[step-manufacturing] Minutes of April 8 Conference Call

[Martin Hardwick]

Attendees
Martin Hardwick, STEP Tools, USA
Mikael Hedlind, KTH, Sweden
David Loffredo, STEP Tools, USA
David Odendahl, Boeing, USA
Fred Proctor, NIST, USA
Sid Venkatesh, Boeing, USA
Bengt Olsson, Sandvik, Sweden
Fiona Zhao, NIST, USA/New Zealand
Bob Erickson, Pratt & Whitney, USA
Leon Xu, Boeing, USA
Erik Jacobson, GE Energy, USA*
*Ronnie Fesperman, NIST, USA
Aydin Nassehi, University of Bath, UK
Buzz Callaghan, IQL, USA
Andreas Archenti, KTH, Sweden

We continued our discussion on how to measure and predict machine tool 
accuracy. Many factors impact machine tool accuracy including the servo 
motors, the machine geometry, the bending force, and thermal 
conditions.  KTH, NIST and IQL (US Army) have on-going projects that are 
investigating how to measure and predict machine tool accuracy. So far 
the results are highly encouraging. Making the initial measurements is 
time consuming, but once the measurements are made they are reliable and 
consistent, and their continued validity can be verified using a Ballbar 
test.

The results of the measurement tests can be represented as stacked 
Homogeneous Transformation Matrices' (HTM's) for the machine tool axes. 
There are emerging ASME standards for these results- B5.59-1 and B5.59-2.

We discussed how to apply machine tool accuracy to STEP-NC. There will  
be many applications. Two key ones are:

1. Predicting if a machine can produce a part that will meet its tolerances.
2. Correcting a program by modifying its nominal tool paths for the 
accuracy of the machine.

The STEP-NC program describes how the part is to be machined and what 
tolerances are required for the final part and also for intermediate 
parts as well. The machine tool model defines the kinematics of the 
machine and with the HTM information added predicts the as-executed tool 
paths. We can define the machine tool models in CAD systems as AP-214 or 
AP-203 data. Using the Siemens NX export extension developed by KTH, or 
by hand-editing, we can add the machine tool kinematics to the STEP 
AP-214 file. The next step is to add the HTM accuracy data to the 
kinematic data to produce an AP-214 file that can be used to predict 
machining accuracy.

A recording of the call is on the ftp site at the address below. The 
next call will be at the usual times on Friday April 22.
ftp://www.steptools.com/private/Undecided/stepmanuf_telecon_20110408.wmv

Action Items
1. STEP AP-214 to be shared with ASME B5.59 experts.
2. ASME B5. 59 to be shared with STEP experts.

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