DESIGN VALIDATION AND DEVELOPMENT OF PLASTIC INJECTION MOULD CAVITY FOR CONTAINER PLASTIC PRODUCT

Transcription

1 UNIVERSITI TEKNIKAL MALAYSIA MELAKA DESIGN VALIDATION AND DEVELOPMENT OF PLASTIC INJECTION MOULD CAVITY FOR CONTAINER PLASTIC PRODUCT Thesis submitted in accordance with the partial requirements of the Universiti Teknikal Malaysia Melaka for the Bachelor of Manufacturing Engineering (Manufacturing Design) By CHIN KAT MENG

2 ABSTRACT Plastic Injection Moulding is one of the popular commercial manufacturing in plastic industry, it has the ability to produce any complex design product. This project, aims to validate design of the plastic container to be manufactured by using plastic injection molding. The design of the product needs to convert into cavity and core of the mould and the form of mould cavity is done by using several advanced manufacturing processes to fabricate the product. This project begins with the validation of the dimension of the mould by measuring the existing mould using CMM machine. The procedures of handling mould and the method to measure the mould dimension will be state out. The next step is modeled process using CAD/CAM software to construct the 3D model. The CAD/CAM software used in this modeling process is CATIA, because it has wide flexibility and capabilities in the 3D modeling. After the modeling, a process plan is generated and the mould fabrication processes will be carried out using various type of manufacturing process. The design feature and process parameter is analyzed and verified. The project is concluded with a discussion of the manufacturing process in general, including some of the future developments, and some of the recommendations iv

3 ABSTRAK Plastic Injection Moulding adalah salah satu proses pembuatan komersial yang popular dalam perindustrian plastik, ia dapat menghasilkan pelbagai jenis produk rekabentuk kompleks. Projek ini, bertujuan untuk mengesahkan rekebentuk kotak plastik yang digunakan dalam mesin suntikan plastik. Rekabentuk plastik produk itu perlu ditukar dalam bentuk acuan dengan menggunakan beberapa jenis proses pembuatan termaju untuk menghasilkan produk ini. Projek ini dimulakan dengan mengesahkan ukuran acuan dengan menggunakan mesin CMM. Seterusnya ialah menunjukkan langkan-langkah untuk menguruskan acuan dan cara-cara untuk mengukur ukuran acuan itu. Permodelan 3D akan menggunakan perisian CAD / CAM sebagai satu alat model untuk membina 3D model. Perisian CAD / CAM yang akan digunakan dalam proses permodelan 3D adalah CATIA, kerana ia mempunyai fleksibiliti yang luas dalam permodelan 3D. Selepas permodelan 3D, menghasilkan suatu proses rancangan dan proses fabrikasi acuan akan mengikut rancangan yang ditentukan. Fabrikasi acuan akan dijalankan dengan menggunakan berbeza jenis mesin dan proses. Projek ini ditamatkan dengan satu penbincangan berkaitan dengan proses pembuatan, serta termasuk beberapa cadangan untuk masa hadapan.

4 CHAPTER 1 INTRODUCTION This project is to design and develop a cavity insert of mould for the container plastic product by using CAD/CAM software and advanced manufacturing process. Develop a mould cavity is require combination of several stages until to the final product and is aimed to the mould are able to function as well. In the design and develop of a mould which needed many of the computer-aided design or manufacturing software and machine to complete the design and development of a mould. Listings below show the stages of design and development of a cavity mould: Design and determination on specification and dimension of the product Technical Drawing Generation in 2D and 3D with full scale of dimension Study the structure of the mould, characteristics Modeling the mould cavity for the product Mould fabrication and construct Select the appropriate process for fabrication and planning the process sequences 1

5 1.1 Background of the Problem This project is continuous of previous study. Previous study is focus on the analysis and design the mould for Container Plastic Product. While in this project will concentrate on the validate the previous design s dimension and plan a process to develop the mould for container plastic product. The development process of the mould is generally a critical way for the newcomer in the mould industry. Mould development require years of experience and knowledge or either the effort or money are sacrificed will just waste it without any return rate. So it is very difficult for a new comer in this field to develop a mould without years of experience. 1.2 Statement of the Problem The most efficient way to improve the knowledge in the mould development is research on the existed mould development procedure in the market. Apply these methods or the systems into the mould development process. From the development process try to analysis all the failure and successful factor and sure its all these result and study will be the best experience and knowledge base for the next mould development process. Below is the list of the problems statement: Unsure dimension accuracy provided by the previous study. Process selection and process planning for mould development 2

