造形品の二次硬化方法

SLA光造形方式の3Dプリンタをご利用の場合、造形品の二次硬化が必要になります。二次硬化は、造形品の強度を最大限に引き出すと同時に安定性も高めます。しかし、熱と光に対する反応は個々のレジンによって微妙に異なるため、それぞれの材料特性を最大限に引き出せるようにするには、最適な硬化時間や硬化温度を個別に設定する必要があります。

造形品の二次硬化ガイドをダウンロードいただくと、後処理の基礎や後処理がFormlabsのレジンにどのような作用をもたらすのかについて詳しくご確認いただけます。

Any resin used in SLA 3D printing can be thought of as a highly cross-linked macromolecule, or a continuous network of polymer chains (monomers and oligomers). Within that macromolecule, there are still some reactive groups that can further cross-link the polymer network when exposed to light and heat.

As more cross-links form, material properties, such as modulus and tensile strength, improve. The objective of post-curing is to link as many of these unreacted groups as possible to bring a part to its maximum material properties.

Once optimal material properties are reached, further post-curing of certain resins can sometimes cause brittleness or warping. The post-curing protocol must therefore be specific for both time and temperature in order to avoid curing too much, and will be unique to each resin and part geometry.

Optimal post-curing starts with heat. Rising temperatures increase the energy, and therefore mobility, in the polymer network. This gives reactive groups a higher probability of finding each other and creating more connections. Formlabs post-curing machines, the Form Cure and the Form Cure L, both use a heater to help the curing chamber quickly reach the desired temperature and then maintain it throughout the postcure.

Once the desired temperature is reached, light is introduced. Photons of light activate remaining photoinitiators, causing nearby reactive groups to form bonds and finish the cross-linking process. With each new cross-link the polymer network becomes more securely linked together and material properties improve.

As more cross-links form in the resin, the network slightly densifies, resulting in some minor shrinkage of the whole part. This is normal for any parts produced with a resin 3D printer. PreForm, Formlabs’ free print file preparation software, automatically compensates for this shrinkage to ensure your post-cured prints are dimensionally accurate to your original CAD designs.

材料特性を最大限に引き出すための最適な二次硬化の温度と時間は、使用する材料や用途に応じて変わります。Formlabsスタンダードレジンの場合、Form Cure V2でわずか1分ほどで二次硬化が可能です。一方、高い強度や剛性、耐熱性が求められる場合に使用するFormlabsのエンジニアリング系レジンの場合、それぞれの特性を最大限発揮させるための推奨の二次硬化時間は最長120分です（二次硬化に使用するハードウェアの種類によります）。

Formlabsは、自社開発するレジンの最適な硬化設定を確認するための研究を社内で立ち上げました。この研究を担当した材料開発チームの科学者たちは、ASTM規格に準拠する計測試験を通じて、各材料の機械的特性が高低様々な温度でどのように変化するかを検証しました。

Form Cure v2、Form Cure V1、Form Cure L V2、Form Cure L V1で各材料を二次硬化する際の推奨硬化設定に関する最新情報は、Formlabsの公式ウェブサイトで入手できます。推奨の硬化設定で二次硬化を完了した後の機械的特性の数値は、材料データシートに記載されています。このデータシートはFormlabsのウェブサイトからダウンロードできます。

As more dental and medical professionals adopt 3D printing in their workflows, 3D printing companies have to ensure that the entire process is controlled to consistently manufacture high performing parts with biocompatible safety for the end user. Biocompatibility requirements require careful adherence to these pre-approved processes, and this applies to the post-cure step of the printing process as well.

Formlabs technology has been validated in FDA-cleared workflows, which means that for each resin intended for use in a biocompatible application, there are certain printing, washing, and curing steps that must be followed without deviation in order for the final part to be considered a biocompatible device.

The Form Cure and Form Cure L are important parts of these workflows. After careful testing and a thorough regulatory process, the validated settings for post-cure times ensure that each printed part for biocompatible applications has optimal mechanical properties and is consistently safe for use.

Find specific post-curing recommendations for each material in the Manufacturing Guide for each material.

An ideal post-cure setting achieves the properties you need in optimal time. Formlabs developed an in-house post-cure study to identify optimized settings for each individual Formlabs Resin. Using the ASTM method, our materials scientists tested a variety of mechanical properties at various temperatures for each material.

