XV Congresso e Exposição Internacionais

da Tecnologia da Mobilidade São Paulo, Brasil

21 a 23 de novembro de 2006

AV. PAULISTA, 2073 - HORSA II - CJ. 1003 - CEP 01311-940 - SÃO PAULO – SP

FILIADA À

SAE TECHNICAL 2006-01-2626 PAPER SERIES E

Methodology of plastic parts development in the automotive industry

Guido Muzio Candido PTI - Engenharia e Projetos LTDA.

Filippo Santolia Junior

PTI - Engenharia e Projetos LTDA.

Marcos R. F. de Melo PTI - Engenharia e Projetos Ltda

Gustavo A. B. dos Santos

PTI - Engenharia e Projetos Ltda

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2006-01-2626

Methodology of plastic parts development in the automotive industry

Guido Muzio Candido Filippo Santolia Jr.

Marcos R. F. de Melo Gustavo A. B. dos Santos

PTI Engenharia e Projetos LTDA.

Copyright © 2006 Society of Automotive Engineers, Inc

ABSTRACT

Nowadays, the increasing use of plastic in the automotive industry complies with the desires of weight and cost reduction, material recyclability and increased performance. Today you can find plastic components in almost all subsystems of the vehicle, including the engine compartment, the interior cabin to the outside of the vehicle. Apart from the low weight, which can be translated to lower fuel consumption, the customer also gains with a gradual increase of plastic impact resistance due to the latest developments. It also contributes to automakers design and production versatility, useful life and keeping part quality related to steel (there is no corrosion).

Faced with this scenario, the purpose of this paper is to introduce an automotive injection moulding plastic component methodology in order to obtain technical and economical benefits of the latest designs with reduced part development time, reduced tooling costs, flexibility and design of style and quality.

INTRODUCTION

Plastic materials have expanded their application in the automotive industry in the 80's, during the oil crisis. At that time, automakers were developing a way to make lighter cars and reduce fuel consumption without loss of final product quality.

After several years, plastic is still being developed in this area and it is not just because of economic reasons. Besides weight, cost and production time reductions, these materials allow the development of modern style designs. The plastic raw material is immune to corrosion and can increase the security of the passengers, for having high mechanical resistance and supporting high temperatures.

In 2002, the European automotive industry used annually about 2 million tonnes of plastic. It was verified that the average application of the material per vehicle was about 110 kg. Studies show that each 100kg of plastic can substitute 200kg to 300kg of mass from previous materials [1].

The use of plastic as an alternative for the European automotive sector contributed to the reduction of annual fuel consumption of 12 million tonnes and the CO2 emission of 30 million tones [1].

In Brazil, by the end of the 80's, the average of plastic used in national vehicles was about only 30 kg. In 2002, each vehicle used 60 to 90 kg of plastic, being 63% in interior components, 15% in the exterior components, 9% in the engine, 8% in electrical systems and 5% in the chassis. Currently, with the advance of technology, it is presumed that the percentage of use of plastic will increase still more.

In automobiles, plastic is used in the instrument panel, door panels, in door handles, the bumpers and even the fuel tank. Some models can even have body structure made of plastic. In trucks, the considerable lightening was acquired with the use of plastic material, allowed the increase of load capacity [1].

In specialized literature, where the growth of plastic application in vehicles is well documented, the main cited advantages, over all, in relation to steel, are the reduction of weight and the absence of corrosion. The decision of automakers to adopt these, or any new component, or material on a bigger scale depends more, each time, on the evaluation of the contribution that brings for the increase of efficiency. This purpose is increasingly relevant in consideration of the intense competition that the material is submitted. Amongst these criteria of evaluation, the following stand out:

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• Offering consumers of better quality in performance terms, durability and appearance.

• Total cost of production, including final assembly, must be lower than previous or substituted ones.

• Cost and quality of the part, including service and replacement must be competitive.

• Weight should be reduced.

