Definition of sheet metal
Up to now, there has not been a complete definition of sheet metal.
According to a definition in a foreign professional journal, sheet metal can be defined as: sheet metal is a comprehensive cold processing process for sheet metal (usually less than 6mm), including shearing, punching/cutting/compounding, folding, welding, riveting, splicing, forming (such as automobile body), etc.
Its remarkable feature is that the thickness of the same part is consistent.
In general, the basic equipment of a sheet metal factory includes shear machine, CNC punching machine/laser, plasma, waterjet cutting machine/combination machine, press brake machine and various auxiliary equipment such as decoiler, leveler, deburring machine, spot welder, etc.
Generally, the most important three steps of a sheet metal factory are shearing, punching/blanking and bending.
Selection and blanking of sheet metal materials
Common sheet metal material types:
- Steel plate;
- Aluminum plate;
- Copper plate;
- Stainless steel plate.
Type and specification of steel plate:
Classification by thickness: thin plate, medium plate, thick plate, extra thick plate.
Classification according to production method: hot rolled steel plate, cold rolled steel plate.
Classification according to surface characteristics: hot-dip galvanized sheet, electro galvanized sheet, tinplate, color coated steel sheet.
H0T ROLLING STEEL
The code of hot rolled plate (H0T ROLLING STEEL) is expressed as: SPHC S Steel, P – Plate, H – Heat, C-commercial, generally refer to hot rolled steel plates and strips.
SPHD stands for hot rolled steel plates and strips for stamping.
SPHB – hot rolled steel plate and strip for deep drawing.
- Hardness HRB
- H=above 89.
- Tensile strength is above 41~52kgf/mm.
Specification range: thickness 1.4~6.0mm, maximum width 1524mm, generally 1250mm or 1220mm, material length can be cut to any size as required.
Generally 2500mm or 2440mm.
Material characteristics: the surface of the material is black gray luster, not easy to scratch, but easy to rust, so it must be removed during processing.
It is not suitable for electroplating (colorful zinc plating, white zinc plating, nickel plating, tin plating, etc.).
Suitable for baking paint, powder spraying and other structural parts.
COLD ROLLING STEEL
COLD ROLLING STEEL, the code is SPCC.
The third letter C is the abbreviation of Cold.
SPCD stands for cold rolled carbon steel sheet and strip for stamping, and SPCE stands for cold rolled carbon steel sheet and strip for deep drawing.
Quenching and tempering code of cold-rolled carbon steel sheet and strip: annealed state is A, standard quenching and tempering is S.
- Minimum tensile strength is 270MPa
- Maximum yield limit is 210MPa.
- Hardness HRB:
- 1H=above 85;
Specification range: 0.25-3.0mm thick, materials above 3.0mm must be customized, with width of 1220mm and 1250mm, and length can be cut to any size as required.
Generally 2440mm and 2500mm.
Material characteristics: the surface is iron gray luster, and the surface is easy to scratch and rust.
During processing, attention must be paid to protection and rapid change of sequence.
Suitable for electroplating (multicolored zinc plating, self zinc plating, nickel plating, tin plating, etc.), paint baking, powder spraying, etc.
Electrolytic plate: code SECC, E-E1 ectroplate, its base material is SPCC, its chemical composition and mechanical properties are the same as those of cold rolled plate.
Electrolytic plates also have stretching materials such as SECD and SECE.
The thickness specification of electrolytic plate is 0.3-2.0mm.
The application characteristics of materials are different according to different treatment methods of SECC. See the following table for details:
Type of surface treatment
General surface treatment
Good corrosion resistance, suitable for bare state
Chromic acid passivation+oiling
Very good corrosion resistance
Phosphating treatment (including sealing treatment)
It has certain corrosion resistance and good painting performance
Phosphating treatment (including sealing treatment)+oiling
It has certain corrosion resistance, good painting performance, and can prevent rust during transportation and storage
Phosphating treatment (excluding sealing treatment)
It has certain corrosion resistance and good painting performance
Phosphating treatment (excluding sealing treatment)+oiling
It has certain corrosion resistance, good painting performance and rust prevention.
Fingerprint resistant processing
Applicable to the production of electrical, electronic devices, computer chassis, movement and other parts of zinc plating products·
Hot rolling steel
The code of hot rolling steel is SPGC, and its base material is also SPCC.
