Week12. Molding and Casting¶
This week I worked on defining my final project idea and started to getting used to the documentation process.
Here is this week assignment:¶
Group assignment:¶
review the safety data sheets for each of your molding and casting materials, then make and compare test casts with each of them compare printing vs machining molds
Individual assignment:¶
design a mold around the process you’ll be using, produce it with a smooth surface finish, and use it to cast parts extra credit: use more then two mold parts
Group assignment¶
Group assignment can be viewed at this link. - week12 Group assignment
Safety rules for using silicone¶
Understand the Material: Before using silicone, carefully read the product’s instructions and the Safety Data Sheet (SDS) to be aware of its chemical properties and potential health hazards.
Personal Protective Equipment (PPE): Wear proper personal protective equipment, including but not limited to gloves, safety goggles, and long-sleeved clothing, to protect your skin and eyes from irritation by silicone or its ingredients.
Ventilation: Work in a well-ventilated area to avoid inhaling vapors or gases. If indoor ventilation is insufficient, use exhaust fans or conduct the operations outdoors.
Prevent Skin and Eye Contact: Avoid direct contact with silicone on the skin. In case of contact, wash immediately with plenty of water. If silicone gets into the eyes, rinse immediately with plenty of water and seek medical attention.
Use of Tools: Use clean, dry tools to handle the silicone to prevent the introduction of impurities, which might affect the cure of the silicone and the quality of the final mold.
Mix in Proportion: Follow the manufacturer’s instructions carefully for mixing ratios, ensuring that the two components (usually silicone comes as a two-part system with a base and a curing agent) are thoroughly mixed to achieve optimal performance.
Avoid Food Contact: Do not eat, drink, or smoke while handling silicone to prevent accidental ingestion of chemicals.
Safe Storage: Ensure that silicone is stored out of the reach of children and away from sources of ignition, high temperatures, and direct sunlight, and make sure containers are tightly closed to prevent moisture absorption or contamination.
Disposal of Waste: Dispose of waste silicone and containers correctly, do not litter, and adhere to local regulations and standards for the disposal or recycling of chemical waste.
Emergency Preparedness: Have emergency procedures in place so that you know how to respond in case of accidental spills or contact and are aware of the locations of nearby emergency facilities.
Safety rules for using AB resin¶
When working with AB resin, which is a two-component resin system typically made up of a resin (Part A) and a hardener (Part B) that cure together through a chemical reaction to form a hard plastic, the following considerations should be kept in mind:
Accurate Ratio: Ensure you measure the correct ratio of Part A to Part B as per the product’s instructions or technical specifications to ensure the cured product has the intended properties.
Thorough Mixing: Mix the two parts thoroughly to avoid any uncured regions or poor performance due to incomplete mixing.
Temperature Control: AB resin can be sensitive to temperature during the mixing and curing process. Both high and low temperatures can affect the curing speed and final properties, so follow the recommended operating temperatures.
Working Time: AB resin has a specific working time (Pot Life) post-mixing. After this time, the resin will start to cure and become unworkable, so complete your application within this window.
Good Ventilation: Ensure good ventilation during the working process as some AB resins may release harmful substances such as volatile organic compounds (VOCs) during mixing and curing.
Protective Measures: Operators should wear appropriate personal protective equipment (PPE), such as gloves, protective goggles, and a mask, to prevent contact with and inhalation of chemicals.
Clean Tools: Clean all tools and mixing equipment immediately after use since the cured resin can be difficult to remove once it has set.
Safe Storage: Store unused portions of Parts A and B sealed separately to prevent moisture absorption or contamination, following the manufacturer’s storage recommendations.
Shelf Life: Be aware of the shelf life of the AB resin; materials past their expiration may not cure properly.
Test on a Small Scale: Before large-scale use, it’s wise to conduct a small-scale mixing and curing test to ensure the material’s performance meets requirements.
These considerations are important for ensuring the safety during the use of AB resin and the quality of the final product. Always read the material’s technical data sheets (TDS) and safety data sheets (SDS) for detailed usage instructions and safety information before proceeding.
Safety rules for paraffin wax¶
When creating molds using paraffin wax, you should consider the following:
Melting Point: Ensure that you melt the paraffin wax at the appropriate temperature. Overheating can degrade the wax or increase the risk of burning or fire.
Mold Design: Design your mold to accommodate the properties of wax. This includes accounting for shrinkage as the wax cools and solidifies.
Ventilation: Work in a well-ventilated area to minimize the inhalation of fumes that can be emitted from the melting wax.
Safety Precautions: Wear protective gear, such as gloves and eye protection, to prevent burns from hot wax.
