AUTOMATED ASSEMBLY SYSTEMS

TYPES OF AUTOMATED ASSEMBLY SYSTEMS

Assuming that the product design is compatible with automated assembly, there are several different ways to characterize the operation and configuration of the automated assembly system. One way to classify the system is by the type of work transfer system that is used in the system. The types are :

• Continuous transfer system
• Synchronous transfer system
• Asynchronous transfer system
• Stationary base part system

In the stationary base part system, the base part (to which the other components are added is placed in a fixed location, where it remains during the assembly work.
Another way of classifying automated assembly systems is by their physical configuration. The possible configurations include :

• Dial-type assembly machine
• In-line assembly machine
• Carousel assembly system
• Single-station assembly machine

The dial-type machine is shown in Figure below. In the typical application, base parts are loaded onto fixtures or nests that are attached to the circular dial. Components are added and/or fastened at the various work stations located around the periphery of the dial. The dial indexing machine is the most common system in this category. It operates with a synchronous or intermittent motion, where the cycle consists of the process time plus indexing time. Several of the mechanisms can be used to provide this motion. Although less common, dial-type assembly machines are sometimes designed to use a continuous motion rather than an intermittent motion.
The in-line assembly machine consists of a series of automatic work stations located along an in-line transfer system. It is the automated version of the manual assembly line. Continuous, synchronous, or asynchronous transfer systems can be used with the in-line configuration.
The operation of dial-type and in-line assembly systems is similar to the operation of their counterparts described in Chapter 4 for machining (and other processing) operations. Sub assemblies at various stages of completion are processed simultaneously at separate work stations. For synchronous transfer of work between stations, the ideal cycle time equals the operation time at the slowest station plus the transfer time between stations. The production rate, at 100% up time, is the reciprocal of the ideal cycle time. Owing to jams of the components at the workstations and other malfunctions, the system will probably not operate at 100% up time. We will analyze the operation of these automated assembly systems in a subsequent section of this chapter.

In a sense, the carousel assembly system represents a hybrid between the circular flow of work provided by the dial assembly machine and the straight work flow of the in-line system. The carousel configuration is illustrated in Figure 7.2. This type assembly system can be operated with continuous, synchronous, or asynchronous transfer mechanisms to move the work around the carousel. The carousel configuration with synchronous transfer of work is often used in partially automated assembly systems.

   

        In the single-station assembly machine, the assembly operations are performed at a single location (stationary base part system). The typical operation involves the placement of the base part at the workstation where various components are added to the base. The components are delivered to the station by feeding mechanisms, and one or more work heads perform the various assembly and fastening operations. The single-station cell is sometimes selected as the configuration for robotic assembly applications. Parts are fed to the single station and the robot adds them to the base part and performs the fastening operations.