The thickness specification is 0.3~3.0 mm. The types of zinc flakes on the surface are: normal zinc flakes (Z), smooth zinc flakes (G), small zinc flakes (X), smooth small zinc flakes (GX), zero zinc flakes (N), and zinc iron alloy (R).
Tin plate: commonly known as tinplate, it is mainly used as anti-corrosion and ultra deep drawing packaging materials, with thickness ranging from 0.20.6mm.
Aluminum plate: The aluminum materials used as plates mainly include the following 2 types: industrial pure aluminum and rust proof aluminum.
These two materials have good plasticity, good weldability and high corrosion resistance, but poor cutting ability.
The aluminum plate has the following states: 0 – full annealing state, H – work hardening state, followed by two Arabic numerals to indicate the additional heat treatment mode.
The first digit in the HXX status code indicates the basic processing procedure for obtaining the status;
The second digit indicates the work hardening degree of the product.
H1 – simple work hardening state. It is applicable to the condition that the required strength is obtained only through work hardening without additional heat treatment.
H2 – work hardening and incomplete annealing. It is applicable to the products whose work hardening degree exceeds the specified requirements of finished products and whose strength is reduced to the specified index after incomplete annealing.
H2 has the same minimum ultimate tensile strength value as the corresponding H1, but the secondary elongation is slightly higher than H1.
H3 is the state of work hardening and stabilization treatment.
It is applicable to products with stable mechanical properties after low temperature heat treatment after work hardening or due to the heating effect in the processing.
H4 – work hardening and painting alloy. It is applicable to the products with incomplete annealing caused by painting after work hardening.
The aluminum content of industrial pure aluminum is more than 99.00%, usually with the following grades: 1050, 1060, 1070, 1100, 1200.
The plate specifications are 1250X2500 or 1000X2000.
The thickness ranges from 0.3-7.0mm.
Anti rust aluminum mainly includes 3003, 3A215052, 5A02, 5A03, 5A05, 5A06.
The aluminum alloy beginning with “3” is mainly composed of manganese, and the aluminum alloy beginning with “5” is mainly composed of magnesium.
The plate specification is basically the same as that of duralumin.
Stainless steel plate: stainless steel plate mainly includes SUS300 series and 400 series.
Among them, 300 series are austenitic stainless steel and 400 series are ferritic stainless steel, which are magnetic and easy to corrode. Its specification is 2mX1m.
Copper plate: Common copper plates include pure copper plate and brass plate.
Pure copper plate has good conductivity, heat conduction, corrosion resistance and processing performance. Its copper content is greater than 99.95%.
The strength of brass plate is slightly higher than that of pure copper plate, and it has good plasticity. Its specification is 1500mmX600mm.
Equipment used for sheet metal blanking, working principle and scope of work.
At present, the equipment used for sheet metal blanking mainly includes: CNC punch, ordinary punch, laser cutting machine, etc.
Working principle of CNC punch: the position of upper and lower dies is fixed, the plate is fixed on the workbench with clamping jaws, and the plate is driven to move by the workbench to process the required workpiece shape.
Working range: 2500X1250x5.0mm.
Processing characteristics: high precision, flexible processing.
Disadvantages: Limited by the mold.
CNC punch manufacturers mainly include: TRUMPF, FINN-POWER, TAILIFT, AMADA, etc.
Blanking by ordinary punch (hard mold): blanking by ordinary punch (hard mold) must be matched with shearing machine.
The shearing machine can cut out the maximum shape of the workpiece before the punch can process the required shape of the workpiece.
Features of shearing blanking: high efficiency, suitable for mass production.
The disadvantage is that mold development requires a certain lead time and cost.
The equipment of shearing and punching machine mainly includes: CNC shearing machine series, ordinary shearing machine series, ordinary punching machine series, high-speed punching machine series, etc.
During the blanking process, the cutting of the plate can be roughly divided into the following four layers: R angle (5%), smooth surface (60%), cracked surface (30%), and burr surface (5%).
As shown below:
LASER cutting machine blanking:
Working principle of LASER cutting machine: use the energy of photons in concave convex mirror focus laser generator to melt metal materials, and then use high-pressure shielding gas N2 or O2 to blow off the melting part for processing.
Processing characteristics: high precision, flexible processing, not limited by the mold.
