Using offline programming keeps that CMM on track.
Coordinate measuring machines (CMMs) relieve some of the back-up that occurs in inspection, but they do little good when they have to be taken offline to program a new part. In some cases, a CMM could be offline for several days while programming a difficult part.
Offline programming is the key to keeping your CMM maintaining throughput. Offline programming provides a way to program parts without having a physical part in front of the operator. This means you can program a part days or weeks ahead of schedule.
Offline programming is done by using a CAD model. Whether you have a manual or a DCC CMM, a model can be used to generate a CMM program. A CAD model can be provided by the customer, or generated in your engineering department. This model provides all the math data needed to generate a CMM program. Nominal data used to create the model are used by the offline program to generate all the CMM moves and measurements. To further elaborate, the vectors used to drive a
DCC CMM come directly from the CAD model. This means the probe on your CMM will drive normal to the surface being measured and will eliminate any cosine error, ensuring that your measurement data are accurate.
In the past, CMM offline programs were expensive and out of the reach of many operations. With costs starting in the $15,000 range, it became hard to justify the return on investment. That has changed. For example, NewCastle Measurement's Offline is a CAD-based full-functioning soft ware program that costs much less - with software maintenance costs below $1,000.
It is important to make sure any offline package is compliant with the current DMIS standards. This ensures that the offline program will write the correct DMIS code for any CMM manufacture's software.
Moreover, all offline CMM programming software should have these basic tools:
Probe system: Building a probe representation is necessary to view just how your probe system will move around the part. With a built-in catalog of probes and styli building, the probe system has become simplified.
Probe orientations can be defined by the user or, in the case of NewCastle Offline, can be picked directly off a model feature. This will guarantee you have the correct orientation for that feature.
Simulation mode: An offline programming package should have a simulation mode. This will allow you to run your program in the offline mode the probe will simulate your probe path.
Clearance planes: This method of programming will allow you to mea sure a part without having to insert intermediate points, also known as gotos. A user-defined clearance box is placed around the part, and it defines how much clearance the probe will have when moving from one side of the part to another. This box can be defined by simply using a slider bar that moves the box closer to or farther away from the part.
Clearance planes help establish a system that provides collision avoidance, not just collision detection. Detection will determine only that you will strike the probe on the part; avoidance will create the path to avoid this collision.
Transparency: Model transparency is a tool that allows the programmer to change the opacity of the model. This gives the programmer the ability to view a feature's point displacement down inside the feature without having to perform time-consuming rotations. The transparency can be quickly adjusted by using a slider bar on the main toolbar.
Datum macros: Easy-to-use datum-alignment macros will help speed up the programming process by simplifying the setup of the part alignment. It is important to have a macro system that will help resolve any alignment issues and align the actual part to the model's coordinate system.
Training: Any offline CMM programming software should be user-friendly and easy to use. Training should be structured so that a user can access it any time. Web-based training is becoming one method of handling customers' different needs.
Easy-to-use features such as a single-click tool for feature element definition makes learning all the feature types a snap.
Offline vs online
There are still those who would rather be able to "touch the part" while programming. However, the inherent problem with this method is that the part you are writing your program with is out-of spec or not the current blueprint design. Another issue is generating the correct vector direction angles for a DCC CMM. These are extracted from the model in offline programming, ensuring a correct angle. NewCastle Measurement LLC, www.rsleads.com/707tp-153
Mark Boucher is co-owner of NewCastle Measurement LLC.
By Mark Boucher, NewCastle Measurement
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|Publication:||Tooling & Production|
|Date:||Jul 1, 2007|
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