5-axis Milling Research Articles

On modelling and analysis of voxel-based force prediction for a 3-axis CNC machining

ABSTRACT Determination of cutting forces is the main requirement for understanding the machining process and optimising its parameters for achieving higher productivity and surface finish. This paper presents an exploratory study and the development of a model to estimate cutting forces for a 3-axis CNC milling process using a voxel-based CAD model. The developed algorithm takes the NC code, workpiece/tool material properties, and the tool geometry data as inputs. The cutting tool engagement with the workpiece is computed using a discretized (voxelized) model. The calculated voxel engagement was finally used to calculate the cutting forces using the analytical method. The algorithm was implemented and tested for various case studies and the in-house experimental data for different types of end mill tools. Finally, the effect of variation in the size of the voxel and the number of flutes was studied. The model showed a good correlation and was found to be accurate (~80%) and robust.

EVALUATION OF 3-AXIS AND 5-AXIS MILLING STRATEGIES WHEN MACHINING FREEFORM SURFACE FEATURES

The article deals with the comparison and evaluation of milling strategies, which are available in CAM systems and are used for the production of components with freeform surfaces. For the purpose of the experiment a test sample with a repeating shape feature was designed. First half of the test sample shape features were machined using 3-Axis milling strategies while second half was performed with strategies available on 5-Axis CNC machining centre. Simulated machining times as well as virtually machined surfaces using color maps with deviation values were evaluated by employed CAM software. Obtained data was used to evaluate the performance of 3-Axis and 5-Axis milling centre both individually and mutually. These results will be used to compare software data with data obtained from real sample production. The main goal is to verify the reliability of the results provided by CAM systems in the production of parts with freeform feature surfaces.

Patient satisfaction of teeth prepared with vertical versus deep chamfer finish line for monolithic zirconia crowns (Randomized Clinical Trial)

Aim: Evaluate the patient satisfaction of monolithic zirconia crowns with vertical preparation technique and compare them to deep chamfer finish line preparation in single crowns restoring posterior teeth. Materials and methods: Fourty full coverage zirconia crowns were fabricated for posterior teeth. The patients were divided into two groups according to the preparation designs. Group1: (control group) horizontal finish line and Group2: (intervention group) vertical finish line. Monolithic zirconia was used for the final restorations. EXOCAD software was used to design the try-in & final restorations which were later produced by five axis milling machine. The cementation was done by using self-adhesive resin cement. Patient satisfaction was assessed immediately after cementation using the “Visual Analogue Scale” VAS. These measurements were repeated after one, three, six, nine, and twelve months respectively. Result: independent t-test was used to compare between the two groups. No statistically significant difference was detected between both groups for patient satisfaction over one year. Conclusion: Both horizontal finish line and vertical finish line revealed successful clinical performance in terms of patient satisfaction for zirconia full coverage restorations.

Comparison of loupes versus microscope-enhanced CAD-CAM crown preparations: A microcomputed tomography analysis of marginal gaps

