Sheet metal processing, a common manufacturing process, consists of six main steps, which I will detail below: sheet metal design for processing -> laser cutting or (CNC punching) -> bending -> welding and forming -> electrostatic powder coating or (liquid painting) -> packaging and shipping.
1. Drawing Design: Generally, customers provide drawings or samples, and engineering personnel measure, design, unfold, and create detailed processing and assembly diagrams to submit to the production department for manufacturing.
2. Laser Processing: Large laser cutting machines can cut materials such as carbon steel and stainless steel. Laser cutting offers clean, smooth, and aesthetically pleasing edges with precise dimensions, especially advantageous for parts with curves, a process that CNC punching cannot replace.
3. CNC Punching: CNC punching is mainly for products with thinner material, typically less than 2.5mm thick. It is suitable for sheet metal parts with many holes or those that require special molds for processing. CNC punching is cost-effective for large-scale production.
4. Bending: After cutting, most parts require bending. Our company has several computer-controlled bending machines, which not only operate quickly but also ensure precise processing of workpieces.
5. Welding and Forming: After cutting, parts generally need to be assembled. There are various assembly methods, including non-welding techniques like screws and rivets. However, for most external mechanical casings in sheet metal, welding is used. Our company typically employs argon arc welding, spot welding, and CO2 welding. After welding, the workpieces are ground and polished to ensure durability and aesthetics.
6. Electrostatic Powder Coating: This is mainly for carbon steel workpieces. The process typically includes degreasing, rust removal, surface conditioning, phosphating, electrostatic powder coating, and high-temperature curing. This process leaves the workpiece surface aesthetically pleasing, rust-free for several years, and is cost-effective.
Liquid Painting: This process differs from electrostatic powder coating and is generally used for large workpieces that are difficult to transport. Liquid painting is convenient and cost-effective. It usually involves two steps: applying primer and then the topcoat after the workpiece has been treated.
7. Packaging and Shipping: A 100% inspection is conducted before packaging, and inspection data is provided. Shipping requirements and packaging methods are confirmed on-site by the customer's representative and recorded for the customer's reconfirmation.
Process Technology Introduction
1. Sheet Metal Processing Methods:
(1) Non-mold processing: This involves using equipment like CNC punch machines, laser cutters, shearing machines, bending machines, and riveting machines to process sheet metal, generally used for sample production or small-scale production, and is more costly.
(2) Mold processing: This involves using fixed molds to process sheet metal, typically including cutting dies and forming dies, mainly used for mass production and is less costly.
2. Sheet Metal Processing Techniques
Cutting: CNC punching, laser cutting, shearing machines
Forming – Bending, stretching, punching: bending machines, punch presses, etc.
Other processing: riveting, tapping, etc.
Welding
Sheet Metal Connection Methods
Surface Treatment: Powder coating, electroplating, brushing, silk screening, etc.
1. Sheet Metal Processing Techniques - Cutting
The main methods of cutting sheet metal include CNC punching, laser cutting, shearing machines, and mold cutting. CNC punching is a commonly used method, laser cutting is often used in the prototyping stage due to its high processing cost, and mold cutting is used for large-volume processing.
Here, we primarily focus on CNC punching for sheet metal cutting.
CNC punching, also known as turret punching, can be used for cutting, punching holes, stretching holes, and pressing ribs, with a processing precision of up to +/-0.1mm. The thickness of the plates that can be processed by CNC punching includes:
- Cold-rolled plate, hot-rolled plate ≤ 3.0mm
- Aluminum plate ≤ 4.0mm
- Stainless steel plate ≤ 2.0mm
(1) Punching requires small dimensions. The minimum size of the hole depends on the shape of the hole, the mechanical properties of the material, and the thickness of the material.
(2) The spacing between holes and the edge distance in CNC punching. The minimum distance from the edge of the punching hole to the outer edge of the part has certain limitations depending on the shape of the part and the hole. When the edge of the punching hole is not parallel to the outer edge of the part, this distance should be no less than the thickness of the material, t; when parallel, it should be no less than 1.5t.
(3) When stretching holes, the minimum distance from the edge is 3T, the minimum distance between two stretching holes is 6T, and the minimum safe distance from a stretching hole to a bending edge (inner) is 3T+R (T is the thickness of the sheet metal, R is the bending radius).
(4) When punching holes in stretched and deep-drawn parts, a certain distance should be maintained between the hole wall and the straight wall.
2. Sheet Metal Processing Techniques - Forming
Forming in sheet metal mainly involves bending and stretching.
