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Source: Business-improvement.eu
Lean: Value adding organization
Picking with augmented reality at KONIProduction of shock absorbers in One Piece Flow (OPF)
OPF at KONI thanks to just-in-time supply

By Dr Jaap van Ede, editor-in-chief Business-improvement.eu, 16-01-2018

Gearing production activities perfectly to one another is not sufficient for production in One Piece Flow! The supply of parts, tools and information must seamlessly connect to this. To this end, operators at KONI receive all the parts and tools just-in-time via roller conveyors, and at the same time, work instructions appear on their screens.

This way, KONI is able to make 20% more shock absorbers with the same resources. A story about operators playing tag along the production line, shoppers with augmented reality glasses who provide them in time with goods, and custom made software that connects people, materials and information.

The 160-year-old KONI is part of the American multinational ITT since 1972. KONI was founded by Arie de Koning, who started the production in his father's saddlery. De Koning decided to develop a new generation of shock absorbers, after examining what was wrong with the existing ones on the market.

The rest is history. Today, KONI has been specialized in the production of hydraulic shock absorbers for 85 years. Their head office and R&D-department are located in Oud-Beijerland, in the Netherlands. Here, also shock absorbers are produced for cars, buses, trailers and defense vehicles. In the same factory they also make specials, such as shock absorbers for bridges.

KONI produces hydraulic shock absorbers
KONI produces hydraulic shock absorbers


Being an automotive supplier, KONI has to be able to deliver just-in-time to their customers. This means frequent delivery in small quantities, in line with the Lean production in almost all automotive factories. To make this possible, it is best if the production within KONI’s own factory is also Lean.

In Lean, production chains that create one end product per fixed time interval (the takt time of the line), are the holy grail. This is called production in a One Piece Flow (OPF). Each takt time, at every work station, one product is processed and then moved to the next station.

This makes it possible to make just the amount of shock absorbers the customers asked for, after which these are immediately delivered to them. As a result, KONI does not need to keep stock that reduces their amount of working capital. In addition, production errors are detected early, and do not lead to large batches of defective products. The reason: a problem is often quickly detected at one of the next production steps. This means that you only have to reject or adjust a few products.

However, production in OPF was not easy to achieve at KONI. The reason: they make no less than 4000 variants of shock absorbers, based on 12000 parts!

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Value Based Six Sigma
‘We have plenty of process improvement knowledge’, says Erik Bleeker, One Piece Flow project manager at KONI. ‘A Six Sigma program has been running here for a long time, and is now called Value Based Six Sigma. With this we emphasize that we put value-creation for our customers and shareholders first. You could say that we apply a form of Lean Six Sigma. As a result we have enough Black Belts, full-time process improvers.’

The improvement knowledge is not limited to those experts. Also the operators have a lot of ideas. ‘On the basis of these ideas, many improvement projects were already carried out, including Blitz Kaizens. In addition, we already experimented with One Piece Flow. However, in retrospect, many of our improvement actions were too local in character. The cohesion was missing. '

Cohesion between all activities is a prerequisite for Lean production, since One Piece Flow is not only elegant, but also vulnerable. In its early days Lean was referred to by the term fragile production. ‘It is not sufficient to form a chain of closely connected production steps, with only small stocks in between. In such a chain one single problem at one single production step is enough to stop the complete line. We did not take enough precautions, to prevent this. Especially the timely supply of tools and materials was not guaranteed.’

As a result, after each experiment with OPF, the operators rapidly returned to batch production. They started to work again on large quantities of products at the same time, to ensure that their own production step would always have plenty of work to do. ‘In the event of problems with OPF production, such a relapse to batching is always waiting in ambush. It seems to be human nature to work that way.’

Perhaps the explanation for this are emotional disadvantages related to single-piece production. Then, after completing a single task on a single product, you have to switch to what could be a new task on another product. Besides that, you become dependent on the production step preceding you. When this step does not deliver the next intermediary product to you in time, you have to wait.

One Piece Flow has (much larger) advantages elsewhere in the supply chain, like reducing the amount of stock, but those advantages are not ‘felt’ by the operators. And besides this, it could be that humans simply don’t have enough experience with a supply chain in which stocks costs money, and in which it is important that mistakes are detected as early as possible. ‘This might very well be the case. Whole books have been written about this subject.’

Three conditions
In order to have lasting success with OPF production, three conditions must be met:

  1. Balancing: all steps in the production chain must function reliably, and must be - and stay - attuned to each other.

  2. Just-in-time supply, perpendicular to the OPF line: Operators must get all the required materials and information at the right time at their workstations, to make it possible that they can continue to work. Materials can be parts, tools and/or molds. Information mainly consists of work instructions for tasks to be performed at a particular moment.

  3. Connection: A software system is needed to support the two points mentioned above, by connecting people and machines. Think of software that (a) ‘tells’ the pickers in a warehouse, which materials they have to bring to which workstations along the OPF line, and (b) ‘tells’ the workstations which type of semi-finished products will arrive there at which moment, so that appropriate work instructions can be displayed.

As we will see later, KONI was able to meet all these three conditions!

