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Technical Articles :: CNC Controls

Omative Adaptive Control & Monitoring Systems for improving Productivity in CNC Machines


Omative Systems ,Israel
Adaptive control and monitoring

 REAL-TIME adaptive control & MONITORING (acm)

now MADE a reality BY OMATIVE SYSTEMS,ISRAEL
Background
While CNC technology coupled with CAD/CAM systems (enabling more flexibility in batch production) has long provided an agile alternative to the more conventional rigid manufacturing technologies, major inefficiencies still remain. Present day CNC technology requires users to determine appropriate cutting parameters even when sophisticated CAD/CAM systems are used to generate NC programs. NC programming - whether based on CAD/CAM or otherwise - is virtually carried out in a vacuum.
The control mechanisms of present day CNC machines are limited to geometry and kinematics. As such, they follow pre-programmed constant speed and feed rates during each cutting operation. Consequently, machines do not have the flexibility to adapt to the dynamic changes that occur during cutting. This inflexibility would be acceptable if cutting conditions were uniform during machining. But conditions do vary continuously during cutting for the following reasons:
  • Workpiece surface is often not even, whether the raw material is a bar stock, forging or casting;
  •  Tool sharpness declines during machining due to tool wear;
  • Workpiece material is generally not homogeneous and material hardness varies within each workpiece;
  • Material hardness and workpiece dimensions vary from piece to piece and even more so from batch to batch;
  • Cooling qualities vary during machining resulting in temperature variations;
  •  Fixture’s stability may be affected by dynamically varying forces; and
  •  NC programs may contain errors.
 
As a result of these variations during the cutting process, actual cutting loads vary continuously - in turn resulting in:
  • Breakage of tools, part and spindle
  • Long cycle times
  • Variations in tool deflection - hence inconsistent dimensional accuracy
  • Damaged internal grain structure and stress areas in the part.
 
While there is need to control cutting loads in order to contain these problems, current CNC machines do not have the capability of controlling the cutting dynamics as they keep speeds and feeds constant during each cutting pass.
 
The CNC Conundrum
Advances in CAD/CAM technology have caused machine shops to focus most of their attention to “defining the required geometry” and ignore dynamic aspects. With all these continuously occurring variations, NC programmers must be conservative when determining cutting parameters, resulting in inefficient machining and long cutting cycles. Alternatively, in an attempt to shorten cycle times, NC programmers have to set aggressive cutting parameters, often resulting in catastrophic damage to tools, parts and machine.
No matter how optimized NC programs may be, they cannot account for the dynamic variations that occur during cutting and are unable to adapt to continuously varying cutting conditions. At best, very long NC programs may be created with different feed rates for each segment. But even this attempt fails to adapt cutting parameters in real-time to real-life cutting conditions.
OMATIVE's Dynamic Optimization Solution
The dilemma of conservative programming vs. the need for speed is solved through the implementation of “Adaptive Control & Monitoring " technology. Effective Adaptive Control & Monitoring (ACM) fully optimizes the cutting process, in real time, based on continuously monitored cutting conditions. ACM is the CNC technology of tomorrow - available today.
Such systems are indispensable if expensive CNC machines are ever to run at their full capacity and if cutting tools are to be utilized to their maximum life, rather than incurring in-process catastrophic breakage and production disruption. In addition, machine operators are not required to intervene in the machining process to watch and manually tune the machine. 
Drastic cost reductions, dictated by an increasingly competitive market, require manufacturers to cut all elements of machining costs. These include machining cycle times, machine operating costs, tooling costs, NC programming costs and the cost of long lead-times. Real time in-process ACM technology addresses all of these economic issues.
ACM systems maintain a constant cutting load by automatically adjusting cutting feeds in real time. As dynamically operating real-time systems, OMATIVE ACM products can be integrated into the CNC machine, continuously sensing the actual cutting conditions and overriding the pre-programmed feeds in real time.
 
