The Perfect Ingredients for an Innovative Assembly Line

Synergy, flexibility, traceability and efficiency are very current terms which, in the case of the pulley assembly line installed in the Agla Power Transmission plant, find a concrete example and a real application. The plant, the result of the long-term partnership between Cosmec Group and Mitsubishi Electric Europe, is actually complex and at the same time flexible, capable of responding – in a very short time – to a precise production requirement but already potentially able to adapt to future developments and requests in a very dynamic sector such as the automotive industry, especially E-mobility. It is not by chance that, starting from three initial part-numbers, Agla Power Trasmission has already produced five different types of pulleys for brands such as Audi, BMW, Luk (Schaeffler Group) and Volkswagen, making full use of those properties of flexibility strongly sought after, with extreme foresight, right from the development phase of the line by Cosmec and Mitsubishi.

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But let’s begin at the beginning by stating that this assembly line gathers and synthesises in the best possible way all the experience and knowledge garnered by Cosmec Group in the production of special machinery and plants for different areas of the industry, for which it has become a reference point over the years, especially in the field of in-line quality control and assembly lines automated to customer specifications. An industrial path which led the company to contact Agla Power Transmission, a concern near Turin which has been operating for almost fifty years as a company specialised in the moulding and assembly of components for the automotive sector. A consolidated relationship which over time has seen Cosmec develop and manufacture various innovative assembly systems for the Piedmontese company, but always studied purposely to produce a specific type of product, right up to the present line dedicated to pulleys which combines special requirements such as a very rapid format change and total traceability of whatever happens within the plant. Inside the line there are four Mitsubishi Electric robots, two SCARA and two anthropomorphous robots, each one well integrated into the system with a specific task, but above all its iQ platform which oversees the entire management of the complex process automation, confirming a long-standing partnership and winning synergy with Cosmec Group; but we shall come back to this aspect later on.

Several part numbers require flexibility

Let’s begin our story by talking about the requirement which led Agla to radically change its production approach by moving from the concept of the dedicated line to the flexible cell; Igor Bigolin, Industrialization Engineer of Agla Power Transmission who welcomed us into the company, helped us to clarify this aspect: “Agla creates customised projects which it develops in co-design with the customer and, before this Cosmec-Mitsubishi Electric cell, the choice had always been to have dedicated production lines which, however, have the “limit” of being able to accommodate only one part number and may not be set differently, if not with long lead times and high costs. Since the market is rather lively, especially in consideration of the new concepts which are gradually becoming established in the field of e-mobility, we decided to change our strategy and try to recover our investments as much as possible by acquiring production means capable of responding to contingent needs but which could be ready for future ones, therefore able to cope with the new production volumes, expected to become increasingly important and demanding, having to produce pulleys for petrol, diesel, electric and hybrid engines. Hence the request made to Cosmec Group to study an extremely flexible line to produce pulleys able to accommodate more part numbers, which at the moment have already become five compared to the three initially planned”.

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The primary need was therefore to make production flexible, especially in view of potential future demands from the automotive world, where the quantities and types of objects can change rapidly. “How? We made an initial hypothesis by summing up the amounts of various part numbers we had in production – Bigolin explained – and we understood that a flexible and highly technological line would be the winning solution. Clearly, it had to be a flexible cell with a set-up of stations which could be completed in a short time and in masked time, where possible, considering that even those operations which cannot be changed in a short time were nevertheless designed to have a setting time of less than an hour. I am talking, for example, about the operation of changing moulds in the rubber press in the pulley discs. This time saving is fundamental, having different set-ups every seven or ten days”. Agla produces mainly for the warehouse according to a forecast of pulley requirements and the minimum batch of pulleys as they are produced; the time component is therefore fundamental. When fully operational, the line can produce about 820,000 items, which corresponds to a takt time guaranteed by Cosmec of about 23 seconds. The potential bottleneck is linked to the pulley balancing operation: if the system detects imbalances it is necessary to apply from one to five blind holes on the pulley, an operation that can lead to a maximum production time of 25 seconds.

