design & optimization of textile machine holder through cae software

DESIGN & OPTIMIZATION OF TEXTILE MACHINE HOLDER THROUGH CAE SOFTWARE

A THESIS PREPARED BY

JOY A. J.

i

ABSTRACT Holder is one of the components used in Textile machines to gauge the yarn formed from the cotton.

The objective of this project is to optimize the design of the component, holder through CAD & CAE Software (Pro-E, MPA, and Moldex3D) so as to enhance its performance in the end to end application.

The project flows in three stages as follows:  Tool Inspection  Study on optimization of molding conditions

 Analysis of component design through CAD and CAE software Purpose of this study based on the feedback from customer after couple of month’s usage holder is starting to lose its dimension stability, thus quality yarn goes down.

ii

TABLE OF CONTENTS CHAPTER NO.

1

2

3

TITLE

PAGE NO.

ABSTRACT

i

LIST OF TABLES

iv

LIST OF FIGURES

v

INTRODUCTION

1

1.1 HOLDER

1

1.2 APPLICATION OF HOLDER

1

1.3 INJECTION MOULDED HOLDER

4

INJECTION MOULDING

7

2.1 FILLING PHASE

7

2.2 PACKING PHASE

8

2.3 COOLING PHASE

9

MATERIAL SURVEY

11

3.1 PLASTIC MATERIAL DESCRIPTION

11

3.2 FIBER REINFORCED COMPOSITE

15

POLYMER 4

PROBLEMS ENCOUNTER

16

5

METHADOLOGY

18

6

TOOL INSPECTION

19

7

OPTIMIZATION OF MOLDING WINDOW

20

THROUGH CAE S/W

8

7.1 MOLDING WINDOW

20

MOLDFLOW ANALYSIS RESULTS AND DISCUSSION 8.1 GATE LOCATION

23 23

iii

8.2 FILLING / MELT FRONT TIME

28

8.3 FILLING/ INJECTION PRESSURE

34

8.4 FILLING / FLOW FRONT TEMPERATURE

37

8.5 FILLING / QUALITY PREDICTION

40

8.6 FILLING / COOLING QUALITY

44

MOLDEX3D ANALYSIS RESULTS & DISCUSSION

48

9.1 WARPAGE

48

10

DESIGN THROUGH CAD S/W – Pro E

58

11

RESULT COMPARISON

59

12

CONCLUSSION

60

9

REFERENCE

iv

LIST OF TABLES CHAPTER NO.

TITLE

PAGE NO.

7.1

Molding Window – Green

20

7.2

Molding Window – yellow

21

7.3

Molding Window – Red

21

8.1

Trouble Shooting Flow Front temperature

38

8.2

Quality Prediction – Green

41

8.3

Quality Prediction – Yellow

41

8.4

Quality Prediction – Red

42

11.1

Results Comparison

59

v

LIST OF FIGURES FIGURE NO.

TITLE

PAGE NO.

1.1

Holder Loading in Field

2

1.2

Textile Machine Frame

3

1.3

Metallic Holder

5

1.4

Plastic Holder

5

1.5

Plastic Holder part drawing

6

2.1

Injection molding machine

10

3.1

Process Temperatures of PA66-Ultramid A3WG10

12

3.2

Mechanical Properties of PA66-Ultramid A3WG10

12

3.3

Viscosity Curve of PA66-Ultramid A3WG10

13

3.4

PVT Curve of PA66-Ultramid A3WG10

13

3.5

Heat Capacity Curve of PA66-Ultramid A3WG10

14

3.6

Thermal Conductivity Curve of PA66-Ultramid A3WG10

14

4.1

Problems Encountered in existing tool

17

5.1

Methodology

18

6.1

Existing Tool with Single gate

19

7.1

Molding Window for Apron Gauge

22

8.1

Best Gate Location

26

8.2

Existing Gate Location

27

8.3

Optimized Gate Location

27

8.4

Filling, Melt Front Time – Existing

33

8.5

Filling, Melt Front Time – Optimized

33

8.6

Injection pressure – Existing

36

8.7

Injection pressure – Optimized

36

8.8

Flow Front Temperature – Existing

39

8.9

Flow Front Temperature – Optimized

39

vi

8.10

Quality Prediction – Existing

43

8.11

Quality Prediction – Optimized

43

8.12

Cooling Quality – Existing

47

8.1

Cooling Quality – Optimized

47

9.1

Warpage X-displacement – Existing

54

9.2

Warpage X-displacement – Optimized

54

9.3

Warpage Y-displacement – Existing

55

9.4

Warpage Y-displacement – Optimized

55

9.5

Warpage Z-displacement – Existing

56

9.6

Warpage Z-displacement – Optimized

56

9.7

Warpage total displacement – Existing

57

9.8

Warpage total displacement – Optimized

57

10.1

Optimized Tool Design with two gate points

58

CHAPTER I INTRODUCTION 1.1 HOLDER

Holder is one of the components used in Textile machines to gauge the yarn formed from the cotton. Since its function is to gauge the yarn into fine threads of desired thickness, it is expected to possess the following factors:  Low co-efficient of friction To allow smooth spinning of yarns  Low wear and tear To ensure smooth rolling of the conveyor belt  Temperature Stability To maintain the quality of warp yarn  Low vibration at high speeds  Dimensional stability  Parallelism  Concentricity

A Textile machine consists of one Holder for a pair of spindles and hence this requires easy maintenance and repalcebility as well. A wrong design of this component will lead to the collapse of the entire textile machine. So the design quality of the component should be assured to be the most perfect one.

