4 Steps to better machining
- July 6, 2002
CAM software enhancements offer machining benefits
by John Welch
“In the Ontario market we have seen a high surge of CNC multi-axis machinery being shipped out to various types of manufacturing outfits,” says Marty Cornacchi, vice president, operations, CAM Focus Consultants, Richmond Hill, ON, a supplier of CAM software for manufacturers.
“This high demand for equipment has pushed the Canadian manufacturing sector to reach into new areas of production and allow for growth. Along with complex CNC machinery, the demand for sophisticated CAM software has also risen due the need of programming state-of-art CNC machines faster, smarter, and easier.”
Five axis machining strategies are particularly important for mould and die manufacturing, as they enable continuous machining of significantly larger areas with shorter tool lengths on vertical or steep walls, improving process parameters and surface quality.
Now further developments in CAM software provide even more benefits. These developments include: automatic tool-axis adjustments to avoid collisions, automated rest machining, automatic indexing, and shape offset roughing and finishing.
In five axis machining, to make generating an NC program as easy as possible, you need a CAM system that exploits the performance range of each machine tool and takes machine kinematics into account. Compared to three axis milling, in five axis simultaneous machining, the movements of the tool reference point and the movements of the machine’s linear axes (pivot point path) are different. This is because movements of the rotary and tilting axes result in compensation movements in the linear axes.
Successful milling projects strike a balance between programming effort, cutting time, machine movement, surface finish, and tool usage—factors that may vary in significance depending upon the shop in question.
Automated collision avoidance must be the core of any five axis strategy. For complex milling areas, it is difficult, and sometimes even impossible, to find a constant definition for tool orientation. Five axis simultaneous movement with fully automated calculation of tool angles solves this problem. Traditional programming solutions require a programmer to sketch geometry to define rotary axis movement, then simulate the resulting milling operation to check collision. This process must be repeated until the programmer correctly guesses proper tool inclination.
Modern CAM software should calculate a collision-free toolpath from the beginning, taking into account the tool, toolholder, spindle geometry, and machine kinematics. The rotary axis should be automatically adjusted to minimize machine movement while completing the
Traditional rest machining is a labour-intensive process that has typically involved mentally dividing a job into many separate areas to define machining orientations for each. Today, rest machining strategies are available that mathematically define the minimum required 3+2 machining orientations and the resulting toolpath for all separate project areas in a single operation.
This reduces programming time for complex geometries. If a collision is detected in one of the rest machining areas during toolpath calculation, minimal simultaneous five axis motion can be activated and the tool axis adjusted to avoid the collision—all without user intervention. This optimizes machining time by maximizing the use of 3+2 and minimizes five axis simultaneous motion.
It is now possible to automatically control both rotation axes independently so only one of the two rotation axes is used to achieve continuous, collision-free machining. This 4+1 machining style is particularly advantageous because rotation axes are typically different in terms of technical capabilities and precision due to different masses to be moved or different drive power. Some of today’s CAM solutions go one step further and provide automatically indexed axes. Tool angle is calculated so tool orientation within a milling area on the surface is not changed. If necessary, the milling area can be automatically subdivided further, or local simultaneous movements can be generated.
In one example, a metal injection mould with more than 350 flat and more than 370 steep rest material areas with different angles was machined in a single operation. All the user had to do was define the preferred lateral tilt. This cut the required programming time significantly.
Automatic indexing enables another machining strategy that moves only once around the C axis in small steps in a single 360° rotation. Compared to conventional five axis machining, this can always maintain the programmed feedrate even when using a slow worm drive. And because unnecessary movements are avoided, this process is also easy on the machine, saving significant costs.
Shape Offset Roughing, Finishing
Modern high performance roughing algorithms have proven ideal for hard milling applications. These volumetric roughing processes prevent the cutter from cutting deeply in corner areas or having a sudden change in direction. They also provide ideally distributed milling paths, climb-only milling strategies, and dynamically adjusted feedrates. They have been proven to allow for the most efficient removal of large volumes of material, plus the constant cutter load extends both tool and machine life. Today, this approach is available for five axis applications for geometries with concave or convex floor conditions using shape offset strategies.
Z-level roughing and Z-level finishing are the traditional programming approaches that have been used successfully for years. In some applications, such as tire mould programming, the toolpath projected on the geometry by Z-level has proven to be inefficient due to a non-constant floor condition resulting in multiple retracts. Shape offset roughing and finishing, named due to the toolpaths offset from a shaped surface rather than projected at Z-level, overcomes this issue and allows for the inclusion of bull-nose tools and end mills.
A programmer need only select the floor of the surface, and from this input, they may choose to rough, floor finish, or both wall and floor finish. Since the toolpath accounts for the shape of the surface, bull-nose and end mills may be employed and the tool is constantly engaged in material.
Modern CAM software can do much to shorten the learning curve for programmers with less experience while providing a competitive edge for the veterans. SMT
John Welch is account manager for Open Mind Technologies USA Inc.