Milling Mode Research Articles

The influence of the composition of atmosphere on the mechanisms of degradation of graphite in planetary ball millers

This study focuses on the degradation process of graphite in a planetary ball miller. It is shown that this degradation is only related to the milling mode. The sliding mode is very gentle toward the graphite structure whereas the shock milling mode leads to the quick degradation of the graphite structure producing poorly organized nanoparticles. Nevertheless, the milling mode is not determined by the ball miller rotation speed but by the ability of graphite to form a lubricating layer. The development of this lubricating layer in only possible in presence of oxygen which annihilates the reactive sites created during milling by forming oxygen groups. In this case, the sliding mode predominates. When the oxygen disappears or under inert atmosphere, the reactive sites stick to the ball surface, destroying the graphite lubricating layer and resulting in shock milling mode. This explains the link between the milling atmosphere and the graphite structure evolution in planetary ball millers. This also explains why the graphite structure evolution is far less sensitive toward environment in a vibratory ball miller in which the sliding milling mode is not possible.

Synthesis of Mg 15Fe materials for hydrogen storage applying ball milling procedures

The effects of different synthesis procedures on the microstructure and hydrogen uptake characteristics of the Mg 15Fe materials were studied. The applied processes of synthesis consisted basically on ball milling in argon atmosphere followed by a hydriding reaction. Two mill devices with distinct milling modes were employed, i.e. a low energy mill (LEM) (Magneto Uni-Ball-Mill II) and a high energy mill (HEM) (Fritsch Planetary Mill, P6). The HEM sample showed better Mg–Fe mixing degree than the sample obtained from the LEM process due to the small particles of Fe resulting from the larger amount of mechanical energy transferred to the materials by the HEM device. The better Mg–Fe contacting was responsible for the higher hydrogen capacity and faster hydrogen uptake rate of the high energy milled material. Therefore, the HEM procedure was more effective than the LEM. The hydrogen uptake properties of the HEM synthesized material were compared with other Mg-based materials obtained via inert and reactive ball milling without a subsequent activation step. This study showed that Mg 15Fe mixture of powders synthesized via reactive ball milling in hydrogen (RBM–LEM) has higher hydrogen capacity (5.5 wt% H) and faster kinetics than samples with the same composition milled in argon (LEM – 1.65 wt% H and HEM 1.87 wt% H). Nevertheless, a superior hydrogen capacity (6.5 wt% H) were obtained by adding LiBH 4 to Mg 15Fe via HEM in argon atmosphere.

A New Algorithm for the Numerical Simulation of Machined Surface Topography in Multiaxis Ball-End Milling

In milling process, surface topography is a significant factor that affects directly the surface integrity and constitutes a supplement to the form error associated with the workpiece deformation. Based on the tool machining paths and the trajectory equation of the cutting edge relative to the workpiece, a new and general iterative algorithm is developed here for the numerical simulation of the machined surface topography in multiaxis ball-end milling. The influences of machining parameters such as the milling modes, cutter runout, cutter inclination direction, and inclination angle upon the topography and surface roughness values are studied in detail. Compared with existing methods, the basic advantages and novelties of the proposed method can be resumed below. First, it is unnecessary to discretize the cutting edge and tool feed motion and rotation motion. Second, influences of cutting modes and cutter inclinations are studied systematically and explicitly for the first time. The generality of the algorithm makes it possible to calculate the pointwise topography value on any sculptured surface of the workpiece. Besides, the proposed method is proved to be more efficient in saving computing time than the time step method that is commonly used. Finally, some examples are presented and simulation results are compared with experimental ones.

