Fundamentals and Classification of Machine Tools

Introduction

Machine tools are machines used to shape, size, finish, inspect, or otherwise process workpieces by means of controlled relative motion between a tool and a workpiece. They form the technological foundation of manufacturing because they transform engineering drawings and digital product definitions into physical components. Examples include lathes, milling machines, drilling machines, grinding machines, machining centres, electrical-discharge machines, and additive–subtractive hybrid systems.

A machine tool is more than a power-driven cutting machine. It is an integrated system comprising a structure, drive system, motion-generating mechanisms, control system, workholding devices, tooling, lubrication, guarding, and often measurement and feedback equipment. Its design determines accuracy, productivity, surface quality, safety, energy consumption, and the range of components that can be produced.

Understanding machine-tool functions and classifications is essential before studying machine-tool design. Classification provides a logical way to compare machines, select suitable equipment, specify performance, and identify the design requirements of new machines.

Learning Objectives

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

1. Define a machine tool and distinguish it from a general-purpose machine.
2. Explain the principal functions and elements of a machine tool.
3. Use fundamental terminology related to cutting, motion, axes, accuracy, and productivity.
4. Classify machine tools using several technically meaningful criteria.
5. Describe primary, secondary, and auxiliary motions.
6. Interpret Cartesian coordinate systems and standard axis conventions.
7. Explain important machine-tool performance measures.
8. Trace the development from conventional machines to CNC and smart manufacturing systems.
9. Select an appropriate machine category for a given manufacturing task.
10. Recognize the limitations, safety requirements, and emerging trends affecting machine-tool design.

1. The Function of a Machine Tool

The central function of a machine tool is to generate a specified geometry on a workpiece by controlling relative motion between a cutting tool and the workpiece. Material may be removed as chips, displaced plastically, fractured, melted, vaporized, or deposited, depending on the process.

A machine tool normally performs five related functions:

• Locating: establishing the position and orientation of the workpiece and tool.
• Supporting: providing sufficiently rigid support for the workpiece, tool, and moving members.
• Driving: supplying power and speed for cutting and feed motions.
• Guiding: constraining motion along accurate paths.
• Controlling: coordinating motion, speed, feed, sequencing, and safety functions.

The desired result is not merely material removal. A successful operation must achieve the required dimensional accuracy, geometric accuracy, surface integrity, production rate, cost, and safety level.

1.1 Machine tool and machine tool system

The term machine tool traditionally refers to a powered machine that holds and moves a tool relative to a workpiece. In modern manufacturing, it is more useful to view the machine as a system. The system includes:

• machine structure, including bed, column, table, slides, and base;
• spindle or tool/workpiece rotation unit;
• feed drives and guideways;
• workholding and toolholding devices;
• numerical controller and human–machine interface;
• sensors, encoders, probes, and feedback loops;
• cutting-fluid, chip-removal, lubrication, and guarding systems.

The structure must resist static and dynamic loads. The drives must generate adequate torque and speed. Guideways must provide controlled motion with low friction and high geometric accuracy. The controller must execute commands while preventing collisions and unsafe operation.

1.2 Generating and forming principles

Machine tools produce surfaces primarily through two principles:

1. Generating: the final surface results from the envelope traced by a cutting edge or tool motion. Turning a cylindrical surface is a typical example.
2. Forming: the tool has a shape that is substantially reproduced on the workpiece. Form milling with a form cutter is an example.

Many practical processes combine both principles. In CNC milling, for example, a ball-nose cutter may form part of a surface while simultaneous programmed motion generates the overall geometry.

2. Fundamental Terminology

Workpiece, tool, and cutting zone

The workpiece is the material being processed. The cutting tool is the active device that removes or modifies material. The cutting zone is the region where the tool and workpiece interact. Heat, stress, friction, and wear are concentrated in this region.

The cutting speed, v, is the relative surface speed at the cutting zone. For a rotating workpiece of diameter D and rotational speed N,

when consistent units are used. If D is in metres and N is in revolutions per second, v is in metres per second. In common workshop units, with D in millimetres and N in revolutions per minute,

where v is in metres per minute. The factor 1000 converts millimetres to metres. This relation assumes a circular work surface and neglects small differences caused by tool geometry or elastic deflection.

