Laser Welding

Laser are now being used in the automotive industry to produce seam or stitch welds, as alternatives to conventional resistance spot welding, which are used extensively for attaching auto body panels to sub-assemblies.  The advantages of laser welding over resistance spot welding result from the smallness of the laser spot size, the large penetration depth of the weld into the material and the requirement that only single-sided access to the work piece is necessary. Further, the equipment used to carry out the welds can be easily adapted to new vehicle program changes, unlike that used for resistance spot welding. Potential benefits realized by the application of laser welding includes reduced flange widths, increased structural strength and high speed automated processing. Traditionally CO2 lasers have been used for auto body applications. Recent advances have been made with Nd:YAG lasers, which are now capable of producing beam powers of more than 2 kW or more through a fiber optic cable. This is particularly useful for robotic operations, where it is necessary to manipulate the laser beam about a stationary part. laser are also used in the manufacture of tailored blanks, where suitably prepared sheet metal, including differing thickness and  material combinations are butt welded together prior to being pressed into the finished shape. This results in considerable cost and weight savings and increases structural rigidity.

Although at present steel is the main material used in the vehicle manufacturing industry, the use of lighter materials, such as Al, Mg and Ti will in the future become of increasing importance, in order to reduce weight. This, however will require the ability to make satisfactory joins between these materials and steel. Aluminium alloys are invariable less weldable than automotive sheet steels due to its high diffusivity  and the presence of passive oxide layers, which have a significantly higher melting temperature than the base alloy and often a poor electrical conductivity. Laser welding of Al alloys is also problematic due to its high thermal conductivity and high reflectivity of the laser light, but progress is being made using Nd:YAG lasers.

There are number of different laser welding systems available. CO2 and Nd:YAG lasers are already in use in industry. Low power Nd:YAG lasers are used in the electronics industry Rapid improvements in technology means that diode lasers of sufficiently high power and power density for the production of good deep penetration welds are now available.

Laser Welding Process

When welding with laser beam, it is necessary to differentiate between two forms of welding: heat conduction welding and deep penetration welding. Conduction welding occurs at lower power densities or higher welding speeds. The absorbed energy is transferred by heat conduction into the volume of the work piece and produced a broad, shallow pool of molten material.

 In deep penetration welding, the laser beam is focused to a small spot and the power can exceed 5*10^6 Watts/m^2. Sufficient energy is input to vaporizer the material and a vapour-filled channel is formed through which the laser energy penetrates deep into the work piece. Deep seams are produced which increase the absorption efficiency and make greater use of laser beam. The energy required to melt and vaporize the material depends on the physical properties of the material, the wavelength of the laser light and the properties of the surface of the work piece. These welds typically have deep, narrow weld profiles, a small HAZ and little distortion. As a result of the better energy utilization and large depth to width ratio of weld is attainable with deep penetration welding, this is the prime method of welding used in industry with the conventional laser sources.    





 

Surface Tension Transfer (STT)

For many years pipe fabrication have been searching for a faster,easier method to make single-sided low hydrogen open root welds. It is difficult even for skilled welders to weld open root pipe and inflexible positioning makes pipeline welding more difficult, time consuming and expensive.

Higher Strength pipe steels are driving a requirement to achieve a low hydrogen weld metal deposit. GTAW has been only available process capable of achieving the quality requirements but GTAW root welds are very expensive to make. The GMAW process has been avoided because of side-wall fusion and lack of penetration.

Lincoln Electrics has developed and proven the Surface Tension Transfer process to make single-sided root welds on pipe. STT is a patented controlled short-circuit transfer GMAW process made possible by Linchon Electrics exclusive waveform control technology.
STT produces a low hydrogen weld deposit and makes it easier to achieve a high quality root weld in all positions. The STT process as a field proven quality record. STT eliminates the lack of penetration and poor sidewall fusion problems encountered when using the traditional short-arc GMAW process.

Advantages:

Penetration control: Provides reliable root pass, complete back bead and ensured sidewall fusion

1. Cost Reduction: Use 100% CO2 the lowest cost gas, when welding carbon steel

      2. Flexibility: Provides the capability of welding  stainless steel,alloys and mild or high strength                                steels without compromising weld quality

      3. Low heat input: Reduces burn through, cracking and other weld defects.

      4. Low hydrogen weld metal deposit: Hydrogen levels meet the requirements for use on high                                                                           strength pipe steels

      5. High quality open root welds at faster rate travel speed than GTAW

      6. Allow operator to control the heat input into the weld puddle

     7. Its easy to operate.

Technology in Welding

Developments in welding technology applicable to the industry are described in three broad themes; advanced arc welding, friction stir welding and laser processes. In each case, selected advances are reviewed and potential applications and benefits in offshore engineering are presented.

Introduction

Welding is a fundamental technology in the fabrication and repair of virtually all structures in the offshore industry, whether they be above or below sea level, or onshore. It is an enabling technology without which  the offshore industry (and many other industries) could not operate ai its present level of sophistication, and yet welding technology often sits in the background, taken for granted as a mature and established technology. Like most technologies, it is developing steadily over time, allowing new benefits in terms of what can be achieved, and in terms of process economics.

