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    DYNAMIC INDUSTRIES

    Report on

    Manufacturing of an injection mould component as per customers requirement and

    comparison of conventional milling and CNC milling methods.

    By

    Nitish Kumar

    Roll no. 322, GR no. 71122100019

    Submitted for

    Technical internship programme

    TrainingSupervisor and Guide

    Prof. Ravi Terkar

    Associate Professor, MPSTME

    Mr. Anup Parikh

    Chairman, Dynamic Industries Ltd.

    MUKESH PATEL SCHOOL OF TECHNOLOGY MANAGEMENT & ENGINEERING

    SVKM's

    NARSEE MONJEE INSTITUTE OF MANAGEMENT STUDIES

    (Declared as Deemed-to-be University Under Section 3 of the UGC Act. 1956)

    Vile Parle (w), Mumbai-400 056.

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    ACKNOWLEDGMENT

    It gives me immense pleasure to present this training report at DYNAMIC

    INDUSTRIES LTD. This training provided me a golden opportunity to expose myself

    to the industrial environment.

    I am very grateful to my training Guides, Mr Anup Parikh & Prof. Ravi

    Terker for their motivation and continuous support as well as guidance to pursue

    and complete this report. Their wide knowledge and logical way of thinking have

    been of great value for me. They were always there to meet and talk about research

    ideas, to proof read and mark-up my papers, and to ask me good questions to help

    me to think through my research. Without their encouragement and constant

    guidance, I could not have finished this synopsis.

    I would like to thank to Mr Chandrakant Vichrolia, Mr Chetan Majithia & Mr.

    Amol Deshmukh for their valuable support and encouragement during the

    research work.

    Further I believe that the list of people would remain incomplete if I fail to

    mention my supervisors & department colleagues; they were constant source of

    encouragement and timely help.

    Thanks

    Nitish Kumar

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    Contents1 ABSTRACT ................................................................................................................................................... 1

    2 Company profile ......................................................................................................................................... 2

    2.1One-Stop Service .............................................................................................................................. 2

    2.2Quality Policy of Dynamic Industries................................................................................................... 2

    2.3List ofEsteemed Customers........................................................................................................... 3

    2.4Facilities Available at Dynamic Industries........................................................................................... 4

    2.5Some of the products of Dynamic Industries are ................................................................................ 5

    3 INTRODUCTION .......................................................................................................................................... 9

    4 Product Design ......................................................................................................................................... 10

    4.1 Milling14

    4.2Shaping ............................................................................................................................................. 15

    4.3 Grinding...16

    5 Understanding the Basics of the Injection Mould ................................................................................... 17

    5.1Number of Cavities............................................................................................................................ 18

    5.2Runners and Gates ............................................................................................................................ 20

    5.3Venting:............................................................................................................................................. 21

    5.4Cooling: ............................................................................................................................................. 22

    5.5Ejection:............................................................................................................................................. 23

    6 Machining and Finishing processes of mould .......................................................................................... 24

    6.1 CNC machining..24

    6.2CNC Control Systems 25

    6.3 Open Loop Systems ........................................................................................................................... 25

    6.4Close Loop Systems............................................................................................................................ 25

    6.4Features of CNC................................................................................................................................. 26

    6.5Basic CNC Principles .......................................................................................................................... 28

    6.6Motion Control.................................................................................................................................. 29

    6.7Types of CNC machines...................................................................................................................... 31

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    6.8Importance of higher axes machining ............................................................................................... 31

    6.9Applications Of Cnc Machines ......................................................................................................... 32

    6.10OTHER FUNCTIONS OF CNC.. .......................................................................................................... 33

    7 Electrical discharge machine ................................................................................................................ 35

    7.1Characteristics of EDM.. ................................................................................................................ 36

    7.2DIELECTRIC.................................................................................................................................... 37

    8 MAIN PROJECT.. ................................................................................................................................ 41

    8.1Observations ................................................................................................................................. 44

    8.2 Results..44

    9 Conclusion.44

    10 References...45

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    ABSTRACTDynamic Industries is an upcoming mould making and moulding company specialized in

    Automobile, Air-conditioners, Water Purifier System, Bio-medical, Television and House

    Hold Industries.

    My project is related to the production, design & manufacturing of an injection mould

    component known as Shroud in this case.

    In my training here, Ill be monitoring and studying the mould making process starting

    from the product design to the final trial & correction, alongside with the use of CNC

    milling machines and its comparison with conventional milling so as to know which is

    better and what are their advantages and disadvantages.

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    Company profile

    Dynamic Industries is an upcoming mould making and moulding company specialized in

    Automobile, Air-conditioners, Water Purifier System, Bio-medical, Television and House

    Hold Industries.

    Industries Serviced:

    Automobiles Water Treatment Consumer Appliances Electrical and Electronics Thermoforming Bio-Medicals

    One-Stop Service:

    We have integrated product development, mould design and

    manufacturing facilities along with injection moulding facilities

    to provide one-step service.

    Quality Policy of Dynamic Industries:Quality policy is to achieve sustained, profitable growth by providing services which

    consistently satisfy the needs and expectation of our customers.

    To achieve and maintain a level of quality which enhances the company's reputation

    with customers.

    To provide a quality product that satisfies our customer's requirement, deliver on time.

