Magnesium alloy handlebar precision plastic forming research

 

(1 Luoyang Han forging Co., Luoyang 471003; 2 Henan University of Science and Technology, Luoyang 471003)

 

Abstract: tension, compression tests on cast AZ91D magnesium alloy in stress-strain curves were studied. Experimental results show that the cast magnesium alloy at elevated temperatures exhibited lower flow stress, plastic forming process can be achieved. Plastic forming process in the optimization scheme based on the use superplastic bulging and bending technology of magnesium alloy motorcycle handlebar tube plastic processing test, and successfully prototyped a qualified products.

 

Keywords: AZ91D; motorcycle handlebar tube; superplastic bulging; bending

 

Magnesium is the most abundant crustal elements of one of its abundance ranks eighth, about two crustal composition. 5%; the density of aluminum, 2/3, a specific strength and specific stiffness are high. Because of its light weight, seismic, high damping, high thermal conductivity, anti-electromagnetic interference and easy to recycle, etc., growing automotive, electronic communications, aerospace and other fields of all ages. In recent years, with the price of magnesium alloy processing technology and gradually break through the bottleneck of the two, the global amount of magnesium alloy increased sharply expanding range of applications, is becoming the steel, aluminum metal structure after the third largest engineering materials, known as "21st Century Green Engineering Materials" [1]. Magnesium hcp crystal structure at room temperature and low-temperature ductility is poor. Current research and application of magnesium alloys are mainly concentrated in the casting of magnesium alloys, especially die-cast magnesium alloy, wrought magnesium alloy research and application in its infancy. Magnesium alloy lower ductility at room temperature, but its specific tissue, deformation temperature and deformation rate, a superplastic deformation capacity, a high elongation can be obtained and a small deformation resistance, it can use its specific temperature preferably the plastic deformation to achieve complex shapes forming structure

 

[2]. The author in the cast magnesium alloy AZ91D plasticity research, based on the research of magnesium alloy large displacement motorcycle handlebar tube plastic processing technology, a brief introduction precision plastic forming technology of magnesium alloy forming the application.

 

A magnesium alloy motorcycle handlebar

 

Normal motorcycle handlebar tube (see Figure 1a) by the use of plastic pipe bending process to process, and the inner tube, the outer diameter remains unchanged. In imports, the greater use of large displacement motorcycle hits magnesium alloy tube, shape is the middle coarse, fine ends, but maintain the same wall thickness. The advantage is the quality of light, not only to improve fuel economy composite indicator, but also improve vehicle noise, vibration, and thermal deformation of magnesium alloy and excellent energy absorption capacity can significantly improve driving safety performance. Magnesium alloy motorcycle handlebar tube (see Figure 1b), precision plastic forming using superplastic bulging and bending processes. The key is: straight tube bulging stage is necessary to achieve bulging middle part, but also to ensure undistorted part of the wall with two consistent.

 

2 AZ91D stress - strain curve

 

Cast magnesium alloy AZ91D uniaxial tensile test in WQ4100 having a constant strain rate tensile capabilities. Temperatures range from 280 ~ 400 ℃, initial strain rate of 1 × 10 - 4 ~ 1 × 10 - 1 s - 1. AZ91D magnesium alloy stress - strain curve shown in Figure 2, 340 ℃ under different strain rates when the stress - strain curve shown in Figure 2b. As can be seen from the figure, the higher strain rate (1 × 10 - 1 s - 1) when stretching deformation at the beginning stage, with the rapid increase in true strain, decreased rapidly after reaching the peak does not appear over held by plastic deformation quasi-steady deformation stage; when the strain rate drops below 1 × 10 - 4 s - 1, the beginning of the deformation curve showing the strain hardening effect, the true strain reaches 0. 15, the stress-strain curve corresponding steady state flow into the stage where, alloys exhibit good superplastic elongation of 487% of its.

