The essence of the SMED philosophy is to eliminate the concept of a manufacturing batch while minimizing machine setup time. For companies that want to increase their flexibility and at the same time reduce their stock levels, it is critical to minimize the times for both tool changes and preparations.
Introduction
This need in turn is inserted within the philosophy of reducing time or maximum speed, which today invades everything, from the capacity for quick attention, to the reduction of response times, shorter periods from research and design to the start of the production and placing of the product on the market, and the reduction in production times. Time is worth money, and every day this becomes more important both from the point of view of customer satisfaction, as well as from the cost and competitive capacity of the company.
Eliminate the concept of a manufacturing batch while minimizing the preparation time for machines and materials, this is in essence the SMED philosophy. Today it is committed not only to reduce preparation times to a minimum, but also repair and maintenance times.
In the late 1960s Toyota took more than four hours to change models on an 800-ton stamping press, when its Volkswagen equivalent required just two hours. The engineer Shigeo Shingo before a research activity assigned by the director of Toyota, Mr. Ohno, (aimed at strengthening and making the Just in Time Production System feasible, with the clear and precise objective of reducing waiting times and levels of inventories of both products in process and finished products (both being cataloged among the seven classic changes), proceeds to develop a system that made it possible to reduce the time indicated above to just three minutes.
The implementation of the SMED had begun, thus overcoming one of the greatest obstacles that Toyota had at that time to implement “just-in-time” production, a system that would become famous throughout the world as the Toyota Production System (TPS).
When a company has worked on reducing the setup time of a particular machine for several years, it finds that it is possible to radically reduce the changeover time from several dozen hours to less than ten. Later and for the same machine, times of tens of minutes can be achieved. A little later you can talk about change times of less than ten minutes. Some companies have even achieved the end goal: changes at the first touch, where time is almost equal to zero. No company can afford to stop working on reducing turnaround times until reaching this goal. It is not about analyzing whether or not it is possible, but about seeing what needs to be done and how long it will take to achieve it.
Not only Toyota serves as an example, we can also mention the company Kodak (USA) who in 1984 managed to reduce the changeover time from approximately two hours to thirty minutes in terms of plastic injection press; a few months later, it was reduced again to six minutes.
Although there are a large number of techniques aimed at increasing or improving productivity, the reduction in preparation times deserves special consideration and is important for three reasons:
- When the turnaround time is high, the production batches are large and, therefore, the investment in inventory is high. When changeover time is negligible, the required quantity can be produced daily, almost totally eliminating the need to invest in inventory. Quick and simple changeover methods eliminate the possibility of errors in tool and fixture settings. New shifting methods substantially reduce defects and eliminate the need for inspections. Quick shifting can increase machine capacity. If the machines are running seven days a week, 24 hours a day, one option to have more capacity, without buying new machines, is to reduce your changeover and setup time.
One of the most important advantages of reducing set-up times to single digits is that the company can go from working against warehouse to manufacturing to order. Since investment in finished product inventory is the greatest asset for some factories, its conversion into cash can be used to finance other investments or reduce debt.
The SMED is undoubtedly a highly innovative concept generated by the Japanese within the field of industrial engineering. It should be noted that in Japanese companies, the reduction of preparation times falls not only on the engineering staff, but also on the Quality Control Circles (QC).
It is worth mentioning that currently such a work philosophy is not only applied in the changes of tools and preparation of machines and equipment, but also in the preparation and set-up of operating rooms, preparation of air shipments, care of Formula One cars and others. activities related to services.
Methodology for changing methods
As in the case of other working methods, various techniques are used, being them:
- Pareto analysis: designed to differentiate the trivial many from the vital few. In other words, focus on those few activities that absorb most of the change and / or preparation time. The six classic questions: What? - How? - Where? - Who? - When? and the respective Why ?, corresponding to each of the respective answers, with the aim of eliminating the unnecessary, combining or reordering the tasks and simplifying them. The five Why? successive: for the purpose of detecting possibilities for change, simplification or elimination of tasks included in the process of changing tools or preparing machines or equipment. This technique is fundamentally focused on finding the root cause,that is, in the factors that in this specific case determine the preparation or change of tools times.
