I Principi Fondanti del TPS: la Struttura Filosofica alla Base dellaLean Production

• The foundation of the TPS house
• Problem Solving
• Fishbone diagram
• A3 method
• Heijunka
• A practical example of Heijunka Box
• Standardised Work
• SDCA & PDCA
• Kaizen
• The interconnection of the three principles

I principi fondanti del Toyota Production System sono organizzati in quattro livelli (Toyota Way): filosofia di lungo termine, processo ottimizzato, sviluppo delle persone e problem solving sistematico. Non sono tecniche isolate ma un sistema coerente: adottarne solo alcuni produce miglioramenti temporanei. Il rispetto per le persone e il miglioramento continuo sono i due pilastri culturali che rendono il TPS sostenibile nel tempo, distinguendolo da qualsiasi altra metodologia produttiva.

I Principi Fondanti del TPS. C’è un errore che molte aziende commettono quando si avvicinano alla Lean Production: trattano il Toyota Production System come un catalogo di tecniche. Prendono le 5S, aggiungono qualche kanban, disegnano una cella a U, e si aspettano i risultati di Toyota. Poi, dopo qualche mese, i miglioramenti si assottigliano, le abitudini vecchie riaffiorano, e il cantiere lean si esaurisce senza aver cambiato davvero nulla.

La risposta, quasi sempre, è la stessa: hanno copiato gli strumenti senza comprendere la filosofia che li genera e li sostiene. Il TPS non è un insieme di tecniche: è un sistema di pensiero. Un sistema costruito su principi filosofici precisi che guidano ogni decisione, dalla progettazione degli impianti alla gestione delle persone, dalla pianificazione strategica alla risposta quotidiana ai problemi. Comprendere questi principi è il prerequisito per qualsiasi implementazione lean duratura.

The foundation of the TPS house

The foundations of the TPS house are represented by:
Heijunka: i.e. levelling. In order to ensure that production avoids waste, is efficient and responds quickly to market demands, it is essential not only to plan but also to balance production. The Kanban method and the OEE indicator are some of the tools that help to level demand.
Standardised Work (standardised work): i.e. the set of operating procedures developed by all company personnel involving machinery and materials aimed at maximising the quality and efficiency of processes, while ensuring a high degree of predictability and safety at work.
Kaizen: that is, change for the better, continuous improvement. Every day is a quest for perfection that must never end. Apply the Kaizen It does not require large investments, but it does require the optimisation of available resources used to eliminate inefficiencies. It leverages specific problem-solving techniques.

PROBLEM SOLVING

The term Problem Solving generally refers to an attitude aimed at finding a solution.
Within the scope of Lean Production, various problem-solving techniques have been developed, all aimed at improving the ability to make quick and effective decisions with a view to continuous improvement.

Fishbone diagram

First, the negative effect, problem or defect under analysis is briefly described. The categories in which the main causes are thought to lie are then identified. These are then connected by diagonal lines to the main line connecting the problem, as shown in the figure (the categories shown in the figure are those most commonly used in industrial manufacturing).
For each of these categories, we then move on to a detailed identification of the underlying causes. Other problem-solving methods include the A3 method and the 5 Whys method.

A3 method

Its name derives from the size of the document used (an A3 sheet), which illustrates the entire process of achieving a goal or solving a problem. The A3 Technique is not only used for problem solving, but is also a model that encourages collaboration, learning and continuous improvement at every organisational level. The thinking behind its use is problem solving through sharing.
The A3 Method follows the logic of the PDCA (Plan – Do – Check – Act) cycle. The A3 report must first of all have a title, a date and the names of those responsible for updating it, as it is a tool that is modified and updated over time.
Usually, the form is completed
carrying out the following steps in sequence:

PLAN
Description of the problem: the “why” it was necessary to address the topic is described;
Current status and future : description of the current situation and the problem, and description of the ideal situation;
Process analysis: The root causes of the problem are investigated using analysis techniques (Value Stream Map, 5 Whys Method, etc.)., Fishbone diagram);
DO
Countermeasures: based on the critical issues identified, the countermeasure to be implemented is identified for each of them (methods, responsibilities, implementation times);
CHECK
Results: the results or failures achieved are reported;
ACT
Follow-up: verification of results and, in case of failure, the analysis cycle is restarted.

Heijunka

Heijunka is the levelling of production that balances the workload within the production cell, while also minimising supply fluctuations.

In order to correctly size the Heijunka Box, it is necessary to know the Takt Time, which we know to be the maximum time within which a product must be manufactured or a service performed in order to satisfy customer demand. Once the Takt Time for a product line is known, a production schedule must then be defined. Providing the production department with all the production Kanbans at the same time certainly does not help with production planning, and there would be no image of Takt Time in the department.

Therefore, this type of subdivision should be avoided. So what can be done? You can calculate the so-called production pitch, which is equal to the Takt Time multiplied by the quantity of the product that is placed in a package/container or defined on a Kanban card.

A practical example of Heijunka Box

Let us assume that the kanban card shows 10 pieces per package and that the takt time is, for example, 90 seconds/piece: the pitch is calculated as the product of these two quantities.

PITCH = (10 pieces x 90 seconds/piece) = 900 seconds (equal to 15 minutes)

In practice, the pitch tells us that every 15 minutes a Kanban card (work instruction) will be released and the material produced in the previous period will be collected. Once we understand the pitch and its meaning, it is quite straightforward and easy to build the Heijunka Box.

