Punching is divided into general punching and precision punching, due to the different processing methods, the processability of punched parts is also different. At present, the structural parts of our communication products are generally only used for ordinary blanking. The following introduction to the process of blanking refers to the structure of the ordinary blanking process.
2.1 The shape and size of the punched parts are as simple and symmetrical as possible, so that there is a minimum of waste in the layout.
Figure 3.1.1 Layout of a punched part
2.2 Sharp corners should be avoided in the shape and bore of the punched part.
There shall be rounded connections at the joints of straight or curved lines, and the radius of the rounded radius R≥0.5t. (t is the wall thickness of the material)
Figure 3.2.1 Minimum value of radius of rounded corners of the punched parts
2.3 Narrow and long cantilevers and narrow grooves shall be avoided in punched parts
The depth and width of the projecting or concave portion of the punched parts shall, in general, be not less than 1.5t (t is the material thickness), and should avoid narrow and long cantilever and and too narrow groove, in order to increase the edge strength of the corresponding parts of the mold. See Figure 3.3.1.
Figure 3.3.1 Avoid narrow cantilever and groove
2.4 Punching preference for round holes, punching has a minimum size
Punching preference for circular holes, punching the minimum size of holes with the shape of the holes, the mechanical properties of the material and the thickness of the material.
Figure 3.4.1 Example of punched hole shape
Materials Diameter of circular holeb Width of short side of rectangular holeb
High-carbon steel 1.3t 1.0t
Mild steel, brass 1.0t 0.7t
Aluminum 0.8t 0.5t
* t is the thickness of the material, and the minimum size of the punched hole is generally not less than 0.3mm.
* See Appendix A of Chapter 7 for a list of the company's common material grades corresponding to high carbon steel and low carbon steel.
Table 1 List of Minimum Dimensions for Punching
2.5 Hole Spacing and Edge Distance of Holes for Punching
The minimum distance of a part's punched edges from the profile varies with the shapes of the part and holes with some limitations, as shown in Fig. 3.5.1. When the edges of punched holes are not parallel to the edges of the part profile, this minimum distance should not be less than 0.3mm. When they are parallel, the minimum distance shall be not less than the thickness of the material t; when they are parallel, it shall be not less than 1.5t.
Figure 3.5.1 Schematic diagram of the hole margin and hole spacing of the punched parts
2.6 When punching of bending and drawing parts, a certain distance shall be maintained between the wall of the holes and the straight wall of the parts
When punching of the bending parts or drawing parts, the wall of the holes shall be kept at a certain distance from the straight wall of the parts (Fig. 3.6.1). Distance (Figure 3.6.1)
Figure 3.6.1 Distance between the hole wall of the bending and drawing parts and the straight wall of the workpiece
2.7 Screws, bolts and countersunk holes and countersunk seat
Screws, bolts and countersunk holes and countersunk seat of the structure of the size of the selection of the following table to take. For countersunk head screw countersunk seat, if the sheet metal is too thin to ensure that both the hole d2 and countersunk hole D, should be given priority to ensure that the hole d2.
Table 2 for screws, bolts and countersunk holes
*Requirement for the sheet metal thickness t ≥ h.
Table 3 countersunk head seat for countersunk screws and countersunk holes
*Requirement for sheet metal thickness t ≥ h.
Table 4 countersunk head seat for countersunk rivets and countersunk holes
Table 4 for Countersunk head seat and overbore for countersunk head rivets
2.8 Limit values of burrs of punched parts and design notation
2.8.1 Limit values of burrs of punched parts
Burrs of punched parts exceeding a certain height are not permitted, and the limit values of the height of burrs of punched parts (mm) are shown in the following table.
