Rapid Prototyping Tooling And Manufacturing Engineering Essay

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Rapid manufacturing is a concept of producing finished goods on demand without the need of tooling, moulding or machining. These techniques are cost effective solution for the production for small single units. The cost analysis for Stereolithography, Fused Deposition Modelling and Selective Laser Sintering has helped to identify where the major source of the cost for rapid manufacturing are to be found. The cost analysis includes the machine cost, machine cost and labour cost. The overall cost for laser sintering process was found to be the cheapest. The build rate is high and therefore production volume per part is also high. The smooth surface finish is not critical and therefore this process can be used to manufacture the bulb housing for military applications. the materials used also have environmental resistance. This process has already been used in stringent and demanding applications like aerospace industry and can be successfully applied to military applications as well. The application of this process can be improved by considering the issues such as surface finish and dimensional accuracy.

Description of the process.

Stereolithography

In this process to prepare the build, the material used is liquid polymer resin. The energy of the solid state, formerly gas charged, stationary UV laser is imparted on the photopolymer using X-Y scanning mirrors on to the X-Y plane, which causes the material to solidify. The first layer formed is comprised entirely of support structures which cures and is bonded with the platform. Once the support structure is build, the first layer (bottom part) of the part geometry is formed. The laser solidifies the internal area of the entire profile with overlapping passes in the X-Y axes. After a layer is complete the resin flows over the build, which is levelled using the blades. The subsequent layers are build as the platform lowers equal into the vat resin leaving a gap equal to one layer thickness (0.03- 0.25) .The resin level is checked by the sensors in preparation for the curing of the next layer. This process is repeated until the prototype is complete. It offers high dimensional accuracy and surface finish. This is mainly applied for the form and fit models and can be used as a direct rapid manufacturing solution.

Selective laser sintering

In this process the materials are fed to the chamber in the powdered form and then operating temperatures are set just above the melting point of the material. When the operation starts the build piston lowers into the build chamber by one layer thickness (ranges from 0.10-0.15mm). The powder is deposited using a roller. A stationary CO2 laser, ranging from 50-100 mW, is directed to scanning mirrors that redirect the laser for travel in the X-Y lane. The laser imparts thermal energy into the thermal bed which sinters the powder. As no support structures are required the first layer is the actual part geometry. After a layer is complete, the piston lowers and fresh powder is deposited by the roller. The build process repeats for all subsequent layers and the prototype is completed. it offers poor surface finish and dimensional accuracy. This is mainly applied for functional testing and can be successfully applied to the direct manufacturing of production of parts.

Fused deposition modelling

In this process the build temperature is raised to operating level which is just below the melting point of the material.The material is extruded in the form of semi molten material through an extrusion head called the liquefier, which travels in the X-Y plane. When the material is deposited, it bonds to the previous layer and rapidly hardens. As the layer is completed the build plate lowers by one layer thickness (0.13 - 0.30 mm).The first layer of the support structures are deposited to a disposable mat and then the first layer (bottom part) of the actual geometry is built. The surface finish is poorer than stereolithography but it is comparable to the selective laser sintering. It can be used for rapid manufacturing applications with the features the process provides.

Cost Analysis

STEREOLITHOGRAPHY:-

Calculation of machine costs:-

Number per platform (N) = 120

Platform build time (T) = 20

Production rate per hour (R) = N/T =120 / 20

Therefore, production rate per hour R = N/T = 120/20

R= 6

Hours per year in operation (HY) = 8544 x 80%

HY= 6835.2 hrs.

Production volume total per year (V)

V= R x HY

= 6 x 6835.2

V= 41011.2

Machine costs = Machine and ancillary equipment (E) = £500,000

Depreciation period = 8 years

Equipment depreciation per year (D)

D = E/8 = 500000/8

D = £62,500

Machine maintenance per year (M)

M = £70,000

Total machine cost per year (MC)

MC = D + M

= 62,500 + 70,000

MC = £132,500

Machine cost per part (MCP)

MCP = MC/V

= 132,500 / 41011.2

MCP = £3.23 per part

Calculation of labour costs:-

Number per platform (N) = 120

Platform build time (T) = 20

Production rate per hour R = N/T = 120/20

R= 6

Hours per year in operation

HY = 8544 x 80%

HY= 6835.2

Production volume total per year

V = R x HY

= 6 x 6835.2

V= 41011.2

Machine operator cost per hour (Op) = 15

Set = up time to control machine

Post = processing time per build

Labour cost per build

L= Op x (Set + Post)

= 15 x 4

L= £60

Labour cost per part

LCP= L/N = 60/120

LCP= £0.5 per part

Calculation of material costs:-

Number per platform (N) = 120

Material per part including support (kg) = SLMass =10 gm = 0.01 kg

Material cost per kg = SLcost = £150 per kg.

Material cost per SL part = SLMCP

SLMCP= SLMass x SLcost

= 0.01 x 150

SLMCP= £1.5

Total cost= Machine cost per part + Labour cost per part + Material cost per SL part

= 3.23 + 0.5 + 1.5

Total cost= £5.23 per part

SELECTIVE LASER SINTERING:-

Calculation of machine costs:-

Number per platform (N) = 300

Platform build time (T) = 40

Production rate per hour (R) = N/T = 300/40

R = 7.5

Hours per year in operation

(HY)= 8544 x 70%

HY= 5980.8 hrs.

