“ADVANCED ‘ISA’ SYSTEM FOR IC ENGINES & HYBRID ELECTRIC VEHICLE.”

ABSTRACT  

The advanced ISAD system for internal combustion engines & hybrid electric vehicle applications to reduce emissions, fuel consumption and enhance energy efficiency. The new starter-alternator combination provides a more efficient and higher output platform, which will provide the vehicle designer unique ways to reengineer many functions under the hood. Virtually any accessory, which is presently belted driven, may be converted to an electrically powered counterpart with the ready availability of more electrical power from the larger alternator component of the system. Hydraulic power steering units, belt driven air conditioning compressors, various fluid pumps and their components could be replaced with more efficient electric motor-driven system powered by the ISAD. Starting motor advents of the new ISAD system include a quite start feature because the gears and whine of the traditional starter will be eliminated. This system will be able to increase the starting speed and it also supports the acceleration phase. The total system weight is nearly the same. The ISAD system provides all the functions of the engines starter motor and alternator in one electric system installed between the engine and gearbox without significantly increasingly weight and volume of the vehicle. The system has been demonstrated for passenger’s cars and it can be used in commercial vehicles as well.

During starting, the induction machine cranks the engine with high starting torque. In the generation mode, the power is input to the ISA from automotive engine, which is emulated using permanent magnet DC motor, while the DC bus voltage is maintained at 42V.

This paper includes the comparison between conventional starter, ISG, and ISA. Also this paper contains the principle of ISA mild hybridization and one case study of Valeo and Ricardo for 42V diesel vehicle.

At last we conclude that, the ISAD system is the first step to HEV (Hybrid electric vehicle) technology.

1. INTRODUCTION

1.1 NEED OF ELECTRIFICATION

In last years, the automotive electrical load has increased, by replacing of different mechanical equipments with servomotors, by using electrical equipments that improve the internal combustion engine (ICE) performances, in parallel with the comfort and safety (e.g. positioning and regulation systems, navigation and control systems). Today, the average electrical power load on the automotive alternator is between 750 W and 1 kW. It is expected to increase to 4 – 6 kW, in the next decade. Since, the present automotive 12V System didn’t cover this power. It is likely to adopt the 42 V systems for the new-generation auto vehicles. The changing of this voltage level will be a good opportunity for substituting the automotive starter and alternator, by a single equipment, the integrated starter-alternator (ISA). The conventional Lund ell (claw-pole) alternator is coupled to ICE, by a transmission belt (typically 3:1 ratio), and the starter, a DC brushed motor, accelerates the ICE to cranking speed, due to a large mechanical gear (typically 10:1)

1.2 DEVELOPMENT TARGETS

1. Achieve fuel economy twice as good as or better than that of gasoline-powered vehicle in the same class.

2. Secure driving performance equivalent to that of gasoline-powered vehicles in the same class.

3.  Achieve a 10% exhaust emission levels of current Japanese standard

4. Achieve other performance characteristics comparable to those of conventional models.

1.3 FEATURES

1. “Start-Stop” is a fuel saving function that automatically cuts off the engine when the                             vehicle comes to a stop and restarts it when the driver engages a gear or releases the                  brake (automatic transmissions).

2. “Green-Boost” is the alternator motor mode ability to deliver up to 10 kW more mechanical power to the transmission.

3. Regenerative braking is a feature that makes it possible to regenerate the energy of                 braking phases into useful electric energy.

4. High electrical output: up to 12 kW at 42 Volt.

5. Noiseless and rapid engine starting.

6. Compatible with future 42 Volt electrical networks.

1.4 HYBRID ELECTRIC VEHICLE

A type of vehicle that may address many of the problems associated with electric vehicles is a hybrid electric vehicle (HEV). HEVs combine an electric motor and battery pack with an internal combustion engine to improve efficiency. In some HEVs, the batteries are recharged during operation, eliminating the need for an external charger. In other cases, the vehicle must still be plugged in at the end of the day. Either way, range and performance can be significantly improved over electric vehicles.

The combustion and electric systems of HEVs are combined in various configurations. In one configuration (series hybrid), the electric motor supplies power to move the wheels, while the combustion engine is connected to a generator which powers the motor and recharges the batteries. In another configuration(parallel hybrid), the combustion engine provides primary power, while the electric motor adds extra power for acceleration and climbing, or the electric motor is the primary power source, with extra power provided by the engine. In some parallel hybrid systems, the engine and electric motor work in tandem, with either system providing primary or secondary power depending on driving conditions.

The hybrid drive train allows the combustion engine to operate at or near peak efficiency most of the time. This can lead to significantly higher levels of overall vehicle system efficiency. The higher efficiency of these vehicles allows them to achieve very high fuel economy and lower emissions. For example, the hybrid Honda Insight is rated at 61 miles per gallon (mpg) in the city, and 70 mpg on the highway. A gasoline-fueled Honda Civic Hatchback, by comparison, achieves a rating of 32 mpg city and 37 mpg highway.24 Fuel economy improvements can help cut demand for foreign petroleum, and the higher efficiency enables hybrid vehicles to attain, and even surpass, the range of conventional vehicles, even with a smaller fuel tank. Furthermore, since these vehicles utilize conventional fuel, the fueling infrastructure problems associated with electric vehicles can be eliminated.