Dependence of Structural Evolution an Hydrogen Storage Mechanism on Milling Parameters during controlled Reactive Milling of Graphite in Hydrogen

t Graphite was mechano-chemically processed in hydrogen using controlled reactive ball milling (CRBM). As-milled and heat treated products were characterised using techniques of combustion analysis, X-ray diffractometry (XRD), selected area electron diffracton (SAED) and high resolution transmission electron microscopy (HRTEM). Both the mechanisms of hydrogen uptake and of hydrogen evolution during subsequent heat treatment were found to be dependent on the mode of milling. Samples milled under a ball-particle impact mode absorbed more hydrogen (2.7wt%) than the samples milled under shearing mode, but the fraction of hydrogen released during subsequent low temperature heat treatment (220-500°C) was significantly less than for the samples milled under shear. XRD of the shear milled product showed increased, but varying c-axis lattice parameters while XRD of the impact milled product showed complete loss of (002) graphite and formation of peaks which could be associated with CnHx species. Low temperature heat treatment of the shear milled product resulted in significant disorder in the graphite structure, characterised by a loss of diffraction peak contrast and high background scattering in both XRD and selected area electron diffraction patterns. In contrast there was little change in XRD patterns from impact milled samples during low temperature heat treatment. For the shear milled samples which were heat treated for short times there was also an associated loss of contrast from graphene layers in HRTEM images, however, HRTEM contrast from samples shear milled and heat treated for longer times showed an increased fraction of graphene sheets in the product. It was concluded that hydrogen uptake under impact mode milling was predominately via an irreversible mechanism involving destruction of graphene sheets and reaction to from product including CnHx -type molecules. However, hydrogen uptake under shearing mode milling occurred via a partially reversible mechanism involving absorption between graphite layers and expansion of the graphite inter-sheet spacing.

DSC study of the effect of milling conditions on the hydrogen storage properties of boron

Two milling modes (shearing and impact) were applied to investigate the hydrogen storage properties of boron. It was found that the shearing mode leads to 2.05 wt% hydrogen trapped in boron, while impact mode to 2.93 wt%. Differential scanning calorimetry (DSC) was used to study thermally induced transformations in freshly milled and aged samples. The DSC traces obtained from freshly milled samples through the shearing and impact modes are dissimilar and are also very different from those obtained from the aged samples. The origins of these differences are discussed in relation to the milling mode applied.

Generate rough tool-paths from unorganized point-cloud directly

An approach is presented to generate rough interference-free tool-paths directly from massive unorganized data in rough machining that is performed by machining volumes of material in a slice-by-slice manner.Unorganized point-cloud is firstly converted to cross-section data.Then a robust dam-structure named tool-path net is constructed to save tool-path data.Optimal algorithms for partitioning sub-cut-areas and computing interference-free cutter-locations are put forward.Finally the tool-paths are linked in a zigzag milling mode,which can be transformed into a traveling sales man problem.The experiment indicates optimal tool paths can be acquired,and high computation efficiency can be obtained and interference can be avoided successfully.

The influence of ball milling process on formation and electrochemical properties of amorphous MgNi hydrogen storage alloys

The present work investigated the influence of ball milling parameter, such as milling mode, milling velocity and milling time, and element addition on the microstructure and electrochemical properties of MgNi alloys prepared by mechanical alloying (MA). It has been found that partially amorphized MgNi (a-MgNi) alloy was obtained through an intermediate product of crystal (c-) Mg 2Ni with continuous milling mode at a certain velocity. The fully amorphized MgNi alloy was gained by milling with intermittent mode, and the time required to form the amorphous phase is strongly affected by milling velocity and intermittent condition. The a-MgNi alloy can be prepared by continuous milling mode when nonmetallic elements, such as B and Si, are suitably added into powder mixture of Mg and Ni. The initial discharge capacities of a-MgNi hydrogen storage alloy changed in a zigzag trend with the prolonging of milling time. The maximal electrochemical capacity is the MgNi alloy with the structure of nearly full amorphous phase.

Effects of iron oxide (Fe 2O 3, Fe 3O 4) on hydrogen storage properties of Mg-based composites

