Week 14 – Molding and Casting

Group Assignment

We learned about the mixing ratios for e to make soft mold and mixing ratio of resin to cast the final object.

My Learning from group assignment : We used Aditya Silicone Ribber RTV 1010 with harder/curing agent Aditya curing agent to make mixture for soft silicone mold. Every 1 kg of liquid silicone, we need 20-25 grams of hardener. The settling time of the mixture is 8 to 10 minutes, the viscosity changes after that it starts becoming harder so we need to pore into he hard mode with in 8-10 minutes. Avoid air bubbles while mixing, remove bubbles using vacuum pump then pour the mixture into the mold, always pore with tiny string in the small gaps first, tap the mold for even distribution/settlement. The soft mold curing time is 12-24hrs.

My Learning from group assignment : We used Aditya Epoxy resin part A and part B in the 2:1 ratio to make mixture for final hard Object. Every 2 part of A shall be mixed with 1 part of B. We pour the water into the mold to measure the amount of resin, we measure resin by mass and then calculate the ratio. For example, Resin ratio 2A: 1B, 40.5g part A, 20.25g part B. Do not vacuum the mixture because it makes the transparent clean mixture yellowish. Use mold releasing spray 1083 on the mold before pouring the resin. Setting time for resin is less than silicone, It takes around 18 hours to completely cured, You can speed up the process by adding UV.

As a part of group assignment, I tried poring resin into one of already available silicone mold, as I wanted to see how transparent clean object will look like thus I did not add any alcohol based color to it and kept it transparent. later I wanted to try embedding LEDs into transparent resin.

The link to our group assignment is below:

Group Assignment

Design (According to Constrains and Lab Machine capability)

First thing first - Constrains: The job piece size we were allocated to is 76mm X 76mm X 38 mm, so I need to make my design with in this boundary. The minimum tool size that our lab has is Flat End Bit 3.175 mm for milling and Ball End Bit 3.175 for finishing curve surfaces after Flat End Bit milling. We also have 6mm FLat End Bit. The Tool Depth varied between 25mm to 32mm (this is also subjected to bit incursion in the tool holder) . As we have 3 axis machine, the tool shall have straight access to for milling the machine cannot insert the tool at any angel with z axis. The outer walls shall have 1° - 2° Tapper Angle so that the silicone mold can come out easily. The side wall and bottom thickness of minimum 5mm should be left. Last but important, to provide registration in case of two part dies.

Model design

First, I made an sketch for size of my logo on the XY plane and then drew a off-set plain above it and used Text on path function to write BMW on a circle then used normal Text function write M3. Then extruded the Badge and use Emboss function to emboss BMW and M3 on the Badge. The I embossed the second and forth quadrants of central circle and then used Revolve function to make circular cure to have BMW logo like feel.

Mold design

As our workpiece size is 76mm X 76mm X 38 mm, so I drew a rectangle using Centre Rectangle function. I need to keep 5mm wall thickness on all 4 side thus I drew another rectangle on same center of 66mm X 66mm to get 5mm wall thickness on all sides.

CAM - Fusion 360

Now, now we need to change the workspace from Design to Manufacturing. Basically, verifying or validating our Computer Aided Design by Computer Aided Manufacturing to ensure the design can be manufactured in the actual machine with tha given machine and tool constrains.

End mills

We used Academy_Fusion360_Tool_Library, which was made and shared by our instructor Revisankar S. I am going to use two end mills to mill my mold and one ball mill to have finished surface.

Step 1, thing is to import Tool Library, click Manage --> Tool Library --> Local --> Right click --> Import Library --> Select library path --> OK --> Close.

[Note : you may not see "M3" at teh bottom of the logo because I add the "M3" test after screen recording below videos.]

Step 2, click on NC Program --> Post --> choose from library --> search --> TRAK --> Select --> ProtoTRAK GCD --> copy to my --> ok.

Step 3, setup origin Setup --> New Setup --> Stock point --> select the point --> Stock tab --> Stock side offset : 0 --> Stock Top offset : 0 --> OK.

