In addition to the shape and accuracy of the part to be processed and the structural equipment available to the company, the processing of the part is also very much related to the material used for the part. Therefore, it is important to analyse and understand the processing properties of different materials, which are of great significance to the processing process of sheet metal parts and the development of production operation specifications.
Process properties of ordinary carbon structural steel
Generally speaking, sheet metal parts are made of ordinary carbon structural steel (e. g. Q195, Q215, Q235, etc. ) and high quality carbon structural steel (e. g. 08, 10F, 20, etc. ), which are most commonly used. There are few restrictions on forming, except that the thickness increase is limited by the deformation rate and the heating is limited by the upper temperature limit.
In the processing of thicker plate material, in order to increase the degree of deformation of the plate material, reduce the deformation resistance of the plate material, more with hot forming or partial heating of the blank deep drawing and forming process, but should avoid heating in certain temperature zones, such as carbon steel heated to 200 ~ 400 ℃, because the aging effect (inclusions in the form of precipitation in the grain boundary slip surface precipitation) to reduce plasticity, deformation resistance increased, this temperature range is called blue brittle zone This temperature range is called the blue brittle zone, when the performance of the steel becomes bad, easy to brittle fracture, the fracture is blue. And in the range of 800 ~ 950 ℃, and will appear hot brittle zone, so that plasticity is reduced, therefore, in the plate hot state deep drawing operation process, should pay special attention to the actual deformation of hot pressing temperature should not be in the blue brittle zone and hot brittle zone. In the operation, should consider the heating equipment and press between the location of the deformation of the hot pressing temperature, and careful use of cooling blowing equipment to avoid the occurrence of blue brittle and hot brittle.
Process properties of alloy steels
The alloy steel commonly used in the manufacture of sheet metal structural parts is usually 16Mn, 15MnV and other low alloy high strength structural steel, their process properties are as follows.
●16Mn. 16Mn steel is generally supplied in hot-rolled condition, no heat treatment is required, especially for rolled steel less than 20mm thick, its mechanical properties are very high, therefore, hot pressing is generally used directly after. For thickness greater than 20mm steel plate, in order to improve the yield strength and low temperature impact toughness of steel, can be used after normalizing treatment.
In addition, its gas cutting performance and ordinary low carbon structural steel the same. Gas cutting edge 1mm within the hardening tendency, but due to the hardening area is very narrow, can be eliminated by welding. Therefore, the gas cut edge of this steel does not require mechanical processing and can be welded directly.
The performance of carbon arc gas planing is also the same as that of ordinary low carbon structural steel. Although there is a hardening tendency within the edge of the gas planing, the hardening area is also very narrow and can be eliminated by welding, therefore, the gas planing edge of this steel grade does not require mechanical processing and can be directly welded. The result is essentially the same hardness of the heat affected zone as when welding is carried out after machining.
Compared with Q 235, 16Mn steel yield strength are above 345MPa, higher than Q 235, so the cold forming force is greater than Q 235 steel. For large thicknesses of hot rolled steel, the cold forming properties can be greatly improved by normalising or annealing. However, when the thickness of the plate reaches a certain thickness (t ≥ 32), it must be cold-formed after the stress relief heat treatment.
When heated to more than 800 ℃, can obtain good hot forming properties, but 16Mn steel heating temperature should not exceed 900 ℃, otherwise, easy to appear overheating organization, reduce the impact toughness of steel.
In addition, 16Mn steel by three times the flame heating orthopedic and water cooling after the mechanical properties of no significant change, with the original base material with the same resistance to brittle damage, therefore, the steel can be water fire orthopedic, but the dynamic load structure is not suitable for water fire orthopedic.
●15MnV. thin 15MnV and 15MnTi steel plate, its shear and cold rolled properties and 16Mn steel similar, but the plate thickness t ≥ 25mm hot-rolled steel plate, in the shear edge is easy to hidden due to shear of the cold hardening caused by small cracks. This crack may have been produced before the steel factory. Therefore, quality checks should be strengthened, but once found, should be removed after gas cutting or mechanical processing of the cracked edge. In addition, the thicker 15MnV steel hot-rolled plate, cold rolled easy to produce fractures, can be normalized by 930 ~ 1000 ℃ to improve its plasticity and toughness, improve the cold roll performance.
In addition, this type of steel hot forming and hot orthopedic performance, heating temperature of 850 ~ 1100 ℃ hot forming, multiple heating on the impact of yield strength is not significant; and good gas cutting performance, carbon arc gas planing performance is also good, carbon arc gas planing on the performance of welded joints without adverse effects.
With the same process performance of 15MnV class steel also includes 15MnTi, 15MnVCu, 15MnVRE, 15MnNTiCu, etc. .
