Analysis of performance and optimization of Iron Roughneck Tong Dies parameters

Abstract

In automated drilling operations within the oilfield industry, the Iron Roughneck represents the most advanced torque screwing equipment currently available. It is primarily used for the make-up and break-out of drill pipes, casings, and other drilling tools, making it an indispensable component of modern drilling automation. Among its key components, the Tong Dies play a crucial role, as their quality directly affects the operational efficiency of the Iron Roughneck and the service life of tubular components. However, research on Tong Dies remains limited, with most existing studies employing orthogonal optimization methods. While these studies address localized optimization issues, they have yet to achieve a globally optimal design. This study systematically analyzes the key factors influencing the performance of Iron Roughneck Tong Dies based on their actual working conditions. The analysis includes the biting depth of the Tong Dies on the drill string and the equivalent friction coefficient between the Tong Dies and the drill pipe. Building on these insights, a global parameter optimization is conducted for critical design parameters, including the tooth apex angle, tooth height, and tooth spacing. The goal is to identify an optimal parameter combination that maximizes the equivalent friction coefficient while maintaining a minimal biting depth, thereby improving performance. Furthermore, by conducting a strength analysis of the Tong Dies and comparative experiments before and after optimization, this study verifies the significant performance improvements achieved through optimization. The findings provide a theoretical foundation and an optimization methodology for the design and application of Iron Roughneck Tong Dies.

Introduction

With the continuous development of oil exploration and extraction, the automation level of oil drilling equipment has also been steadily improving¹. As one of the most critical automated devices for make-up and break-out operations, the Iron Roughneck has been increasingly introduced into oil drilling processes².

The Iron Roughneck is a multifunctional, safe, and highly efficient drill string make-up and break-out device. During operation, it is remotely controlled via an integrated control console to perform the make-up and break-out of oilfield tubular components³. As a critical auxiliary device in automated oilfield drilling equipment, the Iron Roughneck features a compact structure, powerful functionality, and ease of installation and operation. It is widely used in onshore and offshore drilling platforms as well as various field drilling environments⁴.

As a key component of the Iron Roughneck, the performance of the Tong Dies directly affects the operational efficiency of the equipment. Since the Tong Dies is a wear-prone part, enhancing its durability is crucial. To extend its service life, it is necessary to increase its strength and mitigate issues such as wear and fracture of the jaw teeth during make-up and break-out operations⁵.

Currently, Yancheng Teda Drilling Equipment Co., Ltd. has developed a friction-type Tong Dies, which enables the make-up and break-out of oil pipes without causing damage to them⁶. Additionally, Great Wall Drilling Engineering Co., Ltd. has introduced a non-marking friction-type Tong Dies, which effectively addresses the issue of biting marks on drill pipes and other tubular components during operation⁷. This innovative Tong Dies significantly reduces damage to tubular components, thereby extending their service life. Furthermore, the Institute of Metal Research, Chinese Academy of Sciences, has developed a composite petroleum drilling tong⁸. This Tong Dies consists of a base plate and composite teeth, where the base plate is made of high-toughness structural steel , and the teeth are composed of a metal-based composite material. The teeth can be designed in linear, curved, or patterned structures, and they are bonded to the tooth plate through diffusion welding. After diffusion welding, the transition layer exhibits a higher concentration of alloy elements, and quenching and tempering treatment further enhances the strength of the base material. This ensures crack resistance during use and provides wear resistance several times higher than that of conventional steel. The key advantage of this Tong Dies lies in its significantly extended service life and substantially reduced overall cost. Keystone’s B-type rotary Tong Dies is made of alloy steel and undergoes heat treatment to enhance its mechanical strength and wear resistance⁹. Vermeer Corporation has applied laser cladding technology to the Tong Dies, significantly improving its resistance to sliding wear and maximizing its durability. French oil major Total pioneered the application of Wire Arc Additive Manufacturing (WAAM) technology to 3D print Tong Dies¹⁰. This advanced manufacturing process effectively mitigates the impact of hydrocarbon-induced shock frequently encountered during well construction, thereby enhancing the structural integrity and operational reliability of the Tong Dies¹¹.

