Benefits of automating complex assembly and testing processes, exemplified by production lines for shock absorbers and gas springs

The potential of ELPLC S.A. primarily lies in the ability to design and implement prototype stations, workstations, and lines that precisely meet the needs and address the issues present in industrial production and assembly processes. Based on a technical analysis of specific technological processes, concepts for machines that automate factory work worldwide are developed.

Our potential is comprised of a team of over 160 specialists: designers, programmers, mechatronics engineers, automation engineers, and operators. Our in-house Research and Development Department significantly expands our capabilities in executing R&D projects. A prime example is the current product innovation project POIR.01.02.00-00-0056/18-00 – “Innovative Technological Line for the Assembly and Testing of Shock Absorbers and Gas Springs,” intended for international Tier 1 component manufacturers. The R&D work, aligned with National Smart Specialization No. 14 on the automation and robotics of technological processes, has already yielded numerous benefits. This includes devices such as a damping force characteristic tester for shock absorbers and gas springs, a gas filling and closing station for shock absorbers, and a gas filling and closing station for gas springs. It is worth taking a closer look at these solutions, especially the benefits their implementation brings to production.

Testing the Damping Force Characteristics of Car Shock Absorbers – Technological Requirements

When attempting to automate the process of testing the damping force characteristics of shock absorbers, it is necessary to use appropriate drives that induce movement to measure the relationship between vibration amplitude and frequency, considering different damping coefficients. As practice shows, most testers cannot simulate the movements that reflect the real working conditions of a shock absorber. Additionally, the characteristic test requires the smallest possible measurement error, which in standard applications can be as high as 10%. Furthermore, a short cycle time and precise displacement measurement over a wide range are necessary. For proper testing of the shock absorber characteristics, it is essential to measure the force with specified accuracy.

Automation of the Shock Absorber Damping Force Characteristic Testing Process – ELPLC S.A. Conceptual Assumptions

Given the above technical requirements specified by manufacturers worldwide, ELPLC S.A. undertook the challenge of designing a system that allows for determining the damping force characteristics of a shock absorber. This challenge was not randomly taken on by ELPLC S.A. The extensive R&D experience gained from automotive projects guaranteed an appropriate approach and design background. Additionally, the company’s portfolio already included several prototype and dedicated solutions in the form of robotic and modular production lines and systems, including both automatic and semi-automatic assembly stations. This includes a range of innovative and successfully operating solutions such as leak testers and various types of control and measurement workstations, including those based on complex vision systems, working in quality control in highly precise technological processes in the automotive industry.

During the design phase, it was necessary to use technical solutions that could simulate the work of the shock absorber, allowing measurements to be taken with errors resulting from the technical specifications of the automotive industry standards. Additionally, the machine’s versatility, enabling the testing of many shock absorber references of different diameters and heights, was expected. A crucial assumption was the modular design, allowing the machine to be adapted to the factory’s conditions. The designed testing station had to ensure an appropriate return on investment, primarily determined by the cycle time.

The design of the control and visualization system for the tester’s operation was based on Industry 4.0 standards with full traceability functionality. This includes data collection, real-time machine status monitoring, diagnostics, and data analysis. The ability to properly operate the machine with possible integration with other IT systems in the factory played a significant role. Another aspect of compatibility with Industry 4.0 is the line’s adaptation to work with AGVs/AMRs.

To meet the set requirements, ELPLC S.A. designed a damping control system based on examining the vibration characteristics of the shock absorber, with movement induced by linear motors. The testing station design includes two such devices. These are Siemens linear motors – they drive the testing actuator. This way, a compression force (Fmax) of 10350N was achieved. Ensuring the measurement’s accuracy required damping force measurement, handled by an HBM strain gauge (12.5 kN) with an appropriate analog-to-digital converter. It is noteworthy that the test force of 6.5 kN is confirmed by simulation with a specified reserve. For the measurement to be accurate, it had to be taken in a strictly defined position of the shock absorber, considering a set travel range from 0 to just over 400mm. – The designed station had to ensure such a position.

