Open systems bring control to shopfloors.
The large firms, comprising roughly 8% of the machine tool industry, have long enjoyed the benefits of adaptive control because companies their size can more readily afford to be experimental with technology. However, the vast majority of machining, approximately 92%, takes place in small shops (one to five machines) and medium shops (five to 50 machines) where technology investments tend to be more conservative.
Today, open systems are making adaptive control possible for all shops--large and small. Open systems are giving small shop owners with existing CNC technology the power to write programs, optimize productivity, improve the return on investment of their CNCs, and effectively boost their bottom lines.
Though the term adaptive control has been tossed around the industry for more than two decades, its proprietary connotations have often left the little guys dreaming of on-staff software engineers and big budgets. Where adaptive control once meant a machinist's subjective ear was trying to detect that unusual whir or hum signaling an impending break, suddenly, new, easy-to-use objective enhancements have turned up the volume.
Now, even the smallest shop contending with troublesome "tool wear" can feasibly adapt an existing, open CNC and effectively optimize its machining processes. Third-party vendors are opening the door with innovative add-on devices and Windows-based software that can link to any CNC and monitor and control cutting conditions to optimize productivity. These new technologies cannot only instruct the CNC to set optimal feedrates by tailoring each task to cutting force variations but also compensate for tool wear and alert the operator to potential problems.
With high speed communication between the PC or third-party add-on and the CNC, feedrates can be adjusted in real time to maintain a constant load. Adaptive control units measure the cutting load directly from the spindle, while precise system calculations adjust feedrates to compensate for load variations. An increase in the load triggers a decrease in the feedrate, and conversely, a decrease in load triggers an increase in the feedrate. The end result is maximum production efficiency with minimum risk of tool, workpiece, or machine damage.
For most shops, converting a CNC for adaptive control is as simple as using the high speed window within the CNC to read and write real time information. A PC and third-party software can access the data collected by the CNC, tapping into critical information like motor load current, motor torque--including a spindle or spindles, tool data, and commanded feedrates. From this data, the enduser can write the required adaptive algorithms within a user-friendly environment and customize the system for each application.
Never a dull moment
As an example of adaptive control's power and its impact on the small machine shop, consider a common situation in which a tool is becoming dull. While the tool may not be dull enough to require replacement, in a traditional shop the affected machine speed would be adjusted to accommodate the expected productivity of the remaining tool life. Here, many disasters wait. Cutting time increases, productivity decreases, leadtimes lengthen--all are part of the gamble. Worst case scenario: catastrophic tool failure. One tool breaks setting off a domino effect that can damage the machine, subsequent tools, and workpieces.
Many factors affect tool wear, making it seemingly unpredictable. Yet, it is known that tool wear, more specifically the load at the cutting tool tip, is directly proportional to the amount of current drawn by the machine's motor. In this case, an adaptive control device can allow a machine operator to set high and low current parameters. A tool that is becoming dull will cause the amount of current drawn by the motor to increase. The current increase sends a signal to the CNC to adjust the feedrate, thereby significantly limiting the number of opportunities for catastrophic tool failure. When conditions dictate, the computer provides a warning before the tool breaks. If the tool breaks while the machine is operating, the feedrate drops to zero to prevent further damage. Some applications go even further by retracting the tool to the Z axis, so the operator is not required to manually remove the tool.
Replacing worn tools before they break can save other tools and machinery, as well as protect the operator from risk of injury. Over time, operators gain confidence in their machines and capitalize on their new found ability to safely and efficiently oversee several machines at once.
In addition to safeguarding operators and machinery, CNC adaptive controls can provide valuable, timesaving history files for tools, materials, and machinery. When cutting a piece of steel for example, speed parameters and related conditions can be collected and stored in memory. Any time that specific combination of tool, material, and machine are needed, an operator can call up those parameters from the history files and quickly get the job up and running.
Typically, CNC controls create history files one of two ways. The first and fastest way to create a history file is to allow the system to set the parameters--like maximum safe load-based on information supplied by the operator. While this allows for quick setup, it does not guarantee optimal output as the system's prescribed parameters tend to be more conservative than parameters based on actual conditions.
To get the most out of machining, many operators create history files by running through one cycle on the machine and letting the system record the actual conditions. This allows the system to monitor the cycle and determine the true target load for maximum output based on real conditions. In either case, "cutting air" moves are performed at the CNC's highest possible feedrate, ensuring that every cut on every workpiece is run as fast as the strength of the tool will allow.
Aggressive competition among small- and mid-sized job shops continues to feed this new phase of adaptive control. Looking to increase productivity by decreasing cutting time, more and more small shop owners are discovering that adaptive control is a viable option for their CNCs already in service. Bringing protection from tool wear and the guarantee of peak productivity, adaptive control is sharpening the competitive edge of the small- and medium-sized shops with shorter leadtimes due to fewer broken tools--savings that are also realized by machine shop customers.
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|Title Annotation:||machine tool industry|
|Comment:||Open systems bring control to shopfloors.(machine tool industry)|
|Publication:||Tooling & Production|
|Article Type:||Statistical Data Included|
|Date:||Aug 1, 1999|
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