●09Mn2Cu, 09Mn2. this type of steel has better cold stamping performance. 09Mn2Cu, 09Mn2, 09Mn2Si thick steel plate cold roll process, hot pressing process, gas cutting, carbon arc gas planing, flame straightening and Q235 as well.
●18MnMoNb. The notch sensitivity of this type of steel is high, the flame gas cutting of the cut has a tendency to harden, in order to prevent cracking when bending, should be gas cutting of the steel plate by 580 ℃ insulation 1h, stress relief annealing.
Process performance of stainless steel
There are many types of stainless steel, according to the chemical composition can be divided into two categories, namely, chromium steel and nickel-chromium steel. Chromium steel contains a large amount of chromium or then contains a small amount of nickel, titanium and other elements; nickel-chromium steel contains a large amount of chromium and nickel or then contains a small amount of titanium, molybdenum and other elements. According to the different metallographic organisations, they are divided into several categories such as austenitic, ferritic and martensitic. Due to the different chemical composition and metallographic organization, the mechanical properties of various types of stainless steel, chemical properties, physical properties also have a large difference, so that the application of stainless steel material process difficulty relatively increased.
There are two types of stainless steel grades commonly used.
Category A: martensitic chromium steel, such as 1Cr 13, 2Crl 3, 3Crl 3, 4Crl 3, etc.
Category B: belongs to the austenitic nickel-chromium steel, such as 1Cr18Ni9Ti, 1Cr18Ni9, etc.
The above two types of stainless steel have the following processing properties.
●In order to obtain good plasticity, should make the material in the soft state, so to heat treatment. Class A stainless steel softening heat treatment is annealing, Class B stainless steel softening heat treatment is quenching.
●In the soft state, the mechanical properties of the two types of stainless steel have good processability, especially with good stamping deformation processability, suitable for deformation of the basic process of stamping, but the material characteristics of stainless steel compared with ordinary carbon steel, is very different, even if the stainless steel material for deep drawing, the vertical plasticity of the anisotropic properties of the value is much lower than ordinary carbon steel, and at the same time, because of the high yield point, cold work Hardening is serious, so not only in the deep drawing process is easy to produce wrinkles, and the plate material in the concave die corner of the bending and reverse bending deformation caused by the rebound, often in the side wall of the parts to form a depression or deflection. Therefore, for the deep drawing of stainless steel, there is a need to have a very high compression force, and requires careful adjustment of the mould.
Due to the cold hardening phenomenon of stainless steel is very strong, deep drawing is easy to produce wrinkles, so in the actual operation process, to take some of the following measures in order to ensure the smooth operation of deep drawing: generally in each deep drawing after the intermediate annealing, stainless steel is not like soft steel can be after 3 ~ 5 times for intermediate annealing, usually after each deep drawing to intermediate annealing; deformation of large deep drawing parts, the final After deep drawing and forming, to be followed by the elimination of residual internal stress heat treatment, otherwise deep drawing parts will produce cracks, to the internal stress of the heat treatment specification is a stainless steel heating temperature of 250 ~ 400 ℃, B stainless steel heating temperature of 350 ~ 450 ℃, and then in the above temperature insulation 1 ~ 3h; using warm drawing method can get better technical and economic results, for example, for 1Cr18Ni9 Stainless steel heated to 80 ~ 120 ℃, can reduce the material processing hardening and residual internal stress, improve the degree of deep drawing deformation, reduce the drawing coefficient. But austenitic stainless steel heated to a higher temperature (300 ~ 700 ℃), and can not further improve its stamping process. When deep drawing complex parts, should choose to use hydraulic press, ordinary hydraulic press and other equipment, so that it is not high deep drawing speed (0. 15 ~ 0. 25m/s or so) under the deformation, can get better results.
●Compared with carbon steel or non-ferrous metal, another characteristic of stainless steel stamping is the high deformation force and the large elastic jump back. Therefore, to ensure the accuracy of the size and shape of the stamped parts required, sometimes to increase the trimming, correction and the necessary heat treatment.
●Austenitic stainless steel yield strength varies greatly between different varieties, therefore, in the process of shearing, forming, pay attention to the processing equipment capacity.
Process performance of non-ferrous metals and alloys
For non-ferrous metals and alloys in the forming process of contact with the equipment, the smoothness of the surface of the moulds are higher requirements.
●Copper and copper alloys. Commonly used copper and copper alloys are pure copper, brass and bronze. Pure copper and grades H62 and H68 brass, stamping process are good, compared to H62 than H68 cold work hardening more intense.
Bronze is used for corrosion resistance, springs and wear-resistant parts, and the performance varies considerably between grades. Generally speaking, bronze is poorer than brass for stamping, and bronze is stronger than brass for cold hardening, requiring frequent intermediate annealing.
