By Elizabeth Norwood, Senior Chemist, MicroCare
Metal injection molding (MIM) is ideal for producing complex small metal parts. This is thanks to its precision, efficiency, and near-net-shape capabilities compared to traditional, subtractive machining methods like turning, grinding, or cutting.
A process that is helping to speed up MIM manufacturing is debinding using a vapor degreaser. Vapor degreasing with optimized debinding fluids accelerates the removal of binders from fragile green parts, reducing the time between molding, and sintering finished components. This throughput increase enables substantially higher production volumes and allows manufacturers to maximize profits.
The art of efficient binder debinding
MIM success often comes from the careful selection of the specialized combination of the feedstock comprised of fine metal powders and the binder formulation. The chosen binder imparts critical strength and plasticity so the feedstock can mold effectively into delicate and intricate green part shapes. Popular MIM binder components include paraffin wax, carnauba wax, stearic acid, and specialty polyethylene or polypropylene waxes.
In the molding process, the binding agents are crucial but sacrificial. They need partial removal before exposing green parts to the high heat necessary for sintering. The careful extraction of binders is vital to prevent deformation and cracking during sintering, ensuring a uniform compression and even sintering of green parts.
Debinding before sintering is a delicate balance, selectively removing a precise amount of binders in the shortest time with minimal damage to the part’s structure. As binders are progressively removed, green parts become porous and fragile. Preserving an essential amount of binder within the green parts is crucial to provide the required strength and dimensional stability for the forthcoming sintering process.
Any remaining binder within the parts is burned off during this removal in the high heat of the sintering oven. This final step transforms green parts into their finished solid state.
The efficiency of debinding is paramount, as rapid and consistent removal of the binder translates to reduced time between injection molding and the sintering of finished parts. This increase in throughput and enables significantly higher production volumes.
Comparing MIM debinding processes
Various techniques are used to remove binders from MIM green parts, each with pros and cons:
- Thermal Debinding – Heats parts for up to 24 hours, enabling the binder to remove the wax binders and any additives. This process is very slow.
- Catalytic Debinding – Utilizes nitric, oxalic, or other acidic gases to rapidly dissolve binders via catalyst acceleration in just a few hours. Fast, but requires significant safety measures when handling hazardous acids.
- Aqueous Debinding – Dissolves water-soluble binders in hot water or alkaline baths. Limited effectiveness for insoluble binders which remain behind. There are also environmental concerns as the wastewater must be filtered and prepped for proper disposal.
- Solvent Debinding – Employs debinding fluids and a vapor degreaser system to dissolve and extract binders via solvent penetration which is a quick and efficient method.
Advantages of solvent debinding for maximum MIM throughput
Of all MIM debinding approaches, solvent debinding is the fastest way to deliver superior part quality by gently removing the binder without surface or structural defects.
The process heats a non-flammable debinding fluid into a vapor within the closed system of the vapor degreaser. As the vapors rise, they penetrate the green parts, dissolving the binders rapidly and uniformly.
Upon reaching the condensing coils at the top of the machine, the vapors are cooled back into a liquid state. This liquid is then collected, recycled, and ready for another cycle. The continuous recycling of the debinding fluid, lasting for hundreds of hours, minimizes the need for frequent replacement or refreshment, making vapor degreasing an economically viable and environmentally sustainable solution.
The choice of binder removal method depends on the material of the part and the type of binder used. Common methods include immersion in boiling debinding fluid, exposure to vaporized debinding fluid in a vapor degreaser, or a combination of both. All methods aim to allow the debinding fluid to penetrate the part, dissolve the binder, and create sufficient porosity to facilitate the evaporation of the binder before sintering.
Additional benefits of solvent debinding include:
- Speed – Very fast binder removal significantly reduces overall processing time.
- Quality – Gently eliminates binder without cracking, distortion, porosity, or other defects.
- Consistency –Automation ensures repeatable results across long runs.
- Flexibility – Accommodates wide range of MIM alloys, binders and geometries using the same process.
- Safety – Sealed vapor degreaser equipment prevents worker exposure.
- Sustainability – Fluid is recycled on-site for extended life.
Selecting an optimal MIM debinding fluid
Not all debinding fluids offer equal performance. Carefully evaluating the following properties when selecting a fluid is crucial:
- Strength – Must have high solvency to dissolve binders but not excessive to prevent part erosion.
- Viscosity and Surface Tension – Low levels allow the fluid to penetrate narrow channels or blind features and holes fully.
- Low Boiling Point – Due to its ability to heat rapidly and maintain operating temperature with minimal energy input, the low boiling vapor degreasing fluid offers significant energy savings and overall cost reductions.
- Evaporation Rate – Fast drying prevents residual fluid retention within the green part’s porous structure. The optimal selection of debinding fluid can significantly reduce debinding times by up to 75% compared to other methods, improving throughput, and reducing overall manufacturing costs.
- Materials Compatibility – The debinding fluid does not react with metal powder or binder components. Modern debinding fluids exhibit excellent compatibility with various materials, including stainless steel, tool steel, ferrous and nonferrous alloys, and various ceramics, ensuring the safety of delicate uncured substrates and preserving the integrity of molded green parts.
- Safety – Non-flammable debinding fluids enhance worker safety. Their azeotropic properties ensure thermal stability, eliminating fire or explosion risks.
- Stability – Unlike earlier versions, modern debinding fluids remain stable without additional stabilizers or scavengers, reducing maintenance time and costs, except under extreme conditions.
Modern debinding fluids offer superior debinding performance
Modern debinding fluids can be seamlessly integrated into existing vapor degreasers, eliminating the need for new equipment, downtime, or employee retraining. Moreover, these fluids prioritize worker safety, boasting excellent worker safety and environmental profiles. Compared to their predecessors, such as TCE (100-ppm PEL) and nPB (0.1 ppm PEL), modern fluids exhibit significantly higher permissible exposure limits (PELs) of around 200-250 ppm. Additionally, their low global warming potential (GWP) values under 10 and zero ozone-depleting potential (ODP) make them environmentally friendlier choices.
Adopting next generation debinding fluid used within vapor degreasers is helping companies make MIM parts fast. This method delivers unparalleled speed, safety, consistency, and sustainability – enabling manufacturers to reduce the time between molding and sintering finished parts significantly.
Vapor degreasing excels at fast, uniform binder removal from delicate green parts without compromising quality. Closed-loop solvent recycling adds economic and ecological viability, minimizing waste. The process can readily accommodate various MIM alloys and part geometries with adjustable parameters.
As MIM technology advances, integrating modern vapor degreasing and debinding fluids helps position manufacturers as leaders in shaping the industry’s future. Adopting these innovations allows producers to redefine standards around throughput, quality, and sustainable practices.
Elizabeth Norwood is a Senior Chemist at MicroCare, which offers precision cleaning solutions. She has been in the industry more than 25 years and holds a BS in Chemistry from the University of St. Joseph. Norwood researches, develops, and tests cleaning-related products. She currently has one patent issued and two pending for her work.