104 Basic CNC Tube Bender Programming
Main Part Programming Screen - Using the example tube from section 103, this is what a typical CNC tube bender programming screen might look like:
| |
Y Move |
Speed |
B Move |
Speed |
C Move |
Speed |
Stack |
Option |
| Bend 1 |
5 |
100 |
0 |
100 |
90 |
100 |
1 |
|
| Offset |
|
--- |
|
--- |
|
--- |
--- |
--- |
| Bend 2 |
4 |
100 |
-90 |
100 |
90 |
100 |
1 |
|
| Offset |
|
--- |
|
--- |
|
--- |
--- |
--- |
| Bend 3 |
4 |
100 |
-90 |
100 |
90 |
100 |
1 |
|
| Offset |
|
--- |
|
--- |
|
--- |
--- |
--- |
| Bend 4 |
5 |
100 |
|
100 |
|
100 |
1 |
|
| Offset |
|
--- |
|
--- |
|
--- |
--- |
--- |
| Bend 5 |
|
100 |
|
100 |
|
100 |
|
|
| Offset |
|
--- |
|
--- |
|
--- |
--- |
--- |
YBC's, LRA's, PRB's are all different ways (from a variety of manufacturers) to describe the same thing. The Y, L, or P stand for distance between bends (DBB). The B, R, or R stand for the rotation between bends or plane of bend (POB). The C, A, or B stand for the degree of bend (DOB). Currently, most controls designers seem to have settled on YBC's since they are the accepted standard description for the three main axis of motion on a CNC tube bender. These values describe what the tube should look like when the machine finishes bending it - and what machine motions are required to make the part correctly.
Speed - Most of todays' machines are capable of speeds and accelerations that can "whip" the tube out of shape while bending, rotating, or moving to the next carriage position. The speed values can be adjusted downward, usually for longer tubes towards the end of the bending program.
Stack - Many machines allow more than one one bend die to be used, some as many as five. This column is where the particular bend die in a stack is selected for a given bend.
Options - Most CNC benders feature several optional moves to help get the part out of the tooling and position it for the next bend. Many also feature other alternatives like push bending (calandering), cut off, or punching holes. This column is where these features can be selected.
Offset - For ease of recognition, it is a good idea to preserve the original data from the part drawing in the bend data for each row or bend step. In order to get a part to fit it's checking fixture or CMM program, changes usually have to be made to compensate for material stretch, springback, radial growth, and weld seam position. Offsets allow the small addtions or subtractions required to get a good part.
Basic information:
The program needs to have over all tube length and either the exact location of the back of the tube (cut to length variations go to the first straight) or the front of the tube (cut to length variations go to the last straight).
Actual cut length of tube
Length of tube inside the collet
Length of tube ahead of the tangent point prior to the first bend
Load position for the Carriage
Carriage position for the first bend
Crash avoidence information:
Obviously requires accurate information to avoid expensive noises.
Pressure die length (for each stack, if used)
Wiper die length (for each stack, if used)
Bend die centerline radius (for each stack, if used)
Pressure die reach (for each stack, if used)
Length of collet beyond carriage nose
Multi Stack Machine Information:
Tube outside diameter - To calculate minimum horizontal carriage and mandrel moves to clear tube from bend die lips.
Bend die centerline heights - To calculate vertical carriage and mandrel moves to position the tube at each bend die.
All Electronic Bender Information:
Clamp die reach - From fully retracted position, how far in should the servo drive go before the clamp die(s) touch the tube.
Pressure die reach - From fully retracted position, how far in should the servo drive go before the pressure die(s) touch the tube.
Mandrel positions - At bending position, partially back, fully back.
Tweaking the first and last straight lengths:
This will be mentioned again in section 206, but it bears repeating. Some CNC tube bender control programs do this better than others, but usually, there is a method specific to each manufacturer. Please bear in mind that this is dependent upon whether the cut to length variance is at the first or last straight. When adjusting the first straight, the last straight changes in the opposite direction. Many times, to compensate, an adjustment of the over all tube length is also required to get the part to behave properly. Some times simply adjusting the over all tube length will do the job.
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