Although significant progress has been made in the research on Iron Roughneck Tong Dies, several challenges remain. During the torquing process, the clamping hydraulic cylinder drives the breakout tong to grip the drill string. At this moment, the Tong Dies directly contacts the drill string. If the load distribution between the Tong Dies and the drill string is uneven, stress concentration is likely to occur under the combined effect of clamping force and torque. This can lead to deep tooth marks on the drill string surface, accelerating Tong Dies wear and reducing the service life of both the Tong Dies and the drill string connection. Moreover, when the tooth marks left by the Iron Roughneck are relatively shallow, the equivalent friction coefficient tends to be lower¹². A lower equivalent friction coefficient results in reduced transmission efficiency, which is detrimental to the effectiveness of the Iron Roughneck during the torqueing process¹³.

To address the aforementioned issues, this study investigates the Tong Dies from the following aspects: Theoretical analysis of the key factors influencing the performance of Iron Roughneck Tong Dies. Based on this analysis, constraint equations are established for the biting depth of the Tong Dies on the drill string and the equivalent friction coefficient between the Tong Dies and the drill string. A parameter optimization approach is applied to optimize the key parameters of the Tong Dies, with the objectives of extending their service life and maximizing the equivalent friction coefficient to enhance torque transmission efficiency. Once the optimal parameters for the Tong Dies are identified, a strength analysis is conducted to ensure that the optimized design meets the required strength criteria. Finally, simulation experiments are performed to validate the effectiveness of the optimized Tong Dies design.

Performance parameters of Iron Roughneck Tong Dies and drill string

The structure of the new integrated iron roughneck is shown in Fig. 1, which mainly consists of the mast, base, clamp body, and extension mechanism.

Figure 1.

Overall structure of the Iron Roughneck. 1. Mast, 2. Clamp Body, 3. Base, 4. Extension mechanism.

According to the design requirements and with reference to relevant standards and specifications, the key parameters of the Tong Dies and drill string are determined, as shown in Table 1. The jaw of the clamp is shown in the Fig. 2.

Table 1.

Key parameters of Tong Dies and drill string.

Name	Parameter
Clamping method	Parallel Clamping
Clamping diameter range
Maximum make-up torque
Maximum break-out torque
Maximum clamping force
f	0.15
Tong dies type	Triangular tooth angle
Tong dies material	20CrMnTi
Tong die tooth apex angle
Tong die tooth spacing
Tong die tooth height
k	1.5
m	8
n	2
l

Figure 2.

Jaw structure diagram.

Performance analysis of Iron Roughneck Tong Dies

When the Tong Dies come into contact with the drill string, a slight deformation occurs under the clamping force. To simplify the analytical process, the theoretical model must satisfy the following two assumptions: Both the Tong Dies and the drill string are considered elastic bodies, and the elastic deformation occurring during the torqueing process is assumed to be small-scale deformation. The Tong Dies are symmetrically distributed on both sides of the drill string, and the drill string itself exhibits symmetry. Environmental factors are not considered, and the force conditions on both sides of the Tong Dies and the drill string are assumed to be identical¹⁴.

Analysis of biting depth of Iron Roughneck Tong Dies on drill string

The top-view cross-sectional schematic diagram of the Tong Dies gripping the drill string during the torqueing process of the Iron Roughneck is shown in Fig. 3.

Figure 3.

Top-view cross-sectional schematic diagram of Tong Dies and drill string in clamping state.

Throughout the torqueing process, the clamping hydraulic cylinder drives the Tong Dies toward the drill string until the tooth tips of the Tong Dies make contact with the outer surface of the drill string. The clamping hydraulic cylinder maintains hydraulic pressure, thereby applying a radial force P to the Tong Dies. Subsequently, the torqueing hydraulic cylinder is activated, generating a torque T. At this stage, the friction force between the Tong Dies and the drill string enables the transmission of torque T to the drill string, as illustrated in Fig. 3.

During the clamping process of the breakout tong Tong Dies on the drill string, the Tong Dies bite into the surface of the drill string, leading to elastic and plastic deformation in sequence. At the initial contact between the Tong Dies and the drill string surface, elastic deformation occurs. As the clamping force increases, the tooth tips of the Tong Dies and the drill string surface material gradually reach their ultimate stress limit. This causes yielding in the metal contact region, leading to plastic deformation. As the biting depth of the Tong Dies into the drill string surface increases, the contact area between the Tong Dies and the drill string surface continuously expands¹⁵. When the generated tangential frictional torque is sufficient to overcome the breakout resistance torque, the Tong Dies cease further penetration into the drill string, reaching a stable equilibrium state, as illustrated in Fig. 4.

