Stainless steel is widely used in industrial production because of its excellent performance. Still, its stamping processing performance is poor. The surface of the parts is easy to scratch, and the die is easy to produce bond tumors, resulting in stamping quality and production efficiency being greatly affected. This requires the stamping process from the die structure, die materials, heat treatment, lubrication, etc., to improve the quality of parts and die life and to better solve the problems in the stainless steel stamping process.
Stainless steel sheet stamping characteristics
(1) high yield point, hardness, cold hardening effect is significant, easy to crack, and other defects.
(2) poor thermal conductivity than ordinary carbon steel, resulting in the required deformation force, punching force, and deep drawing force.
(3) The plastic deformation is hardened when deep drawing and the thin plate is easy to wrinkle or falls off the bottom when deep drawing.
(4) deep-drawing molds are prone to bonding tumors, resulting in serious scratches on the outer diameter of the parts.
(5) When drawing deep, achieving the expected shape is difficult.
To solve the problem of stainless steel sheet stamping deep drawing way
Analysis that the above problems arise from the performance of stainless steel itself, mainly affected by the following five factors: one is the performance of raw materials; two is the structure of the die and stamping speed; three is the material of the die; four is the stamping lubricating fluid; five is the arrangement of the process route.
(1) The quality of the raw material plate is also an important factor influencing stamping performance, and formal raw materials conforming to national standards must be procured. For hard-state materials, annealing must be done before stamping processing to improve the processing performance.
(2) Structure of the die and stamping speed To improve the drawing difficulty, the crimping surface of the crimping ring 2 can be made beveled, as shown in the attached figure. In this way, when drawing deep, the blank 3 is in full contact with the crimping surface, and the concave die is under the action of the crimping circle, which can make the material in the rounded part of the concave die bear a larger crimping force, thus improving the difficulty of drawing deep.
The punching speed when punching stainless steel is 1/3 smaller than that of carbon steel, and practice has proved that the effect of using a hydraulic press is better than that of a mechanical press.
(3) choose an anti-sticky die material stainless steel deep drawing process; the main problem is sticky die serious, resulting in serious die loss, affecting the quality of the appearance of the parts, so, to solve such problems, we must use anti-sticky die material. The current anti-adhesive mold materials are ① carbide class: tungsten carbide steel junction carbide, non-stick mold, and high mold life. The best anti-adhesive, but the mold material and heat treatment costs are higher, suitable for mass production. ②Copper-based alloys: cast and hard aluminum bronze, non-stick mold, public life. Heat treatment is simple and suitable for small and medium-sized production use. ③3054 alloy cast iron, non-stick mold, life is generally. Surface quenching is required, suitable for small and medium-sized production.
In actual production, each unit can choose suitable materials according to its heat treatment equipment, production, cutting, and processing capacity, and requirements of stamping parts.
In general, the hardness of cemented carbide and alloy cast iron dies should reach 60~64 HRC, and the surface roughness value Ra=0.4μm; copper-based alloy dies to need to be quenched, and the hardness is about 150HBS, and the surface roughness value Ra=1.6μm can meet the common requirements of stainless steel deep drawing. For the surface quality requirements of stainless steel deep drawing parts, the surface of the mold is best to polish so that the surface roughness value of Ra = 0.4 ~ 0.2μm; lower surface roughness value can play a friction reduction and improve the role of anti-viscosity, which is beneficial to improve the surface quality of stainless steel stamping parts, not sticky die.
In recent years, there has been constant new polishing technology; according to information, electrochemical polishing, ultrasonic polishing, abrasive injection, and other new processes can reduce the surface roughness value of the cavity in a short period and improve wear resistance; these are worth exploring and using.
(4) stamping lubricating oil material in a deep drawing to its appropriate lubrication can reduce the friction coefficient between the material and the die so that the drawing force decreases, lubrication compared with no lubrication, the drawing force can be reduced by about 30%. And can improve the degree of material deformation, reduce the limit of deep drawing coefficient, reduce the number of deep drawings, and, more importantly, ensure the workpiece’s surface quality, not cause surface abrasion.
For the deep drawing of barrel-shaped parts, if the inner surface quality requirements are not high, the convex die does not need to be coated with a lubricant to help reduce the drawing coefficient. Generally, it can be coated with lubricant on the strip material and then placed on the concave die stamping deep drawing.
For stainless steel stamping deep drawing, choose a viscous lubricating fluid, use chlorinated vinyl paint (G01-4), spray the surface of the plate material, deep drawing, and then coat with machine oil; the surface of the stamping parts are protected, good quality. However, the environmental performance of chlorinated vinyl paint is poor; more importantly, it needs to be cleaned with banana water after deep drawing; the smell is big and impacts the operator’s health. In recent years, new stainless steel deep drawing oil and water-based deep drawing liquid constantly come out; they have a good effect, good environmental performance, and can be used as an alternative to chlorinated vinyl paint stainless steel deep drawing lubricant. For example, in FH100 type deep drawing oil, the effect is good and has been promoted in the production of use.
(5) arrange a reasonable process route for stainless steel materials with not only high strength and deformation resistance in the process of deep drawing to bear plastic deformation and processing hardening so that the mechanical properties of the material change, but its strength and hardness will also be significantly increased. Its plasticity will be reduced, metal cold working deformation, grain fragmentation, and lattice distortion, in a state of instability, that is, the residual internal stress. This internal stress makes the deformation of the deep drawing parts tend to change the shape of the state, resulting in finished products or semi-finished products being stored for a long time to produce deformation or cracks.
In order not to make deep drawing parts and semi-finished products due to deformation resistance and strength increase and to crack and rupture phenomenon, the production process must be reasonable arrangement process route, select the appropriate drawing coefficient, and reasonable intermediate annealing. In general, stainless steel sheets can be selected near the lower limit of the first drawing coefficient after the drawing coefficient to take the median value. Stress relief annealing temperature of 1050 ~ 1100 ℃, insulation 5 ~ 15min, air cooling. In addition, the shape requirements of strict.