Maintaining the maximum permissible load during each cutting operation, enables the highest permissible feed rate to be applied at all times, resulting in faster and safer processes. Furthermore, constant cutting forces ensure that the tool deflection is constant during machining and dimensional accuracy is consistent throughout the product.
 
Adaptive Control & Monitoring on the Shopfloor : Omative ACM is compatible
Viertually with any CNC Controller in the World either as an Integrated Software
Version or with Add on Hardware along with the ACM Software
ACM systems are available for milling, drilling, turning, creep feed grinding and gear hobbing. They can be obtained in an add-on configuration for any CNC machine Controller in the World or as a pure-software option available for full integration into Sinumerik 840D, Heidenhain iTNC530, Fanuc i-series, Fidia X-Power and Bosch-Rexroth CNCs.
The constant cutting load maintained by ACM systems takes into account the variations in the cutting conditions during the cut and ensures that machine cycle times are minimized for each tool and machines are run at the maximum permissible capacity.
One of the most attractive features of ACM systems is that they calculate the optimal feed rate, in real-time, based on the most basic parameters for each specific tool and material. These parameters may be input, if necessary, from an external tool library. The operator is not required to know specific load threshold for each tool, as the internal expert system determines these limits automatically.
With these systems, NC programmers can be aggressive and program feeds as though tools were new and sharp. During cutting, the add-on systems automatically compensate for tool wear, since feed rates are continuously adjusted as a function of the extent of tool wear. ACM systems also give operators a quantitative indication of tool wear during the cut. Operators no longer have to run the machine until the tool gives out. Based on the systems’ indication, operators can replace the worn tools in time, without incurring costly and disruptive tool breakage or replacing the tool sooner than necessary.
Automatic Tool Protection
In addition to detecting tool wear, ACM systems also protect tools from breakage through their sensitivity to the spindle load. Fewer broken tools also reduce scrap and the need for rework. Breakage protection is provided through an alarm system that alerts the machine operator/supervisor when acute overload conditions occur and, if necessary, automatically stops the machine.
Automatic Load Compensation for Tool Wear
Since the spindle loads increase gradually as tools wear, ACM's automatic and real time feed adjustment ensures that the appropriate feed rate is always applied according to the amount of tool wear.
Using ACM, NC programmers do not need to be conservative in programming feeds. Feeds may be programmed as though the tool were new and sharp. During actual cutting, ACM compensates for tool wear automatically throughout the process. This means that cycle times are always minimized and not traded off against tool life. ACM
systems ensure automatic optimization of the machining process to reduce cycle times, increase tool utilization and prevent tool breakage, thus enhancing the machine capacity. In this way, users typically increase productivity by as much as 40%.
Real-time Dynamically Reactive Systems versus Off-line Virtual Systems
Off-line software systems that interface with CAM systems in an attempt to optimize feed rates in the NC program, differ from on-line and real-time ACM systems in that ACM systems constantly sense load variations and react to them in real-time. Therefore, with ACM systems:
a.      Machining cycle times are reduced to the minimum.
b.      Tools are protected from premature breakage; at the same time, parts are protected from the consequences of unexpected tool breakage.
c.      Tool wear is monitored and displayed for the operator’s timely tool replacement.
d.      Tool breakage is detected.
e.      Automatic feed rate adjustment frees the operator to attend to other, additional important tasks. Unmanned machining becomes a reality.
f.        Tool life may be enhanced in many applications.
 
Conclusion
Effective implementation of Adaptive Control technology with its tremendous advantages is undoubtedly indispensable to CNC metal machining shops if they are to achieve drastic cost reductions, dictated by increasingly competitive market. In reducing machining costs, consideration should be given to savings in all of the cost elements. These include: machining time, operator costs, tooling costs, CNC programming costs, production disruption costs and the cost of long lead-times. Savings in these costs and additional savings resulting from increased flexibility and less reliance on the human factor, which are now enabled for the first time, render the implementation of Adaptive Control & Monitoring technology indispensable in metal cutting applications.
The OMATIVE line of ACM products, at the cutting edge of Adaptive Control & Monitoring technology has achieved these objectives for its current users and can do so for every machine shop.

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