When we intend to implement a lean manufacturing or lean manufacturing system in our processes, it is common to face the restriction of the generation of safety inventories, either product in transit or finished product, as the effect of two main causes, these are sudden breakdowns, and time lost in enlistment processes due to possible reference changes.
In the case of enlistment or preparation time, the traditional solution that seeks to mitigate its impact is the planning of large production batches, minimizing the number of changes, but affecting the flexibility of production, and managing collaterally to increase inventory levels.
What is the SMED technique?
One of the most successful techniques in reducing time lost per preparation is the SMED (Single Minute Exchange Die) methodology. This methodology developed by Shigeo Shingo is of Japanese origin, and was first implemented for Toyota in the 1970s. The hypothesis underlying the SMED implies that a reduction in preparation times allows us to work with smaller batches, i.e. shorter manufacturing times, resulting in a substantial improvement in delivery times and product levels in transit.
The implementation of the SMED method consists in the development of four phases:
1. Separate internal operations from external operations
This first phase involves differentiating between preparation with the stopped machine (internal preparation) and preparation with the machine in operation (external preparation). In the first case, reference is made to those operations that inevitably require the machine to be stopped. The second case refers to the operations that can be performed with the machine running. The first step is to differentiate this type of operations, that is, when the machine is stopped, no external preparation operation should be performed. In operations with the stopped machine, only the removal and placement of the particular elements of each product (moulds, dies, adjustments etc.) must be carried out. A support activity that can support this phase is the realization of a video, which will help us to separate these operations and see the real time of change, as well as the time improvements.
For example, the preparation or enlistment of Team A involves the realization of activities 1, 2, and 3; however, after the separation phase it was identified that activity 3 corresponds to an external cleaning, which can be performed with the equipment in operation, why was it included in the preparation? It is normal that this question has no answer, or that its answer is: Because it has always been done like this.
From now on, when performing only activities 1 and 2, we will be able to observe an improvement in the preparation time of Team A.
2. Convert internal operations to external
It is clear that this activity should be carried out as long as possible. However, the conversion of internal to external activities is not limited in any way to preparation activities on the machine when the machine is operating, since there are countless activities that constitute a conversion of internal to external activities without safety commitments, such as pre-heating of injection molds, prior to being mounted on the machine. The SMED method has been successfully applied in Formula 1, specifically in the well-known “Pit stop”, and at these stops we can see great application of this phase of the method, such as the presets that have the elements of fastening of the tires, this constitutes the conversion of an internal activity into an external one.
3. Organizing external operations
This phase is based on the arrangement of all tools and materials (arrays, fasteners, etc.) that support external operations. These elements must be arranged next to the machine after any repair of the components to be entered. It is usual that at this stage some type of investment must be made in maintenance, storage, food or transport assets. For example, in the enlistment of injection molds, a critical activity is the transport of these, which is why a specialized crane or forklift with specific adjustments is a very good tool, also, the place where the molds are stored has a corollary effect on the distance traveled (involves time) to make a possible change. To have a clear view of this phase, it is recommended to observe the arrangement of the tools in a “pit stop”.
4. Reduce the time of internal operations
This phase is basically to minimize adjustment processes. This type of process is considered to be between 50% and 70% of internal preparation operations. One of the best reduction methods is the standardization of the characteristics of the moving elements of the machines. Another key aspect in this phase goes through the parameterization and adjustment times to achieve the quality of the product, in this case, we should focus on setting a standard of the operations of the tooling change process that directly relates to the quality parameters. In this case, engineering improvements are frequently used to obtain such results.
Example of applying the SMED method
The following example was drawn from the “Production and Logistics” Innovation Guide to illustrate the actual application of the SMED method:
Gallina Blanca Purina (now Affinity Petfoods) established the SMED systematic methodology in the Monjos plant for the change of granulator matrices to produce feed and extruders to produce Petfoods. The change time of the granulator matrices increased from 58 to 23.5 minutes, i.e. it was halved.
In this way, more than twice as many different products could be produced at the same time and the flexibility of the installation was thus doubled.