Disadvantages: low efficiency, high processing cost.
The laser equipment manufacturers mainly includes: TRUMP, HANKWANG, AMADA, BYSTRONIC, etc.
Bending, stamping, bench work process
With the rapid development of the machinery manufacturing industry, the technical level of the front-line production staff is required to be higher and higher.
In order to meet the needs of customers, the current technicians not only need to be skilled in practical operation, but also master basic theories and relevant knowledge, have the ability to analyze and solve problems and are good at innovation.
In order to meet the needs of customers, they constantly improve their processing methods, process system principles and applications in folding, stamping, bench work, and expand the use of efficient processing methods and equipment.
With the content of integrating modern equipment with practice, we seek to further improve the operation level and production efficiency, and strive to take into account the actual difficulties of grassroots producers and the requirements for solving problems in the original design, especially put forward solutions to solve problems, and process them to meet the requirements of the product.
We will list and discuss them item by item, and have corresponding help based on practicality and effectiveness
The working principle of bending forming – bending forming is to fix the upper and lower dies on the upper and lower worktables of the press brake machine respectively, use the servo motor to transmit the relative motion of the worktable hydraulically and combine the shape of the upper and lower dies to realize the bending forming of the sheet metal.
The precision of each bending can reach 0.1mm.
Common bending forming: generally, we can use the bending machine to complete the forming of 90-degree bending and non 90-degree bending, hemming (including the gap less than the plate thickness), offset bending, etc.
Type of press brake dies:
When bending two adjacent edges, if there is a binding relationship between them, consider opening process holes (the diameter of process holes shall not be less than the thickness of the plate) at the corners of the bending edge, and leave a reasonable gap (0.15 times the thickness of the plate) according to the thickness of the plate.
As for the minimum distance from the hole to the edge of the bent part, we usually take 1/2 of the die slot width+0.5 (as shown in the below figure).
When designing sheet metal parts, we should try to avoid the situation that the distance between the folded edge or the hole and the edge is less than the size requirement
The width of the lower die groove is determined according to the plate thickness (T), as shown in the table: Unit: mm
|Plate thickness T||0.5-3||3.0-8||9-10||>12|
|Die opening width||6T||8T||10T||12T|
According to the bending size, consider the feasibility of processing and the reasonable selection of tools, as shown in Fig. A and B, and consider the displacement and upper die selection according to the actual processing needs.
When there are press rivets (PEM fasteners) on the bending parts, punching convex bulges and cracking, it should also be considered that they should not be too close to the bending edge, otherwise they will interfere with the bending tool.
When hemming the edge, the gap tolerance between the two edges of the electroplated part can be appropriately enlarged, so as to facilitate the cleaning of the inside of the dead edge during electroplating, and prevent the acid solution from washing out temporarily and flowing out after a period of time to corrode the electroplated coating.
Stamping forming is a processing method that uses the power generated by the flywheel driven by the motor to drive the upper die, combined with the relative shape of the upper die and the lower die, to separate or deform the sheet metal, so as to obtain the required parts.
The stamping work is mostly carried out at room temperature, so it is also called cold stamping.
The precision of stamping forming depends on the precision of the die, and the general hardware die can reach more than 0.1m.
Punches can be divided into ordinary punches and high-speed punches.
There are many basic stamping processes, including blanking holes, corner bending, drawing, etc.
But from the working principle, it can be divided into two categories, namely separation process and deformation process.
Separation process refers to the stamping process in which the stress of the blank material exceeds the strength limit after being subjected to external force, resulting in shear fracture.
Such as punching, blanking, cutting, notching, etc. It is usually called “blanking” in the stamping process.
Deformation process refers to the stamping process in which plastic deformation occurs when the stress of rough materials exceeds the yield limit but is lower than the strength limit after being subjected to external forces.
For example, bending, drawing, flanging, forming, etc.
Stamping processing generally needs to be matched with the shearing machine.
The shearing machine can cut out the maximum shape of the workpiece, and the punch can process the required shape of the workpiece.
Features of shearing blanking: simple, high production efficiency, suitable for mass production of products.
The products are widely used in the modern sheet metal industry due to their high precision, good consistency, free from human factors in the processing process, easy to ensure quality, high material utilization rate, and simple operation, and some complex forming must rely on a punch to complete.
