Analysis and Optimization of Telescopic Drill Rod Structure Based on SolidWorks

In this paper, the structural performance of the telescopic drill pipe structure is optimized and analyzed. The main working principle of the telescopic drill pipe is to drive the two internal telescopic rods through the two-stage telescopic cylinder, so that it can produce stable reasoning and motion characteristics. The 3D model of the telescopic drill pipe is also established by using SolidWorks software. The simulation of SolidWorks module is used to analyze the dynamic characteristics of the two-stage telescopic drill pipe, including the first five modal shapes, static stress and fatigue life of the structure. The distribution law of the maximum stress distribution point and the easily damaged position is found, and the structural design is optimized, which provides a reliable structural design scheme for improving the fatigue strength of the telescopic rod and prolonging the life cycle of the equipment.


Introduction
Existing rotary drilling rigs typically increase drilling depth by adding drill rods.However, when the drill rig needs to use augers or screw drills, it requires frequent raising of the auger or screw drill during the drilling process to clear debris.If the traditional drill rod method continues to be used, it necessitates repetitive operations of connecting and disconnecting the rods, consuming a significant amount of time.To address this issue, a multi-stage telescopic drill rod for rotary drilling rigs is proposed [1][2][3].
During the drilling process with a rotary drill head, the torque generated by the drill head is transmitted to the telescopic drill rod.The 2-stage telescopic drill rod module, subjected to the reverse torque from the rotary drill head under alternating loads, experiences time-varying stresses within its structure.If the excitation frequency of the reverse torque covers the modal frequencies of the 2-stage telescopic drill rod module, although the stress levels on the structure surface may be below the static fatigue limit, they could still lead to fatigue failure due to the accumulation of fatigue damage [4][5][6].
In this paper, based on SolidWorks Simulation software, the 2-stage telescopic drill rod module of the telescopic drill rod is modeled.The stress levels on its components are analyzed, and through simulation and analysis, a validation check is conducted to provide guidance for the design of this telescopic drill rod.

Structure Design
SolidWorks 3D modeling software was utilized to establish a telescopic drill rod model.Figure 1 depicts the overall view of the extended drill rod [7], figure 2 illustrates the structure of the retracted drill rod, and figure 3 provides a cross-sectional view of the retracted drill rod.

Working Principle
Telescopic Drill Rod Device: The outer rod cylinder mounting section 5 is fixed at the tail end of the telescopic outer rod module 1.Three 1st stage guide bar guide blocks 8 are evenly fixed at the head of the telescopic outer rod module 1, and the first dust seal 12 is also fixed at the head of the telescopic outer rod module 1.The 1st stage telescopic rod cylinder connection section 6 is fixed at the tail end of the 1st stage telescopic rod module 2. Three 1st stage guide bars 9 are evenly distributed on the outer wall of the 1st stage telescopic rod module 2. Three 2nd stage guide bar guide blocks 10 are evenly fixed at the head of the 1st stage telescopic rod module 2, and the second dust seal 13 is also fixed at the head of the 1st stage telescopic rod module 2. The 2nd stage telescopic rod cylinder connection section 7 is fixed at the tail end of the 2nd stage telescopic rod module 3. Three 2nd stage guide bars 11 are evenly distributed on the outer wall of the 2nd stage telescopic rod module 3. The drill head connection section 14 is fixed at the head of the 2nd stage telescopic rod module 3.
The 2nd stage telescopic rod cylinder connection section 7 of the 2nd stage telescopic rod module 3 is fixed on the cylinder fixing 2nd stage plate 18 of the multi-stage telescopic cylinder 4. The 1st stage telescopic rod cylinder connection section 6 of the 1st stage telescopic rod module 2 is fixed on the cylinder fixing 1st stage plate 17 of the multi-stage telescopic cylinder 4. The outer rod cylinder mounting section 5 of the telescopic outer rod module 1 is fixed on the cylinder outer rod connection hole 16 of the multi-stage telescopic cylinder 4 via the cylinder connection pin shaft 15.
The telescopic drive of the 1st stage telescopic module 2 and the 2nd stage telescopic module 3 is synchronized through the telescopic extension and retraction of the multi-stage telescopic cylinder 4. The cooperation of the grooves of three 1st stage guide bar guide blocks 8 with three 1st stage guide bars 9 ensures the stable extension of the 1st stage telescopic rod module 2. The cooperation of the grooves of three 1st stage guide bar guide blocks 10 with three 2nd stage guide bars 11 ensures the stable extension of the 2nd stage telescopic rod module 3.

Analysis of the 2nd Stage Telescopic Rod Module Model
SolidWorks 3D modeling software was utilized to create the telescopic drill rod model, as shown in figure 3. The simulation module is loaded to analyze the 2nd stage telescopic rod module, depicted in figure 3. (1) Adding materials and properties, applying constraints and loads.The main body of the 2nd Stage Telescopic Rod Module is made of 960E quenched and tempered high-strength circular tubing, and the related welded components are constructed from 960E quenched and tempered high-strength steel plates.The corresponding steel materials are selected from the SolidWorks material library.
To simulate the stress analysis of the telescopic drill rod under the most severe working conditions, the model is set to represent the telescopic rod at its innermost end, with the multi-stage telescopic cylinder fully extended.In this configuration, the torque applied to the system can be simplified, as shown in figure 4.