Figure 4.

Structural schematic diagram of Tong Dies biting into the outer wall of the drill string.

In Fig. 4, the parameters are defined as follows: represents the tooth front angle, represents the tooth back angle, represents the tooth apex angle, R represents the radius at the drill string joint, r represents the radius of the transition fillet at the tooth apex angle, t represents the biting depth of the Tong Dies into the drill string, s represents the biting width of the Tong Dies on the drill string, h represents the height of the Tong Dies, q represents the circumferential distance between the tips of two adjacent Tong Dies teeth, and represent the pressures exerted on the front and rear surfaces of the tooth, respectively. Since the make-up and breakout processes are inverse operations, the tooth front angle during the make-up process is equivalent to the tooth back angle during the breakout process,. Under these conditions,the cross-section of the Tong Dies forms an isosceles triangle.

At this moment, the biting depth can be calculated based on the yielding degree of the Tong Dies tooth tip.

1

In the Tong Dies biting drill string model, the following relationship exists:

2

In the given equation:

• Yield strength of the Tong Dies material

• Safety factor

• Number of Tong Dies in the circumferential direction

• Number of Tong Dies in the vertical direction

• Length of each Tong Dies along the drill string axis

From Eqs. (1) and (2), it follows that:

3

From Fig. 4, it can be concluded that:

4

By transforming Eq. (4), we obtain:

5

Substituting Eq. (5) into Eq. (3), we obtain:

6

Through the theoretical analysis of the biting depth of the Tong Dies, a functional relationship between the biting depth and key parameters such as the tooth apex angle, tooth height, and tooth spacing is derived. This provides a theoretical basis for the optimization design of the key parameters of the Iron Roughneck Tong Dies.

Analysis of the equivalent friction coefficient between Iron Roughneck Tong Dies and drill string

The primary function of the Iron Roughneck Tong Dies is to transmit the torque required for make-up and break-out operations while minimizing damage to the outer surface of the drill pipe. Since the tooth tips of the Tong Dies are prone to stress concentration when in contact with the drill pipe, the radial force exerted as a normal force on the drill pipe’s outer wall often leads to plastic deformation at the contact points. This allows the Tong Dies to embed into the drill pipe surface, ensuring a secure grip for effective make-up and break-out operations¹⁶. In the structural model formed by the Tong Dies and the drill pipe, the equivalent friction coefficient is defined as the ratio of the resistance force preventing the drill pipe from rotating about its axis to the normal force exerted on the Tong Dies P. It is denoted as:

where:

• Equivalent friction coefficient

• Tangential resistance force preventing drill pipe rotation

• Normal force exerted on the Tong Dies

This equivalent friction coefficient serves as a key parameter in evaluating the gripping performance and torque transmission efficiency of the Tong Dies.

For the orthogonal transformation of , P, and , we have:

7

• Friction Coefficient Between Tong Dies and Drill String

When the Iron Roughneck performs make-up and break-out operations, the tooth front angle experiences a significantly larger normal force, while the tooth back angle is subjected to a much smaller normal force. Therefore, in theoretical analysis, the effect of the tooth back angle’s normal force can be neglected, setting . Substituting this into Eq. (7), we obtain:

8

Thus, we have:

9

Thus, since:

10

Substituting Eq. (10) into Eq. (9), we obtain:

11

Through the analysis of the equivalent friction coefficient, a functional relationship between the equivalent friction coefficient and key parameters such as the tooth apex angle, tooth height, and tooth spacing is derived. This provides a theoretical basis for the optimization design of the key parameters of the Iron Roughneck Tong Dies.

Parameter optimization design of Iron Roughneck Tong Dies

Establishment of the mathematical model for Iron Roughneck Tong Dies optimization

Taking the biting depth on the drill string as the constraint and the equivalent friction coefficient at the contact between the Tong Dies and the drill string as the optimization objective, a parameter optimization mathematical model for the Tong Dies is established¹⁷. The key structural dimensions, including the tooth apex angle, tooth spacing, and tooth height, are selected as design variables, with their respective parameter ranges defined. The formulation of the parameter optimization mathematical model for the Tong Dies is as follows:

