Shaping & Grinding and Realated Operations

LECTURE-05SHAPING & RELATED OPERATIONS

NIKHIL R. DHAR, Ph. D.DEPARTMENT OF INDUSTRIAL & PRODUCTION

ENGINEERINGBUET BANGLADESH

Department of Industrial & Production Engineering 26/2

Shaping and Planing

Shaping and Planing among the oldest techniques

Shaping is where the workpiece is fed at right angles to the cutting motion between successive strokes of the tool.

Planing the workpiece is reciprocated and the tool is fed at right angles to the cutting motion.

These process require skilled operators and for the most part have been replaced by other processes


Classification of Shapers

Horizontal-push cut Plain (Production work) Universal (Tool room work)

Horizontal-draw cutVertical Slotter Key seater

Special purpose-as for gear cutting


Horizontal Push Cut Shaper

The shaper is a relatively simple machine. It is used fairly often in the toolroom or for machining one or two pieces for prototype work. Tooling is simple, and shapers do not always require operator attention while cutting. The horizontal shaper is the most common type, and its principal components are shown below, and described as follows:


Ram: The ram slides back and forth in dovetail or square ways to transmit power to the cutter. The starting point and the length of the stroke can be adjusted. Toolhead: The toolhead is fastened to the ram on a circular plate so that it can be rotated for making angular cuts. The toolhead can also be moved up or down by its hand crank for precise depth adjustments.


Clapper Box: The clapper box is needed because the cutter drags over the work on the return stroke. The clapper box is hinged so that the cutting too] will not dig in. Often this clapper box is automatically raised by mechanical, air, or hydraulic action. Table: The table is moved left and right, usually by hand, to position the work under the cutter when setting up. Then, either by hand or more often automatically, the table is moved sideways to feed the work under the cutter at the end or beginning of each stroke.


Saddle: The saddle moves up and down (Y axis), usually manually, to set the rough position of the depth of cut. Final depth can be set by the hand crank on the tool head. Column: The column supports the ram and the rails for the saddle. The mechanism for moving the ram and table is housed inside the column.


Tool holders: Tool holders are the same as the ones used on at engine lathe, though often larger in size. The cutter is sharperred with rake and clearance angles similar to lathe tools though the angles are smaller because the work surface is usually flat. These cutters are fastened into the tool holder. just as in the lathe, but in a vertical plane. Workholding: Workholding is frequently done in a vise. The vise is specially designed for use in shapers and has long ways which allow the jaws to open up to 14" or more, therefore quite large workpieces can be held. The vise may also have a swivel base so that cuts may be made at an angle. Work that cannot be held in the vise (due to size or shape) is clamped directly to the shaper table in much the same way as parts are secured on milling machine tables. Shaper Size: The size of a shaper is the maximum length of stroke which it can take. Horizontal shapers are most often made with strokes from 16- to 24" long, though some smaller and larger sizes are available. These shapers use from 2- to 5-hp motors to drive the head and the automatic feed. Shaper Width: The maximum width which can be cut depends on the available movement of the table. Most shapers have a width capacity equal to or greater than the length of the stroke. The maximum vertical height available is about 12" to 15".


Types of Work

The tool post and the tool slide can be angled as seen below. This allows the shaper to be used for different types of work

The tool post has been turned at an angle so that side of the material can

be machined

The tool post is not angled so that the tool can be used to

level a surface.

The top slide is slowly feed into the material so that a ‘rack’ can be machined for a rack

and pinion gear system.


Quick Return Mechanism

The shaping machine is used to machine flat metal surfaces especially where a large amount of metal has to be removed. Other machines such as milling machines are much more expensive and are more suited to removing smaller amounts of metal, very accurately. The reciprocating motion of the mechanism inside the shaping machine can be seen in the diagram. As the disc rotates the top of the machine moves forwards and backwards, pushing a cutting tool. The cutting tool removes the metal from work which is carefully bolted down.


Planing Machines

Planing is used for large workpieces too big for shapersPlaning machines have largely been replaced by planing millsIn planing, large workpieces and their support tables are slowly moved against the tool head.

Figure: Schematic of planers. (a) Double-housing planer with multiple tool heads and a large reciprocating table; (b) single-housing or open-sided planer.


Common Shaping and Planing Geometry

Figure: Types of surfaces commonly machined by shaping and planing.

