Auckland, New Zealand
Introduction
Steel welded pipes are hollow metal made from either rolled steel plate or forming a hot billet. Manufacturing and processes are diverse depending on every thickness, applications, sizes, and materials. Piping systems are normally found in chemical plants, refineries, gas plant, and petrochemical plants which transport fluid from one process to another. Severe conditions in the plant such as vibrations, sludge flow, toxicity of fluid, fluctuated pressure, corrosion, and erosion are some major considerations in designing and choosing the right pipes. There are several methods in producing metal pipes namely Furnace Weld (commonly known as Continuous Weld), Electric Resistance Weld (ERW), Submerged Arc Weld (SAW), Gas Metal Arc Welding (GMAW) and seamless (SMLS) method [1]. In this simulation, the programmer used Gas Arc Welding method. It starts with the welding process to post-annealing and post-weld heat treatment method.
Project background
Single-pass welded pipe is used in low-pressure pipelines which are commonly seen in closed-loop sewers, gravity-fed water line, rainwater drain lines, etc. Pipes account for a considerable amount in the total plant cost, typically one-third of the whole expenditures. Piping systems are the connecting lines in the industries and the presence of the piping systems are vital in manufacturing and Oil & Gas plants. [2]
Figure 1 shows the enormity of piping in Oil & Gas plant. With that, the demand for a higher production requires cost-efficient, process reliability and repeat accuracy. These parameters can be greatly achieved with robotics and automation at hand.
Figure 1
With this project, we can achieve total automation in the welding process, annealing, and post-weld heat-treatment process. Low-pressure piping can withstand 100 KN of inside pressure and weld can be tested through some non-destructive test and the strength can vary depending on the number of the pass, filler used and the quality of the process. Welding by the use of robots is more accurate and efficient. Annealing, in material science, is a type of heat treatment process that modifies the physical and most of the time, the chemical properties of a material to augment or increase its ductility and reduce its hardness. It involves the heating the pipe above its recrystallization temperature, then maintaining a appropriate temperature, and then cooling. The process involves heating the welded pipe to 30 to 50 Degree Centigrade above the critical temperature of the welded pipe and then maintaining the temperature for a specific period of time, then allowing the welded pipe to slowly cool down inside the machine itself without any forced means of cooling [3]. In the simulation, the programmer only shows a definite time to show it undergo annealing and transfer the welded pipe to the gantry system. Post Weld Heat Treatment process is heating a weldment at a controlled rate to temperature range specified. By heating the weld zone, the yield strength of the weld zone is lowered and the realization of the residual stresses occurs by plastic flow combined with a small but real creep effect. The purpose of this is tempering the longitudinal weld of pipe and heat affected zone which improves ductility, toughness, and hardness. The simulation only shows the transfer of a welded pipe by the use of single-axis gantry to the PWHT process.
Problem Statement
People have been working together with a machine over the years, from operating simple house appliances to driving a vehicle. We collaborate with machines to provide us convenience in work like repetitive activities or sometimes in hazardous work but in early years, human failed to work with the machine because of issues of safety. Moreover, automation and robotics aren’t cheap or easy to initialize or start-up, it requires a skilled programmer to make a robot works. But over the years, with the help of technological advancement, this problem was eventually solved and people can work together with machines without any cage separated them. Industries and manufacturing companies shift quickly to automation for fast speed work, higher accuracy, and high volume production line. Humans are increasing so fast and also the demands for every human need are also proportionally increasing. So automation and robotics had evolved to collaborate with humans and adjust to the cognition of a worker. When it comes to pipe welding, a welder exactly knows what makes a good weld and has the muscle memory to make a welding pass on the perfect path. This ability can take a lot of experience to develop and this contributes to a factor of a skilled welder shortage. On the other hand, robots can work consistent physical activities much better than humans, can perform better and creates fewer errors. Robots can now make the same output of weld like an experienced welder can do with more efficient and productivity. [4]
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This project provides an alternative way of manufacturing of longitudinal welded pipes. Every company has its techniques and specific welding machine used. The programmer used a stationed welding robot while the rolled metal sheet is moving along with the roller. Work transfer used in this project is automatic belt conveyor and pneumatic pushers to move the welded pipes to the annealing process. A single axis gantry was used for transferring the annealed pipe to further heat treatment procedure and testing.
Project Objectives
To develop an automated process of rolled steel plate utilizing a robotic welding machine, single axis gantry, pneumatic actuators, and different types of sensors commonly used in Industry.
To create a complete system from welding process, annealing process and PWHT using transports like rollers and conveyors.
To apply the knowledge gained from easyPLC ladder programming and simulations.