12

13

14

Solution of the mathematical model

In the research and application of intelligent optimization algorithms, Genetic Algorithm (GA), Particle Swarm Optimization (PSO), Ant Colony Optimization (ACO), and Simulated Annealing (SA) are four of the most representative metaheuristic methods. Each of these algorithms exhibits distinct advantages and applicability in addressing different types of optimization problems. GA possesses strong global search capabilities and high coding flexibility, making it suitable for solving nonlinear, multimodal, non-differentiable, and multi-objective optimization problems¹⁸. Moreover, its inherent parallelism allows for easy scalability to large-scale problems. PSO is structurally simple with fewer parameters, demonstrating excellent convergence speed in continuous domains, though it is prone to premature convergence and sensitive to initial parameter settings¹⁹. ACO, with its positive feedback mechanism and effective path-finding capabilities for combinatorial optimization, is widely applied in graph-based problems; however, it suffers from high computational complexity, slow convergence, and a tendency toward early stagnation²⁰. SA simulates the physical annealing process, offering a strong ability to escape local optima, but it generally has low convergence efficiency and unstable performance²¹.

Through a comprehensive comparison, GA stands out with its stable optimization performance, strong robustness, high adaptability, and extensive practical verification across engineering domains. Therefore, in the context of the problem studied in this paper, the Genetic Algorithm is selected as the solution approach, as it effectively balances global exploration and convergence quality, providing a reliable foundation for solving the mathematical model.

Solving the above mathematical model using the the genetic algorithm (GA) involves several steps²². First, the population is initialized by randomly generating a set of potential solutions, which are then evaluated based on their fitness to measure the quality of each individual. Based on fitness values, a roulette wheel selection mechanism is employed to select superior individuals for the next generation²³. Next, the selected individuals undergo crossover operations, allowing genetic recombination to simulate biological evolution²⁴. Additionally, a mutation operation is introduced, where some individuals undergo random variations to enhance population diversity and prevent premature convergence to a local optimum²⁵. After generating the new generation, the algorithm re-evaluates the fitness of each individual and updates the population accordingly to ensure the inheritance and improvement of high-quality genetic traits²⁶. This process iterates continuously until the termination condition is met (such as reaching the maximum number of iterations or finding an optimal solution). Finally, the algorithm outputs the optimized results. The optimization process of the genetic algorithm is illustrated in Fig. 5. The logic of the genetic algorithm is detailed in Algorithm 1.

Figure 5.

GA process.

Algorithm 1.

Genetic Algorithm for Maximizing under Constraint

Optimization results

In the GA, iterations are performed under two different conditions: varying population sizes and different iteration counts, aiming to find the optimal solution. The crossover probability and mutation probability are set to 0.8 and 0.01, respectively, while the number of iterations is set to 300. The iteration performance under different population sizes is shown in Fig. 6. As observed in Fig. 6, under the same number of iterations, the iteration performance is optimal when the population size is set to 100. Therefore, the population size is determined to be 100 for the optimization process.

Figure 6.

Algorithm iteration graphs for different population sizes. (a) Genetic iteration graph for population size of 60; (b) Genetic iteration graph for population size of 80; (c) Genetic iteration graph for population size of 100; (d) Genetic iteration graph for population size of 120.

When the population size is set to 100, the iteration optimization is performed under different iteration counts to examine the convergence behavior, as shown in Fig. 7.From the figure, it is evident that the convergence performance is optimal when the iteration count is 300. Furthermore, as observed from Figs. 6 and 7, the algorithm successfully converges under all conditions.

Figure 7.

Algorithm iteration graphs for different iteration counts. (a) Iteration graph for 100 iterations; (b) iteration graph for 200 iterations; (c) iteration graph for 300 iterations; (d) iteration graph for 400 iterations.

By inputting all constraint conditions into MATLAB, an optimal set of values was obtained through the optimization process. Compared to the original values, significant improvements were observed, and the algorithm efficiently converged to the global optimal solution. The design variable values obtained for different population sizes, different iteration counts, and the optimized design variables are shown in Tables 2, 3, and 4, respectively. The iteration results demonstrate that the algorithm effectively optimizes the overall performance of the Iron Roughneck Tong Dies, highlighting the value of both the mathematical model and the optimization algorithm.

Table 2.

Design variable values for different population sizes with 300 iterations.

Population size		q (mm)	h (mm)
60		8.05	4.65	1.057
80		6.68	4.29	1.058
100		8.85	5.10	1.058
120		7.41	4.32	1.056

Table 3.

