Internal Threads Research Articles

Innovative high-strength screw connections for additive manufactured thermoplastic components

AbstractComponents that are additively manufactured by material extrusion (MEX) are exposed to complex challenges due to their layered structure. Anisotropy and the risk of delamination must be given special consideration, especially when they are exposed to high loads. In case high-loaded components have additionally to be connected to other parts or assemblies via screw connections, the connection area in the MEX-manufactured component is a limiting factor for usability. This article presents a novel method in which a preheated metallic threaded sleeve with internal and external threads is inserted into the component in order to create a high-strength threaded anchoring. This prevents pre-damage such as delamination in advance. As part of preliminary investigations, a selection of relevant parameters was first made. An open parameter test rig was developed with which the threaded sleeves could be applied into test specimens with high repeat accuracy. The effectiveness and the increase in the achievable pull-out forces were demonstrated by means of pull-out tests. It was also shown that the heat input via the outer thread flanks during application has a positive influence on the overall strength of the component.

Multi-objective collaborative optimization of internal thread cold extrusion process based on response surface method

Multi-objective collaborative optimization of internal thread cold extrusion process based on response surface method

The Tightening and Untightening Modeling and Simulation of Bolted Joints

Although bolted joints may appear simple and are easy to manipulate, they are challenging to model and analyze due to their complex structural patterns and statically indeterminate nature. Ensuring the structural integrity of these joints requires maintaining proper bolt preload and clamping force, which is crucial for preventing failures such as overload, excessive bearing stress, fatigue, and stripping caused by seizing or galling. Achieving the necessary clamping force involves carefully controlling the input tightening torque, which is divided into the pitch torque and the friction torques at the bolt or nut bearing surfaces and in the engaged threads. The resulting clamping force is critical for generating the required force within the bolt. However, the achieved bolt force depends on several factors, such as friction at the joint’s contact surfaces, grip length, and the relative rotation between the bolt and nut during tightening. Friction at the contact surfaces, particularly beneath the bolt head or nut and between the threads, consumes a significant portion of the applied tightening torque—approximately 90%. This paper explores the three existing bolt internal pitch, bearing, and thread friction torques that are generated by the external applied torque in a bolted joint, as well as their contributions and variations throughout a loading cycle composed of three phases: tightening, settling, and untightening. An analytical model is developed to determine these torque components, and its results are compared with those obtained from finite element (FE) modeling and experimental testing from previous studies. Finally, this study examines the torque–tension relationship during bolt tightening, offering insights into the required accuracy of bolt and clamped member stiffness. The bolt samples used in this study include M12 × 1.75 and M36 × 4 hex bolts.

Repair of mandrels of a continuous mill through the use of adapters

The article describes the repair of mandrels used on a continuous type PQF mill by using adapters made from billets. The starting materials are the tailstocks that have been taken out of service.The process of repairing the mandrels allows the mandrel to be used in further work until the final regrinding to the last size range of the mandrel diameter.The technological process of repair begins with turning the surface of the mandrel to the required size, grinding the surface, the process of cutting off the rear part of the mandrel, including the threaded connection. After the tailstock part has been cut off, the tailstock section is replaced with a transition piece manufactured in‑house. The adapter is a part with a fine tapered thread on one side, which is intended for connection to the mandrel, and with an internal thread on the other side, which serves to connect the rear part of the mandrel to the tailstock.The provided technology will reduce the cost of purchasing new replacement tools by increasing the life cycle of the mandrel, and will reduce the number of mandrels that have become unusable by restoring the tailstock part.

A full-morphology measurement method and system for tubing internal thread based on rotating-mirrored structured light vision

The major methods of tubing internal thread (TIT) measurement are low efficiency, poor accuracy and incomplete measurement. Therefore, a new full-morphology measurement method and system based on rotating-mirrored structured light vision (RMSLV) is proposed in this paper. Firstly, a measurement model of RMSLV is proposed, which establishes the mathematical relationship between two-dimensional (2D) pixel and three-dimensional (3D) topography data. Subsequently, a step-by-step calibration method for this model is put forward to accurately solve model parameters, so that the high-precision restoration from 2D images to intricate 3D full-morphology of TIT is realized. Finally, the measurement system is built, and the verification experiments are conducted. The results indicate that the system’s measurement accuracy of taper, pitch and tooth height is 6.61 times, 5.60 times and 4.48 times higher than traditional equipment, and the efficiency is exponentially improved. This study provides an effective means for highly precise and fast measurement of the TIT.

