Test fixture for cyclic impact testing 1

[badger2011]

I am trying to perform a test to mimic the impact of a hammer onto the back of a screwdriver....many times.

I want to run the test until failure of the screwdriver or 5000 cylces, which ever comes first. My fixture will need to supply the force of a one pound steel weight dropping 3.5 ft (or equivalent). I would like to automate it.

Do you have an suggestions for how I can build a test machine or know of an outside testing company who would perform this for me?

My initial search came up with many "Charpy" style impact tests, nothing automated or cyclic. I did come across one fixture used in furniture testing. It drops a 200# bag onto a chair from about 3 feet high (very expensive and overkill for my application).

I currently have a fixture that has pulleys, a cord, and a weight that can be operated by pulling the cords and then letting go to drop the weight; this weight falls onto the head of a fixtured screwdriver. This fixture is already built so if I could find a way to automate the "pulling" of the cord ---approximately 3.5 ft of cord --- perhaps this would be easiest; but I am welcome to any and all ideas.


Thank you in advance for any insight or tips you can offer me!

 

[rb1957]

set up the hammer to strike the screwdriver, then use a cam to raise and lower the hammer.

pulling on the rope could also be done with the rope being tied off on a rotating wheel/disc

 

[MintJulep]

Put weight on guide rods.

Find appropriate length V or flat belt and two pulleys, plus a drive motor.

Glue a block to the belt.

Arrange things so that the block comes up under the weight and lifts it. When the block gets to the top the block will pull out from under the weight as the belt travels around the top pulley.

Weight falls.

Start again.

 

[1gibson]

I like the idea of a cam to lift the hammer, then let it fall.

Not sure how to address this, but I think your test results will be pretty conservative if your cycle time is fast enough to leave heat in the plastic from the repeated impacts.

Conservative is good though.

 

[badger2011]

Thank you all for you responses!


MintJulep, I think the belt/pulley system will work well in retro-fitting my current set-up.

I need to carry 4 lbs of weight up the 3.5 ft. Assuming my pulley is 4" dia. I will need a motor to supply 24 ft-lb of torque. I found a website called orientalmotor.com that specs out the drive motors. I will look into purchasing one tomorrow.

Thanks again for your input! Much appreciated.

 

[MintJulep]

Check your math.