Conventional Milling Process Research Articles

Effect of machining method and margin design on the accuracy and margin quality of monolithic zirconia crowns

The machining accuracy and marginal integrity of monolithic zirconia crowns with minimal invasive preparations may impact the long-term survival rate of tooth and periodontal health, but studies on the effect of machining method are lacking. The purpose of this in vitro study was to digitally evaluate the machining accuracy and margin quality of monolithic zirconia crowns fabricated using gel deposition and conventional soft milling processes by comparing 2 different margin types. A total of 40 monolithic zirconia crowns were produced using gel deposition (Self-glazed Zirconia Group, SGG, n=20) and soft milling (Milled Zirconia Group, MG, n=20). Each group was further divided into 2 subgroups with different margin designs (chamfer and feather-edge). The trueness and fit of crowns were compared using root mean square (RMS) values. Furthermore, the margin quality was examined before and after final sintering with a scanning electron microscope (SEM). The Scheirer-Ray-Hare and 2-way ANOVA test analysis nonparametric and parametric data, respectively (α=.05). The trueness analysis revealed that SGG had significantly lower RMS values for both the cameo and intaglio areas compared with MG (P<.001). In addition, crowns with a feather-edge margin exhibited significantly lower marginal RMS values than those with a chamfer margin (P<.01) according to the fit assessment. Followed by milling processes, SGG exhibited a constantly homogeneous microstructure compared with MG. Marginal defects were detected in both groups except for the SGG with the chamfer margin. SGG exhibited better accuracy associated with ductile-regime machining than MG, and SGG with chamfer margins displayed flaw-free margin areas. Moreover, the feather-edge margin showed improved marginal fit compared with the chamfer margin.

Study on hybrid 3D printing and milling process for customized polyether-ether-ketone components.

Polyether-ether-ketone (PEEK) has been widely applied in various fields due to its excellent mechanical properties and biocompatibility. The efficient and high-quality customized manufacturing of PEEK components are investigated in this study by the hybrid 3D printing and milling process. At first, the alternating hybrid process is selected and verified by comparing two typical hybrid process categories and conducting experiments, respectively. Second, a set of procedures are designed to automate the engineering application of the hybrid process trying to avoid the disadvantages of manual programing. Then, considering the tool length and possible interferences during the hybrid process, a model segmentation algorithm, namely, the exchange principle of avoiding interference (EPAI) is proposed. Based on the introduced EPAI and the programing language Python, the additive and subtractive hybrid manufacturing (ASHM) data processing procedure is proposed and realized by post-processing of the conventional 3D printing codes. Finally, the feasibility experiments have been conducted. The experimental results verify the hybrid manufacturing process in the fabrication of parts with complex internal features. The surface roughness Ra and dimensional error L of the parts have been reduced by 75.5% and 85.2%, respectively, while the shear strength τ has been increased by 14.1%. Compared with conventional milling process, the material consumption is reduced by 48.7%.

Hybrid manufacturing cost models: Additive friction stir deposition, measurement, and CNC machining

Based on its potential to reduce lead times, hybrid manufacturing, which often includes both additive manufacturing and machining processes, is receiving more attention from manufacturers as they seek to increase their supply chain resilience and efficiency. A new solid-state additive manufacturing, referred to as additive friction stir deposition (AFSD), has shown the potential to become an important process for hybrid manufacturing. To justify the selection of a hybrid manufacturing approach, the cost needs to be estimated for comparison to conventional approaches. Historically, hybrid manufacturing costs have been difficult to estimate due to the complexity and diversity of the manufacturing processes. This paper proposes cost models that include additive friction stir deposition, structured light scanning, milling, and turning, which can be combined in hybrid manufacturing process planning. These cost models are demonstrated in a case study and cost estimates are compared for hybrid and conventional (machining-only) manufacturing approaches. For the selected case, the hybrid manufacturing process cost was $1007.58, while the conventional milling process cost was $833.60. The results of the case study show that both labor and material costs must be considered to make an informed decision between hybrid and conventional manufacturing approaches.

Optimization of Vitamin B1, B2, and B6 Absorption in Nang Tay Dum Floating Rice Grains.

