Multimethodology based on Design-to-Value (DtV), integrated with simulation techniques and prioritization of teamwork for the optimization of a pneumatic rack & pinion actuator

The investigations here presented focus on the redesign and innovation of a pneumatic rack and pinion actuator for valve actuation, as a case study for investigating the potential of a multimethodology based on the Design to Value (DtoV) process, coupled with design techniques utilizing FEA simulations and giving high priority to teamwork. The final objective of this case study is to show how it is possible to optimize the design, increasing weight efficiency while maintaining performance, and to simplify it, with a reduction of components construction complexity, according to the growing demand for a lean production. The principle that guided all the activities was valorizing the power of teamwork, focusing the team on Safety and Reliability. In an initial phase, all the instruments foreseen by “Design-to-Value” process have been applied, obtaining a classification of the contents of the product constituting its sources of value. Subsequent outputs are proposals for efficient construction solutions, driving a second phase, dedicated to the re-design of the actuator. The peculiarity of this project has been to combine the “Design by Formulas” techniques with advanced FEA simulations (“Design by Analysis”), aiming to stress, deformation, and topology optimization. A two-step experimental validation is used, based on a preliminary “mockup” prototype followed by a complete detailed prototype, for confirming the results of the calculations and simulations, by directly performing a series of in-depth tests. Preliminary obtained results show that the approach based on the described multimethodology, makes it possible to optimize the design of the actuator, maintaining safety, reliability, and performance. In the case studied, the weight reduction is expected to be 8% and economic efficiency increase is expected to be near 20%.


Objectives of the activity
In this paper are reported the results of the investigations and of the activities performed during a project of optimization of a rack & pinion actuator, as a case study of application of a multimethodology based on Design to Value (DtoV) process, coupled with design techniques exploiting the potential of FEA.During all the activities the prioritization of teamwork has been a fundamental approach, as show in figure 1.
The rack & pinion actuator is a mature product which however has constant demand from the valve automation sector.First objective of the optimization is to align its features with those that have been identified as the most important sources of value perceived for this product by customers and operators in the sector.Second one is to ensure that the design complies with the most stringent requirements of IOP Publishing doi:10.1088/1757-899X/1306/1/012013 2 the latest versions of the international reference standards (actuators, pressure vessels).Concomitant objectives driving the design choices are to simplify the design, following the growing demand for lean production, increase lightness, maximize economic efficiency.The main final purpose is to design a safety and reliable product.

Product description
The studied product is the "rack and pinion" pneumatic actuator, designed in 1984, shown in Figure2.
An aluminum alloy hollow center body contains two pneumatic pistons, mounting linear gears (the racks), engaging a circular gear located on a vertical shaft (the pinion).This mechanism converts the linear motion of the pistons into the rotary motion of the pinion.The actuator is suitably powered by a pneumatic control system so that to obtain clockwise and anti-clockwise rotations and operate valves with 90° stroke, such as ball or butterfly valves.In the external chambers between pistons and lateral closing flanges, compression springs can be located, making a "spring return" function available.In this configuration the force for performing one of the two strokes is generated by the potential energy accumulated by compressing the springs under pressure action during the previous stroke.In "double acting" function both strokes are operated by pressure.

Design-to-Value: introduction to the process and initial activities
Design-to-Value (DtV) is an effective process, developed in the field of "value engineering", for obtaining product innovation, involving several activities aimed to maximize the value of the new design [1].DtV approach focuses on the value attributed to the product by the customers, in function of available features.Its maximization guides the decisions for the design optimizations [2].Among main elements of value, DtV takes into consideration safety, reliability, ease of use and maintenance, weight optimization and economic efficiency.Through DtV an attempt is made to understand which characteristics of the product are the most interesting for customers and industry experts, and to translate them into design choices.DtV allows modeling the characteristics of a product, based on what satisfies the real needs, ensuring that the product is perceived as having a high value [3].
During the application of DtV process, some fundamental steps can be identified, based on cooperation and exchange of inter-functional knowledge among the people involved in the project: 1 -Creation of an Inter-functional Team -A team is set up, made up of representatives of all company functions interacting with the product: design, production, assembly, quality assurance, sales, marketing, after market and customer care. 2 -Understanding the value for the customer -It is fundamental during this step to acquire and analyze information about needs, problems, and suggestions from the customers, by means of investigations, including quantitative and qualitative surveys.
3 -Generating improvement ideasthis activity is based on periodic inter-functional meetings and workshops, actively involving the entire team.Brainstorming activities, based on teamwork, allow the team to generate ideas about new features and innovative solutions, that could improve the design, always giving the highest priority to product safety and reliability.In the studied re-design, concerning a product that has been on the market for many years, opportunities have been investigated also concerning materials and production processes not available at the time of initial design.Ideas in the following areas have been identified: a. improvement of the topology of components, b. ideas for reducing the number of components, c. ideas for simplifying the functioning of product functions (for example, angular strokes adjustment system), d. ideas for simplifying the assembling activities.
In the context of DtV, improvement indices can be introduced, for monitoring performances of the new product.Here a mass reduction index Iw and a cost efficiency index Ic have been introduced, showing the percentage improvements, with equal safety and reliability, with respect to the old model, taken as a baseline to evaluate the impact of new design improvements.
Improvements of social and environmental value also are among the objectives of this application of DtV.The re-design is in fact an occasion to move towards solutions having a low environmental footprint.Investigations about the major or minor energy-intensive production processes have been carried out.In addition, components simplification with reduction of machining time allows for a reduction in the total energy required for production.Finally, it has been possible to estimate the total CO2 reduction linked to actuator manufacturing by means of a software dedicated to these evaluations.