6 1.3 Objectives In this final project objective is to study on design and develop cavity of a mould, the objectives are listing below: Learn to use CAD/CAM software to design a mould Understanding the Mould Structure and its function especially in the cavity side of the mould Learn to choose most appropriate manufacturing process for the mould construction Aims to obtain tolerance of the mould dimension become as precise as possible 1.4 Scope The scope of this final project is listing below: Study, verify the dimensions of container plastic product. Confirmation on the dimension is precise and suitable for fabricated Study function of the components and configuration of the mould. These include understand all the components in the mould and its each function Developed cavity of the mould by using most suitable manufacturing process. 3

7 1.4.4 Planning the whole process for the mould fabrication, the process planning include tools and process used in the fabrication and methods of removal material. 1.5 Importance of the Project This project enable to widen the knowledge in the injection moulding process including design and development of a mould. Form this project surely will improve the understanding the whole mould structure, components, features and its components function. Beside that, through this project can gain more understanding in the mould design and mould development process. All these knowledge are very useful when involve in the mold making industrial. 1.6 Organization of the Report Chapter 1: Introduction In this chapter, will explain the objective and the scope of this project. Beside, in the introduction has been stated out the problems statement of the se project and the importance of this project for the future study. Chapter 2: Literature Review Literature review will study on all the research and study has been done and relevant to this project. The literatures are providing very useful information and knowledge to important to finish project. Chapter 3: Methodology In the methodology, will explain the all the procedure and progress to finish this project including release mould, assembly and disassembly mould 4

8 procedure, measuring process by using the CMM, and the manufacturing process involved during the machining job. Chapter 4: Development of Cavity mould and Dies In this chapter, will explain the process plan to machining the mould cavity and dies by using several manufacturing process. Chapter 5: Result Finished mould cavity and the dies will be show at this chapter. Chapter 6: Discussion In this chapter, will discuss on the adjustment and few considerations should be concerns of. These factors will help to improve the quality and the accuracy of the mould. Chapter 7: Conclusion and Recommendation Conclude what has been gained during the whole progressing of this project. Beside that, recommend some opinion to improve the process planning quality. 5

9 1.7 Flow Chart of the Project 1.8 Schedule of the project Figure 1.1: Flow chart of the project Figure 1.2 below show the plan of schedule for the first part of the project: Task/Week Literature Review Mould Study Data Collection Refinement Analysis 6

10 Verification Drawing Writing Up Figure 1.2: Schedule of project Figure 1.3 below show the plan of schedule for the second part of the project: Figure 1.3: Schedule for the second part of the project Task/Week Process Planning - Process selection - Tools selection - Graphic process flow - Die fabrication - Operation details Fabrication Writing Up 1.9 Summary Overall in this project will more concentrate on the mould design, material selection for product and the mould base, analysis and modeling the cavity mould, measure the existing mould by using CMM, study the injection moulding machine function and selection development process for the mould fabrication. 7

11 CHAPTER 2 LITERATURE REVIEW 2.1 Introduction This chapter s content is literature review on mould development process and mould structure (features and components). Mould development will be review by the stages and the process to develop a mould from the design product to the machining stages. Beside that, will review on the CAD/CAM software used in the mould development process and material selection for the plastic product. 2.2 Mould Development Process A new procedure has been proposed for the developments of mould by Z.lou, H,Jiang, X. Ruan (2004). The procedure should implement through an integrated, knowledge-based system to improve mould design efficiency and shorten design time. Normally, the conventional designer will separate the mould design are divide into three stages : detailed design of the mould, design of the mould-base and ordering the mould base from the manufacturer. In the new mould development process was purpose by Z.lou, H,Jiang, X. Ruan, firstly the design mould-base according to dimension of the product. Secondly, begin to design the detail of the 8

12 mould while ordering the mould base from the manufacturer. The step of the design the detail of mould and ordering the mould-base are carry out at the same time, enable to shortening the product development cycle as shown in Figure 2.1. Figure 2.1: New Mould Design Process, Z.lou, H,Jiang, X. Ruan [1] According to K.Shelsh-Nezhad (1997) after the mould design has been determined, the designer will be determine the other element of the mould there are: Cavity and Core Plate determining the dimension of the plate, Cavity calculation Calculating the shrink ratio in the part and part s profile, Set- in calculation calculating the dimension of set-in and other factors for set-in, Slide calculation considering the dimension of the mold-base for the slide subsystem, Calculating the number of plates determining the dimensions of the plates in the mold-base on the gate and product information, Mold-base creating in the mold-base model based on the information above, Mold-base check - checking the interference of additional structures (spring, ejector pin, etc.), Injection machine choice checking the installation method and interference between the mold-base and the machine as shown in Figure

