Thin Wall Technology

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Technology Guide

Advanced Technology For THINWALL DESIGN & PROCESSING

Thinwall

SM

GE Plastics

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Contents Introduction

Material Selection

About GE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .iii About GE Plastics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .iii About engineering Thermoplastics . . . . . . . . . . . . . . . .iv

Thinwall Technology What is Thinwall Technology . . . . . . . . . . . . . . . . . . . .1-2 Thinwall Technology Benefits . . . . . . . . . . . . . . . . . . .1-2 Thinwall Technology Market Opportunities . . . . . . . .1-3 Standard Molding vs. Thinwall Molding . . . . . . . . . . .1-3 Thinwall Nomenclature . . . . . . . . . . . . . . . . . . . . . . . . .1-4 Total Systems Approach . . . . . . . . . . . . . . . . . . . . . . . .1-5

Design Considerations Design Considerations . . . . . . . . . . . . . . . . . . . . . . . . . .2-2 Impact . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-3 Mode of Failure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-4 Design Strategies for Load Absorption . . . . . . . . . .2-5 Design Strategies for Load Transfer . . . . . . . . . . . . .2-5 Basic Impact Analysis . . . . . . . . . . . . . . . . . . . . . . . .2-6 Advanced Impact Analysis . . . . . . . . . . . . . . . . . . . .2-6 Stiffness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-6 Material Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-7 Part Geometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-9 Ribs, Bosses and Gussets . . . . . . . . . . . . . . . . . . . . .2-9 Sink Marks and Voids . . . . . . . . . . . . . . . . . . . . . . . .2-10 Component Assembly . . . . . . . . . . . . . . . . . . . . . . . .2-11 Snap Fits/Press Fits . . . . . . . . . . . . . . . . . . . . . . .2-11 Manufacturability . . . . . . . . . . . . . . . . . . . . . . . . . . .2-13 Shrinkage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-14 Warpage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-17 Mold Filling and Gating . . . . . . . . . . . . . . . . . . . . . . .2-18 Flow Length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-19 Melt Flow Index . . . . . . . . . . . . . . . . . . . . . . . . . .2-20 Fill Times . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-20 Mold-Filling Analysis . . . . . . . . . . . . . . . . . . . . . . . . .2-20 COVER: Thinwall technology is broad reaching and applies to a variety of markets including telecommunications, computers, business equipment, appliances and automotive. SM

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-2 Materials Requirements . . . . . . . . . . . . . . . . . . . . . . . .3-3 Resin Flow Length . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-3 Spiral Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-3 Melt Flow Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-4 Impact Strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-4 Low Temperature Impact . . . . . . . . . . . . . . . . . . . . . .3-4 Aesthetics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-5 Stiffness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-5 Heat Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-5 Flame Retardance . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-6 Mechanical Integrity . . . . . . . . . . . . . . . . . . . . . . . . . .3-6 LEXAN® PC Resins . . . . . . . . . . . . . . . . . . . . . . . . . . .3-7 CYCOLAC® ABS Resins . . . . . . . . . . . . . . . . . . . . . . . .3-7 CYCOLOY® PC/ABS Resins . . . . . . . . . . . . . . . . . . . . .3-7 Property Considerations . . . . . . . . . . . . . . . . . . . . . . . .3-8 Flow vs. Impact . . . . . . . . . . . . . . . . . . . . . . . . . . .3-8 Aesthetics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-9 Stiffness vs. Impact . . . . . . . . . . . . . . . . . . . . . . . .3-9 Material Evaluation . . . . . . . . . . . . . . . . . . . . . . .3-10 Materials Portfolio . . . . . . . . . . . . . . . . . . . . . . . . . .3-10

Processing Molding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-2 Tooling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-6 Machinery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-10

Finishing Operations Screws and Inserts . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-2 Ultrasonic Welding . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-3 Shielding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-5

Appendix UL 1950 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-2 Key Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-3

Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7-2 Literature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7-8 Sales Office . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7-9

All statements in this guide are subject to the disclaimer contained on page 7-7.

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© Copyright 1998 General Electric Company

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Introduction About GE The General Electric Company has its roots in the age of invention when, more than 120 years ago, it was founded by pioneering inventor Thomas Edison. Closely following its founder’s philosophy of innovation and the creative application of technology, GE has grown to become one of the largest and most diversified companies in the world. Today, GE products and services make a positive contribution to virtually every sector of commerce and industry. From jet engines to financial services, from lighting and medical systems to factory automation, power generation, transportation and construction.

About GE Plastics Of all GE businesses, one of the fastest growing is GE Plastics. Today, GE Plastics has emerged as the leading producer of engineering thermoplastics. Through application development centers around the world, customers can access data from GE designers, engineers, and tooling, processing and finishing experts, utilizing the most sophisticated equipment and systems available. Working closely with customers is at the core of the GE Plastics’ business culture. Today’s customers need to get the job done better, more costeffectively and within tighter schedules. Having a concentration of molding equipment, testing laboratories and product specialists close to the action permits a cross flow of information that can lead to important breakthroughs and exciting new product developments. At the nucleus of this unmatched global technical network are the worldclass facilities at GE Plastics’ headquarters in Pittsfield Massachusetts. Realizing that speed is the key to profitability today, these support services are backed up by production plants in several locations in the U.S., Europe, Australia, Japan and Mexico.