GENERAL ASPECTS OF DESIGN FOR INJECTION MOULDING PLASTIC PARTS

The development of injection moulding plastic components can be defined as being a set of procedures (processes), through which, using adequate tools (means), find a solution that meets the necessities of customers and contemplates the aspects, recommendations, impositions, limitations, and restrictions related to the distinctly involved fields of knowledge in this activity (information). These fields are constituted by engineering design knowledge, materials, process, mould tooling and costs.

The development of these components involves the design phases: informational, conceptual, preliminary and detailed [2]. Amongst them, it is the distinguished concept phase, when the definition of the product characteristics must be made to determine its performance and its lifecycle. In short, this phase involves, initially, the definition of the project specifications followed by the generation of design alternatives of concept of the product will be made.

In the process of definition of the design specifications of these products, the dependence and the interdependence between the corporate requirements, legal requirements, the strategies and recommendations of project must be considered.

According to Ferreira (2002)[3], in a synthesis of the development phases, are the following (shown in Figure 1):

• Informational phase: or design criteria means definition of the objectives of the product, survey of the necessities of customers, establishment of the design requirements, definition of design restrictions and project specifications definition;

• Conceptual phase: functional structure of the product, generation of alternatives of the concept of the product;

• Preliminary phase: design development of a geometric model of the product, analyses of mechanical, structural, thermal resistances and rheological analysis;

• Detailed phase: elaboration of the detailed drawings of the end item, development of the manufacturing tooling.

Figure 1. Phases of injection moulding plastic components development [2].

The practical application of concurrent engineering for teams specialized in the development of plastic products reflects the work in parallel of the different necessary stages for the conclusion of the project. According to Malloy(1994) [4], this type of approach provides a reduction of the development time, improvement of the final product quality and minimizes the possibility of imperfections in the project or design problems, as schematized in Figure 2.

Figure 2. Concurrent engineering applied in the plastic

product development [4].

METHODOLOGY OF PLASTIC PARTS DEVELOPMENT IN THE AUTOMOTIVE INDUSTRY

The development of plastic components in the automotive industry has specific characteristics that can differentiate it, in some aspects, of considered and studied

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processes for the development of plastic components for general purpose. This difference occurs, mainly in the phases of informational and conceptual design and automotive components normally already possess preset requirements, restrictions and functional characteristics. The methodology of development of injected plastic components in the automotive industry can be described by the following sequence:

SEQUENCE OF INJECTION MOULDING PLASTIC COMPONENT DEVELOPMENT IN THE AUTOMOTIVE INDUSTRY:

1 Establishment of the design parameters: 1.1 Survey of the reference information (other models, latest standards in the market, etc.); 1.2 Market research; 1.3 Benchmarking; 1.4 Estimate of product lifecycle; 1.5 Economic planning of the project considering:

1.5.1 Functional characteristics of the product (mechanical, aesthetic, structural, optical, etc.); 1.5.2 Amount of functional items that can design into the part without impacting in the final cost; 1.5.3 Minimum number of parts to be used in the assembly.

2 Estimation of general characteristics of the component:

2.1 Survey of the required properties of material considering:

2.1.1 Structural requirements; 2.1.2 Tolerances of assembly and functionality; 2.1.3 Environment of the part (contact and interfaces with other substances and parts); 2.1.4 Maximum temperature to which the part will be subjected; 2.1.5 Desired useful life; 2.1.6 Conditions of assembled components; 2.1.7 Type of surface finishing required.

2.2 Determination of the raw material; 2.3 Determination of the basic dimensions of the component; 2.4 Estimation of the thickness; 2.5 Determination of the desirable maximum weight; 2.6 Aesthetic factors of the component (color, texture, brightness, apparent geometry, etc.).

3 Production of the style surface: 3.1 Creation of the assembly theme; 3.2 Construction of the preliminary physical model (mock-up);

3.3 Tests applied in the preliminary physical model such as wind tunnel or other ones; 3.4 Three-dimensional measurement of the surface of the model; 3.5 Conversion of reference geometry into a surface in a CAD (computer aided design) application; 3.6 Manipulation of the surface in CAD.

