Machinability Physics of Metal Cutting Objectives Be able

Machinability & Physics of Metal Cutting

Objectives • Be able explain machinability • Understand how material is removed from and the effects it has on the surface finish of a work-piece • Analyze and troubleshoot chip formation

What is machinability? • Machinability is the ease with which a material can be machined, the wear created to the cutting edge, surface finish obtained and power consumption.

What factors play a role in machinability? • Mechanical properties of material (Hardness, Yield, Shear, etc. ) • Geometry of tool tip (Rake angle, relief angle) • Tool Type (HSS, Carbide, CBD, PCD)

Machinability Chart Carbon Steel 1015 1018 1020 1022 1030 1042 1050 1095 1117 1137 1141 annealed 1144 stressproof 1212 1213 12 L 14 1215 72% 78% 70% 64% 54% 42% 91% 72% 70% 81% 76% 85% 83% 100% 136% 170% 136% Alloy Steel 2355 annealed 4130 annealed 4142 annealed 41 L 42 annealed 4150 annealed 4340 annealed 4620 4820 annealed 52100 annealed 6150 annealed 8620 86 L 20 9310 annealed 70% 72% 66% 77% 60% 57% 66% 49% 40% 66% 77% 51% Aluminum Stainless Steel / Super alloy 302 annealed 45% 303 annealed 78% 304 annealed 45% 316 annealed 45% 321 annealed 36% 347 annealed 36% 410 annealed 54% 416 annealed 110 % 420 annealed 45% 430 annealed 54% 431 annealed 45% 440 A 45% aluminum, cold drawn 360% 15 -5 PH condition A 48% aluminum, cast 450% 17 -4 PH condition A 48% aluminum, die cast 76% A 286 aged 33% Hastelloy X 19% Tool Steels A-2 A-6 D-2 D-3 M-2 O-1 O-2 42% 33% 27% 39% 42% Cast Iron ASTM class 25 ASTM class 30 ASTM class 35 ASTM class 40 ASTM class 45 ASTM class 50 55% 48% 48% 36%

Traditional Metal Cutting • To machine, the tool or work-piece must rotate or move in a linear direction. • In order to remove material, the cutting tool must engage the work-piece. The rate of speed at which this engagement occurs is called Feed-Rate controls the thickness of the chip and is a major factor in the type of chip that is formed. • Depth of cut, also known as in-feed is the depth of material set to be removed by the cutting tool.

Chip Removal in Traditional Machining Operations

Physics of Chip Removal • Metal chips are sheared not “cut” from the work piece

Physics of Chip Removal • Deformation Zone / Plastic Deformation

Physics of Chip Removal • Elongation of the crystalline structure occur in the direction of the cut.

Physics of Chip Removal • Plastic Flow

Physics of Chip Removal • Rupture Chip

Physics of Chip Removal • Affect of rake angle on chip thickness

Chip Formation • Three basic types of chips in machining – Discontinuous chip – Continuous chip with Built up edge

Chip Formation • Discontinuous chip – Brittle work materials (e. g. Cast Irons) – Low Cutting Speed – Large feed and depth of cut – High tool chip friction (small rake angle)

Chip Formation • Continuous chip – Ductile work materials (e. g. Low carbon steel) – High cutting speeds – Small feeds and depths of cut – Sharp cutting edge on tool – Low tool-chip Friction

Chip Formation • Continuous chip with BUE (Built up edge) – Ductile materials – Too low rake angle – Lack of cutting fluid – Feed rate – Tool life affected

Chip Formation • BUE breaking off tool face onto new work surface

Questions?