Basic CNC programming concepts
CNC CAD CAM part programming provides tools that allow manufacturers to bring products to market faster and more economically than ever before. The CAM machining process involves the use of “toolpaths.” A toolpath is the specified path of a cutting tool when actually machining a part from a block of material or workpiece on a CNC machine tool. The material can be aluminum, steel, titanium, plastic, wood, or any other materials depending on the application.
There is a 2D toolpath and a 3D toolpath. 3D toolpaths are not flat and have a three-dimensional surface contour. An example of this is that cars have become more curved and aerodynamic over the past 20 years. You will notice that consumer products have taken on a “modern” look that is no longer as prismatic as it was 20 years ago. This is directly attributable to advances in CAD-CAM software technology and the ability to design 3D models in Computer-Aided Design (CAD) technology and CNC machining (CAM).
Roughing and finishing toolpaths
“Roughing toolpaths are typically used in the initial stages of machining because they allow the machinist to remove a large amount of material with a large end mill. And roughing is used in CNC machining to save time and maximize metal removal. Visit also: CNC machine parts
The concept is to remove the maximum amount of material in the minimum amount of time with minimum tool wear. CAM technology offers many types of roughing strategies that can be used in 2D and 3D machining as well as 4th and 5th order toolpaths. These include:
– Pocket milling
– Drilling, tapping, and boring
– Roughing with grooves
Each of these types usually has a list of parameters including tool path reference, tool approach and departure operations, machining or grouping functions to optimize the machine program for the cutting sequence, variable depth of cut, tool feed and speed information, and more. All of this information is mathematically translate into a numerical code call “G-code”. This is the origin of “NC” programming.
A “finishing toolpath” is use after roughing to run the tool over the remaining material and remove what’s left to produce a smooth, almost polish surface. There are different finishing trajectories such as planar, spiral and radial finishing trajectories. There is also an equidistantly offset contour toolpath. Also known as a “constant scallop” or “constant point,” all of which serve the same purpose. These finished toolpaths are refer to in CAD-CAM as “semi-finished” toolpaths and straight “finished” toolpaths.
Equidistantly offset toolpaths are powerful and highly efficient CNC machining tools because they maintain accurate cutter feeds for tool size regardless of surface complexity. This type of cutter path is use with very high feed tolerances to produce a nearly polished surface in tool and mold making and other types of 3D machining. This type of 3D machining path is commonly find in advance CAD-CAM products use in mold making, aerospace, medical device manufacturing, and other industry segments, depending on the application.
What is a “REST” treatment?
The “REST” machining was originally develope to remove all remaining material after roughing or finishing. The idea for the name comes from the “Machine the REST” part. Typically, CAD-CAM loads machining operations into a “job tree” in the software interface, one machining operation at a time using a toolpath. Higher-level CAD-CAM combines machining operations into a combination of strategies and even adds machining functions within the machining strategy. This hybrid strategy concept is ideal for machinists who want to reduce cycle times and make programming more efficient. This could be, for example, a combination of roughing-roughing/resting or finishing-roughing/resting.
Thus, the CAM programmer loads the roughing operation into the CAM tree and then the REST roughing operation. Then the termination strategy and the REST termination function are load into the tree. Each operation can fully edited in the tree and linked to the CAD model of the part. This means that when the part model changes, all toolpaths are also automatically update. This is a very time-saving aspect of modern CAD-CAM technology that is in high demand.
REST finishing also allows the programmer to enter the original diameter of the finishing tool. The final diameter of the REST finishing tool will be smaller. And then the software will automatically know how much material was remove in the initial step. The software then automatically applies the REST toolpath based on the diameter of the REST finishing tool. It’s that simple. Once the entire toolpath has been generated by the CAM system, the software should have a built-in simulation that allows the programmer to sit back, simulate the toolpath and watch as the part is cut from the material. This allows the programmer to visualize the entire process, calculate machine cycle times, catch grooves or tool and toolholder collisions, and more. Simulation is very important in CNC machining because it saves the programmer from costly mistakes that can occur.
The CAM machining steps in CNC part programming are simple.
- face milling (optional)
- pre-drilling and drilling (optional)
- roughing REST machining
- REST finishing
- pencil milling
The “REST” roughing and finishing operations in processes 4 and 7 are very important aspects of the CAM programming process and are available for both simple and complex CNC part production. CAM programmers will find it useful to learn REST machining for implementation in CNC manufacturing processes.
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