The only hybrid vehicles currently available in the U.S. market are the Honda Insight, the Honda Civic Hybrid, and the Toyota Prius. Over the next few years, however, most major manufacturers plan to introduce hybrid passenger vehicles. Further, while the currently available hybrids are smaller cars, manufacturers are also developing larger hybrids such as mini-vans and sport utility vehicles.25

Until recently, HEVs were treated as conventional vehicles because they run on gasoline or diesel fuel. However, the Internal Revenue Service announced on May21, 2002, that it will allow taxpayers to claim a clean-burning fuel vehicle tax deduction of $2,000.26

2. ELECTRIC MOTOR TECHNOLOGIES

In this section, the three most common electric motor technologies and the power electronic devices with control circuits in vehicle applications are discussed. The three motors are the permanent magnet (brushed and brushless type) motors, induction motors, and switched reluctance motors. Among those three motor configurations, the permanent magnet motor type is more widely applied in the vehicles because of its merits. An electric motor is a well-known device that converts electrical energy to mechanical energy using magnetic field linkage. An electric motor consists of two major elements: (1) a fixed stator with current-carrying windings or permanent magnets, (2) a rotating rotor which provides a magnetic field produced by additional current carrying windings or attached permanent magnets between the rotor and stator magnetic fields. Modern electric motor advances have resulted from developments and refinements in magnetic materials, integrated circuits, power electronic switching devices, computer modeling and simulation, and manufacturing technology, rather than by fundamental changes in operating and control principles. The dramatic improvements in permanent magnet materials and power electronic devices over the last two decades have led to the development of brushless permanent magnet motors that offer significant improvements in power density, efficiency, and noise/vibration reduction. Also, because there is no electrical Sparks, there is less radiated noise.

2.1 PERMANENT MAGNET MOTORS

The permanent magnet machine is highly coveted for its high power density and high efficiency.  This is mainly due to the high energy density NdFeB and SmCo magnets, which are commercially available today. In other words, advancements in high-energy permanent magnet materials and magnet manufacturing technologies enabled the manufacturing of high power density and high efficiency permanent magnet motors at a reasonable cost. Also, the availability of fast switching high power semiconductor devices with low on-state voltage drop such as MOSFETs and IGBTs. Ever increasing high-speed microprocessors/digital signal processors have contributed to permanent magnet electric motors. While the cost for semiconductors and the permanent magnets is still high at the present time, trends for cost reduction are continuing and encouraging.

2.1.1 BRUSH TYPE PERMANENT MAGNETIC MOTOR

There are two types of permanent magnet motors: brush and brushless. Today’s vehicle applications almost exclusively use brush type permanent magnet motors.

The brush permanent magnet motors have four general characteristics that cause them to be useful for vehicle application:

1)      Desirable torque versus speed,

2)      Simple control of torque and speed,

3)      High electromagnetic power density, and

4)      Inverters are not required.

Nevertheless, there are six general characteristics that detract from more wide applications in the automotive industry:

1)      friction between the brushes and the commutator,

2)      brushes and commutators require maintenance,

3)      current is supplied to the armature through the brushes and commutator,

4)      brushes and commutators are open and produce sparking,

5)      cooling of a DC motor is difficult, and

6)      Switching of large currents is required for control of DC motors.

The brushless motors are becoming stronger candidates over traditional brush type motors for the following reasons: higher efficiency, higher power density, better heat dissipation, and increased motor life. In addition, brushless motors experience no losses due to brush friction and they deliver higher torque compared to a brushed type motor of equal size and weight.

2.1.2 BRUSHLESS TYPE PERMANENT MAGNET MOTOR

Electronically commutated, brushless permanent magnet motors are however, becoming prime movers in vehicle propulsion, industrial drives, and actuators as a result of improvements in permanent magnet materials, advances in the power electronic devices, and power integrated circuits in the last two decades. Not only have there been gradual improvements in Alnico and Ferrite (ceramic) alloys, but the rapid development of rare-earth magnets, such as samarium-cobalt (Sm -Co) and neodymium-boron-iron (Nd B Fe) around 1980, have provided designers with a significant increase in available field strength. This new high density, brushless, permanent magnet motor system provides a very high torque to inertia ratio.

2.1.3 PERMANENT MAGNET MATERIAL

Figure 4 summarizes the four most common permanent magnet materials used today by motor manufacturers. In most cases, the higher remanence with higher coercivity in a permanent magnet is desired by motor designers. The alnico magnet provides a fairly high remanence flux density but a low coercive force. When the coercive force is low and two opposing magnetic poles are in proximity of each other, the magnetic poles can weaken each other and there is a possibility of permanent demagnetization by the opposing field.

Unlike an alnico magnet, the ferrite magnet has a low flux density, but a high coercive force. It is possible to magnetize the ferrite magnet across its width as a result of this high coercive force. Ferrite magnets are most widely used in electric motors because their material and production costs are low. The cost of a typical ferrite magnet material at this time is about 6-8 times lower than the Nd B Fe. Nonetheless, output power to weight ratio is 1.22, ferrite, vs. 1.36, Nd B Fe. This means that the ferrite magnet motor will be about 20% heavier for the same output compared with the Nd B Fe magnet motor. Another measurement is an output power per unit cost of active material. It is predicted that the output power per unit cost is about 4 times lower for ferrite magnet motor compared to the Nd B Fe magnet motor. Delco Remy uses the ferrite and Nd B Fe magnets for different starter motor applications. Rare-earth magnets have both high magnetic remanence, and high coercive force. Since the initial cost is high, these permanent magnets are used in applications such as high performance and high-energy density motor applications. For a given volume, the flux density is twice that of the ferrite, leading to a larger torque production. Nd B Fe magnetic materials are superior to any other magnetic material now on the market. The only disadvantage of using an Nd B Fe magnet, as opposed to an Sm Co magnet, is that the high-energy density Nd B Fe permanent magnet has a maximum operating temperature of 100 to 150 degrees C, as compared to 200-300 degrees C for Sm Co, alnico, and ferrite.

