plastic report 02-02-2012
TRANSCRIPT
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POLITECNICO DI TORINO AUTOMOTIVE ENGINEERING
ENGINE VALVE COVER FOR A
V4 ENGINE BY INJECTION
MOLDINGPRODUCTION TECHNOLOGIES FOR BODYCOMPONENTS
GROUP 10
Zeyd Okutan - 172754
Sinan Sevgin Remzi 173061
Antoni Fernandez Mas
170390
Cem Bugra Evci
Bojun Wang
Academic Year 2011 - 2012
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INDEX
1. INTRODUCTION ......................................................... ................................................................. ............ 3
2. PART SELECTION AND ANALYSIS ................................................................. .................................. 4
a. Description of the Part .............................................................. ....................................................... 4
b. Drawings ........................................................ ................................................................. ....................... 4
c. Part Orientation & Mold Parting Plane ............................................................... ....................... 6
d. Part Thickness & Undercut ................................................................ ............................................. 8
3. MOLD DESIGN AND SIMULATION ................................................................. .................................. 8a. Plastic Material Selection ......................................................... ....................................................... 9
b. Molding Parameters Selection ......................................................... .......................................... 11
c. Simulation Results ........................................................... ... Error! Bookmark not defined.
d. Mold Feeding System Design ............................................................ .......................................... 18
e. Augmentation in Mold Design and Parameters .......................................................... ......... 20
f. New Simulation Results ............................................................ .................................................... 21
g. Resume of Optimized Design ............................................................ .......................................... 224. CONCLUSIONS ............................................................. ................................................................. ......... 22
a. VISI Flow Software ........................................................... ............................................................... 22
b. Problems of Design Process .............................................................. .......................................... 22
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1.INTRODUCTIONIn this case study, there is the design and the production process of a plastic part which
is used in real time applications of a V4 engine. This part has the purpose of covering the
valve system. Valve covers are generally produced with various plastic production
technologies, as plastic injection molding, which is the process chosen for this project.
Furthermore, for the production of engine valve covers, various materials and
composites are used in the industry. Depending on the design, costs and production
technologies, very different types of solutions can be chosen.
In this project, the design of the component is done with Solidworks 2010, which is one
of the CAD program available to make different amendments and improvements on the
model.
After the proper design, the model is analyzed in Visi 19, this CAE software allows the
simulation of the plastic injection molding process. After the simulations and analysis,
the quality of the injection, the process conditions, material type and design are
discussed as conclusion.
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2.PART SELECTION AND ANALYSISa. Description of the PartV4Valve Engine Cover
Valve cover parts are generally designed to protect the valves and engine system. They
provide the valve gaskets, oil cap and some more mounting hardware. It is very
important to have a easy-removal ability. This component must ensure a perfect
isolation from the external ambient avoiding the contamination of the lubricant, as the
oil is pumped up through the pushrods and dispersed underneath in order to lubricate
the various engine parts. Beside from this, the valve also protects the various valve train
components, particularly the valves and the rocker arms. The tightening of seals and
cylinder head are important also providing easy access and each time that the valve
cover is removed; however, there is a need to replace the valve cover gasket with a new
one.
Picture I
1: A Plastic Twin Valve Cover produced by Nissan 2: Another Plastic Valve Cover for V4 engine 3: YamahaVMAX V4 Engine 4:Motus Katech KMV4 engine
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b. Drawings2D Drawings
Picture II
2D & 3D Drawing of General View of the Part
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2D Critical Section Views
c. Part Orientation & Mold Parting Plane
Picture III
Critical Section Views of the Model:
Section A has the maximum
thickness of 14mm material and
Section-B has 11mm.
The piece present one undercut
section. This could be solved with a
lifter. As no specific requirements
are request to that region, it could
be cancelled simplifying the molds
lay up, and hence the overall cost
of the molds is reduced.
