Manufacturing process -1

Navroz Navodia(N3)

Slotting machines can simply be considered as vertical shaping machine where the single point reciprocates vertically.

The work piece is mounted on the table, it is given slow longitudinal and / or rotary feed.

The feed can be given by hand or by power.

The circular feed permits machining of a curved surface whereas the plane surface are cut by using either of the table cross feed.

Slotter machine

Photographic view of slotter

It is principally used for internal cutting like internal

cutting slots.

For making keyways.

Large internal and external gears can be machined using

indexing arrangement of rotary table.

Keyseaters, a specially designed slotter is used to make

internal keyways.

There are four types of slotter

1. Puncher slotters

2. General production slotter

3. Precision tools room slotter

4. keyseaters

It is heavy rigid machine used for removing large amount of metal from heavy forged, stamped or roughly sawn work piece.

It can remove surplus material from roughly finished work piece.

It can also finish the job. The ram is driven by a spiral clock and pinion

arrangement whereas the pinion is driven by speed reversible electric motor.

A square table is fitted for plane work whereas round tables is fitted for circular cutting.

These slotter have a

solid body that can be

tilted for machining

inclined surfaces.

They are lighter high speed slotters and used for tool room work with accurate machining.

They are used for taking lighter cuts with accurate dimension.

Special jigs and fixtures are used to produce large number of identical job.

Keyseaters are special type of slotters designed for machining keys in wheel and gear hubs.

There are generally four drive mechanism.

1. Slotted disc mechanism

2. Variable speed reversible motor drive

3. Hydraulic drive

4. Slotted link drive.

The pinions which is in mesh with main gear gets its

motion from the drive motor through belt drive.

The gear is coupled to the slotted driving disc.

The circular motion of the slotted disc is converted into

the vertical reciprocating of the ram with the help of

connecting rod.

The stroke length can be changed by changing the

position of crank pin relative to center of slotted disc.

A range of ram speed is obtained with the help of multispeed gear box provided with motor.

It is used in large modern slotters

Hydraulic drive is used for precision work

The piston axis vertical in this drive instead of horizontal used in shapers but the rest arrangement is similar.

This drive is smooth and free from vibration.

Slotted link drive is used for heavier type of slotting machine.

The drive from the electrical motor is transmitted to helical stroke wheel through a gear box and clutch.

The wheel carries a bronze sliding die block which slides on the face of a large oscillating link connected to the ram of the slotter.

The stroke of the slotter is adjusted by varying the radius at which the sliding die block rotates with the stroke wheel.

The vertical position of the ram can be changed through a pair of bevel wheels.

It is a machine tool designed to machine metal by combining the line motion of a job andthe perpendicular feed of the tool.

The type of work is similar tothat done on shaper but it takes larger workpeices.

Double housing planer

They are of six types

1. Double housing planar

2. Open side planer

3. Universal planer

4. Pit type planer

5. Plate or edge planer

6. Divide Type Planer

It is the most common type of planer.

It consists of mainly a massive bed on which the worktable reciprocates, and two vertical columns or housing, one on each side of the bed.

Each column carries a tool head that can be slide up and down on the column.

A cross rail fitted between the two columns may carry one or more tool heads that can slide horizontally on the cross rail.

All the tool heads can be clamped in position, and can be used collectively or individually depending on the requirements.

Open side planer consists of only one vertical column or housing on which the cross rail is mounted.

The column and the cross rail carry single and double tool heads respectively.

This type of machine permits machining of wide work pieces.

The main feature of a universal planer is that it can cut on both forward and reverse strokes.

Different cutting edges operate for cutting in the two strokes.

A pit type planer differs from other planer in the sense that, the table and the work piece resting on it remain stationary and the tool reciprocates across the work surface.

This type of machine is preferred for very large work, where the weight of the work piece and the tool required table would make reciprocating movement difficult.

The job is either mounted on a stationary table, or on the floor inside a pit, and hence the name pit type planer.

One or two tool heads can be mounted on the cross rail and two side tool posts the housings, if required.

The entire unit travels along the horizontal ways and fro and, thus the tool moves past the work surface during operation.

All feeds are automatic and reversible and are designed to operate either at both end of the planing stroke or at one end only.

This type of machine is used for machining the edges of heavy workpieces.

The workpiece is clamped on the bed and the side mounted carriage supporting the cutting tool is reciprocated along the edge of the workpiece.

Cutting can take place during both directions of carriage travel

A large screw drive is used for moving the carriage.

It is also called tandem planer and consists of two worktables,

which may be reciprocated together or separately.