(1) **Sheet Metal Bending**
i. The basic principle of bending processing order: bend from inside to outside, from small to large, first bend special shapes, then bend general shapes, ensuring that earlier stages do not affect or interfere with subsequent stages.
ii. Minimum bending radius:
When materials are bent, the outer layer is stretched while the inner layer is compressed. With a fixed material thickness, the smaller the internal radius, the more severe the stretching and compression; when the stretching stress on the outer corner exceeds the material's ultimate strength, cracks and breaks occur. Therefore, in the structural design of bent parts, overly small bending radii should be avoided. The table below shows the minimum bending radii for commonly used materials.
(2) Sheet Metal Stretching
Sheet metal stretching is mainly completed by CNC or standard punches, requiring various stretching punches or molds. The shapes of stretched parts should be as simple and symmetrical as possible, ideally formed in one stretch. Parts requiring multiple stretches should allow for potential surface marks during the stretching process. Subject to assembly requirements, a certain degree of slope on the stretching sidewalls should be permitted.
3. **Sheet Metal Other Forming Techniques:**
i. **Reinforcement Ribs** – Pressing ribs into sheet metal parts to increase structural rigidity.
ii. **Louvers** – Louvers are commonly used for ventilation and heat dissipation in various covers or casings.
iii. **Flanged Holes (Stretch Holes)** – Used to process threads or to increase the rigidity of openings.
4. **Sheet Metal Processing Techniques - Welding**
When designing sheet metal welding structures, the principle of "symmetrically arranging weld seams and points, and avoiding convergence, accumulation, and overlap" should be implemented. Secondary weld seams and points can be interrupted, whereas primary ones should be continuous. Common welding methods in sheet metal include arc welding and resistance welding.
i. **Arc Welding**
Sufficient space must be provided for welding between sheet metal parts, with a welding gap of 0.5-0.8MM, and the weld seam should be uniform and smooth.
ii. **Resistance Welding**
The welding surface should be flat, without wrinkles, springback, etc.
5. **Sheet Metal Processing Techniques - Connection Methods**
Here we introduce the connection methods used in sheet metal processing, mainly including riveting, welding (described above), pull-out riveting, and TOX riveting.
i. **Riveting**: This rivet is often referred to as a pop rivet, and joining two pieces of sheet metal together with a pop rivet is known as riveting. Common riveting shapes are shown in the diagram.
ii. **Pull-out Riveting**:
One part has a pull-out hole, and the other part has a countersunk hole. The riveting die makes them into a non-detachable connection. Advantages include the pull-out hole and its corresponding countersunk hole having a positioning function, high riveting strength, and high efficiency through die riveting.
iii. **TOX Riveting**:
The connected parts are pressed into a die by a simple punch. Under further pressure, the material inside the die "flows" outward. This results in a round connection point that is both edge-free and burr-free, and it does not affect the corrosion resistance, even if the sheet has a plating or painting layer, as the plating and painting also deform and flow with the material. The material is squeezed to the sides, into the sheet by the die side, thus forming a TOX connection point. The following page shows a diagram:
6. **Sheet Metal Processing Techniques - Surface Treatment**
Surface treatment of sheet metal can provide anti-corrosion protection and a decorative effect. Common surface treatments for sheet metal include powder coating, galvanizing, hot-dip galvanizing, surface oxidation, surface brushing, and silk screening.
Before surface treatment, the sheet metal surface should be cleaned of oil, rust, weld slag, etc.
i. **Powder Coating**: There are two types of surface spray for sheet metal: liquid paint and powder paint. We commonly use powder paint. By spraying powder, electrostatic adsorption, and high-temperature curing, a layer of various colors of paint is applied to the surface of the sheet metal to beautify the appearance and increase the material's anti-corrosion properties. It is a commonly used surface treatment method.
ii. **Galvanizing, Hot-Dip Galvanizing**: Surface galvanizing is a common method of anti-corrosion treatment for sheet metal and can also enhance the appearance. Galvanizing can be divided into electro-galvanizing, which has a bright and smooth appearance and a thin zinc layer, and hot-dip galvanizing, which has a thicker zinc layer and can form a zinc-iron alloy layer, offering stronger corrosion resistance than electro-galvanizing.
iii. **Surface Oxidation**: Here we mainly introduce the anodic oxidation of aluminum and aluminum alloys. Anodic oxidation of aluminum and aluminum alloys can be colored in various colors, providing protection and a good decorative effect. It can also produce an anodic oxide film on the material's surface, which has high hardness and wear resistance, as well as good electrical insulation and thermal insulation.
iv. **Surface Brushing**: The material is placed between the upper and lower rollers of the brushing machine, which has a sanding belt attached to it. Driven by a motor, the material passes through the sanding belts, leaving traces on the surface. Depending on the sanding belt used, the traces can vary in coarseness, mainly serving to beautify the appearance. Brushing is generally considered for aluminum materials.
v. **Silk Screening**: The process of silk screening various markings on the material's surface, generally available in flatbed and pad printing methods. Flatbed silk screening is mainly used for general flat surfaces, but pad printing is required for areas with deeper recesses. Silk screening requires a silk screen template.