The design has been realized in
order to avoid this area. The
modification doesnt affect on the
piece function. The new piece
design is shown on parting line
section, where no undercuts arepresent.
UNDERCUT
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The mold design is divided in two parts male and female parts. The male part
corresponds to the movable plate coming from the top, enclosing the piece geometry
with the female. The movable plate will shape the inner part of the valve cover, so no
aesthetical requirements are request. The fixed plate draws the external aesthetic part
of the piece, as the valve cover normally present a rough surface, a embossing treatmentto the fixed plate must be performed. The parting plane corresponds to the inner surface
and the contact surface of the piece.
Picture IV Parting line
Now its possible to notice that no undercuts are present on the piece.
Picture IV Contacting surface
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d. Part Thickness & UndercutWith the new design of the piece, no undercut are present and the part orientation is
quite smooth. The movable plate comes from top to the bottom side of the part. As the
fillers are on the sides, there is no undercut appears in the filling system design.
The designed part has some variable thickness values for different sections. (Shown
above picture III). The thickness values are changing between 5 mm to 24 mm. The
maximum thickness is designed as 24 mm on one section. It could cause shrinkage and
sink marks during cooling.
e. Analysis of Part Extraction and DraftingTo ensure a good quality piece, a draft angle of 0.5 has been adopted for all the parallel
surfaces to the movement direction. It will ensure an easy removal and no superficial
defects on the piece. The corner radius of the model are compressed between 0.9 6
mm to avoid sharp angles on the piece surface.
Picture VI Filled Sections of the PartPart extraction will be made by the several number of pins constructed on the male part.
When the molds are separated, the ejector retainer plain pushes the ejectors to the inner
part of the piece, so no witness marks will appear on the piece aesthetical surface.
3.MOLD DESIGN AND SIMULATION
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a. Plastic Material SelectionThe mechanical requests for an engine valve cover are high, as it must be stiff enough to
support the vibrations and loads transmitted by the engine block, and must present a
high thermal stability, as it will be in contact with the warm oil for the valve lubrication
and heat release of the mechanical parts of the engine. Those requirements restricts thematerial selection. Its important to have a polymer with high mechanical properties
with a high service temperature maintaining a reasonable price for the mass production.
Nowadays for the high production of vehicles on automotive field the thermoplastic PP
is spread used because of its price and aesthetics performance, is specially used on
dashboards and interior plastics. When mechanical performance are request, PP doesnt
match the requirements of design. For that reason is usually reinforced with short glass
fibers but it decreases the aesthetics of the piece and is not used for visible parts. To
overpass this problem ABS polymer is used.
The PA6 polymer appear as the best solution for the engine cover. It has better
mechanical properties than the ABS and presents a better thermal properties with a
similar price.
MECHANICAL CHARACTERISTICS
PROPERTIES PA6 Unfilled PP ABS
Density (g/m3) 1.15 - 1.17 0.89 - 0.90 1.04 - 1.07
Young's Modulus (GPa) 3.36 - 3.53 0.89 - 1.24 2.21 - 2.62
Tensile Strenght (MPa) 82.1 - 90.5 27.6 - 37.9 42 - 46
Elongation at break(%) 20 - 45 200 - 500 15.26 - 20.86THERMAL AND PROCESSING PROPERTIES
PROPERTIES PA6 Unfilled PP ABS
Glass temperature (C) 44 - 56 -10 100 - 110
Melting Point (C) 227 - 238 150 - 175 210 - 220
Service Temperature (C) - 70 - 105 -10 - 105 -20 - 80
Viscosity (Shear Rate 1000 1/s)
(Pas)82 (270C) 116 (260C) 170 (240C)
Transition Range Temperature
(C)165 - 175 175 - 186 157 - 167
No - Flow Temperature (C) 165 165 157
Ejection Temperature (C) 145 145 137
MANUFACTURING PROPERTIES
PROPERTIES PA6 Unfilled PP ABS
Prize (/kg) 2.78 - 3.06 0.94 - 1.02 2.33 - 2.57
Production Energy (MJ/kg) 99.4 - 110 77.3 - 85,4 95.4 - 105
Recycle Fraction 0.45 - 0.55 0.45 - 0.55 0.45 - 0.55
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To ensure the mechanical properties of the piece, glass fiber reinforcement is advisable.
