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NC verification.

Computer aided manufacturing (CAM) programs have done much to automate the generation of numerical Control (NC) code.

In some leading edge machine shops, going from art (the CAD drawing) to part (the NC code) has become a reality. However, if material, machine, or tool specifications change, even the best CAM programs have to be "tweaked" before and after producing NC code for a new part.

In many machine shops, NC code is still produced by programmers without the aid of full-fledged CAD/CAM programs, or at the machine by an operator. Regardless of whether the NC code is produced with a full-blown CAD/CAM program, at the machine, or somewhere in between, the resulting program has to be verified before it can be confidently released to production.

Even though pen plots and wire frame simulations can be used to improve NC code, for many, actually machining a part using polyurethane foam or aluminum is still the only acceptable means of verifying the code. By some estimates, US manufacturers spend over $2 billion a year on tape tryouts (TTOs) alone--using hundred thousand dollar milling machines to cut polyurethane or aluminum prototypes.

A relatively new technology, called NC Verification (NCV), greatly reduces the time and cost of producing NC programs by simulating tool paths and material removal in software. On a monitor, programmers can watch a high-quality display of a cutter moving through its specified path. As the curer moves, it removes material from a stock model and the designed part emerges as it would on a machine. The software and resulting display answers questions such as:

* Did the cutter remove the necessary stock?

* Did the cutter remove any material it should not have?

* Did the cutter hit any clamps or fixtures on approach?

* Did the cutter pass through the floor or side of a pocket, or through a rib?

* Were the tool paths as efficient as they could be?

Even with NCV, some errors can slip by. Problems such as tool chatter and stock warpage (due to heat stresses created during machining) are beyond the scope of current technology. However, NCV catches the majority of errors before shop floor resources are used. NCV can even identify some errors that traditional TTOs miss. For example, the NC code used to produce a part that had been cut in foam and cleared for production revealed 14 fatal errors when run through an NCV program. The program identified errors such as:

* Islands of material left behind were scattered over one side of the part. Due to the brittleness of the polyurethane test piece, slender islands simply broke off during the TTO.

* Tool tabs were machined away. The error was obvious when the program's color coding distinctly showed what material had been machined away and what had not.

* Rapid tool movement in the tool tab. Rapid tool movement is flagged by the NCV program and available for review by the programmer. A moments inattention during a lengthy TFO on the shop floor can allow such errors to slip by.

Additional benefits

NCV programs run in a fraction of the time needed to run a TTO. For example, on a graphics workstation, NCV typically takes only 5% of the time physical verification requires. Also, verification is available immediately. A programmer may wait a week or more for use of a milling machine to try out a program. When several runs are needed to debug a progam, waiting time for physical verification can be substantial.

The rapid turnaround time NCV affords programmers encourages them to use NCV to fine-tune NC programs for maximum efficiency. This benefit can be especially valuable for long production runs. Without NCV, program optimization is rare. Not many programmers would risk altering an NC program that already cuts the right shape just to make it 5% faster.

Companies find it costly and time-consuming to provide NC programmers with adequate training and practice. NCV can be used in a similar fashion to the way flight simulators are used by airlines to train pilots, providing immediate feedback as to the cause of an error. When the user points to a scallop or gouge, the system displays the identifier of the motion responsible for that cut. This allows the immediate location of the offending motion in the input file. Potential NC programmers can be trained rapidly and without danger.

The use of NCV reduces the wear on milling machines. When polyurethane foam is cut, it rises in the air and then falls into machine gears where it acts as a grinding paste. Machines used for TFOs typically require four times the maintenance of those doing production work.

NCV programs free up machines to do what they were purchased to do: cut metal to fill shop orders.

NCV programs provide the benefits of program optimization, improve product lead times, assist in training, and can add up to a return on investment of as little as three months.

NCV choices

Several software solutions exist for companies wishing to employ NCV. Some are packaged as part of a complete CAD/CAM package. Others are offered as standalone programs.

CGTech's Vericut (also reviewed in T&P's Feb 1992 Manufacturing Solutions section, page 60) interactively simulates, verities, and displays the metal removal process of an NC tool path, and runs on most workstations and 386/486-based PCs.

Vericut can depict milling, drilling, and turning operations with two-axis through five-axis simultaneous motion. The tool paths to be tested can be passed to the verification worksmtion across any network and from any computer. Vericut can read tool paths from most major CAD/CAM software packages including CADAM, Dassault, Cimlinc, Computervision, MCS, EDS, and Point Control, as well as AutoCAD and CADKey-based NC packages.

