DESIGN OF MULTI-SPINDLE DRILL HEAD WITH DIFFERENT PITCH HOLES

MULTI-SPINDLE DRILL HEAD WITH DIFFERENT PITCH HOLES

CONCEPT

Drilling is the most widely used process for producing one or multiple holes in a work piece. In this article we are going to deal with the engineering design and fabrication of a multi-spindle drill head that can be used to drill holes for different pitch circle diameters.
The purpose is to minimize the production time for drilling multiple holes in a work piece for different Pitch Circle Diameters (PCD). This design employs adjustable transmission systems along with a gear arrangement. The design of the spindle head is done using the CAD/CAM software.

PROBLEMS IDENTIFIED

  1. Production time is greatly increased if we use general purpose machines that have single spindle drilling head.
  2. The total cycle time increases when general purpose machine is used since multiple operations cannot be done in the same machine.
  3. Since multi-spindle drill head is used in work piece the tool breakage or work piece wear and tear is common because of many holes in the work piece.
  4. Manufacturer’s emphasis on quality but the demand to meet the scheduled delivery is delayed due to the conventional drilling machines slow rate of productivity.

SOLUTIONS TO PROBLEMS

  • The problem 1 can be solved by using multiple drill tools connected to the planet gears.
  • The problem 2 can be rectified if we use a multi head spindle that can carry out a number of operation in a single setting.
  • The problem 3 can be solved by limiting the number of holes drilled in the work piece.
  • The problem 4 can be overcome and the demands to meet the delivery time can be met if multi-spindle heads are used instead of general purpose machine.

METHODOLOGY

For the fabrication of gang drilling multi spindle head we had the following techniques:

1) Using 3 jaw chuck mechanism
2) Using main gear with four idler gears arrangement
3) Using timing gears, timing belts, slots and idler gears.

USING 3 JAW CHUCK MECHANISM
Working:
The jaws are kept at an equal distance and equal angles from each other in the spline keyway. The drill tools are placed below the jaw chuck. As we adjust the jaw, all the jaws move together at the same distance in the keyway. The spindle is attached to the jaws which transmits the rotational energy from the motor to the drill tools. As the drill tools come in contact with the work piece machining is done.

Problems Faced:

  • The designing of spiral mechanism was complicated.
  • Weight of the 3-jaw chuck is high.

USING SUN AND PLANET GEARS
Construction & Working:
The power from the motor is transmitted to the main spindle, the main spindle is attached to the sun gear which in turn is attached to four planet gears the collets are placed at the bottom each planet gears and the drill tools are attached to the collets.
As the spindle rotates the main gear starts rotating which in turn transmits the motion to the four planet gears, as the planet gear rotates the drill tool attached to it starts rotating. When it comes to contact with the work piece the machining is done. This is for drilling holes for a single PCD.
To drill multiple holes with various PCD`s the sun gear has to be in accordance to the pitch circle diameter.
The diameter of pitch circle can be determined using the formula
PCD = D + 2r
D is diameter of the sun gear
r is radius of planet gear(constant)

Problems Faced:

1.Removing and changing the main gear every time to drill holes for various pitch circle diameter.
2.More time consumption for the arrangement of main gear.
3.It was an existing technique.

USING TIMING BELTS AND TIMER GEARS, SLOTS & IDLER GEARS
Construction & Working
The machine spindle is connected to the main spur gear. The spindle transmits power from the motor to the main gear. The timing gears are placed at right angles to each other in equal distance from the main gear.
The spur gears transmits the motion to the timing gears using two idler gears that are placed in between the main gear and timing gear.
The timing gear are connected externally to the timing belt that have teeth or vertical slots for timing gear to mesh with it hence reducing the slippage. The base plate contains slots for timing gears to move within the given range. The timing belt contains two roller that are used to adjust the belt tension when the timing gears are moving between the slots.
A screw arrangement is placed in the slot area to hold the turning gear with the collet at a specific distance in between the slots.
The power from the motor is transmitted from the spindle to the main gear. The rotation of spur gear causes the two idler gears to rotate which in turn transmits power to the turning gears.
Since the turning gears are connected to the turning belt the power is transmitted to it which causes the timing gears to rotate.When the four timing gears rotate at a constant speed the drill tools comes in contact with the work piece and the machining is done.
Changing the PCD
The timing gears placed in the slots have a set of screws attached to them and the screw is used to adjust and hold the timing gears in the slots. The tightening gears that are kept outside the timing belt are tightened using screws so that the belt tension remains constant. Then the holes can be drilled at different pitch circle diameter. (Note that first the timing gears are placed at the end of the slots then reduced to change the PCD).

