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Tube Bending Tech: In-depth Q&A

1. What is steel?

Answer: Steel is an iron-carbon alloy with a carbon content less than 2.11%.

2. What is high carbon steel?

Answer: High carbon steel is steel with a carbon content greater than 0.6%.

3. How many categories can steel be divided into based on its usage?

Answer: It can be divided into structural steel, tool steel, and special-purpose steel.

4. How many types of steel are there based on edge shape?

Answer: It can be divided into plates, tubes, profiles, and wires.

5. What are the two main methods for steel deformation correction?

Answer: There are cold work correction and heat correction.

6. How many types of cold work correction methods are there?

Answer: There are manual correction and mechanical correction.

7. What types of heat correction are there?

Answer: There are full heat correction and partial heat correction.

8. How many shapes are there for the heating area of the partial heat correction?

Answer: There are three shapes: point, line, and triangle.

9. What kinds of deformation can angle steel have?

Answer: There are twisting, bending, and angle deformation.

10. What kinds of deformation can channel steel have?

Answer: There are twisting, bending, and flange local deformation.

11. What is cold work correction?

Answer: Correction carried out at room temperature is called cold work correction.

12. What is bending forming?

Answer: Bending forming is the process of bending the blank to the desired shape.

13. What is plasticity?

Answer: Plasticity is the ability of a metal material to undergo permanent deformation without breaking under external force.

14. What is toughness?

Answer: Toughness is the ability of a metal material not to be destroyed under impact load.

15. What is bending forming?

Answer: Bending forming involves bending a flat blank, profile, or tube to a certain angle and curvature to form a part of a certain shape.

16. What is springback phenomenon?

Answer: During bending, the material undergoes elastic deformation. Once the external force is removed, the part of the elastic deformation restores to its original state, causing changes in the shape and angle of the bent part.

17. What factors affect bending forming?

Answer: The factors include bending force, springback phenomenon, minimum bending radius, and cross-sectional shape.

18. How to determine the size of the bending force?

Answer: It is determined by the mechanical properties of the material being bent, the bending method, and the shape of the bent part.

19. What factors influence bending springback?

Answer: These factors include the mechanical properties of the material being bent, the relative bending radius of the material, bending angle, and some other factors.

20. What factors affect the minimum bending radius?

Answer: These factors include the mechanical properties of the material being bent, the bending angle, the bending direction of the material, the surface quality of the material, the quality of the sheared surface, and other factors.

21. What factors influence the change in cross-sectional shape during bending?

Answer: Primarily, these are relative bending radius, cross-sectional geometry, and bending method.

22. What measures are often taken to resolve spring back issues when using contact bending?

Answer: Correcting the mold shape, applying pressure correction method, adding flange devices, and reducing mold clearance.

23. What is press bending?

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Answer: It is a manufacturing process where bending molds are used on a press machine.

24. What types of bending deformation exist in material?

Answer: There are free bending, contact bending, and corrective bending.

25. What is roll bending?

Answer: It is a manufacturing method of bending formation on a rolling machine.

26. What forms of material deformation occur during press bending?

Answer: These include free bending, contact bending, and corrective bending.

27. What factors influence the changes in the cross-sectional shape of the material during bending?

Answer: Factors are relative bending radius, cross-sectional geometry, and bending method.

28. What are the main steps in manual tube bending?

Answer: These include marking out, sand filling, and heat bending.

29. What is referred to as the minimum bending radius?

Answer: The smallest limit at which a material can be bent without the risk of damage or breakage is referred to as the minimum bending radius of that material.

30. How would you explain the neutral layer?

Answer: During material bending, the outer layer is stretched, and the inner layer is compressed. The transition layer on its cross-section, which is neither stretched nor compressed and where the stress equals zero, is known as the neutral layer.

31. What is spring back?

Answer: The phenomenon of material returning to its original shape due to its elasticity after the external force is removed during the bending process is known as spring back.

32. What is drawing?

Answer: It is a stamping process using a press machine and corresponding molds to make open hollow parts from sheet metal.

33. What is a drawing ratio?

Answer: The ratio of the cross-sectional area of the material after each draw to the cross-sectional area before the draw is called the drawing ratio. The drawing ratio actually reflects the degree of deformation of the drawn part.

34. What types of external forces can cause deformation in structural parts?

Answer: These include bending forces, torsion forces, impact forces, tensile forces, and compressive forces.

35. What can external forces cause inside a component? What might remain when the external forces are removed?

Answer: External forces can cause internal forces within a component. When the external forces are removed, some internal stress may remain.

36. Does the degree of cross-sectional deformation during tube bending depend on the values of relative bending radius and relative wall thickness?

Answer: Yes.

37. When bending a tube, if the relative bending radius and relative wall thickness values are larger, does that mean the deformation is greater?

Answer: No.

38. If the curvature of the bent pipe is not enough, but it’s close, can one increase the curvature by cooling the outside of the pipe with water to contract the inside metal?

Answer: Incorrect.

39. In general field pipe bending, when the roundness requirement for the bending deformation cross-section is not very strict, is it often the case that no anti-deformation device is installed for coreless bending?

Answer: Incorrect.

40. Are pipe bending machines divided into mechanical transmission and gear transmission types based on the transmission method?

Answer: Incorrect.

