Pre-drilled Holes Research Articles

Surface Modification and Nanocomposite Layering of Fastener-Hole through Friction-Stir Processing

This investigation studied the surface modification and nanocomposite layering of the cylindrical surface of a fastener-hole using friction-stir processing. A tapered tool rotates and transverses a predrilled hole that gradually expands and simultaneously stirs the surface. The stirring modifies the hole's cylindrical surface to help improve the hardness and resist against fatigue loading. Introduction of nanoparticles between the tool and the hole during the friction stirring results in formation of a nanocomposite layer that further improves the fatigue performance. The process development and resulting changes in surface finish, hardness, compressive residual stress near the hole, and fatigue life are presented; the strengthening mechanisms and their relationship with the process parameters are discussed.

Investigate the Effect of Pre-drilling in Friction Drilling of A7075-T651

Friction drilling is a non-traditional hole achieving method that is a clean, chip-less process, which is called thermal drilling, form drilling, flow drilling, and friction stir drilling. In this study pre-drilling friction drilling was investigated for improving the bushing shape of A7075-T651, which is a brittle cast material. During the process, surface roughness and bushing shapes were analyzed and generated frictional heat was measured by the virtue of thermocouples. Experiments were carried out to 4 mm and 6 mm in thicknesses of A7075-T651 aluminum alloy at 1200, 1800, 2400, 3000, and 3600 rpm spindle speeds, 20, 40, 60, 80, and 100 mm/min feed rates with using high-speed steel rotating conical tool, whose diameter is 8 mm. Consequently, the bushing shapes were advanced without cracks and petal formation in pre-drilling Friction drilling in comparison with without pre-drilling process. With increasing pre-drilled hole diameter the generated frictional heat was decreased. The achieved temperature was realized to be 1/2–1/3 of the melting temperature of the workpiece. Surface roughness values were decreased with decreasing or increasing both spindle speed and feed rate correspondingly.

Experimental investigation of hole quality during reaming applications using multi-blade tools

In practice, economical reaming of precision holes requires the use of multi-blade reaming tools. The main objective of precision machining processes is to minimize any deviations arising from dimensional and shape tolerances. However, process errors such as misalignment errors between the axes of the tool and the pre-drilled hole can occur during reaming processes, thus affecting the machining outcome. This experimental study aims to investigate the influence of process errors and tool geometry on the resulting hole quality while reaming valve guides made of sintered steel alloys. There is particular emphasis on the guiding function of reaming tools with regard to varying chamfer dimensions and back taper ratios at the secondary cutting edge. The experimental results indicate that an enlarged contact zone between the secondary cutting edge and the workpiece material will lead to improved straightness tolerances.

Experimental Investigations on Micro Milling of Stavax Stainless Steel

Micro mechanical milling of Stavax (modified AISI 420) stainless steel which is commonly used in the plastic injection molding industry due to its high corrosion resistance, machinability and wear resistance is studied in this paper. The goal of this study is to investigate the influence of process input parameters such as cutting speed, depth of cut, feed per tooth, radial immersion percentage, and plunging method on process outputs during circular pocketing operation. Tool wear, machining forces and surface roughness measurements are considered to identify the relationships between process inputs and outputs. It is observed that plunging method has a significant influence on tool wear which in turn affects micro milling forces and surface quality. The positive impact of micro milling with a pre-drilled hole is demonstrated. The relationship between radial immersion and feed per tooth is shown to be important in terms of tool wear and surface roughness.

