Avoid These 7 Costly 3D Printing Material Mistakes

The first mistake starts in the quote spreadsheet. A buyer compares material price per kilogram and picks the cheapest column, then discovers the part needs a heat deflection temperature the resin cannot reach. Price per kilogram tells you almost nothing about cost per good part. What matters is whether the material holds the load, survives the temperature, and passes the test fixture on the first build.

Build orientation is the second trap. FDM, SLS, and SLM parts are anisotropic: strength along the layer lines is lower than strength across them. A bracket printed flat may carry 60 MPa in tension; the same bracket printed upright can fail at half that load. The material datasheet rarely states the orientation used for the test.

The fix for both is a mechanical requirement matrix written before you contact a supplier. List tensile strength, modulus, elongation at break, impact resistance, heat deflection temperature, continuous service temperature, chemical exposure, and fatigue life. Then mark which of those are critical and which are nice to have. When a supplier proposes a material, you can check it against the matrix in minutes instead of arguing about datasheet numbers.

Orientation deserves its own note on the drawing. State the load direction relative to the part, not just the material. For a hinge pin loaded along its axis, layer lines should run parallel to the pin. For a pressure cap, they should run perpendicular to the sealing face. A one-line note here prevents a rebuild that costs more than the part.

• 1
  Price per kg is a distractorCompare cost per accepted part, not cost per kilogram of feedstock.
• 2
  Anisotropy is realLayer direction can cut tensile strength by 30–50% in polymer prints.
• 3
  Write the matrix firstEight properties, each marked critical or optional, before any quote.

Nylon and TPU absorb water from the air. A spool left on the shelf for two weeks can gain enough moisture to cause steam voids during extrusion, and the printed part will have visible porosity and lower elongation. Drying the filament before the run is standard practice, but the part also needs protection after it leaves the printer.

The same logic applies to the service environment. A part that lives in a humid warehouse will behave differently from one mounted on an engine block. UV exposure degrades many photopolymers within months. Chlorinated water attacks some stainless grades. Oils and hydraulic fluids swell certain elastomers.

The fix is a short environment list on the drawing. Include indoor or outdoor, temperature range, humidity, contact chemicals, cleaning agents, and UV exposure. That list steers material choice more than any datasheet comparison. It also tells the finisher whether an anodize, a powder coat, or a sealing step is needed.

For parts that see repeated moisture cycles, specify a material with low water absorption or add a barrier finish. Nylon 12 and PEEK handle humidity better than PA6. Stainless 316L resists chlorides better than 17-4PH in some conditions. Small substitutions at the drawing stage save field returns later.

Surface roughness is not cosmetic on a printed part. As-printed SLM surfaces sit around Ra 8–12 μm, which is too rough for a sliding fit or an O-ring seal. If you plan to fix it later with machining or polishing, that step costs more than choosing a process that starts closer to the target.

Specify the finish from the start. A sealing face may need Ra 0.8–1.6 μm, which usually means a light machining pass on the printed blank. A non-critical cover can stay as-printed. Writing the Ra value next to the feature removes the guesswork and stops the supplier from quoting a blanket polish that doubles the price.

Total cost of ownership follows the same pattern. Add up feedstock, machine time, support removal, heat treatment, finishing, inspection, and the scrap rate. A cheap material with a 15% reject rate loses to a more expensive one with a 2% reject rate. Ask for cost per accepted part, not cost per printed part.

At GreatLight we run both additive and subtractive processes, so the comparison is sometimes uncomfortable. A part quoted as SLM may come out cheaper as a 5-axis machined blank with a printed prototype for fit check. The right answer depends on quantity, tolerance, and how soon you need metal.

• 1
  As-printed SLMRa 8–12 μm typical; sealing faces need a machining pass.
• 2
  SLA and SLSSmoother surfaces, but lower temperature and strength limits.
• 3
  Cost per accepted partInclude finishing, inspection, and scrap in the comparison.

A printed metal part is not the same as a wrought bar of the same alloy name. SLM 17-4PH has a different microstructure from wrought 17-4PH, and its ductility and weldability differ. AlSi10Mg prints well and machines reasonably, but it is not the same as 6061-T6 for structural fatigue. If a downstream weld or a tight thread is planned, verify that the printed grade supports it.

The cleanest way to avoid this is to let the process drive the material. If the part needs a welded joint, a rolled thread, or a mirror finish, CNC from wrought stock is often the safer route. If the geometry has internal channels that no cutter can reach, printing is the answer, and the material should be chosen for printability first. Mixing the two logics on one part is where costs appear.

Traceability closes the loop. Aerospace, medical, and automotive customers need batch-level documentation: powder lot, machine, build parameters, heat treatment, and inspection results. Without it, a failed part cannot be traced, and the whole lot is suspect.

We hold ISO 9001:2015, IATF 16949:2016, ISO 13485:2016, and ISO 27001:2022 certifications, and inspection reports are available on request. Raw material check, in-process monitoring, and final inspection run on every order. That paperwork is part of the part, not an add-on.

• 1
  Printed ≠ wroughtSame alloy name, different microstructure and ductility.
• 2
  Process drives materialWeld, thread, or polish first; then pick the route.
• 3
  Batch documentationPowder lot, build parameters, heat treat, inspection records.