The disadvantage is that the development of stamping die requires a certain lead time and cost.
Bench worker processing
The application of benchwork in the field of sheet metal mainly includes tapping, drilling, counterboring, spot faceting, reaming, riveting (PEM), pulling, trimming, shaping, deburring, undercutting (profiles, pipes) and other processes.
Drilling, reaming, countersinking and reaming are three methods for bench workers to rough, semi finish and finish machining holes.
During application, it shall be selected according to the accuracy requirements and processing conditions of the hole.
Bench workers drill, expand and countersink on a drilling machine.
Reaming can be done manually or by a drilling machine.
Therefore, to master the operation technology of drilling, expanding, dimming and reaming, you must be familiar with the cutting performance of drilling, expanding, spot facing, reaming and other tools, as well as the structural performance of drilling machines and some fixtures
The cutting amount shall be reasonably selected, and the specific methods of manual operation shall be skillfully learned to ensure the processing quality of drilling, expanding, boring and reaming.
Because the efficiency mainly depends on manual operation, and the efficiency and quality are not suitable for modern industrial production, we must reduce the work of benchwork in this area as much as possible during structural design.
The internal thread or external thread shall be machined on the working internal hole or external cylindrical surface with a tap and a round wrench.
This is the tapping and threading technology that bench workers usually use.
Threads processed by bench workers are usually of small diameter or unsuitable for machining on machine tools.
In order to make the processed thread meet the technical requirements, in addition to the bench workers’ proficiency in the key points and methods of thread processing, the designers should also try their best to make the designed products meet the processing requirements, such as the selection of tapping material thickness, the size of tapping screw bottom hole, etc.
The tapping bottom hole and pitch of some metric threads are shown in the table below:
Common coarse thread pitches are as follows:
|External diameter of thread||M2.5||M3||M4||M5||M6||M8||M10||M12|
|Screw pitch (mm)||0.45||0.5||0.7||0.8||1||1.25||1.5||1.75|
Sawing is used to cut materials or saw grooves on workpieces that meet technical requirements.
The main equipment is profile cutting machine.
Pressure riveting (PEM): PEM fasteners can be divided into carbon steel, stainless steel and aluminum. Neither stainless steel nor aluminum can be electroplated.
During design, these two types of fasteners must be riveted after forming and electroplating.
The commonly used riveting equipment mainly includes oil press and punch.
Welding, grinding and polishing process
The purpose of polishing is to use materials such as grinding wheel, abrasive belt, cloth wheel and polishing wax to polish the polished materials to achieve smooth and mirror surface under high-speed rotation.
Grinding and polishing process
- Grinding machine;
- Abrasive belt machine;
- Cloth wheel, polishing wax (soil)
The cutting amount of polishing on the surface is very small, so it is strictly prohibited to stick sand particles on the polishing cloth wheel to damage the workpiece surface:
Some of the company now adopts the operation mode of electroplating after polishing the iron material (SPCC): first rough polish the workpiece surface with abrasive belt (# 240), and then fine polish it with pressure oil for 4 times;
The polishing shaft must be screened with carborundum, which is used on the cloth wheel with adhesive and roll bonding;
The choice of carborundum is hardness and shape (polygon is preferred)
The inspection after polishing is usually based on the magnifying glass.
Sand holes and polishing marks should be avoided (depending on the customer’s standard):
The qualified products of polishing inspection must be isolated from the workpiece with EPE, cardboard and other materials to prevent collision damage.
Grind the weld bead and protrusion with abrasive materials such as sanding machine and abrasive belt to achieve smooth appearance.
- Grinding machine;
- Grinding wheel
(Louver wheel, bending wheel and cutting wheel)
Selection of grinding wheel
The grinding materials are different due to iron, copper and aluminum.
Because the aluminum chips (materials) and copper chips are soft and easy to fill the gap of the grinding wheel, a coarse grinding wheel is used (the number is high, such as # 60, # 80, # 100, etc.)
The cutting force of the grinding wheel varies with different brands, and the selection is generally based on trial;
From the microscopic point of view, the cutting materials (diamond and other hard materials) adhered to the grinding wheel blade, which are angular rather than round sand particles, have a strong cutting force, and the wear resistance depends on the quality of the adhesive and the hardness and toughness of the diamond;
From the experiment, it is known that the cheap grinding wheel is not necessarily in line with the requirements of the cost.
