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Computer aided design and analysis of the sprue system of an injection mould for optical data storag

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Title: Computer aided design and analysis of the sprue system of an injection mould for optical data storag


1
Computer aided design and analysis of the sprue
system of an injection mould for optical data
storage replication
  • D. S. Trifonova, Y.E. Toshevb
  • a.Institute of Information Technology, Bulgarian
    Academy of Sciences, 1113 Sofia, Bulgaria
  • b.Institute of Mechanics and Biomechanics,
    Bulgarian Academy of Sciences, 1113 Sofia,
    Bulgaria4M Partner No 28 BAS, Bulgarian Academy
    of Sciences

2
Introduction
  • Optical disc moulding
  • The experience gained up to now in injection
    moulding of optical disc substrates has shown
    that the mould occupies a central place and is
    the most significant part in the production
    process.
  • The obtaining of the geometrically simple
    substrate, being a circular washer with width of
    1,2 mm, diameter of the central hole 15 mm and
    external diameter varying from 120 mm up to 300
    mm, together with the necessity for precise
    copying of the information structure, the
    accuracy of the geometric dimensions and the low
    level of birefringence, imply high requirements
    towards the mould connected with precise
    construction and tolerances of the order of
    microns.

3
Definition of the technical problem in the
optical disc moulding
  • A statement of the problem for optical disc
    moulding starts with the fundamental difficulty
    of filling and packing a mould cavity of much
    greater length than depth, without incurring high
    levels of moulded-in stress and orientation.
  • The approach applied up to now in solving the
    problem of cavity filling and formation of the
    central hole substrate has not declined from the
    basic method - filling through a thin film circle
    gate located at the place, where the central hole
    is to be formed. This requires the use of a
    complex and precise cropping punch system,
    removing the circle gate, in order to form the
    central hole.

4
The purpose of the paper
  • To develop 3D CAD models of two basic types of
    the sprue system and to provide a primary
    investigation to determine a range of gate size
    parameters and correct gate location towards
    central hole thickness, so that an easy mould
    cavity filling is to be attained, using the
    developed 3D CAD models and computer simulation
    techniques.

5
3D CAD models of the the sprue system
  • A flow chart of the stages, necessary for the
    purpose of the present work is developed (see
    Fig. 1)
  • Two basic types of the sprue system design of an
    optical disc mould are considered.
  • The first type of the sprue system design
    concept is based on a well-known type of the type
    of a sprue system, in which the central hole of
    the polymer substrate is formed by breaking off
    the circle gate from the polymer substrate (see
    Fig. 2).

6
  • The other type of the sprue system is known as a
    system, in which the central hole of the polymer
    substrate is formed by direct punching of the
    central gate from the polymer substrate using a
    punch bush, which is moved against the air supply
    bush (see Fig. 3 and Fig. 4).
  • A modified sprue system design is realized. The
    central hole is formed by moving ? bending bush
    and a punch bush in a direction, opposite to the
    sprue bush. The central gate is bent and at this
    moment the punch bush splits the gate from the
    polymer substrate. This gives a possibility to
    change the gate position towards the central hole
    (see Fig. 5).

7
  • The 3D CAD models of the sprue systems are built
    on the base of an integrated 3D CAD model of the
    sprue system and the polymer substrate,
    considered as one object. All of the considered
    above sprue systems consist of a central sprue,
    melt distribution area and a circle gate (see
    Fig. 2).
  • All the experiments are carried out in the case
    when the polymer substrate outer diameter is
    equal to 120. 20 mm and the polymer substrate
    thickness is 1. 30 mm. The gate depth and the
    position of the gate towards the central hole
    thickness are chosen as variable parameters (see
    Fig. 2, Fig. 4 and Fig. 5).

8
Fig. 1. Flow chart of the investigation scheme.
9
Fig. 3. A Sprue system with direct punching of
the central gate.
  • Fig. 2. Section - view of the first type of the
    sprue system.