4 Establishment of the requirements of the project and relative parameters to the manufacturing process:

4.1 Requirements for the application of the design parameters; 4.2 Requirements for application of the characteristics of the component; 4.3 Research of requirements of the current law in the market territory; 4.4 Survey of the corporate requirements of component design.

5 Adaptation of the style surface to the relative requirements of the design and parameters of the manufacturing process:

5.1 Communization with reference to existing components; 5.2 Forecast of future modification of design parameters; 5.3 Addition of details in geometry to attend specific requirements (legal, aesthetic petitions, of security, etc.), considering:

5.3.1 Details of safety characteristics; 5.3.2 Details of characteristics of component interface or joints; 5.3.4 Details for assembly characteristics.

5.4 Addition of details in geometry to attend relative parameters to manufacturing process considering:

5.4.1 To avoid sharp edges in the part (as shown in Figure 3) to minimize the effect of the concentration of stress (Figure 4). Regions with small radii will present structural fragility of the part;

Figure 3. Different hole profiles in a plastic part [5].

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Figure 4. Stress concentration factor given by the relation of the minimum radius and part thickness (R/T) [6].

5.4.2 To avoid threads moulded in the plastic parts, because they are complicate to mould and process; 5.4.3 To avoid types of holes that will need side actions of sliders in the mould. This type of system increases significantly the mould cost and becomes more complex in its operation during the process (Figure 5).

Figure 5. Different holes in plastic parts and its adaptation [5].

Other design good practices recommended to plastic parts holes profiles are illustrated in Figures 6, 7 e 8.

Figure 6. Good practices for blind holes [6].

Figure 7. Good practices for depth holes [6].

Figure 8. Minimum distance between holes and part edges [6].

5.4.4 Changing of the surface for increasing rigidity, using more rigid formations without addition of mass, depending on the mechanical forces operating on the part (Figure 9).

Figure 9. Example of increasing rigidity of a part without addition of thickness or ribs [7].

5.4.5 Apply draft angle for moulding ejection on the surfaces of the component considering the direction in which will be

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moulded. They must also be applied in the direction of the moulding of auxiliary movement systems in regions of texture application without detriment of final product quality and its extraction from the mould, as shown in Figure 10;

Figure 10. Examples of the application of draft angle for moulding ejection [8].

For surfaces without surface graining a minimum draft angle of 0.5 degrees is recommended. For graining walls the depth of the texture regards to addition in the draft angle according to the type of graining. Figure 11 graphically shows the geometric relation of draft angles, height of the part and distance between the base and the top of the core in the mould.

Figure 11. Relation to draft angles, part height and distance to core top and bottom [6].

5.4.6 Develop the parts, simplifying the parting regions (contact between core and cavity of the mould) and facilitating easier maintenance of the injection mould tool. The parting line (PL) of regions of sharp edges must be avoided (Figures 12, 13).

Figure 12. Types of parting lines for different

geometries, according to injection moulding fabrication.

Figure 13. Parting line details [7].

6 Adaptation of the surface to suit the interfaces with other components:

6.1 Application of style surface requirements to the interfaces with other components (gaps and flushness).

7 Detailing of the functional characteristics of the component:

7.1 Application of estimating thickness considering:

7.1.1 Keep a constant thickness on all contours of the part, preventing stress concentration in transition regions that can cause embrittlement (Figures 14, 15);

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Figure 14. Application of constant thickness

recommended [8].

Figure 15. Apply constant thickness to corner radius on the part [9].

In the cases which the variation of thickness of the part is inevitable, a gradual transition as recommended as indicated in the last drawing of Figure 16.

Figure 16. Types of different thickness transitions, E represents shorter thickness [6].

7.2 Application of structural details considering: 7.2.1 Addition of ribs is a common way to increase the rigidity of plastic parts without additional thickness (as shown at Figure 17). The positioning of the ribs in the products must follow the load direction to obtain better results of mechanical structure (Figure 18);

Figure 17. Recommended profile for ribs [6].

