Sheet metal performance mainly involves material characteristics, manufacturing processes and design optimization. Firstly, the choice of sheet metal material has a significant impact on its performance.
For example, ferritic stainless steel and austenitic stainless steel, due to their variable chromium content, have different corrosion resistance and mechanical properties. Aluminum alloy sheets, depending on the alloying element content, are divided into several series, with the 2000 series being commonly used for its excellent comprehensive performance.
Furthermore, materials such as SGCC and SECC also differ in hardness, ductility and weldability.
In terms of manufacturing processes, advances in sheet metal processing technology are crucial to improving the functionality and safety performance of sheet metal parts. Using advanced techniques such as CNC punching and laser cutting can improve the accuracy and quality of sheet metal parts. In addition, controlling process flow such as cold forming, welding and painting is also a key factor in improving sheet metal performance.
Design optimization is another critical aspect of improving sheet metal performance. Avoiding flat design can increase the strength of the sheet metal, as pure flat sheet tends to deform under stress.
Additionally, determining the correct hole sizes, internal radii, and design details such as height and radius of curvature are equally important to ensure the shape accuracy and structural stability of sheet metal parts.
Mechanical properties of sheet metal
① Tensile strength
The maximum stress a sheet metal material undergoes before breaking is known as tensile strength. The unit of measurement is N/mm 2 or MPa, and is represented by the symbol σb. Tensile strength is one of the indicators of the overall strength of a metal.
②Bending resistance
The maximum stress that a cross section undergoes when a load is applied between two points of a sample is called its flexural strength. The unit of measurement is N/mm 2 or MPa, and is represented by the symbol σbb. Flexural strength is one of the indicators of the overall strength of a metal.
③ Compressive strength
The maximum stress that a sheet metal material can withstand under pressure without breaking is known as compressive strength. The unit of measurement is N/mm 2 or MPa, and is represented by the symbol σbc.
④ Yield strength
Yield strength refers to the stress of a metal sample during the stretching process, when the load is no longer increasing but the sample continues to deform. The unit of measurement is N/mm 2 or MPa, and is represented by the symbol σs. Flow resistance is the pressure value at the yield point.
For materials that do not have an obvious yield strength, the value of stress that produces a permanent strain of 0.2% is often taken as the yield strength.
⑤ Shear strength
Refers to the maximum load of the original cross-sectional area of the shear area before shearing the sample.
The unit is: N/mm 2 or MPa and the symbol is στ.
⑥ Elastic Limit
It refers to the maximum stress of the sample under the condition that the test piece deforms after the external force disappears and can recover the original condition.
The unit is: N/mm 2 or MPa and the symbol is σe.
⑦ Fracture surface shrinkage percentage
It is the percentage of the original cross-sectional area that is contracted after tensile loading.
The symbol is ψ and is one of the plastic indices of materials.
⑧ Stretch rate
It refers to the percentage of elongation of the sample material and the original length after the sample material ruptures.
Elongation is also one of the plastic indicators of materials and the symbol is δ.
⑨ Hardness
It refers to the material's ability to resist strong pressure on its surface.
There are three types of hardness: Brinell hardness, Rockwell hardness and Vickers hardness.
Generally, the hardness of steel increases with increasing carbon content in the steel.
⑩ Brinell Hardness (HB)
One way to represent hardness and measure it is through the Brinell hardness test. This test involves tempering a steel ball and then pressing it into the surface of the material under a specified load for a set period of time. The relationship between the applied pressure load and the area of the indentation is then calculated, and this relationship represents the Brinell hardness.
⑪ Rockwell hardness (HR)
Another method of representing and measuring hardness is the Rockwell hardness test. This test involves pressing a diamond cone or steel ball after quenching into the surface of the material and then determining the hardness based on the depth of the indentation.
Rockwell hardness is divided into three categories: HRA, HRB and HRC, which are based on different test items and pressures.
RH: The hardness value is obtained by applying 1470N of pressure using a diamond head with a 120 degree cone angle to the test samples. It is suitable for measuring surface quenching layer, carburizing layer and hard alloy materials.
HRB: The hardness value is obtained by applying 980N of pressure with a 1.59mm diameter steel ball. It is suitable for measuring soft metals such as non-ferrous metals, annealed metals and standard steel.
