The following points highlight the twelve main types of drilling machines widely used in industries. The are: 1. Portable Drilling Machine 2. Sensitive Drilling Machine 3. Upright or Column Drilling Machine 4. Upright or Column Drilling Machine 5. Gang Drilling Machine 6. Multi-Spindle Drilling Machine 7. Vertical Turret Type Drilling Machine 8. Automatic Drilling Machine and Few Others.
Type # 1. Portable Drilling Machine:
It is a small compact drilling machine used principally for drilling operations which can be performed on a regular drill press. The most renewed example of this class is the hand drill. It is equipped with a small electric motor which gives power while working and is specified by the maximum drilling capacity.
Type # 2. Sensitive Drilling Machine:
It is a light, simple, bench type machine for light duty working. It is usually supplied with a friction drive to give an infinite speed ratio. The horse power is small. 800 to 9000 r.p.m. is a typical range of this machine, with the maximum drilling capacity of 12.5 mm. The major components of this machine are spindle, column, table and the base.
Machines of this type are usually hand fed and operate on the principle of rack and pinion drive. The drill head is counterbalanced and fed through a hand lever system. This arrangement allows the operator to feed the force acting on the drill and hence the term ‘sensitive’.
Type # 3. Upright or Column Drilling Machine:
These are similar to sensitive drilling machines, except that they have power feeding mechanism for rotating the drill and are designed for heavier work. Generally these machines have box type column which is more rigid and consequently adapted for heavier work. The table can be given precise movement by a lead screw and graduated sleeve system.
It has several spindle speeds offered in several speed ranges from 75 to 3500 r.p.m. The feed clutch is automatically controlled so that spindle will be disengaged when it reaches its upper and lower limit of travel.
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It has also free engagement of taps through clutch and rapid reversing mechanism for withdrawals. Such a machine is ideally suited for small and big shops. The size of the work that can be accommodated is limited by the distance between the spindle and the column.
Type # 4. Radial Drilling Machine:
It is the largest and most versatile of the drilling machines and is very well suited for drilling large number of holes. It is a single spindle machine intended for handling large and heavy work or work which is beyond the capacity of the small drilling machines. It consists of vertical column with a radial arm that can be swung through an arc of 180° or more.
On the radial arm, which is power driven for vertical movement, is an independently driven drilling head equipped with a power feed. The drilling head may be moved along the arm by hand or power on a gear and rack arrangement. To drill a hole the following procedure is followed.
The arm is raised or lowered as needed, the drill head is positioned and locked on the arm, the arm is locked in that position, the spindle speed and feed are adjusted, and the depth is set. The drill will then feed down and returns when the proper depth has been reached. The arm and column may then be unlocked and the drilling head moved to a new position without disturbing the work.
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Universal radial drills allow the radial arm to the rotated on a horizontal axis, providing the angular hole drilling. Spindle speeds ranging from 20 to 1600 r.p.m. and feed from 0.05 to 3 mm per revolution are available. Sometimes the drilling head is provided with a swivelling arrangement to facilitate angular cutting.
Fig. 18.3 shows in schematic form a radial drilling machine.
Fig. 18.4 shows the photo of a radial drilling machine and its design features are listed below:
i. Higher output easy rotation of the arm and swinging of the drill head assembly on thrust bearing locates the distant points very easily and quickly.
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ii. Easy to operate easy movement of the machine maintains the efficiency of the operator at all times. All operating controls such as switch, locking levers are in easy reach of the operator.
iii. Base, main arm and pillar are of Graded castings. These are designed to withstand heavy cutting forces with minimum deflection and wear of the machine.
iv. The outer pillar rotates about inner pillar on roller and ball bearings fitted at the bottom and top of the inner pillar. This arrangement rotates the arm to a light touch. Pillar can be rigidly locked by operating the lever.
v. Low maintenance cost, longer life sliding of the drill head and parts such as wedges, screws, nuts, etc., are eliminated. This reduces the maintenance cost and increases the life of the machine.
vi. This drilling machine can serve the slow speed operations like reaming, tapping, etc., with optional back gear unit.
vii. Taps to pre-set depth.
viii. The electrical control unit which facilitates reversing of the spindle at the pre-set depth, especially in blind tapping.
ix. Knob, switch for forward, reverse and stop.
Fig. 18.3 show five principal types of drilling machines.
Type # 5. Gang Drilling Machine:
Gang drilling machines have two or more drill heads mounted on the same table. These can be run either simultaneously or in sequence. Spindles are lined in a row, driven either manually or by power. Each spindle can be independently set for speed and depth. Such a machine is useful when a workpiece is to have several operations performed, such as drilling, counter boring, reaming etc., or for drilling holes of several different sizes.
