What is sheet metal?

Sheet metal is a metal product processing technology, and there is no complete definition of sheet metal so far.
According to the definition of foreign journals, sheet metal can be defined as a comprehensive cold working technique for thin metal sheets (usually less than 8 mm). These include cutting, stamping / cutting / compositing, folding, riveting, splicing and molding (eg car body). Its feature is the uniform thickness of the same parts.

Process characteristics

Sheet metal is characterized by light weight, high strength, good conductivity (which can be used for electromagnetic shielding), low cost and mass production. Widely used in fields such as electronics, telecommunications, automobiles, and medical devices. For example, in computer cases, mobile phones and MP3s, sheet metal is an essential part. With the increasing use of sheet metal, the design of sheet metal parts has become an important part of the product development process. Since the mechanical engineer must be skilled in the design of sheet metal parts, sheet metal design not only meets the functional and appearance requirements of the product, but also makes stamping dies easy to manufacture and low cost. increase.

Sheet metal processing characteristics

Main material

There are many sheet metal materials suitable for stamping. Sheet metal materials widely used in the electrical and electronic industries

  1. Normal cold rolled sheet SPCC:
    SPCC refers to the continuous rolling of a steel ingot into a coil or sheet of the desired thickness by a cold rolling mill. Although the surface of the SPCC is not protected, it is easily oxidized in the air, especially in humid environments, with a fast oxidation rate and deep red rust.
  2. Galvanized steel sheet SECC:
    As a typical cold-rolled steel coil, SECC substrates become electro-galvanized products after degreasing, pickling, electro-plating and various post-treatment processes on continuous electro-galvanizing lines. SECC not only has the mechanical properties and similar processing properties of ordinary cold-rolled steel sheet, but also has excellent corrosion resistance and decorative appearance. In electronic products, the consumer electronics and furniture markets are highly competitive and can be replaced. For example, computer chassis typically use SECC.
  3. Hot-dip galvanized steel sheet SGCC:
    A hot-dip galvanized steel coil is a semi-finished product after hot-rolling pickling or cold-rolling. After washing, annealing and immersing in a hot-dip zinc bath at about 460 ° C., a zinc layer is plated on the steel sheet. After conditioning, leveling and chemical treatment. SGCC materials are harder than SECC materials, have poor ductility (avoid deep drawing designs), have a thick zinc layer, and have poor weldability.
  4. Stainless steel SUS301:
    The Cr (chromium) content is lower than that of SUS304, and the corrosion resistance is poor. However, after cold working, good tensile strength and hardness are obtained, and elasticity is good. Used for debris, springs and EMI.
  5. Stainless steel SUS304:
    One of the most widely used stainless steels contains Ni (nickel) and therefore has higher corrosion and heat resistance than steels containing Cr (chromium). It has very good mechanical properties, but it is neither heat treated nor elastic.

Sheet metal technology

The basic equipment for sheet metal processing is generally a variety of auxiliary equipment such as shearing machines, CNC punching machines, lasers, plasmas, cutting machines, bending machines, drilling machines, and anchorers, straighteners, deburring machines, and spot welders. device

In general, the four most important steps in a sheet metal process are shearing, stamping / cutting, folding / rolling, welding and surface treatment. The word sheet metal comes from British metal sheets. Usually, some metal sheets are plastically deformed by hand or mold to form the desired shape and size. It can be further molded into more complex parts by welding or a small amount of machining. For example, chimneys commonly used in housing, tin stoves and car casings are sheet metal parts.

Sheet metal processing

Specifically, for example, a metal plate for manufacturing a chimney, an iron drum, an oil tank for a fuel tank, a ventilation duct, a large elbow, a hemispherical dome, a funnel, or the like is used. The main processes are shearing, bending, fastening, welding and riveting. Geometric knowledge is required.

Metal sheets are sheet metal parts, that is, other methods of processing parts that are generally defined as stamping, bending, stretching, and parts having a certain thickness during processing. Castings, forgings, machined parts

Sheet metal technology

For the modern sheet metal process,

Filament power winding, laser cutting, heavy processing, metal bonding, metal wire drawing, plasma cutting, precision welding, roll forming, sheet bending, mold forging, water jet cutting, precision welding, etc.

Surface treatment of sheet metal parts is a very important part of sheet metal processing because it has the effect of preventing the parts from rusting and making them look beautiful. Sheet metal surface pretreatment is mainly used to remove oil, scale, rust, etc. Post-treatment is mainly spray (bake) coating, spray coating, and rust preventive plating.

