bdd 40903 injection mold design chapter 1.pdf
TRANSCRIPT
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BDD 4 9 3
INJECTION MOLDDESIGN
BDD 40903 Prepared by : Mohd Hilmi Othman
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CHAPTER 1
Introduction(2 hours)
Injection molding concept
Mold structure and components
Mold type
Mold material
Surface treatment
Mold development processType and classification of plastic materials
Melting and solidification
Shrinkage
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Advantages:
Short production cycle Achievable accuracy
Highly efficient production
Producing large variety
Extreme tolerances
Intricate shapes.
Good strength-to-weight ratio,
Good appearance and surface
definition
Good in quality control.
1. Groover, M.P.Fundamentals of Modern Manufacturing: Materials, Process, and System.3rd Ed. Asia: John & Wiley Sons, Pte Ltd, 2007.
2. Osswald, T.A. Turng, L.S. Gramann, P.Injection Molding Handbook. 2nd Ed. Hanser Verlag Publications. 2007.
Injection molding concept
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BDD 40903 Prepared by : Mohd Hilmi Othman
Injection molding concept (2)
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Injection molding concept (3)
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Injection
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Injection molding concept (4)
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Mold structure and components
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Mold structure and components (
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Mold type
Standard Molds
The standard mold is the most simple d
divided in two side :
a) Cavity side
Cavity side is the side that construct to
material from nozzle to cavity parts, basic
of sprue, runner.
b) Core side
Core side construct to make shape for c
system and ejection system, at this sid
system will be designed.
Standard mold have one parting line,
opening direction. This type of mold us
plastic parts that doesn't have undercut,
screw.
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http://bp1.blogger.com/_oF_1Qcfku_w/R2xigNC7BEI/AAAAAAAAAV8/7AApHY-BIbg/s1600-h/standard-2-plate-mold.jpghttp://bp1.blogger.com/_oF_1Qcfku_w/R2xigNC7BEI/AAAAAAAAAV8/7AApHY-BIbg/s1600-h/standard-2-plate-mold.jpg -
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Slide mold
Development from this mold type is the used slider parts in various molds types; basic sli
horizontal movement of mold to vertical movement, this types of molds is used to
undercut.
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Mold type (2)
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Three plate mold
Basically three plate molds has two p
floating plate, whereby the floating pla
by support pin. Since the mold has tw
the runner system can be located on on
plate or by making a special plate that
plate, known as runner plate. Three
used because of their flexibility in gati
types of molds is flexible even use in m
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Mold type (3)
http://bp2.blogger.com/_oF_1Qcfku_w/R2xxRdC7BGI/AAAAAAAAAWM/rDA-ApWqEp4/s1600-h/3plate.jpghttp://bp2.blogger.com/_oF_1Qcfku_w/R2xxRdC7BGI/AAAAAAAAAWM/rDA-ApWqEp4/s1600-h/3plate.jpg -
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Split Cavity Mold
Basically the split cavity is same as
mold, but the cavity have split block tproduct or external threads. This type
when the slider is not enough to make
the threads. the disadvantages of this m
for little parts, the construction will diff
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Mold type (4)
http://bp3.blogger.com/_oF_1Qcfku_w/R2zVhtC7BHI/AAAAAAAAAWU/EhBk6H2Fe9w/s1600-h/split-cavity.jpghttp://bp3.blogger.com/_oF_1Qcfku_w/R2zVhtC7BHI/AAAAAAAAAWU/EhBk6H2Fe9w/s1600-h/split-cavity.jpg -
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Mold Material
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The plastic part is when a plastic material is
heated until it becomes soft enough to be injected
into a closed mold.
The finished part is ejected out once it has cooled
enough to solidify and is completely formed.
It is possible to create a part with intricate
features, although the more complex the part the
more complex the mold, and ultimately more
expensive it is.
