Casting Low Melting Point Metal with zp150 Powder

Metal Casting with Bismuth Using Z Corp Printer Technology

By Emil Reyes

RAPID Technology LLC

OVERVIEW In this application note, we will show you the basics of casting metal parts in ZP150 powder using low melting point metal. This process is great for making metal prototypes for small parts like jewelry. The low melting point metal makes it possible to cast parts at temperatures from 117 to 440 degrees Fahrenheit depending on what alloy you choose. A home stove, or preferably an outdoor grill or burner can be used. Many readily available cooking implements can be used to make this process easier, with great results.

IMPORTANT NOTE Though this process is workable, note that you do so at your own risk. Emil Reyes, RAPID Technology LLC and Z Corporation are not responsible for any injuries or damages that may occur from using this application note. The risk of severe burns, fire, and fume inhalation exist – you will be working with molten metal, so keep safety in mind as you plan out your casting.

SAFETY FIRST

• Prepare your area. Choose an unencumbered, low traffic area that you have control over.

• Use a well-ventilated area, preferably outdoors. Though we have done this indoors in a large room, the process does cause an unpleasant odor. We cannot speak to any fumes or gasses that may occur should something go wrong.

• A vapor-filtering respirator is highly recommended for use while heating and working with hot metal.

• Use safety goggles; I can’t imagine how painful hot metal or debris in the eye would be.

• If using open flame burners or grills, have a fire extinguisher nearby. • Have a few extra potholders and insulated gloves handy. • A First Aid kit is always a good item to have available.

EQUIPMENT REQUIRED

• Safety equipment: goggles, respirator, fire extinguisher, first aid kit • Low melting point metal ingots • Your prepared mold • Your grill, burner or stove • Metal pot – We use $15 stainless steel cooking pots we got from a local

discount store. Choose the right size for the amount of metal you will use - usually a small sauce pot will do just fine.

• A metal soup ladle – You will use the ladle to control the pour into your mold. You should heat your ladle in the melted metal to ensure smoother pouring. Irregular and hard-to-control pouring is caused by the metal cooling and solidifying on a cold ladle. Ladles with silicon or wood handles work fine; just make sure the handle can withstand the temperature you are using. We just use a metal ladle with a straight handle.

• Potholders or insulated gloves for handling hot equipment. • A metal funnel if needed – You should heat this in the metal before pouring. • Aluminum Foil – Put some foil down to protect your work area.

LOW MELTING POINT METAL Low melting alloys also go by the name of CerroSafe or Cerro Metal. These metals are Bismuth based as the majority of the alloy and then consist of different amounts of antimony, cadmium, lead, tin and indium. The different alloys will have varying melting points, with different properties once cast. We get our metal ingots from www.rotometals.com but you can obtain ingots elsewhere. The Rotometals site has a nice chart which lists the alloys and their approximate melting times.

Though there are many alloys available, we have only tested the 281 and the 158-190 alloys. We were happy with the results of the 281 that gave a smoother, more silver-like finish over the 158-190. Pleased with the results, we had no reason to try other alloys. You will have to experiment with the different alloys to get the appropriate look and feel for your project. Rotometals casts their ingots in cupcake molds and sells them by the pound.

Figure 1 - A rotometals cupcake ingot

MAKING YOUR MOLD Mold making is more of an art form than a science, and can take years of practice to be able to produce good mold designs. I will not go into too much detail on making your mold. We have made our molds in both Maya and Blender using Boolean techniques, and both have been successful. We have had success with infiltrated and un-infiltrated molds. Regardless of how you make it, there are some things you will want to plan into the design of your mold. Plan your cast for pouring:

• Plan a route for the metal to travel • Create holes so that air can escape (see Figure 2) • Appropriately widen where you intend to pour (see Figure 2) • External walls should be thick enough to resist warping, particularly if using

an un-infiltrated mold • Molds are typically for one time use

Figure 2 - Funnels and air drainage paths should be planned in advance (mold created by Kalei Lee)

HEATING There is no real trick to melting the metal. Depending on what alloy you choose, the time and heat required will vary. The metal melts evenly, and usually quite quickly.

POURING For safety when pouring, we usually put aluminum foil down on our work space. We also wrap the mold in foil leaving the pour and air drainage holes exposed. This way, if there is any leakage or a wall breaks, the foil will help to contain it. To keep the pouring controlled, use your ladle, and be careful not to pour more metal than the mold can contain.

COOLING To ensure that air bubbles don’t set in, you can let your mold cool on a vibrating surface. We have set parts to cool on our air conditioning unit to work out any air pockets. To speed the cooling process, we have also put the mold in a freezer unit.

REMOVING YOUR PART If using an un-infiltrated mold, the mold should break or come apart easily. If using an infiltrated mold, depending on the complexity of your part, you may have to pry or break the mold apart.

CLOSING Be safe and have fun casting your own metal parts! If you have any questions, I would be happy to answer them. I can be reached by email at: emil.reyes@thinkrapid.com