Chapter 1 MACHINE TOOLS AND MACHINING OPERATIONS Prof. Dr. S Chapter 1 MACHINE TOOLS AND MACHINING OPERATIONS Prof. Dr. S. Engin KILIÇ

MACHINING IS THE REMOVAL OF THE UNWANTED METAL FROM A WORKPIECE IN THE FORM OF CHIPS SO AS TO OBTAIN A FINISHED PRODUCT OF DESIRED SIZE, SHAPE, AND FINISH.

History of Machining Before 18th century main material used was wood. Development of metal machining starts with invention of steam engine (1776). The production of cylinders of the engine was a problem. Wilkinson invented horizontal boring machine to cope with this problem.

Fundamentals of Machining The principle used in all machine tools is generating the surface required by providing suitable relative motions between cutting tool and the work piece. Metal removed is called chip. Two types of relative motion must be provided by a metal cutting machine tool: Primary and feed motion.

Fundamentals of Machining The primary motion is the main motion provided by a machine tool or manually to cause relative motion between the tool and the work piece so that the face of the tool approaches to the work piece material. Usually the primary motion absorbs most of the total power required to perform a machining operation.

Fundamentals of Machining The feed motion is a motion that may be provided to the tool or work piece by a machine tool which, when added to the primary motion, leads to a repeated or continuous chip removal. This motion may proceed by steps or continuously; in either case it usually absorbs a small proportion of the total power required.

Relative motion between tool and workpiece Primary motion Secondary motion Cutting motion Feed motion Feed speed Cutting speed

Classification of the chip removing methods according to relative motions

Resultant cutting motion in cylindrical turning

ISO Machine Tool Axis Definition

RIGHT HAND RULE

RIGHT HAND RULE Vertical Machine Horizontal Machine

Types of cutting tools CUTTING TOOL SİNGLE POİNT CUTTİNG TOOL MULTI POİNT CUTTİNG TOOL ABRASIVE TOOL

Typical single-point cutting tool

Machine tools using single-point cutting tools Lathes Shapers Planers Boring M/C’s

Drilling M/C’s Milling M/C’s Broaching M/C’s Hobbing M/C’s Machine tools using multiple-point cutting tools Drilling M/C’s Milling M/C’s Broaching M/C’s Hobbing M/C’s

Machine tools using abrasive tools Grinding M/C’s Honing M/C’s

Machine Tool Provides work holding tool holding relative motion between tool and workpiece

LATHES

Bed Headstock Assembly Tailstock Assembly Carriage Assembly Components of a Lathe Bed Headstock Assembly Tailstock Assembly Carriage Assembly Quick-change Gear Box Lead Screw and Feed Rod.

A typical turning machine z X Y

Engine Lathe z X Y

Automatic screw machines Swiss-type automatic screw machines Types of Lathes Engine lathe Tool-room lathe Turret lathe CNC lathes Automatic screw machines Swiss-type automatic screw machines

Cutting Tools For cutting tools used in lathes, geometry depends mainly on the properties of the tool material and the work material.

Tool geometry for a single point tool Base Face Major flank Corner Major cutting edge Minor flank Minor cutting edge Tool axis Shank Cutting part

Tool geometry for a single point tool

Tool geometry for a single point tool

Operations that can be performed on a lathe Turning Boring Facing Parting (Cutoff) Threading

Typical Lathe Operations

Typical Lathe Operations

Turning is the machining operation that produces axisymmetrical parts

Turning The process of machining external cylindrical surfaces Usually performed on a lathe

Turning defined as the machining of an external surface with the work-piece rotating, with a single-point cutting tool fed parallel to the axis of the work-piece at a distance from the work axis to remove a layer from the outer surface of the work.

