Martensitic materials result from a specific type of phase transformation that produces the structure known as martensite. Martensitic transformations were first observed and described in steels although they occur also in may other materials, such as e.g. in Titanium alloys.  It received its name from Professor Adolf Martens who suggested that the martensitic reaction is displacive in nature and forms through a highly ordered crystallographic shear transformation, which involves no change in chemical composition or atomic diffusion, i.e. no atomic redistribution between phases. Recent atom probe tomographic analysis reveals though that atomic relaxation and short range diffusion can take  place during martensitic transformations. However, many martensitic reactions normally occur athermally, i.e.  via a diffusionless transformation or with only very local diffusion and martensite is then formed upon cooling from a higher temperature phase which is referred to as the parent phase.  In steels this parent phase is known as austenite and this is also the term often used to describe the parent phase in shape memory alloys although technically speaking this is mostly incorrect. Although the early work describes the formation of martensite as being free from nucleation and growth, it is now accepted that the basic characteristics of martensite type transformations are in fact consistent with the general nucleation - growth framework. The martensite reaction in plain carbon steels proceeds from an equilibrium austenite phase to a non-equilibrium (metastable) low temperature martensite phase. Since the martensite is metastable it will only form through very rapid cooling. In fact the rate of growth is so high in these reactions that the volume change associated with the reaction is controlled almost entirely by the nucleation rate. In many martensitic transformations however, the low temperature phase is itself an equilibrium phase rather than a metastable one. In these cases the phase transformation occurs by the fast growth martensitic mode even with very slow cooling rates. The transformations in these systems occur martensitically but there is no need for a rapid quench to secure the fast growth mode as there is in steel. This is the case with shape memory alloys and many pure elements.

Up milling and down millingwhich is better

In this exploration, we delve into the fundamental differences between up milling and down milling, examining their respective advantages, limitations, and applications. You can also find out more about our cnc tips.

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Up milling, also known as conventional milling, in up milling, the thickness of the chips starts at zero and gradually increases until the end of the cut. The milling process includes a polishing effect. The cutting forces tend to lift the workpiece (there is a tendency to raise the workpiece).

To improve the fundamental understanding of the multi-scale characteristics of martensitic microstructures and their micro-mechanical properties, a multi-probe methodology is developed and applied to low-carbon lath martensitic model alloys. The approach is based on the joint employment of electron channeling contrast imaging (ECCI), electron backscatter diffraction (EBSD), transmission electron microscopy (TEM), atom probe tomography (APT) and nanoindentation, in conjunction with high precision and large field-of-view 3D serial sectioning. This methodology enabled us to resolve (i) size variations of martensite sub-units, (ii) associated dislocation sub-structures, (iii) chemical heterogeneities, and (iv) the resulting local mechanical properties. The identified interrelated microstructure heterogeneity is discussed and related to the martensitic transformation sequence, which is proposed to intrinsically lead to formation of a nano-composite structure in low-carbon martensitic steels.

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Down milling is often considered better due to its advantages like improved chip evacuation, reduced cutting forces, potentially longer tool life, and smoother surface finish. However, the choice between up milling and down milling depends on factors like material, machine setup, and desired outcome.

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Climbmilling

A milling machine has the same capability as a drill press but also has the capability to cut with the side of cutting tools. This is the key difference.

Plainmilling

Surface quality: up milling typically achieves higher surface quality because the cutting process is more stable, reducing the likelihood of vibration and workpiece lifting. This helps to reduce surface roughness and improve the surface finish of the workpiece.

This article was written by engineers from the BOYI team. Fuquan Chen is a professional engineer and technical expert with 20 years of experience in rapid prototyping, mold manufacturing, and plastic injection molding.

Owing to the layer-by-layer build-up of additively manufactured parts, the deposited material experiences a cyclic re-heating in the form of a sequence of temperature pulses. In the current work, this “intrinsic heat treatment (IHT)” was exploited to induce the precipitation of NiAl nanoparticles in an Fe-19Ni-xAl (at%) model maraging steel, a system known for rapid clustering. We used Laser Metal Deposition (LMD) to synthesize compositionally graded specimens. This allowed for the efficient screening of effects associated with varying Al contents ranging from 0 to 25 at% and for identifying promising concentrations for further studies. Based on the existence of the desired martensitic matrix, an upper bound for the Al concentration of 15 at% was defined. Owing to the presence of NiAl precipitates as observed by Atom Probe Tomography (APT), a lower bound of 3e5 at% Al was established. Within this concentration window, increasing the Al concentration gave rise to an increase in hardness by 225 HV due to an exceptionally high number density of 10^25 NiAl precipitates per m3, as measured by APT. This work demonstrates the possibility of exploiting the IHT of the LMD process for the production of samples that are precipitation strengthened during the additive manufacturing process without need for any further heat treatment.

In up milling, the rotation direction of the cutting tool is opposite to the feed direction of the workpiece, resulting in cutting forces directed upwards and the chips gradually increasing from thin to thick. Conversely, in down milling, the rotation direction of the cutting tool aligns with the feed direction of the workpiece, causing cutting forces to be directed downwards and the chips decreasing gradually from thick to thin. These two cutting methods exhibit differences in cutting forces, surface quality, chip morphology, and tool wear, so the choice between them should consider factors such as material properties, surface roughness requirements, and machine tool performance.