Fundamental concepts of SMED
For the purpose of reducing preparation times, four key concepts must be taken into consideration, consisting of:
- Separate the internal preparation from the external one. Internal preparation should be understood as all those activities for which it is necessary to stop the machine or equipment. While the external includes all those activities that can be carried out while the machine is in operation, convert as much as possible of the internal preparation into external preparation. In such a way, many activities that must in principle be carried out with the machine stopped can be advanced while it is in operation. Example: The pressure casting machine can be preheated using the excess heat from the oven that serves this machine. This means that the test shot to heat the metal mold of the machine can be eliminated. Elimination of adjustment processes.Adjustment activities can represent between 50 and 70 percent of total internal activities. For this reason, it is important and imperative to systematically reduce the setting time in order to reduce the total preparation time. The key is not to reduce the setting, but to 'eliminate' it through creative thinking (eg, adjusting the tools in one motion - one touch up). Eliminate the setup phase itself. In order to dispense with preparation entirely, two criteria can be adopted. The first is to use a uniform product design or use the same part for different products; and the second approach is to produce the different parts at the same time. The latter can be achieved by two methods.The first method is the set system. For example, on the same die, two different shapes are carved. The second method consists of punching the different pieces in parallel, using several lower-cost machines.
Application techniques
Six techniques are used in the SMED to apply the four concepts previously exposed.
Technique No. 1: Standardize external preparation activities. The operations of preparation of the molds, tools and materials must become habitual and standardized procedures. Such standardized operations should be recorded in writing and posted on the wall so that operators can view them. Later, the workers must receive the corresponding training to master them.
Technique No. 2: Standardize only the necessary parts of the machine. If the size and shape of all dies are fully standardized, the setup time will be greatly reduced. But since this is expensive, it is advisable to standardize only the part of the function necessary for the preparations.
Technique No. 3: Use a quick fixation element. Although the most widespread fastening element is the bolt, given that it fastens in the last turn of the nut and can loosen at the first turn, various elements have been devised that allow a more effective and efficient fastening. Such items include the use of the pear-shaped hole, the U-shaped washer, and the grooved nut and bolt.
Technique No. 4: Use a complementary tool. It takes a long time to attach a die or jaws directly to the punch press or lathe chuck. Consequently, the die or jaws must be attached to a complementary tool in the external preparation phase, and then in the internal preparation phase this tool can be attached to the machine almost instantly. To make this feasible, it is necessary to standardize the complementary tools. Mention may be made, as an example of this technique, the mobile rotary table.
Technique No. 5: Make use of parallel operations. A large die press or large die casting machine will have many clamping positions on all four sides. The setup operations of such machines will be time consuming for the operator. But if two-person parallel operations are applied to such machines, useless movements can be eliminated and thus setup time reduced.
Technique No. 6: Use of a mechanical preparation system. When setting the die, use could be made of hydraulic or pneumatic systems for simultaneous clamping of several positions in a matter of seconds. On the other hand, the heights of the dies in a punch press could be adjusted by an electronic mechanism.
Most common problems when making tool changes or preparations
When setup activities take too long or setup time varies considerably, the following issues or issues may be occurring:
- Preparation completion uncertain Preparation procedure not standardized Procedure not properly observed Materials, tools and templates are not ready prior to start of preparation operations Docking and separation activities They last too long The number of adjustment operations is high The preparation activities have not been adequately evaluated Non-random variations in the preparation times of the machines.
These obstacles can and should be overcome through daily investigation and repeated questioning of preparedness conditions in the workplace.
Importance of the Five "S" in the application of SMED
The activities of Organization-Order-Cleaning-Standardization and Discipline are essential and fundamental for a correct and optimal implementation of the SMED system.
Being able to quickly find the tools, having all the equipment and workplace in a clean state, and having visual elements that allow the best adjustment, are benefits that the systematic application of the Five "S" brings with it.
Procedures to improve preparedness
In addition to video recordings and time and motion studies related to setup activities, there are four more procedures for improvement. The first is to separate the internal preparation from the external preparation. The second, in reducing internal preparation time by improving operations. The third, to promote a further reduction in internal preparation time by improving the team. And, the fourth is the challenge of reducing it to zero.