Turning process and adjustable parameters Feed Depth of cut (back engagement) Spindle speed

Turning process

Average cutting speed nw:rotational frequency of workpiece dw:diameter of workpiece dm:diameter of machined surface

Metal removal rate F : Feed ap : back engagement (depth of cut) nw : rotational frequency of workpiece dm: diameter of machined surface

Boring involves the enlarging of an existing hole, which may have been made by a drill or may be the result of a core in a casting

Typical boring operation

Metal removal rate f : feed ap : back engagement nw : rotational frequency of workpiece dm: diameter of machined surface

Facing is the process to produce a flat surface normal to work axis in turning

Typical facing operation

Maximum cutting speed nw: rotational frequency of workpiece dm: diameter of machined surface

Metal removal rate Zw,max f :feed ap :back engagement nw :rotational frequency of workpiece dm :diameter of machined surface

Parting is the operation by which one section of a work-piece is severed from the remainder by means of a cutoff tool

Typical parting operation

In threading primary motion of tool is combination of –C’ and –Z’ to generate a helix on the workpiece by setting the gears that drive the lead screw to give the required pitch of the machined threads.

Typical threading operation

Vertical Boring Machine Similar to lathes but with a vertical axis to accommodate large and heavy workpieces

A typical Vertical Boring Machine

Horizontal Boring Machine They are very versatile and thus particularly useful in machining large parts

Essential features of Horizontal Boring Machine A rotating spindle that can be fed horizontally. A table that can be moved and fed in two directions in a horizontal plane. A headstock that can be moved vertically

Horizontal Boring Machine X Y

Shaping and Planing Shaping is used to produce flat surfaces only suitable for small parts in low –batch quantities

Among the oldest single-point machining processes Shaping and Planing Among the oldest single-point machining processes Largely replaced by milling and broaching In shaping, workpiece is fed at right angles to the cutting motion between successive strokes of the tool.

A shaper and a planer from 18th century Shaping and Planing A shaper and a planer from 18th century

Classification of shapers according to their general design features Horizontal Pull-cut Push-cut Vertical Regular Keyseater Special

Horizontal Push-cut Shaper Y X

A typical vertical shaper

Vertical Shaper (Slotter) X Y Z Vertical and inclined surfaces External and internal cylindrical surfaces Circular feeding of table between strokes Keyseater specially designed for mach. keyways inside wheel and gear hubs

Shaping and Planing Planing is used to produce flat surfaces on workpieces that are too large to be accommodated on shapers.

Classification of Planers according to their general design features Double-housing type planers Edge planers Open side planers Pit planers

Typical Planers Z X Y

Machines Using Multipoint-Cutting Tools

Drilling Machine (Drill Press)

Drilling Used to produce holes. Constitutes about 25% of all machining processes

Parts of a Typical Drilling Machine Powerhead Column Spindle Table Base

Various types of Drilling Machines Gun (deep hole) drilling Gang Drilling Turret Drilling

Typical operations performed on drilling machines Center Drilling Reaming Spot Facing Spot facing

Drilling, formulations ac :undeformed chip thickness f :feed Кr :Major cutting edge angle

lw:lenght of specimen f:feed nt:rotational frequency of the tool Machining time: lw:lenght of specimen f:feed nt:rotational frequency of the tool

Metal removal rate: f:feed nt:rotational frequency of the tool dm:diameter of the machined surface

Metal removal rate for hole enlargement: f:feed nt:rotational frequency of the tool dm:diameter of the machined surface

MILLING

A process by which a surface is generated by progressive chip removal. Milling A process by which a surface is generated by progressive chip removal. Performed on a wide variety of milling machines. The cutting tool is used is known as milling cutter.

Major components of a milling machine

Types of milling machines Horizontal Milling Machines Vertical Milling Machines

Milling operation

Milling operation with coolant

Horizontal Milling Machines In horizontal milling machines the milling cutter is mounted on a horizantal arbor driven by the main spindle.

A typical Horizontal Milling Machine

Used to generate a horizantal surface on the workpiece Slab Milling Operation Used to generate a horizantal surface on the workpiece

Slab milling formulations    

Maximum undeformed chip thickness:    

Time for machining:    

Metal removal rate: Zw= ae. ap.vf ae :working Engagement ap :width of cut Vf :feed speed of the workpiece

Vertical milling machines In vertical milling machines the milling cutter is mounted on a vertical arbor driven by the main spindle

Vertical milling operations End Milling Face Milling

A Vertical Milling Machine

Used to generate surface that is at right angle to the cutter axis Face milling Used to generate surface that is at right angle to the cutter axis

Various face and end milling operations

In Face Milling feed is ; f:feed Vf:Feed speed of the workpiece nt:rotational frequency of the cutter

Maximum undeformed chip thickness: Vf:Feed speed of the workpiece nt:rotational frequency of the cutter N:Number of teeth on the cutter