2.2 INDUCTION MOTORS

Alternating current (AC) induction motors are the most common of all types of electric motors manufactured for the general use in household applications, industrial drives, and electric propulsion. These motors are rugged, relatively inexpensive, and require very little maintenance. They range in size from a few watts to about 15,000 hp. The induction motors have certain inherent disadvantages including speed which, is not easily controlled, plus it runs at low lagging power factors when lightly loaded, and the starting current is usually five to seven times full-loaded current.

Induction motors have relatively low manufacturing cost and are mechanically rugged because they can be built without slip rings or brush and commutators. Consequently much attention has been given to induction motors for automotive applications in the areas of vehicle propulsion, engine starting, braking, electricity generating, speed reversal, speed change, etc. In spite of many interests in vehicle applications, the costs of the power electronic components are still relatively high, especially in the low power region. Furthermore, in many automotive applications it is either not possible or not desirable to use a mechanical sensor for speed or angle, etc. This means, a simple and affordable control system, using only the voltage and the current of the induction motor as measured quantities, is necessary. A sensor less controller technology has been demonstrated using a switched reluctance motor by many academia and industrial teams.

3. CONVENTIONAL STARTER, ISG & ISA.

3.1 STARTER AND GENERATOR: -

Fig3.1: - Delco self starter generator unit

The automotive starter (sometimes called a cranking motor) dates back to the early part of the automotive industry. In 1912 the Cadillac Motor Car Company introduced the electric self- starter to replace the hand crank. Frank and Perry Remy of the Remy Electric Company were also early innovators in the automotive industry. Remy Electric also developed and introduced starting motors in the same time period. This innovation in essence broadened the accessibility of the automobile from those strong enough to hand crank to virtually everyone. There have been many developments and refinements in the starting motor since its introduction in 1912 (see Figure 7). The primary innovations focused on the engagement method, changing from six to 12 volts, and gear reduction. From the 1980s to today the industry has focused on size and weight reduction as well as reliability and durability improvement.

3.2 INTEGRATED STARTER GENERATOR

An integrated starter-generator can be used in conventional vehicles to reduce fuel consumption and improve acceleration. As with a hybrid vehicle, using the high-torque device allows the engine to shut off when the vehicle is stopped. When power is applied, the engine can restart in less than one second.45 It is believed that the integrated starter-generator could improve fuel economy of conventional vehicles by as much as 20%. However, because the integrated starter-generator requires considerable amount of electrical power, it is being developed concurrently with 42-volt electrical systems.

3.3 ISA SYSTEM DISCRIPTION

A block diagram of the overall system is illustrated in the figure. As indicated in the figure, the system is based on an induction machine mechanically coupled to an engine, and it is fed by a 36V battery through a three phase IGBT inverter. The controller has been implemented using dSACE 1104 control card. The control algorithm derives PWM signals for the three phase inverter by taking speed, IM line currents and DC voltage as inputs.

1.1kW/22V Induction machine has been used for the prototype hardware. The induction machine line to line voltage of 22V is chosen because of the 42V DC bus voltage and to ensure that the inverter operates in boost mode, so that motor current is in continuous conduction at all times.

3.4 SPECIFICATIONS

In practice, the available 30-36V battery voltage at motoring and required 30-36V charging voltage at generating is the main problem during electric machine design. Besides the dilemma from voltage specifications, the requirement of a wide speed range and the high temperature of cooling media in the ISA system. The ambient temperature range from -40°C to 125°C, which is a typical for an air cooled ISA machine. If the machine cooled by liquid, the available engine coolant temperature will be up to 135-140°C, unless a separate liquid cooling loop is introduced. The speed of electric cool machine runs from 0-6000 r/min for the crankshaft mounted ISA system, which is the same as engine speed. The maximum operating speed electric machine run as high as 13,800-19,200 r/min for the belt driven ISA system with the belt transfer ratio of 2.3-3.2.

In the 42V DC electric system, the motoring performance specifications should met over at lower voltage level of 30-33V dc, although the maximum available battery voltage is 36V at the dc input of the electric machine drive. If the 14V electric system is used for the ISA system onboard vehicle, the motoring operations of the machine have to be fully functional at 10-11V dc voltage in spite of the battery voltage of 12V. the low available voltage is caused by a low battery charge state and internal resistance as well as ambient temperature. If a three phase induction machine is used for ISA machine and the space vector control is introduced for its control, it needs to meet all motoring specifications at the minimum available line to line voltage of 21-23V ac and 7-8V ac in rms value for the 42V dc and the 14V dc systems, respectively.

2. Automotive direct-drive integrated starter-alternator requirements and selection

The proposed solution is represented by a direct-drive, where the electrical machine of ISA is coaxial with the shaft of the ICE and the transmission (clutch and gear box).

(Figure 2)

The integration of the starter and alternator in just one electrical machine will make more efficient the use of electrical equipment, and eliminate the space and weight problems, improving in the same time the performances and reducing the generator and starting noises. Another advantage is that ISA eliminates mechanical elements, such as transmission belt, pulleys and flywheel.

ISA allows at start the operation in motor regime, as a starter, and after that, will work in generator regime, providing electrical energy as an alternator. In motor regime, the ISA system should reach 500 rpm in maximum 3-5 s, overcoming a load torque of 80 – 150 Nm. In generator regime, the ISA system transforms the mechanical energy in a.c. electrical energy, which after rectification recharges the automotive battery. Table 1

Table:-Automotive starter/alternator performance requirement

Summarizes the automotive starter and alternator performance requirements, for both, conventional and integrated system. The interior permanent-magnet synchronous machine (IPMSM) has been selected to fulfill the above-stated performance requirements for an automotive ISA (Figure 3).

