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Automation in Manufacturing Systems
Flexible Manufacturing Systems
Beginning with the definition of a flexible manufacturing system, there are three types of productions being used in the industry; low production, medium production, and high volume production. In medium production, there is a variety of components need to be manufactured and the volume of the production is in medium range. To cater the needs of such mid volume production, the flexible manufacturing systems are widely used in the industry. The flexible manufacturing system is a production method that is designed to easily adapt to the changes in the type and quantity of the product being manufactured. As mentioned, this is the best suited manufacturing methodology for mid variety, mid volume production, such that that it can easily adapt the changes in the type and the quantity, in the variety and in the quantity of the product that to be manufactured. It is best suited for batch production, which is having mid variety and medium volume. In general, a flexible manufacturing system has many equipment which are arranged in logical order, that will be seen in the next slides. The equipment or the machines and the computerized systems which are part of the FMS are configured, they are arranged in a logical fashion so that a variety of parts can be manufactured to handle the changing levels of the production, to check to handle the changing levels of production, to handle various part families. Part family is nothing, but a group of products which are having either geometric similarity or manufacturing similarity. Let us move ahead and look at what are various elements or what are various types of equipment which are the part of the FMS system. The first group of equipment or the first group of machines is the CNC machine. CNC is nothing but Computer Numerical Control machines. This CNC technology is applied to various operations such as machining operation, turning operation, grinding operations, gear cutting operations and variety of other machine tools which are computer numerical controlled. So, these are called as the CNC machines. CNC machines can be called as the backbone of the flexible manufacturing systems. Next group of equipment which are widely used, which are important in FMS are material handling systems. Material handling does the material handling of the component or the tools or even convey the raw materials. The tools maybe the dies and moulds and also, the maintenance material. All these are come in the material handling system. To carry out automatic material handling, various types of equipment are used. These are rail guided vehicles, automatic guided vehicle, and robots. RGVs, AGVs, and industrial robots are used to handle the material. Material handling also include the feeding of the component to the machine and then removal of the component from the machine or in other words, loading and unloading of the machine also come comes into the material handling systems. Basically robots are used for feeding the work parts to the machines, loading the work parts to the machines, and unloading the work parts from the machines. Third group of FMS equipment is the auxiliary equipment. Auxiliary equipment include pallet stores load and unloading stations, tool storage or tool stores, presetting of the tools, presetting involves taking care of the cutting tools. Tool presetting takes a considerable time in manufacturing operation. If this operation can be done offline, a lot of lead time in the manufacturing can be saved. That is why, dedicated tool presetting stations are designed in FMS, where the tools are being set and get ready, such that, they can directly be utilized for actual manufacturing operation. In washing stations, the work parts which are processed have to be cleaned. We need to have a washing stations and then measuring equipment. To check the size shape, to check the surface quality of the process part, a dedicated station is needed, where all the measuring equipment are arranged and the work parts will be examined. There they will be inspected whether the quality of the product is as per the desired specifications are not. The last and the most important component of the FMS is its brain, that is the central computer. So, central computer is controlling the operations of the CNC machines, material handling systems, and auxiliary equipment. The computer has various software installed. These are simulation software and DNC software. DNC is direct numeric control. In this philosophy, a single computer is controlling the operations of a variety of machine tools and as such, they are called as direct numerical control. Now, let us see how a typical flexible manufacturing system works. For that purpose, on the figure, a typical arrangement is shown, where the various elements of the flexible manufacturing systems are shown. These are CNC machines. Here in the figure, a CNC milling center, a turning center can be observed. This is also CNC operated; CNC turning center, CNC milling center, then the stores. But these stores or the storage system is automated. The components are stored in an automatic mode and it has the automatic retrieval as well. The system is widely known in the industry as ASRS, i.e. automated storage and retrieval system. The conveying arrangement can also be seen. In these FMS automated guided vehicles are used. The entire operations or the coordination among all this equipment will be done by a computer that is the central computer. The shown configuration is a typical one used for the education purpose only. In industry little more complicated or little more different configurations are used and the configurations vary from the industry to the industry. They are customized configurations and are designed as per the need of that part family, as per the requirement of the company or as per the investment capability of the company. A video was shown in the lecture which gave a glimpse how exactly the typical flexible manufacturing system works. Afterwards we will be shown, one by one what are the various equipment used. In the figure, an automated storage and retrieval system and a crane stacker can be observed. The retrieval system is having a crane stacker. Now, this stacker goes inside, it takes the components that to be machined in the flexible manufacturing system. The components are then taken and these components will be fed to the conveyor, which will take the components and load the automated guided vehicle. The figure shows an automated guided vehicle. This automated guided vehicle is moves and reaches to its destination, the components are then taken through the conveyor on automated feeding system. The first operation will be carried out on the CNC turning center. The automatic feeding system has taken the component that is to be turned on the CNC turning center. The component has been taken and will be feed to the machine. The machine has a three jaw automatic chuck (chuck is holding the component). It is a pneumatic operated chuck, the feeder will leave the jaw and immediately the chuck will hold the jaw. The component is now held in the chuck. The machine door will be automatically closed. The central computer will now give the instruction to the CNC machine tool to carry out the desired manufacturing operation. The turning operation means, there is reduction in the size, reduction in the diameter of the axisymmetric parts. After machining of the work parts or after processing of the work parts, the same feeding mechanism will approach the work part, the chuck will open and immediately the feeder will hold the work part and will safely unload the work part from the CNC turning center. The conveyor then moves and comes to the pallet, it will get loaded on the top portion of the AGV.
