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Mar 18, 2011
- Foundry: "designer" materials for castings
- Robots producing core packages out of very fine sand
- From a fine art to a perfect process: iron casting in Mannheim
- One of the world's largest machine shops for the "5 Cs" of CV engines
- The first composite camshaft for heavy engines
- Spectacular and unique machining processes
- The "Illig factor" – benchmark for cleanness in the motor industry
- Assembly: engines built under essentially clean room conditions
- Engine testing by directional microphone
- Mannheim plant at the heart of international co-ordinated production
- New production facility protects both neighbours and environment
Mannheim, 17 March 2011. Quality without compromises is the key focus of the new engine manufacturing facility at the Mannheim production plant. For the production of the new OM 47x engine family, every detail of the manufacturing process has been optimised. The three areas of foundry, machining and assembly work perfectly together like the cogs of a well-oiled wheel. Their common goal: to build perfect-quality engines. To this end, several hundred million euros have been invested in a new manufacturing facility at the Mannheim plant.
The "synchronous plant"
Within the space of just six days, a new-generation Mercedes-Benz engine has to pass through every stage of the manufacturing process, from its origins as molten iron in the foundry through to the machining and then assembly shops. Such an ambitious target can only be met if production processes are perfectly organised. With this in mind, the Mannheim plant has chosen to adopt the system of the "synchronous plant": the three production areas of foundry, machining and assembly work as an integrated system in a continuous flow of production that only requires 50% of the inventory levels maintained for earlier model series.
There is no room for errors in this system. They are precluded by excellently trained staff, the sophisticated production system, the very best possible machinery and a whole series of statistical quality checks. All areas work closely together, physically as well as conceptually, ensuring that internal supply routes are kept as short as possible.
Top quality is also ensured from the very outset by the very thorough preparation undertaken. The first engines from the new Mercedes-Benz OM 47x generation were produced on the assembly line as early as last summer. The second stage, which ran from the end of 2010, involved the very thorough training of all staff. The series production that has just begun is seen as a preliminary to the steep ramp-up that will follow in the third quarter of this year. By the time all the engines in the new range have been introduced, the Mannheim production plant will be able to handle the annual production of more than 100,000 engines of this generation.
Foundry: "designer" materials for castings
The company's in-house foundry is the first stop in the engine manufacturing process. Classic images of scorching heat, extreme working conditions and of iron-casting as the high art of metalworking are totally outdated concepts at the Mannheim plant's foundry. This is an extremely high-tech manufacturing facility, and the most advanced casting facility in the world, with the highest level of productivity and lowest wastage rate. Unlike in other engine manufacturing plants, the foundry at the Mannheim plant is an integral part of the production process. Crankcases, cylinder heads and flywheels for the new generation of engines are all produced in the foundry.
Many of the casting processes have been patented; the foundry has worked with several universities to develop its own special materials for this new generation of engines. The cast iron for the crankcase, for example, is made of a special blend of ingredients. This unique compound is only to be found in the melting furnaces of the Mannheim plant. It is not available to purchase, and its precise composition is a secret. In fact it elevates the properties of the castings made virtually to the same high level as cast iron with vermicular graphite. This material is used to meet the particularly exacting requirements for the cylinder head.
Robots use the finest sand to produce core packages
The extreme precision of the manufacturing process becomes especially obvious in the fully automated core shop. For the first time, robots are being used here to create the packages out of sand cores – a tremendous technical challenge. The material that is being used in Mannheim is highly refined and free from dust: the size of the sand grains is set at a diameter of 0.35 mm, with an accepted tolerance for the average grain size of just 0.02 mm. While it is the cores made out of resin-bonded binder systems that define the internal shape of the castings, the external shape of the casting model is determined by clay-bonded sand cores. The Mannheim sand system has a recirculation rate of 90%, another feature to set a benchmark in environmental terms!
Casting temperatures of around 1400 degrees, rest period after casting
Casting is a largely automated process, conducted away from air and atmospheric influences. The precisely defined casting temperatures are 1395 degrees Celsius for crankcases and 1450 degrees for cylinder heads. The castings are then allowed to rest in their sand and on a bed of sand for an initial cooling period of at least four hours – any other handling would make the material brittle and friable. By this time the castings still have a temperature of around 650 degrees, at which point they are left to cool at ambient temperatures for a further 12 hours. Once they have cooled to room temperature, they can be taken to the next stage.