Design variable values for different iteration counts.

Iteration count		q (mm)	h (mm)
100		8.05	4.61	1.058
200		7.73	4.79	1.055
300		8.85	5.10	1.058
400		7.33	4.45	1.057

Table 4.

Comparison of design variable values before and after optimization.

Design variable	Original parameter range	Optimized parameter	Rounded parameter
q (mm)
h (mm)
		1.058	1.06

From Table 2, it can be observed that the optimized objective function values show minimal variation, with the fastest convergence speed occurring at a population size of 100. To enhance computational efficiency, a population size of 100 is selected. From Table 3, it is evident that different iteration counts lead to variations in the objective function values. At 300 iterations, the convergence speed and equivalent friction coefficient are optimal. To ensure stable optimization results, the optimal algorithm graph corresponds to the iteration graph with a population size of 100 and 300 iterations. The comparison of design variable values before and after optimization under the optimal parameters is presented in Table 4.

From the results, it can be observed that the optimized equivalent friction coefficient is 1.06, which is higher than the current equivalent friction coefficient provided by the Iron Roughneck Tong Dies, while ensuring that the biting depth remains below 1 mm. This enhances the performance of the Tong Dies while reducing damage to the drill string.

Strength analysis of the optimized Tong Dies and drill string

Compressive stress strength analysis of Tong Dies and drill string

Under the action of the make-up torque, a compressive force is generated between the front face of the embedded Tong Dies tooth and the drill string surface²⁷. At this moment, the compressive stress on the front face of the Tong Dies tooth and the drill string is equal. Therefore, the compressive strength conditions for both the Tong Dies and the drill string are the same. The force distribution is illustrated in Fig. 8.

Figure 8.

Force analysis diagram of Tong Dies biting into the drill string.

In Fig. 8, P represents the normal force transmitted from the clamping hydraulic cylinder to the Tong Dies, and Q represents the tangential force between the Tong Dies and the drill string. The tangential force Q is orthogonally decomposed along the friction force direction and its perpendicular direction, resulting in two components: , the force component perpendicular to the compression surface. , the force component along the compression surface.

The tangential force Q exerted by the Tong Dies on the drill string is used to transmit the torque T. At this point, the tangential force acts on the drill string with the minimum lever arm . If the number of Tong Dies is mn, the expression for the tangential force Q can be derived as:

15

The relationship between the component force and the tangential force Q is:

16

According to Figs. 4 and 8, the area where the component force perpendicular to the compression surface acts on the drill string is:

17

In , according to the sine formula, we can obtain:

18

By further simplification, we obtain:

19

Substituting into Eq. (19), we obtain:

20

Combining Eqs. (15), (16), (17), and (20), the compressive stress between the Tong Dies and the drill string is obtained as:

21

To ensure that the Tong Dies and the drill string meet the compressive strength requirements during the torqueing process, the torque T must satisfy the following relationship:

22

Where is the allowable compressive strength of the Tong Dies material.

In Eq. (22), t and r are relatively small compared to R. By neglecting their numerical values while retaining their order of magnitude, we obtain:

23

Since the Tong Dies needs to bite into the drill string to provide a larger equivalent friction coefficient, the compressive force exerted by the Tong Dies on the drill string must exceed the required compressive strength. Therefore, the following condition must be satisfied:

24

Conducting a compressive stress intensity analysis of the Tong Dies and drill string based on Eq. (24), the analysis results are shown in Fig. 9.

Figure 9.

Analysis of the compressive stress intensity between the Tong Dies and the drill string.

From this, it can be seen that the Tong Dies meets the requirements of Eq. (24), allowing it to bite into the drill string and provide a larger equivalent friction coefficient. This confirms that the optimized Tong Dies meets the expected performance requirements.

Analysis of the shear stress intensity of the Tong Dies

From the geometric relationship in Fig. 8, it can be determined that under the action of the clamping force P, the tip of the Tong Dies bites into the surface of the drill string. The contact area under the action of the clamping force P is given by:

25

After the Tong Dies bites into the drill string, it is subjected to shear stress under the action of torque. At this moment, the Tong Dies experiences a tangential force Q, which generates shear stress over the same area that bears the normal stress caused by the clamping force P. Therefore, the shear stress on the Tong Dies is given by:

26

Substituting Eq. (15) into Eq. (26), we obtain:

27

To ensure that the Tong Dies meets the shear strength requirements during the torqueing process, the torque T must satisfy the following relationship:

28

Where is the allowable shear strength of the Tong Dies material.