Fig. 3. Section - view of the first type of the
sprue system.
Fig. 3. Section - view of the first type of the
sprue system.
10
Fig. 4. 3D CAD Model of the sprue system with
direct punching of the central gate.
Fig. 5. 3D CAD Model of the Modified Sprue
System.
11
Mould filling simulation and results
  • For a primary verification of the advantages of
    the 3D CAD models, a mould filling simulation
    program MoldflowXpress (integrated with
    SolidWorks) is used.
  • A polycarbonate plastic material Makrolon (PC) of
    the BAYER AG supplier is used. A PC Intel Pentium
    processor (2.7 GHz) with 1200 MB DDRAM is used.
  • A number of simulations of the two types of the
    gate system at values of the gate depth equal to
    0.20 - 0.40 mm at intervals of 0.10 mm and at
    different positions of the gate towards the
    central hole thickness are provided.
  • The parameters selected in three variants of the
    processing conditions are combined (a) ?melt
    2800 ? ?mould 800? (b) ?melt 3000 ? ?mould
    1000 ? (c) ?melt 3200 ? ?mould 1200 ?. In
    many cases the results show that the mould cavity
    filling process is not sufficiently good at the
    parameters above given.

12
  • The main significant results of our investigation
    are shown below (Table 1).
  • The results of the experiments with the sprue
    system, in which the central hole is formed
    breaking off the circle gate show, that it is
    easy to fill the mould cavity, when the gate size
    is equal to d 0.29 0.31 mm and d 0.37
    0.40 mm only in the case, when ? melt 3200 ?
    and ? mould 1200 ?.
  • The results of the experiments with the sprue
    system, in which the central hole is formed by
    direct punching of the circle gate show, that it
    is easy to fill the mould cavity, when the gate
    depth is equal to d 0.28 0.31 mm in the
    cases (b) ?melt 3000 ? ?mould 1000 ? and
    (c) ?melt 3200 ? ?mould 1200 ?.

13
Table 1. Mould Filling Simulation Results
14
  • The results of the experiments with the modified
    sprue system show, that it is easy to fill the
    mould cavity, when the gate depth is equal to d
    0.20 0.30 mm in the cases (b) ? melt 3000 ?
    ? mould 1000? and (c) ? melt 3200 ? ? mould
    1200 ?.
  • Only for example a plot view of the mould filing
    simulation is shown (see Fig. 6).
  • The best results are obtained with modified sprue
    system, when the gate depth is equal to d 0.31
    - 0.40 mm at all of the processing parameters
    (a) ? melt 2800 ? ? mould 800? (b) ? melt
    3000 ? ?mould 1000 ? (c) ?melt 3200 ? ?
    mould 1200 ?.

15
Fig. 6. Mould filling simulation Modified sprue
system gate depth d 0. 40 mm ?melt 3200 ?,
?mould 1200 ?.
16
Conclusions
  • 3D CAD models of two basic types of the sprue
    system of an optical disc mould are developed.
  • The first type of the sprue system is known as a
    system, in which the central hole of the polymer
    substrate is formed by breaking off the circle
    gate from the polymer substrate.
  • The other type of the sprue system is known as a
    system, in which the central hole of the polymer
    substrate is formed by direct punching of the
    gate from the polymer substrate.

17
  • On the bases of a previous authors punch system
    design, a modified sprue system design is
    realized.
  • The modified system gives a possibility to change
    the gate position towards the central hole.
  • The gate depth and the gate location towards
    central hole thickness are defined as variable
    parameters and are combined with different
    variants of the processing conditions.

18
  • By means of the simulation program
    MoldflowXpress, a range of values of the gate
    size for all of the given above sprue system are
    obtained, in which an easy mould cavity filling
    is achieved.
  • The best results are obtained, using the modified
    sprue system, when the gate is symmetrically
    located towards central hole thickness.
  • The approach presented can be used as a ground
    for future development of the mould filling
    simulation, oriented towards more precise
    determination of the resulting injection
    pressure, the residual stresses distribution and
    the temperature distribution.
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