8 Computer Integrated Manufacturing--the dawning of a new age.

Just as Beretta completed the renovation of manufacturing machinery in its plants, yet another new technology began to emerge. Robots for loading and unloading parts in machines, untended mobile carriers for transporting pallets from one part of a plant to another, and flexible manufacturing cells capable of a tenfold increase over traditional machinery in the variety of parts that could be made were all making their debuts, and with them came the potential to automate the manufacturing process from one end to the other, from loading machines, through changing, setting, and operating tools, to unloading processed parts.

In 1987 Beretta engineers introduced, as pilot projects, two new technologies: a flexible manufacturing system (FMS); and computer-aided design/computer-aided manufacturing (CAD/CAM, the CIM integration of computer-aided design and CNC machines). CAD/CAM eventually became Computer-Integrated Manufacturing (CIM). The effects at Beretta are shown in Table 8.1. (1)

8.1. Beretta's FMS

A flexible manufacturing system is a computer-controlled configuration of semi-independent workstations, connected by automated material handling systems, designed to efficiently manufacture more than one kind of part at low to medium volumes. Beretta's first project was the installation of a flexible manufacturing system for manufacturing a major gun part, the "receiver." The system designed for production of the Beretta receiver (Figure 8.1) consists of three CNC machining centers connected by a material handling system that incorporates a conveyor arranged in a loop. The loop constitutes a buffer area; pallets on which the workpieces are mounted keep moving until the machine required for the next operation becomes available. The system is capable of fabricating forty-five discrete parts. With the exception of inspection, all system operations are under computer control.

[FIGURE 8.1 OMITTED]

In most FMS installations incoming raw workpieces are hand fixtured onto pallets at a workstation. Once information on a fixtured workpiece (typically an identifying number) has been entered to inform the FMS that it is ready, the FMS supervisor (supervisory computer) takes charge, performing all the necessary operations to completion in any of a number of machines, moving workpieces between machines, responding to contingencies, and assigning priorities to the jobs in the system.

The supervisor first sends a transporter to the load/unload station to retrieve the pallet. The loaded pallet then keeps moving in a loop until a machine becomes available to perform the first operation. When a shuttle (a position in the queue) is available, the transporter stops and a transfer mechanism removes the pallet, freeing the transporter to respond to the next move request.

Parts received by the machine must be accurately located relative to the machine tool spindle. The inspection to accomplish this can be done manually, using standard instruments, or by coordinate measuring machines. The appropriate machining offsets are calculated from the measurements and communicated to the supervisor.

Meanwhile, the supervisor has determined whether all of the tools required for the machining operations are present in the tool pocket of the machining center, and requested needed tools from either off-line tool storage or a tool crib/tool chain within the system. When all the required tools are loaded, the supervisor downloads the NC part program to the machine controller from the FMS control computer.

The process of making sure that the part is, in fact, what the computer thinks it should be is termed qualifying the part. Qualifying includes making sure that all previous operations have been completed, that the part is dimensionally within tolerance limits, and that it is accurately located. Tools, too, must be qualified. Tool geometry, length, diameter, and wear are all examined, either manually or under computer control. When both the workpiece and the tool have been qualified, the tool, part, or program offsets necessary to correct for systematic error have to be established.

When the set-up activities are completed, machining begins. The FMS monitors the tool during machining. If it breaks, a contingent procedure is invoked. Some advanced FMSs have in-process inspection and adaptive control whereby a continuous measurement of metal removal is taken to determine whether the operation is within defined process parameters. Compensating corrections for any deviations are made during machining, without stopping. Adaptive control in FMS is still very rudimentary and technically quite difficult with [late 1980s] technology. (2)

The finished, or machined, part is moved to the shuttle to await a transporter. After being loaded onto the transporter, the pallet is moved to the next operation, or else circulates in the system or is unloaded at some intermediate storage location until the machine required for the next operation becomes available.

The computer controls the cycles just described for all parts and machines in the system, performing scheduling, dispatching, and traffic coordination functions. It also collects statistical and other manufacturing information from each workstation for reporting systems. As all the activities are under precise computer control, effects of part program changes, decision rules for priority assignment, contingent control, and part-portfolio mix can be captured, at least in principle.

The pre-FMS line layout for making receivers is shown in Figure 8.2. The 41 machines in this line compare with the FMS line's 24, configured as eight parallel three-machine cells (the number of cells dictated by the volume of work). Each cell in the FMS receiver line fabricates a complete receiver and is managed by a single worker. The FMS reduces minimum efficient scale by an order of magnitude, from 41 machines to three, and is flexible and versatile enough to accommodate other prismatic parts as well as receivers.

[FIGURE 8.2 OMITTED]

It will eventually be possible to load a machine on the FMS line at the beginning of a shift with thirty-five pallets, each containing a blank receiver, and have the entire lot completely machined by the end of the shift without an operator being present. Although untended operation has not yet been achieved at Beretta, it is not only possible, as a number of Japanese machine tool vendors have shown, but achievable in the next decade. [19] When it comes it will in all likelihood once again radically alter the nature of work.

What we can expect from a world of untended flexible manufacturing is summarized below.

* The worker is likely to be completely separated from the physical elements of work--metal, lubricants and oil, executing procedures, and turning out parts. Work will, instead, become an act of conception, of creating new products and processes.

* All of the tools, fixtures, and programs needed by a system will have to be conceived, built, and developed before it can make the first product. Thus, all of the controllable costs will be sunk before the first product comes off the line, after which the unit cost will be the same whether the firm makes one unit or many.

* In order to achieve untended manufacture the craft of machining needs to be developed into a science of manufacturing. Every possible contingency needs to be anticipated and an appropriate response provided in the form of a tightly specified procedure.

8.2. Knowledge and Problem Solving in FMS (3)

With each epochal change, from Statistical Process Control to Numerical Control to Flexible Manufacturing Systems, the necessary knowledge became more extensive, more formal, and at a higher stage. Concurrently, the process of problem solving, which generates much of that knowledge, also had to change. The reason is that with each epoch, line operators got farther away from the physical elements of work, so that their intuitive pattern recognition and expertise were not accessible. In the SPC era and before, master mechanics working with general purpose machines usually accrued years of experience, during which they accumulated a wealth of idiosyncratic knowledge about how to perform in a wide variety of circumstances. They talked in terms of a "feel" for the machine, the tools, and the parts they worked on. It was through this feel that they were capable of producing parts to exacting specifications. Watching them work, one had a sense that they recognized errors (e.g., vibration, chatter, structural deformation due to thermal forces) as they were happening and adapted their procedures to compensate for them. This, in engineering terminology, is an advanced form of adaptive control in an ambiguous environment. Such adaptive error recognition and compensation requires either very elaborate expertise with a complex web of relationships, such as the experiential and partly tacit knowledge of the skilled machinist, or alternately a high stage of formal knowledge approaching full scientific understanding of the machinery, sensor, and controller technology, as well as of the product, the process, and all their interactions.