13 Figure 2.2: Flow Diagram in Mould-base Design [24] Knowledge-based system(kbs) (2003) is software built on the product model that is able to store and process the knowledge relevant to this product model, including the product s design analysis and manufacturing methods; Z.Fang(2001), M.A. Moss (1999), V.C. Mountiantis(1999). In the mould-base KBS, there is a mould library, inside the library consists of many design cases, model of mouldbased and other parts. So the KBS can helping in the mould design to easier the design process and the library inside the KBS will also aided in the development of the mould [2]. 3D mould-modeling by using CAD system is the design mainstream. Reason is CAD system provide the flexibility has let the software developers create application that are easy to use. L.Kong, J.Y.H. Fuh, K.S. Lee, X.L. Liu, L.S. Ling, Y.F. Zhang, and A.Y.C. Nee [2]. CAD system has grown become wide range of capabilities and the application is ranging from education to 3D mechanical design. The mould 10

14 development divided into 4 phase: product design, mould ability assessment, detailed part design, insert/cavity design and detailed mould design. L.Kong, J.Y.H. Fuh, K.S. Lee, X.L. Liu, L.S. Ling, Y.F. Zhang, and A.Y.C. Nee (2003) stated the parting design moulds into 6 steps in the 3D modeling. Step 1 : Determination of the parting direction Direction of the core and cavity open are the parting direction. Step 2 : 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 hole. Step 3 : Determination of parting lines and the extruding direction Parting line is the intersection between the two groups surfaces there are core and cavity. Step 4 : Generation of the parting surfaces a surface are mating surface of the core and cavity. Usually the parting surface as splitting surfaces to separate the mould into two block, cavity and core. Step 5 : 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. Step 6 : 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 as shown in Figure

15 Figure 2.3: Parting Design Module, L.Kong, J.Y.H. Fuh, K.S. Lee, X.L. Liu, L.S. Ling, Y.F. Zhang, and A.Y.C. Nee [2] According to the Wong Choon Tat, Shamsuddin Sulaiman, Napsiah, A.M.S.Hamouda (2002), plastic product almost used in every filed field of our live: space travel, transportation, packing, medicine, toys bridge building and sport. Injection moulding is where the molten plastic fill into the mould(desired shape) so the Injection of plastic into the mould has been categories into 3 phase: Filling Phase, Pressurization Phase and Compensating Phase. Filling Phase this phase where the molten material are filling the cavity of the product inside the mould. The molten material contact to the wall of the mould will solidify very fast than other area. Pressurization Phase Even all the cavity is filled with the molten material but at the corner or edges, or the angle may not fulfill with the molten plastic because of the path is too narrow, so extra pressure and material need to complete the fullness of the cavity. Compensating Phase Plastic is a high shrinkage material, from the molten phase to the solid phase it will shrinkage around 25%, after the pressurization phase, should pack the material into the mould [4]. 12

16 S.H. Tang, Y.J. Tan, S.M. Sapuan, S. Sulaiman, N. Ismail, R. Samin (2007) The machining processes that have been done are such as drilling, milling and tapping. The sequence for machining processes is important to get a good quality of work and also saving the machining time. In machining process, there are some steps that should be highlight and pay attention. For drilling process, especially for cooling channel, the drilling machine that has been used is radial drilling machine instead of vertical drill press. This is because the spindle speed for radial drilling machine is controlled by gear while the vertical drill press is used belt. Thus, the radial drilling machine can produce higher drilling torque as compared to the vertical drill press [8]. Suqin Yao (2003) stated that process sequence divide into 2 principles Principle 1: The setup sequence must be arranged according to the sequence of design features. Principle 2: The setup sequence must be arranged according to the feature s pre-defined process sequence. The process sequence should always follow the basic manufacturing principle, there is doing rough cuts first, and semi and finish cuts in a prescribed order. Beside that, Suqin Yao (2003) had categories manufacturing plan generation into 4 steps, there are 1) Machine tool selection, 2) Part layout design, 3) Global process sequence and tool path generation, and 4) Cycle time calculation for mass production [31]. Shaw C. Feng and Eugene Y. Song (2003) stated that process planning is a key activity for designers to evaluate manufacturability and manufacturing cost and time in the early product development stage. So it is important to integrate the design and process planning message exchange to save time and cost of development [32]. The design and process planning integration show in the Figure

17 Figure 2.4: Design and Process Planning Message Exchange for Integration 2.3 Mould Design New mould design, there are few important information must defines before go further any design process to avoid the mistake cause the plastic product out of dimension and the defect can not be adjust anymore by controlling the parameter of the machine [4]. List of few main point should be take account are material for mould and plastic product, mould base type, number of cavities and customer needs as shown in Figure

