- Email: [email protected]
A helical wedge rolling process for producing a ball pin
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Available Availableonline onlineatatwww.sciencedirect.com www.sciencedirect.com Procedia Manufacturing 00 (2018) 000–000 Procedia Manufacturing 00 (2018) 000–000
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www.elsevier.com/locate/procedia www.elsevier.com/locate/procedia
Procedia Manufacturing 27 (2019) 27–32 Procedia Manufacturing 00 (2017) 000–000 www.elsevier.com/locate/procedia
ICAFT/SFU/AutoMetForm ICAFT/SFU/AutoMetForm 2018 2018
A A helical helical wedge wedge rolling rolling process process for for producing producing aa ball ball pin pin
Manufacturing Engineering a* Society International Conference 2017, MESIC 2017, 28-30 June a a b a*, J. Tomczaka, T. Bulzaka, S. Martyniukb Z. Pater 2017, Vigo (Pontevedra), Spain Z. Pater , J. Tomczak , T. Bulzak , S. Martyniuk a a
Mechanical Faculty, Lublin University of Technology, 36 Nadbystrzycka Str., 20-618 Lublin, Poland Mechanical Faculty, Lublinb University of Technology, 36 Nadbystrzycka Str., 20-618 Lublin, Poland bSIGMA S.A, 6 Barak, 21-002 Jastków, Poland SIGMA S.A, 6 Barak, 21-002 Jastków, Poland
Costing models for capacity optimization in Industry 4.0: Trade-off between used capacity and operational efficiency Abstract Abstract
a a,* Wedge Rolling b The paper describes a new metal forming process called Helical (HWR). Combining the advantages of cross A. Santana , P. Afonso , A. Zaninb, R. Wernke The paper describes a new metal forming process called Helical Wedge Rolling (HWR). Combining the advantages of cross wedge rolling and skew rolling methods, this process allows for continuous forming of axisymmetric parts. HWR is characterized wedge rolling and skew rolling methods,a this process allows 4800-058 for continuous forming of axisymmetric parts. HWR is characterized University of Minho, Guimarães, by high efficiency and low material losses. What may present a difficulty is thePortugal design of tools that will enable the formation of by high efficiency and low material losses. bWhat may present a difficulty isSC, theBrazil design of tools that will enable the formation of Unochapecó, 89809-000 Chapecó, parts with required shape. To overcome this and ensure effective design, numerical modelling is performed. The paper describes parts with required shape. To overcome this and ensure effective design, numerical modelling is performed. The paper describes the numerical modelling of a HWR process for a ball pin. The paper also presents the design of a stand for rolling tests (prototype the numerical modelling of a HWR process for a ball pin. The paper also presents the design of a stand for rolling tests (prototype helical-wedge rolling mill) and experimental results (obtained output: 30 pieces per minute). helical-wedge rolling mill) and experimental results (obtained output: 30 pieces per minute). Abstract © 2018 The Authors. Published by Elsevier B.V. B.V. 2019 The © 2018 Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) Under theopen concept of "Industry productionlicense processes will be pushed to be increasingly interconnected, This is an access article under the4.0", CC BY-NC-ND (https://creativecommons.org/licenses/by-nc-nd/4.0/) Selection and peer-review under responsibility of the scientific committee of ICAFT/SFU/AutoMetForm 2018. Selection andbased peer-review undertime responsibility the scientific much committee ICAFT/SFU/AutoMetForm 2018. information on a real basis and,ofnecessarily, moreofefficient. In this context, capacity optimization
goes beyond thetool traditional of capacity maximization, contributing also for organization’s profitability and value. Keywords: rolling; geometry;aim machine; helical-wedge rolling. Keywords:lean rolling;management tool geometry; machine; helical-wedge rolling. Indeed, and continuous improvement approaches suggest capacity optimization instead of maximization. The study of capacity optimization and costing models is an important research topic that deserves contributions from both the practical and theoretical perspectives. This paper presents and discusses a mathematical 1. Introduction 1. Introduction model for capacity management based on different costing models (ABC and TDABC). A generic model has been developed and it was to analyze idle the capacity and is to design the maximization organization’s Skew rolling is aused process in which material shapedstrategies between towards angle placed rolls rotatingofin the opposite Skew rolling is a process in which the material is shaped between angle placed rolls rotating in the opposite value. The The trade-off capacity maximization vs operational efficiency and (helical) it is shown that capacity directions. inclined position of the rolls causes the material to makeisahighlighted axial-rotational movement during directions. The inclined position of the rolls causes the material to make a axial-rotational (helical) movement during optimization might hide operational inefficiency. rolling. A characteristic feature of the skew process is primarily high productivity and the ability to manufacture a rolling. A characteristic featureElsevier of the skew process is primarily high productivity and the ability to manufacture a © 2017range The Authors. Published by B.V.low material losses [1]. wide of high accuracy products with wide range of high accuracy products with low material losses [1]. Peer-review underof responsibility of the scientific committee the Manufacturing Engineering