Plastics Product Design Part 12 doc

420 Plastics Engineered Product Design metalworking permits tolerances as low as one tenth of those on the drawing, assuming the latter being reasonable for plastics. Under difficult circumstances, it has been proved to be a good practice if critical dimensions are kept smaller in the mold first, and then being revised after a test run under production conditions thus permitting machining the cavity if required. In any case, close tolerances should be applied on such dimensions only as directly related to invariable mold dimensions. Any otlier dimension, which is related to a mold dimension in two different mold parts, should allow a generous tolerance. Economical production requires that tolerances not be specified tighter than necessary. However, after a production target is met, one should mold “tighter” if possible, for greater profit by using less material. Many plastics change dimensions after molding, principally because their molecular orientations or molecules are not relaxed. To ease or eliminate the problem, one can change the processing cycle so that the plastic is “stress relieved,” even though that may extend the cycle time. Also used is heat-treat, the molded part based on experience or according to the resin supplier’s suggestions. Theoretical efforts to forecast linear shrinkage have been limited because of the number of existing variables. One way to solve this problem is to simplifjr the mathematical relationship, leading to an estimated but still acceptable assessment. This means, however, that the number of necessary processing changes will also be reduced. The parameters of the injection process must be provided. They can either be estimated or, to be more exact, taken fi-om the thermal and rheological layout. The position of a length with respect to flow direction is in practice an important influence. This is so primarily for glass-filled material but also for unfilled thermoplastics. The difference between a length parallel to (0”) and perpendicular to (90”) the flow direction depends on the processing parameters. Measurements with unfilled PP and ABS have shown that a linear relationship exists between these points. Regarding this relationship, when designing the mold it is necessary to know the flow direction. To obtain this information, a simple flow pattern construction can be used. However, the flow direction is not constant. In some cases the flow direction in the filling phase differs from that in the holding phase. Here the question arises of whether this must be considered using superposition. In order to get the flow direction at the end of the filling phase and the beginning of the holding phase (representing the onset of shrinkage), an analogous model was developed that provides the flow direction at 6 - Plastic performance 421 the end of the filling phase. For a flow with a Reynolds number less than 10, which is valid regarding the processing of thermoplastics, the following equation can be used: A@ = 0. For a two-dimensional geometry with quasistationary conditions, this equation is valid: Instead of the potential @, it is possible to introduce the flow-stream function I,Y for a two-dimensional flow. The stream lines ( I,Y = constant) and the equipotential lines are perpendicular to each other. To express this, the following Cauchy-Rieman differential can be used: A differential (two dimensional/quasi) equation has the same form as is used for a stationary electrical potential field, as it can be realized with an unmantled molding out of resistance paper and a suitable voltage. To control the theoretically determined flow with respect to the orientation direction, a color study was made. The comparison between flow pattern, color study, and analogous model is shown in Figs. 6.8 and 6.9. For a simple geometry the flow pattern method describes the flow direction in the filling phase as well as the holding phase (Fig. 6.8). This description changes when a core is added and the flow is disturbed (Fig. 6.9). In this case the flow at the beginning of the holding phase differs from the flow pattern as it is shown in the color study as well as in the analogous model. Even the welding lines are broken in the holding phase so that at this place another flow direction than that in the filling phase is found. With further measurements this influence has to be tested by using more-complcx moldings. Available are computer sohare programs that provide guide lines to melt flow behavior in the mold cavities (Chapter 5). Recvcled Plastic When plastics are granulated the probability is its processability and performance when reprocessed into any product may be slightly reduced; could be significantly rcduced. Fig. 6.10 shows how properties per ASTM tests for different plastics can effect properties of 422 Plastics Engineered Product Design Figure 6.8 Comparison between an analogous model, flow pattern studies Figure 6.9 Comparison between an analogous model, a flow pattern studies with a core added fig re 6.1 0 Example of the effect of recycling plastics once through a granulator (a) (b) (CI 'a: :::m - 6 - Plastic performance 423 __ ~~ .D Figure 6.11 Example of the effect of recycling plastics more than once through a granulator 5 2 4 85 - n - 0 c 0 80- 25 40 60 85 1st 2nd 3rd 4th recycled (once through a granulator) plastics mixed