ABSTRACT An Automatic Tool Changer is equipment that reduces cycle times by automatically changing tools between cuts. Automatic tool changers are differentiated by tool-to-tool time and the number of tools they can hold. CNC machines are in general, more expensive than general purpose manoperated machine tools, special attention is given to the design of the NC machines and production tooling in order to reduce the time spent in both work and machine set up. Tooling systems for NC are designed to eliminate operator error and maximize productive machine hours. CNC tool changers allow a machine to perform more than one function without requiring an operator to change the tooling. A CNC tool changer can quickly change the end effectors without the requirement of multiple robots. Tool changers can be a manual tool changers or automatic tool changers. A CNC tool changer fulfills the requirement of multiple tooling for a wide variety of machine tools. A CNC machine tool raises the productivity by automatically translating designs into instructions for a computer controller on a machine tool. The spindle axis of a CNC machine tool fixes the chucks which is integral to the lathe’s functioning. A CNC tool storage system is an organized, efficient, and secure method of storing tools at all stages and time. The main component of a CNC tool storage system is a CNC tool holder. A CNC tool holder is suitable for vertically storing all types of preset tools.
1
Index 1. Automation and requirement of Automation
Automation in production system – Automated manufacturing Systems – Fixed Automation, Programmable Automation and Flexible Automation – Automation Principles and strategies – USA principle, Automation Migration Theory, Ten strategies for automation – Reasons for Automation 2. Toolings For Numerical Control
Toolings for Numerical Control – Alternatives for Automatic tool changing – semiautomatic tool changing – preset tooling
3. Automatic Tool Changer – An Idea
Automatic Tool Changer – What is automatic Tool Changer – Why Automatic Tool Changer is needed – Types of Automatic tool Changer – tool Change system with gripper Arm – Description of gripper arm - Tool Change system with Chain Magazine – Tool Change system with Disc Magazine 4. Project Details
Project Concept – Description of Parts – Construction of Parts – Degrees of Freedom – Details About main Parts – Rack and Pinion Mechanism For gripper Arm - Relay what is Relay and How it works – Relay Specifications – How an electric motor works – Specifications of Gear motors – Idea about circuit – Circuit Diagram and description of Circuit Diagram 5. NC Systems
Brief introduction about NC and CNC systems and NC controllers 6. Conclusion 7. References
2
Automation and Requirements of Automation AUTOMATION IN PRODUCTION SYSTEMS Some elements of the production systems are likely to be automated, where as the others will be operated manually or clerically. For our purposes here, automation can be defined as a technology concerned with the application of mechanical, electronic and computer based systems to operate and control production. In modern production systems, the two categories overlap to some extent, because the automated manufacturing systems operating on the factory floor are themselves often implemented by computer systems and connected to the computerized manufacturing support systems and management information system operating at the plant and enterprise levels. The term computer integrated manufacturing is used to indicate this extensive use of computers in production systems.
Manufacturing Support systems
Facilities: Factory Equipment
Potential computerization applications
Potential Automation applications
Opportunities of automation and computerization in production system
3
AUTOMATED MANUFACTURING SYSTEMS Automated manufacturing systems operate in the factory on the physical product.
They
perform
operations
such
as
processing,
assembly,
inspection, or material handling in some cases accomplishing more than one of these operations in the same system. They are called automated because they perform their operations with a reduced level of human participation compared with the corresponding manual process. In some highly automated systems, there is virtually no human participation. Examples of automated manufacturing systems includes:
Automated machine tools that process machine parts
Transfer lines that perform a series of machining operations
Automated assembly systems
Manufacturing systems that use industrial robots to perform processing or assembly operations
Automatic material handling and storage systems to integrate manufacturing operations
Automatic inspection system for quality control
Automated manufacturing systems can be classified into three basic types 1. Fixed automation 2. Programmable automation 3. Flexible automation All the three types of automation differ in certain specific ways as per their characteristics. They are discussed in detail below.
