10. Molding and casting:¶
Highlights of the week:¶
Group Assignment:¶
There are a lot of materials available in the lab. So, we all decided to distribute material and study individually. Later, we all came together for a discussion.
1.Ecoflex Silicone Rubber: Ecoflex rubbers are mixed 1A:1B by weight or volume and cured at room temperature with negligible shrinkage. Low viscosity ensures easy mixing and de-airing.Cured rubber is very soft, very strong and very “stretchy”, stretching many times its original size without tearing and will rebound to its original form without distortion.
A. Mixed Viscosity:3,000 cps
B. Specific Gravity:1.07 g/cc
C. Specific Volume:26 cu.in./lb.
D. Pot Life:45 minutes
E. Cure Time:4 hours
2.Moldsil Silicone:
is a condensation curing type Silicone RTV, recommended for mold making applications. This is a flowable grade, having high mechanical strength and cures with various catalyst options (depending on the application requirements) at room temperature to a flexible elastomer, well suited for detailed and exact reproduction of artifacts, figures, architectural items and similar objects.
A. Catalyst Options:
a. CAT-24: Slow Catalyst
b. CAT-16: Medium speed Catalyst
c. CAt-04: Rapid Catalyst
3.Instamold:InstaMold allows for the most perfect reproductions of all 3 dimensional objects and shapes in a matter of minutes. Mold making compound is activated by water.InstaMold is completely harmless to use for body casting and the material will not adhere to the originals of our casting.
A. Mixing Proportions for Thick Strong Mix: 1 part InstaMold : 2 Parts Water
B.Characteristics: Greater Volume of Mix,Slow Setting,Average Retention of shape & size, Withstands average handling and Retains fine detail
C.Setting time at 70F: 4 - 6 Minutes
4.Epoxy:Epoxy resins, also known as polyepoxides, are a class of reactive prepolymers and polymers which contain epoxide groups.They react (cross-linked) either with themselves through catalytic homopolymerisation, or with a wide range of co-reactants including polyfunctional amines, acids (and acid anhydrides), phenols, alcohols and thiols (usually called mercaptans). These co-reactants are often referred to as hardeners or curatives, and the cross-linking reaction is commonly referred to as curing.
5.Flexwax Perfect for making molds from three dimensional objects by simply melting, brushing it on, and allowing to harden. Molds made with Flexwax can be remelted and used again and again. Flexwax is AP Non-Toxic.
At room temperature, the mold is moderately flexible, so we can allow some shallow undercuts without any problem. Molds made with Flexwax can be remelted and used again and again.
6.Hydro-stone: Hydro-stone is one of the hardest and strongest gypsum-cement. We are using for casting which produces extremely hard surface. The important thing, always add powder to the water, never the reverse. (Sprinkle the powder into water slowly and evenly.)
We designed 2 test parts a flower and moon.
A. Designed the test parts and converted .stl file to .rml in offline Fab modules to be cut on Modella-20.
B.Gave rough and finish cut using end mill 1/8” Square end and 1/8” ball end respectively.
C. Used Moldsil Silicone and CAT-16 hardner for negative mold.
D. After drying the negative mold was ready for casting.
E. Used Epoxy resin with hardner to get the final shape of flower and moon.
F. Also used hydrostone for casting to feel the difference and observe the properties.
Individual Assignment:¶
Project-1: Sunglasses¶
Fashion of sun glasses has attarcted me from quite a long time. After 9 assignemsnts I have become a little more comfortable with design so I planned to design sun glasses. I have kept the sizing small deliberately because I will trying my hands on moulding.casting for the first time and the material should not be wasted.
1.Design:¶
A.Sketch: Using the tools LINE, SPLINE, RECTANGLE,TRIM etc. designed sun glasses.
B. 3D: The sketch was “EXTRUDE” and “CHAMFER” showing how the sun glasses and the stick would lok on the mould. Negative mould will have the extruded parts of the positive mould pierced. So, the glasses frame and stick was extruded to 4mm.
2. Positive Mold:¶
I.Step 1-Machineable Wax:¶
Sticked double side tape on one plain side of the machineable wax. An extremely thin white layer sticked on the surface of the wax.
