Metal materials commonly used in equipment parts are stainless steel, copper, aluminum, zinc alloy, magnesium alloy, steel, iron, etc.
Metal products are often divided into cold treatment and heat treatment according to different processing methods. Different types of metal forming methods also differ. Cold working, such as sheet metal materials, is mainly carried out through cold forming, bending, deep drawing and other processes. , formation. Heat treatment, such as casting parts, is mainly done by melting metal raw materials into a liquid state and casting them into molds.
It is generally accepted that all sheet metal materials of the same thickness are collectively referred to as sheet metal. Commonly used sheet metal materials are stainless steel, galvanized steel sheet, tinplate, copper, aluminum, iron and so on.
❶Principle of uniform product thickness
Sheet metal is a material with uniform thickness, so when designing a structure, it should be given attention, especially where there are many bends, it is easy to get uneven thickness.
❷Principle of easy reduction
Sheet products are processed from sheets. Before processing, the raw material is flat. Therefore, when designing sheet metal parts, all bends and inclinations must be able to unfold in the same plane. There should not be interference with each other. For example, the sheet metal design shown in Fig. 1-1 does not meet the requirements because they interfere with each other after deployment.
(Figure 1-1 Sheet metal parts will interfere with each other after alignment)
❸ Choose the right sheet metal thickness principle
The thickness of sheet metal parts is available in various specifications ranging from 0.03 to 4.00 mm, but the greater the thickness, the more difficult it is to process, the more processing equipment is required, and the scrap rate also increases. The thickness should be selected according to the actual function of the product. As long as strength and function are satisfied, the thinner the better. For most products, the thickness of sheet metal parts should be controlled below 1.00mm.
❹According to the principle of processing technology
Sheet metal products must conform to the processing technology and be easy to manufacture. Products that do not conform to the processing technology cannot be manufactured and are unqualified designs.
The following classification discusses the technological requirements for the design of sheet metal products.
Productivity of conventional stamping design
Conventional stamping: currently the most commonly used
Precision stamping: It requires precision dies and high-precision stamping equipment, and the cost is higher than conventional stamping. It is usually used in more precise products.
(1) The shape of perforated parts should be as simple as possible, without narrow consoles and slots
As a rule, the depth and width of the protruding or concave part of the stamping part should be at least 1.5 / t (t is the thickness of the material). Increase the edge strength of the corresponding parts of the mold, as shown in Figure 1-2.
Fig. 1-2. Avoid narrow and long consoles and grooves
(2) The shape of the perforated parts should minimize waste when placing the sample, thereby reducing the waste of raw materials
An improvement on the design shown in fig. 1-3 to the design shown in fig. 1-4 will lead to more products with the same raw material, which will reduce waste and reduce costs.
Figure 1-3 Initial Design
Fig. 1-4. Improved Design
(3) The shape and inner hole of perforated parts must not have sharp corners.
Sharp corners will affect mold life. When designing the product, attention should be paid to the transition of rounded corners in the corner joints. The radius of the rounded corners is R≥ 0.5t (t is the thickness of the material), as shown in fig. 1-5.
Figure 1-5. Design with rounded corners
(4) Holes and square holes in perforated parts
The punch hole is preferably round. When punching, the punch is limited by the force of the punch. The diameter of the punch hole should not be too small, otherwise the punch will be easily damaged. The minimum punch hole size depends on the shape of the hole, the mechanical properties of the material, and the thickness of the material. Table 1-1 lists the minimum piercing dimensions for commonly used materials, and t is the thickness of the sheet metal material.
Table 1-1 Minimum punch size for commonly used materials
(5) Distance between punch holes and distance to the edge of the hole.
In sheet metal design, there must be enough material between holes and between holes and edges to avoid tearing during stamping. As shown in fig. 1-6 is a schematic diagram of the minimum distance between holes and the minimum distance to the edge of holes, and t is the thickness of the sheet metal.
Figure 1-6 Schematic diagram of the minimum distance between holes and the minimum distance to the edge of holes
(6) When punching curved and drawn parts, a certain distance between the wall of the hole and the straight wall must be maintained.
When punching holes in stretched products, to ensure the accuracy of the shape and position of the holes, as well as to ensure the strength of the mold, a certain distance between the wall of the hole and the straight wall should be kept, as shown in the figure. in fig. 1-7.
Figure 1-7 Punching holes in stretched products
(7) When designing sheet metal parts, try to avoid sharp corners.
Sharp notch angle will cause the shape punch to be sharp, which is easy to damage the punch, and it is also easy to get cracks on the sharp notch corner of the product. The product shown in fig. 1-8(a), has sharp corners, and in fig. 1-8(b) shows sharp corners after rounding, and t is the thickness of the sheet metal.
