Swarf

The metal chip is a mechanically- separated particles from a machined metal workpiece.

Chip formation

The chip formation takes place during the machining of metals in three repeating phases. First the upsetting takes place, the wedge penetrates into the material and the material solidifies and shrinks. The pressure is maintained, the compressive and shear stress in the workpiece to increase the breaking strength and a chip is sheared. The shearing is effected at the location of the maximum shear stress, the so-called shear plane, which forms the shearing angle with the workpiece surface. The chip is now flowing from on the rake face of the wedge and, when he comes across another resistor, compressed again.

With geometrically undefined cutting edges, the process of the chip formation is different, as many cutting edges have an irregular shape and the depth of cut of the individual grains is very small. Further, the grains slip on the workpiece surface only.

Thus, the chips consume much space and can be removed easily, can be taken with chip breakers and Spanleitplatten on the chip formation by breaking or redirecting the chip influence.

Chip types

Under a Spanart refers to a particular lever shape that results in a function of the chip formation. Using the Spanart the clamping operation can be assessed. On the formation of the Spanart the cutting geometry, the formability of the material, the Spanungsgrößen, the cutting speed and the coolant used act. The differences between the three ( depending on the source, four ) single chip types are fluid. With some materials, all kinds clamping can be achieved by changing the clamping conditions.

Tensile tension

If a brittle material machined by a machining process, usually the tear tension arises (also called Bröckel tension ). Small rake angle and low cutting speeds also favor the formation of tear chips. Due to the wedge prior cracks in the workpiece, the clamping solves without significant deformation. By breaking out of the chip, the surface of the workpiece after tear chipping the material is rough. An example of a material which occur during the drawing chips is brass.

When working with wood, see: precleavage

Shear tension

The shear tension is caused by a deformation in the shear zone. The material of the chip is strained beyond the formability. The tension crack parallel to the plane in individual plates apart. The high temperatures ensure that blades are welded together.

Continuous chip

The swarf is also formed by a deformation in the shear zone, but the tension is continuously flowing over the cutting edge on. In this case, the deformation capacity of the material is not exceeded. The transformation is thus uniformly in all layers. This creates a continuous tension. The swarf produced at a high cutting speed and high temperatures as well as a continuous cutting action as it is the case in turning and drilling. Another formation condition is the positive rake angle. (For a long and thin aluminum clamping also called angel hair )

A neat, long chip flow is the most elegant type of metal machining. The main drawback is the risk of the coil formation, thus impairing the automatic operations. Thus the material is flowing chip forming materials only for small production lots or large lots if the flow process of the chip thus band chips can be avoided interrupted at regular intervals. For the mass production if possible short-breaking cutting steels preferred which contain an increased proportion of sulfur and phosphorus, which favor the chip breaking, however, have an adverse effect on strength and ductility.

Lamella clamping

With variation of the chip thickness due to a non-uniform material structure, it can result in the formation of a lamellar chip. The structure is similar to the shear span, but there are no fragments, but it is a pure transformation instead.

Lamellar chips are continuous chips with distinct lamellae.

Chip shape

The chip shape describes the shape of the chip after leaving the tool. The formation of the chip-forming is primarily of the material of the workpiece and the cutting conditions. The single chip shapes are according to their outward appearance, on the bulk density (for steel in t / m³), classified according to the potential hazard of the operator and of the possible damage to the tool, workpiece and machine.

Are considered to be unfavorable, especially band chips and thread chips, since they form balls of tension, thereby endangering the safety at work. They also damage the workpiece surface, hindering the chip flow and automatic chip removal.

Also screws chips (also called spiral chips) should be avoided, but depending on the length they are still considered satisfactory. The negative impact on the workpiece and the clamping case are not as pronounced as in tape and thread chips. Chip fragments ( or disintegration chips ) are also to be avoided because they compromise by the operator, and roving syringes clog guides. On modern machines with enclosed working space and secure guides but this is not a problem

The best chips are screw breakage chips, spiral fracture spiral shavings and chips. They endanger the operator little, can be easily transported away and have a high bulk density.

Clamping tonnage

The clamping tonnage R is the ratio between the dimensions of a disorderly chip quantity and the volume of material in the same amount of chips. The smaller the number, the less space is needed for the chip and the easier they can be handled. The table shows the main chip shapes and their chip space indicated by numbers.