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Digitizing a cylinder head for CNC porting
by Bill Anderson
Janurary 2013
I’ve spent some time working on digitizing the CV-385 port (a port for Pontiac CV1 heads), and I thought I’d walk you guys through the "Reverse-Engineering" phase of getting a new port into our CAD system, this is part of the very first steps in digitizing a port shape with our system ...
... the pic's show what we call a "Point Cloud" which is nothing more than a large amount of small points collected by the CMM, and you basically have to trace over the entire surface until you have a really nice coverage of points through the entire shape, as you do not want any small holes, this can cause problems later when the 3D Mesh phase begins ...
... you can see that the shape is not yet completed, and this really is the hardest part of digitizing a port.
As you see the shape develop on the screen, it will become apparent the shape does not look correct ?? ... This is due to the fact that the CMM is programmed to the "Center" of the probe and that is the shape you'll be seeing until the "Point Cloud" is completed, afterwards we'll need to adjust the tool offset to the correct size and then you'll see the actual size and shape of the CV-385, but before then the port will look bloated in areas like the guide boss, and the floor wing, but this is perfectly normal, all you're seeing is the shape generated from the center of the probe, once the correct ".250" offset is entered, the shape will grow a total of .500 in size throughout the entire shape …
... Ok, here we have pic's showing the CV-385's "Point Cloud" being refined using the Verisurf software which runs inside of MasterCam X6 ...
... So everyone understands, the "Point Cloud" is gathered or recorded by simply tracing over the port's surface with the Master3DGage, which looks like a small robotic arm with a special port probe we had made that can reach all of the port's surface, it basically has a .500 diameter ceramic ball on the end of a steel shaft, and you're just dragging the ceramic ball over the surface, the entire surface that is, which obviously takes some time to get correct ...
... After the complete "point Cloud" has been recorded, this now becomes the first stage of smoothing & refining the port surface, which is for now represented by the "Point Cloud".
You can see the "Point Cloud" has already become noticeably smoother and more refined looking at this stage…
... Now we move on to the next two stages which is to crop the ends of the point cloud at the (Throat) & (Intake Flange) for generating a "3D Mesh" with the refined "Point Cloud" ...
... The pic's below illustrate what the "Cropping" process looks like, this process is to provide a nice clean cut edge to both ends of the port, as this will be very important once the "Splining" stage begins ...
... After the 3D Mesh is generated you'll notice that the ports size still looks incorrect, almost as if the shape were under a vacuum even, pulling the surface inward, this is most noticeable in areas like the guide-boss or the floor-wing, this is due to the software using the center of the .500 diameter probe, which will be adjusted later to the correct tool offset of .250 diameter ...
... The Verisurf software generates the 3D Mesh by using a bunch of small and properly located triangulated surfaces over the surface of the Point Cloud, if you look closely at the two pic's below you'll see the triangulated shapes ...
... At this stage you'll notice some surface texture already present in the 3D Mesh, this is normal at this stage and will be addressed in the following steps, it is difficult to see that part from a Jpeg image, but I'm just referring to what you would see if you were in front of the computer performing this work ...
... Now a 4 step process begins ...
1. ("filter/refine/smooth 3DMesh")
2. ("Export to Back to Cloud & Filter Cloud")
3. ("Export Refined Cloud Back to 3D Mesh")
4. (filter/refine/smooth 3D Mesh")
... Depending on how good of a job you have done recording the original "Point Cloud" determines how many times you'll need to repeat this 4 step process ...
... So as the 4 step process begins you'll see a big difference in the surface of the 3D Mesh, and this process stops once the surface has a very nice uniform appearance, now if a problem occurs with the first 3D Mesh generation, you can go back to the original point cloud and use the Master3DGage to record more point cloud data in the problem area to resolve the problem, but this is why you want to record a very dense point cloud over the entire surface before you generate the 3D Mesh the first time because it will save you extra work later ...
... Notice the "Tool Offset" has not been corrected at this stage as the shape is still not to size, which will be very noticeable once the offset is corrected ...
... The "Tool Offset" will now be corrected for the .250 radius of the probe. This step will usually rough up the edges to the ends of the port that we previously cropped at the point cloud stage ...