Assessment Question #1 Match the following acronyms with their appropriate descriptions. Choose the correct answer from the drop-down list.
FMS: It is a production method designed to adapt to the changes in the volume or batch production.
CNC: It is the automated control of machine tools.
DNC: It is a process set in a manufacturing unit where the machines are controlled by a programmed computer by a direct link.
ASRS: It consists of computer-controlled systems for automatically placing and retrieving loads from storage units.
CNC Machining Center
In order to understand the CNC machining center, we have taken here the example of CNC milling operation. Milling operation is a material removal operation, in which a hard tool is used. The hardness of the tool is much more than the work piece and we are having a relative motion of the hard tool, high strength tool material with the work piece. When there is a relative motion,there is a sheer plastic deformation of the softer material which is the work piece. In this case we can seethe hard tool is rotating about the z axis and the work part is moving along x and y axis. We can also see schematically that the tool is rotating and when the work piece is fed along the z direction, then we achieve deeper cavities or deeper features. The feature depth is controlled by giving the feed along the z direction in multiple number of passes. To have broader features that are be machined we have to give the feed along x and y direction. If the material is given feed along x and y directions, then we can generate the features on the surface which is called surface milling. When we want to mill pocket by cutting along the z direction, it is called as pocket milling. Milling tools may have two flutes or two cutting edges or it may have four flutes or four cutting edges. There are many tools which have a flat end and are called as flat end mill. When the tool end is of ball shape, it is called as ball end mill. Variety of such tools are used to generate various complicated surface using the milling operation. However, the conventional milling machine is having a drawback that very high level of surface finish, freeform surfaces cannot be manufactured, and it is very difficult to achieve the accuracy or the resolution in microns. The reason is obvious that there is human intervention and it is difficult for a human being to control the feed that is to be given to the work piece. A typical conventional milling machine is shown. It has a work table. On this work table, the workpiece is mounted and there is a spindle. On the spindle, the cutting tool is held, on work table there is a clamping vice., The workpiece is clamped or fixed in the clamping vice. . The work movement is manual and this manual work movement is carried out by the control wheels and the handlers. The spindle is rotated by a DC motor and various speed levels can be obtained by using a gearbox. We set a spindle speed and then we can have the relative motion of the tool with the work part by rotating the handlers. It is very difficult for the human being to have a proper feeding of the workpiece by rotating the wheels in a consistent manner. For this purpose, the CNC based machine tools are developed by using the various building blocks that we have seen in our previous class. The CNC machine tool is solving or overcoming the limitations of a typical milling machine. How? The work table movement is automatic. Thus, a machine tool is developed with automatic movement of the work table. For this purpose, we are using the precise lead screw arrangement and these precise lead screws are being driven by the servo motors in conventional milling machine and the tool changing is manual. This takes a lot of time. In CNC machine tools; the tool changing is automatic which is saving lot of lead time. The tool is moving along the z axis automatically. The safety operations are also there; door on and off, then auxiliary operations like coolant on and off. All these operations are carried out in an automatic mode. The CNC machine tool has a controller or the brain as the microprocessor which is nothing, but the system which is having logic gates, memory elements, battery and some memory storages and these microprocessors are working as per the instructions given by the programmer. The software is installed in the microprocessor according to the instructions written in the software, the microprocessor carries out various functions. Processor basically generates the pulses that are needed to actuate the drive mechanisms. In CNC machine tools basically we are using electrical drives, electrical motors to generate the pulses, and the microprocessors are producing the signals to drive these electrical motors. In addition to this the microprocessors generate the signals to make the compressor on and off, to control the directions of various control walls, and also to control the door opening and closing. all these operations are taken care by in the microprocessor. Thus, in this way we can improve the surface quality, enhance the capability of a typical conventional milling machine to generate very complicated shapes. A turbine blade is shown as an example. The shape of the turbine blade is complicated. All the blades are thin, they are intact with its core and are precise as per as their thickness is concerned.
