1. Brief Introduction On Sheet Metal Fabrication
1.1 Brief Introduction On Sheet Metal Fabrication
This specification states the technological requirements to be noted in every basic processing method,like blanking,bending,stretching, forming and welding.
1.2 Key Word
Sheet metal, blanking, bending, stretching, forming, layout, minimum bending radius, burrs, resilience, return fold and welding.
According to the different processing methods, cutting can be divided into punching, blanking, shearing, laser cutting and wind cutting.Because of the different metal fabrication methods, the processing technology of blanking is also different.Main sheet metal blanking methods are NCT punching and laser cutting.
2.1 The punching is processed by CNC punching machine. The range of sheet thickness for processing is as following:
cold roller steel, hot roller steel is less than or equal to 3.0mm; aluminum sheet is less than or equal to 4.0mm; stainless steel is less than or equal to 2.0mm.
2.2 The minimum size of punching is related to the shape of the hole, the mechanical properties of the material and the thickness of the material.
Figure 2.2.1Example of punching hole shape
Table 1 Minimum size list for punching holes
|Material||Circular Hole Diameter b||Short Side Width Of Rectangular Hole b|
|High carbon steel||1.3t||1.0t|
|Low carbon steel and brass||1.0t||0.7t|
● T is material thickness, and the minimum size of punching is not less than 1mm.
2.3 Hole spacing and hole margin of punching process
The minimum distance between the outer punching edge and the edge of punched hole is restricted by the shape of the part and hole, as shown in Figure 2.3.1. When the punching edge of hole is not parallel to the outer edge of the part, the minimum distance shall be not less than t of the material thickness; when parallel, it should be not less than 1.5T.
Figure 2.3.1 sketch map of the hole margin and hole spacing of punching parts
2.4 when the bending parts and drawing parts are punched, the distance between the hole wall and the straight wall of the part should be kept at a certain distance.
When punch bending parts or deep drawing parts, the hole wall should be kept at a certain distance from the straight wall of the work piece. (Fig. 2.4.1).
Fig. 2.4.1 the distance between the hole wall of bending parts, drawing parts and the vertical wall (straight wall) of the workpiece.
2.5 Screw, bolt hole and countersunk seat
The size of screws, through holes for bolts and countersunk seats shall be selected according to the table. For the countersunk seat of countersunk head screws, if the plate is too thin to ensure the hole D2 and the countersunk hole D at the same time, priority shall be given to ensuring D2.
Table 2 Through holes for screws and bolts
Table 3 the countersunk head and through hole for chamfer head screw
"h" - height of screw head for reference
Required sheet thickness t≥h
Table 4 the countersunk head and through hole for countersunk rivet
"h" - height of rivet head for reference
Required sheet thickness t≥h
2.6 Laser cutting is done by laser cutting machine. The max cutting thickness of steel is less than or equal to 20.0mm and the max cut thickness of stainless steel is less than 10.0mm. It can cut thick material with high speed. And its defect is that it can not do forming process. The mesh parts should not be processed by this way because the cost is high.