163 lines
7.0 KiB
Plaintext
163 lines
7.0 KiB
Plaintext
---
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title: Make plaster moulds for large products
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slug: make-plaster-moulds-for-large-products
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description: Here, we outline the process of making and using plaster molds. It’s an excellent low-tech method for creating larger, more intricate products.
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tags: ["product","injection","extrusion","mould"]
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category: Moulds
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difficulty: Medium
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time: < 1 week
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location:
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---
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import { Image } from 'astro:assets'
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# Make plaster moulds for large products
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<Image src={import('./michael-makes-stool-1.jpg')} alt="Make plaster moulds for large products" />
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Here, we outline the process of making and using plaster molds. It’s an excellent low-tech method for creating larger, more intricate products.
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## Steps
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### Step 1: Consider pros and cons
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Before you begin, it is important to note that there are some drawbacks to using this method. Plaster molds are not durable, so this may not be suitable as a common method for processing plastic.
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However, it is an excellent way to create large, solid products and can be used as a prototyping technique. For instance, if you want to test the shape of a mold before it is milled into a block of aluminum.
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You will need:
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- Extruder machine
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- Shredded plastic
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- Casting plaster
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- Mold release
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- A model or object to replicate
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- Melamine or plywood
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- Heat gun
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- Paint, chopped fiberglass, shellac (optional)
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<Image src={import('./IMG_3710.jpg')} alt="IMG_3710.jpg" />
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<Image src={import('./IMG_3598.jpg')} alt="IMG_3598.jpg" />
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### Step 2: Make a model to replicate
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You will need a model or object to cast your plaster mold around. This could be anything, such as a model you made, a 3D print, or a toy. Consider how many parts your mold requires. Our product necessitated a two-part mold.
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In this instance, the desired shape was cut out of foam using a homemade hot wire and hand sanding.
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Pay close attention to the surface finish. Any small bumps or dents will be visible in the final product. If necessary, continue sanding, filling, and painting.
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<Image src={import('./IMG_3506.jpg')} alt="IMG_3506.jpg" />
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<Image src={import('./IMG_3587.jpg')} alt="IMG_3587.jpg" />
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<Image src={import('./IMG_3519.jpg')} alt="IMG_3519.jpg" />
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### Step 3: Make a box to cast your mould
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Construct a box around your model, ensuring everything is sealed and secure to prevent it from floating when pouring the plaster. Melamine is an effective material for the box, though plywood is also suitable.
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Consider using a mold release, such as petroleum jelly, to facilitate easier separation of the plaster mold.
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Incorporating reference pins can be useful for aligning the molds accurately in future stages.
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<Image src={import('./IMG_3594.jpg')} alt="IMG_3594.jpg" />
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<Image src={import('./IMG_3537.jpg')} alt="IMG_3537.jpg" />
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<Image src={import('./IMG_3529.jpg')} alt="IMG_3529.jpg" />
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### Step 4: Mix and pour the plaster
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Mix the casting plaster according to the manufacturer's specifications. In this instance, chopped fiberglass (fibreglass) is added to enhance the mold's durability.
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Pour the mixture into the box, generally aiming for a depth twice that of the model.
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Immediately after pouring, gently tap the box with a hammer for a few minutes to allow any air pockets to rise to the surface.
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Let the plaster cure for a couple of days before demolding.
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<Image src={import('./IMG_3541.jpg')} alt="IMG_3541.jpg" />
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<Image src={import('./IMG_3599.jpg')} alt="IMG_3599.jpg" />
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### Step 5: Air dry and seal
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Once you have both parts of your mold, it is advisable to let them air dry for a couple of days. You will notice when they are touch dry (and significantly lighter), indicating readiness to proceed.
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As an optional step, apply a layer of shellac on the plaster surfaces. Upon curing, you may then apply a mold release agent, such as silicone oil or petroleum jelly, to ensure that plastic does not adhere to your mold, allowing for repeated use.
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<Image src={import('./IMG_3599.jpg')} alt="IMG_3599.jpg" />
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<Image src={import('./IMG_3548.jpg')} alt="IMG_3548.jpg" />
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<Image src={import('./IMG_3654.jpg')} alt="IMG_3654.jpg" />
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### Step 6: Drill injection + relief holes
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Prepare the mold for your machine by clamping its parts together to ensure proper alignment. A large hole is required to connect to the extruder machine.
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Additional smaller holes are necessary in various locations to serve as indicators that the plastic has reached certain points, and they also help to prevent pressure build-up.
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<Image src={import('./IMG_3667_copy.jpg')} alt="IMG_3667 copy.jpg" />
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<Image src={import('./IMG_3677_copy.jpg')} alt="IMG_3677 copy.jpg" />
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### Step 7: Heat your mould
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Since this is a slow injection molding process, it is essential to ensure the inside of the mold remains consistently hot. This can be achieved in various ways; in this instance, large holes were drilled to circulate hot air through the mold from two heat guns.
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<Image src={import('./IMG_3666_copy.jpg')} alt="IMG_3666 copy.jpg" />
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### Step 8: Inject (using the extruder)
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Begin by heating your plaster mold. As it heats, activate your extruder and prepare the plastic. Once the mold is sufficiently heated, commence the injection process. The duration may vary, from several minutes to several hours, depending on the product's size. In this instance, it took approximately 2.5 hours to fill the mold.
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When the plastic reaches all reference points you've drilled, the product is fully injected. At this juncture, deactivate your heat guns and extruder. Ensure all holes are plugged to maintain pressure within the mold.
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<Image src={import('./IMG_3668_copy.jpg')} alt="IMG_3668 copy.jpg" />
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### Step 9: Demould
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You will need to allow sufficient time for everything to cool at room temperature. Due to the insulating properties of the plaster, this process can take up to 12 hours, depending on the dimensions of your product.
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Carefully remove your product from the mold, ensuring that the mold remains intact for future use.
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<Image src={import('./IMG_3706_copy.jpg')} alt="IMG_3706 copy.jpg" />
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### Step 10: Post processing
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If the process is executed correctly, only minimal post-processing should be necessary. This entails cutting off the injection point and the relief channels.
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Additionally, you may tidy up the part line. It is advisable to do this with a knife.
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<Image src={import('./IMG_3697.jpg')} alt="IMG_3697.jpg" />
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<Image src={import('./stool-detail.jpg')} alt="stool-detail.jpg" />
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### Step 11: That's it!
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This technique, though somewhat time-consuming, offers a straightforward approach to mold-making. It is not a substitute for machined molds but serves well in prototyping larger and more organic shapes. Here is the final product: a stool crafted from old polypropylene chairs, showcasing the vast potential of this method.
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An aspect to consider is the contrast between the plastics used in the extruder. In this example, the color choices were similar, resulting in minimal contrast. This element can be adjusted to achieve the desired appearance.
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<Image src={import('./michael-makes-stool-1.jpg')} alt="michael-makes-stool-1.jpg" />
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<Image src={import('./michael-makes-stool-2.jpg')} alt="michael-makes-stool-2.jpg" />
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