Since starting this corporate blog back in September of 2010, this current series on Dynamic Stock Models has not only been rewarding to write, but has generated some commentary among Twitter and certain CADCAM forums.
There still seems to be many people that think a Dynamic Stock Model simply is used to constrain cutterpaths from one cutterpath to the next. While this is in part true for a Static Stock Model, it is far from explaining all the benefits of using a Dynamic Stock Model. For a description of some of the differences between the two, read Part 2 of this series.
This post is going to highlight some other benefits of stock models, especially Dynamic Stock Models.
Dynamic Stock Model: Knows stock condition during calculation
As previously mentioned, the Dynamic Stock Model knows the stock condition during calculations (as necessary). So besides the reliability, efficiency and safety this provides for toolpath calculations it can also benefit certain other cutterpaths.
Trochoidal Cutterpaths
Trochoidal Cutterpath
Many CAM systems have a form of Trochoidal movements in roughing applications. Recall that the reason for making the Trochoidal movement is to not allow the tool to exceed a particular width of cut. In an extreme case, instead of cutting with 100% of the cutter width, Trochoidal cutterpaths can allow for cleaning out and entire area with a non full, 100% width, cut.
The real question to ask is, how is the CAM system determining the actual cut width on the cutter? Most systems are doing this by examining the individual cutterpath offsets and corners and finding the theoretical width. The better way, of course, is to base it on the actual stock remaining at that point in time, which is exactly how the Dynamic Stock Model works. Actual measured cut width versus calculated theoretical width logically makes sense.
Plunge Roughing
Plunge Roughing
Plunge Rough
Many people have tried Plunge Roughing with mixed results. Part of the problem is the retract movement of the cutter after the plunge cut. As the picture at the right shows, it is best if after the vertical cut, that the tool move up and away from the wall it just cut against, then retract for the next cut. This movement keeps the inserts from rubbing on the way back up, extending tool life and increasing safety. Again, if you are not updating the Stock Model in a Dynamic fashion, as it is calculating, then you can not know where there is and is not material and you can not perform the step away prior to the retract the safest way.
RestMachining
WorkNC was the first CAM system to introduce automatic remachining. Where a smaller tool is used to mill residual material leftover from larger tools, all in a completely automatic fashion.
Typically in RestMilling, one can input a reference cutter or less commonly use a stock model. With the reference cutter, the CAM algorithm finds all the theoretical areas of additional material by analyzing the CAD model and looking at the corners and valleys in the part. Quality of the areas found to remachine are only as good as the algorithm used to find it.
Utilizing the stock model, the remachining areas will be based on the actual remaining stock, and not theoretical corners. This method can also be more efficient, especially in the instance of using different cutter shapes when finishing. In the pictures below, the part was finished with three different sized and shaped cutters, a flat, a ball and a bullnose cutter. Utilizing a reference cutter for calculations means you have to go with the ball cutter. Notice the difference in the remachining cutterpaths between using a reference cutter, and the actual stock model, making a huge difference in mill time and efficiency.
Stock Model Remachining
Remachine to Reference Cutter
Conclusions
From the previous blogs, and this one, hopefully you understand the differences in Stock Models a little better, and also what some of the advantages of using a Dynamic Stock Model over a Static one are, such as:
- Utilizing Shorter Tools for more of your milling
- Extending Tool Life
- Increasing Efficiency and Productivity by optimizing cutterpaths
- Increasing Safety for unattended machining
- Automating routines such as Rough and Finish Remachining
