Machining Science and Process Mechanics

Introduction and Context

Machining is the controlled removal of material from a workpiece to produce a required geometry, dimensional accuracy, surface finish, and functional surface condition. In CNC manufacturing, the programmed tool path determines where material is removed, while machining science explains how removal occurs. Understanding chip formation, cutting forces, heat, tool wear, and surface integrity is therefore essential for selecting cutting parameters and achieving reliable production.

Machining is neither a purely geometric operation nor a simple shearing process. The tool interacts with the workpiece through severe plastic deformation, friction, heat generation, elastic recovery, and sometimes chemical or abrasive action. These phenomena influence dimensional error, tool life, energy consumption, productivity, and the quality of the finished component.

This chapter develops the mechanics of conventional cutting, with emphasis on concepts directly applicable to CNC turning, milling, drilling, and related processes. The same principles also support process planning for hybrid and additive–subtractive manufacturing systems.

Learning Objectives

After studying this chapter, the reader should be able to:

1. Explain chip formation using the primary, secondary, and tertiary deformation zones.
2. Distinguish continuous, segmented, discontinuous, and built-up-edge chips.
3. Calculate cutting speed, material removal rate, cutting force, power, and specific cutting energy.
4. Explain the effect of tool geometry, workpiece material, and cutting parameters on forces and temperature.
5. Describe tool-wear mechanisms and apply Taylor’s tool-life relationship.
6. Select cutting fluids according to machining requirements and environmental constraints.
7. Explain machinability and surface integrity, including residual stress and thermal damage.
8. Develop a defensible starting set of cutting parameters for a CNC operation.

1. The Mechanics of Chip Formation

1.1 Material removal as plastic deformation

In ductile machining, the tool penetrates the workpiece and compresses the material ahead of its rake face. The material then undergoes intense plastic deformation and flows upward as a chip. Most deformation occurs in a narrow region called the primary shear zone. Additional deformation occurs as the chip slides along the tool rake face and as the newly generated surface passes over the tool flank.

A useful idealization is orthogonal cutting, in which the cutting edge is perpendicular to the cutting velocity and chip flow is two-dimensional. Although real cutting is usually oblique and three-dimensional, orthogonal cutting provides a foundation for understanding force and chip mechanics.

Figure: Idealized orthogonal cutting model showing the shear plane and chip flow.

1.2 Deformation zones

Three zones are commonly identified:

• Primary deformation zone: material shears along an approximately inclined plane or narrow band. This zone determines much of the chip compression and cutting energy.
• Secondary deformation zone: friction and plastic deformation occur where the chip slides over the rake face. This zone is a major source of heat.
• Tertiary deformation zone: rubbing and ploughing occur between the tool flank and the newly machined surface. This zone affects surface finish, residual stress, and flank wear.

The actual shear region is not an infinitely thin plane. The shear-plane model is an approximation useful for analysis, especially when deformation is concentrated and the work material is reasonably homogeneous.

1.3 Chip ratio and shear angle

Let the uncut chip thickness be t₁ and the chip thickness after cutting be t₂. The chip ratio is:

Here, r is dimensionless. Since the chip is usually thicker than the uncut layer, 0 < r < 1. Under orthogonal cutting, with rake angle α and shear angle φ, geometry gives:

Angles are measured in consistent units, normally degrees for reporting or radians in analytical work. This expression assumes plane-strain orthogonal cutting, a defined single shear plane, negligible elastic recovery, and uniform chip width.

A larger shear angle generally reduces the shear-plane area and therefore reduces cutting energy. Positive rake angles commonly increase the shear angle, while high friction tends to reduce it.

The chip thickness ratio can be measured experimentally. For example, if t₁ = 0.20 mm and t₂ = 0.50 mm, then r = 0.40. With a rake angle of 10°, the shear angle is approximately 24°. This calculation is an estimate because real chips may have curved shear bands, segmentation, or nonuniform thickness.