The associated electronic power converter is considered of bi-directional AC-DC three-phase bridge type in IGBT technology (Fig. 4).

The control of ISA system means the current control by hysteresis regulators, in function of the motor speed error. The main challenge in the selection of an ISA direct-drive is the fulfillment of performance at the lowest possible system cost.

The main data and parameters of the IPMSM designed for automotive direct-drive ISA are the

following:

- Rated voltage: U = 42 V;

- Output power: P = 6 KW;

- Stator phase resistance: Rs = 0,0103;

- d – axis inductance: Ld = 0,06497 * 10-3 H;

- q – axis inductance: Lq = 0,30505 * 10-3 H;

=0,063 Wb;

- Permanent magnet excitation flux: PM

- Number of poles pairs: p = 12;

4. PRINCIPLE OF ISA MILD HYBRIDIZATION

Vehicle speed is controlled by the driver through either the accelerator pedal or the brake pedal. Depending on the driving mode, either a positive or a negative torque is requested from the engine; however, in case of braking, if the negative torque provided by the engine is insufficient, friction torque in the wheels provides an additional braking torque which results in energy loss. The engine speed is determined by the transmission and the gear ratio between the engine crankshaft and the wheel. Consequently, the engine torque is the only available variable that can be adjusted in order to operate the engine in efficient BSFC regimes. For a parallel hybrid configuration, power can be provided for propulsion by both the thermal and electrical paths. The ISA is mechanically coupled to the engine, as depicted in Figure.

Figure 4.1: Schematic diagram of the HMMWV power train incorporating the ISA

(T-Turbine, C-Compressor, D-F- Front Differential, D-Rear Differential, EM- Exhaust Manifold, IM- Intake Manifold, ISA-Integrated Starter Alternator, T/C- Torque Coupler, Trans-Transmission)

Hence, the ISA speed is determined by the engine speed by means of a constant ratio. As a consequence, the additional power available by the ISA can only be regulated by adjusting the ISA torque. The latter can be either positive or negative contingent upon the mode in which the ISA is operating, as designated by the power management algorithm. In the motor mode, the ISA contributes power to the driveline by drawing electrical energy from the battery. In the generator mode, the ISA absorbs power from the driveline and charges the battery.

In cruising, the power requested from the power train by the driver is expressed by positive amount of torque, TDRIVER, given a fixed engine speed:

Tdriver = TISA + TEngine

The power management algorithm comes to a decision regarding the ISA torque, TISA, based on the current SOC, in order to utilize the most proper engine operating point as far as fuel consumption is concerned. Conversely, when braking is demanded by the driver, the power is expressed by a negative torque TDRIVER:

T Driver= T Engine+ T ISA+ T Brake

A fraction of this torque is absorbed by the engine, ENGINE, whereas the ISA absorbs the maximum absolute amount within the constraints imposed by the battery and the ISA. If a residual amount remains, this must be handled by the friction brakes, TBRAKE. Consequently, the ISA can recover the energy that otherwise would be lost by means of friction brakes so as to charge the battery.

5. CASE STUDY

Valeo and Ricardo team for 42-V diesel vehicle

Valeo's high-efficiency integrated starter-alternator system, which will be mounted on the crankshaft between the engine and the transmission, performs a number of key functions. The integrated unit uses electronic control to crank the engine, providing stop-and-go capability. When a driver stops at a traffic light, for example, the engine is automatically cut, both saving fuel and reducing emissions. As soon as the driver engages a gear again, the engine automatically and quietly restarts. NVH improvements are inherent when at standstill because of the absence of engine noise. The quiet starting is realized through the use of the integrated starter-alternator in motor mode. Since this unit is fully integrated into the powertrain and replaces the traditional starter motor, engaging the starter's gear on the ring gear is no longer. The starting time is 0.3 s as opposed to 1 s with a conventional starter motor, leading to further reduction in emissions.

.

The special design of the Valeo integrated starter-alternator means it can provide additional torque into the powertrain over the full range of engine speeds. During acceleration, the starter-alternator is used as an electric motor to give an extra boost to the engine; despite the smaller engine size, the i-MoGen powertrain can supply similar torque to the much larger and heavier 2.0-L diesel engine.

In a conventional vehicle, the kinetic energy of a vehicle is lost as heat when the driver applies the brakes. With the high-output starter-alternator, a part of this energy can be saved, using the alternator to generate electric energy. As soon as the driver presses the brake pedal, an electronic communication is sent to the integrated starter-alternator that immediately converts kinetic energy from the vehicle to electrical energy that can be stored in the battery. It is then possible to re-use this energy, which is the basic principle behind regenerative braking.

The maximum electrical output power from the Valeo integrated starter-alternator unit—when running in alternator mode—is 6 kW, which is three times higher than conventional alternators. This high output is necessary to allow the operation of high- power electrical components such as the electrical HVAC compressor or the electrically heated diesel particulate filter, a Ricardo solution that efficiently destroys harmful diesel particulate.

As part of the integrated starter-alternator system, Valeo will integrate a dc/dc converter to supply 14 V to the low-power electrical components that are not converted to 42 V. Such a high capacity dc/dc converter is expected to be a requirement in future 42-V vehicles where specific components will require lower voltage.

A key requirement for 42-V systems is the reliability of available power. Valeo is collaborating with a battery expert to develop and integrate fault-tolerant batteries with a battery state-of-charge function to guarantee the reliability of all its 42-V systems.