Statement of problemLong-term restoration success depends on a precision marginal fit to prevent marginal leakage and caries. The successful fit of a computer-aided design and computer-aided manufactured (CAD-CAM) crown may be affected by different workflow variables, including preparation, scanning, crown design, milling, sintering, and cementation. Discrepancies in any of these steps may result in poor marginal and internal fit. Evidence suggests that tooth preparation may be the most important step in the workflow for a successful outcome. Compared with the traditional means of crown preparation using the naked eye or loupes, the dental operating microscope provides higher magnification and more direct illumination. However, the impact of high magnification during preparation on the marginal quality of CAD-CAM crowns is unclear. PurposeThe purpose of this in vitro study was to compare marginal fits of CAD-CAM crowns fabricated after initial preparation with loupes and subsequent preparation refinement with either loupes or a microscope. The null hypothesis was that no significant difference would be found in the marginal gap between the preparations with loupes and those with a microscope. Material and methodsMounted extracted molars (N=18) received initial crown preparations with a coarse grit, rounded shoulder, diamond rotary instrument with loupes of ×3.0 magnification. The teeth were then randomly divided into 2 groups and refined for an additional 2 minutes with fine grit, rounded shoulder, diamond rotary instruments with either loupes (LOUP) or a microscope up to ×10.0 magnification (DOM). The prepared teeth were scanned with an intraoral scanner to fabricate zirconia-reinforced lithium silicate crowns manufactured with a 4-axis milling machine, sintered in a dental furnace in accordance with the manufacturer’s instructions, and cemented with self-adhesive resin cement. All teeth with crowns were mounted and scanned with a microcomputed tomography (μCT) system at 21-μm nominal voxel size. The resulting Digital Imaging and Communications in Medicine (DICOM) images were imported into a semiautomatic segmentation software program. Marginal and absolute gaps were measured at 24 consistent circumferential points per specimen. Absolute gaps were labeled, and the total volume was calculated. Paired and unpaired t tests were used for statistical analysis (α=.05). ResultsThe mean marginal gap was 145.0 ±259.6 μm for LOUP and 35.6 ±110.6 μm for DOM, with a statistically significant difference (P<.001). The mean gap volume for LOUP was 0.975 ±0.811 mm3, and 0.250 ±0.477 mm3 for DOM, also statistically significantly different (P=.023). A significant difference was found between the absolute and marginal gaps for LOUP (P=.007), but for DOM, the difference was not significant (P=.063). ConclusionsThis study demonstrated that the higher magnification used during tooth preparation played a significant role in the size of marginal gaps present around CAD-CAM crowns. Crown preparations finished by using fine grit diamond rotary instruments with a microscope at higher magnification than loupes resulted in a more precise marginal fit with smaller gaps.

A novel incremental sheet metal forming process for long and open section profiles

Complex components from High Strength Steel (HSS) can be formed with Flexible Roll Forming (FRF). However, flange wrinkling limits the part shape complexity that can be achieved and hence limits its application in the automotive industry. A novel forming technology is introduced in this study, Incremental Shape Rolling (ISR), where a pre-cut blank is clamped between a top and bottom die and then a single forming tool incrementally forms the material according to the bottom die’s geometry. It is believed that ISR can significantly reduce the wrinkling issue compared to FRF. In the contrast to the incremental sheet forming process, ISR allows the manufacture of long and open sections from HSS sheets. In this work, the experimental prototyping trials of the ISR process are performed using a 5-axis milling machine and then are used to validate the FEA model which is developed to simulate and analyse the deformation behaviour of the ISR process. The results show a clear development of transverse tensile strain along the flange which can overcome the wrinkling issue when the ISR process is applied to complex profiles.

Influence of Ball-End Milling Strategy on the Accuracy and Roughness of Free Form Surfaces

Freeform surfaces are present on an increasing number of engineering products. Three- and multi-axis computer numerical control milling machines are commonly used for improved production. Computer-aided manufacturing (CAM) systems are used almost exclusively for the creation of programs for a variety of machining centers. This study compared the quality of freeform surfaces made by 3- and 5-axis milling using three commonly used strategies (linear, offset, and spiral). The CAM system-predicted surfaces were also compared with the actual surfaces. A test sample with a freeform surface was used for the experiments. Considering the size and distribution, the discrepancy between the predicted surface deviations and the deviations in the produced samples was proven. Maximum negative surface deviations, when 5-axis milling, employed linear and spiral strategy of 29% and 71% less than those produced by the 3-axis milling. On the contrary, positive deviations were 48% smaller. A comparison of the scans showed that the two strategies (linear and spiral) yielded better results for 5-axis milling, and the offset strategy was better for 3-axis milling. Evaluation of the achieved surface roughness showed that the milling method did not significantly affect the surface quality in the linear strategy. However, other two strategies (offset and spiral) achieved better results with 5-axis milling compared to 3-axis milling. The proposed method of evaluating the accuracy of machined free form surfaces can be used in experimental as well as production activities.

