Sheet metal processing flow

With the development of today's society, the sheet metal industry has also grown rapidly. Sheet metal is now involved in various industries. Every sheet metal part has a specific processing process, also known as a process flow. To understand the sheet metal processing process, you must first understand the selection of sheet metal materials.

1. Material Selection: Commonly used materials for sheet metal processing include cold-rolled sheet (SPCC), hot-rolled sheet (SHCC), galvanized sheet (SECC, SGCC), copper (CU), brass, copper, beryllium copper, aluminum sheet (6061, 6063, duralumin, etc.), aluminum profiles, and stainless steel (mirror, brushed, or matte finishes). The material selection varies depending on the product's function, generally considering the product's application and cost.

1. Cold-rolled SPCC sheet, primarily electroplated and painted, is low-cost and easy to form. Material thickness ≤ 3.2mm.

2. Hot-rolled SHCC sheet, with a T ≥ 3.0mm, also electroplated and painted. It is low-cost but difficult to form and is primarily used as a flat sheet.

3. Galvanized sheet: SECC and SGCC. SECC electrolytic sheet is divided into N and P grades. N grade is primarily untreated and is costly, while P grade is used for spray-coated parts.

4. Copper: Primarily used for conductive parts. Its surface treatments include nickel plating, chrome plating, or no treatment, resulting in high cost.

5. Aluminum: Generally uses surface chromate (J11-A) or oxidation (conductive oxidation, chemical oxidation). Cost is high. Silver plating and nickel plating are also available.

6. Aluminum profiles: Parts with complex cross-sectional structures, widely used in various plug-in boxes. Surface treatment is similar to that of aluminum sheet.

7. Stainless steel: Primarily used without any surface treatment and is costly.

II. Drawing Review: To develop a part's process flow, you must first understand the various technical requirements of the part drawing. Drawing review is the most important step in developing a part's process flow.

1. Check that the drawings are complete.

2. Drawing view relationships, whether annotations are clear and complete, and dimension units.

3. Assembly relationships, key dimensions for assembly requirements.

4. Differences between new and old versions of drawings.

5. Translation of foreign-language drawings.

6. Conversion of table and part codes.

7. Feedback and resolution of drawing issues.

8. Materials.

9. Quality and process requirements.

10. Officially released drawings must be stamped with a quality control stamp.

3. Expedited Development Considerations: The expanded drawing is a plan view (2D) expanded from the part drawing (3D).

The expanded method should be reasonable, ensuring material savings and processability.

2. Appropriate selection of clearances and hemming methods: For T=2.0 or less, the clearance is 0.2, and for T=2-3, the clearance is 0.5. The hemming method should be:

Long edge hemming short edge (for door panels).

3. Consider the tolerances for external dimensions: negative tolerances are maximized, positive tolerances are halfway; for hole dimensions: positive tolerances are maximized, negative tolerances are halfway.

4. Burr direction

5. Draw cross-sectional views for the positions and directions of threading, riveting, tearing, and punching embossing (burrs).

6. Verify the material and plate thickness, using the plate thickness tolerance.

7. For special angles, the inner radius of the bend (generally R=0.5) should be determined by trial bending and unfolding.

8. Highlight areas prone to error (similarities or asymmetries).

9. Enlarged views should be provided for areas with large dimensions.

10. Areas requiring spray protection must be indicated.

IV. The process flow for sheet metal processing can vary depending on the structure of the sheet metal part, but generally does not exceed the following points.

1. Blanking: There are various blanking methods, the main ones being the following.

①. Shearing Machines: Shearing machines are used to cut simple parts from strips of stock. They are primarily used to prepare for die blanking and forming. They offer low cost and accuracy below 0.2°, but can only process strips or blocks without holes or corners.

②. Punching Machines: Punching machines use a single or multiple steps to punch out various shapes from flat sheets after unfolding the part. Their advantages are reduced labor time, high efficiency, high precision, and low cost, making them suitable for mass production. However, mold design is required.

③. NC blanking: NC blanking requires programming a CNC machining program. Using programming software, the unfolded diagram is converted into a program that the NC blanking machine can recognize. These programs are used to punch out various shapes from the flat sheet, one cut at a time. However, their structure is affected by the tool structure. The cost is low and the accuracy is below 0.15°.

