MORE THAN A YEAR AGO, AFTER THE DEVELOPMENT OF THE SIC-Y-TIP NOZZLE, I DEDICATED A LITTLE TIME TO STUDY A PRINTING PLATE THAT COULD SATISFY ALL MY PROFESSIONAL NEEDS REGARDING FDM 3D PRINTING.
PERSONAL NEEDS NOT SATISFIED BY THE STANDARD PRODUCTS OFFERED BY THE MARKET.
IN GENERAL, THE PROJECT WAS TO INVESTIGATE THE POSSIBILITY OF A SOLUTION THAT COULD REALIZE SOME NECESSARY FEATURES FOR MY PROFESSIONAL USE OF 3D PRINTED PARTS WITH FDM TECHNOLOGY,
THE DESIRED FEATURES IN BRIEF:
-) AVOID AT THE MAXIMUM, IF NOT EXCLUDING ALL, THE USE OF SUPPORT PLATFORMS FOR THE MODELS (BRIM AND RAFT, ESPECIALLY THIS LAST), REGARDLESS OF THEIR SIZE AND / OR GEOMETRY.
-) OBTAIN EXCELLENT HOT ADHESION AND SIMPLE RELEASE OF THE MODEL AFTER COOLING THE PLATE.
-) EXCLUDE THE POSSIBILITY OF WARPING OR BAD ADHESION OF THE MODEL, EVEN FOR LARGE PARTS OR MULTIPLE PARTS WHICH COULD OCCUPY THE ENTIRE PRINT SURFACE.
-) OBTAIN FIRST DEPOSITED SURFACES ON THE PRINTING TABLE WITH A SURFACE FINISH SIMILAR, IF NOT BETTER, TO THAT OF THE LATEST LAYERS.
-) AVOID TO THE MAXIMUM NEED FOR POST-PROCESSING OF THE FIRST DEPOSITED SURFACES.
-) LIMIT, WHERE POSSIBLE, THE USE OF CHEMICAL ADDITIVES (GLUES) TO FAVOR THE ADHESION OF THE FIRST LAYER AND / OR OTHERWISE, CHOOSE THE MOST SUITABLE BASED ON THE MATERIALS USED.
-) AVOID REMOVAL OF THE PRINTING TABLE FROM THE PRINTER AS MUCH AS POSSIBLE.
-) AVOID THE NEED FOR ITS ADJUSTMENT AFTER A FIRST EXCELLENT ADJUSTMENT OF THE GLOBAL PLANARITY.
-) FOR INTENSIVE USE OF ABOUT 18-20 HOURS / DAY, AVOID IT REPLACEMENT FOR THE LONGEST POSSIBLE TIME. (IN THE ORDER OF THOUSANDS OF WORKING HOURS).
THIS RELATED TO THE USE OF THE FOLLOWING MATERIALS:
PLA, PET-G, ASA, ABS, PC, TPU 95-SH-A, PET-CF, NYLON-66, NYLON-CF, NYLON-GF, NYLON 12.
FOR SUPPORT MATERIALS: BVOH, ACQUASYS 120, PVA.
BRANDS OF THE FILAMENTS USED: RAISE3D, POLYMAKER, BASF INNOFIL, BASF-XSTRAND, FILAMENTUM, FABBRIX, FORMFUTURA, INFINITE).
IN THIS WAY, THE STUDY HAD TO TAKE INTO CONSIDERATION MANY PARAMETERS THAT I DESCRIBE BELOW BUT, ABOVE ALL AND FIRST, THE OBSERVATION OF THE PHENOMENON FOR MY OPINION, THE MOST DETERMINED: THE ONE RELATING TO THE LOCAL OVERHEATING IN THE STORAGE OF THE FIRST LAYERS OF EXTRUDED FILAMENT.
REGARDLESS OF THE TYPICAL EFFECTS OF EXTRUSION TECHNOLOGY IN FREE AIR COOLING: SOME MATERIALS (THE SIMPLEST TO PRINT) HAVE LONG COOLING TIMES SO MUCH AS TO REQUIRE, FORCED COOLING.
OTHERS MATERIALS, (THE MOST COMPLEX), A VERY FAST COOLING TIME THAT INDUCES, FROM THE WIRE EXTERIOR EXTRUDED SURFACE AND ITS CORE, IMPORTANT RESIDUAL STRESS.
THESE LATEST REQUIRE A HIGH PRINTING PLATE TEMPERATURE (SOMETIMES ALSO THE HEATING OF THE ENTIRE PRINTING CHAMBER) TO PREVENT OR MINIMIZE THE RESIDUAL STRESS DESCRIBED ABOVE AND ALSO PROMOTING THE BEST ADHESION BETWEEN THE LAYERS OF THE ENTIRE MODELS.
THE PHENOMENON OF LOCAL OVERHEATING
IN THE EXAMPLE REPRESENTED IN FIG. 1 IT’S OBVIOUS HOW THE HIGH ΔT BETWEEN THE TEMPERATURE OF THE PRINTING TABLE AND THE TEMPERATURE OF THE FILAMENT JUST EXTRUDED, INVOLVES STRONG THERMAL STRESS.
