The short answer
On metal 3D-printed RFQs, **hot isostatic pressing (HIP)** is not the same as a [residual-stress or warpage note](https://3dwk.com/resources/slm-residual-stress-warpage-notes-for-buyers), a [support-removal and skim step](https://3dwk.com/resources/slm-support-removal-and-skim-notes), or a general “heat treat as needed.” HIP is a special process that uses high temperature and high pressure in an inert gas to close internal porosity in an SLM part. It does not replace machining of datums, and it does not by itself set the as-printed surface. Silence on whether HIP is required, on the alloy condition after HIP, and on which faces still need machining stock, is what widens many [quote-new.php](https://3dwk.com/quote-new.php) **rates.v1.1** estimate bands—not the furnace cycle time alone.
This guide is for buyers packaging SLM titanium or aluminum parts where a notes cloud says “HIP if needed” with no sequence. Illustrations use an **Example part** only—not a customer fitting. Sibling notes live in [SLM versus CNC hybrid strategies](https://3dwk.com/resources/slm-vs-cnc-hybrid-part-strategies) and [Ti-6Al-4V CNC versus SLM cost and lead time](https://3dwk.com/resources/ti6al4v-cnc-vs-slm-cost-lead-time); here we focus on **HIP packaging** so estimators do not have to guess whether a Ti-6Al-4V bracket must be HIPed before datum machining.
What HIP means for quoting
A **HIP pack** names whether HIP is required, the alloy and target condition (or “HIP + heat treat per drawing”), and which faces or bores still carry machining stock after the cycle. It is not a substitute for [build-orientation notes](https://3dwk.com/resources/slm-build-orientation-notes-for-buyers) or [downskin roughness notes](https://3dwk.com/resources/slm-downskin-roughness-notes-for-buyers). A general “densify as needed” cloud does not tell the shop whether to plan a third-party HIP load, or how much stock to leave on datum A. Process pages for titanium and aluminum SLM ([SLM Ti-6Al-4V aerospace](https://3dwk.com/en/slm/ti-6al-4v/aerospace.html), [SLM Ti-6Al-4V](https://3dwk.com/en/slm/ti-6al-4v.html), [SLM AlSi10Mg aerospace](https://3dwk.com/en/slm/alsi10mg/aerospace.html)) assume HIP is called only when the buyer actually needs internal-porosity close-out.
Do not bury “HIP as needed” inside a notes cloud. Put **HIP REQUIRED ON TI-6AL-4V AFTER SUPPORT REMOVAL; THEN MACHINE DATUM A AND BORE C (LEAVE 0.4 STOCK PER FACE BEFORE HIP); NO HIP-AND-SHIP ON AS-PRINTED COSMETIC RIBS** on the PDF and mirror it in RFQ text. Background: [DFM checklist before an online CNC quote](https://3dwk.com/resources/dfm-checklist-before-online-cnc-quote), [what files to send for a CNC quote](https://3dwk.com/resources/what-files-to-send-for-cnc-quote), [when to specify heat treat after CNC](https://3dwk.com/resources/when-to-specify-heat-treat-after-cnc).
When HIP is worth calling—and when it is not
HIP is typically specified when internal voids would affect fatigue, pressure tightness, or a required material condition—common on Ti-6Al-4V structural or pressure-adjacent parts, and sometimes on AlSi10Mg. Many fixtures and non-fatigue brackets can skip HIP if you say so, and stay with stress relief plus machining. HIP does not erase a rough downskin or a support scar; those still need orientation, [support removal](https://3dwk.com/resources/slm-support-removal-and-skim-notes), or a skim. Do not invent certificates; if you need a named procedure or a third-party report, write that requirement.
Titanium and AlSi10Mg powder planning bands sit in the published SLM material ranges under **rates.v1.1** tables; powder $/kg is rarely the HIP story—the extra special-process step, batching, and post-HIP machining stock are.
Sequence, stock, and dimensional change
Say whether HIP comes after support removal and before datum machining, and how much stock to leave on faces that must be true after the cycle. HIP plus a heat-treat condition can move a thin wall slightly; leaving no stock on a tight bore is a common trap. Cosmetic ribs that will never be machined should be called out as as-printed so the shop does not invent a skim. [Residual-stress and warpage notes](https://3dwk.com/resources/slm-residual-stress-warpage-notes-for-buyers) stay in the pack: HIP is not a silent substitute for a distortion plan.
Tolerance and inspection traps
Calling “HIP as needed,” mixing HIP with a “net-shape, no machining” note on the same tight datum, or asking for 100% porosity maps without a method, all force **needs_manual**. Default prototype lots to a written “no HIP” or “HIP required” flag, and put machining stock only on the faces that must be true. Related: [ISO 2768 general tolerances on CNC RFQs](https://3dwk.com/resources/iso-2768-general-tolerances-cnc-rfq) when those faces are later milled, and [what needs_manual means](https://3dwk.com/resources/what-needs-manual-means-preliminary-quote).
Illustration 1 shows an **Example part** Ti-6Al-4V fitting with labeled HIP plus 0.4 mm stock on datum A and bore C, versus as-printed cosmetic ribs.
Example part walkthrough
**Example part:** Ti-6Al-4V SLM fitting ~70 × 40 × 35 mm, HIP required after support removal, 0.4 mm machining stock per face on datum A and bore C, cosmetic ribs left as-printed, ISO 2768-m on the milled faces. With STEP + **HIP REQUIRED AFTER SUPPORTS; LEAVE 0.4 STOCK ON A AND C; RIBS AS-PRINTED**, expect a usable automatic planning band on [quote-new.php](https://3dwk.com/quote-new.php). Same geometry with silent “full densification as needed, net datums” often lands DFM notes or **needs_manual**—without inventing any customer PO or certificate.
Illustration 2 contrasts a vague RFQ (“HIP if required / applicable spec”) versus a labeled HIP-and-stock pack and the clearer estimate path.
What widens bands fastest
Unlabeled “densify as needed,” HIP required but zero stock on a tight bore, HIP skipped in text but implied by a material condition, and porosity reports with no method. Quantity breaks help unit price but do not erase special-process ambiguity—see [how quantity breaks change CNC unit cost](https://3dwk.com/resources/how-quantity-breaks-change-cnc-unit-cost) and [powder-reuse notes for SLM buyers](https://3dwk.com/resources/powder-reuse-notes-slm-buyers).
What to do next
Mark whether **HIP is required, the condition, and which faces keep machining stock**, then upload on [quote-new.php](https://3dwk.com/quote-new.php). Service pages: [3D printing](https://3dwk.com/3d-printing-service.php), [materials](https://3dwk.com/materials.php). Treat **rates.v1.1** min/mid/max as estimates, not invoices. If the UI shows **needs_manual**, answer the HIP questions rather than forcing a fake price.
Common questions
Does every SLM part need HIP?
No. Many prototypes, fixtures, and non-fatigue brackets can skip HIP if you write “no HIP.” Call HIP when internal porosity would affect fatigue, pressure tightness, or a required material condition.
Does HIP replace machining of datum faces?
No. HIP can close internal voids; it does not make a downskin or a support scar into a datum. Leave stock on faces and bores that must be true, and say so.
Is HIP the same as stress relief?
No. Stress relief is a thermal cycle aimed at residual stress. HIP adds high pressure to close internal porosity and is usually a separate special-process step, often combined with a stated heat-treat condition. Name both if you need both.
Can I ask for HIP on AlSi10Mg the same way as on Ti-6Al-4V?
You can require it, but write the alloy and the condition. The two alloys do not share one silent HIP recipe. If HIP is not required on the aluminum lot, say “no HIP.”