Society International The process helical-wedge rolling combines theoffeatures of skew rolling and cross-wedge rolling Conference [2]. Wedges The process of helical-wedge rolling combines the features of skew rolling and cross-wedge rolling [2]. Wedges 2017. shaping the material are placed on rollers' barrels along the helix, which allows continuous rolling from one to shaping the material are placed on rollers' barrels along the helix, which allows continuous rolling from one to several dozen forgings from one section of the feed rod. During rolling, the wedges cut into the material, shaping Keywords: Cost Models; ABC;from TDABC; Capacity; Operational several dozen forgings oneCapacity sectionManagement; of the feedIdlerod. During rolling,Efficiency the wedges cut into the material, shaping 1. Introduction * Corresponding author. Tel.: +48 81 5384242; fax: +48 81 5384194 * The Corresponding author. Tel.: +48 5384242; fax: +48 81 5384194 for companies and their management of extreme importance cost of idle capacity is 81 a fundamental information E-mail address: [email protected] E-mail address: [email protected]
in modern production systems. In general, it is defined as unused capacity or production potential and can be measured 2351-9789 2018 The Authors. Published by Elsevier B.V.hours of manufacturing, etc. The management of the idle capacity in several©ways: tons of production, available 2351-9789 © 2018 The Authors. Published by Elsevier B.V. This is anAfonso. open access under the761; CC BY-NC-ND (https://creativecommons.org/licenses/by-nc-nd/4.0/) * Paulo Tel.:article +351 253 510 +351 253license 604 741 This is an open access article under the CC fax: BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) Selection and peer-review under responsibility of the scientific committee of ICAFT/SFU/AutoMetForm 2018. E-mail address: [email protected] Selection and peer-review under responsibility of the scientific committee of ICAFT/SFU/AutoMetForm 2018.
2351-9789 © 2017 The Authors. Published by Elsevier B.V. Peer-review under of the scientificbycommittee the Manufacturing Engineering Society International Conference 2017. 2351-9789 © 2019responsibility The Authors. Published Elsevier of B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) Selection and peer-review under responsibility of the scientific committee of ICAFT/SFU/AutoMetForm 2018. 10.1016/j.promfg.2018.12.039
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Z. Pater et al. / Procedia Manufacturing 27 (2019) 27–32 Author name / Procedia Manufacturing 00 (2018) 000–000
subsequent features on the material. The oblique position of the rolls causes axial displacement of the material between rolls and in this case fulfills the role of a specific feeder. The cutting of the shaped forgings from the remaining part of the batch is carried out using special knives placed on the wedges in the calibration zone [3]. Helical-wedge rolling is used on a large scale in the production of steel balls used on grinding media in ball mills [4]. Skew rolling technology produces balls 15-125 mm. The efficiency of such a process is very high, because it is possible to obtain part during one rotation of the rolls. Additionally, by increasing the multiplication of the number of rolls, it is possible to increase the production efficiency [5]. Skew rolling is also used in the production of a wide range of elements of various shapes, which, like balls, are used in ball mills. The potential of helical-wedge rolling is much less used in the production of stepped axisymmetrical forgings or preforms. One of the first applications of helical-wedge rolling technology took place in 1949 in a passenger car factory in the former USSR [7]. This process has been used for rolling preforms, from which forged connecting-rods were forged in subsequent operations. Currently, work on this rolling process is carried out at the University of Science and Technology Beijing. A number of helical-wedge rolling technologies for balls, cylpeps, forged as well as graduated axisymmetrical shafts [8] were developed there. In Europe, work on the skew and wedge rolling process is carried out in Poland by the employees of the Lublin University of Technology [9]. In order to carry out research work at the Lublin University of Technology, a skew rolling mill was designed and manufactured to enable hot rolling of steel. At the Lublin University of Technology there is also a prototype rolling mill for rapid prototyping of helical-wedge rolling technology. This rolling mill enables quick verification of the technology using modeled materials (e.g. plasticine). The rolls for rapid prototyping are made with 3D printing technology. Although there are references to the process of helical-wedge rolling for forgings other than forging of balls, there is no detailed analysis of this type of process. The only current information on this subject is presented in publications [10, 11], the results of which are limited only to numerical modeling using the finite element method. 2. Helical-wedge rolling process parameters Fig. 1 presents the forging of a ball pin with dimensions as well as drawings of rolls designed for helical wedge rolling of this part. In the rolling process a roll with a diameter of 290 mm was used, on which a wedge with the following parameters was wound: forming angle = 30° and spreading angle = 9°. To ensure axial displacement of the batch material in the roll groove, the rolls were inclined in the opposite directions at an angle of 3.5° to the rolling axis.