Phase 1: Differentiation of external and internal preparation. By internal preparation, as already stated above, all those activities are included that in order to carry them out requires the machine to stop. While the external preparation refers to the activities that can be carried out while the machine works. The main objective of this phase is to separate the internal preparation from the external preparation, and convert as much of the internal preparation into external preparation as possible. To convert internal preparation into external preparation and reduce the time of the latter, the following four points are essential:
- Pre-prepare templates, tools, dies and materials Maintain dies in good operating condition (TPM) Create tables of operations for external preparation Maintain good order and cleanliness in the storage area of removed templates and dies (Five "S").
The most important of these four points is the last one: keep the storage area for tools, templates and dies clean and tidy. If tools are stored haphazardly in a toolbox, workers will waste time searching for the ones they need; it is the typical useless operation that does not create additional value.
Phase 2: Internal preparations that cannot be converted to external should be subject to continuous improvement and control. For this purpose, the following points are considered key for their continuous improvement:
- Keep tools and dies storage areas clean and orderly (Five "S"). Monitor the effects of changes introduced in the sequence of operations. Monitor the personnel needs for each operation. Monitor the need for each operation.
Continuous examination of the points described above will reveal opportunities for improvement.
Phase 3: Equipment improvement. All measures taken to reduce set-up times have hitherto been related to operations or activities. The next strategy focuses on team improvement. Here are some ways to make this feasible.
- Organize external preparations and modify equipment in such a way that different preparations can be selected at the touch of a button Recycle heat from machining operations and use it for preheating ovens Modify equipment structure or invent tools that allow reduction of setup and start-up Eliminate adjustments required to set height or position of dies or templates by using limit switch or convert manual to automatic adjustments Review Sequence of Operations sheet standard and train operators when upgrading equipment.
Phase 4: Zero Preparation. The ideal preparation time is zero. To achieve this, it is necessary to use a common part for several products. This could be achieved in the development and design phase of the new models.
Conclusions
The time invested in preparation and change of tools and tools is one of the key factors for a world-class manufacturer. The reduction of tool change times allows a reduction in the size of the batches, thereby making it possible to reduce inventories in process. The reduction of batches in turn makes it possible to reduce cycle times; reducing the latter allows the company to respond more quickly to customers, reducing or eliminating the need to maintain inventories of finished products.
A typical factory will have numerous tool change processes, and an important part of the continuous improvement will be directly related to the gradual and systematic reduction of these change times.
The Just in Time Production System is not feasible if the batch sizes are large, and such batches can only be reduced if the times for the change of tools and preparation of the equipment are reduced.
In the past, the need to speed up tool changes was not widely considered, but the wide acceptance of Just in Time has made this issue a focus of many manufacturing plants.
Many companies have verified that tool change times (in the order of 50 to 75%) can be significantly reduced simply by studying the problem and subsequent improvement in the organization of activities. Further reductions can be achieved through relatively minor modifications to machines, tools, fixtures, or product. Only after such simple improvements have been made is it necessary or necessary to make capital investments of a certain level.
The current cost of obtaining significant improvements in terms of time is feasible merely with the time allocated first to the training of the operators and secondly to the attention that they pay daily to the machines, and that of the necessary technicians and engineers. for advisory and support activities.
As there are relatively few factories without switching costs, most have the opportunity to reduce them, and reduce the associated inventory investment. The preparation costs are not limited to conventional mechanical workshops, they also affect the process and assembly industries, such as pharmaceuticals, paper, food, chemicals, and electronics among many others.
The important point is that the operations of preparing machines and changing tools, tools, templates and accessories are one of the most substantial wastes in manufacturing. It is enough to consider that if in a factory all operations related to tool changes and setup times (re-tooling times) are reduced to a minimum, they can usually reduce manufacturing costs by 20% or more.
Annex - Checklist to be carried out with the machine running
Die
- Is it in the right place? Has every piece of the die been checked? Is it really clean? Is it cracked?
Tools
- Are there spanners? Are there screwdrivers? Are there spring pliers? Are there clean rags? Are there level gauges? Are there brushes? Are all tools in their correct place?
Control means
- Are the required micrometers available? Are there adjustable gauges? Are there tube gauges? Are there magnifying lenses? Are dial gauges available? Are all inspection tools available? Are gauges available for measurement? Is everything in perfect condition? Are all the means of control in the correct place?
Bibliography
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