For six months I worked inside Bosch Rexroth’s additive manufacturing lab to answer a single question: can we make filament-based metal printing competitive with metal injection molding (MIM) that has been optimised for decades? Hitting that bar demanded a mix of material science, rigorous experimentation, and navigating a large corporate R&D environment to secure the lab time, furnaces, and metrology the project needed.
Building the Material Stack
The thesis started with custom filament development. I blended metallic powders with polymer binders, tuned plasticisers, and measured rheology to keep extrusion reliable while maximising metal content. Each recipe included detailed documentation of viscosity, shrinkage, and surface finish so I could link material behaviour with later test data.
- Produced and extruded multiple batches of metal-polymer feedstock with varying powder loadings and binder chemistries.
- Benchmarked commercial filaments to understand baseline behaviour versus our in-house blends.
- Instrumented prints with inline temperature and flow measurements to correlate printability with final densification.
Designing a DOE Campaign
Because each print-and-sinter cycle consumed days of lab time, guessing was not an option. I designed a fractional factorial Design of Experiments (DOE) matrix covering extrusion temperature, flow, layer height, sintering pressure, ramp rates, and dwell times. Bosch’s lab technicians helped execute the plan while I tracked sample IDs through every process step.
- Used Minitab to plan and analyse DOE runs, capturing interaction effects between print settings and pressure-sintering parameters.
- Ran green density, dimensional accuracy, and post-sinter density measurements for every specimen.
- Modelled the results statistically to predict optimal parameter windows before committing to confirmation builds.
Introducing the “Bricklayer” Toolpath
Traditional slicers place identical line paths layer after layer, trapping voids vertically. I hypothesised that staggering every second line by half a bead width—like offset brick courses—would collapse those voids. Implementing the strategy required custom G-code post-processing and close monitoring of extrusion stability.
- Created a toolpath post-processor that offsets alternating raster lines while preserving wall integrity.
- Captured microscopy of cross-sections that showed the Bricklayer pattern reduced straight-line porosity compared to standard rasters.
- Measured a meaningful uplift in green-part density, translating into higher final density after sintering.
Pressure-Sintering Breakthroughs
Pressure-assisted sintering was the final lever. Working with Bosch furnace technicians, I tuned atmosphere composition, pressure ramps, and dwell times. Combining the DOE insights with Bricklayer prints produced two optimal recipes that delivered density values within striking distance of MIM parts.
- Confirmed dimensional stability and density using Archimedes testing, micrographs, and hardness checks.
- Validated the findings across repeated builds to ensure the optimised settings were robust, not one-off successes.
- Documented a full process guide for Bosch, from filament prep through furnace cooldown, so the work could transfer to other teams.
Operating Inside a Large Organisation
The technical work only happened because I learned how to navigate Bosch’s structure. I coordinated with safety teams, scheduled scarce furnace time weeks ahead, and communicated findings to senior engineers who controlled resources.
- Prepared weekly briefings that translated statistical outputs into clear decisions for non-specialist stakeholders.
- Championed additional microscopy sessions and binder inventory by showing the projected ROI on process yield.
- Built relationships across materials science, production, and quality departments, which opened doors for follow-on experiments.
Lessons I Took With Me
- Rigorous experimentation beats intuition—especially when every run is expensive.
- Toolpath innovation can rival material tweaks for improving additive manufacturing results.
- Influencing a large organisation requires clear storytelling and relentless follow-up, not just good data.
- Material science discipline—sample prep, documentation, traceability—keeps ambitious R&D projects credible.
This thesis cemented my interest in high-performance manufacturing and gave me a playbook for running complex experiments while partnering with corporate R&D teams.
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