Plastic Report 02-02-2012

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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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Automotive Engineering - a.a. 2011/2012Production technologies for body components

Engine Cover for a V4 Engine by Injection Moulding 2

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


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


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


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


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.

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Plastic Report 02-02-2012