1. Core Principle: The Deep Logic of Photopolymerization Reaction
1. Components and Reaction Mechanism of Photosensitive Resin
•Core components of the resin: Low-viscosity prepolymers (such as epoxy acrylate, polyurethane acrylate) make up the majority, accounting for 70%-90%, determining the basic properties such as hardness and toughness after curing.
•Key additives: Photoinitiators (accounting for 1%-5%) act as the “switch”, absorbing 405nm (mainstream) or 365nm ultraviolet light, decomposing to generate free radicals that trigger the crosslinking of prepolymer molecules.
•Other components: Reactive diluents (reduce resin viscosity for better flow), stabilizers (prevent premature curing of resin in the absence of light), pigments (adjust color).
•Reaction process: Free radicals initiate the opening of double bonds in prepolymer molecular chains, rapidly forming a three-dimensional network structure, with liquid resin curing within 0.1-5 seconds, and the curing shrinkage rate typically being 2%-8% (the lower the shrinkage rate, the less deformation of the model).
2. Underlying Influences of Molding Parameters
•Wavelength matching: Photoinitiators must correspond to the wavelength of the light source, 405nm resin is compatible with most civilian devices, 365nm resin cures faster but is more irritating.
•Exposure energy: Single-layer curing must reach the “critical exposure energy (Ec)”, insufficient energy will lead to incomplete curing and poor interlayer adhesion; excessive energy will cause the model to yellow and details to blur.
•Pentration depth (Dp): The effective depth at which light can cure the resin, typically 0.1-0.3mm, determines the maximum single-layer curing thickness; resin exceeding Dp cannot cure and will remain liquid.
2. Three Mainstream Technologies: In-Depth Analysis of Parameters, Structures, and Applicable Scenarios
1. SLA (Stereolithography)
•Core structural details:
◦Light source: Mostly fiber-coupled UV lasers (power 50-200mW), with spot diameters as small as 0.02mm, scanning speeds of 3000-10000mm/s.
◦Galvo system: Composed of X/Y axis galvanometers, controlling the rapid scanning of the laser beam, with scanning paths including “zigzag scanning“ and “spiral scanning“, the latter reduces layer lines.
◦Platform: Driven by ball screw, with repeat positioning accuracy of ±0.005mm, ensuring uniform layer thickness.
•Key parameters:
◦Layer thickness: 0.01-0.1mm, commonly used for fine printing is 0.02-0.05mm.
◦Exposure time: Single layer 5-15 seconds, the first layer exposure time needs to be extended by 50%-100% (to enhance adhesion to the platform).
◦Scanning spacing: 0.02-0.05mm, the smaller the spacing, the finer the surface, but the slower the speed.
•Applicable scenarios: High-precision parts, models with small details (such as jewelry wax molds, miniature architectural parts), high-precision medical models (such as orthopedic guides).
2. DLP (Digital Light Processing)
•Core structural details:
◦Light source: LED UV light source (power 10-50W), reflecting light through DLP chip (Texas Instruments DLP micro-mirror array) to form a planar image.
◦DLP chip: The number of micro-mirrors determines the resolution (e.g., 1920×1080 pixels), pixel size 30-50μm, directly affecting the minimum detail size of the model.
◦Optical system: Includes UV lens group, which needs regular cleaning to avoid dust affecting light transmission uniformity.
•Key parameters:
◦Layer thickness: 0.02-0.15mm, speed is 2-3 times faster than SLA (curing the entire layer at once).
◦Exposure time: Single layer 2-8 seconds, first layer 10-20 seconds.
◦Light source attenuation: After using 2000 hours, the light source intensity will decrease by about 30% , requiring adjustment of exposure time compensation or replacement of the light source module.
•Applicable scenarios: Medium precision models, batch printing (such as mass production of figurines), dental prosthesis bases.
3. LCD (Liquid Crystal Display)
•Core structural details:
◦Light source: Backlight module (mostly LED array), wavelength 405nm, brightness adjustable (1000-3000cd/m²).
