Carbide End Mill Sets

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High-speed machining (HSM) with micro tooling operations offers many benefits when working with nonferrous metals or plastics. However, there are several things that need to be taken into considerations including the challenges of micro tooling, available technology, as well as feeds and speeds.

Micro tooling is what its name implies. This process uses mills and drills with a diameter of 0.250″ or less and is necessary for complex, extremely detailed machining. Micro tooling is best used with high-speed spindles. There are no absolute parameters for high-speed machining other than the machining with spindle speeds of 25,000 rpm or more.

Some of the challenges that face micro tooling are that the machine tool industry has to rethink its manufacturing process in order to meet the demands of the smaller tool diameters. The smaller tool diameters require higher rpm speeds that cannot be achieved on conventional spindles. In addition, CNC machines that use tools with less than a -inch diameter, and operate at speeds at or below 10,000 RPMs, generally do not have favorable feedrates.

Traditional machining methods because of the size of the tools and the low speed of operations are typically unsuited for intricate and detailed machining. Therefore, in order to machining using micro tooling on traditional machines they have to operate at reduced speeds, which in turn caused the fragile tools to break. One reason for this is that fact that the larger sturdier tools are more resistant to the effects of chips, while the smaller tools are susceptible to breakage. It is a fact that the majority of tool breakage is due to improper chip evacuation.

In order to reduce the risk of breakage, chips have to be removed from the cutting channel. For small tools to adequately remove chips, they have to operate at even faster spindle speeds.

In order for micro tooling to be an economical and efficiently method of machining, its three elements have to be examined.

Machining is an occupation, which involving power-driven tools, including lathes, milling machines, or drills, to shape metal. Machining is a vital part of the manufacturing of nearly every metal product as well as several plastic parts.

Machining Operations:

The majority of machining operations can be divided into two separate categories, those that remove metal from the workpiece and those, which shape the metal into the product.

Machine tools that cut or remove material from a workpiece would include a lathe, which shapes the material by rotating it along its axis while pressing the material against a set or fixed cutting or abrading tool. Drills or punch press removes material by drilling or punching a hole into the material. Other tools, which remove material from the workpiece, include milling machines, saws, and grinding tools.

Machines that form and shape metal into products would include forging machine, which hammers or molds hot metal into shape. When metals have been softened or when placed under pressure, dies and molds can be used to shape the metal. Presses shape and form metal by flatten the metal into desired shapes.

Machining is usually performed in machine shops that consist of one or several major machine tools. Machine shop can exist as a small business or as an internal machine shop that supports the needs of the business.

Reamers are used to shape or enlarge holes or bores. Reamers are made with both helical flutes as well as straight flutes. The helical flutes offer a shearing cut and are specially useful in reaming holes that have keyways or grooves, due to the fact that helical reamers are bridged, thus preventing binding or chattering.

Hand reamers are made in both solid and expansion forms. The expansion form is very useful when having to repair or when it is necessary to enlarge a reamed hole by a few thousandths of an inch. The expansion reamer is split through the fluted section and is expanded by screwing in a tapering plug.

Reamers are tapered slightly on the end to facilitate starting them properly. The actual diameter of the reamer shanks may vary from 0.002 to 0.005 inch under the reamer size. The part of the shank, which is squared, should be turned smaller in diameter than the shank, so that when applying a wrench, no burr will be raised, which could mar the reamed hole if the reamer is passed through.

Milling machines use milling cutters to remove material from the workpiece. Characteristically, the milling cutter revolves at calculated revolutions per minute (RPM), and the material is fed to the revolving cutter at a calculated feed rate, which are referred to as cutting speed/ feet per minute. Cutting speed is the difference between the milling cutters and the surface of the workpiece that it is processing.

There are several different types of milling cutters, as well as materials that they are fabricated from, each specially designed for a particular job requirement and cutting speed.

Mill cutters are typically made from four basic types of materials, however these materials can have various coating

High-Speed-Steel also referred to as HHS. HHS was once the material of choice for end mills, however it is being replaced by tungsten carbide as the material of choice for end mills. HHS is still used for milling aluminum, mild steel, and other soft metals.

Cobalt high-speed steel-Mill cutters made from this are harder than those made from HSS. Cobalt high-speed end mills hold their keen edge longer, however, are more brittle.

