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Using Gouge Checking in Multi-axis Machining to Control Lead/Lag & Side Tilt

Daniel Lyon

Using gouge checking in multi-axis machining can either be a huge time saver or an angry road to toolpath that looks like a 3yr olds artwork. Understanding some of the options you have available is crucial. Here we’re going to look at a complicated situation where we’re using gouge checking to control both lead/lag angles and side tilt. 

Tilted_Lead_Lag___Side.png

 

If you're machining parts such as custom wheels or jet engine components that contain spoke/blade type geometries (which have both an inner hub and an outer rim) it can be difficult to control the lead/lag and side tilt as the tool approaches the hub or rim. You could of course use a curve or a point above the part to drive the tool from and tweak the values/sketch until you get the desired result but this can result in a lot of time spent adjusting the sketch/point position and regenerating and little control over the contact point and orientation. One method is to use the gouge checking to control the lead/lag and side tilt. 

When programming any multiaxis operation, it’s good to have a logical plan of action to tackle the problem. Here's a common method that I use:

1, Get the desired pattern working first. Use the options in the pattern tab and establish a clean looking toolpath that you're happy with. In the case of the wheel above I used the Flowline between Curves option and drove the toolpath off of the upper and lower edges of the spoke and used Zigzag to walk back and forth along the spoke.

2, Next on the list is to set the Entry/Retract such as Clearance Planes and the Leadins and Leadouts.

3, Control the Links between cuts and links along cuts if there are any breaks. I used Blend Splines for the links between cuts here to smooth the transitions between each pass. I also wanted to trim the start & end of each pass to avoid undesirable tilts & rotations as the tool approached the hub and the outer rim. I did this by using the extend/trim option on the Finish tab.

 Pre-Trim___Blend_Spline.png                                       Blend_Spline.png

                              Before using Direct links & no trim                                                                                                      Trimmed toolpath with Blend Spline links

4, Axis Control – Define the number of axes and tilt control strategy. In the example of the wheel I wanted to swarf cut the spoke in 5 axis so I used the Tilted Relative to Cutting Direction option with a side tilt of 90°.  To avoid any unwanted rotations as the tool ran along the length of the spoke I opted to use the Ortho to Cut Direction At Each Contour so that I could use the smoothing option.

5, Use Gouge/Collision Checking – In this case I could’ve changed the side tilt strategy to stand the tool up more and use a longer tool but that negates some of the benefits of using 5 axis. I wanted to keep my tool short and use slightly more aggressive cuts but I had to avoid the collisions with the holder and tool as it approaches the rim and hub. I opted to use gouge checking and had CAMWorks decide where it needed to adjust the lead/lag and side tilt angles in the collision regions. Since I wanted to swarf cut the spoke I used the default Tilt Angles of 0-90 degrees. To allow the tool to adjust the lead & lag angles as it approaches the rim and the hub I used the default Cut Angle values of -90° & +90° so that the tool could angle itself away from those collision areas. To maintain the swarf cutting I’d defined on the axis control tab I used the Initial Orientation Limit and allowed the tool axis to deviate up to 60° for those regions where collisions would occur. Initially I saw some undesirable rotations/oscillations as the tool progressed along the spoke.  To solve this I refined the max angle step to from 3° to 1° so that if a collision was detected it would only have to tilt to 1° away rather than the original 3°.

See attached video clips in.swf format (open with internet explorer) showing oscillations & smoothed out toolpath.

One final step I needed to do was machine the remaining spokes. To prevent me having to repeat this whole procedure 11 more times I simply mirrored the toolpath using the option on the Advanced tab and then patterned the multi-surface feature 6 times.

The key thing here is having a logical approach. Get the pattern right to start with and proceed from there making incremental changes. Don’t be tempted into changing too many parameters at once unless you understand the implications.  

 

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