"Teardown Analysis"
In the context of DtV process a very effective technique consists in examining a sample of the product having old design, by completely disassembling it and focusing on the analysis of its components during brainstorming meetings [1], as shown in figure 3. Thanks to Complete disassembly it is possible for the team to have physically available on a workbench every single component, so that it can be easy to indepth analyze it.
Furthermore, during teardown it is possible to study the actions to be performed during the procedures for assembling/disassembling, in search for design changes making them faster and easier.Finally, entire functions of the product are analyzed, for example, the angular adjustment of the strokes, in search of more efficient construction solutions.Ideas born during the teardown are then added to the bucket of ideas identified during previous DtV steps.

"Design Change Proposals"
The proposals emerged during surveys, teamwork meetings and "teardown analysis" constitute a large pool, from which to draw the best ideas to be included in the final plan of the design improvement initiatives [4].For each idea, the team highlighted the pros and cons, and ideas receiving a final positive opinion have been formalized in final "Design Change Proposals" (DCP), implemented in the next project phase, dedicated to detailed design.The main agreed DCPs are the following ones: 1. Re-design of the stroke adjustment system, by implementing a solution based on a cam (Figure 4 and Figure 5).

Detailed design phase
The path followed for executing the design plan is based on two successive and complementary phases.The first phase has been named "design by Formulas", borrowing this term from a standard for pressure vessels, EN 13445-3 "Unfired pressure vessels -part 3: design".It includes verifications performed by issuing electronic spreadsheets with structural verifications.These analyses are used to make the first choices regarding the structural characteristics of each component.
The second phase focuses on the use of simulation techniques, based on Finite Element Method (FEM).During this phase different design concepts are simulated, so that it is possible to arrive to experimental validation phase with design solutions that proved to be most promising, after careful optimization activities, based on "topology optimization" concept [5].

"Design by Formulas"
During this phase the verification of the safety and reliability of the components is performed by means 1306 (2024) 012013 IOP Publishing doi:10.1088/1757-899X/1306/1/0120135 of formulas for structural verifications, included in electronic spreadsheets.These formulas constitute the basic tool for choosing the minimum dimensions and thicknesses guaranteeing the components mechanical strength under the mechanical and pressure solicitations.
Starting shapes could then be refined and optimized thanks to simulation techniques, in the following design phase.For this case study the spreadsheet containing structural calculations was elaborated by using the formulas present in the manual "Roark's Formulas for stress and strain" [6].During verifications the components have been simplified, by schematizing them with simple geometric shapes and by dividing them into sections, for which suitable formulas are present.
In addition, being powered by pneumatic pressure, a rack and pinion actuator also represents a pressure vessel, even if its main function is delivering a torque.The safety of the design in presence of pressure loads is an absolute priority, and main industry standards require that actuator pressure containing parts are designed in compliance with recognized international standard for pressure vessels (EN13445-3, ASME BPVC Sec.VIII, …).
A spreadsheet complying with formulas of EN13445-3 standard has been then issued.Pressure containing parts are central body, lateral closing flanges and flange fixing screws.Pistons are housed inside the central body, and therefore do not contain the pressure towards the external environment.Pressure containing parts can simultaneously be subjected to loads of a different nature, in addition to pressure load, for which no formulas are available in the standards (for example, concentrated loads or earthquake solicitations).For these situations, main standards provide for the possibility to use FEA, defined as "design by analysis".In studied actuator this situation occurs for central body and lateral closing flanges (Figure 6), and the performed verifications are described in next paragraph.
At the end of "design by formulas", a prototype, consisting of a detailed 3D model where all the parts have been preliminary verified, is ready to enter in the next phase.