The problem by adding short fibers is reflect with an increase of the viscosity during the
manufacturing process, which means an increase of the process cost because higher
pressures and stiffer molds are needed.
MECHANICAL CHARACTERISTICS
PROPERTIES PA6 Unfilled PA6GF10 PA6GF30
Density (g/m3) 1.15 - 1.17 1.22 - 1.24 1.35 - 1.42
Young's Modulus (GPa) 3.36 - 3.53 5.37 - 5.64 8. 62 - 11
Tensile Strenght (MPa) 82.1 - 90.5 124 - 137 165 - 190
Elongation at break(%) 20 - 45 3.26 - 3.76 2.2 - 3.6
THERMAL AND PROCESSING PROPERTIES
PROPERTIES PA6 Unfilled PA6GF10 PA6GF30
Glass temperature (C) 44 - 56 44 - 56 44- 56
Melting Point (C) 227 - 238 210 - 230 210 - 220Viscosity (Shear Rate 1000 1/s)
(Pas)82 (270C) 116 (260C) 203 (270C)
Transition Range Temperature
(C)165 - 175 175 - 186 157 - 167
No - Flow Temperature (C) 165 165 157
Ejection Temperature (C) 145 145 137
MANUFACTURING PROPERTIES
PROPERTIES PA6 Unfilled PA6GF10 PA6GF30
Prize (/kg) 2.78 - 3.06 2.97 - 3.27 3.08 - 3.40
Production Energy (MJ/kg) 99.4 - 110 109 - 121 109 - 121
Recycle Fraction 0.45 - 0.55 0.09 - 0.11 0.09 - 0.11
On the previous table its possible to see the influence of the percentage of the glass fiber
reinforcement on the mechanical and thermal and processing properties. By increasing
the percentage of fibers, the mechanical properties increases and the viscosity increases.
Its also interesting see how the melting point decreases by increasing the rate of
reinforcement, it is because the percentage of PA6 decreases and less temperature is
needed to melt the polymer.
Its importing to highlight that the glass fiber reinforcement also decreases the
shrinkage of the piece during cooling, which is a really advantageous point, especially for
the PA6 material that suffers a great shrinkage.
The final polymer for the realization of the engine cover will be PA6 GF10 because it
offer the perfect balance between performance and processing properties.
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b. Molding Parameters Selection and Simulation Results
FILLING PHASE
The injection points has been positioned on the same face in order to achieve an uni-
directional flow, even spaced to balance the flow. In this way the shrinkage will be
uniform, preventing stresses and warpage that could damage the piece.
Filing Analyze Trial 1st Filing Analyze Trial 2nd
In the filling analyze, for the first approximation we just used the parameters that the
program has suggested. After the quality of the filling analyze is checked, its seen that
the temperature isnt in the acceptable limit.
Then, the injection time is decreased to
get an acceptable temperature. On the third
trial, we got the acceptable quality for
temperature and other parameters are still in
the good region.
Filing Analyze Trial 3rd
FILLING ANALYSE - INJECTION PARAMETERS
1st Trail 2nd Trial 3rd Trail
Injection Time [s] 9.57 7 6.5
Flow Rate [cm^3/s] 44.989 61.506 66.237
Melt Temperatrue [] 280 280 280
Mold Temperature [] 85 85 85
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After selecting the filling parameters, lets evaluate the flow inside the mold.
Shear stress, Weld lines (yellow) and Air trapped (green)
The maximum shear stress is located at the ending area of filling. This zone doesnt
perform any special purpose, so no problems during its product life could appear due to
shear stress.
