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Injection Moulding Technology - Part 3 CoWC 0410 Injection Moulding Technology Part 3 Mould Design & Construction.

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Presentation on theme: "Injection Moulding Technology - Part 3 CoWC 0410 Injection Moulding Technology Part 3 Mould Design & Construction."— Presentation transcript:

1 Injection Moulding Technology - Part 3 CoWC 0410 Injection Moulding Technology Part 3 Mould Design & Construction

2 Injection Moulding Technology - Part 3 CoWC 0410 To gain an understanding of general mould design and construction techniques, and to become familiar with the purpose and function of the various component parts. Session aim

3 Injection Moulding Technology - Part 3 CoWC 0410 By the end of the session you will be able to: Detail the requirement for venting the mould. Identify the component parts of a two plate mould. List two advantages and limitations for various gate design alternatives. State the three elements of the feed system. Identify applications for typical runner less mould designs. Explain the importance of mould temperature control. Session objectives

4 Injection Moulding Technology - Part 3 CoWC 0410 Mould material Cost restraints Mould making techniques Moulding machine Component material Quantity Post moulding operations Mould life Component detail Mould Design Mould Design

5 Injection Moulding Technology - Part 3 CoWC 0410 Core plateSplit line Cavity plate Fixed back plate Sprue Cooling channel Guide bush Air vent Dowel or Guide pin Ejector plate Runner Cold Slug Well Sprue puller pin Push back pin Moving backplate Support blocks and risers Two Plate Mould Tool Locating ring Sprue bush Ejector pin

6 Injection Moulding Technology - Part 3 CoWC 0410 Question 1 List the advantages & disadvantages of a multi-plate mould?

7 Injection Moulding Technology - Part 3 CoWC 0410 Multi-plate mould tool

8 Injection Moulding Technology - Part 3 CoWC 0410 Higher cost of tooling. More moving parts. Critical opening stroke. Runner wastage. Centre gating of multi cavity. Side gating easily achieved. Multi-point gating easily achieved. Automatic de-gating. Advantages Disadvantages Multi-plate mould tool Stripper plate

9 Injection Moulding Technology - Part 3 CoWC 0410 Question 2 On a mould that incorporates a hot runner, what might soft start facility be used for?

10 Injection Moulding Technology - Part 3 CoWC 0410 Hot runner

11 Injection Moulding Technology - Part 3 CoWC 0410

12 Injection Moulding Technology - Part 3 CoWC 0410 Ideally the sprue bush, hot tips and the manifold should have separate controllers and thermocouples. On the example four zones are required. The hot runner

13 Injection Moulding Technology - Part 3 CoWC 0410 Hot runner systems Increases the mould height. Material delivered to the cavities in the same condition as the melt left the barrel. Saved material waste from the sprue & runner. The 2 plate tool

14 Injection Moulding Technology - Part 3 CoWC 0410 Question 3 Please list 3 advantages and 3 limitations when using hot runner moulds?

15 Injection Moulding Technology - Part 3 CoWC 0410 Limitations of a hot runner Increased set-up times. Warm up period required. Increased tooling costs. Manifold leaks. Higher maintenance costs. Degradation with certain polymers. Heat expansion problems.

16 Injection Moulding Technology - Part 3 CoWC 0410 When a hot runner leaks ….it leaks !

17 Injection Moulding Technology - Part 3 CoWC 0410 Advantages of a hot runner No feed system to be removed. Reduced mould open stroke. Reduced shot weight. Injection time reduced. Automatic de-gating. Easier to balance gates. Increased number of cavities possible.

18 Injection Moulding Technology - Part 3 CoWC 0410 When using hot runner moulds Avoid regrind to avoid blocked nozzles. Avoid heat sensitive polymers. Do not flick off cold slugs. Keep systems fully maintained.

