Sheet metal processing & Process flow.

With the development of today’s society, the sheet metal industry has also developed rapidly. Now sheet metal involves all walks of life. For any sheet metal part, it has a certain processing process, which is the so-called process flow. To understand the sheet metal processing process, you must first know the selection of sheet metal materials.

1. Selection of materials
   The materials commonly used in sheet metal processing are cold-rolled sheet (SPCC), hot-rolled sheet (SHCC), galvanized sheet (SECC, SGCC), copper (CU) brass, red copper, beryllium copper, aluminum sheet (6061, 6063, Hard aluminum, etc.), aluminum profiles, stainless steel (mirror surface, brushed surface, matte surface), depending on the function of the product, the selection of materials is different, generally it is necessary to consider the use and cost of the product.
2. Cold-rolled sheet SPCC, mainly used for electroplating and baking varnish, low cost, easy to form, material thickness ≤ 3.2mm.
3. Hot-rolled sheet SHCC, material T≥3.0mm, also use electroplating, baking varnish parts, low cost, but difficult to shape, mainly use flat parts.
4. Galvanized sheet SECC, SGCC. SECC electrolytic plates are divided into N material and P material. N material is mainly not used for sheet metal surface treatment, which has high cost, and P material is used for sprayed parts.
5. Copper: It is mainly used as a conductive material, and its surface treatment is nickel plating, chrome plating, or no treatment, and the cost is high.
6. Aluminum plate; generally use surface chromate (J11-A), oxidation (conductive oxidation, chemical oxidation), high cost, silver plating, nickel plating.
7. Aluminum profiles; materials with complex cross-sectional structures, which are widely used in various sub-boxes. The surface treatment is the same as that of the aluminum plate.
8. Stainless steel; mainly used without any surface treatment, and the cost is high.
9. Drawing review. To write the process flow of parts, you must first know the various technical requirements of the part drawings; then the drawing review is the most important link in the preparation of the part process flow.
10. Check that the drawing is complete.
11. The drawing view relationship, whether the labeling is clear and complete, and the dimension unit is marked.
12. Assembly relationship, key dimensions of assembly requirements.
13. The difference between the old and new versions.
14. Translation of pictures in foreign languages.
15. Code conversion at the table.
16. Feedback and resolution of drawing problems.
17. Material
18. Quality requirements and process requirements
19. Officially issued drawings must be affixed with a quality control seal.
20. Precautions for expansion, the expansion diagram is a plan view (2D) expanded based on the part drawing (3D)
21. The expansion method should be consistent, and it should be convenient to save materials and processability
22. Reasonably choose the gap and wrapping method, the gap below T=2.0 is 0.2, the gap between T=2-3 is 0.5, and the wrapping method adopts the long side to wrap the short side (door panel type)
23. Reasonably consider the tolerance dimensions: the negative tolerance goes to the end, and the positive difference goes to half; the hole shape size: the positive difference goes to the end, and the negative difference goes to half.
24. Burr direction
25. Pull out teeth, press riveting, tear, punch bumps (bags), etc., and draw a cross-sectional view
26. Check the material, plate thickness, and plate thickness tolerance
27. For special angles, the inner radius of the bending angle (generally R=0.5) should be determined by trial bending.
28. Where there are error-prone (similar asymmetry) places should be highlighted
29. Larger places should be enlarged
30. The area to be protected by spraying must be indicated
31. The technological process of sheet metal processing, according to the difference in the structure of the sheet metal parts, the technological process can be different, but the total does not exceed the following points.
32. Cutting: There are various ways of cutting, mainly in the following ways
    ①. Shearing machine: It is a simple material that uses a shearing machine to cut strips. It is mainly prepared for mold blanking and forming. The cost is low and the precision is lower than 0.2, but it can only process strips or blocks without holes and corners.

②. Punching machine: It is to use the punching machine to punch out the flat parts after the parts are unfolded on the plate in one or more steps to form various shapes of materials. Its advantages are short working hours, high efficiency, high precision and low cost. It is suitable for mass production. But to design the mold.

③. NC blanking, when NC blanking, you must first write the CNC machining program, use the programming software to write the drawn expansion diagram into a program that can be recognized by the NC digital drawing machine tool, and let it punch each piece on the flat plate according to these programs. The structure is a flat piece, but its structure is affected by the tool structure, the cost is low, and the accuracy is 0.15.

④. Laser blanking is to use laser processing technology to cut out the structural shape of the flat plate on a large flat plate. Like NC blanking, it is necessary to write a laser program. It can produce various complex shapes of flat parts, with high cost and an accuracy of 0.1 .

