How to measurehardenability

Fig.3: The Jominy and quench test The Jominy test is now widely used to determine hardenabilities in the range Di = 1-6; beyond this range the test is of limited use. The results can be readily converted to determine the largest diameter round bar which can be fully hardened. Fig. 4 plots bar diameter against the Jominy positions at which the same cooling rates as those in the centers of the bars are obtained for a series of different quenches. Taking the ideal quench (H = ‡) the highest curve, it can be seen that 12.5 mm along the Jominy bar gives a cooling rate equivalent to that at the center of a 75 mm diameter bar. This diameter reduces to just over 50 mm for a quench in still water (H = 1). With, for example, a steel which gives 50 % martensite at 19 mm from the quenched end after still oil quenching (H = 0.3), the critical diameter D0 for a round rod will be 51 mm. The diagram in Fig. 4 can also be used to determine the hardness at the center of a round bar of a particular steel, provided a Jominy end quench test has been carried out. Fig.4: Equivalent Jominy positions and bar diameter, where the cooling rate for the bar center is the same as that for the point in the Jominy specimen. For example, if the hardness at the center of a 5 cm diameter bar, quenched in still water, is required, Fig. 3 shows that this hardness will be achieved at about 12 mm along the Jominy test specimen from the quenched end. Reference to the Jominy hardness distance plot, then gives the required hardness value. If hardness values are required for other points in round bars, e.g. surface or at half radius, suitable diagrams are available for use.

Depending on the material being milled, and what task should be performed, different tool types and geometry may be used. For instance, when milling a material like aluminum, it may be advantageous to use a tool with very deep, polished flutes, a very sharp cutting edge and high rake angles. When machining a tough material such as stainless steel, however, shallow flutes and a squared-off cutting edge will optimize material removal and tool life.

Hardenabilitydefinition Engineering

In the Grossman test, the transverse sections are metallographically examined to determine the particular bar, which has 50% martensite at its center. The diameter of this bar is then designated the critical diameter D0. However, this dimension is of no absolute value in expressing the hardenability as it will obviously vary if the quenching medium is changed, e.g. from water to oil. It is therefore necessary to assess quantitatively the effectiveness of the different quenching media. This is done by determining coefficients for the severity of the quench usually referred to as H-coefficients. The value for quenching in still water is set at 1, as a standard against which to compare other modes of quenching. Using the H-coefficients, it is possible to determine in place of D0, an ideal critical diameter Di which has 50% martensite at the center of the bar when the surface is cooled at an infinitely rapid rate, i.e. when H = ‡. Obviously, in these circumstances D0 = Di, thus providing the upper reference line in a series of graphs for different values of H. In practice, H varies between about 0.2 and 5.0, so that if a quenching experiment is carried out at an H-value of, say, 0.4, and D0 is measured, then the graph can be used to determine Di. This value will be a measure of the hardenability of given steel, which is independent of the quenching medium used. Fig.1: Steel Ni-0.75Cr-0.4C. Hardness data from transverse sections through water-quenched bars of increasing diameter The Jominy and quench test While the Grossman approach to hardenability is very reliable, other less elaborate tests have been devised to provide hardenability data. Foremost amongst these is the Jominy test, in which a standardized round bar (25.4 mm diameter, 102 mm long) is heated to the austenitizing temperature, then placed on a rig in which one end of the rod is quenched by a standard jet of water (Fig.2). Fig.2: The Jominy test: A - specimen size; B - quenching rig This results in a progressive decrease in the rate of cooling along the bar from the quenched end, the effects of which are determined by hardness measurements on flats ground 4 mm deep and parallel to the bar axis (Fig. 3). A typical hardness plot for a En 19B steel containing 1% Cr, 0.25% Mo and 0.4% C, where the upper curve represents the hardness obtained with the upper limit of composition for the steel, while the lower curve is that for the composition at the lower limit. The area between the lines is referred to as a hardenability or Jominy band. Additional data, which is useful in conjunction with these results, is the hardness of quenched steels as a function both of carbon content and of the proportion of martensite in the structure. Therefore, the hardness for 50% martensite can be easily determined for a particular carbon content and, by inspection of the Jominy test results, the depth at which 50 % martensite is achieved can be determined. Fig.3: The Jominy and quench test The Jominy test is now widely used to determine hardenabilities in the range Di = 1-6; beyond this range the test is of limited use. The results can be readily converted to determine the largest diameter round bar which can be fully hardened. Fig. 4 plots bar diameter against the Jominy positions at which the same cooling rates as those in the centers of the bars are obtained for a series of different quenches. Taking the ideal quench (H = ‡) the highest curve, it can be seen that 12.5 mm along the Jominy bar gives a cooling rate equivalent to that at the center of a 75 mm diameter bar. This diameter reduces to just over 50 mm for a quench in still water (H = 1). With, for example, a steel which gives 50 % martensite at 19 mm from the quenched end after still oil quenching (H = 0.3), the critical diameter D0 for a round rod will be 51 mm. The diagram in Fig. 4 can also be used to determine the hardness at the center of a round bar of a particular steel, provided a Jominy end quench test has been carried out. Fig.4: Equivalent Jominy positions and bar diameter, where the cooling rate for the bar center is the same as that for the point in the Jominy specimen. For example, if the hardness at the center of a 5 cm diameter bar, quenched in still water, is required, Fig. 3 shows that this hardness will be achieved at about 12 mm along the Jominy test specimen from the quenched end. Reference to the Jominy hardness distance plot, then gives the required hardness value. If hardness values are required for other points in round bars, e.g. surface or at half radius, suitable diagrams are available for use.

