ME 5390

ADDITIVE

MANUFACTURING

SEMESTER

PROJECT

Design of conformally cooled

injection mold using AM

capabilities

Rudra Potdar Honeykumar Vishwakarma Dec 11, 2017

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Contents 1. Introduction and Project Description ............................................................................................. 2

1.1 Project Objective ..................................................................................................................... 2

1.2 Project Scope .......................................................................................................................... 2

1.3 Project Requirements ............................................................................................................. 2

2. Additive Manufacturing Process Discussion ................................................................................... 3

2.1 Process Selection .................................................................................................................... 3

2.2 Direct Metal Laser Sintering.................................................................................................... 3

2.3 Process Mechanics .................................................................................................................. 3

2.4 Requirements .......................................................................................................................... 4

2.5 Materials ................................................................................................................................. 4

2.6 Capabilities of DMLS ............................................................................................................... 4

2.7 Advantages .............................................................................................................................. 5

2.8 Limitations............................................................................................................................... 6

2.9 Process Diagram ...................................................................................................................... 6

3. Component Design .......................................................................................................................... 7

3.1 Advantages of AM and benefits of new design ...................................................................... 7

4. Build Preparation ............................................................................................................................ 9

4.1 Generating STL file .................................................................................................................. 9

4.2 Importing STL file into KISSlicer Software ............................................................................... 9

4.3 Process Parameters............................................................................................................... 10

4.4 Print Preview ......................................................................................................................... 10

4.5 Print ....................................................................................................................................... 10

5. Build Execution and Post-Processing ............................................................................................ 11

5.1 Build Execution...................................................................................................................... 11

5.2 Post Processing ..................................................................................................................... 12

6. Conclusion ..................................................................................................................................... 13

6.1 Project Outcome ................................................................................................................... 13

6.2 What worked/what didn’t .................................................................................................... 14

6.3 Learnings ............................................................................................................................... 14

7. References .................................................................................................................................... 15

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1. Introduction and Project Description

1.1 Project Objective The objective of this class project was to design a conformally cooled injection mold using AM

capabilities. Additive manufacturing enabled the following improvements:

1. Conformal Cooling Channels: Complex geometries of conformal cooling channels were

possible since complexity is free with AM

2. Reduced Cycle Time: Conformal cooling cools the part fast, reducing cycle time which

increases productivity

3. Reduced Part Cost: When productivity increases, part cost is reduced

4. Reduced Time for tooling: Since tool would be manufactured using AM technology,

less time and effort would be needed to design the tool compared to traditional

tooling where a number of considerations have to be taken into account for tooling

5. Improved Part Quality: Conformal channels result in improved cooling. With better

cooling parts have less warpage and show fewer deviations from original CAD design

6. Faster Design Iterations: Since time for tooling is less and complexity is free, changes

can be incorporated faster

7. Customization: Low volume parts or custom parts would require less time and cost if

built by this method. Also, these parts would have improved quality

1.2 Project Scope The scope of this project is designing an

injection mold for a force gauge housing.

This mold has complex conformal

cooling channels around the part

contour which are made possible by

additive manufacturing. The project is

focused on the design of the mold (core

and cavity) rather than the plastic part.

The force gauge housing is just for

reference. This could be any low to mid

volume plastic part.

1.3 Project Requirements The force gauge housing is a plastic part.

The mold would be made of steel.

1. Must last for the desired number of cycles

2. Cooling channel profile should be optimally designed to make the most effective use

of AM capability

3. Considerations such as draft, injection locations, gate locations, alignment pins should

be taken into account to facilitate smooth ejection of parts and repeatability

Figure 1.1 Core, Cavity and Part

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2. Additive Manufacturing Process Discussion

2.1 Process Selection Metal AM parts can be built using the following processes –

• Direct Metal Laser Sintering (DMLS)

• Electron Beam Melting (EBM)

• Binder Jetting (BJ)

• Direct Energy Deposition (DED)

Surface finish and feature resolution of the mold is an important criterion since it affects the

quality of the molded part. EBM process would be undesirable since it provides moderate

surface finish and feature resolution.

Main advantages of Binder Jetting process are that it’s faster, different material compositions.

BJ process postprocessing steps such as infiltration and sintering are required. Therefore,

using BJ is not advantageous.

Direct Metal Laser Sintering provides excellent surface finish and feature resolution. It gives

better mechanical properties. Hence, we select Direct Metal Laser Sintering. Looking at costs,

Laser sintering is found to be the most cost-effective.