1.4 Types of chips

Continuous chips form when a ductile material is cut under stable conditions, usually with a sharp tool, suitable rake angle, and moderate-to-high cutting speed. They can produce good surface finish but may create dangerous entanglement in CNC equipment. Chip breakers and high-pressure coolant are often used to control them.

Discontinuous chips form as separate fragments. They are common in brittle materials such as cast iron, or when ductile materials are machined at low speed, with excessive feed, or under conditions of unstable deformation. They may reduce chip-entanglement risk but can increase vibration and surface roughness.

Segmented or saw-tooth chips contain repeated localized shear bands. They are common when machining titanium alloys, nickel-based alloys, hardened steels, and other materials with low thermal conductivity or strong strain-rate sensitivity. Their formation causes fluctuating forces and temperature.

Built-up-edge chips occur when work material adheres to the tool near the cutting edge. The adhered material may periodically grow and break away, causing dimensional variation, poor surface finish, and unstable forces. It is promoted by unsuitable speed, high friction, insufficient lubrication, and certain workpiece–tool material combinations.

2. Cutting Geometry and Kinematics

2.1 Important tool angles

Tool geometry affects chip flow, cutting forces, heat, edge strength, and surface integrity. Important angles include rake angle, clearance angle, cutting-edge inclination, approach angle, and nose radius.

A positive rake angle generally lowers the force required to shear material and improves chip flow, but it reduces the wedge angle and may weaken the cutting edge. A negative or small rake angle strengthens the edge and is useful for hard or interrupted cutting, but generally increases forces and heat.

The clearance angle prevents the flank from rubbing against the workpiece. Too little clearance increases rubbing and heat; too much clearance weakens the wedge. Nose radius affects finish and edge strength. A larger radius can improve finish at an appropriate feed, but it increases radial force and may promote chatter in a flexible setup.

2.2 Cutting speed, feed, and depth of cut

For turning, cutting speed is related to workpiece diameter and spindle speed by:

where V is cutting speed in m/min, D is workpiece diameter in mm, and N is spindle speed in rev/min. Therefore:

These equations assume the diameter at the cutting point is used and neglect effects such as tool nose geometry and eccentricity.

For milling, the cutting speed is similarly:

where D is cutter diameter. The feed rate is:

where v_f is table feed in mm/min, f_z is feed per tooth in mm/tooth, z is the number of teeth, and N is spindle speed in rev/min.

2.3 Material removal rate

For turning, an approximate material removal rate is:

where MRR is in mm³/min, V is in m/min, f is feed in mm/rev, and a_p is depth of cut in mm. The factor 1000 converts metres to millimetres.

For milling, a commonly used approximation is:

where a_p is axial depth of cut in mm, a_e is radial width of cut in mm, and v_f is feed in mm/min. These are geometric estimates; actual removal can differ because of tool engagement, runout, interrupted cutting, and machine limitations.

3. Cutting Forces and Power

3.1 Force components

In orthogonal cutting, the measured forces are commonly resolved into:

• F_c, the cutting-force component in the cutting-velocity direction;
• F_t, the thrust-force component normal to the cutting direction.

The resultant force is:

The power required for cutting is approximately:

where P_c is cutting power in watts, F_c is in newtons, and v is cutting speed in m/s. If speed is supplied in m/min, use v = V/60. Motor power must be higher than cutting power because of transmission and machine losses:

where η is overall efficiency, with 0 < η ≤ 1.

The specific cutting energy is:

It is often expressed in J/mm³ when power is in J/min and material removal rate is in mm³/min. Specific energy includes deformation and friction losses and is not identical to a material’s tensile strength.

Worked Example 1: Turning power and removal rate

A steel bar of diameter 50 mm is turned at 800 rev/min with feed 0.25 mm/rev and depth of cut 2 mm. The measured cutting force is 1,200 N. Determine cutting speed, removal rate, and cutting power.

First,

V = π(50)(800)/1000 = 125.7 m/min.

The removal rate is:

MRR = 1000(125.7)(0.25)(2) = 62,850 mm³/min.

