Tube Insertion Force Calculations

Post a sketch of the parts....and tell us what the materials are.
Without a pic we can't really comment usefully...

I could make fatuous witty replies, but my tothache has gone now so I won't

I believe you'll find some help on the website at New Age Industries (http://www.newageindustries.com/). Or contact them for direct help. This is right in their special area.

As you work this out you may need to consider temperature dependency of the plastic. If you have a narrow window of acceptable force, temperature may need to be kept relatively uniform.

If I understand your question correctly, you are trying to insert a plastic tube (OD) into a female port, rather than push a plastic tube (ID) OVER a male barbed fitting. Is that correct?

You could probably calculate some theoretical insertion force, based on the diameters of the tube (ID and OD) and port, as well as angle of the internal "barb", or rib, where the surfaces meet and the strength of the materials (although you neglected to say what they are other than "plastic"). In reality, insertion force will depend on many factors, not the least of which is the friction between the two materials. Another factor is the stiffness of the tubing, i.e. a less stiff tube will tend to to "mushroom" out, increasing its OD and therefore friction and required compressive force, as you push it into the port. Also, variations due to allowable tolerances for both tube and port will make some difference.

The best idea would be to set up an experiment to measure insertion force. You will need two fixtures, one to hold and clamp multiple tubing samples and another to hold and clamp parts representing the port, either actual sample parts (best idea for meaningful data) or test parts machined to the same dimensions as the port. Machined parts would not be as good as actual sample parts, because the molded surface will have different frictional characteristics than machined surfaces. One of these fixtures would have to be fixed, the other moveable. It does not matter which, since the motion is relative. Also, one of the fixtures must be mounted on a compressive force gages which records the maximum force, where breakage could occur. Again, since this would be almost a static problem, it really does not matter which side gets the force gage, as the contact force should be transmitted equally. In my experience it usually works out best to fix the force gauge to a table-top rather than putting it on the travelling side, but this is not a requirement. You also need to insure that travel will stop before the tube hits the dead end, because that will cause a force spike that does not relate to the required insertion force.

20 trials should give you some pretty good data points, 50 would be better. If you can identify cavity numbers on the molded plastic parts try to get a representative of each. The you can use a spreadsheet to record the data and to calculate the mean and standard deviation or even chart the distribution (Excel has a vary nice histogram function, but you may have to activate the Add-in to use it).