The sheet metal fabrication process can be different according to the differences of sheet metal structure. But generally, it will be as following:
A. Blanking: there are various methods of material cutting, mainly including:
Shearing machines are used to cut strips and simple shaped sheets. It is mainly used for mould blanking. The cost is low and the precision is less than 0.2mm, but only blanks or blocks with no holes or corners can be processed.
(2)Manual Stamping Machines:
It is the use of stamping machines in one or more steps to stamp blanking material into different shapes after unfolding parts. Its advantages are short working hours, high efficiency, high precision, low cost, and suitable for mass production,but need to process with customized mould.
(3)NC Punch Press:
The NC program must first be programmed when processed by CNC punch press. The unfolding drawing should be written as a recognizable program for the NC numbering process machine by using the programming software, and then it can punch on the sheets material by the way of one-punch-one-cut according to these programs. We can get flat base parts of different shapes on the basis of variety of punch tools. The cost is low and the accuracy is 0.15mm.
By using laser cutting, we can cut a variety of flat patterns on a large flat plate.Same with NC punch press, it can cut complicate flat parts of different patterns by writing laser cut program . But it is on high cost than other cutting methods. The accuracy is 0.1mm.
Mainly it is used for cutting for aluminium profile, pipe (tube), rod; low cost, low precision.
B. Fittering: countersunk, tapping, reaming, drilling. Common countersunk angle is 120 degree for riveting, and 90 degrees for countersunk screws.
C. Flanging: that is to draw a slightly larger hole on a smaller base hole, and then tapping, which is mainly used on sheet metal process of thin plate to increase its strength and number of threads and avoid sliding. We can make flanging 40-60% higher under the condition of 30-40% thinner on material thickness. The maximum height of flanging can be made by 50% drawing. When material is thick, like more than 2.0, 2.5, we can drill directly.
D. Manual stamping: It is a processing process by using die forming. The common punching process includes corner cutting, blanking, punching and embossing (bumping), drawing, forming, etc. Tasks are completed with corresponding mould, such as blanking die, hole punching die, tearing die, hole drawing die, forming die, etc. Need to pay attention to its operating location and directionality.
E. Riveting: we have press rivet nuts, screws, bolt, etc., which are completed by hydraulic press riveting machines or punch press machines, riveting them to the sheet metal work. Pay attention to directionality.
F. Bending is folding a 2D flat panel into a 3D part. The processing requires a brake press machine and a corresponding bending die to complete, and it also has a certain bending sequence. The principle is that the first bend does not interfere with the next bend.
(1) Bend coefficient is calculated as follows: T=3.0mm, 6 times of the thickness equal to the lower groove width, eg: 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
(2) Folding bed mold (bending mould) classification: straight knife, machete (80°C, 30°C)
(3)When aluminum plate bended, there will be a crack, which can be solved by increasing the width of the lower groove and increasing the upper mold R angle (annealing can avoid cracks)
(4)Precautions when bending:
●Drawing dimension: the requirements of sheet thickness, quantity;
●Appearance, crease is not allowed on electroplating chrome parts .
(5)The relationship between bending and riveting process is usually followed by riveting first and then bending. However, in some cases, bending, riveting and re-bending are required.
G. Welding is a fabrication or sculptural process that joins materials, usually metals or thermoplastics, by causing fusion, which is distinct from lower temperature metal-joining techniques such as brazing and soldering, which do not melt the base metal.
(1) Classification: a. fusion welding: argon arc welding, CO2 welding, gas welding, manual welding; b. pressure welding: spot welding, butt welding, collision welding c. brazing: electric chrome welding, copper wire
(2) Welding methods: a. CO2 gas shielded arc welding; b. argon arc welding; c. spot welding, etc.;d. robot welding.
The selection of welding method is based on the actual requirements and materials. Generally speaking, CO2 gas shielded welding is used for iron plate welding; argon arc welding is used for stainless steel, aluminum plate welding and robot welding. It can save time, improve work efficiency and welding quality, and reduce work strength.
(3) Welding symbols: Δ fillet welding, Д I welding, V welding, single side V welding, V welding (V) with blunt side, spot welding(O), plug welding or groove welding(∏), flanged edge welding(χ), single side V welding with blunt side(V), U welding with blunt side, J welding with blunt side, sealing welding, seam welding.
(4) Arrow lines and connectors
(5) Welds missing and its preventive measures.
Spot welds: hit bumps to increase strength of welding, imposing welding area; CO2 welding: high productivity, low energy consumption, low cost, strong rust resistance TIG: slow joining speed, low efficiency, high production cost, and tungsten inclusion, but it has the advantages of better welding quality. Non-ferrous metals such as aluminum, copper and magnesium can be welded.
(6) Welding deformation causes:
● Insufficient preparation before welding, additional welding jig (fixture)
● Bad improvement process on welding fixture
● Bad welding sequence
(7) Welding deformation correcting method
● Flame correction method
● Vibration method
● Hammering method
● Artificial correcting method
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