Antifriction characteristics of the magnetron sputtered MoS2 coating of ITER blanket module bolted joints in high vacuum at elevated temperature [formula omitted] =250 °C

The high values of bolt preload force Fa = 90–1200 kN created by the ITER remote handling system can be achieved by using dry coating lubricants such as magnetron sputtering film MoS2 or WS2. An expression was determined to estimate the contact pressure based on the number thread turns and the width of the thread contact area in fastened assemblies that used the Spiralock technology. This study investigated the tribological aspects of the magnetron sputtering MoS2 coating at different thicknesses hc = 6.4–21 μm, contact pressures pa = 20–1200 MPa against the spherical pin (austenitic stainless steel 316L(N)-IG) at elevated temperatures of T = 250 °C in vacuum pv = 10−2–10−3 Pa. Friction data for “humid” and “dry” rectangular specimens with MoS2 coating were obtained and compared. With an increase in the thickness of the coating from 6.4 μm to 21 μm, we obtained a distinct stabilization the friction coefficient of the low friction coating for each given regime of wear that diminished from 0.09 ± 0.010 to 0.05 ± 0.005. The wear mechanism of the “layered MoS2 coating/metal substrate” tribosystem resulted in significant plastic deformation along the sliding direction of the MoS2 solid lubricant as well as microgrooving and microploughing of the coating by the asperities of the flat contact spot of the spherical pin. Regardless of the type of bolted pair alloys used, we concluded that it is necessary to deposit a low friction coating on both the internal and external threads of the ITER blanket module bolted joints that use the Spiralock technology.

Internal Thread Defect Generation Algorithm and Detection System Based on Generative Adversarial Networks and You Only Look Once.

In the field of industrial inspection, accurate detection of thread quality is crucial for ensuring mechanical performance. Existing machine-vision-based methods for internal thread defect detection often face challenges in efficient detection and sufficient model training samples due to the influence of mechanical geometric features. This paper introduces a novel image acquisition structure, proposes a data augmentation algorithm based on Generative Adversarial Networks (GANs) to effectively construct high-quality training sets, and employs a YOLO algorithm to achieve internal thread defect detection. Through multi-metric evaluation and comparison with external threads, high-similarity internal thread image generation is achieved. The detection accuracy for internal and external threads reached 94.27% and 93.92%, respectively, effectively detecting internal thread defects.

Numerical simulation and experimental investigation of coating influence on extrusion tap wear

In order to improve the service life of extrusion taps and reduce their wear, this paper adopted the coating-simulation technology to investigate the influence laws of tool coating type and coating thickness on extrusion torque, extrusion temperature and wear amount. The validity of the numerical simulation results is confirmed through internal thread extrusion experiments. The results showed that the extrusion torque and extrusion temperature of single-layer coating and composite coating showed a tendency of decreasing and then increasing with the increase of the coating thickness; the extrusion torque and extrusion temperature of the double-layer coating increased with the increase of the coating thickness; the wear amount of the three types of coatings increased with the increase of the coating thickness. The TiAlN single coating demonstrates the most pronounced impact on decreasing extrusion torque and temperature (3.82 N·m and 88.4 °C), resulting in a smooth extrusion process. The TiAlN–TiAlN double coating exhibits the lowest wear amount of 0.076 mm. The utilization of numerical simulation proves to be a dependable approach for evaluating the efficacy of tool coatings, and reasonable selection of coating type and thickness can effectively reduce the extrusion torque, extrusion temperature and wear amount.

Biomechanical Evaluation of a Locally Manufactured Modular External Fixator for Tibial Shaft Fractures

Background: Modular external fixations used in the Philippines are manufactured abroad, leading to high costs and limited availability, making them unaffordable for most Filipino patients. The reliability of some external fixators is limited because not all have undergone biomechanical testing. Objective: This study aims to determine the biomechanical stability of locally manufactured modular external fixator clamps (iFIX) versus commercially available fixators (Roger-Anderson) for tibial shaft fractures. Methodology: The biomechanical stability (stiffness, yield, ultimate strength) under loading of the local prototypes compared with the commercially available fixators. Result: No slippage was observed in all rods, pins, and clamps in all groups. No bending occurred in any rods or pins in all groups. There was also no apparent deformation of the internal threading of the pins within the tibial analogs. The commercial fixator group’s ultimate load to failure up was double (110.57% difference) that of the local prototype. Conclusion: The differences in the biomechanical performance between the iFIX and Roger-Anderson clamps may be attributed to variations in clamp material composition. The iFIX fixator exhibited lower stiffness but did not display deformation under axial loading, component displaced slippage, or thread loosening, making it comparable to the commercial fixator.