18 Figure 2.5: Mould Design Procedure [4] Charles Shaw [5] stated that the melts front moves through the mould, molten plastic contacts with wall of the mould and immediately begins to cool and solidly. Thus the first resin to contact the wall is further along in the cooling process at the end of filling than the last resin to be injected. In additional,thicker portions of the mould cool slower than thinner portions. This diference in cooling time aerates uneven volumetric contraction in the part, which lead to warpage of the plastic product. If the part do not design properly, the warpage to the product will exceed the required tolerances, the produced part is fail. 15

19 From the information of (DSM Engineering Plastic mould construction) [18]. A general injection mould is consists of a stationary or injection side which the stationary side containing one or more cavities and while the injection side is moving or ejection side. Below is Figure 2.6 about the mould structure and part: Figure 2.6: Mould Structure provide by DSM The design of a mould is constructed is depending on the following elements: Product shape, Total number of cavities, Type of gating system, and Venting System. Table 2.1: Part and Mould Characteristic 16

20 Table 2.2: Mould Accuracy Standard Respective tolerances with different product function and design is of economic importance. During the mould design progress should be determined that dimensions with tight tolerances or lose tolerances because this will have a influence on the cost. Even slightly over different on the tolerances may bringing a huge influence tool costs, injection molding conditions, and cycle time. It is recommended to indicate only necessary dimensions with tolerances on a technical drawing Number of cavities and Surfaces Finish (DSM Engineering Plastic Mould Structure) Example of determined the number of cavities. A given molding machine has a maximum barrel capacity of 254 cm3, a plasticizing capacity of 25 g/s, 45 mm screw and a clamping force of 1300 kn. A PC part of 30 cm3, (shot weight 36 g) and a projected area of 20 cm2 including runners requires about 5 kn/cm2 clamping force [18]. The maximum number of cavities based on the clamping force would be 12. It is advisable to use only 80% of the barrel capacity, thus the number of cavities in this example is limited to 6. When very short cycle times are expected the total number of cavities may be further reduced. A 6-cavity mold in this example requires a shot weight of 216 g. The cooling time must be at least 8.7 seconds. 17

21 Patricia Miller, (2007) say that choosing the right tooling material for plastic molding is becoming ever more difficult. In light of intense competition, as well as the cost of raw materials, which is driving the price of materials for molds up, it becomes increasingly more important to be selective in the choice of mold materials. There are things that can be done to help the moldmaker make the best selections for the application at hand, and these things are not simply looking at the price per pound [15]. But in order to do this, the moldmaker must consider other factors. This starts at the beginning of the moldmaking cycle, as the part to be manufactured is being proposed. The major areas to be considered in a mold design include: Size and complexity of the part or mold, Production quantity required, Type of plastic molding material required and its impact on the molding environment, Mechanical requirements for the mold, Physical property requirements for the mold [17] (thermal conductivity, stiffness, thermal expansion), Stability requirement of mold during operation, Assembly issues (mating material criteria, coatability), Design features (sharp corners, thin sections, sealing methods), Surface condition requirements (polishing, texturing demands), Manufacturing methods (electro discharge machining, hard milling). Cost savings can occur in all these areas, but for this discussion four areas of alloys will be addressed: New high hardness matrix alloys, Thermally conductive alloys, Corrosion resistant materials, and Prehardened alloys [16]. According to the M.K.A.Ariffin, S.Sulaiman, M.M.Hamdan, Z.Leman, N.Ismail (2002) integrating the computer software such as CAD/CAM, Moldflow makes mould making industries becomes easier compare to the traditional method which has been prove time consuming and very costly. A mould is actually the part of the injection moulding which produce the product. The product quality is depends on the mould itself, thus if any defect or design errors will also affected the end product quality. so it is important to make sure the mould quality [3]. 18