④. Laser blanking uses laser cutting to create structural shapes on large flat plates. Like NC blanking, laser programming is required. It can produce a variety of complex flat plate shapes, but at a high cost and with an accuracy of less than 0.1.

⑤. Sawing Machine: Primarily used for cutting aluminum profiles, square tubes, drawing tubes, round bars, etc. It offers low cost but low accuracy.

Fixer: Countersinking, tapping, reaming, and drilling. Countersinking angles are typically 120° for rivets, 90° for countersunk screws, and tapping imperial base holes. Flanging, also known as punching or drilling, involves creating a slightly larger hole from a smaller base hole, followed by tapping. This process is primarily used on thin sheet metal to increase strength and thread count, while preventing thread slippage. It's generally used for thin sheet metal, where shallow flanges around the hole are normal and maintain minimal thickness change. A 30-40% reduction in thickness is permitted, resulting in a 40-60% increase in flange height compared to the normal flange. A 50% thinning allows for maximum flange height. For thicker sheet metal, such as those above 2.0 mm and 2.5 mm, direct tapping is possible.

Punching: A process utilizing dies to form parts. Common punching operations include punching, corner cutting, blanking, embossing, tearing, punching, and forming. These operations require appropriate dies, such as punching, embossing, tearing, punching, and forming dies. During operation, proper positioning and directionality are crucial. Press riveting: Our company primarily rivets nuts, screws, and captives. This process is performed using a hydraulic riveting press or punch press to attach the parts to sheet metal. Expansion riveting is also available, but attention must be paid to directional control.

Bending: Bending involves folding a 2D flat sheet into a 3D part. This process requires a folding machine and corresponding bending dies. There is also a specific bending sequence. The principle is to bend parts that will not interfere with the next cut first, and parts that will interfere last. The number of bends is calculated based on the groove width of six times the plate thickness for T=3.0mm or less. For example: 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 machine tool types: straight and curved (80°C, 30°C)

If cracks occur when bending aluminum plates, increase the groove width of the lower die or increase the R of the upper die (annealing can prevent cracks).

Bending precautions: I. Drawing, required plate thickness and quantity; II. Bend direction; III. Bend angle; IV. Bend dimensions; VI. Appearance: Chrome-plated parts must not have creases.

Regarding the relationship between bending and riveting, riveting is generally performed first, followed by bending. However, if the parts will interfere after riveting, bending is performed first, followed by riveting. Some parts require a combination of bending, riveting, and then bending. Welding: Definition: The process by which atoms and molecules of the materials being welded are integrated within the crystal lattice.
① Classification: a. Fusion welding: argon arc welding, CO2 welding, gas welding, manual welding. b. Pressure welding: spot welding, butt welding, butt welding. c. Brazing: electrochromium welding, copper wire welding.

② Welding Methods: a. CO2 gas shielded welding. b. TIG welding. c. Spot welding, etc. d. Robotic welding.

The choice of welding method depends on the specific requirements and material. Generally, CO2 gas shielded welding is used for welding iron plates; TIG welding is used for welding stainless steel and aluminum plates. Robotic welding can save time, improve work efficiency and welding quality, and reduce workload.

③ Welding symbols: Δ fillet weld, D/I weld, V-weld, single-sided V-weld (V), blunt-edged V-weld (V), spot weld (O), plug or slot weld (∏), flange weld (χ), blunt-edged single-sided V-weld (V), blunt U-weld, blunt J-weld, bottom weld, butt weld

④ Arrow lines and joints

⑤ Welding defects and their prevention measures: Spot welding: If strength is insufficient, bumping can be used to increase the weld area. CO2 welding: High productivity, low energy consumption, low cost, and strong rust resistance. TIG welding: Shallow penetration, slow welding speed, low efficiency, high production cost, and the possibility of tungsten inclusion defects, but with the advantage of good weld quality. It can weld non-ferrous metals such as aluminum, copper, and magnesium.

⑥ Causes of Welding Deformation:

Insufficient pre-welding preparation, requiring additional fixtures

Poor welding fixtures, process improvements

Improper welding sequence

⑦ Methods for Correcting Welding Deformation:

Flame Correction

Vibration Correction

Hammer Correction

Artificial Aging