with virgin plastics. The data presented are (a) tensile strength, (b) tensile elongation, and (c) unnotched Izod impact test. Fig. 6.11 shows effect on repeating recycling plastics where data presented are (a) tensile strength and (b). Thus it is important to evaluate what the properties of the recycled material provides. The size reduction, and particularly its uniformity, exerts a substantial influence on the quality of the recycled plastics. Recycled plastics is usually nonuniform in size so that processing with or without virgin plastics is subject to operating in a larger fabricating process window (Chapter 1 ) . Different approaches are used to improve performances or properties of mixed plastics such as: (1) additives, fillers, and/or reinforcements (use specific types such as processing agent, talc, short glass fibers), (2) active interlayers (crosslinking, molecular wetting), and (3) dispersing and diffusing (fine grinding, enlarging molecular penetration via melt shearing). Most processing plants have been reclaiming/recycling reprocessable TP materials such as molding flash, rejected product, film trim, scrap, and so on during the past century. TS plastics (not remeltable) have been granulated and used as filler materials. If possible the goal is to significantly reduce or eliminate any trim, scrap, rejected products, etc. in an industrial plant because it has already cost money and time to go through a fabricating process; granulating 424 Plastics Engineered Product Design - just adds more money and time. Also it usually requires resetting the process to handle it alone (or even when blending with virgin plastics and/or additives) because of its usual nonuniform particle sizes, shapes, and melt flow characteristics. Perhaps it was overheated during the cutting action of a granulator, etc. Keeping the scrap before/afier granulating clean is an important requirement. When fiber RPs are granulated, the lengths of the fibers are reduced. On reprocessing with virgin materials or alone, their processability and performance definitely change. So it is important to determine if the change will affect final product performances. If it will, a limit for the amount of regrind mix should be determined or no recycled RP is to be used. Consider redesigning the product to meet the recycled performance or use it in some other product. Engineering data information source ___ In addition to what has been presented throughout this book such as the sobare on designing products in Chapter 5, this section provides source information concerning plastic material data basis. The available information worldwide has reached a volume that makes it impossible for one to review all the sources. In order to retrieve the desired or needed information, indexes and abstracts are continuously prepared by individual libraries, technical organizations, and professional societies. By the 1960s computers became available for storing and manipulating information. This lead to the creation and marketing of automated data banks. Available for manual searching are abstracts that typically provide the name of the author, a brief abstract of the article, the title of the article, and identifl where the article was published. Alphabetical author and subject indexes are usually provided, and an identifling number is assigned to refer to the abstract. Many abstracts are published monthly or more frequently. Annual cumulations are available in many cases. A comprehensive listing of abstracts and indexes can be found in Ulrich’s International Periodical Directory (annual from R R Bowker, New York). Most of the major indexes and abstracts are now available in machine- readable form. For a comprehensive list of databases and online vendors see Information Industry Market Place (International Directory of Information Products & Services from R. R Bowker, New York). The names of online databases frequently differ from their paper counterparts. Engineering Index (monthly from Engineering Information Inc.) for 6 - Plastic performance 425 ^. ,._I example, offers COMPENDEX and Engineering Meetings online. Many of the professional societies producing online databases will undertake a literature search. A society member is frequently entitled to reduced charges for this service. In addition to indexes and abstracts, periodicals, encyclopedias, and handbooks are available online. There seems to be virtually no limit to the information that can be made available online or on CD-ROMs, which can be networked in large institutions with many potential users. Thc high demand for quick information retrieval ensures the expansion of this service. In addition to the online indexes, several library networks and consortia, such as OCLC, the Online Computer Library Center, located in Columbus, Ohio, produce online databases. These are essentially equivalent to the catalogs of member libraries and can be used to determine which library owns a particular book or subscribes to a particular periodical. Publication The major emphasis on information is placed on publications and services designed to identifjr and obtain information. Because of space limitations references to individual works, which contain the required information, are limited to a few. The most important source of information is the primary literature. It consists mainly of the articles