"Design by Analysis"
FEA simulations are a very powerful tool, here used for two concomitant purposes.On one side, to carry out a further in-depth verification of the design choices, on the other one, to achieve an accurate "design optimization".
In a first step, simulations allow to verify that stress levels in the components are aligned with those found by means of formulas [7].In addition, they are used for verifying the conformity to pressure vessels international standards, in this case to requirements of "Annex B -Design by Analysis -Direct Route" of EN13445-3.In a second extremely important step, FEA are used to perform an optimization of the shape and dimensions of each component, a set of characteristics often defined as "topology" [8].It is possible to model the component geometry, reinforcing the areas where a high strength is needed and lightening other ones where reinforcing material is not necessary [9,10].Two examples are reported below, for describing more clearly how this approach was used.
1) Optimization of a component -piston An integrated approach between structural calculations and FEA was extensively used for one of most important actuator components, the piston.Structural checks by formulas are very difficult for this component, having a complex shape, connected to other components through constraints in different points, and is possible only by schematizing it in a simplified way.Simplifications introduced in the calculations do not allow for a precise evaluation of the distributions of deformations and stresses in the different areas, and consequently it is not possible to precisely evaluate if, with hypothesized thicknesses, the material is used in the best way.Alternatively, accepting to have lower safety factors in calculations and then lower thicknesses, could lead to increase the probability to revise the design during the experimental validation.To complement the calculation-based method, it is therefore possible to use FEA.For the piston it was possible: -to simulate the real constraints and real contacts existing with surrounding components; -to identify areas subject to high stress concentrations and verify the possibility to accept small local plasticizations under certain conditions; -to study the detailed maps and trends of deformation and stress in the component.A detailed representation of the distribution of these quantities makes it possible: A) to strengthen weak areas, if present, B) to identify, vice versa, less stressed areas, and, if possible, remove or redistribute material.This shape improvement process is also called "topology optimization" and is a very effective tool for increasing the weight efficiency, while maintaining the functionality and respecting the constraints given by connections with other components [11].
The deformation levels present in the old piston were used as a "baseline" to define levels of acceptability, causing not excessive stress and then wear on the sliding ring guiding the piston inside the center body.The old piston did not present problems of this type and therefore the hypothesis was to maintain in the new prototype aligned values of deformations.In a first phase then simulations were carried out on old piston, to find reference values to compare with the new ones.The model for the simulations of the new prototype was initially a subassembly, where interactions with other components through different types of contacts ("bonded", "frictionless", "frictional") are possible, so as to have a detailed representation of the stresses in the region.In a second phase, FEA on models of the single piston, with constraints calibrated by means of the results of the complex model, allowed to speed up the analyzes, with the possibility to perform many simulations, each one associated to small geometry improvements.When the component is subject to design pressure (10,5 barg), stress values with a minimum safety factor of 1.5 with respect to yield value are considered as acceptable, with exception of small surface areas considered as "peak stress".The expected average stress, when the supply pressure is about half of the design pressure, can be considered at values below of the fatigue limit.
Several iterations have been carried out, as shown in figure 7, gradually optimizing the use of the material, and checking to remain within acceptable stress and deformation limits [12,13].At the end of the optimization process it has been possible to achieve a total weight reduction equal to 6%.

1) Verifications of center body and angular strokes regulation system
Thanks to FEA simulations it has been possible to verify the central body accurately and in accordance with EN134445-3 requirements.This component is in fact subjected to an additional concentrated load with respect to pressure, for which "Design by Analysis" is suggested.The component contains in fact the threaded holes for the grub screws of the angular strokes adjustment system.This system has been totally re-designed, with a construction solution based on a cam.The cam is connected to the pinion, allowing to stop its angular travel when it goes into contact with two grub screws, located frontally in the center body.Regulating the cam travel it is then possible to regulate actuator strokes.
A FEA model of the complete actuator assembly was prepared, where the contacts and reactions among all the components were simulated.By applying a pressure to the pistons, it has been possible to evaluate the entities and directions of the forces exchanged among the components, in particular, at the contact between cam and grub screw, as shown in figures 8 and 10.A special function was also included, allowing to simulate the presence of a real thread between grub screw and center body, even if, from a 3D point of view, components are modeled as smooth cylindrical surfaces.
Using this approach, the new cam system has been thoroughly verified and the geometry of the center body has been verified following topology optimization principles [14], guaranteeing at same time compliance with EN13445-3 requirements.In summary, accurate FEAs on critical components are a big help to confirm and optimize the design choices, correcting situations that could present criticalities (for example by updating fillet radii and other areas subjected too high peak stresses).Thanks to them, during the subsequent phase of the project dedicated to experimental tests on prototypes, it is expected to encounter a lower number of situations requiring modifications to the design, and in that case to deal with minor changes.

