Sheet metal processing

Sheet metal processing is a hub technology that sheet metal technicians need to grasp, and it is also an important process in sheet metal product forming. Sheet metal processing includes traditional cutting, blanking, bending and forming methods and process parameters, as well as various cold stamping die structure and process parameters, various equipment working principles and operating methods, and new stamping technology and new technology. Parts sheet metal processing is called sheet metal processing.

Sheet metal processing is called sheet metal processing. Specifically, for example, the use of plates to make chimneys, iron barrels, fuel tanks, oil tanks, ventilation pipes, elbows, elbows, squares, funnels, etc. The main processes include shearing, bending, bending, forming, welding, riveting, etc. Certain geometric knowledge. Sheet metal parts are thin sheet metal parts, that is, parts that can be processed by stamping, bending, stretching and other means. A general definition is a part with a constant thickness during processing. Corresponding to castings, forgings, machining parts, etc.

Material selection

The materials generally used in sheet metal processing are cold rolled plate (SPCC), hot rolled plate (SHCC), galvanized plate (SECC, SGCC), copper (CU) brass, red copper, beryllium copper, aluminum plate (6061, 5052) 1010, 1060, 6063, duralumin, etc.), aluminum profiles, stainless steel (mirror surface, brushed surface, matte surface), depending on the role of the product, the choice of materials is different, and generally need to be considered from the product’s use and cost.

(1)    Cold rolled sheet SPCC, mainly used for electroplating and baking varnish parts, low cost, easy to shape, and material thickness ≤ 3.2mm.

(2) Hot-rolled sheet SHCC, material T≥3.0mm, also uses electroplating, paint parts, low cost, but difficult to form, mainly flat parts.

(3) SECC, SGCC galvanized sheet. SECC electrolytic board is divided into N material and P material. N material is mainly used for surface treatment and high cost. P material is used for sprayed parts.

(4) Copper， mainly used conductive material, the surface treatment is nickel plating, chrome plating, or no treatment, high cost.

(5) Aluminum plate， generally use surface chromate (J11-A), oxidation (conductive oxidation, chemical oxidation), high cost, silver plating, nickel plating.

(6) Aluminum profiles，materials with complex cross-section structures are widely used in various sub-boxes. The surface treatment is the same as the aluminum plate.

(7) Stainless steel，it is mainly used without any surface treatment, and the cost is high.

Commonly used materials

1. Galvanized steel sheet SECC

The substrate of SECC is ordinary cold-rolled steel coil, which becomes electro-galvanized product after degreasing, pickling, electroplating and various post-treatment processes on the continuous electro-galvanizing production line. SECC not only has the mechanical properties and similar processability of general cold-rolled steel sheet, but also has superior corrosion resistance and decorative appearance. It is highly competitive and replaceable in the market of electronic products, home appliances and furniture. For example, SECC is commonly used in computer cases.

2.Ordinary cold rolled sheet SPCC

SPCC refers to the continuous rolling of steel ingots through cold rolling mills into steel coils or sheets of required thickness. There is no protection on the surface of SPCC, and it is easily oxidized when exposed to the air, especially in a humid environment, the oxidation speed is accelerated, and dark red rust appears. The surface should be painted, electroplated or other protection when in use. SPCC refers to the continuous rolling of steel ingots through cold rolling mills into steel coils or sheets of required thickness. There is no protection on the surface of SPCC, and it is easily oxidized when exposed to the air, especially in a humid environment, the oxidation speed is accelerated, and dark red rust appears. The surface should be painted, electroplated or other protection when in use.

3.Hot-dip galvanized steel sheet SGCC

Hot-dip galvanized steel coil refers to the semi-finished product after hot-rolling and pickling or cold-rolling, which is washed and continuously immersed in a molten zinc bath at a temperature of about 460°C, so that the steel sheet is coated with a zinc layer and then quenched and tempered SGCC material is harder than SECC material, has poor ductility (avoid deep drawing design), thicker zinc layer, and poor weldability.