It is adopted for short runs, where tooling cost of a multi-spindle machine is too great. Fast movement of the work from one spindle to another is an important, feature of this machine. The number of spindles is practically unlimited, but the four spindles are the most common. Machines of this type are used for any straight line, multiple hole drilling applications, as in pipes, channels, castings, angles and plates.
Type # 6. Multi-Spindle Drilling Machine (Fig. 18.6):
These have been developed for the purpose of drilling several holes simultaneously. These machines are essentially production machines, and once set-up, will drill many parts, with such accuracy that all the parts are interchangeable. Multi-spindle machines differ in the manner in which the drills are held and the way in which feed is accomplished.
Generally multi-spindle machines are of vertical-type. The head assembly has number of fixed upper spindles driven by pinions surrounding a central gear. A corresponding number of spindles are located below this gear and are connected to the upper ones by a tubular drive-shaft and two universal joints. These, thus can lower the spindles. The drills may be adjusted over a wide area.
The entire head assembly carrying all the spindles travels on vertical double-V ways. In some machines, table moves upwards and drilling heads are fixed. The drilling cycle consists of the rapid advance of drills to the work, proper feed, and rapid return of drills to the starting position.
For drilling closely spaced holes, some of the holes are drilled first by a set of spindles, the job is then repositioned and other set of closely spaced holes are then drilled by another set of spindles.
A special type of multi- spindle machine is way-type. It has usually two, three or four ways, each of them is inclined at same angle. When several holes in different planes are to be drilled, this type of machine is needed.
Type # 7. Vertical Turret Type Drilling Machine:
This machine has a turret which houses various tools such as drill, ream, spot-face, counter bore, tap in any desired sequence. The various spindles on this indexing turret can be indexed manually or automatically. These spindles cannot be driven until they come to the drilling position.
Type # 8. Automatic Drilling Machine:
These are used for high production work. These are built of a number of unit heads with single or multiple spindles in angular, horizontal or vertical positions in various combinations on a special base. Indexing table and work holding fixture at each station are also provided.
Type # 9. Deep-Hole Drilling Machine:
These machines are used for drilling such holes whose length exceeds three times the drill size. The examples of this class are rifle barrels, long spindles, connecting rods and certain oil-well drilling equipment. They are of vertical or horizontal type, single spindle or multi-spindle and may vary as to whether the work or the drill is made to revolve.
Type # 10. Turret Drilling Automatics (Refer Fig. 18.7):
i. High-speed operation
ii. Extremely short set-up time
iii. Quality of production
iv. Robust design
v. Versatility
vi. Comfortable operating
vii. Several machines per operator
viii. Pendulum machining.
Type # 11. Special Turret Drilling Automatics (Refer Fig. 18.8):
The universal application and great flexibility of turret drilling automatics, with their high speed and robust construction, lead to trouble-free production machines. For unusual requirements, special machines, tailored to a particular operation or series of operations can be used.
The drawings below give an idea of various types of construction:
Drawing 1:
The turret head with 6 or 9 quick change spindle is the main component and starting point for design of special turret drilling automatics.
Drawing 2:
Special machine with 9 spindles in bed design with turret adjustable for height, for large workpiece.
Drawing 3:
2-way horizontal machine. 2 out of total of 12 or 18 tools can work simultaneously.
Drawing 4 and 5:
Six-station indexing chuck round table automatic for machining 5 sides of hydraulic blocks. While the deep hole drilling unit prepares the piston bore(s) for honing, the high-speed 9-spindle turret heads machine all connection holes from 5 sides.
On the round table are 6 hydraulic indexing chucks with horizontal axes, which automatically index the clamped workpiece 4 x 90°.
Type # 12. Drill Mill Centre (Refer Fig. 18.9):
Features:
i. The X, Y, Z axes slideways are composed as one unit. Best suited for manufacturing system with pallet changer, robots, indexer or where transfer line for the table is fixed and all the movements for X, Y, Z axes are done on the column side.
ii. Having a slanted bed surface. The cut chips are completely cleared for the working surface and the bed.
iii. The CNC system and electric system are installed at the back of the machine, therefore minimizing floor space requirement and facilitating the location and installation.
iv. The most suitable speed can be chosen within 200 to 3000 rpm, 300 to 6000 rpm, or 600 to 12000 rpm because the frequency converter is used for the change of spindle speed.
v. Simply constructed turret tool changer is used for the machine.
vi. The rapid traverse rates are provided for fast positioning.