 

Three magnesium alloy handlebar precision plastic forming

 

3. A magnesium alloy handlebar superplastic bulging

 

The test device from the mold, the tube sealing means, heating means, pneumatic and hydraulic auxiliary body bulging bodies, shown in Figure 3. Die by the upper mold 1, the lower mold 5, the main provider of bulging cavity tube, the tube is formed into the desired shape precision; tube sealing mechanism controlled by the plug and plug 2,7 3,8 composed of hydraulic cylinders for sealing the tube and the tube bulging required to provide axial feeding pressure; heating mechanism consists of six heating rods to provide heat required for heating the tube; pressure bulging mechanism consists of a pneumatic cylinder composed by hydraulic pump to cylinder oil-filled cylinder air compressor needed to achieve a certain pressure bulging pressure; hydraulic auxiliary mechanism is dominated by the fuel tank, hydraulic pumps, hydraulic valves and other components of controllable circuit, in accordance with the bulging complete certain required actions. 1) Load path selection. Impact tube bulging bulging process factors are mainly internal pressure and axial pressure matching relationship. According to theoretical calculations and DYNAFORM numerical simulation results, the range of the axial pressure is small, the axial pressure is 1. 5 MPa, the design of the load path 4, as shown in Figure 4. The results showed that the loading path 4 loading condition, after bulging minimum thickness along the axial pipe, and the thickness variation along the axis error is 1. 4%.

 

2) forming process. Mold (1,5) is heated to a specific temperature, the magnesium alloy preheated straight pipe (6) into the mold cavity in the mold and to the certain pressure F; hydraulic cylinder (3,8) push block head (2,7) forward, so that the pipe ends and plugs sealing the tube ends to exert some pressure; to the pneumatic cylinder (4) within the oil-filled, up to a certain pressure, pressure, so that the tube bulging with mold cavity fully fit. Finally, remove the cylinder pressure, plug back, magnesium alloy straight tube bulging complete.

 

The test apparatus, the hydraulic pressure is converted into a key part of the air pressure cylinder (4), when the hydraulic oil into the cylinder of compressed air, the cylinder and the mold cavity through the plug communicating pipe, thereby enabling the tube to generate high pressure chamber , prompting the tube bulging.

 

3) Mold heating mechanism. Magnesium alloy tube superplastic bulging, the mold must be heated to superplastic temperature. Heating device placed in the upper and lower mold, the heat source is six heating rods, each length 1 200 mm, power 1 000W. Molds play a hole, insert the thermocouple with triac temperature controller.

 

4) sealing device designs. Tube bulging end seals to maintain the pressure of the key. This process is used in the form of cone-shaped seal punch pressed into France, this sealing method has good sealing effect, high production efficiency, easy operation and so on. Taking into account the test uses the bulging pressure medium is a gas, the sealing more stringent requirements, you can do some work on the sealing plug hard chrome plated and polished. During the test proved the effectiveness of this sealing method.

 

5) hydraulic system design. Hydraulic System (hydraulic machine hydraulic system itself except) main function is: through hydraulic / pneumatic converter device provides the required bulging pressure; through certain actions when the pipe ends to provide bulging desired axial compressive force and management end sealed to prevent leaks.

 

3. Two magnesium alloy handlebar tube bending forming

 

Magnesium alloy motorcycle handlebar tube bulging finished, enter the bending phase. Due to bending accuracy and appearance of higher quality requirements, after the shape of the motorcycle handlebar integrated analysis method of forming the final selection of bending, ie hydraulic press using a mold tube bending processing methods. The process is simple, accurate dimensions. After the bulging straight pipe bent into a mold out two outside the arc, and then bend the two inner arc. Since magnesium alloy is poor ductility at room temperature, the bending is easy to crack or break phenomenon magnesium alloy tube before bending should first be heated, the heating temperature can be 180 ~ 250 ℃. Motorcycle handlebar magnesium alloy precision plastic forming product shown in Figure 5.

 

4 Conclusion

 

Although magnesium alloy lower ductility at room temperature, the plastic processing capacity is poor, but in the 350 ~ 450 ℃ significantly improve the plastic, suitable for plastic molding, precision plastic forming techniques can be used magnesium alloy products for plastic processing.

 

Using superplastic bulging, bending process can be realized cast AZ91D magnesium alloy motorcycle handlebar tube plastic processing. The bulging of magnesium alloys Fig. 5 Motorcycle Handlebar after Bulging & Bending tube temperature at 180 ~ 250 ℃ under the conditions of the second bend, get qualified motorcycle handlebar tube, uniform and smooth transition, bend without cracking or breaking phenomenon. But bulging stage temperature, pressure and bulging pressure axial coordination between needs further study.