Selecting the appropriate materials for prototyping is crucial to represent the final product accurately. Prototyping enables designers and engineers to test concepts, refine designs, and validate functionality before moving to full-scale production. It’s essential to use materials that can endure prototyping demands while closely simulating the end product’s mechanical properties.
With various materials available for injection molding, choosing the right one is critical to creating effective prototypes. Acrylonitrile butadiene styrene (ABS) and polylactic acid (PLA) are commonly used plastics in injection molding prototypes. Each has unique advantages and disadvantages, making it important to consider the specific needs of your prototype.
Understanding Prototyping Materials
Prototyping materials encompass plastics, metals, and other substances used for creating preliminary models. These models allow for refining functionality, conducting user tests, and making adjustments without the high manufacturing costs. Injection molding, a process that heats and injects plastic into a mold, is a popular method for prototyping and mass production due to its efficiency in creating detailed parts.
Choosing the right plastics is essential for successful injection molding. Materials need to fill molds without defects and accurately withstand any post-processing. Prototyping materials must be similar to final production materials in attributes like heat or chemical resistance, elasticity, and moldability. If there’s a significant difference, the prototype may not accurately represent the final product, leading to costly and time-consuming revisions.
Introduction to ABS and PLA
ABS is an extremely versatile thermoplastic made from three distinct monomers: acrylonitrile provides thermal stability, butadiene improves impact resistance, and styrene gives rigidity and ease of processing. The combination creates a durable plastic with high strength and flexibility compared to rivals.
ABS is also dimensionally stable across a wide temperature range, resisting warping or deformation up to approximately 221°F. It can be easily machined and finished with coatings or metallic platings for functional or aesthetic requirements. These properties make ABS a go-to choice for consumer products, automotive parts, protective equipment, toys, and prototypes.
PLA (Polylactic acid) is a biodegradable, plant-based alternative created from renewable ingredients like corn starch, cassava, or sugarcane. Because it is biodegradable, it is commonly used for medical implants like stents and implantable drug dispensers designed to biodegrade over time. While PLA is easy to process and more environmentally friendly than oil-based plastics, its mechanical performance limits use cases compared to plastics like ABS.
PLA’s tensile strength and heat resistance are inferior to ABS in injection molding applications. PLA begins softening at temperatures above 140°F, making it more prone to warping. The material also becomes brittle when subjected to basic solutions or weathering effects over time. These drawbacks necessitate more careful design considerations compared to durable ABS.
The underlying compositional differences between oil-based ABS and plant-sourced PLA dictate divergent material characteristics that significantly impact injection molding suitability. Where ABS offers strength, flexibility, and is easy to manipulate into detailed molds, PLA suffers fundamental limitations like brittleness, poor stability, and lower heat thresholds that rule out intricate applications.
Why ABS is Preferable for Injection Molding Prototyping
Durability and Impact Resistance
ABS has inherently superior durability than brittle PLA due to its elastomeric properties. The butadiene segments allow ABS resins to flex and stretch, while acrylonitrile and styrene provide strength, making ABS an ideal choice for functional prototypes undergoing rigorous testing. PLA is prone to fracturing when dropped or impacted and is unable to emulate the resilience of final ABS production plastics.
Thermal Properties
With a glass transition temperature of 221°F compared to PLA’s 140°F, ABS remains dimensionally stable across the high temperatures involved in injection molding processes. This prevents warping while allowing very precise mold flows to fill intricate cavities. PLA risks deformation, shrinking, and sinking at the temperatures required for fast, high-volume injection cycles.
Flexibility and Machinability
ABS strikes an excellent balance between rigidity for precision and flexibility for releasing injection molded parts without distortion or cracking. The material can flex slightly to fill complex curves and negative spaces without collapsing or sacrificing surface quality. PLA’s comparative rigidity limits possible prototyping geometries due to the increased likelihood of cracking upon demolding.
Surface Finish and Post-Processing
With suitable viscosity and flow properties, ABS easily achieves glossy, glass-smooth finishes out of the mold. The symmetry and strength also make ABS the preferred plastic for bonding, painting, smoothing, and other secondary finishing processes often required for prototypes. PLA’s susceptibility to moisture absorption and crystallization makes achieving the surface qualities or post-processing seen in ABS challenging.
Considerations When Choosing ABS for Prototyping
Environmental Factors
While extremely useful for prototyping, ABS does come with environmental considerations regarding its oil-based composition and difficulties recycling certain grades. The non-biodegradability and presence of hazardous Bisphenol-A in some variants make responsible disposal important. However, the durability of ABS leading to long lifecycles offers a form of efficiency. Overall, designers should account for environmental impact along with performance needs when selecting ABS.
Cost Implications
ABS remains highly cost-effective for low- to mid-volume injection molding orders compared to alternatives like PLA or nylon. Less defective parts, quicker cycle times, and better versatility to adapt prototypes across the testing process also boost value. If design requirements align with ABS properties, it offers outstanding “bang for your buck” even with added finish work.
Sustainability
Despite being petroleum-based, ABS’s long lifespan and recyclability offer a form of sustainability. Its durability means less frequent replacements, and its recycling ability reduces the environmental footprint by minimizing the need for new resources. This aligns with the principles of a circular economy. PLA, celebrated for its biodegradability and renewable origins, faces scrutiny over its decomposition rate and resource use. While industrially compostable, PLA can decompose in non-optimal conditions for up to 80 years. Additionally, the production of PLA is resource-intensive, requiring 2.7 grams of corn to produce 1 gram of PLA, raising concerns about the ethical use of agricultural resources.
Project Requirements
The most crucial factor when weighing ABS against other plastics is properly matching material performance to application requirements. Considerations like temperature or chemical resistance needs, lifetime and aging properties, post-processing needs, expected user conditions, and performance validation targets should dictate material selection. ABS balances superior mechanical properties and processability to a wide spectrum of prototypes. However, unique electrical or medical devices may consider finding a material specialty suited to their niche.
If you are still unsure whether PLA or ABS makes the most sense for achieving your next prototype milestones, the experts at Protoshop can help review application details and provide straightforward plastic resin recommendations. By precisely aligning prototype requirements to material characteristics, together, we can enable your prototypes to effectively inform downstream decisions, uncover insights, and hit development targets right on schedule.