published in periodicals and of papers presented at conferences. New discoveries are first reported in the primary literature. It is, therefore, a major source of current information. Most engineers are familiar with a few publications, but are not aware of the extent of the total production of primary literature. As an example there is the publication Machine Design that issues 22 per year. It covers design engineering of manufactured products across the entire industry spectrum. It offers solutions to design problems, new technology developments, CAD/CAM updates, etc. It is published by Penton Media, Inc., 1100 Superior Ave., Cleveland, OH 44114; Tel 216-696-7000; Fax 216-696-8765; website wvw. machinedesign. com . Engineering Index (Engineering Information Inc. published monthly) abstracts material fiom thousands of periodicals and conferences. It is known as Compendex in its electronic version. Handbooks and encyclopedias are part of the secondary literature (included in the Bibliography section). They are derived from primary sources and make fiequent references to periodicals. Handbooks and encyclopedias are arranged to prescnt related materials in an organized fashion and provide quick access to information in a condensed form. 426 Plastics Engineered Product Design While monographs include books written for professionals, they are either primary or secondary sources of knowledge and information. Textbooks are also part of the tertiary literature. They are derived from primary and secondary sources. Textbooks provide extensive explanations and proofs for the material covered to provide the reader with an opportunity to understand a specific subject thoroughly. Thomas Register Use has always been made by many of the Thomas Register of American Manufacturers. These books may occupy considerable real estate either in your office, your company’s library, or somewhere in purchasing. The people at Thomas Register have developed (since 2000) two things that are of considerable help to those who have come to rely on this reference. The first are Thomas Register CD-ROMs, and the second is the Thomas Register web site. One can get at the Thomas Register web site at www.thomasregister.com. The first time user must register to use it, but registration is free. The Thomas Register web site offers several distinct advantages over the traditional printed version. The first few advantages are obvious and not really exciting. One is simply real estate. Finding a place to store (much less use) the bound versions of the register is difficult. If you have access to the Internet, you have access to the register. The second big advantage is, in theory, how current the information is. One would assume that an electronic version would be updated morc often than volumes you have sitting on your bookshelf. The improvement in storage space is met with the CD-ROM version as well. Once registered, you can move directly to the search portion of the site, where you are allowed to search on a company name, product or service, or brand name. Selecting one of these three categories and entering the appropriate key word or words, the register quickly returns a set of broad categories. For example, searching under the word “extrusion” under products/services yielded 157 product headings. Obviously this contains a significant number of categories that are not appropriate for plastics extrusion, but serves as an example. Each product heading is reported along with a set of columns recording the number of companies found, (and now the bigger and vcry exciting advantages of the web site) the number of companies with on-line catalogues, the number of companies with literature requests via fax, and the number of companies with on-line ordering and links to web sites. Selecting one of the broad product headings gets one into the listings of the individual companies themselves, where, if available, one can 6 - Plastic performance 427 jump to an on-line catalogue, on-line ordering, or move to the company’s web site. If none of these features are available, there is a short blurb about the company, location, phone numbers, and what type of products they offer, very similar to the “bare-bones” listing in the bound versions of the register. The designers of the Thomas web site have done an excellent job in that they split the screen when you jump to a company web site. The left-hand side of the screen gives you the Thomas Register choices of contacting the company, etc. while the right hand side is the site of the individual company. As with any conventional desk reference, the primary means of contact with the bound versions of the Thomas Register is the telephone. With the web site, to be able to go from a search for a list of suppliers of a given item or service (either nationally or by state) to order from an on- line catalogue is a huge advantage and one would suspect, an advantage for a company that offers that option. A cursory stroll through a few randomly chosen categories shows that not everyone is offering on-line catalogues and on-line ordering. Look for these services to grow considerably as more and more people begin to rely on the Internet for goods and services. Thomas Regional Directory Company has been in business since 1977, and publishes 19 Regional Industrial Buying Guides, in print and on CD- ROM, and now on a