The choice of the Siemens linear motor was also influenced by its maximum speed (Vmax) reaching 90m/min. This parameter allowed for a shorter testing cycle time. The force measurement is complemented by the control of the distance traveled in a unit of time. For this purpose, the IMS-I measurement system by Bosch Rexroth was used.

ELPLC S.A.’s Competitive Advantage

The technical solutions implemented by ELPLC S.A., along with appropriate control systems, ensured the automatic operation of the testing station. The measurement error achieved was 1.5%. It is worth noting that in solutions based on hydraulic drives, this parameter can be as high as 10%. A cycle time of 6.8 seconds was also achieved – in the case of hydraulic drives, it is 7.2 seconds. The measured displacement exceeds 450mm (standard is up to 350mm).

In turn, the force measurement is +/- 10 kN (standard is +/- 5 kN). Thanks to the system’s appropriate dynamics resulting from its weight, the resolution of the displacement measurement system, and the stability of the readings, an optimal speed range of 0.5mm/s – 1000mm/s was achieved. This allowed for functional testing of most shock absorbers available on the market.

Testing the Characteristics of Shock Absorbers in a Technological Assembly Line – Assumptions

However, the R&D work on the shock absorber characteristic testing station went much further. In response to market needs, it was assumed that the designed machine could be one of the modules in a comprehensive assembly line for car shock absorbers.

During the data collection phase for designing the line, ELPLC S.A.’s designers and engineers continuously consulted on the concepts and technical parameters of individual stations. Process engineers from shock absorber factories worldwide expected a universal machine that allows for assembling various shock absorber references. It was noted that the produced shock absorbers have tubes with diameters from 30 to 60mm, with heights ranging from 120 to 600mm. It was necessary to consider different diameters (from 30 to 300mm) and the position (from 25 to 100mm) of the spring seat ring. Individual stations and transport sections of the line had to work with the finished product with a height ranging from 300 to 1000mm. Additionally, the need to maintain a specific gas pressure in the shock absorber (from 0 to 25bar) and the appropriate gas force in the shock absorber (from 20 to 500N) was emphasized. The assembly process also required working with end caps of different diameters (40-80mm) with a maximum component weight of up to 8 kg.

There was also a need to meet several additional requirements regarding maintaining parameters such as force (45-150kN), as well as the damping force of the shock absorber (-6500 – 6500N), occurring in its proper working position (from 0 to 400mm). It was also necessary to maintain the required working speed (from 0.5mm/s to 1000mm/s).

Additionally, factory representatives emphasized the need for the line to check the basic dimensions of the shock absorber. The importance of precise oil dosing in quantities ranging from 60 ml to 600ml was noted.

The technological line designed and produced by ELPLC S.A. is characterized by automatic operation, durability, and high assembly and testing accuracy. The line does not require production workers for full operation. It only requires loading containers with components at the loading station (module 1) and receiving loaded containers. The technological line, including control cabinets, can be adapted to the factory’s logistics layout. Special high IP protection connectors are provided for connecting the line to the control cabinets.

Process Flow and Technical Parameters of the Shock Absorber Assembly Line

After loading the line by the operator at the initial station, the shock absorber is filled with oil (module 1). The shock absorber is then sealed in module 3. It is worth noting that the sealing operation uses the technology of rounding the upper part of the cylinder while simultaneously gassing and maintaining the required gas pressure in the shock absorber.

In module 2, the described damping force characteristic test of the shock absorber is conducted. The next step is to check the key dimensions of the shock absorber (housing length from 120 to 600mm). This task is carried out at station C4 of module 1, using the Cognex vision system and the Edmunds 6mm Techspec 2/3″ fixed focal length lens.

A crucial step in the assembly process is the precise dosing of oil into the shock absorber chambers (module 1). For this purpose, a Prema hydraulic cylinder was used. Oil dosing can be compared to the operation of a syringe applying the appropriate amount of oil. The cylinder piston is connected to a screw drive powered by a Siemens servo drive. Depending on the type of shock absorber, the amount of dosed oil ranges from 60 to 600ml.