Facemilling

For example regarding the crystallography of martensite most of the original pioneering works were based on transmission electron microscopy observations. TEM provides sufficient spatial resolution to resolve fine martensitic features such as e.g. laths, however, it provides only limited statistics of larger martensitic constituents (e.g. prior austenite grains) due to its limited field of view arising from the specimen and beam geometries. It is the development of the electron backscatter diffraction (EBSD) technique that enabled the systematic  characterization of the hierarchical martensitic microstructure spanning multiple scales, i.e. ranging from prior austenite grains of hundreds of microns down to laths of tens of nanometers. Yet, it is also clear that the standard 2D EBSD-based analysis provides a rather simplified representation of the lath martensite crystallography. For example, 3D EBSD and 3D FIB analyses, as well as TEM observations reveal significant heterogeneities in the size and morphology of martensite sub-units even within a single alloy, which cannot be fully captured by stand-alone 2D investigations. Also, even in optimized conditions, EBSD cannot resolve the fine details of the martensitic sub-structure.  Regarding martensite composition, similar progress was made due to the advances in another key technique, namely, atom probe tomography (APT). Similar to EBSD providing wider access to martensite crystallography, APT triggered investigations of e.g. carbon (C) Cottrell atmospheres, compositional relaxation and segregation, precipitation reactions in martensite and retained as well as reversed austenite layers in martensite. Arguably the most critical among these is the analysis of C in martensite, since interstitial C plays one of the major roles in the properties of martensite From these multiple studies we can in principle use several types of categories when describing  these features in more detail. These are: Crystallography Mesoscopic morphology Interface types

Up milling (climb milling) offers reduced workpiece deflection and lower cutting temperatures but suffers from poor chip evacuation and higher cutting forces at the start. Down milling (conventional milling) provides better chip evacuation and lower cutting forces but may cause workpiece lift and higher cutting temperatures. The choice between the two depends on factors like material properties and machining requirements.

The established terminology to describe martensite, specifically lath martensite, has been continuously developing over the years with the gradually improving different  types of experimental observations which step-by-step gave additional insights that  some of the original terminology did not contain or reflect.

It offers better chip evacuation, reduced cutting forces directed into the workpiece, potentially longer tool life, and smoother surface finish. These benefits contribute to improved machining efficiency and higher-quality finished parts.

BoYi stands as an ideal partner for CNC milling services, delivering precision, efficiency, and reliability. With state-of-the-art equipment and a skilled team, BoYi ensures superior quality and accuracy in every project. Whether it’s rapid prototyping or high-volume production, BoYi commitment to excellence makes them a preferred choice for meeting diverse machining needs.

Up and down millingprocess

Machining efficiency: Although up milling typically achieves higher precision, the cutting speed may be limited due to lower cutting forces, affecting machining efficiency. On the other hand, down milling, with its higher cutting forces, may be more suitable for applications requiring higher machining speeds.

This means that our knowledge about martensite today is more precise and detailed compared to the rough and in part historical categories and terms we use to describe it. Hence these are some of the typical terms that we use in metalllurgy which are relatively ill-defined owing to the long history of being studied.

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In summary, while up milling and down milling achieve similar results in terms of material removal, they differ in terms of cutting forces, surface finish, and tool wear. The choice between them depends on factors such as the material being machined, the rigidity of the setup, desired surface finish, and the type of CNC machine being used.BOYI provides a chart to summarize and facilitate everyone’s decision-making.

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Up and down millingpdf

The cutting method refers to the relative motion between the cutting tool and the workpiece during the machining process.

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Conventionalmilling

Dimensional accuracy: In up milling, the direction of cutting forces helps to keep the workpiece stable, thus usually achieving better dimensional accuracy. In contrast, down milling may be affected by cutting forces causing workpiece lifting, which can result in larger dimensional deviations.

Down milling, also known as climb milling, in down milling, the thickness of the chips is at its maximum at the beginning, decreasing as the cut progresses, resulting in reduced chip deformation. The cutting forces are directed towards the workpiece.

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020 inches per revolution, while the finishing feed rate be between.002 and.004 inches per revolution. When referring to a milling machine, the term feed ...

Cutting process stability: The cutting process in up milling is relatively stable, with chip evacuation being smoother, thereby reducing vibration and instability factors during machining, and enhancing machining precision.

Advantagesanddisadvantages ofup milling and down milling

In the realm of CNC machining, where precision and efficiency reign supreme, up milling and down milling are two techniques used in CNC (Computer Numerical Control) machining, especially in milling operations. These techniques refer to the direction of the cutting tool’s rotation in relation to the direction of the workpiece feed.

For achieving good surface quality, we typically use down milling. Down milling is suitable for machining ductile materials and when high material removal rates are required. It can also be utilized for harder metals like titanium, vanadium titanium alloys, and metal ceramics. Throughout the machining process, it can execute various cutting forms including grooves, holes, boring, helical milling, recesses, and chamfers.

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The multi-scale complexity of lath martensitic microstructures requires scale-bridging analyses to better understand the deformation mechanisms activated therein. In this study, plasticity in lath martensite is investigated by multi-field mapping of deformation-induced microstructure, topography, and strain evolution at different spatial resolution vs. field-of-view combinations. These investigations reveal site-specific initiation of dislocation activity within laths, as well as significant plastic accommodation in the vicinity of high angle block and packet boundaries. The observation of interface plasticity raises several questions regarding the role of thin inter-lath austenite films. Thus, accompanying transmission electron microscopy and synchrotron x-ray diffraction experiments are carried out to investigate the stability of these films to mechanical loading, and to discuss alternative boundary sliding mechanisms to explain the observed interface strain localization.

Up milling is suitable for machining brittle materials and when cutting forces need to be minimized. However, it may not be as efficient as down milling in certain applications, especially when dealing with ductile materials or when higher material removal rates are required.