Fracture in control rods of helicopters: Same failures but different reasons

This paper presents two incidences of failures of collective control rods which resulted in accidents to a particular type of helicopter. The control rods were made of 2024 Al-alloy tubes fitted with fork at one end and a spherical bearing at the other end (eye-end). In terms of physical appearance, the two failures in the control rods were identical to each other wherein there was fracture in the Al-alloy tube at the eye-end. Fractography study confirmed that in both the cases, multiple fatigue cracks had initiated over a sector at the internal thread roots on the Al-alloy tubes corresponding to 1st/2nd thread on the eye-end stud. After initiation, the cracks had propagated progressively into the tube-wall and then along the circumferential direction. As the crack propagation progressed, the load bearing capacity of the tubes diminished resulting in final overload fracture under the operational load at the time of accidents. Although failures in both the control rods looked alike in terms of failure location, fracture pattern and fracture mechanism, the primary reasons of failures were found to be different. Investigation revealed that premature fatigue crack initiation was due to non-uniform stress distribution on the internal threads of the control tube with increased level of stress over a sector. In one case, the non-uniform stress distribution resulted from thread manufacturing deficiency, and in the other case, it was due to incorrect assembly at the eye-end.

Residual Debris within Internal Features of As-received New Dental Implants.

To investigate residual debris within internal features of new 'as received' dental implants. A total of 15 new dental implants representing various dental implant brands were obtained in sealed containers from the manufacturers. Batch numbers and implant types were documented. In a controlled setting, implants were carefully unpacked, and their internal aspects were visually examined. Further analysis involved light microscopy imaging to document and photograph any foreign material. The internal aspect of the implants were sampled with both an endodontic paper cone and a fine bristle brush swab. These were inserted into the implant, rotated three times, then removed and examined under a microscope at 30x magnification. Post sampling some of the brushes/swabs were washed with alcohol to remove debris that could be further examined under magnification. Inspection of the implants without magnification revealed no visible foreign materials. However, under light microscopy (x10 and x30), all 15 implants exhibited small black particles at various internal sites, including connections, threads, and deep within screw channels. Swabs evaluated at magnification detected what appeared to be metal particles in all 15 implants, ranging from distinct metal shards to smaller particles. This study suggests that implant manufacturers have not effectively removed all machining debris from within implant bodies, potentially producing prosthetic and clinical complications.

Experimental and numerical study on the effect of load direction on the bolt loosening failure

The loosening is one of the main failure modes of bolted joints. Currently, researchers only focused on bolt loosening behavior under simple axial or transverse loads. Understanding the loosening failure mechanism of bolted joints under complex load is important for improving reliability. A multi-directional loading test device was designed, and bolt loosening experiments were conducted. The effect of load direction and amplitude on bolt loosening behavior were investigated. The results indicate that bolt loosening can be divided into two stages. Load direction and load amplitude are critical factors determining the loosening trend in the later stage. In addition, a refined finite element model of bolted joints was established to verify and explain the experimental results. The FEA results show that the relative sliding between internal and external threads and the stress redistribution on the threads are the main reasons for the bolt loosening. The smaller the angle between the load direction and the tangential direction of the contact surface, the relative sliding more likely to occur.

Advanced CNC thread milling: a comprehensive canned cycle for efficient cutting of threads with fixed or variable pitch and radius

This paper presents the design, implementation, and experimental validation of a novel canned cycle for CNC milling machines, enabling the precise and efficient cutting of threads with fixed or variable pitch and radius. Conventional canned cycles are limited to fixed pitch threads, restricting the versatility of CNC milling machines in thread machining applications.The development process involves integrating a sophisticated control algorithm into the CNC milling machine's software, giving the operator remarkable control over the thread cutting process. This algorithm allows the operator to choose between external or internal threads, set both initial and final radii, determine initial and final pitches, specify the number of turns, and select the left or right-hand thread type. Such flexibility enables the creation of threads with diverse geometries. Furthermore, the proposed canned cycle provides the capability to switch between roughing and finishing passes by adjusting the step motion along the prescribed helical curve.Simulation tests conducted under various threading cases clearly demonstrate the efficiency of the proposed canned cycle. These results showcase its capability to address a wide range of machining scenarios, offering practical solutions applicable across a spectrum of applications.