22 Nagahanumaiah, K.Subburaj, B.Ravi [6] manufacturability evaluation involves determining the technical and economical feasibility of a mold produced by a selected rapid tooling process. The proposed RT manufacturability evalustion approach comprises three steps: 1) primary manufacturability evaluation of functional elements of tooling including cavity, cores and side cores, 2) compatibility of cooling lines, with RT mold properties, and 3) the cost effectiveness of RT mold. S.H. Tang, Y.M. Kong, S.M. Sapuan, R. Samin, S. Sulaiman (2006) The plastic injection molding process is a cyclic process. There are four important stages in the process. These stages are filling, packing, cooling and ejection. The plastic injection molding process begins with feeding the resin and the appropriate additives/colorant. The filling stage in which the mould cavity is filled with hot polymer melts at injection temperature. After the cavity is filled, in the packing stage, additional polymer melt is packed into the cavity at a higher pressure to compensate the expected shrinkage as the polymer solidifies. This is followed by cooling stage where the mould is cooled until the part is sufficiently rigid to be ejected. The last step is the ejection stage in which the mould is opened and the part is ejected, after which the mould is closed again to begin the next cycle [9]. 2.4 Introduction of Mould An injection mould is an arrangement of steel parts, in one assembly. It has one or several cavity spaces built in it to the plastic product shape; where molten plastics are injected into filling the cavity / cavities to form the plastic products [25]. Two members form this space: 1. The cavity, which is female portion of the mould, gives the moulding its external form. 2. The core, which is male portion of the mould, forms the internal shape of the moulding. 19

23 Figure 2.7: Basic Injection Mould Structure The different design principles of functional units can be used as a basis for the classification of injection moulds. Moulds can be categorized by the following criteria: 1. the processed material material of the product which the plastic are heated to molten form and inject into the mould cavity, 2. The basic design type of mould, 3. The runner system a system where a path for the molten plastic flow from the barrel of the machine into the mould, 4. The ejector system design of the ejector system in the core side to eject the plasticized product from the core, 5. The number of cavities total number of the cavities or product produce in the one run of the injection process, 6. The profile of parting lines the separate line of the product where a line for the product separate in the cavity and core side, 7. The size of mould the dimension of the mould includes length, width and thickness. 20

24 2.4.1 Function of Mould The mould s function of the mould has divide into 5 categories there are: Receive the molten plastic: which the mould will ready a opening to allow the molten plastic flow into the mould cavity, Distribute the molten plastic: after the molten plastic flow into the mould the molten plastic will distribute by gate system of the mould, Form and shape the plastic product: through the gate system the molten plastic will fill up the cavity of the mould and ready to form and shape the product in the cavity mould, Cool the moulded product: after the cavity has been fill up with the molten plastic the next stage is solidification of the molten plastic which the plastic will cool, Eject the moulded product: after a few second the plastic is reach the solid stage the plastic product will be eject by the ejection system of the mould from the mould. All above functions only can be achieved, the mould must consists of functional system listing below: Sprue and runner system The path for the molten plastic materials from the plasticating unit (barrel) of the moulding machine and inject into the mould cavity.it consists of the following parts: a. Sprue It is formed in the sprue bushing. The contact in surfaces with the machine nozzle is generally curved. Plain or flat surface is seldom used because they require higher sealing pressure. There are some important guidelines to follow:- 21

25 The sprue diameter should be 0.5mm bigger than the nozzle orifice, to avoid undercut. The sprue has to be easily remove and therefore, has to be tapered with recommended draft of 3 included angle (min. of 1 with the best finishing). The sprue must not freeze before the mould cavity is filled, to permit transmission of pressure. The sprue bushing must be hardened, available as standard item and easily replaced. Figure 2.8: Sprue Brush b. Runner -It guides and distributes the molten plastic to the gate Figure 2.9: Runner, and Gate illustration 22

26 c. Cold Slug Cold runner systems must have cold slug wells, to accommodate cold slugs. Cold slugs are formed when the material at the tip of the machine nozzle that is trapped by the cold well before it enters the cavity. The residual material at the machine nozzle loses heat and solidifies before the next injection cycle starts. Figure 2.10: Cold Slug Designation d. Gate The functions of the gate are:to control the flow of the material into the cavity, to permit easy of separation of the moulded product from the runner system, to permit automatic separation between the moulded product. 23

27 e. Core and cavity inserts The cavity and core is the heart of the injection mould. This is where the shaping and forming the plastic product takes place. First the molten plastic flows through the sprue/runner system or the hotrunner system, then it solidifies in the cavity. Finally, it is ejected from the core. Generally the cavity is located on the fixed or stationary halve, while the core is on the movable halve of the mould. The numbers of cavities are determined by one or all of the following:-design of product, Quality of product and Quantity to be produced Cavity Layout It should consider these guidelines: All cavities should be filled at the same time, to avoid short moulding and flashing. Runner flow length should be as short as possible, to avoid pressure loss and material waste. There should be sufficient space between cavities for proper cooling and ejection Parting Line This is the opening between the cavity and core halves that release the moulded product and the runner. Its position is determined by the following[10]:- a. mould design or/and b. product design. The 2-plate, slider and hot runner moulds usually have a single parting line. However, 3 plates may have more than one parting line. 24