Carbide End Mill Sets

Archive for the ‘Common Questions’ Category

High-speed-steel is used in the manufacture of machine tool bits and cutters and is often seen abbreviated as HSS. High-speed-steel is a composition of steel that contains a combination of more than 7 % tungsten, molybdenum, vanadium, and cobalt and more than 0.60% carbon and can withstand greater temperatures without losing its temper/ hardness. This makes HSS a far superior material than older high carbon steel tools. Because high-speed-steel does not loss its temper, it can cut at higher speeds than high carbon steel.

Coatings such as titanium nitride (TiN) are added to increase the life of high-speed-steel tools. Several coatings also increase the tool’s hardness as well as provide a lubrication, which permits the cutting edge to cleanly pass through the material without any of the material sticking to the cutting edge. Coatings also help decrease the temperature, which is associated with the cutting process. This also helps to increase the tool life.

High-speed-steel?s main use is in the manufacturing of various cutting tools including drills, gear cutters, milling cutters, saw blades, taps, tool bits, etc. However, lately, there has been an increase amount of punches and dies manufactured from high-speed-steel.

For low speed applications that require a very sharp/keen edge, high carbon steel still remains the best choice especially for files, chisels, and hand plane blades.

MIT Servomechanisms Laboratory developed the CNC in the late 1940s and early 1950s. CNC is the abbreviation for Computer Numerical Control or sometimes known as Computerized Numerically Controlled machine. CNC refers specifically to the computer, which controls machine tools for the purpose of repetitively manufacturing complex parts from metal or other materials. The staff of Servomechanisms Laboratory aggressively promoted the introduction and use of CNC for industrial processes by sponsoring conferences as well as summer sessions, which were aimed at industry personnel. The development of the CNC had a profound impact on the machine tool industry.

The introduction of CNC machines made it possible to cut curves as simply as straight lines. In addition, it has reduced the number of machining steps, which require human action to complete. As the machine tool industry became increasingly automated due to CNC machining, improvements in consistency and quality were achieved. To increase productivity, several CNC machines could be combined in a series to form a station, which is commonly referred to as a “cell.? This enables the progressive machining of a workpiece that requires several operations.

Today, CNC machines are controlled from files created by computer-aided manufacturing, (CAM), software. This makes it possible for a workpiece or a complete assembly to go from design directly to manufacturing eliminating the drafting process of the manufactured part or assembly.

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, machine tools 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.

When using a silicon carbide grinding wheel, it has to either be absolutely dry, or have enough coolant to flood both the wheel and tool.

Dry grinding is the method most commonly used because when an operator uses wet grinding, they tend to us an insufficient amount of coolant in order to have a better visual of the grinding operation. Unfortunately, this increases the likely hood of checking or cracking.

However, wet grinding does have several advantages over dry grinding. When sufficient amounts of coolant are used on the wheel: The wheel can be used approximately one grade harder than in dry grinding, which increases the life of the wheel. The use of sufficient amounts of coolant prevents thermal stresses and cracks. There is also less of a tendency for the wheel to load. A dust exhaust system is not required with wet grinding.

When used correctly, both wet grinding and dry grinding provide satisfactory results.

A list of the three main coatings used today:

Titanium nitride (TiN) TiN-coated carbide end mills must be run at speeds and feed rates close to that of uncoated carbide end mills. However, the TiN coating provides a better wear and lubricity to the end mill.

Titanium carbon nitride (TiCN) TiCN coatings are perfect for slow feeds and speeds, however it is often the choice coating for high-speed steel end mills. For carbide tools coated with TiCN, you can run at speeds approximately 80 % faster than uncoated solid carbide end mills. However, TiCN is prone to failure under extreme heat, which is why it is often used in slower feed and speed applications.

Titanium aluminum nitride (TiAlN) or Aluminum titanium nitride (AlTiN) TiAlN- or AlTiN-coated end mills are becoming increasingly popular. The aluminum in both coatings helps to create a gaseous aluminum oxide layer at the cutting edge that can reach temperatures greater than 1800-degrees. This layer of aluminum oxide gas protects the carbide in the tool from the damaging effects of heat. This is why these two coatings have become popular for high-speed and hard milling, especially in dry cutting. Aluminum titanium nitride contains greater amounts of aluminum than titanium aluminum nitride.

