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AP206
Machinecapabilityc
heck
Machine capability check
Problem
In order to run a machining process it is necessary for part tolerances to fall within the short-term capability of the machine tool. Implementing Patterns such as AP203 (Job set-up), AP301(Cutter parameter update) and AP302 (Dynamic re-machining) can help a machine tool adaptto real production conditions in order to maintain process capability. However, some sources ofprocess variation cannot be accounted for using such methods. For example: Where no mechanism exists to adjust an error, even when the error and its magnitude have
been correctly identified. For example, it may not be possible to correct for extreme backlashon machine axes, or to automatically correct in instances where a piece of swarf causesgross part mis-alignment
Where the variation in error changes at a rate faster than it is possible to correct for it, forexample extreme temperature variation
Solution
Use an inspection probe to perform a machine capability test before machining. Commencemachining only if the machine is within the capability limits defined for the component.Measuring known reference features shows the machine is capable of positioning itselfaccurately and repeatably, or if there is a capability problem.
For example, the following scenarios may be checked: A fixture is automatically loaded and clamped on a machine tool. Occasionally, swarf may
become trapped between the fixture and the clamp, causing an angular error which can bemeasured
It may be known that extreme temperature variation causes a particular machine tool to varyin performance. It is possible to test for thermal effects immediately before a cutting cycle bymeasuring a known artefact, golden part or machine reference feature
Benefits
Programs can automatically alert an operator if the machine appears to be out of alignment Machining will not begin unless confidence in machine capability has been established
Perform machinecapability checks
Ismachine within
defined capabilitylimits?
No, haltmachining
Yes, continuemachining
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Case study
Renishaw uses workpiece inspection probes in its own factories to establish machine capability. TheRenishaw Advanced Milling Turning and Inspection Centre (RAMTIC) is a vertical machining centreequipped with standard Renishaw probing technology, custom fixture, indexing trunnion and tooling
loading systems. RAMTIC machines are also loaded with an artefact: a known golden part which isregularly calibrated and used as a reference part for machine checks.
RAMTIC systems perform machine capability checks with three tests:
Indexer repeatability test:measure artefact features with artefact on top of indexer, performindexer moves away from and back to measurement position, re-measure and compare artefactfeatures, stop machining process if the difference is out of tolerance.
Indexer alignment test:measure points on the top of the artefact spanning the X-axis with theartefact at positions either side of the indexer top position, compare centre points at each inspectionposition, calculate indexer misalignment, stop machining process if out of tolerance.
Checks for thermal distortion:measure key features on the artefact to establish reference pointsfor thermal tracking, stop machining process if thermal drift is out of tolerance - see AP303, Thermalcorrection - machine drift and AP306, Thermal Correction - workpiece expansionfor information
about correcting for thermal effects.
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Example: checking the correct orientation of an automatically loaded pallet table
Only continue machining if the A and B axes are correct to within 1
Sample Productivity+ probe software program
Using data from measured plane, determine if the absoluteangle error in A or B axes is greater than or equal to 1. Ifyes, the program jumps to Out_of_Alignment label and amachine alarm is raised.
If error in A and B axes is less than 1 the component ismachined before jumping to the end of the program.
Measure plane and establish X, Y, Z position data.
RENISHAW ACCEPTS NO RESPONSIBILITY FOR ANY PROBLEMS OR DAMAGE ARISING FROM THE USE OF ANY SAMPLE CODE AND ADVISES THOROUGH
CHECKING OF OUTPUT VARIABLES FOR THE SELECTED INSPECTION PACKAGE AND THE AVAILABILITY OF SPARE AND UNUSED VARIABLES FOR
INDIVIDUAL APPLICATIONS.
SAMPLE PRODUCTIVITY+ PROGRAMS ASSUME THE USE OF ACTIVE EDITOR PRO 1.70.20SAMPLE INSPECTION PLUS PROGRAMS ASSUME USE WITH FANUC TYPE CONTROLS
N10
T01 M06 Select the probe
G54 X0. Y0. Start position
G43H1 Z100. Activate offset 1 and go to 100 mm above
G65 P9810 Z10. F3000 Protected positioning move to Z10
G65 P9818 Y50. Z0. Measuring cycle
IF[ABS[#144]GT1.]GOTO100 If the angle error is greater than 1 jump to an alarm
G65 P9810 X0. Y110. F3000 Move to next position
G65 P9810 Z-10. F3000
G65 P9843 X0. D50. Measuring cycle
IF[ABS[#144]GT1.]GOTO100 If the angle error is greater than 1 jump to an alarm
G65 P9810 Z10. F3000
G65 P9810 X110. Y0. F3000 Move to second position
G65 P9810 Z-10. F3000
G65 P9843 Y0. D50. Measuring cycle
IF[ABS[#144]GT1.]GOTO100 If the angle error is greater than 1 jump to an alarm
G65 P9810 Z100.
G0 G91 G28 Z0. Return to home position
G90
GOTO110
N100
#3000=99(AXIS OUT OF ALIGN) Alarm for the axis alignment
N110 (END)
Sample Inspection Plus software program
The statement referenced by the ABS function within the Condition Builder of Productivity+ Active Editor Pro must be surrounded by parentheses - round brackets. Even ifthe target NC platform requires square brackets, the Condition Builder must use round brackets; the post processing process will convert them as necessary for the target
machine.
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8/10/2019 AP206_machine_capability_check.pdf
4/4Issued 0912 Part no. H-5650-4010-02-B
2010-2011 Renishaw plc. All rights reserved.Renishaw reserves the right to change specifications without notice
RENISHAW and the probe emblem used in the RENISHAW logo are registered trademarks of Renishaw plc in the UK and other countries.apply innovation, Productive Process Pyramid, Productive Process Patterns, Productivity+, AxiSet, Rengage, Trigger Logic, ToolWise,Sprint, MicroHole, PassiveSeal and SwarfStop are trademarks of Renishaw plc.All other brand names and product names used in this document are trade names, ser vice marks, trademarks or registered trademarks oftheir respective owners.
RENISHAW HAS MADE CONSIDERABLE EFFORTS TO ENSURE THE CONTENT OF THIS DOCUMENT IS CORRECT AT THE DATE OFPUBLICATION BUT MAKES NO WARRANTIES OR REPRESENTATIONS REGARDING THE CONTENT. RENISHAW EXCLUDES LIABILITY,HOWSOEVER ARISING, FOR ANY INACCURACIES IN THIS DOCUMENT.
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