manual bending of round flat steel ring

Flat steel is one of the common profiles. Because of its thick material, manual bending needs to be made with molds for bending. The designed flat steel rim mold is shown in the figure.

Round flat steel rim mold
Round flat steel rim mold
  • The design principles and characteristics of the mold. In order to make the shape of the flat steel ring meet the design requirements, the tire bottom plate 1 and the tire plate 2 are designed to be round in the mold, and the diameter of the tire plate 2 should be increased by a certain amount of shrinkage in consideration of the shrinkage after cooling (according to the material The shrinkage rate is increased by 0.1%~0.2% of the diameter), and the edges and holes must be machined to improve the structural accuracy. The thickness of the tire plate 2 should be 1~1.5mm larger than the thickness of the bent flat steel, and its purpose is to contain the red hot flat steel.

In addition, roller 8 must be machined to improve the structural accuracy and the quality of the flat steel ring. It is designed in the form of an I-beam with a large upper part and a small lower part. The main purpose is to make the structure strong enough to make the flat steel ring lean on the tire. The height of the groove should be greater than the height of 1, 2 plates, and 1~1.5mm. The inner plane of the upper wing plate plays the role of anti-wrinkle rolling, the upper and lower wing plates jointly play a guiding role, and the inner plane of the web plays a role of roll forming.

The fixed pressing plate 10, the nut 11, and the crank 12 are matched with compressed flat steel to prevent the flat steel from twitching and shifting during simmering.

In order to eliminate the straight section of the flat steel ring and become a full circle, holes 1 and 2 are designed.

  1. Heat the lower flat steel material in the furnace to an orange color, 900~1000℃, and braise it slightly.
  2. Fix the fixed pressure plate 10 at the position of hole 1, close it with the roller 8, quickly pass through the flat steel end, press it tightly, and then turn the handle 3 to bend. When it is turned close to the fixed pressure plate 10, The two ends are overlapped to eliminate the straight section, and the fixed pressing plate 10 is quickly moved to hole 2 and fixed, and the bending is continued until the head and the tail overlap and cannot move forward.
  3. Remove the fixed pressing plate 10, take out the flat steel ring with the blank, and divide the overlapped part to obtain the pure round flat steel ring.

Manual bending of the question mark ring

The picture shows the central question mark-shaped ring, which is made of round steel with a diameter of 420mm. Because the production batch is not large, it is generally made by hand bending with a mold.

Question mark ring
Question mark ring
  1. The design of the mold. According to the size given in the figure, in order to ensure that the diameter of the middle hole is equal to 40mm, the shaped cylindrical pin should be a fixed structure, the right cylindrical pin can be a fixed or movable structure, and the left side must be a movable cylindrical pin. The distance should be larger than the circle, the steel diameter is 2~3mm.
  2. The method diagram (a) in the case of bending the eccentric ring. Insert the round steel between the central cylindrical pins and bend the eccentric ring from position 1 to 2 in the direction of the arrow. Figure (b) is the center ring that is bent into the design requirement. Arrow 2 is reported to the position of 3. At this time, the cylindrical pin is inserted into the left hole, and the round steel is pulled from 3 to 4, and the ring can be bent. to make.
The mould of the question mark ring (1-4 is the bending sequence)
The mold of the question mark ring (1-4 is the bending sequence)

Manual groove system of small truncated cone

The truncated cone is also a fan-gold component that is often encountered in production. Its elementary line is radial, with a small distance between the small ends and a large distance between the large ends. Generally, large-scale truncated cones are formed by bending the surface with a plate rolling machine, and small-sized truncated cones are generally formed by manual grooves when the sheet material is thinner and cannot be bent by the rolling machine. Similarly, for the convenience of groove system and assembly, it is generally formed into two halves and then welded together. When the height is less than 100mm and a beautiful appearance is required, it can also be made into a single piece, which is then grooved and welded to form.

Làm khuôn

The mold of the hand-grooved truncated cone can be made of straight channel steel or radial orifice. The former has more defects and the latter has fewer defects. Generally, the taper of the mold made should be the same as The taper of the frustum is the same, and the same taper is helpful to improve the quality of the part, and there are fewer defects, and the difference is not conducive to the improvement of the quality of the part, and there are more defects. Figure 1-1 shows the mold form of a small truncated cone made by hand groove.

