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  • INSTITUTE OF TECHNOLOGY, NIRMA UNIVERSITY, AHMEDABAD – 382 481, 08-10 DECEMBER, 2011

    1

    Optimisation: Need of today’s competitive age

    A case study on simulation using AutoCAST

    A. Harshwardhan Pandit, B. Uday Dabade

    A. P.G. student, Department of Mechanical Engineering, Walchand College of Engineering, Sangli.

    B. Asst. Professor, Department of Mechanical Engineering, Walchand College of Engineering, Sangli.

    Abstract-- In today’s competitive age foundries are required

    to be more active, efficient. They need to respond fast. More

    and more competition calls for the fast response to buyer. In

    this quest maintaining quality is also a key issue. In

    particular, one is interested in quantifying the performance

    of a system under study for various values of its input

    parameters. Such quantified measures of performance can be

    very useful in the managerial decision process. The cost

    concerns of the metal casting company focus on the extra

    time and energy spent in changing the setup configurations in

    the manufacturing system. The methods layout of a casting is

    an important activity in tooling development. It involves

    critical decisions regarding part orientation in mold, parting

    line, cores, cavity layout, feeders, feedaids and gating system.

    An improper layout leads to either poor quality or low yield,

    affecting manufacturing costs and productivity. The objective

    is to design the methoding system and optimize it.

    Optimisation can be achieved with various techniques. In this

    paper optimisation of methoding parameters with the help of

    simulation is discussed and it is tried to minimize efforts and

    avoid conventional trial and error practice. The simulation

    model is built to assess the methoding parameters.

    Index words—Casting, simulation, optmisation,

    I. INTRODUCTION

    n a business and manufacturing environment, most of

    the organisations optimize their production schedules

    and flow lines in order to meet the customer demands. The

    main objective is to satisfy customer demands with

    minimum production cost. In the competitive business

    environment today, many industries focus attention

    especially on rapidity for responding to their customers’

    needs. For this reason, continuous improvements are

    needed to increase response times to customer changes.

    Methods design is usually carried out manually on the part

    to be cast. The tooling is then fabricated; trial castings are

    produced in the foundry in small batches, and inspected. If

    these castings contain defects, then the methoding is

    modified and the process is repeated. Each such iteration

    can take up several days which delays delivery schedule,

    lead time and hence the customer is dissatisfied. After a

    few iterations, the foundry may find the best alternative for

    the methoding which may help to solve the problems

    stated earlier. It may also help to increase yield, reduce the

    rejection rates. This is especially true in the case of large

    castings, where the cost of a trial or repair can be too

    excessive. Casting simulation can take care of the above

    problems as the virtual trials do not involve wastage of

    material, energy and labor, and do not hold up regular

    production.

    In this process of simulation we first create the solid model

    of casting and then a suitable methoding is generated by

    iterations using software. However, most of the simulation

    programs available today are not easy to use. They may

    take longer times depending upon the user expertise

    available and their accuracy is affected by material

    properties and boundary conditions specified by users. The

    problem is the preparation of 3D model of the casting

    along with mold, cores, feeders, gating, etc., which

    requires CAD skills and takes considerable time for even

    simple parts. Methoding is an important task in casting

    production, directly affecting casting quality and yield. It

    involves several decisions, such as the size of mold box

    and number of cavities, orientation of casting in the mold,

    location of the parting line, design of core prints, and the

    location, shape and size of feeders and gating elements.

    The methoding is validated and improved through several

    iterations of design, pattern modification, trial production

    and inspection. The goal is to consistently produce castings

    with zero internal defects (such as shrinkage porosity,

    inclusions, blowholes, cold shuts and inadequate

    mechanical properties), while ensuring the maximum

    possible yield.

    I

  • INTERNATIONAL CONFERENCE ON CURRENT TRENDS IN TECHNOLOGY, ‘NUiCONE – 2011’

    2

    Fig.1. Optmisation in foundry at various stages [1]

    For achieving an end, some means is required. If casting is

    an end, gating can be considered as a means. An efficient

    and effective means is a prerequisite to achieve a

    satisfactory and desired level of end in good manner.

    Gating:

    Various parts of gating system like sprue, runner etc., have

    some specific purpose. Sprue is required for facilitating the

    pouring operation. Metal has to be transferred from ladle

    to casting at sufficient pressure without causing it to

    freeze. Sprue serves as a means to create the pressure in

    the system. Without sprue head, travel to casting shall not

    be at required pressure. Runner helps in transferring the

    pressure from sprue through the mould up to the casting

    like a conductor in electrical system. Finally, ingates are

    required to pass on the metal to the casting which act as a

    connectors. Choke in gating system acts like a current

    limiter. Gating should ensure that metal reaches the

    remotest portion of the casting. For this, it shall be

    necessary to have large enough sizes of runner bars

    carrying the metal to the inaccessible portion of the

    casting. At times, some special method shall be required to

    reach the casting. It is very much required that all the

    portions of the casting be filled nearly simultaneously.

    Here, proportioning of gating system plays a role. A long

    casting may require several ingates along the length.

    Streamlining of the gating components helps in ensuring

    smooth flow.

    Risering:

    Riser acts like a reservoir or UPS. When power fails UPS

    starts its function. Similarly, after pouring stops, risers

    keep on feeding the liquid metal to the casting. It is very

    important to have proper connections between riser and

    casting. Otherwise, feeding shall not be effective.

    II. NEED FOR OPTIMISATION

    Optimisation is the process of finding the best way of

    using your resources, at the same time not violating any of

    the constraints that are imposed. By "best" we usually

    mean highest profit, or lowest cost. Even after spending

    significant resources i.e. man-hours, materials, machine

    overheads and energy etc for casting development, one of

    the following situations may arise during regular

    production [2]:

    (a) Under design: resulting in high percentage of defective

    castings. This usually happens when the number or size of

    feeders and gating elements are inadequate, or their

    placement is incorrect. Sometimes the cause is an

    undersized neck or a thin intermediate casting section,

    which prevents feed metal flow from the feeder to the hot

    spot inside the casting.

    (b) Over design: leading to acceptable quality level, but

    poor yield and thereby higher cost. In this case, the number

    and/or size of feeders and gating elements are much higher

    than their respective optimal values. This situation usually

    arises because of lack of time or resources to fine-tune the

    methoding solution or to try other alternative solutions.

    (c) Borderline design: irregular defect levels during

    regular production, although sample castings are defect-

    free. This happens when the methoding solution is just

    optimal (perhaps by accident), which will produce good

    castings only under controlled conditions. This is difficult

    to expect in practice, especially with manual molding and

    pouring.

    Foundries try to reduce rejections by experimenting with

    process parameters (like alloy composition, mold coating,

    and pouring temperature). When these measures are

    ineffective, then methods design (gating and feeding) is

    modified. When even this is not effective, then tooling

    design (part orientation, parting line, cores and cavity

    layout) is modified. The effect of any change in tooling,

    methods or process parameters is ascertained by pouring

    and inspecti