4.Stainless steel SUS304

One of the most widely used stainless steels. Because it contains Ni (nickel), it has better corrosion resistance and heat resistance than Cr (chromium) steel. It has very good mechanical properties, no heat treatment hardening phenomenon, and no elasticity.

5.Stainless steel SUS301

The content of Cr (chromium) is lower than that of SUS304, and the corrosion resistance is poor. However, it can obtain good tensile force and hardness in stamping after cold working, and has good elasticity. It is mostly used for shrapnel springs and anti-EMI.

Drawing review

To compile the process flow of a part, we must first know the various technical requirements of the part drawing; the drawing review is the most important link in the compilation of the part process flow.

(1) Check whether the drawings are complete.

(2) The relationship between the drawing and the view, whether the label is clear, complete, and the unit of dimension.

(3) Assembly relations, key dimensions of assembly requirements.

(4) The difference between the old and new versions of the graphics.

(5) Translation of pictures in foreign languages.

(6) Conversion of table codes.

(7) Feedback and disposal of drawing problems.

(8) Material.

(9) Quality requirements and process requirements.

(10) The official release of the drawings must be stamped with a quality control seal.

Precautions

The expanded view is a plan view (2D) based on the part drawing (3D).

(1) The expansion method should be suitable, and it should be convenient to save materials and processability.

(2) Reasonably choose the gap and edging method, T=2.0, the gap is 0.2, T=2-3, the gap is 0.5, and the edging method adopts long sides and short sides (door panels).

(3) Reasonable consideration of tolerance dimensions: negative difference goes to the end, positive difference goes half; hole size: positive difference goes to the end, negative difference goes half.

(4) Burr direction.

(5) Draw a cross-sectional view in the direction of extraction, pressure riveting, tearing, punching convex points (package), etc.

(6) Check the material and thickness of the board to the board thickness tolerance.

(7) For special angles, the inner radius of the bending angle (generally R=0.5) needs to be flexed and unfolded.

(8) Places that are prone to error (similar asymmetry) should be highlighted.

(9) Enlarged images should be added where there are more sizes.

(10) The area to be protected by spraying must be indicated.

Manufacturing processes

According to the difference in the structure of sheet metal parts, the process flow can be different, but the total does not exceed the following points.

1. Cutting: There are various cutting methods, mainly the following methods.

①Shearing machine: It is a simple piece of material that uses a shearing machine to cut strips. It is mainly used for mold blanking and forming preparation. The cost is low, and the accuracy is less than 0.2, but it can only process strips or blocks with no holes and no corners. .

②Punch: It uses the punch to punch out the flat parts after unfolding the parts on the plate in one or more steps to form various shapes of materials. Its advantages are short man-hours, high efficiency, high precision, low cost, and it is suitable for mass production. , But to design the mold.

③NC CNC blanking. When NC blanking, you must first write a CNC machining program. Use the programming software to write the drawn unfolded image into a program that can be recognized by the NC digital drawing processing machine, so that it can punch each on the plate step by step according to these programs. The structure is a flat piece, but its structure is affected by the structure of the tool, the cost is low, and the accuracy is 0.15.

④Laser cutting is the use of laser cutting to cut the structure and shape of the flat plate on a large flat plate. The laser program needs to be programmed like NC cutting. It can load various complex shapes of flat parts with high cost and lower accuracy. 0.1.

⑤Sawing machine: Mainly use aluminum profiles, square tubes, drawing tubes, round bars, etc., with low cost and low precision.

 2.Fitter: countersinking, tapping, reaming, drilling.

The counterbore angle is generally 120℃, used for pulling rivets, and 90℃ used for countersunk screws and tapping inch bottom holes.

 3.  Flanging: It is also called hole-drawing and hole-turning, which is to draw a slightly larger hole on a smaller base hole, and then tap it. It is mainly processed with thinner sheet metal to increase its strength and the number of threads. , To avoid sliding teeth, generally used for thin plate thickness, normal shallow flanging around the hole, the thickness is basically unchanged, and the thickness is allowed to be thinned by 30-40%, 40-higher than the normal flanging height can be obtained. For a height of 60%, the maximum flanging height can be obtained when the thinning is 50%. When the thickness of the plate is larger, such as 2.0, 2.5, etc., it can be tapped directly.

