The benefits of automating complex assembly
and testing processes, based on the dampers line

Damian Żabicki, 2022.05.23, Automatization and Robotization

The potential of ELPLC S.A. it is primarily the possibility of designing and implementing prototype stations, stands and lines tailored to the needs and problems occurring in industrial production and assembly processes. Based on the technical analysis of a specific technological course, machine concepts are created that automate and robotize prodution lines around the world.

Our potential consists of a team of over 160 specialists: designers, programmers, mechatronics, automation specialists and operators. Our own Research and Development Department allows for a significant expansion of competences in the implementation of R&D projects. A perfect example here is the product innovation implemented under the project POIR.01.02.00-00-0056 / 18-00 - "Innovative technological line for the assembly and testing of dampers and gas springs" intended for international manufacturers of Tier1 components. R&D works in line with the Polish National Smart Specialization No. 14, concerning the automation and robotization of technological processes, have already brought a number of benefits. These are the devices developed, such as the tester of the damping force characteristics, the station for filling gas and closing the dampers, as well as the station for filling gas and closing gas springs. It is worth taking a closer look at these solutions, and above all the benefits of their implementation into production.

Testing the damping force characteristics - technological requirements

When trying to automate the process of testing the damping force characteristics, it is necessary to use appropriate drives, forcing movement to measure the relationship between the vibration amplitude and their frequency, taking into account different damping factors. As practice shows, most of the testers are not able to simulate the movements that reflect the damper work in real conditions. In addition, the characteristic test requires the smallest possible measurement error, which in standard applications can be as much as 10%. In addition, short cycle times and precise displacement measurement over a large range are a must. For the proper performance of the damper characteristics test, it is necessary to measure the force with a certain precision.

Automation of the process of testing the damping force characteristics - concept assumptions of ELPLC S.A.

Zrobotyzowany ciąg montażowy

In view of the above technical assumptions, specified by manufacturers all over the world, ELPLC S.A. has attempted to design a system that allows to determine the damping force characteristics. Taking up this challenge by the company ELPLC S.A. was not accidental. Extensive research and development experience gained in previous projects in the automotive industry was a guarantee of an appropriate approach and design skills. In addition, the company's portfolio already contained a number of prototype and tailor made solutions in the form of robotic and modular production lines and systems, including assembly stations, both automatic and semi-automatic. It is also a significant number of innovative and successfully working solutions in the form of leak testers, various types of control and measurement stations: including those based on complex vision systems, working in quality control in very precise technological processes of the automotive industry.

Konepcja zrobotyzowanej linii

At the design stage, it was necessary to apply technical solutions that had to simulate the damper's work, allowing measurements to be made with errors resulting from the specifications of the technical standards of the Automotive Industry. In addition, the universality of the machine was expected, allowing the testing of many references of dampers or gas springs of various diameters and heights. An important assumption was a modular design that allows the machine to be adapted to the facility conditions of the factory. The designed test station had to ensure an adequate return on investment, which was primarily determined by the cycle time.

The design of the control and visualization system of the tester's work was based on the assumptions of the Industry 4.0 standard with full traceability functionality. It is about the possibility of collecting data, viewing the current state of the machine, carrying out diagnostics and data analysis. An important role was played by the ability to properly operate the machine with possible integration with other IT systems operating in the factory. Another manifestation of Industry 4.0 compatibility is the line's adaptation to work with AGV / AMR.

In order to meet the assumed requirements, the company ELPLC S.A. designed a damping control system based on the study of damper vibration characteristics, with forced movement with electromagnetic linear motors. Two devices of this type are used in the construction of the test station. These are Siemens linear motors - they drive the test effector. In this way, a compression force (Fmax) of 10,350N was obtained. To ensure the appropriate accuracy of the measurement, it was necessary to measure the damping force, for which the HBM strain gauge (12.5 kN) with an appropriate analog-to-digital converter is responsible. It should be emphasized that the test force, amounting to 6.5 kN, is simulation-confirmed with a defined margin. To be accurate, the measurement must be performed in a strictly defined position of the damper, taking into account the assumed path from 0 to just over 400mm. - The designed station had to provide such a position.