4
1. Fixed Automation Fixed automation is a system in which the sequence of processing operations is fixed by the equipment configuration. Each of the operations in the sequence is usually simple, involving perhaps a plain linear or rotational motion or an uncomplicated combination of the two; for example, the feeding of a rotating spindle. It is the integration and coordination of many such operations into one piece of equipment that makes the system complex. Typical features of fixed automation are: High initial investment for custom-engineered equipment High production rates Relatively inflexible in accommodation product variety The economic justification for fixed automation is found in products that are produced in very large quantities and at high production rates. The high initial cost of the equipment can be spread over a very large number of units, thus making unit cost attractive compared with alternative methods of production. Example of fixed automation includes machining transfer lines and automated assembly machines. 2. Programmable Automation In programmable automation, the production equipment is designed with the capability to change the sequence of operations to accommodate different product configurations. The operation sequence is controlled by a program which is a set of instructions coded so that they can be read and interpreted by the system. New programs can be prepared and entered in to the equipment to produce new products. Some of the features that characterize programmable automation include:
High investment in general purpose equipment
Lower production rates than fixed automation
Flexibility
to
deal
with
variations
and
changes
in
product
configuration 5
Most suitable for batch production
Programmable automated systems are used in low and medium volume production. The parts or products are typically made in batches. To produce each new batch of a different product, the system must be reprogrammed with the set of machine instructions that correspond to the new product. 3. Flexible Automation Flexible automation is an extension of programmable automation. A flexible automation system is capable of producing a variety of parts with virtually no time lost for changeovers from one part style to the next. There is no lost production time while reprogramming the system and altering the physical setup (tooling, fixture, machine settings). It is a case of soft variety, so that the amount of changeover required between styles is minimal. The features of flexible automation can be summarized as follows:
High investment for a custom engineered system
Continuous production of variable mixture of products
Medium production rates
Flexibility to deal with product design variations
Examples of flexible automation are the flexible manufacturing systems for performing machining operations that date back to the late 1960s.
6
AUTOMATION PRINCIPLES AND STRATEGIES There are mainly three approaches for dealing with automation projects 1. The USA principle 2. Ten strategies for automation 3. Automation migration strategy The USA principle The USA principle is a common sense approach to automation projects. Similar
procedures
have
been
suggested
in
manufacturing
and
automation trade literature, but none has a more captivating title than this one. USA stands for: Understand the existing process Simplify the process Automate the process A statement of the USA principle appeared in the APICS (American Production and Inventory Control Society) article. The article was concerned with implementation of enterprise resource planning but the USA approach is so general that it is applicable to nearly any automation project. 1.
Understand the existing process
The obvious purpose of the first step in the USA approach is to comprehend the current process in all of its details. What are the inputs? What are the outputs? What exactly happens to the work unit between input and output? What is the function of the process? How does it add value to the product? What are the upstream and downstream operations in the production sequenced, and can they be combined with the process under consideration?
7
Mathematical models of the process may also be useful to indicate relationships between input parameters and output variables. What are the important output variables? How are these output variables affected by inputs to the process, such as raw material properties, process settings, operating parameters, and environmental conditions? This information may be valuable in identifying what output variables need to be measured for feedback purposes and in formulating algorithms for automatic process control. 2. Simplify the process
Once the existing process is understood, then the search can begin for ways to simplify. This often involves a checklist of questions about the existing process. What is the purpose of this step or this transport? Is this step necessary? Can this step be eliminated? Is the most appropriate technology being used in this step? How can this step be simplified? Are there necessary steps in the process that might be eliminated without detracting from function? Some of the ten strategies of automation and production systems are applicable to try to simplify the process. Can steps be integrated into a manually operated production line? 3. Automate the process
Once the process has been reduced to its simplest form, then automation can be considered. The possible forms of automation include those listed in ten strategies discussed in the following section. An automation migration strategy might be implemented for a new product that has not yet proven itself. Ten strategies for automation Following the USA principle is a good first step in any automation project. As suggested previously, it may turn out that automation of the process is unnecessary or cannot be cost justified after it has been simplified.
8
If automation seems a feasible solution to improve productivity, quality or other measure of performance, then the following strategies provide a road map to search for these improvements. These strategies are as relevant and appropriate today as they did in 80s. They are referred as strategies for automation because some of them are applicable whether the process is a candidate for automation or just for simplification. 1. Specialization of operation
The first strategy involves the use of special purpose equipment designed to perform one operation with the greatest possible efficiency. This is analogous to the concept of labor specialization, which is employed to improve the labor productivity. 2. Combined operations
Production occurs as a sequence of operations. Complex parts may require dozens, or even hundreds of processing steps. The strategy of combined operation involves reducing the number of distinct production machines or work stations through which the part must be routed. This is accomplished by performing more than one operation at a given machine, thereby reducing the number of separate machines needed. Since each machine typically involves a setup, setup time can usually be saved as a consequence of this strategy. Material handling effort and non operation time are also reduced. Manufacturing lead time is reduced for better customer service. 3. Simultaneous operations
A
logical
extension
of
the
combined
operations
strategy
is
to
simultaneously perform the operations that are combined at one workstation. 4.