End mills are sold in both imperial and metric shank and cutting diameters. In the USA, metric is readily available, but it is only used in some machine shops and not others; in Canada, due to the country's proximity to the US, much the same is true. In Asia and Europe, metric diameters are standard.

A wide variety of materials are used to produce the cutting tools. Carbide inserts are the most common because they are good for high production milling. High speed steel is commonly used when a special tool shape is needed, not usually used for high production processes. Ceramics inserts are typically used in high speed machining with high production. Diamond inserts are typically used on products that require tight tolerances, typically consisting of high surface qualities (nonferrous or non-metallic materials).

Using the H-coefficients, it is possible to determine in place of D0, an ideal critical diameter Di which has 50% martensite at the center of the bar when the surface is cooled at an infinitely rapid rate, i.e. when H = ‡. Obviously, in these circumstances D0 = Di, thus providing the upper reference line in a series of graphs for different values of H. In practice, H varies between about 0.2 and 5.0, so that if a quenching experiment is carried out at an H-value of, say, 0.4, and D0 is measured, then the graph can be used to determine Di. This value will be a measure of the hardenability of given steel, which is independent of the quenching medium used. Fig.1: Steel Ni-0.75Cr-0.4C. Hardness data from transverse sections through water-quenched bars of increasing diameter The Jominy and quench test While the Grossman approach to hardenability is very reliable, other less elaborate tests have been devised to provide hardenability data. Foremost amongst these is the Jominy test, in which a standardized round bar (25.4 mm diameter, 102 mm long) is heated to the austenitizing temperature, then placed on a rig in which one end of the rod is quenched by a standard jet of water (Fig.2). Fig.2: The Jominy test: A - specimen size; B - quenching rig This results in a progressive decrease in the rate of cooling along the bar from the quenched end, the effects of which are determined by hardness measurements on flats ground 4 mm deep and parallel to the bar axis (Fig. 3). A typical hardness plot for a En 19B steel containing 1% Cr, 0.25% Mo and 0.4% C, where the upper curve represents the hardness obtained with the upper limit of composition for the steel, while the lower curve is that for the composition at the lower limit. The area between the lines is referred to as a hardenability or Jominy band. Additional data, which is useful in conjunction with these results, is the hardness of quenched steels as a function both of carbon content and of the proportion of martensite in the structure. Therefore, the hardness for 50% martensite can be easily determined for a particular carbon content and, by inspection of the Jominy test results, the depth at which 50 % martensite is achieved can be determined. Fig.3: The Jominy and quench test The Jominy test is now widely used to determine hardenabilities in the range Di = 1-6; beyond this range the test is of limited use. The results can be readily converted to determine the largest diameter round bar which can be fully hardened. Fig. 4 plots bar diameter against the Jominy positions at which the same cooling rates as those in the centers of the bars are obtained for a series of different quenches. Taking the ideal quench (H = ‡) the highest curve, it can be seen that 12.5 mm along the Jominy bar gives a cooling rate equivalent to that at the center of a 75 mm diameter bar. This diameter reduces to just over 50 mm for a quench in still water (H = 1). With, for example, a steel which gives 50 % martensite at 19 mm from the quenched end after still oil quenching (H = 0.3), the critical diameter D0 for a round rod will be 51 mm. The diagram in Fig. 4 can also be used to determine the hardness at the center of a round bar of a particular steel, provided a Jominy end quench test has been carried out. Fig.4: Equivalent Jominy positions and bar diameter, where the cooling rate for the bar center is the same as that for the point in the Jominy specimen. For example, if the hardness at the center of a 5 cm diameter bar, quenched in still water, is required, Fig. 3 shows that this hardness will be achieved at about 12 mm along the Jominy test specimen from the quenched end. Reference to the Jominy hardness distance plot, then gives the required hardness value. If hardness values are required for other points in round bars, e.g. surface or at half radius, suitable diagrams are available for use.