As reported by the FAO, in 2022, approximately 735 million people experienced undernourishment, underscoring the critical need for effective strategies to address micronutrient deficiencies. Among these strategies, the mass fortification of staple foods, particularly rice-a dietary staple for half of the global population-has emerged as one of the most effective approaches. Conventional milling processes diminish the nutritional content of rice, necessitating the development of fortification methods to enhance its nutrient profile. This study investigates advanced fortification techniques to improve the nutritional value of rice, focusing on vitamins B1, B2, and B6, with guidelines from the US Institute of Medicine's Dietary Reference Intakes. The results indicate that implementing ultrasonic treatments and optimal soaking conditions (60 °C for 60 min) significantly enhances the absorption of these vitamins. Effective parameters included a concentration of 1500 ppm for vitamin B1 and higher levels for vitamins B2 and B6, with a rice-to-vitamin solution ratio of 1:4. These conditions yielded an absorbed vitamin B1 content of 1050 mg/kg, bringing the fortified rice closer to meeting recommended intake levels. Given the global average daily consumption of 100 g of rice per person, this research demonstrates the feasibility of fortifying rice to address nutrient deficiencies effectively and contribute to improved dietary health worldwide. Further enhancement of vitamin B2 and B6 levels remains essential for optimal fortification, highlighting the potential of fortified rice as a sustainable solution for improving global nutrition.

Perhitungan Ongkos Pemesinan Konvensional Menggunakan Macro Vba Excel pada Studi Kasus (Produk Roda Gigi Payung Ø65mm × Z24)

In the conventional machining process, production costs are essential to know to determine the cost of making a product in any industrial manufacturing such as the SMK N 2 PEKANBARU machining workshop. Machining production costs are calculated based on machining time per product and machining operation costs. In calculating conventional machining costs, the VBA Excel macro is an application that can be used to calculate production costs. The Ø65mm × z24 umbrella gear product which is the research case study is a product that is machined by two conventional machining processes, namely lathe machining and milling machining. From the results of the research, the cost of conventional lathe machining, namely making gear wheels, is IDR 47,841/product, and the conventional milling process, namely making Z24 gears, is IDR 40,002/product, while the machining cost for lathe mastercam simulation is IDR 33,187/product and the machining cost for milling mastercam simulation is IDR 20,340/product. Machining costs are the product of operating costs per minute (cm) and machining time (tm). So, from the results of calculating machining and production costs, it is known that the product manufacturing costs or production costs for Ø65mm × Z24 umbrella gears are in the range of IDR 111,827 - IDR 146,143/product.

The use of crude carbon dots as green, low-cost and multifunctional additives to improve the curing, mechanical, antioxidative and fluorescence properties of epoxy natural rubber/silica composites

Rubbers are acknowledged as strategically important and irreplaceable materials in daily life, and rubber additives are indispensable components for the practical application of the rubber vulcanizate. Developing novel rubber additives is highly desirable, and pursuing multifunctional rubber additives has been one of the major tasks in the field of rubber. Herein, the crude carbon dots (CCDs) without any purification were used as rubber additives for epoxy natural rubber/silica system by conventional milling process. Our results revealed that the CCDs have outstanding advantages, they could not only endow the rubber with charming fluorescence and excellent anti-aging capability, but also improve the curing rate and mechanical performance of rubber composite. Moreover, with the incorporation of CCDs, the rolling resistance of the rubber composite could be remarkably reduced, which is promising for the application of green tyres. Overall, this work convincingly provides novel inspiration to develop novel low-cost yet multifunctional additives for rubber.

An innovative formulation approach for low-melting ingredients: optimizing an alternative melt suspension technique for Pyraclostrobin suspension concentrate

The agrochemical industry is now focusing more on safer formulations with lowest dose rate. Suspension Concentrate formulations are one of the safest and most commonly utilized type in agrochemical industry. In this study, a suspension concentrate was developed and compared using a novel melt suspension technique alongside the conventional milling process. The objective was to determine the effectiveness of the new technique in terms of particle size reduction, processing time, and storage stability. In the melt suspension process, the low melting active ingredient(fungicide), was melted along with suitable surfactants and antifreeze in water and homogenized at high rotation per minute (2000). The same fungicide suspension concentrate was also prepared using milling process for comparison. Stability studies were conducted following the Food and Agricultural Organization procedure for both suspensions concentrate products. The storage stability results showed that particle size variation was just 0.8 ± 0.84% (w/v), antifungal content variation during storage stability studies was (±3.12 g/L) only, all other physical parameters results variations were < ± 0.5% w/v. Prepared suspension concentrates were further analyzed using three analytical techniques, Ultraviolet-Visible spectroscopy, high-performance liquid chromatography, and Fourier-transform infrared spectroscopy. The study suggests that the melt suspension technique can be an alternative to the normal milling process for preparing stable suspension concentrate, particularly for low melting point compounds.

