ME 383 Exam 3- CH 21: Theory of Metal Machining

Other machining operations:

Shaping and planning Broaching Sawing

21.4 Name the three most common machining processes.

The three common machining processes are (1) turning, (2) drilling, and (3) milling.

21.13 MC Which of the following cutting conditions has the strongest effect on cutting temperature: (a) feed or (b) speed?

B speed

Finishing

completes part geometry § Final dimensions, tolerances, and finish § Low feeds and depths, high cutting speeds

Negative rake angles

• Make the tool more blunt, increasing the strength of the cutting edge. • Increase the cutting forces. • Can increase friction, resulting in higher temperatures. • Can improve surface finish.

Four Basic Types of Chip in Machining

1. Discontinuous chip 2. Continuous chip 3. Continuous chip with Built-up Edge (BUE) 4. Serrated chip

Types of Conventional Machining (4)

1. Turning and related operations 2. drilling and related operations 3. milling 4. other machining operations

Machine Tool

A power‐driven machine that performs a machining operation, including grinding

21.2 MC A lathe is used to perform which one of the following manufacturing operations: (a) broaching, (b) drilling, (c) lapping, (d) milling, or (e) turning?

E, turning

21.2 What distinguishes machining from other manufacturing processes?

In machining, material is removed from the workpart so that the remaining material is the desired part geometry.

High cutting temperatures result in the following:

Reduce tool life Produce hot chips that pose safety hazards to the machine operator Can cause inaccuracies in part dimensions due to thermal expansion of work material

Serrated Chip

Semicontinuous - saw-tooth appearance Cyclical chip forms with alternating high shear strain then low shear strain Associated with difficult-to-machine metals at high cutting speeds

21.17 What is the specific energy in metal machining?

Specific energy is the amount of energy required to remove a unit volume of the work material.

21.1 MC Which of the following manufacturing processes are classified as material removal processes (two correct answers): (a) casting, (b) drawing, (c) extrusion, (d) forging, (e) grinding, (f) machining, (g) molding, (h) pressworking, and (i) spinning?

(e) and (f)

Types of material removal processes (3)

1) conventional machining 2) Abrasive processes 3) Nontraditional machining

Types of Nontraditional Machining (4)

1. Mechanical Energy processes 2. Electrochemical Machining 3. Thermal energy processes 4. Chemical Machining

21.11 MC Which one of the following metals would usually have the lowest unit horsepower in a machining operation: (a) aluminum, (b) brass, (c) cast iron, or (d) steel?

A aluminum

21.8 What is a machine tool?

A machine tool can be defined as a power-driven machine that positions and moves a tool relative to the work to accomplish machining or other metal shaping process.

21.7 Explain the difference between roughing and finishing operations in machining.

A roughing operation is used to remove large amounts of material rapidly and to produce a part geometry close to the desired shape. A finishing operation follows roughing and is used to achieve the final geometry and surface finish.

21.19 What is a tool-chip thermocouple?

A tool-chip thermocouple is comprised of the tool and chip as the two dissimilar metals forming the thermocouple junction; as the tool-chip interface heats up during cutting, a small voltage is emitted from the junction that can be measured to indicate cutting temperature.

21.1 What are the three basic categories of material removal processes?

As organized in this text, the three basic categories of material removal processes are (1) conventional machining, (2) abrasive processes, and (3) nontraditional processes.

21.7 MC The chip thickness ratio is which one of the following: (a) tc/to, (b) to/tc, (c) f/d, or (d) to/w, where tc = chip thickness after the cut, to = chip thickness before the cut, f = feed, d = depth, and w = width of cut?

B to/tc

21.9 MC According to the Merchant equation, an increase in rake angle would have which of the following results, all other factors remaining the same (two best answers): (a) decrease in friction angle, (b) decrease in power requirements, (c) decrease in shear plane angle, (d) increase in cutting temperature, and (e) increase in shear plane angle?

B and E

21.10 MC In using the orthogonal cutting model to approximate a turning operation, the chip thickness before the cut to corresponds to which one of the following cutting conditions in turning: (a) depth of cut d, (b) feed f, or (c) speed v?

B, feed

Discontinuous Chip

Brittle work materials Low cutting speeds Large feed and depth of cut High tool‐chip friction

21.12 MC For which one of the following values of chip thickness before the cut to would you expect the specific energy in machining to be the greatest: (a) 0.010 inch, (b) 0.025 inch, (c) 0.12 mm, or (d) 0.50 mm?

C

21.5 MC A roughing operation generally involves which one of the following combinations of cutting conditions: (a) high v, f, and d; (b) high v, low f and d; (c) low v, high f and d; or (d) low v, f, and d, where v = cutting speed, f = feed, and d = depth?

C low v, high f and d

21.8 MC Which one of the four types of chip would be expected in a turning operation conducted at low cutting speed on a brittle work material: (a) continuous, (b) continuous with built-up edge, (c) discontinuous, or (d) serrated?

