Progressive Plants Look to On-Machine Probing by
Thomas R. Cutler
Measuring and quality control on the machine tool is gaining increasing importance in progressive manufacturing plants. Much of probe programming is related to accurately defining the probe purpose and objective. While this may sound like a basic statement, there is almost no end to what a relatively simple in-process probing can do. Fortunately, most probe manufacturers have developed a series of canned routines for common probing problems.
From one off prototype to large runs there are strategic frameworks, methodologies, enabling technologies and automation which can significantly improve operating performance and market share; these tools result in an increased bottom line.
Machine Tool Probes, Button and Laser Type Tool Setters, and Process Control Software using Probe Data come with their own series of challenges according to Cliff Jones, President of Advanced Probe Technologies. Jones asserts, â€śOn-Machine probing is a great way to reduce costs, downtime and operator error. Although measuring a part when it's clamped into a machining center uses up metal-cutting time, doing so can actually save minutes upstream and downstream of the machining cycle. The whole idea behind on-machine probing is to eliminate variation in a process. Anytime, variation shows up there it turns into repairs, rework, or dollars lost. â€ś
The Puyallup, Washington based firm has identified some of the key challenges firms face in addressing on-machine probing including:
Calibration of the probe
Difficulty writing extensive probing programs
Understanding machine tool probe language
In process verification of a part on the machine
In process verification of part stock
Backlog on CMMâ€™s
Reduction of scrap
None or limited static process control
Lack of in process control/inspection
Inconsistent inspection results
Reduction in variability
Reduction of human error
Embracing new technology
Expensive tooling fixtures
Examples include finding the center of a hole, finding the center of a slot, and finding the edge or corner of a work-piece. Unfortunately, these simple routines seldom allow the probe user to do all that may be necessary for their probing requirements, meaning custom programs must be written.
Probing routines can be very complicated to write even for seemingly simply applications. In many cases, a great deal of logic must be built into the routine. Arithmetic capability is often needed as well along with geometrical calculations of complex shapes. A probing program to the depth of a pocket is not so simple if the probing cannot take place due to clamping or some other obstruction. Advanced Probe Technologies, Jones insists, â€śYou have to get the control to retain the current reference position in the Z axis so it will be able to compare it later, after the lower surface is probed. Worse yet, once the probing routine measured the pocket depth, what will it do if the pocket is too shallow? Too deep?â€ť Standard CNC programming commands are just not designed for probe programming. Probes require the control to be much more intelligent than when running standard CNC programs.
CNC machine tools and programming systems for 5-axis machines are quite commonplace. What is less common is the understanding required to get the very best performance out of this equipment, even with sophisticated CAD/CAM systems. â€śReal 5-axis programming is still something of a black hole. True 5-axis probing (or even 4-axis probing) happens when the rotary axis or axes are in the head and actually change the tool axis angle. The tool axis no longer is pointing (normal) towards the XY plane. Even machines that have controllers capable of 3 dimensional tool offsetting do not control the probe adequately,â€ť according to Jones.
Multi-axis machine tool probing is needed; it is where the machining head is actually rotated to the base plane of the machine. This is achieved via 5 axis custom probe macros, except they are capable of accurately positioning the probe tip in the multi axis mode and providing accurate data real time to the user. There is no "post processing" of the data to provide meaningful results. It is all right there as soon as soon as one probes a point or a circle. Few firms have been programming 5-axis CNC machines for more than a decade and even fewer understand how to develop and deliver proven, highly effective solutions that brings greater process control, higher machine utilization, and lean efficiencies to multi-axis or even multi-head machine tools.
The probe technologies are central to an effective lean initiative. According to Advanced Probing Technologiesâ€™ leader, â€śTime is always equated with money, and is an important aspect of any production run. But an even more important aspect is that of the team-building that occurs when the quality function is shared with the shop floor. While control of the process and analysis of the part data stays with the quality department, the actual data collection is performed by the machine operators building an increased understanding between two historically embattled departments.â€ť
Thomas R. Cutler is the President & CEO of Fort Lauderdale, Florida-based, TR Cutler, Inc, (www.trcutlerinc.com). Cutler is the founder of the Manufacturing Media Consortium of three thousand five hundred journalists and editors writing about trends in manufacturing. Cutler is a member of the Society of Professional Journalists, Online News Association, American Society of Business Publication Editors, Committee of Concerned Journalists, as well as author of more than 300 feature articles annually regarding the manufacturing sector. Cutler is also the developer of lean technology C.E.O (Continuous Experiential Optimization). Cutler can be contacted at firstname.lastname@example.org.
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