In the selection, we must obtain a variety of brand products, do the experiment with the same workpiece, divide the unit price by the grinding wheel with the longest grinding time, and its value is lower than other products.
Generally, the grinding is divided into coarse grinding and fine grinding. It is better to separate the coarse grinding and fine grinding by different people.
Continuous production is more cost-effective;
Due to the large cutting amount, rough grinding is generally carried out with curved grinding wheel and 5-inch grinder, and the number of grinding wheel is usually # 60~# 120;
Fine grinding is for the purpose of finishing and smoothing, and generally 150~# 320 is used for grinding;
The cutting amount of fine grinding is small, so it is forbidden to use fine grinding wheel or louver wheel to grind.
Precautions for grinding
1. Dust (will damage the machine and human health);
2. Safety of grinding (use fireproof cloth motor);
3. Do not polish dust in confined space;
4. The appearance requirements must be clear.
Role of electroplating
2. Decoration protection;
3. Special functions (wear resistance, heat resistance, magnetism, etc.)
- Post plating treatment
After processing, there will be a layer of oil stain on the surface of the workpiece, which can be divided into saponified and non saponified oils according to chemical properties.
Saponified oil can saponify with alkali, such as animal oil and vegetable oil.
Mineral oil, such as paraffin and lubricating oil, cannot saponify with alkali, which is collectively called non saponified oil.
According to the nature of grease, the common methods of oil removal are:
1. Wipe and degrease manually
When there are many oil stains, the grease on the workpiece surface can be wiped off with a cloth.
2. Organic matter degreasing
According to the principle of similar dissolution, the oil can be dissolved with organic solvent to achieve the purpose of oil removal.
3. Chemical degreasing
Alkali reacts with saponified oil and emulsifier reacts with non saponified oil to achieve the purpose of oil removal.
4. Emulsifying process
The lipophilic group of the emulsifier is combined with the oil, and the hydrophilic group of the emulsifier is also dissolved in water.
With stirring, the emulsifier gradually removes the oil on the surface of the workpiece.
5. Electrochemical degreasing
After power on, H2 or O2 is separated from the surface of the workpiece, which makes the oil film fall off from the surface of the workpiece and turn into small oil drops.
In addition, the electrolyte itself also has saponification and emulsification, so it can obtain very good oil removal effect.
1. Manual derusting
Remove the rust on the workpiece surface by grinding.
2. Chemical derusting
HCl or H2SO4 is used to react with rust to achieve rust removal.
Remove a very thin oxide film on the surface of the workpiece.
Take galvanizing as an example, immerse the workpiece in the electrolyte containing the plated metal ions (Zn2+) as the cathode, add the anode (using iron plate or stainless steel as the anode), connect the DC current, and deposit a layer of zinc on the workpiece surface.
In this process, not only metal zinc is deposited on the cathode surface, but also H2 is generated, while O2 is generated on the anode surface.
Post plating treatment
Zinc is easily oxidized and corroded in the atmosphere.
After galvanizing, chromate treatment will be carried out to make the surface produce a chemical conversion film, also called passivation film.
The appearance of the passivation film is light blue, rainbow color, golden yellow, military green and black.
Because r6+is highly toxic, according to environmental requirements, it is an inevitable trend for hexavalent chromium passivation to trivalent chromium passivation, and its performance is equivalent to that of hexavalent chromium passivation film.
Galvanizing process flow of the company
Hot degreasing → initial stage electrolysis → water washing → water washing → hydrochloric acid → water washing → water washing → final stage
Electrolysis → water washing → water washing → neutralization → water washing → prepreg → galvanization → water washing → water washing → ultrasonic wave → light emitting → water washing → water washing → blue and white passivation → water washing → water washing → hot water washing → drying → multicolored passivation → water washing → hot water washing → drying
What is painting?
The operation process of turning coating into coating is called coating.
The main content of coating technology is that the coating is formed by coating and curing to form a good coating with the coated object and has some necessary properties to achieve the expected date.
Materials that can be coated on the surface of objects and can form certain properties can be called coatings.
Type of coating
Powder, liquid, two-component, single component, self drying, baking, reaction, etc.