2.2 Direct Metal Laser Sintering Direct Metal Laser Sintering is a Powder bed Fusion processes. It consists of three parts – A

thermal source (Laser), a method that controls powder fusion in a specific area and a powder

layering system.

2.3 Process Mechanics As shown in Figure 2.1, in MLS, an appropriate powder layer is spread across the build

platform using a counter-rotating powder leveling roller. A laser beam is focussed and

directed onto the powder bed through mirrors controlled using a galvanometer. It fuses the

powder and forms the slice cross-section. After a layer is formed, the build platform is lowered

by the one-layer thickness and a new layer of powder is laid by the counter-rotating roller.

The beam scans subsequent cross sections. This process is repeated, and the entire part is

built.

The build process takes place inside an enclosed chamber filled with nitrogen gas to prevent

oxidation and powder degradation. The powder in the build platform is maintained at an

elevated temperature just below the melting point and the glass transition temperature of

the material with the help of infrared heaters or resistive heaters. Powder preheating

minimizes the laser power requirements of the process and prevents warping of the part

during build due to non-uniform expansion and contraction.

After the part is built a cool down period is required for the parts to uniformly come down to

ambient temperature so that they can be handled. Powder left on the bed may also degrade

due to non-uniform cooling. The next step is to remove the part from the powder bed and

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clean off loose powder from the parts. In this process, the surrounding powder serves as a

support for the part being built eliminating the need for external supports.

2.4 Requirements

• Material must have good enough mechanical properties so that the mold lasts for

required injection cycles

• Component should not warp

• Surface finish and accuracy of the component should be excellent

2.5 Materials Stainless Steel / 17-4 PH is selected for the mold since the mold needs good mechanical

properties and it is cost effective. It has good machining characteristics and high corrosion

resistance and high strength.

2.6 Capabilities of DMLS

• Complex parts can be built

• Final DMLS parts are near 100% dense

• Functional parts can be built in single build

• Capable of producing parts with less residual stress, less warpage, and curl

• Number of parts can be simultaneously built in a single build

• Supports are not required since it is a self-supporting process

• Powder can be reused

Figure 2.1 Schematic of the Selective Laser Sintering process

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Figure 2.2 DMLS materials

2.7 Advantages

• Complex geometries

• Consolidation of parts to reduce development time

• High accuracy in fine details

• The support material is not required since powder bed provides the support. It is a

self-supporting process.

• Strong and durable components

• Internal conformal cooling channels can be created easily.

• Relatively inexpensive if compared with the tooling cost required for traditional molds.

• A number of parts can be nested and built simultaneously in a single build, thus

dramatically improving the productivity of this process compared to processes that

require supports and post-processing.

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2.8 Limitations

• Size of parts is limited by the size of powder bed in the machine

• Stresses may develop between steel plate building platform and built part can warp

the part

• Wall thickness on a part created using DMLS is limited to double the spot size of the

laser

• Limitation on overhang

2.9 Process Diagram

DESIGN• CAD of the Part

STL• Part is saved in STL file format in CAD Software

SLICE• Part is Sliced in Slicing Software (G code)

TRANSFER• File is transferred to machine

SETUP• Machine is set up for the build

BUILD• Sliced file is loaded on machine and built

POSTPROCESS

• Part is removed from bed and cleaned

INSTALL• Part is ready for use in application

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3. Component Design

3.1 Advantages of AM and benefits of new design The new design takes advantage of the following unique capabilities of AM

1. Shape Complexity

AM enables complex curved internal cooling channels for conformal cooling which can

eliminate problem of hotspots which is encountered in conventional molds since the

cooling channels are restricted to straight hole profiles

2. Cavity and Core parts of the mold can be built simultaneously

3. Conformal cooling results in high-quality cooling of the part and time required to reach

ejection temperature reduces resulting in reduced cycle time.

4. Time for tooling is eliminated

5. Customization is easy, only the CAD model needs to be modified for making variants

6. Quality of the molded part is improved

Figure 3.1 Core, Cavity and Part exploded view

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Figure 3.2 Cooling analysis of part with straight channels: Traditionally manufactured mold enables only straight cooling channels, Analysis done in Autodesk Moldflow Ad

Figure 3.3 Cooling analysis of part with conformal channels: Additive manufactured mold enables conformal cooling channels, Analysis done in Autodesk Moldflow Adviser.