Feed is the commanded relative movement of the tool and workpiece per revolution, tooth, or unit time. In turning, feed per revolution is often denoted by f in millimetres per revolution. In milling, if f_z is feed per tooth, z is the number of teeth, and N is rotational speed in revolutions per minute, the table feed is

where v_f is in millimetres per minute, provided f_z is in millimetres per tooth.

Depth of cut, a_p, is the thickness of material removed in a direction normal to the machined surface. It is distinct from feed and cutting speed.

Cutting and non-cutting motions

The cutting motion produces the relative velocity responsible for chip formation. The feed motion progressively brings new material into the cutting zone. Approach, return, indexing, and tool-change motions are non-cutting or auxiliary motions. They do not directly produce the machined surface but strongly affect cycle time.

Accuracy-related terms

• Accuracy: closeness of a manufactured feature to its specified value.
• Precision: closeness of repeated results to one another.
• Repeatability: ability to return to the same position under the same conditions.
• Reproducibility: consistency under changed conditions, such as different operators or times.
• Resolution: smallest command or measurement increment that a control or sensor can distinguish.
• Geometric accuracy: accuracy of straightness, squareness, parallelism, angularity, and positioning.
• Surface finish: texture characteristics of a surface, often represented by parameters such as arithmetic mean roughness, R_a.

Accuracy and precision are not identical. A machine may repeatedly produce the wrong dimension, demonstrating high precision but poor accuracy.

3. Classification of Machine Tools

No single classification is sufficient for all engineering purposes. A machine may be classified simultaneously by its process, cutting action, number of axes, control method, orientation, production role, or degree of automation.

3.1 Classification by manufacturing process

This classification is useful when selecting a process, but it does not fully describe machine architecture. For example, a machining centre may perform milling, drilling, tapping, boring, and probing.

3.2 Classification by principal cutting motion

Machines may be grouped according to which member carries the main cutting motion:

• Rotary-workpiece machines: the workpiece rotates, as in turning.
• Rotary-tool machines: the tool rotates, as in milling and drilling.
• Reciprocating-tool machines: the tool moves back and forth, as in shaping.
• Reciprocating-workpiece machines: the workpiece reciprocates, as in some planing machines.
• Continuous abrasive machines: an abrasive wheel or belt rotates continuously.

This distinction helps determine spindle design, bearing loads, workholding requirements, and drive power.

3.3 Classification by degree of specialization

• General-purpose machines perform a broad range of operations and are common in repair and prototype work.
• Special-purpose machines are designed for a limited operation or component family, often providing high productivity.
• Single-purpose machines perform one principal operation.
• Universal machines accept many attachments, tool arrangements, or workpiece configurations.
• Flexible manufacturing machines can produce varied parts with rapid changeover and programmable control.

A dedicated transfer machine can be highly productive for large volumes, whereas a CNC machining centre may be economically superior for moderate volumes and frequent product changes.

3.4 Classification by control method

Numerical control does not automatically guarantee accuracy. Machine condition, thermal stability, tooling, fixturing, programming, and measurement remain critical.

3.5 Classification by machine configuration and axes

Common configurations include horizontal, vertical, gantry, bridge, column-and-knee, bed-type, turret, Swiss-type, and parallel-kinematic machines. Configuration affects accessibility, stiffness, chip evacuation, work envelope, and cost.

A three-axis machine generally provides linear motion along three mutually perpendicular axes. A fourth axis may provide rotary positioning or continuous rotation. Five-axis machines coordinate three linear and two rotary axes, allowing improved access to complex surfaces and fewer setups.

The number of axes should not be confused with the number of controlled motions at one instant. A machine may have several axes but restrict simultaneous interpolation between them.

4. Machine Motions and Coordinate Systems

4.1 Primary, secondary, and auxiliary motions

The primary motion creates the cutting velocity. The secondary or feed motion controls the rate at which uncut material enters the cutting zone. Auxiliary motions include clamping, indexing, tool changing, pallet changing, coolant delivery, chip removal, and probing.

In a conventional lathe, spindle rotation is the primary motion and carriage movement is the feed motion. In a milling machine, cutter rotation is primary while table or spindle translation supplies feed. In grinding, wheel rotation is primary, while workpiece rotation and traverse provide feed-related motions.

