What is stereolithography 3D printing

What is stereolithography 3D printing

History

Stereolithography or "SLA" which sometimes refereed as resin 3D printing is one of 3D printing technologies that is widely used in industry. In the early 1980s, Japanese researcher Hideo Kodama  invented the stereolithography by using ultraviolet (UV) light to cure photosensitive polymers.

How it works

Photopolymers are sensitive to ultraviolet light, so the resin is photochemically solidified and forms a single layer of the desired 3D object. Then, the build platform lowers one layer and a blade recoats the top of the tank with resin. This process is repeated for each layer of the design until the 3D object is complete.

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CAD 3D model with supports in the SLA machine software

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Laser scanning one layer of the 3D model

Completed parts must be washed with a solvent to clean wet resin off their surfaces. It is also possible to print objects "bottom up" by using a vat with a transparent bottom and focusing the UV or deep-blue polymerization laser upward through the bottom of the vat. An inverted stereolithography machine starts a print by lowering the build platform to touch the bottom of the resin-filled vat, then moving upward the height of one layer.

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SLA 3D print with support material

The UV laser then writes the bottom-most layer of the desired part through the transparent vat bottom. Then the vat is "rocked", flexing and peeling the bottom of the vat away from the hardened photopolymer; the hardened material detaches from the bottom of the vat and stays attached to the rising build platform, and new liquid photopolymer flows in from the edges of the partially built part. The UV laser then writes the second-from-bottom layer and repeats the process. An advantage of this bottom-up mode is that the build volume can be much bigger than the vat itself, and only enough photopolymer is needed to keep the bottom of the build vat continuously full of photopolymer.
This approach is typical of desktop SLA printers, while the right-side-up approach is more common in industrial systems. Stereolithography requires the use of supporting structures which attach to the elevator platform to prevent deflection due to gravity, resist lateral pressure from the resin-filled blade, or retain newly created sections during the "vat rocking" of bottom up printing. Supports are typically created automatically during the preparation of CAD models and can also be made manually. In either situation,

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Removing the support material

The supports must be removed manually after printing. Other forms of stereolithography build each layer by LCD masking, or using a DLP projector. Stereolithography is an additive manufacturing process that, in its most common form, works by focusing an ultraviolet (UV) laser on to a vat of photopolymer resin. With the help of computer aided manufacturing or computer-aided design (CAM/CAD) software, the UV laser is used to draw a pre-programmed design or shape on to the surface of the photopolymer vat.

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Sanding the 3D printed model

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Post-processed SLA 3D printed assembly

PartzPro Frequently Asked Questions

The "Open-Book" Business Model

Q: Why is there a factory invoice in the box?
That is your Commercial Import Invoice. Because we ship Factory Direct to your door, international customs requires an invoice that travels with the package.
  • Transparency & Compliance: This invoice lists the origin factory (showing you exactly who made your parts) and declares the exact value you paid at checkout.
  • Why it matches your payment: We ensure the commercial invoice matches your transaction value so that Customs calculates your duties correctly and legally, preventing delays or penalties at the border.
Q: Why don't you offer Instant Quotes?
Because "Instant" usually means "Inaccurate." Competitors use algorithms to guess the price based on geometry averages. This often leads to:
  • The "Bait & Switch": They quote low instantly, then email you 24 hours later to raise the price once a human actually looks at it.
  • The "Risk Buffer": They inflate the price by 30% just to cover the errors their algorithm makes.
We measure twice, cut once. We have the factory validate the CAM strategy before we give you a price. You wait a few hours, but the price you get is the price you pay—guaranteed. No surprises.
Q: If I have the factory’s info, why shouldn't I just go direct next time?
First, strictly speaking, you cannot. To protect our platform, our Terms of Use include a Non-Circumvention clause that prohibits direct transactions with our suppliers for 24 months.