The choice of the Siemens linear motor was also determined by its maximum speed (Vmax) reaching 90 m / min. This parameter allowed to shorten the test cycle time. The force measurement is supplemented by a track per unit time check. The IMS-I measuring system - Bosch Rexroth was used for this.

Advantages of the ELPLC S.A. concept.

ELPLC's design solutions, along with appropriate control, ensured automatic operation of the testing station. The measurement error was obtained at the level of 1.5%. It should be emphasized that in solutions based on a hydraulic drive, this parameter is even 10%. The cycle time of 6.8 s was also achieved - in the case of hydraulic drives it is 7.2 s. The measured displacement exceeds 450mm (standard is up to 350mm).

What's more, the measurement of the force is +/- 10 kN (standard +/- 5 kN). It should be emphasized that thanks to the appropriate dynamics of the system resulting from its weight, as well as the resolution of the linear movement measurement system and the stability of the readings, the optimal speed range was obtained: 0.5mm / s - 1000mm / s. This allowed for the performance of functional tests of most dampers available on the market.

Testing the characteristics of dampers in the technological assembly line - assumptions

Linia montażu amortyzatorów

However, the research and development work on the station for testing the characteristics of dampers went much further. In response to market needs, it was assumed that the designed machine may be one of the modules of a comprehensive assembly line for automotive dampers or gas springs.

At the stage of collecting data for line development, ELPLC's designers and constructors consulted the concepts and technical parameters of individual stations on an ongoing basis. Process engineers of dampers factories located all over the world expected a universal line that would allow the assembly of various dampers references. It was also noted that the manufactured dampers have pipes with a diameter of 30 to 60 mm, with a height between 120 and 600 mm. It was necessary to take into account different diameters (from 30 to 300 mm) and the position (from 25 to 100 mm) of the spring bed ring. Individual stations and transport routes of the line had to work with the finished product with a height range of 300 to 1000 mm. Additionally, the necessity to maintain a specific gas pressure in the damper (from 0 to 25 bar) and the correct gas force (from 20 to 500N) was emphasized. In addition, the assembly process required working with pads of various diameters (40-80mm) with a maximum weight of components of up to 8 kg.

There was a need to meet a number of additional requirements in terms of maintaining parameters such as force (45-150kN), as well as the damping force (-6500 - 6500N), occurring damper's appropriate working position (from 0 to 400mm). It was necessary to keep the speed requirements (from 0.5mm / s to 1000mm / s).

In addition, factory representatives emphasized the need for the line to perform control the basic dimensions of the dampers. The necessity of precise dosing of the oil in the amount between 60 ml and 600 ml was pointed out.

ELPLC's line is primarily characterized by automatic operation, durability and high accuracy of assembly and performance tests. No production staff is needed to fully operate the line. It is only required to deliver the containers with components to the loading station (module 1) and to pick up the loaded containers. The technological line, including the control cabinets, can be adapted to the logistic system of the factory. To connect the line with control cabinets, special connectors with a high IP protection level are provided.

The course of the process and technical parameters of the dampers assembly line

Linia montażu amortyzatorów z widocznym testerem CTS

After the line is loaded by the operator at the beggining, the damper is filled with oil (module 1). The closing of the damper takes place in module 3. It should be emphasized that the closing operation uses the technology of rounding the upper part of the cylinder while gassing and maintaining the required gas pressure inside.

In module 2, the already described test of the damping force characteristic is carried out. The next step is to check the key dimensions of the damper (housing length from 120 to 600mm). This operation takes place at the C4 station of module 1, using the Cognex vision system and the 6mm Techspec 2/3" prime lens.

An important stage in the assembly process is the precise dosing of oil into the damper chambers (module 1). A Prema hydraulic cylinder was used for this. Dosing the oil can be compared to the work of a syringe applying the right dose of oil. The actuator piston is connected to a helical drive, powered by a Siemens servo drive. Depending on the type of damper, the amount of the dosed oil varies from 60 to 600 ml..

Thanks to the use of appropriate design solutions and the versatility of the line, it is possible to assembly dampers with a pipe with a diameter between 30 and 60mm. It should be borne in mind that the diameter of the shock absorber pipe mounted on the line affects not only the transport pallet but also the operation of the damping force test station and the gas filling and closing station. Therefore, retooling systems cooperating with a specific pipe diameter have been used. In order to adjust the line flow to the damper pipe height, at all stations there is an appropriate clearance, allowing the safe passage of the pipe and the mounted piston rod.

