Introduction to Sheet Metal Processing
1 Introduction
1.1 Introduction
The basic processing methods for sheet metal parts are as follows: sheet metal, bending, stretching, forming and welding. This specification describes the process requirements to be noted for each type of processing.
1.2 Keywords
Sheet metal, underfeeding, bending, stretching, forming, row of samples, the minimum bending radius, burrs, rebound, dead center, welding
2 underfeeding
Underfeeding according to the different processing methods can be divided into the general punching, number of punches, shearing machine opening, laser cutting, air cutting, as a result of the different methods of processing, underfeeding the processing of the process of craftsmanship is also different. different. Sheet metal under the way mainly for the number of punching and laser cutting
2.1 digital punching is a CNC punch processing, sheet metal thickness processing range of cold rolled sheet, hot rolled sheet less than or equal to 3.0mm, aluminum less than or equal to 4.0mm, stainless steel less than or equal to 2.0mm
2.2 punching a minimum size requirements
Punching the minimum size of the hole with the shape, mechanical properties and thickness of the material. mechanical properties and material thickness.
Figure 2.2.1 Examples of punched hole shapes
Materials Circular hole diameter b Rectangular hole short side width b
High-carbon steel 1.3t1.0t
Low-carbon steel, brass 1.0t0.7t
Aluminum 0.8t0.5t
* t is the thickness of the material, and the minimum dimensions of the punched holes are generally not less than 1mm.
* High-carbon steel, low carbon steel, brass 1.0t0.7t
T is the material thickness. p>* For a list of the company's common material grades corresponding to high-carbon steel and low-carbon steel, see Chapter 7, Appendix A.
Table 1: List of Minimum Dimensions of Punching Holes
2.3 Hole Spacing and Edge Distance of Holes for Digital Punching
The minimum distance between the edge of the hole for a part's punched hole and the profile varies according to the shapes of the part and hole and is subject to certain limitations, as shown in Fig. 2.3.1. When the edge of the hole for a punch hole and the edge of the profile of the part are not parallel, this minimum distance should be not less than 1mm. When the punched edge is not parallel to the edge of the part shape, the minimum distance shall be not less than the thickness of the material t; when it is parallel, it shall be not less than 1.5t.
Figure 2.3.1 Schematic diagram of the hole edge distance and hole spacing for punched parts
2.4 When punching holes in bending and deep-drawing parts, a certain distance should be maintained between the wall of the holes and the straight wall of the workpiece
When punching holes in bending or deep-drawing parts, the hole walls and the straight wall of the workpiece should be kept at a certain distance from each other ( Figure 2.4.1)
Figure 2.4.1 Distance between the hole wall of bending and drawing parts and the straight wall of the workpiece
2.5 Screws, bolts and countersunk holes and countersunk seat
Screws, bolts and countersunk holes and countersunk seat of the structure of the dimensions 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 holes 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 seats and countersunk rivets used for Countersunk head seat for countersunk head rivets and apertures
2.6 Laser cutting is a laser machine flight cutting process, plate thickness processing range of cold rolled plate hot rolled plate less than or equal to 20.0mm, stainless steel less than 10.0mm. Its advantages are processing plate thickness, cutting workpiece shape speed, processing flexibility. The disadvantage is that it can not be processed into shape, mesh parts should not be processed in this way, high processing costs!
3 Bending
3.1 Minimum bending radius of the bent parts
When the material is bent, its rounded area, the outer layer receives stretching, 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
108, 08F, 10, 10F, DX2, SPCC, E1-T52, 0Cr18Ni9, 1Cr18Ni9, 1Cr18Ni9Ti, 1100-H24, T20.4t
215, 20, Q235, Q235A, 15F0.5 t
325, 30, Q2550.6t
41Cr13, H62 (M, Y, Y2, cold rolled) 0.8t
545, 501.0t
655, 601.5t
765Mn, 60SiMn, 1Cr17Ni7, 1Cr17Ni7-Y, 1Cr17Ni7-DY, SUS301, 0Cr18Ni9, SUS3022.0t
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 5 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 parts with 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 6 hole edge distance on the bent parts
3.4 Local bending process notch
3.4.1 Bending line of the bending parts should 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 bending fracture, can be moved a certain distance from the bending line to leave the size of the sudden change (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. Fig. 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 (Fig. 4.4.2.1)
Fig. 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 to the design
In order to ensure accurate positioning of the blank in the mold, to prevent bending of the blank offset and scrap, should be added to the design of the process of positioning holes in advance, 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 Resilience of bent parts
There are many factors affecting the resilience, 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 thickness of the plate, i.e., r2 ≤ 8t. (See Figure 5.1.1)
4.3 Circular stretching parts of the inner diameter
Circular stretching parts of the inner diameter of the cavity should be taken as D ≥ d + 10t, so that in the stretching of the platen compression does not wrinkle. (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, and in order to minimize the number of times of stretching it should be taken as far as possible as r3 ≥ H/5 so that it can 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 following figure.
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 7 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 8 Limit dimensions of pitch and pitch
5.3 Shutters
Louvers are usually used for ventilation and heat dissipation on various covers or housings, 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 Structure of hole flanging with threaded holes
Thickness of threaded material t flanging inner hole D1 flanging outer hole d2 flanging height h pre-punched hole diameter D0 flanging radius
2.57.042.81.25
7.34.53
37.04.83.41.5
Table 9 Dimensional parameters of bore flanging with threaded holes
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, brazing, and sheet metal products are mainly welded by arc welding and gas welding.
6.2 Electric arc welding has the advantages of flexibility, mobility, wide applicability, all-position welding; the equipment used is simple, good durability, low maintenance costs. However, the labor intensity is large, the quality is not stable enough, determined by the level of the operator.
Suitable for welding more than 3mm of carbon steel, low alloy steel, stainless steel and copper, aluminum and other non-ferrous alloys
6.3 Gas welding flame temperature and properties can be adjusted, the heat source in the arc welding than the heat-affected zone is wide, the heat is not as centralized as the arc, the productivity is low
Apply to the thin-walled structures and small pieces of the weld, can be welded to steel, cast iron, aluminum, copper and its alloys, cemented carbide and so on