4.2 Cartesian coordinate system

Most CNC machines use a right-handed Cartesian coordinate system. The three principal linear axes are conventionally named X, Y, and Z. The Z-axis is generally associated with the principal spindle axis. Positive direction is determined by the right-hand convention and machine standard. Rotary axes are commonly designated A, B, and C as rotations about X, Y, and Z respectively.

Machine coordinates are fixed by the builder. Work coordinates are established by the programmer or setup technician and may be shifted using work offsets. Tool offsets account for tool length, radius, or geometry. Confusing machine, work, and tool coordinate systems can cause incorrect machining or collision.

A programmed point can be represented as a position vector:

where x, y, and z are coordinates measured in the selected length unit. This representation describes position only; it does not specify velocity, acceleration, orientation, or tool compensation.

4.3 Interpolation

Interpolation is the calculation of intermediate points between programmed positions. Linear interpolation generates a straight tool path. Circular interpolation generates an arc defined by its plane, centre or radius, direction, and end point. Spline or higher-order interpolation may be used for complex free-form surfaces.

The programmed path is not necessarily the actual path. Servo lag, backlash, structural deflection, thermal expansion, and controller limits can produce deviations. Consequently, machine design and calibration are as important as the numerical program.

5. Machine-Tool Performance Measures

5.1 Productivity and cycle time

Productivity describes the useful output obtained from resources such as machine time, labour, energy, and floor space. A simple cycle-time model is

where t_c is total cycle time, t_m is machining time, t_h is handling and loading time, t_a is auxiliary time such as tool changes and inspection, and t_i is idle or delay time. The terms must be defined consistently and should not overlap.

For a turning pass of length L, with feed per revolution f and spindle speed N, the ideal cutting time is

where L is in millimetres, f in millimetres per revolution, and N in revolutions per minute; the result is in minutes. This formula assumes constant speed and feed, neglects approach and overtravel, and applies to a single continuous pass.

Worked example. A turning pass has a cutting length of 180 mm, feed of 0.20 mm/rev, and spindle speed of 900 rev/min. Therefore,

t_m = 180/(0.20 × 900) = 1.0 minute.

If loading takes 0.40 min, tool change and measurement take 0.20 min, and delay time is 0.10 min, the total cycle time is t_c = 1.0 + 0.40 + 0.20 + 0.10 = 1.70 min. The calculation is idealized; acceleration, deceleration, chip evacuation, and actual operator practice may increase the time.

5.2 Material removal rate and power

For a simplified orthogonal cutting approximation, material removal rate may be estimated as

where Q is material removal rate, v_f is feed velocity, a_p is axial or depth engagement, and a_e is radial or width engagement. The product has units of volume per unit time. The exact interpretation depends on the process and engagement geometry.

Cutting power is related to cutting force and cutting speed:

where P_c is cutting power in watts, F_c is the tangential cutting force in newtons, and v is cutting speed in metres per second. This relation is dimensionally consistent because one newton-metre per second equals one watt. Motor power must exceed cutting power because transmission, bearing, and drive losses are present.

5.3 Accuracy, stiffness, and thermal behaviour

Machine accuracy is influenced by geometric errors, kinematic errors, load-induced deflection, thermal expansion, vibration, tool wear, fixturing, and measurement uncertainty. Static stiffness relates displacement to applied force in a defined loading condition. A simplified relation is

where k is stiffness in newtons per metre, F is applied force, and δ is displacement in metres. This is a linear approximation and is valid only when the structure behaves approximately elastically over the considered range.

High stiffness reduces deflection, but excessive mass may reduce acceleration and energy efficiency. Good design therefore balances stiffness, damping, mass, thermal stability, accessibility, and cost.

5.4 Overall equipment effectiveness

In production environments, Overall Equipment Effectiveness (OEE) is often expressed as

where each factor is expressed as a fraction between 0 and 1. Availability commonly reflects operating time relative to planned production time; performance compares actual speed with an ideal or standard speed; quality reflects good units relative to total units. Definitions must be agreed within the organization because maintenance, setup, and planned stoppages may be treated differently.

6. Evolution of Machine Tools

Early machine tools were manually operated and relied on the operator’s judgment, mechanical skill, and physical control. Lathes, shapers, drilling machines, and milling machines gradually gained power drives, standardized tooling, leadscrews, gearboxes, and improved guideways.

The next stage introduced mechanical automation through cams, templates, copying systems, automatic bar feeders, and transfer lines. These systems achieved high production rates but were costly and inflexible when product designs changed.

