Machining Cutting Speeds and Feeds

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Questions and Answers

What is a primary characteristic of high speed steel?

It can be quenched only in oil

It has a lower wear resistance compared to alloy tool steels

It retains its hardness up to 500°C

It retains its hardness up to 600°C (correct)

Which alloying element is the major component in tungsten type high speed steels?

Tungsten (correct)

Cobalt

Vanadium

Molybdenum

Which high speed steel grade is primarily used for turning carbon and alloy steels of hardness up to 375 BHN?

M-7

T-2

M-2 (correct)

T-1

What are molybdenum type high speed steels known for?

Having greater toughness at the same hardness level Signup and view all the answers

What is the purpose of adding cobalt to high speed steel?

To increase red hardness Signup and view all the answers

What method is used to determine the temperature distribution on the rake face of a cutting tool?

Embedded thermo-couples Signup and view all the answers

Which of the following is a key characteristic of a satisfactory calibration in measuring thermal e.m.f?

Same plot shape for increasing and decreasing temperatures Signup and view all the answers

What limitation does a radiation pyrometer have when measuring temperature?

Dependent on accurate determination of emissivity Signup and view all the answers

What is the role of a standard thermo-couple (chromel-alumel) in the calibration process?

To record the bath temperature Signup and view all the answers

Which statement accurately reflects the method of using a radiation pyrometer?

It compares radiation intensities with known temperature strips Signup and view all the answers

What aspect is observed when plotting E1 versus temperature in thermo-couple calibration?

Linearity of the plot during temperature increase and decrease Signup and view all the answers

What is the main drawback of using radiation pyrometers for temperature measurement?

They can only measure surface temperatures Signup and view all the answers

What is the purpose of a chip breaker in machining processes?

To control chip formation Signup and view all the answers

Which tool angle is typically used to improve the cutting efficiency for hard materials?

Negative rake angle Signup and view all the answers

Which of the following accurately describes discontinuous type chips?

They are preferred due to lower cutting forces Signup and view all the answers

What defines the term 'tool signature' in machining?

The arrangement of various tool angles Signup and view all the answers

In metal machining, what is often the primary factor that leads to flank wear on a cutting tool?

Inadequate cooling Signup and view all the answers

What characterizes orthogonal cutting in machining processes?

The cutting edge is perpendicular to the cutting surface Signup and view all the answers

Which factor does not directly contribute to the formation of built-up edge on a cutting tool?

Low cutting temperature Signup and view all the answers

Which of the following factors has the greatest impact on tool life during a machining process?

Cutting speed and feed rate Signup and view all the answers

What is the effect of using a negative rake angle when machining materials?

Increases cutting forces required Signup and view all the answers

What are the principal elements of metal machining?

Cutting tool, workpiece, and coolant Signup and view all the answers

Which material has the highest machinability index?

Aluminium alloys Signup and view all the answers

What is a common remedy for reducing flank wear in cutting tools?

Select a tougher grade Signup and view all the answers

What kind of wear is characterized by small cracks normal to the cutting edge?

Small cutting edge fracture (frittering) Signup and view all the answers

Which material has a machinability index of 60?

C - 45 steel Signup and view all the answers

What action should be taken to remedy excessive notch wear?

Select a more wear-resistant tool Signup and view all the answers

What is one way to increase tool life during machining?

Increase coolant flow Signup and view all the answers

How does the machinability index of brass (red) compare to that of stainless steel?

It is significantly higher Signup and view all the answers

What condition is most likely to lead to insert breakage?

High cutting speed Signup and view all the answers

Which of the following materials has the worst machinability index?

Stainless steel Signup and view all the answers

What does plastic deformation in machining typically indicate?

Overheating of the material Signup and view all the answers

What is a primary factor that affects tool wear during machining?

Temperature Signup and view all the answers

What can be one consequence of tool wear?

Loss of dimensional accuracy Signup and view all the answers

What technique can be used to measure heat distribution in machining?

Indirect Calorimetric techniques Signup and view all the answers

What happens to a tool once it has worn out?

It can be reconditioned or replaced. Signup and view all the answers

What is a common method for reconditioning a worn-out tool?

Grinding Signup and view all the answers

What role do temperature-sensitive paints play in machining?

They help determine overall temperature distribution. Signup and view all the answers

What is one impact of frequent tool changeovers in machining?

Increased machine downtime Signup and view all the answers

Which of the following best describes the consequence of unsatisfactory performance due to tool wear?

Increased surface roughness and power requirements Signup and view all the answers

Why is the study of tool wear important?

It impacts performance and economic costs of machining. Signup and view all the answers

What effect does increasing the feed rate have on tool life?

It increases cutting temperature, leading to decreased tool life. Signup and view all the answers

Which setting is recommended for obtaining a finer finish during machining?

