Brief introduction of sheet metal processing technology
1 Introduction
1. 1 Introduction
According to the basic processing methods of sheet metal parts, such as blanking, bending, stretching, forming and welding. This specification describes the technological requirements that should be paid attention to in each processing mode.
1.2 Keywords
Sheet metal, blanking, bending, stretching, forming, layout, minimum bending radius, burr, springback, dead edge and welding.
2 blanking
According to the different processing methods, blanking can be divided into ordinary punching, multiple punching, shearing machine cutting, laser cutting and gas cutting. Because of the different processing methods, the blanking processing technology is also different. The blanking methods of sheet metal mainly include punching and laser cutting.
2. 1 Punching is processed by numerical control punching machine. The processing range of plate thickness is cold-rolled plate, hot-rolled plate is less than or equal to 3.0mm, aluminum plate is less than or equal to 4.0mm and stainless steel is less than or equal to 2.0 mm.
2.2 There is a minimum size requirement for punching holes.
The minimum size of punching hole is related to the shape of hole, the mechanical properties of material and the thickness of material.
Figure 2.2. 1 Example of punching shape
Diameter of circular hole of material B and width of short side of rectangular hole B.
High carbon steel1.3t1.0t.
Low carbon steel and brass 1.0t0.7t
Aluminum 0.8t0.5t
* t is the material thickness, and the minimum punching size is generally not less than1mm.
* See the list of common company materials corresponding to high carbon steel and low carbon steel in Appendix A of Chapter 7.
Table 1 List of Minimum Stamping Dimensions
2.3 Hole spacing and hole edge of several punches
The minimum distance between the punching edge and the shape of the part is defined according to the shape of the part and the hole, as shown in Figure 2.3. 1. When the stamping edge is not parallel to the shape edge of the part, the minimum distance should not be less than the material thickness t; Parallel, should not be less than1.5t.
Fig. 2.3. 1 Schematic diagram of hole edge and hole spacing of blanking parts
2.4 When stamping bending parts and drawing parts, a certain distance should be kept between the hole wall and the straight wall.
When stamping bent or stretched parts, a certain distance should be kept between the hole wall and the straight wall of the workpiece (Figure 2.4. 1).
Figure 2.4. 1 Distance between hole wall of bending parts and deep drawing parts and straight wall of workpiece
2.5 Through holes and countersunk seats for screws and bolts
The structural dimensions of screws, bolt holes and countersunk seats are selected according to the following table. For the countersunk head seat of countersunk head screw, if the plate is too thin to ensure the through hole d2 and countersunk head hole D at the same time, the through hole d2 should be ensured first.
Table 2 Through holes of screws and bolts
* require sheet metal thickness t ≥ h.
Table 3 Countersunk seats and through holes of countersunk screws
* require sheet metal thickness t ≥ h.
Table 4 Countersunk seats and holes of countersunk rivets
2.6 Laser cutting is a flight cutting process with a laser machine. The processing range of plate thickness is less than or equal to 20.0mm for cold-rolled plate and less than 10.0 mm for stainless steel ... Its advantages are large plate thickness, fast cutting speed of workpiece shape and flexible processing. Its disadvantage is that it cannot be processed and shaped, and the mesh parts should not be processed like this, and the processing cost is high!
3 bending
3. 1 Minimum bending radius of bending part
When bending the material, the outer layer is stretched and the inner layer is compressed in the fillet area. When the thickness of the material is constant, the smaller the internal R is, the more serious the tension and compression of the material will be. When the tensile stress of the fillet exceeds the ultimate strength of the material, cracks and fractures will occur. Therefore, the structural design of bending parts should avoid too small radius of bending fillet. The minimum bending radius of materials commonly used in the company is shown in the following table.
Minimum bending radius of serial number material
108、08F、 10、 10F、DX2、SPCC、E 1-T52、0Cr 18Ni9、 1Cr 18Ni9、 1Cr 18Ni9Ti、 1 100-H24、T20.4t
2 15、20、Q235、Q235A、 15F0.5t
325、30、Q2550.6t
4 1Cr 13, H62(M, y, Y2, cold rolled) 0.8t
545、50 1.0t
655、60 1.5t
765Mn、60SiMn、 1Cr 17Ni7、 1Cr 17Ni7-Y、 1Cr 17Ni7-DY、SUS30 1、0Cr 18Ni9、SUS3022.0t
The bending radius refers to the inner radius of the bending part, and t is the wall thickness of the material.
T is the thickness of the material, M is the annealed state, Y is the hard state, and Y2 is the hard state of 1/2.
