ME 383 Exam 3- CH 23: Cutting Tool Technology

Three Modes of Tool Failure

1. Fracture failure: Cutting force becomes excessive and/or dynamic, leading to brittle fracture 2. Temperature failure: Cutting temperature is too high for the tool material 3. Gradual wear: Gradual wearing of the cutting tool

23.6 MC Steel-cutting grades of cemented carbide are typically characterized by which of the following ingredients (three correct answers): (a) Co, (b) Fe, (c) Mo, (d) Ni, (e) TiC, and (f) WC?

A, E, F

Coated Carbides

Cemented carbide insert coated with one or more layers of TiC, TiN, and/ or Al2O3 or other materials

Cemented Carbides

Class of hard tool material based on tungsten carbide (WC) using powder metallurgy techniques with cobalt (Co) as the binder

Twist Drill

Most common cutting tools for hole‐making

23.8 Identify three desirable properties of a cutting-tool material.

Three desirable properties are (1) toughness to resist fracture failure, (2) hot hardness to resist temperature failure, and (3) wear resistance to prolong the life of the tool during gradual wear.

Lubricants

designed to reduce tool-chip and tool-work friction -Usually oil‐based fluids -Most effective at lower cutting speeds -Also reduce temperature in the operation

Hot Hardness

ability to retain hardness at high temperatures

Tool Life Criteria in Production

1. Complete failure of cutting edge 2. Visual inspection of wear by the machine operator 3. Fingernail test across cutting edge 4. Changes in sound emitted from operation 5. Chips become stringy and difficult to dispose 6. Degradation of surface finish 7. Increased power 8. Workpiece count 9. Cumulative cutting time

23.1 MC Of the following cutting conditions, which one has the greatest effect on tool wear: (a) cutting speed, (b) depth of cut, or (c) feed?

A

Cutting Fluids

Any liquid or gas applied directly to the machining operation to improve cutting performance

23.13 Why are ceramic cutting tools generally designed with negative rake angles?

Ceramics possess low shear and tensile strength but good compressive strength. During cutting, this combination of properties is best exploited by giving the tool a negative rake angle to load the tool in compression.

23.19 Why are cutting fluid filter systems becoming more common and what are their advantages?

Cutting fluid filter systems are becoming more common due to the environmental protection laws and the need to prolong the life of the fluid before disposal. Advantages of filter systems include longer fluid life, reduced disposal costs, better hygiene, lower machine tool maintenance, and longer cutting tool life.

23.20 Dry machining is being considered by machine shops because of certain problems inherent in the use of cutting fluids. What are those problems associated with the use of cutting fluids?

Cutting fluids become contaminated over time with a variety of contaminants, including tramp oil, garbage, small chips, molds, fungi, and bacteria. In addition to causing odors and health hazards, contaminated cutting fluids do not perform their lubricating function as well as when they are fresh and clean.

23.7 MC If you had to select a cemented carbide for an application involving finish turning of steel, which C-grade would you select (one best answer): (a) C1, (b) C3, (c) C5, or (d) C7?

D

High Speed Steel (HSS)

Highly alloyed tool steel capable of maintaining hardness at elevated temperatures better than high carbon and low alloy steels

23.16 Name the four categories of cutting fluid according to chemistry.

The four categories of cutting fluids according to chemistry are (1) cutting oils, (2) emulsified oils, (3) chemical fluids, and (4) semi-chemical fluids.

23.4 Identify the mechanisms by which cutting tools wear during machining.

The important tool wear mechanisms are (1) abrasion, (2) adhesion, (3) diffusion, and (4) plastic deformation of the cutting edge.

23.18 What are the methods by which cutting fluids are applied in a machining operation?

The most common method of application is flooding, in which a steady stream of fluid is direct at the operation. Other methods include mist application, fluid-hole delivery through the tool, and manual application (e.g., using a paint brush).

23.5 What is the physical interpretation of the parameter C in the Taylor tool life equation?

The parameter C is the cutting speed corresponding to a one-minute tool life. C is the speed-axis intercept on the log-log plot of the tool life data.

23.12 Name the seven elements of tool geometry for a single point cutting tool.

The seven elements of single-point tool geometry are (1) back rake angle, (2) side rake angle, (3) end relief angle, (4) side relief angle, (5) end cutting edge angle, (6) side cutting edge angle, and (7) nose radius.

23.2 Name the three modes of tool failure in machining.

The three tool failure modes are (1) fracture failure, (2) temperature failure, and (3) gradual wear.

23.15 Name the two main categories of cutting fluid according to function.

The two functional categories of cutting fluids are: (1) coolants and (2) lubricants.

23.1 What are the two principal aspects of cutting-tool technology?

The two main aspects of cutting tool technology are (1) tool material and (2) tool geometry.

23.9 What are the principal alloying ingredients in high-speed steel?

Principal alloying ingredients in HSS are (1) either tungsten or a combination of tungsten and molybdenum, (2) chromium, (3) vanadium, and (4) carbon. Some grades of HSS also contain cobalt.

23.21 What are some of the new problems introduced by machining dry?

Problems with dry machining include (1) overheating the tool, (2) operating at lower cutting speeds and production rates to prolong tool life, and (3) absence of chip removal benefits that are provided by cutting fluids in grinding and milling.