There are six materials that are commonly used
for creating mold, which are Aluminum, Copper
Alloy, Plaster, Polymers, Steel and Wood.
i ( )
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Mold Material (2)
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How Material Selection Effects Mold DesignOne aspect to consider is that each material has its own specific shrinkage factors. Eve
exception of water expands when it is heated and contracts when it is cooled. In inj
contraction was labeled as the materials shrinkage. The shrinkage factor of the ma
account when designing the cavity of the mold so that when the part contracts it will
dimensional requirements of the original design.
Some materials dissipate heat differently than others, which can result in variation i
during the molding process. This has a big impact on how the water cooling lines are p
ensure even cooling.
Another related factor is the viscosity of the material. Viscosity is the measurement of
material in its liquid form. Higher viscosity means thicker material, and greater injection
through the mold. Also these materials require larger diameter in the runners and gates t
to flow easily into the cavity. The melt index is a good tool in determining the flowab
plastic.
M ld M i l (3)
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Mold Material (3)
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http://injectionmold.cc/mold-design-and-manufacturing-process
Mold design and manufacturing processStudies have shown that life of the mold depends on heat
treatment, material selection, construction, machiningand
many other factors.
Based on the statistical analysis of a large number of failures
mold, the failure of mold design due to improper heat
treatment accounts is about 45%, selection and mold structure
is irrational about 25%, about 10% of process problems, and
lubricants and equipment questions about 20%. Therefore, in
the mold design and manufacturing process, material
selection, mold structure, heat treatment, machining processes
and improve working conditions for mold can improve the
quality and service life.
Improper heat
Selectio
Lu
Failure of m
M ld M t i l (4)
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Mold Material (4)
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The rational use of mold material Selection of mold material, should be selected according to different
production batches and process methods.
In mass production, the mold should be used durable materials, such as
cemented carbide, high toughness & high wear-resistant tool steel.
For small quantities or new product trial can be zinc alloy, bismuth-tin
alloy.
As mold material it should be easily deformed, easy to fracture failure
common mold, the need to use high-strength, high toughness material;
good toughness, and strength.
Die-casting mold was good to adopt high thermal fatigue resistance, high
temperature strength alloy steel.
Plastic mold should be chosen for easy cutting, dense, and good polished
performance material.
In addition, by using different hardness or different materials for matched
mold, a mold life can be increased by 5 to 6 times. b
M ld M t i l (5)
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Mold Material (5)
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The mold heat treatment process From the die failure analysis, it shows that 45% of die failure is due to
improper heat treatment.
Abrasion usually occurred at the surface. Fatigue and fracture often startfrom the surface, so the surface processing quality requirements are very
high.
But in fact due to the presence of traces of machining, surface oxidation and
decarbonization of inevitable heat treatment, the surface properties of the
mold was worse than the substrate.
Adoption of new technology heat treatment is an effective measure to
improve mold performance. Mold heat treatment process includes a substrate and a surface hardening
treatment toughening.
The main purpose is to strengthen the surface of the mold surface, by
improving the wear resistance, corrosion resistance, and lubricating
properties.
M ld M t i l (6)
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Mold Material (6)
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Mold machining process Mold machining process directly affects the quality of life of the
mold and products.
Complex structure and the process requires special tooling, new
processing methods. Due to the variety of shapes and molds, with
high precision dimension, therefore the needs of additional process
such as EDM, WEDM and precision grinders was required.
Therefore, a special die EDM has been developing rapidly. This
method does not require the tool material and application of
mechanical forces in the process, but the direct use of electrical,
chemical, light and sound on the work piece can be processed to
achieve the shape and size and the surface roughness of the request.
Practice has proved that with the right process, the surface
roughness improvement had doubled the die life span, increased by
50%, which is particularly important for the plastic mold.
Electr
Mac
S f T t t
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Surface Treatment
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Why strive for a high surface finish?
The increased use of plastic products has created a
higher demand for mirror finish of molding tools. The
highest demands for surface finish are in the optical
lens mold whereby an extreme requirement on
polishability is desired.