    We are committed to continuously improve our processes to provide goods and services

    at a better value to our customers.

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    List ofEsteemed Customers:

    Mutual Industries Ltd. Ronch Polymers Ltd.

    TVS Motor Company Ltd.

    Sundaram Auto-Components Ltd.

    Tata Auto-Components Pvt. Ltd.

    Banco Products (India) Ltd.

    Alkraft Thermo technologies Pvt. Ltd.

    Kabra Extrusiontechnik Pvt. Ltd. Jyoti Plastic Works Pvt. Ltd.

    Polysmart Technologies Pvt. Ltd.

    Auro Plastic Injection Moulders Pvt. Ltd

    Hitachi Home & Life Solution Ltd

    Rajoo Engineers Ltd.

    Tata InfoTech Ltd.

    Sui Generics Transpo International

    Polyset Plastics

    Transasia Bio Medicals

    Kirti Industries Ltd.

    Rita International

    Harita Infoserve Ltd.

    Lear Corporation Supreme Treaves Pvt. Ltd.

    Vipul Plastocrafts

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    Facilities Available at Dynamic Industries:

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    Some of the products of Dynamic Industries are:

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    Mould Process Chart of the Company:

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    INTRODUCTION:

    The whole process of manufacturing of moulds comprises of

    following stages:

    General Mould Manufacturing Chart

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    Product Design:

    The product design is given by the customer to the manufacturer. Product design is

    made on the 3D designing softwares like Unigraphics, PRO-E etc. by the customer and

    then it is sent to the manufacturer and the manufacturer improves it further if there is

    any problem in the design so as to get the required mould.

    Pre machining:

    Pre machining of raw material is done to get the uniform surface for machining before it

    is sent for further machining like in CNC and EDM.

    The three basic steps involved in Pre machining are:

    Milling:

    A milling machine is a machine tool that removes metal as the work is fed against a

    rotating multipoint cutter. The milling cutter rotates at high speed and it removes metal

    at a very fast rate with the help of multiple cutting edges. One or more number of

    cutters can be mounted simultaneously on the arbor of milling machine. This is the

    reason that a milling machine finds wide application in production work. Milling

    machine is used for machining flat surfaces, contoured surfaces, surfaces of revolution,

    external and internal threads, and helical surfaces of various cross-sections. In many

    applications, due to its higher production rate and accuracy, milling machine has even

    replaced shapers and slotters.

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    Milling Machine

    PRINCIPLE OF MILLING:

    In milling machine, the metal is cut by means of a rotating cutter having multiple

    cutting edges. For cutting operation, the workpiece is fed against the rotary cutter. As

    the workpiece moves against the cutting edges of milling cutter, metal is removed in

    form chips. Machined surface is formed in one or more passes of the work. The work

    to be machined is held in a vice, a rotary table, a three jaw chuck, an index head,

    between centers, in a special fixture or bolted to machine table. The rotatory speed of

    the cutting tool and the feed rate of the workpiece depend upon the type of material

    being machined.

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    Principle of Milling

    The rotational axis of the milling cutter may be horizontal. This is called plain milling.

    Plain milling is usually carried out on a horizontal milling machine.

    When the rotational axis of the milling cutter is perpendicular to the machined

    surface, the process is called face milling or end milling. Vertical milling machines are

    the machines mostly used for this type of milling.

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    Milling Methods:

    Up-milling:In the up-milling, the metal is removed in form of small chips by a cutter rotating

    against the direction of travel of the workpiece. In this type of milling, the chip

    thickness is minimum at the start of the cut and maximum at the end of cut. As a

    result the cutting force also varies from zero to the maximum value per tooth

    movement of the milling cutter. The major disadvantages of up-milling process are the

    tendency of cutting force to lift the work from the fixture and poor surface finish

    obtained. But being a safer process, it is commonly used method of milling.

    Up Milling

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    Down-milling:In this method, the metal is removed by a cutter rotating in the same direction of feed

    of the workpiece. The effect of this that the teeth cut downward instead of upwards.

    Chip thickness is maximum at the start of the cut and minimum in the end. In this

    method, it is claimed that there is less friction involved and consequently less heat is

    generated on the contact surface of the cutter and workpiece. Down milling can be

    used advantageously on many kinds of work to increase the number of pieces per

    sharpening and to produce a better finish. With down milling, saws cut long thin slots

    more satisfactorily than with standard milling. Another advantage is that slightly lower

    power consumption is obtainable by climb milling, since there is no need to drive the

    table against the cutter.

    Down milling

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    Shaping:Process of removing metal from surface by the use of a single point cutting tool held in

    ram that reciprocates the tool in a linear direction across the work piece held on thetable of the machine.

    Shaper

    The main motion shown is performed either by the tool. It consists of two strokes, the

    working (cutting) stroke and the return (idle) stroke. The speed of the return stroke is

    greater than that of the cutting one for saving the time. The feed is performed by the

    workpiece.