Integration of operations
Another strategy is to link several workstations together into a single integrated mechanism, using automated work handling devices to transfer parts between stations. 9
5.
Increased flexibility
This strategy attempts to achieve maximum utilization of equipment for job shop and medium volume situations by using the same equipment for a variety of parts or products. It involves the use of the flexible automation concepts. 6.
Improved material handling and storage
A great opportunity for reducing nonproductive time exists in the use of automated material handling and storage systems. Typical benefits include reduced work in progress and shorter manufacturing lead times. 7.
Online inspection
Inspection for quality of work is traditionally performed after the process is completed. This means that any poor quality product has already been produced by the time it is inspected. Incorporating inspection into the manufacturing process permits corrections to the process as the product is being made. 8.
Process control and optimization
This includes a wide range of control schemes intended to operate the individual processes and associated equipment more efficiently. By this strategy, the individual process times can be reduced and product quality improved. 9. Plant operations control Whereas the previous strategy was concerned with the control of the individual manufacturing process, this strategy is concerned with control at the plant level. 10. Computer integrated manufacturing
Taking the previous strategy one level higher, we have the integration of factory operations with engineering design and the business functions of the firm. CIM involves extensive use of computer applications, computer data bases, and computer networking throughout the enterprise.
10
The ten strategies constitute a checklist of the possibilities for improving the production system through automation or simplification. They should not be considered as mutually exclusive. For most situations, multiple strategies can be implemented in one improvement project. Automation migration strategy
Owing to competitive marketplace, a company often needs to introduce a new product in the shortest possible time. As mentioned previously, the easiest and least expensive way to accomplish this objective is to design a manual production method, using a sequence of workstations operating independently. If the product turns out to be successful, and high future demand is anticipated, then it makes sense for the company to automate production. A typical automation migration strategy is the following: Phase 1: manual production using single station manned cells operating independently. This is used for introduction of the new product for reasons already mentioned: quick and low cost tooling to get started. Phase
2: Automated production using single station automated cells operating independently. As demand for the product grows, and it becomes clear that automation can be justified, then the single stations are automated to reduce labor and increase production rate.
Phase
3:
Automated
integrated
production
using
a
multistation
automated system with serial operations and automated transfer of work units between stations.
11
REASONS OF AUTOMATING Companies
undertake
projects
in
manufacturing
automation
and
computer integrated manufacturing for a variety of good reasons. Some of the reasons used to justify automation are the following: 1.
To increase labor productivity
Automating a manufacturing operation usually increases production rate and labor productivity. This means greater output per hour of labor input. 2. To reduce labor cost
Ever increasing labor cost has been and continuous to be the trend in the world’s industrialized societies. Consequently, higher investment in automation has become economically justifiable to replace manual operations. 3. To mitigate the effects of labor shortages
There is a general shortage of labor in many advanced nations, and this has stimulated the development of automated operations as a substitute for labor. 4. To reduce or eliminate routine manual and clerical tasks
An argument can be put forth that there is social value in automating operations that are routine, boring, fatiguing, and possibly irksome. 5. To improve worker safety
By automating a given operation, and transferring the worker from active participation in the process to a supervisory role, the work is made safer.
12
6. To improve product quality
Automation not only results in higher production rates than manual operations; it also performs the manufacturing process with greater uniformity and conformity to quality specifications. 7. To reduce manufacturing lead time
Automation helps to reduce the elapsed time between customer order and
product
delivery,
providing
a
competitive
advantage
to
the
manufacturer for future orders. 8. To accomplish processes that cannot be done manually Certain operations cannot be accomplished without the aid of a machine. These processes have requirements for precision, miniaturization, or complexity of geometry that cannot be achieved manually. 9. To avoid the high cost of not automating
There is a significant competitive advantage gained in automating a manufacturing plant. The advantage cannot easily be demonstrated on a company’s project authorization form. The benefits of automation often show up in unexpected and intangible ways, such as an improved quality, higher
sales,
better
labor
relations,
and
better
company
image.
Companies that do not automate are likely to find themselves at a competitive disadvantage with their customers, their employees and the general public.