◦LCD screen: UV-specific screen (ordinary LCD screens cannot transmit UV light), pixel size 25-50μm, resolution determines the printing area (e.g., 10.1 inch screen, resolution 2560×1600, area about 21×13cm).
◦Resin tank: The bottom is made of a transparent release film (PTFE material), thickness 0.1-0.2mm, wear of the release film can cause models to stick to the bottom, requiring regular replacement (100-200 hours of printing).
•Key parameters:
◦Layer thickness: 0.02-0.2mm, the best cost-performance ratio, the first choice for civilian entry-level.
◦Exposure time: Single layer 3-10 seconds, first layer 15-30 seconds (LCD screen transmittance is lower than DLP, requiring longer exposure).
◦Screen lifespan: 1000-1500 hours, prolonged high-brightness use will accelerate aging, resulting in black spots and uneven light transmission.
•Applicable scenarios: Personal hobbies (figurines, models), entry-level prototype production, teaching experiments.
3. Photosensitive Resins: Classification, Characteristics, and Selection Details
1. Classification by Chemical System (Core Impact on Performance)
•Acrylate resins: The most common, fast curing speed, high hardness, low cost, but slightly higher shrinkage rate (4%-8%), average toughness, suitable for printing structural parts and figurines.
•Epoxy acrylate resins: Low shrinkage rate (2%-4%), strong adhesion, better toughness and high-temperature resistance, suitable for high-precision parts and molds.
•Polyurethane acrylate resins: Excellent toughness, strong impact resistance, suitable for printing flexible parts and bionic models, but more expensive.
2. Detailed Parameters of Functional Resins
|
Resin Type |
Key Performance Parameters |
Applicable Scenarios |
Usage Notes |
|
Rigid Resin |
Shore D 85-95, tensile strength 30-50MPa, elongation at break 2%-5% |
Structural parts, molds, main body of figurines |
High brittleness, avoid dropping and collision |
|
Flexible Resin |
Shore A 50-85, tensile strength 5-15MPa, elongation at break 50%-200% |
Sealing rings, soft toys, bionic skin |
Must be fully UV irradiated after curing, otherwise prone to stickiness |
|
Transparent Resin |
Light transmittance 85%-95%, refractive index 1.5-1.6, Shore D 80-90 |
Light covers, optical parts, display models |
Post-processing requires sanding and polishing (400-2000 grit sandpaper), avoid scratches affecting light transmission |
|
High-Temperature Resistant Resin |
Heat distortion temperature (HDT) 80-150℃, Shore D 90-95 |
Small mechanical parts, mold inserts, electronic enclosures |
Layer thickness needs to be reduced during printing (0.02-0.03mm), to avoid internal stress leading to cracking |
|
Dental Resin |
Biocompatibility (compliant with ISO 10993 standards), Shore D 75-85 |
Dentures, crowns, orthodontic brackets |
Must use medical-grade resin, high-temperature sterilization required after printing (121℃, 30 minutes) |
|
Castable Resin |
Ash content < 0.1%, no residue after burning, shrinkage rate < 3% |
Jewelry wax molds, metal casting prototypes |
Must be quickly cleaned and cured after printing to avoid moisture absorption affecting casting results |
3. Key Details for Resin Usage
•Storage conditions: Temperature 15-25℃, cool and dark, sealed storage, must be used within 1 month after opening, otherwise viscosity will increase due to moisture absorption.
•Viscosity requirements: The viscosity of the resin during printing should be between 50-200mPa・s (25℃), too high viscosity will lead to poor flow and uneven interlayer coverage, can be slightly heated (not exceeding 30℃) to reduce viscosity.
•Expiration judgment: If the resin shows precipitation, discoloration, abnormal increase in viscosity, or the curing speed significantly slows down during printing, it indicates that it has expired and should not be used.
4. Complete Printing Process: Practical Details from Slicing to Post-Processing
1. Slicing Software Parameter Settings (Taking Chitubox as an Example)
•Model placement:
◦Fine surface facing up (to reduce support marks), large models tilted 15-30° placement (to avoid large flat surfaces, reducing bubble retention).
◦Models with a low center of gravity can be placed flat, while those with a high center of gravity need increased support density to prevent tipping during printing.
