Month: January 2022

Waste and OEE

It doesn’t matter where I go – scrap is the form of waste most prominent in the minds of manufacturing companies.  To my knowledge, steel is the material most roll formed in North America and around the world.  In many companies the price of steel is a constant concern, because it can fluctuate wildly and it’s frequently the single biggest cost when it comes to calculating margin.  I’ve seen companies make more money buying and re-selling coils than they could by turning that coil into finished product and selling it to their customers – at least when the market was particularly volatile.

I think the main reason companies focus on scrap is because it’s right there.  You can see it, touch it, smell it, and weigh it.  There’s a problem with the focus on scrap, because its usually not the biggest contributor to waste.  Scrap is usually the third-biggest contributor to waste.

It’s important to note that I’m not saying you should ignore scrap or that you shouldn’t care about it.  You should.  In most roll forming applications, it should be relatively easy to hold scrap percentage to 0.5% or less.  If you’re close to that value on your production lines, then you’re doing pretty well.

Speed-loss is usually a bigger contributor to waste than scrap.  And the most common form of waste is downtime.  If you have a lot of excess capacity in your plants, then downtime waste might not be an important concern for your company.  If you’ve captured a lot of the market and your customers are saturated so that your Sales function cannot sell the capacity you already have, then you’re doing very well and this blog post might not be for you.  If your company isn’t sitting pretty at the top of the heap, or if you’re struggling to find capacity without buying new equipment then you should continue reading.

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Continuous Press and Servo Feed Calculations

If you’re setting up a punching operation with pneumatic or hydraulic presses, the servo feeds are relatively simple, because you have full control over the presses and when they’re fired.  Mechanical presses running in continuous require a balance of timing and accelerations.  If your timing is off, you could break tooling or miss your target.  If your accelerations are off, the feed rolls could slip and induce a variance or even leave marks on the part.

Timing is directly impacted by production rate and press angle.  The higher the rate, the faster the press has to run.  The faster the press runs, the more acceleration you need to make servo moves.  Ultimately, production rate is capped by the capability of the press motor/drive and the maximum acceleration rate of the servo motor.

The most efficient way to dial in a particular production line is to setup the servo to handle the most extreme production rate and minimize setup changes for less-demanding applications.  The demands of production – balancing speed, quality, wear, and cost – might require a unique set of parameters for every job a line might run.  This post will walk through the math of using press speed and part/punch distance to calculate the speeds and accelerations required from the servo.

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Press Consistency

Unless you’re using a servo, press consistency is crucial to length accuracy in flying punch and cut applications.  Without servo positioning, timing variances in the press will directly relate to length tolerance error, and the faster you run the line, the worse even small timing variances will affect length.

For instance, if you’re running a roll former at 400 fpm, that’s 80 ips.  At that speed a timing variance as small as ±0.003 s will cause a total length variance of ±0.24″!

Even the best 24 VDC relays have a switching time of ± 0.003 s.  Thus, running a press fire output through an electro-mechanical relay could easily induce a total length variance of almost 0.5″.  That assumes you have no encoder tracking issues.

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We Don’t Know What Our Margins Are – How Do We Take Decisions?

During my time in the Roll Forming Industry, I have been in dozens of companies across the United States and around the world.  Frequently, I have found myself in conference rooms with C-level groups trying to implement a new ERP system.  Since I worked for a company that made MRP scheduling software for manufacturers, we were a critical vendor and typically brought in early in the process to consult.

In these meetings, I have heard the same conversation over-and-over.  The first time I heard it, I was shocked, but since then I realize most companies must operate the same way.  It usually comes from someone in Accounting, and it goes something like this, “We don’t even look at the paperwork that comes off the floor anymore.  It’s usually meaningless.  Every time we’ve tried to reconcile what the Operators write down with what we measure coming off the line, it’s either wildly inaccurate, or there’s so much error it doesn’t matter.  We know what we spent last month to purchase things.  We know what we shipped out.  The rest must be waste.  We just have no idea where all the waste is coming from.”

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