Convert cutting speed to m/s: v = 125.7/60 = 2.095 m/s. Thus:

P_c = 1200 × 2.095 = 2514 W ≈ 2.51 kW.

If machine efficiency is 85%, required motor power is approximately 2.51/0.85 = 2.95 kW. The selected machine should provide additional capacity for acceleration, transient loads, tool wear, and interrupted engagement.

3.2 Merchant force analysis

For orthogonal cutting, the friction force on the rake face and the normal force are:

The apparent friction coefficient is:

The shear force along the shear plane is:

and the shear-plane area is:

where b is the width of cut. The average shear stress is τ_s = F_s/A_s. These relationships assume orthogonal cutting, uniform stress, a single shear plane, and force measurements resolved in the correct directions. They are useful engineering approximations rather than complete descriptions of three-dimensional machining.

4. Heat Generation and Temperature

Machining heat is generated mainly in the primary shear zone, secondary tool–chip contact zone, and tertiary tool–workpiece contact zone. The total heat rate is related to the mechanical power dissipated, but heat partition among chip, tool, workpiece, and coolant varies with speed, geometry, thermal conductivity, contact length, and cooling conditions.

The chip often carries away a large proportion of heat at high cutting speed. However, the tool tip can still reach a high temperature because the contact area is small and the heat flux is intense. Excessive temperature softens many tool materials, accelerates diffusion and oxidation, promotes crater wear, and can thermally damage the workpiece.

Temperature is influenced by:

• cutting speed, usually the most influential basic parameter;
• feed and depth of cut, which increase force and heat generation;
• tool geometry and rake angle;
• workpiece and tool thermal conductivity;
• friction and built-up edge;
• coolant delivery and concentration;
• tool wear and contact length.

Temperature measurements may use thermocouples, infrared methods, thermal paints, or embedded sensors. Each technique has calibration, response-time, emissivity, or disturbance limitations. Temperature should not be inferred solely from visible chip colour, particularly in automated production.

5. Tool Wear and Tool Life

5.1 Principal wear mechanisms

Flank wear develops on the clearance face because of abrasion, adhesion, diffusion, and rubbing. It directly changes the effective tool geometry and can produce dimensional error and poor surface finish.

Crater wear develops on the rake face where the chip slides. It is associated with high temperature, diffusion, adhesion, and chemical interaction. Excessive crater wear weakens the cutting edge.

Notch wear occurs locally at the depth-of-cut line. It may result from work-hardening, oxidation, or abrasive interaction with a hardened surface layer.

Chipping and fracture occur when the cutting edge is overloaded, weakened by excessive wear, subjected to interrupted cutting, or exposed to vibration. They are often sudden and catastrophic.

Plastic deformation occurs when temperature and stress exceed the hot strength of the tool material. The edge may collapse or deform even without a conventional wear scar.

Tool wear is monitored by direct methods, such as optical measurement of flank-wear land, and indirect methods, such as spindle power, acoustic emission, vibration, force, or surface-finish monitoring. In industrial CNC systems, indirect signals can support predictive maintenance, but they require process-specific calibration.

5.2 Taylor tool-life relationship

For a fixed tool–workpiece pair and a specified failure criterion, the basic Taylor relationship is:

where V is cutting speed, T is tool life, n is the experimentally determined exponent, and C is the Taylor constant. Units of V and C must match. The equation assumes that other influential parameters remain constant.

A more general empirical form is:

where f is feed, a_p is depth of cut, and m and p are empirical exponents. The exponents and constant must be obtained for the relevant tool, workpiece, cooling condition, and failure criterion; they should not be transferred uncritically between operations.

Worked Example 2: Tool life

A carbide tool follows VT^0.25 = 600, with speed in m/min and life in minutes. Estimate life at 300 m/min.

T^0.25 = 600/300 = 2. Therefore T = 2⁴ = 16 min. If speed is increased to 400 m/min, life becomes T = (600/400)⁴ = 5.06 min. This illustrates the strongly nonlinear effect of speed on tool life.