But practically, clients stay for the "US Shield." When you order through PartzPro, your money is held in US-based Escrow. We handle the legal leverage, language barriers, and financial security. If you go direct, you lose that protection and have zero recourse if something goes wrong.
Q: What exactly does your Service Fee cover?
Your fee covers Financial Security (Escrow), Vendor Vetting, AI Engineering Analysis, and Project Management. We act as your US-based legal firewall. We find the best factories, negotiate the rates, and hold the money until the job is done right.

Logistics, Customs & AI Technology

Q: Who handles the HTS Codes and Customs paperwork?
Our AI does the heavy lifting; you just confirm the release. We don't leave you guessing on complex government tariffs.
  • Heavy AI Analysis: Our proprietary AI Assistant performs a 40-point analysis of your part's geometry and material. It automatically searches the official US Government HTS database to generate a precise HTS Code Breakdown for your specific parts.
  • The Process: This data is provided to the carrier (DHL/FedEx/UPS). When the broker contacts you, the classification is already estimated—you simply confirm it to release the shipment.
Q: Who pays the duties?
You do—which saves you money. Because we ship DAP (Delivered at Place), you pay the exact duties owed to the government based on the AI-generated HTS code.
  • Why this is better: Competitors who offer "Free Shipping/DDP" often inflate the price to cover the worst-case tariff scenario. By paying the actual duties yourself, you ensure you are never overcharged for import taxes.
Q: How fast is shipping?
Since we skip the "Middleman Warehouse," our standard international shipping is extremely fast (typically 3–5 days transit). Your parts fly directly from the machine shop to your desk.

Quality Assurance & Liability

Q: Competitors inspect parts at a US warehouse before shipping. Why don't you?
Because "double handling" kills speed and adds unnecessary cost. We operate on a "Dock-to-Stock" model. The factory performs the rigorous QC, and parts ship directly to you.

We treat you like a professional: we know you will verify the fit and function of your parts upon arrival. By removing the redundant middleman inspection, we save you 30% on cost and 3–5 days on lead time.
Q: What happens if the parts arrive out of spec?
You are protected by the PartzPro Escrow Guarantee. Because we hold the funds, the factory does not get paid until you verify the order.

The Process: You have a 3-Day Inspection Window upon delivery to verify fit and function. If parts are non-conforming, simply upload a photo and inspection report within that window. We will either force an immediate priority remake at the factory’s expense or issue a refund.
Q: Does your AI just check for geometry errors?
No. Our AI Cost-Driver Audit goes beyond simple DFM (Design for Manufacturing). It helps you perform Value Engineering by highlighting features that are disproportionately expensive (e.g., deep pockets, tight radii, non-standard threads). We show you the cost drivers so you can engineer the price down before you order.

Payments & Corporate Orders

Q: We are a company, not a hobbyist. Can we pay via Purchase Order (PO)?
Yes. We specialize in serving agile engineering departments and mid-sized manufacturing firms.
  • How to order with a PO: You can select "Pay via PO / Wire" at checkout or email our sales team directly with your PO attached. We will verify your company details and send a payment link or wire instructions immediately so production isn't delayed.
Q: Do you offer Net-30 Terms?
We offer terms to qualified business partners after an initial credit review. Please contact our sales team to set up your corporate account. For new customers, we recommend using our PO-to-Wire workflow for the fastest start.

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Please be advised that the content presented on our blog and throughout our website is intended strictly for informational purposes. It is designed to serve as a preliminary guide and reference point for our customers embarking on their projects. We endeavor to provide insightful and useful information, but it is imperative for each individual and organization to undertake their own comprehensive research and assessment before making any decisions related to their designs or component usage.Our blog and website content should not be considered as a replacement for specialized advice suited to your unique requirements. For more detailed terms and conditions, kindly refer to our Terms of use. The responsibility for the application of any information obtained from our blog or website in your designs, applications, or parts usage, rests solely with you, the reader or user. Our goal is to inform, advise, and inspire; however, the ultimate application and use of this information is under your discretion and liability.