Rapid prototyping crankshafts in metal? Solid, substantial, drop-it-on-your-foot-and-break-it (foot)-type material like a billet of pre-hardened 4340 steel?
That's what they're working with at Mazak Corp.'s National Technology Center (NTC; Florence, KY). Engineers are transforming billets into full-size, machined crankshafts within eight hours. Grind it, balance it, then put it on a test stand or into an engine: this is a bona-fide crank.
They're calling the process "RPM": rapid prototype machining. The capability is based on special software that they've developed at the NTC in response to a request from one of the two U.S.-based OEMs for fast crankshaft capability. It is being made available to all companies that are interested in having the means to make one-offs fast.
Mazak engineers are taking a different approach to attain this capability. Whereas there is an increasing number of people who are creating CAD solid models of what they want to create, there is often a difficulty, explains Martin Roderick, Mazak applications engineer, in quickly transforming the math models into a form that can be used for machining. "So, instead of taking information from the solid model, we use the database that's used to create the CAD file," he says. Or they can actually create the program without a database at all, but create the design and the required machining program right on a PC screen, whether it is a PC in an office, or the PC that's part of the company's Mazatrol Fusion 640 CNC control, which is not a PC front-end on a CNC control, but actually a PC and a CNC.
|By combining a software tool that rapidly creates a machining program for crankshafts with a standard array of tools, users will be able to create a functional prototype cranks within a single shift.|
To create the crankshaft design without the database, one begins with a screen that shows a long, thin rectangle that's segmented into squares at the top of the screen, and a drawing of a crankshaft below it. The drawing has its various features (pin, counterweight, journal, main journal) labeled. It is simply a matter of using a mouse or touchpad to drag a feature from the drawing to the rectangle in the required sequence. Once the overall design is laid out, a second screen asks for information relating to the dimensions (e.g., diameter, angle, radius) of the features. Another screen asks for tooling information (e.g., rpm, feedrate, depth of cut). (If the CAD database is used along with a predefined set of tools, then all of these steps can be performed automatically.)
Once the information is entered, it is a matter of simply pushing a button and then obtaining a G-code program that can be used by machines that aren't equipped with Mazak's proprietary Fusion 640 control.
But one of the things that facilitates the RPM program is the capability of the machine tool. Development of RPM for cranks at the NTC was done on the company's Integrex 200Y machine. Although the Integrex is nominally a CNC turning center with an 8-in. through-hole chuck, a 30-hp spindle motor, a 20.47-in. swing, and a maximum machining length of 40 in., it is much more than a turning machine. It is also equipped with a 10-hp spindle that can provide speeds up to 6,000 rpm for rotary tools. Tools that can be employed include face mills up to 3-in. in diameter, 1-in. end mills, and 1-in. drills. The standard automatic toolchanger (ATC) handles 20 tools; an option can bring the number to 80.
Roderick emphasizes the importance of standard tooling being used instead of the specials that are characteristic of crankshaft machines. If the necessary tools were extensively specials, then the time to make the tooling would take the rapid out of the system. Roderick admits, however, that Mazak engineers did have to come up with one special, an adjustable tool to generate undercuts around pin journals because a catalog version of such a tool could not be found.
A given software/equipment-tooling setup would be established for a family of crankshafts (i.e., cranks that can fit within a defined machining envelope and with features that can be produced with the tooling package). Roderick says that the RPM capability will be developed for other automotive components, including camshafts, pistons and pulleys.