However, in general there are other advantages for
high surface finish, including:
a) Easier ejection of the plastic parts from the
molding tool
b) Reduced risk of local corrosion
c) Reduced risk of fracture or cracking due to
temporary overloading or pure fatigue.
www.acerosuddeholm.com/spanish/files/polishing-english.pdf
S f T t t (2)
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BDD 40903 Prepared by : Mohd Hilmi Othman
Judging surface finish Two things are important when judging the surface of the
mold:
a) The surface must first have a geometrically correctshape without any long macro waves.
b) Secondly, the mirror finish of the mold surface must be
free from scratches, pores, orange peel, pitting (pin-
holes) etc.
The surface finish is normally judged by the naked eye. There
are certain difficulties involved in such a visual evaluation. A
flatsurface can look perfect despite the fact that it is notgeometrically completely flat. Thus, the eye can be fooled.
In more sophisticated cases, the finish can be judged by
instrumental methods, such as optical interference techniques.
Surface Treatment (2)
Optical I nterf e
S f T t t (3)
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Factors which affect polishability
The surface smoothness which can be achieved by
polishing steel depends on factors such as:
a) Tool steel quality
b) Heat treatment
c) Polishing technique.
In general, it can be stated that polishing technique is the
most important factor.
If a suitable polishing technique is used, it is almost
possible to achieve acceptable results, providing the
correct heat treatment and the good quality tool steel is
used.
However, if an unsuitable technique is used, even the best
steels can be ruined.
Surface Treatment (3)
Rating of hardness and
Mold Development Process
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Mold Development Process
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Initial
Design
Review part design
and specifications
Develop preliminary
mold design and
quote
Feed System Design
Structural System
Design
Ejector System
Design
Cooling System
Design
Machining, Polishing,
Assembly and Trials
Moldings
OK?
Source: David O. Kazmer,Injection Mold DesignEngineering, Carl Hanser Verlag, 2007.
Type and classification of plastic mate
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Type and classification of plastic mate
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Polymers
All plastics are polymers, but not all polymers are plastics.
The simplified diagram below shows the relationship between monomers and polymers.
Identical monomers can combine with each other to form homopolymer, which cbranched chains.
Different monomers may combine together to form copolymers, which also may be bran
Type and classification of plastic materi
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Type and classification of plastic materi
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The chemical properties of a polymer depends on:
The type of monomer or monomers that make up the polymer. The
chemical properties of homopolymer 1 are different from those of
homopolymer 2 or the copolymers. The arrangement of monomers within the polymer. The chemical
properties of the straight polymers are different from those of the
branched polymers
The monomers that are found in many plastics include organic compounds
like ethylene, propylene, styrene, phenol, formaldehyde, ethylene glycol,
vinyl chloride and acetonitrile.
Because there are so many different monomers that can combine in many
different ways, it can make many kinds of plastics.
Type and classification of plastic materi
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Type and classification of plastic materi
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Two types of plastic are thermoplastic and
thermosetting.
For thermoplastics the chemical structure remainsunchanged during heating and shaping. It can be
reused after re-melting.
Examples of Thermoplastics
Acrylonitrile butadiene styreneABS
Polycarbonate - PC
Polyethylene - PEPolyethylene terephthalate - PET
Poly(vinyl chloride) - PVC
Poly(methyl methacrylate) - PMMA
Polypropylene - PP
Polystyrene - PS
Expanded PolystyreneEPS
Type and classification of plastic materi
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Type and classification of plastic materi
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For thermosets, it will undergo a curing process
during heating and shaping, causing a permanent
change (cross-linking) in molecular structure. Once
cured, they cannot be re-melted.
