Our common sheet metal processing is mainly composed of six steps, which are introduced in detail as follows:
- Drawing design
- Laser processing / NC stamping
- Welding forming
- Electrostatic powder / liquid paint
- Packing and delivery
Steps To Complete The Production Of Sheet Metal Products
1. Drawing design
General customers provide drawings or samples, which are measured, designed and developed by the company’s engineering personnel to form processing breakdown drawing and assembly drawing and submit to the production department for processing.
Laser cutting machine can cut carbon steel, stainless steel and other materials. After processing, the section of the workpiece is neat, smooth and beautiful, and the size is accurate. It has more advantages for the workpiece with arc. It is an irreplaceable processing method for general CNC stamping.
3. CNC stamping
CNC Turret punch is mainly for products with thin material thickness, generally less than 2.5mm, which is more suitable for sheet metal parts with more holes or need to open a special mold to process. When the batch is large, CNC stamping has a certain cost advantage.
If most of the workpieces need to be bent after cutting, then the press brakes are needed to finish the bending process. The CNC press brake is better cause they’re not only fast, but also more accurate.
5. Welding forming
Generally, the workpiece needs to be assembled and formed after blanking.
There are many assembly methods, some directly with screws, riveting and other non welding process
General mechanical shell sheet metal use welding molding, the company generally adopts argon arc welding, touch welding, carbon dioxide welding
After welding, the workpiece is polished, so that the workpiece is firm and beautiful.
6. Electrostatic powder spraying
Electrostatic powder spraying mainly aims at carbon steel parts
In the process, the first step is to remove oil and rust, surface cleaning, phosphating treatment, electrostatic powder spraying, high temperature baking and other processes. After treatment, the surface of the workpiece is beautiful, it will not rust for several years, and the cost is low.
Liquid paint: this process is different from electrostatic powder spraying. Generally for large workpieces, liquid paint has the advantages of convenience and low cost when it can’t be transported. Liquid paint is generally divided into two steps. After the workpieces are treated, the primer is applied and then the paint is applied.
7. Packing and delivery
Carry out 100% inspection before packaging and provide inspection data.
The delivery requirement and packing method are confirmed by the customer’s representative on site. The record is hereby made for the customer’s confirmation
Process flow of sheet metal products
1. Sheet metal processing method:
(1) Non mold processing
The technology of sheet metal processing by punching, laser cutting, shearing machine, folding machine and riveting machine is generally used for sample production or small batch production with high cost
(2) Mold processing
Through the fixed mold for sheet metal processing, there are blanking mold, forming mold, mainly used for mass production with low cost.
2. Sheet metal processing technology
- Blanking: CNC punch, laser cutting, shearing machine
- Forming: bending, stretching, hole punching – press brake machine, punch machine, etc
- Other processing: riveting, tapping, etc
- Connection method of sheet metal
- Surface treatment: powder spraying, electroplating, wire drawing, silk screen printing, etc
The blanking methods of sheet metal include punching, laser cutting, shearing machine, die blanking, etc
At present, CNC punching is the common method; laser cutting is mostly used in the proofing stage, with high processing cost; die blanking is mostly used for mass processing.
Next, we mainly introduce the blanking of sheet metal with CNC punches.
The CNC punch, also known as turret punch, can be used for blanking, punching, drawing hole, pressing bar, etc. its machining accuracy can reach + / – 0.1mm. The thickness of the sheet that can be processed by numerical punching is as follows:
- Cold-rolled plate, hot rolled plate ≤ 0 mm
- Aluminum plate ≤ 0 mm
- Stainless steel plate ≤ 0 mm
(1) Small size is required for punching.
The small size of punching is related to the shape of the hole, the mechanical properties of the material and the thickness of the material. (as shown in the figure below)
|Materials||Hold dia. b||Rectangular hole
short side width b
|High carbon steel||1.3t||1.0t|
|Low carbon steel, brass||1.0t||0.7t|
(2) The distance between holes and distance between hole edges
The small distance between the punching edge and the shape of the part is limited by the shape of the part and the hole
When the punching edge is not parallel to the contour edge of the part, the small distance should not be less than the material thickness T; when parallel, it should not be less than 1.5T. (as shown in the figure below)
(3) When drawing holes, the small distance between the drawing hole and the edge is 3T, the small distance between the two drawing holes is 6T, and the small safe distance between the drawing hole and the bending edge (inside) is 3T + R (t is the sheet metal thickness, R is the bending radius)
(4) When drawing bending parts and deep drawing parts, a certain distance should be kept between the hole wall and the straight wall. (as shown in the figure below)
Sheet metal forming is mainly sheet metal bending, stretching.
① Basic principles of bending sequence:
Bending from inside to outside; bending from small to large; bending special shape first, then bending general shape; the former process has no influence or interference on the subsequent process.
② Small bending radius of bending parts:
When the material is bent, the outer layer of the fillet is stretched and the inner layer is compressed.