Roughing: the purpose is to remove a big chunk of material from workpieces, sometimes to get rid of excess material in order to get closer to the final shape.[2] It attempts to get really close to the finalized shape. Traditionally it's the first major operation in the machining process.

Contouring/Profiling: this is a process used to mill different surfaces such as flat or irregular ones. This type of process can be done during the roughing or finishing phase of the overall operation.[3]

What is hardenabilityin Materials Science

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Fig.4: Equivalent Jominy positions and bar diameter, where the cooling rate for the bar center is the same as that for the point in the Jominy specimen. For example, if the hardness at the center of a 5 cm diameter bar, quenched in still water, is required, Fig. 3 shows that this hardness will be achieved at about 12 mm along the Jominy test specimen from the quenched end. Reference to the Jominy hardness distance plot, then gives the required hardness value. If hardness values are required for other points in round bars, e.g. surface or at half radius, suitable diagrams are available for use.

The Grossman test Much of the earlier systematic work on hardenability was done by Grossman and coworkers who developed a test involving the quenching, in a particular cooling medium, of several cylindrical bars of different diameter of the steel under consideration. Transverse sections of the different bars on which hardness measurements have been made will show directly the effect of hardenability. In Fig 1, which plots this hardness data for an SAE 3140 steel (1.1-1.4% Ni, 0.55-0.75% Cr, 0.40% C) oil-quenched from 815‹C, it is shown that the full martensitic hardness is only obtained in the smaller sections, while for larger diameter bars the hardness drops off markedly towards the center of the bar. The softer and harder regions of the section can also be clearly resolved by etching. In the Grossman test, the transverse sections are metallographically examined to determine the particular bar, which has 50% martensite at its center. The diameter of this bar is then designated the critical diameter D0. However, this dimension is of no absolute value in expressing the hardenability as it will obviously vary if the quenching medium is changed, e.g. from water to oil. It is therefore necessary to assess quantitatively the effectiveness of the different quenching media. This is done by determining coefficients for the severity of the quench usually referred to as H-coefficients. The value for quenching in still water is set at 1, as a standard against which to compare other modes of quenching. Using the H-coefficients, it is possible to determine in place of D0, an ideal critical diameter Di which has 50% martensite at the center of the bar when the surface is cooled at an infinitely rapid rate, i.e. when H = ‡. Obviously, in these circumstances D0 = Di, thus providing the upper reference line in a series of graphs for different values of H. In practice, H varies between about 0.2 and 5.0, so that if a quenching experiment is carried out at an H-value of, say, 0.4, and D0 is measured, then the graph can be used to determine Di. This value will be a measure of the hardenability of given steel, which is independent of the quenching medium used. Fig.1: Steel Ni-0.75Cr-0.4C. Hardness data from transverse sections through water-quenched bars of increasing diameter The Jominy and quench test While the Grossman approach to hardenability is very reliable, other less elaborate tests have been devised to provide hardenability data. Foremost amongst these is the Jominy test, in which a standardized round bar (25.4 mm diameter, 102 mm long) is heated to the austenitizing temperature, then placed on a rig in which one end of the rod is quenched by a standard jet of water (Fig.2). Fig.2: The Jominy test: A - specimen size; B - quenching rig This results in a progressive decrease in the rate of cooling along the bar from the quenched end, the effects of which are determined by hardness measurements on flats ground 4 mm deep and parallel to the bar axis (Fig. 3). A typical hardness plot for a En 19B steel containing 1% Cr, 0.25% Mo and 0.4% C, where the upper curve represents the hardness obtained with the upper limit of composition for the steel, while the lower curve is that for the composition at the lower limit. The area between the lines is referred to as a hardenability or Jominy band. Additional data, which is useful in conjunction with these results, is the hardness of quenched steels as a function both of carbon content and of the proportion of martensite in the structure. Therefore, the hardness for 50% martensite can be easily determined for a particular carbon content and, by inspection of the Jominy test results, the depth at which 50 % martensite is achieved can be determined. Fig.3: The Jominy and quench test The Jominy test is now widely used to determine hardenabilities in the range Di = 1-6; beyond this range the test is of limited use. The results can be readily converted to determine the largest diameter round bar which can be fully hardened. Fig. 4 plots bar diameter against the Jominy positions at which the same cooling rates as those in the centers of the bars are obtained for a series of different quenches. Taking the ideal quench (H = ‡) the highest curve, it can be seen that 12.5 mm along the Jominy bar gives a cooling rate equivalent to that at the center of a 75 mm diameter bar. This diameter reduces to just over 50 mm for a quench in still water (H = 1). With, for example, a steel which gives 50 % martensite at 19 mm from the quenched end after still oil quenching (H = 0.3), the critical diameter D0 for a round rod will be 51 mm. The diagram in Fig. 4 can also be used to determine the hardness at the center of a round bar of a particular steel, provided a Jominy end quench test has been carried out. Fig.4: Equivalent Jominy positions and bar diameter, where the cooling rate for the bar center is the same as that for the point in the Jominy specimen. For example, if the hardness at the center of a 5 cm diameter bar, quenched in still water, is required, Fig. 3 shows that this hardness will be achieved at about 12 mm along the Jominy test specimen from the quenched end. Reference to the Jominy hardness distance plot, then gives the required hardness value. If hardness values are required for other points in round bars, e.g. surface or at half radius, suitable diagrams are available for use.