Production volume total per year (V)

V= R x HY

= 7.5 x 5980.8

V= 44856

Machine costs = Machine and ancillary equipment = E = £400,000

Depreciation period = 8 years

Equipment depreciation per year

(D) = E/8

= 400,000/8

D = £50,000

Machine maintenance per year (M) = £20,000

Total machine cost per year

(MC) = D + M

= 50,000 + 20,000

MC = £70,000

Machine cost per part (MCP) = MC/V

= 70,000 / 44856

MCP = £1.56 per part

Calculation of labour costs:-

Number per platform (N) = 300

Platform build time (T) =40

Production rate per hour (R) = N/T = 300/40

R= 7.5

Hours per year in operation (HY)

HY= 8544 x 70%

HY= 5980.8 hrs.

Production volume total per year

V= R x HY

= 7.5 x 5980.8

V= 44856

Machine operator cost per hour (Op) =15

Set = up time to control machine

Post = processing time per build

Labour cost per build (L)

L= Op x (Set + Post)

= 15 x 8

L= £120 per build

Labour cost per part

LCP= L/N

= 120/300

LCP= £0.4 per part

Calculation of material costs:-

Number per platform (N) = 300

Material per part including support (kg) = SLSMass

SLSMass= 50 gm.

SLSMass= 0.05 Kg

Material cost per kg = SLScost

SLScost= £30 per kg.

Material cost per SLS part = SLSMCP

SLSMass x SLScost

= 0.05 x 30

SLSMCP= £1.5

Total cost= Machine cost per part + Labour cost per part + Material cost per SLS part

= 1.56 + 0.4 + 1.5

Total cost= £3.46 per part

FUSED DEPOSITION MODELING:-

Calculation of machine costs:-

Number per platform (N) = 49

Platform build time (T) = 25

Production rate per hour (R) = N/T = 49/25

R= 1.96

Hours per year in operation (HY)

HY= 8544 x 90%

HY= 7689.6 hrs.

Production volume total per year (V)

V= R x HY

= 1.96 x 7689.6

V= 15071.616

Machine costs

Machine and ancillary equipment (E)

E= £80,000

Depreciation period = 8 years

Equipment depreciation per year (D)

D = E/8

= 80,000/8

D = £10,000

Machine maintenance per year (M)

M = £10,000

Total machine cost per year (MC)

MC = D + M

= 10,000 + 10,000

MC = £20,000

Machine cost per part (MCP)

MCP = MC/V

= 20,000 / 15071.616

MCP = £1.326 per part

Calculation of labour costs:-

Number per platform (N) = 49

Platform build time (T) = 25

Production rate per hour (R) = N/T = 49/25

R= 1.96

Hours per year in operation

HY= 8544 x 90%

HY= 7689.6 hrs.

Production volume total per year

V= R x HY

= 1.96 x 7689.6

V= 15071.616

Machine operator cost per hour (Op)

Set = up time to control machine

Post = processing time per build

Labour cost per build

L= Op x (Set + Post)

= 15 x 2

L= £30 per build

Labour cost per part

LCP= L/N

= 30/49

LCP= £0.612 per part

Calculation of material costs:-

Number per platform (N) = 49

Material per part including support (kg) = FDMMass =10 gm = 0.01 kg

Material cost per kg = FDMcost

FDMcost= £250 per kg.

Material cost per FDM part = FDMMCP

FDMMCP= FDMMass x FDMcost

= 0.01 x 250

FDMMCP= £2.5

Total cost= Machine cost per part + Labour cost per part + Material cost per FDM part

= 1.326 + 0.612 + 2.5

Total cost= £4.438 per part

Selection and justification

The process selected to manufacture the bulb housing for military application is selective laser sintering. The total cost of the part manufactured by this process is cheapest as compared to the other processes. The machine cost and cost per part and properties of the material are the limitations of stereolithography which does not make this suitable for this application. The material used in the process is not affected by moisture and chemical agents. The build time is for the part is considerably less. The machine is capable of building a higher number of parts by stacking vertically. Thus a high production volume per year can obtained as compared to the other processes. The process does not require support structures. The post processing time is minimized as compared to the processes. The labour costs are minimal for the selective laser sintering as compared to the process considered. The material costs are high as it was assumed that the material cannot be recycled. But the sintered material only comprised one tenth of the material with more efficient packing of parts and the cost should be able to reduce significantly. The thermoplastic materials can be easily machined. The machine cost is high, however in the long run, this cost should reduce significantly as the material cost and the labour cost are minimal and the cost per part is cheaper

Issues

There are some limiting factors in the applicability of this process which include the surface finish and dimensional accuracy. The dimensional accuracy is poor and surface finish is rough and porous. It is also not suitable for the applications where tight tolerance parts are to be manufactured. It cannot manufacture translucent and aesthetically appealing components. The production volume is not specified, it can be expensive for low production volumes because the initial setup cost (machine cost) is high considering the small manufacturing industry.

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