Numerical control emerged when coded instructions controlled machine motions. Early systems used punched tape and dedicated electronic hardware. Computer numerical control replaced much fixed hardware with programmable memory and software. CNC enabled rapid program modification, coordinated interpolation, tool compensation, automatic tool changing, canned cycles, probing, and integration with computer-aided manufacturing.

Modern machines increasingly incorporate:

• direct-drive spindles and high-speed motors;
• linear motors and precision ball screws;
• scale feedback and advanced servo control;
• in-process probing and tool-breakage detection;
• thermal compensation;
• digital twins and virtual commissioning;
• network communication and production monitoring;
• predictive maintenance based on sensor data;
• energy and coolant monitoring.

A smart machine tool is not simply a CNC machine connected to a network. It combines physical equipment, sensing, computation, communication, and decision support. The value of “smart” functionality depends on data quality, valid models, cybersecurity, operator competence, and the ability to act on information.

7. Conventional, CNC, and Smart Manufacturing: A Comparison

CNC technology improves repeatability and reduces dependence on continuous manual handwheel control, but it introduces new responsibilities: program verification, coordinate management, tool data control, backup, access control, and systematic maintenance.

8. Selecting a Machine Tool: An Applied Framework

Selection should begin with the product and process rather than with a machine catalogue. Important questions include:

1. What material and hardness must be processed?
2. What features, tolerances, surface finishes, and geometric relationships are required?
3. What is the component size and mass?
4. What production quantity and product variety are expected?
5. How many setups are needed?
6. What tooling, workholding, inspection, and coolant systems are required?
7. What are the available power, floor space, skills, and maintenance resources?
8. What safety, environmental, energy, and data requirements apply?

For example, a cylindrical shaft with several diameters and threads may be produced on a CNC turning centre. A prismatic component with pockets, drilled holes, and tapped features may be better suited to a vertical machining centre. A hardened bearing race requiring very close size and finish may require grinding after heat treatment.

The technically best machine is not always the economically best choice. Capital cost, utilization, tooling cost, setup time, maintenance, training, energy, quality losses, and expected product life must be considered together.

9. Illustrative Case: Choosing Equipment for a Variable-Volume Component

Background

A small manufacturer produces an aluminium housing with two machined faces, four drilled and tapped holes, a pocket, and two locating bores. Annual demand varies between 2,000 and 8,000 units. Several design revisions are expected.

Problem

The existing manual milling and drilling operations require three setups and produce inconsistent hole-location accuracy. Inspection and rework consume significant time. Management must decide whether to purchase a CNC vertical machining centre or a dedicated special-purpose machine.

Analysis

A dedicated machine could reduce cycle time at the upper demand level, but it would require expensive fixtures and redesign if the housing changes. The CNC machine can combine milling, drilling, tapping, probing, and bore interpolation in one main setup. Its higher flexibility is valuable because demand and geometry are uncertain.

Suppose the CNC cycle consists of 8.0 minutes of machining, 1.5 minutes of loading and unloading, and 0.5 minutes of probing and tool-change activity. The cycle time is therefore 10.0 minutes. At 420 productive minutes per shift, the theoretical output is 42 parts per shift, before allowances for breaks, downtime, and quality losses.

A production plan should not treat this theoretical value as guaranteed capacity. If availability is 0.90, performance is 0.85, and quality is 0.98, the corresponding OEE estimate is

OEE = 0.90 × 0.85 × 0.98 = 0.7497 ≈ 75.0%.

The effective good output is approximately 42 × 0.7497 ≈ 31.5 parts per shift under the stated assumptions.

Approach and solution

The manufacturer selects a CNC vertical machining centre with a rotary fourth axis provision, probing, tool-life monitoring, and a modular fixture. The process is validated using simulation and first-article inspection. Work offsets are established by probing, while tool length and diameter offsets are measured using a tool presetting system.

Outcome

The number of setups falls from three to one main setup. Hole-location consistency improves, and engineering changes are implemented through revised programs and fixtures rather than a complete machine redesign. The machine is not necessarily the fastest option at maximum volume, but it provides better flexibility and lower technical risk over the expected product life.

