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Drop Testing

Postby Lowe9 » March 7th, 2018, 3:13 pm

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I'm looking for some insight into how drop testing is performed during the prototype phase of a project. My firm is consulting for a medical device company and the project is stalled due to the need to meet all of the "Product Requirements" as laid out in the "Product Specification" document; two of which relate to dropping the product from different heights onto vinyl covered concrete and having the product survive. Without being able to prove the design meets these requirements, the company will not move forward with injection mold tooling.

We're at the point where a prototype design is finished and 10x cosmetic cast urethane prototypes have been made and assembled with electronics. The units work great and the client loves how they look. We originally thought we could meet these requirements with FEA testing but the studies take 16+ hours to run and provide no insight if the impact will damage the electronics or touch screen LCD. We are now proposing using the existing urethane tooling to mold additional prototypes out of a very mechanically comparable urethane resin.

We had considered machining parts for drop testing, but the final product will be molded from a very niche resin (not ABS or ABS/PC blend, HDPE, HIPS, PA, etc) that I'm sure is impossible to find in billet size pieces.

We are confident in the results from drop testing mechanically similar urethane parts, but our client is concerned about getting a false pass from not using the final plastic resin. Any insight on getting over this hurdle so the client can commit to tooling is much appreciated!

Re: Drop Testing

Postby Cyberdemon » March 7th, 2018, 8:35 pm

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Lowe9 wrote:I'm looking for some insight into how drop testing is performed during the prototype phase of a project. My firm is consulting for a medical device company and the project is stalled due to the need to meet all of the "Product Requirements" as laid out in the "Product Specification" document; two of which relate to dropping the product from different heights onto vinyl covered concrete and having the product survive. Without being able to prove the design meets these requirements, the company will not move forward with injection mold tooling.

We're at the point where a prototype design is finished and 10x cosmetic cast urethane prototypes have been made and assembled with electronics. The units work great and the client loves how they look. We originally thought we could meet these requirements with FEA testing but the studies take 16+ hours to run and provide no insight if the impact will damage the electronics or touch screen LCD. We are now proposing using the existing urethane tooling to mold additional prototypes out of a very mechanically comparable urethane resin.

We had considered machining parts for drop testing, but the final product will be molded from a very niche resin (not ABS or ABS/PC blend, HDPE, HIPS, PA, etc) that I'm sure is impossible to find in billet size pieces.

We are confident in the results from drop testing mechanically similar urethane parts, but our client is concerned about getting a false pass from not using the final plastic resin. Any insight on getting over this hurdle so the client can commit to tooling is much appreciated!


Drop testing on prototype parts is only a short lived first step. No product is completed in a single build cycle, and if you are doing an electronics device then you need to plan for a typical series of EV (engineering validation), DV (Design Validation) and MV (Manufacturing Validation) builds.

I designed rugged mobile devices for a decade and all of them usually required at least 5 build cycles. You can use cast parts for certain pieces or pre-EV prototypes, but the reality is in order to pass drop testing you need to account for stresses which occur in the plastic as part of the molding process. That will reveal areas that fail or crack due to bad weld lines, improper gating or processing issues like temperature, etc.

Once you perform the drop testing you'll see where the failures occur and have to perform multiple rounds of tooling modifications and re-testing to validate that the changes worked. FEA testing can certainly help here, but real world testing will be what shows the failures.

If it's any consolation vinyl over concrete (usually a 4' retail spec) is usually easier to pass with fewer revisions since it's typically less stressful. Many of the devices I worked on were spec'ed 6' or 8' to concrete to simulate falling from a ladder or fork truck.

Re: Drop Testing

Postby Generatewhatsnext » March 8th, 2018, 5:54 pm

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+1 to Mike's reply - and within those multiple steps of validation, you can employ low cost aluminum tooling to short run plastic parts in your spec'd materials, but that approach is very costly once you've set everything up - and even then, as Mike said you'll not have the true picture of weaknesses from moldflow, gating, etc of the final tool.
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Re: Drop Testing

Postby yo » March 8th, 2018, 6:41 pm

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Everywhere I've worked the NPD team had a pretty airtight process for pre-production units and the testing associated with each. To quote one of my engineering coljeguase it is "non-trivial" :-) ... Like Mike said, usually EV1, EV2, DV1, DV2, then a short pre production run of the line, then MP1, MP2, and so on. What has the client done in the past?

Re: Drop Testing

Postby Cyberdemon » March 9th, 2018, 10:53 am

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Generatewhatsnext wrote:+1 to Mike's reply - and within those multiple steps of validation, you can employ low cost aluminum tooling to short run plastic parts in your spec'd materials, but that approach is very costly once you've set everything up - and even then, as Mike said you'll not have the true picture of weaknesses from moldflow, gating, etc of the final tool.


Most of our product wound up eventually eliminating the soft tooling phase and going straight to steel. It was found to be more cost and time efficient over the number of projects running to go to steel, and pay for the modifications - even if it meant cutting a new core/cavity or adding inserts than it was to run a soft tool and then re-tool the final part. It sometimes lead to very constrained design decisions (IE you can only modify the part so much in a tool safe direction before you hit a cooling line or some existing feature) but at scale it had a substantial cost and lead time reduction.

Re: Drop Testing

Postby Lowe9 » March 27th, 2018, 5:53 pm

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Thanks all for the feedback. The clients internal corporate structure dictated that each of the product requirements set out in the product spec document were met before any kind of tooling was purchased. But without the tooling, you can't do a proper drop test in the actual material with real world molding conditions. Chicken and the egg.

In the end, the client accepted our engineering rational that dropping urethane parts cast from a mechanically similar resin would be an acceptable action short of buying soft tooling. The parts are simple enough that we should be able to discuss gating and moldflow with the toolmaker to eliminate problem areas. We dropped the parts over 20 times with no issue. Our client also has a tumble test that we're going to run one of the units in for additional testing.

As an aside, shooting 240fps high speed footage on a phone is surprisingly effective at capturing the impacts.

Re: Drop Testing

Postby yo » March 27th, 2018, 5:55 pm

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Glad to read there was resolution and you are moving forward!


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