Assessment Question #2 Which of the following images is an example of a CNC (Computer Numerical Control) machine?. Click on the correct area of the image (a blue circle with a cross will appear).
Correct Answer: the second image from the left
CNC Machine Tools
To machine these complex surfaces, we need Computer Numerical Control technology. The CNC technology or the term CNC has 3 letters C and N C. What is the meaning of N C? N C is Numerical Control. In this numerical control, coded instructions are used. These coded instructions have various numbers, letters, alphabets and symbols. These instructions will be passed to or they will be fed to the machine control unit. Machine control unit is a part of CNC machine tool. Machine control unit reads these instructions, follows them and generates electrical pulses. These electrical pulses are running the motors of the CNC machine tool. Motors are the basic drives of the CNC machine tool. The accurate passage of electrical pulses are done by the machine control unit. Moreover, the machine control unit is getting the feedback from various sensors and based on that sensor feedback it may take the decision to adjust or change or to vary the number of pulses that are to be generated and given to the motors. This is called the control. The operation of the drives and control of the drives will be done by the machine control unit. As the motors are running, we are getting the required operation. In CNC milling machine operation the machining would be carried out. What exactly these coded instructions are carrying the information? These instructions are having the information related to the distances. These coded instructions have the distances, information related to the position, information related to the activation of various functions to carry out various auxiliary operations such as coolant on coolant off, safety door on safety door off, changing of the tool. All these functions will be carried out and these instructions are provided in the coded form. All the symbols, letters and numbers together are written in a standardized way, which is called the G and M code; the preparation and the miscellaneous code. We will be studying about this in the later classes when we will study the CNC technology in detail. Numerical control was started in early 50s in USA. The instructions were written in the form of magnetic strips and punch cards. To write a simple program, very long length punch cards were used. In order to change or edit the program, we have to discard the entire punch card. This is a very cumbersome and lengthy process to develop and write a program on the punch card. With the use of computers, this problem of editing has now been solved. The computers are helping us to have graphical user interface and now we can write the program in an offline mode. We can write the program on computers, change the program easily on computer console screen and can easily edit the program. Machine and online programming has now become possible with the computers. In addition to the online editing of the program and online simulation of the program, we can now incorporate automatic tool change operations, automatic pilot changing operation. The machine can communicate with other machines and the central computer through network communications. Thus, the communications may be done in a wired mode or the wireless mode. This is a very interesting feature of the CNC machine tools, the machines can now run unattended. We will be looking at various tool changing, pallet changing aspects of the CNC machine tools in the coming slides. I In a typical conventional machine tool; very limited number of cutting tools can be mounted, which have to be changed manually. This is a time consuming task. In CNC machine tool operations, we use Automatic Tool Changing facility or ATCs. In addition to that we should hold multiple number of cutting tool. If we take the example of a CNC drilling machine, the operation is very special that the machine tool should manufacture variety of types of; the machine tool should carry out variety of the drilling operations from small to larger size of holes that are to be drilled. For this purpose we may need to have large number of drill bits. We may also need to have the large number of the semi-finishing tools, which are called reamers and finishing tools in a drilling operation. For this purpose various types of arrangements are available in CNC machine tool industry. The umbrella type storage device is a circular magazine and these circular magazines can hold up to 30 number of the tools. But, if wewant to store say from 80 to 120 number of tools, then we use chain type of arrangement. These ATC facilities have the storage devices as well as mechanisms which are required to remove the tool from the spindle of the machine, which is called unloading of the tool and then loading of the tool to the machine. The removed tool will be taken to the magazine, which and stored at an empty slot. The designated or the desired tool will be taken from the magazine and that will sit at the spindle of the machine tool. This is the automatic tool changing operation. This saves lot of time and enhances the production. Production rate enhancement is the ultimate aim to provide the tool magazines. The next type of arrangement that is required in CNC machine tool is the