Most of the brass and bronze in the hot state (600 ~ 800 ℃ below) has a good stamping process, but the heating will bring a lot of inconvenience to the production, and copper and many copper alloys in the state of 200 ~ 400 ℃, but plasticity than the room temperature has a large reduction, and therefore generally do not use the hot state stamping.
●Aluminium alloys. The aluminium alloys commonly used in sheet metal components are mainly hard aluminium, rust-proof aluminium and wrought aluminium.
Rust-proof aluminium is mainly aluminium-manganese or aluminium-magnesium alloy, the heat treatment effect is very poor, only through cold hardening to improve the strength, it has moderate strength and excellent plasticity and corrosion resistance. Hard aluminium and wrought aluminium are aluminium alloys that can be strengthened by heat treatment. Most wrought aluminium is an aluminium-magnesium-silicon alloy, with high strength in the hot state, poor heat treatment strengthening effect, and good plasticity in the annealed state, suitable for stamping and forging processing. Hard aluminium is an aluminium-copper-magnesium alloy with high strength and good heat treatment strengthening effect.
Rust-proof aluminium can be annealed to obtain maximum plasticity, hard aluminium and wrought aluminium can be annealed and quenched to obtain maximum plasticity. They have a higher plasticity in the quenched state and a better overall mechanical property for stamping, thus having a better stamping process than the annealed state.
Hard aluminium and wrought aluminium belong to the heat treatment can strengthen the aluminium alloy, they have a characteristic, that is, after quenching with the extension of time gradually strengthen, this phenomenon is called "ageing strengthening". Age strengthening has a certain development process and the rate of development varies from one grade to another. As these aluminium alloys have the characteristics of age strengthening, therefore, the stamping process of these aluminium alloys must be completed before the development of age strengthening is completed, generally the workshop requires the process to be completed within 1. 5h after quenching.
In aluminium alloys, aluminium and magnesium alloys (mostly rust-proof aluminium) are more strongly cold hardened, so when using such materials to manufacture complex parts, usually 1 to 3 times intermediate annealing. After deep drawing and forming, the final annealing is carried out to eliminate internal stress.
To improve processability, stamping is also used in the production of aluminium alloys in a warm state. Warm stamping is mostly used for cold-hardened materials. After warming (about 100-200°C), the material retains some of its cold-hardening and improves its plasticity, which improves the degree of stamping deformation and the dimensional accuracy of the stamped parts.
When warm stamping, the heating temperature must be strictly controlled, too low will cause cracks in the stamped parts, too high will cause a sharp reduction in strength and also cracks. During the stamping process, the convex die tends to overheat and when it exceeds a certain temperature, it will cause the stamping material to soften strongly and cause the deep-drawn part to fracture. Keeping the temperature of the convex die at less than 50~75°C can improve the degree of deformation of warm deep drawing. In warm stamping, special heat-resistant lubricants must be used.
●Titanium and titanium alloys. Titanium and titanium alloys are less processable, with higher strength, high deformation forces and strong cold work hardening, and are mostly used for hot stamping, except for a few grades that can be cold stamped for parts with little deformation. The heating temperature for hot stamping is high (300-750°C) and varies according to the grade. Too high a heating temperature will make the material brittle and is not conducive to stamping. As titanium is a very chemically active element, the temperature required for the chemistry of oxygen, hydrogen and nitrogen are not high, and the compounds generated with oxygen, hydrogen and nitrogen are the main factors that produce brittleness, therefore, the heating of titanium and alloys is strictly limited. When high temperature processing is required, it must be carried out in a protective gas or in a fully protected, leak-free package for integral heating. When operating stamped parts of titanium and titanium alloys, the lowest possible stamping speed should be adopted.
In addition, titanium can be cut off by mechanical methods, such as sawing, high-pressure water cutting, lathe, tube cutting machine tools, etc. , sawing speed should be slow, never use oxygen - acetylene flame and other gas cutting through heating, but also should not use the wheel saw cutting, to avoid the heat-affected zone of the incision by the gas pollution, at the same time, the incision at the burr is too large, but also to increase the process of burr processing.
Titanium and titanium alloy tube can be cold bent, but the rebound phenomenon is obvious, usually at room temperature is two to three times the stainless steel, therefore, the cold bending of titanium tubes to deal with the amount of rebound, in addition, the cold bending bending radius of titanium tubes shall not be less than 3. 5 times the outer diameter of the tube. Cold bending, in order to prevent the local appearance of ellipticity super poor or the phenomenon of wrinkling, can be filled with dry river sand in the tube and tamped with a wooden hammer or copper hammer. Bender cold bending, the mandrel should be added. When hot bending, the preheating temperature should be 200 to 300 ℃.
For 90 ° flanging, should be used 30 °, 60 °, 90 ° three sets of moulds pressed in stages to avoid cracks.