41. There are two stroke switches on the pipe bending machine, which control the required bending length by adjusting the position of the stop blocks, right?

Answer: Correct.

42. The features of a hydraulic pipe bending machine are smooth transmission, reliability, low noise, compact structure, and capability to bend different pipe blanks, correct?

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Answer: Incorrect.

43. What are the two main categories of roll bending machines?

Answer: Vertical and horizontal types.

44. Horizontal roll bending machines are divided into three-axis and four-axis types, what are the two types of three-axis?

Answer: Symmetric and asymmetric types.

45. When bending a pipe, what force does the material on the outer side of the neutral layer experience that causes the pipe wall to thin? What force does the material on the inside experience that causes the pipe wall to thicken?

Answer: The material on the outer side experiences tensile stress, which thins the pipe wall, and the material on the inside experiences compressive stress, which thickens the pipe wall.

46. When bending a pipe, due to its ring-shaped cross-section and insufficient rigidity, what is likely to happen when it is bent in a free state?

Answer: It is likely to flatten and deform.

47. What are the main steps in manual pipe bending?

Answer: The main steps are sand filling, marking, heating, and bending.

48. When bending a pipe blank with a seam, where should the seam ideally be positioned?

Answer: At the neutral layer.

49. What test must be conducted on the bent part of the pipe, and what should be checked for?

Answer: A pressure test must be conducted to check for leakage.

50. How does an asymmetric three-roll shaft round machine eliminate the straight head at the start?

Answer: In an asymmetric three-axis round machine, the straight head is only at the start of the workpiece. Simply roll the workpiece over after the first round, and the straight heads at both ends can be eliminated.

51. What does mechanical performance include?

Answer: It includes strength, hardness, plasticity, toughness, fatigue strength, and others.

52. What is deformation?

Answer: It refers to the change in shape and size of metal materials under the influence of external forces.

53. What types of deformation can metal materials undergo?

Answer: They can undergo tension, compression, bending, twisting, and shearing.

54. What is the elastic limit?

Answer: It refers to the maximum force a material can withstand in the elastic phase.

55. What is the hardness of a material?

Answer: It is the ability of a material to resist the penetration of other objects into its surface.

56. What are the different ways to express hardness?

Answer: There is Brinell hardness, Rockwell hardness, and Vickers hardness.

57. What is the processability of metal materials?

Answer: It refers to whether the properties of metal materials are easy to process and shape.

58. What does the processability of metals include?

Answer: It includes castability, weldability, forgeability, machinability, and heat treatment capability.

59. What is alloy steel?

Answer: It is a type of steel that intentionally adds some alloying elements to carbon steel to improve certain mechanical properties of the steel.

60. What are the types of alloy steel?

Answer: They are classified into alloy structural steel, alloy tool steel, and special-purpose steel.

61. What is the minimum bending radius?

Answer: It is the smallest radius to which a material can be bent without causing damage.

62. What are the common methods to reduce springback in bent parts?

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Answer: There are methods such as the die modification method and overbend correction method.

63. What are the factors that affect the minimum bending radius of a material?

1. The mechanical properties and heat treatment state of the material
2. The bending angle of the workpiece
3. The geometric shape and size of the material
4. The bending direction
5. Other aspects, such as the thickness of the material, the quality of the surface and side, etc.

64. How is the neutral layer of a material defined during bending?

Answer: During the bending process of the material, the outer layer is stretched, the inner layer is compressed, and there must be a transition layer on its cross-section that is neither stretched nor compressed, where the stress is almost zero. This transition layer is called the neutral layer of the material.

65. There are many types of mandrels for bending with a mandrel, including round-head, sharp-head, hook-style, and which other types?

Answer: And unidirectional joint style, universal style, etc.

66. What is free bending, and what method does it use on a bending machine to control what kind of deformation in the bending process?

Answer: Free bending is a method that does not use a mandrel and uses an anti-deformation process on a bending machine to control the deformation of the bending cross-section.

67. When the bending radius of a tube is more than how many times the diameter, is free bending generally used?

Answer: More than 1.5 times.

68. What is extrusion bending, and how does it form the bend in the tube?

Answer: Extrusion bending is the process of pressuring the tube blank onto a mold with a bend at room temperature to form a tube elbow.

69. During extrusion bending, in addition to the moment of the bending force, what other forces does the tube blank experience?

Answer: The tube blank also experiences axial and frictional forces in the opposite direction to the axial force.

70. How can the ovality of the cross-section be reduced when bending a tube?

Answer: To reduce the ovality of a tube’s cross-section during bending, common methods include filling the tube with a filler material, applying a conical groove roller on the outside of the tube, or inserting a mandrel into the tube.

71. What are the advantages of a spoon-type mandrel?

Answer: The spoon-type mandrel has a larger external support surface which provides superior anti-flattening effects compared to a pointed type. It prevents surface wrinkling during tube bending, is relatively easy to manufacture, and thus is widely used.

72. What types of transmission are there in a tube bending machine?

Answer: Mechanical and hydraulic transmissions are used in tube bending machines.

73. What is the main cause of tube cracking?

Answer: Tube cracking is primarily caused by excessive clamping force.

74. What is the main reason for the cross-section of the bend to become elliptical during mechanical cold bending of a tube?

Answer: Insufficient counter-bending and better plasticity allow for a smaller deep drawing ratio.

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