The economically optimum speed is not necessarily the speed giving maximum tool life. It depends on tool cost, tool-change time, machine cost, part value, and required quality.

6. Machinability

Machinability is the relative ease with which a material can be machined to an acceptable result. It is multidimensional rather than a single intrinsic material property. Common indicators include:

• achievable tool life at a specified speed;
• cutting force and power;
• surface roughness and dimensional stability;
• chip-control behaviour;
• tendency to form built-up edge;
• sensitivity to work hardening and thermal damage.

Free-machining steels may contain sulphur, lead, or other additions that improve chip breaking and reduce friction, although environmental and health regulations influence material selection. Aluminium alloys are often highly machinable but may adhere to tools. Titanium alloys can be difficult because of low thermal conductivity, high strength at temperature, and chemical affinity for tool materials. Nickel-based superalloys retain strength at high temperature and generate severe thermal and mechanical loads.

Machinability must always be considered with the selected tool material and process. A workpiece that is easy to turn with a sharp carbide tool may be difficult to drill, mill, or finish after heat treatment.

7. Cutting Fluids and Lubrication

Cutting fluids perform four principal functions:

1. Cooling: removing heat from the tool, chip, and workpiece.
2. Lubrication: reducing friction at tool–chip and tool–workpiece interfaces.
3. Chip evacuation: transporting chips away from the cutting zone.
4. Corrosion control: protecting machine and workpiece surfaces.

Fluid types include straight oils, soluble oils, semi-synthetic fluids, and synthetic fluids. Minimum-quantity lubrication supplies a very small amount of lubricant in an air stream. Cryogenic cooling uses substances such as liquid nitrogen or carbon dioxide to reduce temperature without conventional flood-fluid disposal, but it requires appropriate equipment and safety controls.

Flood cooling is not automatically beneficial. In interrupted cutting, thermal shock can damage carbide or ceramic tools. In deep-hole drilling, delivery pressure and direction may be more important than volume. For some aluminium operations, fluid chemistry must be controlled to avoid staining or corrosion. Fluid concentration, contamination, bacterial growth, tramp oil, mist exposure, and disposal require a documented maintenance programme.

Best practice includes selecting fluid according to tool and workpiece materials, directing it accurately to the cutting zone, maintaining concentration within the supplier’s range, using guarding and mist extraction, and recording fluid condition. Personnel exposure and waste management are occupational and environmental responsibilities, not merely process-cost issues.

8. Surface Integrity

Surface integrity includes both surface topography and the altered metallurgical and mechanical condition beneath the surface. It includes roughness, waviness, residual stress, microhardness, plastic deformation, white layers, burns, cracks, and contamination.

8.1 Surface roughness in turning

For an ideal sharp tool in turning, the theoretical arithmetic roughness is often approximated by:

where R_a and f are in the same length units and r_ε is tool nose radius. This expression assumes a geometrically ideal feed mark, a sharp tool, negligible vibration, no built-up edge, and no material tearing. Actual roughness is usually higher because of tool wear, machine deflection, runout, chatter, material behaviour, and edge radius.

A larger nose radius or lower feed can reduce theoretical roughness, but a larger radius increases radial force and may cause chatter. Surface-finish selection must therefore be linked to machine stiffness and workholding.

8.2 Residual stress and thermal damage

Mechanical deformation can produce compressive or tensile residual stress. Compressive stress may improve fatigue resistance in some applications, while tensile stress can promote crack initiation and stress-corrosion failure. Excessive heat may cause tempering, rehardening, white-layer formation, distortion, or thermal cracking in hardened steels and superalloys.

Surface integrity is especially important for aerospace, biomedical, energy, and precision components. A visually acceptable surface can still possess harmful subsurface deformation or residual stress. Inspection may require roughness measurement, hardness testing, metallographic sectioning, residual-stress analysis, or nondestructive testing.

