Temperature Control, Dispensing Precision Key to Auto-Component Assembly

After the loading station, the distributors pass through a furnace on the way to the dispensing unit. The operator can monitor all important system data on the control panel.

The encapsulation of ignition distributors by a Tier 1 supplier of automotive components requires special materials and a dispensing system with precision temperature controls and exact material metering. The requirements are very demanding: the encapsulating compound that fills the distributor modules must act as a high-quality insulator, protecting the electronics from continuous high voltage. The material must not contain any air inclusions (bubbles). Bubbles lead to sparking, which destroys the printed circuit board in the distributor. The encapsulating compound consists of two parts; one is filled with a glass fiber.

Kern-Liebers Dispensing Technology developed a solution for this very difficult application in cooperation with the manufacturer of the ignition modules. During system development, attention is focused on temperature monitoring since acceptable results can only be obtained when specified temperatures are stringently maintained. System temperature is continuously monitored at 20 measuring points and corrected if necessary. Both material reservoirs are temperature-controlled, one at 80 deg C, the other at 60 deg C, preventing the formation of bubbles and allowing the material to reach the required fluidity.

The parts are preheated to 60 deg C and filled with two-component material mixed 1:1. The components are heated to 60 deg C and 80 deg C respectively to ensure the necessary fluidity for perfect, bubble-free encapsulation.

A vacuum system used in the reservoirs reduces the pressure to 3 millibars, removing trapped air bubbles. The parts are preheated to 60 deg C, ensuring the mixed material retains it fluidity during dispensing. The material is fed to the mixing unit by a reliable and proven media-transfer system. This system and all transfer hoses are temperature-controlled, keeping the material flowing properly. A material ratio of 1:1 is precisely mixed with Kern-Liebers metering pumps, ensuring an accurately mixed final compound.

Curing takes place in two 5-meter, continuous furnaces, the first at 80 deg C and the second at 120 deg C. Overly high temperatures are also not permitted since the module electronics are temperature-sensitive and can be ruined by excessively high temperatures. The system controller has the temperature indicators along with pressure sensors for the material reservoirs. The operator keeps all system data in sight because it is displayed on a monitor at the loading and unloading position.

While the primary issue was handling the difficult encapsulating material in the ignition-module application, another current project requires speed as the key to success. Foamed gaskets are applied to connectors in a system without a human operator; the cycle time is 2.8 seconds.

For more information on dispensing systems and their various applications, contact Mike Erby, Kern-Liebers USA Inc., 1510 Albon Road, Holland, OH 43528; phone 419-865-2437; fax 419-865-2738; e-mail merby@kl-usa.com; or visit the Web site www.kern-liebers.com. Or Circle No. 204