Are you constantly struggling to meet due dates? The more you try to accelerate and push jobs into production the more delays get high? Queues and buffer are always full, but production yield and throughput are not satisfactory? Lead Times seems to be unpredictable and answering to customers’ enquiries is cumbersome? If the answer, to one or all these questions, is yes, do not feel bewildered, this situation is common, but a straightforward solution exists. So, keeps on reading, goods news are here to come.
Consider a sink. You can control the inlet flow by adjusting a faucet, but you cannot control the outlet flow, as it depends on the section of the drain, which is fixed. So, if the input flow is higher than the maximum outlet, the level of the water in the sink will rise, but the output flow will remain constant. Your manufacturing systems behaves, exactly, in the same way. The input flow represents the jobs, the level of the sink is the Work-In-Process, the output flow is the throughput rate, and the section of the drain is the bottleneck. An input flow greater than the output flow is thus meaningless, but certainly we cannot operate without a minimum level of water in the sink. If so, any variation in the input rate would stop the output flow, which is definitely something that you must avoid.
So, moving back to a manufacturing system, what you need to do is simple: first, you have to detect the bottleneck(s) and, next, you must control the input flow, to assure that the bottleneck is always fed. If so, your production will flow smoothly, and you’ll be amazed at how much easier planning will be.
Ok, enough with theory, let’s turn operational. The key point is that, to control WIP you need to measure and visualize it, and a possible way to do so is to generate “cards” any time a job is released or moved in the shop floor. Cards, either physical or electronic, signal what is being processed and where, and may be of different colors to convey additional information such as the job’s routing, the customer and so on. Anyhow, the key point is that the number of cards that can be simultaneously used is fixed, as this threshold defines the maximum admittable WIP level. If all cards are used no other jobs can be released, as they would only increase queues and times, without positively affecting the throughput rate.
The set of alternative card-based solutions is wide, ranging from the basic 2-Kanbans, perfect in case of low variety system with stable demand, to the more complex POLCA system, suited for job shops with variegated demand. Unfortunately, simple rules for proper selection and dimensioning do not exist. But do not be puzzled, we can support you in this process, from the system conceptualization to its final deployment in the shop floor. Indeed we can: