Visual Management

Our eyes are heavily linked to the thought processes of our brains

Our eyes are heavily linked to the thought
processes of our brains


Seeing is believing. We rely heavily on sight to guide our actions. Accordingly, seeing something for ourselves is a powerful way of having us believe it. When we plan systems to control manufacturing activity, the ones that use things that we can see to guide our decisions work the best. This week I was attempting to solve an accuracy deficiency on a high RPM vertical CNC machining center. This machine is used to cut graphite to make EDM electrodes for mold making. The CAD/CAM cutter path software guided shapes, cut using diamond tipped tools, need to be accurate to better than 0.001 inch (0.04mm) on all surfaces. This shape accuracy is needed to obtain the taper needed to eject parts from the mold. 0.001 inch is a tiny distance that is difficult to see and measure. A experimental method that I call a 6 time repeat study is very effective adding visibility to the task. In this case, we machined a test shape using the CNC. After the graphite was cut we used a yellow paint marker to color all surfaces that were machined. The exact same cutting program was run again. Low and behold, one face showed uncut and completely yellow.
A painted test block shows the backlash in the X CNC axis

A painted test block shows the backlash in the X CNC axis


My machinist could not understand why I called the test a 6 time repeat study. We had only run the program twice. I indicated that once the machine flunks it is no longer necessary to run the remaining passes. Had the part been black on all sides after the first rerun we would have run the program five more times painting in between every cut to confirm that the machine consistently cuts accurately. I had originally thought that my problem was a worn spindle bearing due to the 15000 RPM cut. The actual test part only has a hint of the zebra stripe that a worn spindle bearing creates. The 6 time repeat test for metal cutting CNC machines is similar. I machine a precision bore as the test. A black Sharpy is used for coloring the bored hole between each repeat.

Segeo Shingo correctly taught that every manufacturing operation needs to leave a visual indication that it has been begun. He was careful to distinguish visually confirming that an operation has been begun from inspecting that it has been properly performed. His experience matches mine. For every part that is made with an operation that has been improperly performed, 9 parts are made with that same operation missed. A good example is a rough boring operation. After the part is finished machined there is no way to visually tell that the roughing bore (or drill) actually happened. A missed rough bore is a problem because the only way to achieve the desired roundness in a precision bore is to set the rough cut size so that it only leaves 0.010 inch (.4 mm) stock for the final cut. I am happy to report that the advent of CNC machining centers gives us a few more options. One of my favorite tools is to use a helix orbit to add a counter bore. I make this cut using the roughing cutter after it finishes its bore so that I can either gage or visually confirm that the cutter has not chipped. (In the pictured example, the helixed counterbore using the robust roughing cutters also protected the fragile finishing cutter from the weld located at the start of the bore.)

Adding a CNC helixed counter bore made by the roughing tool makes visually confirmation possible

Adding a CNC helixed counter bore made by the roughing tool makes visual confirmation possible


A classic example of a manufacturing operation that leaves no visual witness is bolt torquing. This becomes a problem when multiple bolts are needed to secure the joint. On a excavator, the turret is secured with 24 to 36 bolts depending on size. If one of these bolts is not tight, the operation of the unit will work it loose and zipper apart the entire joint. The repair, in one years time, is a $20,000 warranty cost. Confirmation of proper bolt torquing is further complicated by the locktite used to seal rust out of the thread. Checking bolt torque a day later only confirms that the locktite is working. This is where Shingo’s visual management concept fits in. Every operation needs to leave a visual witness that it has occurred. This warranty cost was eliminated by redesigning the bolt tightening wrench so that it left a mark when it was used to tighten a bolt. It became possible to visually see walking by that every bolt was tightened.
Final torque wrenches should leave a visual mark when they are used

Final torque wrenches should leave a visual mark when they are used


Not every application can tolerate a scratch in the paint. I have also modified open end wrenches and sockets so that they leave an imprint on the bolt head or nut when the torquing operation is performed.

Feedback

It is easier to hit the target when you employ feedback

It is easier to hit the target when you employ feedback

When I first embarked on a campaign to knock seconds out of my CNC cycle times, a few eyebrows were raised. The doubters lacked the experience to realize that just about every quality deficiency or design change would add task steps and cutting time to the CNC cycle. Multi million dollar CNC machining centers usually do not have spare capacity. The direct feed back made this a good starting Kaizen project to tackle with my machining team. Our successful effort was just in time to support the next generation of models which included additional machined features. Next on the Kaizen plate was an attack on cutting tool usage. Even though we utilized the excellent feedback loop of a run chart, the actual life of the cutting edge was poor. Fortunately introduction of TiALN coating of the carbide inserts eliminated the size drift of the bored hole.
Surface technology advances dramatically increase cutter life

