Super-Plastic | Super-Plastic Forming Process

Super Plastic Forming Process

Introduction

Manufacturing of complex lightweight automotive structure that meet cost and product goals is a competitive challenge facing industry. Super plastic forming process (SPF) is appreciated tool for the fabrication of complex parts used in the aircraft and automobile industries. Super plastic forming process of sheet metal has been used to make very complex shapes and integrated structures that are frequently lighter and stronger than the assemblies they replace. Super plasticity in metals is well-defined by very high tensile elongations, ranging from two hundred to several thousand percent. Superplasticity is the capability of certain materials to undergo great elongation at the proper temperature and strain rate.

01 - SUPER PLASTIC - advantages of SUPER PLASTIC

 

The process is usually conducted at high temperature and under organized strain rate, can give a ten-fold increase in elongation related to conventional room temperature processes. Components are formed by applying gas pressure between one or more sheets and a die surface, producing the sheets to stretch and fill the die cavity. The development of pressures must be closely controlled throughout the process since the alloys of interest only shows Super plastic performance for certain temperature dependent range of strain rates. particular alloys of titanium, stainless steel, and aluminium are commercially available with the fine-grained microstructure and strain rate sensitivity of flow stress that are essential for Super plastic deformation.

SPF can yield parts that are impossible to form using conventional methods. During the SPF process, the material is heated to the SPF temperature inside a sealed die. Inert gas pressure is then applied, at a controlled rate forcing the material to take the shape of the die pattern. The flow stress of the material at the time of deformation increases rapidly with increasing strain rate. Super plastic alloys can be stretched at higher temperatures by several times of their original length without breaking.

Some of the materials developed for super plastic forming are

1. Bismuth-tin (200% elongation)

2. Zinc-aluminium

3. Titanium (Ti-6AI-V)

4. Aluminium

5. Aluminum-lithium alloys

Super-Plastic Forming-Process

01 - SUPER PLASTIC - SP FORMING PROCESS

This technique consists in hot forming up to 1000 °Celsius super plastic alloys by using an inert gas pressured up to 50 bars. Combined with diffusion bonding, this method permits honeycomb structures made of several sheets in a single operation.

The blank is loaded in the form of die. The hot press heats the die and the blank to the material super-plastic temperature.

Forming:

Once the temperature is reached, it is exactly controlled, while the gas pressure slowly expands the blank. The gas keeps expanding the part to fit the die. The material at the super-plastic temperature can permit up to 500% elongation.

Release:

At the end of the forming cycle, the part perfectly conforms to the die, even in its smallest details.

Applications

The method is increasingly being applied in the aerospace industry as a way of producing very complex geometries.

Trends in Common Rail Fuel Injection System | Common Rail Fuel Injection System

Components of a common rail system

01 - common rail system - Components of a common rail system

In the common rail system, a pressure sensor measures the fuel pressure in the rail, its signal valve is compared with the desired value stored in the engine computer. If the measured value and the desired value are different, an overflow orifice in the pressure regulator on the high pressure side is opened or closed. The overflow returns to the fuel tank.

The fuel injectors are opened and closed by the engine computer at defined times. The duration of injection, the fuel pressure in the rail, and the flow area of the injector determine the injected fuel quantity. The injector solenoid valves are controlled according to the accelerator position and the engine information.

The electronic management in the newer fuel injection systems is time based control systems-injection timing can therefore be very flexible and highly precise.

The current advanced fuel injection system such as common rails can account for 30 to 40 percent of the total engine cost.

Third generation common rail technology is currently available on the Mercedes E 280 CDI vehicles sold in our country.

Trends in common rail injection system

In the first and second generation of bosch’s common rail the injection process is controlled by a magnetic solenoid on the injectors. With an electronic solenoid on the injector nozzle, and electronic controls, pilot injection becomes possible.

In pilot injection technique, a small quantity fuel is injected before the main injection. A typical injection period is 300milliseconds. Too small or too early pilot injection raises the noise, too large increases the particulate emission. In short the quantity decreases with increasing engine speed and its interval.

The third generation common rail injection units utilize piezo-electric injector, which use piezo crystals for even more precise metering and accurately timed delivery. Piezo crystals deform when a current is applied across them and return to their original form as soon as the current supply is switched off. The injector actuators consists of several hundred thin piezo crystal wafers. In a piezo inline injectors, the actuator is built into the injector body very close to the jet needle. The movement of the piezo packet is transferred friction-free, without using mechanical parts, to the rapidly switching jet needles.

The piezo injectors effect a more precise metering of the amount of fuel injected and an improved atomization of the fuel in the cylinder.

The third generation common rail fuel injection technology enabled fuel injectors to run with pressure as high as 2000 bar, while microsecond fuel delivery timing is possible.

The rapid speed upon which the injectors can switch makes it possible to reduce the intervals between injections and split the quantity of fuel delivered into a large number of separate injections for each combustion stroke.

01 - common rail system - Single fuel injector unit

System changes

In modern common rail system, injection is split into several individual injection such as preinjection, main injection and post injection. This change will also help in reducing the emissions.

Diesel engine with common rail split injection system has become even quieter, more fuel efficient, cleaner and more powerful.