web site (www.thomasregional.com). The Thomas Regional Dircctory is listed as a “partner” to the Thomas Register. Thomas Regional provides access to a searchable database of more than 480,000 manufacturers, distributors, and service companies organized under 4,500 product/service categories in 19 key U.S. industrial markets. As with the Thomas register, one can search by product/ service or company name in the region of interest to you. As Thomas Regional points out in their own introduction. You can also refine your search based on company type (manufacturer, distributor, manufacturer’s rep, and service company), geographic location (state, city/county, area code), trade name, key words, and other specifications such as IS0 9000 certified, and minority and woman-owned businesses. View also supplier brochures, catalogs, line cards, and fax forms and contact suppliers directly via our Contact Company feature. Thomas Regional also offers listings (by region) of trade shows and special events, including locations, dates, contacts, listings of industry and professional organizations, and government and business resources. Where available, each reference has a link to the web site of the organization in question. They will begin offering some new features 428 Plastics Engineered Product Design that capitalize on their database of companies. As Thomas Regional points out in a press release published on their web site, industrial buyers today face the same recurring problems with the large search engines that researchers, consumers, and virtually everyone else encounters. Thcse searches generally produce hits in the range of thousands to millions, with far too little of it on target. For that reason, Thomas Regional will be creating a series of web sites that provide buyers with “vertical portals” to specific industries. Thcsc portals provide access to Thomas Regional’s extensive databases of industrial suppliers, organized according to industry or trade. Thomas Regional is leveraging the usefulness of its content through comprehensive databases that fulfill the specific need of each industry. Thomas Regional claims that ultimately over 90 industrial “communities” will have their own Thomas-powered web sites tailored to their interests, which will go a long way to improve the efficiency and speed of their searches. The first of these vertical web sites has been launched for the facilities management and engineering profession and may be found at www.facifitiesengineering.com. Industry Societies When discussing the subject of periodicals published by societies and commercial publishers, articles are identified usually by issue, and/or volume, date, and page number. Bibliographic control is excellent, and it is usually a routing matter to obtain a copy of a desired article. However, some problems exist such as periodicals that are known by more than one name, and the use of nonstandard abbreviations. Using the International Standard Serial Number (ISSN) that accurately identifies each publication solves both of these problems. With the increasing size and use of automated databases one should consider using ISSN or some other standard. An important source of the latest information is &om papers presented at conferences where the sponsoring agency is frequently a professional society (such as Society of Plastics Engineers) or a department of a university (such as the Plastics Dept., University of Massachusetts Lowell). These conferences are usually annual affairs. Encyclopedia and Industrial Books There are many hundreds of encyclopedias and handbooks covering science and technology. Internet sites with comprehensive catalogs of books include amazon.com and barnesandnoble.com. The date of publication should be checked before using any of these works if the required information is likely to have been affected by recent progress. The following list represents only a sampling of available works of outstanding value. The concern with industrial health and safety has placed an additional responsibility on the designer to see that materials and products are handled in a safe manner. Sax's Dangerous Properties of Industrial Materials (Kluwer, 1996) provides an authoritative treatment of this subject. This book also covers handling and shipping regulations for a large variety of materials and products. Designers are concerned with the interaction between humans and machines. This area has become increasingly sophisticated and specialized. Books on Human Factors have been written for the design engineer rather than the human factor specialist. The books provide the engineer with guidelines for designing products for convenient use by people. Standards Government agencies, professional societies, businesses, and organiz- ations devoted almost exclusively to the production of standards produce codes, specifications, and standards. In USA the American National Standards Institute (ANSI located in New York City) acts as a clearing house for industrial standards. ANSI frequently represents the interests of USA industries at international meetings. Copies of standards from most industrial countries can be purchased tkom ANSI as well as from the originators. Copies of standards issued by government agencies are available from several centers maintained by the government for thc distribution of publications. Most libraries do not collect government specifications. Many of the major engineering societies issue specifications in areas related to their functions. These specifications are usually developed, and revised, by membership committees. The American Society of Mechanical Engineers (ASME) has been a pioneer in publishing codes concerned with areas in which mechanical engineers are active. As an example in 1885 ASME formed a Standardization Committee on Pipe and Pipe Threads to provide for greater interchangeability. A frequently used collection of specifications is the Annual Book of Standards (53-55) issued by the American Society for Testing and Materials (ASTM). Committees drawn primarily from the industry [...]