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Software answers post processing problems.

A post processor, sometimes called a code generator, is used to convert programmed instructions generated by offline CAM software into CNC programs that can be read by a machine tool's control. The post processor determines the order in which CNC code is output and matches CNC program requirements to the capabilities of the machine tool's control. For example, the post processor determines whether the tool change happens before or after the coolant is turned off. Another example is the ability to output plane switching, which utilizes arcs, allowing faster machining and producing smoother surface finishes. The post processor recognizes this feature of the control and outputs CNC codes as arcs in the appropriate G-code format.

Most CAM systems come with a number of generic or standard post processors that allow very basic instructions to be generated for machine tools. However, they are not designed to take advantage of all the capabilities of a specific machine tool's control, such as subroutines. Therefore, the NC programmer may have to edit code before it can be run; cycle times may be longer than if the post processor was designed for the specific control.

A standard or generic post was developed for a specific machine. If the control has features that aren't supported by the post, then the NC programmer will not be able to take advantage of them without editing code every time a new program is generated. Most shops have a preferred method of outputting code. For example, different shops have a preference for the order in which the steps required for tool changes occur. In the past, only two options were available: edit code or pay for development of a custom post processor.

Some CAM systems provide tools that allow a generic post processor to be modified. The cost for these tools is high. Plus these tools require an in-depth and steep learning curve before the NC programmer can perform even basic modifications to the post processor. Another method CAM developers have devised to enable the NC programmer to customize his own post processors is a generic post processor that can be reconfigured with a question-and-answer interface. Often the question-and-answer routines are lengthy and include a poor interface with cryptic questions and a poor level of control cycle support. The method for sequencing code is cryptic and, when questions don't address the needs of the NC programmers, difficulties can surface.

Custom post processors pose a few difficulties - they can take months to develop and revise, and the cost for multiple controls can be prohibitive. Custom post processor generation requires the NC programmer to answer about 30 pg of questions about specific features of the control. If the NC programmer answers incorrectly or forgets a specific feature, the post processor will require revisions. Likewise, if the programmer doesn't include all the features requested in the 30-pg questionnaire in the post processor, it will need revisions. Additionally, the NC programmer may not know about missing features until they are actually needed and that can then be the difference between profit and loss on a specific job.

Processed solution

Based on Microsoft Wizard technology, EdgeCAM's Code Wizard allows the NC programmer to edit a post processor and tailor it to each machine tool's control in minutes. It allows program defaults, such as no flood coolant, spindle direction, and gear ranges, and allows the NC programmer to reorder code to the sequence preferred in the shop. It also allows the use of advanced features on the machine tool's control, such as using plane switching to convert linear moves to circular moves to provide smooth surfaces and reduce cycle time.

Clicking a button launches Code Wizard's list of standard control templates, such as Fadal, Haas, Fanuc, GE, Heidenhein, and Siemens, etc. Each control template has already been preloaded with defaults to minimize configuration time. The only task that remains is to review and/or reset defaults so that the post processor matches specific control features, techniques, and practices in the shop.

Once the appropriate control template has been selected, a series of templates prompt the NC programmer with a series of questions. It takes about 5 to 10 min to answer all the questions and compile the post processor into machining language. For example, one template covers units of measure (metric and imperial), initial plane, rapid rates, maximum angular feed, and radius compensation factor. Another template includes toolchanges, feedrates, and average toolchange time (so cycle time can automatically be calculated). A gear template allows definition of gear ranges for machine tools with gearboxes.

For rotary milling, the NC programmer can define around which axis rotation takes place and select primary and secondary axes for rotation. A format table allows decimal places to be adjusted and leading and trailing zeros to be set.

The G-code template allows specific codes to be set to a desired number. For example, metric measurements can be defined as G71 or G21 depending on the control. The M-code template enables subroutine call and subroutine end. Program defaults, such as flood coolant on or off and spindle direction, can be set.

A full variable trace can be generated so that the post processor can be debugged. It will display a line that tells the NC programmer where the source of a G-code is located. When the questions have been completed, the Code Constructor template can be opened allowing the content and order of a line of code to be defined. For example, the contents of a drill cycle code line are displayed, such as retract code, X move, Y move, Z depth, replane, tool length offset, coolant, and speed. The order can be rearranged or split into two lines of code to suit the needs of the shop. Hard codes and comments can also be added, which will always appear.

Because EdgeCAM is a Windows operation, the Code Wizard can run in one window, simultaneous to the editor running in another window so the NC programmer can view code changes as the post processor is modified. It's a very powerful tool for getting the exact desired code output.

The last step is to click on the Compile button and convert the post processor to machine language for faster code output. Then the post processor is completed.

Once the post processor has been compiled, code is output to take advantage of the features of a specific machine tool's control, as well as the specific needs of the shop. In addition, as many custom posts as are required can be generated for the machine tools in the shop. When a program is ready to be post processed, call up the right post processor.

Code Wizard eliminates delays caused by waiting for custom posts, eliminates the need to edit code before it goes to the machine tool, and takes advantage of the specific features of each control. It is simple to use with minimal training and is a very good solution for most machine tool controls on the market today.
COPYRIGHT 1997 Nelson Publishing
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1997 Gale, Cengage Learning. All rights reserved.

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Title Annotation:CAM software
Publication:Tooling & Production
Date:Jun 1, 1997
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