A single reference point in automation, for real process efficiency

The key elements to guarantee the necessary flexibility of execution are the robots and vision systems, together with the choice of having a free pallet line management which is certainly more functional and in line with what is required compared to the concepts linked to rotary tables. “The previous systems made for Agla were rotary table systems – explains Paolo Andreoni, CEO of Cosmec Group – a more compact but decidedly more rigid solution, therefore less in line with the required flexibility demands. The pallet line, on the other hand, combined with the iQ platform and Mitsubishi Electric robots, implies that there is no need to make any changes between one product step and the next: all that it takes is to load the appropriate program and the robot, seeing the pulley, is already able to recognize it, manage it and orient it correctly according to the part number chosen. Apart from the mould for the press, which is changed in masked time, the rest of the line is set automatically once the part program for that type of part has been recalled, including laser markers used to engrave on each pulley the DataMatrix necessary to satisfy the other great need, that is, the complete traceability of each item produced”.

“For us it was fundamental to have a competent partner like Mitsubishi Electric Europe by our side – Andreoni explained – able to provide us with a complete automation solution, from robots to the management and process control platform. By default, where we can choose, we always use this Mitsubishi Electric platform, which allows us to focus on the real problems of the machine without wasting time on automation issues; therefore, having integrated robots with a control board in the PLC, ease of communication and an entire chain of command by the same manufacturer allows us to reach the goal which for us is the operation of the overall system and not automation in particular. Mitsubishi Electric provides us with a reliable and consolidated complete solution for the control of process automation; having a single manufacturer produce everything from the contactor to the robot means no integration problems and for us this is a huge advantage which we never give up, especially in the case of complex systems like this one. Not many companies are able to provide this service, besides, in this specific case, we have the robot CPUs directly integrated into the PLC rack, therefore with a very easy and direct data transfer, which is another advantage”. “We integrated the iQ automation platform which enables the creation of a multi-CPU system, which means managing the logic of the entire plant, that is, PLC, motion, robot, CN and make it work with a single brain” Marco Filippis, Product Manager Robot and Export Marketing Coordinator at Mitsubishi Electric, explained. “This allows first of all to have a single data access point and a single exit point, besides having a shared memory allowing, at the same time, a global view of all the variables involved in the plant and to see in real time what is happening on the whole line. Another advantage of the system is the use of a single communication BUS, so there is a single ribbing for the entire information flow, which, given the complexity of the system, is another important advantage of Mitsubishi Electric”.

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Perfectly integrated robots

Inside this assembly line there are four Mitsubishi Electric robots of two different types, two SCARA and two anthropomorphous ones, engaged in the various phases of the cycle. But what were the reasons behind their choice? Even in this case, it was the experience of the system integrator – that is, Cosmec Group – and the type of application or handling to be carried out depending on whether it is necessary to move on the plane or in space.
“Our first choice always falls on the SCARA because for us it is a “friendly” robot which is easy to use – Paolo Andreoni stated – especially when it is not necessary to have a six-axis movement. Clearly where it is not possible, for example when gripping the rubber rings to position them on the automated system which feeds them into the lubrication bath before press-fitting, we use an anthropomorphous machine. In this specific case, we exploit the full potential of the SCARA machines to control the loading and unloading operations of the press and to manage the pulleys before the balancing phase, while we use the anthropomorphous machines for the above-mentioned handling of the tyres and inside the pulley check and control station. In each of the four robots, however, we are talking about oversized machines compared to what would have been the correct choice for the current processing requirements. Not knowing yet how far we might go in the near future with this line for production, we decided to play safe right from the start with top notch machines and load performance superior to real needs”. “In the robotic control cell, the use of an anthropomorphous robot is essential because an indefinite amount of checks with profile gauges and vision systems are carried out and also in this case – Bigolin pointed out – the choice of Mitsubishi Electric has secured an important advantage in that it allows the profile gauge to be correlated with the rotation of the robot’s wrist, which makes it possible to carry out a more accurate check. In practice, thanks to a special gripper, each item is checked while still in the “hand” of the robot with the optimum inclination for a correct back light check; the position of the robot’s wrist is correlated with what the vision system says. There are eight vision systems integrated in the plant”. “One of the aspects of Mitsubishi Electric’s robotics which Cosmec likes – Marco Filippis again explained- is the fact that our controller may be completely open; it is, in fact, possible to go as far as removing the robot’s singularity points, something many of our competitors do not do, because they provide a closed system. From the integrator’s point of view, an open system has enormous potential, as this integrated robotic testing and control cell shows”.

