Vertical machining centers for volume production: at this model plant for lean manufacturing. Parker Hannifin personnel became convinced that the simple approach was the strongest choice for the application. Part of the lesson learned at this plant is that the most difficult part of going lean may lie in the discussion

Modern Machine Shop, Dec, 2004 by Peter Zelinski

Parker Hannifin's plant in Beaufort, South Carolina, makes truck engine components--units for fuel filtration, oil filtration and cooling. The plant is part of the company's Racor division. To produce well in excess of 1,000 assembled products on a busy day, the plant has to be able to machine almost 10,000 cast aluminum workpieces daily. That demand might tend to suggest some traditional high-volume machining approach, such as transfer machines or horizontal machining centers. But the management of this plant, and company managers in other locations, ultimately became convinced of an alternate view--that the right solution for this application would come from simple, compact 30-taper vertical machining centers instead.

Joe Juliano, the plant's engineering services manager, is one of the people who had to be convinced. When the new production process was being conceived 3 years ago, he was an advocate for horizontal machining centers, and he was prepared to fight for this approach. All that he had read about lean manufacturing suggested to him that this style of machining fit best with Parker Hannifin's priorities for lean production in the new plant. A vertical was a low-cost machine for small volumes, and a horizontal was a more sophisticated machine better suited for higher volumes and higher demands or so his thinking went. Only when he had a chance to see vertical machining centers running high-volume parts in a Toyota supplier's facility did he recognize how well vertical machines would fit with his own application.

The priorities for that application can be summarized plainly. The plant needs the productivity to meet customers' demands and the responsiveness to react to changes. Verticals meet the productivity requirement because their low unit cost lets the shop run more spindles for the money, compared to the other approaches. These machines meet the responsiveness demand because they are, to put it simply, simple. They can be brought on- and off-line with little difficulty; their work can be exchanged between machines; and adding an additional vertical machine as the demand warrants is relatively inexpensive.

The stress on simplicity in this process can't be overstated. As a "model lean plant" for the company, the Racor facility is one of the most prominent plants within Parker Hannifin, even though the plant is not one of the more automated facilities, nor is it one of the more "high tech." Parts arriving at each vertical machining center are not machined in a single setup. They are transferred from machine to machine. And work-handling devices don't perform this transfer automatically, but instead parts are transferred piece by piece from machine to machine by human hands.

One consequence of this approach, says Mr. Juliano, is that the workholding is at least as important to this process as the machine tools.

Workholding And Handling

The plant has vertical machining centers grouped in three cells. One of the details the company wishes to keep secret is the precise number of machining centers used in this plant--but the number is between 10 and 20. Each of the three cells runs a particular set of part numbers, and different part numbers use a particular cell in different ways.

Sometimes a part goes to three machines in sequence. Sometimes two machines both perform a long first operation in parallel, while a third machine performs the short second operation all alone. And some times, one machine out of three sits idle, because only two machines are needed to run a particular part. Keeping all of the machines cutting is not a priority in this plant. Meeting quality demands, meeting quantity and delivery demands that change daily, and keeping labor efficiently engaged are all higher priorities than this.

Here is how a machining cycle works: An operator walks to a machine tool with a workpiece in hand. The machine tool door is open because the previous machining cycle has just been completed. The operator unloads the current piece and loads the next piece. Walking to the next machine, the operator hits a switch that triggers the door to close, the fixture to clamp and the machining cycle to begin. The operator then arrives at the next machine with the partially completed workpiece in hand. The door to that machine is open, and the sequence begins again.

Is it costly to use human labor in this way, mechanically performing workpiece transfer? In cases where the work transfer truly is mechanical, the answer may be yes. The plant will evaluate automation for some of its work transfer in the future. However, the value of every operator extends beyond the movement of parts. All employees in the machining cells have duties apart from those cells. And within the cell, one of the employee's functions is to perform a visual inspection of every completed part. A quick look to confirm that everything seems right is an important element of the shop's quality control system, and human attention is a particularly effective tool for accomplishing this step.