    Shaping Process:A shaper operates by moving a hardened cutting tool backwards and forwards across

    the workpiece. On the return stroke of the ram the tool is lifted clear of the workpiece,

    reducing the cutting action to one direction only. The workpiece mounts on a rigid,

    box shaped table in front of the machine. The height of the table can be adjusted to

    suit this workpiece, and the table can traverse sideways underneath the reciprocating

    tool which is mounted on the ram, the table motion is usually under the control of an

    automatic feed mechanism which acts on the feedscrew. The ram slides back and forth

    above the work, at the front end of the ram is a vertical tool-slide that may be

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    adjusted to either side of the vertical plane. This tool-slide holds the clapper box and

    toolpost from where the tool can be positioned to cut the straight, flat surface on the

    top of the workpiece. The tool-slide permits feeding the tool downwards to put on a

    cut it or may be set away from the vertical plane, as required. The ram is adjustable for

    stroke and, due to the geometry of the linkage, it moves faster on the return (non-

    cutting) stroke than on the forward, cutting stroke.

    Grinding:Grinding is a metal cutting operation performed by means of a rotating abrasive wheel

    that acts as a cutting tool. It is used to finish work pieces which must show a high

    surface quality, accuracy of shape and dimensions. It is considered as a finishingoperation because it removes comparatively little metal, usually 0.25 to 0.50 mm and

    the accuracy in dimensions is in the order of 0.000025 mm.

    Grinding Machine

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    Understanding the Basics of the Injection Mould:

    Mould Cavity Space:

    The mould cavity space is a shape inside the mould, ` excavated''in such a manner thatwhen the moulding material is forced into this space it will take on the shape of the

    cavity space and, therefore, the desired product. The principle of a mould is almost as

    old as human civilization. Moulds have been used to make tools, weapons, bells,

    statues, and household articles, by pouring liquid metals (iron, bronze) into sand forms.

    Such moulds, which are still used today in foundries, can be used only once because the

    mould is destroyed to release the product after it has solidified. Today, we are looking

    for permanent moulds that can be used over and over. Now moulds are made from

    strong, durable materials, such as steel, or from softer aluminum or metal alloys andeven from certain plastics where a long mould life is not required because the planned

    production is small. In injection moulding the (hot) plastic is injected into the cavity

    space with high pressure, so the mould must be strong enough to resist the injection

    pressure without deforming.

    Mould Cavity Space and Parting Line

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    Number of Cavities:

    Many moulds, particularly moulds for larger products, are built for only one cavity

    space but many moulds, especially large production moulds, are built with 2 or more

    cavities. The reason for this is purely economical. It takes only little more time to inject

    several cavities than to inject one. For example, a 4-cavity mould requires only

    (approximately) one-fourth of the machine time of a single-cavity mould. Conversely,

    the production increases in proportion to the number of cavities.

    Today, most multicavity moulds are built with a preferred number of cavities: 2, 4, 6, 8,

    12, 16, 24, 32, 48, 64, 96, and 128. These numbers are selected because the cavities can

    be easily arranged in a rectangular pattern, which is easier for designing and

    dimensioning, for manufacturing, and for symmetry around the center of the machine,

    which is highly desirable to ensure equal clamping force for each cavity. A smaller

    number of cavities can also be laid out in a circular pattern, even with odd numbers ofcavities, such as 3, 5, 7, and 9.

    Cavity Shape:

    The shape of the cavity is essentially the ``negative'' of the shape of the desired product,

    with dimensional allowances added to allow for shrinking of the plastic.

    The shape of the cavity is usually created with chip-removing machine tools, or with

    electric discharge machining (EDM), with chemical etching, or by any new method that

    may be available to remove metal or build it up, such as galvanic processes.

    Cavity and Core:

    By convention, the hollow (concave) portion of the cavity space is called the cavity. The

    matching, often raised (or convex) portion of the cavity space is called the core. Most

    plastic products are cup-shaped. This does not mean that they look like a cup, but they

    do have an inside and an outside. The outside of the product is formed by the cavity, the

    inside by the core.

    Usually, the cavities are placed in the mould half that is mounted on the injection side,

    while the cores are placed in the moving half of the mould. The reason for this is that

    all injection moulding machines provide an ejection mechanism on the moving platen

    and the products tend to shrink onto and cling to the core, from where they are then

    ejected.

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    The Parting Line:

    To be able to produce a mould (and to remove the moulded pieces), we must have at

    least two separate mould halves, with the cavity in one side and the core in the other.

    The parting line can have any shape, but for ease of mould manufacturing, it is

    preferable to have it in one plane. The parting line is always at the widest circumference

    of the product, to make ejection of the product from the mould possible.

    With some shapes it may be necessary to offset the parting line, or to have it at an angle,

    but in any event it is best to have is so that it can be easily machined, and often ground,

    to ensure that it shuts off tightly when the mould is clamped during injection. If the

    parting line is poorly finished the plastic will escape, which shows up on the product

    as an unsightly sharp projection, or ` flash,'' which must then be removed; otherwise,

    the product could be unusable. There is even a danger that the plastic could squirt out

    of the mould and do personal damage.

    Parting Line

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    Runners and Gates:

    We must add provisions for bringing the plastic into the cavity spaces. This must be

    done with enough pressure so that the cavity spaces are filled completely before the

    plastic ` freezes,'' that is, cools so much that the plastic cannot flow anymore. The flow

    passages are the sprue, from where the machine nozzle contacts the mould, the

    runners, which distribute the plastic to the individual cavities, and the gates, which are

    (usually) small openings leading from the runner into the cavity space.