13
Tooling for Numerical Control TOOLING FOR NUMERICAL CONTROL Since NC machines are in general, more expensive than general purpose man-operated machine tools, special attention is given to the design of the NC machines and production tooling in order to reduce the time spent in both work and machine set up. Tooling systems for NC are designed to eliminate operator error and maximize productive machine hours. They do this in one or more of the following ways: 1. Using quick change tool holders 2. Automatic tool selection 3. Automatic tool Changer 4. Presetting of tool 5. Facilitating tool selection and tool changing through the numerical control program While tooling for NC machines might appear to be specialized, the actual components and principles involved have much in common with what would be considered proper practice for conventional machine tools. 1. Tool Holders
Quick change tool holders are designed so that cutting tools can be readily positioned with respect to the spindle axis of the machine. This requires that tolerances on length and/or diameter be held on all tools used in the machine. Arbor type cutters such as face mills and shell end mills are held in arbor type tool holders. Shank type mills are held in positive lock holder. Drills, reamers and boring tools are held in a straight shank collet type holder. Taps are held in a tension and compression collet type holders. 14
2. Automatic tool selection
Automatic tool selectors in NC make all the tool changes required to complete a predetermined sequence of machining operations on a part. There are two basic approaches to automatic tool selection:
When relatively small number of different tools is required, automatic tool selector is the turret type. The turret is rotated under program control to bring the proper tool into position. The tools are held in preset tool holder adapters which are mounted into turret spindles.
An automatic tool changer and magazine of tools is frequently used in preference to the turret approach, when the number of tools to be used is large. Each tool is inserted in a common spindle as required. The tools which are mounted in uniform holders, are automatically picked up, placed into the spindle and locked in place. When the operations using that tool are completed it is returned to the tool storage magazine.
For changing tools rapidly it is better to place tool in magazine or turret in the order in which they will be used. 3. Automatic Tool Changer
For three axis machines which perform a wide variety of operations tool changes a programmed into the tape for fully automatic selection and replacement. The automatic tool change system may consist of following elements:
Rotary tool storage magazine for numerous tools.
Automatic tool changer to remove tool holders from the machine spindle and replace them with tape programmed tools.
15
Basic tool holders adaptable to a multiplicity of cutting tool types and work specifications.
Tool coding rings and system for selection of proper tools in accordance with tape signals.
In operation, the automatic tool change is accomplished in four steps:
By tape command (and from any location the magazine) the tool magazine rotates to proper position to bring the pre selected tool into place for particular operation. One end of the tool change your arm then grasps the tool while the opposite end grasps the tool to be replaced in the spindle.
The tool changer arm moves out away from the spindle removing one tool from the magazine and other tool from the spindle.
4. Preset Tooling
In machining relatively small batches of work very considerable savings can be made by reducing the machine down time during the period needed for the initial machine tool setup i.e. when preparing two machines a batch of different components. This reduction in setup time favourabaly influences the breakeven point towards the use of NC machine tool.
Since the cost per minute of maintaining an NC machine in production is much greater than the cost of a tool setter working on a bench with special tool setting equipment there arises the necessity for presetting the tools to be used by NC machines.
In other word the advantage of presetting tool in the tool room on precision
tool
presetting
machine
can
readily
be
seen
by
calculating the cost of operator mistakes and machine down time on jobs which require continuous machine cycling. The time and costs for any interruption for trial cuts or to adjust tooling would be prohibitive.
16
AUTOMATIC TOOL CHANGER AUTOMATIC TOOL CHANGER An Automatic Tool Changer is equipment that reduces cycle times by automatically changing tools between cuts. Automatic tool changers are differentiated by tool-to-tool time and the number of tools they can hold. CNC tool changers allow a machine to perform more than one function without requiring an operator to change the tooling. A CNC tool changer can quickly change the end effectors without the requirement of multiple robots. Tool changers can be a manual tool changers or automatic tool changers. A CNC tool changer fulfills the requirement of multiple tooling for a wide variety of machine tools. Why Tool Changer is needed? Tool changer is equipment which is used in CNC machines to reduce the cycle time. The term applies to a wide variety of tooling, from indexable insert, single point tools to coded, preset tool holders for use in automatic tool changers. It includes power-actuated, cross-slide tooling and turret tool holders for single spindle chuckers, interchangeable-block boring tools. A number of basic types of tool holders are available that accommodate most
face
mills,
end
mills,
drills,
reamers,
taps,
boring
tools,
counterbores, countersinks, and spot facers. Arbor type cutters such as face mills and shell end mills are held in an arbor type tool holders. Shank type mills are held in positive lock holder. Drills, reamers and boring tools are held in a straight shank collet type holder. Taps are held in a tension and compression collet type holders.