Experimental Investigation on Axial Ultrasonic Vibration Assisted Milling of Cr12MoV

The conventional milling process is difficult due to the high strength and hardness of Cr12MoV, which can cause the rapid tool wear, premature failure,and poor milling quality of work platform. The ultrasonic vibration machining technology has been founded to be effective in the milling process of hard-to-cut materials like die tool steel and nickel alloys. The ultrasonic vibration assisted milling (UVM) technology is carried out the axial milling of Cr12MoV in this paper, and the average impact force Fi is influenced by the vibration amplitude A, the vibration frequency f, and equivalent mass of the vibrating part M. The mean value of cutting force Fx, Fy, and Fz decreases by 25%, 15.04%, and 17.46%, respectively. With the increase of vibration amplitudes, the value of surface roughness firstly decrease and then increase, and it is obviously lower than conventional milling. The experimental results demonstrated that the UVM technology is a feasible method for the low cutting force and high quality process of cutting Cr12MoV.

Effects of process parameters on cutting forces, material removal rate, and specific energy in trochoidal milling

Trochoidal milling has been developed to enhance tool life during slot machining. It is characterized by reduced cutting forces, cutting temperature, and tool wear as compared to conventional milling processes. It is effective in machining difficult-to-cut materials, high-speed machining, and groove corners. However, this process has not been deeply investigated enough to discover its advantages and optimize its parameters. A full factorial design of 144 experiments has been applied in this paper to investigate extensively the effects of axial depth of cut, feed rate, and trochoidal step on material removal rate, cutting forces, and specific energy in trochoidal milling. Trochoidal step and axial depth of cut almost have the same contributions on cutting forces by 32% and 31% respectively, followed by feed rate by 25%. Feed rate, trochoidal step, and axial depth of cut influence the material removal rate by 37%, 30%, and by 19% respectively. The contributions of feed rate, trochoidal step, and axial depth of cut on relative specific energy are 57%, 24%, and 8% respectively. The increase of axial depth of cut increases the maximum resultant force till a threshold value, then it stabilizes. This behavior occurred due to the increase of the maximum engagement angle to a certain limit, then it does not increase any more. Both feed rate and trochoidal step linear affect maximum resultant force and material removal rate, while the relationships are non-linear for specific energy. It is recommended to machine slots in full depth with the highest possible trochoidal step and feed rate, considering the increase of tool wear and surface roughness. It is preferred to use a cutting tool of a large helix angle and small diameter to reduce the threshold axial depth of cut. Overall, this study is significant in characterizing, designing, and optimizing of trochoidal milling through experimental work.

Evaluation of profile accuracy and surface integrity for Inconel 718 blade machined by ultrasonic peening milling

The blade is the most important component of the aero-engine in an aircraft. Aero-engine blades comprise thin-walled structures with complex curvatures, which are processed and manufactured by difficult-to-cut materials, such as Inconel 718. The blade profile accuracy and surface integrity are difficult to achieve using the conventional milling (CM) process only, as it directly affects the overall performance and reliability of the aero-engine. In this study, the deformation theory of thin-walled blades during the milling process was systematically analyzed, and the effectiveness of the ultrasonic peening milling (UPM) process in controlling the profile accuracy and surface integrity of Inconel 718 blades was evaluated. This study employed a simplified model of an Inconel 718 blade machined by UPM and CM and compared the milling forces under the milling processes. The profile accuracy (with straight or curved geometry) and surface integrity of the blades are measured and evaluated after the milling tests. The validation results show that UPM has significant advantages in terms of reducing milling forces, increasing blade profile accuracy, and improving the surface integrity during the milling process. This study affords a new process to enhance milling profile accuracy and achieve surface integrity control of Inconel 718 blades.

