INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERING AND TECHNOLOGY (IJMET) International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 ISSN 0976 6340 (Print) ISSN 0976 6359 (Online) Volume 4, Issue 6, November - December (2013), pp. 227-240 IAEME: www.iaeme.com/ijmet.asp Journal Impact Factor (2013): 5.7731 (Calculated by GISI) www.jifactor.com IJMET I A E M E OPTIMIZING INJECTION MOULDING TOOL COST BY USING VIRTUAL SOFTWARE TECHNIQUES Sri. P V S M VARMA, Sri. P N E NAVEEN Mechanical Engineering Department, Godavari Institute of Engineering & Technology, E.G.Dt. A.P. ABSTRACT Now a day s Die design is the major part in product development. Die design will cause of the increase in component cost, machining complexity. For avoiding these problems we are taking virtual software support. In this thesis paper I am working on injection moulding die design optimizing. To provide an initial design of the mould assembly for customers prior to receiving the final product CAD data is a preliminary work of any final plastic injection mould design. Traditionally and even up till now, this initial design is always created using 2D CAD packages. The information used for the initial design is based on the technical discussion checklist, in which most mould makers have their own standards. This technical discussion checklist is also being used as a quotation. This paper presents a methodology of rapid realization of the initial design in 3Dsolid based on the technical discussion checklist, which takes the role of the overall standard template. Information are extracted from databases and coupled with the basic information from customer, these information are input into the technical discussion checklist. Rules and heuristics are also being used in the initial mould design. A case study is provided to illustrate the use of the standard template and to exhibit its real application of rapid realization of the initial design for plastic injection moulds. In this paper we are avoiding the all the problems involved in die design and how to make standard template for the die design. INTRODUCTION BASICS OF INJECTION MOLDING DESIGN Designing plastic parts is a complex task involving many factors that address a list of requirements of the application. How is the part to be used? How does it fit to other parts in the assembly? What loads will it experience in use? In addition to functional and structural issues, processing issues play a large role in the design of an injection molded plastic part. How the molten 227
plastic enters, fills, and cools within the cavity to form the part largely drives what form the features in that part must take. Adhering to some basic rules of injection molded part design will result in a part that, in addition to being easier to manufacture and assemble, will typically be much stronger in service. Dividing a part into basic groups will help you to build your part in a logical manner while minimizing molding problems. As a part is developed, always keep in mind how the part is molded and what you can do to minimize stress. APPLICATIONS Plastic injection molding is the preferred process for manufacturing plastic parts. Injection molding is used to create many things such as electronic housings, containers, bottle caps, automotive interiors, combs, and most other plastic products available today. It is ideal for producing high volumes of plastic parts due to the fact that several parts can be produced in each cycle by using multi-cavity injection molds. Some advantages of injection molding are high tolerance precision, repeatability, large material selection, low labor cost, minimal scrap losses, and little need to finish parts after molding. Some disadvantages of this process are expensive upfront tooling investment and process limitations. POLYMERS BEST SUITED FOR INJECTION MOLDING Most polymers may be used, including all thermoplastics, some thermosets, and some elastomers. There are tens of thousands of different materials available for injection molding. The available materials mixed with alloys or blends of previously developed materials means that product designers can choose from a vast selection of materials to find the one that has exactly the right properties. Materials are chosen based on the strength and function required for the final part; but also each material has different parameters for molding that must be considered. Common polymers like Epoxy and phenolic are examples of thermosetting plastics while nylon, polyethylene, and polystyrene are thermoplastic. MAIN AIM OF THE THESIS The most