𝑇 = −𝑇 (ℎ)
We take the yield strength of the material as the compressive strength here σs Calculate its minimum stress area, which is the minimum contact area Smin between the 2nd level guide strip guide block 10 and the 2nd level guide strip 11.
We hereby confirm that the length of the second level guide strip guide block 12 is L(4)=500mm， and the contact thickness of the second level guide strip 11 is L(5)=12mm.

𝑆 = 𝐿 (4) × 𝐿 (5)
According to this value, the contact area S is 6000 mm 2 which is much larger than the minimum contact area Smin.
(2) Meshing of the Level 2 telescopic rod module.Utilizing an automatic transitional meshing approach with well-maintained grid density set at 20 mm and a tolerance of 1 mm, the mesh is divided into tetrahedral regular grids.

Modal Analysis
When performing modal analysis, only constraints are applied without applying any external loads.The solver is automatically selected, and after running the simulation, the modal results are obtained, as shown in table 1 and figure 5 The head of the telescopic rod deforms around the circumference of z Due to the working frequency of the rotary drilling head being 10 Hz, the analysis results indicate that the working frequency of the rotary drilling head falls within the range of the first five natural frequencies of the Level 2 telescopic rod.Therefore, resonance is likely to occur.

Static Load Stress Analysis
Fatigue is typically divided into high-cycle fatigue and low-cycle fatigue.High-cycle fatigue occurs under conditions of high repetition of loading cycles.The fatigue studied in this paper falls under high-cycle fatigue.Based on stress fatigue theory, a static stress analysis should be conducted first.After preprocessing, running the simulation case yields stress and displacement contour maps for the telescopic drill pipe under the influence of the gravitational force of the rotary drilling head and the reactive force of the rotary drilling head.As shown in figure 6, the maximum stress is observed at the contact point between the Level 2 guide block 10 and the Level 2 guide strip 11 (excluding the welded area), measuring 342 MPa.The maximum displacement [8] is located at the top of the telescopic drill pipe, measuring 11m.

Fatigue Analysis
Defining the event as a constant amplitude cycle, incorporating the aforementioned static stress analysis as the event, and setting the cycle count to 10,000, as the rotary torque varies from 0 to maximum and then back to 0, the load type is selected based on 0 (LR=0).The mean stress correction is set to Soderberg [9].Running the simulation case yields the fatigue life contour map for the telescopic drill pipe, as shown in figure 7. From figure 7, it is evident that the lifespan is shortest at the rear end of the telescopic drill pipe (excluding the welded area), measuring 3.62 × 10 4 cycles.Given that the working frequency of the rotary drilling head is 65 Hz, this lifespan is equivalent to approximately 10 hours.If the rotary drilling head system operates in this state for an extended period, the telescopic drill pipe is prone to damage at this location.

Improvement Measures
From the above simulation results, it is evident that the vulnerable area at the top of the telescopic drill pipe requires structural design improvements by increasing stiffness.Operators, during usage, should also take measures to minimize frequent starts and stops, thus extending the equipment's lifespan.Based on stress and displacement contour maps (Figure 6), it is observed that the maximum deformation of the telescopic drill pipe occurs at its rear end.Strengthening the design of the rear structure reduces the deformation, and an optimized improved model is depicted in figure 8. Through calculation and analysis, the natural frequencies of the first five orders of the optimized model are 25.48 Hz, 25.73 Hz, 62.07 Hz, 64.31 Hz and 158.83Hz, which are less than the service frequency of rotary head of rotary head, and the service life is more than 1014 times, fully meeting the working reliability and operation stability of telescopic drilling rod [10].

Conclusion
This paper first analyzed the structure of the telescopic drill pipe, followed by a detailed analysis of the structural model of the Level 2 telescopic rod module.The modal analysis and fatigue analysis are carried out respectively under the worst working conditions, and the first 5 natural frequencies and service life of the two-stage telescopic drill pipe are obtained.After improvement, the first 5 orders of natural frequency are increased, the minimum natural frequency is increased from 6.816Hz to 25.48Hz, and the maximum natural frequency is also increased to 158.83Hz, but they are still less than the use frequency of the drill, and the service life is more than 1014 times.The optimization results show that the improved method is correct, and the theoretical method has certain reference significance for the structural design of the two-stage telescopic rod module in the future.

Figure 1 .
Figure 1.Overall view of the extended drill rod.

Figure 2 .
Figure 2. Structure of the retracted drill rod.

Figure 4 .
Figure 4. Force analysis of telescopic drill pipe.T: Counter-torque generated by the rotation of the rotary head; F(1): Support force experienced by Level 2 guide strip; F(2): Support force experienced by Level 2 guide strip; F(3): Support force experienced by Level 2 guide strip; L(1): Lever arm of force F1.T=280000 N• m; L(1)=184mm.F1, F2 and F3 are tangent to the center circle in the direction of equal size, respectively T(1)T(2)T(3).The distances are F(1) F(2) F(3), making the sum of their torques T(h);

Table 1 .
. Characteristics of the first 5 natural frequency vibration modes of the second level telescopic rod.