CNC Analysis Aids Machine Design

Moore Tool (Bridgeport, Connecticut) currently designs, engineers and builds machines in conjunction with its sister company, Producto, in a 200,000-square-foot facility with approximately 200 employees. When the company set out to build a five-axis, high speed machining center for use in the production of critical components, it faced numerous challenges. The machine was intended to serve critical needs of the turbo machinery, mold and die, scroll compressor and medical markets. To help meet the needs of these applications, a control supplier analyzed the machine's control system in order to optimize the performance of this particular design.

The machine needed to possess capabilities such as high speed (30,000 rpm to 40,000 rpm) cutting capability when milling materials ranging from aluminum to hardened steel and titanium; dynamic response; good stability and vibration damping; automation adaptability; a user-friendly Windows working environment; onboard cooling; substantial onboard memory in a CNC without external devices for downloading complex programs; and, above all, high precision.

Moore Tool embodied a "from the ground up" approach to develop its Five-Sided Precision (FSP) line of machining centers. Speed and accuracy were considered when evaluating the needs of working with various materials, as were the differing requirements of production and part accuracy. The requirements of machining aluminum and titanium with high production rates can differ when compared to the intricate contours and features of mold components produced directly in hardened steel. Adding the requirements for efficient graphite machining also produces significant challenges.

The company says the need for a combination of high precision and high material removal rates was evident. The complex contour surface profiling on leading and trailing edges of blades, and especially blisks and IBRs, made a high speed processor essential to maintain acceptable feed rates. The machine configuration, particularly as it relates to the position and configuration of the rotary tables and spindle, would also play an integral role in meeting the needs of Moore Tool's customers.

The machine's CNC is an 840D from Siemens (Elk Grove Village, Illinois). To maximize machine performance, Siemens performed a detailed dynamic analysis of the machine, control and servodrive system. This service is called "Mechatronics." Data gathered during the Mechatronics process are used to optimize the complete machine concept.

In complex blade contour and finishing operations, the CNC provides an aerospace-specific software feature, CompCAD, by which the control's compressor function smoothes point-to-point programming. The real benefit of the control is realized when processing the part using Non-Rational Uniform B-Splines (NURBS), with which the machine can reach an advanced level of smooth contouring and chatter elimination. This is achieved by using splines in an axis-specific tolerance window. According to the manufacturer, contour violations are thus avoided; the efficiency of acceleration/deceleration curves is increased; and slowdowns/speed-ups at block transitions are virtually eliminated.

According to Moore Tool's engineers, in programming, the open architecture of the CNC, along with its high speed, user-defined macros and block search capabilities, have made it an "ideal choice" for the FSP300X. They go on to say that the ability of the CNC to handle large programs, which are typical for intricate mold and die applications, without "drip feed" is also noteworthy.

Optional features that are available with the machine include high-frequency spindle options as high as 80,000 rpm; a range of robotic part loaders, all of which are designed and built by Moore Tool, with the control parameters incorporated into the host CNC; a graphite machining package; a laser toolsetter with measurement and compensation standards; and various customized configurations. The machine can be enhanced with Siemens' Simodrive 611D drive packages.