1.2 APPLICATION OF HOLDER

Holder was used in two types of textile machines. 1. Speed frame Machine

1

2. Ring frame Machine The function of Holder remains the same in both the machines i.e., to gauge the yarn into fine threads, and the requirements too.

Fig. 1.1 Holder Loading in Field

2

Fig. 1.2 Textile machine Frame

Earlier Holder was primarily made of metal and this posed several disadvantages as follows:  Deformation: Because of the continuous load applied over holder and pressure over the rollers to squeeze the yarn into fine threads, the metal component exhibited permanent deformation which led to non-uniform thread sizes and also breakage in the continuous thread flow.  Rust Formation: Being a metal, to protect the part from rusting, a coating should be provided and the coating quality should be continuously monitored. This naturally increased the manufacturing, maintenance cost and time.  Manufacturing Cost: Compared to Plastics, the manufacturing cost and the processing time of metallic holder was more.  Replacement Difficulty: The repalcebility of metallic holder was difficult and more time consuming.  Wear and Tear of Roller Belt: Since the metal is in regular contact with the roller belt wearing occurs. 3

1.3 INJECTION MOLDED HOLDER

Metallic Holder being studied for its varied disadvantages, the component was decided to be made of plastic.

The engineering plastic material used for Holder was PA66 - 50% GLASS FIBER FILLED The grade selected was BASF / PA66 / ULTRAMID A3WG10 / 50% GF FILLED

Thermoplastics generally have extreme design flexibility and hence our desired need could be brought out with ease. They could be made accustomed to any environment by incorporating additives and processing agents. Plastics are  Cheap Raw material.  Easy to be processed.  No Rust formation and therefore low maintenance.  Easy assembling and dismantling.

4

Fig. 1.3 Metallic Holder

Fig. 1.4 Plastic Holder

5

Fig. 1.5: Plastic Holder – Part Drawing 6

CHAPTER 2 INJECTION MOLDING The injection molding process can be broken into three phases: 

Filling phase



Packing phase



Cooling phase

2.1 FILLING PHASE During the filling phase, plastic is pushed into the cavity until the cavity is just filled. As plastic flows into the cavity, the plastic in contact with the mold wall quickly freezes. This creates a frozen layer of plastic between the mold and the molten plastic. At the interface between the static frozen layer and the flowing melt, the polymer molecules are stretched out in the direction of flow. This alignment and stretching is called orientation. The flow front expands as material from behind is pushed forward. This outward flow is known as fountain flow. The edges of the flowing layer come into contact with the mold wall in a near perpendicular direction and freeze. The molecules in the initial frozen layer are therefore not highly orientated, and once frozen, the orientation will not change. The frozen layer gains heat as more molten plastic flows through the cavity, and looses heat to the mold. When the frozen layer reaches a certain thickness, equilibrium is reached. This normally happens early in the injection molding process, after a few tenths of a second. 7

2.2 PACKING PHASE The packing phase begins after the cavity has just filled. This involves further application of pressure to the material in an attempt to pack more material into the cavity, in order to produce uniform shrinkage at reduced levels and consequently, reduce component warpage. Once the material has filled, the mold cavity and the packing phase has begun, material flow is driven by the variation of density across the part. If one region of a part is less densely packed than an adjacent region, then polymer will flow into the less dense region until equilibrium is reached. This flow will be affected by the compressibility and thermal expansion of the melt in a similar way to which the flow is affected by these factors in the filling phase. The material's PVT characteristics provide the necessary information (density variations with pressure and temperature, compressibility and thermal expansion data) so that when combined with the material viscosity data accurate simulation of the material flow during the packing phase is possible. In practice, due to limitations of pressure and available unfrozen flow channel, it is not possible to pack enough material into the mold to fully compensate for shrinkage. The uncompensated shrinkage must be allowed for by making the cavity bigger than the desired part size.

2.3 COOLING PHASE The cooling phase occurs after the end of packing. The cooling phase is the period of time from the end of packing to the instant that the mold clamp opens. Cooling of the plastic occurs from the commencement of the filling phase, so that this phase can be considered as the extra time required, after the packing time, to

8

cool the part sufficiently for ejection. This does not necessarily mean that all sections of the part or runner system need be 100% frozen. The material at the center section of the part wall reaches its freeze temperature and becomes solid during cooling time. The rate and uniformity at which the part is cooled affects the finished molding quality and production costs. Mold cooling accounts for more than twothirds of the total cycle time in the production of injection molded thermoplastic parts.

9

Fig. 2.1 Injection Molding Machine 10

CHAPTER 3 MATERIAL SERVEY

3.1 PLASTIC MATERIAL DESCRIPTION Generic Class PA66 (Polyamide 66, or Nylon 66, or poly (hexamethylene adipamide))

Applications PA66 is heavily used in the automotive industry, appliance housings, and generally where impact resistance and strength are required.

Chemical and physical properties PA66 homopolymer is produced by the polymerization of hexamethylene diamine and adipic acid (a dibasic acid). Among commercially available polyamides, PA66 has one of the highest melting points. It is a semicrystalline material. The grades have strength and stiffness which is retained at elevated temperatures. Moisture absorption depends on the composition of the material, wall thickness, and environmental conditions. Dimensional stability and properties are all affected by the amount of moisture absorption which must be taken into account for product design. Various modifiers are added to improve mechanical properties; glass is one of the most commonly used filler. The viscosity is low and therefore, it flows easily. This allows molding of thin components. PA66 is resistant to most solvents but not to strong acids or oxidizing agents.

