Most mechanical products are assembled from parts. After designing the parts, they must be manufactured. Before FMS, parts for batch production were created in machine shops by skilled machinists, who would use general purpose machines such as laths, drills and so on in sequence to create the parts. To discuss the automation of such a machine shop(creation of an FMS), we must first consider the functions to be accomplished at each machine:
a. Move the proper workpiece to machine
b. Load workpiece onto the machine
c. Select proper tool
d. establish a set machine speeds
e. control machine motion
f. sequence different tools
g. unload part
In mass production, the large volume makes having a special purpose machine for each operation economical, but in batch production, it simply is not economical to have special purpose machines for each operation, because they would sit idle most of the time. The goal in improving the efficiency of batch parts manufacture has been to create computer controllers which will make general purpose machines flexible enough to create multiple parts automatically. Since 1960, considerable advances in FMS have been made from the numerically controlled machine to the current flexible manufacturing cell, several general purpose machines linked and controlled by a computer.
A schematic drawing of an FMS is shown below.
The current leader in this area are the Japanese. Fanuc, Ltd. created a plant in the 80s that makes robots and CNC machine tools. The plant is essentially an automated machine shop that produces parts for these machines. Robots carry the parts from one group of machines to another. Vehicles automatically store finished parts and retrieve raw workpieces. There are 19 day shift workers and one night shift worker.
The use of FMS instead of a general purpose machine shop staffed by skilled machinists can reduce the cost of manufacturing parts by a factor of 5 to 10. With a general purpose machine shop, the machinists spend a large portion of their time setting up the machines for the next operation. With a FMS, this set up time is greatly reduced by the computer which sets up the machines automatically. Because the set up time is greatly reduced, machine time in creating parts increases from 3- 10%to 50%of the total time. Also, FMS requires from 10 to 30%of the skilled labor which a general machine shop requires. Besides reducing labor costs and increasing the output of the machines, a FMS has two other advantages over a general purpose machine shop. With a FMS, production can rapidly shift from one part to another. Thus, a FMS can match supply to demand with very little inventory. In addition, the use of FMS has led to much greater quality control.
The problems with FMS are the cost of setting up the stations and the fact that technical expertise is required to set them up and run them. If a component breaks, the FMS cell shuts down. Despite these limitations, FMS has moved from the experimental to the rapid growth stage. The demand by larger firms for higher quality control in order to install just in time parts management has created incentives for small firms to install FMS in order to achieve higher quality control. An example of a small firm which installed an FMS cell is Frost, Inc. with 1985 sales of $16M. For a $5.1M investment, sales per employee have climbed from $86,000 top $130,000. Quality control has improved from 1 reject in 4 to 1 reject in 20. Gross margins have increased to 35%in spite of price decreases of 21%since 1983. With its FMS, Frost could shift from the production of one item to another in minutes instead of 12 hours or more. Frost converted to automation at 1/3 the cost of the expert plans. To capitalize on its experience with FMS, Frost has set up a consulting company to advice other firms desiring to follow suit.