I STARTED FROM THIS SIMPLE CONSIDERATION AND OBSERVATION OF THE PHENOMENON, MAIN CAUSE, IN MY OPINION, OF THE PROBLEMS AND, CONSEQUENTLY, ALSO THE MAIN KEY FOR SOLVING.
WE WILL SEE, BELOW, HOW MANY OTHER PHYSICAL PARAMETERS ARE RELATED TO THE PHENOMENON OF LOCAL OVERHEATING OF THE FIRST LAYER AND HOW THEY CAN PROMOTE OR LESS THE CORRECT EXECUTION.
PHYSICAL PARAMETERS CONSIDERED FOR THE PRINT PLATE
- PLANARITY -GLOBAL –
IT IS DETERMINED, IN ADDITION TO AN EXCELLENT CONSTRUCTIVE FLATNESS OF THE PLATE, ALSO BY ITS PERFECT POINT-TO-POINT “Z” ADJUSTMENT ONCE MOUNTED ON THE PRINTER.
2. PLANARITY -LOCAL –
REPRESENTS THE POSSIBILITY OF PLANAR DIFFERENCE BETWEEN VARIOUS AREAS OF THE PLATE, DUE TO CONSTRUCTIVE DEFECTS, IMPROPER USE, OR LOCAL DEFORMATIONS. (THESE LATEST ARE ALMOST ALWAYS DETERMINED BY THE PHENOMENON OF LOCAL OVERHEATING).
3. BENDING STIFNESS – K-
PARAMETER DETERMINED BY THE PRODUCT OF YOUNG’S MODULUS (E) RELATED TO THE BENDING STRESS, MULTIPLIED BY THE CUBE OF THE THICKNESS (S) OF THE TABLE / PRINT SURFACE.
K=ES3
A LOW BENDING STIFFNESS IS SYNONYMOUS OF AN EXCELLENT APPROXIMATE CORRECTION OF LOW FLATNESS (IN PARTICULAR THE LOCAL ONE) BUT IMPLIES WORST REACTIONS REGARDING THE PHENOMENON OF LOCAL OVERHEATING REPRESENTED IN FIG. 1
4. SURFACE ENERGY
SURFACE ENERGY, IN SHORT, IS THE EXCESS ENERGY ON THE SURFACE OF A MATERIAL RESPECT TO ITS MASS.
THERE ARE THREE CATEGORIES OF MATERIALS IN GENERAL: WITH LOW, MEDIUM AND HIGH SURFACE ENERGY.
THIS FEATURE DETERMINES THE “ADHESIVE” CAPACITY OF A MATERIAL BOTH ON ITSELF OR ON OTHER MATERIALS WITH DIFFERENT NATURE.
MORE ITS VALUE IS HIGH, AND MORE THE “ADHESIVE” FEATURE INCREASES AND VICEVERSA.
AN EXCESSIVE SURFACE ENERGY DETERMINES, IN THE CASE OF FDM 3D PRINTING, AN EXCELLENT ADHESION BUT A WORST DETACHMENT OF THE MODEL FROM THE PRINTING TABLE.
VICEVERSA, A LOW SURFACE ENERGY, COMPLETELY PREVENTS THE ADHESION OF THE FIRST LAYER.
SO, IT IS A MATERIAL WITH MEDIUM-HIGH SURFACE ENERGY AND AN ENERGY CHANGE CAPABILITY CORRELATED WITH ITS TEMPERATURE, THE RIGHT PARAMETER THAT CAN SATISFY THE NEEDS OF ADHESION AND RELEASE OF THE MODEL.
P.S.: MATERIALS WITH LOW SURFACE ENERGY ADHERE, AND NOT SIMPLY, ALMOST ONLY ON THEMSELVES.
5. THERMAL CONDUCTIVITY
IT IS THE INHERENT CAPACITY OF THE MATERIAL TO CONDUCT HEAT INTERNALLY TO ITS MASS, REFER TO TIME UNIT.
A LOW THERMAL CONDUCTIVITY OF THE PRINT SURFACE MATERIAL CAN ONLY WORSE THE PHENOMENON OF LOCAL OVERHEATING IN FIG.1:
BY FAVORING ITS “CHANGE OF STATE” (FROM LIQUID TO SOLID) TOO FAST, IT CAN CAUSE INTERNAL TENSIONS IN THE FILAMENT UNTIL THE DETACHMENT FROM THE PLATE, ESPECIALLY CONCERNING TO THE MOST EXTERNAL AREAS OF ITS PATH.
A GOOD THERMAL CONDUCTIVITY OF THE PLATE IS ABLE TO SPREAD BETTER THE TEMPERATURES OF THE FILAMENT STORED, FAVORING ITS QUITE COOLING AND A MUCH LESS DRASTIC CHANGE OF STATE AND THEREFORE, FREE AS POSSIBLE, OF RESIDUAL INTERNAL STRESS.