Research on tap breakage monitoring method for tapping process based on SSAELSTM fusion network

Aiming at the problems of high tap breakage rate during tapping of small-diameter internal threads and the difficulty of feature extraction and fusion in characterising tap breakage, this paper proposes a tap breakage monitoring method based on stack sparse autoencoder long-short-term memory (SSAELSTM) fusion network. Specifically, based on change rule of torque in the tapping process and the analysis of the processing mechanism, the normal label and the breakage label are defined, and 36 groups of feature in the multi-feature domain of the torque signal are extracted, constituting a labelled set of feature. Additionally, a stacked sparse autoencoder network (SSAE) is employed to fuse the feature that serve as inputs to the long short-term memory network (LSTM) for recognition, and the classification errors of LSTM are back-propagated to SSAE to optimize the weights of the LSTM and SSAE networks. Finally, 31 SSAELSTM fusion network models with different structures are constructed, and the final tap breakage monitoring model is determined by comparing the performance indexes. Compared with the features before fusion, the constructed model fusion effectively reduces the amount of data and improves the correlation with the labels. Compared with other network models, it was found that SSAELSTM fusion network is superior to other models in both accuracy and robustness, providing breakage warning for the tapping process, and laying the foundation for subsequent decision-making to avoid tap breakage.

Research on Extrusion Forming Process of Micro Internal Thread for Nickel-plated Aluminum Alloy Parts

Abstract With the development of electronic products in the direction of miniaturization and lightweight, the specifications of thread gradually become minor, and the high-precision forming of micro threads has become an urgent problem to be solved. In this paper, the extrusion forming process of the micro internal thread was mainly studied on the nickel-plated aluminum alloy parts. The process route suitable for the internal thread forming on electroplated parts was designed, and the key parameters of thread bottom hole diameter and thread tapping speed were determined by experiment. Aiming at the typical problem of internal thread blocked by a broken tap, a thread repair method based on laser ablation was proposed and the laser processing parameters were optimized. Eventually, the manufacturing of M1 micro internal thread on nickel-plated aluminum alloy parts was successfully realized.

Analysis of secondary makeup characteristics of drill collar joint and prediction of downhole equivalent impact torque of Well SDTK1

Based on the three-dimensional elastic-plastic finite element analysis of the 8” (203.2 mm) drill collar joint, this paper studies the mechanical characteristics of the pin and box of NC56 drill collar joints under complex load conditions, as well as the downhole secondary makeup features, and calculates the downhole equivalent impact torque with the relative offset at the shoulder of internal and external threads. On the basis of verifying the correctness of the calculation results by using measured results in Well GT1, the prediction model of the downhole equivalent impact torque is formed and applied in the first extra-deep well with a depth over 10 000 m in China (Well SDTK1). The results indicate that under complex loads, the stress distribution in drill collar joints is uneven, with relatively higher von Mises stress at the shoulder and the threads close to the shoulder. For 203.2 mm drill collar joints pre-tightened according to the make-up torque recommended by American Petroleum Institute standards, when the downhole equivalent impact torque exceeds 65 kN·m, the preload balance of the joint is disrupted, leading to secondary make-up of the joint. As the downhole equivalent impact torque increases, the relative offset at the shoulder of internal and external threads increases. The calculation results reveal that there exists significant downhole impact torque in Well SDTK1 with complex loading environment. It is necessary to use double shoulder collar joints to improve the impact torque resistance of the joint or optimize the operating parameters to reduce the downhole impact torque, and effectively prevent drilling tool failure.

Internal thread defect detection system based on multi-vision.