19 Injection Moulding Technology - Part 3 CoWC 0410 Question 4 What is the primary function of a stack mould?

20 Injection Moulding Technology - Part 3 CoWC 0410 Braun Ireland Stack mould - reduced projected area

21 Injection Moulding Technology - Part 3 CoWC 0410

22 Injection Moulding Technology - Part 3 CoWC 0410 Valve to Valve

23 Injection Moulding Technology - Part 3 CoWC 0410 Spring opening

24 Injection Moulding Technology - Part 3 CoWC 0410 Question 5 What are the different types of ejector pins and methods of ejection?

25 Injection Moulding Technology - Part 3 CoWC 0410 Combination round/blade ejection Blade ejectors Round ejectors

26 Injection Moulding Technology - Part 3 CoWC 0410 Sleeve ejection Core pin Sleeve

27 Injection Moulding Technology - Part 3 CoWC 0410 Good even ejection around bosses but quite expensive. Sleeve ejection

28 Injection Moulding Technology - Part 3 CoWC 0410 Stripper plate ejection Stripper block

29 Injection Moulding Technology - Part 3 CoWC 0410 Air off - spring returns valve to its rear position Air ejection

30 Injection Moulding Technology - Part 3 CoWC 0410 Question 6 When would mechanical or hydraulic core movement be used?

31 Injection Moulding Technology - Part 3 CoWC 0410 Mechanical core pin movement

32 Injection Moulding Technology - Part 3 CoWC 0410 Core pulling

33 Injection Moulding Technology - Part 3 CoWC 0410 Points to remember: If in doubt ASK! Core movement by hydraulics Machines will need to be programmed. There are many different sequences. Must know the sequence, before opening or closing the mould.

34 Injection Moulding Technology - Part 3 CoWC 0410 Question 7 When designing a mould, utilising a cold runner system, what are the primary considerations to be addressed?

35 Injection Moulding Technology - Part 3 CoWC 0410 The feed system

36 Injection Moulding Technology - Part 3 CoWC 0410 Runner shape Which shape will give the best flow? 10 deg

37 Injection Moulding Technology - Part 3 CoWC 0410 Runner layout

38 Injection Moulding Technology - Part 3 CoWC 0410 Runner layout

39 Injection Moulding Technology - Part 3 CoWC 0410 General guidelines Single Mould As the number of cavities increases, so must the machine tonnage 2,4,6,8,12,16,24,32,48,64 cavities are typical. No odd numbers!

40 Injection Moulding Technology - Part 3 CoWC 0410 Question 8 Please list advantages & disadvantages for the selected gates: Sprue gate Pin gate Diaphragm gate Tab gate Flash gate Fan gate Tunnel gate

41 Injection Moulding Technology - Part 3 CoWC 0410 Tab gate Diaphragm gate Sprue gate Pin gate Gates Flash gate Fan gate

42 Injection Moulding Technology - Part 3 CoWC 0410 Runner Submarine/tunnel gate Component Sprue Gate

43 Injection Moulding Technology - Part 3 CoWC 0410 Submarine/tunnel gate

44 Injection Moulding Technology - Part 3 CoWC 0410 Gate considerations Size in relation to section thickness of the moulding. Always feed into the thickest section. Position gate to give even filling.

45 Injection Moulding Technology - Part 3 CoWC 0410 Question 9 Why is mould venting required?

46 Injection Moulding Technology - Part 3 CoWC 0410 Exhaust grooves Vent depth 0.025mm Mould venting To prevent burning/dieseling.

47 Injection Moulding Technology - Part 3 CoWC 0410 Question 10 What are the general considerations for the correct moulding temperature?

48 Injection Moulding Technology - Part 3 CoWC 0410 Mould temperature control As uniform as possible, to ensure the mould is cooled equally in all areas. Mould temperature has the greatest influence on part quality. High enough to allow filling of the mould, without premature freezing of the polymer melt.

49 Injection Moulding Technology - Part 3 CoWC 0410 Piping up considerations 1in 2in 1out 2out

50 Injection Moulding Technology - Part 3 CoWC 0410 Core Coolant flow Used as an alternative to cooling channels. Cool core pin technology

51 Injection Moulding Technology - Part 3 CoWC 0410 Beryllium copper insert to improve cooling

52 Injection Moulding Technology - Part 3 CoWC 0410 Cooling baffles Baffles may be offset to achieve turbulent flow. Must be piped correctly.