CDH: The hardness value is obtained by applying 588N of pressure using a diamond cone with apex angle of 120 degrees on the test samples. It is suitable for measuring hard metals such as tempered steel and hardened steel.
Chart of mechanical properties of metals
For metal mechanical properties chart including shear strength, tensile strength and yield strength, you can check here.
What are the specific differences between SGCC and SECC materials in terms of hardness, ductility and weldability?
The differences between SGCC and SECC materials in terms of hardness, ductility and weldability are manifested in the following ways:
Hardness: SGCC material is harder than SECC material. This can be attributed to the reduction annealing process during hot-dip galvanizing, which makes SGCC a little harder.
Ductility: SGCC has lower ductility. Due to its higher hardness, SGCC is prone to fracture or damage during stamping or deep drawing projects, therefore, deep drawing projects should be avoided in its application.
Weldability: SGCC has worse weldability. This may be due to its thicker zinc layer, which can peel off easily during welding, affecting the welding quality. In contrast, although SECC is also a galvanized steel sheet, its formability and paintability are superior to SGCC, which may indirectly reflect its advantage in weldability.
What are some success stories or theoretical foundations for preventing deformation of flat sheets under force through design optimization?
To avoid the problem of deformation of flat sheets under force through design optimization, the following methods can be adopted:
Add reinforcing ribs: By adding reinforcing ribs to the sheet metal part, the strength and rigidity of the sheet metal part can be improved. This method is simple and effective and is suitable for situations where structural stability needs to be improved.
Add bends, flanges or hemmed edges: These process operations can add extra layers of metal to the edges of the sheet metal part, thereby improving its tensile and compressive capabilities. This design method helps to disperse stresses, reduce local stress concentration, thereby increasing overall structural strength.
Add embossed protrusions through wave formation: By adding embossed protrusions to the surface of the sheet metal part, it can not only beautify the appearance, but also increase the load-bearing capacity and deformation resistance of the sheet metal part. This method is suitable for application scenarios with high structural performance requirements.
Rational structural design: The design of sheet metal parts needs to consider the requirements and characteristics of its processing technology, while taking into account batch size, cost and production efficiency. Rational structural design is a prerequisite to ensure that sheet metal parts have high strength and rigidity.
Use the design during the plastic deformation phase: According to the theory of plasticity, when the local material of the structure enters the plastic deformation phase, the stress will be redistributed to make the stress distribution more uniform, thereby improving the load-bearing capacity of the structure. Therefore, considering adequate plastic deformation in the design can make the structure more stable under force, avoiding deformations caused by excessive stress concentration.
In sheet metal design, how significant is the impact of correct hole sizes, internal radii, and bend heights and radii in improving sheet metal performance?
In the design of sheet metal parts, the correct hole size, internal radius, and height and radius of curvature significantly impact sheet metal performance. Firstly, the positioning of the hole must take into account the influence of the manufacturing process. For example, holes positioned too close to the edge can deform or even crack due to material stretching, highlighting the importance of proper hole design to avoid manufacturing issues.
Furthermore, the minimum size of the drilled hole is related to the shape of the hole, the mechanical properties of the material and the thickness of the material. These factors must be considered during design to ensure that the punching process does not damage the punch or compromise the quality of the final product.
The bending height must be at least twice the sheet thickness plus the bending radius. This design principle helps ensure uniform plastic deformation of the material during the bending process, thereby improving the precision and quality of sheet metal parts.
If the design requires a straight edge height less than twice the thickness of the sheet metal, measures should be taken to increase the bending height to avoid processing shallow grooves in the bending deformation zone before bending, ensuring the quality of the fold formation.
The number of bending operations in sheet metal part manufacturing also directly affects mold cost and bending accuracy. Reducing the number of bending operations can lower mold cost and improve bending accuracy, so it is crucial to minimize bending operations during design.
In addition, the external shape and internal holes of perforated parts must avoid sharp corners, as sharp corners may affect the service life of the mold. This is another important factor to consider when designing sheet metal parts.
The correct hole size, inside radius, and height and radius of curvature are vital to improving sheet metal performance. By reasonably designing these parameters, manufacturing problems can be effectively avoided and the quality and precision of sheet metal parts can be improved. Simultaneously, it can also help reduce costs and improve production efficiency.