Fig. 1. Roll and ball pin forging used in the analyzed process of helical-wedge rolling
Z. Pater et al. / Procedia Manufacturing 27 (2019) 27–32 Author name / Procedia Manufacturing 00 (2018) 000–000
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Prior to the experimental tests, numerical modeling of the analyzed process was carried out in the Forge NxT 1.1 software based on the finite element method. In numerical modeling, as well as in experimental studies, a rod made of C45 steel with dimensions of 28 mm and length of 350 mm was used as a workpiece. The material model of C45 steel is described by the following equation: ߪ ൌ ͶͳͲͷ݁ ሺିǤଷହହ்ሻ ߮ሺିǤଵଷ்ିǤହሻ ݁
షబǤబబబబమషబǤబమఴభ ቁ ക
ቀ
߮ሶ ሺǤଵ଼்ିǤଶସଵሻ
(1)
where: ߪ is the yield stress [MPa], φ is the effective strain, ߮ሶ is the strain rate [1/s], T is the temperature [°C]. Tetragonal elements with an average size of 0.75 mm were used to discretize the workpiece. Before the rolling process, the material was heated up to 1100°C in the induction heater. The temperature of the rolls during the process was 50°C. Thermal contact between the rolled material and the tools describes a heat transfer coefficient of 10 kW/m2K. Mechanical contact was described by the Tresca friction model, for which the friction factor was 0.9. The rotational speed of the rolls was 30 rpm. The numerical model of the analyzed process is presented in Fig. 2, while the mill and the tools used in the experimental tests are shown in Fig. 3. The rolls have a segmental structure, this solution was used to facilitate the assembly of tools on the rollers of the rolling mill.
Fig. 2. Numerical model of the helical-wedge rolling process
Fig. 3. Test stand: a) skew rolling mill, b) rolls segments and guiding device
3. Helical-wedge rolling process parameters The next stages of forming of the ball pin are shown in Fig. 4. In the first stage of rolling between the adjacent wedges, a part of the material from which the ball of the pin is shaped is closed. The first wedge is also shaped by the narrowing, which will form a graduated shank. In the further rolling stage, successive wedges reduce the material diameters eventually shaping the forged core. Fig. 4a also shows the distribution of strain intensity on the surface of the shaped element. The largest strain values are located in areas where the largest cross-sectional area of the starting material is reduced. The deformation in the area of the ball is the result of slight upsetting of the material. Fig. 4b shows the distribution of strain intensity in the axial section. This distribution shows that the strain values in the central part of the forging are smaller than on the surface. This is the result of intensive material flow in the circumferential direction as a result of friction forces. In the obtained strain distribution an analogy can be found to the deformation distributions obtained in the typical cross-wedge rolling process [12]. Fig. 5 shows the numerically determined distribution of the material failure criterion based on the model described by Cockcroft-Latham. The criterion of damage in the analyzed case was used in two ways. In the first case, it was used to analyze the possibility of cracks forming in the shaped forging. In the second case, the critical trigger value was estimated based on the Cockcroft-Latham criterion. The critical value of the trigger characteristic is used to initiate the deletion of finite elements, which allows the division of the batch material. In the analyzed case, this feature was used to cut forgings by knives located on wedges in the calibrating part of the roller. It was arbitrarily assumed that the trigger's critical value is 2.75. The results obtained in Fig. 5 show that in the area of
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Z. Pater et al. / Procedia Manufacturing 27 (2019) 27–32 Author name / Procedia Manufacturing 00 (2018) 000–000
forgings the maximum values of the failure criterion do not exceed 1.37. Only in the area in which the forgings are cut, the criterion of destruction reaches a critical value. Confirmation of the correctness of the assumed critical value of the trigger is the fact that during the experimental tests the individual forgings from the rolled material were separated, as shown in Fig. 6. The Cockroft-Latham failure criterion compares the behavior of the material with uniaxial state of tensile stress relatively accurately. In the analyzed case of rolling there is a complex state of stress, which is additionally variable in time [13]. This phenomenon is commonly known as the Mannesmann effect. In order to estimate the cracks in this type of processes correctly, it is necessary to develop a new model of material cracking with a variable state of stress or to set limit values for existing criteria taking into account the complex state of stress that occurs in rotational shaping processes.
Fig. 4. Distribution of strain intensity: a) view on the surface of the part, b) view in the axial section
Fig. 5. Distribution of the standardized failure criterion according to Cockcroft-Latham: a) view on the surface of the part, b) view in the axial section
Fig. 7 presents the temperature distribution in the formed material after a time of about 8 s. The shaped forging after the rolling process has a high temperature of over 1000°C. In the central part of the forgings as well as in the rod, which has not entered into the roll gap, the temperature remains high as it is close to the initial temperature of 1100°C. In the area of the smallest diameters of forging, the temperature rises above the initial value due to the change of the work of plastic deformation into thermal energy. The process of helical-wedge rolling is a very efficient process and should be carried out using long-life stock. The use of a long feed reduces the amount of final waste per one forging, however, it involves the risk of excessive cooling of the final batch material. In connection with the above, the material should be heated continuously during the rolling process with the use of induction heaters prior to the rolling process.