    Runners, Gates and Sprue

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    Venting:

    As the plastic flows from the gate into the cavity space, the air trapped in it as the

    mould closed must be permitted to escape. Typically, the trapped air is being pushed

    ahead by the rapidly advancing plastic front, toward all points farthest away from the

    gate. The faster the plastic enters which is usually desirable the more the trapped air is

    compressed if it is not permitted to escape, or vented. This rapidly compressed air heats

    up to such an extent that the plastic in contact with the air will overheat and possibly be

    burnt. Even if the air is not hot enough to burn the plastic, it may prevent the filling of

    any small corners where air is trapped and cause incomplete filling of the cavity. Most

    cavity spaces can be vented successfully at the parting line, but often additional vents,

    especially in deep recesses or in ribs, are necessary.

    Another venting problem arises when plastic fronts flowing from two or moredirections collide and trap air between them. Unless vents are placed there the plasticwill not ``knit'' and may even leave a hole in the wall of the product. This can be the casewhen more than one gate feeds one cavity space, or when the plastic flow splits in twoafter leaving the gate, due to the shape of the product or the location of the gate.Within the cavity space, plastic always flows along the path of least resistance, and ifthere are thinner areas, they will fill only after the thicker sections are full.

    Venting in an Injection Mould

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    Cooling:

    Cooling and productivity are closely tied. In injection moulding, the plastic is heated in

    the moulding machine to its processing (melt) temperature by adding energy in theform of heat, which is mostly generated by the rotation (work) of the extruder screw.

    After injection, the plastic must be cooled; in other words, the heat energy in the plastic

    must be removed by cooling, so that the moulded piece becomes rigid enough for

    ejection. Cooling may proceed slowly, by just letting the heat dissipate into the mould

    and from there into the environment. This is not suitable for large production, but for

    very short runs ``artificial'' cooling of a mould is not always required. However, for a

    production mould, good cooling to remove the heat efficiently is very important.

    Moulds are usually built with cooling channels. These channels are usually connected in

    series with one inlet and one outlet for water flow.

    Cooling of an Injection Mould

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    Ejection:

    After the plastic in the cavity spaces has cooled sufficiently and is rigid enough and

    ready for removal, the mould halves move apart, allowing sufficient space between the

    mould halves for removal of the product. As with cooling, the complexity of any

    provision for ejection from the mould is a question of the desired productivity. Some

    products don't need any provision within the mould for ejection. For example, a quick

    blast from an air jet applied manually by an operator and directed at the parting line can

    lift a (simple) product off the core or out of the cavity, but this would not be practical in

    most moulds, and is rarely used for real production.

    Locating ejectors is important. Balanced pressure on the part by all ejectors is

    important. Accurate location of ejectors on part walls, ribs, and bosses is highly

    desirable. Part appearance and function must be taken into consideration when

    designing the ejection system. Stripper Plate ejection is highly preferred due to the evenpressure and minimal witness marks on the part.

    Usually, the products are ejected by one of the following

    methods:

    (1) Pin (and sleeve)

    (2) Stripper plate or stripper ring

    (3) Air alone(4) Air assist

    (5) Combination of any of the above (1), (2), (3), and (4)

    (6) Unscrewing, in case of screw caps, etc.

    Use of Ejector Pin and Ejector Plate in a Mould

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    Machining and Finishing processes of mouldCNC Machining:It is a process used in the manufacturing sector that involves the use of computers to

    control machine tools. Tools that can be controlled in this manner include lathes, mills,

    routers and grinders. The CNC in CNC Machining stands for Computer Numerical

    Control.

    On the surface, it may look like a normal PC controlling the machines, but the

    computer's unique software and control console are what really sets the system apart

    for use in CNC machining.

    Under CNC Machining, machine tools function through numerical control. A computer

    program is customized for an object and the machines are programmed with CNC

    machining language (called G-code) that essentially controls all features like feed rate,

    coordination, location and speeds. With CNC machining, the computer can control exact

    positioning and velocity. CNC machining is used in manufacturing both metal and plastic

    parts.

    First a CAD drawing is created (either 2D or 3D), and then a code is created that the CNC

    machine will understand. The program is loaded and finally an operator runs a test of

    the program to ensure there are no problems. This trial run is referred to as "cutting air"

    and it is an important step because any mistake with speed and tool position could

    result in a scraped part or a damaged machine.

    Computer Numerical Control (CNC) is a specialized and versatile form of soft

    Automation and its applications cover many kinds, although it was initially developed to

    control the motion and operation of machine tools.

    Computer Numerical Control may be considered to be a means of operating a machine

    through the use of discrete numerical values fed into the machine, where the requiredinput technical information is stored on a kind of input media such as floppy disk, hard

    disk, CD ROM, DVD, USB flash drive, or RAM card etc. The machine follows a

    predetermined sequence of machining operations at the predetermined speeds

    necessary to produce a work piece of the right shape and size and thus according to

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    completely predictable results. A different product can be produced through

    reprogramming and a low-quantity production run of different products is justified.

