What is Cutting Tools ?
In the context of machining, a cutting tool or cutter is any tool that is used to remove material from the workpiece by means of shear deformation. Cutting may be accomplished by single-point or multipoint tools. Single-point tools are used in turning, shaping, planing and similar operations, and remove material by means of one cutting edge. Milling and drilling tools are often multipoint tools. Grinding tools are also multipoint tools. Each grain of abrasive functions as a microscopic single-point cutting edge (although of high negative rake angle), and shears a tiny chip.
Cutting tools must be made of a material harder than the material which is to be cut, and the tool must be able to withstand the heat generated in the metal-cutting process. Also, the tool must have a specific geometry, with clearance angles designed so that the cutting edge can contact the workpiece without the rest of the tool dragging on the workpiece surface. The angle of the cutting face is also important, as is the flute width, number of flutes or teeth, and margin size. In order to have a long working life, all of the above must be optimized, plus the speeds and feeds at which the tool is run.
Linear cutting tools include tool bits (single-point cutting tools) and broaches. Rotary cutting tools include drill bits, countersinks and counterbores, taps and dies, milling cutters, reamers, and cold saw blades. Other cutting tools, such as bandsaw blades, hacksaw blades, and fly cutters, combine aspects of linear and rotary motion
Cutting tools with inserts (indexable tools)
Cutting tools are often designed with inserts or replaceable tips (tipped tools). In these, the cutting edge consists of a separate piece of material, either brazed, welded or clamped on to the tool body. Common materials for tips include cemented carbide, polycrystalline diamond, and cubic boron nitride. Tools using inserts include milling cutters (endmills, fly cutters), tool bits, and saw blades.
Solid cutting tools
The typical tool for milling and drilling has no changeable insert. The cutting edge and the shank is one unit and built of the same material. Small tools cannot be designed with exchangeable inserts.
To use a cutting tool within a CNC machine there is a basic holder required to mount it on the machine’s spindle or turret. For CNC milling machines, there are two types of holder. There are shank taper (SK) and hollow shank taper (HSK).
The detailed instruction how to combine the tool assembly out of basic holder, tool and insert can be stored in a tool management solution.
The cutting edge of a cutting tool is a very important for the performance of the cutting process. The main features of the cutting edge are:
- form of the cutting edge: radius or waterfall or trumpete
- cutting edge angles (free angle and rake angle)
- form and size of the chamfers
The measurement of the cutting edge is performed using a tactile instrument or an instrument using focus variation.
To produce quality product, a cutting tool must have three characteristics:
- Hardness: hardness and strength at high temperatures.
- Toughness: so that tools do not chip or fracture.
- Wear resistance: having acceptable tool life before needing to be replaced.
Cutting tool materials can be divided into two main categories: stable and unstable.
Unstable materials (usually steels) are substances that start at a relatively low hardness point and are then heat treated to promote the growth of hard particles (usually carbides) inside the original matrix, which increases the overall hardness of the material at the expense of some its original toughness. Since heat is the mechanism to alter the structure of the substance and at the same time the cutting action produces a lot of heat, such substances are inherently unstable under machining conditions.
Stable materials (usually tungsten carbide) are substances that remain relatively stable under the heat produced by most machining conditions, as they don’t attain their hardness through heat. They wear down due to abrasion, but generally don’t change their properties much during use.
Most stable materials are hard enough to break before flexing, which makes them very fragile. To avoid chipping at the cutting edge, some tools made of such materials are finished with a sightly blunt edge, which results in higher cutting forces due to an increased shear area, however, tungsten carbide has the ability to attain a significantly sharper cutting edge than tooling steel for uses such as ultrasonic machining of composites. Fragility combined with high cutting forces results in most stable materials being unsuitable for use in anything but large, heavy and rigid machinery and fixtures.
Unstable materials, being generally softer and thus tougher, generally can stand a bit of flexing without breaking, which makes them much more suitable for unfavorable machining conditions, such as those encountered in hand tools and light machinery.
Sumber dari : wikipedia