Sites: GlobalSpec.com | GlobalSpec Electronics | CR4 | Electronics360
Login | Register
The Engineer's Place for News and Discussion®

GEA's Global HVAC Technology Blog

GEA's Global HVAC Technology Blog covers a range of topics including:

  • Core HVAC Technologies
  • Technology & Patent Evaluation
  • Manufacturing Technologies
  • Product Quality Improvement
  • Materials/Failures/Corrosion
  • Product/Technology Commercialization
  • Business Strategy Development
  • New Factory Design & Equipment

We'll draw upon our range of experts to provide comments, insights, technical articles and a little humor from time to time

We encourage your participation and feedback!

Previous in Blog: Is Low-Cost Chinese Labor Affecting Your U.S. Exports?   Next in Blog: Do Your Exports Really Have a Cost Disadvantage from Chinese Labor?
Close

Comments Format:






Close

Subscribe to Discussion:

CR4 allows you to "subscribe" to a discussion
so that you can be notified of new comments to
the discussion via email.

Close

Rating Vote:







16 comments

Cast Iron Is Not Cheaper Than Brains

Posted July 19, 2011 9:15 AM by geanorm

Editor's Note: CR4 would like to thank PJ Sikorsky, Metallurgical Consultant, for contributing this blog entry, which originally ran here.

I can't begin to remember how many times over the past 30 years I've felt the bile rise in my system as I've heard design engineers suggest that it doesn't matter what material(s) are used to build parts and components. I suppose it's natural for any of us to feel unloved and underappreciated in our professional endeavors. As a materials engineer working for two different major manufacturers over my career I often felt that materials selection was not given as much attention during the design process as it deserved. There are 5 repetitive problems I have observed related to material(s) selection over my career:

1. Material Selection after the part/component is 'designed'.
2. Material Selections not reviewed over time.
3. Materials copied from old designs.
4. Material substitutions fail.
5. Bad material selections - the gift that keeps on taking.

In the remainder of this blog post I'll briefly describe each of these problems. I'll devote subsequent posts to each of these issues individually in more detail.

1. Material Selection after the part/component is 'designed'.

Many times a design engineer comes to the materials engineer after lines are committed to paper and the part is 'designed' - the question often is 'Okay, what should we make this out of?' The shortcoming of this approach is that once parts are designed, materials options are limited. Done right, Material Selection is integral with the design process and parts are designed around specific material characteristics.

2. Material Selections are not reviewed over time.

Even when Material Selection is done right, the materials world is a dynamic place and what makes sense today, may not make sense tomorrow. For many years copper was less expensive per pound than aluminum (for most of my career, copper was $0.65/pound while aluminum was around $1.00/pound), today copper is 4.5 times more expensive than aluminum per pound - does copper still make sense for heat exchanger tubing or headers or connecting tubing now that aluminum is so much less expensive? Maybe, maybe not, but it is obviously a different question now than it was before.

3. Materials copied from old designs

This is similar to #2 above, but it also can create problems for other reasons: What is the right material for a one pound widget may not be the right material for an 'identical' 10 pound widget - material properties do not necessarily scale with the geometry of a part. Where a part is manufactured may impact the material selection - what makes sense for a part made in the US, may not be appropriate for a part made in China.

4. Materials substitutions fail.

Whether we try to convert parts from metal to plastic, or from metal castings to powdered metal, materials substitutions fail. The primary reason is that when materials change, part design needs to change. A plastic gear, even though it may serve the same function as a metal gear, if designed properly, should look different than a plastic gear. If we simply try to drop in a plastic material into the same geometry as a part that was originally made from metal we are almost assured of failure.

5. Bad Material Selection - the gift that keeps on taking

Oftentimes during the development process, problems are discovered too late in the game to 'redesign' parts before going into production. Instead, we call on some materials 'magic' and we implement special coatings, or heat treatments or exotic materials into the existing designs just to get us into production. Our intentions are always good - we say we'll come back later and redesign the parts so that we can revert to more standard/affordable materials - but the reality is that we rarely have the time to go back and redesign and instead we pay for the premium material throughout the life of the component design, and in those cases where we simply copy material selections from old designs into new designs, we pay the premium forever.