53 Injection Moulding Technology - Part 3 CoWC 0410 Spiral flow cooling in Material entering the mould will be at its hottest in out

54 Injection Moulding Technology - Part 3 CoWC 0410 Machine Practical 1

55 Injection Moulding Technology - Part 3 CoWC 0410 Injection Moulding Technology Part 3 Mould Design & Construction

56 Injection Moulding Technology - Part 3 CoWC 0410 Injection Moulding Technology Part 3 Plastics Materials

57 Injection Moulding Technology - Part 3 CoWC 0410 Aim To provide an understanding of plastics materials technology and processing behaviour when injection moulded.

58 Injection Moulding Technology - Part 3 CoWC 0410 Describe, in simple terms, the molecular structure of plastics materials. State three methods of classifying plastics, giving examples. Describe the MFI test and it’s relevance. Identify five common additives to modern plastics. Objectives By the end of the session you will be able to:

59 Injection Moulding Technology - Part 3 CoWC 0410 What are plastics? Synthetic -Man made Organic -Based on carbon Polymers - Describes the MOLECULES of polymers Many units

60 Injection Moulding Technology - Part 3 CoWC 0410 Polymerisation example cc H H H H cc H H H H c c HH HH cc HH HH ETHYLENE Monomer

61 Injection Moulding Technology - Part 3 CoWC 0410 c H H c c H H POLYETHYLENE polymer ETHYLENE monomer Polymerisation example Catalyst - heat, pressure and time cc H H HH c H H H cc HH H H c

62 Injection Moulding Technology - Part 3 CoWC 0410 Polymer examples Polypropylene polymer Propylene monomer Polystyrene polymer Styrene monomer Polyvinylchloride polymer Vinyl Chloride monomer Polycarbonate polymer Phosgene Bis-Phenol Acetone monomer

63 Injection Moulding Technology - Part 3 CoWC 0410 Summary Polymer chains have a coiled spring like structure. About 5,000 times longer than their diameter. Chains are upwards of 1,000,000 repeat units long. Processing of polymers reduces the chain length and hence the loss of properties when using regrind.

64 Injection Moulding Technology - Part 3 CoWC 0410 Classifying plastics Thermosets Example - Bakelite Curing/solidification Heat & Pressure Cross-linking reaction Flows due to pressureHeat Melt

65 Injection Moulding Technology - Part 3 CoWC 0410 Classifying plastics Bakelite Rubber Epoxy Melamine Polyester (Chemical change - Boiled egg) Thermosetting

66 Injection Moulding Technology - Part 3 CoWC 0410 Thermoplastics Example - Polyethylene Melt Flows under pressure Heat Cool/remove heat Solidification Classifying plastics

67 Injection Moulding Technology - Part 3 CoWC 0410 Thermoplastics Polyethylene Polystyrene Polycarbonate Nylon Polyester (Physical change - Ice to water) Classifying plastics

68 Injection Moulding Technology - Part 3 CoWC 0410 Commodity Engineering Classifying plastics

69 Injection Moulding Technology - Part 3 CoWC 0410 Commodity £600 - £950 £500 - £900 £600 - £900 £600 - £1200 £900 - £1500 £ £2500 Polypropylene HDPE LDPE Polystyrene SAN Acrylic ABS Price/tonnePlastic Prices are only approximate Classifying plastics

70 Injection Moulding Technology - Part 3 CoWC 0410 Engineering PlasticPrice/tonne PET Acetal (POM) Nylon (PA) PBT PC PAI PEEK £ £1200 £ £1900 £ £2400 £ £2700 £ £3500 £ £40000 £ £69000 Prices are only approximate. Manifold PA66 GF35 Classifying plastics

71 Injection Moulding Technology - Part 3 CoWC 0410 Amorphous versus Semi-crystalline! What are the differences? Classifying plastics

72 Injection Moulding Technology - Part 3 CoWC 0410 Structural changes of polymers Semi-Crystalline Ordered structure Molten state Amorphous Random structure Flow COOL

73 Injection Moulding Technology - Part 3 CoWC 0410AmorphousSemi-crystallineThermoplastics Polycarbonate A.B.S. Polystyrene S.A.N. Acrylic Polyethylene Polypropylene Nylon Acetal Polyester Classifying plastics

74 Injection Moulding Technology - Part 3 CoWC 0410AmorphousSemi-crystalline Wide melting rangeNarrow melting range Generally clear Generally opaque Property differences High mould Shrinkage 1.5%-2.5% Low mould shrinkage 0.5% Why is crystallinity important?