 

 

6. ADVANTAGES, DISADVANTAGES & APPLICATIONS

6.1 ADVANTAGES

1. Reduce fuel consumption.
2. Reduce emission.
3. Enhance energy efficiency.
4. Weight is less
5. High power generation.
6. Quick start & stop.
7. Well engine performance.
8. Big cities getting more advantage.

6.2 DISVANTAGES

1.        Requirement of mass production.

2.        Audible normally associated with engine cranking.

3.        Battery required is of high voltage.

6.3 APPLICATIONS

      1.    Vehicle magnetic air conditioner

      2.    Camless electromagnetic valve  System.

      3.    Turbocharger generator

      4.    Permanent magnet traction wheel motor

      5.    Electric variable transmission

7. CONCLUSION

The automotive industry trends and prediction of the future electrical system was presented. Today’s 2 kw platforms need to be replace with 20 kw or even 50 kw platforms on which host of electrically generated functions will be enabled -some of which we have not even conceived .The three major motor configuration and enabling technologies that support more electrical system to vehicle application were presented. Some devices on the vehicle that are now driven mechanically could be driven electrically, since the needed power will be availed by ISA system. Component such as air conditioner compressor, the water pump and the power steering system can then be operated only on demand, instead of remaining a continuous parasitic load on the engine when they are in the “off” part of their operating cycle. This will further reduce fuel consumption and emission. The ISA system is the first step to HEV technology.

8. REFERENCES

1. www.indiacar.com
2. www.automotiveengineering.com
3. www.automobile.com
4. www.google.com
5. IEEE industry applications magazine.
6. Automotive Research Center, The University of Michigan() SAE technical paper series-by Andreas Malikopoulos, Zoran Filipi and Dennis Assanis)

“ROBOT WELDING TECHNOLOGY”

 

A SEMINAR ON

 “ROBOT WELDING TECHNOLOGY”

                 SUBMITTED BY,Mr.BORATE SUHAS DHONDIBA

 

ABSTRACT

                Welding is manufacturing process in which to pieces of metal are   joined by usually by heating them until molten and fused and by applying pressure. Welding operations performed by robot vastly.  Welding of two types on e is arc welding and another spot welding.

          In arc welding two metals are joined along its continuous path.  An electric arc is generated there.

               Spot welding is the largest application for industrial robots in US, accounting for about for 35 percent of installed robots.  Welding robots typically use point-to-point programming to maneuver a welding gun.  Robots weld more consistently faster and with higher quality than humans

 

================

1.  Robot welding

When should robots be used for welding?

             A welding process that contains repetitive tasks on similar pieces might be suitable for automation. The number of items of any type to be welded determines whether automating a process or not. If parts normally need adjustment to fit together correctly, or if joints to be welded are too wide or in different positions from piece to piece, automating the procedure will be difficult or impossible. Robots work well for repetitive tasks or similar pieces that involve welds in more than one axis or where access to the pieces is difficult. 

Why robot welding? 

             The most prominent advantages of automated welding are precision and productivity. Robot welding improves weld repeatability. Once programmed correctly, robots will give precisely the same welds every time on work pieces of the same dimensions and specifications.

            Automating the torch motions decreases the error potential which means decreased scrap and rework. With robot welding you can also get an increased output. Not only does a robot work faster, the fact that a fully equipped and optimized robot cell can run for 24 hours a day, 365 days a year without breaks makes it more efficient than a manual weld cell. 

           Another benefit of automated welding is the reduced labor costs. Robotic welding also reduces risk by moving the human welder/operator away from hazardous fumes and molten metal close to the welding arc.

What welding processes are suitable for robot welding?

           Most production welding processes can be used in automated applications. The most popular, used in perhaps 80 percent of applications, is the solid wire GMAW process. This process is best for most high production situations because no post weld cleanup is required

 

2. WELDING PROCESSES

         Welding is the most economical and efficient way to join metals permanently. Welding is used to join all of the commercial metals and to join metals of different types and strengths. 

 

        A weld is produced either by heating the materials to the welding temperature with or without the application of pressure alone with or without the use of filler metal. There are different kinds of welding processes who all use different sources of heat, for instance arc welding which uses an electric arc as a heat source. Another commonly used welding process is spot welding (resistance welding).  

      Welding is considered to be the most complex of all manufacturing technologies. In order to transform welding from a manual operation to an automated production process, it is necessary to understand the scientific principles involved.

2.1. ROBOT ARC WELDING

       Robot welding means welding that is performed and controlled by robotic equipment. In general equipment for automatic arc welding is designed differently from that used for manual arc welding. Automatic arc welding normally involves high duty cycles, and the welding equipment must be able to operate under those conditions. In addition, the equipment components must

have the necessary features and controls to interface with the main control system. 

      A special kind of electrical power is required to make an arc weld. A welding machine, also known as a power source, provides the special power. All arc-welding processes use an arc welding gun or torch to transmit welding current from a welding cable to the electrode. They also provide for shielding the weld area from the atmosphere. 

     The nozzle of the torch is close to the arc and will gradually pick up spatter. A torch cleaner (normally automatic) is often used in robot arc welding systems to remove the spatter. All of the continuous electrode wire arc processes require an electrode feeder to feed the consumable electrode wire into the arc.

    Welding fixtures and work piece manipulators hold and position parts to ensure precise welding by the robot. The productivity of the robot-welding cell is speeded up by having an automatically rotating or switching fixture, so that the operator can be fixing one set of parts while the robot is welding another.

To be able to guarantee that the electrode tip and the tool frame are accurately known with respect to each other, the calibration process of the TCP (Tool Center Point) is important. An automatic TCP calibration device facilitates this time consuming task.

