ENB331 Materials and Manufacturing 2 Week 3.docx

6 Pages
Unlock Document

Queensland University of Technology
Prasad Yarlagadda

ENB331 Lecture Materials and Manufacturing 2 Cutting Tool Technology Cutting Tool Failure: Preferred Mode: Gradual Wear Fracture Failure Fracture and temperature are premature failures; Cutting force becomes excessive and/or dynamic leading to gradual wear is preferred because it leads to the brittle fracture longest possible use of the tool. Gradual wear occurs Thermal Failure at two locations on a tool: Cutting temperature is too high for the tool material 1. Crater Wear – occurs on top rake face Gradual Wear 2. Flank wear – occurs on flank Gradual wearing of the cutting tool Crater Wear Flank Wear Wear Patterns on Tools (a) Flank wear and crater wear in a cutting tool; the tool moves to the left. (b) View of the rake face of a turning tool, showing various wear patterns (c) View of the flank face of a turning tool, showing various wear patterns. (d) Types of wear on a turning tool: a. Flank wear b. Crater Wear c. Chipped Cutting Edge d. Thermal Cracking on rake Face e. Built up Edge f. Catastrophic Failure Dull tool in Orthogonal Machining Schematic illustration of a dull tool with respect to the depth of cut in orthogonal machining (exaggerated). Note that the tool has a positive rake angle, but as the depth of cut decreases, the rake angle effectively can become negative. The tool then simply rides of the workpiece (without cutting) and burnishes its surface; this action raises the workpiece temperature and causes surface residual stress. 1 Week 3 Tuesday, 27 August 2013 ENB331 Lecture Materials and Manufacturing 2 Tool Wear vs Time Effect of Cutting Speed on Tool Wear Effect of Cutting Speed on Tool Life Taylors Tool Life Equation n and C are parameters that depend V = cutting speed on feed, depth of cut, work material, T = Tool life tooling material and the tool life N = Slope of the plot criterion used. C = the intercept on the speed axis at one minute tool life (i.e. cutting speed required for one min tool life) Tool life criteria in production Cumulative Cutting time Increased Power Chips become ribbon-like, stringy, and Workpiece Count Degradatino of surface finish difficult to dispose of Changes in sound emitted from Fingernail test across cutting edge Visual inspection of flank wear (or operation Complete failure of cutting edge crater wear) by the machine operator) 2 Week 3 Tuesday, 27 August 2013 ENB331 Lecture Materials and Manufacturing 2 Tool Geometry Single point tools Multiple Cutting Edge Tools Used for turning, shaping and planing, threading, boring Drilling, reaming, tapping, milling, broaching and sawing. Holding the tool Typical Insert Shapes Feed Marks on a Turned Surface Twist Drills Most common cutting tools for hole-making, usually made of high speed steel. Rotation and feeding of drill bit result in relative motion between cutting edges and workpiece to form the chips.  Cutting speed varies along cutting edges as a function of distance from axis of rotation  Relative velocity at drill point is zero, so no cutting takes place  A large thrust force is required to drive the drill into the hole 3 Week 3 Tuesday, 27 August 2013 ENB331 Lecture Materials and Manufacturing 2 Twist Drill Operation Problems Chip Removal: Flutes must provide sufficient clearance to allow chips to be extracted from bottom of hole during the cutting operation Friction makes matters worse: Rubbing between outside diameter of drill bit and newly formed hole. Delivery of cutting fluid to drill point to reduce friction and heat is difficult because chips are flowing in opposite direction. Milling Cutters – Principal Types 1. Plain milling cutter: used for peripheral or slab milling 2. Face milling cutter: Teeth cut on side and periphery of the cutter 3. End milling cutter: Small diameter plain milling tool Plain Milling Cutter Face Milling Cutter End Milling Cutter Looks like a drill but but designed for primary cutting with its peripheral teeth, applications include; Face milling, profile milling and pocketing, cutting slots, engraving, surface contouring, die sinking. Tool Materials Tool failure modes identify the important properties that a tool material should possess: (a) Toughness – to avoid failure (b) Hot Hardness – ability to retain hardness at high temperatures (c) Wear resistance – hardness is the most important property to resist abrasive wear. High Speed Steel (HSS) Two basic types (AISI) Highly alloyed tool steel capable of maintain hardness (a) Tungsten-type, designated T-grades at elevated temperatures better than high carbon and (b) Molybdenum-type, designated M-grades low alloy steel. (c) Alloying elements – C,Si,Cr,V,W,Mo,Co One of the most important cutting tool materials Typical alloying ingredients: Tungsten, Molybdenum, Especially suited to applications involving complicated Chromium, Vanadium, Carbon, Cobalt. tool geometries such as drills, taps, milling cutters andTypical Composition broaches.
More Less

Related notes for ENB331

Log In


Don't have an account?

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.