How to Read a Die Caster's Capability Sheet

Why This Document Deserves an Hour of Your Time

Most buyers comparing Aluminum Die Casting suppliers skim the capability sheet for two things: a machine big enough, and an ISO certificate. Both boxes get ticked in ninety seconds.

That is a mistake, though not for the obvious reason. Suppliers rarely lie here. The real issue is that capability sheets are written by marketing from notes supplied by production, and nobody reconciles the two. What reaches the website is a set of best-case figures stripped of the conditions that made them true.

This is the checklist our engineering team uses to evaluate a subcontract partner. It applies equally when the sheet being audited is ours.

Test One: Does the Sheet Contradict Itself?

Start here. It costs three minutes and tells you more than any certificate.

Read the narrative paragraphs, then the specification table, then compare. On a surprising number of die casting services pages you will find a minimum part weight stated one way in the prose and another in the table, envelope dimensions that disagree, or a tonnage range excluding a machine listed in the equipment inventory below it.

None of these are lies. They are a page assembled over five years by people who each edited one section. But consider what it tells you: no engineer read the finished document.

Key point: internal consistency is a proxy for document control, and document control governs drawing revisions, process parameters and inspection records once your programme is running.

Test Two: Is the Tonnage Qualified by Projected Area?

Clamp force is determined by projected area, not part weight. Metal in the cavity pushes the die halves apart with a force equal to projected area — runners and overflows included — multiplied by intensified cavity pressure. For aluminium that pressure runs 6,000 to 8,000 psi, giving a rule of thumb of two to four tons per square inch.

A wide, flat die cast housing with a 245 in² footprint needs roughly 735 tons even at under two pounds. A compact valve body weighing six times more but occupying 38 in² needs about 114 tons. The light part needs the bigger machine — which is why quoting die Casting Parts by weight alone routes work to the wrong press.

"What is the largest projected area you can run, and on which machine, with runners included?"

A supplier answering in square inches is quoting from process knowledge. One redirecting to part weight is quoting from a sales sheet.

Test Three: Is Wall Thickness Tied to Flow Length?

"Thin walls as low as 0.04 inch" is a claim you will see often. One millimetre. Achievable — and meaningless without a second number.

Wall thickness is not an independent variable. It is a ratio against flow length. A 1.0 mm wall fills easily 30 mm from the gate. The same wall 200 mm away will cold shut: the metal front loses superheat, begins to solidify, and two fronts meet without fusing. The part looks complete and leaks under pressure test.

A minimum wall published without a flow length qualifier was either measured on a coupon beside the gate, or taken from a part whose geometry kept every thin section close to a feed path. Neither tells you whether your part will fill.

Buyers who learn this often overcorrect and thicken everything.

Eight millimetres is not a safe wall — it is the hardest section to cast properly. Solidification time scales with the square of thickness, so a heavy section stays liquid after the gate has frozen and no feed path remains to compensate for shrinkage. The result is internal microshrinkage, found only when the part is machined open or fails a pressure test. The workable range sits between 2.0 and 5.0 mm; above that you need coring and ribs, not more metal.

Test Four: Which Tolerance Class Is Being Quoted?

Three tolerance classes get published under one heading, and the spread between them is an order of magnitude.

A page advertising "±0.02 mm precision" on cast metal is describing a secondary machining operation while implying a casting capability. The claim survives because it is technically defensible — the finished die cast metal part does hold ±0.02 mm, just not as cast. The consequence is cost: specifying it across a parting line buys a machining operation, a fixture and an inspection step that nobody quoted.

"Is this tolerance as-cast or after machining, and does the datum cross the parting line?"

Key point: mark on the drawing which dimensions are critical-to-function. Untagged drawings force the supplier to treat everything as critical, converting as-cast features into machined ones and inflating price without improving the part.

Test Five: Does the Mould Life Figure Come With a Maintenance Clause?

The claim to be most sceptical of: "tooling withstands 75,000 to 250,000 shots without requiring maintenance."

The shot count is plausible. "Without maintenance" is not, and it reveals a misunderstanding of how dies age.