1. Drawing Design: Generally, customers provide drawings or samples, and engineering personnel measure, design, unfold, and create detailed processing and assembly diagrams to submit to the production department for manufacturing.
2. Laser Processing: Large laser cutting machines can cut materials such as carbon steel and stainless steel. Laser cutting offers clean, smooth, and aesthetically pleasing edges with precise dimensions, especially advantageous for parts with curves, a process that CNC punching cannot replace.
3. CNC Punching: CNC punching is mainly for products with thinner material, typically less than 2.5mm thick. It is suitable for sheet metal parts with many holes or those that require special molds for processing. CNC punching is cost-effective for large-scale production.
4. Bending: After cutting, most parts require bending. Our company has several computer-controlled bending machines, which not only operate quickly but also ensure precise processing of workpieces.
5. Welding and Forming: After cutting, parts generally need to be assembled. There are various assembly methods, including non-welding techniques like screws and rivets. However, for most external mechanical casings in sheet metal, welding is used. Our company typically employs argon arc welding, spot welding, and CO2 welding. After welding, the workpieces are ground and polished to ensure durability and aesthetics.
6. Electrostatic Powder Coating: This is mainly for carbon steel workpieces. The process typically includes degreasing, rust removal, surface conditioning, phosphating, electrostatic powder coating, and high-temperature curing. This process leaves the workpiece surface aesthetically pleasing, rust-free for several years, and is cost-effective.
Liquid Painting: This process differs from electrostatic powder coating and is generally used for large workpieces that are difficult to transport. Liquid painting is convenient and cost-effective. It usually involves two steps: applying primer and then the topcoat after the workpiece has been treated.
7. Packaging and Shipping: A 100% inspection is conducted before packaging, and inspection data is provided. Shipping requirements and packaging methods are confirmed on-site by the customer's representative and recorded for the customer's reconfirmation.
Process Technology Introduction
1. Sheet Metal Processing Methods:
(1) Non-mold processing: This involves using equipment like CNC punch machines, laser cutters, shearing machines, bending machines, and riveting machines to process sheet metal, generally used for sample production or small-scale production, and is more costly.
(2) Mold processing: This involves using fixed molds to process sheet metal, typically including cutting dies and forming dies, mainly used for mass production and is less costly.
2. Sheet Metal Processing Techniques
Cutting: CNC punching, laser cutting, shearing machines
Forming – Bending, stretching, punching: bending machines, punch presses, etc.
Other processing: riveting, tapping, etc.
Welding
Sheet Metal Connection Methods
Surface Treatment: Powder coating, electroplating, brushing, silk screening, etc.
1. Sheet Metal Processing Techniques - Cutting
The main methods of cutting sheet metal include CNC punching, laser cutting, shearing machines, and mold cutting. CNC punching is a commonly used method, laser cutting is often used in the prototyping stage due to its high processing cost, and mold cutting is used for large-volume processing.
Here, we primarily focus on CNC punching for sheet metal cutting.
CNC punching, also known as turret punching, can be used for cutting, punching holes, stretching holes, and pressing ribs, with a processing precision of up to +/-0.1mm. The thickness of the plates that can be processed by CNC punching includes:
- Cold-rolled plate, hot-rolled plate ≤ 3.0mm
- Aluminum plate ≤ 4.0mm
- Stainless steel plate ≤ 2.0mm
(1) Punching requires small dimensions. The minimum size of the hole depends on the shape of the hole, the mechanical properties of the material, and the thickness of the material.
(2) The spacing between holes and the edge distance in CNC punching. The minimum distance from the edge of the punching hole to the outer edge of the part has certain limitations depending on the shape of the part and the hole. When the edge of the punching hole is not parallel to the outer edge of the part, this distance should be no less than the thickness of the material, t; when parallel, it should be no less than 1.5t.
(3) When stretching holes, the minimum distance from the edge is 3T, the minimum distance between two stretching holes is 6T, and the minimum safe distance from a stretching hole to a bending edge (inner) is 3T+R (T is the thickness of the sheet metal, R is the bending radius).
(4) When punching holes in stretched and deep-drawn parts, a certain distance should be maintained between the hole wall and the straight wall.
2. Sheet Metal Processing Techniques - Forming
Forming in sheet metal mainly involves bending and stretching.
(1) **Sheet Metal Bending**
i. The basic principle of bending processing order: bend from inside to outside, from small to large, first bend special shapes, then bend general shapes, ensuring that earlier stages do not affect or interfere with subsequent stages.
ii. Minimum bending radius:
When materials are bent, the outer layer is stretched while the inner layer is compressed. With a fixed material thickness, the smaller the internal radius, the more severe the stretching and compression; when the stretching stress on the outer corner exceeds the material's ultimate strength, cracks and breaks occur. Therefore, in the structural design of bent parts, overly small bending radii should be avoided. The table below shows the minimum bending radii for commonly used materials.
