Cheaper to manufacture (milling) from one part, or to manufacture and assemble many parts? 1

[dejan95]

I have a question about price of a manufactured part. I would only need one. Probably made with milling.

I'm creating a new design for a tool on the picture bellow:

Would it be cheaper to manufacture this design from one part, or to manufacture separate parts (5 parts in total) and assemble them with screws? Off course this design is not finished yet, I'm only wondering for current design.

Material is aluminium.
Thank you in advance!

Best regards!

 

[Jboggs]

One of the ways I answer that question for myself is very simple. How much of the original piece will remain? Will most of it end up as chips on the floor? If so I look for another method.

Have you considered welding instead of bolting? Probably not a significant difference. Another one of my favorite ways to decide these questions (since I'm not a machinist) is to simply ask the shop that will be making it. Explain your end goal and let them choose the best way to get there. They know the factors that affect their price better than you do. Questions like available materials on the shelf, available equipment on the floor, available skillsets in their workforce.

 

[Tmoose]

Sometimes the "best" method is the one that results in lots of chips on the floor.

I'm guessing about the scale of the fairly simple rendered part, but machining material removal rates aluminum can be quite aggressive.
The precision require is also an important unknown.

6:50 here.

https://www.youtube.com/watch?v=rjyuqhs8scA

Then again, fabrication and assembly time in-house can be a bargain, or even "free."

 

[EdStainless]

Will you ever need to modify it or replace parts = make it an assembly
Is strength and holding tolerances critical = machine it
Chips are cheap since you are only making one.
If I had a big mill and a skilled machinist I was make it solid.
Is making different parts out of different materials helpful? = assemble
At the minimum if this is being used on production and made from Al you should use thread inserts if assembled.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[MintJulep]

For what you show I think milling will be less.

 

[Scuka]

Think about the operations required.

If part is made of one piece, you need to saw cut the rectangular stock to length, mill the longitudinal channel, mill the transversal channel, and add chamfers. Maybe mill width and height, depending on whether the overall size is equal to one of the standard stock sizes (it's preferable to make it so whenever possible).

If made as an assembly, you need 5 saw cuts from 3 different stock bars (as opposed to earlier 1). Then you have to put each of them individually into the machine to drill the holes for assembly and mill out all the other features. So that's 5 cuts, 5 individual machine preparations, several more holes. How do you imagine that to be cheaper?


In simple parts and low volumes, it's the preparation that chews up most of the time (and money), not the actual machining. So your goal is to reduce the number of operations.

If 1, 2, and 5 could be made by, say, laser cutting with no additional machining required, then arguably, assembly could maybe be cheaper. But if you need to mill all 5 parts, forget it.

 

[JohnRBaker]

Back in my days as a machine designer, I participated in several 'Value Engineering' reviews and one of the ways that we found to reduce the cost of something was to reduce the number of parts that had to assembled. Now this came about from two different issues. The first was attempting to get a component to do multiple duties so that another part(s) could be eliminated. An example might be to have a single bracket support more than one item, like a limit switch and the junction box that it's wired to.

The second, was more in line with the OP's question, that is reduce the number of parts needed to meet the requirements of a single part. This is where we'd decide if it was cheaper to machine an albeit more complex single part versus fabricating it either by welding or just manufacturing separate pieces that had to assembled together. Generally speaking, but depending on the final complexity, the least number of individual parts was generally the desirable outcome.

John R. Baker, P.E. (ret)
Irvine, CA
Siemens PLM:
UG/NX Museum:

The secret of life is not finding someone to live with
It's finding someone you can't live without

 

[mfgenggear]

dejan95

since it is quantity of one, it will be more precise if machined from one piece. regardless of cost.
if precision is required, if assembled then jig boring or jig grinding will be required. that will raise the cost.
not mentioned here is hardness and if it will require heat treating . treat will change the outcome.
one would have to know the fit, form and function to get a better answer

 

[dejan95]

Thank you very much guys. This really answers all my questions!

 

[BrianPetersen]

If you are going to machine it in one piece, design it in a way that CAN be machined in one piece.

It needs to be able to be clamped down in a desired orientation, the features to be machined in that setup need to be accessible to the tool and spindle in an orientation that is practical on the machine that you are using, if the part needs a setup change that involves re-orienting it then make sure the first setup involves machining appropriate datum edges and clamping surfaces as needed, etc. To a certain extent, the part has to be designed and toleranced according to the way you want to machine it.

 

[Stick.]

To piggyback on BrianPetersen's point, if you're able to work closely with the machinist making your part let them know if you're open to design changes to make their life easier (but always insist on approving the changes). Things like letting them add fixturing holes, adding a radius to a sharp inside corner, changing a sharp inside corner to a radiused corner, changing a feature size to align with standard tooling, etc can drop machining costs significantly.

 

[aldumoul]

As a general rule… more parts = more cost. This is because there will be a lot more setups on machining centers. Let’s say your 4 parts take two setups each, now you you have 8 setups. That could equate to 4 hours of time. Not to mention, if you have them saw cut 4 pieces you can almost double that. Material is also cheaper if you just buy one piece of something.

It is always good to get the machinist/toolmakers involved, and ask them before design. I often have them stop by and look at my model so I have their buy in.