A Presentation on:HELICAL GEARSCONICAL GEARSSPIRAL BEVEL GEARS

Application- MARINE

Presented By:SOMESH SAURABH BT13MEC081SONU VERMA BT13MEC082DEBA PRAKASH BT13MEC099

PHYSICAL AND MECHANICAL PROPERTIES OF SAE-8620 STEEL

COMPOSITION

Carbon Manganese Nickel Chromium Molybdenum

0.18-0.23 0.70-0.90 0.40-0.70 0.40-0.60 0.15-0.25

MECHANICAL PROPERTIES

NORMALIZED AT 915˚ C

Tensile

Strength

(MPa)

YieldingStrength (MPa)

Elongation/50 mm

BHN Hardness (HB)

635 360 26.3 183

ANNEALED AT 870˚ C

Tensile

Strength

(MPa)

YieldingStrength (MPa)

Elongation/50 mm

BHN Hardness (HB)

540 385 31.3 149

Since marine gears are high speed gears and also there are chances of high shocks during operation so the gears surfaces must be strong enough to withstand dynamic loading and wear resistance. So, in order to get these properties we do Heat Treatment that includes:

1.Pre-hardening processAnnealing- Improves machinability- Involves heating to

870C and then slowly cooled to 315C in a furnace.

Normalizing- Controlling dimensional variations during hardening processes.

- Heating to 800C and then cooling in atmospheric air to relieve residual stresses.

Heat Treatment

2.Hardening Process

Case Hardening- To produce hard, wear-resistant surface layer on top of a ductile, shock-resistant core.

- Idea is to keep the core of gear teeth at a level of 30-40 HRC to avoid tooth breakage while hardening at outer surface up to 50 HRC to increase pitting resistance.

Carburizing- A Time-proven process in which a carbon-rich atmosphere surrounding the workload is used to chemically react with the surface of the parts to allow an adequate quantity of carbon to be absorbed at surface and diffused into the material.

SIZE AND WEIGHT OF GENERAL HELICAL GEARS USED IN MARINE

APPLICATIONS

Diameter (mm)

Thrust (kN) Approximate Weight (metrictonnes)

1000 245 2.5

2000 1000 17

•MARINE GEARS ARE MADE HAVING FACE WIDTH UPTO 1000 mm

• THEY ARE SUPPOSED TO TRANSMIT POWER UPTO 15 MW (20,000 HP)

MANUFACTURING PROCESSES INVOLVED

CASTING : Centrifugal casting is used for manufacturing these large gear blanks.

• In this method the mould is rotated about its central axis and there exists a continuous pressure as metal is solidifying

• This method is predominantly used for radial symmetrical casting

GENERATION OF TEETH BY MACHINING ON CASTED BLANKS

HOBBING

•Hob teeth are shaped to match the tooth space and are interrupted with grooves to provide cutting surfaces. It rotates about an axis normal to that of the gear blank, cutting into the rotating blank to generate the teeth.

•It is the most accurate of the roughing processes since no repositioning of tool or blank is required and tooth is cut by multiple hob-teeth.

•Excellent surface finish is achieved.

FINISHING OPERATIONS

• Grinding : In grinding , a contoured grinding wheel is run over machined surface of the gear teeth using computer control .

• Small amount of metal removal with high surface finish is obtained

• Lapping : Lapping employs an abrasive-impregnated gear or gear-shaped tool that

is run against the gear to abrade the surface.

• In lapping the abrasive tool drives the gear to an accelerated and controlled run-in

to improve surface finish and the accuracy.

• The figure shows the lapping operation for spiral bevel gears in employed in

marine.

MACHINES AND MATERIAL HANDLING SYSTEM

Flat AGVs for heavy and large gears

Grinding MachineHobbing Machine

Rate of Production= 15pc/day

Number of Shifts= 2 shifts/day

Time for one Shift= 8hrs

Heat treatment processes are not included in the FMS Layout but it will come after hobbing process.

Part mix is assumed on the basis of the number of gears present in a standard gearbox of marine engine.

Assumptions for FMS

Number of Servers per Station

Station Description Number of Servers

1. Loading/Unloading 2

2. Hobbing 2

3. Grinding 2

4. Lapping 2

5. Inspection 1

Total number of Servers=9

Operations to be performed by FMSPart Part Mix

(Pj)Operation Descriptio

-nStation Process

Time(min)Frequency

A 1 Loading 1 10 1

(Helical 2 Hobbing 2 60 1

Gear) 0.6 3 Grinding 3 40 1

4 Lapping 4 30 1

5 Inspection 5 10 .5

6 Unloading 1 5 1

B 1 Loading 1 2 1

(Conical 2 Hobbing 2 20 1

Bevel 0.2 3 Grinding 3 15 1

Gear) 4 Lapping 4 10 1

5 Inspection 5 5 .3

6 Unloading 1 2 1

Contd...

Part Part Mix Operation Descriptio-n

Station Process Time(min)

Frequency

C 1 Loading 1 2 1

(Spiral 2 Hobbing 2 20 1

Bevel 0.2 3 Grinding 3 15 1

Gear) 4 Lapping 4 10 1

5 Inspection 5 5 .3

6 Unloading 1 2 1

Line-Sketch of FMS

Work Load at each Station=Wli= ∑∑tijk.fijk.pj

Bottleneck Station = max(Wli/Si)

Rp* = (No. of servers on bottleneck station)/(Work load on bottleneck station)

Production Rate, Rp= Pj.Rp*

Utilisation, Ui =(Wli/Si).Rp*

Formulae used for calculations

Calculations For Bottleneck Station

Stations Workload(WLi)(min.)

No. of Servers(Si) Wli/Si

1 10.6 1 10.6

2 44 2 22

3 30 2 15

4 22 2 11

5 3.6 1 3.6

Maximum Value of Wli/Si= 22 (Station 2).Station 2 (Hobbing Station) is Bottleneck Station.

Utilization of Each Station

Station Description Utilization

1. Loading/Unloading 47.7%

2. Hobbing 100%

3. Grinding 67.5%

4. Lapping 49.5%

5. Inspection 16.2%

Overall Utilization of Stations=62.2%

Rp*= (No. of servers on bottleneck station)/(Work load on bottleneck station)

Rp*=2.72 pc/hr

Production Rate for Part A (Helical Gear)=1.632 pc/hr

Production Rate for Part B (Conical Bevel Gear)=.544 pc/hr

Production Rate for Part C (Spiral Bevel Gear)=.544 pc/hr

Production Rates of each Part

TESTING OF MANUFACTURED GEAR

PARKINSON’S GEAR TESTING METHOD

•The standard gear is mounted on a fixed spindle and the gear to be tested is mounted on another spindle which can slide over a carriage

•The dial indicator gives the deviation of teeth profile of gear being tested

A flexible manufacturing system (FMS) is a manufacturing system in which there is some amount of flexibility that allows the system to react in case of changes, whether predicted or unpredicted.

Most FMS consist of three main systems. The work machines which are often automated CNC machines are connected by a material handling system to optimize parts flow and the central control computer which controls material movements and machine flow.

FMS