General considerations:

• Low cost
• Long shelf-lives, long pot-lives, low toxicity
• Strong layer to layer binding
• The temperature at which the materials are deposited, shaped or cured should not damage previously shaped features.
• Material shrinkage should be minimized for the dimensional accuracy of the SDM process.
• Part and support materials should exhibit good machinability.
• Good mechanical properties and chemical stability for part material
• Part and support materials should solidify without the formation of internal voids.
• Part and support materials should have physical properties such as low viscosity and good machininability that favor the process control of SDM.
• Part and support materials must be physically and chemically compatible.
• Part material should be easily taken out of the support material after the process.

Other considerations specified by biomimetic robot fabrication

• Good binding strength between soft and hard polymer materials.
• Good interlayer shear strength between the embedded strain gages and the surrounding polymer material.
• Good binding property between polymer materials and metals.
• The temperary material should be easy to clean in order to make internal cavities such as valves.
• The embedded sensors, tubes and actuators should lead to minimum trapped air in the polymer material after casting.

Possible material combination matrix for polymer SDM
 

	Thermoset Support Material	Thermoplastic Support Material
Thermoset Part Material	Category A  Part: SLA resin  Support: Solder Mask	Category B Part: Polyurethane or Epoxy Support: Wax
Thermoplastic Part Material	Category C  Part: Wax  Support: Solder Mask	Category D  Part: Polycarbonate or Filled Wax  Support: ACR200

Category A: Thermoset materials must be highly crosslinked than the support materials so that the support materials will be removable via solvents which will not harm the part materials. The only major SDM combination from this category is acrylate Stereolithography resin part material with solder mask support material.

Category B: The material combinations from this category is currently used for making biomimetic robot legs. Thermoplastic support materials can be removed by heating or heated solvents, since thermoset part materials will not melt when heated. If thermoset part materials cure exothermically, however, their heats of polymerization must not cause thermoplastic support materials to melt or flow. SDM material combinations in this category include polyurethane or epoxy part materials and wax support materials. Heat resistance of support materials limites the cure speed of part materials since fast-curing part materials may generate enough heat to melt support materials. Therefore, most of the SDM thermoset part materials in this category cure at intermediate speeds. However, these part materials tend to have low heat resistance, making them soften at the deposition temperatures required by the support materials. This can weaken parts during construction, leading to greater distortion.

Category C: Thermoset support materials must be chosen so that heat generated during curing does not melt thermoplastic part materials. Support materials must also be chosen to have sufficient heat resistance to withstand the deposition of hot, liquid thermoplatic part materials.
 
 

Category D: This is a difficult combination to develop because of the different temperature requirements for adhesion and geometry preservation.

Material combinations experimented at Stanford University with promising results:
 
 
 

combination	part material	Support material	Support material removal	Comments
UV-curable part + water solvable support	Somos 2100 Acrylate Stereolithography resin	Solder mask	Complete removal by water	Reduced process cycle time  Insufficient strength
Castable thermoset part + chemically solvable support	LUC-4180 Polyurethane	Protowax	Partial removal by melting, complete removal by  BIOACT 280	Adequate strength, good toughness, performance was limited by available support materials, long curing time, relatively poor interlayer strength
Castable Epoxy part + wax support	Ciba TDT205-3 Epoxy	KC3230A Protowax	Complete removal by BIOACT280	Rapid cure speed, successive layers can be machined two hours after casting
Castable Epoxy part + wax support	ADTECH EE-501/530 Epoxy	Protowax	Complete removal by BIOACT 280	Strongest material for multilayer structure, long curing time (24hrs), increased process difficulty
Castable Polyurathene part + different wax supports	IE-50A, IE-90A, IE-65DC, IE-70DC polyurathene	Blue wax,  Red wax, green wax	Blue wax is removed by machining, red wax is removed by heating, green wax is removed by water	Good combination for making graded material parts. Bubbles exist when embedding components. IE-50A is too soft to machine. IE-90A can be faced, but not good for contouring

 

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Last updated: 11/22/1999