    CNC Control Systems:

    Open Loop Systems:

    Open loop systems have no access to the real time data about the performance of the

    system and therefore no immediate corrective action can be taken in case of system

    disturbance. This system is normally applied only to the case where the output is almost

    constant and predictable. Therefore, an open loop system is unlikely to be used to

    control machine tools since the cutting force and loading of a machine tool is never aconstant. The only exception is the wire cut machine for which some machine tool

    builders still prefer to use an open loop system because there is virtually no cutting

    force in wire cut machining.

    Block diagram of an open loop system

    Close Loop Systems:

    In a close loop system, feedback devices closely monitor the output and any disturbance will be

    corrected in the first instance. Therefore high system accuracy is achievable. This system is more

    powerful than the open loop system and can be applied to the case where the output is subjected to

    frequent change. Nowadays, almost all CNC machines use this control system.

    Block diagram of a close loop system

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    Features of CNC:

    Computer NC systems include additional features beyond what is feasible with

    conventional hard-wired NC. These features, many of which are standard on most

    CNC Machine Control units (MCU), include the following:

    Storage of more than one part program:

    With improvements in computer storage technology, newer CNC controllers havesufficient capacity to store multipleprograms. Controller manufacturers generally

    offer one or more memory expansions as options to the MCU

    Various forms of program input:Whereas conventional (hard-wired) MCUs are limited to punched tape as the

    input medium for entering part programs, CNC controllers generally possess

    multiple data entry capabilities, such as punched tape, magnetic tape, floppy

    diskettes, RS-232 communications with external computers, and manual data

    input (operator entry ofprogram).

    Program editing at the machine tool: CNC permits a part program to be edited while it resides in the MCU computer

    memory. Hence, a part program can be tested and corrected entirely at the

    machine site, rather than being returned to the programming office for

    corrections. In addition to part program corrections, editing also permits cutting

    conditions in the machining cycle to be optimized. After the program has been

    corrected and optimized, the revised version can be stored on punched tapeor other media for future use.

    Fixed cycles and programming subroutines: The increased memory capacity and the ability to program the control computer

    provide the opportunity to store frequently used machining cycles as macros,

    which can be called by the part program. Instead ofwriting the full instructions for

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    the particular cycle into every program, a programmer includes a call statement

    in the part program to indicate that the macro cycle should be ex ec ut ed . These

    cycles often require that certain parameters be defined, for example, a bolt hole

    circle, in which the diameter of the bolt circle, the spacing of the bolt holes, and

    other parameters must be specified.

    Interpolation: Some of the interpolation schemes are normally executedonly on a CNC system because of computational requirements. Linear and circular

    interpolation are sometimes hard-wired into the control unit, but helical, parabolic,

    and cubic interpolations are usually executed by a stored program algorithm.

    Positioning features for setup: Setting up the machine tool for a

    given work part involves installing and aligning a fixture on the machine tooltable. This must be accomplished so that the machine axes are established with

    respect to the work part. The alignment task can be facilitated using certain

    features made possible by software options in the CNC system. Position set is one

    of the features. With position set, the operator is not required to locate the

    fixture on the machine table with extreme accuracy. Instead, the machine tool

    axes are referenced to the location of the fixture using a target point or set of

    target points on the work or fixture.

    Cutter length and size compensation: In older style controls,cutter dimensions hade to be set precisely to agree with the tool path defined

    in the part program. Alternative methods for ensuring accurate tool path

    definition have been incorporated into the CNC controls. One method involves

    manually entering the actual tool dimensions into the MCU. These actual

    dimensions may differ from those originally programmed. Compensations are then

    automatically made in the computed tool path. Another method involves use of a

    tool length sensor built into the machine. In this technique, the cutter is mounted

    in the spindle and the sensor measures its length. This measured value is then

    used to correct the programmed tool path.

    Acceleration and deceleration calculation: This feature isapplicable when the cutter moves at high feed rates. It is designed to avoid tool

    marks on the work surface that would be generated due to machine tool dynamics

    when the cutter path changes abruptly. Instead, the feed rate is smoothly

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    decelerated in anticipation of a tool path change and then accelerated back up to

    the programmed feed rate after the direction change.

    Communications interface:

    With the trend toward interfacing and networking inplants today, most modernCNC controllers are equipped with a standard RS-232 or other communications

    interface to link the machine to other computers and computer- driven devices.

    This is useful for various applications, such as

    (1)downloading part programs from a central data file;

    (2)collecting operational data such as workpiece counts, cycle times, and

    machine utilization; and

    (3)interfacing with peripheral equipment, such as robots that unload and load

    parts.

    Basic CNC Principles:

    All computer controlled machines are able to accurately and repeatedly control motion

    in various directions. Each of these directions of motion is called an axis. Depending on

    the machine type there are commonly two to five axes. Additionally, a CNC axis may be

    either a linear axis in which movement is in a straight line, or a rotary axis with motion

    following a circular path.

    Linear Axis and Rotary Axis of CNC

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    Motion Control:

    The most basic function of any CNC machine is automatic, precise, and consistent

    motion control.

    Rather than applying completely mechanical devices to cause motion as is required on

    most conventional machine tools, CNC machines allow motion control in a

    revolutionary manner.

    All forms of CNC equipment have two or more directions of motion, called axes. These

    axes can be precisely and automatically positioned along their lengths of travel.

    The two most common axis types are linear (driven along a straight path) and rotary

    (driven along a circular path).