Methodology
Plc, Working and Application
PLC is the major components in the industrial system. They replace electromagnetic relays. The languages still use symbology from the evolution of the relays to using the computer to control manufacturing systems. Using a computer then uploading it to a machine to run using relays as logic is challenging and will consume a lot of time. This is a transition from relays to using bits in memory. PLC is a specialized computer because it has no printer, display, keyboard or hard drive and it cannot be easily noticed since there is no need to operate them. They are installed in a control panel on a factory floor. Relay is also used in PLC but in a digital sense and relay required more downtime to keep it running than newer PLC base control. Moreover, relay generates a lot of electricity, making a lot of heat and soot’s and most especially taking up a lot of space in a working space.
An installed PLC is consists of CPU module and Input and Output devices referred to as Input and Output. Mostly the Input and Output is part of the Central Processing Unit(CPU). The CPU communicates with the Input and Output so in most cases they share a storage room that physically holds them together and connects them electronically. In other equipment, the Input and Output modules can be far away from the CPU and just connected with cables communicating the data so that the PLC is not limited to a building. Since a PLC is a computer there is no need to limit it to digital inputs and outputs. Over the years the manufacturer includes the analogs numerical inputs and outputs. To make these devices useful they included capability of calculation and programming. Most PLC is programmed using an application running in a standard desktop or laptop PLC. They communicate with the PLC using the Ethernet or a proprietary communication bus depending on the manufacturer. Unfortunately, the PLC manufacturers have failed to agree on how we control logic. Most of the manufacturers claim different forms of programmable logic ladder, the specifics of it are different depending for each manufacturer. This includes the different ways of doing the same things, and also one can found differences in the arrangement in which the processes in the CPU can do the various pieces of logic. One attempt to bring some order into this kind of chaos is the IEC 61131-3:2013 standard from the American National Standard Institute (ANSI). The excerpt from the webpage, define some programming languages with different strength and weaknesses.[5]
Robots (Welding robot and Gantry)
Robot welding is a programmable tool which is mechanized to perform weld. Robot welding is commonly used in relatively high production applications such as automotive or steel manufacturing processes. Growth of this technology was primarily limited because of some myths like only high quantity production can have a robotic technology, the robotic operator should be rocket scientist, skilled and well-compensated employee, Robots cannot be used a very large assembly, etc. But in reality programming, a robot is simple and can be easily trained to every employee. No robot can solve 100% of welding quality. If a certain assembly is not designed properly or the joints are not prepared correctly, problems with quality will certainly appear. [6] Hundreds of benefits of robotic welding have proven for many manufacturers because of repeatable ability, exponential accuracy and throughput. On the other hand, most gantry system is operated manually through hoist. But in this simulation, the gantry arm is operated by PLC programming inputs.
Project Design
The project is basically run by Nirtec PLC programming software in which the programmer can use a personal computer or laptop to conduct the automation and interactive 3D simulations. The programmer can use Ladder, script, logic, or grafcet to create a program for automation. In this project, the ladder program was mainly used with a few basic commands from a script to give commands to the gantry. The machine simulator which is a 3D tool that the programmer utilizes lets you use real physical components to make the idea possible. The work part creator was used to show the production of a rolled steel plate was done beforehand. The items will be transferred by a roller which is automated and controlled on and off by a start button. All the rolled steel plate will undergo a welding process by the welder robot. An inductive sensor is installed right beside the welder robot to detect the un-welded pipe to start the seaming process. It will take a certain time to finish the welding to accomplish the single pass. Then the welded pipe will be transported again to a small conveyor which can be started by a photocell sensor. When the welded pipe reaches the small conveyor, a two pneumatic actuator will push the welded pipe to the quenching bath for heat-treatment process. Finally, the gantry robot will pick the welded pipes one by one for a couple of minutes to transfer them to a pallet for hydro-testing and inspection. The Nirtec easyPLC is designed to work in a laptop by a USB type license and install the program (EasyPLC Editor, HMI system, Virtual PLC CPU and Machine Simulator)so a student or a programmer can work anytime and anywhere.[7]
Selection System Parameters
The initial point to determine a solution for automation is to understand what is to be achieved. Before one can design a program, a task should break down into a simple number of a task or in understandable elements into which it can be easily depicted. The next step is to know exactly what are the input and output devices available. A specific device has a specific function or operation. Like for example, a simple conveyor it requires input such as push-button or a sensor before it can give output or movement. Since we are using a licensed PLC, communication or sharing of application data to a simulator becomes feasible. The programmer just needs to learn the method of connecting the PLC program to the machine simulator. Through that, uploading to the simulator is very convenient even you are modifying your program in the ladder.
