Hot Metals For Medical Robotics Devices

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I grew up in a family of teachers, writers and musicians (though my mother should have been a mechanical engineer). So having a son who is obsessed with manufacturing processes (his favorite show is How It’s Made) gives me a chuckle. It’s not enough for him to know that his new Razor is made of metal; he needed to know if it was “stainless steel” (it’s actually aluminum). And so when his robotic engineer cousin Scott showed up with the toy Capsela well, let’s put it this way, we didn’t hear a peep out of our son.

Scott designs robotic medical equipment during the day and nifty gadgets at night. I thought it would be interesting to get his perspective on the use of metals in the medical device industry as well as test a few industry stereotypes.

Lisa: Can you explain the types of metals that you are specifying into designs and why?

Scott: When we use sheet metal, we use cold rolled steel primarily because it is easy to form. We also specify quite a bit of yellow zinc chromate (this is plating to make it conductive). For medical devices you obviously have to make sure people can’t get electrocuted – everything has to be “grounded”. These metals are used for enclosures. When you make an enclosure with electronics of say 120v you have to be sure that there is a proper ground. We use 5052 aluminum sheet metal for other enclosures because it’s more formable and used when we need something that is lighter in weight. These are for electronic circuit boards and sub-components. For the robotic arms we specify 6061 aluminum where strength is important. Most custom structural components are made from steel ¼”- ½” plate for strength. We have to pay special attention to structural compliance issues. For example, any bending could create some inaccuracy of our system. Therefore, we need to use very stiff materials. For really important parts requiring alignment such as a kinematic mount ” we specify stainless 440C For our arm/system it’s a very heavy base. We are trying to look at alternative materials such as carbon fiber (to reduce the weight) but there is a tradeoff between cost and weight. Titanium is an alternative material but there is a tradeoff in using it.

Lisa: What do you make of this stereotype of the medical device industry “money is no object or the industry doesn’t care about cost”?

Scott: Well certainly the days of 1970’s defense spending are over. There is not a lot of extra money sloshing around. As engineers of these devices, we have more of a focus on getting something to work properly vs. saving money initially. We have to make sure that something works safely and effectively. The trade-off is time vs. money. If you know that 6061 aluminum will work, perhaps something cheaper will work but you don’t want to lose time on the design side to experiment. If you are start-up, you have to get something done on time that works. Cost reduction comes second. But in regard to your question, for a medical device company selling disposables, the “minting” money piece is probably a fairer stereotype but medical device capital equipment is something different altogether.

Lisa: Have you been impacted by these material price increases?

Scott: No because we’re mostly prototyping. We just finished a prototype design and it was just transferred to manufacturing. Now they are procuring parts for production. This is the second version of the robot and we are just now ramping up for a new production line. We’re going to look at our BOM’s and look at the most expensive items and then go for cost reductions. Right now we’re using a target cost.

Lisa: Does the notion of “green” relate at all to medical devices or because of their nature, it’s the kind of thing that doesn’t really matter (green that is)?

Scott: Actually, it is something that we think about. If we can easily make a decision that meets ROHS requirements that doesn’t hurt the cost, we’ll do that. But there is an exemption for ROHS for medical devices and military which makes sense. We also think about recycle-ability of materials. How do we design our product for recycling to minimize the overall environmental impact?

My personal opinion [Lisa] is that the medical device industry could improve their profitability by better managing their metals buy. But as Scott rightly points out, the tradeoff analysis is considerable!

–Lisa Reisman

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