When magnesium powder containing small additions of certain multiple valence transition metal oxides (TMOs) is ball milled in hydrogen, the hydrogenated Mg-based product can show remarkable improvements in hydrogen absorption/desorption properties. Using a magnetically controlled Uni-Ball-Mill, small amounts of the iron oxides, Fe 2O 3 and Fe 3O 4, were ball milled with Mg powder in a hydrogen atmosphere (Mg to Fe atomic ratio; 20:1). Milling products as well as samples used in hydrogen absorption/desorption experiments were characterized by scanning electron microscopy (SEM), X-ray diffractometry (XRD), differential scanning calorimetry (DSC) and thermogravimetric (TG) analysis. TG analysis combined with DSC revealed a higher hydrogen storage capacity for the Mg + Fe 2O 3 + H 2-milled product (6 wt% H) compared with 5 wt% H for Mg + Fe 3O 4 + H 2. XRD revealed that during heating, both iron oxides were reduced to pure Fe, a result not previously reported for similar materials milled using different milling devices. For both samples, there was little difference found in the decomposition temperature of the as-prepared MgH 2 and rehydrogenated composites. However, storage capacity degradations were observed for the rehydrogenated composites (4 wt% H storage capacity for MgH 2 + Fe 2O 3 and 4.4 wt% H for MgH 2 + Fe 3O 4). The higher capacity degradation of rehydrogenated MgH 2 + Fe 2O 3 composite is also believed to be a result of the reduction reaction, during which more magnesium was consumed than was consumed by the same amount of Fe 3O 4. The results also were related to the particular ball-milling equipment and low-energy shearing milling mode employed, which promoted the development of a nanostructural hydride product which subsequently changed structure significantly during the first desorption cycle.

A New Method to Prepare Maleic Anhydride Grafted Poly(propylene)

AbstractSummary: A new method to prepare maleic anhydride grafted poly(propylene) (MAPP) was developed successfully. The grafting reaction of maleic anhydride (MA) onto poly(propylene) (PP) was performed with the aid of ball‐milling, and the grafting mechanism was proposed based on the experimental results. MAPP was prepared by ball‐milling of PP powder, MA, and peroxide initiator in balls‐containing jars with a planetary ball mill for a certain time. Factors were considered on reaction time, rotational speed of the mill, cyclic milling mode, kind and concentration of peroxide, and concentration of MA. Results show that MAPP obtained contains the main structures of end‐grafting type (both single and oligomeric) and bridge‐grafting type. Compared with the conventional melt‐mixing method, MAPP obtained through the ball‐milling method reveals alleviated degradation of PP or even increased molecular weight of resultant MAPP. This novel method has also the advantages of lower process temperature and solventless, energy efficient, low cost and simple running process. Furthermore, it is very easy to get purified products.Key steps for preparing MAPP through ball‐milling.magnified imageKey steps for preparing MAPP through ball‐milling.

X-ray diffraction and Mössbauer studies of mechanically alloyed Fe–Ni nanostructured powders

Fe–10 wt% Ni and Fe–20 wt% Ni nanostructured alloys were prepared using a planetary ball mill P 4 vario mill from Fritsch. The Fe (Ni) BCC solid solution was identified by X-ray diffraction, allowing also to follow the size and shape of crystalline grains. The higher the shock power, the smaller the grain size. The Mössbauer spectra of the nanostructured powders recorded at 77 and 300 K differ according to the shock power and the friction energy component while the hyperfine structure gives relevant information on the local structure environment of Fe atoms in relation with the milling mode process (shock or friction mode).

Structural stability of sodium borohydride (NaBH 4) during controlled mechanical milling

The complex hydride NaBH 4 was subjected to controlled mechanical milling (CMM) under various milling modes in the magneto-mill Uni-Ball-Mill 5. X-ray diffraction was employed to study the variation of lattice parameter and crystallite (grain) size within the powder particles with milling time up to 200 h. It is found that the lattice parameter of the compound varies only modestly during prolonged milling (max. ∼0.15% after 50 h) and its rate of increase is only slightly faster under high-energy impact (IMP2) mode as opposed to low-energy shearing (LES) mode. Essentially there is no formation of true nanostructure in the powder particles and the average crystallite (grain) size remains on the order of a few tens of nanometers. A bimodal or even multimodal crystallite size distribution within powder particles of NaBH 4 is observed after CMM. The results clearly demonstrate a high structural stability of the compound under heavy deformation conditions imposed by milling.