The topic will be about the recent developments in a selection of welding processes which may have potential for use in the industries.

1. Advanced Arc Welding 
2. Friction Stir Welding 
3. Laser Welding     

Pre- Crash Sensors for Pre-Crash Safety(part 2)

Many research and development have been conducted  to meet society needs for safer vehicles. Particularly, occupant protection system such as air bags, developed and introduced in order to reduce occupant injuries in crashes, are currently installed in most vehicles making significant contribution to safety.

Meanwhile, many studies have been made into the development of active safety technologies that help to avoid crash accidents. Unfortunately the current situation is that the active safety technologies are not sufficient spread. Adaptive cruise control has been commercialized since 1995, but its primary use has not been convincing.Some audible warning system  are also being offered, but have not yet reached widespread use.

Toyota Motors corporation has explored the possibility of producing an active safety system employing Intelligent Transport System (ITS) technologies,through participation in the Advanced Safety Vehicle (ASV) projects started in 1991 and led by ministry of land , infrastructure and transport.

Critical basis ITS technologies for application to ASV includes a surround monitoring sensor and an obstacle determination algorithm which combines information from the surround monitoring sensor with other information to identify obstacles with which the vehicle is likely to actually crash.

The sensors and crash determination algorithm for an active safety system should be capable of reliably determining that  a crash will not occur in non-crash situation. Advanced technologies are required to make these predictions and judgments correctly while also taking into account the driver's operation and behavior and this has hampered widespread of active safety systems.

Pre-crash safety system has been developed which operates only when it is judged that a crash cannot be avoided by most drivers under normal driving conditions. Determining unavoidable crashes is restricted to a short time period immediately before the crash so as to improve the reliability of the judgement. In addition the pre-crash system is made with a mechanism and system that will not place the driver and the running vehicle in an unsafe condition even if the system is operated unnecessarily. As a result the world's first commercial system has been achieved.

mechanical views: PRE- CRASH SENSOR FOR PRE-CRASH SAFETY Part 1

mechanical views: PRE- CRASH SENSOR FOR PRE-CRASH SAFETY Part 1: Improvement of vehicle safety performance is one of the targets of the ITS development.A pre-crash safety system has been developed that ut...

PRE- CRASH SENSOR FOR PRE-CRASH SAFETY Part 1

Improvement of vehicle safety performance is one of the targets of the ITS development.A pre-crash safety system has been developed that utilizes ITS technologies. The pre-crash safety system reduces collision injury by estimating TTC (time-to-collision) to preemptively activate safety devices, which consist of "pre-crash seat belts" system and "pre-crash brake assist" system.

The key technology of these systems is a "pre-crash sensor" to detect obstacles and estimate TTC. The pre-crash Sensor uses millimeter-wave radar to detect preceding vehicles, oncoming vehicles, roadside objects, etc. on the road ahead. Furthermore, by using a phased array system as a vehicle radar for the first time, a compact electronically scanned millimeter wave radar with high recognition performance has been achieved.

With respect to the obstacle determination algorithm, a crash determination algorithm has been newly developed, taking into account estimation of the direction of advance of the vehicle, in addition to the distance, relative speed and direction of the object.   

V2V (Vehicle to Vehicle) Communication

The objective of ambient intelligence is to create an intelligent daily space, which is immediately usable and integrated into our homes, our offices, our roads, our cars, and everywhere. This new concept must be invisible; it must blend in with our normal environment and must be present when we need it.

One of the application of this concept consists of providing our cars and roads with capabilities to make road more secure (information about the traffic, accidents, dangers, possible detours, weather, etc.) and to make our time on road more enjoyable (Internet access, network games, helping two peoples follow each other on the road, chat, etc). These applications are typical example of what we call an Intelligent Transport System (ITS) which goal is to improve security, efficiency and enjoyment in road transport through the use of new technologies for information and communication.

Traditional traffic management systems are based on centralized infrastructures where cameras and sensors implemented along the road collect information on density and traffic state and transmit this data to a central unit to process it and make appropriate decisions. This type of system is very costly in terms of deployment is characterized by a long reaction time for processing and information transfer in a context where information transmission delays is vital and is extremely important in this type of system. In addition, these devices on roads requires periodic and expensive maintenance. Consequently, for large scale deployment of this type of system, important investment is required in communication and system infrastructure. However, with the rapid development of wireless communication technologies, location and sensors, a new decentralized architecture based on vehicle to vehicle communications has created a very real interest in these last few years for car manufacturers, R&D community and telecom operators. This type of architecture relies on a distributed and autonomous system and is made up of the vehicles themselves without the support of fixed infrastructure for data routing.  

The main objectives of an intelligent transportation system includes:

1. the improvement of trip security
2. the improvement of global efficiency of the transportation system by reducing travel time and congestion
3. the integration of transportation in a durable development policy particularly by reducing gas emissions for light vehicles and heavy trucks and  by optimizing maintenance of the infrastructure
4. the improvement of user comfort by providing him with a selection of information, decision support, guidance and internet access services.