Injection molding of thermosetting materials such as low profile SMC/BMC composites found increasing application in the transportation industry in the eighties. Such automotive parts as front end panels and rear/hatchback doors have grown in usage. The rear doors have reached exceptional production levels of 2500/day in a single plant. The injection process offers the advantages of greater automation for the mass production of body panel parts compared to compression molding. However, the injection molding of fiber reinforced low profile composites suffers from a severe reduction in physical properties. This is particularly true for impact strength which can be one-third that of similar compression molding materials. A primary reason for this is due to the degradation of the reinforcement during the processing/molding. Efforts at increasing the physical properties through processing changes have many times caused problems with the surface smoothness of the moldings. Should major improvements in impact strength be coupled with excellent surface appearance the injection process could be applicable to automotive hoods, doors, deck lids, etc. The resultant application of automation could provide a more favorable cost structure for these composites versus metal even at high volumes of production. This paper reports on a concerted study of this problem involving examination of the organic matrix system, shrinkage control materials, interfacial agents, glass sizing changes, chemical thickening and various processing parameters and injection molding machines. This work has resulted in truly super Class A surface molding at impact strengths 80% above those of the best standard injection materials. Progress of this nature signals the beginning of a new day in low profile thermoset injection molding.

Atkins, K.E., Seats, R.L., Rex, R.C.

Geometries of Simple Hinges Hidden by Flush Contoured Surface Doors

910878

2/1/1991

Doors are very important parts of transportation products as exemplified by the large number of them. In addition to doors for occupants to enter and exit there are doors for access to engine, cargo, luggage, air flow, fuel fill, etc. For transportation products, doors are usually designed to be flush with surrounding surfaces -- and most of them have hidden hinges . There are only a few mechanical alternatives to provide for the opening of doors and the use of simple pivoting hinges is predominant. There are two kinds of simple pivot hidden hinges -- in swinging and outswinging. These are named according to the initial motion of the edge of door with respect to its adjacent surface. Inswinging hinges are most prevalent for occupant entry/exit doors since they are required for most rear doors and they provide more pleasing cut line shapes for current surfaces, usually at lower cost. The door cut lines for hidden hinges which studio designers initially style on proposed products frequently cannot be achieved due to the inherent limitations. While achievable cut lines can be developed using trial -and- error methods, quicker and more reliable results together with a true understanding of the problems requires an analysis which identifies causes and simplifies their visualization. Such an analysis has led to a system for establishing the limits of surfaces and cut lines which has been named the “Volume-in- Space” method. It was developed originally for automotive occupant doors but is also applicable to other transportation items such as doors for luggage, engine, air flow, fuel, etc. as well as other pivoted parts such as convertible tops and aerodynamic suspension arms -- and even non- transportation hinged applications such as cabinets and machinery housings. As the top end view of a hinge center line for automotive occupant doors is observed, there are four basic limits to the volume in which the edge of the door must be contained. These limits are (1) the Swing-By Limit, determined by the requirement of the door swinging clear as it passes by the adjacent panel (or door) at initial movement, (2) the Molding Clearance Limit, determined by the requirement that any randomly located molding on the vehicle surface must not be contacted when the door is fully opened, (3) the Swung Limit, determined by the requirement that the door and the body parts must not contact each other when the door is swung fully opened, and (4)) the Inner Limit, determined by the most inward exterior surface possible with respect to the hinge on the door or other hardware in the door. By examining the parameters which affect each limit, projections can be made regarding ways of increasing the size of the limiting “Volume- in-Space”. Additional discussion is included on advantages for occupant entry/exit which have been gained in some products by orientating the hinge centerline at angles up to 4° from vertical. There are also opportunities for improving the door openings for both body structure and occupant entry/exit.

Glossop, Donald L.

Economic Criteria for Sensible Selection of Body Panel Materials

910889

2/1/1991

In order to determine the best way to evaluate materials selection from an economic standpoint, a discussion of conventional cost estimation is given versus a more precise technique, Technical Cost Modeling. Automotive body panels are used as an application for the costing techniques; conclusions about fabrication costs and parts consolidation are drawn with regard to these parts.

Busch, John V., Dieffenbach, Jeff R.

High-Volume SMC Exterior Body Panels - An Evolution in Productivity

880360

2/1/1988

There are many advantages of using SMC assemblies for automotive exterior body panels. However, in the past SMC has been considered only for low-volume production because SMC molding was a slow process. Today, with process innovation which has evolved over the past several years, the advantages of SMC components can be applied to high-volume automotive lines.

Smith, Rueben L.