It is quite well known that, mounting and setting of work pieces

on the worktable consumes more time thereby restricting the

machine for continuous mass production applications. In such

cases, divided table planer can be used, where in, one

worktable can be used for setting up a new work piece, while

the second worktable carrying work piece is being machined.

The two tables can be joined together to hold large work pieces.

There are different planer drive mechanism such as

1. Open and crossed belt drive

2. Table drive by reversible motor

Four pulley belt drive Two pair of loose and fast pulleys are driven at

different speeds from the same pulley with open crossed belts.

At the end of each stroke a belt shifter changes the position of both the belts simultaneously thereby reversing the table

To reduce the slip and angle of lap the cross belt is used for forward motion.

Three belt pulley drive The central pulley is loose on the shaft while the

two outer ones are fixed.

Drive between two shafts is through gears and an additional gear is there on one side for reversal motion.

At the end of each stroke the belt shifter shifts the belt from one to other

The loose pulley enables the machine to be stopped temporarily for checking the job without having to stop the driving motor.

Many planers are equipped with a variable

speed electric motors for driving the bull gear

through a train of gears

The speed and direction of the rotation of the

D.C motor can be easily controlled with

suitable controlling devices.

The feed mechanism is provided intermittently between two strokes.

Cross feed and down feed are given on the tools on the cross rail.

The down feed is needed for machining vertical and angular surface while cross feed is given while machining horizontal surfaces.

Both feed are given with the help of screw and nut mechanism and can be given manually or automatically.

The automatic feed drive for a planer are provided by two methods

1. By friction disc

2. By electric drive

It consists of a friction disc D at the bottom and a rack and pinion drive at the top.

The friction disc D is connected to a table drive shaft with a flexible connection formed through leather washers.

A T-slot is cut radially on the face of feed disc within which block B slides over a screwed shaft.

At the end of screwed shaft is a knurled knob K which can be turned to adjust the position of block B with respect to the centre of the disc.

The sliding block is connected at one end to a connecting rod C which at the other end is connected at the rack R through a guide G.

A projection pin connected to the disc body extends beyond the body of the disc.

‣ When the table drive shaft starts rotating during the cutting stroke the motion is transmitted to the disc but when the projecting pin hits a fixed pin P1 fitted to a machine body, the disc starts slipping even though the drive shaft continuous to rotate.

‣ When the table is reversed the disc rotates through the same angle in opposite direction due to the projecting pin hitting the second fixed pin P2.

‣ The rotary motion of the feed disc is transmitted through rack R to pinion L mounted on shaft S1.

‣ Gears G1 and G2 are mounted on shaft S1,butG2 is keyed to shaft while G1 is free.

‣ Double pawl M is pinned on face of G1 and any one end of pawl is meshed with gear G2.

‣ When left end of pawl is meshed with G2, upward movement of rack rotates gear G2 in clockwise direction and also rotation of gear G1clockwise because of pawl connection.

‣ Downward movement of rack will move gear G2 in anticlockwise direction but no motion is transmitted to G1 because pawl’s bevel edge will slip over teeth of gear G2.

‣ Gear G1meshes with gears G3 and G4 mounted on shafts S2 and S3 which are down feed and cross feed shafts of planer.

‣ The feed motion is transmitted to tool heads by shafts S2 and S3.

‣ Direction of feed movement can be reversed by changing position of double pawl.

‣ Amount of feed can be varied by operating knurled knob K which changes eccentricity of block B.

Modern planer which have an electrical drives also use an electrical feed mechanism.

A separate motor is used on these planer to provide feed motion.

The motor is energised at the same time as the table reversing mechanism and rotates through different part revolution after which it is automatically tripped.

For best planer use many tool head should be used as possible.

For roughing and finishing cut , the first tool may do roughing cut and other tool head may follow it doing finishing cut.

If the medium sized parts are lined up in a row on the planer table and are machined at the same time ,it is known as string or multiple machining.

Planer tools are same as general type of lathe but they are heavier in construction.

The common operations include Planning of:

1. Horizontal flat surface

2. Vertical flat surface

3. Planning at an angle

4. Planning at curved surface

5. Planning different type of slot, grooves etc.

In shaper the work piece is held stationary on the table while in planer tool is stationary and work piece moves back and forth.

Planer holds heavier work pieces compared to shaper. A planer is heavier and can give much heavier cuts

compared to a shaper. Shaper uses one cutting tool while planer using

several cutting tool simultaneously. The drive on a shaper is slotted lever crank

mechanism while planers are operated by fast and loose pulleys.

Planers give better accuracy than shaper because of their better rigidity.

Shaper is more economical for cutting small and medium size work pieces.

Work piece can be clamped in shaper more easily compared to planner.