Drawings for Every Machining Operation?

[tlwhite0311]

I have recently moved into a Mfg. Eng. role after 4 years in a more design centric role. This company is a large production/job shop that producers aerospace and defense parts. One thing they have their engineers doing is creating drawings for every machining operation. This requires the parts to be remodeled in CAD with colors and the features added incrementally in model configurations (it's Solidworks I don't know what they are in other CAD packages, if I remember Creo called them Simplified Reps.) to show the operator exactly what they are to do in that op. I have never seen this done before, I have visited countless shops for my own projects, where the operators have the customer print on the floor. It seems to me that this is a massive waste of time and resources, essentially doing everything twice. Their argument is that the operators need to have no ambiguity for what they have to do at each op. I feel that if the program and fixture is correct, there is no way the operator could change anything or add any features.

My question is, is this typical? Am I correct in my assumptions or is there something I am missing?

 

[CWB1]

Yes and no. For complex parts its normal for shops to have markups referencing work instructions, inspections, etc. Its also normal to have a few reasonably large print levels - casting, rough-machined casting, finish machined part, etc. That said, it'd be strange to see separate prints for each machine/op/etc as described.

 

[mfgenggear]

OP
Yes it is normal. Especially for complex parts that require rough machining before heat treat, stock allowances for post machining of heat treated parts.. especially case harden parts. With cad it makes the dimensional control, and stack up of machining more feasible. Taking that burden off the operator.
My suggestion to you it do a write up and discuss it with a lead or supervisor.
Especially if you are not strong in machining.

 

[Gr8blu]

It may be a result of the company's customer base (i.e. aerospace and defense contracts). If those users require "step by step" instruction on the documentation, then it may be a carryover to ALL drawings regardless of end user. It can also be how the company is "protecting" itself from possible future legal issues - if the machinist has absolutely no way to set things up differently from the drawing (because they don't necessarily know all the steps involved before and after their specific operation), the outcome should be exactly the same. Any part variability then comes down to either material or tooling - not process.

I do agree, though, that MOST machining drawings allow some flexibility in how the machinist accomplishes a specific outcome by giving multiple operations on the same drawing.

I have also seen a multi-step approach (i.e. casting or forging, rough machining, final machining, etc.) as separate drawings because the amount of effort at a given operation may vary - and there may be multiple stations doing the same task. For example: rough machining takes 2 hours and can be done by one station. Final machining takes 5 hours (for whatever reason) and is performed on three other stations. This means no one station becomes a production bottleneck - at least in theory.

 

[mfgenggear]

There are also operations that are processed in house by different machining centers that are specific, and operations that have to be off loaded to an outside vendor. Complex parts require many different types of machining.
Cnc turn, cnc mill, jig bore, or jig grinding, od and Id grinding, wire or conventional edm broaching, and more. Sheet metal parts require bunch of different machines.

 

[EdStainless]

ours were fairly simple parts and we lumped multiple operations together.
In many cases it wasn't that the operator couldn't figure out how to do it, but we wanted it done the same way every time.

 

[NOLAscience]

Maybe they are going to replace workers and the workers' input with AI and automation

 

[dgeesaman]

I have recently moved into a Mfg. Eng. role after 4 years in a more design centric role. This company is a large production/job shop that producers aerospace and defense parts. One thing they have their engineers doing is creating drawings for every machining operation. This requires the parts to be remodeled in CAD with colors and the features added incrementally in model configurations (it's Solidworks I don't know what they are in other CAD packages, if I remember Creo called them Simplified Reps.) to show the operator exactly what they are to do in that op. I have never seen this done before, I have visited countless shops for my own projects, where the operators have the customer print on the floor. It seems to me that this is a massive waste of time and resources, essentially doing everything twice. Their argument is that the operators need to have no ambiguity for what they have to do at each op. I feel that if the program and fixture is correct, there is no way the operator could change anything or add any features.

My question is, is this typical? Am I correct in my assumptions or is there something I am missing?

There are internal/manufacturing drawings and component design drawings. And all sorts of overlap.

The scope can be anything that makes sense for you. Many companies have manufacturing drawings that are derived from the component drawing. That sort of causes overlap. If you force design to break down the product design drawings to suit manufacturing preferences only your only controlled definition of the product, quickly makes a mell of a hess. If these are parts of your own design, the change management and engineering process becomes almost impossible if Engineering can't define a component in its entirety on their own. From a design, inspection, and Engineering perspective I strongly prefer one drawing per part.

The other issue is that cost can become extremely murky especially if you want to compare outsourced vs. in-house costs per component. A drawing per part allows the part to be defined by its functional requirements and also have it outsourced. If you break it into drawings for your manufacturing processes, you have blinded yourself to any other possibilities.

David

 

[mfgenggear]

The final acceptance is the engineering drawing. Manufacturing drawings are derived from the engineering drawing. And is now more easily manufactured and is also favorable for quality to inspect make sense.
Of what they are to inspect. Even for out sourced operations. Is very specific. Every department is on the same page.
There will alway also be changes and improvements. But now there is historical record and break down. Of manufacturing, inspection and cost. Simple as that.

 

[MintJulep]

I've never seen that done to the level you describe.

I like the part about no ambiguity.

I hope there's a favorable cost:benefit ratio for it.

Why don't you ask about when and why they started, and if it's paid off in terms of less reworked and scraped parts.