(2) Sheet Metal Stretching
Sheet metal stretching is mainly completed by CNC or standard punches, requiring various stretching punches or molds. The shapes of stretched parts should be as simple and symmetrical as possible, ideally formed in one stretch. Parts requiring multiple stretches should allow for potential surface marks during the stretching process. Subject to assembly requirements, a certain degree of slope on the stretching sidewalls should be permitted.
3. **Sheet Metal Other Forming Techniques:**
i. **Reinforcement Ribs** – Pressing ribs into sheet metal parts to increase structural rigidity.
ii. **Louvers** – Louvers are commonly used for ventilation and heat dissipation in various covers or casings.
iii. **Flanged Holes (Stretch Holes)** – Used to process threads or to increase the rigidity of openings.
4. **Sheet Metal Processing Techniques - Welding**
When designing sheet metal welding structures, the principle of "symmetrically arranging weld seams and points, and avoiding convergence, accumulation, and overlap" should be implemented. Secondary weld seams and points can be interrupted, whereas primary ones should be continuous. Common welding methods in sheet metal include arc welding and resistance welding.
i. **Arc Welding**
Sufficient space must be provided for welding between sheet metal parts, with a welding gap of 0.5-0.8MM, and the weld seam should be uniform and smooth.
ii. **Resistance Welding**
The welding surface should be flat, without wrinkles, springback, etc.
5. **Sheet Metal Processing Techniques - Connection Methods**
Here we introduce the connection methods used in sheet metal processing, mainly including riveting, welding (described above), pull-out riveting, and TOX riveting.
i. **Riveting**: This rivet is often referred to as a pop rivet, and joining two pieces of sheet metal together with a pop rivet is known as riveting. Common riveting shapes are shown in the diagram.
ii. **Pull-out Riveting**:
One part has a pull-out hole, and the other part has a countersunk hole. The riveting die makes them into a non-detachable connection. Advantages include the pull-out hole and its corresponding countersunk hole having a positioning function, high riveting strength, and high efficiency through die riveting.
iii. **TOX Riveting**:
The connected parts are pressed into a die by a simple punch. Under further pressure, the material inside the die "flows" outward. This results in a round connection point that is both edge-free and burr-free, and it does not affect the corrosion resistance, even if the sheet has a plating or painting layer, as the plating and painting also deform and flow with the material. The material is squeezed to the sides, into the sheet by the die side, thus forming a TOX connection point. The following page shows a diagram:
6. **Sheet Metal Processing Techniques - Surface Treatment**
Surface treatment of sheet metal can provide anti-corrosion protection and a decorative effect. Common surface treatments for sheet metal include powder coating, galvanizing, hot-dip galvanizing, surface oxidation, surface brushing, and silk screening.
Before surface treatment, the sheet metal surface should be cleaned of oil, rust, weld slag, etc.
i. **Powder Coating**: There are two types of surface spray for sheet metal: liquid paint and powder paint. We commonly use powder paint. By spraying powder, electrostatic adsorption, and high-temperature curing, a layer of various colors of paint is applied to the surface of the sheet metal to beautify the appearance and increase the material's anti-corrosion properties. It is a commonly used surface treatment method.
ii. **Galvanizing, Hot-Dip Galvanizing**: Surface galvanizing is a common method of anti-corrosion treatment for sheet metal and can also enhance the appearance. Galvanizing can be divided into electro-galvanizing, which has a bright and smooth appearance and a thin zinc layer, and hot-dip galvanizing, which has a thicker zinc layer and can form a zinc-iron alloy layer, offering stronger corrosion resistance than electro-galvanizing.
iii. **Surface Oxidation**: Here we mainly introduce the anodic oxidation of aluminum and aluminum alloys. Anodic oxidation of aluminum and aluminum alloys can be colored in various colors, providing protection and a good decorative effect. It can also produce an anodic oxide film on the material's surface, which has high hardness and wear resistance, as well as good electrical insulation and thermal insulation.
iv. **Surface Brushing**: The material is placed between the upper and lower rollers of the brushing machine, which has a sanding belt attached to it. Driven by a motor, the material passes through the sanding belts, leaving traces on the surface. Depending on the sanding belt used, the traces can vary in coarseness, mainly serving to beautify the appearance. Brushing is generally considered for aluminum materials.
v. **Silk Screening**: The process of silk screening various markings on the material's surface, generally available in flatbed and pad printing methods. Flatbed silk screening is mainly used for general flat surfaces, but pad printing is required for areas with deeper recesses. Silk screening requires a silk screen template.