Examples of Thermosets
Epoxide (EP)
Phenol-formaldehyde (PF)
Polyurethane (PUR)
Polytetrafluoroethylene - PTFE
Unsaturated polyester resins (UP)
Melting and solidification
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Melting and solidification
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Melting and solidification are the two phenomena that
frequently occur in nature and in many technological
processes. Good examples of the phenomena that occur in
nature are ice melting and water freezing, ground freezing(the uppermost surface layer), solidification of vulcanic
lava and the melting processes that evolve deep under the
earth surface. Examples of the phenomena that occur in
many technological processes are the freezing and thawing
of food products, casting, production of plastic products,
welding, electrolytic machining and thermal energy
accumulators, which make use of the metal or wax meltingor freezing phenomena. In the cases when pure metals, ice
or eutectic alloys undergo a phase change, one can observe
a clear cut line between a liquid and a solid and a definite
melting point tm
Melting and solidification (2)
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Short question
What is the difference between liquid and fluid?
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Melting and solidification (2)
Melting and solidification (3)
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Polymer Melts
To shape a thermoplastic polymer it must beheated so that it softens to the consistency of
a liquid
In this form, it is called apolymer melt
Important properties of polymer melts:
Viscosity
Viscoelasticity
Melting and solidification (3)
Polymer meltis forced to flow
Polymer meltspinning
Melting and solidification (4)
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Viscosity of Polymer Melts
Fluid property that relatesshear stress to shear rateduring flow
Due to its high molecular weight, apolymer melt is athick fluid with high viscosity
Most polymer shaping processes involve flow throughsmall channels or die openings
Flow rates are often large, leading to high shear ratesand shear stresses, so significant pressures are
required to accomplish the processes. Viscosity of a polymer melt decreases with shear rate,
thus the fluid becomes thinner at higher shear rates
Melting and solidification (4)
Viscosity relationships fotypical polym
Melting and solidification (5)
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Viscosity and Temperature
Viscosity decreases with temperature, thus thethinner at highertemperatures fluid becomes
Viscoelasticity
It is the property of a material that determines thestrain it experiences when subjected to combinationof stress and strain
Possessed by both polymer solids and polymer melts
Example: die swell in extrusion, in which the hotplastic expands when exiting the die opening
Melting and solidification (5)
Viscosity as a function of temselected polymers at a shear r
Shrinkage
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Shrinkage
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When plastic material is injected into a cavity, it starts to
cool down, whereby its volume decreases. A measure for
this volume decrease is given by the difference between
melt density and solid density. As cooling rates in thecavity are very high and non-uniform, the frozen material
will also incorporate internal stresses. These stresses may
relieve after ejection from the cavity, which process can be
accelerated by keeping the part at elevated temperatures.
Shrinkage can be defined by the following formula:
S = (D - d) / D ( 100%).
D = dimension of mould cavity.
d = dimension of moulded part.Mold shrinkage percen
type of ma
Shrinkage (2)
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BDD 40903 Prepared by : Mohd Hilmi Othman
Shrinkageto be distinguished are:
shrinkage in flow direction ;
shrinkage normal to flow;
shrinkage in thickness direction.
The sum of these three shrinkages must be equal to the volumetric
shrinkage of a material, which can be obtained from the difference
between melt density and solid density, or from pVT-diagrams.
Besides on material, shrinkage is further dependent on processing
conditions, (such as injection-speed, hold-pressure, hold-pressure time,
runner/gate-dimensions and mold temperature), on part shape, (during
injection the flow-direction may change) and part thickness, (thicker
parts have usually a thicker central layer with less orientation). The
shrinkage contribution caused by stress relieve after ejection from the
mould is called Post Mold Shrinkage.
g ( )
3 Dimens
Shrinkage (3)
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Shrinkage Factors
g ( )
Fillers in the plastictend to reduce shrinkage
Injection pressure higher pressures force more material
into mold cavity to reduce shrinkage
Compaction time- similar effect
longer time forces morematerial into cavity to reduce shrinkage
Molding temperature- higher temperatures lower polymer
melt viscosity, allowing more material to be packed into
mold to reduce shrinkage.