Engineering and Design Support for Hot-Die Forgings

Die design and process engineering come with the quotation, not as an extra: a drawing is reviewed and returned with a written manufacturability note in 3 working days, the die layout follows before any die block is ordered, and the first article is measured 4–8 weeks after die design release, for parts from 0.1 to 500 kg in envelopes up to 1,200 × 800 mm. Projected area, shrinkage, draft angle and the tolerance stack are all fixed before the cavity is cut, which is what keeps die corrections off the critical path.

What the drawing review actually checks

The review is not a courtesy read. It is the point where a part moves from "can be drawn" to "can be forged", and every item below is answered in writing so that the quotation and the die layout rest on the same assumptions.

Most rejections at first article trace back to one of these six items being left to the die maker to "sort out". Fixing them on paper costs nothing; fixing them in hardened H13 costs a die set.

Tonnage and stage count come from projected area, not from part weight

A common RFQ mistake is to size the press from the weight of the finished part. The press sees the projected area of the forging at the parting line, including flash, multiplied by the flow stress of the material at the temperature the die actually runs at. The working form is F = K × σ_f × A, where A is the projected area in mm², σ_f is the flow stress in MPa at forging temperature, and K is a constraint factor that accounts for flash restraint and strain rate.

K is where suppliers differ by a factor of two. For open-die work in a single blow it is near 1.2; for a closed impression with a flash land it runs 3 to 5; for a deep, thin-walled cavity with a long metal path it can reach 6 to 8. Sizing with K = 1.5 on a closed-die job produces a press that deflects under load and a die that cracks at the fillet.

The number of stages follows from the same geometry. A simple axisymmetric part with a 1.5:1 height-to-diameter ratio forges in one or two blows; a part with a long axis, a thin web or a reverse draft needs a blocker, a buster and a finisher. Each extra stage is another die impression and another set of tolerances to stack.

Shrinkage, draft and radii: the three numbers that decide die success

Shrinkage is applied to the die cavity, never to the finished drawing. Steel contracts roughly 1.2–1.5% between the last blow and room temperature; the exact figure depends on grade, section thickness and how fast the part leaves the die. Thin sections cool faster and shrink less in absolute terms but the pattern differs, which is why a shrink rule applied uniformly to a part with a 12 mm web and a 90 mm hub still needs correcting on the second die.

Draft is stated on the drawing as a finished-part requirement, but it is a die requirement. On hot-die work the values below are what keeps the part from dragging. Where a customer drawing shows zero draft, the note that comes back will say what the minimum is and what it costs to machine the wall afterwards instead.

Radii are the cheapest die-life decision available. An internal corner at R1 will crack in H13 within a few thousand blows; the same corner at R4 lasts an order of magnitude longer and fills more reliably, because metal flows into a radius instead of stopping against a wall.

Design calculations that come with the quotation

Four calculations are run routinely because they decide cost more than the part geometry does. They are returned as one page with the quotation, so that a purchasing decision can be checked rather than trusted.

What to send with the RFQ

A drawing in PDF is enough to start; a 3D model in STEP or IGES shortens the review by a day because the projected area and stock volume are read directly. The list below is what removes the follow-up questions.

• 2D drawing with GD&T, datums, and a clear statement of which surfaces are as-forged and which are machined
• 3D model in STEP AP214 or IGES, nominal, without the machining allowance applied
• Material grade and the standard it is ordered to (GB/T, ASTM, JIS, EN)
• Annual volume, batch size, and whether the volume is expected to grow
• Any second operation already fixed — heat treatment, coating, machining, assembly
• Acceptance standard for NDT, if the part is safety-related
• Target landed cost or target weight, if either is already fixed by the programme

Frequently asked questions

How long does the drawing review take?

Three working days from receipt of a drawing and a material grade. A STEP model shortens it because the projected area and stock volume are read from the solid rather than reconstructed from the drawing. The note comes back in writing and lists every assumption made.

Can you forge to a drawing that has no draft angle?

Not as drawn. A hot-die forging needs 5–7° on outer walls and 7–10° on pockets for steel. Where the drawing shows zero draft, the part is either forged with draft and then machined on that wall, or the die is built with a split that hides the draft on a non-functional face. Both are priced differently, and the note says which one is being quoted.

What tolerance can be held as-forged?

As-forged geometry follows ISO 8062 class C. On small parts that is roughly ±0.3 mm on general dimensions, widening to ±0.5 mm at 100 mm and about ±1.0 mm above 300 mm. Critical dimensions are machined to ±0.2 mm where the drawing calls for it. Anything tighter is a machining requirement, not a forging requirement, and should be priced and inspected as one.

Do you charge for the die layout?

The layout is part of the quotation package, not a separate engineering fee. What is charged separately is the die itself, and the die becomes the customer asset once the first article is approved.

Who owns the die after the project ends?

The customer. Die ownership, the right to move the die, and the condition it is returned in are stated in the quotation. Die drawings and the electrode set travel with it so that a second source can continue production.

Can you work from a competitor drawing or a sample part?

Yes, with one caveat: a sample part carries the previous supplier assumptions, including draft and parting line that may not suit the volume you are planning. Reverse engineering is quoted with a dimensional report against the sample first, so that deviations are known before the die is cut.

All figures are typical reference values for the materials and processes named. Final acceptance criteria are fixed by the drawing, the applicable standard (ISO 8062, ISO 2768, ASTM E140, EN 10204, ASTM A388) and the agreed inspection plan.

Engineering: wuq268022@gmail.com · +86-512-6808-6677