The castings at this stage do not have a shiny metal surface but are black. Each component is coated in a very fine layer of sand, with the discoloration due to the fact that the core sand is mixed with carbon to prevent it reacting with the iron during the casting process. The sand is then removed by being jet-blasted with grains of steel. The few burrs still left on the castings are then removed in what is known as the trimming process.
Channels and ducts already cast into the cylinder head
It's worth taking a closer look at the finished castings. The cylinder head in the new engines, for example, is the most complex to be found anywhere in this size of engine. The water ducts and oil and fuel return lines are already cast in the cylinder head. This obviates the need for many of the pipes that normally run round the outside of the engine, so reducing complexity during assembly and resulting in an exceptionally leakproof engine.
From a fine art to a perfect process: iron casting in Mannheim
The success of the new manufacturing technology: iron-casting has been transformed from a skilled art into a highly efficient process. As lead engine production plant, the Mannheim plant has now rolled out this process to other plants in the Group. So now, for example, the crankcases for the new 12.8-litre Mercedes-Benz OM 471 are cast according to exactly the same principles at Atlantis Foundries in Cape Town/South Africa. They are then delivered to Mannheim for further processing, making them among the most far-travelled components in the new engine family.
One of the world's largest machine shops for the "5 Cs" of CV engine manufacturing
Machining takes place right next to the foundry. With an annual processing capacity of 100,000 tonnes of cast iron, this is one of the largest facilities of its type in the world. All the key metal components, the "five Cs" of cylinder head, camshaft, crankcase, crankshaft and connecting rod, undergo machining here. And in the machine shop, as well as in the foundry, the production experts at the Mannheim plant have stretched the technological boundaries to achieve extreme manufacturing tolerances. Several examples serve to demonstrate this.
The first composite camshaft for heavy engines
Among the highlights of the engine and manufacturing technology that goes into the new generation of engines is the world's first composite camshaft for heavy-duty commercial vehicle engines. The separation of shaft and cams in a composite camshaft permits the selection and use of the ideal materials for each individual component. It is a process that requires tremendous expertise.
The shaft itself is not solid but, for weight reasons, is in fact a hollow tube. During preheating, the cams expand; they then shrink into precisely the right position as they cool. This process results in an extremely close-fit, firm join with a high degree of dimensional accuracy: the cams fit to 2 µ (1 µ, or "Mu", corresponds to a thousandth of a millimetre). The composite camshafts have considerable advantages over the conventional single-piece camshaft produced in a machining process: the weight is halved, the production costs are around a third lower and there is considerably less wastage.
Spectacular and unique machining processes
There are further spectacular processes to be discovered in the machining section of the Mannheim plant. For example the deep hole drilling used for ducts inside the cylinder head: the holes drilled can be up to 900 mm deep and are not even 10 mm in diameter. The drilling is precise to exactly 10 µ, in other words to a hundredth of a millimetre.
For the first time, the camshaft produced in Mannheim is ground in just one step rather than in two, as hitherto. The level of precision achieved is thus far greater, because the shaft only has to be inserted into the machine once. After this single grinding process, the shafts are, at most, 0.2 mm out of true, so only minimal aftertreatment is required.
Another of the further special processes undertaken here is the plateau honing of the cylinder liners for the new engines. The cylinder wall is honed (smoothed) as usual in a cross-grinding process, after which any rough, protruding peaks are trimmed in a further finishing process, using a special stylus. This produces a plateau-like surface with oil-retaining pockets. In conventional manufacturing processes, this surface is produced during the stabilising phase of new engines by the friction of the oil control rings against the cylinder liner. This stabilising period, and the wear and tear that it involves, is therefore eliminated in the new-generation engines. The result is a more even spread of oil over the cylinder liner, while the piston rings no longer become pitted. As a further effect, oil consumption falls by about two thirds.
Production in the machining area is a hybrid process, comprising both transfer lines and a number of machining stations. These are modular in design: as series production of the new engine generation is ramped up, the number of stations can be continually increased through investment in additional machines.
Clinical standards of cleanness throughout the manufacturing process
The precision of the work undertaken in the foundry and assembly areas is matched by exceptional cleanness. Before each next step in the process, all components are thoroughly cleaned in one of a variety of ways. This may be by steel grit blasting, ultra-sound or by jet-cleaning with various fluids. Thus even larger castings, such as a crankcase, are just as clean inside as the bought-in plastic wiring. The maximum particle size is less than 1 µ. For comparison purposes: a human hair is around 0.1 mm in diameter, or 100 µ.