Table 5 List of Minimum Bending Radius of Common Metal Materials in the Company
3.2 Height of straight edge of bending part
3.2. 1 Minimum straight edge height requirement in general
The height of the straight edge of the bending part should not be too small, and the minimum height should be (Figure 4.2. 1): h > 2t.
Figure 4.2. 1. 1 Minimum height of straight edge of curved part
3.2.2 Height of ruler with special requirements
If the design requires that the straight edge height h of the bent part is less than h≤2t, the height of the bent edge should be increased first, and then processed to the required size after bending; Or after machining a shallow groove in the bending deformation zone, bend it (as shown in the following figure).
Fig. 4.2.2. 1 Height requirements of straightedge under special circumstances
3.2.3 Height of straight edge with inclined surface at bending side
When there is a bent piece with an oblique angle on the side surface of the bent edge (Figure 4.2.3), the minimum height of the side surface is: h = (2 ~ 4) t > 3 mm.
Fig. 4.2.3. 1 Height of straight edge with oblique angle on bent edge side
3.3 Bend the hole edge on the component.
Hole edge: punch first and then bend, and the position of the hole should be outside the bending deformation zone to avoid hole deformation during bending. See the table below for the distance from the hole wall to the bending edge.
Table 6 Hole edges on bent parts
3.4 local bending process incision
3.4. 1 The bending line of the bending part should avoid the position where the size changes suddenly.
When bending an edge locally, in order to prevent stress concentration cracking at sharp corners, the bending line can be moved for a certain distance, leaving a sudden change in size (Figure 4.4. 1. 1 a), or opening a process tank (Figure 4.4. 1. 1 b), or punching a process hole (Figure 4.4.1b). Pay attention to the size requirements in the drawing: s ≥ r; Groove width k ≥ t; Groove depth L≥ t+R+k/2. Fig. 4.4. 1. 1 local bending design processing method
3.4.2 When the hole is located in the bending deformation zone, the form of incision is adopted.
An example of cutting when the hole is in the bending deformation zone (Figure 4.4.2. 1).
Figure 4.4.2. 1 Example of incision form
3.5 Bending edge with bevel edge should avoid deformation zone.
Fig. 4.5. 1 Bending edge with bevel edge should avoid deformation zone.
3.6 Design Requirements for Edge Killing
The length of the dead edge is related to the thickness of the material. As shown in the figure below, under normal circumstances, the minimum length of dead edge L ≥ 3.5t+R. ..
Where t is the wall thickness of the material, and r is the minimum internal bending radius of the previous process (as shown in the right figure below).
Figure 4.6. 1 Minimum length of dead edge l
3.7 Process locating holes added during design
In order to ensure the accurate positioning of the blank in the mold and prevent the blank from deviating in the bending process and producing waste products, the process positioning holes should be added in advance in the design, as shown in the following figure. Especially for parts that have been bent for many times, the process hole should be taken as the positioning benchmark to reduce the accumulated error and ensure the product quality.
Fig. 4.7. 1 Process locating holes added during multiple bending.
3.8 When marking the relevant dimensions of bending parts, the manufacturability should be considered.
Figure 4.8. 1 Example of marking bent parts
As shown in the above figure, a) punching first and then bending, L dimensional accuracy is easy to ensure and processing is convenient. B) and c) If the accuracy of dimension L is required to be high, it is necessary to bend the hole first and then process it, which is troublesome to process.
3.9 Springback of Bending Parts
There are many factors affecting springback, including mechanical properties of materials, wall thickness, bending radius and positive pressure during bending.
3.9. 1 The greater the ratio of fillet radius to plate thickness, the greater the springback.
3.9.2 Examples of methods for restraining design rebound.
At present, manufacturers mainly avoid the springback of bending parts when designing molds. At the same time, some structures have been improved in design to reduce the rebound angle, as shown in the following figure: Pressing the stiffener in the bending area can not only improve the rigidity of the workpiece, but also help to restrain the rebound.
Fig. 4.9.2. 1 Examples of methods for restraining springback in design.
4 stretching
4. 1 Requirements for fillet radius between bottom and straight wall of drawing parts
As shown in the following figure, the fillet radius between the bottom of the drawing piece and the straight wall should be greater than the plate thickness, that is, r1≥ t. In order to make the drawing smoother, generally, r 1=(3~5)t, and the maximum fillet radius should be less than or equal to 8 times the plate thickness, that is, r 1≤8t.