PROBLEMS FACED
1.The transmission of power is not equally transmitted to the timing gears
2.The range of PCD was limited due to the tension on the belt
3.Heavier weight of the spindle head
4.Backlash in the belt could not be controlled effectively

COMPONENTS USED
The components used in this multi spindle drill head are
1. Gears
2. Adjustable transmission systems (ATS)
3. Bearings
4. Top plates
5. Bottom plates
6. Drill chuck
7. Drill tool
8. Shank
9. Key
10. Shaft

GEARS
Gears are used to transmit power from the main spindle to the transmission systems.
Main Gear
Quantity – 1
No. of teeth – 32
Gear width – 20mm
Outer Diameter – 60mm
Inner Diameter – 20mm

MULTIHOLEFigure:Gear assembly
Secondary Gears
Quantity – 4
No. of teeth – 20
Gear width – 20mm
Outer Diameter – 38mm
Inner Diameter – 20mm
ADJUSTABLE TRANSMISSION SYSTEMS
It is made up of adjustable shafts with universal joints at both the ends that are used to transmit power from gear to the drill tools. It is made up of steel
Quantity – 4
Length – 360mm (max), 260(min)

MULTIHOLE1Figure : Adjustable transmission systems

BEARINGS
It constraints the relative motion and reduces friction between moving parts
Specifications
Bearings for main gear
Size-6204Z at top, 6203Z in bottom of the main gear
Quantity – 2
Outer Diameter of 6204Z – 45mm
Inner diameter of 6204Z – 20mm
Outer Diameter of 6203Z – 35mm
Inner diameter of 6203Z – 20mm
Bearing for secondary gear
Size – 6203Z
Quantity – 8
Outer Diameter – 35mm
Inner Diameter – 20mm
Bearing for bottom plate
Size – 6202Z
Quantity – 8
Outer Diameter – 30mm
Inner Diameter – 20mm

MULTIHOLE3Figure: Bearings 6202, 6203, 6204

TOP PLATE
Top plates are used to house the gear assembly
Top plate-2
Diameter-170mm
Thickness-10mm

MULTIHOLE4Figure : Top plate 1

MULTIHOLE5Figure: Top plate 2
BOTTOM PLATE
Bottom plate is made of cast iron the bottom plate has arrangement for slots. Bottom plate 1 has markings for various PCD`s. The difference between two PCD marking is 5mm. Bottom plate 2 is used to support the spindle head and observe the vibration.
Quantity-2
Diameter-280mm
Thickness-12mm

MULTIHOLE6Figure: Bottom plate with slots

DRILL CHUCK
Drill chucks are used to hold the drill tools of range 1.5mm – 10mm
Quantity – 4
Outer diameter – 34mm
Inner diameter – 12mm

MULTIHOLE7Figure: Drill chuck
DRILL TOOL
Quantity – 4
Drill tool size – 5mm
Length – 85mm
MULTIHOLE8Figure: Drill tool

SHANK
Shank is used to transmit the power from the motor to the main gear. It is taper turned.
Taper turning
Maximum diameter – 39mm
Minimum diameter – 20mm

MULTIHOLE9Figure: Shank
KEY
Keys are used to transmit power from gear to shaft and to avoid slippage.
Quantity – 5
Length – 20mm
Width – 6mm
Thickness – 6mm

MULTIHOLE10Figure: Key
SHAFT
Shafts in the top plate are used to connect secondary gears to the transmission systems, shafts in the bottom plate are used to connect the transmission systems and the drill chuck.
Shaft connecting gear and transmission systems
Shaft of 20mm diameter is step turned to 16mm

MULTIHOLE11Figure: Shaft connecting gear and the transmission sysytems
Shaft connecting transmission systems and drill chuck
Shaft of 22mm diameter is step turned to 15mm and it is threaded to
12mm

MULTIHOLE12Figure: Shaft connecting transmission systems and the drill chuck

READ FABRICATION OF MULTI DRILL HEAD




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