Material wall thickness Material tensile strength (N/mm2)
>100～250 ＞250～400 ＞400～630 ＞630
f m g f m g f m g f m g
＞0.7～1.0 0.12 0.17 0.23 0.09 0.13 0.17 0.05 0.07 0.1 0.03 0.04 0.05
＞1.0 ～1.6 0.17 0.25 0.34 0.12 0.18 0.24 0.07 0.11 0.15 0.04 0.06 0.08
＞1.6 ～2.5 0.25 0.37 0.5 0.18 0.26 0.35 0.11 0.16 0.22 0.06 0.09 0.12
＞2.5 ～4.0 0.36 0.54 0.72 0.25 0.37 0.5 0.2 0.3 0.4 0.09 0.13 0.18
* Grade f (Precision) is suitable for parts with high requirements; grade m (Medium) is suitable for parts with medium requirements; and grade g (Roughness) is suitable for parts with general requirements.
Table 5 Limit values for burr height of stamped parts
2.8.2 Requirements for marking burrs in design drawings
* Direction of burr: BURR SIDE.
* Part to be burred: COIN or COIN CONTINUE. Generally do not press burr all over the entire structural part break, which will increase the cost. Try to use in the following cases: exposed breaks; sharp edges often touched by human hands; holes or grooves that need to be passed over the cable; parts with relative sliding.
Figure 3.8.2.1 Example of burr labeling in sheet metal structural design drawing
3 Bending
3.1 Minimum bending radius of a bent part
When a material is bent, on the fillet area, the outer layer receives stretching and the inner layer is compressed. When the material thickness is certain, the smaller the inner r, the more serious the material's stretching and compression; when the tensile stress of the outer fillet exceeds the ultimate strength of the material, cracks and breaks, therefore, the structural design of the bending parts should be avoided too small bending radius of the fillet. The minimum bending radius of the company's commonly used materials are shown in the table below.
No. Material Minimum Bending Radius
1 08, 08F, 10, 10F, DX2, SPCC, E1-T52, 0Cr18Ni9, 1Cr18Ni9, 1Cr18Ni9Ti, 1100-H24, T2 0.4t
2 15, 20, Q235, Q235A, 15F 0.5 t
3 25, 30, Q255 0.6t
4 1Cr13, H62(M, Y, Y2, cold rolled) 0.8t
5 45, 50 1.0t
6 55, 60 1.5t
7 65Mn, 60SiMn, 1Cr17Ni7, 1Cr17Ni7-Y, 1Cr17Ni7-DY, SUS301, 0Cr18Ni9, SUS302 2.0t
The bending radius is the inner radius of the bent part,t is the wall thickness of the material. t is the wall thickness of the material, M is the annealed condition, Y is the hard condition, and Y2 is the 1/2 hard condition.Table 6 list of minimum bending radius of metal materials commonly used in the company
3.2 Straight edge height of bending parts
3.2.1 Minimum straight edge height requirements in general
The straight edge height of the bending parts should not be too small, the minimum height according to the requirements of the (Fig. 4.2.1): h>2t.
Figure 4.2.1.1 Bending part of the Minimum straight edge height
3.2.2 Special requirements of the straight edge height
If the design needs to bend the straight edge height h ≤ 2t, then first of all to increase the height of the edge of the bending, bending and then processed to the required size; or in the bending of deformation zone after processing a shallow groove, and then bent (as shown in the figure below).
Figure 4.2.2.1 Requirements for straight edge height in special cases
3.2.3 Height of straight edge with beveled side
When bending a bent part with a beveled side (Fig. 4.2.3), the minimum height of the side is: h=(2~4)t>3mm
Figure 4.2.3.1 Straight edge with beveled side Height
3.3 Hole side distance on the bent part
Hole side distance: first punching and then bending, the location of the hole should be outside the bending deformation zone, to avoid bending the hole will produce deformation. The distance from the hole wall to the bending edge is shown in the table below.
