Upon receiving the sheet metal bending part blueprint, one should initially select the appropriate punching and blanking methods based on the internal and external geometry, size, and production volume of the bending part.
Methods include laser cutting, CNC punching (turret punching), shearing, die punching, and wire cutting. Subsequently, the blank development view of the bending part should be drawn based on the sheet metal bending part blueprint.
Note that CNC press machines (turret press machines) are influenced by the tooling. For irregularly shaped workpieces and irregular hole processing, larger burrs (which need to be deburred) may appear on the edges, simultaneously impacting the precision of the workpiece.
Laser processing, on the other hand, is not limited by tooling and has smooth cross-sections, making it suitable for irregular workpiece processing. However, processing smaller workpieces may be time-consuming.
Workbenches should be placed near CNC press machines (turret press machines) and laser cutters to facilitate the placement of sheets onto the machine platform for processing and reduce the workload of lifting sheet materials. Any usable offcuts should be placed in designated areas to provide material for bending trials.
After the workpiece is blanked, corners, burrs, and intersections must be properly finished (sanded). Flat files should be used to finish at tool junctions, large burrs should be finished with a grinder, and small inner hole intersections should be finished with the appropriate small file to ensure aesthetic appearances.
This finishing also ensures accurate positioning for bending, maintaining consistency in the position of the workpiece on the press brake machine and safeguarding the dimensional consistency of batch products.
Once blanking is complete, different bending parts should separately proceed to the next operation according to the technical requirements of the part blueprint. These operations include bending, riveting, flanging, threading, spot welding, embossing, form trimming, and secondary cutting.
Sometimes, after one or two bending operations, it may be necessary to first rivet nuts or studs to avoid difficulties in performing riveting after additional bending.
When the bending parts need to be embossed and trimmed by the die, consider processing these first to avoid interference that may prevent completion of the fabrication after other operations.
If hooks are present on the upper or lower cover, and if welding is not possible after bending, then welding should be done prior to bending.
During the bending process, one must initially determine the bending tool and lower die to be used based on the shape, drawing dimensions, and material thickness of the bent part. This helps avoid interference between the product and the bending tool or lower die (different types of bending tools and lower dies may be used within the same product), causing part deformation.
The choice of lower die slot width should be determined according to the thickness of the sheet and the tonnage of the bending machine. The next step is to determine the sequence of bending.
The general rule is to bend internally before externally, smaller parts before larger, and special shapes before standard ones. For sheet metal parts that need to be flattened, the part should initially be bent to 30°, and then flattened using a hemming die.
When riveting nuts or studs onto the bent parts, consider the potential impact of the height of the nuts or studs on bending. You can select identical or different dies, then adjust the pressure of the press to ensure the riveted nuts or studs are flush with the part surface, avoiding waste caused by improperly tightened or protruding nuts or studs.
Welding of sheet metal parts typically uses processes such as laser welding, hydrogen arc welding, spot welding, CO2 shielded welding, stick arc welding (commonly known as manual arc welding), and gas welding. For spot welding, consider the position of the welded parts first.
In mass production, manufacture positioning jigs should be considered to ensure the accuracy of the spot welding position. To ensure solid welding, pre-form protrusions on the sheet metal parts to be welded, allowing the protrusions to make contact with the flat plate before electricity is applied, thus ensuring consistent current at each point.
Spot welding may leave weld scars and spatter on the part surface, necessitating a desplattering process. Argon arc welding and CO2 shielded welding are mainly used for welding larger parts or corner welding of individual parts (such as the four corners of box-shaped parts).
However, be aware that the heat generated by argon arc welding and CO2 shielded welding can easily deform the part. After welding, use a grinder and surface grinder on the part, especially at the corners.
After bending, welding, and other processes, parts generally require surface treatment. Depending on the material of the sheet metal part, different surface treatments are needed. For regular thin steel sheet parts, the surface generally requires electroplating and then painting.
However, painting cannot be done immediately after electroplating; first, a phosphating treatment is needed, then painting after heating. Before painting the surface of electroplated parts, they should be cleaned, degreased, and heated. Stainless steel parts usually don’t require painting, and surface treatments can be applied before bending for mirror finish, matte, or brush finish panels.
If painting is required, the painting surface must undergo a sanding process. Alloy saw plates generally use an anodic oxidation surface treatment. If painting is required, chromate treatment should be applied before painting. The base color of the oxidation should be chosen based on the color of the surface painting, with black and natural oxidation being commonly used.
Before entering the painting process, protect areas of the part (not to be painted) with threads or conductive holes, by inserting a soft rubber rod in the hole or screwing in a screw. High-temperature tape can be used to protect surfaces.
Protective measures should be taken for nuts, studs, and threaded holes on the part to avoid additional thread-chasing after painting. When high surface quality is required, conduct a putty application before painting. Special high-temperature-resistant stickers should be used to protect grounding symbols during putty application.
Before entering the assembly process, remove the protective stickers from the part, ensuring that there is no paint or dust inside the threaded holes. Throughout the process, gloves should be worn to prevent dust and fingerprints from adhering to the part.
