Developing Built time model of Powdered Bed Fusion Technology In Additive Manufacturing

Satyajeet Udavant sudavant@purdue.edu

Purdue School Of Engineering, Indianapolis

Resources

Additive Manufacturing Lab in Science and Engineering department -- Purdue School of Engineering

Other online resources

Professor

Dr. Andreas Tovar

Keywords Additive manufacturing, EBM printer, binder jetting, material jetting, alternatives for design and

material, design parameters, powder technology

OBJECTIVE

To Design and develop a built time model of a Powdered bed Fusion unit

A) Without Delay time

B) With delay time

BACKGROUND

Few of the additive manufacturing (AM) technique that uses a laser as the power source to sinter powdered material

(mostly metal), aiming the laser automatically at points in space defined by a 3D model, binding the material together

to create a solid structure is categorized as powdered bed fusion processes. It is similar to direct metal laser sintering

(DMLS); the two are instantiations of the same concept but differ in technical details. Selective laser melting (SLM)

uses a comparable concept, but in SLM the material is fully melted rather than sintered, allowing different properties

(crystal structure, porosity, and so on). SLS (as well as the other mentioned AM techniques) is a relatively new

technology that so far has mainly been used for rapid prototyping and for low-volume production of component parts,

or customized parts needed in medical industry (typically orthopedic)

Because finished part density depends on peak laser power, rather than laser duration, a SLS machine typically uses a

pulsed laser. The SLS machine preheats the bulk powder material in the powder bed somewhat below its melting

point, to make it easier for the laser to raise the temperature of the selected regions the rest of the way to the melting

point.

Other additive manufacturing processes are:

Stereolithographic SLA

Fused deposition method FDM

Filament Fabrication FFF

Digital light processing DLP

Laminated object manufacturing LOM

Though the printer-produced resolution is sufficient for many applications, printing a slightly oversized version of the

desired object in standard resolution and then removing material with a higher-resolution subtractive process can

achieve greater precision.02mm

Technology of Powdered bed fusion

Fig 1 Fig 2

Above figure shows the methods used in these technologies.

Following are the examples of various design and complex geometries that are possible.

Fig 3

PROBLEM STATEMENT

Consider a powder bed additive unit (see Fig. 4). Assume that the part platform is to be filled with parts and the

platform is L (mm) long and W (mm) wide. The printhead width is H (mm). Assume that a layer requires three

passes of the printhead, the printhead can print in both directions of travel, and the layer thickness is T (mm).

Assume that a delay of D (sec) is required for cleaning the printheads every K layers. The height of the parts to be

printed is P (mm)

Fig. 4: Schematic of a powder bed additive manufacturing unit. Source:

Table 1: Values of the variables in the powder bed additive manufacturing process.

L W H T D K P Tb

300 185 50 0.04 10 20 60

300 185 50 0.028 12 25 85

260 250 60 0.015 12 25 60

340 340 60 0.015 12 25 60

490 390 60 0.015 12 25 80

A) Develop a build time model to compute build time Tb (sec) using the variables listed in the problem statement.

Assumptions

Since the object to be built is not known but the parts should fill the build platform, there for lets assume the build

time to be total build time for parts.

Print head speed is S mm/sec

To compute the total no of passes we need to consider two cases depending upon the part width(H).

Case I

When the part width(Partwidth) is less than or equal to the width of print head we have,

Then

N1 = no of parts spaced along the Y axis

N1 = W/H (approximated to greatest integer).

Example: when W= 260

H = 60

N1 = 4.33 parts can accommodate along y axis. That means 4 complete parts.

N1 = 4 parts.

Case II

When the part width is greater than the width of print head we have, approximately 1.25+ times more, but less than

2H,

Then

N2 = no of parts spaced along the Y axis

N2 = [(W/H) -1]

(approximated to greatest integer).

Example: when W= 260

H = 60

N2 = 4.33 parts but Partwidth is more than H, therefore there is not much extra space for the

4 th part to fit in.

That means 4-1 parts

N2 = 3 parts (maximum can be accommodate along Y Axis)

For simplification we will consider CASE I for this problem.

S mm /sec is the print head speed.

Pp is total of passes required to lay one layer. It varies with N1

Example

Since, one layer needs 3 passes, 3 rows of parts need 9 passes so as to cover the entire build platform.

Pp is given by,

Pp = N1*3

Dtotal -Total distance travelled by print head to complete one layer over all parts in platform.

Dtotal = Pp*L

Print time = Dtotal / S

Delay due to print head cleaning,

No.L- Number of layer is given by print ht and thickness P/T

No.L = P/T

CF- Cleaning frequency is number of times print head is cleaned

CF = No.L / K

Actual CF- is greatest integer of cleaning frequency.

Delay due to print head cleaning = CF*D

Now,

Build time Tb = print time + delay due to print head cleaning

Tb = S/ N1*3*L + D*P/( T* K)

(B)Compute the build time Tb (sec) for a layer of parts given the variable values in Table 1.

L(mm) W(mm) H(mm) N1= W/H Max complete

N1 Pp D-total (mm) print time(min)

300 185 50 3.7 3 9 2700 270

300 185 50 3.7 3 9 2700 270

260 250 60 4.166667 4 12 3120 312

340 340 60 5.666667 5 15 5100 510

490 390 60 6.5 6 18 8820 882

D(sec) K P(mm) No.L CF Actual CF cleaning

delay(min)

10 20 60 60 3 3 0.5

12 25 85 102 4.08 4 0.8

12 25 60 72 2.88 2 0.4

12 25 60 72 2.88 2 0.4

12 25 80 96 3.84 3 0.6

Total Build Time:

print time(min) cleaning delay(min)

Tb(min)

270 0.5 270.5

270 0.8 270.8

312 0.4 312.4

510 0.4 510.4

882 0.6 882.6

(C)Assume a recoating time Tr = 10 sec. Compute the new build times Tb (sec).

Recoating happens after every layer

Therefore recoating time = No.L*10

Tb (min) Recoating delay (min) Tb with recoating(min)

270.5 10 280.5

270.8 17 287.8

312.4 12 324.4

510.4 12 522.4

882.6 16 898.6

Above results are near to practical data that we acquire in similar practices. Build time validates when compared to

similar technologies, available in market.

CONCLUSION

Hence we successfully developed the built time model of the given problem statement.