Table 7 hole edge distance on the bending
3.4 Local bending process notch
3.4.1 Bending line of the bending parts should be avoided to avoid the location of the size of the sudden change
Local bending of a section of the edge, in order to prevent the sharp corners of the concentration of stress generated by the curved cracks, can be bending line moved a certain distance away from the dimensional changes (Figure 4.4.1.1 a), or open the process slot (Figure 4.4.1.1 a) , or cut a process slot (Fig. 4.4.1.1 b), or punch a process hole (Fig. 4.4.1.1 c). Note the dimensional requirements in the figure: S ≥ R; slot width k ≥ t; slot depth L ≥ t + R + k/2. Figure 4.4.1.1 Design treatment of local bending
3.4.2 Notch form adopted when the hole is located in the bending deformation zone
Example of notch form adopted when the hole is located in the bending deformation zone (Figure 4.4.2.1)
Figure 4.4 .2.1 Example of a notch form
3.5 Bending edge with a beveled edge should avoid the deformation zone
Figure 4.5.1 Bending edge with a beveled edge should avoid the deformation zone
3.6 Design requirements for hitting the dead center
The length of the dead center for hitting the dead center is related to the thickness of the material. As shown in the figure below, the general minimum length of the dead edge L ≥ 3.5t + R.
Where t is the wall thickness of the material, R is to beat the dead edge of the previous process (as shown in the figure below, the right) of the minimum internal bending radius.
Figure 4.6.1 Minimum length of the dead-edge L
3.7 Process positioning holes added at design time
In order to ensure accurate positioning of the blank in the mold, to prevent bending of the blank offset and scrap, should be added in advance at the time of design of the process positioning holes, as shown in the figure below. Especially the parts of multiple bending and forming, must be process holes as a positioning reference, in order to reduce the cumulative error, to ensure product quality.
Figure 4.7.1 Process positioning holes added during multiple bending
3.8 Labeling of dimensions related to bent parts, taking into account the manufacturability
Figure 4.8.1 Example of labeling of a bent part
As shown in the figure above, a) punching the hole and then bending it, the accuracy of the L dimensions can be easily ensured, and it is easy to process. b) and c) if the accuracy of the L dimensions is required to be high, it is need to bend first and then process the hole, processing trouble.
3.9 Springback of bent parts
There are many factors affecting the springback, including: the mechanical properties of the material, wall thickness, bending radius, and the positive pressure during bending.
3.9.1 The greater the ratio of the radius of the inner corner of the bent part to the thickness of the plate, the greater the rebound.
3.9.2 Examples of ways to inhibit rebound from the design
Bending parts of the rebound, is mainly by the manufacturer in the mold design, to take certain measures to avoid. At the same time, from the design to improve some of the structure to promote the springback angle of the simple less as shown in the following figure: in the bending area of the press reinforcement, not only can improve the stiffness of the workpiece, but also conducive to the inhibition of springback.
Figure 4.9.2.1 Examples of design methods to suppress springback
4 Tension
4.1 Requirements for the radius of the fillet between the bottom of the tensioned part and the straight wall
As shown in the figure below, the radius of the fillet between the bottom of the tensioned part and the straight wall should be greater than the thickness of the plate, i.e. r1 ≥ t . In order to make the stretching proceed more smoothly, r1=(3~5)t is generally taken, and the maximum fillet radius should be less than or equal to 8 times of the plate thickness, i.e., r1≤8t.
Figure 5.1.1 Fillet radius of tensile member
4.2 Fillet radius between the flange of the tensile member and the wall
The fillet radius between the flange of the tensile member and the wall should be greater than 2 times of the plate thickness, i.e., r2≥2t. 2t, in order to make the stretching more smoothly, generally take r2 = (5 ~ 10)t, the maximum flange radius should be less than or equal to 8 times the plate thickness, that is, r2 ≤ 8t. (See Figure 5.1.1)
4.3 Circular tensile member of the inner diameter
Circular tensile members of the internal diameter should be taken as D ≥ d + 10t, so that in the stretching of the platen compression will not be wrinkled. (See Fig. 5.1.1)
4.4 Radius of fillet between two adjacent walls of rectangular tension member
The radius of fillet between two adjacent walls of rectangular tension member should be taken as r3 ≥ 3t, in order to minimize the number of times of stretching it should be taken as far as possible, r3 ≥ H/5, so as to be pulled out at one time.
