This article covers the basics of Part Avoidance, which when used effectively, can speed up your cutting times, prevent head crashes, and generate better head-down paths to prevent potential tip-ups.
Using part avoidance with Auto NC
You can enable Part Avoidance from the Auto NC dialog to have it automatically appear after NC is applied, or manually select it afterward applying auto or manual NC.
To enable Part Avoidance automatically when applying Auto NC:
- Go to the Nesting NC tab and click Auto NC.
- Set your parameters as usual, then go to the Advanced NC tab and enable Part Avoidance.
You can then configure three different settings that determine which rapid moves will be head-down:
- Max Head-down Length - Specifies the distance the machine head can move from the inside of a feature to the next feature while keeping the head down. A head-up is applied if the distance is more than the value entered.
- Clearance Diameter - Specifies how close the cutting head can get to a part before a head-up is applied (this distance is calculated as half of the clearance diameter). The clearance diameter should generally be larger than the head diameter to provide sufficient head clearance.
- Max Traverse in Cut Feature - The maximum distance the machine head or tool moves with the head down while within an internal contour.
- After you have set these parameters, click OK to apply Auto NC. You will then see dot-dash lines for the head-down rapid moves in the nest NC rather than the simple dotted line for the standard rapid (head-up) moves.
Using auto part avoidance after applying auto/manual NC
To use Part Avoidance after NC has been applied to the nest:
- Go to the Nesting NC tab and look for the Motion Optimization group.
- Click the arrow under Part Avoid and select Auto Part Avoid. is in the dropdown of Part Avoid.
- You can then configure all the same settings listed above using the Auto Part Avoid dialog.
Application #1: Head-down rapid moves
The first and most common use of Part Avoidance is to keep the rapids as head-down moves between contours that are within a given distance of each other.
This reduces the amount of time it takes for a machine to cut a nest, because it doesn't have to retract every time it re-pierces.
You will notice that many rapids were kept as a head-down moves in above example to decrease the cutting time. Other rapid moves stayed the same as they did not fit within the defined parameters.
It is important to specify a valid Max Head-down Length to take advantage of this feature. If Max Head-down Length is set to 0, all the rapids will be changed to head-up moves, since the total length of successive rapids is checked against this parameter.
Note that the color of head-down moves has been changed here for clarity. You can set this color value in the Configuration from the Color Scheme tab (it's the Flame Off Head Down option).
Application #2: Moving leadins
The second application of Part Avoidance is its ability to move leadins. SigmaNEST will move the leadins on a part in order to minimize the head movement, creating the possibility for more head-down moves between contours.
To allow SigmaNEST to do this, make sure one of the Move Leadins options is selected.
With these settings you can restrict leadin movement to either dynamic leadins only or both dynamic and fixed leadins. You can further restrict this to internal leadins only by selecting the Move Only Internal Leadins check box.
Applying these leadin settings to the same nest will give different results. When compared to the previous nest NC, there are more head-down moves in this one resulting in faster cutting time.
Application #3: Move around hazards
The third application of Part Avoidance is to move rapids away from internal contours that have already been cut. This avoids head crashing by not traveling over potential tip-ups.
This particular application of Part Avoidance does increase the cutting time, but there is much less risk of ever hitting a tipped internal. To apply this setting, all you have to do is select the Move Around Hazards check box.
The rapid lines drastically change direction in order to move around the internal contours that have already been cut. This allows the machine to continue running with a much smaller risk of hitting tipped up internal contours.
Note that if the Clearance Diameter specified in the settings is too high, the offset zones around internals and rapids might end up interfering with one or more contours in either direction, making it impossible to find a valid feature avoidance path.
In this case, you will see several head-up moves crossing over cut features. If instead, you use a smaller clearance diameter, you should get a valid head-down movement that does not pass through any scrap regions or already cut contours.