Hardenabilityvs hardness

Fig.2: The Jominy test: A - specimen size; B - quenching rig This results in a progressive decrease in the rate of cooling along the bar from the quenched end, the effects of which are determined by hardness measurements on flats ground 4 mm deep and parallel to the bar axis (Fig. 3). A typical hardness plot for a En 19B steel containing 1% Cr, 0.25% Mo and 0.4% C, where the upper curve represents the hardness obtained with the upper limit of composition for the steel, while the lower curve is that for the composition at the lower limit. The area between the lines is referred to as a hardenability or Jominy band. Additional data, which is useful in conjunction with these results, is the hardness of quenched steels as a function both of carbon content and of the proportion of martensite in the structure. Therefore, the hardness for 50% martensite can be easily determined for a particular carbon content and, by inspection of the Jominy test results, the depth at which 50 % martensite is achieved can be determined. Fig.3: The Jominy and quench test The Jominy test is now widely used to determine hardenabilities in the range Di = 1-6; beyond this range the test is of limited use. The results can be readily converted to determine the largest diameter round bar which can be fully hardened. Fig. 4 plots bar diameter against the Jominy positions at which the same cooling rates as those in the centers of the bars are obtained for a series of different quenches. Taking the ideal quench (H = ‡) the highest curve, it can be seen that 12.5 mm along the Jominy bar gives a cooling rate equivalent to that at the center of a 75 mm diameter bar. This diameter reduces to just over 50 mm for a quench in still water (H = 1). With, for example, a steel which gives 50 % martensite at 19 mm from the quenched end after still oil quenching (H = 0.3), the critical diameter D0 for a round rod will be 51 mm. The diagram in Fig. 4 can also be used to determine the hardness at the center of a round bar of a particular steel, provided a Jominy end quench test has been carried out. Fig.4: Equivalent Jominy positions and bar diameter, where the cooling rate for the bar center is the same as that for the point in the Jominy specimen. For example, if the hardness at the center of a 5 cm diameter bar, quenched in still water, is required, Fig. 3 shows that this hardness will be achieved at about 12 mm along the Jominy test specimen from the quenched end. Reference to the Jominy hardness distance plot, then gives the required hardness value. If hardness values are required for other points in round bars, e.g. surface or at half radius, suitable diagrams are available for use.

End mills are typically made on CNC (computer numeric controlled) tool and cutter grinder machines under high-pressure lubricants such as water, water-soluble oil, and high-flashpoint oil. Grinding inside the machine is accomplished with abrasive wheels mounted on a spindle (and in some cases, multiple spindles). Depending on what material is being ground, these wheels are made with industrial diamond (when grinding tungsten carbide), cubic boron nitride (when grinding cobalt steel), and other materials (when grinding, for instance, ceramics), set in a bond (sometimes copper).