Utilizing a fine feed rate. Signup and view all the answers

When selecting the depth of cut, what is the most critical consideration in roughing operations?

Using the largest depth of cut possible. Signup and view all the answers

Which characteristic is essential for inserts that can handle higher feeds effectively?

A single-sided structure. Signup and view all the answers

What is a primary cause of power issues in machining when using coarse feeds on an inadequate machine?

Slipping of the drive or belt. Signup and view all the answers

What is the relationship between feed and nose radius in rough turning operations?

Feed rate should be 0.5 times the square of the nose radius. Signup and view all the answers

Which approach should be taken to improve surface finish when machining?

Selecting the finest feed rate that meets finish specifications. Signup and view all the answers

What is the required hardness of a cutting tool material compared to the work material to ensure reasonable tool life?

At least 35% to 50% harder than the work material Signup and view all the answers

Which of the following properties is not typically required for effective cutting tool materials?

Decreased thermal conductivity Signup and view all the answers

What property allows a tool material to withstand sudden loading without breaking or chipping?

Impact toughness Signup and view all the answers

Which group of materials is classified as 'Tool Steels'?

Plain Carbon Steels, Medium Alloy Steels, High Speed Steels Signup and view all the answers

What is a major consideration when selecting tool materials for machining operations?

The compatibility with the machine tool being used Signup and view all the answers

What value range is typically assigned to the exponent 'n' for high-speed steel (HSS) tools?

0.1 to 0.15 Signup and view all the answers

Which of the following factors does NOT affect tool life significantly?

Color of the tool Signup and view all the answers

According to the content, what is the relationship between cutting speed and tool life?

Tool life decreases exponentially with increased cutting speed Signup and view all the answers

What does a higher variable 'm' indicate in the equation for tool life?

Greater impact of depth of cut Signup and view all the answers

Which material is associated with the highest range of 'n' values?

Ceramic Signup and view all the answers

What is a primary component that influences cutting temperature, hence affecting tool life?

Tool geometry Signup and view all the answers

Which factor is NOT part of the definition of machinability?

Operator's experience Signup and view all the answers

In the logarithmic relationship of tool life, what does 'C' in the equations typically represent?

A constant based on material properties Signup and view all the answers

According to the content, what is the consequence of increased feed rate on tool life compared to cutting speed?

Decreases tool life at a lesser rate than increased speed Signup and view all the answers

What is a key reason why there has not been an exact quantitative definition of machinability?

The complexity and variability of influencing factors Signup and view all the answers

How does the cutting speed influence the heat generated during machining?

It increases the heat generated proportionally. Signup and view all the answers

What is the relationship between feed rate and cutting temperature during machining?

The effect of feed on cutting temperature is less than that of cutting speed. Signup and view all the answers

How does the rake angle affect heat generation in metal cutting?

A positive rake angle increases material deformation and heat generation. Signup and view all the answers

What effect does the nose radius of a cutting tool have on cutting temperature?

A larger nose radius improves heat removal, reducing cutting temperature. Signup and view all the answers

How do cutting fluids contribute to reducing cutting temperature?

They facilitate chip formation and carry away generated heat. Signup and view all the answers

In terms of heat generation, which tool geometry characteristics significantly impact cutting temperature?

Rake angle, plan approach angle, and nose radius all affect cutting temperature. Signup and view all the answers

What is the primary consequence of using increased depth of cut during machining?

It has a minimal impact on cutting temperature compared to feed and speed. Signup and view all the answers

Which statement is true regarding the heat removal capabilities of the tool shank?

A larger cross-sectional area of the tool shank increases heat removal efficiency. Signup and view all the answers

What is a key requirement for calibration of the thermal e.m.f during heating?

Consistency in output irrespective of temperature changes Signup and view all the answers

Which technique involves monitoring infrared radiation from the cutting zone?

Radiation pyrometry Signup and view all the answers

What limitation does the embedded thermocouples technique have?

It involves considerable effort and complexity Signup and view all the answers

What critical factor affects the accuracy of radiation pyrometers?

The emissivity of the surfaces being measured Signup and view all the answers

What does a satisfactory calibration plot of E1 versus temperature indicate?

There is a consistent relationship without temperature-dependent error Signup and view all the answers

Why is it important to compare intensities of radiation at different points in the cutting zone?

To determine the temperature distribution across various materials Signup and view all the answers

What is a drawback of the radiation pyrometer method?

It only indicates surface temperatures, not internal ones Signup and view all the answers

What role does the standard thermo-couple (chromel-alumel) play in temperature measurement?

It provides the thermal e.m.f necessary for calibration Signup and view all the answers

What is the primary objective of using thermal e.m.f measurements in machining?

To determine the temperature distribution during machining Signup and view all the answers

What is a key characteristic of satisfactory calibration in thermal e.m.f measurement?