Fig. 5. 1. 1 Drawing Parts Fillet Radius Dimensions
4.2 Radius of fillet between flange and wall of tension member
The radius of fillet between the flange and the wall of the drawing piece should be more than twice the thickness of the plate, that is, r2≥2t. In order to make the drawing smoother, r2=(5~ 10)t is generally adopted, and the maximum flange radius should be less than or equal to 8 times the thickness, that is, r2≤8t. (See Figure 5. 1. 1)
4.3 Diameter of Inner Cavity of Circular Drawing Part
The diameter of the inner cavity of the circular drawing part should be D ≥d+ 10t, so that the drawing delay platen will not wrinkle. (See Figure 5. 1. 1)
4.4 Radius of fillet between two adjacent walls of rectangular drawing parts
The radius of fillet between two adjacent walls of rectangular drawing parts should be r3 ≥3t. In order to reduce the number of drawing times, r3 ≥H/5 should be taken as far as possible for one drawing.
Figure 5.4. 1 Radius of fillet between two adjacent walls of rectangular extruded parts
4.5 When a circular flangeless drawing part is formed at one time, the dimensional relationship between its height and diameter is required.
When a circular flangeless drawing part is formed at one time, the ratio of height h to diameter d should be less than or equal to 0.4, that is, H/d ≤0.4, as shown in the following figure.
Fig. 5.5. 1 Dimensional relationship between height and diameter of circular flangeless drawing parts during one-step forming.
4.6 Matters needing attention in dimensioning design drawings of stretched parts
Due to the different stress in different places, the thickness of the stretched material will change. Generally speaking, the center of the bottom keeps its original thickness, the material at the corner of the bottom becomes thinner, the material near the top of the flange becomes thicker, and the material at the corner around the rectangular drawing piece becomes thicker.
Standard method for drawing product dimensions of parts.
When designing a stretched product, the dimensions on the product drawing should clearly indicate that external dimensions or internal dimensions must be guaranteed, and both internal and external dimensions cannot be marked at the same time.
4.6.2 Marking Method of Dimensional Tolerance of Stretched Parts
The tolerance of the inner radius of the concave-convex arc of the drawing part and the height dimension of the cylindrical drawing part formed at one time is bilateral symmetrical deviation, and the deviation value is half of the absolute value of the national standard (GB) 16 precision tolerance, and it is marked with a plus sign or a minus sign.
5 molding
5. 1 stiffener
Pressing ribs on plate metal parts is helpful to increase structural stiffness. See Table 6 for the structure and size selection of reinforcing ribs.
Table 7 Selection of Stiffener Structure and Size
5.2 Limit dimensions of convex spacing and convex edge spacing
The limit dimensions of convex spacing and convex edge spacing are selected according to the following table.
Table 8 Limit dimensions of convex spacing and convex edge spacing
5.3 shutters
Shutters are usually used in various housings or enclosures for ventilation and heat dissipation. The forming method is to cut the material with one side of the punch, and the rest of the punch will stretch and deform the material at the same time, forming an open wave shape.
See fig. 6.3. 1 for the typical structure of shutters.
Figure 6.3. 1 louver structure
Shutter size requirements: A ≥ 4t; b≥6t； h≤5t； l≥24t； r≥0.5t .
5.4 hole flanging
There are many kinds of hole flanging, and this specification only aims at the inner hole flanging of the thread to be processed, as shown in Figure 6.4. 1.
Fig. 6.4. 1 Schematic diagram of inner hole flanging structure with threaded hole
Thickness of spiral material t Flange inner hole D 1 flange height h Pre-punched hole diameter D0 Flange fillet radius d2 of Flange outer hole
2.57.042.8 1.25
7.34.53
37.04.83.4 1.5
Table 9 Size parameters of inner hole flanging with threaded hole
6 welding
6. 1 Classification of welding methods
Welding methods mainly include arc welding, electroslag welding, gas welding, plasma arc welding, fusion welding, pressure welding and brazing, and the welding of sheet metal products mainly includes arc welding and gas welding.
6.2 Arc welding is flexible, flexible and widely applicable, and can be used for all-position welding; The used equipment has simple structure, good durability and low maintenance cost. But the labor intensity is high and the quality is not stable enough, which depends on the level of the operator.
Suitable for welding carbon steel, low alloy steel, stainless steel, copper, aluminum and other non-ferrous alloys above 3 mm
6.3 The temperature and properties of gas welding flame can be adjusted, and the specific heat of arc welding heat source has a wide influence area, and the heat is not as concentrated as arc, resulting in low productivity.
Used for welding thin-walled structures and small parts, such as steel, cast iron, aluminum, copper and their alloys, cemented carbide, etc.
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