As a seasoned professional in metal fabrication, I frequently encounter issues related to bent parts. Understanding what the common defects of bent parts are is essential for ensuring high-quality production and minimizing waste. In this article, I will discuss the typical defects we face, such as warping, cracking, and incorrect angles, and explore their causes. By identifying these issues early in the process, we can implement effective solutions and improve our bending techniques. Join me as we dive into the common defects that can impact the integrity of bent parts and how to address them effectively.

Common defects and process measures for Bent Parts

⒈Bending fracture：After shearing or blanking, the material often has burrs or fine cracks on the edges. When bending, it tends to form stress concentration and is broken. The following figure shows that the workpiece is fractured when the workpiece is fractured, and the cracking position occurs in the shearing of the workpiece. Belt and rolling belt.

The technical measures taken for this are:

①The workpiece after shearing or punching is guaranteed to be cut in the direction of bending, that is, under pressure, as shown in the figure, the forming effect is better.

②The workpiece is deburred before bending, and the bend can be ground with a manual grinder.

⒉ Rebound：During the bending process of the metal material, both plastic deformation and elastic deformation exist simultaneously. At the end of the bend, a rebound occurs due to the recovery of the elastic deformation, as shown. The rebound phenomenon directly affects the dimensional accuracy of the workpiece and must be controlled.

The technical measures taken for this are: 

①Angle compensation method. If the workpiece is bent at an angle of 90°, the lower opening angle of the bending machine can be selected as 78°.

②The pressurization duration increases the correction method. At the end of the bending, the pressure correction is performed to extend the contact time between the upper mold and the lower groove of the bending machine, so as to increase the degree of plastic deformation at the rounded corner of the lower groove, so that the rebound tendency of the fiber in the tension and compression zone resists each other, thereby reducing the rebound. 

⒊ Bulge：For the bending of the medium-thick plate (thickness t≥6mm), the situation is special. The fiber structure becomes longer during the bending process in the vicinity of the bending line, causing the convex portion to form a convexity at the rounded corner, and by observing the workpiece in the workshop, The size of the rounded protrusions increases as the thickness of the plate increases. For some workpieces with high-quality requirements, the rounded protrusions will affect the dimensional accuracy of the welding or assembly and need to be removed by technological measures.

The technical measures taken for this are:

① If the hot cutting equipment is used for cutting, the craftsman will make the inward concave arc centering on the bending line with the bending line as the center, and remove the excess sheet, as shown in the figure, where R is the arc. radius. 

② For workpieces that have not been subjected to sheet metal cutting, the bent parts is manually ground to the required dimensional accuracy after the bending is completed. If the assembly accuracy is high, the workpiece needs to be milled.

⒋Slide：

① Case 1: The bending line and the edge line of the workpiece are not parallel when the workpiece is to be bent, that is, one end has a fulcrum on the lower groove of the bending machine, and the other end has no fulcrum. The workpiece is shown in the figure, where L is the length of the kerf. 

②Case 2: The bend line of the bend to be bent is parallel to the edge line of the bent parts, but there are no fulcrums on the lower groove of the bender at both ends.

The technical measures taken for this are:

① Increase the kerf processing.

For case 1: the craftsman adds a slit to the blanking line along the direction of the workpiece bending line, the length of which is the workpiece: the bending line is outwardly offset, and the offset width is half of the width of the lower groove of the bending machine.

②Increase margin processing.

For Case 2: The craftsman increases the size of the blanking map so that the edge has a fulcrum on the lower groove of the bending machine to satisfy the bending. After the bending process is completed, the cutting allowance is processed according to the product drawing, and the cutting mouth is trimmed to meet the product quality requirements.

⒌ Indentation or scratching：When the workpiece is bent, it is pressed by the upper die and the lower groove of the bending machine, and there are different degrees of indentation or slip. Generally, the surface roughness of carbon steel parts is not high, and slight flaws do not affect them.

①For the carbon steel material, increase the width of the lower groove to increase the radius of the forming fillet and reduce the extrusion of the lower groove to the workpiece.

②For special stainless steel materials, prepare for the bending before the bending, and lay the paper on the lower groove of the bending machine. If both sides of the workpiece need protection, the workpiece can also be separated in the direction of the bending line. If there are better production conditions, the anti-indentation pad can be used.