11

The material used in this project is ULTRAMID A3WG10 which is a 50% glass fiber reinforced and heat aging resistance injection molding PA66 grade.

Fig. 3.1 Process Temperatures of PA66-Ultramid A3WG10

Fig. 3.2 Mechanical properties of PA66 / Ultramid A3WG10 12

Fig. 3.3 Viscosity curve for PA66 / Ultramid A3WG10

Fig. 3.4 PVT curve for PA66 / Ultramid A3WG10

13

Fig. 3.5 Heat capacity curve for PA66 / Ultramid A3WG10

Fig. 3.6 Thermal conductivity curve for PA66/Ultramid A3WG10

14

3.2 FIBER-REINFORCED COMPOSITE POLYMER

The fiber-reinforced composite products with stiffness properties are usually superior to those of unreinforced polymer products. During the recent years, the injection molding of fiber-reinforced thermoplastics has been very popular. A lot of automobile plastic parts are made of fiber-reinforced engineering plastic for its superior mechanical properties and high heat distortion temperature. Since the reinforced composites have anisotropic properties, it makes the injection molding process of fiber-reinforced thermoplastics be more complicated. The thermal and mechanics properties of the composite strongly depend on the fiber orientation pattern. The property of the composite is stronger in the fiber orientation direction and weaker in the transverse direction. However, at the same time, the thermal shrinkage is larger in transverse direction and lower in fiber orientation direction. The molded product may have high internal stress and warpage at unexpected locations. Therefore, during the design phase of a new product, we must take account of processing details to understand the fiber orientation and warpage behaviors more comprehensively.

The fiber orientation and anisotropic shrinkage in injection molding are complex phenomena. It’s difficult to identify and examine by the traditional 2.5D model for complicated geometry and thick parts. When the fiber-reinforced polymer is injection molded, the flow during mold filling creates the pattern of fiber orientation in the part. This leads to push the mechanics properties to be anisotropic. Essentially, the fiber orientation shows a full 3D phenomenon. The direction of orientation may be in the any 3D direction.

15

CHAPTER 4 PROBLEMS ENCOUNTERED

The product design of Holder and the material selected for the application was analyzed to be perfect.

In its application field of gauging the yarn into fine threads of desired thickness, we encountered following problems in the component.  Parallelism: Parallelarity was lost in the existing component and it led to the non uniformity of thread thickness.  Concentricity: The existing Holder loses concentricity and therefore the roller belt movement was disrupted.  Dimensional Stability: Yielding of the existing component during its continuous cycle of gauging the yarn affected its dimensional stability.

In order to overcome the above said difficulties the component was taken through the following stages:  TOOL INSPECTION  STUDY ON OPTIMISATION OF PROCESS CONDITIONS  ANALYSIS

OF

THE

COMPONENT

SOFTWARES

16

USING

CAD/CAE

Fig. 4.1:Problems encountered in the Application field with molded Holder 17

CHAPTER 5 METHADOLOGY

Tool Inspection

Study on Optimization of Molding Conditions

Analysis of the Component design through CAE software (Moldflow, Moldex3D & ProE)

System Review

Conclusion

Fig. 5.1 Methodology

18

CHAPTER 6 TOOL INSPECTION Tool Inspection was mainly carried out to verify whether there are any deviations or deformations which could be the cause for the component’s failure in the field. The tool designed for the existing component was inspected for its dimension and tool rigidity.  It was found that, all dimensions were within the tolerance limit.  The tool deformation due to continuous production was found to be negligible.  The shrinkage specified for the component in designing the tool was also correct as per material details.

SINGLE GATE Fig 6.1 Existing Tool

Fig. 6.1 Existing tool with single gate

19

CHAPTER 7 OPTIMIZATION OF MOULDING CONDITIONS THROUGH CAE S/W

7.1 MOLDING WINDOW A process window or molding window, defines the limits of molding conditions under which an acceptable part can be produced. If molding conditions fall within this region, then a good part can be made. The Molding Window display is a plot over the ranges of the melt temperature and the injection time for a given mold temperature. The Molding Window result can include red, yellow and green areas:  Green

: These are the best processing conditions for this part

 Yellow

: These conditions may cause molding or part quality problems, but the part would be moldable

 Red

: Don't use these processing conditions

Green - An area of Molding Window is green if all of these cases are true: Table - 7.1 – Molding window -Green The part is not a short shot. The injection pressure required to fill the part is less than 80% of maximum machine injection pressure. The flow front temperature is less than 10°C above the injection (melt) temperature. The flow front temperature is greater than 10°C below the injection (melt) temperature.

20

P < 0.8 * Pmax

T < Tmelt + 10°C

T > Tmelt - 10°C

The shear stress is less than the maximum specified.

-

The shear rate is less than the maximum specified.

-

Yellow - An area of the Molding Window is yellow if all of these cases are true:

Table – 7.2– Molding window -Yellow The part is not a short shot. The injection pressure required to fill the part is less than the maximum machine injection pressure capacity.

P < Pmax

Red - An area of the Molding Window is red if either of these cases is true:

Table – 7.3– Molding window -Red The part is a short shot. The injection pressure required to fill the part is greater than the machine injection pressure specified.

