Title: Computer aided design and analysis of the sprue system of an injection mould for optical data storag
1Computer 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
2Introduction
- 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.
3Definition 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.
4The 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.
53D 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).
8Fig. 1. Flow chart of the investigation scheme.
9Fig. 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.
10Fig. 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.
11Mould 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 ?.
13Table 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 ?.
15Fig. 6. Mould filling simulation Modified sprue
system gate depth d 0. 40 mm ?melt 3200 ?,
?mould 1200 ?.
16Conclusions
- 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.