As three gates has been selected to balance the flow and due to the shape of the piece,
the flow is divided and so weld lines (yellow lines) are created. They are located mainly
on the edge holes which could cause failures during the product life. In order to avoid
that, metallic inserts will be set up on those holes that will link the valve cover with the
engine block.
Due to the fact that great thickness gradient appears through the piece, its important to
evaluate hesitation in order to avoid possible air traps, overpack, sink marks or void
defects. After simulation air traped appear (green line), fortunately the area where its
located doesnt affect the performance of the piece asits just a contact surface.
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HOLDING PHASE
After computing several test, holding time is limited to 130 seconds because, is the limit
time determined with no-flow in the injection points. In this way the shutoff of therunners is set adequatelly to avoid overpack and reverse flow.
HOLDING PHASE - IMPORTANT PARAMETERS
1st Trail 2nd Trial 3rd Trail 4th Trial
Holding Pressure [MPa] 25 50 50 50
Hold Time [s] 140 140 98 130
Cooling Time [s] 189 189 189 250
Accrording to the holding phase results, we compared the important values of each trial
by checking the solid fraction,frozen skin and volumetric shrinkage. The results are
tabled below:
HOLDING PHASE ANALYSE - RESULTS
1st Trail 2nd Trial 3rd Trail 4th Trial
Solid Fraction [%] 35 35 35 47
Frozen Skin [%] 53 53 53 75
Volumetric Srinkage [%] 5 4 4.6 4
After the results of the 4th trial, its possible to ensure a safe extraction of the piece as
the frozen skin is almost freezed (75%) and the hole solid fraction is near the halfpercent.
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Optimizated result of the Holding Phase 4th trial
Frozen Skin [%], weld lines (yellow) and air trapped (green)
In the Frozen Skin result, possible to see that nearly all the part is frozen. Only a few
small parts arent frozen very well. All in all, in these region we have at least 75% frozen
skin which is a good value. Ejectors will not be set near those areas. Its possible to see
that the air trapped is mainly located on the areas with lower fraction of frozen skin.
Solid Fraction [%], weld lines (yellow) and air trapped (green)
Minimum Solid Fraction is about 47%. The result is good because we can see that, nearly
all part of the piece is 100 % solid. The areas with a lower solid fraction could present
warpage problems due to differential cooling rates. They are located where a great
thickness variation is located. A high thickness gradient means great cooling rates that
will introduce differential orientations introducing residual stresses on the piece. Its
important to control those areas by the mold cooling system.
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SHAPE ANALYSE
As said before, the six perimetrical holes will set metalic inserts for the linkage between
valve cover and engine block. For that reason, fixation points on the holes are createdsimulating the inserts, in this way, no deformation is achieved on these parts.
Before computing the holding analysis, its possible to evaluate the final shrinkage of the
piece.
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SHRINKAGE EFFECT - WRAPPAGE
Shrinkage is 1.77mm so this warpage is not so high for plastic injection.
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ALL EFFECT WARPAGE
In shape analysis, we see 1.34mm warpage if we choose the all effect.
By increasing the hole magnitude of deformation is possible to see the tendency on
deformation of the piece. In this way is easiest to realize where are located and which
influence have the deformations on the working conditions of the piece.
Its possible to observe that the piece present a double concave curvature, one which
connects the 2 longer edges of the piece (small) and another that links the shorter ones.
The beginner presents a really low influence, and so by screwing the piece onto the
engine block the deformations will disappear. The other deformation tendency presents
a more or less flat behavior on the plane containing the oil gasket (enclosed by the six
holes for the screws) and a sharp deformation on the last area. As the main objective of
the piece, oil sealing, is achieved, the deformation behavior doesnt influence on the
working conditions of the piece.