4.  Punch: It is a processing procedure that uses mold forming. Generally, punching processing includes punching, corner cutting, blanking, punching convex hull (bump), punching and tearing, punching, forming and other processing methods. The processing needs to have corresponding processing methods. The mold is used to complete the operations, such as punching and blanking molds, convex molds, tearing molds, punching molds, forming molds, etc. The operation mainly pays attention to position and directionality.

5.  Pressure riveting: As far as our company is concerned, pressure riveting mainly includes pressure riveting nuts, screws, and so on. The operation is completed by hydraulic pressure riveting machine or punching machine, riveting them to sheet metal parts, and riveting Way, need to pay attention to directionality.

6.  Bending: Bending is to fold 2D flat parts into 3D parts. The processing needs to be completed with a folding bed and corresponding bending molds, and it also has a certain bending sequence. The principle is that the next cut does not interfere with the first folding, and the interference will occur after the folding.

The number of bending strips is 6 times the thickness of the plate below T=3.0mm 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.

Bending bed mold classification, straight knife, scimitar (80 ℃, 30 ℃).

　There are cracks when the aluminum plate is bent. The width of the lower die slot can be increased, and the upper die R can be increased (annealing can avoid cracks).

　Precautions when bending: Ⅰ Drawing, required plate thickness and quantity; Ⅱ bending direction; Ⅲ bending angle; Ⅳ bending size; Ⅵ appearance, no creases are allowed on the electroplated chromed material. The relationship between bending and pressure riveting process is generally the first pressure riveting and then bending, but some materials will interfere with the pressure riveting, and then press first, and some require bending-pressure riveting-then bending and other processes.

 7. Welding: Welding definition: The distance between the atoms and molecules of the welded material and the Jingda 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: electric chromium welding, copper wire.

② Welding method: a CO2 gas shielded welding. b Argon arc welding. c Spot welding, etc. d Robot welding.

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

③ Welding symbol: Δ fillet welding, Д, I type welding, V type welding, single side V type welding (V) V type welding with a blunt edge (V), spot welding (O), plug welding or slot welding (∏) , Crimp welding (χ), single-sided V-shaped welding with blunt edge (V), U-shaped welding with blunt, J-shaped welding with blunt, back cover welding, and every welding.

④ Arrow wires and connectors.

⑤ Missing welding and preventive measures.

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

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

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

⑥ Reasons for welding deformation: insufficient preparation before welding, additional fixtures are needed. Improving process for poor welding jigs. The welding sequence is not good.

⑦ Welding Deformation Correction Method: Flame Correction Method. Vibration method. Hammering method. Artificial aging method.

other apps

The processing steps of processing parts in the sheet metal workshop are: product pre-test, product processing trial production and product batch production. In the product processing trial production step, it should communicate with customers in time, and after obtaining the evaluation of the corresponding processing, the product can be mass-produced.

Laser drilling technology is the earliest practical laser technology in laser material processing technology. Laser drilling in the sheet metal workshop generally uses pulsed lasers, which have higher energy density and shorter time. It can process small holes of 1μm. It is especially suitable for processing small holes with a certain angle and thin material, and it is also suitable for processing strength and hardness. Deep small holes and tiny holes in parts of higher or more brittle and softer materials.

The laser can realize the drilling of the combustor parts of the gas turbine, and the drilling effect can realize the three-dimensional direction, and the number can reach thousands. Perforated materials include stainless steel, nickel-chromium-iron alloys, and HASTELLOY-based alloys. The laser drilling technology is not affected by the mechanical properties of the material, and it is easier to realize automation.

With the development of laser drilling technology, the laser cutting machine has realized automated operation. The application in the sheet metal industry has changed the processing method of traditional sheet metal technology, realized unmanned operation, greatly improved production efficiency, and realized the whole process. The automatic operation has promoted the development of the sheet metal economy, and has improved the punching effect to a higher level, and the processing effect is remarkable.