Quality of Drilled and Milled Rivet Holes in Carbon Fiber Reinforced Plastics

In this paper, a conventional drilling process and a circular milling process are compared with respect to delamination and fiber protrusion when machining carbon fiber reinforced plastics (CFRP). The tool design (tool orthogonal clearance, drill-point angle) and the parameters (feed rate, cutting speed) are varied when drilling. The axial feed force and the spiral angles of the cutting edges can cause damages to the CFRP when circular milling. In this study, the possibilities to reduce those errors by the application of end mills with no spiral angle at the circumference cutter and no feed in axial direction are investigated. This milling process requires pre-drilled holes, and the final rivet hole dimension is then machined by circled movements without any motion in axial direction. For this special circular milling process, the tool design (rake angle of the circumference cutters) as well as the setting parameters (depth of cut, feed rate, cutting speed, up and down milling) are varied. The machining quality of both processes is compared. This is done by measuring the delaminations using an optical microscope. The fiber protrusion are visually identified with the help of an adapted imageprocessing algorithm. The diameters of the rivet holes are measured on two planes of the hole by a coordinate measuring machine. The cylindricity of the holes is determined using an instrument for roundness measurement.

Nonlinear finite element models for the embedded through-section FRP shear-strengthening method

The embedded through-section (ETS) strengthening method is a promising technique recently developed to increase the shear strength of deficient reinforced concrete (RC) beams. The method uses an adhesive to bond fiber-reinforced polymer (FRP) bars embedded through pre-drilled holes into the concrete core. The motivation for this work is the fact that a full understanding of the ETS technique can be achieved through finite element models. Two-dimensional finite element models have been developed to address the CFRP bar/concrete interfacial behavior of the ETS pull-out test. In the model, discrete truss elements are oriented above and below the CFRP bar to connect the bar to the two sides of the concrete. The Cosenza–Manfredi–Realfonzo (CMR) bond stress–slip model is used to represent the bond behavior. Numerical predictions show that the CFRP bar/concrete interfacial profiles are useful in determining the optimum lengths of the CFRP bars. The study has been extended to investigate FRP shear-strengthened beams using the ETS method by developing a three-dimensional finite element model. Nonlinear material behavior of the plain concrete, steel reinforcing bars and CFRP bars has been simulated using appropriate constitutive models. Results are presented in terms of ultimate load-carrying capacities, load–deflection relationships, and axial strains in the CFRP bars. The numerical predictions are compared with experimental data, and very good agreement is obtained.

Anatomic Reconstruction of the Distal Radio-ulnar Ligament for Distal Radio-ulnar Joint Instability : A Case Report

Abstract Stability of the distal radio-ulnar joint (DRUJ) is provided by bony architecture and by soft tissues such as the triangular fibrocartilage complex (TFCC), the joint capsule, and surrounding muscles. Many authors have made various attempts to restore DRUJ stability surgically following trauma. The objective of this study was to analyse clinical outcomes after anatomic reconstruction of the distal radio-ulnar ligaments in a 26 years male with post-traumatic chronic instability of the DRUJ. Anatomic reconstruction of the major structures responsible for joint stability is the most important principle for the treatment of instability of an injured joint with an intact articular surface by using a palmaris longus tendon graft whose ends were anchored in pre-drilled holes in the radius and the ulna. Anatomical reconstruction of the distal radioulnar ligaments is thought to be an effective procedure for treating post-traumatic DRUJ instability.

Cement augmentation of lag screws: an investigation on biomechanical advantages

In trauma surgery, lag screws are commonly used. However, in osteoporotic bone, anchorage can be considerably compromised. This study investigates the biomechanical potential of cement augmentation in terms of improved fixation. 36 Surrogate osteoporotic bone specimens were utilised in three biomechanical experiments, each comparing 6 augmented with 6 non-augmented samples. Standard partially-threaded lag screws (Synthes) were placed following surgical standard. For the augmented groups, 0.4ml of polymethylmethacrylate was injected into the pre-drilled hole prior to screw placement. Interfragmentary compression was determined using a cannulated ring compression sensor. Maximum torque was recorded with a torque wrench. Compressive relaxation after 24h, relaxation after loosening and re-tightening the screw as well as maximum compression and torque at failure were measured. Mean relaxation was significantly lower for the augmented group (p<0.01). After 24h, a remaining fragmental compression of 62% for the augmented and 52% for the non-augmented specimens was found. Loosening and re-tightening of the screw did not affect the compressive relaxation when augmentation was applied (p=0.529), compared to an increased relaxation after re-tightening in the non-augmented group (p=0.04). The mean maximum compression and torque until failure were significantly higher for the augmented group (p<0.001). Cement augmentation of lag screws can improve fixation stability in terms of installing and maintaining interfragmentary compression. Effects of relaxation can be reduced and re-tightening of screws is possible without compromising the fixation. Particularly in reduced bone mass, augmentation of lag screws can markedly increase the security of the technique.