Learning points

• Machine selection must reflect volume, variety, and future change.
• Combining operations can reduce accumulated setup and datum errors.
• Theoretical capacity must be adjusted for availability, performance, and quality.
• Probing and tool management are process-control systems, not merely accessories.
• Human training and program governance remain essential in CNC production.

10. Challenges, Safety, and Responsible Use

Machine tools present hazards including rotating components, ejected workpieces, sharp chips, cutting fluids, noise, electrical energy, stored pneumatic or hydraulic energy, and unexpected automatic motion. Guards, interlocks, emergency stops, safe workholding, correct tool clamping, and lockout procedures are fundamental. Safety systems must not be bypassed to save time.

Important professional practices include:

• verify programs using simulation, dry runs, and controlled single-block operation;
• establish correct work and tool offsets;
• inspect fixtures, tools, guards, and coolant condition;
• control access to CNC programs and machine parameters;
• maintain traceable calibration and inspection records;
• manage chips and fluids to reduce environmental and health risks;
• apply cybersecurity controls to networked machines;
• treat sensor-based recommendations as decision support requiring engineering validation.

Smart manufacturing also creates governance questions. Who owns machine data? How should data be protected from unauthorized alteration? Can an adaptive system change cutting parameters without approval? What evidence is required to validate an AI-based tool-wear prediction? Responsible implementation requires clear authority, audit trails, fail-safe limits, and human oversight.

11. Contemporary Developments and Best Practices

Current machine-tool development emphasizes higher productivity with lower energy and improved quality. Important directions include hybrid machines that combine additive deposition and subtractive machining, autonomous tool management, model-based definition, cloud-connected production systems, and machine learning for anomaly detection.

However, advanced technology should solve a defined manufacturing problem. A reliable foundation consists of:

1. stable process planning and standardized workholding;
2. accurate machine geometry and regular calibration;
3. verified tooling and cutting data;
4. disciplined program and offset management;
5. appropriate sensing and data collection;
6. preventive and predictive maintenance;
7. operator and engineer training;
8. measured improvement using quality, time, cost, and energy indicators.

Technology is most effective when integrated with sound mechanical design and process knowledge. Data cannot compensate for an unstable fixture, inadequate rigidity, poor tooling, or incorrect datum selection.

Chapter Summary

Machine tools are integrated systems that locate, support, drive, guide, and control tools and workpieces to produce specified features. Their performance depends on structure, drives, guideways, tooling, workholding, control, measurement, thermal behaviour, and human practice.

Machine tools can be classified by process, principal cutting motion, specialization, control method, configuration, orientation, and number of axes. Turning machines rotate the workpiece; milling and drilling machines generally rotate the tool; grinding uses abrasive action; non-traditional machines use electrical, thermal, chemical, or other mechanisms.

Primary motion produces cutting speed, feed motion advances material into the cutting zone, and auxiliary motions support handling, tool changing, probing, and chip removal. Cartesian coordinates, work offsets, tool offsets, interpolation, and axis conventions are fundamental to CNC operation.

Important performance measures include cycle time, material removal rate, cutting power, stiffness, accuracy, repeatability, surface quality, availability, performance, quality, and OEE. Conventional machines rely heavily on operator skill; CNC machines provide programmable repeatability and flexibility; smart manufacturing systems add sensing, communication, analytics, and adaptive decision support.

Machine selection must match material, geometry, tolerance, quantity, variety, setup requirements, cost, safety, skills, and future change. Advanced systems are valuable only when supported by stable processes, data governance, cybersecurity, maintenance, and trained personnel.

Key Terms

Machine tool: Powered equipment that controls relative motion between a tool and workpiece to produce a manufactured feature.

Workpiece: Material or component being processed.

Cutting speed: Relative surface speed at the cutting zone.

Feed: Relative advance of the tool and workpiece during processing.

Depth of cut: Thickness of material removed in a direction normal to the machined surface.

Primary motion: Motion that produces the principal cutting velocity.

Auxiliary motion: Supporting motion such as tool changing, clamping, or indexing.

Generating: Producing a surface through the envelope of tool motion.

Forming: Producing a surface substantially through the shape of the tool.

CNC: Computer numerical control of machine-tool functions and motion.

Interpolation: Calculation of intermediate points along a programmed path.

Work offset: Coordinate transformation locating the programmed work datum.

Tool offset: Compensation for tool dimensions or geometry.

Accuracy: Closeness to a specified or true value.