75 Injection Moulding Technology - Part 3 CoWC 0410 Amorphous plastics Melt and solidify over a WIDE temperature range. Semi-crystalline plastics Melt and solidify over a NARROW temperature range. (i.e they have a crystalline melting point) Flow behaviour Amorphous + Ease of flow + Temperature Semi-crystalline (PA) (PMMA)

76 Injection Moulding Technology - Part 3 CoWC 0410 Homo-polymers The homo-polymer chains comprise of the same repeat unit for their entire length. Examples: HDPE, PA, POM, PVC, PS, PP.

77 Injection Moulding Technology - Part 3 CoWC 0410 Co-polymers Co-polymer chains comprise of two or more different repeat units, which are linked together. Examples: ABS, SAN, POM, PP, HIPS. (ABS – Acrylonitrile-Butadiene-Styrene)

78 Injection Moulding Technology - Part 3 CoWC 0410 Blends Blends & Alloys Two or more different polymers in the same matrix but not linked. Noryl PPO/PS HIPSHigh Impact Polystyrene Alloys Two or more different polymers in the same matrix plus a chemically adhesive additive. Xenoy Bayblend PC/PBT PC/ABS

79 Injection Moulding Technology - Part 3 CoWC 0410 Why use additives? Additives in polymers Modify service performance. Modify processing performance.

80 Injection Moulding Technology - Part 3 CoWC 0410 Assist processing Modify bulk mechanical properties Modify bulk mechanical properties Reduce costs??? Reduce costs??? Heat stabilisers Lubricants Plasticisers Reinforcing fillers Toughening agents Powdered fillers e.g. talc or chalk Types of additives Essential additives = Flexible PVC

81 Injection Moulding Technology - Part 3 CoWC 0410 Modify surface properties Modify optical properties Prevent ageing Others Anti-static agents Pigments and dyes U.V. stabiliser Blowing agents Flame retardants Additional additives

82 Injection Moulding Technology - Part 3 CoWC 0410 Melt Flow Index apparatus (MFI)

83 Injection Moulding Technology - Part 3 CoWC 0410 Melt Flow Index apparatus Barrel Insulation Polymer Melt Die Thermometer inside an oil filled well Weight Avg. weight of extruded plastic in 10 mins.

84 Injection Moulding Technology - Part 3 CoWC 0410 Chain lengths can be shortened by processing or regrinding. Chain length Effects of processing First pass Lower viscosity Higher MFI Lower strength material

85 Injection Moulding Technology - Part 3 CoWC 0410 Melt Flow Index The bigger the value - the easier the flow. Values can reflect relative chain lengths. Low shear (not representative of injection moulding) Spiral flow test better. Summary Used as a quality control for incoming material. Specific test conditions must be used.

86 Injection Moulding Technology - Part 3 CoWC 0410 Cycolac, Lustran, TerluranABS Delrin, Hostaform, KematalAcetal (POM) Plexiglas, Lucite (Perspex)Acrylic (PMMA) Lupolen, Rigidex, VestolenHDPE Styron, LacqreneHIPS Ultramid A, Zytel 66, Maranyl A Nylon 66 (PA 66) Common trade names Trade names Family names Santoprene, EPDMTPE’s

87 Injection Moulding Technology - Part 3 CoWC 0410 Moisture absorption - Hygroscopic Not affected - drying not usually required. POM, PE, PP, PS, PVC Water absorbed - may need drying. PMMA, ABS, SAN, PP + talc Damaged by water - needs drying. PC, PET, PA, PBT, PUR Pre-treatment of plastics