With raw material costs accounting for 50-80% of piece part cost it seems intuitive that choosing the 'right' material is critical to managing cost, yet we often treat this part of the design process as an afterthought. We'll explore each of the repetitive problems described above in more detail in subsequent posts and we're available to help you improve Material Selection.

- PJ Sikorsky

Reply

Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.
Guru
Popular Science - Weaponology - New Member United Kingdom - Member - New Member

Join Date: May 2007
Location: Harlow England
Posts: 15415
Good Answers: 549
#1

Re: Cast Iron Is Not Cheaper Than Brains

07/19/2011 11:44 AM

Nice blog... it raised a smile as I've met some of those problems even tho' I'm not actually a mech eng'.
Same sort of thing happens in electronics, some bright spark will decide to substitute a cheaper or even a 'better' part, which doesn't work of course, or worse still fails 2 weeks after switch on. The flip is... We've allways done it like this.
Del

__________________
health warning: These posts may contain traces of nut.
Reply
Guru

Join Date: Aug 2010
Location: Melbourne, Australia
Posts: 593
Good Answers: 19
#3
In reply to #1

Re: Cast Iron Is Not Cheaper Than Brains

07/20/2011 12:20 AM

I agree

Reply
Guru
Engineering Fields - Aerospace Engineering - Member United States - Member - Army Vet in the aviation industry

Join Date: Mar 2008
Location: Bridgewater, Va.
Posts: 1396
Good Answers: 70
#2

Re: Cast Iron Is Not Cheaper Than Brains

07/19/2011 11:35 PM

I smiled at your blog as well.

After many years in the aviation industry, I just don't get it when people decide they have better ideas in material selection. Particularly when the FAA says otherwise, based on tried and true practice.

Dave G.

Reply
Guru

Join Date: Jan 2008
Posts: 1756
Good Answers: 59
#4

Re: Cast Iron Is Not Cheaper Than Brains

07/20/2011 5:23 AM

Having spent a life in the electronic industry, I can attest to all five of them. I have seen the best, where proper material selection led to no failure in a few ten millions of connector pins in a lifetime (mine). Corrections, there was one. When I finally tracked it down, I was compelled to carefully dissect it. It was a manufacturing defect.

On the other hand, I had to deal with an RCA manufactured controller on a recurring basis. The electronic design was fine for the time. Materials selection was straight from hell. Electronic boards were mostly ok, copper traces tin plated, gold plated fingers. But, the board edges were beveled (what for, I cannot fathom). The exposed glass fibers scoured the sockets every time a board was inserted. Can you spell SHORT CYCLE LIFE for those sockets?

The sockets were not replaceable, as they were soldered into a backplane, AND wire wrapped for most signals. Additionally, the contacts were made of steel, tin plated on the card's side. Gold contacting tin over steel. Corrosion, big time!!

I am not finished. The pins for soldering and wrapping were nickel plated (with copper underneath) to make it fit for soldering and wire wrapping. Guess what? When Mount St Helen volcano blew its top, I had some 2 years repairing corrosion problems from fine volcanic dust and sulfur dioxide. The most memorable were, when a signal got lost on a straight wire from here to there. The copper corroded somehow, and the nickel plating delaminated from the steel pin.

Why this cockamamie construction, I cannot fathom. But, it definitely contributed to RCA's reputation of unreliability and eventual demise. For those too young to know: wire wrapping is an excellent, gastight manual wiring, mostly backplanes. It was designed for base metal to base metal cold welding contacts. How does it supposed to work over mechanically weak plating?!?

Oh, YES I have plenty of appreciation for materials science, and bruises to prove.

--------------------------------------------------------------------------

Clausewitz: war is simple. But the simple things are most difficult to execute.

Reply
Power-User
Canada - Member - New Member

Join Date: Mar 2011
Posts: 128
Good Answers: 8
#5

Re: Cast Iron Is Not Cheaper Than Brains

07/20/2011 5:44 AM

Yeah, to me the argument about the best material for a home-built vehicle is like the eternal Ford-Chevy debate. The best material, out of the ones in successful use for similar stuff, is the one you enjoy working with and have the tools for.

