Basic Manufacturing Process - Ch. 7.1


Q.1    What do you mean by machining.
Ans.    Machining: -

        Conventional machining, one of the most important material removal methods, is a collection of material-working processes in which power-driven machine tools, such as lathes, milling machines, and drill presses, are used with a sharp cutting tool to mechanically cut the material to achieve the desired geometry. Machining is a part of the manufacture of almost all metal products, and it is common for other materials, such as wood and plastic, to be machined. A person who specializes in machining is called a machinist. A room, building, or company where machining is done is called a machine shop. Much of modern day machining is controlled by computers using computer numerical control (CNC) machining. Machining can be a business, a hobby, or both.
    The precise meaning of the term “machining” has evolved over the past 1.5 centuries as technology has advanced. During the Machine Age, it referred to (what we today might call) the “traditional” machining processes, such as turning, boring, drilling, milling, broaching, sawing, shaping, planing, reaming, and tapping, or sometimes to grinding. Since the advent of new technologies such as electrical discharge machining, electrochemical machining, electron beam machining, photochemical machining, and ultrasonic machining, the retronym “conventional machining” can be used to differentiate the classic technologies from the newer ones. The term “machining” without qualification usually implies conventional machining.
    Machining can be defined as the process of removing material from a workpiece in the form of chips. The term metal cutting is used when the material is metallic. Most machining has very low set-up cost compared to forming, molding, and casting processes. However, machining is much more expensive for high volumes. Machining is necessary where tight tolerances on dimensions and finishes are required.
The Machining section is divided into the following categories:
Drilling :              

Turning :

Milling :               
Grinding :
Chip Formation :
Machining Operation: -
    There are many kinds of machining operations, each of which is capable of generating a certain part geometry and surface texture.
    In turning, a cutting tool with a single cutting edge is used to remove material from a rotating workpiece to generate a cylindrical shape. The speed motion in turning is provided by the rotating workpart, and the feed motion is achieved by the cutting tool moving slowly in a direction parallel to the axis of rotation of the workpiece.
    Drilling is used to create a round hole. It is accomplished by a rotating tool that is typically has two cutting edges. The tool is fed in a direction parallel to its axis of rotation into the workpart to form the round hole.
    In boring, the tool is used to enlarge an already available hole. It is a fine finishing operation used in the final stages of product manufacture.
    In milling, a rotating tool with multiple cutting edges is moved slowly relative to the material to generate a plane or straight surface. The direction of the feed motion is perpendicular to the tool’s axis of rotation. The speed motion is provided by the rotating milling cutter. The two basic forms of milling are -
Peripheral milling, Face milling.
    Other conventional machining operations include shaping, planing, broaching and sawing. Also, grinding and similar abrasive operations are often included within the category of machining.

Q.2    Classified the lathe machine?
Ans.    Lathe: -

        A lathe is a machine tool which spins a block of material to perform various operations such as cutting, sanding, knurling, drilling, or deformation with tools that are applied to the workpiece to create an object which has symmetry about an axis of rotation.
    Lathes are used in woodturning, metalworking, metal spinning, and glassworking. Lathes can be used to shape pottery, the best-known design being the potter’s wheel. Most suitably equipped metalworking lathes can also be used to produce most solids of revolution, plane surfaces and screw threads or helices. Ornamental lathes can produce three-dimensional solids of incredible complexity. The material can be held in place by either one or two centers, at least one of which can be moved horizontally to accommodate varying material lengths. Other workholding methods include clamping the work about the axis of rotation using a chuck or collet, or to a faceplate, using clamps or dogs.
    Examples of objects that can be produced on a lathe include candlestick holders, cue sticks, table legs, bowls, baseball bats, musical instruments (especially woodwind instruments), crankshafts and camshafts.
Types of Lathe: -
Speed Lathe: -
    It is the simplest of all types of lathe. It has a bed, a head stock, a tailstock and a tool post but no feed box and lead screw. The tool is mounted on adjustable slide and fed to work purely by hand control. The spindle speed is high, with usual range 1200 to 3600 rpm.
    Depth of cut and chip thickness is very very small. In head stock only 2 or 3 speeds are available.
Application: -
    Wood working, polishing and centering.
The Engine lathe or Centre lathe: -
    The term “ engine”is associated with lathes because in olden times these were driven by steam engine. The engine lathe has got parts same as speed lathe. Only the stock is robust and contains additional mechanism to give multiple spindle speeds. Cross and longitudinal feeds are available with the help of carriage, lead screw.
Applications: -
    Drilling, taping.
The Bench Lathe: -
    It is the smallest lathe mounted on bench, has practically all the parts of an engine lathe.
Applications: -
    Small and precision work.
The Tool Room Lathe: -
    It is having all features similar to an engine lathe. It is much more accurately built and has a wide range of speed from very low to quite high up to 2500 rpm. Apart from other parts of engine lathe this lathe has a chuck, taper turning attachment, thread chasing dial, rests.
Application: -
    Mainly used for precision work on tools, dies, gauges.
Turret Lathe: -
    In it, several tools are set on a revolving turret to facilitate doing large number of operations on a job in minimum time.
An indexable square tool post is provided at cross slide.
Applications: -
    Turret is used to perform large number of operations simultaneously and is widely used for repetative batch production.
Capstan Lathe: -
    It is similar to turret lathe and sin corporate capstan slide which moves on an auxiliary slide and can be clamped at any position.
Applications: -
    Best suited for fast production of small parts.
Gap Bed Lathe: -
    In these lathes, a gap is provided on bed near the head stock with view to handle jobs having flanges or some projections.