There are other coatings available on the market today, however, they are variations of the main three. When machining nonferrous materials, aluminum, brass, and plastics non-coated carbide end mills that have polished flutes are recommended in order to prevent edge buildup. These materials require finely keen edges and end mills that are coated don’t allow as sharp an edge.

These are only a few of the factors to consider using carbide end mills. Other factors include the specific geometries of the end mill, rake angles, gash lands, relief angles, as well as programs, and the machine. Understanding the process as well as the material that will be machined is only the first step in deciding which end mill should be selected for the application.

When manufactures of machine tools simply scale down a tool’s geometry, it produces unacceptable feedrates as well as unacceptable finishes. Smaller tools with smaller diameter require increased spindle speeds. Higher rpm rates require tools, which are properly balanced and have increased chip room for proper chip evacuation in order to prevent chip burn-up. Therefore, HSM applications require small tools that are optimized for this purpose.

Use of Low-Viscosity Coolant:

Just by the nature of the process of high-speed machining with micro tooling heat. In fact, the process creates enough heat that can require the use of coolants, even though HSM technology contains advantages, which reduce heat. There are, however certain applications that still require the use of an efficient coolant system.

Coolants perform two task, first the reduce heat and second they serve as a lubricant, which enabling the tool to move smoothly over the surface of the workpiece. Micro tooling requires a lubricating agent that has a viscosity lower than water in order for the coolant to make it to the cutting edge of the tool at the higher spindle speeds. Emulsion-based coolants are ineffective as a lubricant for HSM with micro tooling because they have a higher viscosity than water.

Ethanol can be used in micro-volume coolant spray systems and is suitable for nonferrous metals as well as some plastics. However, oil-based coolants are required on steel-based materials because of the risk of sparks that can be produced by the carbide tooling on steel surfaces can produce a safety hazard when the sparks come in contact with the ethanol.

Although ethanol is flammable, its low evaporation point makes it an efficient coolant for HSM operations. Other benefits of ethanol include that fact that it doesn?t leave any residue on the machined parts, and eliminates the process of degreasing.

Improving HSM Technology:

Machining involves math, a lot of math. We use math to calculate the areas and dimensions of plane figures, we use math for measurements and inspections, to check pitch, to calculate clearance angles, and speed and feed rates, in fact there probably isn?t a step of machining that does not relay on a mathematical formula. Therefore, it is perfectly logical and mathematically sound when we state that a smaller tooling requires a higher spindle speed in order to machine the parts efficiently. This is due to the fact that the higher spindle speed is required to efficiently evacuate chips to prevent chip burn-up.

HSM technology does use higher rpm rates, however it also uses considerably increased feedrates as well. When the spindles spin fast, there’s not enough time for heat to feed back into the workpiece and cause concerns. However, the tool continuously cuts chips from the workpiece, which produces heat and friction on both sides of the tool and chip. Approximately 60% of the heat is inside the chip. HSM process is based on evacuating the chips, thus removing the heat along with the chip to provide a cleaner cut. However, if the tooling cannot or has insufficient chip evacuations, then the heat is not removed, creating chip-burn and eventually the tooling cracks, and breaks. A better principle would be machining process that is based on cooler tooling, meaning lower machining forces to reduce vibration. Higher spindle speeds reduce the amount of chip load to < 0.005″, which in turns reduces the amount of forces between the tool and the workpiece. A higher speed lower force machine produces less heat, which decreases tool deflection resulting in a better surface quality, as well as better accuracy.

Dynamics of Machining:

Improved Micro tooling designs, low-viscosity coolant, and improved HSM technology can drastically improve the dynamics of machines, which perform HSM with micro tooling. Traditional machines are heavier meaning that they do not have the speed or feed rates required for micro tooling. Therefore, you cannot expect the same quality, precision, and tolerances from retrofitting a high-speed spindle onto a traditional machine as you would from a high-speed machine with micro tooling that is designed precisely.

Machines can either be large and powerful capable of using tools with large diameter spindle sized, or they can be lightweight, designed specifically for micro tooling. When you attempt to merge the two, it is like trying to breed a Great Dane and a Tea Cup Chihuahua. Therefore, to achieve proficient high-speed machining there has to be improved micro tooling designs, the use of low-viscosity coolants, and improved HSM technology. HSM with micro tooling provides less force, reduced heat, which means less tool breakage, and a better surface finish. In addition, there is the elimination of deburring and the degreasing process.