TYPICAL COMPONENTS OF AN INTEGRATED ROBOTIC ARC-WELDING CELL:

1. Arc welding robot
2. Power source
3. Welding torch
4. Wire feeder
5. Welding fixtures and work piece positioners

6. Torch cleaner

7. TCP calibration unit

2.1.1 ARC WELDING ROBOT

      During the short time that industrial welding robots have been in use, the jointed arm or revolute type has become by far the most popular. For welding it has almost entirely replaced the other types except for the Cartesian, see (robot kinematics), which is used for very large and very small robots. The reason for the popularity of the jointed arm type is that it allows the welding torch to be manipulated in almost the same fashion as a human being would manipulate it. The torch angle and travel angle can be changed to make good quality welds in all positions. Jointed arm robots also allow the arc to weld in areas that are difficult to reach. Even so, a robot cannot provide the same manipulative motion as a human being, although it can come extremely close. In addition, jointed arm robots are the most compact and provide the largest work envelope relative to their size. Usually arc-welding robots have five or six free programmable arms or axes.                                                           

      Off-the-shelf programmable robot arms are today available from different suppliers such as ABB, FANUC, PANASONIC, KUKA, MOTOMAN.

 

2.1.2 ARC WELDING POWER SOURCES

      A welding power source must deliver controllable current at a voltage according to the requirements of the welding process. Normally, the power required is from 10 to 35 V and from 5 to 500 A. The various welding processes and procedures have specific arc characteristics that demand specific outputs of the welding machine.

      Automatic arc welding machines may require power sources more complex than those used for semi-automated welding. An automatic welding machine usually electronically communicates with the power source to control the welding power program for optimum performance. A power source for arc welding is designed to provide electric power of the proper values and characteristics to maintain a stable arc suitable for welding. 

      There are three types of arc welding power sources, distinguished according to their static characteristics output curve. The constant-power (CP) is the conventional type of power source that has been used for many years for shielded metal arc welding using stick electrodes. It can be used for submerged arc welding and gas tungsten arc welding.  The constant-voltage (CV) power source is the type normally used for gas metal arc and flux cored arc welding using small-diameter electrode wire. The constant-current (CC) power source is normally used for gas tungsten arc and plasma arc welding. 

      The selection of a welding power source is based on

1.      The process or processes to be used

2.      The amount of current required

3.      The power available at the job site

4.      Economic factors and convenience

2.1.3 WELDING TORCH

      A welding torch is used in an automatic welding system to direct the welding electrode into the arc, to conduct welding power to the electrode, and to provide shielding of the arc area. There are many types of welding torches, and the choice depends on the welding process, the welding process variation, welding current, electrode size and shielding medium. Welding torches can be categorized according to the way in which they are cooled. They may be water-cooled with circulating cooling water or air-cooled with ambient air. A torch can be used for a consumable electrode welding process such as gas metal arc or flux cored arc welding, and shielding gas may or may not be employed. 

      A torch can be described according to whether it is a straight torch or has a bend in its barrel. A torch with a bend is often used for robotic arc welding applications to provide access for the weld.

     

      The major function of the torch is to deliver the welding current to the electrode. For consumable electrode process this means transferring the current to the electrode as the electrode moves through the torch. 

      A second major task of the torch is to deliver the shielding gas, if one is used, to the arc area. Gas metal arc welding uses a shielding gas that may be an active gas usually carbon dioxide or a mixture of an inert gas, normally argon, with CO₂ or oxygen.

      The welding torch is mounted to the robot flange with a matching mounting arm. Preferably an anti collision clutch is used to prevent damages on expensive weld equipment in case of sticking electrode and crashes during installation and start-up.

2.1.4 WIRE FEEDER

      Wire feeders are used to add filler metal during robotic welding. This allows flexibility in establishing various welding wire feed rates to suit specific requirements for an assembly. Normally, the wire feeder for robotic welding is mounted on the robot arm, separate from the power supply. For robotic welding, a control interfaces between the robot controllers, the power supply and wire feeder is needed. The wire feeding system must be matched to the welding process and the type of power source being used. 

      There are two basic types of wire feeders. The first type is used for the consumable electrode wire process and is known as an electrode wire feeder. The electrode is part of the welding circuit, and the melted metal from the electrode crosses the arc to become the weld deposit. There are two different types of electrode wire feeders. The constant-power power source requires a voltage-sensing wire feed system in which the feed rate may be changing continously. The constant-voltage system requires a constant feed rate during the welding operation.

      The second type of wire feeder is known as a cold wire feeder and is especially used for gas tungsten arc welding. The electrode is not part of the circuit, and the filler wire fed into the arc area melts from the heat of the arc and becomes the weld metal.

 

 

 

 

 2.1.5 WORKPIECEFIXATION AND POSITIONING

      In order to join parts successfully in a robotic welding application, individual parts must be aligned precisely and held securely in place while the welding is proceeding. An important consideration, then, is the design of a fixture which holds the individual parts in the proper alignment. The tool must allow for quick and easy loading, it must hold the parts in place securely until they are welded together and must allow the welding gun unrestricted access to each weld point. 

One starting point for positioning the workpiece for robotic welding may be the fixture already used for manual welding even though specialized positioners are used to improve the versatility and to extend the range of robotic arc welding systems. The usable portion of a robot work envelope can be limited becuse the

welding torch mounting method does not allow the torch to reach the joint properly. Special positioners eliminate some of these limitations by making the workpiece more accessible to the robot welding torch. 

      The positioners used with robots also have to be more accurate than required for manual or semiautomatic welding. In addition the robot positioner controls must be compatible and controllable by the robot controller in order to have simultaneous coordinated motion of several axes while welding.