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    TYPES OF CNC MACHINES BASED ON AXES:

    2 & 3 axes CNC machines:CNC lathes will be coming under 2 axes machines. There will be two axes along which

    motion takes place. The saddle will be moving longitudinally on the bed (Z-axis) and the

    cross slide moves transversely on the saddle (along X-axis). In 3-axes machines, there

    will be one more axis, perpendicular to the above two axes. By the simultaneous

    control of all the 3 axes, complex surfaces can be machined.

    3 Axes CNC Machine

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    4 & 5 axes CNC machines:4 and 5 axes CNC machines provide multi-axis machining capabilities beyond the

    standard 3- axis CNC tool path movements. A 5-axis milling centre includes the three

    X, Y, Z axes, the A axis which is rotary tilting of the spindle and the B-axis, which can

    be a rotary index table.

    5 Axes CNC Machine

    Importance of higher axes machining:Reduced cycle time by machining complex components using a single setup. In

    addition to time savings, improved accuracy can also be achieved as positioning

    errors between setups are eliminated.

    Improved surface finish and tool life by tilting the tool to maintain optimum tool to

    part contact all the times.Improved access to under cuts and deep pockets. By tilting the tool, the tool can be

    made normal to the work surface and the errors may be reduced as the major

    component of cutting force will be along the tool axis.

    Higher axes machining has been widely used for machining sculptures surfaces in

    aerospace and automobile industry.

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    APPLICATIONS OF CNC MACHINES:

    CNC machines are widely used in the metal cutting industryand are best used to produce the following types of product:

    Parts with complicated contours. Parts requiring close tolerance and/or good repeatability. Parts requiring expensive jigs and fixtures if produced on conventional machines. Parts that may have several engineering changes, such as during the

    development stage of a prototype.

    In cases where human errors could be extremely costly. Parts that are needed in a hurry. Small batch lots or short production runs.

    Some common types of CNC machines and instruments

    used in industry are as following: Drilling Machine. Lathe/ Turning Centre. Milling/ Machining Centre. Turret Press and Punching Machine. Wire cut Electro Discharge Machine (EDM). Grinding Machine. Laser Cutting Machine. Water Jet Cutting Machine. Electro Discharge Machine. Coordinate Measuring Machine Industrial Robot.

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    OTHER FUNCTIONS OF CNC:

    Modern CNC systems have some specially designed functions to

    simplify the manual programming.

    Some of the functions are:

    a. Mirror Image:This is the function that converts the programmed path to its mirror image, which

    is identical in dimensions but geometrically opposite about one or two axes.

    b. Programme Repetition and Looping:In actual machining, it is not always possible to machine to the final dimension in

    one go. This function enables the looping of a portion of the programme so that

    portion can be executed repeatedly.

    c. Pocketing Cycle:Pocketing is a common process in machining. This is to excavate the material

    within a boundary normally in zigzag path and layer by layer. In a pocketing cycle,

    the pattern of cutting is pre-determined. The user is required to input parameters

    including the length, width and depth of the pocket, tool path spacing, and layerdepth. The CNC system will then automatically work out the tool path.

    d. Drilling, Boring, Reaming and Tapping Cycle:This is similar to pocketing cycle. In this function, the drilling pattern is pre-

    determined by the CNC system. What the user has to do is to input the required

    parameters such as the total depth of the hole, the down feed depth, the relief

    height and the dwell time at the bottom of the hole.

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    Uses of CNC milling in plastic injection mould making

    Some of the main operations done by CNC milling are:

    Mould base work. The insert pockets, the core and cavity pockets, interlockpockets, slide openings, many water-lines, in fact, just about everything you find

    in a mould base.

    Roughing and semi-finishing of cores and cavity blocks. Now, with hard-milling acommon operation, many cores and cavities are finished in the CNC. As much of

    the detail as possible is milled because it is so much faster than EDM or grinding.

    Electrodes are made in the CNC. Both copper and graphite electrodes are madehere. Once the program is made, you can make as many duplicates as you want,

    even for replacement parts far in the future.

    All kinds of inserts, slide components, lifter details, and other features used ininjection moulds.

    Another close relative is the 5 axis CNC milling machine. These are highlysophisticated machines that are becoming increasingly common. They are very

    versatile and able to machine 5 sides of a workpiece in one setup, plus the

    infinite number of angles sometimes required.

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    ELECTRICAL DISCHARGE MACHINE

    Electrical Discharge Machining (EDM) is a controlled metal-removal process that is used

    to remove metal by means of electric spark erosion. In this process an electric spark is

    used as the cutting tool to cut (erode) the workpiece to produce the finished part to thedesired shape. The metal-removal process is performed by applying a pulsating

    (ON/OFF) electrical charge of high-frequency current through the electrode to the

    workpiece. This removes (erodes) very tiny pieces of metal from the workpiece at a

    controlled rate.

    In EDM, a potential difference is applied between the tool and workpiece. Both the tool

    and the work material are to be conductors of electricity. The tool and the work

    material are immersed in a dielectric medium. Generally kerosene or deionized water is

    used as the dielectric medium. A gap is maintained between the tool and the workpiece.