Chatter detection for micro milling considering environment noises without the requirement of dominant frequency

Existing chatter detection methods were mainly developed for conventional milling processes, and did not consider the influences of environment noises. Thus, they are not suitable for micro milling, in which the widely used small cutting parameters easily lead to the occurrence of non-negligible noises. This article proposes a new variable forgetting factor recursive least-squares (VFF-RLS) algorithm to filter out the chatter-independent component, which is composed of environment noises and periodic components, for the signals sampled from the micro milling process. It is theoretically found that with the aid of VFF-RLS algorithm, there is almost nothing in the filtered signal for stable cuts, while chatter components will be dominant in the filtered signal for unstable cuts. This important finding confirms that some features can be easily extracted from the filtered signal to directly reflect the stable or unstable machining states without the requirement to measure the system’s dominant frequency, which is necessary for some existing methods to obtain the frequency band where chatter vibrations appear. Subsequently, a streaming feature selection considering feature interaction (SFS-FI) method is established to select optimal features and remove irrelevant and redundant features. Then, a chatter detection model is developed based on the selected features. Finally, a series of micro milling tests with various axial depths of cut and spindle speeds prove that the proposed model can accurately identify the cutting state, even for slight chatter and stable cuts with small little depths of cut, which are more easily disturbed by environment noises. Results confirm that the detection accuracy is larger than 99 %, and this fact means that the proposed method is effective and practical for detecting chatter occurring in micro milling processes.

Optimisation of surface residual stresses using ultrasonic-assisted milling for wire-arc additive manufactured Ni alloy components

Nickel alloys are cost intensive materials and generally classified as difficult-to-cut material. However, machining of these materials is needed especially in case of alloy 36 (1.3912), which is commonly used in mould construction for the production of fibre-reinforced composites. With regard to repair, modification and manufacturing of such components, additive manufacturing offers significant economic advantages. Nevertheless, subsequent machining steps are needed to achieve the final component contour and defined surface conditions. Dependent on the material and machining process conditions, detrimental tensile residual stresses may be the result on the machined surface, having negative impact on the component performance and safety. In this investigation, machining experiments were carried out on wire arc additive manufactured components made of alloy 36, varying the cutting speed and the feed rate. In addition, the conventional milling process (CM) was compared with a modern, hybrid machining process, the ultrasonic-assisted milling (US). The cutting forces and the surface-near residual stresses were analysed using X-ray diffraction. A significant improvement of the machinability as well as the surface integrity by using the ultrasonic assistance was observed, especially at low cutting speeds. The CM induced mainly tensile residual stresses, the US mainly compressive residual stresses.

Machinability improvement in milling of SiCf/SiC composites based on laser controllable ablation pretreatment

The poor machinability of SiCf/SiC composites greatly limits its application and promotion. The laser-induced ablation products of SiCf/SiC composites are powdery, loose and porous. Milling of laser ablated samples demonstrated that the force and heat were almost negligible when milling ablation products. Accordingly, a laser ablation pretreatment milling (LAPM) process of SiCf/SiC composites was proposed. Under the LAPM process, after the laser ablation treatment with controllable depth, the cutting allowance could be achieved in only one pass, which greatly improved the machining efficiency compared with the conventional milling process. The material removal rate was greatly improved on the premise of ensuring the machining quality. Taking the milling of tensile specimens as an example, compared with conventional milling, the total processing time of the specimen was reduced by 31.29 % by LAPM process. Therefore, LAPM provides a potential feasible process scheme for greatly improving the machinability and machining efficiency of SiCf/SiC composites.

Mechanical and Aging Properties of Hydrogenated Epoxidized Natural Rubber and Its Lifetime Prediction.