3D software, SolidWorks, UG, Pro / E, SolidEdge, TopSolid and CATIA all have sheet metal component design capabilities. Mainly, edit 3D graphics to get the data necessary for sheet metal processing (expansion, bending line, etc.)
CNC punching machines, lasers, plasmas, water jet cutting machines, combination machines, CNC bending machines, etc. provide data.

Technical design

While meeting the requirements of product function and appearance, the design of the metal plate should ensure that the stamping process is simple, the stamping die is easy to manufacture, the sheet metal stamping quality is high and the size is stable. be.
Detailed guidelines for sheet metal design can be found in “Machinability of Parts Structure Design” and “Manufacturing and Assembly Product Design Guidelines” of the Machinery Industry Press.

Sheet Metal process

After receiving your drawing, we will select different blanking methods according to different drawings such as lasers, CNC punching machines, shear plates, molds and batch sizes, and develop according to the drawings. CNC punching machines are affected by tools, but in the case of irregular machining or irregular hole drilling, there are large burrs on the edges and deburring is performed at the same time, which affects the machining accuracy. Machining profiled workpieces, but machining small workpieces takes time. Placing the workbench next to the CNC and laser helps to install the board on the machine to reduce the workload of the lift plate.

Some of the edging materials that can be used are placed in designated locations to provide materials for testing during bending. After punching the workpiece, edge joints, burrs, and finishing (grinding) required the necessary contact for dressing using a flat boring tool at the tool joint. The small diameter connector is fitted with a corresponding small plaque to ensure the appearance. At the same time, shape trimming ensures positioning during bending so that it is placed on the bending machine at the same time during bending. Make sure the products in the same batch are the same size.

Sheet metal process design

After the blanking is complete, the next process is started and different workpieces enter the corresponding process according to the processing requirements. There are bends, rivets, boring, tapping, spot welding, bulges, steps, and nuts and studs may be pushed after one or two bends. In order to avoid interference after first processing the other steps, it is necessary to treat the position and step of the protrusion mold first and consider that the required machining cannot be completed. If the upper or lower case has hooks and cannot be welded after bending, it must be processed before bending.

When performing bending, the curvature of the tool and sipe must first be determined based on the paper size and material thickness. Avoiding collisions between the product and the tool and causing deformation is important for the choice of top mold (the same product can use different mold top molds). The choice of lower die depends on the thickness of the sheet. The second step is to determine the order of flexion. The general law of bending is first and foremost inside and outside, large at first and small after the first special | normal. First, push the work in the blind spot to bend the work from 30 ° to 40 °, and then crush the work with the leveling die.

When riveting, consider the height of the studs, select the same mold, and then adjust the press pressure so that the studs are level with the surface of the workpiece. Avoid studs that are not pushed or extruded over the surface of the workpiece and discard the part.

Welding Argon arc welding, spot welding, carbon dioxide welding, manual arc welding, spot welding must first consider the welding position of mass-produced workpieces, position fixtures to ensure accurate spot welding. Please consider.

By impacting the protrusions of the welded workpiece to ensure a firm weld, the protrusions make uniform contact with the flat plate prior to electric welding, ensuring uniform heating at each point. The welding position can also be determined. Again, welding is required. To adjust the preload time, pressure retention time, maintenance time, and downtime, make sure the workpiece is spot welded. After spot welding, a weld mark will be created on the surface of the workpiece. Process with a flat mill. Argon arc welding is primarily used when two workpieces are large and connected together. Alternatively, the workpiece can be machined to achieve a smooth, smooth surface. The heat generated during argon arc welding can deform the workpiece. After welding, especially in the corners, it should be machined using a grinder and a flat grinder.

surface treatment

Workpieces must be surface treated after bending, riveting, etc., and different plates have different surface treatments.
After processing the cooling plate, surface plating is usually performed. No spraying is required after plating. It is treated by phosphating and sprayed after phosphating.

The surface of the plate is clean, degreased and then sprayed.

Stainless steel sheets (mirror panel, fog panel, line drawing panel) can be pulled out before bending.

The aluminum plate is usually oxidized and a different oxidized background color is selected depending on the spray color. Commonly used black and natural oxidation; aluminum plates should be sprayed after chromate oxidation treatment. Surface pretreatment can cleanse the surface, significantly improve the adhesion of the coating film, and double the corrosion resistance of the coating film.

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