The "Illig factor" – benchmark for cleanness in the automotive industry
The almost clinical levels of cleanness are continuously monitored and documented by the plant's own washing and cleaning laboratory. This involves the minute residual dirt particles being separated out and inspected under special microscopes. A so-called "Illig factor" has now in fact been named after the head of the laboratory at the Mannheim plant. This relates to a formula for the technical cleanness of fabricated parts, which became a valid unit of measure for the whole motor industry last autumn and is now enshrined in the literature of the German association of the automotive industry, the VDA.
A high level of cleanness is one of the stringent quality assurance requirements along the way to achieving a target of zero errors. A whole range of tests before and after each machining step is also part of this process. These ensure that each individual part is tested several times. All parts therefore have to pass repeatedly through extensive checks at what are known as quality gates, before and after being worked on in the foundry and in the machining area.
Assembly: engines built under what are essentially clean room conditions
Precision and cleanness are similarly key factors when it comes to the assembly of the new engine generation. In Hall 150, built for the production of the new engine generation in 2007, a constant slight overpressure is maintained in order to prevent dust penetrating in from outside. In- and out-going deliveries take place through an air lock outside the hall itself.
The process of assembling the engines is just as sophisticated and, in many key respects, has been designed by the employees themselves: the engine fitters spent a whole week assembling engines in a specially created work area, watched by workplace safety and quality assurance colleagues. They were thus able to simulate each individual stage, documenting them in the production training system along with all the "tips and tricks" learned along the way. Together, they created a new assembly system that is second to none, anywhere in the world.
The daily routine of each assembly line is organised jointly by managers and staff as part of the shop floor management process. The production teams meet each morning at 7.30 a.m. to discuss the key data from the previous day, any potential problems and the staffing schedule. At 1 p.m., any issues that have still not been resolved are discussed again. This process has now even been standardised for use all over the world.
Step one: etching the model plate
During the assembly process, the engines glide from station to station in Hall 150 on automatically guided vehicles. The first step in the manufacturing process is what is known as etching: in a small cabin, the engine model plate on the crankcase is etched with a special stylus. The assembly then begins, with the crankshaft and cylinders and so ultimately to the sump – the crankcase is complete.
Meanwhile, the pre-assembly of the cylinder head, including the valves, is taking place. The pre-assembly stations are docked directly on to the assembly line in a fishbone pattern. The cylinder head is mounted onto the crankcase with 36 screws. A fully automatic multi-head screwdriver with four spindles tightens them in a set sequence with a pre-determined torque.
Once the cylinder head has been attached, it is followed by the camshafts and the rocker arms for the valve actuation. The adjustment of the valve clearance is undertaken by a technician at a workstation that was designed here at the plant. With the assembly of the gear drive, the engine is already mechanically functional. The flywheel, the installation of the wiring harnesses, engine control unit, filter modules and turbocharger follow. The engine is then coated in a clear varnish. All components of the new engine family thus shine in their original colour.
Engines log in at each station
Technology helps the engine fitters with their work. Each engine logs in independently at the relevant work station using its own specific data. The fitter then selects the required parts from a so-called pick-to-light racking system. The term is, in essence, self-explanatory: the technician takes the parts out of the racking one by one, until the green light in the appropriate section goes out. The data input from the engine also automatically sets the tightening torque and the angle of the screws.
Better safe than sorry…
Should any problems ever arise during assembly, the fitter can press an alarm button to call for help. If 70 percent of the time allocated at a specific station has passed without the problem being resolved, a member of the support team will step in to help. Problems are tackled immediately and on the spot: there is no way of channelling an engine out of the line.
A series of quality checks are integrated into the assembly process. Each individual engine is carefully examined at several points during manufacture before finally passing through the distinctive pillars of the quality gate at the end of its line. At this point the engine is checked by two technicians, according to the four-eye principle. They check the seals and electrics of the engine, while even the crankshaft is rotated and the resulting friction registered.
At the quality gates, staff use various lists to make the relevant checks. First of all, there is a general checklist for that specific gate. If a fault has actually been identified by the OEM or customer, every single engine produced will be checked on this point until a full three weeks have passed without the specific problem arising again. If a fault is identified on an individual engine, the measures taken to resolve it are also checked. During the production start-up phase for the new engine generation, there are even experts on hand to monitor the fault-finding process: they purposely build in small faults and then check if they are found.