Figure 18. Recommended rib lay-out [9].

7.2.2 The addition of gussets for structural reinforcement in the regions of adjoining angled walls and internal details subjected to flexing. These reinforcements can increase the rigidity of the part with little addition of mass and without compromising the process (Figures 19 and 20);

Figure 19. Examples of addition of gussets [5].

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Figure 20. Recommended design for gussets [6].

7.2.3 To avoid sharp or very close internal walls that can cause thin section regions in the core of the mould, presenting future problems on process involving premature breakage of mould tool (Figure 21);

Figure 21. Example of part with problems of mass concentration and sink marks [5].

7.3 Elaboration of details for attachments and assembly considering:

7.3.1 Addition of details for specific attachments (threading, riveting, clips, push pins, etc.); 7.3.2 Addition of details for adhesion of components; 7.3.3 Addition of details for living hinges (Figure 22);

Figure 22. Example of living hinge design [8].

7.3.4 Addition of details for metallic inserts in the part; 7.3.5 Addition of details for assembly with snap-fits. The most common type of assembly currently applied to plastic parts. It does not require other components and involves, in the majority of the cases, only the mechanical effort of assembly, disassembly and locking (Figure 23);

Figure 23. Examples of snap-fit design [10].

7.3.6 Addition of details for assembly locks (Figure 24);

Figure 24. Example of pressure operated plastic locks

[7].

7.3.7 Addition of details for alignment of the assembly, preventing loss of time in the assembly process, to guarantee positioning in all the parts assembled (shown in Figure 25);

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Figure 25. Example of alignment feature design [11].

7.3.8 Addition of details for welded junctions (sonic weld, vibration, induction, heat, etc.).

8 Analysis and simulation of detailed geometry:

8.1 Study of the conditions of component function; 8.2 Determination of the types of analyses to be carried out (rheological, structural, thermal, etc):

8.2.2 Structural analysis; 8.2.1 Rheological analysis; 8.2.3 Thermal analysis; 8.2.4 Interaction between different analyses.

8.3 Evaluation of the results of the analyses; 8.4 Optimization of the component based on the analyses results.

9 Manufacture of tooling for first prototypes:

9.1 Revision of the product for manufacturing process; 9.2 Support for manufacture of the mould tool; 9.3 Evaluation mould tool functioning (try-out).

10 Phases of Prototypes:

10.1 Analysis of performance of the prototype; 10.2 Initial phase of production.

The proposition of this methodology is generated from

observation of the practice for designing automotive injected plastic components, of inquiries and the research carried out in this area, as well as the study of literature. With the objective to reflect the relations between the involved fields of knowledge in this activity, to satisfy the necessities of the sector and accordingly to deal with the development of the injected components using the philosophy of concurrent engineering, in other words, involving the engineering departments of product, processes, production tooling and manufacture.

The described sequence does not have to be a serial process, in which each activity would be completed after the termination of the previous one. With the application of the techniques of simultaneous engineering, exemplified by Malloy (1994), the development of the activities and phases of the project must be in parallel, as shown previously in Figure 2.

It is possible to associate the stages of development sequence of injected plastic components in the automotive industry with the different phases of the project, in view of the fact, the activities can often being carried out by different teams of professionals.

Figure 26 demonstrates the stages of the sequence of development that can be related with the teams that compose the work and its activities in whole development time. This methodology provides a reduction in the total time of development and makes possible improvement of the product quality [4].

Figure 26. Detailed concurrent engineering applied in plastic products development.

On the other hand, the implantation of concurrent engineering in a development process requires integrating tools that make possible a higher degree of information synergy between the work teams.

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This concurrent engineering technique in this study is applied to the long one of the complete process of development of products. Mascarenhas (2002) and Santos (2004) [12,13] also analyze its application in a more detailed way e, focused in the phase of tooling engineering (injection mould design), evaluating the interaction and execution of each activity in such work.