Curve-guided 5-axis CNC flank milling of free-form surfaces using custom-shaped tools

A new method for 5-axis flank milling of free-form surfaces is proposed. Existing flank milling path-planning methods typically use on-market milling tools whose shape is cylindrical or conical, and is therefore not well-suited for meeting fine tolerances for manufacturing of benchmark free-form surfaces like turbine blades, gears, or blisks. In contrast, our optimization-based framework incorporates the shape of the tool into the optimization cycle and looks not only for the milling paths, but also for the shape of the tool itself. Given a free-form reference surface and a guiding path that roughly indicates the motion of the milling tool, tangential movability of quadruplets of spheres centered along a straight line is analyzed to indicate possible shapes and their motions. This results in G1 Hermite data in the space of rigid body motions that are interpolated and further optimized, both in terms of the motion and the shape of the milling tool itself. We demonstrate our algorithm on synthetic free-form surfaces and industrial benchmark datasets, showing that the use of custom-shaped tools is capable of meeting fine industrial tolerances and outperforms the use of classical, on-market tools.

Comparison of Simulated Machining Time with Real Machining Time at Free-form Surfaces Milling

The presented results are part of more extensive experiments, which aim to verify the reliability of the results provided by CAM systems in the production of parts with shaped surfaces. The article deals with the comparison of production times obtained from programming and simulation systems with real production times. For production planning and organization processes, information on estimated production time is an important input. A free-form sample was designed for the experiment. Finishing of the sample surfaces was accomplished by 3-axis and 5-axis milling using three different strategies. The machining times obtained by the simulation in the CAM system, the times from the simulation mode of the machine control system and the real machining times were evaluated. Data discrepancies were shown, with in almost all cases the real machining times being longer than the times given by the simulations. The results were supplemented by outputs from software that optimizes the feed during milling thus reducing the production time. The tests proved the validity of its use.

Accuracy of Dental and Industrial 3D Printers.

This in vitro study evaluated the dimensional accuracy of three 3D printers and one milling machine with their respective polymeric materials using a simplified geometrical model. A simplified computer-aided design (CAD) model was created. The test samples were fabricated with three 3D printers: a dental desktop stereolithography (SLA) printer, an industrial SLA printer, and an industrial fused deposition modeling (FDM) printer, as well as a 5-axis milling machine. One polymer material was used per industrial printer and milling machine while two materials were used with the dental printer for a total of five study groups. Test specimens were then digitized using a laboratory scanner. The virtual outer caliper method was used to measure the linear dimensions of the digitized 3D printed and milled specimens in x-, y-, and z-axes, and compare them to the known values of the CAD model. Data were analyzed with Kruskal-Wallis one-way ANOVA on Ranks followed by the Tukey's test. Milled specimens were not significantly different from the CAD model in any dimension (p > 0.05). All 3D printed specimens were significantly different from the CAD model in all dimensions (p = 0.01), except the dental SLA 3D printer with one of the polymers tested (Bis-GMA) which was not significantly different in two (x and z) dimensions (p = 0.4 and p = 0.12). The milling technology tested provided greater dimensional accuracy than the selected 3D printing. Printer, printing technology, and material selection affected the accuracy of the printed model.

Influences of modal shape and tool orientation on evolution of dynamic responses in 5-axis milling of thin-walled parts

Influences of modal shape and tool orientation on evolution of dynamic responses in 5-axis milling of thin-walled parts

Evaluation of the influence of different milling parameters and tool wear on the rim zone of a 5-axis milled large gear

Machining of gears by 5-axis milling allows additional degrees of freedom in gear design compared to conventional hobbing processes. Changes in the machining technology influence the surface integrity and, thus, the service life of the machined gears. For this reason, different machining parameters were investigated regarding their effects on the surface layer and subsequently on service life. In this paper, the residual stresses and microstructures of a large gear manufactured by 5-axis milling and the service life of test gears are analyzed. With the results from this paper, the surface integrity and service life can be predicted depending on the machining parameters.