An end mill is a type of milling cutter, a cutting tool used in industrial milling applications. They can have several end configurations: round (ball), tapered, or straight are a few popular types. They are most commonly used in "milling machines" that move a piece of material against the end mill to remove chips of the material to create a desired size or shape. It is distinguished from the drill bit in its application, geometry, and manufacture. While a drill bit can only cut in the axial direction, most milling bits can cut in the radial direction. Not all mills can cut axially; those designed to cut axially are known as end mills.

The Jominy and quench test While the Grossman approach to hardenability is very reliable, other less elaborate tests have been devised to provide hardenability data. Foremost amongst these is the Jominy test, in which a standardized round bar (25.4 mm diameter, 102 mm long) is heated to the austenitizing temperature, then placed on a rig in which one end of the rod is quenched by a standard jet of water (Fig.2). Fig.2: The Jominy test: A - specimen size; B - quenching rig This results in a progressive decrease in the rate of cooling along the bar from the quenched end, the effects of which are determined by hardness measurements on flats ground 4 mm deep and parallel to the bar axis (Fig. 3). A typical hardness plot for a En 19B steel containing 1% Cr, 0.25% Mo and 0.4% C, where the upper curve represents the hardness obtained with the upper limit of composition for the steel, while the lower curve is that for the composition at the lower limit. The area between the lines is referred to as a hardenability or Jominy band. Additional data, which is useful in conjunction with these results, is the hardness of quenched steels as a function both of carbon content and of the proportion of martensite in the structure. Therefore, the hardness for 50% martensite can be easily determined for a particular carbon content and, by inspection of the Jominy test results, the depth at which 50 % martensite is achieved can be determined. Fig.3: The Jominy and quench test The Jominy test is now widely used to determine hardenabilities in the range Di = 1-6; beyond this range the test is of limited use. The results can be readily converted to determine the largest diameter round bar which can be fully hardened. Fig. 4 plots bar diameter against the Jominy positions at which the same cooling rates as those in the centers of the bars are obtained for a series of different quenches. Taking the ideal quench (H = ‡) the highest curve, it can be seen that 12.5 mm along the Jominy bar gives a cooling rate equivalent to that at the center of a 75 mm diameter bar. This diameter reduces to just over 50 mm for a quench in still water (H = 1). With, for example, a steel which gives 50 % martensite at 19 mm from the quenched end after still oil quenching (H = 0.3), the critical diameter D0 for a round rod will be 51 mm. The diagram in Fig. 4 can also be used to determine the hardness at the center of a round bar of a particular steel, provided a Jominy end quench test has been carried out. Fig.4: Equivalent Jominy positions and bar diameter, where the cooling rate for the bar center is the same as that for the point in the Jominy specimen. For example, if the hardness at the center of a 5 cm diameter bar, quenched in still water, is required, Fig. 3 shows that this hardness will be achieved at about 12 mm along the Jominy test specimen from the quenched end. Reference to the Jominy hardness distance plot, then gives the required hardness value. If hardness values are required for other points in round bars, e.g. surface or at half radius, suitable diagrams are available for use.

What is hardenabilityof steel

It is becoming increasingly common for traditional solid end mills to be replaced by more cost-effective inserted cutting tools (which, though more expensive initially, reduce tool-change times and allow for the easy replacement of worn or broken cutting edges rather than the entire tool). Another advantage of indexable end mills(another term for tools with inserts) is their ability to be flexible with what materials they can work on, rather than being specialized for a certain material type like more traditional end mills. For the time being however, this only generally applies to larger diameter end mills, at or above 3/4 of an inch. These end mills are generally used for roughing operation, whereas traditional end mills are still used for finishing and work where a smaller diameter, or a tighter tolerance, are required; modular tooling introduces additional margins of error that can compound with each new component, whereas a solid tool can provide a smaller tolerance range for the same price level.

explain using a sketch howhardenabilityof steelsismeasured.

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Although coatings have a typical color, manufacturers may modify the coating process or add additives to change the appearance without affecting the performance as part of their branding. Bright blues, reds and turquoise are among the "unnatural" colors.

There are four critical angles of each cutting tool: end cutting edge angle, axial relief angle, radial relief angle, and radial rake angle.