Fig. 6. Ball pins after the rolling process in the rolling zone of the mill
Z. Pater et al. / Procedia Manufacturing 27 (2019) 27–32 Author name / Procedia Manufacturing 00 (2018) 000–000
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Fig. 7. Temperature distribution (°C): a) view on the surface of the part, b) view in the axial section
Validations of numerical calculations were carried out on the basis of a comparison of the shape of the workpiece at particular stages of the rolling process, which is shown in Fig. 8. A product from experimental tests was obtained by stopping the rolling mill during the rolling process. When comparing the obtained results, it can be stated that they remain in a very good agreement with each other. In the rolled up products shown in Figs. 8 and 6, no defects were identified that could disqualify the rolling process. The adopted scheme of cutting off forgings from the rest of the rolled material does not introduce deformation of the spherical part of the forging, which occurred in the case of cross-wedge rolling and was the result of bending of forgings on the cutting knife [12].
Fig. 8. A comparison of shape progression obtained during numerical modeling and experimental research
Comparison of the main dimensions of ball pin obtained during FEM and experimental research is presented in the Table 1. The length dimensions of ball pins produced in research tests are bigger than the nominal design ball pin. While the diameter dimensions are less than or equal to the nominal dimensions. The results obtained by FEM and experimental tests are consistent with each other. Machining allowance for the ball pin forging illustrated in Fig. 1 was set to 1 mm. The dimensions of the ball pin obtained during experimental tests comply with the assumed accuracy. Table 1. Comparison of the main dimensions of ball pin obtained during FEM and experimental research.
Dimension [mm] Nominal Experimental FEM
L1 82,0 82,6 82,5
L2 56,2 56,4 56,5
L3 46,6 46,8 46,4
L4 16,6 16,8 17,0
d1 29,0 28,8 28,9
d2 19,0 19,0 18,9
d3 22,0 21,7 21,8
d4 16,0 15,8 15,9
d5 19,0 19,0 19,1
The energy parameters of the rolling process are presented in the form of diagrams in Figs. 9 and 10, respectively for the forming force and the torque acting on one of the rolls. In both cases the nature of the distribution of the analyzed parameters is cyclical. The duration of one sequence of parameter changes is equal 2 s and corresponds to the duration of one rotation of the rolls. In the final stage of each revolution of the rolls, a drop in force and torque is observed, this decrease occurs when the forging is calibrated and this is typical of the cross-rolling processes. Then,
Z. Pater et al. / Procedia Manufacturing 27 (2019) 27–32 Author name / Procedia Manufacturing 00 (2018) 000–000
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the forming force and torque increase rapidly as a result of cutting the wedge forming the first constriction on the shaped material. The next increase in the force parameters is caused by cutting the next wedge, which is responsible for shaping the smallest grade of the forging. The maximum values of forming force and torque increase with the duration of the process, which of course is the result of the cooling of the material. The maximum values of the forming force do not exceed 60 kN. The torque maximum values reach 2000 Nm and they are relatively small.
Fig. 9. Distribution of the forming force acting on the roll during the rolling of the ball pins
Fig. 10. Distribution of the torque acting on the roll during the rolling of the ball pins
4. Summary The process of helical wedge rolling of ball pins forgings has been designed and analyzed in a numerical and experimental way. The obtained results clearly indicate the possibility of using this technology in industrial conditions. The main advantage of the presented process is high efficiency, which exceeds previously used technologies of crosswedge rolling and die forging. Based on the analysis, it can be concluded that the helical wedge rolling process ensures obtaining high accuracy products. In addition, the adopted cut-off scheme of finished forgings from the rest of the rod seems to be more accurate than the division scheme for forgings rolled in a double system by cross-wedge rolling technology. It has been confirmed in experimental studies that the assumed critical value of the trigger of 2.75, which initiates the removal of finite elements to separate the forgings, is correct. The obtained stress distributions, damage criteria and temperature are very similar to those occurring during cross-wedge rolling. Acknowledgements The research has been conducted under the project No. 2017/25/B/ST8/00294 financed by the National Science Centre, Poland. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13]
Z. Hu, B. Wang, Z. Zheng, Research and industrialization of near-net rolling technology used in shaft parts, Frontiers of Mechanical Engineering, 13 (2018) 17-24. Z. Pater, Analysis of the Helical-wedge rolling process for producing a long stepped shaft, Key Engineering Materials, 622 (2014) 893-898. Z. Hu, B. Wang, J. Liu, et al., Technology of Skew Rolling. Beijing, Chemical Industry Press, 2014, 4-5. M.V. Filippova, M.V. Temlyantsev, V.N. Peretyat’ko, E.E. Prudkii, Rolling of metal balls, Steel in Translation, 47 (2014) 435-439. Z. Pater, J. Tomczak, J. Bartnicki, M.R. Lovell, P.L. Menezes, Experimental and numerical analysis of helical-wedge rolling process for producing steel balls, International Journal of Machine Tools & Manufacture, 67 (2013) 1-7. H. Yang，L. Zhang, Z. Hu, The analysis of the stress and strain in skew rolling, Advanced Materials Research, 538-541 (2012) 1650-1653. V.Z. Smirnov. V.P. Anisiforov. M.V. Vasilchikov, et al., Poperechnaya prokatka v mashinostroyenii, GNTIML, Moskva 1957. Z. Hu, C. Yang, B. Wang, Development of part rolling technology in China, Journal of Mechanical Engineering, 48 (2012) 7-12. Z. Pater, FEM analysis of the multi-wedge helical rolling process for a workholding bolt, MATEC Web of Conferences, 80 (2016) 1-6. Z. Pater, J. Tomczak, FEM modelling of a helical wedge rolling process for axisymmetric parts, Advances in Science and Technology Research Journal, 12 (2018) 115-126. Z. Pater, Analysis of the helical wedge rolling process for producing a lever preform, Global Journal on Technology, 7 (2015) 58-64. T. Bulzak, Z. Pater, J. Tomczak, Numerical and experimental analysis of a cross wedge rolling process for producing ball studs, Archives of Civil and Mechanical Engineering, 17 (2017) 729-737. Z. Pater, et al., Preliminary analysis of a rotary compression test, Advances in Science and Technology Research Journal, 12 (2018) 77-82.