Natural rubber (NR) has restricted its application due to its potential for thermal- and oil-resistant materials. The weakness of NR can be eliminated by chemical modification to enhance aging properties. Formic acid and hydrogen peroxide have been used to prepare partially epoxidized natural rubber (ENR) in the latex state. Its residual unsaturated units were then modified using hydrazine and hydrogen peroxide to obtain hydrogenated ENR (HENR). 1H-NMR characterized the resulting products. NR and modified NRs were compounded and then vulcanized using a conventional milling process. This paper compares NR, ENR having 49.5% epoxide group content, and HENR having 49.5% epoxide group content and 24% hydrogenation degree in terms of tensile, thermal, oil, and ozone properties. Morphology and lifetime prediction were studied. Overall results show that the tensile strength of the HENR composite (14.7 MPa) was 79 and 71% lower than that of ENR (18.6 MPa) and NR (20.8 MPa) composites, respectively. In contrast, the modulus at 100% elongation of the HENR composite (2.0 MPa) was 167 and 200% higher than that of ENR (1.2 MPa) and NR (1.0 MPa) composites, respectively. Morphological studies of the tensile fractured surface of the vulcanizates, using scanning electron microscopy, confirmed a shift from ductility failure to brittle with the presence of the epoxide groups and low unsaturated bonds in the backbone chain. The results demonstrated that HENR could act as an ideal material, providing better thermal, oil, and ozone resistances while maintaining the mechanical properties of the rubber. The kinetic analyses of the thermal degradation of NR, ENR, and HENR were studied using thermogravimetric analysis (TGA) at three heating rates. Kissinger–Akahira–Sunose (KAS) was employed to calculate the activation energy (Ea). The obtained data were used to predict the lifetime under the established temperature range and 0.05 conversion level. Overall, the results represented that HENR had a longer lifetime than NR and ENR for a temperature range between 25 and 200 °C, indicating that HENR had excellent thermal stability than NR and ENR. Therefore, the HENR should extend the applications to include gaskets and seals, especially for the automotive and oil industries.

Investigation of deviation and surface topography in ultrasonic vibration-assisted milling

Thin-walled structures have many applications in the aerospace industry. An important feature of them is their high strength to weight. When milling the thin-walled part, the thickness decreases step by step by cutting, which causes the process to be complex and dependent on process parameters. In the present study, thin-walled aluminum structures are investigated using conventional and ultrasonic milling processes, and distortion, surface roughness, surface texture, and average thin-wall forces are also investigated. Therefore, 18 tests are performed on parts made of 7075T6 aluminum alloy using various feeds, spindle speeds, and machining modes. The results showed that the machining type and spindle speed had 47% and 33% effect on distortion, respectively. In addition, the results showed that by applying vibrations to the milling, the amount of distortion can be reduced by up to 30% and effectively optimized. This technique is suitable for manufacturing industries that require high dimensional accuracy. Also, the surface texture and burr formation are investigated. In particular, the surface roughness in ultrasonic milling decreased compared to conventional milling.

Improved Cutting Force Modelling in Micro-Milling Aluminum Alloy LF 21 Considering Tool Wear

Aluminum alloy LF 21 has a strong ability to reflect electromagnetic waves. LF 21 waveguide slit array structure is widely used in waveguide radar antenna. The stiffness of the slit array structure is relatively weak. So, the structure is prone to deformation under the cutting force in the conventional milling process. Micro-milling technology can realize high-precision machining of mesoscale parts/structures and is a potential effective machining technology for the waveguide slit array structure. However, the diameter of the micro-milling cutter is small, and the feed per tooth is comparable to the arc radius of the cutting edge, so the micro-milling cutter is prone to wear. In addition, the effects of elastic recovery of material, the minimum cutting thickness and friction of cutting dead zone on micro-milling force cannot be ignored. A simulation model of micro-milling aluminum alloy LF 21 processes based on DEFORM 3D is built by combining the theory of cutting and the technology of process simulation. Prediction of tool wear is achieved. The quantitative relationship between the arc radius of the cutting edge and tool wear is clarified for the first time. The authors built an improved cutting force model in micro-milling LF 21 considering tool wear and cutter runout with the minimum cutting thickness as the boundary. The validity of the built micro-milling force model is verified by experiments.

Adapting the Surface Integrity of High-Speed Steel Tools for Sheet-Bulk Metal Forming

New manufacturing technologies, such as Sheet-Bulk Metal Forming, are facing the challenges of highly stressed tool surfaces which are limiting their service life. For this reason, the load-adapted design of surfaces and the subsurface region as well as the application of wear-resistant coatings for forming dies and molds made of high-speed steel has been subject to many research activities. Existing approaches in the form of grinding and conventional milling processes do not achieve the surface quality desired for the forming operations and therefore often require manual polishing strategies afterward. This might lead to an unfavorable constitution for subsequent PVD coating processes causing delamination effects or poor adhesion of the wear-resistant coatings. To overcome these restrictions, meso- and micromilling are presented as promising approaches to polishing strategies with varying grain sizes. The processed topographies are correlated with the tribological properties determined in an adapted ring compression test using the deep drawing steel DC04. Additionally, the influence of the roughness profile as well as the induced residual stresses in the subsurface region are examined with respect to their influence on the adhesion of a wear-resistant CrAlN PVD coating. The results prove the benefits of micromilling in terms of a reduced friction factor in the load spectrum of Sheet-Bulk Metal Forming as well as an improved coating adhesion in comparison to metallographic finishing strategies, which can be correlated to the processed roughness profile and induced compressive residual stresses in the subsurface region.