Thanks to the appropriate design solutions and the line’s versatility, it is possible to assemble shock absorbers with tube diameters ranging from 30 to 60mm. It should be noted that the diameter of the shock absorber tube mounted on the line affects not only the transport pallet but also the operation of the damping force characteristic testing station and the gas filling and rolling station. Therefore, systems for retooling tools cooperating with a specific tube diameter were used. To adapt the operation to the shock absorber tube height at all stations, an appropriate clearance was provided, allowing the safe passage of the tube and the attached piston rod.

Parameters such as diameter (from 30mm to 300mm) and position (from 25mm to 100mm) of the spring seat ring are achieved at all key modules. The diameter of the spring seat ring is a shock absorber parameter that can significantly increase the component’s dimensions. As a result, the ELPLC S.A. line’s transport system can transport shock absorbers with ring diameters from 30mm (smallest cylinder diameter) to 300mm.

Since ELPLC S.A. focused on the line’s versatility during the design phase, the total height of the handled finished product ranges from 300 to 1000mm. Components of these heights can freely pass through the entire transport section of the line. For this property, pallet tooling with the lowest possible support point of the shock absorber was used, and in some places, upper tools with reduced height were provided.

In module 3, the shock absorber is filled with nitrogen and sealed by rolling. It is assumed that the gas pressure in the shock absorber ranges from 0 to 25bar. Direct pressure application to the shock absorber is done in the head.

The gas force in the shock absorber is 20N – 500N. An HBM strain gauge with a transducer was used to measure the gas force. The specially designed rotary system plays a crucial role. The measurement range was chosen to cover 90% of the parameters of commonly produced shock absorbers.

The caps of the assembled shock absorbers can have diameters ranging from 40 to 80mm. These elements are picked up from the pallet using a gripper. Interchangeable jaws allow the gripper to clamp over such a wide range of caps. ELPLC S.A.’s innovative solution is a special quick-change system for the gripper jaws with positioning. The maximum weight of the components for assembly is 8 kg.

Derivative Projects

Designing the shock absorber characteristic testing station allowed ELPLC S.A. to undertake several additional R&D projects alongside the comprehensive assembly line.

Thanks to the assumptions, design concepts, and thorough process analysis, a gas filling and closing station was also designed, integrating two processes into one. This solution halved the cycle time. Instead of two operations, usually carried out on separate machines – preliminary closing with gas filling and final closing, these tasks are performed in one motion. The availability of a continuous force value chart facilitates data analysis and quality control.

It is worth noting that gas filling and closing stations are a common element of the gas spring production lines manufactured by ELPLC S.A. They operate in both automotive factories and other industries, such as furniture manufacturing. Additionally, alongside the implementation project of the shock absorber damping force characteristic testing station, work was conducted on using HoloLens 2 technology as a key element of Industry 4.0 and modern machine operation. It is based on smart augmented reality glasses. This allows for quick diagnostics and detecting machine operation irregularities. Moreover, using such a solution, especially during COVID-19 restrictions, shortens the time for retooling, servicing, and inspections and reduces the likelihood of machine failures and unplanned downtimes. Using the glasses, data from the process can be remotely collected for automation purposes or to indicate faults and locations of machine failures to maintenance personnel.

Conclusions from the ELPLC S.A. Case Study

The station designed by ELPLC S.A. is a solution that global manufacturers expected for automating the shock absorber damping force characteristic testing process. They emphasized the need to reduce the cycle time to at least 6.8 seconds, achieve a measurement error of 1.5%, measure displacement exceeding 450mm, and measure force at +/- 10 kN. For shock absorber manufacturers, achieving optimal testing speed in the range of 0.5mm/s to 1000mm/s was important, which ELPLC S.A. achieved thanks to the system’s appropriate dynamics related to its weight, resolution of the displacement measurement system, and stability of readings. As a result, the designed station allowed for functional testing 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 assembling and testing shock absorbers. This solution is ELPLC S.A.’s response to the needs of manufacturers seeking automation of the shock absorber assembly process, considering automatic operation, high assembly accuracy, performed tests, and durability. For full line operation, zero operators are required. The line only requires loading (module 1) and unloading, for example, using AGVs/AMRs. This translates to a quick return on investment and eliminates manual assembly, along with the associated errors and risks.