C, discontinuous

21.3 MC With which one of the following geometric forms is the drilling operation most closely associated: (a) external cylinder, (b) flat plane, (c) round hole, (d) screw threads, or (e) sphere?

C, round hole

21.6 What are the parameters of a machining operation that are included within the scope of cutting conditions?

Cutting conditions include speed, feed, depth of cut, and whether or not a cutting fluid is used.

21.4 MC If the cutting conditions in a turning operation are cutting speed = 300 ft/min, feed = 0.010 in/rev, and depth of cut = 0.100 inch, which one of the following is the material removal rate: (a) 0.025 in3/min, (b) 0.3 in3/min, (c) 3.0 in3/min, or (d) 3.6 in3/min?

D, 3.6 in^3/min

21.6 MC Which of the following are characteristics of the orthogonal cutting model (three best answers): (a) a circular cutting edge is used, (b) a multiple-cutting-edge tool is used, (c) a single-point tool is used, (d) only two dimensions play an active role in the analysis, (e) the cutting edge is parallel to the direction of cutting speed, (f) the cutting edge is perpendicular to the direction of cutting speed, and (g) the two elements of tool geometry are rake and relief angle?

D, F, G

Continuous with Build Up Edge (BUE)

Ductile materials Low‐to‐medium cutting speeds Tool-chip friction causes portions of chip to adhere to rake face BUE forms, then breaks off, cyclically

Continuous Chip

Ductile work materials High cutting speeds Small feeds and depths Sharp cutting edge Low tool‐chip friction

21.9 What is an orthogonal cutting operation?

Orthogonal cutting involves the use of a wedge- shaped tool in which the cutting edge is perpendicular to the direction of speed motion into the work material.

21.10 Why is the orthogonal cutting model useful in the analysis of metal machining?

Orthogonal cutting is useful in the analysis of metal machining because it simplifies the rather complex three-dimensional machining situation to two dimensions. In addition, the tooling in the orthogonal model has only two parameters (rake angle and relief angle), which is a simpler geometry than a single-point tool.

Roughing

Removes large amounts of material from starting work part § Some material remains for finish cutting § High feeds and depths, low speeds

Turning

Single point cutting tool removes material from a rotating workpiece to form a cylindrical shape

21.15 Describe in words what the Merchant equation tells us.

The Merchant equation states that the shear plane angle increases when rake angle is increased and friction angle is decreased.

21.12 Identify the four forces that act upon the chip in the orthogonal metal cutting model but cannot be measured directly in an operation.

The four forces that act upon the chip are (1) friction force, (2) normal force to friction, (3) shear force, and (4) normal force to shear

21.11 Name and briefly describe the four types of chips that occur in metal cutting.

The four types are (1) discontinuous, in which the chip is formed into separated segments; (2) continuous, in which the chip does not segment and is formed from a ductile metal; (3) continuous with built-up edge, which is the same as (2) except that friction at the tool-chip interface causes adhesion of a small portion of work material to the tool rake face, and (4) serrated, which are semi-continuous in the sense that they possess a saw-tooth appearance that is produced by a cyclical chip formation of alternating high shear strain followed by low shear strain.

21.16 How is the power required in a cutting operation related to the cutting force?

The power required in a cutting operation is equal to the cutting force multiplied by the cutting speed.

21.3 Identify some of the reasons why machining is commercially and technologically important.

The reasons include the following: (1) it is applicable to most materials; (2) it can produce a variety of geometries to a part; (3) it can achieve closer tolerances than most other processes; and (4) it can create good surface finishes.

21.14 What is the relationship between the coefficient of friction and the friction angle in the orthogonal cutting model?

The relationship is that the coefficient of friction is the tangent of the friction angle (μ = tan β).

21.18 What does the term size effect mean in metal cutting?

The size effect refers to the fact that the specific energy increases as the cross-sectional area of the chip (to x w in orthogonal cutting or f x d in turning) decreases.

21.5 What are the two basic categories of cutting tools in machining? Give two examples of machining operations that use each of the tooling types.

The two categories are (1) single-point tools, used in operations such as turning and boring; and (2) multiple-edge cutting tools, used in operations such as milling and drilling.

21.13 Identify the two forces that can be measured in the orthogonal metal cutting model.

The two forces that can be measured in the orthogonal metal cutting model are (1) cutting force and (2) thrust force.

Drilling

Used to create a round hole, usually by means of a rotating tool (drill bit) with two cutting edges

Machining

material removal by a sharp cutting tool, e.g., turning, milling, drilling

Abrasive processes

material removal by hard, abrasive particles e.g. grinding

Nontraditional processes

various energy forms other than sharp cutting tool to remove material

Milling

~ Rotating multiple-cutting-edge tool is moved across work to cut a plane or straight surface ~Two forms: peripheral milling (left) and face milling

positive rake angles

• Make the tool more sharp and pointed. This reduces the strength of the tool, as the small included angle in the tip may cause it to chip away. • Reduce cutting forces and power requirements. • Helps in the formation of continuous chips in ductile materials.

Types of Abrasive Processes (2)

1. Grinding operations 2. other abrasive processes