9. Selecting Cutting Parameters

Parameter selection should be treated as a constrained engineering decision rather than a search for the highest nominal speed. A practical sequence is:

1. Identify workpiece material, hardness, geometry, rigidity, and prior surface condition.
2. Select tool material, coating, grade, geometry, and edge preparation.
3. Consult validated manufacturer data for a starting cutting-speed range.
4. Calculate spindle speed from diameter and cutting speed.
5. Select feed from tool capability, required roughness, chip control, and force limits.
6. Select depth of cut according to stock allowance, rigidity, power, and tool engagement.
7. Verify spindle torque, motor power, workholding, tool overhang, coolant delivery, and machine envelope.
8. Conduct a controlled trial and inspect tool wear, chips, forces, finish, and dimensional error.
9. Adjust one principal variable at a time unless a designed experiment is being performed.
10. Document the validated process window.

For a turning operation, spindle speed may be calculated as N = 1000V/(πD). The selected value should be checked against the machine’s maximum speed and constant-surface-speed control. During facing, the diameter changes continuously, so CNC control may vary spindle speed to maintain the programmed surface speed; maximum-speed limits must be set to prevent overspeeding near the centre.

Parameter selection is also a systems problem. A tool may tolerate a high feed, but the machine may lack torque. A high-speed spindle may provide sufficient power but insufficient stiffness. A stable cut may become unstable when the tool extends farther from the holder. Consequently, cutting data should be validated in the actual machine, holder, workholding, and component configuration.

10. Applied Case: CNC Turning of a Hardened Steel Sleeve

Background

This illustrative case concerns a CNC turning cell producing hardened steel sleeves. The sleeve requires a 0.8 μm Ra finish on an outside diameter and a tight dimensional tolerance. Initial production shows short tool life, occasional chatter, and inconsistent size.

Problem

The initial process uses a small nose-radius carbide insert, high feed, and flood coolant directed near—but not consistently at—the cutting edge. Operators report that some parts meet roughness requirements while others show feed marks and oversize dimensions.

Analysis

Inspection finds progressive flank wear and occasional edge chipping. The small nose radius reduces radial force but produces a pronounced theoretical feed pattern at the selected feed. The workholding is adequate, but tool overhang is longer than necessary. Chatter appears when the insert reaches moderate wear. Intermittent coolant contact may also produce thermal cycling.

The team calculates the spindle speed using the actual work diameter rather than the nominal bar diameter. Cutting power is checked against machine capacity, and a lower feed is evaluated using the theoretical roughness relationship. Because the material is hardened, the process is treated as thermally and mechanically demanding; tool grade and edge preparation are reviewed rather than changing speed alone.

Approach and solution

The revised process uses a more suitable hard-turning insert, reduced tool overhang, a modestly larger nose radius, and a feed selected to satisfy both finish and force constraints. Cutting speed is reduced slightly to establish tool-life stability, while coolant delivery is made consistent. The operator records flank-wear measurements after a defined number of parts and uses a wear limit before dimensional drift becomes unacceptable.

A controlled trial compares three speeds and two feeds. The selected condition is not the fastest trial; it provides stable chips, acceptable power, predictable wear, and consistent roughness. Tool offsets are updated using a documented measurement procedure rather than manual adjustment based only on visual inspection.

Outcome

Tool life becomes more predictable, chatter is reduced, and the proportion of parts meeting the roughness requirement increases. The process also reduces unplanned tool changes. The result demonstrates that surface quality depends on the combined effects of geometry, rigidity, wear state, cooling, and parameters—not on feed alone.

Learning points

• Use actual cutting diameter in speed calculations.
• Separate tool-wear diagnosis from chatter diagnosis.
• Validate cutting data in the complete machine–holder–tool–workpiece system.
• Use measurable wear and quality criteria for tool changes.
• Optimize stability and capability, not only nominal productivity.

