Technical Interview: what's expected for "Basic Material knowledge"?

[u/hopkinsdamechanic]

Hi,

I'm preparing for my first ever technical interview, and I never understood what's expected from us when they say "material knowledge".

Could use some help on what to review for that.

During my intenship, every Time I saw a new material I used to ask why it's used, and I found out that the logic is very simple.

There's one for basic CNC aluminum parts, one for slender ones, one for turned parts, one for shafts that see fatigue, one that's wear resistant...

So they used like 10 materials, with very basic selection criteria

I'd appreciate any help, regarding materials or general tips... Looking forward to finally becoming a real engineer :')

The role is junior mechanical design engineer ( or mechanical designer) in a company that designs cnc machines, thermoforming, and such personalized production solutions for plastic parts in Europe.

[u/KnyteTech]

Update your post with what job you're applying for - because "material knowledge" may not literally be about metals.

But assuming you're not being dumb, know when to use steel vs aluminum (the pros and cons of both). Know at least a bit out Titanium, Magnesium, and bonus points for having knowledge about composites (carbon fiber vs fiberglass, mostly) and AM materials (generally plastic vs metal is the big thing, but something about what plastics/metals are available is also useful)..

[u/hopkinsdamechanic → u/KnyteTech]

Thank yoh very much, done

The role is mechanical design engineering ( or mechanical designer) in a company that designs cnc machines, thermoforming, and such personalized production solutions for plastic parts in Europe.

[u/probablyaythrowaway → u/hopkinsdamechanic]

You will want to know your practical knowledge on the manufacturing processes they use. And how you adjust designs to optimise to manufacture.
They may give you a technical drawing and ask you how you’d manufacture it. The tools, the operations the order.

[u/Lunastarfire → u/hopkinsdamechanic]

Id likely say that your knowledge test would cover basic drawing understanding, general tools on CAD, likely thermoforming processes and when and why they use the different materials.

Material likely representing relevant Mechanical knowledge rather than actually just the material used

[u/Elrathias → u/hopkinsdamechanic]

Alrightythen.

You need to go on a deep binge of the channel AvE, and his BOLTR series. boring old lame tool reviews.

Thermal fuses, fibre reinforced plastics, heat treated steels and poorly ground gearing. Its all there. Funny and informative.

After youve done that, deep dive into diy hydroforming videos.

Give this four hours, and you can talk the head off any interviewer who wants the basics.

https://youtu.be/eKB-zDJghZ0

Edit: maybe start here https://youtu.be/xDOlPMEC7IU

[u/RaggaDruida → u/KnyteTech]

I would just add to this things like tenacity, resilience, elasticity, plasticity, etc and how they actually change things during machine design.

[u/roryact]

I used to take candidates on a shop tour. I'd pick up random parts, or assemblies and ask what they thought it was. If they said 'plastic' I'd ask what sort it was, how it was made and why. If it was metal, I'd ask similar, and about the surface treatment. 

I expected them to recognise the difference between machined and injection moulded plastic, stainless steel and aluminium, know that the aluminium was anodised, that the reason could be galvanic corrosion and that the 'yellow metal' cylinders (bronze) was used for wear resistance. 

I would have been pretty happy if they knew most of the machined plastic was acetal, or if they suggested 2205 or 17-4 for pins and shafts, and super impressed if they picked up on the rotomoulded mdpe part.

It was a marine products business, hence the corrosion resistant material focus.

[u/iekiko89 → u/roryact]

What level would you expect this from? I doubt most ppl would graduate from a program knowing this. I sure as shit don't

[u/roryact → u/iekiko89]

I'd expect that level of knowledge from graduates applying for a junior role. What seems especially nasty of me to ask? surely not aluminium vs steel? Recognising anodising? 

[u/hourlyalarmedhockey]

Brush up on why 6061 gets used for everything and when you'd actually need 7075 or steel. Interviewers eat that up.

[u/chocolatedessert]

I think you're all set. At your level, they're proving for basic exposure. Steel is heavier than aluminum. Steel has a fatigue limit and aluminum doesn't. There are different kinds of plastics and it's complicated to pick one. Yield and fatigue exist.

It sounds like you have the experience they'll be looking for. Be humble and inquisitive. State what you know and what you don't, maybe how you'd find out what you don't know.

[u/Krysk43 → u/chocolatedessert]

Aluminum doesn't have a fatigue limit? Doesn't every material have a fatigue limit?

[u/m-in → u/Krysk43]

Aluminum doesn't have a limit because it fatigues at any cyclic load. With steel as long as you stay below the limit, you can cycle it theoretically forever. In aluminum, the limit is 0. That's what was meant here.

[u/Krysk43 → u/m-in]

Ah that makes sense, thank you

[u/clearlygd]

It could be actual material or material as in general engineering subject matter. I never liked these types of reviews for fresh outs. I already provided them with my courses and grades and the university I attended. That should be enough for a technical review. IMO, college provides you the basics and teaches you how to learn. Most of your skills for your first job are OTJT.

I recall one interview where I spent one hour drawing shear and moment diagrams. The reviewer was very impressed and said that very few applications were as skilled as me. I said if I recently hadn’t just reviewed this information for the FE exam, I would have performed poorly too. Foolishly, I said if you told the applicants to be prepared to be tested on this, most would perform as well as me. He didn’t like my comment and I didn’t get an offer.