Include setup as part of CAD/CAM

Modern Machine Shop, Oct, 1992 by Chris Koepfer

First, Mr. Eastin programs the fixture. A library of machine speeds and feeds is resident in the CAM software. The programmer defines type of material and selects the tools and the speeds and feeds are automatically calculated. These speeds and feeds can be modified.

Essentially, once the tools are selected and the material specified, all that is left is assigning bolt hole locations for the two part blanks, spotting the locating pins for the second side and specifying the subplate hold-down bolt holes. All of the holes are co-bored except the part hold-down holes, which get tapped.

The workpiece gets programmed next. He generates the NC program using the merged CAD and CAS files, which let him see the workpiece, subplate, and fixture clamps all mounted on the machine table. The program for the first side calls for end milling the workpiece perimeter in two passes, milling five asymmetrical pockets, and milling three flats. For the second side, the workpiece is turned over and positioned against the locating pins. With the exception of milling the perimeter, the second side machining sequence is the mirror of the first.

Both programs are next downloaded to the machining center CNC. Since the machine home position is used to locate the subplate, no fixture offsets are needed the first time the job runs.

On The Shop Floor

The off-line work is complete. Part blanks are ready. The machine is tooled. Clamps are in-house. The subplate is on the machine. It's time to machine the fixture and workpieces--less than a day from the initial CAD input.

The machining of the subplate is straightforward. A spot drill starts the cycle by locating the subplate hold-down bolt holes, workpiece holding and locating pin holes, and setting ball hole. The tapped holes for the workpiece, pins and setting ball get pilot drilled. A half-inch drill prepares the holes for the subplate bolts. Next, a quarter-twenty tap finishes up the workpiece, locator pin and setting ball holes. The drill work is complete with a co-bore of the half-inch holes.

An end mill cleans up the back side of the subplate with a skim cut creating a surface to simplify alignment with the machine's X-axis the next time the plate is used. On subsequent setups, Mr. Eastin only needs to square the subplate with the machine's X-axis, establish an X-Y location using the setting ball, and enter a G-55 offset between the ball and the machine home position and he is ready to run the brackets again.

In about half an hour, the fixture is machined complete. The workpieces are machined alternately (as detailed above), side one workpiece one, turn it over and locate it against the pins for side two, load a blank workpiece for side one, and so on until the order is complete.

Is It For You?

Automating the production process to include machine setup has helped Ejay's compete and succeed. Many of the benefits Ejay's enjoys from its CAD/CAM system are transferable to most job shop operations:

* increased throughput of work

* shortened leadtimes from order entry to shipment