Synthesis and magnetic properties of Sb added MnBi magnets for applications at sub-zero temperatures

MnBi-LTP bulk magnets containing substitutional Sb element were fabricated using gas-atomizing process, surfactant-assisted wet magnetic compaction process, and thermal compaction process. Magnetic properties and microstructures were investigated according to the processing parameters. It was found that substitutional Sb element effectively refined the grain size of gas-atomized powders. The conventional ball milling process was able to pulverize these powders into fine particles with a single crystalline structure and minimize their phase decomposition, resulting in a (BH)max of 11.0 MGOe. By analyzing the effects of the compaction pressure on the density and magnetic alignment during the surfactant-assisted wet compaction process, Mn54Bi45.9Sb0.1 bulk magnet with Hc of 10.0 kOe at room temperature and temperature coefficient Hc of 0.68%/K was successfully fabricated. Furthermore, effects of Sb element on the temperature dependency of Hc in the bulk magnet were discussed.

Structural, Electromagnetic and Microwave Properties of Magnetite Extracted from Mill Scale Waste via Conventional Ball Milling and Mechanical Alloying Techniques.

This study presents the utilization of mill scale waste, which has attracted much attention due to its high content of magnetite (Fe3O4). This work focuses on the extraction of Fe3O4 from mill scale waste via magnetic separation, and ball milling was used to fabricate a microwave absorber. The extracted magnetic powder was ground-milled using two different techniques: (i) a conventional milling technique (CM) and (ii) mechanical alloying (MM) process. The Fe3O4/CM samples were prepared by a conventional milling process using steel pot ball milling, while the Fe3O4/MM samples were prepared using a high-energy ball milling (HEBM) method. The effect of milling time on the structural, phase composition, and electromagnetic properties were examined using X-ray diffraction (XRD) and a vector network analyzer (VNA). XRD confirmed the formation of magnetite after both the magnetic separation and milling processes. The results revealed that Fe3O4 exhibited excellent microwave absorption properties because of the synergistic characteristics of its dielectric and magnetic loss. The results showed that the Fe3O4/CM particle powder had a greater absorption power (reflection loss: <−10 dB) with 99.9% absorption, a minimum reflection loss of −30.83 dB, and an effective bandwidth of 2.30 GHz for 2 mm thick samples. The results revealed the Fe3O4/MM powders had higher absorption properties, including a higher RL of −20.59 dB and a broader bandwidth of 2.43 GHz at a matching thickness of only 1 mm. The higher microwave absorption performance was attributed to the better impedance matching property caused by the porous microstructure. Furthermore, the magnetite, Fe3O4 showed superior microwave absorption characteristics because of the lower value of permittivity, which resulted in better impedance matching. This study presents a low-cost approach method by reutilizing mill scale waste to fabricate a high purity crystalline Fe3O4 with the best potential for designing magnetic nano-sized based microwave absorbers.

Significantly reinforced and long serviceable acrylonitrile butadiene rubber/graphitic carbon nitride composites for future industrial applications

The application of graphitic carbon nitride (g-C3N4) as non-black reinforcing filler is very little-known part in rubber technology. In the present study, g-C3N4 filled acrylonitrile butadiene rubber (NBR) composites were prepared by conventional two-roll milling process to investigate the influence of g-C3N4 on the mechanical and thermal performances of NBR formulations. NBR composite with 3 phr (parts per hundred parts of rubber) g-C3N4 presents considerably higher cure rate index, hardness, tensile strength, storage modulus and thermal stability than unfilled NBR composite. Also, the addition of g-C3N4 successfully enhances the thermal oxidative aging resistance and fuel consumption efficiency of NBR composites. Thus, g-C3N4 can be used in the near future as interesting filler for developing long serviceable NBR composites with good mechanical properties.