With Vericut, the user has complete control over the dimensions, location, and orientation of rough stock, as well as the ability to include fixturing Or clamp holding of the stock. The program allows cutter information to be developed interactively, input using an expanded APT seven-parameter statement, or retrieved -from a tool library.

A new module added to Vericut, called "Optipath," is said to reduce NC machining time by 20% or more. Optipath is a solids-modeling program that enables a modified or variable feedrate to be used when simulating the machining of a part--one that is maximized for the thickness of material being removed. Optipath, in turn, determines the actual feedrates of the NC machine, thus optimizing the time required to cut the part.

Cimplex NCV operates as a standalone application on a range of IBM, Silicon Graphics, and Sun Workstations. A version integrated with other Cimplex applications modules runs on a variety of highperformance UNiX-based graphics workstations.

The program is compatible with most existing CAD/CAM systems that can produce IBM APTAC or APT-CLFILE output, such as CADAM, CATIA, CALMA, and CIMLINC. Cimplex NCV can run to| tally unattended, automatically storing screen images of each error and cutter change. Different colors c an be used to identify curers for multi-axis programs.

Numerical Control Computer Sciences' (NCCS) IPV (In-Process Verification) produces a graphics simulation of the metal-removal process, and has been integrated into its CAM system, NCL. IPV takes verification inside the CAM system and makes it an integral part of the programming effort. The programmer can generate a cutter path, look at the results simulated in realistic solid animation, correct errors or deficiencies, and re-verify the program to ensure that it is efficient and error-free.

Using NCL/IPV, the programmer can verify any portion or all of the tool path during the process of creating the program. Collisions with the raw stock, fixture, or clamps are automatically flagged. Each tool path is verified by using the stock as it appeared at the end of the preceding operation, exactly as it would appear on the machine.

The software runs on UNiX-based workstations from Silicon Graphics, Sun, and Digital Equipment Corp.

SILMA Inc's CimStation NC Verification enables programmers to visualize the complete machining process in 3D simulation, including the NC machine, tool magazine, and individual tools, parts, and fixtures. Unwanted collisions between tools and either the machine, the part, fixturing, equipment, or other tools are easily identified, eliminating risk to the equipment.

The program provides a seamless interface to existing NC environments. Simulations are driven by actual NC machine code data (C-- or M-code). Programmers can easily transfer existing CAD data to CimStation via IGES or direct CAD interfaces. The software is available on UNiX workstations from HewlettPackard, IBM, Silicon Graphics, and Sun Microsystems.

Teksoffs CAD/CAM system 6.0 features NC Verification and Associative Machining modules. NC Verification enables errors in programming to be corrected before the machine is set up by enabling the user to view and dimensionally verify the workpiece as it will be machined, both in-process and as a final part. The program enables the user to visually verify the part, including fixtures and clamps by creating a solid model of the part that can be viewed from any angle, rotated, cross-sectioned, or zoomed-in at any time. The user can visually inspect the inside of pockets or holes through cross-sectioning functions, which are determined by selecting coordinates across the X plane, Y plane, or both. The program also determines cutting times and the volume of material removed.

Associative Machining reduces the time required to generate, modify, or manipulate tool paths by associating groups of information with specific milling or turning processes such as roughing, pocketing, or finishing. This information is then saved and used to generate new tool paths requiring the same processes or can be used to modify or manipulate an existing tool path without starting from scratch. For instance, spindle speed does not have to remain constant; it can be varied at any point along the tool path.

The program'sCMM (coordinate measuring machine) feature enables users to inspect and measure the part created in software. For example, if the user sees gouging, the CMM feature will report the block number of the responsible NC code so the user doesn't have to run the whole program to find the problem area. It also enables the user to determine or verify precise dimensional data between specified locations.

TexSoffs CAD/CAM system was developed for the PC platform to provide a drafting, design, and manufacturing tool with up to five-axis CAM programming, 3D viewing, engineering, and cutting of sculptured surfaces. Complete CNC part programs can be generated from drafting, design, inspection, and prototype development through tool path generation for mill, lathe, punch, laser, plasma, md wire EDM machines.
COPYRIGHT 1992 Nelson Publishing
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1992 Gale, Cengage Learning. All rights reserved.

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Title Annotation:numerical control
Author:Stovicek, Donald R.
Publication:Tooling & Production
Date:May 1, 1992
Previous Article:Saturn system simulates transfer.
Next Article:Measuring complex surfaces.

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