G-code Simulation Ensures Safety and Precise Parts
Not a single part lost to scrap after implementing VERICUT CNC simulation software

Ron Topper, supervisor of Rotor Division Machining and Assembly, looks over a large centrifugal compressor impeller. Many of the parts produced in the rotor department are as large as 80 inches in diameter.

Everyone knows that scrap parts and CNC machine crashes are bad, but when the parts are more than six feet in diameter, a mistake can be disastrous. To ensure operator safety and eliminate scrapped parts, Elliott Group of Jeannette, PA, implemented VERICUT CNC verification and simulation software from CGTech.

For nearly 100 years, companies around the world have hired Elliott Group for the design, manufacture and service of their critical turbomachinery. Elliott’s primary products are centrifugal and axial compressors, steam turbines, power recovery expanders, and lubrication systems for rotating equipment. Elliott products and services are used throughout the world in the oil and gas, refining, and petrochemical industries, as well as in other process and power applications. The company is widely recognized for the quality, efficiency, and reliability of its products and services. Elliott Group is wholly owned by Ebara Corporation headquartered in Haneda, Japan.

Impeller manufacturing applies five-axis milling to ensure the quality of the advanced impeller designs. Impellers are stress relieved, machine finished, balanced statically and dynamically, spin tested, and then mounted with an interference-fit onto the shaft. Shaft-to-impeller keys are used for extra stability in high pressure or high power applications.

Elliott Group Engineer George Slezak is an impeller programmer in Elliott’s Rotor Division. The impellers are very large, expensive, one-of-kind parts. They are primarily run on vertical turret lathe (VTL) machines and have complex profiles, grooves, and tolerances as tight as +-.0005/inch.

“Our Ravensburg machine is very complicated,” said Slezak. “It is a unique machine, used mainly for cutting our turbine shafts. With 8 plus axis, machine tool clearance is always an issue. Some turbine shafts have small gaps between the disks on the shaft. We need to verify that the Ravensburg’s swords or machine quill clear when going in between the disks.”

Using Vericut CNC verification and simulation software from CGTech has given Elliott Group the ability to simulate from the same G codes that drive the machine. In this instance, it is used to simulate the turbine shafts machined on the Ravensburg machine.

Scrapped parts due to programming errors are no longer a problem for Elliott Group since it installed Vericut software.

In 2010, Elliott scrapped 27 parts due to programming errors. Most errors were related to gouging of tools, or to tool holders not clearing. In other cases, the tool rapid-traversed across the part. To make matters worse, the parts produced in the rotor department are as large as 80 inches in diameter.

“Parts this large can come off the machine tool due to a tool crash, seriously injuring anyone in the vicinity,” said Slezak. “CAM systems do not always show the post processor outputs. Our CAM systems only verify CL Data, not the actual g-code that the CNC machine tool reads.”

George Slezak, impeller programmer for the Rotor Division, says Vericut lets programmers know when they need to modify tools to meet clearance issues.

Elliott Group found the answer to its challenges with the installation of full multi-axis VERICUT machine simulation software. The ability to simulate from the same g-codes that drive the machine gives the programmers at Elliott Group the confidence to run parts without the risk of injury due to a machine crash.

“The number one reason VERICUT was chosen was of course SAFETY,” said Slezak. “Worrying about a crash used to be part of our day-to-day routine. Not anymore.”

VERICUT shows material removal at the workpiece level and simulates entire machine tools as they appear on a shop floor. The program also simulates NC machine controls and supports advanced control functions to reduce the possibility of a machine crash. Machine Simulation detects collisions and near-misses between all machine tool components such as axis slides, heads, turrets, rotary tables, spindles, tool changers, fixtures, work pieces, cutting tools, and other user-defined objects. A user can set up near-miss zones around the components to check for close calls, and detect over-travel errors.

George Deitz, VTL operator, works on small centrifugal compressor impellers. Using Vericut software helped the company go from 27 scrapped parts a year to zero.

To get up and running quickly with VERICUT, Elliott Group also purchased an interface to its CAM system. All of the modelled elements from the CAM system are imported into VERICUT, including the raw material, fixtures, clamps, cutting tools and holders, and other machine structures. These elements must be positioned correctly to prevent collision with any other element during the machining process. Slezak utilized the free downloadable training sessions that CGTech offers for many of the CAM interfaces available. “The Quick Start training sessions were very helpful. When we implemented the interface to our CAM system it was very easy to use,” Slezak said.

In 2013, not a single part was lost due to programming error, although output tripled during the same period of time. As a result, Elliott Group management sees VERICUT as a very good risk management tool and a big money saver.“Going from 27 parts scrapped to zero paid for the software and then some,” Slezak said. “Programmers are extremely proud of the software. It saves time and money, and gives programmers piece of mind. We know exactly when we need to modify a tool or change tools to meet clearance issues. Machinists are now more comfortable when they hit Cycle Start, and rarely touch the big red emergency stop button.”