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