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About the Book
Injection moulding, one of the most popular commercial manufacturing techniques in the plastic industry, is an automated, highly cost-effective, precise and competent manufacturing technique having ability to produce complex design products. The design of an injection mould is an integral part of the plastic injection moulding technique which affects the quality of the final product. This book is a stepwise guide to design, manufacturing, and validation of an injection mould for ‘Rotor and Cover’ of a plastic component used in a particular model of a two-wheeler. It is very useful for researchers and the people who are working in the area of tool design and manufacturing.
About Author
Dinbandhu Singh was born in Sohagpur, a small village in Gopalganj District, Bihar, India. He did his schooling from Gita Niketan Awasiya Vidyalaya, Kurukshetra, Haryana. He is an M. Tech in Tool Engineering from R.V. College of Engineering (2011) and B. Tech (2009) in Mechanical Engineering from G. Pulla Reddy Engineering College (Autonomous), Kurnool, Andhra Pradesh. His teaching career started at Al-Habeeb College of Engineering & Technology, Hyderabad, Telangana (then Andhra Pradesh) and later worked at various reputed institutions across the country. Presently, he works as an Assistant Professor in Department of Mechanical Engineering at Vidya Vihar Institute of Technology, Maranga, Purnea, Bihar. He has more than 06 years of teaching experience. His research interests are focused on Material Sciences/Composite Materials. He has published/presented/contributed more than 10 research papers in various international journals and conferences of their repute. He can be emailed at [email protected]
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Veröffentlichungsjahr: 2018
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A Guide to Injection Moulding Technique
To my Family, Friends, Teachers, and all my Students BookRix GmbH & Co. KG81371 MunichCHAPTER 1
INTRODUCTION
OVERVIEW
Injection moulding requires that the material be heated to a plastic state in a barrel and then forced into the mould cavity with a plunger under high pressure. The plasticization of the material in the barrel is facilitated by shear and friction from a rotating screw that also feeds the raw material. In thermoplastics, the material is cooled in the mould until it can be ejected. With thermo-set, the material is heated in the mould to “cure” the material before ejection. The construction of mould depends upon the shape of component, quantity required, its size and complexities of the parting surface/plane.
Before designing the mould, the designer should carefully analyze the shape, size, undercuts, holes, bosses, and sharp corners of the component. One should also try to check from preliminary calculations, the clamping force required, size of insert required, which intern decides the size of the mould, and the injection moulding machine required for production. The number of cavities in mould also plays a main role in deciding the size of the mould. The number of cavities in the mould is sometimes, as per the specification given by the customer. In this book, a family mould is considered for the design of two different types of components.
The book entitles the design, fabrication and validation of the mould for the manufacture of plastic components ‘Rotor and Cover’ weighing five grams, aimed at high productivity. Since this component is an automobile part of a two-wheeler, its life should be for 300000 per mould as per customer specification, which is due to new design change requirement these days. A new mould with higher productivity with flash free component is the primary requirement.
To accomplish this, a careful examination of the component drawing is carried out along with the 3D-solid for its geometric profiles, surface quality, and material specification, in-service condition and so on. Design exercise involves the choice of parting surface, allowance for shrinkage, draft, gate location, venting, thermal balancing of mould and choice of ejection system. The software is designed based on the knowledge of scientific and engineering principles and advanced mathematics. It is not based on intuition or guess. Therefore mould making, using the software is not just an art and but it has become an applied science.
Technology demands a good understanding of the fundamentals of physics, injection moulding process and computer skill in handling CAE and CAD. It may be difficult to combine these skills in one person to begin with. It is knowledge centered technology and demands teamwork and new work culture. For any design to be successful, the designer should have knowledge of different types of plastic materials used in the injection moulding process, their properties and the machine suitable for each of them. The forthcoming section of the review of literature deals with widely used plastic materials, machinery used for processing of components and mould design considerations.
PLASTIC MATERIAL
The selection of plastic material depends on the application of the product. The most commonly used plastic raw materials in injection moulding processes are Polypropylene (PP), Polycarbonate (PC), Polyvinyl chloride (PVC), Acrylonitrile-Butadiene-Styrene (ABS), Polystyrene (PS), PA-66 (Polyamide), etc. Among these, only a few, namely PC, PVC, PP, PA, ABS and Nylon use in automotive components due to their specific characteristics and strength.
In this work, the plastic material used is Nylon-6/6 (13% glass filled) manufactured by Dupont. Zytel is the material specified material by the customer.
ZYTEL 70G13HS1L NC010, BLACK
GenericClass: Nylon 6/6, 13% Glass filled
Tradename: ZYTEL 70G13HS1L
Applications: Automotive (Gears, Bearings and equipment requiring high strength and durability, air intake manifolds, various types of covers, throttle bodies, fasteners, ski bindings, switch gears circuit breakers, etc.)
Injection Moulding Processing Conditions:
Drying: Nylon resins are hygroscopic and drying is required prior to processing. Suggested drying conditions are 80-90oC for a minimum of 4 to 6 hours. Resin moisture content should be less than 0.1%.