Step 4, right click setup --> edit --> setup tab --> operation type --> Milling.

In total, I had four operations - 1 Adaptive cleaning operations with 6mm flat end bit, 1 Adaptive cleaning operations with 3.175mm flat end bit, 1 Pocket operation with 3.175mm flat end bit and 1 Scallop operation with 3.175mm ball end bit - to CAM mu Mold.

Operation 1 Adaptive Cleaning [Rough Cut with 6mm flat end mill]

Step 5, setting up adaptive cleaning function for 6 mm flat End bit.

• Part A, 3D --> Adaptive cleaning --> Tool Tab --> Select --> Local --> Academy_Fusion360_Tool_Library_updated --> 6mm bit with 32 length --> select --> spindle speed : 2500 --> Cutting federate : 900 .
• Part B, Geometry Tab --> Machining boundary : Selection --> Machine boundary selection --> inside wall edge --> Tool Containment --> Tool inside boundary .
• Part C, Heights Tab --> Bottom Hight --> Offset --> 0 mm .
• Part D, Passes Tab --> Maximum rough : 9mm --> radial stock to leave : 0.25.
• Part E, Linking Tab --> Ramp Type --> Plunge --> Retraction Policy : Minimum Retraction --> ok .

Step 6, check simulation, right click --> [T5]Adaptive --> simulate --> stock --> uncheck "toolpath" --> click play.

Operation 2 Adaptive Cleaning [Rough Cut with 3.175mm flat end mill]

Now, I repeated step 5 and step 6 but with below settings.

• Part A, 3D --> Adaptive cleaning --> Tool Tab --> Select --> Local --> Academy_Fusion360_Tool_Library_updated --> 3.175mm Flat bit with 32 length --> select --> spindle speed : 2500 --> Cutting federate : 700 .
• Part B, Geometry Tab --> Machining boundary : Selection --> Machine boundary selection --> inside wall edge --> Tool Containment --> Tool inside boundary .
• Part C, Heights Tab --> Bottom Hight --> Offset --> 0.250 mm .
• Part D, Passes Tab --> Maximum rough : 9mm --> radial stock to leave : 0.25.
• Part E, Linking Tab --> Ramp Type --> Plunge --> Retraction Policy : Minimum Retraction --> ok .

Operation 3 Pocket Cleaning [Rough Cut with 3.175mm flat end mill]

Again, I repeated step 5 and step 6 but with below settings.

• Part A, 3D --> Pocket cleaning --> Tool Tab --> Select --> Local --> Academy_Fusion360_Tool_Library_updated --> 3.175mm Flat bit with 32 length --> select --> spindle speed : 2500 --> Cutting federate : 600 .
• Part B, Geometry Tab --> Machining boundary : Selection --> Machine boundary selection --> Select the square-edge of the logo--> Tool Containment --> Tool outside boundary .
• Part C, Heights Tab --> Bottom Hight --> Offset --> 0.250 mm .
• Part D, Passes Tab --> Maximum rough : 5mm --> uncheck stock to leave .
• Part E, Linking Tab --> Ramp Type --> Plunge --> Retraction Policy : Shortest Retraction --> ok .

Operation 4 Scallop Cleaning [Rough Cut with 3.175mm ball end mill]

Again, I repeated step 5 and step 6 but with below settings.

• Part A, 3D --> Scallop --> Tool Tab --> Select --> Local --> Academy_Fusion360_Tool_Library_updated --> 3.175mm ball bit with 32 length --> select --> spindle speed : 2500 --> Cutting federate : 1000 .
• Part B, Geometry Tab --> Machining boundary : Selection --> Machine boundary selection --> Select the well-edge of mold--> Tool Containment --> Tool center on boundary .
• Part C, Heights Tab --> Bottom Hight --> Offset --> 0 mm .
• Part D, Passes Tab --> Stepover --> 0.150mm--> uncheck stock to leave .
• Part E, Linking Tab --> Retraction Policy : Shortest Retraction --> ok .