To produce shock absorbers in a One Piece Flow, three conditions had to be met
To produce shock absorbers in a One Piece Flow, three conditions had to be met: balancing the production line, just-in-time supply of materials & information, and software that attunes all activities of people and machines

Material flow
The transition to OPF production turned out to be a major operation. KONI called this project material flow.

A logical name: to make OPF possible, materials (and matching information) would have to flow through the factory. ‘The idea for material flow originated three years ago. We have many automotive customers, so it was clear that we needed short lead times, to be able to supply them just-in-time. In addition, we had the ambition to become a best-in-class factory within ITT.’

Blue print
To avoid the earlier pitfall of ‘fragmentary’ improvement actions, first a blueprint was developed for the factory-wide implementation of OPF. ‘To this end, we gathered as much knowledge as possible. This included reference visits.’

KONI also contacted OPF expert Charlie Protzman. This American, who published several books about OPF, is regularly active as a consultant within ITT. ‘A consultant not only contributes via his or her knowledge, but is also an important enabler to start a transition. Protzman is a great supporter of time-motion studies, for example by way of video recordings.’

Hydraulic shock absorbers  - and how KONI makes them

Hydraulic shock absorbers serve to damp both springing in and out. These type of shock absorbers consist of two tubes inside each other, filled with oil. The inner one has a piston rod with a piston at the end, and a foot valve at the bottom.

During ‘springing in’, for example needed when you drive with a car over a bump, the piston rod moves downwards. To make this possible, oil flows upwards via valves through the piston and through the foot valve. The resistance during this process causes the damping. ‘Springing out’ is the reverse process.

The outer tube acts as an oil reservoir, to compensate for the varying amount of volume occupied by the piston rod. During a downward movement (springing in), this volume for example increases.

Bleeker explains what the production process of the shock absorbers at KONI looks like. ‘We start with six-meter-long pipes. First, a CNC machine cuts the inner and outer tube for the desired type of shock absorber to length. Sometimes, this machine also cuts a wire in the tube. Next, a number of welding steps follows, for example to seal the pipes and to install mountings at the top and bottom.’

Then, the final assembly follows. ‘The inner tube is then slid into the outer tube, and the piston rod with the piston and the foot valve is built up from various components. Various valves and seals are also added. After testing, the shock absorber is coated and packed.’

From preparatory phase to final assembly
KONI created a OPF production chain for its entire production and assembly process, from the preparatory phase to the final assembly. ‘There are a few interruptions in this chain with buffer stocks. Buffers are for example located between the welding process and the assembly. In addition, we have multiple OPF chains, because we have several production lines.’

Starting a production order
Starting a production order. After this, software coordinates all the activities of people and machines

In a traditional OPF production line, operators stay at their workplace, where every ‘takt time’ a product to be processed passes. This makes the flexibility very limited. After all, if your predecessor along the line needs a little bit longer than one ‘takt’ to complete his or her work, you have to wait.

To prevent this, you could perfectly balance the line, ensuring that every task takes exactly the same amount of time. However, this becomes impossible if you make many different products with one production line, as KONI does. In addition, having to comply to an exact ‘takt time’ to complete tasks can be stressful.

Therefore, KONI implemented a more flexible OPF variant, the bumping system. Taiichi Ohno from Toyota originally called it the batton zone system.

Bumping has the advantage that the production line constantly rebalances itself. As a result, variable processing times are no longer problematic. In addition, the operators no longer experience the pressure of an exact cycle time, while on average still every ‘takt time’ one finished product leaves the production line.

With bumping, the chain of products being built still moves along the line. ‘However, as operator you now move along’, explains Bleeker. ‘This means that you carry out several tasks consecutively on the same semi-finished product, at several work stations. You continue to do so, until the person in front of you has no work anymore. When this happens, that person walks in backward direction, and takes over your work.’

The words bumping and baton, the latter referring to ‘tagging out’, describe this moment. When you are ‘tagged out’, in your turn you take over the work of the person behind you. And so on. In case you are ‘tagged out’ at the beginning of the production line, you start to assemble a new product.

Bumping ensures that the flow continues, despite variable processing times. You might say that the bumping moments serve as shock absorbers! Theoretically, this makes it even possible to produce faster than in an OPF with fixed processing times. After all, operators never have to wait until a previous task is finished.

With the bumping system, KONI had met the first condition for OPF production. They had realized a chain of well-coordinated production steps.

However, the other two conditions for OPF production, just-in-time supply and connecting people and machines, turned out to be much more difficult to achieve. Not for nothing the absence of those two prerequisites was the reason that previous OPF attempts had only limited (read: local) success!

As early as 2012, KONI invested in a fully automatic warehouse, equipped with a miniload system for the supply and the removal of small containers. This automatic warehouse also includes a maxiload system for the handling of pallets, and a shuttle system. ‘The power of these systems, which automatically collect the materials you need, is at the same time the weakness’, says Bleeker.

Waiting time
There is a waiting time. ‘Current requests are handled first, and only then the order you give the logistics system. As a result, it is not possible to supply just-in-time from such an automated warehouse.’