established method for producing plastic parts in large quantities is plastic injection moulding. This is a highly cost-effective, precise and competent manufacturing method, which can be automated. However, costly tooling and machinery are needed in this manufacturing process. The design of a plastic injection mould is an integral part of plastic injection moulding as the quality of the final plastic part is greatly reliant on the injection mould. A plastic injection mould is a high precision tooling that is being used to mass produce plastic parts and is by itself an assembly of cavities, mould base and standard components etc. Over the years, much research work using computer-aided techniques had been done from studyingthe very specific areas of mould design to studying mould design as a whole integrated system. Many commercial mould design software packages such as IMOLD, PRO/ENGINEER, UG MoldWizard, R&B MoldWorks, etc are also available today in the market for mould makers. However, the systems and software packages mentioned above did not consider the initial design prior to actual mould design. These software packages assist in the preparation of the detailed mould design that includes the core/cavity creation, cooling and ejection design. As a result, mould designers hardly used the mould design software packages when they are doing their initial design because the software does not catered for such a design process. 228
Molding Defects Blister Burn marks Color streaks (US) Delamination Flash Embedded contaminates Flow marks Jetting Polymer degradation Sink marks Short shot Splay marks Voids Weld line Warping Alternative Name Blistering Air Burn/Gas Burn Burrs Embedded particulates Flow lines Descriptions Causes Raised or layered zone on Tool or material is too hot, often caused by a lack of surface of the Plastic part cooling around the tool or a faulty heater Black or brown burnt areas on the plastic part Tool lacks venting, injection speed is too high located at furthest points from gate Plastic material and colorant isn't mixing properly, or Localized change of color the material has run out and it's starting to come through as natural only Thin mica like layers formed in part wall Excess material in thin layer exceeding normal part geometry Foreign particle (burnt material or other) embedded in the part Directionally "off tone" wavy lines or patterns Deformed part by turbulent flow of material polymer breakdown from oxidation, etc. Localized depression (In thicker zones) Non-Fill/Short Partial part Mold Splash Circular pattern around Mark/Silver gate caused by hot gas Streaks Knit Line/Meld Line Empty space within part (Air pocket) Discolored line where two flow fronts meet Twisting Part Distorted part Contamination of the material e.g. PP mixed with ABS, very dangerous if the part is being used for a safety critical application as the material has very little strength when delaminated as the materials cannot bond Tool damage, too much injection speed/material injected, clamping force too low. Can also be caused by dirt and contaminants around tooling surfaces. Particles on the tool surface, contaminated material or foreign debris in the barrel, or too much shear heat burning the material prior to injection Injection speeds too slow (the plastic has cooled down too much during injection, injection speeds must be set as fast as you can get away with at all times) Poor tool design, gate position or runner. Injection speed set too high. Excess water in the granules, excessive temperatures in barrel Holding time/pressure too low, cooling time too short, with sprueless hot runners this can also be caused by the gate temperature being set too high Lack of material, injection speed or pressure too low Moisture in the material, usually when resins are dried improperly Lack of holding pressure (holding pressure is used to pack out the part during the holding time). Also mold may be out of registration (when the two halves don't center properly and part walls are not the same thickness). Mold/material temperatures set too low (the material is cold when they meet, so they don't bond) Cooling is too short, material is too hot, lack of cooling around the tool, incorrect water temperatures (the parts bow inwards towards the hot side of the tool) 229