P > Pmax

The Molding Window uses Part geometry, Injection location, Material(s), Surface finish (gloss), Max. Injection pressure And uses Mold temperature, Melt temperature, Injection time across their ranges and outputs whether Injection pressure, Flow front temperature, Shear stress, Shear rate, Short shot are acceptable or not.

21

Fig.7.1 Molding window for holder – PA66 50% GF filled 22

CHAPTER 8 MOLDFLOW ANALYSIS RESULTS AND DISCUSSIONS 8.1 GATE LOCATION Gates connect the runners to the cavity at the injection location. When designing gates, the following factors are to be considered: 

Quality of the appearance of the molded part.



Removal of the gate.



Complexity of the cavity



Material used.



The volume of the material injected into the mold.

For parts where appearance is important, the gates should be narrow to prevent large blemishes on the surface of the part. A smaller opening will also make degation simpler. Gates should be made short to prevent large pressure drops. Sharp angles between gates and runners should be avoided, as they can contribute to the pressure drop in the system. Corners should be rounded, so they don't inhibit the melt flow. Edge (standard) gate - An edge gate is located on the parting line of the mold and typically fills the part from the side, top, or bottom. Dimensions : The typical gate size is 6% to 75% of the part thickness (t) (or 0.4 to 6.4mm thick (H)) and 1.6 to 12.7mm wide (W). The gate land should be no more than 1.0mm in length (L), with 0.5mm being the optimum

RUNNERS The design of the runner system affects the amount of material used and the quality of the parts produced. If the flow within each cavity is not balanced, overpacking

23

and hesitation can lead to poor part quality. Long or poorly designed runners can cause large pressure drops and require a larger injection pressure to fill the part. In general, runners should be made as short as possible, with the lowest possible shot weight, and which provide balanced flow into the cavities. Higher melt temperatures reduce residual stress levels and the tendency of parts to warp, but high barrel temperatures can cause degradation of the material. To minimize material waste and decrease the barrel temperature required, runners should be designed with a small cross sectional area.

Runner to surface ratio Runners should be modeled with a gradual change in diameter and, where they join a surface, the ratio of runner diameter to surface thickness should not exceed 10:1. Large changes in thickness at the runner/surface interface may cause a rapid change in flow resistance, resulting in flow instabilities.

SPRUE The sprue is the extension of the injection nozzle into the mold. In a mold with a single injection location on a single cavity, the sprue can meet at the cavity wall. The sprue opening should be as small as possible but must fill the cavity adequately. The angle of the taper on a sprue should be large enough to allow it to be easily ejected but not too large because the cooling time and material used increase with the increase in the sprue diameter.

BEST GATE LOCATION The Gate Location analysis determines suitable gate locations using a set of predetermined conditions and the selected material properties. It then rates the model areas for their suitability for an injection location where, the worst position/s (red) is classified as the least suitable, and the best position/s (blue) is classified as 24

the most suitable. There are a number of components which are weighted and summed to produce an overall quality indicator for each location examined. 

Processibility: Is it possible to produce a part if the part is gated at this location. This is the major component in the Gate Location analysis. If the part cannot be produced from an investigate location, the location will appear red. Minimum Pressure : Lower injection pressure usually produces lower shear rate and shear stress levels, or lower clamp tonnage requirements.



Geometric Resistance: Where would gating not cause overpacking? The resistance in the X and Y directions is being normalized. For multiple gated parts, this calculation measures the resistance through each node. If two gates fill with equal flow resistance, then they fill with equal pressure producing no overpacking. If the resistance is different then one gate will fill first resulting in an overpacking situation whilst the other gate continues to fill.



Thickness: Is it possible to pack the part effectively when gating at this location

25

Fig.8.1 Best Gate Location 26

Fig. 8.2 Existing Gate Location

Fig. 8.3 Optimized Gate Location

27

8.2 FILLING MELT FRONT TIME The Fill Time result shows the path that the molten plastic takes through the part, and how long it takes to fill. In this result, all areas of the part that are filled at the same time are given the same color contour. For example, areas of the part that fill first are given a red contour, while those that fill last are blue. Areas of the part that fail to fill appear translucent. Plotting these contours in time sequence gives the impression of plastic flowing through the mold. The primary use of the fill time result is to determine if all flow paths fill at the same time. The fill time result can also be used to understand how weld lines and air traps form. Flow fronts merging to form weld lines, or flow fronts surrounding a region of the cavity trapping a pocket of air (air trap) could be identified from this result. Several problems that can occur during filling can be deduced by animating the fill time result and they are as follows:

Hesitation Hesitation is when flow slows down or stops along a particular flow path. If plastic filling a cavity has the option of filling either a thin section or a thick section, the plastic will tend to fill the thick section first as this route offers less resistance to flow. This can result in plastic in the thin section stopping or slowing significantly. Once the plastic starts to slow down, it will cool more rapidly, so the viscosity will increase. This higher viscosity will inhibit flow further causing even faster cooling and so the problem is self propagating. Hesitation can occur in ribs and in thin section of parts that have significant changes in wall thickness.

28

Hesitation can reduce part quality due to variation in surface appearance, poor packing, high stresses and non-uniform orientation of the plastic molecules. Alternatively, if the hesitation allows the flow front to freeze completely, part of the cavity may remain unfilled (short shot). Trouble Shooting Hesitation 

The polymer injection location can be moved away from the area of hesitation so that the bulk of the cavity fills before the melt reaches the thin area. The absence of alternative flow paths will give less time for the polymer to hesitate.