Production Quality of Shaped Surfaces During Milling

In the context of the development of continuous improvement, increasing the level of quality, safety and protection of the ecological environment, it is necessary to deal with the sensitive phases of the production process and to evaluate the efficiency in terms of time and cost. In the paper, the quality of production in milling (method that is using rotary cutters to remove material) of shaped surfaces is pursued. The quality of the production process leads to the satisfaction of customer needs, and it is essential to focus on the quality/price ratio due to non-conformities. In the paper, the authors use the quality method to provide effective solutions and improve production activities, processes, and systems. This approach stands for a quality management system applied as a perpetual improvement tool, where individual activities consist of four steps: Plan, Do, Check, and Action, with returned stages developing a cycle. This cycle starts with minor to examine potential effects on systems and progresses to more extensive and precise improvements. The results of the implementation of effective solution method can be practiced for constant improvement and as a working model in developing a process or system in an organization. The different stages of the method are applied to set the path tolerance in relation to precision in 3-axis milling. The paper describes area computer numeric control milling center programming during 3-axis finishing milling. The article is focusing on setting the tolerance of tool paths during finishing milling in Computer Aided Manufacturing systems to recommend specific tolerance settings in computer aided Manufacturing systems concerning achieved accuracy, machining time, surface roughness, and quantity of blocks of machine tool control program. Finding suitable tool paths during finishing is very time-consuming and can be expensive. The aim is also to compare the practical results of machining with predicted simulation. The methodology for evaluating this problem is based on the following steps: experimental sample design for production, accuracy prediction of machined samples, production of samples using Computer Numeric Control milling center, analysis of accuracy, and surface roughness for the shape of the workpiece. The result is the variance of the shape accuracy deviations from the specified computer-aided design model of the workpiece, focusing on individual areas of its shape. The workpiece (aluminium alloy), focusing on individual areas of its shape. The research results show milled surface errors depending on the tool path tolerances. Using the effective solution method, it is possible to efficiently set up individual processes to improve the quality of production processes for time and cost.

Patient Satisfaction and Maintenance Requirements of Classical Implant Locators versus Customized Attachments in Mandibular Implant-Retained Overdentures

Objectives: This study was performed to compare implant locators versus customized mandibular implant-retained overdentures considering patient satisfaction and prosthesis maintenance. Materials and methods: 12 completely edentulous patients from the prosthodontic department-Cairo university outpatient clinic were selected according to specific inclusion criteria. The patients were then allocated randomly into two groups using closed envelopes. For both groups, each patient received dental implants in the planned position. The patients were left for 3 months for implant healing. For group (A) the patients received two locator attachments. The attachment collar height was selected based on the soft tissue thickness keeping the retentive part 1 mm above the soft tissue level. The denture was relieved opposite the locator housing and the attachment was picked up using cold-cured resin. For group B, the implants were exposed, and healing collars were placed. After 2 weeks, the implants were scanned using an intraoral scanner. The denture was readapted using a light body closed mouth impression. The relined denture was scanned from both the fitting and the occlusal side. The scanned fitting surface was used to create an inverted virtual model and preceded till creating custom locator attachments. The generated custom attachment abutment was milled from grade V titanium blanks using a 5-axis milling machine. The abutments were anodized into gold color using an electric anodizer. The attachments were then sterilized and placed in the patient mouth as set before in the design. The pick-up of the housing was done in the same manner as group A. For both groups, the patients were given instructions for using and maintaining the overdenture. Initial denture corrections were made in the first 2 weeks if any complaint existed. The patients were recalled periodically at 3 months, 6 months, 9 months &amp; 12 months respectively. Results: Likert scale out of 5 was followed for patient denture satisfaction along 3, 6, 9, and 12 months for groups A &amp; B. Applying an Independent t-test for significance evaluation between group A and group B, precluded the higher significance of group B than group A for all follow up as P-value &lt;0.05.For prosthetic maintenance along twelve months follow-up, group B revealed a lower insignificant different incidence of prosthetic complications than group A using the Chi-square test for significance testing between proportions as P-value &gt;0.05. Conclusions: Customized locator attachments are highly recommended to retain mandibular overdentures, as they exhibited better maintenance values and more wear resistance with minimal loss of retention. Moreover, can be utilized by any presented implant system in the market, in addition, Patients were completely satisfied with their customized locators retaining their implant-supported overdentures.

