ROSS Racing Pistons designs and manufactures high-end aluminum pistons. The company handles 40 to 50 orders each week, and nearly every job is custom. The company also fabricates approximately 1000 pistons in a week, using a process that involves four to five different machining operations performed on high-end computer numerical control (CNC) equipment.
With CNC programming being a critical step in the production process, ROSS’ programmers must work quickly and their programs must be right the first time to avoid delays caused by rework and reprogramming. In the past, using a traditional programming process, the task required about 200 hours per week.
Using macros created with DP Technology’s ESPRIT CAM software, that time has been reduced to only 30 hours per week. And when a programmer wants to make a minor change to an existing macro, which is common, it takes only minutes using ESPRIT instead of the cumbersome C++ programming process required previously. In addition, ESPRIT’s simulation functionality helps avoid errors that lead to rework.
“We can't afford a lot of programming time,” explained Nicholas Plantus, chief engineer at ROSS Racing Pistons. “With ESPRIT, it takes about 20 minutes total to program the five operations needed to get a part ready to run.”
Power and Precision
ROSS Racing Pistons began production of high-end forged aluminum racing pistons in 1979 and the company is still run by one of its founders, Ken Roble. The company offers pistons for so many cars that its catalog runs to 45 pages. While most of the company’s pistons go into drag racers, some are made for other uses, such as in antique and vintage cars for which pistons are no longer made.
The breadth of the company’s product line means that the design team must deal with 900 possible combinations of applications, cylinder heads and compression ratios—the three factors that determine the shape of a piston. “There are so many different possibilities out there that almost every job that we do is different,” said Plantus. To design a new piston, designers work from samples that customers send, as well as drawings or actual cylinder heads. Some customers even send plastic models of their engines’ combustion chambers.
The company’s production equipment includes vertical machining centers, horizontal machining centers, lathes, a turning center, and a 5-axis machining center from vendors such as Okuma, Mori Seiki, Takisawa, and Fadal.
The first step of the production process involves the selection of the appropriate aluminum forging from one of the 95 different forgings the company uses. Forgings range in size from 1.5 to 6.8 inches in diameter.
Actual production begins on a pin-boring machine where pin holes are made. The part then goes to the lathe for OD turning, facing, and creating ring grooves. The next stop is the horizontal machining center, where dome shapes or dish shapes on top of the piston are made, along with the pockets for the valve. This machine also trims the sides of the forging for weight removal, and to make it easier to install the lock rings. When there are valves with compound angles, the part goes next to the 5-axis machine. After that, the vertical machining center is used to remove additional material to further lighten the piston. The last step is the turning center, which is used to make the piston elliptical to compensate for thermal expansion.
Addressing Programming Challenges
Even though nearly every job is unique, many of the new pistons vary only slightly from those that ROSS has already made. Using a traditional approach, however, CNC programming still required 20 hours per order. With that approach, the programmer imported a CAD model into the programming software. He added a model of the workpiece and positioned the part inside. He then selected and organized the features in the part.
The next step was to define the machining operations. For each toolpath, he selected a tool and defined its diameter, length, tool holder, and speeds and feeds.
Macros greatly simplified the creation of the CNC programs by prompting the programmer to enter dimensions and other basic information for each type of part. However, the company’s previous CAM system generated macros using C++. “The guy who was writing the macros for us was pretty good, but when he left, we had nobody who knew C++,” said Plantus.
This meant the company could no longer maintain its existing macros or develop new ones for new piston geometries. Another drawback of the previous CAM system was that it did not let end users generate post processors. The only way to get them was to buy them from the software developer, and that was expensive.
One of the main reasons ROSS chose ESPRIT was because its macro programming language is based on the industry-standard programming language Microsoft Visual Basic for Applications, which many programmers know and is much easier to use than C++. ESPRIT enables programmers to use VBA to access virtually all of its capabilities.
For example, a programmer can create a new dialog box that asks for parameters to define a hole (diameter, depth, XYZ location, hole type). Then the VBA macro automatically creates circles representing the holes, selects the cutting tools, automatically creates the drilling operations, and produces the G-code program all in one step. All of ESPRIT’s menus and tool bars are also accessible from within a macro or add-in program via the ESPRIT API. This allows the macros and programs to adapt the ESPRIT interface to suit the individual needs of a particular application or business. “So far we have created 60,000 lines of code and we are adding to it,” Plantus noted. DP Technology also allows users to develop their own post-processors.
Using macros created in ESPRIT, ROSS has created a fast 5-step process for CNC programming in which programmers simply fill in parameters and make some menu picks. The first step involves importing an IGES file for the dome and a Pro/ENGINEER CAD file for the piston. Using that geometry, he defines the features on the part.
There are normally between 10 and 12 features, and this step takes between one and five minutes. Next, he identifies which machining operations will be required and assigns them to the various machines, which are selected from a menu. Finally, he selects the tool for each operation. At that point, ESPRIT generates the code for each machining operation. This step takes less than one minute—for a total of 20 minutes or less for the entire process.
The programmer then uses the ESPRIT simulation functionality to visualize the cutting process. ESPRIT makes it possible to view each individual cut in the entire machining process as dynamic 3D solids. The programmer can also view a presentation of the part that will be produced by the program and compare the as-machined workpiece to the original design. By zooming in on the simulated mold, the programmer can determine whether or not it matches the customer’s requirements.
The simulation process provides the ideal opportunity to take a close look at the program that has been created up to that point. At times, the simulation will show a problem with a program, which can then be corrected before any time or aluminum is wasted.
ESPRIT’s simulation functionality is more user-friendly, according to Plantus, than what was available in the company’s previous CAM system. For example, ESPRIT allows the user to place the cursor over a geometric feature and read its dimensions. “Simulation using ESPRIT is very accurate, and it’s easier, compared to our old software, to check the geometry and catch mistakes,” he explained.
The ease of creating macros with ESPRIT means that the company’s two CNC programmers have time to do other things, such as setting up jobs on the machines. It is also allowing ROSS to keep up with demand, even as its product line has expanded. “In the past, it could take half a day to program one operation,” Plantus said. “Now that it goes so quickly, we are better able to handle the complexity of our product line.”
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