Dynamic simulation of the self-tapping insertion process of orthodontic microimplants into cortical bone with a 3-dimensional finite element method

The aim of this study was to evaluate the stress state in the cortical bone around an orthodontic microimplant during and after the insertion surgery. The self-tapping insertion of an orthodontic microimplant into 1-mm-thick cortical bone containing a predrilled hole was simulated by using a 3-dimensional finite element method. The entire insertion surgery was replicated by a total of 3601 calculation steps: ie, the first 3600 dynamic steps analyzing the insertion process and an additional static step for analyzing the residual stress state after insertion. Four microimplants were experimentally inserted into rabbit tibiae to measure the insertion torques and compare them with the finite element analysis results. Reasonable agreement was observed between the experimentally measured and the finite element calculated torques, confirming the validity of our finite element simulation, which showed that high stresses can develop in the interfacial bone during microimplant insertion. Hoop stresses above the ultimate tensile strength and radial stresses above the ultimate compressive strength of cortical bone developed in the bone. Furthermore, residual radial stresses higher than the critical threshold stress to trigger pathologic bone resorption were observed after insertion. These high insertion-related stresses implied that it is not the orthodontic force or the timing of its application, but the insertion conditions that can determine the bone's response to the microimplant and its clinical prognosis. This in-vitro finite element analysis showed that, during the self-tapping insertion of orthodontic microimplants, stresses high enough to fracture cortical bone can develop. After the self-tapping insertion, the radial stresses calculated at the interfacial bone were higher than the threshold value to trigger pathologic bone resorption.

Subglacial till and bedrock drilling

Drilling to till and bedrock of ice sheets and glaciers offers unique opportunities for examining processes acting at the bed. Samples of basal and subglacial material contain important paleo-climatic and paleo-environmental records and provide a unique habitat for life, give significant information on sediment deformation beneath glaciers and its coupling to the subglacial hydraulic system, subglacial geology, and tectonics. Retrieving bedrock samples under ice sheets and glaciers is a very difficult task. Drilling operations are complicated by extremely low temperature at the surface of, and within glaciers, and by glacier flow, the absence of roads and infrastructures, storms, winds, snowfalls, etc. Nevertheless, borehole drilling might be considered as the optimal method to access beds of the glaciers and to sample subglacial material. Four types of subglacial drilling technologies are considered: (1) non-rotary sampling; (2) non-core penetrating; (3) pipe-string rotary drilling; (4) electromechanical cable-suspended drilling. The most simple and effective systems for sampling in subglacial soft sediments or unfrozen till from pre-drilled access holes are non-rotary devices like gravity corer and piston corer. The maximal thickness of ice is determined by the length of wire rope attached to the corer and could possibly be more than 4000 m. Potentially, piston sampling can reach a maximal depth of 25 m in soft subglacial lake sediments. In stiffer sediments a hammer corer or vibrocorer should be used. To install different sensors and markers into the soft till beneath glaciers and to measure basal sliding, different types of sediment non-core penetrators were used. Typically the boreholes are pre-drilled by hot-water systems as well. To recover core of the true bedrock the rotary drilling systems are used. The experience of pipe-string rotary drilling in subglacial environment showed that drilling operations were very unstable, and the recovery of subglacial sediment was generally poor. Commercial drilling rigs for drilling up to the depth of 3000 m or more tend to be very heavy and require a large logistical load to move and support. They also require more equipment for the circulation system. Taking into account that they are not adapted for extremely unfavorable conditions in Polar Regions and also need high power consumption, these drill rigs were not considered for subglacial exploration. Electromechanical cable-suspended systems are widely used for core drilling in pure and debris-containing ice. The main feature of these systems is that an armored cable with a winch is used instead of a pipe-string to provide power to the down-hole motor system and to retrieve the down-hole unit. The use of armored cable allows a significant reduction in power and material consumption, a decrease in the time of round-trip operations, and a simplification in the cleaning of the hole from the cuttings. To penetrate frozen till and bedrock the electomechanical drills can be adapted for coring bedrock. This was confirmed by four successful penetrations into the bedrock carried out by U.S. and Russian specialists. The procedure of till and bedrock drilling and the geological description of retrieved debris-containing ice and bedrock cores are given.