Hydrogen storage properties of Mg-based mixtures elaborated by reactive mechanical grinding

The hydrogen sorption properties of Mg + 10 wt% WO3 and Mg + 5 wt% Cr2O3 mixtures made by reactive (under hydrogen) mechanical grinding were studied and compared with those of elemental Mg subjected to a similar preparation procedure. It was observed that both oxides have an important catalytic effect on hydrogen absorption and desorption. Moreover, in the case of Cr2O3 addition, both milling speed (i.e, milling energy and milling mode) and ball to powder weight ratio influence drastically the hydrogen sorption kinetics.

A new approach to analysing machined surfaces by ball-end milling, part II:

This paper presents a procedure for the evaluation of maximum surface roughness using the ridges analysed in part 1 of this paper. Maximum surface roughness is predicted for the plane cutting mode of ball-end milling. Two types of cutting modes, i.e., unidirectional mode and bidirectional mode, are investigated. The various cutting conditions in plane cutting are simplified employing the concept of the path interval ratio, fp/ ft . In addition, mathematical expressions for calculating maximum surface roughness have been described for each case. The predicted results show that the geometrical surface roughness of the bidirectional mode is usually larger than that of the unidirectional mode differing from the results of the conventional roughness model. Maximum roughness and the shapes of the cut remainder are affected by path interval, feedrate and cutting mode. Experiments are carried out at various cutting conditions for both cutting modes. A high level of agreement between the expected surface roughness and measured value confirms the validity of the proposed method.

Influence of operating parameters on the flotation of apatite

Flotation of apatite is complicated, owing to its physicochemical similarity with other minerals in phosphate ores. Despite this, relatively few studies have been done on the effect of operating parameters, such as the mode of milling, pulp conditions and collector dosage on the kinetics of apatite flotation. In this technical note, the results of batch flotation tests and the fitting of a first-order kinetic model to assess the influence of operating variables on the flotation kinetics are discussed. Pulp pH, collector dosage and pulp temperature affected recovery significantly, but the mode of milling (wet or dry) did not. All factors influenced the concentrate grade, except for the collector dosage, while the milling mode was the only factor that did not affect the flotation kinetics significantly.

The application of tool deflection knowledge in process planning to meet geometric tolerances

Machine tool deflections due to cutting forces can result in dimensional errors on workpieces. The problem is most severe when flexible tools such as end mills are used. When dimensioned features are specified with tolerances, process planning should examine the compromise between achieving high productivity rates and meeting dimensions within the specified tolerances. The use of geometric dimensioning and tolerancing permits interaction between size and position and makes bonus tolerances available. The errors occurring in end milling are first examined and modelled using regression methods. A procedure is proposed for selecting optimal feed rates that ensure that tolerances can be met. The process is demonstrated in machining a slot using the down milling mode. The use of a tolerance analysis chart clarifies the results of the test in relation to the tolerance standards. The need to consider the transient errors at the exit of the cut is demonstrated.

Development of the First Force‐Controlled Robot for Otoneurosurgery

In some surgical specialties (eg, orthopedics), robots are already used in the operating room for bony milling work. Otological surgery and otoneurosurgery may also greatly benefit from the enhanced precision of robotics. Experimental study on robotic milling of oak wood and human temporal bone specimen. A standard industrial robot with a six-degrees-of-freedom serial kinematics was used, with force feedback to proportionally control the robot speed. Different milling modes and characteristic path parameters were evaluated to generate milling paths based on computer-aided design (CAD) geometry data of a cochlear implant and an implantable hearing system. The best-suited strategy proved to be the spiral horizontal milling mode with the burr held perpendicular to the temporal bone surface. To reduce groove height, the distance between paths should equal half the radius of the cutting burr head. Because of the vibration of the robot's own motors, a high oscillation of the SD of forces was encountered. This oscillation dropped drastically to nearly 0 Newton (N) when the burr head made contact with the dura mater, because of its damping characteristics. The cutting burr could be kept in contact with the dura mater for an extended period without damaging it, because of the burr's blunt head form. The robot moved the burr smoothly according to the encountered resistances. The study reports the first development of a functional robotic milling procedure for otoneurosurgery with force-based speed control. Future plans include implementation of ultrasound-based local navigation and performance of robotic mastoidectomy.