1-1 Small truncated cone and its mold
1-1 Small truncated cone and its mold

Figure 1-1 (a) is the part drawing of the small truncated cone, and Figure 1-1(b) is the radial mold made. The mold is placed radially with round steel, and the length of the round steel is according to the length of the frustum element line. Add 50~100mm margin to determine, its length l==242mm (120mm is the outer radius of the big mouth, 85mm is the outer radius of the small round mouth, 240mm is The height of the cone); the distance between the small end of the mold can be large or small, but the maximum cannot exceed the diameter of the small end of the cone. In this example, 70mm. The opening spacing n of the large end is equal to the diameter of the large and small ends of the mold. The ratio is determined, that is, n:70=240:170, so n=90mm. Figure 1-1 (c) and (d) are the calculation principles of the diameter of the round steel used in the mold. There are two principles for determining the diameter of the round steel: one is to maintain a certain distance between the frustum and the bottom plate after forming; the other is the circle Steel has a certain rigidity. Since the radii of the forming arcs at both ends of the size are not equal, the distance between the arc and the bottom plate should be calculated separately. Assuming that ∅20mm round steel is used, the distance between the bottom of the small end part and the bottom plate after forming is  l1=20-(8-)=12mm, of which 35mm is the radius of the small end of the mold, as shown in Figure 1-1(c). Similarly, the distance between the bottom of the part at the large end and the bottom plate after forming is l2=20-(120-)=9mm, of which 49.5mm is the radius of the large end of the mold, as shown in Figure 1-1(d), so it is reasonable to take ∅20mm for the diameter of the round steel.

Manual groove method

The manual groove-making method of the truncated cone is basically the same as the arc part of the small sky-circle local pipe. The forming method is mostly done by using a sledgehammer and a grooved arc hammer and then radiating the mold. The groove-making process follows “the two ends first, then the middle, step by step”. The principle of “from shallow to deep” is carried out, and at the same time, the curvature should be checked at any time with the template.

