Some Places where Lean Manufacturing and Industrial Controls Intersect
Lean Manufacturing is a great way to sustain and revive Made in the USA. This month’s newsletter will focus on places where Lean concepts and industrial controls meet – specifically Andon Indicators and Poka Yoke. There is a Lean saying – ‘take care of the pennies and the dollars will flow’. Ben Franklin, an early efficiency innovator said the following about avoiding unnecessary cost: “A penny saved is two pence clear. A pin a day is a groat a year. Save and have.”.
Jeffrey K. Liker in ‘The Toyota Way’ writes about andon indicators – ‘bring problems to the surface, make them visible, and go to work immediately on countermeasures’. There is great value to an andon indicator in a production environment where the cycle time is short – where a lot of good and bad parts can be produced in a short period. The entire staff must be aware of problems and have the proper training and authority to quickly resolve them. An andon indicator can be a large marquee display, prominently positioned in the production area or in the maintenance shop. It can display information for one or several machines. Items to display include actual shift production vs. target shift production, machine warnings, machine failures, number of bad parts produced, raw material delivery required, rework or scrap bin status, low compressed air pressure, remaining run-time until service required, etc… Or an andon indicator can simply be a well-positioned 4-lite stack. ‘Green’ means the machine is running, ‘Red’ means it is faulted or shutdown, ‘Blue’ means that service is due, and ‘Yellow’ means that raw material is low. Andon indicators bring transparency and give all workers timely and highly visual information to help them be successful. These indicators are usually connected to a PLC containing some programming to make them perform as planned. For most facilities, costs to install andon indicators are very cost justifiable.
Poka Yoke (aka Fool Proofing)
Poka Yoke is Japanese for mistake proof. An example is the use of different electronic connectors to avoid them being plugged into the wrong place on a device – which could result in damage. Poka Yoke also has a place in automated manufacturing. There are ‘warning poka yokes’ that alert prior to a mistake and ‘control poka yokes’ that prevent a mistake from happening. For example, an automated machine has an air-operated bad-part-reject mechanism. A ‘warning poka yoke’ would indicate that air pressure is too low or off; a ‘control poka yoke’ would prevent the machine from running under this condition. Some other examples of poka yokes are as follows. After completing a secondary machining operation, an operator is required to press two different bushings into the part. Photo-switches and a beacon could be installed to indicate whether the operator reached into both bins to retrieve each bushing (and prevent an incomplete assembly). Another example could be a laser gage that measures part height or a scale that measures part weight. The measurements are automatically fed into the machine controls. Logic would shut down the machine per defined SPC parameters.
Thunderstorm Season is Here!
Some machines are will shut down from the slightest power flicker during a T-storm. A machine tool that stops in the middle of a cut can damage the tool, the part, or the machine. Or the loss of an air compressor can shut down a production line. In many applications, a properly specified UPS (uninterruptable power supply) installed on the control circuit can ride out the power dips and keep the machinery running.