Stainless steel sheet metal stamping and deep drawing processing points

Stainless steel is widely used in industrial production due to its excellent performance, but its stamping processing performance is poor, the surface of the parts is easily scratched, and the mold is prone to bond tumors, which leads to great influence on stamping quality and production efficiency. This requires starting from the die structure, mold material, heat treatment and lubrication in the stamping process to improve the quality of the parts and die life, and better solve the problems in the stainless steel stamping process.

1. Stainless steel sheet stamping features

(1) High yield point, high hardness, significant cold work hardening effect, and easy to crack defects.

(2) The thermal conductivity is worse than that of ordinary carbon steel, resulting in a large deformation force, and a large punching force and deep drawing force.

(3) The plastic deformation is severely hardened when deep drawing, and the thin plate is easy to wrinkle or fall off.

(4) The drawing die is prone to sticking to the phenomenon of the joint, resulting in serious scratching of the outer diameter of the part.

(5) When drawing deep, it is difficult to achieve the desired shape.

2. Ways to solve the problem of drawing and deep drawing of stainless steel sheet

According to the analysis, the above problems are determined by the performance of stainless steel itself, which is mainly affected by the following five factors: first, the performance of raw materials; second, the structure and stamping speed of the mold; third, the material of the mold; fourth, stamping Lubricating fluid; five is the arrangement of the process route.

(1) The quality of raw material sheets is also an important factor affecting the punching performance. It is necessary to purchase regular raw materials that meet the national standard. For hard materials, annealing must be performed before stamping to improve processability.

(2) Structure of the die and punching speed In order to improve the difficulty of drawing, the presser face of the presser ring 2 can be made oblique as shown in the drawing. When the drawing is deepened, the blank 3 is completely in contact with the pressing side surface and the concave mold under the action of the blanking ring, so that the material of the rounded corner of the concave mold can withstand a large blanking force, thereby improving the difficulty of drawing.

When punching stainless steel, the punching speed is 1/3 smaller than that of carbon steel. It has been proved that the effect of using hydraulic press is better than that of mechanical punch.

(3) Selection of anti-stick mold material In the process of deep drawing of stainless steel, the main problem is that the sticking mold is serious, resulting in serious mold loss and affecting the appearance quality of the parts. Therefore, anti-stick mold materials must be used to solve such problems. At present, the anti-stick mold materials mainly include: 1 hard alloy type: tungsten carbide steel knot hard alloy, non-stick mold, high mold life. It has the best anti-adhesion, but the cost of mold materials and heat treatment is high, which is suitable for mass production. 2 copper-based alloys: cast aluminum bronze and hard aluminum bronze, non-stick mold, life expectancy. The heat treatment is simple and suitable for medium and small batch production. 33054 alloy cast iron, non-stick mold, life expectancy. It needs surface hardening and is suitable for small and medium batch production.

In actual production, each unit can select suitable materials according to its own heat treatment equipment, production capacity, cutting processing capacity, and stamping parts requirements.

Under normal circumstances, the hardness of cemented carbide and alloy cast iron molds should reach 60~64HRC, the surface roughness value Ra=0.4μm; the copper base alloy molds should be quenched, the hardness is about 150HBS, and the surface roughness value Ra= 1.6μm stainless steel deep drawing that meets common requirements. For stainless steel deep drawing parts with high surface quality, the surface of the mold can be polished to make the surface roughness value Ra=0.4~0.2μm. The lower surface roughness value can reduce friction and improve anti-adhesiveness. The role of this is to improve the surface quality of stainless steel stampings, and it is beneficial to not stick the mold.

In recent years, new polishing technologies have been introduced. According to the data, new processes such as electrochemical polishing, ultrasonic polishing, and abrasive spraying can reduce the surface roughness of the cavity and improve the wear resistance in a short period of time. Let's explore and apply.

(4) When drawing the lubricating oil material, it should be properly lubricated to reduce the friction coefficient between the material and the mold, so that the drawing force is reduced, and the drawing force can be reduced compared with the lubrication without lubrication. About 30%. Moreover, the degree of deformation of the material can be improved, the ultimate drawing coefficient can be reduced, thereby reducing the number of drawing times, and more importantly, the surface quality of the workpiece is ensured, and the surface is not scratched.

For the drawing of the cylindrical part, if the inner surface quality is not high, the punch does not need to be coated with lubricating oil, which helps to reduce the drawing coefficient. In general, the lubricating oil can be applied to the strip first and then placed. Stamping and drawing on the die.

When stainless steel is drawn and drawn, it is necessary to use a lubricating oil with a large viscosity. Generally, the surface of the sheet is sprayed with chlorinated vinyl paint (G01-4). When the drawing is deep, the oil is applied, and the surface of the stamping part is protected and the quality is good. However, the environmental performance of chlorinated butyl paint is poor, and the main thing is that it needs to be cleaned with banana water after deep drawing, and the smell is large, which has an impact on the health of the operator. In recent years, new stainless steel deep drawing oils and water-based deep drawing fluids have been continuously introduced, with good effects and good environmental performance. They can be used as stainless steel deep drawing lubricants instead of vinyl chloride paint. For example, FH100 type drawing oil has good effect and has been promoted in production.

(5) Arranging a reasonable process route Stainless steel material not only has high strength, large deformation resistance, but also undergoes plastic deformation during the drawing process to produce work hardening, which changes the mechanical properties of the material, and its strength and hardness are obviously improved, while the plasticity itself It will be reduced, after the metal cold working deformation, the crystal grain is broken, the crystal lattice is twisted, and it is in an unstable state, that is, the residual internal stress. This internal stress causes the deformed drawn member to have a tendency to change shape, resulting in deformation or cracking of the finished product or semi-finished product for long-term storage.

In order not to cause cracking and cracking of the drawing parts and semi-finished products due to the deformation resistance and strength, in the production process, the process route must be reasonably arranged, the appropriate drawing coefficient should be selected, and reasonable intermediate annealing should be performed. Under normal circumstances, the first drawing coefficient of the stainless steel sheet can be selected close to the lower limit value, and the back drawing drawing coefficient is taken as the middle value. The annealing temperature for stress relief is 1050~1100 °C, the temperature is 5-15 minutes, and air cooling. In addition, for workpieces with strict shape requirements, the shaping process can be added after annealing, and the effect is good.

3. Conclusion

In the production practice of our company for many years, by controlling the raw material performance parameters, mold structure, mold materials, lubricating oil, process route, etc., the thin plate stainless steel has stable drawing quality, small deformation and high production efficiency, which has created a good economy for the company.