Machining with CBN Tools Quiz

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Questions and Answers

What is generally NOT recommended for machining conventional materials with cubic boron nitride (CBN) tools?

Using a water-soluble coolant

Using a negative rake angle

Using a large lead angle

Using high cutting speeds (correct)

When using square or triangular CBN inserts, what lead angle is generally advised?

10 degrees

15 degrees, or 45 degrees when possible (correct)

5 degrees

90 degrees

For most applications, what negative rake angle is recommended for cubic boron nitride cutting tools?

0 degrees

20 degrees

15 degrees

5 degrees (correct)

What is the typical range of room temperature hardness for ordinary high-speed steels?

63 Rc to 65 Rc (D) Signup and view all the answers

What is the typical range recommended for the relief angle when using CBN cutting tools?

5 to 9 degrees (B) Signup and view all the answers

Which of the following is NOT a typical factor determining tool life?

The relief angle of the cutting tool (A) Signup and view all the answers

At approximately what temperature do high-speed steels retain enough hardness to cut effectively?

1,000 or 1,100°F (573 or 593°C) (A) Signup and view all the answers

Which of the following is NOT a principal alloying element in high-speed steels?

Nickel (Ni) (B) Signup and view all the answers

What is a common criterion for measuring tool wear when evaluating tool life?

The amount of flank wear on the tool (C) Signup and view all the answers

What is the primary designation prefix for molybdenum high-speed steels?

M (B) Signup and view all the answers

According to the provided content, what type of coolant is recommended when using CBN tools?

Water-soluble type coolant (B) Signup and view all the answers

What does ANSI B94.55M primarily define?

The end of tool life as a given amount of wear on the flank of a tool (D) Signup and view all the answers

What is the effect of adding 5 to 12 percent cobalt to high-speed steel?

It increases hardness at cutting temperatures and enhances wear resistance, but slightly increases brittleness. (C) Signup and view all the answers

Which type of high-speed steel is recommended for machining tough die steels and other difficult to cut materials?

The M40 series of super high-speed steels. (D) Signup and view all the answers

What property makes cobalt high speed steels suitable for roughing cuts in abrasive materials?

High hardness at elevated temperatures (A) Signup and view all the answers

When are the super high-speed steels such as M40 series and T15 usually heat treated to 67-68 Rc?

To reduce their brittleness and tendency to chip, making them more practical for cutting applications. (A) Signup and view all the answers

Which parameter should generally be selected first when determining machining settings?

Depth of cut (C) Signup and view all the answers

What type of cutting speed data is found in the left-most columns of the cutting speed tables?

Traditional speeds for high-speed steel (HSS) tools (B) Signup and view all the answers

What is a key limitation of traditional speeds and feeds when planning machining operations?

Tool life varies greatly, making it difficult to plan for efficient production cycles (B) Signup and view all the answers

What are the two types of combined feed/speed data provided in the speed tables?

Optimum and average (C) Signup and view all the answers

Where can the feed and depth of cut factors be found for turning operations?

Table 5c (A) Signup and view all the answers

What information specifically can be found in the footnotes of Tables 1, 10 and 17?

Important notes concerning use of the tables (C) Signup and view all the answers

What tables provide data for milling operations specifically?

Tables 10 through 15e (B) Signup and view all the answers

In the feed/speed data tables, what does the first number in a feed/speed set typically represent?

Feed in thousandths of an inch per revolution or tooth (C) Signup and view all the answers

What does a blank cell indicate in the feed/speed data tables?

No data existed for that material at the time of publication (A) Signup and view all the answers

What is the primary difference between the 'optimum' and 'average' feed/speed data sets?

Optimum is for lower final cost while maintaining tool life, average is for normal productivity. (A) Signup and view all the answers

According to the tool life equations used in the COMP program, what does 'equivalent chip thickness (ECT)' simplify?

Cutting speed, tool life predictions, and calculation of cutting forces and torques. (C) Signup and view all the answers

According to the information provided, what is one of the main uses for the average feed/speed data?

To provide similar tool life as the optimum data, but with different productivity (C) Signup and view all the answers

What is the main characteristic of the 'optimum' feed value provided in the tables, generally?

It represents the maximum safe feed for a given tool and work material (B) Signup and view all the answers

What was used to determine the feed/speed data in the tables according to the text?

A computer program and a large database of cutting speed and tool life testing data. (B) Signup and view all the answers

When might feeds greater than the optimum feed be acceptable?

When milling, if the radial depth of cut is less than a specified value. (A) Signup and view all the answers

What is the primary concept that Equivalent Chip Thickness (ECT) combines?

Depth of cut, lead angle, nose radius, and feed per revolution. (B) Signup and view all the answers

Who first introduced the concept of Equivalent Chip Thickness (ECT)?

Prof. R. Woxen. (A) Signup and view all the answers

How is Equivalent Chip Thickness (ECT) mathematically defined?