Design and Testing of a WAAM Retrofit Kit for Repairing Operations on a Milling Machine

Repairing, remanufacturing, and refurbishing high value metal components are crucial to move towards a more sustainable economy. Nowadays, repairing operations on high value parts, such as dies, are generally performed using time-consuming manual approaches that rely on the operator’s expertise. The research idea of this paper is to develop a retrofit kit to provide additive capabilities to an existing milling machine, allowing automatic repairing of components thanks to a fast switch between additive and machining operations without a relevant economic investment such the acquisition of a brand-new machine: the final cost of the solution is lower than 10% with respect to the mean cost of a 5-axis milling machine. The additive technology used in this work is Wire Arc Additive Manufacturing (WAAM) that is characterized by a higher deposition rate and a simpler and cost-effective equipment with respect to other techniques (e.g., laser cladding). The design of the system is illustrated in the paper together with the analysis of the results achieved repairing a test case: a die casting mold made of AISI H13 tool steel.

Lithography-based Ceramic Manufacturing (LCM) versus Milled Zirconia Blocks under uniaxial compressive loading: An in vitro comparative study

AimThis in vitro study aimed to compare the mechanical performance of 3D printed versus milled zirconia blocks, when subjected to uniaxial compression load, and to investigate the microstructural characteristics of the 3D printed samples, before and after the application of the load. MethodsTwenty zirconia blocks (5 × 5 × 5mm3) were prepared: 10 (tests) were 3D printed with a Lithography-based Ceramic Manufacturing (LCM) printer (Cerafab S65®, Lithoz, Vienna, Austria), and 10 (controls) were milled with a 5-axis milling machine (DWX-52D®, DGShape, a Roland Company, Hamamatsu, Japan). Compression tests were carried out on all samples, using a load cell of 30 kN and crosshead speed of 0.5 mm/min, in according to the ASTM C1424–15. The elastic modulus of the material was calculated from stress/strain curve by taking compressive stress values between 50 MPa and 100 MPa. Compression data obtained were plotted as stress-strain curves. Finally, the 3D printed test samples were also observed by VEGA3 Tescan scanning electron microscope (SEM) to detect the presence of eventual defects on surface before and after compression. A statistical analysis was performed to compare the elastic modulus and the deformation in compression at maximum load of the test samples that did not break and the control samples. ResultsUnder mechanical compression, four of the test samples reached failure, whereas all the control samples did not reach failure at the limit of the load cell. However, the 3D printed samples that did not break revealed interesting properties, such as a better modulus of elasticity (p = 0.15) and a lower tendency to deformation under compression (p<0.001), when compared to the milled ones. ConclusionsWithin the limits of this study (experimental setting, in vitro design, only one type of force applied) milled zirconia blocks were found more resistant to compression forces than 3D printed ones.

DEPTHS OF CUT IDENTIFICATION IN 3-AXIS MILLING USING CUTTING FORCE SPECTRUM

Cutting forces analysis is one of the most important means of improving machining quality and productivity. In 3-axis milling, the frequency domain analysis of the cutting forces provides information which can be adopted for both predicting and monitoring the cutting process. However, the evaluation of the cutting forces spectra requires the application of specific tools (i.e., Fourier’s Transform) to the time domain representation of the same cutting forces. This paper presents analytical formulations to directly evaluate the cutting force spectra starting from the tool geometry and the cutting parameters. The proposed formulations start from the expression of the cutting forces as a Fourier series and enhance the predictions showed in previous works by reducing the overall number of calculations needed. Then, the proposed formulations are applied to identify both radial and axial depths of cut exploiting the normalized cutting force spectrum. Finally, the proposed formulations and their application were numerically and experimentally validated. This work represents a preliminary step in the development of a monitoring system to identify cutting conditions in 3-axis milling.