Die subpektorale Tenodese der langen Bizepssehne bei Pathologien der langen Bizepssehne und des Pulley-Systems

The presented surgical technique aims at fixation of the long head of the biceps tendon at the proximal humerus, distal to the bicipital groove, after arthroscopic tenotomy. This preserves the length and shape of the biceps muscle belly and avoids groove tenderness. All forms of degenerative changes of the long head of the biceps tendon, biceps instability due to pulley lesions, irreparable SLAP tears. The technique offers a cosmetically favorable outcome compared to a tenotomy. Old complete tears of the long head of the biceps, significant loss of bone density due to osteoporosis, tumor or bone cysts, implants in the proximal humerus, such as intramedullary nails, stem of total shoulder replacement. The presented technique is not indicated for patients with unspecific chronic shoulder pain or if asymmetric shape of the upper arm due to distal migration of the biceps is not relevant. After arthroscopic tenotomy of the long head of the biceps tendon, a small incision at the level of the pectoralis major tendon is made to the axillary fold. The stump of the long head of the biceps tendon is tenodesed to a predrilled hole with a bioabsorbable screw. No active training of the biceps for 6weeks, a sling for comfort is optional until healing of the wound is completed. Clinical studies of several authors have shown significant postoperative increase in all scores evaluated. Safety of the screw fixation and a low complication rate have been proven.

Experimental investigation of residual stresses in cold formed steel sections

Residual stresses play important role for design of steel structural members. Cold formed sections usually have residual stresses caused by roll forming. When compared to stresses caused by the working load, especially for compressed members, the effects of residual stresses can be favorable or unfavorable depending on magnitude, orientation and distribution of these stresses. The research presented in this paper includes experimental investigations of residual stresses, initial imperfections and material properties on cold formed carbon steel open cross sections. Experimental results have been compared to results obtained in similar tests with stainless and high strength steel cross sections. Theoretical and experimental research, conducted for cold formed open cross sections, are important for design of axially compressed members. This paper presents two methods of residual stresses investigation: magnetic method and method of pre-drilled holes and obtained results have been compared with results of residual stresses from other authors.

Performance Analysis and Optimization of a Dual Warhead System

Abstract In modern warfare earth penetrating weapons are often used to defeat enemy’s hardened and deeply buried targets such as aircraft shelters and bunkers. A dual warhead system (DWS) is one of such weapons composed of a forward shaped charge (FSC) and a following through warhead (FTW). In this paper, an analytical model is first proposed to analyze the penetration of an FTW into concrete targets with pre-drilled holes and a DWS is then optimized in order to achieve its best penetration performance. The effects of various parameters on the performance of a dual warhead system penetrating a concrete target are delineated. It transpires that the present model predictions are in good agreement with available experimental data and that the results obtained may be useful for designing such weapon systems.

Performance Analysis and Optimization of a Dual Warhead System

Abstract In modern warfare earth penetrating weapons are often used to defeat enemy’s hardened and deeply buried targets such as aircraft shelters and bunkers. A dual warhead system (DWS) is one of such weapons composed of a forward shaped charge (FSC) and a following through warhead (FTW). In this paper, an analytical model is first proposed to analyze the penetration of an FTW into concrete targets with pre-drilled holes and a DWS is then optimized in order to achieve its best penetration performance. The effects of various parameters on the performance of a dual warhead system penetrating a concrete target are delineated. It transpires that the present model predictions are in good agreement with available experimental data and that the results obtained may be useful for designing such weapon systems.