Nel nostro caso quindi l’Heijunka Box sarà costruito (per un turno di 8 ore) di 32 colonne corrispondenti agli incrementi del pitch nelle 8 ore lavorative. Se il pitch dovesse risultare troppo corto (ad esempio 5 minuti, che porterebbe ad avere 96 possibili posizioni per il pitch), di solito si agisce per il multiplo di pitch (ad esempio in ogni posizione possono essere posizionati 3-4 cartellini Kanban che devono essere fatti in quel periodo incrementale).

Di solito si scende raramente sotto i 10-12 minuti per ogni colonna (5-6 caselle per ogni ora produttiva). Ogni 15 minuti, la persona che gestisce i materiali porta alla produzione il Kanban successivo che sta nella apposita posizione e ritira il Kanban precedente insieme ai prodotti fatti nella fase finale della produzione. Se non è finito tutto il prodotto richiesto nel periodo precedente, si capisce subito che c’è stato qualche problema produttivo che bisogna andare a investigare e scoprirne le cause all’origine.

Si tratta quindi anche di un magnifico controllo visuale della produzione, in quanto quando un capo reparto va a controllare in tempo reale se tutto è a posto, va a controllare l’ora e la situazione sull’Heijunka Box e se non ci sono problemi, tutte le caselle prima di quell’ora dovrebbero essere vuote, invece se ci sono problemi ci saranno alcune caselle ancora piene a significare che si è in ritardo rispetto alla produzione programmata. E questo gli può servire come input per andare a vedere che problemi ci sono ed eventualmente dare delle disposizioni per gli straordinari, per aiuto, per risolvere i problemi e recuperare rispetto al programma.

Anziché avere un programma produttivo dato ad ogni reparto che lo gestisce per sé, come succede nella gran parte delle aziende tradizionali, nelle aziende Lean, attraverso l’utilizzo dell’Heijunka Box e dei cartellini Kanban, si realizza un sistema di trazione dall’ultima postazione lavorativa fino all’inizio del processo. Le quantità di Kanban vengono arrotondate per eccesso. Si dovrebbe comunque cercare di ottenere dei numeri pieni, in quanto ’arrotondamento verso l’alto crea una sovrapproduzione, uno dei sette sprechi che vanno evitati.

A practical example. Let's assume that the average demand is 480 pieces per day. The coverage time is 30 minutes. The safety stock is 10% and the containers hold 5 pieces.
We will need 7 Kanban cards (= 7 containers).

Standardised Work

Standard means rule. The standard affects all company functions (production, production support, administration, etc.) and represents the basis for stability and therefore improvement. Work organised according to an efficient production sequence is called standardised work, not to be confused with the use of standards during work activities.
Standardised work consists of applying three concepts:

• Takt Time
• Working Sequence
• In-Process Stock Standard
  

Takt Time, as already described, is the time that must be used to produce a piece. This time scanning mechanism is based on monthly production scheduling.

Working Sequence refers to the definition of unique sequences of operations for the same process, which leads an operator to produce quality goods efficiently, reducing inventory and the risk of accidents or illness. Standard In-Process Stock is the minimum quantity of components that must always be on hand for production. It allows the operator to do their job continuously, performing the same sequence of operations each time in the same order.

SDCA & PDCA

The’SDCA (Standardise, Do, Check, Act) is a cycle of standardisation of procedures that alternates with the PDCA cycle in a process of continuous improvement.
The standardisation cycle consists of four phases:

1. Standardise processes with actions aimed at standardising rather than improving (STANDARDISE)

2. Implement standardisation measures with relevant training (DO)

3. Verify the results (CHECK)

4. Confirm the new standards and make them operational (ACT)

The four stages of the cycle PDCA are instead:

1. Planning (PLAN)

2. Experimental implementation of what has been planned (DO)

3. Checking results and verifying compatibility with what was planned (CHECK)

4. Implementation of solutions that have passed verification (ACT)

Kaizen

The TPS is based on the philosophy Kaizen.
The Japanese term Kaizen is a combination of two words: KAI, which means change, and ZEN, which means better. Hence the meaning of continuous improvement. It is a fundamental concept in Japanese culture, and therefore also found in TPS.

Working according to the Kaizen philosophy means always striving for continuous improvement, based on the assumption that everything we do can be improved. Even when we think we have achieved perfection, this is not actually the case, as everything can and must be improved; the perfection achieved becomes nothing more than a standard, which can be improved upon. All the concepts found in the Kaizen philosophy are then obviously incorporated into the Lean Production system.

Another fundamental concept of Kaizen is that energy comes from below: analysing Lean Production, we see that decisions or suggestions must come from below and must not be imposed from above, as is the case in other production models. This is also why, in order to apply Lean Production, it is necessary to involve all levels of the hierarchy, even the lowest ones.

Furthermore, Kaizen, like Lean Production, is based on small but continuous changes; these changes should also be inexpensive. It is obvious that this continuous improvement is driven by an underlying dissatisfaction, namely the need to change a certain situation or at least improve it.

The interconnection of the three principles

What makes TPS so powerful is not the individual principles in isolation, but their synergistic integration. Heijunka creates the conditions for standardised work, stabilising processes and making it possible to define repeatable operating sequences. Standardised work, in turn, provides the necessary basis for Kaizen: without a benchmark, it would be impossible to measure whether a change actually represents an improvement.

Il Kaizen, infine, arricchisce continuamente sia l’Heijunka che il lavoro standardizzato. Attraverso il miglioramento continuo, si scoprono modi migliori per livellare la produzione e si affinano gli standard di lavoro. Questo ciclo virtuoso genera un sistema che si auto-perfeziona nel tempo, diventando sempre più efficiente, flessibile e capace di rispondere alle esigenze dei clienti.