Q.3    Describe the various parts of lathe machine?
Related Questions -
Q.    With the help of sketch, explain the basic components of lathe machine.       (AKTU - 2008-09)
Ans.    Descriptions of Various Parts of Lathe: -

        Figure illustrates the basic parts of geared head lathe.
Following are the principle parts:
(i)     Bed.    (ii)  Head stock.     (iii) Tailstock.        (iv) Carriage.
(v)     Feed mechanism.    (vi) Lead screw.    (vii) Tool post and tools.
(i) The Bed: -
    Lathe bed forms the base of the machine. The head stock is located at one end and Tail stock at another. The carriage rests over the bed and slides on it. The bed consists of two heavy metal slides running. Lengthwise, with ‘v’ shape slide ways. The outer guideways provide supporting and sliding surfaces for the carriage, and inner ways for the tailstock. Lathe bed is made of high grade special cast iron having high vibration damping qualities. Lathe bed is secured rigidly over carbinet leg and end leg.
(ii) The Head Stock: -
    The head stock is secured permanently on the innerways at the left hand end of the lathe bed. It provides necessary transmission mechanism with speed changing lever to obtain different speeds.
    The center line of head stock is parallel to the guide ways in both horizontal and vertical planes.
    All the modern lathes employ all geared head stock. However, cone-driven headstock can be used for low cost and simplicity. Sliding gearing is generally employed for obtaining the various speed changes.
    A separate speed changer gear box is placed below headstock to reduce the speed in order to have to have different feed rates for threading and automatic linear movement of carriage.
(iii) Tail Stock: -
    The tail stock has two main uses
(a)     It supports the other end of work when it is being machined between centers.
(b)     To hold a tool for performing operations like drilling, remaining tapping etc. It consists of the dead center, the adjusting screw and hand wheel. The body of  tailstock is bored to form a barrel in which spindle moves in and out. Spindle has a tapered hole in which tool or dead center fits. Spindle moves in when screw is turned anticlockwise with the help of hand wheel. Ultimately end of screw strikes against the tool and tool come out. Spindle has a key to prevent it’s rotation in barrel and a lever to lock the spindle in any desired position.
(iv) Carriage: -
    It is mounted on the Bed of a Lathe and its main functions are to support, guide and feed the cutting tool during the operations.
(v) Feed Mechanism: -
    Power is transmitted to carriage by means of feed mechanism. For this purpose a system of gear trains is provided. The quick change gear is arranged between spindle and lead screw. Rotational speed of lead screw with respect to spindle speed can be adjusted manually by means of gear trains.
(vi) Lead Screw: -
    It is used to transmit power to carriage through gear and clutch arrangement in the carriage apron.
(vii) Tool Post and Tools: -
    The tool post rotates around a large bolt on the top of compound slide and is locked and held in position by clamping lever. It can be set at any desired angle.

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