THE GEOMETRY, SPECIFICATION AND PREDICTIVE FORCE MODELS FOR PLANE FACED BALL-END MILLING CUTTERS AND OPERATIONS

In this paper the geometry and specification of ball-end milling cutters are studied and discussed followed by an outline of the development of computer-aided predictive models for the three force components, torque and power in plane faced ball-end milling operations, based on the ‘Unified-Generalised Mechanics of Cutting Approach’. The models allow for six milling modes, namely; slotting, ‘on-centre’ end-milling and ‘off-centre’ end-milling, each machining at the cutter ball-end cutting edge only or at the cutter ball-end and cylindrical periphery cutting edges for two or more flute cutters. The models include all the tool and cut geometrical variables and the cutting speed as well as the tool-workpiece material combination (via the database of basic cutting quantities). The models are verified through extensive numerical simulation studies and a comprehensive experimental testing programme. Good qualitative and quantitative correlation has been found between predicted and measured fluctuating and average force components and torque.

Mechanically driven crystallization of amorphous MgNi alloy during prolonged milling: applications in Ni–MH batteries

The influence of prolonged ball milling on the characteristics of the Mg:Ni (1:1) compound used as hydrogen storage electrode has been studied. Our results show that an amorphous structure is obtained after 10±1(2) h of milling. This optimal period of milling leads to an electrode capacity of 522 mAh/g. Further milling results in a crystallization of amorphous MgNi into nanocrystalline MgNi 2 and Mg 2Ni, which decreases significantly the electrode performance. Experiments carried out at different milling temperatures (20, 60, 100 °C) demonstrate the limited effect of the vial temperature on the crystalline-to-amorphous transition phenomena. In contrast, the milling mode (continuous or discontinuous milling) has a notable influence on the end-product structure. When milling is performed for 10 h followed by a 20-h rest period and milling for 10 h again, material consists essentially of amorphous MgNi which indicates that the crystallization process does not occur in contrast to the case of continuous milling for 20 h. This result indicates that not only the milling duration but also the milling mode have an influence on the end-product structure. Our high energetic milling conditions which accentuate the mechanical deformations during prolonged and continuous milling are believed to be responsible for the mechanically driven crystallization process.

An experimental study of burr formation in square shoulder face milling

Previous research on burr formation in face milling operations has usually been limited to the study of the rollover burr in the cutting direction and/or to a few machining parameters. This paper presents the results of an experimental study on the influence of the main cutting parameters on the formation of the more important burrs produced in face milling operations, namely exit burr in the cutting direction, exit burr in the feed direction and the burr formed at the top edge in a square shoulder face milling operation. Feed per tooth ( Sz), cutting velocity ( V), axial depth of cut ( a) and exit angle ( EXA) were the cutting parameters investigated. The effects of mode of milling, tool nose geometry and tool coating were also investigated to a lesser extent. The results show that exit angle and depth of cut are the cutting parameters which have a major influence on the exit burr in the cutting direction, whereas the exit burr in the feed direction is mainly affected by depth of cut. The top burr is very small and only slightly influenced by cutting conditions. It is also shown that down-milling can effectively eliminate the formation of burrs in some cases, whereas an unfavourable tool nose geometry can double the size of buns.

The stomatogastric nervous system: a formal approach.

A discrete mathematical formalism (d-space) which is specifically designed to investigate discrete aspects of behavior is applied to the foregut of decapod crustacea. This approach differs from continuous modeling techniques in that the analysis determines a structure in which the observed behavior of the foregut is constrained. A notation for the implementation of the formalism is developed as well as a coordinate system natural to the functioning of the gastric mill. The formalism is used to organize previous observations that suggest potential courses of further experimental investigation. A detailed analysis of observed chewing modes of the gastric mill is presented, along with a discussion of the overall organization of the interrelationships between these modes. The investigation also addresses the relationship between behavioral modes of a pyloric muscle found in the shrimp Palaemon. Two alternative hypotheses are presented to describe the relationship of the behavioral components of the gastric mill: an interlaced control scheme in which the components are freely exchanged, and a top-down control system where the chewing modes are rigidly separated into packages. Flow through regions of state space in time is found to be important in determining the relations between the discrete behavioral components. The behavior of the foregut, like that of other motor control systems, is shown to fit naturally into the d-space formalism.