Components of paint
Resin: A transparent liquid, the main film-forming substance of paint, used to connect pigments, so that paint has luster, hardness, adhesion and other properties.
Solvent: a multi-purpose liquid that dissolves resin, making it easier to mix pigment and resin, and ensuring that paint has proper viscosity for construction.
Pigment: Colored powder in paint. Insoluble in water or solvent.
Filler: constitutional pigment, which can reduce the cost of coating and increase the mechanical properties of coating.
Auxiliaries: Compounds with various characteristics, added to paint to obtain special properties.
Effect of coating
2. Decorative function
3. Sign function
4. Special functions
Making a good coating depends on both the quality of the coating itself and the mature coating technology. The two depend on each other.
The painting process includes:
1. Coating method;
2. Coating tools and equipment;
3. Environmental conditions for painting;
4. Coating curing conditions, etc.
Choosing the right painting process is a necessary condition for obtaining a good coating.
Air pressure spraying, high pressure airless spraying and electrostatic spraying are used for liquid paint.
Electrostatic coating technology shall be used for powder coating.
Electrophoretic coating technology shall be used for electrodeposition coating.
Air spraying is based on the same principle as sprayers.
When the air passes through the nozzle, due to the change of the diameter, the air flow rate increases, forming a vacuum at the nozzle to suck out the paint.
Traditional spray gun
Environmental conditions for painting
The painting environmental conditions have great influence on the painting quality;
Temperature and humidity affect the leveling of coating;
Defects of coating affected by dust prevention measures;
The wind direction and air circulation will affect the construction quality.
Coating curing conditions
Physical film forming:
The film is formed simply by solvent evaporation. Thermoplastic acrylic products;
Chemical film forming:
Make paint or varnish cure and dry, bake, react and initiate through chemical reaction.
Coating process management
Good painting process management is the primary condition to ensure painting quality.
To organize and implement painting construction with a scientific attitude and carry out painting process management, it is necessary to master all technical parameters related to painting construction, fully master professional technical knowledge and rich construction experience.
Technical management of coating operators
Confirm the personnel allocation for coating, coating preparation, commissioning machines and tools, and coating conditions.
Technical management of painting tools and equipment
What type of spraying system shall be adopted according to the requirements of product structure type.
Determination and implementation of painting process;
Quality control management.
Metal pretreatment process
Before the product is coated, the oil stain and oxide generated during the manufacturing process of the product shall be removed, and a phosphate crystal shall be generated on the metal surface to increase the adhesion and corrosion resistance of the coating on the metal surface.
Spraying process is an important process for comprehensive management of all aspects of spraying production, which is different from production management but serves production, providing necessary technical support and decision-making basis for production management.
You need a highly cohesive cooperation team and the spirit of continuous innovation to produce high-quality products that meet customer requirements.
Product assembly and packaging
What should be paid attention to before assembly?
Prepare relevant materials in advance, such as self-made parts, purchased parts, packaging materials, etc;
The equipment and tools are properly prepared (the equipment must be in good condition) and various clamps, inspection tools, jigs, etc;
All operators are fully familiar with the drawings and understand the key quality points, SOP and SIP;
All personnel must be in place.
Mass production can only be started after 100% full inspection of the first article is confirmed as OK;
Self-inspection and mutual inspection shall be carried out to prevent defective products from entering the next process;
During assembly, all materials shall be handled with care, without dragging or pulling, without man-made scratches or bruises;
The defective products found shall be clearly marked and immediately isolated and placed in the defective product area;
During assembly, more clamping tools and inspection tools are used to ensure quality and improve work efficiency;
No missing or wrong installation. Use scientific methods to assemble orderly and efficiently.
Carry out inspection in strict accordance with SIP, such as key dimensions, Class A appearance surface, etc.
During inspection, inspection records must be made to provide the required data for the next production.
Apply to FQC for inspection after 0K inspection, and start packaging after passing the inspection.
Precautions during packaging:
To confirm the correctness of the quantity, it must be ensured that there are no more packages, less packages, missing packages or wrong packages.
Strictly follow the packaging specifications issued by the Engineering Department.
The marks on the outer box shall be clear and correct, such as order number, material number, version, quantity, production date, production factory, etc.
The packaged products must be beautiful and generous, and the materials must be firm to prevent scratches, bruises, extrusion deformation, etc. during transportation.