In Eq. (28), t and r are relatively small compared to R. By neglecting their numerical values while retaining their order of magnitude, we obtain:

29

Conducting a shear stress intensity analysis of the Tong Dies based on Eq. (29), the analysis results are shown in Fig. 10.

Figure 10.

Analysis of the shear stress intensity of the Tong Dies.

From this, it can be seen that the Tong Dies meets the requirements of Eq. (29) and possesses high shear strength, proving that the optimized Tong Dies parameters meet the strength requirements.

Analysis of the shear stress intensity of the drill string

The shear stress on the drill string is mainly caused by the tangential force Q. At this moment, the surface area of the drill string subjected to shear stress is given by:

30

At this moment, the shear stress on the drill string is given by:

31

To ensure that the drill string meets the shear strength requirements during the torqueing process, the torque T must satisfy the following relationship:

32

Where is the allowable shear strength of the drill string joint material.

In Eq. (32), t are relatively small compared to R. By neglecting its numerical values while retaining their order of magnitude, we obtain:

33

Furthermore, since the tong dies need to bite into the drill string to provide a higher equivalent friction coefficient, the shear strength of the tong dies against the drill string must exceed the allowable shear strength requirement, which can be expressed by the following equation:

34

Conducting a shear stress intensity analysis of the drill string based on Eq. (34), the analysis results are shown in Fig. 11.

Figure 11.

Analysis of the shear stress intensity of the drill string.

From this, it can be seen that the tong dies meet the requirements of Eq. (34), allowing them to bite into the drill string and thereby provide a higher equivalent friction coefficient, which indicates that the optimized tong dies meet the expected performance.

Simulation experiment analysis of the Tong Dies

Preprocessing of Tong Dies simulation analysis

The Tong Dies is in direct contact with the drill string, and due to the significant clamping force, the mechanical environment at the Tong Dies tooth tip is highly complex. Therefore, conducting a simulation experiment analysis of the Tong Dies is essential. In the previous study, key parameters such as the Tong Dies Tooth Apex Angle, tooth height, and tooth spacing were optimized based on the equivalent friction coefficient and bite depth. A comparative simulation analysis is now conducted before and after optimization, with the pre-optimization Tong Dies parameters listed in Table 1.

Since the meshing method for the optimized and pre-optimized Tong Dies is the same, the pre-optimized Tong Dies is used as an example to describe the meshing process²⁸. During the meshing process of the Tong Dies and the drill string, mesh refinement was applied to the tooth apex surface of the Tong Dies and its contact region with the drill string. The simulation employed C3D8R elements, with a minimum size factor of 0.1 and an approximate element size of 0.5 mm in the refined region, aiming to accurately capture the stress and strain variations in the contact area²⁹. The focus is on analyzing the stress and strain distribution at the contact surface as well as the bite depth, while the remaining parts are meshed normally. The meshing results of the drill string and Tong Dies are shown in Fig. 12, and the refined mesh of the Tong Dies Tooth Apex Surface is shown in Fig. 13.

Figure 12.

3D model meshing.

Figure 13.

Refined mesh on arc-shaped surface.

When applying constraints, fixed constraints are added to the upper and lower surfaces of the drill string³⁰. Based on actual working conditions, the clamping force is applied to the back surfaces of the two die plates, and the maximum make-up torque is applied parallel to the Tong Dies to simulate real working conditions. The loading conditions of the drill string and Tong Dies are shown in Fig. 3.

Simulation experiment results of the Tong Dies

A simulation experiment was conducted on the clamping process of the Tong Dies before optimization. Initially, a finite element simulation was performed on the pre-optimized Tong Dies to obtain the stress and strain distribution, as illustrated in Fig. 14. The simulation results indicate that the maximum von Mises stress experienced by the pre-optimized Tong Dies is 472.8 MPa, while the maximum strain value reaches 0.7867 mm.

Figure 14.

Simulation diagram of tong dies before optimization. (a) Stress distribution diagram of Tong Dies before optimization; (b) strain distribution diagram of Tong Dies before optimization.