In the past, all materials for three full production days were brought to the factory floor in advance. This was done on the basis of a Material Requirements Planning (MRP). So, materials were ‘pushed’ to the factory floor, instead of ‘pulled’ by the work stations when needed.

‘On our shop floor materials were present for 30 different production orders at average, a huge amount of stock. As a result, operators often had to search for the materials they needed at a particular moment. They walked no less than four kilometers a day! Sometimes, those materials eventually turned out not to be present. Then they had to collect those parts in the warehouse themselves. You can imagine that this made OPF production impossible.’

The solution: a so-called supermarket. This is a small buffer between the warehouse and the shop floor. Logistics assistants or shoppers, KONI calls them water spiders, ‘shop’ in this supermarket and deliver the right materials to the operators in time. This means delivery on the basis of pull, thus only when needed.

A shopper on his way with materials from the supermarket to one of the One Piece Flow production lines
A shopper on his way with materials from the ‘supermarket’ to one of the One Piece Flow production lines

‘In the supermarket, blue containers contain tools, and gray ones contain parts’, explains Bleeker. ‘For small components, required for many types of shock absorbers, we do not keep track of the quantities per container. However, we do ensure that there are always enough full containers for about one day of production. Supplementation from the central warehouse is done on the basis of Kanban. If an operator needs certain parts, a bin with those parts is delivered to him or her. After use, this bin, with the remaining amount of parts therein, is returned to the supermarket. Tools are supplied and returned in the same way.’

The supply of parts for specific types of shock absorbers, is done in a similar way. Two days in advance, those parts are transferred from the central warehouse to the supermarket, and put ready there in bins, in the appropriate quantity for one production order of one type of shock absorber. After use, these bins return empty.

The ‘presentation’ of the bins to the operators is done by placing them on a roller conveyor. This is done just-in-time, in line with the OPF production sequence. After use, the operator places each bin back on the roller conveyor.

15 minutes
Every 15 minutes shoppers supply the production lines from the supermarket. This does not mean, however, that every work station receives materials every quarter of an hour. The supply frequency per work station is much lower. ‘A production order entails on average 70 identical shock absorbers. Although we produce these in a OPF, all parts and tools for one production order are delivered to the workstations in one go.’

An operator works half an hour to three quarters of an hour on one shock absorber, carrying out one or more operations. This depends on the time within he or she is 'tagged out' via the bumping system. ‘We want the materials needed to work on the next shock absorber to be present at every workplace. To garantee this, the replenishment time when a production line switches to another shock absorber type to be assembled, may not exceed 30 minutes. This is accomplished by way of a supply round every 15 minutes. Then, even if a shopper is just on the way with materials to another production line, he or she will still arrive on time with the new materials.’

With their augmented reality glasses the shoppers see what they have to bring to the operators
With their augmented reality glasses the shoppers see what they have to bring to the operators from the ‘supermarket’.

Glass Enterprise Edition
As mentioned earlier, producing in a OPF is very vulnerable to disruptions. One wrong delivery of materials and the whole production line comes to a halt. Therefore it is crucial that the shoppers pick quickly and error-free from the supermarket. ‘We worked with color charts from a printer for a while, but too many mistakes were made.’

A better option seemed to be a barcode scanner. In this case the scanner screen shows the picker what to pick, and after completing this task this is confirmed via barcode scanning. ‘Barcode scanners with screens, however, are heavy and difficult to handle. It turns out that no less than 20% of the time is spent on it. Ultimately, we found a better system: augmented reality with Glass Enterprise Edition glasses.’

Those glasses are a new version of Google Glass, with improved battery, camera and wifi. However, these are no longer sold under the Google brand name. After pilots at, among others, KONI, Glass Enterprise Edition was officially launched in July 2017.

‘Messages on the transparent glass tell our shoppers which bins they have to pick. They confirm every picking action with a small barcode scanner, attached to one of their gloves. Pick by vision, this is called. With this system, the right materials are now brought to the operators in 99.9% of the cases.’

Every picking action is confirmed with a barcode handscanner
Every picking action is confirmed with a barcode handscanner

The last condition to be fulfilled to make OPF possible: digitally connecting everything and everyone!

The shoppers for example need to know which materials they have to bring to which workstations, and the workstations need to ‘know’ in which order different types of shock absorbers will arrive. Only then can the workstations present appropriate work instructions to the operators, and timely send ‘pull’ supply orders to the shoppers. It must always be clear what the current situation in the factory is, the software must have an ‘image’ of it. Finally, the operators and shoppers must be able to report which activities they have completed.

‘We developed the connecting software ourselves. Thereto we adapted our ERP system, which uses an IBM AS400 database. We have two programmers here, and we have a lot of experience with customization.’

The results of the OPF production: 20% more shock absorbers are now produced with the same resources. In addition, the stocks on the shop floor shrunk by 98%, leading to 40% freed space. ‘This space could be used to increase our production capacity.’

In the supermarket now lays an amount of stock for one production day, instead of the amount of stock for three production days that used to be present on the workfloor.

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TWI InstituteArnout Orelio