The “Pit-Stop” Concept Guides the Assembly of Drawers

Designing and building a system for the assembly of sides for metal drawers – as well as related subassemblies – capable of ensuring a production capacity of 700 drawer kits/h, each of which consists of a right drawer side and a left drawer side for a total of 1,400 pieces/h to be assembled. This is the challenge taken up and won by Cosberg, who has developed a system capable, among other things, of rapid production changes, since the final product is made in 21 variants, resulting from the combination of three different heights with seven different lengths. In addition, there is the complexity of the element and its final configuration, since the total components to be assembled for each finished kit are more than 60.

by Fabrizio Garnero

A difficult and complicated production challenge that Cosberg has faced by strengthening the added values that have always characterized its products to reduce “machine downtime”, ensuring timely start-up and doing everything necessary to maintain high production levels. The intent is to get as close as possible to the “Pit-Stop” concept, i.e. machines for which downtime due to, for example, production changes or maintenance is minimized, if not canceled. Just as in Formula 1, where victory or defeat often depends on pit stops, it becomes vital to standardize machines as much as possible and study systems that minimize downtime, while maintaining high flexibility and reliability.

Some machines that make up the entire system for the assembly of drawer sides, able to assemble 1,400 pieces/hour.
Some machines that make up the entire system for the assembly of drawer sides, able to assemble 1,400 pieces/hour.

Therefore, in order to meet the customer’s needs and, at the same time, to pursue the path towards the “Pit Stop” concept, Cosberg has offered and then built four separate systems: two of them assemble the mechanisms called “turrets” and are in turn composed of two rotary tables; one plant assembles the right turrets and the other assembles the left turrets. A third system consists of a rotary table which assembles the “adjustment unit” in the right and left variants. Finally, the fourth system is downstream from the previous three and consists of an in-line machine with free pallets suitable for assembling the drawer covers; among the components used by this line are the three subgroups assembled by the three upstream systems and here is where the complete and finished kits come from.
Choices are made fully observing the Pit-Stop concept
One of the factors that made the customer choose the Cosberg solution was precisely its flexibility, which is essential in this system. Feeding units entirely designed and manufactured by Cosberg have been used on all the machines, in combination with MoxMec solutions, including, for example, the spring routers.

Rotary table made up of 30 stations, which mounts one of the subassemblies.
Rotary table made up of 30 stations, which mounts one of the subassemblies.

For the displacement of components – which takes place from different picking points and planes – and for the positioning of different pieces on the table, in addition to the traditional pick & place modules, both scara and anthropomorphic robots have been chosen.
For screwing, units designed and manufactured by Cosberg were used, consisting of a mechanical part, with great strength and durability, managed by a “commercial” brushless motor that can be easily programmed using the machine HMI, together with a standard motor, which Cosberg also uses for other modules such as arms, riveting units and slides. This avoids the burden of installing another control unit and, instead, achieves a standardization of the different units which facilitates interface programming, use by the operator and management of spare parts, because, with only two product codes, motors operating a multiple units are managed. The latter feature facilitates maintenance work and, above all, reduces the required time, fully observing the Pit-Stop concept. Still with this in mind, the possibility of swiftly replacing the screwing blade is added, just as quick as any motor replacement. This is made easier by the support position. Choosing a standard motor also allows for a simple configuration of units, which does not necessarily require the intervention of an expert technician.

A Scara Robot of the turrets’ assembly plant.
A Scara Robot of the turrets’ assembly plant.

The new Cosberg riveting systems – for eccentric shaping, pins and rivets – are also equipped with brushless motors that allow for control and parameterisation of the riveting process, making possible to program both speed and force. In this way, the same unit can perform operations on different inserts and on different planes and can also compensate for the various tolerances in the insert length. The assembly of the riveting unit on Cartesian axes allows it to be moved in space to perform multiple riveting operations and on different inserts (rivets, pins, eccentric) with a single unit. This allows the same unit to be used also for different pieces, greatly reducing production changeover times, also in line with the Pit-Stop philosophy.
Checks in several phases of these four assembly processes are carried out by means of vision systems entirely programmed by Cosberg, which in addition to contributing to the quality of the final result, allow for remote intervention if assistance is required.