17
TYPES OF AUTOMATIC TOOL CHANGER There are mainly three kinds of tool changers available in market according to the tool magazine arrangements provided. 1. Tool change system with gripper arm 2. Tool change system with chain magazine 3. Tool change system with disc magazine 1. Tool Change system with gripper Arm In this system, there are mainly two elements Disc with magazine Gripper arm In this system, a disc is provided with magazine, in which different types of tools are loaded. It can hold maximum 32 tools. In magazines, all the tools which are required are fixed in the magazines. The tool which is programmed in controller according to the program will be indexed in front of the gripper arm and then the gripper arm grips the tool and performs the operation. After completion of the operation by each tool, the gripper arm places the tool back in to the magazine. Description of the gripper arm The tool changer gripper arm consists of a central aluminum structure with terminal tool grippers of hardened steel. Tool gripping and release are obtained by means of a spring-operated mechanism actuated by the rotation of the arm. The latter, in turning, engages or disengages the grippers from the tools when these are in exchange position. 2. Tool Change system with chain magazine In this kind of system, a chain is provided with magazines for tool holding. This chain can hold numerous tools so it is used in heavy machineries. Starting from 32 it can hold more than 100 tools. 18
These chain is indexed in front of the head stock directly as per the tool programmed position.
Tool Change system with chain magazine
19
In this kind of system there is no arrangement like gripper arm. The chain itself is indexed and the machining is done while keeping the tool in the chain only. 3. Tool change system with Disc magazine In this system, the tools are held in a big disc. This disc is not similar to the disc provided in gripper arm mechanism. In this disc, there are tool grippers provided separately for each magazine these grippers holds the tool and performs machining operation as well.
Tool change system with disc magazine
This system disc can hold 32 to maximum of 64 tools. These type of tool changers are used in medium capacity machineries.
20
Project Details CONCEPT During training, we have seen huge CNC units equipped with automatic tool changers. From there we have got the idea to replicate the same as our project. CNC machines are widely used in industries these days. For saving time consumed in loading and unloading the tools, almost all the CNC machines are equipped with automatic tool changers.
DESCRIPTION OF THE PARTS Here, we have selected the gripper arm type arrangement for our project. We have made the model of gripper arm automatic tool changer. Main Components The main components of the gripper arm arrangement are: 1. Base 2. Griper arm 3. Tool holder 4. Support arm 5. Horizontal rib Description of all the parts used and its function is discussed here. The main parts are base, tool holder, support arm and gripper arm 1. Base:
We have provided 400x600x20 mm wooden base. This base holds the whole arrangement as well as supports it. 2. Gripper Arm:
An aluminum strip is provided on which the gripper arm is fixed. The gripper arm rotates 360 degree and performs the machining operation as per our requirement.
21
The aluminum strip can oscillate about the support arm and gripper arm rotates 360 degree about the pivot point and also reciprocates due to the rack and pinion arrangement provided in the gripper arm. So the machining operation can be performed. The tool gripper mechanism also rotates 360 degree which is provided at the end of gripper arm. So mainly there are three motions 1.
Tool gripper rotation 360 degree
2.
Whole rack and pinion mechanism disc rotates 360 degree
3.
Gripper arm reciprocates due to rack and pinion mechanism
These motions facilitate machining operations in all directions very easily. 4. Tool holder
Tool holder can be any disc or block type arrangement in which the tools can be held. Here, we have provided wooden block with metal strip at the bottom for holding the tools. We have fixed a metal strip with the bottom strip so after putting the tool back into the tool holder, the tool is locked. So basically it is a locking and unlocking mechanism for all the four tools. 5. Support arm
Support arm does not perform any kind of specific function; it just supports the whole assembly mainly, the gripper arm and the horizontal rib. It is a mild steel hollow shaft of 150 mm diameter. It is kept hollow so that all the wires can be passed inside the shaft.
22
Motors There are mainly three motors are used all of different RPM ranging from 15 rpm to 45 rpm. Motors used here are the simple gear motors used for electrical purposes. These motors have the capacity to carry load upto 4-5 kg. and then it can give torque of The motors are called gear motors which are directly available in market. The supply to the motors is given by 9 watts battery. The electric motor is a standard DC electric motor.
DC Electric Motor
On the end of the motor is a small 6-tooth gear. This gear fits into the center of the planetary gear system, as shown here:
A gear attached to the motor fits in the middle of the three smaller gears
23
This gear system is the heart of any electric screwdriver. An electric motor by itself is a pretty weak device. You can grab the axle and stop a small motor's rotation very easily. This means that the chuck moves very slowly relative to the motor, but that the chuck has a great deal of torque (it takes 56 times more strength to stop the motor from spinning because of the gear ratio).