Experimental validation of the new design
Once the detailed re-design of the product was completed, a validation plan has been drawn up, containing all the tests necessary to discover and fix all possible critical points before proceeding with mass production [15].For this case study, a special validation procedure, based on two subsequent steps, has been adopted: 1-a first phase is focused on the creation of a partial prototype called "mockup"; 2-a second phase is focused on a sample identical to the actuator that will go into production.Prototypes are essential for multiple purposes: I. to validate the safety of the pressure containing parts, by performing the tests required by the standards, II. to confirm the good reliability of the product, ensuring that it can perform the emergency functions, when required, with a very low probability of failure.The actuator must in fact be certified as "SIL 3 Capable" (SIL = Safety Integrity Level), according to EN61508 "Functional safety of electrical/electronic/programmable electronic safety related systems".III. to validate good fatigue life under pressure and mechanical loads for all the components.The actuator must in fact be suitable for special applications, requiring performing up to 500,000 cycles during its operational life [16].IV. to check assembling activities, and to confirm the chosen dimensional and geometric tolerances.

Validation based on a "Mockup" prototype
A partial prototype here called "Mockup" has been assembled with the special aim to validate some functions of the actuator.Checks are focused on the new strokes adjustment system and on the new pinion bushings.In fact, dimensions of other important components, the casted pistons and the extruded central body, depend on them.The production processes of these components require to produce stamps, making very difficult to perform changes in component shapes once produced.Then the the chosen approach was to create a preliminary model, as shown in figure 9, composed by: 1) Components in the new version for pinion, pinion guide bushings, stroke adjustment grub screws.
2) The new designed cam.
3) A central body machined from solid.The component features detailed machining for the areas of interest for the tests while for other sections it does not present all the details present in final version.4) For all other parts not directly affected by the tests, components with old design taken from old model.During the assembly phases of the prototype, a problem had to be faced, regarding the assembly tolerances of the cam, that was never previously produced.Excessive backslash was noticed, requiring a design modification for indicating tighter dimensional tolerances.
Checks were performed about the correct assembling and functioning of the pinion bushings, completely re-designed for simplifying the assembly operations.Also, the ease of regulation of the new strokes adjusting system was tested.Once these preliminary checks were completed, tests under load allowed to verify the structural resistance of the new designed parts in static and dynamic conditions.The "mockup" was tested by performing a cyclic test, powering it with high pressure and high flow rates, to obtain high torques and high stroke execution speeds, causing impacts between the cam and the grub screws.The possible cumulative damage caused by the repetition of the impacts can in this way be assessed.After completing 900 cycles, the actuator was disassembled, and components examined.The absence of permanent deformations in grub screws was verified, and pinion and cam were checked for ensuring absence of cracks.Finally, the conditions of the pinion bushings were assessed, for excluding premature deterioration.
The observations on the components after the tests confirmed some behaviors foreseen by FEA with good approximation.For example, the formation of an acceptable small denting on the cam surface, in correspondence to the contact position with grub screw, was noticed, as shown in figure 10.This result is very important and confirms the useful predictions obtained with FEA.The tests on "mockup" prototype confirmed the validity of the completely new design solutions introduced after DtV analyzes, drastically reducing the probability of having to make changes to them in the final prototype.
At the time of writing this text, the tests on the "mockup" have been successfully completed and the procurement of the final parts made by casting and extrusion processes is ongoing.Considering that the experimental results examined in the "mockup" model are aligned with calculations and FEA predictions, it is expected that in final prototype also a certain alignment of the results will be found, allowing to avoid major modifications of big impact.