In this thesis emphasis is done on injection moulding die design optimizing. To provide an initial design of the mould assembly for customers prior to receiving the final product CAD data is a preliminary work of any final plastic injection mould design. A case study is provided to illustrate the use of the standard template and to exhibit its real application of rapid realization of the initial design for plastic injection moulds. In this thesis all the problems involved in die design are avoided and a standard template for the die design is made. STEPS INVOLVED IN THIS PROJECT 1. Study customer requirement 2. Preparing model by CAD software 3. Inspecting CAD Component 4. Adding Material Properties 5. Extracting Core and Cavity 6. Preparing rough assembly for die 7. Preparing Quotation 8. Technical and cost discussion with customer 9. Prepare Final Assembly of die 10. Prepare Raw material required quantity 11. Planning for machining and prepare total approximate machining time 12. Planning for die assembly 13. Planning for trial and dispatch STUDY CUSTOMER REQUIREMENT In this project we are working for Piaggo Automotive Company. Their requirement is making front driver cabin interior component. Initially the company has given outer dimensions of the component and other components that need to be assembled on that component. Also they have given strength requirement and no. of components to produce and maximum weight of the component. Our design team prepared models according to their requirement and shown to customer. Then models are changed by design team according to their requirement. And that component model is sent to the companies design department, production department. Finally the component model is approved according to the company requirement. This is the first step for any component manufacturing before going to die design because if the component shape has irregular shape it increases manufacturing cost as well as component cost. In this process I am involved in doing component modeling. 230
2D DRAWING OF THE COMPONENT GIVEN BY THE COMPANY SAMPLE 3D MODEL DESIGNED FROM 2D DRAWING PREPARING FINAL COMPONENT MODEL BY CAD SOFTWARE Our design team prepared models according to their requirement and shown to customer. Then models are changed by design team according to their requirement. And that component model is sent to the companies design department, production department. This is important stage of the product development because by using the software we can change our model according to customer requirement, manufacturing requirement at any stage before going to die design. It decreases the designing time and also increases quality of the product. In most of the cases, designers do mistake without knowing manufacturing knowledge while doing modeling of the component, that s why I am prescribing that while doing component design, consult with manufacturing and quality departments. This approach is called as Concurrent Engineering. By this approach, we can reduce mistakes in the manufacturing in the design stage itself. Most of the die makers not following this theory, that s why manufacturing lead time is increased. 231
MODIFIED MODEL ACCORDING TO THE CUTOMER REQUIREMENT 2D DRAWING OF THE FINAL MODEL INSPECTING CAD COMPONENT After modeling CAD component, it needs to be inspected according to die design requirements. With my knowledge, the following check list needs to be prepared for any plastic component. a. Maintaining maximum uniform thickness for reducing material flowing problems while injecting material in to the die. 232
b. Avoiding sharp corners due to which material flow struck at the sharp corners. It causes decrease in component strength and also increases stresses in corner. It causes failure of component. In our component we have avoided all sharp corners. c. Maintaining draft angle in die opening and closing direction. It the draft angle is not maintained the component struck in production. The providing of draft angle depends on type of plastic material, size of component and thickness of component. Allow at least minimum draft of ½ Deg to 1 Deg to facilitate removal of parts from the mould. d. Avoiding long flat surfaces. Due to the long flat surfaces, the component will bend and more warpage will come. For avoiding this, the design needs to be modeled with some curved surfaces or ribs are needed to be provided on flat surfaces. e. Allow for shrinkage after moulding. Before Shrinkage After Shrinkage f. Specify only dimensional tolerance as close as actually necessary. A tolerance closer than 0.005 inch, the usual commercial limit, generally increases costs. 233