Machining time if the path of the tool axis passes over the workpiece:   lw :Lenght of the specimen dt :Diameter of the tool v f :Feed speed of the workpiece

Milling time analysis Slab milling: Approach distance, A : A = d (D-d) Time to mill workpiece, Tm: Tm = (L + A)/fr Face milling: Allow for over-travel O where A = O: Full face A = O = D/2 Partial face A = O = w (D – w) Machining time: Tm = (L + 2A)/fr

Machining time if the path of the tool axis does not pass over the workpiece: lw:Length of the specimen ae:Working engagement dt:Diameter of the tool Vf:Feed speed of the workpiece

Milling Operatios

BROACHING

Broaching is the machining of metal by means of a tool which is composed of a series of single point cutting edges each slightly larger than the previous one, made on bar.

Finishes an entire surface in a single pass. Broaching Finishes an entire surface in a single pass. Is used in production to finish holes, splines and flat surfaces. Is one of the most productive of the basic machining processes.

Vertical broaching X Z y

The average metal-removal rate (Zw) can be estimated by dividing the total volume of metal removed by the machining time.

Machining time for broaching: lt:Lenght of the Broach V:Cutting Speed

ac=af=f af:Feed engagement f:Feed Feed is the motion which an imaginary single cutting edge would have to be given by the machine tool to produce the same result as the array of cutting edges with which the tool is actually provided. It is the height difference between the two successive teeth. Uncut chip thickness: ac=af=f af:Feed engagement f:Feed

ABRASIVE MACHINING PROCESSES

Abrasive Machining The basic process in which chips are formed by very small cutting edges that are integral parts of abrassive particles

Two unique characteristics: Abrasive Machining Two unique characteristics: Cutting edge is very small, very fine cuts are possible. Cutting edges are actually extremely hard abrasive particles therefore very hard materials can be machined

Abrasive machining: Grinding A material removing process that involves the interaction of abrasive grits with the work piece at high speeds and shallow penetration depths. Abrasive machining is the oldest machining operation. Cutting edges are very small and can cut simultaneously. Very fine and smooth surfaces can be obtained

Types of grinding operations Traverse Grinding: The primary feed motion is the reciprocating traverse motion along the length (or axis) of the part with an intermittent infeed (cylindrical grinding)/cross feed (surface grinding) at the end of each stroke. Plunge Grinding: Intermittent feed motion is normal to the work surface (infeed) at the end of each stroke of the traverse motion (surface grinding); infeed motion (normal to work surface) without traverse motion (cylindrical grinding).

Types of grinding machines Horizontal-Spindle Surface-grinding Machine Vertical-Spindle Surface-grinding Machine Cylindrical-grinding Machine Internal-grinding Machine

Horizontal-Spindle Surface-Grinding Machine Has a horizontal spindle that provides primary motion to the wheel. The feed motion is the reciprocation of the worktable on which the work is mounted.

Horizontal-spindle surface-grinding machine Traverse grinding

Metal removal rate for traverse grinding: f:Feed ap:Back Engagement Vtrav.:Traverse Speed

Machining time: bw:Witdh of the workpiece F:Feed nr:Frequency of reciprocation

Plunge grinding process with horizontal-spindle surface-grinding machine

Metal removal rate for plunge grinding: f :Feed ap :Back Engagement Vtrav.:Traverse Speed

Machining time: at :tool depth of workpiece f :feed nr :frequency of reciprocation ts :sparking-out time

Vertical-Spindle Surface-Grinding Machine Employs a cup-shaped abressive wheel and performs an operation similar to face milling operation.

