Surface finishing  Surface finishing may be defined as any process that alters the surface of a material for asthetic and functional purposes  It improve appearance and sales value of product  Used to resist wear, electrolytic decomposition, and corrosive wear  Treatment process (chemical or electrical) produces oxide of original metal on surface

Common methods for super finishing process Honing Lapping Polishing Super finishing

HONING Honing is an abrasive machining process that produces a precision surface on a metal workpiece by scrubbing an abrasive stone against it along a controlled path. Honing is primarily used to improve the geometric form of a surface, but may also improve the surface texture. The surface of a honed workpiece

How honing process is done Honing is a controlled, slow velocity,stock removal process that uses fine abrasive stones to remove very small amount of material. The process is used to size and finish drilled holes,remove errors etc. The honing stone usually are held in a honing head, with stone being held against the work with controlled light pressure. The honing tool is guided by the predrilled cavity. The stones are given complex motion to prevent single grit from repeating

Honing is used in For external and flat surfaces varying oscillatory motions are given. Gear teeth Valve seating Roller bearing etc. Super abrasives and hone head for cylinders

Honing tools Honing uses a special tool, called a honing stone or a hone, to achieve a precision surface. The hone is composed of abrasive grains that are bound together with an adhesive. Generally, honing grains are irregularly shaped and about 10 to 50 micrometers in diameter Any abrasive material may be used to create a honing stone, but the most commonly used are corundum, silicon carbide, cubic boron nitride, or diamond.

Some commonly used honing tools

Some processes showing honing

Types of honing machines There are two types of honing machines that are commonly used. They are as follows: 1.Horizontal honing machine 2.Vertical honing machine The classification is done on the basis of the motion of the workpiece and tool. If machine carry a horizontal spindle and workpiece is mounted on a table that can reciprocate to and fro then the honing process is called horizontal honing and if tool is mounted in a vertical spindle and moves up and down then it is called vertical honing process.

Vertical honing machine Horizontal honing machine

Advantages and disadvantages of honing Advantages Highly accurate holes are produced. Very little heat is generated. Tolerances can be easily maintained. Surface finish produced is very smooth. Hole of any dimensions can be honed. High productivity at low cost can be obtained. Disadvantages Impossible to improve lack of straightness in holes. Difficult to hone tough non ferrous metals due to clogging of the pores of abrasive. Amount of stock removal is less.

Lapping Lapping is a machining process, in which two surfaces are rubbed together with an abrasive between them, by hand movement or by way of a machine.

How lapping is done Lapping is an ancient machining technique It is a precision process or combination of processes used to provide flatness, parallelism, size and surface finishes to extremely demanding tolerances. First the workpiece is held in pressure plate onwhich pressure is to be applied. There is a rotating wheel on which a coating of abrasive material is present. Now workpiece and abrasive material are brought in contact by applying pressure on pressure plate and due to thes contact the material is removed.

Lapping is used in Gauges Piston pins Valves Gears Thrust washers Optical parts

Lapping tools Two types of tools are used on the basis of abrasive material Abrasives like, jeweller's rouge, optician's rouge, emery, silicon carbide, diamond, etc. are used. For machine lapping the preferred lap material is cast iron Soft steel, bronze, brass and lead are used in manual lapping.

Some common lapping tools

Some processes showing lapping

Types of lapping Lapping is done by following methods 1.Hand lapping 2.Machine lapping Hand lapping is done by using hand held tools for both flat and external cylinder work Machine lapping is done to obtain highly finished surface on many articles such as worm and worm gears, camshafts, automobile engine parts etc.

Types of lapping machine There are five types of lapping machines and they are discussed below: 1.Vertical lapping machine 2.Flat machine lapping 3.Centreless roll lapping machine 4.Centreless lapping machine 5.Lapping spherical surfaces

Advantages and disadvantages of lapping Advantages Extreme accuracy in both tolerances and geometry. Fast stock removal. No clamping or heat distortion. No expensive tooling required. Very thin and non magnetic parts can be processed. Irregular shaped parts can be easily processed. Disadvantages Since lapping is a finishing operation, parts should not be far from the expected size and geometry before lapping. Reside of compound left on the part after lapping must be removed Trail and error still may be needed to get the optimum results.

Super finishing process Super finishing is a surface improving process that removes the undesirable fragmentation metal, leaving a base of solid crystalline metal It differ form honing in then motion given to the stone.

Types of super finishing It is of two types: 1.Cylindrical super finishing 2.Flat super finishing In cylindrical super finishing a bonded form abrasive stone having a width of about two third of diameter of part to be finished and the same length is operated at low speed and pressure. The motion given to the stone is oscillating with an amplitude of 1.6 to 64 mm at about 450 cycles. The work is rotated at the speed of0.25m/s. In flat super finishing flat surface may be super finished. The upper spindle is spring loaded quill on which stone is mounted The lower spindle carries the work. Both spindles are parallel so that when they rotate the result is a flat smooth surface

Cylindrical super finishing Flat super finishing

Super finishing tools The tools used are basically stones which has a specified kind of abrasive, size type of bond and hardness. These stones are mounted on special attachments. The machine used have the capability to hold stones in adjustable and interchangeable holders.

Advantages and disadvantages of super finishing Advantages Produce excellent surface finish in a minimum time. Type of surface finish may be preselected. Process is easy adapted to high volume productions. Disadvantages Super finishing cannot be used to correct feature location such as concentricity.

Super finishing is used in Automobile component such as gudgeon pins. Aircraft components. Heavy earth moving equipments.