II. Step 2-Cleaned Bed:¶
Used acetone in cotton and cleaned the bed of Modella-20 to remove all the dust and dirt.
III. Step 3-Placed Wax:¶
Sticked the machineable wax on the bed. The wax was sturdy and didn’t move.
IV. Step 4-Terminal:¶
A. Opened the module to convert file and instruct “Modella-20” to cut the design on wax. Here, intrusted the input file fromat as “.stl” and the output process as “.rml” for the design.
B.File Format: Uploaded the “.stl” file saved from Fusion 360 and coverted it into “.png” file format.
C.Path: Clicked “make.path” which created the tool path for the design from “.png” format. This gave me an idea of the path of the end mill.
D.Positioning:The X,Y coordinate of the end mill was adjusted and fixed. The end mill was left free from the collate to free fall and touch the surface of the machineable wax. Tightened the collate and this marked the Z-coordinate.
E. “.rml” file: Instructed to “make.rml” file and “send it!” to the machine the file was ready for operation. Clicked “Begin milling” and the end mill started moving on the tool path.
V. Step 5- Surfacing:¶
Made Surface Plane.The surface of the wax was highly uneven. It took me hours to make it straight.I selected various points on the uneven mould and the end mill cut all the wax above that point.
VI. Step 6-Rough Cut:¶
The end mill moved on the surface to make a hollow 5 sided cube and remove the wax leaving the design extruded.
VII. Step 7-Finish Cut:¶
The finish cut file looked completely different then the rough cut. It basically moved end mill in the horizontal and vertical direction which removed unwanted wax left in the rough cut.
3.Negative Mold:¶
I. Step 1-Volume Measurement:¶
A.Volume of sticks=7+7=14 ml
B.Volume of front frame=26 ml
C.Void Space=Volume of water occupied=Volume of stick 1+ Volume of stick 2+ Volume of front frame=7ml+7ml+26ml=40ml
II. Step 2-Calculations:¶
A. Density of Silicone=1.07 gm/ml
B. Calculated Volume=40ml
C. Weight of Silicone required=Volume*XDensity=40X1.07=42.8 gm
III. Step 3-Weight Measurement:¶
I used Ecoflex 00-30 Silicone which has Part A and B to be mixed in 1:1 proportion.
IV. Step 4-Pouring and Drying:¶
Stirred Silicone well and poured it in the positive mold.
4. Casting:¶
I. Step 1-Volume measurement:¶
Added water in the voild and measured it.
II. Step 2-Weight Measurement and Mixing:¶
Used hardner:epoxy in ratio 1:2 by weight i.e. for 1 parts of hardener we use 2 part epoxy.Stirred it well.
III. Step 3-Drying:¶
Poured Epoxy in negative mold and kept it for drying overnight.
Design files are available here.
Project 2- Bolt¶
1.Design¶
Made a 3D bolt in Fusion 360. Made 2 parts of it front and back. The idea is to make the bolt by molding and casting such that the threads should be in continuation.
Made a 2D design and extruded it. Used “thread” feature in bolt which will fix with nut. Soldified the opposite face in both front and back mold.
I. Front mold¶
II. Back mold¶
2. Positive Mold¶
Modella Player 4: It is a CAM software that imports general-use 3D data, (such as IGES, DXF(3D), or STL), and lets us easily prepare tool paths and output them to the SRM-20.
I. Step 1- Importing File:¶
Click [File] - [Open], and selected the file. I opened the front of bolt in .stl fomrat made in “Fusion 360”
II. Step 2- Set the machine selection:¶
The software could be compatible with many machines.
Selected the Model Name-[SRM-20],Command Set : [RML-1], Spindle Unit : [Standard] and Printer Name : [Roland SRM-20]
III. Step 3-Orinetation and Origin Point of the Model:¶
A. Clicked Model and selected the orientation “Top Surface”. Other features include scale and rotation which I didnot changed.
B. Click the “Origin” tab, selected the origin position at the front left end of the bolt.
IV. Step 4-Set the material:¶
Chose the workpiece material “Modeling Wax” from the pull-down list.It is important to set up the quality of the material before process creation. Because changing the composition also produces changes in the cutting tool and the cutting parameters.
