how to create variable pitch helical spring in nx7.5? please provide the detail steps.
if it requires the use of commands like 'law curve' & 'expression', then pleaze provide detail steps.
There a couple of ways this can be done.
First is that you can create a law curve based on expressions for x and y and a separate law curve for you z values. The expressions for the x and y values are formulas for the x and y values of a circle multiplied by the number of coils, i.e. x=rad*cos(t*360*number_coils) and y=rad*sin(t*360*number_coils). "t" is a built in expression that tells NX to evaluate the formula from 0 to 1. For the z value you can create a sketch that directly plots the values of z. Look at the attached part for an example.
Another way is to create a cylinder whose diameter equals the diameter the spring minus the diameter of the wire and whose length is equal to the spring length. Then, on a datum plane that is tangent to the cylinder create a sketch that is the "unwound" path of the coil. Use "wrap curve" to map this sketch onto the cylinder and then create a "tube" using the wrapped curve. You can get rid of the cylinder and create flattened ends by offsetting the cylindrical wall to make it larger than the spring and doing a boolean intersection of the cylinder and tube. Example part attached.
The original model I uploaded was for a straight wound spring. I apologize for not making that clear. To get a variable pitch the sketch must be modified to control the pitch in a variable manner. Attached are two sketches, one that is progressively wound and one that is a two stage spring. You will need to edit the sketch as needed to get the desired result.