The need of 5 Axis Machining

Some workpieces with complex contoured parts such as mold cavities, blisks, impellers, aerospace related products and other turbine-type parts require five-axis machining capability in order to be manufactured at all. These workpieces incorporate tool orientation which must be controlled to enable reaching the complicated surface to be machined.

In order to achieve the optimum cutting conditions when machining spatially rounded surfaces (free-form surfaces) the tool application angle must be able to be changed. To realize this, in addition to three linear axes, a minimum of two rotary axes are required.

In some cases, where the workpieces can be produced on three-axis machines, economic considerations like the following often reveal that five-axis machining offers lowest total potential costs saved by reducing the volumes of machines, tooling, and fixturing presently required to achieve the same end result;

• Value of increased throughput—including time saved by eliminating separate setups and reducing queue times required for separate-machine operations;
• Value of current in-process inventory that will not be needed with multi-axis machining capability;
• Value of reduced scrap and rework made possible by complete machining in a single setup, reduced part handling, more uniform machining accuracy;
• Value of time and costs saved in quality control and inspection.
  

5 Axis Machining Made Easy with SINUMERIK 840D

Siemens SINUMERIK 840D has been the first choice for many years when there is a need for five-axis machining. Special functions that have been implemented to make your five-axis machining simple and convenient include:

• Special machine kinematics
• 5 Axis transformation
• Orientation interpolation
• High-performance 3D tool correction
• Manual five-axis functions
  

Unique among the features for SINUMERIK 840D are the ability to have control calculate the complex five axis transformations in real time instead of relying on the upstream CAD/CAM Post Processor. Through this capability in conjunction with advanced probing routines eliminates the need for time-consuming finite part alignment, resulting in a substantial reduction in part set up time.

This is achieved by the use of the onboard TRAORI transformation orientation, a SINUMERIK 840D high-level language for kinematic machine transformation. With TRAORI, all programming is related to the tool center point (TCP) moving along the defined workpiece contour. According to the machine kinematic and tool length, the TCP is referenced to the machine pivot point within the work envelope. While changing the tool orientation, contour violation is avoided, since TRAORI enables compensation movement of the involved Cartesian axis.

The "5-axis transformation" is provided for machine tools, which have 3 linear axes (translational axes) X, Y and Z and 2 rotary axes, which rotate around linear axes. This means that a tool, which is symmetrical around its rotational axis (e.g. milling tool, laser beam), can be oriented as required to the workpiece at each point in the machining space.

Furthermore, far less data needs to be transferred from the upstream Post Processor since tool orientation is described by the start and end vectors of the programmed tool path and all intermediate points are calculated within the CNC control itself. With this programming method, the CNC file is a sort of neutral format, hence the same part program can be executed on different machine tool kinematics.

Using SINUMERIK 840D 5 Axis maching package, we can handle the following 3 basic machine types, which differ in the tool and workpiece orientation:

• Type 1: Tool with two-axis swiveling head (rotary axes with axis sequence C A)
• Type 2: Workpiece with two-axis rotary table (rotary axes with axis sequence B C)
• Type 3: Tool with single-axis swiveling head (A) and workpiece with single-axis rotary table (C)
  

General kinematic features: The 3 linear axes X,Y and Z form a right-handed Cartesian coordinate system.Rotary axes A, B and C are located vertically to the appropriate linear axes X, Y and Z. The basic tool setting is in the negative Z axis. The tool length correction is calculated-in when machining.