Chapter 23

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).

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) and (c).

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) and (c).

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) and (d).

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) and (d).

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), and (f).

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).

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), and (g).

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).

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) and (d).

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.

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.

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.

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.

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.

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.

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.

List five characteristics of a good tool material.

The characteristics of a good tool material are the following, as indicated in the video: (1) it is harder than the workpiece, (2) it retains hardness at high temperatures, (3) it resists wear and thermal shock, (4) it has impact resistant, and (5) it is chemically inert.

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.

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.

What are the factors a machinist should know in order to select the proper tooling? List at least five.

The factors a machinist must know in order to select the proper tooling are (1) workpiece starting and finished shape, (2) workpiece hardness, (3) workpiece tensile strength, (4) material abrasiveness, (5) whether the material breaks into short chips or long stringy chips, (6) workholding setup, and (6) power and speed capacity of the machine tool.

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.

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.

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).

According to the video clip, what is the objective in selection of cutting tools for a given operation?

The objective when choosing a cutting tool is to safely machine a workpiece in the shortest amount of time while meeting the part's quality requirement. Furthermore, the tooling should be the least costly and least complex to meet the production demands.

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.

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.

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.

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

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

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.

List the two principal categories of cutting tools.

The two principal categories of cutting tools are (1) single-point cutting tools (used on lathes) and (2) multi point cutting tools (used on mills, drills, reamers, and taps).

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.

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.

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.

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.