Carbide-Mill cutters fabricated from carbide provide increase hardness, which will mill several different types of materials. However, carbide mill cutters are more expensive than cobalt or HSS cutters. When milling with carbide mill cutters it is vital that you have a rigid setup with the proper speeds and feed rates for maximal the use of the solid carbide cutters. Carbide mill are less affected by heat and therefore are often used for medium to large production runs.

Milling cutting fluid is also known as coolants. It is vital that the machinist know and understand what the cutting fluids are for each type of grinding wheel as well as what each do. There are three reasons to use coolants:

1.Coolants are used to cool the cutting edge of the cutter. It is the edge where approximately 30% of the heat is generated, which due to the high heat can cause the cutting edge to lose its sharpness and hardness.

2.The coolant is also a lubricant, which reduces the amount of friction at the cutting point. When there is less friction, there is less heat.

3.Coolants wash away the chips. Removing chips quickly also reduces friction as well as helps to improve the surface finish.

Plain water is seldom used for two reasons, first plain water will rust the grinding wheel, machine tool, and probably the workpiece. The second reason why plain water is not used is because it does not spread evenly.

Therefore chemicals are added to the water to help it spread out over the tool more evenly and to help reduce heat more effectively. Different tools and operations require different types of coolants. An example of this would be the use of a silicon carbide or diamond wheel. The coolant most frequently used is water with a small amount of either soluble oil, Sal soda, or soda ash, which will prevent corrosion. However, one prominent manufacturer recommends for diamond wheels that kerosene be applied to the wheel face with a felt pad. Another manufacturer recommends for diamond wheels that a coolant, which is 80% water and 20% soluble oil, be used.

Other coolants that are commonly used for milling operations are:

Chemical water/ Alkaline Water- Excellent for transferring of heat; usually has a concentration of 3 to 10 % alkaline inorganic and organic compounds. Emulsions/Soluble Oil- Good lubricant but does not transfer heat as well as chemical water; usually has a 3 to 10% concentration. Semi-Chemical fluids-This provide excellent lubrication as well as transfer of heat. This is a mixture of Chemical water and soluble oil with a concentration of 5 to 40%. Cutting Oils-This is mineral oil with additives and is used for cutting steel or when tapping diameters over ?.

It is important to realize however, that there are machining applications were this is coolants are not used and in fact should be avoided.

Milling cutters are used in milling machines and machine centers. How the milling cutter moves within the machine is how it removes the material from the workpiece. There are several various types of milling cutters available including slot drills, end mills, ball nose cutters, ball nose, hobbing cutter and woodruff cutters to name a few.

Slot drills usually have two or three fluted cutter, which cut on their end and flutes. Slot drills are named because of their use in cutting keyway slots. Slot drills are usually used at times when pre-drilling holes for an end mill would be too time consuming or when there isn?t room for the end mill to plunge with a spiral motion.

End mills are typically high-speed-steel cutting tools, which have three or more flutes. End mills are used for remove bulk metal with their flutes. However, if the end mills are ground with cutting edges, which cross the axis then these are suitable for side cutting.

Early End mills as well as most large end mills at each end of the cutters have a recessed center to facilitate re-sharpening, which results in the unavailability of the full cutting edge.

Ball nose cutters resemble slot drills however, the end of the ball nose cutters are semi-circular cutting edges and are perfect for machining 3 dimensional contoured shapes in machining centers such as in molds and dies. Side and face cutters have cutting teeth on its side and circumference. Side and face cutters are available in different diameters and widths. Because the teeth are also located on the side of the side and face cutters, they can make unbalanced cuts, which are cuts make only on one side without redirecting the cutter.

These are only a few of the many different types of milling cutters, which provide a fast, accurate, and precise method of machining. The machined surface can be angular, curved, or flat.

Grinding dressers or wheel dressers are tools used to dress the surface of grinding wheels.

The purpose of dressing grinding wheels is to minimize vibration and enhance the surface finish. Dressing also dislodges abrasive particles and exposing fresh abrasive from the surface of the wheels. Every abrasive grain of a grinding wheel is in fact is a small cutting tool. When these tiny cutting tools or grains become worn, the grinding wheel loses its effectiveness. Evidence of rounded and worn grains is glazing of the wheel and is obvious when the spinning grinding wheel has a reflective surface.