V.Step 5-Process:Created the surface leveling process of material.¶
A. Pressed the “New Process Icon” and chose “Surfacing” out of the 4 processes Surfacing, Roughing, Finishing and Drilling.
B.Selected the cutting tool 3mm Square which will be the end mill size for the operation.
C. Set the area and depth for surface leveling.
D. Set the tool path to “Scan Lines”. This creates a tool path parallel to the specified axis (Parallel with X axis). The path is created in such a way that the outbound movement and return movement lie along the axis.
VI. Step 6-Confirm the Cutting Preview:.¶
Saw tool path and cutting tool movement in Virtual MODELA screen that were set in MODELA Player 4.
VII. Step 7-Preparing the Machine:¶
A. Sticked double sided tape to the wax and pressed it well.
B.Cleaned the Acrylic surface with Acetone and attached the Modeling Wax brick to the Table.
VIII. Step 8- Cutting¶
A. Gave the output command from Modella Player 4
B.Surface leveling of modeling wax Leveling eliminated unevenness in the surface of wax to create a work plane that is parallel with the cutting plane along which the cutting tool moves.
C. Rough Cut- This task cut a rough outline and left the detailed portions. This is an important process for reducing cutting time and increasing the efficiency of the finishing proces.
D. Finish Cut-The finishing process cuts the finely detailed portions according to the shape of the data. A cleaner finish was achieved and it’s quite visible.
3. Negative Mold¶
I. Step 1-Volume measurement:¶
Filled the void space in the mold with water and collected it back in measuring cylinder to measure the total volume 18ml.
II. Step 2-Calculations:¶
A. Density of Silicone=1.07 gm/ml
B. Calculated Volume=18ml
C. Weight of Silicone required=VolumeXDensity=181.07=19.26 gm
III. Step 3-Weight Measurement:¶
A. I used Ecoflex 00-30 Silicone which has Part A and B to be mixed in 1:1 proportion.
B. Weighed 12 gm of each Silicone Part A and B to total 24 gm. I took a little extra because somepart of it sticks to the glass surface.
IV. Step 4-Mixing:¶
Mixed the Silcione really well with Ice Cream wooden stick for 3 minutes.
V. Step V-Pouring and Drying:¶
Poured Silcone in the positive mold and left it undisturbed for drying. It dried in 4 hours and the negative mold was ready! There were no air bubbles which was utmost satisfactory feeling.
4. Casting¶
I. Step 1-Volume measurement:¶
Added water in the voild and measured it.
II. Step 2-Weight Measurement:¶
The bottles for both Epoxy and hardener were unlabeled.My instructor recommended to use it in ratio 1:2 by weight i.e. for 1 parts of hardener we use 2 part epoxy.Here, the density of resin and hardner were also not known so went ahead with approximations.
III. Step 3-Mixing:¶
On adding hardner to Epoxy the liquid turned pale Yellow. Mixed them vigorously with a wooden stick.
IV. Step 4-Pouring and Drying¶
Filled the negative mold with the resin and left them for drying. in open air. It took more than 24 hours to dry completely and it looks beautiful.
Design files are available here.
Trobuleshooting¶
This week was full of problems for me yet the most learning week.
Problem 1-Moldsil Silicone:¶
Used Silicone after a few months and is too viscous. I stirred it vigrously and used it. BUt it didnot take the shape properly. So, I switched to Ecoflex Silicone Rubber.
Problem 2- Modella-20:¶
The screw inside the collate got ripped. Inbetween cutting the end mill was stuck in the modeling wax and the machine stopped. I changed the collate screw to fix the end mill tight.
Problem 3- Modella-20:¶
The origin of the Modella changed twice after rough cut. Since, the finish cut didnot start from the same origin the mold was damaged. I read manual, installed Modella player 4 and cut the bolt on SRM20.
Problem 4- Design¶
I planned to make a single side of bolt and cut it twice. Yet during design it clicked me in that case the threads of bolt will not be in continuation. So, made a 3D design and used it front and back face for molding.