The polymer injection location can be moved to a place that will cause greater pressure to be applied where the hesitation occurred.



It is useful to have thin ribs/bosses as the last point to fill, so all the injection pressure is applied at this point.



The wall thickness where the hesitation occurred, can be increased to reduce the resistance to flow.



A less viscous material can be used (that is, a material with a higher melt flow index).



Plastic can be injected more quickly to reduce the potential of hesitation time.



The melt temperature can be increased so that it flows into the thin area more readily.

29

Overpacking Overpacking is when extra material is compressed in one flow path while other flow paths are still filling. Overpacking occurs when the easiest (shortest/thickest) flow paths fill first. Once this flow path has filled, it will still be under pressure as extra plastic is injected into the cavity to fill the remaining flow paths. This pressure will push more material into the already full flow path, causing it to have a higher density and lower shrinkage than other regions. The overpacked fill path will have frozen under pressure, so stresses will be frozen in. Overpacking generally occurs in sections with the shortest fill time. It can cause a range of problems including warpage due to non-uniform shrinkage, increased part weight due to wasted material and non-uniform density distribution throughout the part.

Trouble Shooting Overpacking To solve problems caused by Overpacking, balance the flow paths. 

Thicken or thin parts of the model to act as flow leaders or deflectors.



The injection location can be moved to a position that will define similar length flow paths.



The cavity can be divided into imaginary sections, and one injection location can be used for each section.



Unnecessary gates can be removed

30

Racetrack effect The racetrack effect occurs when flow races through thick sections of the cavity before the thin sections have filled. Thick sections offer less resistance to flow than thin sections. The racetrack effect indicates unbalanced flow paths and can often cause unnecessary weld lines and air traps Trouble Shooting Racetrack effect Flow leaders and deflectors can be used to ensure all flow paths within the cavity fill at the same time (balanced flow paths). Often the most suitable polymer injection location does not define equal flow paths, and the use of multiple polymer injection locations creates extra unwanted weld lines. Therefore, altering thicknesses within the design specifications can be the most appropriate way to balance flow paths.

Underflow Underflow is when a flow front reverses direction. It occurs when flow fronts from two directions meet; pause momentarily, then one of the flows reverses direction and flows back between the outer frozen layers. When the flow reverses direction the frozen layer partly re-melts due to frictional heating. This flow reversal gives poor part quality, both from surface appearance and structural viewpoints. The filling pattern is to be inspected to assess if underflow is likely to occur.

31

Unbalanced flow Unbalanced flow is plastic completely filling some flow paths in the mold before other flow paths have filled. Unbalanced flow can be the cause of many molding problems such as flashing, short shots, high cycle time, and density differences throughout the part, warpage, air traps and extra weld lines. Flow is balanced when all the extremities of the mold fill at the same time. To recognize unbalanced flow, the different flow paths in the mold should be recognized. These are the different routes that the plastic takes throughout the cavity.

Trouble shooting unbalanced flow By altering the thickness of regions within the part, flow can be hastened or delayed in certain directions to help balance flows. Flow Leaders or Flow Deflectors can be used to uniform the thickness. Position or number of the polymer injection location can be considered to balance the flow.

32

Fig. 8.4 Filling Melt Front Time – Existing

Fig. 8.5 Filling Melt Front Time – Optimized

33

8.3 INJECTION PRESSURE The injection pressure is the pressure that is applied to the ram during the injection phase, causing the material to flow, and can be measured approximately by a transducer located in the nozzle. The injection pressure result uses a range of colors to indicate the region of lowest pressure (colored blue) through to the region of highest pressure (colored red). The color at each place on the model represents the pressure at that place on the model, at the moment the part is filled completely.

Pressure Results Derivation At any point during filling, there is a pressure gradient from a maximum value at the injection location, down to atmospheric pressure at the flow front. The Adviser calculates this pressure distribution continuously throughout cavity filling, and provides two pressure results: Injection Pressure and Pressure Drop. The Injection Pressure result is a contour plot of the pressure distribution throughout the cavity at the end of filling. This is effectively a "snapshot" at one instant of time. The maximum value is at the injection location and the minimum is at the last point of the cavity to fill. The Pressure Drop result is a contour plot showing the pressure required to force material to each point in the cavity. The value calculated is the pressure at the injection location as a point fills and this value is plotted at the corresponding point on the model. Unlike the Injection Pressure result, the Pressure Drop is not displayed for any one moment in time. The values displayed relate to the time that the location is actually filled.

34

The injection pressure can be used in conjunction with the pressure drop result. For example, even if a section of a part has an acceptable pressure drop, the actual injection pressure in the same area may be too high. High injection pressure can cause Overpacking. There are a number of options available to improve the result: 

Increase the injection pressure to improve the confidence of part filling.



Alter the polymer injection location to improve the likelihood of all sections of a part filling; placing the polymer injection location depends greatly on part geometry, material, and processing conditions. Using adequate injection pressure as indicated in the Molding Windows dialog, the injection location can be placed close enough to the problem area, but far enough away from thin areas which may cause hesitation or additional injection points can be added.



Alter part geometry - If the part consists of a complex and thin geometry, this can cause filling difficulties which require high injection pressure to complete the filling. If altering injection pressure is not possible, the part geometry may need to be altered.



Select a different material - By choosing a material with a higher melt flow rate, less injection pressure will be required to fill the part.



Increase the melt temperature value - This will reduce the viscosity of the melt, enabling the melt to flow into the mold more easily. This in turn will reduce the pressure required to fill the mold.