•Support settings:
◦Support type: Use “tree supports“ for fine parts (small support points, less residue), and “linear supports“ for large parts (strong stability).
◦Support density: Support spacing for fine parts 2-3mm, for coarse parts 3-5mm, support diameter 0.2-0.5mm.
◦Support and model angle: 30-45°, too small an angle may cause support breakage, while too large will leave obvious support marks.
•Exposure parameter template (for civilian LCD devices):
◦Rigid resin: Layer thickness 0.05mm, single layer exposure 6 seconds, first layer exposure 20 seconds, bottom exposure times 3 times.
◦Flexible resin: Layer thickness 0.03mm, single layer exposure 8 seconds, first layer exposure 25 seconds, bottom exposure times 5 times.
◦Transparent resin: Layer thickness 0.02mm, single layer exposure 7 seconds, first layer exposure 22 seconds, bottom exposure times 4 times.
2. Real-time Monitoring and Adjustment During the Printing Process
•First layer curing: Observe whether the model is evenly adhered to the platform; if the edges lift, immediately pause and increase the first layer exposure time 10%-20%, and reprint.
•Inter-layer curing: After printing 10-20 layers, pause the device and check whether the inter-layer adhesion is tight; gently touch the side of the model with your hand; no looseness or stickiness is normal.
•Bubble handling: If bubbles appear in the resin tank during printing, pause the print, use a toothpick to pop the bubbles, or wait 5 minutes before continuing.
•Environmental control: Maintain temperature 20-25℃, humidity 40%-60%, too low a temperature will increase resin viscosity, while too high will accelerate premature curing of the resin.
3. Post-Processing: A Key Step in Determining Product Quality
•Cleaning stage:
◦Cleaning liquid: Preferably use isopropyl alcohol (IPA)99% concentration for the best cleaning effect; specialized cleaning liquids (such as Elegoo Wash Cure Plus special liquid) can also be used, which are less irritating.
◦Cleaning method: Small models should be soaked 5-8 minutes, large models should be soaked 10-15 minutes, during which the cleaning container can be gently shaken to remove residual resin in the gaps.
◦Secondary cleaning: After cleaning fine models, quickly rinse with clean IPA once to avoid residual cleaning liquid affecting curing results.
•Curing stage:
◦Curing device: UV curing box (wavelength 405nm, power 36W or more), curing distance 10-15cm.
◦Curing time: Rigid resin 15-20 minutes, flexible resin 20-30 minutes (must be fully cured to exhibit elasticity), transparent resin 10-15 minutes (to avoid over-curing and yellowing).
◦Flip curing: For larger models, after curing for 10 minutes, flip and cure again for 5-10 minutes to ensure complete curing inside and out.
•Sanding and beautifying:
◦Removing supports: Use diagonal pliers to cut off coarse supports, carefully scrape off fine parts with a craft knife to avoid damaging the model.
◦Sanding steps: Start with 400 grit sandpaper, then use 800 grit, 1200 grit, 2000 grit sandpaper to sand support marks; during sanding, a small amount of water can be sprayed to reduce dust.
◦Polishing: After sanding transparent models, polishing paste (such as car polish) can be applied and wiped with a soft cloth to enhance light transmittance; a “resin coating“ (a thin layer of transparent resin applied and cured for 5 minutes) can also be used.
◦Coloring: Acrylic paints or model-specific paints can be used; before coloring, wipe the model surface with alcohol to remove grease and enhance paint adhesion.