Metal removal rate: Vertical-Spindle Surface-Grinding Machine f:Feed ap:Back Engagement Vtrav.:Traverse Speed

Machining time: Vertical-Spindle Surface-Grinding Machine at:tool depth of workpiece f:Feed nw:Frequency of reciprocation worktable ts:Sparking-out time

Cylindrical grinding

Traverse grinding on a cylindrical grinder Max. metal removal rate: f :feed per stroke of the machine table dw :diameter of the work surface Vtrav.:traverse speed

Machining time: Traverse grinding on a cylindrical grinder at:tool depth of workpiece f:Feed nr:Frequency of reciprocation ts:Sparking-out time

Plunge grinding on a cylindrical grinder Max. metal removal rate ap:back engagement dw:diameter of the work surface Vf.:feed speed

Machining time: Plunge grinding on a cylindrical grinder at:tool depth of workpiece vf:Feed speed ts:Sparking-out time

Internal-grinding machine Commonly used for producing internal cylindrical surfaces

Max.metal removal rate: Traverse grinding on an internal grinder Max.metal removal rate: f :feed per stroke of the machine table dm :diameter of the machined surface Vtrav.:traverse speed

The machining time: Traverse grinding on an internal grinder at:tool depth of workpiece f:Feed nr:Frequency of reciprocation ts:Sparking-out time

Max.metal removal rate: Plunge grinding on a internal grinder Max.metal removal rate: ap:back engagement dm:diameter of the machined surface Vf.:feed speed

The machining time is; at:tool depth of workpiece vf:Feed speed ts:Sparking-out time

Abrasive machining: Honing A stock removal process that uses fine abrasive stones to remove very small amounts of metal. Cutting speed is much lower than that of grinding. Used to size and finish bored holes.

Specific Cutting Energy For a given work material machined under given conditions, the energy required to remove a unit volume of material (ρs) can be measured. This mainly depends on the work material.

Pm = ps Zw Machining power Ps:Specific cutting energy Zw:Metal removal rate

Electrical motor power Pm: Power required to perform machining ηm: Overall efficiency of the machine tool

Unit for specific cutting enegy

Specific Cutting Energy ps vs Uncut Chip Thickness ac

Selected Problems 1.1. 2000 bars 80 mm in diameter and 300 mm long must be turned down to 65 mm diameter for 150 mm of their length. The surface finish and accuracy requirements are such that a heavy roughing cut (removing most of the material) followed by a light-finishing cut are needed. Both the roughing and the light finishing cuts are to be taken at maximum power. The light finishing cut is to be taken at a feed of 0.13 mm, a cutting speed of 1.5 m/s. Assume that the lathe has a 2 kW motor and an efficiency of 50 %, specific cutting energy for the work material is 2.73 GJ/m3, the time taken to return the tool to the beginning of the cut is 15 s, and the time taken to load and unload a workpiece is 120s. a) Calculate the total production time in kiloseconds (ks) for the batch of work b) Calculate the machining time of one part in the roughing cut c) Calculate the machining time of one part in the light finishing cut

Selected Problems 1.1. SOLUTION Given: Nb=2000 dw=80 mm dm=65 mm lm=150 mm Psmax= 0.5x2= 1 kW = 1000 W ps=2.73 GJ/m3 flf= 0.3mm vlf = 1.5 m/s tr=15 s tl = 120 s tpr= Nb(tl + tmr + tmlf + 2 tr ) only the machining times for the roughing and the light finishing cuts are unknown Machining time can be found by dividing the volume to be removed for a given operation to the metal removal rate for the operation. Hence we need to find the metal removal rate first.

Selected Problems 1.1. SOLUTION (cont.’d) Zw= Psmax /ps Since for both the roughing and the light cutting operations maximum available power at the spindle are to be utilized; the metal removal rate for both of the operations wiil be the same. Hence: Zw= (1000 J/s)/(2.73 J/mm3) = 366 mm3/s a) tmT= tmr+ tmlf = Vr/ Zw + Vlf / Zw =(Vr+ Vlf)/Zw =VT/ Zw VT= (dw2 - 652).lw/4 = (802+ 652). 150/4 = 256236 mm3 tmT= 256236 /366.3≈ 700 s tpr= 2000(120 + 2x15 +700) = 1700ks

Selected Problems 1.1. SOLUTION (cont.’d) b) tmr= Vr/ Zw = 196985/366.3 ≈ 538 s c) tmlf = Vlf /Zw = 59251/366.3 = 162 s Machining time for light finishing operation can also be found by using the given cutting parameters, i.e. v=1.5 m/s and f= 0,13 mm ap = Zw /(fv) = 366.3/(0.13x1500) = 1.88 mm tmlf =  dlfave lm/vf dlfave = dw+ ap= 65+ 1.88 = 66.88 mm tmlf = ( x 66.88 x 150)/(1500 x 0.13) = 162 s