Figure 5.4.1 Radius of fillet between two adjacent walls of rectangular tension member
4.5 Dimensional relationship between height and diameter of round flange-free tension member when forming at one time
When forming at one time of round flange-free tension member, the ratio of the height H and the diameter d should be less than or equal to 0.4, i.e., H/d ≤ 0.4, as shown in the figure below.
Figure 5.5.1 Dimension relationship between height and diameter of round flangeless drawn parts when forming at one time
4.6 Precautions for dimensioning on the design drawings of tensile parts
Tensile parts change the thickness of the material after drawing due to the varying stresses in various places. Generally speaking, the bottom center to maintain the original thickness, the bottom rounded corner of the material thinner, the top near the flange of the material thicker, rectangular tensile parts around the rounded corner of the material thicker.
4.6.1 Standardized method of product dimensions of tensile parts
When designing tensile products, the dimensions on the product drawing should be clearly indicated that the external dimensions or internal dimensions must be guaranteed, and internal and external dimensions should not be marked at the same time.
4.6.2 Tensile dimension tolerance labeling method
The inner radius of the concave-convex arc of the tensile parts and the height of the cylindrical tensile part of the one-time molding size tolerance for double-sided symmetrical deviation, and the deviation value of the national standard (GB) 16-level precision tolerance half of the absolute value, and crowned with ± sign.
5 Forming
5.1 reinforcement
Pressing rib on the plate metal parts, help to increase the structural rigidity of the reinforcing bar structure and its size selection, see Table 6.
Table 8 reinforcing bar structure and size selection
5.2 hit the limit size of the convex spacing and convex edge distance
Hit the limit size of the convex spacing and convex edge distance are selected according to the following table.
Table 9 Limit dimensions of pitch and pitch
5.3 Louver
Louvers are usually used for ventilation and heat dissipation on various housings or enclosures, and are molded by cutting through the material with one edge of the convex mold, while the rest of the convex mold stretches and deforms the material at the same time to form an undulating shape with an opening on one side.
The typical structure of shutter see figure 6.3.1.
Figure 6.3.1 structure of shutter
Size requirements of shutter: a ≥ 4t; b ≥ 6t; h ≤ 5t; L ≥ 24t; r ≥ 0.5t.
5.4 Hole flanging
Hole flanging type more, this specification is only concerned with the processing of threaded hole flanging. as shown in Figure 6.4.1.
Figure 6.4.1 Bore flanging structure with threaded holes
Threaded material thickness t flanging bore D1 flanging bore d2 flanging height h pre-punched hole diameter D0 flanging radius R
M3 0.8 2.55 3.38 1.6 1.9 0.6
1 3.25 1.6 2.2 0.5
3.38 1.8 1.9
3.5 2 2
1.2 3.38 1.92 2 0.6
3.5 2.16 1.5
1.5 3.5 2.4 1.7 0.75
M4 1 3.35 4.46 2 2.3 0.5
1.2 4.35 1.92 2.7 0.6
4.5 2.16 2.3
4.65 2.4 1.5
1.5 4.46 2.4 2.5 0.75
4.65 2.7 1.8
2 4.56 2.2 2.4 1
M5 1.2 4.25 5.6 2.4 3 0.6
1.5 5.46 2.4 2.5 0.75
5.6 2.7 3
5.75 3 2.5
2 5.53 3.2 2.4 1
5.75 3.6 2.7
2.5 5.75 4 3.1 1.25
M6 1.5 5.1 7.0 3 3.6 0.75
2 6.7 3.2 4.2 1
7.0 3.6 3.6
7.3 4 2.5
2.5 7.0 4 2.8 1.25
7.3 4.5 3
3 7.0 4.8 3.4 1.5
Table 10 Dimensional reference for the flanging of the inner holes with threaded holes
Table 10