... The first pic below shows what the "Extend" function looks like, and this allows the 3D Mesh to then be cropped the same way the point cloud was cropped, as to restore the sharp edges needed at the ends of the port ...
... Now the port is noticeably larger, and is now actual size, so if you were to need measurements or distances, the Verisurf/MasterCam software can be used for this and compared to the actual "Master Port" shape in the cylinder head ...
... So now the 3D Mesh should be complete, as the pic below shows, and the "Auto Surfacing" function in Verisurf can be applied to the 3D Mesh, and if the work was done correctly this is when you get to really see what the port shape looks like in reference to its true size & shape ...
... We like to use many different colors at this stage to really see what my CAD surface looks like, because sometimes you'll get a small wrinkle in the CAD surface, and certain colors can hide these small wrinkles ...
... After all the point clouding, 3D Mesh, refining, and filtering is completed, the port is now comprised of a bunch of small CAD surfaces where the 3D Mesh used to be, and while this may look cool, it makes it very hard on the PC to move and navigate with & around the port, as the file size is now quite large ...
... To fix this the next step is to “spline” the surface of the port, which is a bit of a complicated process, so we'll just keep this part brief ...
... The spline is generated by "Slicing the 3D Mesh" from throat to entry, and once the splines are set in place and are all solid continuous lines, then we like to adjust the splines a little smaller, at the throat especially as this is this a very critical area in the port. It's very nice to have a little extra material to properly rough the surface in this area to size after CNC'ing, and also at the entry just a small amount so after the shape is CNC'd the entry doesn't get flared after de-burring the edges, as the CNC cutter usually leaves a small lip or peeled edge at the entry ...
... Now this is the time to repair or smooth any small wrinkles or waves in the surface you might have by modifying the splines, which is really no fun at all, as this part can be a lot of work, but if you perform the point clouding & 3D Mesh steps correctly, the shape is usually spot on at this point ...
... Once the splines are completed, then another CAD surface can be generated and this time it will be all one surface, not a bunch of small surfaces, which in turn makes the file size considerably smaller and this helps greatly when the "Port Expert" software begins to generate "Tool Paths" for cutting the new shape ...
This pic is after locating all 4 port surfaces.
... Now we have a surface, that is ready to be located into the cylinder head, most of the time shops will pull in the needed data to properly locate a port right on the 5 axis CNC machine. This can be costly due to the fact the 5 axis CNC machine is now being used for digitizing, and not 5 axis porting, which most shops do not like taking too much time here for obvious reasons. If the CNC isn’t cutting, it isn't making much money ...
... That's the beautiful part about our system here at Joe Mondello Racing Engines, 100% of the Digitizing & Locating happens with the Master3DGage on our custom built granite table in a separate room away from the CNC machine ...
... The only thing the CNC machine has to do is "Probe" the dowel holes on the fixture plate, and that only needs to be done once per fixture!!! Meaning, we can be developing new ports and manifolds or be digitizing/locating them at the same time the CNC machine is cutting one of our other digitized & located programs. This is a huge advantage in production, as this greatly speeds up the CNC process and lowers turnaround time for our customers ...
... Another benefit is the Master3DGage is fast, instead of watching the CNC probe everything at a snail’s pace, you are in control of how fast data is recorded, because the Master3DGage is in your hands ...
... Back to location of the port in the cylinder head, this can be tricky and is very easy to get wrong if you are not very careful. The 1st pic below shows what our "Alignment" file looks like, and it is basically all the needed components of the cylinder head, such as deck plane, dowels, guide centers, head bolt holes, and even the pushrod tubes ...
... This file literally took about 15 minutes to generate, which is a big time saver. Locating the ports, is not a fast process, you need to be precise, and we can get ports within an extremely tight tolerance with this process ...
... Depending on the cylinder head, you may need to mirror the ports as they are in the head. This CV-1 head requires this step. Once you have your mirrored layout properly located on the guide centers and deck plane, you should have something that looks like the other pic's below ...
... The next step will be tool path generation, and with the "Port Expert" software we have, this is a snap !!! ... details of that process will be coming soon !
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