11. Challenges, Limitations, and Contemporary Developments

Classical cutting models simplify real machining. They may neglect three-dimensional chip flow, tool edge radius, elastic recovery, temperature-dependent properties, material anisotropy, vibration, runout, and evolving wear. Empirical cutting data are therefore indispensable.

Modern CNC systems increasingly combine force, spindle-power, vibration, acoustic-emission, temperature, and vision data. Machine learning can help classify tool wear or predict surface quality, but models require representative data and must be monitored when tooling, material batches, coolant, or machine conditions change. An unexplained prediction should not override a safety limit or engineering inspection.

Digital twins and process simulations can estimate forces, thermal fields, chatter stability, and tool life before production. Their reliability depends on calibration and accurate representation of machine dynamics. In additive–subtractive systems, machining allowances may vary because deposited material has anisotropic properties, porosity, residual stress, and uncertain stock geometry. Scanning and adaptive tool paths can help, but the underlying mechanics of cutting remain necessary for selecting safe parameters.

Sustainable machining seeks lower energy, reduced fluid consumption, longer tool life, and recyclable or safer materials. A reduction in coolant may increase tool wear or scrap, so sustainability must be assessed over the complete process rather than by fluid volume alone. Life-cycle thinking includes tool manufacture, energy, fluid treatment, rejected parts, and disposal.

Chapter Summary

Machining removes material through severe plastic deformation, friction, and heat generation. Orthogonal cutting models use chip ratio, rake angle, and shear angle to explain chip formation, while real operations also involve three-dimensional chip flow and tool–workpiece contact. Cutting speed, feed, and depth of cut determine removal rate, forces, power, temperature, productivity, and tool life.

Cutting power is approximately the product of cutting force and cutting velocity. Tool wear occurs through flank wear, crater wear, notch wear, chipping, fracture, and plastic deformation. Taylor’s relationship provides a useful empirical connection between cutting speed and tool life, but its constants are specific to the process conditions. Machinability includes tool life, force, chip control, surface finish, and dimensional stability.

Cutting fluids cool, lubricate, evacuate chips, and prevent corrosion, but their selection involves process performance, worker safety, environmental control, and maintenance. Surface integrity includes roughness, residual stress, hardness changes, deformation, and thermal damage. Reliable cutting-parameter selection requires validated data, machine and workholding checks, controlled trials, tool-wear monitoring, and documentation.

Key Terms

Chip formation: The deformation and separation process by which workpiece material becomes a chip.

Primary deformation zone: Region in which the work material undergoes major shear deformation.

Secondary deformation zone: Tool–chip contact region where friction and additional plastic deformation occur.

Tertiary deformation zone: Tool flank–workpiece contact region associated with rubbing and surface alteration.

Chip ratio: Ratio of uncut chip thickness to produced chip thickness.

Shear angle: Angle locating the idealized shear plane relative to the cutting direction.

Rake angle: Tool-face angle influencing chip flow, edge strength, and cutting force.

Cutting speed: Relative speed between the cutting edge and workpiece at the cutting zone.

Feed: Tool advance per revolution, tooth, or other defined cutting cycle.

Depth of cut: Thickness or radial extent of material removed in one pass.

Material removal rate: Volume of material removed per unit time.

Specific cutting energy: Cutting energy required per unit volume of removed material.

Flank wear: Wear land formed on the tool clearance face.

Crater wear: Depression formed on the rake face by chip contact.

Tool life: Usable cutting time before a specified wear or performance limit is reached.

Machinability: Relative ease of producing acceptable machined results.

Built-up edge: Workpiece material adhered near the cutting edge during cutting.

Surface integrity: Topographic, mechanical, metallurgical, and chemical condition of a machined surface.

Residual stress: Stress remaining in a component after external loads are removed.

Minimum-quantity lubrication: Delivery of a very small lubricant quantity, usually entrained in air.

Review Questions

Short Answer Questions

1. What are the primary, secondary, and tertiary deformation zones in machining?
2. Why does a positive rake angle generally reduce cutting force?
3. Distinguish flank wear from crater wear.
4. State two functions of cutting fluids.
5. What is meant by surface integrity?