    Depending upon the applied potential difference and the gap between the tool andworkpiece, an electric field would be established. Generally the tool is connected to the

    negative terminal of the generator and the workpiece is connected to positive terminal.

    When the power is supplied a large number of electrons will flow from the tool to the

    job and ions from the job to the tool. This is called avalanche motion of electrons. Such

    movement of electrons and ions can be visually seen as a spark. Thus the electrical

    energy is dissipated as the thermal energy of the spark.

    The high speed electrons then impinge on the job and ions on the tool. The kinetic

    energy of the electrons and ions on impact with the surface of the job and tool

    respectively would be converted into thermal energy or heat flux. Such intense localised

    heat flux leads to extreme instantaneous confined rise in temperature which would be

    in excess of 10,000oC.

    Such localised extreme rise in temperature leads to material removal. Material removal

    occurs due to instant vapourisation of the material as well as due to melting. The

    molten metal is not removed completely but only partially.

    Generally the workpiece is made positive and the tool negative. Hence, the electrons

    strike the job leading to crater formation due to high temperature and melting and

    material removal. Similarly, the positive ions impinge on the tool leading to tool wear. In

    EDM, the generator is used to apply voltage pulses between the tool and the job. Aconstant voltage is not applied.

    The sparks get distributed all over the tool surface leading to uniformly distributed

    material removal under the tool.

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    EDM

    Characteristics of EDM:

    (a) The process can be used to machine any work material if it is electrically conductive

    (b) Material removal depends on mainly thermal properties of the work material rather

    than its strength, hardness etc.

    (c) In EDM there is a physical tool and geometry of the tool is the positive impression of

    the hole or geometric feature machined

    (d) The tool has to be electrically conductive as well. The tool wear once again depends

    on the thermal properties of the tool material

    (e) Though the local temperature rise is rather high, still due to very small pulse on time,there is not enough time for the heat to diffuse and thus almost no increase in bulk

    temperature takes place. Thus the heat affected zone is limited to 24 m of the spark

    crater

    (f) However rapid heating and cooling and local high temperature leads to surface

    hardening which may be desirable in some applications

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    (g) Though there is a possibility of taper cut and overcut in EDM, but they can be

    controlled and avoided by using Insulation over the EDM tool.

    Prevention of Overcut

    DIELECTRIC

    In EDM, material removal mainly occurs due to thermal evaporation and melting. As

    thermal processing is required to be carried out in absence of oxygen so that the

    process can be controlled and oxidation avoided. Oxidation often leads to poor surface

    conductivity (electrical) of the workpiece hindering further machining. Hence, dielectric

    fluid should provide an oxygen free machining environment. Further it should haveenough strong dielectric resistance so that it does not breakdown electrically too easily

    but at the same time ionise when electrons collide with its molecule. Moreover, during

    sparking it should be thermally resistant as well. Generally kerosene and deionised

    water is used as dielectric fluid in EDM. Tap water cannot be used as it ionises too early

    and thus breakdown due to presence of salts as impurities occur. Dielectric medium is

    generally flushed around the spark zone. It is also applied through the tool to achieve

    efficient removal of molten material.

    ELECTRODE MATERIAL

    Electrode material should be such that it would not undergo much tool wear when it is

    impinged by positive ions. Thus the localised temperature rise has to be less by tailoring

    or properly choosing its properties or even when temperature increases, there would be

    less melting. Further, the tool should be easi.ly workable as intricate shaped geometric

    features are machined in EDM.

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    The basic characteristics of electrode materials are:

    High electrical conductivity electrons are cold emitted more easily and there is less

    bulk electrical heating

    High thermal conductivity for the same heat load, the local temperature rise would

    be less due to faster heat conducted to the bulk of the tool and thus less tool wear

    Higher density for the same heat load and same tool wear by weight there would be

    less volume removal or tool wear and thus less dimensional loss or inaccuracy

    High melting point high melting point leads to less tool wear due to less tool material

    melting for the same heat load

    Easy manufacturability

    Cost cheap

    The followings are the different electrode materials which areused commonly in the industry:

    Graphite

    Electrolytic oxygen free copper

    Tellurium copper 99% Cu + 0.5% tellurium

    Brass

    Tools of EDM

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    EDM Operation on a Mould

    With a combination of EDM and CNC machining, you can obtain injection moulds made

    of aluminium with sharp, clear features.

    The best time to use EDM during the mould building process:

    Table to Show when and Why to Use EDM

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    Mould of fan shroud of TATA Motors EURO V standard

    based car:

    The Final Product:

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    MAIN PROJECT:

    Comparison of CNC milling and Conventional Milling and to

    know which is better:

    Main advantages of CNC over Conventional:Computer numerical control (CNC) machinery has improved woodworking by

    automating critical functions that once required manual input. In doing so, it has made

    high production milling, routing and other practices more feasible in terms of

    manpower, and narrowed the gap between proficient and expert machine

    operators.

    Better Production Capacity:Due to their automatic operation and excellent cutting ability, CNC machines can

    produce multiple pieces in remarkably less time than standard machines. The

    production capacity of a CNC machine depends on its table size and number of cutter

    heads. Opting for an oversized table and five cutter heads can create a dramatic surge in

    production.