Generate G-Code

To generate G code for 6 mm Flat End Mill, click NC Program --> Operations --> checkmark all the operations that I needed with 6mm flat end mill--> Settings --> Post --> ProtoTrak GCD / prototrak --> give File name --> Select Output folder --> Post . Download 6mm Flat End Mill (.gcd File)

To generate G code for 3.175 mm Flat End Mill, click NC Program --> Operations --> checkmark all the operations that I needed with 3.175mm flat end mill--> Settings --> Post --> ProtoTrak GCD / prototrak --> give File name --> Select Output folder --> Post . Download 3.175mm Flat End Mill (.gcd File)

To generate G code for 3.175 mm Ball End Mill, click NC Program --> Operations --> checkmark all the operations that I needed with 3.175mm ball end mill--> Settings --> Post --> ProtoTrak GCD / prototrak --> give File name --> Select Output folder --> Post . Download 3.175mm Ball End Mill (.gcd File)

Machining

machinable WAX

tool changing

setup

running program

Rough cut

Finish cut

Molding

In the group assignment, I learned about the mixing ratios for silicone to make soft mold, we used Aditya Silicone Ribber RTV 1010 with harder/curing agent Aditya curing agent to make mixture for soft silicone mold.

Safety

Safety first - I used Nitrile GLoves to protect my hands and safety goggles to protect my eyes while doing Molding with liquid silicone and hardening agents.

Mixing ratio

Every 1 kg of liquid silicone, we need 20-25 grams of hardener. I used ratio 1000:22. First, I approximate the required silicone my poring water into the hard mold and taking it into transparent glass, then making the level of the water and cleaned the glass with high air-pressure gun. The total weight of my hard mold's liquid silicone was 107.5 gm, I added 2.365 gm of hardener. Total weight added upto 109.865gm.

Removing Bubbles

Now, I used vacuum chamber to remove air bubbles from the mixture, the chamber used high-air pressure line to rotate a vacuum pump. I kept the glass with the mixture inside the chamber and waited for air bubbles to come-up. The air bubbles will come-up and then blast and mixture will settle down.

Pouring Silicone

Now, I clean the hard mold with high pressure water jet chamber and then cleaned and dried the Hard Mold using air pressure gun. Then applied the mold releasing spray on the hard mold and then poured the silicone mixture into the hard mold. Here, while pouring it is important that we pour first in tiny/small gaps of the hard mold with thin pouring of silicone. And then I kept it for settling for 17-20 hours.

After Setting

After about 17 hours, I removed the silicon soft mold from hard mold. I came out well and without any bubbles!

Casting

safety

mixing ratio

pigments (if used)

mold release

pouring

setting

Hero shot and conclusion

Fifth, setting up adaptive cleaning function for 6 mm Flat End bit

• Part A, 3D --> Adaptive cleaning --> Tool Tab --> Select --> Local --> Academy_Fusion360_Tool_Library_updated --> 6mm bit with 32 length --> select --> spindle speed : 2500 --> Cutting federate : 600 .
• Part B, Milling --> 3D --> Geometry Tab --> Machining boundary : Selection --> Machine boundary selection --> inside wall edge --> Tool Containment --> Tool inside boundary .
• Part C, Milling --> 3D --> Heights Tab --> Bottom Hight --> Offset --> 0 mm .
• Part D, Milling --> 3D --> Passes Tab --> Maximum rough : 9mm --> radial stock to leave : 0.25.
• Part E, Milling --> 3D --> Linking Tab --> Ramp Type --> Plunge --> Retraction Policy : Minimum Retraction --> ok .

Seven, Right click [T5] Adaptive3 --> Duplicate

Eight, setting up adaptive cleaning function for 3.175 Flat end bit.