⑤. Sawing machine: mainly use aluminum profiles, square tubes, graphic tubes, round bars,precision etching etc., with low cost and low precision.

2. Fitter: countersunk, tapping, reaming, drilling
   The angle of countersunk hole is generally 120°C, which is used for pull rivets, and 90°C is used for countersunk head screws, tapping inch bottom holes.
3. Flange:
   Also known as pumping holes and turning holes, it is to draw a slightly larger hole on a smaller base hole, and then tap. It is mainly processed with thinner sheet metal to increase its strength and number of thread turns to avoid slippage. Teeth, generally used for thin plate thickness, normal shallow flanging around the hole, the thickness basically does not change, and when the thickness is allowed to be thinned by 30-40%, the height of the flanging is 40-60% higher than the normal flanging. Height: When extruding 50% thinner, the maximum flanging height can be obtained. When the plate thickness is relatively large, such as 2.0, 2.5, etc., it can be directly tapped.
4. punch:
   It is a processing process that uses mold forming. Generally, punching machines include punching, corner cutting, blanking, punching convex hull (bump), punching and tearing, drawing holes, forming and other processing methods. The processing requires corresponding molds. Complete operations, such as punching and blanking dies, convex shell dies, tearing dies, punching dies, forming dies, etc., the operation mainly pays attention to the position and direction.
5. Pressure riveting:
   As far as our company is concerned, pressure riveting mainly includes pressure riveting nuts, screws, loosening, etc., which are completed by hydraulic pressure riveting machines or punching machines, and riveted to sheet metal parts. Pay attention to directionality.
6. bending;
   Bending is to fold a 2D flat piece into a D part. Its processing needs to be completed by a folding bed and corresponding bending molds. It also has a certain bending sequence. The principle is to fold first without interference to the next knife, and to fold later with interference.

The number of bending strips is T=3.0mm and below 6 times the plate thickness to calculate the groove width, such as: T=1.0, V=6.0 F=1.8, T=1.2, V=8, F=2.2, T=1.5, V =10, F=2.7, T=2.0, V=12,

F=4.0

Classification of folding bed molds, straight knife, machete (80°C, 30°C)

When the aluminum plate is bent, there are cracks, you can increase the width of the lower die groove and increase the upper die R (annealing can avoid cracks)

Points to note when bending: Ⅰ drawing, required plate thickness and quantity; Ⅱ bending direction

ⅢBending angle; ⅣBending size; ⅥAppearance, electroplated chrome parts are not allowed to have creases.

The relationship between bending and riveting process, in general, riveting first and then bending, but if there are materials that will interfere after riveting, it is necessary to fold first and then press, and some require bending-riveting-rebending and other processes.

7. welding:
   Welding definition: the distance between the atoms and molecules of the material to be welded and the Jingda crystal lattice form a whole

①Classification: a Fusion welding: argon arc welding, CO2 welding, gas welding, manual welding

b Pressure welding: spot welding, butt welding, bump welding

c brazing: electrochrome welding, copper wire

② Welding method: a CO2 gas shielded welding

b argon arc welding

c Spot welding,PCB Circuit Board Etching etc.

d robot welding

The selection of the welding method is based on the actual requirements and materials. Generally speaking, CO2 gas shielded welding is used for welding iron plates; argon arc welding is used for welding stainless steel and aluminum plates. Robot welding or etching process can save man-hours and improve work efficiency. And welding quality, reduce work intensity.

③ Welding symbol: Δ fillet weld, Д, I-type welding, V-type welding, single-sided V-type welding (V), V-type welding with blunt edge (V), spot welding (O), plug welding or slot welding (∏) , curling welding (χ), unilateral V-shaped welding with blunt edge (V), U-shaped welding with blunt, J-shaped welding with blunt, back-sealing welding, every welding

④ Arrowed wires and connectors

⑤ Missing welding and its preventive measures

Spot welding: If the strength is not enough, bumps can be made, and the welding area is imposed

CO2 welding: high productivity, less energy consumption, low cost, strong rust resistance

Argon arc welding: shallow melting, slow welding speed, low efficiency, high production cost, tungsten inclusion defect, but has the advantage of better welding quality, and can weld non-ferrous metals, such as aluminum, copper, magnesium, etc.

⑥ Reason for welding deformation: Insufficient preparation before welding, need to add fixtures

Improving Process for Bad Welding Fixtures

bad soldering sequence

⑦Welding deformation effect method: flame effect method

vibration method

hammering method

artificial statute of limitations