Parts of an electric motor
You can see that this is a small motor, about as big around as a dime. From the outside you can see the steel can that forms the body of the motor, an axle, a nylon end cap and two battery leads. If you hook the battery leads of the motor up to a flashlight battery, the axle will spin. If you reverse the leads, it will spin in the opposite direction. Here are two other views of the same motor. (Note the two slots in the side of the steel can in the second shot - their purpose will become more evident in a moment.)
24
Nylon cap
The nylon end cap is held in place by two tabs that are part of the steel can. By bending the tabs back, you can free the end cap and remove it. Inside the end cap are the motor's brushes. These brushes transfer power from the battery to the commutator as the motor spins.
Rack and pinion mechanism for gripper arm
Rack
and
pinion
mechanism
is
provided
for
gripper
arm
for
reciprocating movement of gripper arm. The mechanism is fixed in a plate kind of arrangement and in this arrangement, gripper arm is fixed. Due to up and down motion of rack and pinion, the gripper arm moves up and down and the whole mechanism rotates 360 degree for performing the required task. The gripper arm used here is of screw driver kind of arrangement. It is available readily in market with different arrangements for different kinds of screw heads.
25
DEGREES OF FREEDOM Main aspect of this project is its degrees of freedom. It has mainly 10 degrees of freedom. There are mainly 1. Rotational motion of horizontal arm 2. Rotational motion of Rack and pinion disc 3. Reciprocating motion of gripper arm 4. Rotational motion of gripper 5. Reciprocating motion of tool holder lock unlock mechanism Rotational Motion of Horizontal Arm
The horizontal arm is pivoted about the main arm and it can rotate, clockwise as well as anticlockwise about the main arm. This motion facilitates machining in any direction. Rotational Motion of Rack and Pinion Disc
The rack and pinion disc is provided at the end of the horizontal arm. It is pivoted about the upper middle side. It can rotate about the pivot point. This motion facilitates movement of tool gripper in any direction. Reciprocating Motion of Gripper Arm
Rack and pinion arrangement is provided for gripper arm. Gripper arm is fixed with pinion. So reciprocating motion of the gripper arm can be obtained and machining can be done accordingly. Rotational Motion of Gripper
The tool gripper which is almost cylindrical in shape and provided at the end of gripper arm for actually holding the tools can have circular motion. This motion facilitates the tasks like fastening or loosening a screw.
26
CONSTRUCTION We have carried out the construction of the tool changer equipment in following manner.
Firstly, we have attached the main arm (which is of 65 mm diameter) to the base. As mentioned above the base is wooden board of 400x600x20 mm.
On this wooden board, the hollow arm is fixed with two bolts. The arm is kept hollow so that the wirings can be passed inside the hollow arm. On the arm, a motor is fixed. Motor is of 20rpm and it can carry maximum of 4kgs. load.
After fixing the horizontal arm to the main arm, at the end of the horizontal arm, the disc of rack and pinion arrangements is attached. This attachment is also fixed with motor. So the whole rack and pinion disc can rotate 360 degree.
In the rack and pinion arrangement, a gripper arm is attached. Gripper arm is attached so that up and down movement of the gripper arm can be achieved by rack and pinion mechanism.
The
gripper
arm
used
here
is
of
screw
driver
kind
of
arrangement. It is available readily in market with different arrangements for different kinds of screw heads. This kind of tool gripper arrangement is used. The all four tools are arranged in tool holder, and the tool gripper comes down, grips the tool and goes to the required location.
A circuit with eight relays is used for four different tools holding and un-holding. A relay is an electrical switch that opens and closes under the control of another electrical circuit.
The circuit diagram is very simple and it is explained in next
page.
27
Description of the Circuit Circuit diagram is shown in previous page. It is a very simple circuit. It consists of transistors, Relays and motors. The
detail
about
relay
is
given
in
next
pages.
Relay
is
an
electromagnetic switch which is used to convert AC to DC. The motors and all the other parts used in circuit can be run through DC supply. So for converting AC current into DC we have used Relay. P Total P total is maximum total power which can be generated in a transistor. The Specifications All the specifications of the BC547 PNP transistor, we have used, is described in next page.
RELAY A relay is a simple electro mechanical switch made up of an electro magnet and a set of contacts A relay is an electrical switch that opens and closes under the control of another electrical circuit. In the original form, the switch is operated by an electromagnet to open or close one or many sets of contacts. Relays are found hidden in all sorts of devices.