Surface technology advances dramatically increase cutter life

We were happy about the resultant $250,000 annual reduction in cutting tool purchases and the saving in down time related to cutting edge replacement, but we lost our run chart feedback loop. The cutter held bore size until it chipped. We needed a new feed back loop. In the short term we switched to 100% guaging of every part. When an edge chipped we replaced, reset and rebored before removal of the part from the fixture. This proved cumbersome. Our team wanted to automate measurement using the CNC and the probe. Combo cutters were designed and purchased to knock more seconds out of the cycles. We had switched to through spindle oil mist lubricant to save part washing and smell. More feedback required. An artifact was added to the fixture with a reference bore size so that the probe could be calibrated to measure the part at the current ambient temperature. We had lost the temperature stability that comes with flood coolant. We discovered that it was not enough to detect the wear of the finishing cutter. A chipped roughing cutter also spoiled the bore roundness. This is especially true when it is also necessary to cut through weld. Using good visual management feedback practice the roughing cutter was helix orbitted to replace the lead in chamfer with a counterbore.
Counterbores made using the rougher enable visual management of cutter chipping

Counterbores made using the rougher enable visual management of cutter chipping

Finally we closed the loop. The probed rough and finish diameter measurement presented the correct tool for cutting edge swap immediately upon encountering a worn insert. Modern machined accuracy is always the result of properly planned feedback

Kludge

Treasure is camouflaged in the digital jungle

Treasure is camouflaged in the digital jungle

kludge
[klooj]
noun – Computer Slang
1. a software or hardware configuration that, while inelegant, inefficient, clumsy, or patched together, succeeds in solving a specific problem or performing a particular task.

*definition from Dictionary.com

Whoever came up with this term must have been assigned to marry legacy IoT (Internet of Things) digital controls. Lots of ones and zeros show on the logic analyzer, with obscure or forgotten protocols for interpreting what they mean. In the arms race to stay ahead of the newest start-up, many of the companies who built the previous generation equipment with embedded internet communication no longer exist. However, even the first internet connected device is still a part of our IoT infrastructure. At the blinding communication speed of two bits per week, the transmitter shuts off the water feed pump every Sunday when the water tower is full.

We take running water out of our taps for granted

We take running water out of our taps for granted

I used to worry about terrorists gaining control of our infrastructure using the internet. It is theoretically possible to inflict some serious damage and injury. My concern was based on the fact that early IoT devices have very little access protection. Now that I have integrated some legacy systems I realize the lack of standardization will be our saving grace. It is next to impossible to apply experimentally the right combination of ones and zeros without a guide.
I was discussing the evolution of CNC position encoders with the technician who was upgrading the control on one of our CNC machining centers. In mold making, the cutter path software that converts 3D models (3D printing) into physical shapes, originally used a layer by layer contour line approach. We would like to use the more modern climb milling software because it eliminates the contour lines. (and the hours of hand draw polishing to remove them) The upgraded control will position X Y and Z at high speed instead of just X and Y which is all the contour line method requires. The embedded computer in each axis position encoder sends a high speed serial data stream including error correcting bits back to the control. This is a far cry from the first GE (now Fanuc) CNC control retrofitted to a Buffalo milling machine that I first programmed – yes, there is still a lot of legacy stuff in operation out there. This control also had position encoders without the local embedded computer. It only lost about 2500 count per shift (about 1/4 inch of position) and it came with a switch to shut off the Z axis so that you did not mill too deep. We evolved through resolvers and glass scales and back to a smart encoder. Don’t expect to do “big data” analysis of this type of IoT real time data stream. Bad things happen if the transmission of position is interrupted.
Who will bridge the genetation gap?

Who will bridge the genetation gap?


On the hardware side it is very convenient to connect the 10/100 port of my laptop to the ethernet switch. In my latest control I added ethernet cables so that it can be used in convenient locations without exposing it to the open internet. The generation gap became painfully obvious on the software side. The desire of the Windows operating system coders to download daily changes exceeds the ability of any custom low volume application software creator to keep up. We are finding that the latest version of custom application software is obsolete before it is sold. In the short term we will keep the systems synchronized by isolating them from the internet once we solve the inter-connectivity issues. This solution does not work for every IoT software mismatch issue. In my mileage trakker www.mileagetrakker.com IoT connected car application, it is necessary to have a staff who continuously monitors the functionality of the links and keeps up with interfacing with each model and car maker as they evolve. This becomes part of the monthly charge which enables our trakkers to obtain a couple thousand dollars in annual savings. Many of my mileage trakker competitors have gone out of business because they got caught continuously rewriting their cell phone based code in order to keep up with a rapidly changing software platform.
The IoT is evolving like the power grid. New IoT applications emerge based on the cost and performance drivers. Each implementer chooses a variation that matches the application without regard for the broader inter-connectivity issues. This will generate employment for the people with the STEM skills to link users to the vast data pool.

3D Printing – An Invisible Revolution

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3D PRINTING, a current hot news item, is actually the result of a gradual, almost invisible revolution in mold making which has finally reached a transformative point. The point where it can revolutionize the manufacture of equipment, like stock chasers, … Continue reading