Hi, Not realy a ProE question, but I have been looking at a snap fit clip on a plastic part, and need a little help. I have found snap fir calculators on the internet where you enter the type of material and dimensions of the clip. I then get a 'maximum strain percentage' figure (ie. 6.7%). What figure do I compare this to on the material data sheet? Tensile Strain (Yeild?/Break?) Tensile Elongation Flexural Modulus? I have seens equasions where it asks to input 'permissable strain'. How do I find out what the permissable strain of my material is?
Hi Joseph, There are several things to consider when designing a snap fit in plastic and not being familiar with the online snap fit calculator you're using I don't know if it is accurate for all situations or simply for general information. If you put aside all the variables of geometry for a second and focus only on the plastic material, I can tell you that if the calculator you are using does not break down each material by supplier and material grade you may not get the results you want. ABS as an example comes from many sources with many grades of the material and the properties can be very different for each ... which brings up an interesting story ... I once had a company approach me for help that made a plastic part that was identical to their competitor. Both companies made their parts from ABS. The company that contacted me had the mold made and parts run in Korea to save costs. When their parts were wiped with a damp cloth that had been sprayed with a common household cleaning agent the following day the parts were full of hair line cracks. Their competitors parts could be placed in a bucket full of this household cleaner for a week and after taking out the parts there were no cracks at all! This company was in a panic because they had to deliver product. They wanted put me on a plane to Korea the following day to review the mold and recommend what changes should be made to the mold to keep the parts from cracking. I asked them what the material was, ABS ... and then where was the material purchased, a supplier in Korea. I recommended they save their money and instead of sending me to Korea, go directly to GE, purchase 50 lbs. of a specific ABS material, send it to Korea, tell their vendor to run the parts only from the supplied material and send samples back to the U.S. for evaluation. End result? ... problem solved! My recommendation would be to go directly to the material supplier for the plastic material you want to use, tell them what you need and seek their advice. Then if you want to compare what they tell you against the online snap fit calculator you're using you'll get an idea of whether it is very accurate or not. Have a terrific weekend! Robert 3D Accuracy www.3d-accuracy.com