    Increased Cutting Accuracy:CNC milling cuts with more accuracy than standard machinery for an obvious reason:

    software programs control it. In addition to increasing design options, these programs

    refine cutting accuracy, creating consistent precision. CNC millers cut with greater

    accuracy than standard ones, producing intricate designs that would be impossible

    otherwise.

    Faster workpiece machining:Since current model CNC machine tools are guarded (splash guards, windows, etc.) in a

    much better manner than most conventional milling tools, users can apply the most

    efficient cutting conditions to attain the best cycle times. Conventional Milling

    machinists tend to nurse-along their machining operations to minimize the chips and

    coolant are constantly thrown from the work area.

    Complexity of work pieces to be machined:CNC machines can generate very complex motions, making it possible to machine

    shapes that cannot be generated on conventional machine tools.

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    Reduced Rework:As a consequence of increased cutting accuracy, CNC milling machine reduce rework,

    helping the production process to maintain fluidity and economy. As with increased

    cutting accuracy, the reason for reduced rework is computer control that eliminateshuman error.

    Reduced Waste:Reduced rework and reduced waste go hand-in-hand. If your company has a high

    production rate, reducing waste pieces can be a valuable cost saving measure. Trash

    cans full of discarded work pieces are not a sign of booming business; they are a sign

    business is conducted ineffectively from a machining standpoint. CNC machining can

    help to change this.

    Easier to Operate:CNC milling machines require training and practice to operate correctly. But once you

    learn the ropes, their operation becomes second nature. Unlike older machines that

    required constant dexterity from their operators, CNC machines allow operators to

    oversee the production process as they manipulate a computer as needed.

    Feedback to production control:Since CNC milling machines have a built-in computer, they can relay information about

    how they're running to other parts of the company using the same network that othercomputers in the company are using.

    Automatic working:When it comes to actually running production (after programming and setup are

    completed), just about every major problem faced by a conventional milling machinist's

    workload has been solved by CNC machine tools. While a conventional milling machinist

    must be involved with everything happening on a conventional machine, once a CNC

    operator loads a workpiece and activates the cycle, the CNC machine takes over,

    completing all tasks a manual machinist normally does. Specific examples include toolchanging, speed, feed, and coolant selection, generating the motion needed to machine

    work pieces (a conventional machinist turns hand-wheels to cause motion), and in some

    cases, even chip removal.

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    Use of designing software:Modern design software allows the designer to simulate the manufacture of his/her

    idea. There is no need to make a prototype or a model. This saves time and money.

    Experimental Calculation to check whether CNC milling isbetter or conventional milling:

    1. CNC:Running cost per hour: Rs. 600/-

    Labour cost: Rs. 30/- per hour

    Tool set up time: 10 mins.

    Machining Time: 4 Hours.

    The total cost of running the CNC for 4 hours is Rs. 2400/-

    Here, in this case the labour cost will be considered for only one hour because the CNC

    is run by a computer program automatically so there is no need of any labour after

    setting up of CNC.

    2. Conventional Milling:

    Running cost per hour: Rs. 100/-

    Labour cost: Rs. 25/- per hour

    Tool set up time: 20 mins.

    Machining Time: 8 Hours.

    The total cost of running the Conventional milling for 8 hours is Rs. 800/-

    In Conventional milling a person is required to run the machine to get the desired

    output. So, the labour cost after 8 hours will be Rs. 800/-.

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    Observations:

    We can observe that the tool set-up time and machining time on CNC is half of that of

    Conventional milling and the total running time of CNC is also half of Conventional

    milling.

    This shows that a lot of time is saved on CNC than Conventional Milling.

    The machining time of CNC is also half of Conventional Milling machine i.e. in CNC two

    jobs can be machined in 8 hours whereas in Conventional Milling machine only one can

    be completed.

    One of the main thing observed was the surface finishing on CNC milling was much

    better than Conventional milling machine.

    Another main thing observed is that the total cost of CNC milling is much higher than

    Conventional milling machine.

    Result:

    Profit earned by the manufacturer is more on CNC and the customers expense is more

    but at the same time the surface finish on CNC is also of high quality and as per

    customers requirement they want to have a good high quality product. So, CNC milling

    is a much better choice than using conventional milling because it will benefit both the

    manufacturer and the customer.

    CNC machining can be a cost efficient process, particularly for high volume production

    runs.

    Conclusion:After doing my Technical Internship at Dynamic Industries, I have understood how the

    moulds are manufactured and the various machines which are used in manufacturing of

    moulds like CNC, EDM etc.

    By comparing CNC and Conventional milling method, I found that the cost of machining

    of CNC is more than the Conventional milling so the manufacturer will earn more by

    using CNC milling machines instead of Conventional milling methods. But the customerwants that the product should be accurate and of a very high quality and this is achieved

    only in CNC milling so the CNC milling will benefit both the customer and manufacturer.

    So, the CNC milling method is much better than Conventional milling method.

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    References:

    http://www.global-plastic-injection-molding.com http://cncmachinetools.org http://www.automationsol.com http://www.ehow.com Malloy, Robert A. (1994). Plastic Part Design for Injection Moulding. Munich

    Vienna New York.

    Hanser.Todd, Robert H.; Allen, Dell K.; Alting, Leo (1994). ManufacturingProcesses Reference Guide. Industrial Press, Inc.

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