Though PCD veins is not a coating, some end mills are manufactured with a 'vein' of polycrystalline diamond. The vein is formed in a high temperature-high pressure environment. The vein is formed in a blank and then the material is ground out along the vein to form the cutting edge. Although the tools can be very costly, they can last many times longer than other tooling.

There exist end mills with variable flute helix or pseudo-random helix angle, and discontinuous flute geometries, to help break material into smaller pieces while cutting (improving chip evacuation and reducing risk of jamming) and reduce tool engagement on big cuts. Some modern designs also include small features like the corner chamfer and chipbreaker. While more expensive, due to more complex design and manufacturing process, such end mills can last longer due to less wear and improve productivity in high speed machining (HSM) applications.

Whyis hardenabilityimportant

This results in a progressive decrease in the rate of cooling along the bar from the quenched end, the effects of which are determined by hardness measurements on flats ground 4 mm deep and parallel to the bar axis (Fig. 3). A typical hardness plot for a En 19B steel containing 1% Cr, 0.25% Mo and 0.4% C, where the upper curve represents the hardness obtained with the upper limit of composition for the steel, while the lower curve is that for the composition at the lower limit. The area between the lines is referred to as a hardenability or Jominy band. Additional data, which is useful in conjunction with these results, is the hardness of quenched steels as a function both of carbon content and of the proportion of martensite in the structure. Therefore, the hardness for 50% martensite can be easily determined for a particular carbon content and, by inspection of the Jominy test results, the depth at which 50 % martensite is achieved can be determined. Fig.3: The Jominy and quench test The Jominy test is now widely used to determine hardenabilities in the range Di = 1-6; beyond this range the test is of limited use. The results can be readily converted to determine the largest diameter round bar which can be fully hardened. Fig. 4 plots bar diameter against the Jominy positions at which the same cooling rates as those in the centers of the bars are obtained for a series of different quenches. Taking the ideal quench (H = ‡) the highest curve, it can be seen that 12.5 mm along the Jominy bar gives a cooling rate equivalent to that at the center of a 75 mm diameter bar. This diameter reduces to just over 50 mm for a quench in still water (H = 1). With, for example, a steel which gives 50 % martensite at 19 mm from the quenched end after still oil quenching (H = 0.3), the critical diameter D0 for a round rod will be 51 mm. The diagram in Fig. 4 can also be used to determine the hardness at the center of a round bar of a particular steel, provided a Jominy end quench test has been carried out. Fig.4: Equivalent Jominy positions and bar diameter, where the cooling rate for the bar center is the same as that for the point in the Jominy specimen. For example, if the hardness at the center of a 5 cm diameter bar, quenched in still water, is required, Fig. 3 shows that this hardness will be achieved at about 12 mm along the Jominy test specimen from the quenched end. Reference to the Jominy hardness distance plot, then gives the required hardness value. If hardness values are required for other points in round bars, e.g. surface or at half radius, suitable diagrams are available for use.

2 Flute: Allows for more chips to be removed from the part. Primarily used in slotting and pocketing operations in non-ferrous materials.

Pocketing/Slotting: this is a process to make a pocket on the inside of the part. A pocket can be shallow or deep, depending on specs. [7]

Hardenabilitytest

The diagram in Fig. 4 can also be used to determine the hardness at the center of a round bar of a particular steel, provided a Jominy end quench test has been carried out. Fig.4: Equivalent Jominy positions and bar diameter, where the cooling rate for the bar center is the same as that for the point in the Jominy specimen. For example, if the hardness at the center of a 5 cm diameter bar, quenched in still water, is required, Fig. 3 shows that this hardness will be achieved at about 12 mm along the Jominy test specimen from the quenched end. Reference to the Jominy hardness distance plot, then gives the required hardness value. If hardness values are required for other points in round bars, e.g. surface or at half radius, suitable diagrams are available for use.

Several broad categories of end- and face-milling tools exist, such as center-cutting versus non-center-cutting (whether the mill can take plunging cuts); and categorization by number of flutes; by helix angle; by material; and by coating material. Each category may be further divided by specific application and special geometry.

For example, if the hardness at the center of a 5 cm diameter bar, quenched in still water, is required, Fig. 3 shows that this hardness will be achieved at about 12 mm along the Jominy test specimen from the quenched end. Reference to the Jominy hardness distance plot, then gives the required hardness value. If hardness values are required for other points in round bars, e.g. surface or at half radius, suitable diagrams are available for use.