pallets. Pallets are used to stack, store, protect and transport the work part.We need to stack the work parts, stack the finished products, store the work parts and the stored work parts will be fed to the machine whenever and wherever it is required. On the pallet, various work parts are mounted and the machine will carry out the processing operation like machining or drilling or welding. This processing will be carried out on the work part or it may be the washing operation as well. Once the operations are done, then the pallets will be removed manually or by using robots. During the processing time, the other operator can ready the next pallet. Thus, the pallet number 2 will become ready. The work parts are ready which are to be fed to the machine tool for the next set of operations. This again saves the production timeand reduces the lead time in the manufacturing. Designing of the pallet or changing of the pallet, then changing of the pallet transport system or pallet changing system, all varies from machine tool to machine tool. Some of the advanced concepts are coming in the CNC machine tools. These are adaptive controland its usage in the CNC operation. What is the meaning of the adaptive control? In adaptive control, the tool, machine, work piece are protected from the damages caused by the malfunctioning of the machine. we have to protect tools, machine components and work piece from malfunctioning or unexpected changes in the machine behavior. Machine may behave in an unexpected way due to the failure of the tool. If we take the example of the CNC milling operation, there is a huge amount of friction that is occurring between the tool and the work piece. A lot of heat is generated at their contact point and their interface due to which there is wearing and tearing of the tool as well. The tool edge gets blunt which further increases the friction and reduces the sharpness of the tool. We may not get even proper surface finish. At certain point, the tool may fail, and the edges may break down. The broken edges will harm the machine tool. Therefore, the tool condition needs to be continuously monitored. As we get the in situ information or in process information about the health of the tool, we can in a better way control the process. If the tool is getting worn out, the machine tool should give the alarm or the signal to the operator or automatically it should take the decision to change the tool; or it may even adjust the process parameters like speed or feed need to be reduced or adjusted by the machine tool. This concept is called as the adaptive control in which the machine control unit has the capability to get the information from various sensors which are mounted on the machine tool for the monitoring purpose. Based upon the sensory input, the machine control unit will take the decisions to change the process parameters or to change the tool. Tool wear is a critical factor, which affects the productivity of a machining operation. Thus, it is very essential to take care of the automatic tool changing to have an automated machining system, which is the feature of unmanned factories. The unmanned factories required uninterrupted machining operations, which are helpful to achieve the desired production goals and to get better customer satisfaction. We have already seen that this unexpected failure are damaging to the machine tool and the work pieces. What are the ways or what are the methods to monitor the cutting tool failures or to monitor the cutting tool health? Basically there are two methods; first is the offline monitoring system. In offline monitoring system, the cutting tools are taken out from the spindle and then these cutting tools are observed under the tool microscope. Special purpose microscopes are available. These microscopes are used to measure various angles of the cutting tool. Based upon the angles of the cutting edge and the surface of the cutting tool, the operator takes the decision, whether the tool is to be replaced or the cutting edges are to be re-sharpen. Thus, this is the manual mode of the tool monitoring system. This system is time consuming and naturally it is enhancing the lead time. But, the advantage of offline monitoring system is that the human operator can closely monitor the cutting edges and by his or her experience or knowledge he can take the appropriate decision. However, as far as the adaptive control systems are concerned, nowadays people are going for the online monitoring system, that is the second mode. There are various methodologies being used in the online monitoring system.Various options are available in this system. We can go for acoustics or the measurement of forces or based upon the images. Acoustics is nothing but, the sounds are recorded during the cutting operation. If the sound of the cutting operation is normal, it is standard and the cutting edges are intact and fine. If unusual sound is occurring, then we can say that there is some problem. It may be either with the tool or with the work piece. Accordingly, the operator will take the decision or the machine control unit itself will take the decision. The second way is by monitoring the cutting forces. When the tool edge is not proper or blunt; then the required cutting forces are more.
Assessment Question #3 Which of the following ARE considered as CNC machine tools? Choose three answers.