Figure 3.4 Effect of unused area on frost formation

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4. Build Preparation

Figure 4.1 Core, Cavity and the part

4.1 Generating STL file While generating the STL file from CAD file in SolidWorks, it allows you to set the resolution

for the STL file. Depending on the resolution the file size varies. Since the bed size of the

Polyprinter was smaller, the part needed to be scaled down with a factor 0.5

4.2 Importing STL file into KISSlicer Software The next step was to import STL file into KISSlicer Slicing software. The part had to be scaled

to fit the bed dimensions. The part was scaled down by a factor of 0.5. The orientation of the

part was decided. Settings such as Infill % and overhang angle are set. The print command

was given and the time process parameters were checked.

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Figure 4.2 Slicing

4.3 Process Parameters The following process

parameters were checked.

Time: 6 hrs 28 mins

Resolution : 0.2 mm

Supports: On

4.4 Print Preview A print preview was

observed to check whether the part was on the build platform.

4.5 Print Print command was given

Figure 4.3 Process parameters

Figure 4.4 Process parameters

Figure 4.5 Print Preview

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5. Build Execution and Post-Processing

Figure5.1 Build Execution

5.1 Build Execution The parts were built using FDM process on the PolyPrinter.

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5.2 Post Processing Since support material used was the same material as the built part, it was removed

mechanically using files.

Figure5.2 Final parts built

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6. Conclusion 6.1 Project Outcome Following are the results in tabulated form that were achieved by this project

Process Injection Molding with traditional molds

Injection Molding with AM molds and conformal cooling

Time required for tooling and molds

High Significantly less

Cost High Comparatively less

Customization Not possible Possible

Production volume Suitable only for high volumes of parts

Suitable for medium to low volumes of production

Design Freedom Restrictions imposed No restrictions

Cooling efficiency

Comparatively less Comparatively more

No of channels 8 4

Time required to reach ejection temperature

3.1 sec 2.9 sec

Hotspots Cannot eliminate the hotspots since unreachable locations

Hotspots can be eliminated with conformal cooling

Figure5.2 Result for time to reach ejection temperature part in Autodesk Moldflow adviser

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6.2 What worked/what didn’t In the initial simulations for cooling conformal cooling channels simply following the part

profile was used which did not give improved results for cooling.

On examination, it appeared that the new conformal cooling channels were not near the

hotspot. Therefore, it is evident that to make the conformal cooling and AM capabilities

advantageous it is necessary to identify the hotspots and optimize the flow of coolants.

There was slight warpage in the x-direction in the FDM prototype part, However, since the

actual part is designed for DMSL process, warpage will not be much since the powder bed is

heated and uniform cooling of the part is done after the build.

Since the build platform was not sufficient the part was to be scaled down by a factor of 2

Since scaling down reduced the original thickness, the part would have very less thickness.

Hence original part was redesigned with a greater thickness to consider scaling factor and a

minimum wall thickness of FDM process.

Acceptable accuracy and surface finish were achieved.

6.3 Learnings Following were the learnings from this project

1. Cost comparison of various AM processes with conventional processes revealed that

making tooling such as molds for injection molding with additive manufacturing is

comparatively inexpensive

2. Use of AM technology such as DMLS enables complex shapes and geometry. There is

no restriction on design such as undercuts or overhangs or internal features

3. Supports are not required since parts are self-supporting

4. Tooling is not required for AM processes

5. AM enables consolidating number or parts into one part thereby reducing assembly

operations, time and cost

6. Resolution of part affects STL file size. While selecting resolution, process accuracy

should be considered

7. FDM process leads to warpage in long parts due to non-uniform cooling

8. Using AM capabilities is not merely replacing the traditional parts with additively

manufactured parts, but it needs rethinking and optimising the design of the system

itself.

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7. References

1. https://www.britannica.com/topic/selective-laser-sintering

2. https://www.stratasysdirect.com/materials/direct-metal-laser-sintering/

3. Ian Gibson, David Rosen, Brent Stucker “Additive Manufacturing Technologies, 3D

Printing, Rapid Prototyping, and Direct Digital Manufacturing Second Edition”

4. Hopkinson, Neil, and P. Dickens. 2003. “Analysis of Rapid Manufacturing—using Layer

Manufacturing Processes for Production.”

5. http://www.advanc3dmaterials.com/assets/presentation-sls.pdf

6. https://www.protolabs.com/services/3d-printing/direct-metal-laser-sintering/