Facing: is an operation used to face the part down to specified dimension. Facing can be done using end mills or a special face mill.[4][5][6]

Advances in end mill coatings are being made, however, with coatings such as Amorphous Diamond and nanocomposite PVD coatings beginning to be seen at high-end shops (as of 2004).

A very popular helix angle, especially for general cutting of metal materials, is 30°. For finishing end mills, it is common to see more tight spiral, with helix angles 45° or 60°. Straight flute end mills (helix angle 0°) are used in special applications, like milling plastics or composites of epoxy and glass. Straight flute end mills were also used historically for metal cutting before invention of helical flute end mill by Carl A. Bergstrom of Weldon Tool Company in 1918.

The Jominy test is now widely used to determine hardenabilities in the range Di = 1-6; beyond this range the test is of limited use. The results can be readily converted to determine the largest diameter round bar which can be fully hardened. Fig. 4 plots bar diameter against the Jominy positions at which the same cooling rates as those in the centers of the bars are obtained for a series of different quenches. Taking the ideal quench (H = ‡) the highest curve, it can be seen that 12.5 mm along the Jominy bar gives a cooling rate equivalent to that at the center of a 75 mm diameter bar. This diameter reduces to just over 50 mm for a quench in still water (H = 1). With, for example, a steel which gives 50 % martensite at 19 mm from the quenched end after still oil quenching (H = 0.3), the critical diameter D0 for a round rod will be 51 mm. The diagram in Fig. 4 can also be used to determine the hardness at the center of a round bar of a particular steel, provided a Jominy end quench test has been carried out. Fig.4: Equivalent Jominy positions and bar diameter, where the cooling rate for the bar center is the same as that for the point in the Jominy specimen. For example, if the hardness at the center of a 5 cm diameter bar, quenched in still water, is required, Fig. 3 shows that this hardness will be achieved at about 12 mm along the Jominy test specimen from the quenched end. Reference to the Jominy hardness distance plot, then gives the required hardness value. If hardness values are required for other points in round bars, e.g. surface or at half radius, suitable diagrams are available for use.

Additional data, which is useful in conjunction with these results, is the hardness of quenched steels as a function both of carbon content and of the proportion of martensite in the structure. Therefore, the hardness for 50% martensite can be easily determined for a particular carbon content and, by inspection of the Jominy test results, the depth at which 50 % martensite is achieved can be determined. Fig.3: The Jominy and quench test The Jominy test is now widely used to determine hardenabilities in the range Di = 1-6; beyond this range the test is of limited use. The results can be readily converted to determine the largest diameter round bar which can be fully hardened. Fig. 4 plots bar diameter against the Jominy positions at which the same cooling rates as those in the centers of the bars are obtained for a series of different quenches. Taking the ideal quench (H = ‡) the highest curve, it can be seen that 12.5 mm along the Jominy bar gives a cooling rate equivalent to that at the center of a 75 mm diameter bar. This diameter reduces to just over 50 mm for a quench in still water (H = 1). With, for example, a steel which gives 50 % martensite at 19 mm from the quenched end after still oil quenching (H = 0.3), the critical diameter D0 for a round rod will be 51 mm. The diagram in Fig. 4 can also be used to determine the hardness at the center of a round bar of a particular steel, provided a Jominy end quench test has been carried out. Fig.4: Equivalent Jominy positions and bar diameter, where the cooling rate for the bar center is the same as that for the point in the Jominy specimen. For example, if the hardness at the center of a 5 cm diameter bar, quenched in still water, is required, Fig. 3 shows that this hardness will be achieved at about 12 mm along the Jominy test specimen from the quenched end. Reference to the Jominy hardness distance plot, then gives the required hardness value. If hardness values are required for other points in round bars, e.g. surface or at half radius, suitable diagrams are available for use.

The rate at which austenite decomposes to form ferrite, pearlite and bainite is dependent on the composition of the steel, as well as on other factors such as the austenite grain size, and the degree of homogeneity in the distribution of the alloying elements. It is extremely difficult to predict hardenability entirely on basic principles, and reliance is placed on one of several practical tests, which allow the hardenability of any steel to be readily determined.