Smoothness: Ensure the surface of the mold is smooth, as any imperfections will be transferred onto the casted object.
Removal: Make a plan for how you will safely remove the wax from the mold. This may involve melting it out, so consider the mold’s heat resistance.
Application: Paraffin wax is best suited for certain types of casting, such as the lost-wax method. Make sure that the use of a paraffin wax mold is appropriate for the casting material and process.
Cleanup: Have tools and materials ready for cleaning as wax can become difficult to remove once solidified.
Wax Quality: Use appropriate quality paraffin wax that is free from contaminants and designed for mold making to get a better result and reduce defects.
Storage: Store paraffin wax in a cool, dry place away from direct sunlight to maintain its quality and ease of use.
Part 1: 3D Printing¶
We used onshape to make the model. First, I created a circular base in the top view in the draft state.
Then I made a chamfer for the base
Next I want to design a CHAI HUO icon, because it is too complicated to draw on onshape,
so I chose to use Illustrator to draw the icon, as shown below
then export the DXF file, import it into onshape, and then give it performs
an extrusion operation, as shown below
Next, I made a square container 1cm larger than the original size according to the size
of the seal, as shown in the picture
Then use the slicing software to import the prepared 3D model into the slicing software for slicing, and then import the sliced files into the 3D printer.
This is what it looked like after it was 3D printed for the first time, but we felt that the
mold was too big and needed to be reduced.
Later, I consulted Salman, and he said that the cutting tools of the machine tool are round,
so it is best to make the graphics with rounded corners, and also because I thinks squares
look better:) I changed the original circle into a square, as shown in the picture
Part 2: Molding and casting¶
Useful file¶
This is CHAI HUO icon file, made with Illustrator, chaihuo_icon.dxf
and an 3D model file made with onshape. CHAIHUO_seal02.stl
After finishing the 3D printing part, the next step is to make the mold. We chose this kind of silicone as the mold material because this kind of silicone is relatively common and cheap.
In order to make the mold release better, I also bought this release agent.
Before pouring the silicone, we spray the 3D model with a release agent
In order to accelerate the curing of silicone, a curing agent needs to be added. The silicone and curing agent need to be prepared in a ratio of 100:2.
Mix the silicone and curing agent evenly and pour them into the 3D printing mold.
After pouring all the silica gel, many bubbles appeared on the surface, as shown in the picture
We popped the larger bubbles and let them sit for ten minutes, and the bubbles gradually disappeared.
It looks good, we’re going to casting it
This time we need to use AB resin
First, spray the release agent first
Then mix the two liquids AB together in a ratio of 1:1.
Note: AB resin solidifies very quickly and emits heat, so you need to pay attention to the time and be careful as it will burn your hands.
It seems that there are a lot of bubbles. The instructor said that if you do it again in the future, you can use a vacuum machine to eliminate the bubbles.
In view of the low cost and easy demoulding properties of paraffin wax we mentioned before, we chose paraffin wax as the material for CNC processing.
The purchased material is too big, so the size and flatness need to be processed before it can be put into CNC processing.
Done
Start to milling
Because the model we made this time involves small holes and curved surfaces, we chose three types of tools this time. The following one is for basic milling
the following one is for detailed cavity milling
the following one is for curved surface milling.
Done and it looks good
Next, we will redo the molding and casting based on our previous operating experience.
After completing the group assignment together, we discovered that both milling and 3D printing have their respective strengths and weaknesses.
Part 1: Advantages and Disadvantages of 3D Printing 3D printing represents a more modern approach to mold production. Its foremost strength is in fabricating molds with complicated geometries, with its layer-by-layer assembly process offering unparalleled precision in crafting minute details. The downside, though, is that the resulting product surfaces may exhibit stratified textures, a byproduct of the material layering during the printing process. Moreover, for applications that require withstanding high temperatures or pressures, 3D-printed molds might not possess adequate strength. When opting for 3D printing as a mold-making technique, one often needs to balance between the surface quality of the finished product and the complexity of the design.
Part 2: Advantages and Disadvantages of Milling Milling is a classic mold-making technique renowned for producing molds with high-quality, smooth finishes and crisp lines, particularly suited for larger or geometrically simpler items. The primary advantage of milling lies in its ability to create molds with superior surface finishing and clarity of design. However, milling falls short when it comes to intricate details that are smaller than the diameter of the milling bit. Hence, it may not be the go-to option for extremely fine or complex mold structures.
Individual assignment:¶
The example of our group assignment is using my model, so the model mentioned above is also the content of my individual assignment.
Since the time cost and process of 3D printing are much simpler than CNC machining, I will still choose to use 3D printing for molding and casting in the future.