Precision: Closeness of repeated measurements or results to one another.

Repeatability: Ability to reproduce a result under the same conditions.

Stiffness: Force divided by the corresponding elastic displacement.

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

OEE: Product of availability, performance, and quality factors.

Smart manufacturing: Connected manufacturing using sensing, computation, communication, and data-supported control.

Review Questions

Short Answer Questions

1. What are the five principal functions of a machine tool?
2. Distinguish cutting motion, feed motion, and auxiliary motion.
3. State two differences between accuracy and precision.
4. What is the purpose of a work offset in CNC machining?
5. Name four criteria used to classify machine tools.

Long Answer Questions

1. Explain the structure and major subsystems of a modern machine tool.
2. Compare conventional, CNC, and smart manufacturing systems in terms of flexibility, feedback, skills, and risks.
3. Discuss the main classifications of machine tools and explain why one classification is not sufficient for all purposes.
4. Explain Cartesian axes, rotary axes, interpolation, work coordinates, and tool compensation.
5. Discuss the major factors that influence machine-tool accuracy, productivity, and surface quality.

Analytical / Application Questions

1. A turning operation uses a cutting length of 240 mm, feed of 0.25 mm/rev, and spindle speed of 800 rev/min. Calculate the ideal machining time and state the assumptions behind the calculation.
2. A factory is choosing between a dedicated transfer machine and a CNC machining centre for a product with uncertain annual demand and frequent design changes. Recommend a selection approach and justify it using technical and economic criteria.
3. A networked machining centre reports increasing vibration and tool-wear indicators. Propose a responsible diagnostic procedure that uses sensor data without allowing an unverified automated system to create unsafe cutting conditions.

Multiple Choice Questions with Answers

Question 1

Which function of a machine tool establishes the position and orientation of the workpiece and tool?

A. Locating

B. Driving

C. Guiding

D. Cooling

Correct Answer: A. Locating

Question 2

In a conventional lathe, which motion normally produces the principal cutting velocity?

A. Cross-slide movement

B. Spindle rotation

C. Tailstock movement

D. Carriage return

Correct Answer: B. Spindle rotation

Question 3

A turning operation has D = 100 mm and N = 600 rev/min. Using v = πDN/1000, what is the cutting speed?

A. 18.8 m/min

B. 188.5 m/min

C. 1,885 m/min

D. 0.1885 m/min

Correct Answer: B. 188.5 m/min

Question 4

Which machine is generally most suitable for producing pockets, drilled holes, and tapped holes in a prismatic component?

A. Vertical machining centre

B. Centerless grinder

C. Engine lathe only

D. Broaching machine only

Correct Answer: A. Vertical machining centre

Question 5

What does interpolation in a CNC system mean?

A. Measuring tool hardness

B. Calculating intermediate points along a programmed path

C. Clamping the workpiece

D. Changing cutting fluid

Correct Answer: B. Calculating intermediate points along a programmed path

Question 6

Which statement correctly distinguishes precision from accuracy?

A. Precision is closeness to the specified value, while accuracy is repeatability

B. Precision concerns repeated-result closeness, while accuracy concerns closeness to the specified value

C. They are always identical

D. Precision applies only to CNC machines

Correct Answer: B. Precision concerns repeated-result closeness, while accuracy concerns closeness to the specified value

Question 7

A turning pass is 180 mm long, with f = 0.20 mm/rev and N = 900 rev/min. What is the ideal cutting time?

A. 0.10 min

B. 1.00 min

C. 10.0 min

D. 162 min

Correct Answer: B. 1.00 min

Question 8

Which expression represents the simplified relation between cutting power, cutting force, and cutting speed?

A. P_c = F_c/v

B. P_c = v/F_c

C. P_c = F_c v

D. P_c = F_c + v

Correct Answer: C. P_c = F_c v

Question 9

What is a major advantage of a dedicated special-purpose machine over a flexible CNC machine?

A. It always accommodates design changes more easily

B. It can provide high productivity for a narrowly defined operation

C. It requires no workholding system

D. It eliminates all maintenance

Correct Answer: B. It can provide high productivity for a narrowly defined operation

Question 10

If availability is 0.90, performance is 0.85, and quality is 0.98, what is the approximate OEE?

A. 0.25

B. 0.65

C. 0.75

D. 2.73

Correct Answer: C. 0.75