Fig.1: Steel Ni-0.75Cr-0.4C. Hardness data from transverse sections through water-quenched bars of increasing diameter The Jominy and quench test While the Grossman approach to hardenability is very reliable, other less elaborate tests have been devised to provide hardenability data. Foremost amongst these is the Jominy test, in which a standardized round bar (25.4 mm diameter, 102 mm long) is heated to the austenitizing temperature, then placed on a rig in which one end of the rod is quenched by a standard jet of water (Fig.2). Fig.2: The Jominy test: A - specimen size; B - quenching rig This results in a progressive decrease in the rate of cooling along the bar from the quenched end, the effects of which are determined by hardness measurements on flats ground 4 mm deep and parallel to the bar axis (Fig. 3). A typical hardness plot for a En 19B steel containing 1% Cr, 0.25% Mo and 0.4% C, where the upper curve represents the hardness obtained with the upper limit of composition for the steel, while the lower curve is that for the composition at the lower limit. The area between the lines is referred to as a hardenability or Jominy band. Additional data, which is useful in conjunction with these results, is the hardness of quenched steels as a function both of carbon content and of the proportion of martensite in the structure. Therefore, the hardness for 50% martensite can be easily determined for a particular carbon content and, by inspection of the Jominy test results, the depth at which 50 % martensite is achieved can be determined. Fig.3: The Jominy and quench test The Jominy test is now widely used to determine hardenabilities in the range Di = 1-6; beyond this range the test is of limited use. The results can be readily converted to determine the largest diameter round bar which can be fully hardened. Fig. 4 plots bar diameter against the Jominy positions at which the same cooling rates as those in the centers of the bars are obtained for a series of different quenches. Taking the ideal quench (H = ‡) the highest curve, it can be seen that 12.5 mm along the Jominy bar gives a cooling rate equivalent to that at the center of a 75 mm diameter bar. This diameter reduces to just over 50 mm for a quench in still water (H = 1). With, for example, a steel which gives 50 % martensite at 19 mm from the quenched end after still oil quenching (H = 0.3), the critical diameter D0 for a round rod will be 51 mm. The diagram in Fig. 4 can also be used to determine the hardness at the center of a round bar of a particular steel, provided a Jominy end quench test has been carried out. Fig.4: Equivalent Jominy positions and bar diameter, where the cooling rate for the bar center is the same as that for the point in the Jominy specimen. For example, if the hardness at the center of a 5 cm diameter bar, quenched in still water, is required, Fig. 3 shows that this hardness will be achieved at about 12 mm along the Jominy test specimen from the quenched end. Reference to the Jominy hardness distance plot, then gives the required hardness value. If hardness values are required for other points in round bars, e.g. surface or at half radius, suitable diagrams are available for use.

The results can be readily converted to determine the largest diameter round bar which can be fully hardened. Fig. 4 plots bar diameter against the Jominy positions at which the same cooling rates as those in the centers of the bars are obtained for a series of different quenches. Taking the ideal quench (H = ‡) the highest curve, it can be seen that 12.5 mm along the Jominy bar gives a cooling rate equivalent to that at the center of a 75 mm diameter bar. This diameter reduces to just over 50 mm for a quench in still water (H = 1). With, for example, a steel which gives 50 % martensite at 19 mm from the quenched end after still oil quenching (H = 0.3), the critical diameter D0 for a round rod will be 51 mm. The diagram in Fig. 4 can also be used to determine the hardness at the center of a round bar of a particular steel, provided a Jominy end quench test has been carried out. Fig.4: Equivalent Jominy positions and bar diameter, where the cooling rate for the bar center is the same as that for the point in the Jominy specimen. For example, if the hardness at the center of a 5 cm diameter bar, quenched in still water, is required, Fig. 3 shows that this hardness will be achieved at about 12 mm along the Jominy test specimen from the quenched end. Reference to the Jominy hardness distance plot, then gives the required hardness value. If hardness values are required for other points in round bars, e.g. surface or at half radius, suitable diagrams are available for use.

A variety of grooves, slots, and pockets in the work-piece may be produced from a variety of tool bits. Common tool bit types are: square end cutters, ball end cutters, t-slot cutters, and shell mills. Square end cutters can mill square slots, pockets, and edges. Ball end cutters mill radiused slots or fillets. T-slot cutters mill exactly that: T-shaped slots. Shell end cutters are used for large flat surfaces and for angle cuts. There are variations of these tool types as well.

In the early 90s, use of coatings became more common. Coatings can provide various benefits including wear resistance, reduction of friction to assist with chip evacuation, and increased heat resistance. Most of these coatings are referred to by their chemical composition.