The turret assembly plants

Now, let’s analyze in detail the four Cosberg plants starting from the upstream systems intended for the assembly of turrets, which start from a set of 20 components to manufacture 800 pieces per hour each and manage two product variants: high model and low model.
Production change is really quick, as it takes less than 5 minutes, since it is limited to the time necessary to set the product code. Not only that: the system is designed to be connected to the customer’s MES, through which it could automatically start production.
Each plant is composed of two rotary tables: the first counts 30 stations and assembles the mechanism, while the second (8 stations) takes care of the completion and final inspection. In concrete terms, the pre-assembled turret comes out of the first table, which is then transferred to the second rotary table by means of a belt that acts as a buffer.
In the first table, the correct orientation of all the components is checked by special systems before the pieces are positioned and centered perfectly on the table. Among this process, we mention the tapping of a hole on a plate, with a Cosberg tapping machine. At the end, the threaded plate is positioned so as to center it with respect to all the other elements already on the installation, including some rivets that are cadenced thanks to special selectors, characterized by an input and multiple outputs as well as by special units that insert them in the installation. Some components are instead handled by scara robots, capable to precisely manage and position pieces taken from different planes. This first part of turret assembly is completed by the special Cosberg riveting units mounted on X-Y axes, which shape the rivets and the eccentric. Finally, the good pieces are put on a belt to be conveyed to the second table.

In the second table, a grain is screwed using the Cosberg standard screwing unit, equipped – as explained above – with an electric motor equipped with current absorption control, which puts the grain in position. Another standard Cosberg unit takes care of shaping some rivets on the front plate. The process is completed by a device that rearms the turret, so that the spring is compressed and the mechanism is ready to snap, while also controlling force by means of a load cell. The finished and tested subgroup is then unloaded armed, ready to be transferred to the next in-line machine which will use it to assemble the final kits.

Due lineari alimentano un perno e un rivetto, sui quali, grazie a un portale a doppia pinza, viene inserito e centrato un terzo componente.
Due lineari alimentano un perno e un rivetto, sui quali, grazie a un portale a doppia pinza, viene inserito e centrato un terzo componente.

The assembly of the adjustment unit

Now, let’s move on to the “adjustment unit” mounting system, which starts from a set of seven components. A universal installation has been designed for the two product variants: right and left. In this way, the table can manufacture both versions simultaneously or dedicate the entire production to a single model, with no need to be retooled.
The cadence is 1,500 pieces/h, whether 750 pairs of right + left groups are produced, or in the event that production concerns only one of the two models.

The choice of universal fittings allows for a very rapid production change, as it is limited to the time required by the automatic set-up of the individual work units according to the product code chosen: less than 5 minutes in all.
The process starts from loading and feeding a cam on the table, in the right or left version, depending on the production batch set. The same goes for a bracket, which is also loaded in the right or left version, according to the product code being processed. Then an arm picks up the plate and places it on top of the cam, on the table position.
Next, a device inserts four pins. The work is completed by standard Cosberg units which allow for the riveting of 4 rivets simultaneously. Finally, another device unloads the pieces, which will then be used in the following process.

The plant must allow for fast production changeover times and to manage 21 product variants.
The plant must allow for fast production changeover times and to manage 21 product variants.

Everything revolves around clinching

Finally we get to the in line machine. It starts from fourteen components to assemble pairs of covers (right + left) of seven different lengths, each of which can have three heights, therefore the machine must manage twenty-one product variants. The cadence, as mentioned above, is 700 kits (or couples)/h.
Despite the large number of variants to be managed, the production change takes only 15’: limited to the time necessary to (automatically) empty the machine according to the product code chosen and the subsequent manual set-up of some system components.
The unloading of the assembled pieces takes place manually, in the first station of the machine, as well as manual loading of the “covers” and “connection profiles” in the next station, as a visual check of products is required. However, these stations are already set up to be automated, which in the past has already been done on other systems by this customer.
The process begins with the loading of the covers and the connection profiles, in the right and left versions. Subsequently, the connection profiles, both right and left, are hooked by an anthropomorphic robot to the relative covers by means of a rotation movement.
As anticipated, the assembly sequence also involves the use of subgroups mounted by the other plants. Two turrets, one right and one left, are fixed to their respective covers by means of a screw shot and screwed by a Cosberg unit equipped with an electric motor with current absorption control.

