Bronson Precision Products (Bronson, MI), a division of Royal Oak Industries (Lake Orion, MI), is one example of how a shop can utilize secondary machining to simultaneously perform operations across a variety of machines while increasing the number of parts produced per hour. All without damaging parts, creating bottlenecks, expending labor needlessly or tying up money in work-in-progress inventory.

Many of the fuel injection parts this shop produces are complex and require a tricky combination of secondary operations. Take, for example, the housing piece that Bronson manufactures which contains the electromechanical device that actuates the fuel injector plunger. This part requires milling operations at one end, drilling along its entire length and ID and OD turning operations at both ends. In addition, it requires drilling, tapping, grooving and pocket milling at one end; the broaching of two wrench flats on the largest OD; and then final facing and deburring.

When production on the part began, the housings were made from discrete blanks and the initial turning operations were performed on a two-axis turret-type lathe. This arrangement worked fine for producing limited quantities of the part - as long as workers remained at the machine to load and unload parts and make frequent inspections. But, as orders increased, it soon became apparent that something more efficient than the turret-type lathe would be needed. The shop decided to go with a large CNC lathe that combined considerable horsepower and gang tooling capacities with accessories such as an automatic loading and unloading system and an integral gantry loader.

The lathe's automated gantry loader moves the separate workpieces from the staging area to the chuck. A blank that needs turning on either end is machined on the front end, moved from the chuck to a workpiece reversing station, turned around, and sent back to the chuck for back end machining. With its combination of a part banking system and a gantry loader, the lathe can run unattended for great lengths of time. Another advantage is that instead of simply delivering the turned blank to an exit chute, the gantry loader delivers it to a conveyor belt that carries it to an inspection station. After that, it is carried downstream for additional machining operations. By choosing equipment that combines essential operations, rather than purchasing them as separate machines, the shop not only saved money but was able to cut the number of workers from the amount needed to run two machines down to those needed for one.

Bronson also used less-costly conventional systems - such as CNC machine tools - wherever possible. Since conventional CNC machine tools are less expensive than multi-axis turning centers, a greater number can be bought to boost the shop's machining capacity. This makes up for any advantage that the simultaneous operations on a multi-axis machine offers. After automating its secondary operations, the shop's machining cells were rearranged to best suit the abilities of its new systems. In some cases, certain pieces of equipment, like lathes, were allowed to be moved from cell to cell in response to changes in demand.

Matt Kroll, director of technology at Royal Oak Industries, explains the importance of automating secondary operations. "Looking at the cell as a whole, by automating the transfer of parts from machine to machine and the loading and unloading of parts at each machine, we've been able to staff the cell with a relatively small crew given the number of machines involved, holding down labor costs." He adds, "We have also eliminated the potential mistakes that can occur when machines are manually loaded. Manual handling of parts is greatly reduced, and with it damage due to rough handling. In addition, costs associated with storing and keeping track of incomplete parts have been eliminated. Production is less affected by interruptions because of things such as breaks, shift changes, lunch and so forth. Best of all, production is more consistent, and we have better control over part quality."

Combining conventional tooling with equipment that handles more than one key process – as well as reconfiguring machining cells to tackle more of each part's necessary operations – turned out to be a great success. Tellingly, the current system employed by the shop was put into place just before the economy went sour. When the downturn began, the system turned out to be money saver. In Mr. Kroll's words, "We expect our automated cell to meet our needs well into the future, but if our production needs should change, the cell is flexible enough so that we can easily and inexpensively reconfigure it to meet our needs."

Source: Secondary Machining – Without the Tears
Leo Rakowski
Production Machining, Nov. 2001
http://www.production-machining.com/articles/110101.html