A friend of mine was making small talk with an engineer at a famous motorcycle company. "So, you must get to work with some advanced alloys?" he essayed. "Nah, if it breaks, we make it bigger, and if it gets ugly, we chrome it!"

Reply
Guru
Popular Science - Weaponology - New Member United Kingdom - Member - New Member

Join Date: May 2007
Location: Harlow England
Posts: 15415
Good Answers: 549
#6
In reply to #5

Re: Cast Iron Is Not Cheaper Than Brains

07/20/2011 5:53 AM

"Nah, if it breaks, we make it bigger, and if it gets ugly, we chrome it!".
It amazes me how some people have no feel for the materials they use. Personally I tend to under-engineer as I like to see how far you can push materials, its also a lot easier to saw 1/8" steel plate than 1/4".
I find wood to be pretty impressive stuff (but of course different species have different properties, and even the sap wood and heart wood from the same tree may have distinct feel and properties), not to mention Bamboo.
Del

__________________
health warning: These posts may contain traces of nut.
Reply
Guru
Hobbies - Musician - New Member United Kingdom - Member - New Member

Join Date: Mar 2007
Location: England
Posts: 909
Good Answers: 43
#7
In reply to #6

Re: Cast Iron Is Not Cheaper Than Brains

07/20/2011 7:13 AM

I'm not sure I like the term "under-engineer". But minimizing, and pushing to the limits to find where the limits are, this was Colin Chapman's approach, and it worked pretty well for Lotus.

As for wood; possibly the best engineering material ever invented, and certainly the most aesthetically pleasing.

An interesting blog. I too have seen most of Mr. Sikorsky's 5 problems. I don't know why it is not understood that material selection and product/component design go hand in hand.

Reply
Guru
Popular Science - Weaponology - New Member United Kingdom - Member - New Member

Join Date: May 2007
Location: Harlow England
Posts: 15415
Good Answers: 549
#8
In reply to #7

Re: Cast Iron Is Not Cheaper Than Brains

07/20/2011 7:17 AM

Yeah, I know what you mean, but I've built a few projects which needed strategic reinforcement/increase of section on certain parts.
Modern cars are a good example of removing excess wieght and pareing design to the bone. compare a wishbone (or other suspension component) of a modern car to one from the 60s-70s.
You can have too much minimalism
Del

__________________
health warning: These posts may contain traces of nut.
Reply
Guru

Join Date: Mar 2011
Location: Sebastopol, California
Posts: 502
Good Answers: 25
#11
In reply to #6

Re: Cast Iron Is Not Cheaper Than Brains

07/20/2011 10:09 AM

I love bamboo! You can do almost anything with it. Beautiful material.

__________________
Most people are mostly good most of the time.
Reply
Guru
Engineering Fields - Optical Engineering - Member Engineering Fields - Engineering Physics - Member Engineering Fields - Systems Engineering - Member

Join Date: Apr 2010
Location: Trantor
Posts: 3823
Good Answers: 402
#9

Re: Cast Iron Is Not Cheaper Than Brains

07/20/2011 8:49 AM

I empathize with this a lot. In my years as an optics engineer I've heard the same kind of question, 'Here's the mechanical design, now how can we get the optics to work?'

And the change-of-materials mistake reminds me of one of my long-standing pet peeves: putting a counter-sink screw in a plastic part. Sure, counter-sunk screws are OK in metal, but a counter-sunk screw in plastic is a guaranteed way of busting the plastic.