35

Fig. 8.6 Injection Pressure - Existing

Fig. 8.7 Injection pressure - Optimized

36

8.4 FLOW FRONT TEMPERATURE The flow front temperature result uses a range of colors to indicate the region of lowest temperature (colored blue) through to the region of highest temperature (colored red). The colors represent the material temperature at each point as that point was filled. The result shows the changes in the temperature of the flow front during filling. If the flow front temperature is too low in a thin area of the part, hesitation or short shot may occur. If it is too low in an area where weld lines are present, the weld lines may appear worse. In areas where the flow front temperature is too high, material degradation and surface defects may occur. The flow front temperature should be always within the recommended temperature range for the polymer material used. The flow front temperature is one factor used to determine the confidence of fill result. Low melt temperatures will cause yellow or red confidence of fill results. Confidence of fill is determined by both material melt temperature and injection pressure. So there is a need to adjust both processing conditions before an acceptable confidence of fill result is obtained.

37

Table – 8.1 Trouble Shooting Flow front Temperature Difference Temperature too low

Possible Problems

Decrease injection time.

May cause excess shear in the gate if it is restrictive. Too much shear will cause degradation and surface defects.

Increase

the

melt

May increase cycle time and may cause material

temperature.

degradation.

Increase mold temperature.

May increase cycle time.

Increase the thickness in the

May cause a functional problem with the design and

area to permit flow.

increase cost.

For hesitation in thin areas.

Increase the melt temp to flow into thin area more readily.

Move the gate away from the

May cause hesitation or other problems elsewhere in

hesitation area.

the part.

Temperature too high

Possible Problems

Increase the injection time.

This will slow the flow of plastic into the cavity, which will reduce the frictional heating

Increase the part thickness.

A thicker part will also reduce the frictional heating.

Resizing of Gate

Reduce high temperature caused by shear stress in the gate

38

Fig. 8.8 Flow Front Temperature - Existing

Fig. 8.9 Flow Front Temperature - Optimized 39

8.5 QUALITY PREDICTION The Quality Prediction result estimates the expected quality of the part's appearance, and its mechanical properties. This result is derived from the pressure, temperature and other results. Green

: Will have high quality.

Yellow

: May have quality problems.

Red

: Will definitely have quality problems.

Translucent : Will not fill (short shot) The Quality display is derived from combinations of the five results listed below: 

Flow front temperature



Pressure drop



Cooling time



Shear rate



Shear stress For each area of the cavity, the five results are evaluated. If all five results in

an area are acceptable, the area is green. If there is at least one unacceptable result, the area is red. If there are both acceptable and preferred results, the area is yellow. This Quality Prediction result shows there is a problem with this area of the mold. The Quality Prediction result gives a measure of the surface quality of the finished part. Attention should be given to the feed system, as poor design quality can effect the part and reduce quality. An area of the Quality Prediction result is green if all of these cases are true:

40

Table – 8.2 – Quality perdition -Green Description

Equation

The flow front temperature (T) is between the minimum (Tmin)

Tmin < T < Tmax

and maximum (Tmax) recommended temperatures for the material in the material database. The pressure drop (Pdrop) is in the range between 0% and 80% of

Pdrop < (0.8Pmax)

the maximum injection pressure (Pmax). The cooling time (t) is less than 1.5 times the average cooling

t < 1.5tav

time for the part (tav) The shear rate is less than the max. recommended shear rate in the database. The shear stress is less than the max. recommended shear stress in database. An area of the Quality Prediction result is yellow if none of the red conditions is true, and at least one of these conditions is true: Table– 8.3 - Quality perdition -Yellow Description

Equation

The flow front temperature (T) is between the min. (Tmin),

Tmin < T < (Tmax +

temperature for the material and a value 5°C above the max.

5°C)

(Tmax), temperature for the material. The pressure drop (Pdrop) lies in the range between 80% and

(0.8Pmax) < Pdrop
(Tmax + 5°C)

maximum recommended temperature for the material (Tmax). The pressure drop (Pdrop) is greater than or equal to the

Pdrop >= Pmax

maximum injection pressure (Pmax), as set on the Analysis Wizard - Processing Conditions page. The cooling time (t) is more than 5 times above the average cooling time for the part (tav). The shear rate is more than double the maximum recommended in the material record. The shear stress is more than double the maximum recommended in the material record.

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t > 5tav

Fig. 8.10 Quality prediction - Existing

Fig. 8.11 Quality Prediction - Optimized

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8.6 COOLING QUALITY Cooling Quality Analysis plots in the Adviser shows where the heat tends to stay in a part due to its shape and thickness. The part is considered to be located in the center of a block of metal, or a theoretical mold, without any cooling circuits and held there for a fixed period of time. The Adviser then simulates the way heat will leave the hot part naturally and flow towards the extremities of the block. For a cooling quality analysis, it shows the areas whose design facilitates a high (green) amount of cooling, medium (yellow) amount of cooling, or low (red) amount of cooling. Cooling Quality results are a combination of the Surface Temperature Variance (mainly affected by shape) and Freeze Time Variance (mainly affected by thickness) results. If cooling quality is low in a thin area of the part due to surface temperature variance or freeze time variance being significantly lower than the average, hesitation or a short shot may occur, and the result will show a red area. Thicker walls or a higher melt temperature may be necessary. If it is low for the same reason in an area where weld lines occur, those weld lines may be visually more obvious and structurally weaker. In areas where cooling quality is low because of surface temperature variance or freeze time variance being significantly higher than normal, surface defects may occur and/or warpage may result unless significant cooling is introduced to your mold design or the product redesigned. It should be made sure that the flow front temperature is always within the recommended temperature range for the polymer you are using.