Lubrication, press-fitting and balancing are the critical phases

The production cycle of this assembly line is quite articulated and in some ways complex. For the sake of concision we shall limit ourselves to analysing only the most delicate aspects of the process which, as we have seen, has as its most critical phase the press-fitting of the rubber on the pulley hub, on which the actual functionality, reliability and durability of the pulley itself depends. Behind this operation there is a lot of technology for which Cosmec and Agla have worked in close synergy, each bringing their own know-how for the development of apparently secondary but fundamental aspects such as the profiles of the rubber and the position where it will be fitted. “One of our strong points – Igor Bigolin commented – is precisely linked to the profile of the hub and the mass of the pulley in relation to the rubber; it is here that Agla has a strong competence, which has enabled it to obtain twenty international patents, because it is precisely the profile that makes the rubber in the pulley last longer. Another aspect concerns the moulds used, which are also the result of our technical design department”.

“The speed at which the rubber is pressed and the time it stays in the mould vary depending on the item,” Andreoni of Cosmec stated, continuing: “These operations are carried out with a controlled press, where the values of the force and the speed with which the rubber is inserted may be monitored almost to the hundredth of a unit. This is an important operation, because it is what determines the quality and duration of the pulley: if a correct pressing does not take place, it will be visible during the balancing phase”. Once the rubber has been press-fitted, the pulley goes through a drying phase in which excess lubricant is removed, manipulated by means of one of the Mitsubishi Electric SCARA robots and sent to the control phase where the correct insertion of the rubber, radial and axial oscillations and the characteristic dimensions of the pulley according to the specific part number are verified. From here it comes out, if it is correct, to be taken to the balancing machine where it is put into rotation to check its possible unbalance, on which, if necessary, the blind balancing holes are bored with different depths after which, if the unbalance remains, the item is declared not up to standard and discarded”. Upstream of this press-fitting, however, there is another fundamental phase in which the first Mitsubishi Electric anthropomorphous robot integrated in the line is involved, which picks up the various rubber rings from a vertical warehouse and loads them into the lubrication system. The rubber must be soaked in a lubricating liquid for 200/300 seconds (depending on the part number), and with a fairly tight time tolerance. “It is essential for the immersion time to remain in this range considering a buffer of rubber in the immersion tank, so the management of any stop must take this into account”, explains Paolo Andreoni. “If the rubber remains immersed for longer, it is automatically discarded, as well as if it remains exposed to air for too long; discarded rings cannot be reintroduced into the cycle, thus increasing the risk and consequent discard costs”.

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Making the most of limited space

Finally, tackling one of the most complex aspects of the system development phase, namely the line layout, is wothwhile. Actually, one of the biggest problems has been housing such a complex system in such a limited space, together with the need, thinking about future developments, to leave space and therefore elbow room in order to be able to introduce new stations and meet other future needs related to incoming part numbers. “This is a problem we have already had to face when the fourth part number was inserted,” Igor Bigolin concluded. “The customer requested the execution of a laser phasing notch on the outer diameter during assembly; a fiber laser marking source was therefore later integrated. Having foreseen space for future developments allowed us to integrate at a later stage this new machine, and we do not rule out the possibility and need to add more. However, we are confident that we still have some spare room on this line, but above all we know that we can count on the proven synergy between Cosmec Group and Mitsubishi Electric at all times. However, we are confident that we still have some room for manoeuvre on this line, but above all knowing that we can count on the proven synergy between Cosmec Group and Mitsubishi Electric at all times”.