Injection mold
Which mold base to use
Projected area, product height and cavity count — or the part's .stl / .step — and the page returns the series, sub-series and stroke of the standard Polimold mold base, with the steel to spare and the steel that is missing.
The part
Import a model
Designer's settings
Injection machine (optional)
Series
25.35
246 × 346 mm
Sub-series
12
P1 36 · P2 66 mm
Stroke
3
53 mm
Closed mold height
298.00
mm — in the closed mold
Opening needed
88.00
mm — for the part to come out
Clamping force
39.2
tf at 400 bar
Cavity layout
| 2 × 2 | 60.00 × 40.00 mm | grid rotated 90° on the plate |
|---|---|---|
| Useful area needed | 152.00 × 192.00 mm | |
| Useful area | 156 × 196 mm | |
| Spare useful area | 4.00 × 4.00 mm | |
| Wall between cavities (mm) | 32.00 mm | |
| Margin to the useful-area edge (mm) | 20.00 mm | |
| Total projected area | 9,600 mm² |
Plate thicknesses
| Top clamping plate | 27 mm | |
|---|---|---|
| Upper cavity plate | 36 mm | ≥ 32.00 |
| Lower cavity plate | 66 mm | ≥ 57.00 |
| Support plate | 46 mm | |
| Spacer | 96 mm | Stroke 3 |
| Ejector retainer plate | 17 mm | |
| Ejector plate | 22 mm | |
| Bottom clamping plate | 27 mm | |
| Stroke needed | 35.00 mm | 53 mm |
How to order
2535 · ? · 12 · ? · 3 · ?
Polimold's code order is series, type, sub-series, steel, stroke and assembly. Type, steel and assembly are your choice and do not come out of this calculation — the type sets the base-plate width (2 = clamping slot, 4 = with flange).- Note: Clamping force used 400 bar cavity pressure. 300 to 500 bar covers most technical parts; thin walls, long flow paths and reinforced materials call for 600 to 1000 bar. The right figure comes from simulation, not from this page.
53 series · 262 sub-series
The method is the manufacturer's, not mine
The series comes from the useful area
Polimold's catalogue is explicit: the series of a mold base is determined by the useful area available to machine the cavities, through the X and Y dimensions given in the series table.
So the calculation is: how much useful area your cavity layout needs, and which is the smallest series whose X × Y holds it. The page searches in ascending order and stops at the first that fits — testing both orientations of the grid on the plate.
The sub-series comes from the product height
Also from the catalogue: the sub-series is determined by the thickness of the cavity plates, which are tied to the product height, cooling details, slide inserts and other functional features.
The sub-series is the P1 / P2 thickness pair. The page picks the thinnest pair that still holds the cavity depth plus the steel around the cooling channel — and the manufacturer itself notes that slides and special cooling belong in that decision, and those the page does not know.
The stroke comes from the depth in the core
The part must clear the core completely, and the core is as deep as the share of the height left in the bottom plate. The stroke chosen is the smallest in the table that reaches it, plus whatever clearance you set.
The spacer height comes from the stroke table, not from the thickness column. That was established, not assumed — see the note on the real drawing below.
Why cavity spacing comes from the water hole
The easy route would be a "typical 50 mm margin". It errs both ways: wasted steel on a shallow part, and no guarantee of a hole on either.
Between two neighbouring cavities the injection pressures OPPOSE each other and the wall is in compression — a regime with enormous margin in steel. What actually governs the thickness is the cooling channel that has to pass there, with enough steel between channel and each cavity surface.
Hence the rule: wall = channel Ø + 2 × cover, with the cover as a multiple of Ø (1.5 × Ø by default). The same logic sets the minimum cavity-plate thickness, because the channel runs below the cavity floor. Both parameters are overridable.
About importing .stl and .step
STL is read in the page itself, with no dependency — including the case of an assembly exported as several concatenated binary STLs, where an ordinary reader takes only the first solid and says nothing.
STEP loads a CAD kernel compiled to WebAssembly (7.6 MB), only on this page and only when you choose such a file. There is no shortcut: STEP stores surfaces, not triangles, and measuring the box from the file's points would come out SMALLER than the part on a cylinder — the point there is the circle's centre, not its periphery. A round part would get an undersized mold base.
The projected area is the part's SHADOW, rasterised, not the sum of upward-facing faces. On a cup the rim and the inner floor occupy the same region of the plane, and summing would count it twice. Rasterising also discounts a through-hole by itself — steel meets steel there and pressure opens nothing — while keeping a blind hole, which is correct. The result carries a measured uncertainty, not a promise.
The two readers were checked against each other on the same model in STL and in STEP: footprint within 0.15%, volume within 0.23% and all three shadows within 0.47%.
How the catalogue was checked
The data came from the official 2- and 3-plate PDF catalogues. The font that draws almost every number in those files ships with an EMPTY character map, and the embedded subset has no glyph-name table: read the ordinary way, the PDF loses two thirds of its text without any error. The numbers were recovered by matching each glyph's outline against the complete system font — exact outline identity, not resemblance.
So nothing was published without crossing against a source that does not depend on that path. Polimold's per-family PDF uses standard encoding and agrees on 36 of 36 sub-series and 3 of 3 strokes. And the drawing of a REAL mold base (series 35.40, 346 × 396 plates) agrees on 6 of 6 plate thicknesses, with its 76 mm spacer matching stroke 1 of that series.
Further: the five 2-plate sub-series bands come out as complete square grids (6×6, 7×7, 7×7, 8×8, 8×8), with no gaps and no duplicates; and across 53 series × 3 strokes the ejector set always fits inside the spacer, with the stroke fitting the remaining gap. That invariant is what licenses the mold-height formula.
2 plates: 53 series from 156 × 156 to 696 × 996 mm, 262 sub-series. 3 plates: 30 series from 156 × 156 to 396 × 596 mm, 114 sub-series, with the runner plate.
What this page does not know
- Slides and moving cores. Any side action changes the useful area needed and may demand a much larger series. The catalogue names slides as a sub-series factor; here they do not enter.
- Runner system. Gate location, balancing and hot runners do not enter the cavity layout.
- Shrinkage, draft angles and locking. Dimensions are the product's as entered.
- Deflection of a tall core. A deep part with a slender core may need a thicker plate than the channel rule indicates.
- Conformal or insert cooling. The straight-channel rule is the common case, not the only one.
- The 3-plate stack height was not checked against a real drawing, unlike the 2-plate one.
Indicative. The series, sub-series and stroke of a real mold come out of the complete design — slides, cooling, runners and the machine it will run on. Confirm with Polimold before buying steel.