__________________
Whiskey, women -- and astrophysics. Because sometimes a problem can't be solved with just whiskey and women.
Reply
Guru
Popular Science - Weaponology - New Member United Kingdom - Member - New Member

Join Date: May 2007
Location: Harlow England
Posts: 15415
Good Answers: 549
#10
In reply to #9

Re: Cast Iron Is Not Cheaper Than Brains

07/20/2011 9:40 AM

one of my long-standing pet peeves: putting a counter-sink screw in a plastic part. Sure, counter-sunk screws are OK in metal, but a counter-sunk screw in plastic is a guaranteed way of busting the plastic.
Good idea for a pet peeves thread? My pet hate is plastic fingers supposed to act as springs which aren't tapered and then predictably snap off at the root.
Del

__________________
health warning: These posts may contain traces of nut.
Reply
Associate

Join Date: Jul 2011
Posts: 45
#12
In reply to #9

Re: Cast Iron Is Not Cheaper Than Brains

07/20/2011 11:46 AM

Sure there's room for improvement here and perhaps a simpler solution.

But i find it to be my fault 50% of the time.

Tend to overturn the screw bc some part of me wants to secure it for life!

Before i realize what i've done: Crack! followed by "Crap"

I've tried coating the end of the screw with olive oil...

Anyone else find square vs. conical better?

Reply
Guru

Join Date: Sep 2008
Posts: 606
Good Answers: 23
#13

Re: Cast Iron Is Not Cheaper Than Brains

07/20/2011 1:29 PM

Copper was never "cheaper" than aluminum on a per pound basis when you consider the fact that copper has a density 3 times that of aluminum.

__________________
Spinco
Reply
Guru
Popular Science - Weaponology - New Member United Kingdom - Member - New Member

Join Date: May 2007
Location: Harlow England
Posts: 15415
Good Answers: 549
#14
In reply to #13

Re: Cast Iron Is Not Cheaper Than Brains

07/20/2011 3:37 PM

At the risk of being pedantic, it certainly was in 1825.
Copper has been available for much longer.
Del

__________________
health warning: These posts may contain traces of nut.
Reply
Guru

Join Date: Sep 2008
Posts: 606
Good Answers: 23
#15
In reply to #14

Re: Cast Iron Is Not Cheaper Than Brains

07/20/2011 4:25 PM

Regardless of discovery (Bronze age-3000 B.C. vs. 1825) and although ancient Greeks and Romans used Alum as an astringent(hence use but not discovery), the density of aluminium is 2.71g/cc whereas copper is 8.92g/cc or 3.3 times as heavy which the only point I was making.

Hence the cost of a copper part would have to take into account that the part will be 3.3 times as heavy so unless the cost of copper is 1/3 that of aluminium there will be a price advantage to aluminium due to the weight savings. But I still wouldn't recommend using aluminium tubes in a seawater application.

__________________
Spinco
Reply
Commentator

Join Date: Jun 2014
Posts: 69
Good Answers: 4
#16

Re: Cast Iron Is Not Cheaper Than Brains

06/22/2014 11:31 AM

Material selection is very integral to good design as I once learned the way of hard knocks. I had a 4" shaft in hexagonal profile turned down to an approximately 2" splined drive driven from 10 hp planetary reducer to about 25 rpm from 1750.

Well the shaft jammed to a stop and the reducer twisted off the splined turned down on the shaft.

The original shaft was made from 1144SP TG&P. As I found out later after talking to the mill, the material properties of round stock material are certified to 1/3 the depth of the radius. After that, there is no certification.

So I switched to 4340 heat treated to Rc 43-48 and have never had a shaft shear problem since.

By heat treating a finished product the material properties are transferred to the new radius's.

I forgot how to spell the plural of radius.

__________________
Hey Isaac, catch! ...oops, that's gonna leave a mark...
Reply
Reply to Blog Entry 16 comments
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.
Copy to Clipboard

Users who posted comments:

Deefburger (1); Del the cat (5); Easyway (1); Holzfeller (1); Hooker (1); leveles (1); Massey (1); Onthewaytotheforum... (1); Spinco (2); Usbport (1); WAWAUS (1)

Previous in Blog: Is Low-Cost Chinese Labor Affecting Your U.S. Exports?   Next in Blog: Do Your Exports Really Have a Cost Disadvantage from Chinese Labor?
You might be interested in: Hazardous Material Storage, Nondestructive Testing (NDT) Material Testers, Industrial Ceramic Materials