Suggested melt temperature: 280-305 C (Aim: 290C).
Mould temperature: 0-95C can be used recommended is 70C (Mould temperatures control the
gloss Properties; lower mould temperatures produce lower gloss levels).
Injection pressure: 35-140 MPa. Parts should be moulded at the highest practical injection
pressure.
Injectionspeed: Moderate - high.
CHEMICAL AND PHYSICAL PROPERTIES OF NYLON
The polyamides are a group of polymers characterized by a carbon chain with -CO-NH- groups interspersed at regular intervals along it. They are commonly referred to by the generic name nylon and may be produced by the direct polymerization of amino acids or by the reaction of a diamine with a dibasic acid. Different nylons are usually identified by a numbering system, which refers to the number of carbon atoms between successive nitrogen atoms in the main chain. Polymers derived from amino acids are referred to by a single number; for example, nylon-6 is polycaprolactam. Polymers derived from a diamine and a dibasic acid are given two numbers with the first referring to the number of carbon atoms contributed by the diamine and the second referring to the number of carbon atoms supplied by the dibasic acid. Thus Nylon 6/6 is derived from hexamethylenediamine and adipic acid to give the structure shown in Figure 1.1.
Figure 1.1 Nylon 6/6
The general properties of Nylon are presented in Table 1.1.
Mechanical Properties
Conditions
State 1
ASTM
Flexural Modulus (MPa)
4830 - 5175
23 ºC
D790
Tensile Strength (MPa)
104 - 118
at break
D638
Flexural Strength (MPa) at yield or break
190
dry (0.2% water content) D790
Flexural Strength (MPa) at yield or break
104
50% relative humidity
D790
Elongation at break (%)
3 - 5
D638
Hardness
95
Rockwell M
D638
Izod Impact (J/cm of notch)
1/8" thick specimen unless noted
0.5 - 0.6
D256A
ThermalProperties
Conditions
Pressure
ASTM
Deflection Temperature (ºC)
257
0.46 MPa
D648
233-244
1.82 MPa
D648
Physicaland ElectricalProperties
Conditions
State
ASTM
Specific Gravity
1.21 - 1.23
D792
Water Absorption (% weight increase)
7.1
Saturated
D570
1.1
after 24 hrs
D570
ProcessingProperties
Conditions
State
ASTM
Melting Temperature (ºC)
257
Tm, crystalline
Processing Temperature (ºC)
272 - 299
Injection moulding
Moulding Pressure (MPa)
49 - 138
Compression Ratio
3 - 4
Linear Mould Shrinkage (cm/cm)
0.005 - 0.009
D955
Table 1.1 General Properties of Nylon
LITERATURE SURVEY
Coreand Cavityextraction
J.Y.H. Fuhetal [1] recommended 6 steps for parting design module in the 3D modelling.
Determination of the parting direction – Direction of the core and cavity open are the parting direction.
Recognition and patching the ‘through’ hole – if there is hole in the product, must indicate the parting location for the hole and determine the parting surface for these holes.
Determination of parting lines and the extruding direction – Parting line is the intersection between the two groups surfaces there are core and cavity.
Generation of the parting surfaces – a surface are the mating surface of the core and cavity. Usually the parting surface as splitting surfaces to separate the mould into two blocks, cavity and core.
Creation of containing box – Containing box is used to create core and cavity. The size of the containing box is based on the dimension of the object, strength mould, moulding parameter.
Generation of mores and cavities – the box will be split into two mould halves, the core block and cavity block. The empty space inside the containing box is the place where the molten plastic will ne inject and solidify. The flow chart of parting design module is as shown in Figure 1.2.
Figure 1.2 Parting Design Modules [1]
Runner Balancing for Multi cavity Moulds
Kevin Alam et al [2] suggested on optimization of runner balancing in multi-cavity moulds. For runner systems with equivalent secondary runner diameters and lengths, cavities farthest from the injection point will experience greater shrinkage because the longer path length causes an increase of pressure drop. Accordingly, the traditional approach to runner balancing reduces the runner diameters of the closest cavities
and increases the runner diameters of the furthest cavities to balance the pressure drops among them. A larger primary runner diameter also reduces pressure drops to the furthest cavities. Such designs minimize differences in shrinkage among the cavities and decrease the effects of variation on the runner balancing process.
When runner length was manipulated to achieve runner balancing, it became desirable to increase the length of the runners closest to the injection point to increase the pressure drops to these cavities, while decreasing the lengths of the runners furthest from the injection point to decrease the pressure drops to the furthest cavities. Both strategies help balance the pressures among the cavities, which reduce the need to increase the diameters of the primary runner and of the furthest secondary runners to achieve that balance. This ultimately reduces the runner system volume and associated material costs. Thus, the manipulation of the runner lengths and diameters is more effective in balancing the runner system than the manipulation of runner diameters alone.
Cooling Channel Design and Gate Design
