Kanban Types-3 : POLCA
Hello colleagues and welcome to the second part of the Weekly Lean Series in Week-26. Before we start I want to thank all of you who are interested in a lean way of excellence and continuous improvement. I hope to achieve a faster circulation of ideas and information with our new linked-in group , Towards Lean Enterprise .
"Towards Lean Enterprise" linked-in group aims to be a pool of professionals who are joining together to network, to learn, to develop business, to discuss jobs & careers, to talk about certification opportunities, to participate in best practice sharing and maintain and build new relationships. All content sharing is free and not bound to review and feel free to share your ideas helping to build such a network.
Today's topic is actually about another Kanban type, namely POLCA. The pronunciation of the word reminds me of the Czech polka dance and actually this is a little bit of a nice coincidence since POLCA is an acronym for Paired-cell Overlapping Loops of Cards with Authorization; meaning a paired control over multiple processes just like the pairs in Polka control each other :)
Suppose we have got a shop floor focused on cellular manufacturing of parts. This can also be a job shop consisting of different machines or processes. As many of us who have a prior experience will remember ,in such manufacturing environments things can go quite messy due to production happenstances, misinformation , cycle time differences and other issues; causing piles of inventory and decreased throughput. Thus an automatic inter communication of different stations can support the ongoing operation and reduce waste.
This is where POLCA comes to play. As a start Polca is not a traditional Kanban type and this is well reflected in Polca cards. The most important information on these cards are Source and Destination processes. We also add both the specific card information and the deck info of the same type of cards and also support this via barcodes or other digital tracking technologies. It is a very good idea to be able to track such information in your shop floor with the help of a software and this can generate valuable information for future use in PDCA cycle.
As an example here, our shop floor is dedicated to manufacture three different parts, namely Part-A , B and C. Each of these parts needs to follow a different production route to become the final product. For instance part-A follows the route of 1-2-5-8 while B has 7-8-5-6 as a route. At each route the part transports in between pairs of cells also called loops and if the necessary part does not move to next step you cannot continue to finalize the product. Also if you dedicate your resources to WIP that is unnecessary you will again end up with waste.
A key difference of Polca method is that it is a hybrid of both push and pull strategies. Polca cards by itself cannot manage the operation. The additional component is released production orders. These orders sometimes can be generated manually but generally comes from an ERP system. Hence an operator in a Polca governed shop floor has to take two conditions into consideration to process a part. If either of these conditions are not met, parts cannot be processed;
- Is there an order released to the cell with a current or past date of processing ?
- Is there a Polca card available releasing the production ?
Let's explore the logic following an order for Part-A. When orders are released, station-1 starts to manufacture the part since both release conditions are met. When the processing is finished, the part is transferred via M1-M2 polca card to station-2. Upon part arrival, the operator checks whether there is a released order to M2 with a current or past processing date . If there is, he/she will look for an available Polca card. Finding the M2-M5 card, the processing starts at M2 and when it is finished the M1-M2 card is returned back to M1 while the part moves to M5 with M2-M5.
In your shop floor there can be parts with similar routes. In our example, the route was 1-2-5 8 for part-A .Suppose another part has a route as 1-2-3-7. So when the first process ends the part at M2 can be routed either to M3 via M2-M3 or M5 via M2-M5 if there is a released order and an available Polca. Here, apart from the order lists and dates available to the work center, there is no other priority rule defined, it simply shows that the WIP processed by first cell is demanded by multiple flows and parts need to be manufactured as capacity allows it.
The production orders and how they are scheduled is also of high importance. The classic method which many ERP packages have is backwards planning of the orders in accordance with the demanded delivery date and capacity of the processes in the production route of the part. The routes and capacities of work centers are defined in the system and once an order is released for a part, all the production orders for the cells are also released. These orders should be accessible by the operators in the cells either with a digital solution or a very structured visual management tool.
So how many Polca cards are needed ? In our example we had there different parts and with their route information we can tabulate the manufacturing loops that run in our shop floor. Once we have identified them we can check the demand information that drives these loops and cross checking with capacity we can calculate the lead times (LT) in between these loops. However it is much better to have historical data available or data generated by a digital tracking solution for LT calculation. With such information lead times can be more precisely defined. In addition the LT should also include the time necessary to return the Polca card to the original cell. Also a safety (SS) should be added to ensure the smooth flow of the operation. The daily demand (DD) is already known so the formula (LT + SS) X DD will give the necessary amount of cards for each loop . In our example there are 24 Polca card requirements for the shop floor.
Polca is a very interesting method as it combines push and pull strategies in a unique way. Although things can be a little more complicated, once the setting is done correctly, it can work smoothly controlling WIP and ensuring demand orientation.
This is the final part of our mini Kanban series , hope you enjoyed all three and see you next time in another part of the Weekly Lean Series :)