Parameters such as diameter (from 30mm to 300mm) and position (from 25mm to 100mm) of the spring support ring are achieved on all key modules. The diameter of the spring support is a damper parameter that can significantly increase the dimensions of the component. As a result, the line transport system can carry dampers with a ring diameter from 30mm (the smallest cylinder diameter) up to 300mm.

Due to the fact that the ELPLC company, focused on the versatility of the line, hence the total height of the finished product to be handled is from 300 to 1000mm. Components of such heights can freely pass through the entire transport line of the line. To obtain this property, the pallet's tooling with the lowest possible damper support point was used, and in some places bottom tools with a reduced height were provided.

In module 3, the damper is filled with nitrogen and closed by rolling. The gas pressure in the damper is assumed to be between 0 and 25bar. Pressure is applied directly to the damper using the working head.

The gas force in the damper has range 20N - 500N. A HBM strain gauge with a transducer was used to measure the gas force. The specially designed swivel system plays an important role in this. The measuring range was selected in such a way that 90% of it covers the parameters of generally produced dampers.

The covers of the mounted dampers can have a diameter in range 40 - 80mm. These elements are picked up from the pallet by a gripper. Interchangeable jaws allow the gripper to be clamped on a wide range of covers. The innovative ELPLC's solution is a special system of quick gripper jaws retooling with repositioning. The maximum weight of the components for assembly is 8 kg.

Derivative projects

Designing a station for testing the characteristics of dampers allowed ELPLC S.A. for the implementation, in addition to the comprehensive assembly line, several additional research and development topics.

Thanks to the assumptions, accepted design concepts and a very careful analysis of the processes, a gas filling and closing station was also designed, integrating the performance of two processes in one place. This solution allowed to reduce the cycle time by half. This is because instead of two operations, usually performed on separate machines, gas-filled pre-closure and final closure, these operations are performed in a single movement. The availability of a continuous force value diagram facilitates data analysis and process quality control.

It is worth emphasizing that gas filling and closing stations are a frequent element of ELPLC's gas spring production lines. They work both in automotive factories and in other industries - for example in the furniture industry. In addition, the implementation project of the station for testing the damping force characteristics was carried out in parallel with the use of HoloLens 2 technology as a key element of Industry 4.0. and operation of modern machines. It is based on intelligent augmented reality glasses. As a result, it is possible to quickly diagnose and detect bottlenecks in the operation of machines. In addition, the use of such a solution, especially during covid restrictions, allows to shorten the time of retooling, services and inspections, as well as reducing the likelihood of machine failure and unplanned downtime. With the help of AR / MR glasses, you can remotely collect data from the process for the purposes of automation or indicate faults and places of machine failure to maintenance services.

Final conclusions from the case study

ELPLC S.A. station is a solution that manufacturers from all over the world have been expecting when it comes to automating the process of testing the damping force characteristics of shock absorbers. It was emphasized that the cycle time should be shortened to at least 6.8 s, the measurement error was 1.5%, the displacement exceeded 450 mm and the force was measured at the level of +/- 10 kN. For manufacturers of shock absorbers, it is important to obtain the optimal speed during the test in the range from 0.5mm / s to 1000mm / s, which is what the company ELPLC S.A. obtained thanks to the appropriate dynamics of the system related to its weight, the resolution of the road measurement system and the stability of the readings. As a result, the designed station allowed for the performance of functional tests of most shock absorbers available on the market.

It is worth noting that the tester can also be one of the elements of a complete, modular technological line for the assembly and testing of shock absorbers. The solution is, in turn, the answer of ELPLC S.A. for the needs of producers who expect the automation of the shock absorber assembly process, taking into account automatic operation, high accuracy of assembly and tests, as well as durability. To fully operate the line you need ... zero operators. The line requires only loading (module 1) and unloading, e.g. with AGV / AMR. This translates into a quick return on investment and the elimination of manual assembly, and thus a number of errors and risks associated with it.