44

Surface Temperature Variance values that are too low or too high will cause yellow or red Cooling Quality results, as will Freeze Time Variance results that are significantly shorter or longer than the average time to freeze. Cooling Quality analysis simulates the transfer of heat from the plastic to the mold based on a concept of Natural Cooling. The part is considered to be embedded in a large metal block with no cooling channels and heat is assumed to be lost from the outer surfaces of the block. The purpose of this analysis is to identify areas of the part where the part geometry (shape and thickness combined) is expected to cause localized cooling problems, that is, areas of the part that may require more cooling. For each area of the cavity, the two results are evaluated. If both results in an area are acceptable, the area is green. If there is one unacceptable result, the area is red. If there are both acceptable and preferred results, the area is yellow.

An area of the Cooling Quality plot is green if both of these cases are true: 

The freeze time variance for the area is a value between -60% and +100% of the average time to freeze for the entire part.



The surface temperature variance result temperature range for the area is between 10°C under to 10°C over the average surface temperature for the entire part.

An area of the Cooling Quality plot is yellow if none of the red conditions is true, and at least one of these conditions is true: 45



The freeze time variance for the area is a value between -60% to -75% or +100% to +150% of the average time to freeze for the entire part.



The surface temperature variance result temperature range for the area is between 10 to 20 degrees C under or 10 to 20 degrees C over the average surface temperature for the entire part.

An area of the Cooling Quality plot is red if either of these conditions is true: 

The freeze time variance for the area is a value below -75% or above +150% of the average time to freeze for the entire part.



The surface temperature variance result temperature range for the area is more than 20°C under or 20°C over the average surface temperature for the entire part.

46

Fig. 8.12 Cooling Quality – Existing

Fig. 8.13 Cooling Quality - Optimized

47

CHAPTER 9 MOLDEX3D ANALYSIS RESULTS AND DISCUSSIONS 9.1 WARPAGE Warpage is a part defect caused by a non-uniform change of internal stresses. The total warpage in the part can be attributed to the following three factors: 

Variation in shrinkage from region to region (differential shrinkage).



Temperature differences from one side of the mold to the other (differential cooling).



Variations in the magnitude of shrinkage in directions parallel and perpendicular to the material orientation direction (orientation effects).

Differential Cooling Shrinkage due to differential temperature typically results in bowing of the component. Usually this type of shrinkage is due to poor cooling system design. While the part is in the mold, temperature differences from one side of the mold to the other cause variations in shrinkage through the thickness of the component. In addition to this, any temperature differences at ejection will cause further warpage as both sides of the part cool to room temperature. The two main ways of influencing differential cooling are: 

Changing cooling line layout.



Using mold inserts.

One of the easiest things to alter is the coolant temperature. It may be useful to run two additional cooling analyses with the coolant inlet temperatures at, for

48

example, plus and minus 10°F (5°C) with respect to the original inlet temperature used. The results from the cooling analyses will then give some idea of the sensitivity of the part to variations in coolant temperature. If it is not sufficient to simply alter the coolant temperature, we should consider the addition of extra cooling lines in troublesome regions or the use of mold inserts to reduce variations in cooling rates across the part. Differential Shrinkage Differential shrinkage is often caused by variations in crystalline content and volumetric shrinkage. The three main ways of influencing differential shrinkage effects are: 

Designing packing profiles.



Reducing part thickness variations.



Using mold inserts.

Packing profile: The first option to consider when reducing differential shrinkage is the use of a packing profile. This is dependent on the machine response time and its effectiveness may be limited for thin parts, or parts with complex geometries. The advantage of using a packing profile to reduce warpage is that this does not involve changing the design specifications of the part. Reduce part thickness variations: If we decide that changes to the wall thickness may be of more use in reducing differential shrinkage effects for the part, then we can alter the thickness in

49

the region in question and re-analyze the modified part model. This can be an iterative process, until the differential shrinkage level is acceptable. Use mold inserts: The final alternative for reducing differential shrinkage is to consider the use of mold inserts to reduce shrinkage due to variations in cooling rates. Orientation Effects Orientation is caused by the combined effects of material shearing and freezing. This type of shrinkage can produce warpage similar to that from differential shrinkage. The three main ways of influencing orientation (apart from choice of material) are: 

Changing molding conditions.



Changing part thicknesses.



Changing gate locations.

Change molding conditions: It may be possible to reduce orientation by changing the molding conditions (mold temperature, melt temperature, injection speed, etc). In contrast to the other two approaches below, this remedy does not require changes to the part or the mold so is the least expensive option to try. Change gate locations: If molding conditions cannot be used to reduce orientation effects sufficiently, we must decide whether to change the gate type or location, or alter the part thickness. Other changes to the gate, apart from simply changing its location, may include using an end gating, a fan gate or multiple gates. All of these may be 50

done without significantly altering the geometry of simple parts (assuming the mold has not already been cut). Note: Changing a gate location will not alter the design specifications of the part and may be an easier option to try on parts with complex geometry and thickness variations. Once we have decided on an alternative gate location (or type), the required changes are made and the part is reanalyzed. This can be an iterative process, until the orientation level is acceptable. Change part thicknesses: If we decide that changes to the wall thickness may be of more use in reducing orientation effects for the part, then we can alter the thickness in the region in question and re-analyze the modified part model. This too can be an iterative process, until the orientation level is acceptable. Solving one problem can often introduce other problems to the injection molding process. Each option hence requires consideration of all relevant aspects of the mold design specification.