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Notice that between the piece and the engine block, it will be set a sealing sheet element
to ensure no leakages or possible contamination. This sealing sheet will also provide a
cushion tolerance, and possible piece deformations will be damped by this element.
Deformation Magnitude 1 Deformation Magnitude 10
c. Mold Feeding System DesignThe feeding system has been designed by a central sprue connected to the extruder that
finishes into a perpendicular cylinder that fills three parallel runners. Those runnershave a conic gate on its end. The hole runner system represents the 12% of the hole
piece material.
The characteristics of the feeding system are:
Central Conical Sprue D1 = 6 mm , D2 = 1.5mm
Cylindrical Runners D = 5 mm
Conical Gates D1= 5 mm , D2= 1 mm
The runner system has been design to achieve a high pressure drop and a high
temperature, in this way its possible to decrease the flow viscosity entering the piece.
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Once the filling system has been designed, the overall thickness has been checked to
ensure that the geometric parameters are correct. If no errors occurs during this phase
the model was ready for a filling simulation. The first simulation was run with the
optimized parameters of the single piece.
The results obtained were:
An excessive Shear Stress appears so before doing modifications its advisable to detect
were those loads are located. The piece stability must be ensured.
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The simulation shows that the shear stresses are located only on the gates entrance
which is normal and acceptable. It could be noticed that the hole piece is subjected to a
high margin of shear stresses, so the piece its not damaged and the simulation results
are acceptable. Even though, one more simulation has been run increasing the holding
time to 7 seconds trying to downsize the magnitude of the shear stress.
The results highlights that the new parameters diminishes the performance, as
temperature has raised to a non-acceptable limit.
d.Augmentation in Mold Design and ParametersDue to the presence of the feeding system the holding parameters have to be adjusted.
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HOLDING PHASE - IMPORTANT PARAMETERS
No feeding system With feeding system
Holding Pressure [MPa] 50 50
Hold Time [s] 130 185
Cooling Time [s] 250 280
Solid Fraction [%] 47 42,96
Frozen Skin [%] 75 76
Volumetric Srinkage [%] 4 6,17
The main cycle parameters have been increased while the piece quality after process has
been decreased.
e. New Simulation ResultsWith the runners design the solid fraction and frozen skin have changed.
Frozen skin [%], weld lines (yellow) and air
trapped (green)
Solid fraction [%], weld lines (yellow) and
air trapped (green)
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With the feeding system the weld line and air trapped behavior is better, less areas and
located better that the simulation without the runners.
Also the frozen skin and solid fraction distribution is better with the new parameters.
Besides those improvements the overall piece increases its shrinkage, passing form a4% of deformation to 6,17%. As the difference between those values is not so important,
the simulation could be finished.
f. Resume of Optimized DesignThe presence of the feeding system increases the holding and cooling time, those
variations stabilizes the operating parameters and improves the overall quality of the
piece. The greater shearing stress introduced by the runners is reflected with an
increase on the overall shrinkage of the piece.
It could be interesting to check the film gate or fan gate feeding systems as presentbetter filling configurations for our piece.
The feeding system has been only designed for filling one piece for simulation
simplifications. For production purposes this is not a performance solution as the
injection shot must be used to fill more than one piece, in order to increase the cycle
time.
4.CONCLUSIONSa. VISI Flow Software
This CAE software helps to understand the several parameters that are involve on the
injection process. Thanks to this kind of simulators is possible to predict and estimate
the melt flow behavior inside the mold and so, different changes on the injection process
could be done to perform in the best conditions the operation. This helps to reduce the
time to market of a product and reduce the investment on molds, which are really
expensive, and configuring the process which is reflected in a great save of money.
The only negative point to this software is the CAD functions which arent intuitive and
difficult to manage, specially while designing the feeding system.
b. Problems of Design ProcessWe did not have so many problems of mold design. Only during the simulations of the
feeding system some problems related to the shear stress on the runners appear, as no
danger on the piece was created, we could continue with our simulations.