In the realm of industrial inspection, the precise assessment of internal thread quality is crucial for ensuring mechanical integrity and safety. However, challenges such as limited internal space, inadequate lighting, and complex geometry significantly hinder high-precision inspection. In this study, we propose an innovative automated internal thread detection scheme based on machine vision, aimed at addressing the time-consuming and inefficient issues of traditional manual inspection methods. Compared with other existing technologies, this research significantly improves the speed of internal thread image acquisition through the optimization of lighting and image capturing devices. To effectively tackle the challenge of image stitching for complex thread textures, an internal thread image stitching technique based on a cylindrical model is proposed, generating a full-view thread image. The use of the YOLOv8 model for precise defect localization in threads enhances the accuracy and efficiency of detection. This system provides an efficient and intuitive artificial intelligence solution for detecting surface defects on geometric bodies in confined spaces.

Research and Optimization of Extrusion Tap Structure Based on Numerical Simulation and Experimental Analysis.

In order to enhance the quality of thread processing by tap, a systematic analysis of its forming mechanism and factors affecting forming quality is conducted. Effects of the number of edges, the amount of shovel back, the extrusion cone, the calibration part and the extrusion cone angle on the torque and temperature are achieved by finite element analysis and experiments. From the perspective of reducing torque and temperature during the forming process, the optimal combination of tap structural parameters for machining M22×2 internal threads on 42CrMo4 high-strength steel are further obtained through orthogonal optimization. The results show that, unlike the cutting process of threads, the extrusion forming process of threads is a net forming process in which metal undergoes plastic deformation in a limited space, and the metal material continuously flows along the edge of the V-shaped groove of the tap, gradually piling up to form the thread tooth shape. This also caused a noticeable lack of flesh at the top of the extruded thread teeth. Better quality threads can be obtained by machining with optimized structural parameters. The maximum torque and temperature during the machining process are reduced by 22.86% and 20.31%, respectively. The depth of the hardened layer increased by 0.05 mm, and the root and top hardness of the teeth increased by 10 HV0.2 and 5 HV0.2, respectively.

Analysis of the Influence of Thread Parameter Deviation on The Sealing Performance of Drill Pipe Joint Under Axial Load

To explore the influence of the limit deviation of the thread parameters of the drill pipe joint on its sealing performance, based on the API NC38 drill pipe joint, the existence of the limit deviations of the three thread parameters of taper, side angle, and pitch is analyzed. Based on this, a total of 12 finite element models of drill pipe joints including various limit deviations and free combinations of internal and external thread limit deviations are established, and the sealing performance of different structures under the action of make-up torque and axial load is analyzed. The results show that the pitch limit deviation has the most obvious influence on the sealing performance of the drill pipe joint, and the yield failure of the contact surface is easy to occur. The existence of taper limit deviation makes the sealing performance of the drill pipe joint significantly reduced when subjected to tensile load. When the change of the limit deviation of the side angle of the internal and external thread teeth is opposite, the plastic deformation occurs locally in the drill pipe joint, which affects the sealing effect. Therefore, it is necessary to control further the tolerance range of the thread parameters of the drill pipe joint to reduce the risk of sealing failure of the drill pipe joint.

Is fatigue mechanism implicated in intraoral fracture of narrow dental implants? A thorough retrieval analysis of two failed implant fixtures retrieved from a single patient

PurposeThis study aimed to perform a thorough failure analysis of two fractured narrow dental implants after medium-term in vivo use. Materials and methodsThe top parts of two fractured Narrow Dental Implant (NDI) fixtures were retrieved from two different locations at two different times from the same patient. The NDI-specimen-1 was 12-months in service while the NDI-specimen-2 was 17-months in service. In both cases, the top parts of the fractured NDI fixtures that were attached to prosthetic components were retrieved and subjected to thorough, non-destructive and destructive testing. ResultsLight Microscopy (LM) and Scanning Electron Microscopy (SEM) revealed that both the retrieved fractured NDIs failed because of fatigue, characterized by beach and ratchet marks. Macroscopic examination revealed that fatigue cracks initiated at the internal thread surfaces of the implants and propagated around them until final fracture. Both samples fractured near the end of the retaining screw and followed the root of the internal thread. Optical and SEM analyses revealed a uniform distribution of irregularly shaped grains (diameter = 2 to 5 μm). X -ray Energy Dispersive Spectroscopy (EDS) analysis showed that the NDI-specimen-1 was made using Ti-14%Zr with a Vickers Hardens (HV) of 288 ± 5. ConclusionSince the fracture occurred by a fatigue; thus, an increase in fatigue resistance will be beneficial for the longevity of NDI.