Marposs Mida T25G Probe Benefits A flexible, modular system for in-proc-ess probing Resistant to false triggers Outstanding repeatability even with long styli Automatic feedback for tool compen-sation www.marposs.com

Touch Probes Improve Machine Shop's Proficiency

Haas Automation, one of America's most successful machine tool companies, installed new Marposs systems on its CNC lathes to increase production economically. The Marposs Mida T25G probe systems offer Haas increased accuracy and automation.

To cost-effectively meet growing production demands, Haas has instituted an unattended "lights out" third shift. The Marposs Mida T25G probes help to reliably meet size requirements during unattended machining of Haas pulleys and gear blanks, typically run in batches of 1,000 to 2,000 pieces. The in-process probe inspections maintain tolerances of 0.001" on pulley inside diameters (IDs) and outside diameters (ODs), as well as multiple IDs and ODs on the gear blanks.

The in-process gaging system eliminates the need for secondary finishing operations on the pulleys and gears. "Most companies hone or grind the parts after machining in order to bring them to tolerance," says Sean Tillet, Haas' machine shop manager. "We've chosen to eliminate these operations by using in-process touch probing to maintain part size. That way the gear blanks, for example, can go straight to the hob, with no worry that they won't fit into the arbors."

In-process gaging also allows Haas to automatically compensate for variables such as tool wear and thermal drift. "Before the Marposs probes we had to manually test for things like tool wear," explains Tillet. "In the morning we'd experiment with how many pieces we could run in tolerance before tool wear became a factor, or if after a few runs, tool wear leveled off. A couple of hours later and we'd be in production. With the Marposs probes the machines constantly receive information about the run and can adjust to offset such factors."

Marposs probes use a high-frequency system for data transmission. Signals are sent from the probe to the interface and then to the machine tool's CNC. Haas has installed the Mida T25G probes on three of its five CNC lathes. To do their inspection work, the probes are installed into a lathe turret station, just like the cutting tools. The probe is programmed to measure critical machine part diameters by collecting size data at a number of different reference points. The CNC machine equipped with the Marposs probes can self-adjust for thermal growth, tool wear and other undetermined factors. Also, the probes can detect incorrect workpiece mounting and tool breakage.

To ensure measuring consistency, the size data are continuously processed to calculate the differential between the centerline of the work spindle and the centerline of the turret, which sometimes changes due to any number of reasons, including thermal growth. By tracking and nulling out deviations in the spindle-turret relationship, the probe system is able to report true machined part size without regard to any machine movement.

Because touch probes can also detect workpiece type, they can be used for several different types of tasks. Once a probing program is generated for a particular part, it can be saved in the machine's CNC memory. To return to the same type of part to be tested, an operator only needs to call up that program and calibrate the probe.

During the unattended production, the correct probe and probing program are called up automatically for the in-process parts inspection. Tillet offers an illustration: "Let's say you're continuing a run of a thousand pieces of a given pulley. You may have an ID and OD that have to be probed. When the machining cycle gets around to the inspection operation the machine kicks over to a macro program that calls up the right probing program and probe."

In its size-control function, measurements taken by the Mida probe are combined with calculations generated by special Marposs software to maintain a statistical running average of part size. This trend data is transmitted to the machine control and compared against specified print tolerances. When the running average reaches a programmed limit for a given tool and dimension, a tool-wear offset is automatically generated for that tool and dimension to ensure continuous in-tolerance machining.

The bottom-line benefit of the automatic process control is significant. "Without the probes, you'd have to check the parts manually as they come off the machine, and manually program the required offsets," observes Tillet. "Our educated guess, based on the time savings achieved, is that the probes are probably paying themselves off in just four or five months."

Manufacturers are quickly learning that while the CNC machine is capable of making parts quicker and to tighter tolerances, it often can't do so without the help of some means of process control. Mida probes can help CNC machines achieve that potential by accounting for inconsistencies with part material, machine stability, insert quality and the machine operator.