In the next step, the elements are fixed. For this operation, Cosberg has designed a fully electric clinching station: a solution that, in addition to ensuring savings in terms of time and maintenance costs, as well as energy costs, makes it possible – by means of algorithms – to detect the paint thickness and automatically adjust the strength and penetration of the tool that will clinch them, so that they remain constant, thus ensuring a “zero defect” result. Basically, the station adjusts according to the characteristics of the element to be machined and ensures correct sealing even in the presence of any discrepancies.

The assembly of the turrets starts from a set of 20 components.
The assembly of the turrets starts from a set of 20 components.

The final product is 100% traced and tested

Assembly continues with the insertion of rubber in the connection profile and, in the next phase, with the insertion of two other plastic turrets – one right and one left. These turrets, in three height variants, are picked by an anthropomorphic robot, which selects the correct model according to the product code being processed, and places it in the covers. The same anthropomorphic robot also takes care of housing the adjustment unit, which was assembled in one of the systems described above, in the turrets.
The turrets are fixed by screws managed by Cosberg units equipped with a brushless electric motor. The flexibility offered by this unit, which can count on force and torque adjustment thanks to the brushless motor, makes it possible to address at best the screwing problems related to the two different materials (metal first, plastic then). Anthropomorphic robots are used because they guarantee great flexibility, which is very useful for reducing time – as for example in the station just described – or for making particular movements, such as in the case of coupling between the covers and the connection profile. In the last station described, the robot makes it possible to efficiently manage the different turret models, reducing – even for this complex phase – production change to a simple setting of the product code, fully respecting the Pit-Stop philosophy.

System for assembling the “control unit”: it can assemble two product variants at the same time.
System for assembling the “control unit”: it can assemble two product variants at the same time.

Subsequently, another unit with current absorption electric motor screws hooks into the cover. The process ends with a station that laser marks each individual piece, allowing traceability of the production batch and thus meeting the customer’s need to mark each product permanently, associating this with a series of indelible information related to the production process.
Lastly, a check is made on the correct functioning of the mechanisms inside the drawer side. In this way, the final product is not only “traced”, but also 100% tested.

The system for assembling the “control unit” produces 1,500 pieces/hour.
The system for assembling the “control unit” produces 1,500 pieces/hour.

Times for production changes are minimized

In general, in the design and manufacturing of the entire system, Cosberg has been faithful to the principles that have always characterized its products: we speak, for example, of easy maintenance. This, thanks to the application of sensors and actuators (subject to wear) outside the mechanics, is simpler and, therefore, faster and cheaper.

Cosberg’s special riveting units programmed to shape multiple rivets.
Cosberg’s special riveting units programmed to shape multiple rivets.

The same principle is adopted for mechanical parts subject to wear, such as the heads of the rivet insertion units, the screwing units or channels on the linear distributors (designed and manufactured to allow for a quick change without having to disassemble the entire station). In addition to this, there is the standardization described above, which facilitates maintenance and management of spare parts and does not require expert technicians.
Flexibility is another important peculiarity; the time required by production changes is in fact minimized by preparing the machine for the assembly of all the variants, with no need to empty the loaders and thanks to the use of technologies such as anthropomorphic robots that makes it possible to perform multiple operations quickly.

For the assembly of the “adjustment unit” the choice of making universal laying allows a quick production change.
For the assembly of the “adjustment unit” the choice of making universal laying allows a quick production change.

Another key feature of this system is the fact that the rotary tables and the line are built on a cylinder block chassis, thus facilitating disassembly and transport. Thanks to the construction solutions, the entire plant was installed and started in just three days.
It is therefore clear how Cosberg transforms the Pit-Stop principles into concrete solutions, which translate into concrete and measurable advantages in terms of competitiveness for its customers, so that they can win their “Grand Prix”, too.