Latest / Mechanical Engineering Made Simple / (#107) Blueprints for Profit: Hitting the UMC Target with DFM&A, GT, and the 43% Fastener Flaw

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(#107) Blueprints for Profit: Hitting the UMC Target with DFM&A, GT, and the 43% Fastener Flaw · Mechanical Engineering Made Simple

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  Welcome back, design junkies, to Mechanical Engineering Made
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  Simple. Today we're diving deep into
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  basically the blueprints for profit.
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  This deep dive is our shortcut really to understanding those
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  critical decisions, the ones that let you build products
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  efficiently, cost effectively. We're looking at, well,
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  everything from setting that upfront cost target, you know,
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  classifying materials, managing those complex production flows,
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  and using tools like design for manufacturing and assembly.
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  Yeah. And that upfront focus is it's
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  everything, isn't it? The real core challenge is
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  getting that congruence. You need the product design, how
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  it looks, what it does to perfectly mesh with the design
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  of the manufacturing processes. You know, the ones that actually
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  make the thing. Success really boils down to
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  three things. Time to market, cost and
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  quality. Get those early choices right
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  and will those 3 metrics tend to fall into place?
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  Right. So the big goal fundamentally is
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  turning raw stuff into finished products profitably.
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  But you can't just wait until it's on the factory store to
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  figure out the cost. You need that target way
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  earlier, right at the beginning. Absolutely, and the sources we
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  looked at, we're really emphatic about this.
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  These aren't just like nice ideas, they're rules rule #1 the
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  product development team must get a specific unit
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  manufacturing cost, a UMC target right at the start.
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  OK, non negotiable. Non negotiable and rule #3
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  follows right on. They have to be held accountable
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  for hitting that target right? To do that you need to
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  understand the formula. It's UMC equals BL plus MC plus
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  TA. OK.
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  Let's break that down, BL. BL is burden assembly labor.
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  So that's not just the wages, right?
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  It's the direct labor, plus benefits, plus all the relevant
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  overhead costs tied to that labor.
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  Got it. Overhead included.
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  MCMC is material cost, that's the raw materials packaging,
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  plus things like duty freight, insurance, sometimes called DIP,
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  and also material acquisition cost.
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  It all adds up. OK.
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  And TA. TA is tooling amortization,
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  basically the cost of your fabrication tools, your molds,
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  divided by the total number of units you expect to build over
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  the product's entire life. Wow.
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  OK. So there are a lot of sort of
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  hidden layers in there that maybe management sometimes
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  misses. But looking at that equation, BL
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  plus MC plus TA, one of those usually stands out, doesn't it?
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  MC, the material costs. Oh.
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  Absolutely. Consistently dominated.
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  But it's not just big. It's, I mean, some studies say
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  material costs can be like 60, even 80% of the total UMC.
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  Easily, yeah. 60 to 80% is pretty typical, and that right
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  there tells you something huge. Your biggest leverage point for
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  cutting cost isn't usually shaving 5% off assembly labor,
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  it's figuring out how to use less material or cheaper
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  material. So part reduction and smart
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  material choices are just critical.
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  Absolutely critical, which leads us perfectly into DFM and.
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  A design for manufacturing and assembly.
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  Right. It's this technique specifically
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  aimed at slashing product cost by, well, simplifying the design
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  down to its essential components.
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  Yeah, it forces the design team to think about assembly material
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  flow really early on, not just, you know, throwing it over the
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  wall later. Yeah, not as an afterthought.
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  It's exactly the goals are pretty straightforward.
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  Cut the part count, integrate parts and processes where you
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  can, and by doing that minimize the assembly work and cost.
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  I saw this this great cautionary tale in the source material,
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  this fictional Ajax Bull Corporation memo.
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  It perfectly showed what happens when managers think they're
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  doing DFM and A but they're actually undermining the whole
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  concept. This memo basically said
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  manufacturing would only get involved like a couple of times
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  planned occasions because engineering was worried that
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  manufacturing's input would quote drag on schedule and
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  they'd waste time defending and arguing the design.