When the thickness of the material is constant, the smaller the inner R is, the more serious the tensile and compression are;
When the tensile stress of the outer fillet exceeds the ultimate strength of the material, cracks and fracture will occur
Therefore, the structural design of bending parts should avoid too small bending radius.
The small bending radius of common materials of the company is shown in the table below.
Table of minimum bending radius of bending parts:
The bending radius refers to the inner radius of the bending part, and t is the wall thickness of the material.
(2) Sheet metal stretch
Sheet metal drawing is mainly completed by several punches or common punches, and various drawing punches or dies are needed.
The shape of the drawing part should be as simple and symmetrical as possible, and it should be drawn once as far as possible.
For parts that need to be stretched many times, possible traces on the surface during the stretching process shall be allowed.
Under the premise of assembly requirements, the stretching side wall should be allowed to have a certain inclination.
(3) Other forming methods:
① Reinforcing rib – pressing reinforcing ribs on sheet metal parts helps to increase structural rigidity.
Reinforcing rib structure and its size selection
② Louvers – louvers are usually used for ventilation and heat dissipation on various enclosures or casings.
③ Hole flanging (stretch hole) – used to machine threads or to improve the rigidity of openings.
In the design of sheet metal welding structure, the welds and solder joints should be arranged symmetrically, and the convergence, aggregation and overlap should be avoided. The secondary welds and solder joints can be interrupted, and the main welds and solder joints should be connected.
Commonly used welding in sheet metal processing are electric arc welding, resistance welding, etc.
(1) Arc welding
There should be enough welding space between the sheet metal, the welding gap should be 0.5-0.8mm, and the weld should be even.
(2) Resistance welding
The welding surface shall be smooth without wrinkles and springback.
The dimensions of resistance spot welding are as follows
|Thickness t(mm)||Solder joint dia. d (mm)||Min distance from
solder joint to edge f (mm)
|Min width of
welding edge (mm)
4. Sheet metal connection methods
Here we mainly introduce the connection methods of sheet metal in the process of processing, mainly including rivet riveting, welding (described above), hole riveting, tox riveting.
This kind of rivet is often called pull rivet. Two plates are riveted together by pull rivet.
Common riveting shapes are shown in the figure:
(2) Pull out riveting:
One part is a hole drawing, the other is a counterbore, which is made into a non detachable connector by riveting die
Advantages: the hole itself has positioning function.
The riveting strength is high, and the riveting efficiency through the die is also high.
(3) Tox riveting:
The connected part is pressed into the die by a simple punch
Under the action of further pressure, the material in the die flows outward. As a result, a round connection point without edges and burrs is formed, and its corrosion resistance is not affected.
Even if there is a coating or spray coating on the surface of the plate, the original anti-rust and anti-corrosion characteristics can also be retained because the coating and paint layer also deform and flow together.
The material is pushed to both sides and into the panel near the die side to form the tox connection dot.
As shown in the figure below:
5. Surface treatment
The surface treatment of sheet metal can play the role of anti-corrosion protection and decoration.
The common surface treatment of sheet metal includes powder spraying, electro galvanizing, hot-dip galvanizing, surface oxidation, surface drawing, silk screen printing, etc.
The oil stain, rust and welding slag on the surface of sheet metal shall be removed before surface treatment.
(1) Powder spraying
There are liquid paint and powder paint on the surface of the sheet metal.
Powder paint is commonly used.
By means of powder spraying, electrostatic adsorption and high temperature baking, a layer of various colors of coatings is sprayed on the surface of sheet metal to beautify the appearance and increase the anti-corrosion performance of materials. It is a common surface treatment method.
(2) Electro galvanizing and hot dip galvanizing
Galvanizing on the surface of sheet metal is a common surface anti-corrosion treatment method, which can beautify the appearance.
Galvanizing can be divided into electro galvanizing and hot dip galvanizing.
The appearance of electro galvanizing is bright and flat, and the zinc coating is thin, which is commonly used.
The zinc coating of hot-dip galvanizing is thicker and can produce zinc iron alloy layer, and its corrosion resistance is stronger than that of electro galvanizing.
(3) Surface oxidation
Here mainly introduces the surface anodization of aluminum and aluminum alloy.
Aluminum and aluminum alloy surface anodization can be oxidized into a variety of colors, play a protective role and have a good decorative effect.
At the same time, it can produce anodic oxide film on the surface of the material. The anodic oxide film has high hardness and wear resistance, as well as good electrical insulation and thermal insulation.
(4) Surface drawing
The material is placed between the upper and lower rollers of the wire drawing machine. There is an abrasive belt attached to the roller. Driven by the motor, the material can pass through the upper and lower abrasive belts and pull out traces on the surface of the material. According to the different abrasive belts, the trace thickness is also different. The main function is to beautify the appearance
Generally, the surface treatment method of wire drawing is only considered for aluminum.
(5) Silk screen printing
Screen printing on the surface of materials can be divided into flat screen printing and pad printing
Flat screen printing is mainly used in the general plane, but if there are deep pits, you need to use pad printing.
Silk screen printing needs a silk impression.