It must display symmetric behavior for increasing and decreasing temperature Signup and view all the answers

Study Notes

Cutting

Cutting speed is the amount of length passed the cutting edge per unit of time (meters per minute).
Feed is the relatively small movement per cutting cycle (millimetres per revolution or stroke). It’s measured perpendicular to the cutting speed.
Depth of cut is the thickness of the metal layer removed in each pass, perpendicular to feed motion.
Factors affecting cutting speed include work material, tool material, depth of cut and feed, tool life, rigidity of machine and work conditions.
Hard materials require lower cutting speeds; soft materials, higher.
Stronger tool materials allow higher cutting speeds.
Light finishing cuts with fine feed rates allow for higher cutting speeds than heavy roughing cuts.
Tool life decreases with increased cutting temperature and speed.
Rigidity of machine and work support are important for high speeds.
Cutting speed is calculated as V = π DN / 1000 where D=Diameter in mm of work or cutter, and N = revolutions/min of work or cutter. Common values for cutting speed and feed rates are presented in Table 6.2.

Cutting Speeds & Feed Rates (Table)

Data presented in a table format showing cutting speeds(mpm) and feed rates (mm/rev) for various work materials and machining processes(turning, reaming drilling etc.).
Different materials yield varying rates.
Cutting speeds related to tool material(H.S.S., carbide, Stellite) were also included
Examples include Mild Steel, Cast Steel, Grey CI, Aluminum, Brass, Phosphor Bronze.

Selection of Feed

Feed selection depends on: Smoothness required (fine feed for better finish), Power available, condition of the machine, Type of cut (coarse for roughing, fine for finishing), Tool life (lesser feed means longer life).
A rule of thumb example: For rough turning, feed = 0.5 x nose radius (mm/rev.)
Maximum recommended feed rate is approximately 1/3 of the nose radius.
Feeds should be higher for stronger, single sided tools with smaller entering angles, under moderate cutting speeds and machinable materials.

Selection of Depth of Cut

Depth of cut selection depends on the type of cut (larger depths for roughing), Tool life (decreases with increased depth), Power required (multiplied by depth and feed).
A larger ratio of depth to feed usually leads to better surface finish.
Depth of cut is typically 3-5 times the feed for roughing operations.

Thermal Aspects of Chip Formation

Machining creates heat, from plastic deformation, frictional forces on tool face, and adjoining machined surfaces.
Heat generated is distributed among chips, tool, workpiece, and surrounding air.
In general, roughly 50- 86% of heat is dissipated into the chips.
Higher heat dissipation may occur in finishing operations where less material is removed.
Amount and type of heat generated affects tool and workpiece properties (eg., tool hardness, work hardening).
Temperature distribution in the cutting zone is non-uniform, with higher temperatures near the tool face.

Measurement of Temperature in Cutting Zone

Tool-work thermocouples are frequently used. They measure e.m.f generated at points of contact between the tool and workpiece, converting it to temperature using a calibration curve.
Embedded thermocouples are used to measure temperature distribution on cutting tool surfaces.
Radiation pyrometers measure radiative heat from points in the cutting zone.
Temperaturesensitive paints are used to measure temperature variation, especially surface temperatures.
Indirect calorimetric techniques measure temperature differences in layers of the chip/tool.

Tool Wear & Tool Life

Tool wear results from the combined effects of forces, temperature, & sliding action at the tool-workpiece interface.
Tool life is the total operating time before tool failure.
Tool life is influenced by factors including cutting speed, feed, depth of cut, tool geometry, workpiece material, and cutting fluids.
Tool life decreases as temperature increases.
Wear may involve flank wear, crater wear, chipping, or rounding of the cutting edge.
Tool life equations, such as VT = C, and VT^n ⋅ d^m ⋅ f^p = C, are used to analyze factors influencing tool life.

Cutting Tool Materials

Tool materials(steel, carbide, etc.) should be hard, have high wear & abrasion resistance, high hot hardness(resisting temper at machining temps) and good toughness.
Tool materials are often selected considering the cutting method, workpiece material, and required surface finish.
Various Tool Materials including Carbon Steels, Alloy Steels, HSS, Non-ferrous cast alloys, Cemented carbides and CBN were described plus their properties and uses.
In addition, tables showing percentage composition of different cutting tool material variants are included.
Tool materials are prone to deformation and cracking when hardened.
Alloying elements are added to improve properties such as wear resistance, hot hardness, and toughness.
High-speed steels (HSS) are used for high-speed machining of many materials.
Cemented carbides are characterized by very high hot hardness, wear resistance, and high strength, often used in the form of inserts.
Tool wear and failure can be categorized in terms of flank wear, crater wear, edge rounding, and chipping.

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Description

This quiz covers the essential concepts of cutting speeds and feed rates in machining. Understand the factors that influence these parameters, including material types and tool characteristics. Test your knowledge on how to optimize cutting processes for efficiency and tool life.