88 Injection Moulding Technology - Part 3 CoWC 0410 Methods for removing moisture: Pre-treatment of plastics Vacuum oven Dehumidifying dryer

89 Injection Moulding Technology - Part 3 CoWC 0410 Type of material – ABS, PC, PA plus virgin or regrind. Temperature and time required. Volume held in dryer to give correct throughput. Maintenance of dryer. Key drying considerations: Pre-treatment of plastics

90 Injection Moulding Technology - Part 3 CoWC 0410 Injection Moulding Technology Part 3 Plastics Materials

91 Injection Moulding Technology - Part 3 CoWC 0410 Injection Moulding Technology Part 3 Processing & Troubleshooting

92 Injection Moulding Technology - Part 3 CoWC 0410 Processing

93 Injection Moulding Technology - Part 3 CoWC 0410 Mould Closes Mould Opens Cooling Phase Holding Phase InjectionPhase Mould 99% Full Injection Speed & Pressure Apply Locking Tonnage Start Mould Safety Open Period Aims during the injection phase

94 Injection Moulding Technology - Part 3 CoWC 0410 Mould fill analysis

95 Injection Moulding Technology - Part 3 CoWC 0410 Melt flow behaviour Mould cavity Fountain flow Frozen layers

96 Injection Moulding Technology - Part 3 CoWC 0410 Example of skin formation Skin New colour Previous colour

97 Injection Moulding Technology - Part 3 CoWC 0410 Molecular orientation Slow injection speed Low orientation/Stiff flow Mould cavity Thicker frozen layers

98 Injection Moulding Technology - Part 3 CoWC 0410 Molecular orientation Mould cavity Fast Injection Speed High orientation/Easy flow Thinner frozen layers

99 Injection Moulding Technology - Part 3 CoWC 0410 Residual stress Slower filling or colder moulds Mould cavity Thick frozen layers High residual stress !

100 Injection Moulding Technology - Part 3 CoWC 0410 Residual stress Faster filling or hotter moulds Thin frozen layers Low residual stress ! Mould cavity

101 Injection Moulding Technology - Part 3 CoWC 0410 Effect of residual stress Fast fill rate - Lower internal stress Slow fill rate - Higher internal stress

102 Injection Moulding Technology - Part 3 CoWC 0410 Injection phase Aim to fill the mould as quickly as possible. Uniform melt front speed as part fills. Mould cavities fill evenly. Ensure mould is 99% full. Summary

103 Injection Moulding Technology - Part 3 CoWC 0410 Mould Closes Mould Opens Cooling Phase HoldingPhase Injection Phase Gate Freeze-off Hold Pressure & Time Mould 99% Full Injection Speed & Pressure Apply Locking Tonnage Start Mould Safety Open Period Aims during the holding phase

104 Injection Moulding Technology - Part 3 CoWC 0410 Polymer compression Pressure is applied to the melt. Melt density increases. Material shrinkage reduces.

105 Injection Moulding Technology - Part 3 CoWC 0410 Weight Holding time (secs) (gms) Gate freeze-off Gate frozen using 35 o C mould & 230 o C melt Gate frozen using 55 o C mould & 230 o C melt

106 Injection Moulding Technology - Part 3 CoWC 0410 Ensure adequate compression of the melt. Reduce sinks and voids by compensating for the shrinkage of the polymer chains Obtain consistent component quality by establishing gate freeze-off time. Obtain correct component weight/dimensions by the application of a suitable pressure. Rule of thumb: Amorphous plastics require a low holding pressure. Semi-crystalline plastics require a high holding pressure. Holding phase Summary

107 Injection Moulding Technology - Part 3 CoWC 0410 Mould Closes Mould Opens CoolingPhase Holding Phase Injection Phase Screw Back Completed Start Screw Rotation Gate Freeze-off Hold Pressure & Time Mould 99% Full Injection Speed & Pressure Apply Locking Tonnage Start Mould Safety Open Period Aims of the cooling phase

108 Injection Moulding Technology - Part 3 CoWC 0410 Factors to consider Polymer type – Semi-crystalline or Amorphous. HDT – Heat Distortion Temperature. Capacity of temperature control unit. Cooling time versus refill time (open nozzle).