• Part A, Right click T6 Adaptive3 (2) --> Tool Tab --> Select --> Local --> Academy_Fusion360_Tool_Library_updated --> 3.175mm bit Flat End --> select --> spindle speed : 2500 --> Cutting federate : 900 .
• Part B, Geometry Tab --> Machining boundary : Selection --> Machine boundary selection --> inside wall edge --> Tool Containment --> Tool inside boundary .
• Part C, Heights Tab --> Bottom Hight --> Offset --> 0 mm .
• Part D, Passes Tab --> Maximum rough : 5mm --> radial stock to leave : 0.25.
• Part E, Linking Tab --> Ramp Type --> Plunge --> Retraction Policy : Minimum Retraction --> ok .

Nine, check simulation, right click --> [T6]Adaptive --> simulate --> stock --> uncheck "toolpath" --> click play.

Ten, setting up adaptive cleaning function for 3.175 ball end bit.

• Part A, 3D --> Scallop --> Tool Tab --> Select --> Local --> Academy_Fusion360_Tool_Library_updated --> 3.175mm bit Flat End --> select --> spindle speed : 2500 --> Cutting federate : 1000 .
• Part B, Geometry Tab --> Machining boundary : Selection --> Machine boundary selection --> inside wall edge --> Tool Containment --> Tool inside boundary --> Additional offset : -3 mm --> enable Rest machining.
• Part C, Heights Tab --> Bottom Hight --> Offset --> 0 mm .
• Part D, Passes Tab --> radial stock to leave : uncheck.
• Part E, Linking Tab --> Retraction Policy : Shortest path --> Transition type : Smooth --> ok .

Eleven, check simulation, right click --> [T6]Adaptive --> simulate --> stock --> uncheck "toolpath" --> click play.

Ninth, Right click [T5] Adaptive(2) --> Edit --> Tool --> Select --> Local --> Academy_Fusion360_Tool_Library_updated --> 3.175 Ball

Milling

Our lab has 3 axis vertical milling machine, it doesn't have ATC (automatic tool changer), we need ot manually load the tool. It has hand wheels and also servo motors to move the job bed.

We are using CAM Software of Fusion 360 can generate G-Code

The machine has Spring loaded edge finder tool, make sure that we rotate it always below 600 rpm. This tool os ude to find the x edge and y edge.

Check lubricant level and coolant level before starting the machine then turn-on the machine.

Now turn on all motors - press and hold reset button

Tool table - specify tool for operation

DRO for movement manually and automatic

Return 0 - work origin point

Line center - to find object center

JoG mode to move XYZ direction

Prog - select the program

Feed rate max is 5000 rpm

Spindle speed,Clk wise for some tool, Counter clk wise for some tool

Chuck - lock the clutch and press off

Always keep your finger below Chuck flat edge very important.

Vice - work holding device

Molding

Every 1 kg of silicone, we need 20-25 grams of hardener. The settling time of the mixture is 8 to 10 minutes, the viscosity changes after that.

First, we pour water into the mold to measure the amount of silicone required, then measure the weight of the water. Now, we cna take equivalent weight/amount of silicone and add hardener in the above ratio. In the group assignment weight of silicone is 124.2, so hardener 3.5g.

Mix well slowly to avoid air bubbles

Remove bubbles using vacuum pump

Pour the mixture into the mould

Tap the mould for even distribution/settlement

Vacuum pump it again to remove bubbles

Keep it out for curing, It takes around 17-18 hours for curing

Resin

2 part of A and 1 Part of B

Pour water into the mold to measure the amount of resin. measure it by mass and then calculate the Ratio.

For example, Resin ratio 2A: 1B, 40.5g part A, 20.25g part B.

Mix well

Use Vacuum pump to remove bubbles

Use releasing spray on the mould before pouring the resin

Add Alcohol based color, add a tint of color if required (very minimal amount)

Pour in the resin in to silicone mold

Setting time for resin is less than silicone, It takes around 18 hours to completely cured, You can speed up the process by adding UV

New 3D skills learned

Until now, I was struggling to rectangle centered to origin or some point in the sketch. This week I find out the Center Rectangle function. The function can be used by clicking on Sketch → Rectangle → Center Rectangle.

Sketching the Concepts