MOLDEX3D WARPAGE Moldex3D-Warp analyzes the shrinkage and warpage behaviors of the molded part after it is demolded from the mold cavity. Moldex3D-Warp adopts the finite element method and advanced programming techniques to solve the complicated three-dimensional structure analysis problems associated with the shrinkage/warpage behavior of the molding. It can be used to determine the part

51

wall thickness distribution, the layout and the dimension of the reinforcing ribs/rims in the design phase. The cooling channels should be designed in such a way that the warpage of part is minimized. Moldex3D-Warp can be used as a trouble-shooting tool to detect the key issues related to the part warpage due to PVT variation of plastic material or due to unbalanced mold cooling. In addition, Moldex3D-Warp can be used to optimize the process conditions such as cooling time, packing/holding time, holding pressure profile, and etc. Moldex3D-Warp shows how the molded part would deform or warps under the action of process-induced loading. An injection-molding part is shaped from a high temperature melt to a solid state. Variation of temperature and pressure will induce volumetric shrinkage and produce internal forces. Thus, the internal forces cause warpage of a plastic part. In this situation, this internal stress is also named residual stress. There are a lot of factors that will affect plastics’ residual stress, such as material selection, part design, mold design and processing. Displacement Displacement refers to the deformation of part caused by process-induced shrinkage and distortion. It is the difference between the dimension of original part and molded part. For the displacement in the x direction, it represents the displacement of parts along the x direction. Positive value denotes the quantity of distortion along the positive (+) x direction, while negative value is along the negative (-) x direction. Displacement in y axis and displacement in z axis have the same definition as displacement in x direction. Besides, the linear shrinkage in one direction can be defined as the maximum displacement divided by the part’s dimension in this direction.

52

(X, Y, Z) Total Displacement

These displacements mean that all of displacement occurs from the end of filling to be cooled down to room temperature. It includes all factors affecting the behavior of warpage.

53

Fig. 9.1 Warpage X – Displacement Existing

Fig. 9.2 Warpage X – Displacement Optimized

54

Fig. 9.3 Warpage Y – Displacement Existing

Fig. 9.4 Warpage Y – Displacement Optimized

55

Fig. 9.5 Warpage Z – Displacement Existing

Fig. 9.6 Warpage z – Displacement Optimized

56

Fig. 9.7 Warpage Total Displacement Existing

Fig. 9.8 Warpage Total Displacement Optimized 57

CHAPTER 10 DESIGN THROUGH CAD S/W – PRO-E From the observations made through CAE Analysis: Moldflow and Moldex3D, the injection location for the component has been changed. Two gate points at the most appropriate location was given and the runner is designed accordingly. Without altering the component design or the tool splitting, the part quality has been optimized by just a change in the injection location thereby the feed system. Tool has been modified for the proposed feed system through CAD S/W – PRO-E as shown in the figure.

2 GATE POINTS

CAVITY HALF Fig. 10.1 Optimized Tool design with two gate points

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CHAPTER 11 RESULTS COMPARISON Table – 11.1 –Results Comparison EXISTING DESIGN

DESCRIPTION

OPTIMIZED DESIGN

TOOL DESIGN DESIGN CHANGE

SINGLE GATE

2 GATE POINTS

MOLDFLOW ANALYSIS RESULTS GATE LOCATION

55% OK

91%OK

MELT FRONT TIME

0.6 secs

0.35 secs

INJECTION PRESSURE

56.48 MPa

54.46 MPa

FLOW FRONT TEMPERATURE

Non Uniform

Uniform

QUALITY PREDICTION

Not Acceptable

Acceptable

COOLING QUALITY

Not Acceptable

Acceptable

MOLDEX3D ANALYSIS RESULT X-DISPLACEMENT

-0.48 – +0.49 mm

-0.31 – +0.32 mm

Y-DISPLACEMENT

-0.19 – +0.15 mm

-0.08 – +0.11 mm

Z-DISPLACEMENT

-0.81 – +0.75 mm

-0.34 – +0.39 mm

TOTAL DISPLACEMENT

0 – 0.816 mm

0 – 0.408 mm

From the above comparative results, it is very evident that the optimized design is found to be more effective and this design of feed system produces the component with good quality which encounters the problems such as parallelism, concentricity and dimensional stability as that faced in the old design. Field trial was also taken and the new design was approved.

59

CHAPTER 12 CONCLUSION

From the discussions made, it is proved that the new design proposed as per the CAE analysis results was very effective and is found to have enhanced functional performance, such as Warpage, Flow front temperature and Part quality.

By opting CAE softwares to optimize the design the time taken for trials in producing the component and the cost that could have been consumed due to the design alterations directly in the tool with vague idea was reduced to a greater extent.

The Process conditions for producing the component with enhanced quality were also suggested through CAE Analysis study.

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REFERENCES

[1] DESIGN OF MOLDS BY R.J.W. PIE [2] C-MOLD DESIGN GUIDE, AC TECHNOLOGY [3] REITER MACHINE WORKS CATALOGUE [4] SKF ALMANAC – 8TH REVISED EDITION 1995 [5] www.basf.com [6] www.moldex3d.com [7] www.moldflow.com