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Process problems in sheet metal processing

Process problems in sheet metal processing

2021-05-29

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, brushed, matte), 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 is 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, baking varnish parts, low cost, but difficult to form, mainly flat parts.
3. Galvanized sheet SECC, SGCC. 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 uses conductive material, and its surface treatment is nickel plating, chrome plating, or no treatment, which is costly.

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

CNC Turning Aluminum parts-3

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; mainly used without any surface treatment, high cost.
Drawing review
To compile the process flow of a part, we must first know the various technical requirements of the part drawing; then the drawing review is the most important link in the compilation of the part process flow.
1. Check whether the drawing is complete.
2. The relationship between the drawing and the view, whether the marking is clear and complete, and the unit of dimension is marked.
3. Assembling relationship, assembly requires key dimensions.
4. The difference between the old and the new version of the graphics.
5. Translation of pictures in foreign languages.
6. Table office code conversion.
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) developed based on the part drawing (3D)
1. The unfolding 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 by drawing teeth, pressing riveting, tearing, punching convex points (package), etc.
6. Check the material, thickness, and thickness tolerance
7. For special angles, the inner radius of the bending angle (generally R=0.5) depends on the trial bending.
8. Places that are prone to errors (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
①. Shearing machine: It uses a shearing machine to cut simple strips. It is mainly used to prepare and process mold blanking. It has low cost and accuracy below 0.2, but it can only process strips or blocks with no holes and no corners.
②. Punch: It uses a 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.
③. NC 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. According to these programs, you can punch each piece on the plate one step at a time. 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.
④. Laser cutting is to use laser cutting to cut the structure and shape of the flat plate on a large flat plate. The laser program is required to be programmed like NC cutting. It can load various complex shapes of flat parts, with high cost and accuracy of 0.1 .
⑤. Sawing machine: Mainly use aluminum profiles, square tubes, drawing tubes, round bars, etc., with low cost and low precision.
1. 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.
2. Flanging: It is also called hole extraction and hole flanging, 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, there is basically no change in thickness, and when the thickness is allowed to be thinned by 30-40%, it can be 40-higher than the normal flanging height. For a height of 60%, the maximum flanging height can be obtained when the thinning is 50%. When the plate thickness is larger, such as 2.0, 2.5, etc., it can be tapped directly.
3. Punching machine: 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.
4. Pressure riveting: As far as our company is concerned, pressure riveting mainly includes pressure riveting nuts, screws, and so on. It is operated by hydraulic pressure riveting machine or punching machine, riveting it to sheet metal parts, and expanding riveting Way, need to pay attention to directionality.
5. 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 will not interfere with the first folding, and the interference will occur after the folding.
l 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
l Classification of folding bed molds, straight knife, scimitar (80℃, 30℃)
l When the aluminum plate is bent, there are cracks, the width of the lower die slot can be increased, and the upper die R can be increased (annealing can avoid cracks)
l Matters needing attention 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 electroplated chromium materials.
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.
6. Welding: Welding definition: the distance between the atoms and molecules of the welded material and the Jingda lattice is integrated
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 blunt edges (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, every welding
④ Arrow line and joint
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 melting speed, low efficiency, high production cost, tungsten inclusion defects, but has the advantages 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 poor welding fixture
Bad welding sequence
⑦ Welding deformation correction method: flame correction method
Vibration method
Hammering
Artificial aging
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