To see how post-curing influences mechanical properties, this guide looks at changes in the tensile modulus, which shows a change in stiffness of a part, for each resin over time in Form Cure or Form Cure L. An object with a higher tensile modulus will have a greater resistance to changing shape under stress. Modulus of elasticity is closely related to how completely crosslinked photopolymer chains are within the part, which is why Formlabs uses modulus to represent overall completeness of post-curing.

The “green” shape of a model is formed by laser-curing the resin during printing, but some potential polymer connections remain unbonded. Cross-linking the remaining polymer proportionally improves strength, stiffness, and temperature resistance. Post-curing also causes some part shrinkage. Formlabs measures accuracy and mechanical properties based on a standard post-cure of parts, and material settings are tuned to account for shrinkage under the same conditions.

The following graphs will help you understand how Formlabs materials respond to post-curing, viewed as a percentage increase in tensile modulus. Familiarity with post-curing behavior saves time and improves accuracy when post-curing parts for your particular application.

In this example, Rigid 4000 Resin exhibits a sharp rise in modulus of elasticity over the first 15 minutes of post-curing, increasing by 116%. After 15 minutes, no further improvements are observed. 

Rigid 4000 Resin is a glass-filled composite material designed for parts requiring high stiffness and strength, as well as low deformation under load. Post-cure directly increases strength and stiffness by further crosslinking the polymer matrix surrounding microparticles of glass, holding them rigidly in place. Post-cure of Rigid 4000 Resin is substantially impacted by temperature. At higher temperatures, a large improvement in modulus of elasticity is gained over a short period of time. Post-curing beyond 15 minutes will not affect properties but will begin to cause cosmetic yellowing, and is not recommended. For most applications of Rigid 4000 Resin, post-cure for 15 minutes at 80 °C in Form Cure.

The most common issues encountered when post-curing parts are under-curing and warping. If parts seem weaker or less rigid than expected, they may be insufficiently post-cured. Undercuring can occur when a part is particularly thick or large, as larger parts take longer to heat. Light alone cannot post-cure much beyond the surface of a part, which is why Form Cure and Form Cure L apply both heat and light. If a part is significantly larger or thicker than Formlabs’ test geometries, it may require a longer post-curing time or higher temperatures to reach a full internal post-cure.

Warping during post-cure may occur if a part is especially thin, and is not equally exposed to light on all sides. Form Cure and Form Cure L help prevent warp by rotating the part on a turntable during post-curing, and by exposing the part to light from all directions — including underneath the turntable.

Post-cured parts also tend to be more brittle than green parts. Typically, as modulus increases elongation will decrease; because of this, over-cured parts can be undesirably brittle.

二次硬化の方法は、シンプルに（自然な太陽光、ネイルサロンで使っているUV装置、UV硬化装置、DIYのUV硬化ボックスなどを使って）光だけで硬化させる方法から、光と熱の両方を使う方法まで数多く存在します。熱を加えると硬化プロセスが加速し、より完全な結合が可能になります。その結果、硬化した材料は光だけでは達成できない高いレベルの材料特性を発揮できるようになります。

Formlabsは、自社製レジンを短時間に一貫性のある仕上がりで二次硬化を行う独自のソリューションとして、デスクトップサイズと大容量サイズの工業品質のSLA光造形3Dプリンタ用に、Form CureとForm Cure Lを開発しました。Form CureやForm Cure Lなどの後処理装置を使用することで、SLA光造形で3Dプリントした造形品に対し、適切な波長のUV光と温度、時間で二次硬化を行えます。

Form Cure uses a 405 nm light source, which was determined through an extensive internal testing process to be the most effective at creating the best modulus and tensile strength in parts printed on Formlabs printers. In comparison, when the time and temperature were the same, but a 365 nm light source was used, the modulus reaches only 67% as that of the 405 nm samples. There is a significant difference in the post-cured properties at each wavelength, especially so at shorter post-cure times.

Formlabsの二次硬化ガイドをご覧いただくと、二次硬化がFormlabsの各材料の主要特性にもたらす作用のほか、用途別に最適な二次硬化の設定についてもご確認いただけます。

このガイドをダウンロードいただくと、以下のノウハウを得られます。

• 二次硬化がFormlabsの各材料の主要特性にもたらす作用
• 材料の最適な二次硬化の推奨設定（用途別）
• 二次硬化のよくある失敗を防ぐための戦略