109 Injection Moulding Technology - Part 3 CoWC 0410 ? HOT SIDE COLD SIDE Mould Tool Cooling rate, shrinkage & distortion

110 Injection Moulding Technology - Part 3 CoWC 0410 Cooling rate, shrinkage & distortion More shrinkage Cold side Hot side Normal shrinkage effect Residual orientation effect (stress) Hot side Cold side Low orientation High orientation

111 Injection Moulding Technology - Part 3 CoWC 0410 Cooling phase To remove heat at an appropriate rate to promote maximum service properties. To remove the heat from all cavities evenly. To allow the part to be ejected without distortion. To provide sufficient time to plasticise a homogeneous mass of molten polymer. Summary

112 Injection Moulding Technology - Part 3 CoWC 0410 Troubleshooting

113 Injection Moulding Technology - Part 3 CoWC 0410 Troubleshooting ASSESSMENT CORRECTION Is the fault acceptable – check the first off. If not, then check the basics first: The mould (damage, vents). The material (grade, batch, moisture). The machine (wear, malfunction).

114 Injection Moulding Technology - Part 3 CoWC 0410 Residual stress Slower filling or colder moulds Mould cavity Thick frozen layers High residual stress !

115 Injection Moulding Technology - Part 3 CoWC 0410 Residual stress Faster filling or hotter moulds Thin frozen layers Low residual stress ! Mould cavity

116 Injection Moulding Technology - Part 3 CoWC 0410 Relationship between faults & cycle steps OUT OF CYCLECOOLINGHOLDINGINJECTION Note: Note: Some faults can be related to more than one specific part of the injection moulding cycle. Weight Sinking Flash Voids Dimensions Contamination Mica marks DistortionFlash Short Gas trap Jetting Flow lines Weld lines Dieseling

117 Injection Moulding Technology - Part 3 CoWC 0410 Troubleshooting Examine the mouldings and determine the: FaultCauseRemedy

118 Injection Moulding Technology - Part 3 CoWC 0410 Example of Fault - Cause - Remedy Burn mark (Dieseling) REMEDY FAULT CAUSE Trapped gas Clean vents. Reduce Locking tonnage. Reduce injection speeds or profile. Reduce melt temperatures.

119 Injection Moulding Technology - Part 3 CoWC 0410 Short term Locking tonnage Holding pressure time Cooling time Injection speed Holding pressure Change over position Shot weight Decompression Ejector speed Long term Melt temperature Mould temperature (Oil temperature) Determine actual temperatures using a pyrometer for both mould and melt. Back pressure Screw speed Processing variables

120 Injection Moulding Technology - Part 3 CoWC 0410 Systematic approach Eliminate faults in order of priority: Those that potentially damage the mould - Flash - Gas burns/traps Optimise the filling phase % full Filling phase faults - Jetting - Flow lines - Weld lines

121 Injection Moulding Technology - Part 3 CoWC 0410 Systematic approach Holding phase related - Voids - Sinks - Undersized Optimise the holding phase - Holding pressure - Gate freeze-off time - Cushion Size Optimise the cycle time - Cooling time

122 Injection Moulding Technology - Part 3 CoWC 0410 Troubleshooting Summary Adopt a logical and systematic approach Change one condition at a time Consider the interaction of conditions Keep samples Keep notes Be patient Don’t be a knob Twiddler!!

123 Injection Moulding Technology - Part 3 CoWC 0410 Injection Moulding Technology Part 3 Processing & Troubleshooting

124 Injection Moulding Technology - Part 3 CoWC 0410 Blade ejection

125 Injection Moulding Technology - Part 3 CoWC 0410 Round ejection

126 Injection Moulding Technology - Part 3 CoWC 0410 Sleeve ejection Return

127 Injection Moulding Technology - Part 3 CoWC 0410 Return Sprue bush


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