Influence of a diagonal pre-drilled hole on hole quality during the reaming process using multiblade tools

The requirements of production engineering for a precision hole are to ensure the required quality as well as minimal production costs. The interactions between machine, tool and the pre-drilled hole result in uncertainties during the final reaming process. For this purpose the reaming process itself and the appearance of process faults were focused in a large number of publications. Due to the fact that the reaming process is an inherent part of a process chain and thus directly linked to a pre-machining process (drilling process), the influence of a pre-drilled hole is neglected till date. For that reason the present paper deals with the influence of a diagonal pre-drilled hole on the reaming process with multi blade tools. Pretests show that the radial deviation of the pre-drilled hole seems to be an important input parameter for the reaming process within the process chain. Based on this new input parameter the question whether the reaming tool follows the path of the pre-drilled hole or not has arisen. To achieve a better understanding of this issue, cutting tests were accomplished to investigate this influence. For this purpose, holes with different radial deviations were manufactured on a five axis machining center and reamed in a second step. The bored holes were evaluated with the help of a coordinate measuring machine and compared with ideal results. Thus the present paper highlights cause and effect relationships within the process chain drilling/reaming. In addition, a further clamping system with an increased stiffness is also examined to decrease the effects of uncertainties. Furthermore, the results were compared with an open loop chip cross section simulation.

Influence of Column Construction Type on the Bearing Capacity of Bonded Anchors

The anchorage formed by the post-installed steel chemical anchors can be used for new buildings. Thanks to easy and fast installation can be used particularly for reconstructions. Chemical anchors are the most frequently used with concrete and reinforced concrete. On the trade of anchoring, the chemical anchor systems are represented by a number of variants of this anchorage type but, in fact, they always consist of a steel bolt (anchor) installed in a pre-drilled hole. The connection between a steel bolt and concrete or masonry (most frequently) is done by glue, i.e. usually by different types of epoxy.The research presented in this article is focused on a possible application of these anchor types, namely in the connection of a steel beam with a face plate to different types of columns.The analysis of a connection steel beam cantilever stressed by bending moment to the construction of the column with bonded anchors. The loading capacity of anchors connected (bonded) to steel HEB concreted column will be compared to loading capacity of anchors bonded to reinforced concrete column.Comparisons will be done on the basis of experimental tests and subsequently validated by numerical models. Compared resistance of the anchors is different for columns and the rigidity of joints.

Mechanical microdrilling of negative-tapered laser-predrilled holes: a new approach for burr minimization

Despite considerable research effort being concentrated on improving hole quality, minimisation of burrs still remains a key challenge in mechanical microdrilling of ductile materials. Recently, a sequential laser-mechanical microdrilling technique, which was developed by the authors, has proved effective in improving tool life and reducing burr size. The improvement in burr size was achieved by means of laser predrilling a pilot hole before utilising a twist drill to finish the hole. This paper presents further development of the sequential laser-mechanical microdrilling process based on negative-tapered laser-drilled pilot holes. In the sequential laser-mechanical microdrilling process, although a large predrilled hole reduces the burr size, it has a negative effect on roundness and cylindricity of the hole. The results of further studies highlight that a smaller entry hole size supports the drill and suppresses tool wander which, in turn, improves hole cylindricity. Furthermore, a larger exit hole size significantly reduces burr size. Compared to pure mechanical drilling without any pilot hole, the reduction in burr size for the mechanical microdrilling of near zero tapper and negatively tapered laser-predrilled holes was observed to be 2.5 and 6 times, respectively. Moreover, the mechanical finishing of these holes does not compromise tool life and/or surface integrity. Thus, the use of a negative taper laser-predrilled hole presents a significant improvement in burr control in microdrilling of nickel-based super alloys in addition to providing a step change increase in tool life.