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Available Availableonline onlineatatwww.sciencedirect.com www.sciencedirect.com Procedia Manufacturing 00 (2018) 000–000 Procedia Manufacturing 00 (2018) 000–000
ScienceDirect ScienceDirect
www.elsevier.com/locate/procedia www.elsevier.com/locate/procedia
Procedia Manufacturing 27 (2019) 27–32 Procedia Manufacturing 00 (2017) 000–000 www.elsevier.com/locate/procedia
ICAFT/SFU/AutoMetForm ICAFT/SFU/AutoMetForm 2018 2018
A A helical helical wedge wedge rolling rolling process process for for producing producing aa ball ball pin pin
Manufacturing Engineering a* Society International Conference 2017, MESIC 2017, 28-30 June a a b a*, J. Tomczaka, T. Bulzaka, S. Martyniukb Z. Pater 2017, Vigo (Pontevedra), Spain Z. Pater , J. Tomczak , T. Bulzak , S. Martyniuk a a
Mechanical Faculty, Lublin University of Technology, 36 Nadbystrzycka Str., 20-618 Lublin, Poland Mechanical Faculty, Lublinb University of Technology, 36 Nadbystrzycka Str., 20-618 Lublin, Poland bSIGMA S.A, 6 Barak, 21-002 Jastków, Poland SIGMA S.A, 6 Barak, 21-002 Jastków, Poland
Costing models for capacity optimization in Industry 4.0: Trade-off between used capacity and operational efficiency Abstract Abstract
a a,* Wedge Rolling b The paper describes a new metal forming process called Helical (HWR). Combining the advantages of cross A. Santana , P. Afonso , A. Zaninb, R. Wernke The paper describes a new metal forming process called Helical Wedge Rolling (HWR). Combining the advantages of cross wedge rolling and skew rolling methods, this process allows for continuous forming of axisymmetric parts. HWR is characterized wedge rolling and skew rolling methods,a this process allows 4800-058 for continuous forming of axisymmetric parts. HWR is characterized University of Minho, Guimarães, by high efficiency and low material losses. What may present a difficulty is thePortugal design of tools that will enable the formation of by high efficiency and low material losses. bWhat may present a difficulty isSC, theBrazil design of tools that will enable the formation of Unochapecó, 89809-000 Chapecó, parts with required shape. To overcome this and ensure effective design, numerical modelling is performed. The paper describes parts with required shape. To overcome this and ensure effective design, numerical modelling is performed. The paper describes the numerical modelling of a HWR process for a ball pin. The paper also presents the design of a stand for rolling tests (prototype the numerical modelling of a HWR process for a ball pin. The paper also presents the design of a stand for rolling tests (prototype helical-wedge rolling mill) and experimental results (obtained output: 30 pieces per minute). helical-wedge rolling mill) and experimental results (obtained output: 30 pieces per minute). Abstract © 2018 The Authors. Published by Elsevier B.V. B.V. 2019 The © 2018 Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) Under theopen concept of "Industry productionlicense processes will be pushed to be increasingly interconnected, This is an access article under the4.0", CC BY-NC-ND (https://creativecommons.org/licenses/by-nc-nd/4.0/) Selection and peer-review under responsibility of the scientific committee of ICAFT/SFU/AutoMetForm 2018. Selection andbased peer-review undertime responsibility the scientific much committee ICAFT/SFU/AutoMetForm 2018. information on a real basis and,ofnecessarily, moreofefficient. In this context, capacity optimization
goes beyond thetool traditional of capacity maximization, contributing also for organization’s profitability and value. Keywords: rolling; geometry;aim machine; helical-wedge rolling. Keywords:lean rolling;management tool geometry; machine; helical-wedge rolling. Indeed, and continuous improvement approaches suggest capacity optimization instead of maximization. The study of capacity optimization and costing models is an important research topic that deserves contributions from both the practical and theoretical perspectives. This paper presents and discusses a mathematical 1. Introduction 1. Introduction model for capacity management based on different costing models (ABC and TDABC). A generic model has been developed and it was to analyze idle the capacity and is to design the maximization organization’s Skew rolling is aused process in which material shapedstrategies between towards angle placed rolls rotatingofin the opposite Skew rolling is a process in which the material is shaped between angle placed rolls rotating in the opposite value. The The trade-off capacity maximization vs operational efficiency and (helical) it is shown that capacity directions. inclined position of the rolls causes the material to makeisahighlighted axial-rotational movement during directions. The inclined position of the rolls causes the material to make a axial-rotational (helical) movement during optimization might hide operational inefficiency. rolling. A characteristic feature of the skew process is primarily high productivity and the ability to manufacture a rolling. A characteristic featureElsevier of the skew process is primarily high productivity and the ability to manufacture a © 2017range The Authors. Published by B.V.low material losses [1]. wide of high accuracy products with wide range of high accuracy products with low material losses [1]. Peer-review underof responsibility of the scientific committee the Manufacturing Engineering Society International The