CAD-CAM Software Delivers Effective High-Speed Machining


It’s hardly a secret that CAD-CAM software is the driver behind quality, high-speed machining. Machinists have been known to see CNC production increases from their CAM programming by as much as 50 percent or greater. CAD-CAM software that offers high-speed Toolpath strategies opens the door for shops to do more complex CNC work is less time, which in turn will lead to higher, more frequent financial returns. Before I go into detail about why you should be programming with CAD-CAM software that offers high-speed Toolpath strategies, let’s explore how that concept came about.

In the beginning of Numeric Control (NC), each block of data was followed in order, one at a time. As you can imagine this was quite a slow process. This was sufficient enough for 2D operations and linear Milling, but as the machine needed to execute a curve or contour, there quickly became a need for seeing what kind of data was ahead. Otherwise, the machine would cause the cutter to overshoot or undershoot a programmed change in direction. Through this newly found need, look-ahead was developed and is requisite for high-speed machining of any geometry except linear, single-axis moves. If your machine currently doesn’t have look-ahead, then you must upgrade it first before taking on high-speed machining.
CAD-CAM Toolpath
The term Toolpath is used to visualize and describe the path that the CAM software will dictate to the cutting tool so it machines all areas of your part. The Toolpath is being defined by the areas the user has chosen to machine, the size of the tool that’s being used, cutting regions for those tools to reach and the type of machine strategy that’s being used. There is much more data that’s included in the creation of an NC program having to do with post processing parameters such as speeds and feed rates based on strategy, material, tool data and more. Many machine controllers differ on how they want to see g-code for the program to be read properly by the machine; that is Toolpath.
Usually, more than one type of Toolpath is used while machining. There is generally a ‘roughing’ and a ‘finishing’ operation, roughing being the first stage in machining. Roughing means there are multiple Stepdowns by the tool to remove most of the material. The finishing operation will essentially complete the machining phase. There is also a semi-finishing operation to finish the part. An example would be the application of a Z-level roughing operation to remove most of the material, followed by a Z-level finishing operation to ‘semi-finish’ the part, and finally, an ‘Equi-Distant Offset contour’ operation to finalize the part. By integrating high-speed Toolpaths into your daily machining operations you can produce dynamic results quicker than traditional offset Toolpaths; even in 3D machining. CAD-CAM software, like that from BobCAD-CAM, generally offers an advanced roughing operation that provides users the option to use adaptive high-speed machining technique. This gives the programmer an advantage in roughing out 2D or 3D regions on their parts or the whole part. Boundaries can be used to segment the Toolpath into specific areas or deep cavities that require smaller tools. However, this will not replace a REST operation. Advanced REST in machining is used in conjunction with the finishing process to clean the areas that larger tools were unable to reach.
For as long as CAM software has been around, traditional offset Toolpath has been the most common form of Toolpath. There are distinct differences in the different types of Toolpath operations; planar, offset and high-speed. The image below gives you a basic 2D representation of how each differs from another. Number 1 is planar, 2 is offset and 3 represents high-speed.
CNC software Toolpath Types
Planar is the most fundamental of the aforementioned and is generally a back and forth cut across the material. Users should be able to determine a cut direction, “Lace Angle” parameter and a Stepover for the cutter. Tool Lead-Ins and Lead-Outs will often be limited to a plunge, ramp or spiral Lead-In when using this strategy with every option definable through input parameters. Additionally, compensation controls can be available for the finish pass. Offset is the most commonly used function when CNC machining open or closed wall pockets and slots in a 2D/2.5 Axis (X, Y and Z step down) program. Although this operation is similar to planar, the difference comes when you create an offset IN or offset OUT. Meaning, the tools will either start in and work their way out or the tools will start out and work their way towards the inside of the material. A minor downfall of this type of operation is the fact that the Toolpath will have many right or left turns that lead to a lot of stop-and-go occurring. The more often this happens, the more wear and tear there will be on the tool, leading to more frequent replacements needed. Lastly, high-speed machine Toolpath strategies (also known as Trochoidal machining Toolpaths) allow for a controlled arc of engagement which generates low cutting forces on your tools and increases their longevity. Other benefits include the ability to do deeper cutting, as well as the fact that there isn’t constant tool engagement, so no stop-and-go that commonly deteriorates tool life. Perhaps the greatest benefit is the fact that greater speeds lead to higher quality finishes and quicker cycle times.
As time goes on, technology gets more advanced and more affordable, allowing shops to increase productivity. To stay ahead of the curve, increasing your Feedrate is a much more effective way to increase parts produced. An example would be increasing the Feedrate of a ball-nose end Mill in tool steel from 12 to 24 IMP and spindle speed from 4,000 to 8,000 RPM, leading to a 100 percent increase in cutting speed. Most machines are in fact capable of an increase similar to the aforementioned. Additionally, as the cutter makes a chip, the heat created by that action is transferred to the chip. The advantage of high-speed machining is that the elevated speed and feed are so rapid that as the chip is cut and ejected, leaving little to no heat transfers with it to the workpiece. In most cases, this can eliminate the need for coolant. As force is increased to create a chip, the heat that is generated is significant. Coolant reduces the temperature in the cut zone and flushes chips out. However, at higher speeds, the spinning tool throws coolant away from the cut zone; without high-pressure forcing the coolant into the cut zone, it will never touch where it needs to go. In this case, an air blast may be effective for removing troublesome chips from your material. There are many ways to achieve a finished part in the CNC machining industry, but it’s clear that machinists that want to maintain a high level of production are keen to the benefits of high-speed machining.

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