Types Of Chips

Types of chip: The form and dimension of a chip in metal machining indicate the nature and quality of a particular machining process, but the type of chip formed is greatly influenced by the properties of the material cut and various cutting conditions. In engineering manufacturing particularity in metal machining processes hard brittle material have a very limited use, and various cutting conditions. Chips of ductile metals are removed by varying proportions of tear, and slow..

Discontinuous or segmental chips: consist of elements fractured into fairly small pieces ahead of the cutting tool. This type of chip is obtained in machining most brittle materials, such as cast iron and bronze. These materials rupture during plastic deformation, and form chips as separate small pieces. As these chips are produced the cutting edge smoothes over the irregularity, and a fairly good finish is obtained. Tool life is also reasonably good, and the power consumptions low. Discontinuous chips can also be formed on some ductile metals only under certain conditions particularly at very low speeds and if the coefficient of friction is low. With ductile materials, however, the surface finish is bed and the tool life is short. Conditions tending to promote its formations include: brittle materials greater depth of cut, low cutting speed and small rake angle.

Continuous chips: consist of elements bonded firmly together without being fractured. Under the best conditions the material flows by means of plastic deformations and gives a continuous ribbon of metal which, under the microscope, shows no signs of terms or discontinuities. The upper side of a continuous chip has small notches while the lower side, which slide over the tool face, is smooth and shiny. The continuous forms is considered most desirable for low friction at the tool-chip interface, lower power consumption, long tool life and good surface finish.

Built-up edge: implies the building up of a ridge of metal on the top surface of the tool and above the cutting edge. It appears that, when the cut is started in ductile metals, a pile of compressed and highly stressed metal forms at extreme edge to the tool. Conditions tending to promote the formations of built-up edges include: low cutting speed, low rake angle, high feed, and lack of cutting fluid and large depth of cut.

Chip breakers: A continuous-type from a long cut is usually quite troublesome. Such chips foul the tools; clutter up the machine and workplace, besides being extremely difficult to remove from the swarf tray. They should be broken into comparatively small pieces for ease of handling and to prevent it from becoming a work hazard. Hence chip breakers are used to reduce the swarf into small pieces as they formed.

The act that the metal is already work-hardened helps the chip breaker to perform effectively. Various type of chip breakers are made, but all of them consist mainly of a step or groove ground into the leading edge of the tool are a piece of cutting-tool material clamped on the cutting-tool. Effective control of the chip, as it moves across the face of the tool, may also be achieved by proper selection of tool angle, feed, depth of cut and cutting fluids used. A large positive front rake gives rise to a looser chip formation, which follows down the face of the tool, and away from the work piece, leaving the newly cut surface unscratched. A small positive or negative side rake as the effect of decreasing the radius at which the chip coils. Hence the tendency to produce short, easily managed chip. A small depth of cut with a fine feed allows the chip to form into comparatively small pieces or direct it into the swarf tray. The use of a good stream of coolant that as a quenching medium causes, the hot chip to become harder and break into small pieces.

The cutting action of hand tools: All hand tools may also be classified as single-point tools and multi-point tools, and the action of removing metal is one of shear. The fundamental cutting from that has been described before, applies, in principle on even type of cutting edge used for cutting, whether at the bench or in a machine tool. In some cases, at the first instance, it appears does not apply, but upon more detailed examination the fundamental rake or clearance may be found out. In the subsequent paragraphs a few of the common hand tool are described.