---
title: "Automated Finishing for HP MJF PA12 | AMT PostPro"
description: "PostPro3D on HP MJF PA12: no loss of tensile strength, at most 0.4% dimensional change, bores down to 0.3 mm smoothed, and no cytotoxic effects."
canonical: https://amtechnologies.com/resources/whitepapers/automated-finishing-technology-for-post-processing-mjf-parts/
updated: 2026-10-06
type: whitepaper
---
Whitepaper · HP High Reusability PA12

# Automated surface finishing for HP High Reusability PA12

AMT’s patented PostPro3D technology automates the smoothing of thermoplastic 3D-printed parts. This whitepaper tests it on HP Nylon 12 printed on an HP MJF 4200 and reports surface roughness, mechanical properties, dimensions, color, water absorption and cytotoxicity.

[Read the whitepaper (PDF, opens in a new tab)](https://6983077.fs1.hubspotusercontent-na1.net/hubfs/6983077/Website/Whitepapers/AMT_WP_HP%20AUTOMATED%20FINISHING%20FOR%20HP%20MJF%20TECHNOLOGY.pdf?ver=2) [Test your parts](https://amtechnologies.com/test-your-parts/)

Published Nov 7, 2022 Free download, no form

![Cover of the whitepaper “Automated surface finishing for HP High Reusability PA12”](https://amtechnologies.com/img/resources/wp-hp-mjf-pa12-720.webp)

- **With**: HP
- **Material**: HP High Reusability PA12
- **Printing**: HP Multi Jet Fusion 4200
- **Tested on**: PostPro3D
- **Published**: Nov 7, 2022

- 0.4% maximum dimensional change
- 0.3 mm bores smoothed, at the smallest

Source: [HP whitepaper, amtechnologies.com](https://amtechnologies.com/resources/whitepapers/automated-finishing-technology-for-post-processing-mjf-parts/) [PDF (opens in a new tab)](https://6983077.fs1.hubspotusercontent-na1.net/hubfs/6983077/Website/Whitepapers/AMT_WP_HP%20AUTOMATED%20FINISHING%20FOR%20HP%20MJF%20TECHNOLOGY.pdf?ver=2) published Nov 7, 2022

Published Nov 2022. These tests ran on PostPro3D, the earlier generation of AMT’s automated vapor smoothing systems; today’s systems are the [PostPro SF range](https://amtechnologies.com/products/vapor-smoothing/).

## The technology

PostPro3D automates post-processing and integrates into digital manufacturing workflows. Its process, Boundary Layer Automated Smoothing Technology, is a physico-chemical method that smooths complex internal cavities and surfaces with reproducible results and keeps mechanical properties intact. It handles polyamide (nylon) variants, flame-retardant and carbon- or glass-filled nylons, TPU and TPE.[PDF](https://6983077.fs1.hubspotusercontent-na1.net/hubfs/6983077/Website/Whitepapers/AMT_WP_HP%20AUTOMATED%20FINISHING%20FOR%20HP%20MJF%20TECHNOLOGY.pdf?ver=2)

## Test method

Calibration pieces and ASTM D638 Type I tensile samples were printed on an HP MJF 4200 and cleaned of loose powder before processing. Surfaces were evaluated as printed, after cleaning and after post-processing.

## Design considerations

The process is non-abrasive: it redistributes surface material, so delicate structures survive and bores as small as 0.3 mm are smoothed. Uniform results depend on consistent wall thickness, with 1 mm recommended as a minimum.[PDF](https://6983077.fs1.hubspotusercontent-na1.net/hubfs/6983077/Website/Whitepapers/AMT_WP_HP%20AUTOMATED%20FINISHING%20FOR%20HP%20MJF%20TECHNOLOGY.pdf?ver=2)

## Results

- Surface roughness, measured with a Mitutoyo Surftest SJ-210, improved across three standard finishes, with smaller standard deviations
- No loss in ultimate tensile strength; elongation at break increased while Young’s modulus decreased
- Maximum dimensional variation of 0.4%, so tolerances and fine features are kept
- Color and gloss from gray to piano black in one step, and lower water absorption in immersion tests
- No cytotoxic effects from extracts of processed samples[PDF](https://6983077.fs1.hubspotusercontent-na1.net/hubfs/6983077/Website/Whitepapers/AMT_WP_HP%20AUTOMATED%20FINISHING%20FOR%20HP%20MJF%20TECHNOLOGY.pdf?ver=2)

Key finding

No loss in tensile strength; at most 0.4% dimensional change[PDF](https://6983077.fs1.hubspotusercontent-na1.net/hubfs/6983077/Website/Whitepapers/AMT_WP_HP%20AUTOMATED%20FINISHING%20FOR%20HP%20MJF%20TECHNOLOGY.pdf?ver=2)

Full whitepaper

Method, data and charts in the PDF. Free, no form to fill in.

[Download the PDF (opens in a new tab)](https://6983077.fs1.hubspotusercontent-na1.net/hubfs/6983077/Website/Whitepapers/AMT_WP_HP%20AUTOMATED%20FINISHING%20FOR%20HP%20MJF%20TECHNOLOGY.pdf?ver=2)

Related

- [Compatible materials lists](https://amtechnologies.com/resources/documents/)
- [What is vapor smoothing?](https://amtechnologies.com/learn/what-is-vapor-smoothing/)
- [All whitepapers](https://amtechnologies.com/resources/whitepapers/)

Test your parts

## Send us a part. See it smoothed.

We vapor smooth your own parts and send them back with the results. No cost to evaluate · Parts returned · Typical turnaround 2–3 weeks[1]

[Test your parts](https://amtechnologies.com/test-your-parts/) [See the systems](https://amtechnologies.com/products/vapor-smoothing/)

## Sources

1. [PostPro benchmarking: send us your 3D printed parts](https://benchmarking.amtechnologies.com/) · AMT · read Oct 6, 2026