LECTURE-06GRINDING & RELATED OPERATIONS

NIKHIL R. DHAR, Ph. D.DEPARTMENT OF INDUSTRIAL & PRODUCTION

ENGINEERINGBUET


Grinding

The grinding process consists of removing material from the workpiece by the use of a rotating wheel that has a surface composed of abrasive grains. Grinding is considered to be the most accurate of the existing machining processes. Grinding processes are used when high accuracies, close dimensional tolerances, and a fine surface finishes are required. Grinding processes also allow for high production rates. This allows for a lowered cost of production. Hard materials can also be machined.Grinding may be classified as non-precision or precision, according to purpose and procedure.

Non-precision grinding: The common forms are called, snagging and off-hand grinding. Both are done primarily to remove stock that can not be taken off as conveniently by other methods. The work is pressed hard against the wheel or vice versa. The accuracy and surface finish are of secondary importance.

Precision grinding: Precision grinding is concerned with producing good surface finishes and accurate dimensions. Three types of precision grinding exists

External cylindrical grindingInternal cylindrical grindingSurface grinding


Grinding Operations

Surface grinding is most common of the grinding operations. A rotating wheel is used in the grinding of flat surfaces. Types of surface grinding are vertical spindle and rotary tables.

Figure: Schematic illustration of surface-grinding operations. (a) Traverse grinding with a horizontal-spindle surface grinder. (b) Plunge grinding with a horizontal-spindle surface grinder, producing a groove in the workpiece. (c) Vertical-spindle rotary-table grinder (also known as the Blanchard-type grinder).


Cylindrical grinding is also called center-type grinding and is used in the removing the cylindrical surfaces and shoulders of the workpiece. Both the tool and the workpiece are rotated by separate motors and at different speeds. The axes of rotation tool can be adjusted to produce a variety of shapes.

Figure: Examples of various cylindrical grinding operations. (a) Traverse grinding, (b) plunge grinding, and (c) profile grinding.


Internal grinding is used to grind the inside diameter of the workpiece. Tapered holes can be ground with the use of internal grinders that can swivel on the horizontal.

Figure: Schematic illustrations of internal-grinding operations.


Centerless grinding is when the workpiece is supported by a blade instead of by centers or chucks. Two wheels are used. The larger one is used to grind the surface of the workpiece and the smaller wheel is used to regulate the axial movement of the workpiece. Types of centerless grinding include through-feed grinding, in-feed/plunge grinding, and internal centerless grinding.

Figure: Schematic illustration of centerless-grinding operations.


Creep-feed grinding is used for high rates of material removal. Depths of cut of up to 6 mm are used along with low workpiece speed. Surfaces with a softer-grade resin bond are used to keep workpiece temperature low and an improved surface finish.

Figure: (a) Schematic illustration of the creep-feed grinding process. Note the large wheel depth of cut. (b) A shaped groove produced on a flat surface in one pass by creep-feed grinding. Groove depth can be on the order of a few mm. (c) An example of creep-feed grinding with a shaped wheel.


Figure: Schematic illustration of a horizontal-spindle surface grinder

Grinding Machines


Common Grinding Wheels

A grinding wheel is made of abrasive grains held together by a bond. These grains cut like teeth when the wheel is revolved at high speed and is brought to bear against a work piece. The properties of a wheel that determine how it acts are the kind and size of abrasive, how closely the grains are packed together and amount of the bonding material.

Figure: Common types of grinding wheels made with conventional abrasives


Identifying Grinding Wheels

Standard Marking System for Aluminum-Oxide and Silicon-Carbide Bonded Abrasives


Standard Marking System for Cubic-Boron-Nitride and Diamond Bonded Abrasives


Chip Formation

Chip formation and plowing of the workpiece surface by an abrasive grain.

Schematic illustration of chip formation by an abrasive grain. Note the negative rake angle, the small shear angle, and the wear flat on the grain.


Mechanics of Grinding

Grinding is basically a chip removal process in which the cutting tool is an individual abrasive grain. The mechanics of grinding and the variables involved can be studied by analyzing the surface grinding operation as shown in the following Figure.

wear wheelof Volume

removed material of Volume ratio, Grinding

rise eTemperatur

forceGrain

4 , thicknesschip Undeformed

length, chip Undeformed

2/14/34/1

G

v

VCdD

D

d

VC

v

D

d

VCr

vt

Ddl

D=Grinding wheel diameterd= Wheel depth of cutV= Tangential velocityv= Workpiece velocityt=Undeform thickness (grain depth of cut)

C=0.1 per mm2 to 10 per mm2 r= 10 to 20 for most grinding operation


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Shaping & Grinding and Realated Operations

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