3D WERK
CASTING · TROUBLESHOOTING
CASTING DEFECTS GUIDE
Read the defect,
fix the stage it came from.
A failed casting is frustrating, but it is also evidence. The shape and position of a defect point back to the stage that caused it, and that stage is often well before the pour. This guide helps you name what you see, find the likely cause and change the right thing on the next flask.
Before you start
This guide is general information to help you get the most from your WaxJet. It does not replace the Flashforge manuals, the safety data sheets for your materials or your own safety checks. Where they differ, follow the manufacturer's instructions and safety data sheets. Isopropyl alcohol (IPA) is highly flammable, and warm IPA gives off more vapour. Flashforge's manual uses a mix of PPG400, ethanol and IPA at 40 °C, never above 43 °C. Ethanol is also highly flammable. Keep it away from heat, sparks and open flames, heat it only with equipment suited to flammable liquids, use it in a well-ventilated area, and wear suitable PPE such as gloves and eye protection. Investment powder contains crystalline silica, and wax burnout and metal melting give off fumes, so use ventilation and the PPE your safety data sheets list. As a business, you are responsible for work health and safety in your workshop, including risk assessment and how you store, use and dispose of chemicals. See our Terms and Conditions.
THE NUMBERS AT A GLANCE
Often
casting faults trace back to the tree, the investing or the burnout, well before the pour
One change
per flask when you test a fix, so you know what worked
About 730°C
top of a standard gypsum burnout cycle. Never above your powder's maximum
50%+
fresh metal in every melt, with any reused metal cleaned first
Clean white
investment at breakout. Grey means carbon was left behind
WHAT YOU NEED
Loupe or microscope
10x or more, and good light
Data sheets
for your investment, alloy and wax
Jeweller's saw
to cut a reject open at the sprue join
Second thermometer
to check the kiln reads true
Casting log
flask, times, temperatures, metal mix
Digital scale
for the metal and the investment
Before you change anything
Look before you guess. Under magnification, note the shape, size and exact place of the defect. Is it on every piece, or only one part of the tree? One flask, or every flask this week?
Walk back up the chain. Pattern, tree, investing, burnout, then melt and pour. The pour is the last step, not always the cause.
Check the equipment early. A worn thermocouple, a leaking vacuum seal or old pump oil can cost you a whole run of castings.
1
Gas or shrinkage? Read the hole
Porosity comes in two main kinds, and they have different fixes. Look at the holes under magnification, or saw a reject through the worst spot, before you change anything.
Shrinkage porosity
TREE
BURNOUT
Looks like: jagged, spongy or worm-like holes. Under magnification the walls show fern-like crystals.
Gas porosity
MELT & POUR
BURNOUT
Looks like: rounder, smooth-walled holes, often in small groups. Polishing opens them up as pits.
Where: in the heaviest section or right at the sprue join, the last metal to freeze.
Where: often at or just under the surface, and in corners such as where prongs meet.
Why: metal shrinks as it freezes. If the sprue freezes first, no liquid metal is left to feed the piece.
Fix at the tree: sprue to the heaviest section, a little thicker than the part, short and flared. Add a sprue where a heavy area sits beyond a thin one, and keep pieces clear of the button.
Why: gas trapped as the metal froze. It comes from the melt, from carbon left in the mould, or from investment that got too hot.
Fix at the melt: the lowest metal temperature that fills, a reducing flame, half or more fresh metal, and scrap cleaned of investment.
Then the flask: a flask that is too hot can make it worse. Try a cooler flask within your data sheet range.
Fix at the burnout: the full hold at top temperature with good air flow, and never above your investment maker's maximum.
Not sure which one you have?
Look at where the holes are. Holes only at the sprue join or in the thickest part point to shrinkage, usually a spruing problem (see the Casting Tree guide). Holes spread over thin and thick areas alike point to gas. You can have both in one casting.
Fix one thing at a time
Change one thing per flask and write it down. Lower the metal temperature, resize the sprue and change the burnout all at once, and a good casting will not tell you which change worked. When you can, run a few test flasks, each with a single difference.