Correction method of groove system defect

  • Outer peach shape. Figure 1-2 (a) shows the three-dimensional shape of the two mating ports forming an outer peach shape. The reason is that the upper arc shape is not enough when the groove is made (especially the end). Figure 1-2(b) and (c) respectively show the correction methods. Figure 1-2(b) is to correct the upper arc from the outside of the cone, and Figure 1-2(c) is to correct the upper arc from the inside of the cone.
1-2 Correction of outer peach shape
1-2 Correction of outer peach shape
  • Inside peach shape. Figure 1-3 shows the three-dimensional shape of the inner peach shape formed by the two mating parts. The reason is that the upper end of the groove is arced or the pre-bend is arced. Figures 1-3 (b) ~ (d) are respectively shown The method of correction. Among them: Figure 1-3 (b) is the lining hammer method, that is, the lining hammer is placed at the arc, and the force hammer is hit on the edge. It can be corrected by moving while hitting, but it should be noted that the distance between the force point and the force fulcrum should be small ( But it cannot be overlapped); when the plate thickness is large and rigid, it can be operated by two people, and when the rigidity is small, it can be completed by one person. Figure 1-3 (c) shows the cantilever arc discharge method. While setting the arc, you should check with a template at any time, and try not to overcorrect it. This is because the upper arc is more difficult than the arc discharge. Figure 1-3 (d) is the method of suspending the arc on the platform. Make the part of the arc that is too large contact the platform, suspend the side of the mouth, hit the edge hard, that is, it will be corrected, and the hammer must be evenly applied to prevent sharp bends and The edges are not straight.
1-3 Correction of inner peach shape
  • The small end gap is large and the overall length is partially convex. Figure 1-4 (a) shows that the arc at the big end is just right, and only the arc at the small end is short, thus forming a three-dimensional shape with a large gap at the small end. Figure 1-4(b) shows the other parts of the arc are just right, but there are three-dimensional shapes of convex defects in the direction of the local plain lines. These two defects are of the same nature, so the treatment methods are the same. Figure 1-4 (c) shows the arc method from the outside. Figure 1-4 (d) shows the arc method from the inside. For Figure 1-4(a), the upper arc is limited to the small end, and the length must not exceed half of the frustum, otherwise, it will affect the arc of the big end. For Figure 1-4(b), the upper arc can be partially long, either inside or outside.
1-4 Correction of large gaps at the small end and local concave
1-4 Correction of large gaps at the small end and local concave
  • The large end gap is large. Figure 1-5 (a) is a three-dimensional shape with a large gap between the large end of the other pair after spot welding on one side. The reason is that the partial arc at A in the figure is caused by the lack of arc, and the small end is lower by a value e. Figure 1-5(b) shows that the arc of the small port is just right, and the arc of the large end is generally short, so there is a gap between the large end. The reason for the formation of the two is the same, so the treatment method is the same. Figure 1-5(c) shows the method of arcing from the outside. Figure 1-5(d) shows the method of arcing from the inside. But it should be noted that the length of the upper arc must not exceed half of the plain line, otherwise, it will affect the arc at the small end. When dealing with the defect in Figure 1-5(a), only the partial arc of A is required, and its length must not exceed half of the plain line. When the arc is adjusted, the misalignment at the small end will naturally disappear.
1-5 Large end gap correction
1-5 Large end gap correction
  • The whole arc passes or the partial arc passes through the long arc. Figure 1-6(a) shows the arc of the left fan, resulting in a three-dimensional shape with four corners inside and two upper corners high. Figure 1-6(b) shows a partial long arc along the direction of the element line, which results in a three-dimensional shape with a large gap between the mouths. The reasons for the formation of the two are the same, so the treatment methods are the same. Figure 1-6(c) shows the correction method of placing the convex surface on the platform or the ground and hammering along the full length line. In order to improve the arc release efficiency, you can press it with one foot before hitting hard This can prevent springback and improve the correction effect. Samples should be checked at any time during the correction process to prevent letting go, because the arc forming is more difficult than the arc release. Figure 1-6(d) shows the correction method of partial long arc passing, and the operation is the same as that of Figure 1-6(c). Figure 1-6 (e) shows the cantilever type arc prevention method, which can be used for the correction of partial long arcs. During operation, one person should hold the handle firmly and one person should hit the hammer to prevent bounces from injuring people.
1-6 Correction of overall arc over or partial long arc over
1-6 Correction of overall arc over or partial long arc over
  • The upper end covers the lower end and the gap is large. Figure 1-7 is a three-dimensional shape with a large gap between the upper and lower ends. The reason is that the upper-end A is partially arced, and the lower-end B is partially arced. As a result, the upper end is over-covered and raised, and the lower end has a gap and moves out. . The correction can use the arc up and arc methods are shown in Figure 1-5 and Figure 1-6. Through correction, the upper corner of part A will drop, the lower corner of part B will move inward, and the upper corner will rise, and the defect will be eliminated.
1-7 Correction of large gap between the upper end and the lower end
1-7 Correction of large gap between the upper end and the lower end
  • The side of the mouth is not straight. Figure 1-8 (a) is a three-dimensional shape with uneven edges or partial unevenness. The main reason is the uneven hammering force when pre-bending the head. Figure 1-8(b) is a schematic diagram of the correction with the lining hammer method. Also to improve the correction effect, the lining hammer should be lined near the bump to be hit. The hammer should be close to the supporting point. The closer the better, the closer the distance is, the greater the correction force. , But not overlapping. In addition, the contact surface of the force hammer and the lining hammer should be as small as possible during operation. The contact with the hammer edge is much stronger than the contact with the full hammer surface. Figure 1-8(c) is a schematic diagram of the platform suspension method correction. The uneven or convex edge of the board touches the platform, and the bump is hit with a hammer to correct the defect.
1-8 Correction of mouth not straight
1-8 Correction of mouth not straight
  • There is a gap at the big end (or little end). Figure 1-9(a) shows the three-dimensional shape with a gap at the large end of the two pieces after spot welding. The reason for this defect is that the small-end arc is just right and the large-end arc is insufficient. Figure 1 can be used. -5’s upper arc method is solved; you can also spot weld the small port first. Spot weld the two angle sheets of steel at the position with a large gap and draw them together with bolts [see Figure 1-9(a)]; you can also squeeze the large port to make it close [see Figure 1-9(b)]. During operation, attention should be paid to spot welding the small port firmly. It must be firm and not too long. Too short and insufficient strength, leading to cracks in the weld and waste of previous efforts; too long will increase the tensile force of the bolt. When tightening the bolt, check the deformation of the upper spot weld at any time to see if there are cracks and scale peeling. If there is, it should be a timely deal. The treatment method is first to spot weld a small spot on the easily falling apart, and then spot weld another spot after it is completely cold. Do not strengthen the spot welding at a time. This will increase the thermal toughness of the weld and cause the weld to crack.
1-9 Correction of gaps at the small or big end
1-9 Correction of gaps at the small or big end
  • Distortion. Figure 1-10 (a) is a three-dimensional view with one arc just right and the other twisted. The reason for the distortion is mainly due to the improper mold used or not made according to the direction of the frustum. As shown in Figure 1-10 (a), because the upper corner of side A is lower and shifted inward, the lower corner is shifted out, the upper corner of side B is higher and higher, and the lower corner is shifted inward and upward, causing distortion. Figure 1-10(b) is a schematic diagram of the correction of the hanging hammering method. Place side A in the platform, the upper corner is pressed by the platform board, and side B hangs outside the platform, hit the upper corner of side B with a hammer to make it Move it down, and the distortion can be corrected. Figure 1-10(c) is a schematic diagram of the reversing groove arc correction method, that is, the reversing groove system is carried out in a direction about 90° to the original groove system direction, and the upper corner point of side A and the lower corner point of side B are moved outward. The lower corner point of side A and the upper corner point of side B is retracted, and the distortion can be corrected. Figure 1-10 (d) is a schematic diagram of the pressure bar correction method. Place the upper corner point of side B under the pressure bar, and place the lower corner point of side A on the ground (not easy to slide on the ground), with a heavy object as a fulcrum. After the pressure bar is applied, the distortion is smoothly corrected. Figure 1-10 (e) is a schematic diagram of the correction of the bolt drawing method. Figure 1-10(f) is a schematic diagram of the correction of the pad pressing method. When correcting, pay attention to pad a thick plate at the lower end of the non-distorted plate, so that the twisted and raised points have a lower body space. This method is simple and easy to implement, and the use effect is better. Well, it is widely used in production.
Distortion correction
1-10 Distortion correction

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  1. Muhammad viết:

    Professional article! so effective!thanks

    1. Mayo viết:

      thanks for your trust and support.

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