Methods for the Control of Uncertainty in Multilevel Process Chains Using the Example of Drilling/Reaming

Uncertainty during production processes has an important influence on the product quality as well as production costs. For multilevel process chains with serially connected processes, additional uncertainty can be caused by the previous step. The manufacturing of precision holes by drilling and reaming is an important multilevel process chain. The interactions between machine, tool and pre-drilled hole cause process errors during the quality determinant final reaming process. In this paper, a systematic approach for the identification and control of uncertainty during the reaming process is presented. Thus, the influence of key aspects like skewness of pre-drilled hole or the influences of material strength gradients are analyzed. Further, simulation models for the consideration of these uncertainties are presented.

Comparison of Self-Drilling and Self-Tapping Cervical Spine Screws Using ASTM F543-07

Abstract ASTM F543-07 is used to evaluate insertion load (Annex A4), driving torque (A2), and axial pullout (A3) characteristics of self-tapping metallic medical bone screws. F543-07 was designed to evaluate screws that utilize a pre-drilled pilot hole and was not intended for self-drilling screws. The objectives of this study were to (1) adapt the F543-07 test methods to allow evaluation of both self-drilling and self-tapping screws and (2) quantify differences in performance between the two screw types. For all three tests (A4, A2, A3) appropriately sized pilot holes were pre-drilled into the surrogate test medium for all the self-tapping screw designs per ASTM F543-07. No pilot holes were created for the self-drilling screws. During the insertion load tests (A4), a constant rotation was applied to the screws under an initial, near-zero axial force state. While monitoring axial load, torque, and displacement, the axial load was gradually increased. The maximum load at which there was a marked increase in torque and displacement on the graph was indicative of the force required to engage the self-drilling or the self-tapping feature. To measure driving torque (A2), a constant rotation was applied. To maintain screw driver–screw contact, a constant-force axial pre-load was required. The axial insertion load, determined during the insertion load testing (A4), was used as the preload for the driving torque testing. Axial pullout testing (A3) measured the axial tensile force required to remove a screw from the test medium. Quantifiable differences in mean insertion load, driving torque, and pullout load were found, demonstrating that these methods are able to discern differences in performance between different screw designs. Finally, this study demonstrated it is possible to adapt the test methods outlined in ASTM F543-07 to evaluate the insertion load, driving torque, and axial pullout performance of self-drilling screws in addition to self-tapping screws.

Distal Radius Osteotomy with Volar Locking Plates Based on Computer Simulation

Corrective osteotomy using dorsal plates and structural bone graft usually has been used for treating symptomatic distal radius malunions. However, the procedure is technically demanding and requires an extensive dorsal approach. Residual deformity is a relatively frequent complication of this technique. We evaluated the clinical applicability of a three-dimensional osteotomy using computer-aided design and manufacturing techniques with volar locking plates for distal radius malunions. Ten patients with metaphyseal radius malunions were treated. Corrective osteotomy was simulated with the help of three-dimensional bone surface models created using CT data. We simulated the most appropriate screw holes in the deformed radius using computer-aided design data of a locking plate. During surgery, using a custom-made surgical template, we predrilled the screw holes as simulated. After osteotomy, plate fixation using predrilled screw holes enabled automatic reduction of the distal radial fragment. Autogenous iliac cancellous bone was grafted after plate fixation. The median volar tilt, radial inclination, and ulnar variance improved from -20°, 13°, and 6 mm, respectively, before surgery to 12°, 24°, and 1 mm, respectively, after surgery. The median wrist flexion improved from 33° before surgery to 60° after surgery. The median wrist extension was 70° before surgery and 65° after surgery. All patients experienced wrist pain before surgery, which disappeared or decreased after surgery. Surgeons can operate precisely and easily using this advanced technique. It is a new treatment option for malunion of distal radius fractures.