E
Ed-Bal
Hello to everybody:
Recently I was asked by the repetibility of a electrical screwdriver. I made a capability study (I calculate the Cm index), but I really don't know if it's valid or not.
Additional Information:
I work on a company where car door latches are produced. We use a small screw to fix a frameplate. On the drawing, the spec for the screw is: 0.70 +/- 25% Nm (0.525 - 0.875 Nm).
My problem started when I tried to obtain the repetibility of the screwdriver. With the use of a torque analyzer I got 30 readings taken directly from the screwdriver (I call to this dinamic torque), getting values similar to these: 0.95, 0.83, 0.92.
If I measured the torque applied directly on the screw latch (I call to this residual torque), I got values similar to these: 0.65, 0.70, 0.60.
As you see, the specification match perfectly for the torque found on the product, but not for the torque applied directly by the screwdriver.
So, I don't know if it's valid to calculate the average of the readings taken directly from the screwdriver and apply the % tolerance defined for the latch product (not for the screwdriver)? Once having the tolerance I could easily calculate a capability index.
As a second question, I don't know if 1.33 is the minimum value acceptable for Cm capability index or could be less?
I would appreciate all your point of views to clarify my doubts
Thanks & Regards
Eduardo
Recently I was asked by the repetibility of a electrical screwdriver. I made a capability study (I calculate the Cm index), but I really don't know if it's valid or not.
Additional Information:
I work on a company where car door latches are produced. We use a small screw to fix a frameplate. On the drawing, the spec for the screw is: 0.70 +/- 25% Nm (0.525 - 0.875 Nm).
My problem started when I tried to obtain the repetibility of the screwdriver. With the use of a torque analyzer I got 30 readings taken directly from the screwdriver (I call to this dinamic torque), getting values similar to these: 0.95, 0.83, 0.92.
If I measured the torque applied directly on the screw latch (I call to this residual torque), I got values similar to these: 0.65, 0.70, 0.60.
As you see, the specification match perfectly for the torque found on the product, but not for the torque applied directly by the screwdriver.
So, I don't know if it's valid to calculate the average of the readings taken directly from the screwdriver and apply the % tolerance defined for the latch product (not for the screwdriver)? Once having the tolerance I could easily calculate a capability index.
As a second question, I don't know if 1.33 is the minimum value acceptable for Cm capability index or could be less?
I would appreciate all your point of views to clarify my doubts
Thanks & Regards
Eduardo