A production organization strategy in which parts with certain similarities are manufactured according to a common production method
Patrick de Vos, Head of Global Training, Seco Tools20/03/2019
From before the Industrial Revolution until today, manufacturers have shared common goals: to produce a certain number of parts, within a certain period of time and at a certain cost. Manufacturing processes evolved from the production of a single component by hand to series production lines and the production of an increasing number of identical parts: high-volume production with low product combination (HVLM). More recently, digital technology in programming, machine tool controls and part handling systems are facilitating a manufacturing environment known as Industry 4.0, which allows the cost-effective manufacture of very diverse parts in small batches: high combination production of products with low volume (HMLV).
In the era of Industry 4.0, it is fashionable to highlight the most modern production techniques and digitization technologies. However, achieving maximum productivity and profitability is still based on operational excellence. In today’s economic environment, manufacturers generally consider speed to be a key indicator of this operational excellence. A blueprint enters an installation, and eventually a finished piece leaves the plant; manufacturers want the time between the two events to be as short as possible. Efforts to increase speed typically focus on strategies such as lean manufacturing or Six Sigma.
However, these strategies generally refer to HVLM type production, and are not always effective when applied in HMLV type scenarios. An important contributor to optimized HMLV production is the group technology approach, in which sorting and coding parts into machinable families allows a workshop to achieve the highest level of operational excellence. Group Technology
Group technology is a production organization strategy in which parts with certain similarities, such as their geometry, material, manufacturing process or quality standards, are classified into groups or families, and manufactured according to a common production method. Operations are planned for the parts family, rather than for individual parts.
Very often, when production is organized to manage parts families, the arrangement is described as cellular manufacturing. Cellular manufacturing achieved notoriety in the 80s, approximately when the era of HMLV production began. Manufacturers noticed that batch sizes were shrinking, while the variety and new materials of the parts increased. The workshops faced a great diversity of pieces, produced in comparatively small batches. The time spent preparing for production increased exponentially, and manufacturers looked for means to control it.
The creation of part families in group technology is based on the coding and classification of those parts. Each piece is assigned a code consisting of letters or figures, or combinations of both, and each individual letter or figure represents a certain characteristic of the part or a technique that is required to produce such a piece. In image 1, the 6th digit of the code represents the dimensions of the part, the 7th digit corresponds to the raw material, the 8th digit to the original shape of the working material, and the 9th digit to the required quality level. Digits 3 through 5 describe the operations required for machining.
Part codes are used to plan production and to make price quotes regarding an imaginary or non-existent part called a complex workpiece, as shown in the second line of figure 2. Complex, in this case, does not mean difficult, but describes a generic piece that illustrates all the features that a company is capable of creating, such as high and low precision holes, shallow and deep cashiers, characteristics of squared and contoured, etc. The parts in the first line of the figure represent workpieces that can be produced with operations selected from those described in the complex workpiece of the second line. The sum of the production costs of the necessary features offers a representative total cost and simplifies the estimation of the price. There is no need to analyze costs individually.
Production planners and estimators work with a one-part drawing and generate a budget by matching characteristics of that part with those of the complex workpiece, and also determine other production elements, such as required machine tools, whether refrigerant will be needed, etc. In addition, by applying group technology with the help of a sophisticated CAM system, the engineering time prior to machining is further reduced. Another advantage is better communication between the departments of the center, since they all work from the same model of complex workpiece.
The group technology approach was initially experience-based, as the staff developing it interviewed process engineers, programmers, and planners to gather information on the cost of various production operations. Although the development occurred in the 80s, the collection of individual experiences and data, as well as their organization into a system, was a process that resembles today’s artificial intelligence initiatives.
In some cases, group technology drives plant reorganization. In the left section of image 3, the complicated route that the pieces follow in a workshop organized according to a traditional scheme based on the functions of the machines, including turning, milling and grinding, is shown. However, when parts are grouped together and processed as families following a cellular scheme, as shown in the right section of the figure, machine tools can be arranged to streamline the manufacturing flow and minimize the movement of parts within the workshop. Each family of parts is machined as efficiently as possible, without the need for unnecessary carrying within the workshop. The result is a significant reduction in the time needed to produce the parts.
As always, adopting new concepts offers both benefits and challenges. The group technology approach offers advantages in terms of engineering, process planning and manufacturing time savings, but it also comes with a number of challenges. First, to some extent, this approach reduces flexibility. The traditional workshop structure is more flexible if there is a significant increase in demand for a given part configuration that causes a bottleneck in production. In the traditional scheme, other machines in the department can be used to produce the parts. Secondly, managing machine times can also be challenging. If there is a temporary reduction in demand for a piece of the family, the machines in the cellular schema remain idle.
Another potential problem arising from the application of group technology concepts is the tendency to spend an excessive amount of time comparing one coding system to others. However, more important than the coding system itself is that a company must thoroughly know its equipment, its resources and the desired results. In that case, a custom coding system created in-house can be a simple and efficient approach. Possibly rearranging the shop floor to machine part families more efficiently is another plant-specific decision. It may be easier for larger companies to realign their machinery, while smaller workshops may face budget constraints and other factors. Faster and more accurate offers