Engine testing by directional microphone
Finally, every engine undergoes testing at an engine test station. Eight test cells have been created for this purpose in a special testing area within the assembly hall. Each engine undergoes cold as well as brief hot testing. This ensures that the highest quality is maintained, although the test procedures take less than ten minutes. This is the first time in the world that cold and hot testing of heavy-duty engines has been undertaken at a single test station. To help locate potential faults, directional microphones are used to test the engines for structure-born noise.
The assembly shop in Hall 150 is currently undergoing a refit in readiness for the production start-up of the new engines. Once this has been completed, by the end of 2011, this will be the most advanced engine assembly facility in the world.
Perfect logistics in engine despatch
Exceptional efficiency is also the watchword when it comes to the despatch of the engines, which takes place right next to the assembly shop. The truck lane has been lowered here, so that loading can take place on the level. As a result, only a fraction of the number of fork-lift trucks are required, compared with the way things were done in the past, and far fewer fork-lift movements are necessary. The logistics of the despatch process are exemplary: throughput time has been reduced from two days to just four hours. Dockets attached to the completed engines show the precise time of despatch.
Mannheim plant at the heart of international co-ordinated production
The Mannheim plant is the lead plant worldwide for heavy-duty commercial vehicle engine manufacturing at Daimler Trucks. This is where all logistics and quality processes within the co-ordinated production system are controlled, so ensuring the quality and availability of the necessary parts throughout the global network. Production and quality standards, as well as the processes and plant engineering used, are all defined in Mannheim. Mannheim is also responsible for regional supply management co-ordination.
The plant is at the heart of Daimler Trucks' international co-ordinated engine production system. All Mercedes-Benz new-generation engines are produced here, as are the drive units for Fuso in Japan. Detroit Diesel in the US has its own assembly plant covering North America.
The new generation of engines is produced in a sophisticated interplay between the company's sites around the world: once series-production of the Mercedes-Benz engines has started up, the Mannheim plant will produce all cylinder heads, all camshafts and all flywheels, plus the engine blocks for the Mercedes-Benz OM 47x and the crankshafts for the Mercedes-Benz and Fuso engines. The crankcases for some members of the engine family come from the company's Atlantis plant in Cape Town/South Africa. The connecting rods for all heavy-duty engines of the new generation are manufactured centrally in the US.
The Mannheim plant: the best of three worlds
The Mannheim plant benefits from this close inter-continental cooperation. Comparisons between the assembly lines in North America and Mannheim serve to improve quality. There is a constant international exchange of experience: if a problem occurs in one continent, feedback goes immediately to the other two so that specialists from three continents can work on finding a solution. Due to the international time differences, video conferences take place in the mornings with Fuso in Japan and in the evenings with Detroit Diesel in the US.
Each location has something to learn from the others. The shop floor management system used on the assembly lines in Mannheim, for example, came originally from North America. From Japan came an uncompromising focus on quality. In Japan, for instance, the new engine is partially sprayed with white chalk and then allowed to run for several hours as a way of identifying any leakage. In a country where truck drivers tip their cabs on a daily basis for a meticulous visual inspection of the engine, even an engine plate that has not been fitted quite straight is seen as a blemish. On the new-generation Mercedes-Benz engines, even the fixing of the engine plate is done with meticulous attention to accuracy.
New production facility protects both its neighbours and the environment
The new layout of the engine manufacturing facility at Mannheim groups the foundry, machine shop, assembly and despatch in close proximity to one another. This is one of the prerequisites for achieving the highest possible levels of efficiency as well as exceptional quality. In addition, each area in its own right uses highly sophisticated production processes. But the Mannheim engine plant does not sit on an island: its neighbours include several residential areas. The buildings of the engine production facility are therefore constructed in an L-shape, so providing noise insulation for the surrounding area. On the side of the building facing the houses the windows cannot be opened – the interests of local residents were high on the list of priorities during the restructuring of the production facility.
Working in a sea of fresh air
Protection of the environment and an awareness of costs are evident in many places. Inside Assembly Hall 150, the fitters work in a "sea of fresh air": ventilation up to a height of 2.5 metres is provided through columns, so not only ensuring a pleasant atmosphere but also reducing energy consumption on heating and ventilation by about a third.
The tremendously high proportion of core sand re-used in the foundry is a further example of the intelligent way in which concern for the environment and cost awareness have been linked: 92 percent of the material is recycled.