2
Metal that did not arrive
Misrun. Part of the piece is missing, usually far from the sprue, with rounded, shiny edges. The metal froze before it got there.
Cold shut. A seam with rounded edges where two streams of metal met but were too cool to fuse. Look on thin or wide sections.
Poured short. Not enough metal, or the pour stopped. Most printed waxes are lighter than the 1.00 that charts assume, so chart factors under-pour. Weigh every tree and use the formula in the Casting Tree guide.
Check temperatures first. Metal or flask too cold. Raise one of them in small steps, within the data sheet range.
Then the tree and the machine. A sprue too thin or too long, a thin section far from its sprue, weak vacuum (check pump oil and seals), too little spin, or an incomplete burnout.
Then the design. A feature not properly joined in the CAD model can leave a gap metal cannot reach. Changing the sprues will not fix a gap that is in the model, so check the CAD file too.
3
Metal where it should not be
Fins and flashing
INVEST
BURNOUT
Looks like: thin, sharp sheets of metal standing straight off the surface, often with lacy edges.
Why: the investment cracked and metal ran into the crack.
Causes: a fast burnout ramp, the wrong water to powder ratio, a flask moved before it set, a flask left to dry out, patterns too close, or a flask cooled and heated again.
Fix: weigh powder and water exactly, leave the flask alone for the full bench set (typically 1.5 to 2 hours, longer for some powders and big flasks), and follow the maker's ramp.
Nodules
INVEST
Looks like: small round balls of metal on the surface.
Why: an air bubble clung to the wax and the metal filled it.
Causes: poor vacuum (pump oil, leaks), no debubblizer, investment under or over mixed, or too little working time left to vacuum it.
Fix: service the pump, use debubblizer and let it dry, and finish mixing, vacuuming and pouring well inside the working time.
4
Rough, pitted or stained surfaces
Rough or grainy all over
BURNOUT
INVEST
PATTERN
The mould surface broke down: burnout started too soon after investing, heated too fast or too hot, or the wrong water ratio. Rough or dusty wax is copied into the metal too.
Sharp pits, white or grey flecks
TREE
MELT & POUR
Investment or slag in the metal: a sharp corner at a sprue join broke off, the mould eroded, or an old crucible shed. They may only show once you polish.
Pitted surface, grey investment
BURNOUT
Carbon and ash left by a short burnout. Give the full hold at top temperature, with good air flow.
Stain left after pickling
BURNOUT
MELT & POUR
Investment that got too hot, in the kiln or from very hot metal, frees sulphur that reacts with the metal. Stay under your powder's maximum.
Purple or copper stain after polishing
MELT & POUR
Firescale, copper oxide in silver and gold alloys. Keep air off the metal as it melts and cools. Abrasion removes it, pickle will not.
5
Cracks and brittle metal
Hot tear. A jagged crack where thick meets thin or at a sharp inside corner. Soften sharp changes in the design, feed the heavy section, use clean metal, and avoid too much spin or pressure.
Quenched too soon. Wait until the red glow has left the button. Stuller advises letting the flask cool below about 600°C (1100°F) before breakout, especially for nickel white gold. Some red and rose golds are meant to be quenched early, so your alloy data sheet has the final word.
Flask or metal too cold. Can crack castings and leave prongs brittle.
Dirty or tired metal. Investment on old sprues, oxides, repair solder, or metal remelted too often. Use 50% or more fresh metal.
Handled while hot, or brittle white gold that needs the alloy maker's heat treatment.
PRINTED WAX: WHAT TO WATCH
Same rules apply. Printed wax does not prevent casting defects.
Support fully gone. Support left under a prong or in a gallery burns out too and comes back as extra metal.
Clean and dry. Re-rinse any white haze and let the IPA evaporate before spruing.
No shortcuts on the ramp. Wax swells as it warms. In a 2024 lab test, a solid sample of one FDM printing wax pushed about twice as hard as an injection wax, though its porous printed parts did better. The WaxJet's wax was not tested, so keep the full bench set and your maker's ramps.