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Introduction About Engineering Thermoplastics The advantages of high performance engineering thermoplastics have grown dramatically both from new material developments and through a new generation of design engineers. Today, designers who have learned to “think” in plastics can take full advantage of their inherent benefits, rather than just simply translate metal components into plastic. Some of the many potential benefits offered by plastics include: • • • • • • • •

Consolidation of parts Integrated system assembly Molded-in assembly features Unprecedented strength to weight ratios Thinwall technology Elimination of painting and other operations Outstanding impact resistance Excellent chemical resistance

Through re-thinking and re-design, many traditional metal assemblies can be produced in dimensionally stable plastics: with 50% fewer parts, engineered for automated assembly and offering a full range of impact, heat, electrical and chemical properties. This Thinwall Guide is one example of how designers can access and utilize the knowledge and experience available from GE Plastics.

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Technology

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Thinwall Technology This guide has been created to help address problems commonly associated with design, tooling, and molding of plastic parts in wall sections thinner than today’s nominal wall sections. Basic information about products and fundamentals of designing with engineering thermoplastics utilizing “Thinwall ” technology have been provided. With this basic knowledge, proper resin selection, coupled with good design practice, should result in the development of a successful part. SM

What is Thinwall Technology? Thinwall Technology, or Thinwall, gets its name from one of the end results that it provides, a thin wall section. The difficulty is deciding a wall section at which a part goes from being “standard” or “conventional” wall thickness to “Thinwall.” The portable electronics and notebook computer industries have established themselves as being rich in Thinwall applications. With wall thicknesses often less than one half of a millimeter, there is no question that these applications qualify as Thinwall. The smaller the part, typically, the easier it is to fill parts with these small wall thicknesses. Parts that have different geometries, materials, and longer flow lengths, may not be able to be manufactured at these low wall thicknesses, even with current Thinwall technology. The benefits associated with decreasing wall thicknesses below their current values are still measurable and desired even if the final wall thickness is nowhere near those of the aggressive portable electronics industry. The techniques suggested within this guide can be applied to a wide range of markets and injection molded applications. Rather than setting a cut-off value between “standard” and “Thinwall” thicknesses, use of this guide can help attain thinner wall sections.

Thinwall Technology Benefits Reduction of wall thickness has always been important and is an enabling technology in a variety of markets. For small hand held parts, thinner wall sections help reduce weight and overall part size where these traits are critical. For all size parts, Thinwall technology can also help enhance productivity by providing opportunities to reduce costs and cycle times. The rapid growth in demand in the consumer electronics market for smaller, lighter, faster cycling parts created a need for advancements in thinner wall-section applications and technology. Requirements continue to increase for lighter, more compact products, necessitating high-performance housing designs with thinner wall sections – a critical requirement that is challenging engineers, resin suppliers, toolmakers, processors, and original equipment manufacturers (OEMs) alike.

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Thinwall Technology Thinwall Technology Market Opportunities A popular market for Thinwall applications and engineering thermoplastics has been portable electronics where demand for new products has increased an average of 30% each year since the 1980s. Technology advances in the industry are frequent. New technologies and products tend to make current products obsolete quickly. The fast pace has necessitated short product design and life cycles. Thinwall technology has been advancing at an equal pace. With virtually each new product offering has come a decrease in wall thickness. This has brought the wall thicknesses of many injection molded portable electronic applications down to levels previously thought to be impossible. An equally fast paced market with similar goals of light weight and smallest possible package has been the computer notebook industry. It too has relied on Thinwall technology to not only meet these goals, but also to provide lower cost parts. Here, the parts have been larger and the machines to produce them have been more traditional than those used in the portable electronics market. The technology developed within both of these markets is directly translatable to many markets. The trend has been to not only continue to look for ways to drive wall thicknesses down in established markets, but also towards allowing thinner walls on larger and different parts.

Standard Molding vs. Thinwall Molding As an example, today’s injection molding market innovators are typically molding hand held applications at wall sections between 0.030 and 0.060 in (1.0-1.5 mm), with the rest of the market molding at 0.0650.100 in (1.7-2.5 mm). However, the gap between these two groups possibly will increase in the near future as Thinwall technology becomes better understood and standardized. At that time, the market will likely be molding between 0.060-0.080 in (1.5-2.0 mm), while the market innovators will be molding between 0.020 and 0.040 in (0.5-1.0 mm). It is important to note that gains in wall-section reduction don’t always occur without investment – in this case, in tooling and machinery upgrades. Equally important is the fact that productivity and performance benefits of reduced material usage, faster cycle times, and lighter weight can often outweigh most added costs.

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Thinwall Technology Thinwall Nomenclature While it may be difficult to apply a thickness at which an application goes from “standard or conventional” wall thickness to “Thinwall”, for the purposes of discussion three sets of terms with dimensional references will be used:

Standard Wall Thickness Technology [>0.080 in (2.0 mm)] Standard or conventional technology is represented by those applications with wall thickness between 0.125 in (3.2 mm) and 0.080 in (2.0 mm), where conventional design rules apply. Standard engineering thermoplastics are usually sufficient for these applications. In addition, processing and tooling are well understood and standardized. Much information related to wall thicknesses in this range is contained in GE Plastics Injection Molding Processing Guide, PBG-135 and related product line publications. As parts become larger (longer flow lengths), Thinwall processing methodology applies, but if the standard wall thicknesses are used, conventional design rules should be applied.

One Step Thinner Wall Thickness Technology [0.080 and 0.050 in (2.0 and 1.2 mm)] Current Thinwall technology is heavily represented by applications with wall thicknesses between 0.080 and 0.050 in (2.0 and 1.2 mm); where design rules are transitional, where higher flow resins are required, and where processing favors high pressures and fill speeds that necessitate tooling changes. A majority of today’s Thinwall applications fall into this category.

Dedicated Thin Wall Thickness Technology [