Flow Chart
Figure 2 shows represent the complete manufacturing process of a welded pipe. Inside the red dash dotted line shows the process included in the simulation. The purple dash dotted shows the upstream process while inside the green dash dotted line shows the downstream process of the Gas Metal Arc Welding (GMAW) process.
Figure 2
Block Diagram
Figure 3 shows the PLC as the heart of the simulation into which input and output interact with. The common inputs in the simulation are the push buttons and sensors, and then program uploaded in the PLC will give an output to control processes like conveyors, welded and gantry robot, elevator, and pneumatic pusher. It is always consist of three main parts, the input, the CPU (which is the PLC) and the output.
Figure 3
Process Chart
Figure 4 shows the logic arrangement followed by the PLC ladder program. This is the step by step process followed to create the sequencing, input and outputs commands including analog, and order of the simulation.
Figure 4
Project Working Principles
PLC is the workhorse of the simulation process. The programmer uses the Ladder program to create the automation and the sequencing of the process from GMAW (Gas Metal Arc Welding), Annealing process and the Post Weld Heat Treatment process. The whole simulation begins by pressing the start button located at the control panel. The rollers and belt conveyor begins to operate as the work part creator starts to generate a rolled metal sheet. The photo-sensor will detect the presence of the rolled metal sheet and will trigger the welding robot to begin the longitudinal welding process. When the welder robot finished the single-pass welding it will automatically stop and wait for the next rolled metal sheet to come. Another sensor is waiting at the end of the roller to activate the simple conveyor for the annealing process. The pneumatic pusher will impel the pipe to an annealing machine after a few seconds. After a couple of seconds, the elevator will carry the annealed pipe in the upper position for the gantry system to pick. Finally, a single-axis gantry robot will carry the pipe overhead one at a time to transfer the welded pipe to the next roller for the further pipe manufacturing process. Pressing the stop button can end the whole simulation as it is programmed in the PLC. It can be used as an emergency button if something wrong happens in the whole system.
Results and Discussions
I/O System
Table 1
Process
Name
Address
I/O
Type
Gantry
Gantry_Sequence
–
–
Digital
Welding and Transfer
StartButton
I.0.12
Input
Digital
Welding and Transfer
StopButton
I.0.13
Input
Digital
Welding and Transfer
pusherBack
I.0.17
Input
Digital
Welding and Transfer
pusherForward
I.0.18
Input
Digital
Welding and Transfer
PhotoCell1
I.0.2
Input
Digital
Welding and Transfer
PhotoCell3
I.0.20
Input
Digital
Welding and Transfer
PhotoCell2
I.0.3
Input
Digital
Gantry
Gantry_AxisX_Moving
I.0.6
Input
Digital
Gantry
Gantry_AxisY_Moving
I.0.7
Input
Digital
Gantry
GripsPartDetected
I.0.8
Input
Digital
Welding and Transfer
BeltConveyorOn
O.0.0
Output
Digital
Welding and Transfer
PusherAdvance_Output
O.0.1
Output
Digital
Gantry
Axis_X_Dest_Pos
O.0.1
Output
Analog
Welding and Transfer
ElevatorUp
O.0.10
Output
Digital
Welding and Transfer
ElevatorDown
O.0.11
Output
Digital
Welding and Transfer
Roller1
O.0.2
Output
Digital
Gantry
Axis_Y_Dest_Pos
O.0.2
Output
Analog
Gantry
CloseGrips
O.0.3
Output
Digital
Welding and Transfer
WorkPartC
O.0.4
Output
Digital
Welding and Transfer
WelderRobot
O.0.5
Output
Digital
Gantry
Gantry_MoveAxis_X
O.0.7
Output
Digital
Gantry
Gantry_MoveAxis_Y
O.0.8
Output
Digital
Gantry
RotateGrips
O.0.9
Output
Digital
The table 1 show the variables that the programmer used in the simulation. Take note that Input and Output are not assigned in chronological order since a lot of trial and error is done and so some I/O assigned was remove. The programmer do not have the time to arrange the sequence order but the I/O address in the ladder program is matching in the I/O address used in the simulation.
Timers
Figure 5 depicts timers used in the simulation are for the annealing process and gantry movement. In the real annealing process it will take 4 to 8 hours to finish the process. But for this simulation process only, the programmer assigned 5 seconds only to move the elevator up for the next process. For gantry sequence, calling out of timers in input and output is essential. This timer allows the connecting process like the elevator to wait to the gantry arm to move out and pick up the work part. Also, the programmer used timer in every gantry sequence to wait a couple of seconds before doing another movement.
Figure 5
Add Coil
Figure 6 represent the output coil in the PLC programming. This makes the components move or do an action when activated.