SYMPTOM FINDER
Jagged, fern-like holes at the sprue join or in the heaviest part
LIKELY CAUSE
FIX AT
WHAT TO DO
Shrinkage: sprue too thin, too long or in the wrong place, or flask too hot
TREE
Sprue to the heaviest part, a little thicker, short and flared. Try a cooler flask
SYMPTOM
Round, smooth holes at or just under the surface
LIKELY CAUSE
FIX AT
WHAT TO DO
Gas: metal overheated or oxidised, too much reused metal, carbon in the mould
MELT & POUR
BURNOUT
Cooler metal, reducing flame, 50%+ fresh metal, full burnout with good air
SYMPTOM
Piece missing far from the sprue, or a seam with rounded edges
LIKELY CAUSE
FIX AT
WHAT TO DO
Misrun or cold shut: metal or flask too cold, sprue too small, weak vacuum
MELT & POUR
TREE
Raise metal or flask temperature in small steps, bigger or extra sprue
SYMPTOM
Small button or none, pieces unfilled
LIKELY CAUSE
Poured short: not enough metal, or the pour stopped
FIX AT
TREE
WHAT TO DO
Weigh the tree and use the metal formula with your printed wax density
SYMPTOM
Thin, sharp fins standing off the surface
LIKELY CAUSE
Cracked investment: fast ramp, wrong ratio, flask moved or dried out, patterns too close
FIX AT
INVEST
BURNOUT
WHAT TO DO
Weigh exactly, full bench set, maker's ramp, 3 to 5 mm between patterns
SYMPTOM
Small metal balls on the surface
LIKELY CAUSE
Air on the wax: poor vacuum, no debubblizer, mix under or over worked
FIX AT
INVEST
WHAT TO DO
Service the pump, use debubblizer, finish inside the working time
SYMPTOM
Rough or grainy surface all over
LIKELY CAUSE
FIX AT
WHAT TO DO
Mould surface broke down: burnout too soon, fast or hot, wrong ratio, dusty wax
BURNOUT
INVEST
Maker's bench set and cycle, correct ratio, clean wax stored away from dust
SYMPTOM
Sharp-edged pits, white or grey flecks
LIKELY CAUSE
FIX AT
WHAT TO DO
Investment or slag: sharp corners at joins, eroded mould, old crucible
TREE
MELT & POUR
Fillet every join, clean or replace the crucible
SYMPTOM
Pitted surface, grey investment at breakout
LIKELY CAUSE
Carbon and ash left by a short burnout
FIX AT
BURNOUT
WHAT TO DO
Full hold at top temperature, good air flow through the kiln
SYMPTOM
Stained surface that pickle will not shift
LIKELY CAUSE
Sulphur from gypsum investment that got too hot, in the kiln or from very hot metal
FIX AT
BURNOUT
MELT & POUR
WHAT TO DO
Kiln at or under the powder's maximum, metal no hotter than it needs
SYMPTOM
Cracks, or prongs that snap
LIKELY CAUSE
FIX AT
WHAT TO DO
Hot tear, quenched too soon, flask or metal too cold, dirty or tired metal
MELT & POUR
TREE
Wait for the glow to leave the button, check temperatures, clean fresh metal
SYMPTOM
Distorted piece, flaws copied from the wax, drips or bridges
LIKELY CAUSE
FIX AT
WHAT TO DO
Pattern damage, heat, leftover support, or a hot wax pen
PATTERN
TREE
Inspect under magnification, store cool, build the tree from the top down
SYMPTOM
BEFORE THE NEXT POUR: CHECKLIST
Patterns inspected, support gone, fully dry
Sprues on the heaviest part, flared, joins filleted
Tree weighed, metal worked out
Half or more fresh, clean metal
Powder and water weighed to the maker's ratio
Mixed, vacuumed and poured in the working time
Full bench set, flask left alone
Maker's burnout cycle, never above its top
Flask and metal at data sheet temperatures
Quench only when the alloy allows
Only one change from the last flask
Everything written in the casting log
WHERE TO NEXT
GUIDE 13 OF 13 · AFTER CASTING
THE BIG PICTURE
1 · DESIGN
2 · PATTERNS
3 · CASTING
4 · AFTER CASTING