However, loading and unloading stationary jigs of the robot cell can be time consuming and impractical. It is often more efficient to have two or more fixtures on a revolving workpiece positioner, despite a higher initial cost. With a revolving table for instance, the operator can load and unload while the robot is welding. Obviously, this speeds up the process and keeps the robot welding as much of the time as possible.

2.1.6 TORCH CLEANER

      Periodic cleaning of arc welding guns is required for proper and reliable operation of robotic arc welding equipment. The high duty cycle of an automatic operation may require automated gun cleaning. Systems are available that spray an antispatter agent into the nozzle of the gun. Additionally, tools that ream the nozzle to remove accumulated spatter and cut the wire are available. The cleaning system is automatically activated at required intervals by the welding control system. 

2.1.7 TCP-CALIBRATION UNIT

      End-of-arm sensor and tool centre point calibration is a critical aspect of successful system implementation. End-of-arm sensing, in the context of robotic welding, is used to detect the actual position of the seam on the workpiece with respect to the robot tool frame. 

      Analysis of the profile data yields the relative position of the seam with respect to the sensor reference frame. If the sensor reference frame pose is known with respect to the end-frame of the robot, and the tool frame pose is known with respect to the end-frame, then the sensor data may be used to accurately position the tool centre point (TCP) with respect to the workpiece.

      While end-of-arm sensor based control would appear to solve both robot accuracy and workpiece position error problems, this is only so if the sensor frame, end frame, and tool frame are accurately known with respect to each other. 

      Should the sensor be accidentally knocked out of position, the robot system becomes a highly consistent scrap production facility. Indeed, this very concern has been one of the reasons why some companies that would benefit from a sensor based correction system have been reluctant to implement such a system. What is required is not only a technique that enables the frames to be automatically calibrated, but that also enables the system to quickly determine if recalibration is necessary. This second capability is perhaps the more important in practice, since it can be reasonably assumed that any calibration error will be caused by an unanticipated event that could occur during any welding cycle. 

2.2 ROBOT SPOT WELDING

      Automatic welding imposes specific demands on resistance welding equipment. Often, equipment must be specially designed and welding procedures developed to meet robot welding requirements. 

      The spot welding robot is the most important component of a robotized spot welding installation. Welding robots are available in various sizes, rated by payload capacity and reach. The number of axes also classifies robots.  A spot welding gun applies appropriate pressure and current to the sheets to be welded. There are different types of welding guns, used for different applications, available.  An automatic   weld-timer initiates and times the duration of current. 

  

      During the resistance welding process the welding electrodes are exposed to severe heat and pressure. In time, these factors begin to deform (mushroom) the electrodes. To restore the shape of the electrodes, an automatic tip-dresser is used. 

      One problem when welding with robots is that the cables and hoses used for current and air etc. tend to limit the capacity of movement of the robot wrist. A solution to this problem is the swivel, which permits passage of compressed air, cooling water, electric current and signals within a single rotating unit. The swivel unit also enables off-line programming as all cables and hoses can be routed along defined paths of the robot arm.

TYPICAL COMPONENTS OF AN INTEGRATED ROBOTIC SPOT WELDING CELL:

      1) Spot welding robot
      2) Spot welding gun
      3) Weld timer
      4) Electrode tip dresser
      5) Spot welding swivel

 

2.2.1 SPOT WELDING ROBOT

      A robot can repeatedly move the welding gun to each weld location and position it perpendicular to the weld seam. It can also replay programmed welding schedules. A manual welding operator is less likely to perform as well because of the weight of the gun and monotony of the task. 

   

 Spot welding robots should have six ore more axes of motion and be capable of approaching points in the work envelope from any angle. This permits the robot to be flexible in positioning a welding gun to weld an assembly. Some movements that are awkward for an operator, such as positioning the welding gun upside down, are easily performed by a robot. 

 

2.2.2 SPOT WELDING GUNS

Spot welding guns are normally designed to fit the assembly. Many basic types of guns are available, the two most commonly used being the direct acting type, generally known as a “C”-type gun, where the operating cylinder is connected directly to the moving electrode, and the “X”-type (also known as "Scissors" or "Pinch") where the operating cylinder is remote from the moving electrode, the force being applied to it by means of a lever arm. C guns are generally the cheapest and the most commonly used. There are many variations available in each basic type with regard to the shape and style of the frame and arms, and also the duty for which the gun is designed with reference to welding pressure and current. 

 Pneumatic guns are usually preferred because they are faster, and they apply a uniform electrode force. Hydraulic spot welding guns are normally used where space is limited or where high electrode forces are required

2.2.3 WELD TIMER

      An automated spot welding cell needs control equipment to initiate and time the duration of current. A spot weld timer (weld control unit) automatically controls welding time when spot-welding. It also may control the current magnitude as well as sequence and time of other parts of the welding cycle.

2.2.4 ELECTRODE TIP DRESSER

      The function of the electrodes is to conduct the current and to withstand the high pressures in order to maintain a uniform contact area and to ensure the continued proper relationship between selected current and pressure. Uniform contacting areas should therefore be maintained. 

      Good weld quality is essential and depends, to a considerable degree, upon uniformity of the electrode contact surface. This surface tends to be deformed (mushroomed) with each weld. Primary causes for mushrooming are too soft electrode material, too high welding pressure, too small electrode contact surface, and most importantly, too high welding current. These conditions cause excessive heat build-up and softening of electrode tips. Welding of today’s coated materials also tends to contaminate the face of the electrodes. 

      As the electrode deforms, the weld control is called upon to "step" up the welding current in order to compensate for "mushroomed" weld tips. Eventually, the production line will have to be shut down in order to replace the electrodes or to manually go in and hand dress the electrodes. This process will improve the weld cycle but in either case, the line is stopped and time is lost. Furthermore the deformed electrodes have caused unnecessary high consumption of energy and electrodes.