Correct answer: Tool magazines, Automated palletizing, and Tool wear monitoring system
Automated Manufacturing Equipment
Now, as far as automation in manufacturing is concerned, the next type of equipment which is very common and important is the automated storage and retrieval system, which consist of a rack and a stacker crane.And, that rack and stacker crane are being handled automatically by the central computer unit. Thus, this system is basically used to store the raw material, tools, semi-finished products and finished product. When the quantity or volume of raw materials, tools, semi-finished and finished product is very high then, manual handling of all these material or commodities is very difficult. For this purpose we are taking help of the stacker crane and a storage device. A typical automated storage and retrieval systems is shown. Here we can see these are all the racks. The racks has many compartments, the compartments are coded; numbers are given to the compartments. Then, there is a stacker crane. There is a conveyor and that conveyor is taking the commodities to the stacker crane feeding unit. In the next figure, wecan see there is a conveyor over which the commodities are moving. The stacker crane is taking the commodities and then it will store the commodities in the programmed compartment or programmed section of the rack. Thus, automated storage and retrieval systems are helping us for the efficient space utilization. They provide us with the optimized flow of the commodities inside the system. The vertical space inside the factory can be utilized by using the automated storage and retrieval system. The next type of automated equipment that is used in industrial automation is industrial conveyor. These are mechanical handling equipment and with the help of mechatronics we are automating their operations. We need to convey variety of commodities; the raw material, semi-finished goods products, finished goods products, tools, the auxiliary equipment or material required in the manufacturing. A typical conveying system that is a ruler based conveying system is shown. On the conveyor we can see the baskets and the goods are mounted over the baskets. As the baskets are moving over the roller conveyor, the goods are being taken to their respective destinations. The automated or industrial conveyors help in quick and efficient material handling. They are also widely used in packaging industry. Various types of conveyors are used in the industry. First type is belt, where the commodities are being conveyed by using belt conveyors. Then bucket conveyors, buckets are used; basically, bucket conveyors are used in coal or in food industries. Then roller conveyors; roller conveyors are suitable when the commodities are packed in boxes, and are having a flat bottom. Thus, they can roll over the conveyor. Roller conveyors are either gravity operated or they are powered. Electric power is used to drive them. The next type is chain conveyor, then skate wheeled conveyor, screw conveyor, spiral conveyor, vibratory conveyors. Vibrating or vibratory conveyors are used for sorting operation. We are conveying and simultaneously sorting the commodities. A overhead conveyor is shown and this overhead conveyor is used to convey the car body. The car body is mounted on a carrier which moves by a mono rail mounted on the shop floor. In this way we can save the floor space and have the easy movement of the heavy bodies which are hanging inside the shop floor. Thus, the floor space can be utilized for other operations. The next type is the belt type of conveyor with sufficient frictional coefficient to carry or to convey the food products. The belts should be of food grade quality which should not contaminate the food products. Potatoes which are to be moved on the belt conveyor are shown, which may be utilized for its processing further. In this case screws are used. Stainless steel screws are used. Stainless steel is a good quality food processing material and here we can see the grapes which are to be conveyed and further crushed to produce the wine. The grapes that are to be moved are shown in a stainless steel screw conveyor. A very important automation equipment is the industrial robot. A industrial robot as far as ISO 8373:2012, is defined as an automatically controlled, reprogrammable, multipurpose manipulator. It is a mechanical equipment controlled by electronics. It is a mechatronics based equipment, which is reprogrammable, for a variety of operation. It is multipurpose and there are many applications of robots. We will see some of the applications relevant to manufacturing. It is easy to controland can be controlled using sensors and a feedback system. These kind of robots have multiple axes, generally 3 or more axes, and they are very useful and widely used equipment in the industry. Various applications of industrial robots are in welding, welding of the structures mainly in automobile industry, painting of the products, ironing,which is a very useful application in textile industry, assembly which is a very useful application in all manufacturing processes. Pick and placeis a material handling operation, which is used to feed the products inside the manufacturing facility. Palletizing to prepare the pallets and those pallets may be used for the storage purpose to create unit loads on the pallets. Inspection is done in Coordinate Measuring Machines (CMM). Variety of testing can be done on the wear parts using the industrial robots. Why the robots are widely used? Why they are popular? They do have high endurance. So, what is the meaning of endurance? The robots can carry out difficult task without giving away.
Assessment Question #4 Which of the following IS a piece of equipment used in industrial automation? Choose one answer.
Correct answer: Industrial roller conveyor