Thermal fatigue cracking is not a defect. It is the normal life cycle of H13 tool steel. Every shot cycles the cavity surface through a large temperature swing in under a second, and the resulting cyclic strain produces a fine network of heat-check cracks that begins early, progresses gradually, and eventually prints as a visible pattern on the casting. You cannot prevent it — you manage it, through scheduled polishing every 20,000 to 30,000 shots plus localised weld repair where areas degrade faster.

So the real question was never the shot count:

"Who pays for scheduled maintenance, and when does the die need replacement rather than repair?"

A supplier offering "lifetime tooling" without answering that has either priced maintenance into the part price silently, or will raise the subject in year two.

Raise a second-order issue at the same time. When a cavity area degrades, replacing a modular insert costs a fraction of a new tool and turns around in days; replacing the complete die costs full price and five to eight weeks. Which option exists was decided at tool design, not at failure. Modular construction with standardised insert pockets costs slightly more up front and requires in-house EDM. Ask before steel is cut — afterwards the option is gone.

Test Six: Are Porosity Claims Split by Mechanism?

"Low porosity" appears on nearly every metal casting services page and in most OEM casting quotations. It is not a specification, because porosity is not one defect.

The countermeasures are not interchangeable. A supplier who answers a shrinkage rejection by adding vacuum will spend six weeks proving nothing.

For pressure-tight or structural parts, replace "low porosity" with a named standard and a zone map — typically ASTM E505 reference radiographs with an acceptance level per region, or a defined leak rate at a stated test pressure.

Key point: if the acceptance criterion is not written down before tooling, T1 approval becomes a negotiation instead of an inspection.

Test Seven: Are Alloys Grouped by Process?

A materials line reading "aluminium, zinc and magnesium" bundles two different machine architectures.

Cold chamber

• — aluminium and magnesium. Metal is dosed into an unheated shot sleeve each cycle, because molten aluminium attacks a submerged steel injection system. Slower cycle, higher pressure capability.

Hot chamber

• — zinc and some magnesium alloys. The injection mechanism sits in the melt. Faster cycle, lower pressure, and the reason

zinc casting

reaches thinner walls than aluminium.

A cold-chamber-only shop can still quote zinc, but it will be subcontracted. Not disqualifying — problematic only when undisclosed, because it silently adds a handover and removes direct quality control over the aluminum alloy processing manufacturing chain you thought you were buying.

Two alloy constraints are worth checking on any materials list.

6061 cannot be die cast. Silicon at 0.4 to 0.8% sits far below the 7 to 13% of casting alloys, giving a wide freezing range that hot-tears in a steel die. If 6061 appears on a die casting alloy list, that list was copied from a machining or extrusion page. Drawings calling for 6061 need aluminum fabrication from extrusion, or machining from billet.

A380 does not anodise bright. At 3 to 4% copper the intermetallic phases dissolve preferentially and produce a mottled dark film. Bright anodised aluminium casting parts require A360 or A413, chosen before steel is cut — afterwards the options are a new tool or a different finish.

Test Eight: What Is Deliberately Excluded?

The most trustworthy capability sheets state what the supplier will not do. A credible custom die casting operation should say plainly that below roughly 200 units machining from billet skips tooling and ships faster; that high pressure casting cannot deliver T6 properties, because entrained air expands during the 500–540 °C solution soak while the matrix softens and lifts the surface as blisters; and that geometry developing from flat stock belongs in custom metal fabrication rather than a die.

A page claiming every process suits every volume has told you it is a sales document.

Our Capability Sheet, Written to These Rules

Each figure below is a commitment, qualified where a qualifier is needed.

In-house scope: permanent tooling design and manufacture with modular insert construction, cold chamber aluminum die casting, hot chamber zinc, 3/4/5-axis CNC machining, blasting, anodising, powder coating, plating, threaded insert installation, sub-assembly and leak testing. Our metal fabrication line — laser cutting, press brake forming, TIG and MIG welding — often lets a cast body carry fabricated brackets, removing side actions from the die.

Typical aluminium casting products: LED heat sinks, telecom enclosures, motor housings, gearbox covers, valve bodies, furniture hardware and mounting brackets. We hold no stock — every custom casting is built to drawing or sample, with 1-to-1 engineering support and permanent tooling ownership, backed by 30+ years of factory processing experience.

Frequently Asked Questions