Figure 6
Set Coil and Reset Coil
Figure 7 shows the coils are used in the pneumatic pusher, elevator and Gantry system. This is an output feature in the PLC to determine the first and last position. It should be called out in the I/O parameters of a component to make it working along with the PLC program.
Figure 7
Contact and Negate Contact
Figure 8 represent the contacts which are used as the inputs in the PLC program.
Figure 8
Analog Output
Figure 9 shows the analog output is used to give command to the gantry after a sequence is finished. This is the initial position of the gantry when the process is not called out.
Figure 9
Project Simulation
Conveyor and Work Transfer Ladder Diagram
Segment 1: Figure 10 shows the start and emergency stop arrangement. Pressing the start button can make roller and belt conveyor on and keep the elevator in down position.
Figure 10
Segment 2: Figure 11 shows the Roller starts to activate the work-part creator after segment 1. Now the rolled metal sheet will start to move in the roller.
Figure 11
Segment 3: Figure 12 shows the presence of the rolled metal sheet in the PhotoCell will trigger the welder robot to start welding longitudinally. Pressing of stop button in the 3D simulation will cut the operation as this is negated in the segment.
Figure 12
Segment 4: Figure 13 shows that if the welded pipe detected by the sensor, belt conveyor will stop to move to give time for the pneumatic pusher to move the work-part in the elevator.
Figure 13
Segment 5 & 6: Figure 14 shows the segments controls the pneumatic pusher. When the sensor detects the welded pipe then it will be activated. Timer for the elevator is called out in the output side of the pneumatic pusher string.
Figure 14
Segment 7 & 8: Figure 15 shows that the sensor will detect the work-part is now in the elevator then it will wait for 5 seconds before it moves up. Next thing, it will wait for 8 seconds to wait the gantry to pick up the work-part. After this process, the elevator will go back again to its original position.
Figure 15
Single Axis Gantry Ladder Diagram
Segment 1: Figure 16 shows that the elevator upper position with the welded pipe on top, will be the cue for the gantry to move and follow successively the 12 sequence created in this simulation.
Figure 16
Segment 2: Figure 17 shows the Gantry arm will move to the location of the welded pipe and rotate the grips. Then will follow the next sequence.
Figure 17
Segment 3: Figure 18 shows the gantry arm will move downward (Y-axis) and will position within 0.7 seconds.
Figure 18
Segment 4: Figure 19 shows that if the welded pipe and the gantry arm is in correct position, the grip will close.
Figure 19
Segment 5: Figure 20 shows the Gantry will wait for 1 second to initiate sequence 5.
Figure 20
Segment 6: Figure 21 shows that if the welded pipe is detected properly on the grip, the gantry arm will move up (Y-axis).
Figure 21
Segment 7: Figure 22 shows the grips will rotate and move the gantry arm to the other end of the X-axis.
Figure 22
Segment 8: Figure 23 shows the Gantry will wait for 0.7 seconds before initiating sequence 8.
Figure 23
Segment 9: Figure 24 shows the Gantry arm will move down (Y-axis) and output part Gantry sequence number 9 is called out.
Figure 24
Segment 10: Figure 25 shows the command is in reset coil for the timer 2 and Y-axis movement.
Figure 25
Segment 11: Figure 26 shows the Gantry will wait for 1 second before initiating sequence 11.
Figure 26
Segment 12: Figure 27 shows the Gantry arm will open grips while it is in reset coil to drop the welded pipe. Then it will move upward (Y-axis) to execute the last sequence.
Figure 27
Segment 13: Figure 28 shows the Gantry will wait for 0.7 seconds to start the process back to 1 if welded pipe is detected in the elevator’s upper position.
Figure 28
System Simulation Control Process
Figure 29 shows the initial conditions the programmer set for the analog Input and Output of the Gantry system. This can be set in the initial conditionsunder Init_Sequence_1 in the PLC ladder program.
Figure 29
Figure 30 shows the initial position of the Gantry arm and called out in the common area in the PLC under Main Program.
Figure 30
Model and Design
Figure 31 represents the first process of the simulation which is the welding section.
Figure 31
Figure 32 represents the annealing process and Figure 33 shoes the elevator which moves up to trigger the gantry system.
Figure 32
Figure 33
Figure 34 represents a pneumatic pusher which includes in the work part transfer in the whole system.
Figure 34
Figure 35 represents the Gantry robot which transfers the welded pipe to the post weld heat treatment.
Figure 35
Figure 36 represents the final product which is the welded pipes that are ready for shipping.
Figure 36
Figure 37 represents the whole simulation plant which is created in 3D simulation of Nirtec.
Figure 37
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