chip formation
DESCRIPTION
Chip Formation. Machinability. relative difficulty of a machine operation with regard to tool life, surface finish, and power consumption generally softer materials - easier to machine. Metal does NOT split off ahead of cutter as in wood. Metal is sheared off at SHEAR PLANE. - PowerPoint PPT PresentationTRANSCRIPT
Chip Formation
Machinability
relative difficulty of a machine operation with regard to tool life, surface finish, and power
consumption
generally softer materials - easier to machine
Metal does NOT split off ahead of cutter as in wood
Metal is sheared off at SHEAR PLANE
metal is forced ahead of tool
Surface finish affected by:
speeds feeds depth of cut tool shape use of cutting fluid rigidity of the setup
Optimum chip for operator safety is figure “9”
Chip breaker
curls chip to break it off keep from tangling in machine safer
3 basic types of chip formation
1. Continuous chip
Continuous chip characteristics
better surface finish soft or medium hardness materials
that are ductile low coefficient of friction - pass
across top of well polished tool chips curl or are straight and stringy chip breaker used to break the chip
2. Discontinuous chip (segmented)
Discontinuous chip characteristics
materials that fracture easily (cast iron)
fails or breaks after only a small amount of deformation
no chip breaker required chips are cleaned up easily
3. Continuous chip (with built up edge on tool)
Continuous chip (built of edge) characteristics
soft materials - high coef of friction stick to top of entering edge of tool caused by heat and pressure of cutting
action material temporarily welds to tip of
cutting tool then releases rougher surface finish tool life shortened
Solutions for built up edge
• no single solution• change tool geometry• use chip breaker• cutting fluids• best combination of speeds and feeds
Cutting tool geometry
positive rake neutral rake negative rake
Positive rake tools
Positive rake tool characteristics
freer cutting at low speeds pos rake tools, cutting fluids, and
higher speeds decrease tendency for built up edge - however,
large pos rake = continuous chip
Negative rake tools
Negative rake tool characteristics
surface disrupted more require more power stronger and have longer working life
than positive low cutting speeds = poor surface
finish high cutting speeds = good surface
finish
Most carbide tools have negative rake because:
indexable insert can be turned over withstands more cutting pressure higher cutting speeds used