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  Their definition of concurrent engineering was literally
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  engineering designs that manufacturing is forced to
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  agree. Minimal input allowed.
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  That's just setting yourself up for failure.
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  A cost disaster waiting to happen because they completely
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  miss the ripple effect of simplification.
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  When you genuinely cut parts, you don't just save the cost of
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  that part. All the overhead tied to that
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  part, tracking it, storing it, inspecting it.
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  That just vanishes. Your quality goes up instantly.
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  Fewer places for things to go wrong.
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  Assembly time drops and crucially, the whole product
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  development cycle gets shorter. It's a win, win, win.
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  So for you listening, wanting to apply this kind of radical
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  simplification, what are the key principles?
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  How do you actually do it? OK, key DFA principles.
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  First, design parts with self locating features.
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  Make them easy to put in the right place.
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  Self Fastening features help too.
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  OK Second, use multi functional parts.
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  Whenever possible. Combine functions into one
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  piece. Third, eliminate assembly
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  adjustments completely. They are just sources of
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  complexity and air get rid of. The tweaking.
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  Exactly. And 4th Dr. Standardization.
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  Standardized fasteners, components, materials, processes
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  use the same stuff across different products.
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  OK, so we simplified the design. Now, how do we organize all this
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  engineering knowledge, keep track of these parts and
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  processes effectively? That's where Group Technology,
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  or GT comes in. It's all about grouping things.
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  GT essentially takes different work pieces and puts them into
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  logical part families based on similarities and how they're
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  made or how they're designed. And this whole process starts
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  with parts classification and coding, which is really crucial
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  for things like automating processes or even just finding
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  existing design so you don't reinvent the wheel.
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  Right, design retrieval and the theory behind classifying these
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  parts seems pretty straightforward, based on sort
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  of three ideas. Yeah, it's quite elegant
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  actually. Yeah, Premise 1.
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  A part is best defined by its most obvious feature.
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  Its basic shape, you know, is round, flat, cubic.
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  OK, basic shape first, second. Special features, Holes,
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  threads, slots. They're just added on to that
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  basic shape. Superimposed.
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  Exactly. And 3rd, you can fully describe
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  a workpiece by looking at its basic shape, the special
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  features, its overall size, the required precision and finally
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  the material type and form. And that structure leads to
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  these codes, right? Like an 8 digit code often.
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  Yeah, an 8 digit code is common, broken into sections, basic
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  shape, form, features, size, precision, material.
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  These codes aren't the whole story, they're pointers to the
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  detailed info. Now how you structure that
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  classification, there are a couple of ways.
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  There's the E tree concept. Think of it like a strict
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  hierarchy, like a family tree where everything fits neatly
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  into one branch. Mutually exclusive category.
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  One Part 1 family. Right, then there's the entry
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  concept. This allows for non mutually
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  exclusive paths, so a part could belong to multiple groups based
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  on common features. It's useful for attributes like
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  say needs welding or has internal threads, Things that
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  might apply across different basic.
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  Shapes I see. And this isn't just for metal
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  parts, is it? You can classify materials too.
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  Oh definitely a really comprehensive system.
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  Like the engineering materials taxonomy mentioned in the
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  sources goes way beyond just metals.
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  It describes something like 79 different material families,
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  including composites, ceramics, plastics, all sorts.
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  Having that kind of system just makes life easier for everyone,
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  helps designers pick materials faster, improve communication
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  between departments, cuts down search time.
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  It's about systemizing knowledge.
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  OK, so knowledge systematized, parts simplified.
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  Now we need to actually make them and get them to the
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  customer on time. This moves us into production
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  planning, right? Starting with forecasting.
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  Exactly. Factory floor planning
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  forecasting is Step 1 and quantitatively you've basically
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  got 2 main flavors. First is time series analysis.
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  That's using historical data plotted over time, looking at
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  past sales trends, that kind of thing.
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  Looking backwards to predict forwards.
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  Pretty much the second is causal methods.