Long Answer Questions

1. Explain the formation of continuous, discontinuous, segmented, and built-up-edge chips, including the conditions that promote each type.
2. Derive and explain the practical significance of the turning cutting-speed equation.
3. Discuss the major mechanisms of tool wear and the methods used to monitor them.
4. Explain how cutting parameters influence forces, power, heat generation, tool life, and surface finish.
5. Discuss the limitations of Taylor’s tool-life equation and explain how tool-life data should be generated for production.

Analytical / Application Questions

1. A 40 mm diameter bar is turned at 1,000 rev/min with a feed of 0.20 mm/rev and depth of cut 1.5 mm. Calculate cutting speed and approximate material removal rate. State the units and assumptions.
2. A tool obeys VT^0.25=500, with speed in m/min and life in minutes. Compare predicted tool life at 250 m/min and 400 m/min. Explain the production implications.
3. A CNC operation produces acceptable roughness initially but develops oversize dimensions, chatter, and increasing spindle power after several parts. Develop a diagnosis and corrective-action plan using tool wear, rigidity, cutting parameters, coolant, and inspection evidence.

Multiple Choice Questions with Answers

Question 1

Which deformation zone is primarily responsible for shearing the work material into a chip?

A. Primary deformation zone

B. Secondary deformation zone

C. Tertiary deformation zone

D. Elastic recovery zone

Correct Answer: A. Primary deformation zone

Question 2

In orthogonal cutting, if uncut chip thickness is 0.20 mm and produced chip thickness is 0.50 mm, what is the chip ratio?

A. 0.20

B. 0.40

C. 2.50

D. 0.70

Correct Answer: B. 0.40

Question 3

For turning, which equation gives cutting speed in m/min when diameter is in mm and spindle speed is in rev/min?

A. V = DN

B. V = πD/N

C. V = πDN/1000

D. V = 1000πD/N

Correct Answer: C. V = πDN/1000

Question 4

A cutting force of 1,000 N acts at a cutting speed of 2 m/s. What is the approximate cutting power?

A. 0.5 kW

B. 2 kW

C. 500 kW

D. 2,000 kW

Correct Answer: B. 2 kW

Question 5

Which wear form occurs mainly on the tool clearance face and directly affects the generated surface?

A. Crater wear

B. Flank wear

C. Notch wear only

D. Thermal expansion

Correct Answer: B. Flank wear

Question 6

According to the basic Taylor relationship VTⁿ=C, what generally happens to tool life when cutting speed increases?

A. It increases linearly

B. It remains constant

C. It decreases according to an empirical power relationship

D. It becomes independent of tool material

Correct Answer: C. It decreases according to an empirical power relationship

Question 7

Which condition most strongly promotes built-up-edge formation?

A. Low friction and a perfectly sharp edge

B. Adhesion, unsuitable speed, and inadequate lubrication

C. Zero tool–chip contact

D. Only very high thermal conductivity

Correct Answer: B. Adhesion, unsuitable speed, and inadequate lubrication

Question 8

Which statement about specific cutting energy is correct?

A. It is cutting power divided by material removal rate

B. It is always equal to tensile strength

C. It has units of newtons only

D. It is independent of friction and tool geometry

Correct Answer: A. It is cutting power divided by material removal rate

Question 9

The theoretical turning roughness approximation R_a≈f²/(32r_ε) assumes primarily that:

A. The tool is heavily fractured

B. The feed marks are generated by an ideal nose radius

C. The process is always interrupted

D. Coolant eliminates all deformation

Correct Answer: B. The feed marks are generated by an ideal nose radius

Question 10

Why can a larger tool nose radius cause chatter despite potentially improving theoretical roughness?

A. It always eliminates radial force

B. It increases radial force and may reduce stability in a flexible setup

C. It prevents all chip formation

D. It makes cutting speed equal to zero

Correct Answer: B. It increases radial force and may reduce stability in a flexible setup