g. Avoid undercuts which requires cores or split-cavity moulds h. Locate the mould parting in one plane, if possible i. Locate holes at right angles to part surfaces, Oblique holes add to mould costs. j. Avoid long cored holes k. Design projections in order to have circular sections. Irregularly shaped holes are generally more expensive to obtain in the mould l. Locate all holes and projections in the direction of mould opening & closing, if possible. Otherwise, holes must be formed by the use of retractable core pins m. Locate lettering to be embossed or debossed on surfaces perpendicular to the mould closed n. Arrange ejector pin locations so that marks will occur on concealed surfaces o. Design toward uniform section thickness and uniform distribution of mass for optimum flow of the plastic in moulding. p. Design corners with ample radii or fillets. This makes possible a more durable mould and improves the flow of the plastic during moulding q. Use ribs to add strength and rigidity, to minimize distortion from warping and to improve the flow of the plastic during moulding r. Restrict the rib height to not more than twice the thickness of the rib section. Otherwise, sink marks will obtained on the flat surfaces opposite the ribs s. Break up large flat surfaces with beads, steps or other geometric Designs to increase rigidity. Improved appearance too can be obtained. We have to check all of the above points before going to extract core and cavity. If we have done any mistake while checking the model it affects the final product. Again we have to do rework which will cause of increasing die cost and die manufacturing time. 234
ADDING MATERIAL PROPERTIES AND ADDING SHRINKAGE File Properties Material Change Select or Create Material Enter properties Save to Model Ok Ok Process Rotational molding Transfer molding Compressio n molding Injection molding Injection molding vs. other process Max operating temperature Max operating Pressure General operating pressure is less than 260 c 20 Mpa 1.5 Mpa 320 c 76 Mpa 20 Mpa 260 c 55 Mpa 20 Mpa 371 c 250 Mpa 100Mpa 235
ADVANTAGES OF INJECTION MOLDING OVER THE OTHER MOLDING PROCESSES The manufactured object generally requires no further machining. Rate of production is high. Hot mold is used in some special cases only. Waste of material is negligible. CAVITY CORE In this step extracting core and cavity is done in Pro/Engineer. By extracting core and cavity in software we will get exact component from model. PREPARING ROUGH ASSEMBLY FOR DIE In this stage we have to prepare rough assembly of die of the total mould base for knowing how much material required and the manufacturing processes required to prepare the quotation for the die design. 236
PREPARING QUOTATION Based on the rough assembly prepare quotation. S.No Part name Raw material Weight Cost M2 Cost M1(Rs/kg) size(mm) Kg Rs (Rs/Kg) Rs 1 Cavity plate 1380*620*420 2800 EN31(120) 336000 C45 (70) 196000 2 Core plate 1380*620*400 2700 EN31(120) 324000 C45 (70) 189000 3 Core back plate 1380*620*120 134 EN8(60) 8040 M.S (50) 6700 4 Spacer(2Nos) 620*120*350 210*2= 420 M.S(50) 21000 M.S(50) 21000 5 Back plate 1380*620*120 800 M.S(50) 40050 M.S(50) 40050 6 Ejector guide (8Nos) 350*100Dia 200 M.S(50) 10000 M.S(50) 10000 7 Ejector & Retainer 1160*620*45 510 M.S(50) 25500 M.S(50) 25500 plate(2nos) 8 Guide pillar(4nos) 350*100Dia 100 EN31(130) 13000 C45 (80) 8000 9 Guide bush(4nos) 400*90 120 EN31(130) 15600 C45 (80) 9600 10 Ejector pins(25nos) 400*12 OHNS 8750 OHNS 8750 11 Retainer pins(6nos) 400*16 EN31 1200 EN31 1200 12 Other materials 30000 30000 Total material cost 833140/- 545800/- CNC machining cost= Rs.400000/- Jig boring cost=rs.10000/- Drilling & tapping cost=rs. 15000/- Cooling holes cost=rs 8000/- Polishing =Rs 30000/- Transportation=Rs10000/- Other machining=rs60000/- Total machining amount=rs 533000/- 237
TOTAL DIE COST IF WE USE FIRST MATERIALS M1 FOR DIE COMPONENTS Total material & machining cost for first material=rs13,66,140/- Profit+ Risk factor=rs 2,73,860/- Total die cost with first material=rs16,40,000/- TOTAL DIE COST IF WE USE FIRST MATERIALS M2 FOR DIE COMPONENTS Total machining amount=rs533000/- Total material & machining g cost for second material=rs1078800/- Profit+ risk factor=rs1,67,820/- Total die cost with second material=rs1246620/- TECHNICAL AND COST DISCUSSION WITH CUSTOMER In this stage, we have to explain technical points involved and cost to the customer. Basically following points have to be discussed with the customer. a. Material used for component production. Specify 2 to 3 materials to the customer and explain strength and cost of each material. b. Material used for die design for various components in mould base die. Example material used for core, cavity, core and cavity plates, ejector and retainer plates, guide pillars, ejector