process helical-wedge rolling combines theoffeatures of skew rolling and cross-wedge rolling Conference [2]. Wedges The process of helical-wedge rolling combines the features of skew rolling and cross-wedge rolling [2]. Wedges 2017. shaping the material are placed on rollers' barrels along the helix, which allows continuous rolling from one to shaping the material are placed on rollers' barrels along the helix, which allows continuous rolling from one to several dozen forgings from one section of the feed rod. During rolling, the wedges cut into the material, shaping Keywords: Cost Models; ABC;from TDABC; Capacity; Operational several dozen forgings oneCapacity sectionManagement; of the feedIdlerod. During rolling,Efficiency the wedges cut into the material, shaping 1. Introduction * Corresponding author. Tel.: +48 81 5384242; fax: +48 81 5384194 * The Corresponding author. Tel.: +48 5384242; fax: +48 81 5384194 for companies and their management of extreme importance cost of idle capacity is 81 a fundamental information E-mail address: [email protected] E-mail address: [email protected]
in modern production systems. In general, it is defined as unused capacity or production potential and can be measured 2351-9789 2018 The Authors. Published by Elsevier B.V.hours of manufacturing, etc. The management of the idle capacity in several©ways: tons of production, available 2351-9789 © 2018 The Authors. Published by Elsevier B.V. This is anAfonso. open access under the761; CC BY-NC-ND (https://creativecommons.org/licenses/by-nc-nd/4.0/) * Paulo Tel.:article +351 253 510 +351 253license 604 741 This is an open access article under the CC fax: BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) Selection and peer-review under responsibility of the scientific committee of ICAFT/SFU/AutoMetForm 2018. E-mail address: [email protected] Selection and peer-review under responsibility of the scientific committee of ICAFT/SFU/AutoMetForm 2018.
2351-9789 © 2017 The Authors. Published by Elsevier B.V. Peer-review under of the scientificbycommittee the Manufacturing Engineering Society International Conference 2017. 2351-9789 © 2019responsibility The Authors. Published Elsevier of B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) Selection and peer-review under responsibility of the scientific committee of ICAFT/SFU/AutoMetForm 2018. 10.1016/j.promfg.2018.12.039
28 2
Z. Pater et al. / Procedia Manufacturing 27 (2019) 27–32 Author name / Procedia Manufacturing 00 (2018) 000–000
subsequent features on the material. The oblique position of the rolls causes axial displacement of the material between rolls and in this case fulfills the role of a specific feeder. The cutting of the shaped forgings from the remaining part of the batch is carried out using special knives placed on the wedges in the calibration zone [3]. Helical-wedge rolling is used on a large scale in the production of steel balls used on grinding media in ball mills [4]. Skew rolling technology produces balls 15-125 mm. The efficiency of such a process is very high, because it is possible to obtain part during one rotation of the rolls. Additionally, by increasing the multiplication of the number of rolls, it is possible to increase the production efficiency [5]. Skew rolling is also used in the production of a wide range of elements of various shapes, which, like balls, are used in ball mills. The potential of helical-wedge rolling is much less used in the production of stepped axisymmetrical forgings or preforms. One of the first applications of helical-wedge rolling technology took place in 1949 in a passenger car factory in the former USSR [7]. This process has been used for rolling preforms, from which forged connecting-rods were forged in subsequent operations. Currently, work on this rolling process is carried out at the University of Science and Technology Beijing. A number of helical-wedge rolling technologies for balls, cylpeps, forged as well as graduated axisymmetrical shafts [8] were developed there. In Europe, work on the skew and wedge rolling process is carried out in Poland by the employees of the Lublin University of Technology [9]. In order to carry out research work at the Lublin University of Technology, a skew rolling mill was designed and manufactured to enable hot rolling of steel. At the Lublin University of Technology there is also a prototype rolling mill for rapid prototyping of helical-wedge rolling technology. This rolling mill enables quick verification of the technology using modeled materials (e.g. plasticine). The rolls for rapid prototyping are made with 3D printing technology. Although there are references to the process of helical-wedge rolling for forgings other than forging of balls, there is no detailed analysis of this type of process. The only current information on this subject is presented in publications [10, 11], the results of which are limited only to numerical modeling using the finite element method. 2. Helical-wedge rolling process parameters Fig. 1 presents the forging of a ball pin with dimensions as well as drawings of rolls designed for helical wedge rolling of this part. In the rolling process a roll with a diameter of 290 mm was used, on which a wedge with the following parameters was wound: forming angle = 30° and spreading angle = 9°. To ensure axial displacement of the batch material in the roll groove, the rolls were inclined in the opposite directions at an angle of 3.5° to the rolling axis.