Towards understanding and controlling of the surface texture pattern in 5-axis ball-end milling using fast texture simulation

Surface texture is critical for the functionality of industrial parts. This work aims to effectively control the surface texture by applying the phase difference angle between adjacent cutting passes using 5-axis ball-end milling. Because the texture pattern is complicated and is formed by combining feed-interval and step-interval scallops, we propose a level-contour-based fast simulation method to effectively generate the surface texture by inputting the phase difference angle with tilt and lead angles of the cutter. After clarifying the influence of these three parameters on the texture pattern, the desired texture was controlled by modifying the tool path according to the simulated phase difference angle. As a result, the milled surface texture corresponded well with the simulation. The details of the cutting features were efficiently and comprehensively simulated. The mechanism underlying the sudden change in the texture ridge direction was clarified as the major-minor ridge transition when the phase difference angle increased to a certain level, wherein the surface roughness could be decreased because the rearrangement of the cutting region reduced the scallop height. The proposed fast simulation method was also applied to the optimization process with a case study to demonstrate the benefits it can bring to the surface texture design and control.

Forces Shapes in 3-Axis End-Milling: Classification and Characteristic Equations

In 3-axis milling, cutting force analysis represents one of the main methods to increase the quality and productivity of the process. In this context, cutting force shape gives information of both monitoring and prediction of the cutting process. However, the cutting force shape is not unique, and it changes according to the cutting strategy, tool geometry, and cutting parameters. This paper presents a comprehensive approach to predict and classify cutting force shapes in 3-axis milling operations. In detail, the proposed approach starts by classifying the cutting force shapes for a single fluted endmill (i.e., single flute force shape), and, considering how the single flute force shapes may overlap one another, it extends the classification to a general multiple-fluted endmill. Moreover, the method provides, through analytical equations, angles, and magnitude dimensionless parameters of each key point, describing each shape classified. Finally, the proposed approach was experimentally validated through several milling tests in different cutting conditions.

Minimization of surface roughness in 5-axis milling of turbine blades

The Reynolds number of turbine blades can be reduced by decreasing the surface roughness of the blades, which decreases energy loss in energy production systems. Due to the challenges of the polishing process in reducing roughness of machined blades, the application of optimized machining parameters to decrease surface roughness is a practical solution. Virtual machining system is explored in this research to improve the efficiency of machined parts. The aim of this research is to provide a virtual machining system that can predict and effectively reduce roughness in gas turbine blade 5-axis machining operations. The machining parameters were optimized using Genetic algorithm to reduce surface roughness. The turbine blades were machined using a 5-axis CNC machine tool, and the surface roughness of the machined parts was measured using a CMM machine to validate the developed methodology in the study. The optimized machining parameters result in a 26.2% reduction in observed surface roughness and a 27.3% reduction in expected surface roughness in the machined blades. The developed virtual machining system can be used to improve the surface quality of machined turbine blades and hence improve the efficiency of gas turbines during the power production in gas turbines.

Influence of Different Marginal Preparation Designs and Materials on the Marginal Integrity and Internal Adaptation of Endocrown Restorations

ABSTRACT Objective: This in vitro study was performed to assess the marginal accuracy and internal adaptation of CAD/CAM fabricated endocrowns restoring endodontically treated molars with two different designs and materials. Materials and methods: Forty extracted maxillary first molar teeth were divided into two main groups (n=20) according to the preparation designs: group B: (Butt joint) & group S (Shoulder finish line): and each group was subdivided into two subgroups (n=10) according to materials: group E: lithium disilicate glass-ceramic (IPS e.max CAD; Ivoclar Vivadent AG) & group C: hybrid nanoceramic (Cerasmart; GC Corp). A digital scan was made with a digital scanner (Identica Hybrid Scanner; Germany) and virtual endocrowns were milled with a 5-axis milling machine ((Imes-Icore; CORiTEC250i; Germany). The silicone replica technique and a stereomicroscope (25X) were used to measure the marginal and internal gaps of endocrowns at different points. All data were statistically analyzed using three-way ANOVA test with Post Hoc Tukey test to detect pair-wise comparison. Student's t-test also was used. Results: There was a statistically significant difference between the preparation designs on the marginal integrity and internal adaptation (p 0.05). Conclusions: All tested groups showed acceptable marginal and internal gaps mean values. Butt joint design showed a better effect than shoulder finish line design on the marginal integrity and internal adaptation. Cerasmart showed a better effect than IPS e.max CAD on the internal adaptation.