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  This tries to find relationships between what you want to
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  predict, like demand and other independent factors, maybe using
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  tools like regression analysis. OK, so you've got your forecast,
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  now you need a plan to get the materials in house.
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  That's MRP territory materials, requirements, planning.
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  Yes, and MRP is crucial, but it's for a specific situation.
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  The key thing about MRP is you use it when the demand for a
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  component is dependent on something else.
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  Like you only need screws when you're building the main
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  product, and when that demand is irregular and highly varying it
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  jumps around a lot. So not like a steady constant
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  demand you might see for finished goods at a supermarket.
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  Exactly the opposite. Traditional inventory models
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  often assume constant demand, which just doesn't work for
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  components deep inside a bill of materials.
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  You can't just set a simple reorder point.
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  So what's the big win with MRP then?
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  The huge benefit is inventory reduction.
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  It lets a business keep much lower average inventory levels
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  because you're not just holding stock.
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  Just in case you use schedule procurement, you schedule
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  manufacturing to happen just before the parts are actually
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  needed based on that dependent demand.
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  Saves a ton on holding costs. Makes sense.
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  Schedule it tight and then finally the parts arrive at the
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  assembly line. Now we're talking sequencing.
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  Right, getting the work done efficiently on the line.
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  The main goal here is assembly line balancing.
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  You're trying to assign all the little tasks, the work elements,
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  to the different workstations along the line in a way that
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  minimizes the total idle time, what they call balance delay,
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  while making absolutely sure you follow the required order of
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  operations, the precedence relationships.
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  Got to do step A before step B. Precisely.
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  All right, let's shift gears to the actual manufacturing
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  processes, the tools in the toolkit.
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  Sometimes the standard stuff just won't cut it right.
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  Yeah, absolutely. You run into situations where
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  conventional machining, milling, turning, grinding just isn't the
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  right answer. That's when non traditional
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  machining processes become essential.
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  You'd look at these when you need really complex shapes or
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  maybe incredibly small features or when the material is super
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  hard. Think harder than say 400 Brunel
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  OK also when you need extremely tight tolerances or and this is
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  often critical when you absolutely have to avoid heating
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  up the part or leaving residual stresses on the surface.
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  So these are like the special forces of machining.
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  Can you give some examples? Sure, Laser beam machining.
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  LBM uses a super focused beam of light to melt or vaporize
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  material away. Incredible energy density.
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  Like a tiny, precise cutting torch.
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  Kind of, yeah. Then there's electrochemical
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  machining, ECM. This removes conductive material
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  using electrolyte bath and electric current, basically
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  controlled corrosion and you can reverse it sort of for
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  electrochemical debring ECD, just to clean up edges.
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  Clever. And a really common one is
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  electrical discharge machining. EDM uses rapid Starks between a
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  tool and the workpiece in a dielectric fluid.
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  The cool thing about EDM is it works great on really hard
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  materials. Doesn't really care about
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  toughness. OK, powerful tools.
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  Now switching to putting things together.
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  Mechanical fasteners, bolts, rivets.
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  There's some interesting physics there with bolted joints.
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  Yeah, especially with high strength bolts.
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  When you tighten a bolt, you apply a preload.
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  This actually stretches the bolt slightly, makes it longer A.
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  Stiff spring. Exactly, and at the same time it
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  compresses the parts being joined together, the joint
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  itself. You can visualize this with a
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  joint diagram. It plots force versus
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  deflection, showing the stiffness of the bolt, Let's
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  call it case of B and the stiffness of the joint case of
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  J. Case of B for bolt.
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  Case of J for joint stiffness. And how these stiffness is
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  compare is really important for how the joint behaves under
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  load. So a common design goal is what
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  make the joint stiff and the bolt relatively less stiff like
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  a shock absorber as you said, that's.
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  Often the preferred way. Yeah, a stiff joint and a
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  softer, more elastic bolt. Now think about what happens
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  when you apply an external pulling force, a tension load,
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  let's call it L sub X to that assemble joint.
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  That external load gets shared. Part of it increases the tension
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  already in the bolt. That's Delta F sub B.
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  OK, the bolt stretches a bit more.