5. Common Failures: Cause Analysis and In-Depth Solutions
|
Failure Phenomenon |
Deep Cause |
Solution |
|
Model sticks to the bottom, cannot be removed |
Release film wear, excessive first layer exposure time, too small distance between platform and resin tank |
Replace the release film; reduce the first layer exposure time 5%-10%; adjust platform height to increase the distance from the resin tank to 0.1-0.2mm |
|
Inter-layer separation, cracking |
Insufficient exposure energy, excessive layer thickness, expired resin, low environmental temperature |
Increase single layer exposure time 10%-20%; reduce layer thickness to 0.03-0.05mm; replace with new resin; raise environmental temperature to 20℃ or above |
|
Model surface has pits, bubbles |
Resin viscosity too high, bubbles generated during pouring, incomplete coverage between layers |
Heat the resin to 25-30℃ to reduce viscosity; let the resin sit for 30 minutes to de-bubble; reduce layer thickness and increase exposure time |
|
Loss of model detail, blurriness |
Light source intensity decay, low slicing resolution, support blocking details |
Replace the light source module or adjust exposure time compensation; increase slicing resolution (e.g., 1080P or above); optimize support position to avoid fine details |
|
Model turns yellow, becomes brittle |
Over-curing, poor quality resin, prolonged exposure to sunlight |
Shorten curing time 5-10 minutes; replace with high-quality resin; spray a layer of UV protective paint after curing |
|
Solidified clumps appear in the resin tank |
Light source leakage, improper resin storage, device not turning off the light source |
Check the sealing of the device’s light source, repair leakage points; replace with new resin; promptly turn off the light source and cover the resin tank after printing |
6. Equipment Maintenance: Details to Extend Lifespan and Ensure Accuracy
1. Core Component Maintenance
•Resin tank:
◦After each print, pour the remaining resin back into the original bottle (filter impurities with a sieve), and wipe the tank walls and release film with IPA to avoid resin residue curing.
◦Release film check: Check once a week; if scratches, wear, or uneven light transmission appear, replace immediately (replacement cost about 50-200 yuan).
◦Avoid collisions: The resin tank is made of acrylic material, which is fragile; handle with care during transport to avoid contact with hard objects.
•Light source components:
◦SLA laser: Wipe the lens monthly with a lint-free cloth dipped in IPA to avoid dust blocking the laser; calibrate the laser power once a year; if the power drops by more than 30%, the laser needs to be replaced.
◦DLP projector: Clean the lens every 3 months to avoid dust affecting light transmission; after using 2000 hours, check the light source intensity, and replace the light source module if necessary (cost about 500-1500 yuan).
◦LCD screen: Gently wipe the screen surface weekly with a lint-free cloth; avoid using alcohol directly (it will corrode the screen coating); avoid prolonged high-brightness use, and turn off the device when not in use.
•Platform and transmission system:
◦Clean the platform surface monthly to remove residual resin and impurities, keeping the platform level.
◦Apply special lubricant (such as lithium grease) to the ball screw and guide rails every 3 months to reduce friction and ensure transmission accuracy.
2. Daily Maintenance Procedures
•Daily maintenance: Clean the resin tank and platform before and after printing; check resin level and viscosity; when turning off the device, cover the resin tank and seal the resin bottle.
•Weekly maintenance: Check the release film and light source lens; clean internal dust from the device (using a hair dryer on the cool setting); calibrate platform level.
•Monthly maintenance: Lubricate the transmission system; check for loose device wiring; test light source intensity.
•Annual maintenance: Contact the manufacturer for professional calibration (such as laser power, projection accuracy, platform positioning accuracy); replace aging components (such as light source, release film, sealing rings).
7. Advanced Techniques: Improving Print Quality and Expanding Applications
•Reduce curing shrinkage: Preheat the resin to 25-30℃ before printing to reduce viscosity and shrinkage stress; set “gradient layer thickness“ (bottom layer thickness 0.1mm, upper layer thickness 0.02mm) to balance speed and precision.
•Improve surface smoothness: Use “inverse printing“ (printing the model upside down with the fine surface facing down, but requires additional supports); after printing, soak in “resin polishing liquid” for 5 minutes, then cure, achieving a surface roughness of Ra<0.05μm.
•Batch printing: Utilize the maximum area of the device, reasonably arrange multiple models, avoiding too small spacing between models (at least 2mm), to prevent mutual interference; uniformly set support parameters to improve printing efficiency.
•Expand applications: Print molds (such as mother molds for silicone molds), use rigid resin to print the mother mold, sand and polish after curing, then pour silicone to make molds; print composite structures, combining rigid and flexible resins to print parts with both hardness and toughness.