... improve the processes Polymers (20 hour Module) Markets for plastics Commercial production of plastics Physical properties of plastics Fabrication of plastics Applications lntvoduction to Injection Moldin8 (16 hour Module) What is injection molding? Plasticating systems Clamping systems The electrical system 436 Plastics Engineered Product Design The injection mold The molding process Process conditions... Electrical Manufacturers Association National Fire Protection Association Plastics Institute of America Society of Automotive Engineers Society of Plastics Engineers Society of Plastics Industry Underwriters Laboratories Designs Design books are listed in the Bibliography They concentrate on different aspects of designing with plastics of which they have been referenced throughout the book Databases... considered for the new product The application of appropriate data to product design can mean the difference between the success and failure of manufactured products made from any material The available plastic test data requires an understanding and proper interpretation before an attempt can be made to apply them to the product design There are two important sources of information on plastics There is... 438 Plastics Engineered Product Design Plastics Process Conwol (20 hour Module) Principles of process control Instrumentation Data acquisition/monitoring Servo control for injection molding Control of extrusion processes Blow molding/parison control SPC/SQC Integrated manufacturing New developments ThermoforminJ (20 hour Module) Basic process/variations Processing conditions Materials Mold design Product. .. and product failure Once it is recognized that there are certain reservations with some of the properties given on the data sheet, it becomes obvious that it is very important for the designer to have a good understanding of these properties Thus the designer can interpret the test results in order to make the proper evaluation in selecting a material for a specific product 440 Plastics Engineered Product. .. sophisticated tests to determine which plastic best suits a product design or fabricating process For the product designer, however, a few basic tests, such as a tensile test, will help determine which plastic is best to meet the performance requirements of a product At times, the complex test may be required The test or tests to be used will depend on the product s performance requirements To ensure quality... Administration PLASTEC Plastics Technical Evaluation Center PPI Plastics Pipe Institute QPL Qualified Products List SAE Society of Automotive Engineers SPE Society of Plastics Engineers SPI Society o f the Plastics Industry TAPPI Technical Association of the Pulp and Paper Industry Available is a USA government directory list for various forms of testing worldwide that includes plastics The National... available from NIST, NVLAJ? Directory, A124 Building, Gaithersburg, MD 20899 USA 446 Plastics Engineered Product Design Quality control I _ _ _ p Different approaches are used in setting up QC QC as in testing are discussed but often the least understood Usually it involves the inspection of materials and products as they complete different phases of processing Products that are within specifications... obtaining high quality products Quality must be built into a product from the beginning of the design that follows the FALL0 approach (Fig 1.15); it cannot be inspected into the process The target is to control quality before a product becomes defective Quality and Reliability The lying down of levels of quality and reliability necessary to ensure product success and acceptability in a particular market... may work to their f capacity d l 9 Tear down department barriers so that everyone can work as a team member 10 Eliminate items such as goals, posters, and slogans that call for new productivity levels without the improvement of methods 11 Make your organization fiee of work standards prescribing numeric quotas 448 Plastics Engineered Product Design - - 12 Eliminate factors that inhibit employee workmanship . Processing conditions Materials Mold design Product design Secondary operations Twin sheet forming Decorating Trimming/recycling DESIGN RELIABILITY Product design starts when one visualizes. processes Materials Primary equipment Mold design Process controls Auxiliary equipment Troubleshooting Testing 438 Plastics Engineered Product Design Plastics Process Conwol (20 hour Module). variability Polymers (20 hour Module) Markets for plastics Commercial production of plastics Physical properties of plastics Fabrication of plastics Applications lntvoduction to Injection