pins, retainer pins, guide bushes, spacers, back plate c. Finally prepare quotation for the component based on customer specification. From the above quotation, if the materials specified in M2 are used, the total die cost is reduced almost by 3,90,380/-. S.No FINAL QUOTATION AS APPROVED BY THE CUSTOMER Part name Raw material size(mm) Weight Kg Cost Rs M2 (Rs/Kg) 1 Cavity plate 1380*620*420 2800 336000 C45 (70) 196000 2 Core plate 1380*620*400 2700 324000 C45 (70) 189000 3 Core back plate 1380*620*120 134 8040 M.S (50) 6700 4 Spacer(2Nos) 620*120*350 210*2=420 21000 M.S(50) 21000 5 Back plate 1380*620*120 800 40050 M.S(50) 40050 6 7 Ejector guide (8Nos) Ejector & Retainer plate(2nos) Cost Rs 350*100Dia 200 10000 M.S(50) 10000 1160*620*45 510 25500 M.S(50) 25500 8 Guide pillar(4nos) 350*100Dia 100 13000 C45 (80) 8000 9 Guide bush(4nos) 400*90 120 15600 C45 (80) 9600 10 11 Ejector pins(25nos) Retainer pins(6nos) 400*12 8750 OHNS 8750 400*16 1200 EN31 1200 12 Other materials 30000 30000 833140/- 545800/- 238
CNC machining cost= Rs.400000/- Jig boring cost=rs.10000/- Drilling & tapping cost=rs. 15000/- Cooling holes cost=rs 8000/- Polishing =Rs 30000/- Transportation=Rs10000/- Other machining=rs60000/- Total machining amount=rs 533000/- TOTAL DIE COST IF WE USE FIRST MATERIALS M2 FOR DIE COMPONENTS Total machining amount=rs533000/- Total material & machining g cost for second material=rs1078800/- Profit+ risk factor=rs1,67,820/- Total die cost with second material=rs1246620/- In this step we explained about the die cost to the customer. Also explain both merits and demerits of the die manufacturing with two materials. We have taken approval from the customer in cost point of view and productivity point of view. Then we can start our die work without any objections. Otherwise if we didn t explain all these to the customer after starting of die if customer changes his design, there will be lot of lose to us. Here we can reduce total lead time and cost by explaining about the die to the customer. FINAL ASSEMBLY OF DIE After all the technical discussions and cost discussions with the customer, the final quotation is prepared and submitted to the customer. Now the total complete die required should be prepared. Total Die components and their drawings are given below. TOTAL DIE ASSEMBLY 239
PLANNING FOR MACHINING AND PREPARE TOTAL APPROXIMATE MACHINING TIME CNC milling- 400hours, 17 days but we have to put tolerance put 25days +5 weekly half total no of days for CNC are 30 days. Time taken for jig boring is 7days Time taken for drilling are 7 days Time taken for turning operation is 7 days. Time taken for heat treatment 4 days Total time taken for machining are 55 days Time taken for assembling 7days Time taken for part modeling and die design in software 7days. Time taken for trail 2days Time taken for total die manufacturing is 65 days. By knowing time taken for manufacturing we can give die delivery time to the customer. If we prepared our plane we can reduce total lead time of die manufacturing. We can explain about the die to the customer by technically and cost point of view. We can have clear permeation from the customer. Customer also satisfies with our work. In this project we can save 10 days time and lead time cost of 2, 52,300/-. CONCLUSION In product development die design will plays major roll. If we didn t don die design with proper planning. It will cause of increasing total lead time and cost of the die. In this project I rectified above problems by giving proper planning for developing die. In this project I rectified the major problem faced by most of the die makers. I taken virtual software support in all steps. In model developing, shrinkage allowance adding, quotation preparation, output drawings, machining cost, machining time, final assembly preparation. In all aspects of the die design and manufacturing we taken software support, I saved 10 days time and 2,52,500/- cost. Also we can manufacture die with out mistakes. FUTURE SCOPE By following above steps in plastic component die design and manufacturing to any component we can save time and amount. REFERENCES 1. 3D RAPID REALIZATION OF INITIAL DESIGN FOR PLASTIC INJECTION MOULDS by Maria L.H. Low1 and K.S. Lee2. 2. Case study on Injection Moulding tool cost at JDP TOOLS. 3. G. Boothroyd et al., "Design for Injection Molding. 4. Robert A. Malloy, Plastic Part Design for Injection Molding. Cincinnati, OH: Hanser/ Gardener Publication, Inc., 5. Robert G. Launsby and Daniel L. Weese, Straight Talk on Designing. 6. Experiments. Colorado Springs, CO: Launsby Consulting. 240