ECT = A / CEL (C) Signup and view all the answers

What does a constant value of ECT imply regarding tool life, when cutting speed is constant?

Tool life remains constant. (D) Signup and view all the answers

How does an increase in cutting speed affect tool life, when ECT is held constant?

Tool life decreases. (C) Signup and view all the answers

What happens to tool life if ECT is increased while maintaining a constant cutting speed?

Tool life decreases. (A) Signup and view all the answers

Which of the following is NOT explicitly mentioned as an input parameter to calculate ECT for operations beyond simple material removal like turning?

Coolant flow rate. (D) Signup and view all the answers

What do 'optimum' and 'average' feed/speed data represent in the context of ECT?

Same overall tool life, but different ECT, with optimum using maximum ECT and average using half of maximum ECT. (D) Signup and view all the answers

When needing to reduce the size of a cut while staying within the power capacity of the machine, which parameter should be reduced first?

Cutting speed (D) Signup and view all the answers

For indexable insert drilling, the feed/speed data is based on a tool with a specific insert nose radius. What is this radius?

3/64 inch (1.2mm) (C) Signup and view all the answers

When making adjustments to cutting speed for indexable insert drilling, what depth of cut is used in Table 5a?

One-half of the drill diameter (D/2) (A) Signup and view all the answers

For short hole drilling using the provided feed/speed data, approximately what is the expected tool life?

15 minutes (C) Signup and view all the answers

When threading or tapping, the feed used should be equal to which parameter of the thread?

The lead (or pitch) (B) Signup and view all the answers

For tapping and threading, what is the expected tool life at the given feeds and speeds?

45 minutes (C) Signup and view all the answers

When drilling a material with a desired feed of 0.012 in/rev and an optimum feed of 0.016 in/rev, what is the calculated ratio of the feeds?

0.75 (B) Signup and view all the answers

If the speed ratio (Vavg/Vopt) of a machining operation is approximately 2, which of these numerical values is most likely the average to optimum speed ratio given by the text?

95/50 (D) Signup and view all the answers

Study Notes

Machining Operations - Cutting Speeds and Feeds

Materials vary greatly in machining characteristics; certain metals can be grouped based on microstructure and cold work.
Microstructure and cold work significantly affect a metal's machinability.
Harder metals are more difficult to machine than softer ones.
Cutting temperature impacts machining, requiring lower speeds for harder materials to prevent tool failure.
Hardness alone is insufficient for determining cutting speeds; microstructure is crucial.
Microstructures can have same hardness but different machining behavior.
Machining scale differences on ferrous metal castings; various degrees of difficulty.
Electrochemical treatments sometimes eliminate scale effects, but not commonly encountered.
Cutting speed reduction (5-10%) is recommended when dealing with casting scale.
Hard spots and metallurgical differences in a single metal piece, resulting from variations in cooling rate, can affect machinability.
Steel bar stock's hardness generally stronger at the outside of the bar compared to center.

Cutting Tool Materials

High-speed steel (HSS) is a common cutting tool material; various grades with varying temperature hardness.
Tungsten and molybdenum high-speed steels differ slightly in performance.
Cobalt inclusion increases hardness and wear resistance at high temperatures, often used in single-point cutting tools and for abrasive applications.
Cemented carbides (sintered carbides, or simply carbides), superior to HSS in hardness and wear resistance.
Coated carbides, utilizing TiC, TiN, or Al2O3 coatings, enhance performance at faster cutting speeds; superior to uncoated carbides.
Ceramics (aluminum oxide), and cermets often used for high-speed applications in highly abrasive materials.
The hardest known material for cutting is cubic boron nitride (CBN), resistant to high temperatures and suitable for extremely hard and tough materials.
Diamond cutting tools are extremely wear-resistant and recommended for machining abrasive materials.
Diamond tools available in multiple forms: single-crystal, polycrystalline, CVD.

Cutting Speeds and Feeds

Choosing optimum speeds and feeds is essential for minimizing costs and maximizing productivity.
Tool life, defined as the time taken for a tool to reach a specific amount of wear, is affected by cutting conditions: speed, feed, and depth of cut.
Depth of cut is typically chosen first, followed by feed, then cutting speed.
Appropriate cutting speeds and feeds for various materials and tool types are provided in tables; these values offer guides rather than precise specifications.
Cutting speed tables offer two datasets for maximum speed/productivity (optimum) or average speed/less productivity (average for a given tool life).
Tables are organized by material type and cutting tool material for specific machining applications.
Tool life adjustment factors for various feeds and depths of cut are also included.

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Description

Test your knowledge on the machining properties and recommendations for using cubic boron nitride (CBN) tools. This quiz covers tool angles, material hardness, cooling methods, and factors influencing tool life. Perfect for students and professionals in machining and materials engineering.