A finite element simulation was conducted on the optimized Tong Dies, and the resulting stress and strain distributions are shown in Fig. 15. The simulation results indicate that the maximum von Mises stress of the optimized Tong Dies is 364 MPa, while the maximum strain value is 0.5717 mm.

Figure 15.

Simulation diagram of optimized Tong Dies. (a) Stress distribution diagram of optimized Tong Dies; (b) strain distribution diagram of optimized Tong Dies.

A bite depth simulation was performed for both the pre-optimized and optimized Tong Dies over the same time period, with the results shown in Figs. 16 and 17, respectively. The simulation results indicate that the bite depth of the pre-optimized Tong Dies reached 0.35 mm within the simulation time, whereas the bite depth of the optimized Tong Dies remained below 0.35 mm under the same conditions.

Figure 16.

Bite depth diagram of pre-optimized Tong Dies.

Figure 17.

Bite depth diagram of optimized Tong Dies.

As observed from Figs. 14 and 15, the stress and strain of the Tong Dies are primarily concentrated on the curved surface. Due to the line contact between the Tong Dies and the drill string, the maximum stress and deformation occur at the contact line on the tooth tip. Comparing the stress distribution diagrams before and after optimization, it is evident that the von Mises stress of the optimized Tong Dies is lower, indicating improved strength and durability. Additionally, a comparison of the strain distribution diagrams shows that the wear of the pre-optimized Tong Dies is significantly greater than that of the optimized ones. From Figs. 16 and 17, it can be seen that the optimized Tong Dies maintain a shallower bite depth than the pre-optimized ones, even when the equivalent friction coefficient reaches its maximum. Based on the above analysis, it can be concluded that the optimized Tong Dies represent a superior design under the given constraint conditions.

Results

This study addresses the issues of severe Tong Dies wear and low equivalent friction coefficient in existing Iron Roughnecks. The research focuses on two key parameters: bite depth and equivalent friction coefficient. The specific work and conclusions are as follows:

1. Based on the structure and loading conditions of the Tong Dies, theoretical formulas were established for the bite depth of the Iron Roughneck Tong Dies on the drill string and the equivalent friction coefficient between the Tong Dies and the drill string.

2. A parameter optimization was performed on the key parameters affecting the performance of the Tong Dies, and the maximum equivalent friction coefficient was found to be 1.06 under the condition that the bite depth is less than 1 mm.

3. Complete the optimization and solution of the key parameters of the Tong Dies, obtaining the optimal parameter combination: tooth apex angle , tooth spacing 8.9mm, and tooth height 5.1mm.

4. The extrusion stress intensity, shear stress intensity, and biting conditions of the Tong Dies and drill string were checked, verifying that the optimized Tong Dies meet the usage requirements.

5. A simulation experiment was conducted to compare the optimized Tong Dies with the original ones, verifying the correctness of the theoretical analysis and demonstrating a significant improvement in the performance of the optimized Tong Dies.

Although this study has achieved notable progress in the modeling and optimization of Iron Roughneck Tong Dies, there is still room for further improvement. The theoretical model was reasonably simplified during development, but it has not yet fully accounted for large elastic deformations and complex working conditions. The validation was primarily based on simulation, which effectively demonstrated the feasibility of the optimization approach, though certain limitations remain. In addition, the dynamic analysis employed a rigid body model, and future work may consider flexible body modeling to enhance accuracy.

Future research can focus on the following directions: incorporating nonlinear contact mechanics and flexible body modeling to improve simulation precision; integrating material wear behavior for comprehensive performance optimization; conducting co-simulation of the control system and mechanism; and performing field tests to verify the engineering applicability and reliability of the optimized design.

Author contributions

Conceptualization, Y.S. and D.H.; methodology, Y.S. and D.H.; software, Y.S. and D.H.; validation, Y.S., D.H. and X.Z.; formal analysis, Y.S. and C.L.; investigation, Y.S. and D.H.; resources, B.S., D.H. and X.Z.; data curation, Y.S. and D.H.; writing–original draft preparation, Y.S.; writing–review and editing, Y.S., D.H. and C.L.; visualization, D.H.; supervision, Y.S.; project administration, X.Z.; funding acquisition, Y.S. All authors reviewed the manuscript.

Data availability

The datasets used and/or analyzed during the current study are available from the corresponding author Yongbai Sha on reasonable request via e-mail shayb@jlu.edu.cn.

Declarations

Competing interests

The authors declare no competing interests.