There are three types of dressers, star dressers, diamond dressers, and dressing sticks. Star dressers are long handled tools that have a row of free running hard and serrated discs that run at right angles to the handle. The following dressers are diamond dressers, which are shorter handled tools that have either a single diamond or diamond matrix on the broad surface of the dresser. Finally, there are dressing sticks, which are composed of a hard material usually silicon carbide with a stronger bonding agent.

Grinding wheels are composed of an abrasive material that is typically made from a matrix of coarse particles that are pressed and bonded together to form a solid, circular shape. There is a wide variety of profiles and cross sections available depending on the intended use for the grinding wheel. In addition, grinding wheels can also be created from a solid steel or aluminum disc that?s surface is bonded with silicon carbide and diamond particles. The manufacture of grinding wheels is tightly controlled and precise process due to the safety risks of a rotating disc as the structure and standardization necessary to prevent the disc from exploding under the high stresses produced on rotation.

The grinding wheel is the mainstay of the engineering and construction industry and many times the risks involved with them are often overlooked. Therefore, safety should always be priority when working with grinding wheels, especially the wearing of all the appropriate safety gear. In addition, all safety procedures must be followed.

With excessive use it carbide tools will need to be sharpened from time to time in order to maintain their cutting edge. Cemented carbide indexable inserts usually require a special grind in order to form a contour on the cutting edge to suite a special purpose. Brazed type carbide cutting tools are re-sharpened after the cutting edge has become worn. On brazed carbide tools, the cutting-edge wear should not be allowed to become excessive before the tool has been re-sharpened. One method of determining when carbide tools need to be re-sharpened is by periodically inspecting the flank wear and the condition of the face, in addition, when amount of production decrease from that, which is usually achieved after re-sharpening is another indication that the tool requires re-sharpening.

Re-sharpening should never require the removal of more than 0.005 to 0.010 inch of carbide. The typical procedure for re-sharpening depends on the type of grinding operation that is required. If the procedure is to re-sharpen a dull tool, then a diamond wheel of 100 to 120 grain size is normally recommended. However, a finer wheel of 150-grain size is sometimes utilized in order to obtain a smoother finish. Some machine shops prefer to rough grind carbide with a vitrified silicon carbide wheel, the finish grinding is usually accomplished with a diamond wheel, with a final process designated as lapping may or may not be used to obtain an extra-fine finish.

Milling cutters can be sharpened by using the periphery of a disk wheel or the face of a cup wheel. The face of a cup wheel grinds the lands of the teeth flat, while the periphery of a disk wheel will leave the teeth slightly concave back of the cutting edges. The concavity created by the dick wheel will reduce the effective clearance angle on the teeth. This effect is more pronounced with smaller diameter wheels than with larger diameter wheels. It is for this reason that large diameter wheels are preferred for sharpening milling cutters.

Machine tools are powered mechanical devices that are generally used to manufacture metal components of machines by selectively cutting and removing metal. Depending on whom you ask, the creation of machine tools occurred when the direct human involvement was removed from the process of cutting, shaping, or stamping process required in creating the various types of tools. An example of this theory is the lathe machine tool. In 1751, Jacques de Vaucanson mounted the cutting instrument on a mechanically adjustable head, removing the process from the hands of the operator. However, many historians will argue that machine tools did not come about until after the development of the steam engine and the Industrial Revolution.

Today, they are powered by electricity and can be operated manually, or under automatic control. The early machines had flywheels that stabilize their motion as well as an intricate system of levers, and gears that controlled the machine as well as the piece that were being produced.

Numerical control or NC machines were developed after World War II. These machines used a series of numbers punched onto paper tape or cards to control their motion. Then by the 1960s, computers were gradually added to the machines to allow for more flexibility in the process. These new computerized machines were then know as computer numerical control machines, or CNC for short. With the development of the NC and CNC machines, more pieces that are complex could be produced. The reason for this is that these machines could precisely repeat sequences over and over.

It wasn’t long before these machines drastically changed the cutting and shaping of tools being used. An example of this change is the drill machine, which because of computerization can contain a magazine loaded with a variety is sizes of drill bits used to produce various size holes. In the past, the machinist would have to either manually change out the bit or completely relocate the piece being worked on to another station in order to perform the different operations. Both methods took time, thus reduced productivity.

Once the NC and CNC proved to increase production, the next step was to combine various machine tools together with each being controlled by a single computer. These combined machine tools were then known as machine centers, and like their predecessors, have dramatically changed the way parts are created. Today, highly complex machine parts can be finished in a matter of minutes instead of the hours that it used to take.