Fig. 1. Roll and ball pin forging used in the analyzed process of helical-wedge rolling
Z. Pater et al. / Procedia Manufacturing 27 (2019) 27–32 Author name / Procedia Manufacturing 00 (2018) 000–000
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Prior to the experimental tests, numerical modeling of the analyzed process was carried out in the Forge NxT 1.1 software based on the finite element method. In numerical modeling, as well as in experimental studies, a rod made of C45 steel with dimensions of 28 mm and length of 350 mm was used as a workpiece. The material model of C45 steel is described by the following equation: ߪ ൌ ͶͳͲͷ݁ ሺିǤଷହହ்ሻ ߮ሺିǤଵଷ்ିǤହሻ ݁
షబǤబబబబమషబǤబమఴభ ቁ ക
ቀ
߮ሶ ሺǤଵ଼்ିǤଶସଵሻ
(1)
where: ߪ is the yield stress [MPa], φ is the effective strain, ߮ሶ is the strain rate [1/s], T is the temperature [°C]. Tetragonal elements with an average size of 0.75 mm were used to discretize the workpiece. Before the rolling process, the material was heated up to 1100°C in the induction heater. The temperature of the rolls during the process was 50°C. Thermal contact between the rolled material and the tools describes a heat transfer coefficient of 10 kW/m2K. Mechanical contact was described by the Tresca friction model, for which the friction factor was 0.9. The rotational speed of the rolls was 30 rpm. The numerical model of the analyzed process is presented in Fig. 2, while the mill and the tools used in the experimental tests are shown in Fig. 3. The rolls have a segmental structure, this solution was used to facilitate the assembly of tools on the rollers of the rolling mill.
Fig. 2. Numerical model of the helical-wedge rolling process
Fig. 3. Test stand: a) skew rolling mill, b) rolls segments and guiding device
3. Helical-wedge rolling process parameters The next stages of forming of the ball pin are shown in Fig. 4. In the first stage of rolling between the adjacent wedges, a part of the material from which the ball of the pin is shaped is closed. The first wedge is also shaped by the narrowing, which will form a graduated shank. In the further rolling stage, successive wedges reduce the material diameters eventually shaping the forged core. Fig. 4a also shows the distribution of strain intensity on the surface of the shaped element. The largest strain values are located in areas where the largest cross-sectional area of the starting material is reduced. The deformation in the area of the ball is the result of slight upsetting of the material. Fig. 4b shows the distribution of strain intensity in the axial section. This distribution shows that the strain values in the central part of the forging are smaller than on the surface. This is the result of intensive material flow in the circumferential direction as a result of friction forces. In the obtained strain distribution an analogy can be found to the deformation distributions obtained in the typical cross-wedge rolling process [12]. Fig. 5 shows the numerically determined distribution of the material failure criterion based on the model described by Cockcroft-Latham. The criterion of damage in the analyzed case was used in two ways. In the first case, it was used to analyze the possibility of cracks forming in the shaped forging. In the second case, the critical trigger value was estimated based on the Cockcroft-Latham criterion. The critical value of the trigger characteristic is used to initiate the deletion of finite elements, which allows the division of the batch material. In the analyzed case, this feature was used to cut forgings by knives located on wedges in the calibrating part of the roller. It was arbitrarily assumed that the trigger's critical value is 2.75. The results obtained in Fig. 5 show that in the area of
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forgings the maximum values of the failure criterion do not exceed 1.37. Only in the area in which the forgings are cut, the criterion of destruction reaches a critical value. Confirmation of the correctness of the assumed critical value of the trigger is the fact that during the experimental tests the individual forgings from the rolled material were separated, as shown in Fig. 6. The Cockroft-Latham failure criterion compares the behavior of the material with uniaxial state of tensile stress relatively accurately. In the analyzed case of rolling there is a complex state of stress, which is additionally variable in time [13]. This phenomenon is commonly known as the Mannesmann effect. In order to estimate the cracks in this type of processes correctly, it is necessary to develop a new model of material cracking with a variable state of stress or to set limit values for existing criteria taking into account the complex state of stress that occurs in rotational shaping processes.