Parts of a relay
28
A simple electromagnetic relay, such as the one taken from a car in the first picture, is an adaptation of an electromagnet. It consists of a coil of wire surrounding a soft iron core, an iron yoke, which provides a low reluctance path for magnetic flux, a moveable iron armature, and a set, or sets, of contacts; two in the relay pictured. The armature is hinged to the yoke and mechanically linked to a moving contact or contacts. It is held in place by a spring so that when the relay is deenergized there is an air gap in the magnetic circuit. When an electric current is passed through the coil, the resulting magnetic field attracts the armature and the consequent movement of the movable contact or contacts either makes or breaks a connection with a fixed contact. If the set of contacts was closed when the relay was de-energized, then the movement opens the contacts and breaks the connection, and vice versa if the contacts were open. If the coil is energized with DC, a diode is frequently installed across the coil, to dissipate the energy from the collapsing magnetic field at deactivation,
which
would
otherwise
generate
a
voltage
spike
dangerous to circuit components. Some automotive relays already include that diode inside the relay case.
CONSTRUCTION OF A RELAY Relays are amazingly simple devices. There are four parts in every relay:
Electromagnet
Armature that can be attracted by the electromagnet Spring
Set of electrical contacts
29
Working principle of a relay
In this figure, you can see that a relay consists of two separate and completely independent circuits. The first is at the bottom and drives the electromagnet. In this circuit, a switch is controlling power to the electromagnet. When the switch is on, the electromagnet is on, and it attracts the armature (blue).
30
NC System – An Idea NC SYSTEM Many
of
the
achievements
in
computer-aided
design
and
manufacturing have a common origin in numerical control (abbreviated as
NC).
The
conceptual,
framework
established
during
the
development of numerical control is still undergoing further refinement and enhancement in today’s CAD/CAM technology. Numerical control can be defined as a form of programmable automation in which the process is controlled by numbers, letters and symbols. In NC the numbers form a program of instructions designed for a particular workparts or job. NC technology has been applied to the wide variety of operations, including drafting, assembly, inspection, sheet metal press working, and spot welding. However, numerical control finds its principle applications in metal machining processes. The machined work parts are designed in various sizes and shapes, and most machined parts that are produced in industry today are made in small to medium size batches.
31
BASIC COMPONENTS OF AN NC SYSTEM An operational numerical control system consists of the following three basic components. 1. Program of instructions 2. Controller unit, also called a machine control Unit 3. Machine tool or other controlled process The general relationship among the three components is illustrated in figure. The program of instructions serves as the input to the controller unit, which in turn commands the machine tool or the other process to be controlled. In NC system you need to write the part programs required to run the machine tool manually. Programs are listing of codes in a proper sequence that as instructions for the machine. The program of instructions is the detailed step by step set of directions which tell the machine tool what to do. It is a multifunction machine which incorporates several time saving features into a single piece of automated production equipment. All the components are explained in detail below.
Part program
Controller
Machine Tool
NC system
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1.
Program of Instructions The program of instructions is the detailed step by step set of directions which tell the machine tool what to do. It is coded in symbolic form on some type of input medium that can be interpreted by the controller unit. The most common input medium today is 1 inch wide punched tape. Over the years, other forms of input media have been used, including punched cards, magnetic tapes, and even 35-mm motion picture film.
2.
Controller Unit The second basic component of the NC system is the controller unit. This consists of the electronics and hardware that read and interpret the program of instructions and convert it into mechanical actions of the machine tool. The typical elements of a conventional NC controller unit include the tape reader, a data buffer, signal output channels to the machine tool, feedback channels from the machine tool, and the sequence control to co-ordinate the overall operation of the foregoing elements. Here, some systems are provided with Automatic Tool Changer so there will be no operator required for changing the tools and the tool changing time will also be reduced so the machining operation will be performed fast.
3.
Machine tool or other controlled process The third basic component of an NC system is the machine tool or other controlled process. It is the part of the NC system which performs useful work. In the most common example of an NC system, one designed to perform machining operations, the machine tool consists of the work table and spindle as well as the motors and controls necessary to drive them. It also includes the cutting tools,
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work fixtures and other auxiliary equipment needed in the machining operation. CNC SYSTEM In a CNC system, a dedicated computer is used to perform all basic NC functions. Part program of CNC is similar to part program of an NC system. This program is entered only once, and it serves as input for the computer. The CNC systems have more computational capability, more reliable and are flexible compared to NC system.
Part program
Computer
Machine Tool
CNC System
DEFINITION OF CNC A system in which the actions are controlled by direct insertion of numerical data at some point. The system automatically interprets at least some portion of this data. DNC SYSTEM The DNC system uses a central computer, which sends control signals to number of local CNC machines. Program is stored in the memory of host computer, when a machine tool needs control commands, host computer
instantaneously
communicates
with
it
and
perform
operation.