Validation of a complete prototype
The second part of the validation will be based on a prototype identical to the final model intended to production.All possible problems regarding the components not already checked with "mockup" could be discovered, and final changes could be carried out before the start of production.Tests of fundamental importance for the safety and reliability of the product will be performed, as briefly described below: I) Quality, dimensional, tolerances and assembling checks.II) Pressure tests -Tests listed below are essential to preserve the health of the operators, placing safe products on the market.These tests are the first ones to be carried out, both during prototype validation and once production started.
IOP Publishing doi:10.1088/1757-899X/1306/1/01201310 A) Leakage test at low pressure, for checking the correct functioning of sealing systems, B) Structural pressure tests, at pressure equal to 1.5 times the design pressure: 1,5 x Pd = 1,5 x 10.5 barg = 15,75 barg C) "Burst pressure test", performed only during validation, for checking the behavior of the actuator before being subject to structural collapse, in case of improper use or failures of the pneumatic supply system.Actuator is gradually powered up to a pressure equal to 2.5 times the design pressure: 2,5 x Pd = 2,5 x 10.5 barg = 26,25 barg Components are expected to plasticize and have permanent deformations.Some O-rings may be extruded, and the actuator begins to leak.Such a behavior without explosions can be assessed as positive.III) Verification of actuator performances -Torques delivered by the actuator at different angular positions are measured by means of a calibrated dynamometric brake.Torques aligned with the expected ones will confirm that the new components involved in torque transmission do not present unwanted deformations, increasing friction, and then causing a reduction in transmissible torque.IV) Cyclic endurance Test -Test finalized to verify the reliability and the good fatigue life of actuator components, by analyzing their behavior when subjected to a very high number of cycles [16].In accordance with reference standard EN15714-3:2022 "Industrial valves -Actuators -Part 3: Pneumatic part-turn actuators for industrial valves -Basic requirements", the minimum number of cycles to be performed without failures for actuators in this torque range is equal to 500,000 cycles.V) OK to launch the first production batch

Conclusions
The results of the activities carried out in the context of this case study show that a multimethodology based on the Design-to-Value process, integrated with innovative design techniques based on FEA simulations, and valorization/maximization of teamwork, make it possible to obtain a significant improvement in the re-design of a product, as shown in figure 11, maintaining constant safety, reliability, quality and performances.4 -Last but not least, increase of economic efficiency, maintain high standards of safety and reliability.

OLD DESIGN NEW DESIGN
Weight efficiency brings to an immediate benefit in terms of costs.Furthermore, components simplification with a reduction in machining time, led to a consequent further reduction of costs.
Finally, studies about simplification of assembling activities led to increase productivity.The expected achievable cost reduction for the present case study can be estimated with the following cost efficiency index Ic.Ic = (new costold cost) / old cost = -18% (2) The next steps of the investigations will be the application of FEA tools dedicated to Explicit Dynamics and Fatigue, for augmenting the details of predictions achievable with simulations, and entering in validation phase of other actuator sizes with a still more verified design.The current limitations to the integration in the design of components obtained by addictive manufacturing will also be investigated.
"Secret ingredient" fundamental for the good result of all the activities has been the collaboration.Teamwork and know-how exchange aimed at mutual enrichment are essential components for increasing the commitment of the team during all the project phases.

Figure 1 .
Figure 1.Fundamental components of the studied methodology applied for Actuator Optimization.

Figure 2 .
Figure 2. old design version of the studied rack and pinion actuator.

Figure 3 .
Figure 3. Moments of the teardown Analysis, during in-depth study of each component.

2 .
Optimization of the geometry of the casted lateral closing flanges.3. Optimization of the geometry of the extruded central body.4. Optimization of the geometry of the casted pistons. 5. Re-design of piston guide pads.6. Re-design of pinion bushings.7. Simplification of the system for fastening the pinion to the center body.8. Introduction of a new nameplate using QR code technology.

Figure 4 .
Figure 4. Old Angular Strokes Adjustment system based on lateral screws and complex machining.

Figure 5 .
Figure 5. New system based on a cam system and simplified components.

Figure 6 .
Figure 6.Lateral closing flanges are subjected to pressure or spring loads.According to EN13445-3, for spring loads verifications by means of FEA are possible.

Figure 7 .
Figure 7. Steps of the topology optimization analysis of the piston.

Figure 8 .
Figure 8. FEA simulations used for topology optimization and verification of compliance to EN13445-3 of the center body.

Figure 9 .
Figure 9. Moments of the validation by means of a "mockup" prototype.From left: (a) center body obtained by machining a solid block, (b) assembling of the prototype, (c) execution of cyclic test with angular deformations measurement.

Figure 10 .
Figure 10.Images showing Consistency between the results obtained with FEA and results of experimental tests on the cam -grub screw connection.

Figure 11 . 1 ) 3 -
Figure 11.Comparison between the actuator before and after the value-driven design optimization activites.

Figure 12 .
Figure 12.Increase of product efficiency in terms of weight and cost reduction.