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  And the other part of the load reduces the clamping force that
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  was compressing the joint. That's delta F sub J With a
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  stiff joint and a softer bolt, the bolt takes most of that
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  external load fluctuation. The change in the clamping force
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  on the joint is relatively small, which is good.
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  You want the bolt to handle the stress, not the joint faces
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  separating. Right.
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  You don't want the joint Oing oen.
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  Recisely, but here's a critical detail that often gets missed.
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  Fasteners aren't static. Once you tighten them they relax
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  retty raidly. Actually, right after you
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  tighten them, that initial preload you work so hard to
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  achieve it decreases. It just fades.
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  How much? It can be significant.
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  The sources cited studies showing this relaxation, this
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  load loss, can vary wildly. In one case, it ranged from just
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  5% all the way up to 43% of the initial tension wait. 43% That's
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  almost half the clamping force just disappearing due to
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  relaxation. Potentially, yeah, if you don't
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  account for. It wow, OK, that single
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  statistic makes understanding bolt relaxation absolutely
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  crucial. You have to design that margin
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  in. You absolutely do.
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  It highlights the need for precision not just in
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  manufacturing, but in assembly and design calculations too.
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  OK, final stretch quality control.
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  We've designed it, built it, fastened it.
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  Now we check it. Let's quickly clarify 2 terms.
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  People sometimes mix up tolerance and allowance.
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  Good idea. They sound similar but mean
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  different things. Tolerance is the total amount of
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  variation allowed in a specific dimension.
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  It's the plus or minus range. The designer gives the machinist
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  the acceptable wiggle room, basically.
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  OK, tolerance is allowable error on one part.
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  What's allowance? Allowance is about mating parts.
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  It's the minimum clearance space or maximum interference intended
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  between two parts when they fit together.
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  It defines the tightest possible fit the design permits.
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  So allowance is about the gap between parts.
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  God. Right now, when you're actually
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  monitoring production quality on the floor, use capability
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  limits, and these are usually calculated as the process
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  average X bar ±3 standard deviations, 3 Sigma.
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  X bar ±3 3 Sigma, the classic process capability measure.
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  Exactly, and what that tells you is that your process running
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  normally can produce about 99.73% of its output naturally
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  within those limits. The rule of thumb is simple.
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  If the designers specified tolerance limits are tighter
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  than the machines natural capability limits, the plus -3
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  Sigma range, then you can't rely on statistics.
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  You need 100% inspection for that feature to ensure every
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  part meets the spec. Makes sense if the spec is
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  tighter than what the process can reliably hold.
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  You have to check every single one.
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  OK, so this whole journey from UMC targets DFM and a
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  classification planning, advanced processes fast and
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  details quality checks. It all seems to point towards
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  this bigger vision of integration, right?
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  Computer integrated manufacturing.
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  CIM. Absolutely, that's the ultimate
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  goal for many. CIM aims to link all these
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  islands together, integrating things like CAD and Cam,
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  numerical control machines, robotics using group technology
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  for efficiency, automated material handling, all
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  coordinated ideally by a central computer controlled system
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  working in a hierarchy. Connecting all the dots.
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  Connecting all the dots and maybe a final thought to tie it
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  all together. The real key to being truly
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  competitive in manufacturing today goes back to the very
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  beginning. Recognizing that the initial
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  decision to simplify the part count way back in that DFM and a
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  stage that single choice echoes through everything else.
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  It directly impacts the UMC calculation because material
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  cost drops. It minimizes set up time on your
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  NC machines because you handle fewer unique parts.
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  It inherently reduces the opportunities for defects that
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  quality control has to catch. So simplification isn't just one
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  step, it's the engine driving efficiency across the entire
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  system. That's it exactly.
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  Start simple, stay efficient. To my fellow design junkies,
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  another session in the books. Thanks for grinding with me and
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  sharpening your engineering edge one problem at a time.
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  This show exists because there are people out there who
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  actually care about building things that work, who chase
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  precision, who think in port curves and tolerances instead of
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  trends. If you're one of them, you're in
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  the right place.