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Host computer
CNC Computer
M/c. Tool
CNC Computer
M/c. Tool
CNC Computer
M/C. Tool
DNC System [
NEED FOR CNC In conventional machines, after loading the work piece, you have to manually operate different hand wheels to feed the cutting tool into the work piece.
ADVANTAGES OF CNC MACHINES With a CNC system you can:
Reduce non-production time
Achieve manufacturing flexibility
Increase in production rate
Produce parts with complex shapes
Improve quality
Achieve good surface finish and accuracy
In short, CNC offers ACCURACY, REPEATABILITY, RELIABILITY and PRODUCTIVITY.
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TYPES OF CNC MACHINES 1.
Single spindle drilling machine
2.
Turning center or CNC lathe
3.
Milling center
4.
Machining center
5.
CNC Non conventional machines (EDM, AJM etc.)
COMPONENTS OF CNC SYSTEM
Part program
Computer
Machine control unit (MCU)
Processing machine
1. Part Program Before making a part program, you need to understand the: 1. Given part drawing. 2. Different machining operations to be performed on the job. 3. Sequence through which these operations are to be performed. 4. Cutting conditions to be selected. 2.
Machine Control Unit
It is a main part of CNC system. This unit interprets the program of instructions and sends it to the next step in the process. All control signals to the machine tool are generated here, based on the instructions given in the part program. The MCU reads the part program, and then sends the control signals to the control unit of the machine tool in the form of electrical pulses. The drives in the machine
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tool convert these electrical pulses into the equivalent mechanical motions.
Control signals
MCU (Interpretatio n)
Inform of ele. Pulses
M/C. TOOL (Conversion)
MCU
3. Processing Machines Processing machines are designed to execute the metal machining work as per the signals received from MCU. Different types of machines are developed for different operations. These include conventional
and
non-conventional
machine
tools.
Conventional
machine tool includes lathe, milling, drilling etc. non-conventional machines are machines that uses non-conventional energy, such as thermal energy, chemical energy etc. Examples are, Electro Chemical Grinding (ECG), Electro Discharge Machining (EDM) etc.
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CLASSIFICATION OF CNC SYSTEMS 1. TYPE OF MACHINE: Point to point machining Continuous path machining 2. PROGRAMING METHOD: Incremental Absolute 3. TYPE OF CONTROL LOOPS: Open loop Closed loop DEVICES FOR DRIVING CNC SYSTEMS Electrical devices Hydraulic devices
Electric devices use different type of motors such as stepper motor or DC motor.
Hydraulic devices use actuator and other set up.
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CONCEPT OF PART PROGRAMMING
In CNC machine tools, the operations to be performed are given in a coded form, which is known as part program.
Manual part programming is a very tedious work. For manual programming a programmer must have sufficient knowledge of machining processes and part programming techniques.
The programmer has to prepare a part program with a proper sequence of operations and appropriate selection of cutting parameters such as feed and speed.
In such cases chances of committing errors are high while developing a part program. There for the concept of computer assisted
part
programming
came
into
existence
so,
computational errors are eliminated.
Programming software does the calculations required to produce the component and the programmer communicates with this system, through the system language, which is based on English words.
TYPES OF PROGRAMMING LANGUAGES
APT (Automatically programmed tools)
COMPACT – 2
ADAPT (Adaptation of APT)
EXAPT (Extended subset of APT)
AUTOSPOT
SPLIT
These languages are utilized as per type of machine, but APT is widely used.
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CONCLUSION An Automatic Tool Changer is equipment that reduces cycle times by automatically changing tools between cuts. Automatic tool changers are differentiated by tool-to-tool time and the number of tools they can hold. We have made the simplest model of an automatic tool changer. In this model, there is scope of as many modifications as we want. By more investment, it can be made more sophisticated as per our requirement. For example, by using the disc instead of tool holder we have used, more tools can be accommodated. By using timers for operations, the time required for a particular operation can be fixed and as per that time, the tool changing procedure can be carried out. So, in this way, more modifications can be done in the model we have made.
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REFERENCES Books
Automation principles and strategies by Mikell Groover
Production Technology Part II by O.P.Khanna
Computer Aided design and manufacturing by Mikell P. Groover & Emory W. Zimmers
Websites
www.ati-ia.com
www.howstuffworks.com
www.wikipedia.com
www.atc.cnc.in
www.industrialautomation.com
[email protected]
www.controldevices.com
Magazines
Electronics 4 you
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