      In automatic tip dressing, a tip dresser is mounted on the line where it can be accessed by the welding robot. The robot is programmed to dress the electrodes at regular time intervals. The dressing can be done after each working cycle, after every second cycle, and so on. It depends upon how many spot-welds are done in each cycle. For welding in galvanized sheet, dressing after about 25 spot-welds is recommended. The dressing takes approximately 1 to 2 seconds, and is performed when the work pieces are loaded, unloaded and transported.  Maintaining proper electrode geometry minimizes production downtime and utility costs and increases weld efficiency.

2.2.5 SPOT WELDING SWIVEL

      A major advancement in resistance spot welding is the swivel. This unit permits passage of compressed air, cooling water, electric current and signals through different channels within a single rotating unit. 

   This invention greatly improves total efficiency of robotic spot-weld installations. Electrical connection between swivel and transformer is minimal thus permitting maximum utilization of access to spot-weld areas.

Basic advantages are:

·         Less work space needed -No mass of cables and hoses hanging from the robot arm, resulting in floor space economy.

·         Improved accessability - Since no limitation on the robot wrist caused by any cables or hoses.

·         Improved safety - Greatly improved safety factors through reduction of air, electric and water lines; now limited to quick-connect piping, and hoses within robot arm.

·         Saving in capital equipment - Compact weld-gun assembly accessable to areas formly blocked by transformer, cables, and control boxes. More welds per station means big savings through fewer work stations and less capital equipment.

      Reduced try-out costs - No un-defined cables exist on the robot, which reduces programming time to minimum. True off-line programming is now a real. The swivel, which fits directly onto the weld-gun fixture plate without any hoses or cables, ensures the highest quality condition of the spot weld. No electrical degeneration on cables and no hoses that wear.

 

 

 

 

 

 

 

 

2.3 LASER ROBOT WELDING

      Today, there are more and more three-dimensional welding applications. Typical of many is the welding of roofs in the automobile sector. Here, the focusing unit of the laser is mounted on a 6-axis buckling arm robot, which executes the movements in space. Most frequently used are Nd: YAG lasers, which allow flexible application of the laser light through optical fibers. But CO₂ lasers combined with flexible mirror movement  can also be used.

This is how bodies are created in car construction that are significantly stiffer in case of a crash, for example, and thus provide greater safety for passengers.

Furthermore, laser welding always requires access from one side only, so newdesigns are now possible that could not nave been implemented by means of traditional resistance spot welding.

 

3. Welding Safety

      Welding is an established manufacturing process with known potential hazards. Potential safety hazards associated with arc welding include arc radiation, air contamination, electrical shock, fire and explosion, compressed gases, and other hazards. Robots were originally designed to perform the job functions of a human. They were designed to relieve humans of the drudgery of unpleasant, fatiguing, or repetitive tasks and also to remove humans from a potentially hazardous environment. In this regard, robots can replace humans in the performance of dangerous jobs and are considered beneficial for preventing industrial accidents. On the other hand, robots have caused fatal accidents.

      The introduction of robots requires appropriate safety features in order to protect both those working directly with the robot and others in the workshop who may not be aware of its potential dangers. This can be provided in a number of ways.

      One of the best solutions for robot safety is to purchase a complete welding cell from a robotic integrator. A complete cell includes barriers, all necessary safety devices, and a method of loading and unloading the workstation.

      Each robot installation must be carefully planned from safety viewpoint to eliminate hazards. When the robot is in operation it is necessary that people remain outside the work envelope. Barriers or fences should be in place around the robot. All doors and maintenance openings must be protected by safety switches, and the weld areas must be safe guarded so that the power is immediately removed from the robot when a door is opened.. Emergency stop buttons should be placed on all operator panels, robot cabinets and robot programming panels. Barriers must be designed to completely surround the robot and eliminate the possibility of people climbing over or under to get inside the barrier. Signal lights must be arranged on the robot or in the robot area to indicate that the robot is powered. 

 

4. ADVANTAGES IN USING WELDING ROBOT 

      At present relatively few figures are available on the economics of robot Welding machines, but it has been found that numbers of components produced by A robot are 2.5 to 3.5 times greater than that produced manually over the same Span of the time. It can be said that for an output of more than 100 parts/month which takes two or three shift per day there is an increase in number of parts output without difference in quality, which is not necessarily so with manual shift   work.

      Use of robot welding increases the flexibility. Because it is easy to change the robot work from to another just by changing the program. When the same time of work is already done, the same programme can be fed and the time and cost of programming can be eliminated completely.

      Day by day the cost of welding consumable are increasing. Using robots by Slightly changing the edge preparations from normal gap to narrow gap welding lot of consumable can be served with improved weld quality (decrease in grain size, distortion). In addition to increase the productivity it maintains the desired quality throughout the reducing the rework scrap.

      It reduces welder fatigue and welder exposure to the more hazardous atmosphere.

                                       

                                 

                                       CONCLUSION

      At present relatively few figures are available on the economics of robot Welding machines, but it has been found that numbers of components produced by A robot are 2.5 to 3.5 times greater than that produced manually over the same Span of the time. It can be said that for an output of more than 100 parts/month which takes two or three shift per day there is an increase in number of parts output without difference in quality, which is not necessarily so with manual shift   work.

 

REFERENCES

1.      www.ukros.com/robot_welding

2.      www.weldingengineer.com

3.      www.autotech-robotics.com

4.      www.robot-automation.com

5.      www.robot-welding.com