ANALYSIS AND CONCLUSIONS

Nowadays, product engineering in automotive industries makes use of innumerable tools that assist the development with quality, making possible the development of vehicles with cost and mass reduction, developed in shorter periods of time. This process of continuous improvement and optimization of the design comes to face up to a competitive global market with a greater variation of automotive products for even more demanding consumers.

Faced with this panorama, the work presents an optional method for developing automotives products focused on injection moulded plastic component design based on specialized literatures and practical experiences of automotive designs for interiors and exteriors parts of the vehicles. This methodology can provide reduction of the total time of development, with the application of multidisciplinary teams working a simultaneous engineering technique. A great improvement in final product quality is possible.

Despite the design process of a plastic component is complex, this article shows simple techniques used in companies specialized in thermoplastic material manufacturing, for example GE Plastics, Bayer and plastic transformation companies, in the case the suppliers of auto-parts that work on product development together with the automakers.

The objective of proposals shown on this paper is to minimize costs and avoid possible problems occurrences in the injection mould performance. In some examples it will not be possible to incorporate all the design improvements, but these recommendations will, at least, increase understanding in the thermoplastic component design good practices.

ACKNOWLEDGMENTS

The authors also express its gratitude for the support and help to PTI Engenharia e Projetos LTDA., Ford Motor Company (Brazil) and Polytechnic School – University of São Paulo (Brazil) that have contributed to conclude this paper.

REFERENCES

[1] QUICKPLAST; The triumph of plastics in automotive segment. Available from: http://www.pecasplasticas.com/artigos_newsletter_otriunfodoplastico.asp. Accessed on March 13th 2006. [2] FERREIRA, C.V.; Integrated product development. Presentation in the week of product development at Senai-Cimatec. Bahia, Brazil, 2004. [3] FERREIRA, C.V.; Methodology for the phases of informational and conceptual design of injected plastic components integrating the design processes and cost estimates. PhD thesis. Federal University of Santa Catarina, Santa Catarina, Brazil, 2002. [4] MALLOY, R. A.; Plastic part design for injection moulding. Munich. Ed. Hanser 1994. [5] IMM MAGAZINE; A series of plastic part design archives. Available from: http://www.immnet.com. Accessed on May 5th 2005. [6] DSM ENGINEERING PLASTICS. General design guidelines. Available at: http://www.dsm.com/en_US. Accessed on June 3rd 2006. [7] GE PLASTICS; Injection moulding design guidelines. Available from http://www.geplastics.com . Accessed on April 10th 2004. [8] SANTOS, G.A.B.; Introduction to plastics technology and injection moulding design. Course given for PTI Engenharia e Projetos. Bahia, Brazil 2006. [9] BAYER S.A.; Design guide for injection moulding 2005. Available from: http://www.bayer.com. Accessed on January 16th 2006. [10] DUPONT S.A.; The 10 more tips of design – Available from: http://www.dupont.com.br . Accessed on January 16th 2006. [11] BONENBERGER, P.R.; The first snap-fit handbook. Munich; Ed. Hanser, 2000. [12] MASCARENHAS, W.N.; Systematization of the process of dimensional lay-out injection moulded plastic components. Master engineer dissertation. Federal University of Santa Catarina, Santa Catarina, Brazil, 2002. [13] SANTOS, G.A.B.; Development of injection mould and process planning of thin walled plastic part with application of concurrent engineering: a case study. Research article. Polithecnic School, Bahia Federal University, Bahia, Brazil, 2004.

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AUTHORS

Guido M. Candido,Msc - PTI Engenharia e Projetos LTDA. e-mail: gcandido@ptiengenharia.com Filippo Santolia Jr,Msc - PTI Engenharia e Projetos LTDA. e-mail: fsantolia@ptiengenharia.com Marcos R. F. de Melo - PTI Engenharia e Projetos LTDA. e-mail: mmelo@ptiengenharia.com Gustavo A. B. Santos - PTI Engenharia e Projetos LTDA. e-mail: gusbusson@hotmail.com

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