Figure 1-8 Machining a sharp gap corner
(1) Minimum Bend Radius for Bent Sheet Metal Parts
When the material is bent, the outer layers are stretched and the inner layers are compressed in the fillet area. When the thickness of the material is constant, the smaller the internal fillet, the greater the tension and contraction of the material; when the tensile stress of the outer rounding exceeds the tensile strength of the material, cracks and breaks occur; if the fillet is bent. If it is too large, it will be affected by the rebound of the material, and the accuracy and shape of the product is not guaranteed. Refer to Table 1-2 for information on the minimum bend radius of designed bendable parts.
Table 1-2. Minimum bending radius of the most commonly used materials
(2) Curved straight edge height
The height of the straight edge of the curved part should not be too small, otherwise it will be difficult to meet the product accuracy requirements. As a rule, the minimum height of the ruler is calculated in accordance with the requirements shown in fig. 1-9.
Figure 1-9. Design with minimum straight edge height
If the height of the straight side of the bent part is less than the minimum design height of the straight side due to product design requirements, shallow grooves can be machined in the bending deformation zone before bending, as shown in fig. 1-10. The disadvantage of this method is that it reduces the strength of the product and is not suitable if the sheet metal material is too thin.
(3) Minimum hole margin for a curved part.
There are two ways to make holes in bending parts: first bending and then punching, and first punching and then bending. The calculation of the distance to the stamping edge after bending is primarily related to the requirements of stamping parts; punching first and then bending must make a hole outside the bending deformation zone, otherwise it will cause the hole deformation and easy cracking in the hole. The requirements are shown in fig. 1-11.
Figure 1-11 Curved part minimum hole margin
(4) When bending the adjacent edge close to the edge of the bending edge, the bending edge should be at a certain distance from the fillet, as shown in Figure 1-12, the distance L≥0.5t, where t is the thickness of the gold plate.
(5) Design of technological cutouts for bending parts
If one edge is only partially bent, a technological notch with a width of at least 1.5 t must be provided to prevent cracking and deformation, and the depth of the technological notch must not be less than 2.0t + R, where t is the thickness of the sheet metal, asshown in fig. 1-13.
Figure 1-13. Process break diagram
(6) The design of the dead edge of the bending part.
The dead edge of the bent part means that the bent surface is parallel to the bottom surface, commonly referred to as the dead edge. The previous process of hammering the edge is to bend the curving edge at a certain angle and then hammer it to fit.
The length of the dead edge depends on the thickness of the material. Generally, the minimum dead edge length is L≥3.5t+R, where t is the sheet metal thickness and R is the minimum inside bending radius of the previous dead edge process, as shown in Figure 1-14.
Figure 1-14 Dead side length calculation
(7) Construction of technological holes of curved parts
When designing a U-shaped bend, it is best to have the same length on both sides of the bend to avoid product deflection during bending and waste. When adding process positioning holes during design, especially for a part that has been bent and formed multiple times, process holes should be designed as positioning references to reduce cumulative errors and ensure product quality, as shown in Figure 1-15.
Figure 1-15 Construction of technological holes of curved parts
Stretching sheet metal parts: The process of drawing sheet metal parts into round or square shapes with sidewalls around them, such as aluminum washbasins, stainless steel cups, etc.
2. Sheet metal stretching precautions
(1) The minimum fillet radius between the bottom and the wall of the part to be stretched should be greater than the thickness of the plate, that is, r1>t, for smoother stretching, usually take r1 =(3～5)t, the maximum fillet radius should be less than 8- multiple of the sheet thickness, i.e. r1<8t.
Requirements for the size of the rounding radius of the drawn parts are given in the table
Rounding radius of the drawn part
(2) The minimum radius of the fillet between the flange and web of the tensioned part must be more than twice the sheet thickness, i.e. r2 > 2t; The corner radius must be less than 8 times the sheet thickness, i.e. r1<8t. (Example Fig. 1-16)
Figure 1-16 Dimensional relationship between height and diameter of round parts for deep drawing without flanges
(3) The minimum fillet radius between two adjacent walls of a rectangular stretch element should be r3≥3t. To reduce the number of stretches, try setting r3≥1/5H so that one stretch can be performed.
(4) Due to different loads on the parts being stretched, the thickness of the material after stretching changes. As a rule, the original thickness is maintained in the center of the bottom, the material in the rounded corners of the bottom becomes thinner, and the materialal in the upper part at the flange becomes thicker; the material at the rounded corners around the rectangular stretch portion becomes thinner. thicker. When designing tensile products, make it clear on the drawings that external dimensions or internal and external dimensions must be guaranteed, and internal and external dimensions cannot be indicated at the same time.
(5) The material thickness of tensioned parts generally takes into account the law that the thicknesses of the top and bottom walls are not equal during the deformation process (i.e., the top is thicker and the bottom is thinner). When the round non-flange draw part is formed at one time, the ratio of height H to diameter D must be less than or equal to 0.4.
In general, when designing a tensioned part, pay attention to keep the shape of the tensioned part as simple as possible, the shape should be as symmetrical as possible, and the depth of the stretch should not be too large.