Cutting Fluid Filtration Advantages:

Prolong cutting fluid life between changes Reduce fluid disposal cost Cleaner fluids reduce health hazards Lower machine tool maintenance Longer tool life

Tool Geometry Two categories:

Single point tools -Used for turning, boring, shaping, and planing Multiple cutting edge tools - Used for drilling, reaming, tapping, milling, broaching, and sawing

Synthetic Diamonds

Sintered polycrystalline diamond (SPD) - fabricated by sintering very fine‐grained diamond crystals under high temperatures and pressures into desired shape with little or no binder

23.11 Identify some of the common compounds that form the thin coatings on the surface of coated carbide inserts.

The common coatings are: TiN, TiC, and Al2O3.

23.6 In addition to cutting speed, what other cutting variables are included in the expanded version of the Taylor tool life equation?

The expanded version of the Taylor equation can include any of the following: feed, depth of cut, and/or work material hardness.

23.17 What are the principal lubricating mechanisms by which cutting fluids work?

There are two lubricating mechanisms that are believed to be effective in metal cutting: (1) boundary lubrication, which involves the formation of a thin fluid film to help separate and protect the contacting surfaces; and (2) extreme pressure lubrication, in which a thin solid layer of a salt such as iron sulfide is formed on the tool surface to provide lubrication.

Cutting Fluids Pros

Two main problems addressed by cutting fluids: 1. Heat generation at shear and friction zones 2. Friction at tool-chip and tool-work interfaces Other functions and benefits: -Wash away chips (e.g.,grinding and milling) -Reduce temperature of work part for easier handling - Improve dimensional stability of workpart

23.3 What are the two principal locations on a cutting tool where tool wear occurs?

Wear occurs on the top face of the cutting tool as crater wear and on the side or flank of the tool, called flank wear. Portions of flank wear are often identified separately as notch wear, corresponding to the surface of the work; and nose radius wear, corresponding to the tool point.

Cubic Boron Nitride

Next to diamond, cubic boron nitride (cBN) is hardest material known

Coolants

designed to reduce effects of heat in machining -Water used as base in coolant‐type cutting fluids -Most effective at high cutting speeds where heat generation and high temperatures are problems -Most effective on tool materials that are most susceptible to temperature failures (e.g., HSS)

Toughness

to avoid fracture failure

23.4 MC Which of the following is not a common ingredient in cemented carbide cutting tools (two correct answers): (a) Al2O3, (b) Co, (c) CrC, (d) TiC, and (e) WC?

A, C

23.8 MC Which of the following processes are used to provide the thin coatings on the surface of coated carbide inserts (two best answers): (a) chemical vapor deposition, (b) electroplating, (c) physical vapor deposition, (d) pressing and sintering, and (e) spray painting?

A, C

23.2 MC As an alloying ingredient in high-speed steel, tungsten serves which of the following functions (two best answers): (a) forms hard carbides to resist abrasion, (b) improves strength and hardness, (c) increases corrosion resistance, (d) increases hot hardness, and (e) increases toughness?

A, D

23.5 MC An increase in cobalt content has which of the following effects on WC-Co cemented carbides (two best answers): (a) decreases hardness, (b) decreases transverse rupture strength, (c) increases hardness, (d) increases toughness, and (e) increases wear resistance?

A, D

23.7 What are some of the tool life criteria used in production machining operations?

As identified in the text, tool life criteria used in production include (1) complete failure of the tool, (2) visual observation of flank or crater wear, (3) fingernail test to feel flank wear, (4) sound of the tool, (5) chip disposal problems, (6) degradation of finish, (7) power increase, (8) workpiece count, and (9) length of cutting time for the tool.

23.9 MC Which one of the following materials has the highest hardness: (a) aluminum oxide, (b) cubic boron nitride, (c) high-speed steel, (d) titanium carbide, or (e) tungsten carbide?

B

23.3 MC Cast cobalt alloys typically contain which of the following main ingredients (three best answers): (a) aluminum, (b) cobalt, (c) chromium, (d) iron, (e) nickel, (f) steel, and (g) tungsten?

B, C, G

23.10 Which of the following are the two main functions of a cutting fluid in machining (two best answers): (a) improve surface finish on the workpiece, (b) reduce forces and power, (c) reduce friction at the tool-chip interface, (d) remove heat from the process, and (e) wash away chips?

C, D

23.10 What is the difference in ingredients between steel cutting grades and nonsteel-cutting grades of cemented carbides?

In general, non-steel cutting grades contain only WC and Co. Steel cutting grades contain TiC and/or TaC in addition to WC-Co.

Cermets

Metal + Ceramic Materials Combinations of TiC, TiN, and titanium carbonitride (TiCN), with nickel and/or molybdenum as binders

Ceramics

Primarily fine‐grained Al2O3, pressed and sintered at high pressures and temperatures into insert form with no binder

23.14 Identify the alternative ways by which a cutting tool is held in place during machining.

There are three principal ways: (1) solid shank, in which the cutting edge is an integral part of the tool shank, an example being high speed steel tooling; (2) brazed inserts, used for some cemented carbides; and (3) mechanically clamped inserts, used for most hard tool materials including cemented carbides, coated carbides, cermets, ceramics, SPD, and CBN.