Fig. 4. Distribution of strain intensity: a) view on the surface of the part, b) view in the axial section
Fig. 5. Distribution of the standardized failure criterion according to Cockcroft-Latham: a) view on the surface of the part, b) view in the axial section
Fig. 7 presents the temperature distribution in the formed material after a time of about 8 s. The shaped forging after the rolling process has a high temperature of over 1000°C. In the central part of the forgings as well as in the rod, which has not entered into the roll gap, the temperature remains high as it is close to the initial temperature of 1100°C. In the area of the smallest diameters of forging, the temperature rises above the initial value due to the change of the work of plastic deformation into thermal energy. The process of helical-wedge rolling is a very efficient process and should be carried out using long-life stock. The use of a long feed reduces the amount of final waste per one forging, however, it involves the risk of excessive cooling of the final batch material. In connection with the above, the material should be heated continuously during the rolling process with the use of induction heaters prior to the rolling process.
Fig. 6. Ball pins after the rolling process in the rolling zone of the mill
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Fig. 7. Temperature distribution (°C): a) view on the surface of the part, b) view in the axial section
Validations of numerical calculations were carried out on the basis of a comparison of the shape of the workpiece at particular stages of the rolling process, which is shown in Fig. 8. A product from experimental tests was obtained by stopping the rolling mill during the rolling process. When comparing the obtained results, it can be stated that they remain in a very good agreement with each other. In the rolled up products shown in Figs. 8 and 6, no defects were identified that could disqualify the rolling process. The adopted scheme of cutting off forgings from the rest of the rolled material does not introduce deformation of the spherical part of the forging, which occurred in the case of cross-wedge rolling and was the result of bending of forgings on the cutting knife [12].
Fig. 8. A comparison of shape progression obtained during numerical modeling and experimental research
Comparison of the main dimensions of ball pin obtained during FEM and experimental research is presented in the Table 1. The length dimensions of ball pins produced in research tests are bigger than the nominal design ball pin. While the diameter dimensions are less than or equal to the nominal dimensions. The results obtained by FEM and experimental tests are consistent with each other. Machining allowance for the ball pin forging illustrated in Fig. 1 was set to 1 mm. The dimensions of the ball pin obtained during experimental tests comply with the assumed accuracy. Table 1. Comparison of the main dimensions of ball pin obtained during FEM and experimental research.
Dimension [mm] Nominal Experimental FEM
L1 82,0 82,6 82,5
L2 56,2 56,4 56,5
L3 46,6 46,8 46,4
L4 16,6 16,8 17,0
d1 29,0 28,8 28,9
d2 19,0 19,0 18,9
d3 22,0 21,7 21,8
d4 16,0 15,8 15,9
d5 19,0 19,0 19,1
The energy parameters of the rolling process are presented in the form of diagrams in Figs. 9 and 10, respectively for the forming force and the torque acting on one of the rolls. In both cases the nature of the distribution of the analyzed parameters is cyclical. The duration of one sequence of parameter changes is equal 2 s and corresponds to the duration of one rotation of the rolls. In the final stage of each revolution of the rolls, a drop in force and torque is observed, this decrease occurs when the forging is calibrated and this is typical of the cross-rolling processes. Then,
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the forming force and torque increase rapidly as a result of cutting the wedge forming the first constriction on the shaped material. The next increase in the force parameters is caused by cutting the next wedge, which is responsible for shaping the smallest grade of the forging. The maximum values of forming force and torque increase with the duration of the process, which of course is the result of the cooling of the material. The maximum values of the forming force do not exceed 60 kN. The torque maximum values reach 2000 Nm and they are relatively small.
Fig. 9. Distribution of the forming force acting on the roll during the rolling of the ball pins
Fig. 10. Distribution of the torque acting on the roll during the rolling of the ball pins
4. Summary The process of helical wedge rolling of ball pins forgings has been designed and analyzed in a numerical and experimental way. The obtained results clearly indicate the possibility of using this technology in industrial conditions. The main advantage of the presented process is high efficiency, which exceeds previously used technologies of crosswedge rolling and die forging. Based on the analysis, it can be concluded that the helical wedge rolling process ensures obtaining high accuracy products. In addition, the adopted cut-off scheme of finished forgings from the rest of the rod seems to be more accurate than the division scheme for forgings rolled in a double system by cross-wedge rolling technology. It has been confirmed in experimental studies that the assumed critical value of the trigger of 2.75, which initiates the removal of finite elements to separate the forgings, is correct. The obtained stress distributions, damage criteria and temperature are very similar to those occurring during cross-wedge rolling. Acknowledgements The research has been conducted under the project No. 2017/25/B/ST8/00294 financed by the National Science Centre, Poland. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13]
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