Professional Custom Metal Die Casting OEM: How the Process Really Works

• 1
  What a Metal Die Casting OEM Partner Actually Does
• 2
  How Alloy Choice Sets Your Real Limits
• 3
  Draft, Wall Thickness and Shrinkage: The Three Numbers That Decide Feasibility
• 4
  Post-Processing: Where the Casting Becomes a Real Part
• 5
  When Die Casting Is the Wrong Answer
• 6
  Die Casting or CNC Machining: Which Fits Your Part

Die casting is a molding process for metal. A steel die is cut with a cavity shaped like your part. Molten alloy is pushed into that cavity under pressure, held while it solidifies, then the die opens and ejector pins push the part out. Cycle times usually land between 20 and 90 seconds depending on part mass and wall thickness.

A metal die casting OEM supplier does more than run the press. The work starts at DFM review, where draft angles, parting lines, wall thickness and gate locations are checked against your drawing. It continues through die design, first-article inspection, trimming, CNC finishing of critical features, surface treatment and final inspection reports.

That full chain matters because a casting straight out of the die is close to net shape, not finished. Holes can often be cored instead of drilled. Cored holes smaller than about 2.5 mm in diameter are risky, since the core pin bends or breaks under repeated thermal cycling. Bosses, ribs and mounting pads can all be formed in the cavity if the geometry allows it.

The engineering meaning is simple. Every feature you leave to the die costs tooling money once and saves machining cost on every part. At low volume the die never pays for itself. At high volume it usually does, and the crossover point is what a good OEM partner should calculate with you before you commit.

Aluminum, zinc, magnesium and copper alloys behave differently in the same die. Aluminum ADC12 flows well and takes thin walls, but it is aggressive on tool steel and shortens die life compared with zinc. Zinc alloys like Zamak cast at lower temperature, hold tighter tolerances and finish better, which is why small precise parts often go that route.

Magnesium AZ91D is the lightest common option, roughly 35 percent lighter than aluminum for the same volume. It also needs tighter process control because the melt oxidizes quickly. Magnesium dust and chips require dedicated handling. If your part is weight-critical and the volumes justify it, magnesium is worth the extra discipline.

Copper alloys give the best thermal and electrical conductivity, but the higher melt temperature wears dies faster. You pay for that in tooling maintenance. For heat sinks and busbars the trade is often still worth it.

Aluminum 6061 and ADC12 cover most general housings. Stainless and titanium are not die casting alloys at all. They are machined, and mixing them into a casting conversation usually means the part should be CNC cut from billet instead.

Porosity is the other alloy-driven factor. Gas trapped during filling becomes internal voids. Vacuum-assisted casting pulls gas out of the cavity before the shot, which reduces porosity in thick sections. It costs more per part and is not needed for every geometry.

Draft is the taper on every vertical face that lets the part slide out of the die. Typical values run 1° to 3° on inside walls and 0.5° to 1.5° on outside walls. Textures and deep ribs need more. A part with zero draft can be cast, but it will drag, scratch and raise ejection force until something cracks.

Wall thickness drives cooling time and defect risk. Aluminum parts usually sit between 1.5 mm and 4 mm. Below 1 mm the metal freezes before it fills the far end of the cavity. Above about 6 mm the center cools slower than the skin, and shrinkage porosity forms in the middle. Thick sections should be cored out or redesigned as ribs.

Shrinkage is predictable, not random. Aluminum shrinks roughly 0.6 percent, zinc about 0.5 percent, magnesium around 0.7 percent as it solidifies. The die cavity is cut oversized to compensate. If your drawing calls for a 100 mm span in aluminum, the tool is built near 100.6 mm so the cooled part lands on nominal.

Tolerance is where casting alone runs out of road. As-cast linear tolerances commonly hold around ±0.1 mm on small features and loosen as dimensions grow. When your print says ±0.005 mm, that feature is machined after casting, not cast. Planning which surfaces are cosmetic and which are functional saves both tooling cost and argument later.

Trimming removes runners, gates and flash. It is quick, but the trim die has to be built alongside the casting die or you create a bottleneck at the press. Deburring follows, usually tumbling or manual work on functional edges.

CNC finishing is the step that turns a rough casting into a usable component. Mounting faces, bearing bores, threaded holes and sealing surfaces get machined to ±0.005 mm where the design needs it. We run 127 high-precision CNC machines, including 16 simultaneous 5-axis centers, so the same shop that casts the part also machines it. That avoids the tolerance stack you get when two suppliers each hold half the print.

Surface treatment comes last. Anodizing, plating, powder coating, bead blasting and laser marking are all available. Laser marking has a minimum character height of 1.5 mm, which matters if you plan a serial number or data matrix on a small boss.

Inspection closes the loop. Every part is checked before shipment, with raw material verification, in-process monitoring and final inspection. Reports are available on request. For automotive and medical programs the paperwork trail is not optional, and it is easier to build it in from the start than to reconstruct it later.

Die casting loses when volume is low. A die is a fixed cost. If you need 50 parts, that cost lands on each one and the per-unit price looks absurd next to machining from billet. Rapid prototyping and short-run CNC are the honest answer at that stage.

It also loses when the part is mostly one thick block. Casting a 30 mm solid section invites porosity and long cycle times. Machining from plate is faster and more predictable. Thin, ribbed, complex shells are where casting wins.

Very tight tolerances across many features are another warning sign. If half the drawing is ±0.01 mm, you are paying for a die and then machining most of the part anyway. Ask whether the geometry could be simplified and cut directly from aluminum 6061 or 7075.

Finally, consider material. If the design calls for 316L stainless or Ti-6Al-4V, die casting is off the table. Those go through CNC machining and, for magnesium or specialty alloys, vacuum casting for low-volume bridge production.