6. COEFFICIENT OF LINEAR THERMAL EXPANSION
THE COEFFICIENT OF LINEAR THERMAL EXPANSION OF THE PRINT SURFACE MUST BE ABLE TO FOLLOW THE VARIATIONS IN TEMPERATURE AND, CONSEQUENTLY, THE DIMENSIONAL VARIATIONS OF THE STORED WIRE.
AN EXCESSIVE EXPANSION, AS WELL AS ITS OPPOSITE, WOULD BE HARMFUL IN ORDER TO AVOID RESIDUAL STRESSES OF THE FIRST DEPOSITED LAYER.
7. THERMAL INERTIA
CONNECTED TO THE TWO PREVIOUS PARAMETERS (5-6), IS CLEAR THAT THE THERMAL INERTIA OF THE PRINT SURFACE, IN ORDER TO OBTAIN A GOOD ADHESION RESULTS OF THE FIRST DEPOSITED LAYER, MUST BE ENOUGH HIGH, FOR THE GREAT DIFFERENCE OF THE TWO MASSES INVOLVED.
THIS PARAMETER IS MAYBE ONE OF THE MOST IMPORTANT FOR THE PHENOMENON OF LOCAL OVERHEATING.
THIS LEADS A SLOW HEATING / COOLING TIME BUT A BETTER MAINTENANCE OF THE CONSTANT TEMPERATURE WHICH, AS WE DESCRIBED ABOVE, IS VERY IMPORTANT FOR THE PURPOSES OF THE DEPOSITION OF THE FIRST LAYER WITHOUT ADHESION PROBLEMS AND, ESPECIALLY, WITH THE ITS BEST THERMAL STABILITY.
8. BOUNDARY CONDITIONS
AS DESCRIBED WITH REGARD TO LOCAL OVERHEATING (FIG. 1), DURING THE DEPOSITION OF THE FIRST LAYER, WITH ΔT BETWEEN THE MELTED FILAMENT AND THE ADHESION SURFACE ALSO OF 200° C, THE INDUCED STRESS, BOTH IN THE FILAMENT AND IN THE SURFACE, HAVE VALUES NOT NEGLIGIBLE.
THEREFORE, THE TRIGGERING OF LOCAL DEFORMATIONS CAN ALSO INDUCE DEFORMATIONS THAT AFFECT THE GLOBAL PLANARITY OF THE PLATE ESPECIALLY IN RELATION WITH IT’S STIFFNESS.
FIG. 3 SHOWS THE TREND OF THE DEFORMATION OF UNCONSTRAINED PLATE WITH HIGH BENDIING STIFFNESS, SUBJECT TO A STRONG, PARTICULARLY CONCENTRATED AND / OR LOCALIZED OVERHEATING.
THE BOUNDARY CONDITIONS AT THE EDGE OF THE PLATE ARE VERY IMPORTANT TO MAINTAIN ITS CORRECT FLATNESS AND ARE WELL DESCRIBED, IN RELATION TO THE LENGTH MEASURES OF ITS SIDES, BY THE SCIENCE OF ENGINEERING CONSTRUCTION.
THESE CONSTRAINTS, IN THE SPECIFIC CASE, MUST ALSO CONSIDER THE LINEAR EXPANSION TO WHICH THE PLATE IS SUBJECT.
IN THIS WAY, THE CONSTRAINTS MUST THEREFORE CONTAIN THE VERTICAL REACTIONS AND LEAVING THE HORIZONTAL REACTIONS FREE TO SLIDE.
IN FIG.4, ON THE OTHER END, IT IS POSSIBLE TO SEE THE DEFORMATION TREND OF A PRINTING SURFACE/PLATE SUBJECT THE SAME TO A STRONG, PARTICULARLY CONCENTRATED AND / OR LOCALIZED OVERHEATING BUT WITH A LOW BENDING STIFFNESS.
IN THIS CASE THE BOUNDARY CONDITION ARE MUCH FURTHER AWAY FROM ITS TERMINAL EDGE AND CONCENTRATED VERY CLOSE TO THE HEAT SOURCE.
THIS CONDITION (SEE FOR EXAMPLE THE PRINTING OF POM – FIG.2) IS MUCH MORE DIFFICULT TO CONTROL. IS SIMPLE UNDERSTAND THAT THIS PARAMETER IS VERY IMPORTANT AND IT IS ONE OF THE MOST IMPORTANT AND MOST DIFFICULT TO CONTROL WHEN DESIGNING THE PRINTING PLATE/SURFACE
9. RESISTANCE TO WEAR FOR MECHANICAL STRESS
SOMETIMES, IN THE FDM 3D PRINTING TECHNIQUE, FOR AN INCORRECT Z OFFSET OR FOR USE OF CHEMICAL GLUES WITH HIGH ADHESIVE POWER, EXCESSIVE ADHESION OF THE FIRST LAYER OF THE FILAMENT ON THE PRINT SURFACE MAY OCCUR.
ITS REMOVAL, UNDER THESE CONDITIONS, MAY REQUIRE THE USE OF MECHANICAL TOOLS WHICH, SOMETIMES, CAN CAUSE IRREPARABLE DAMAGE TO THE SURFACE UNTIL THE NEED FOR ITS REPLACEMENT.
10. RESISTANCE TO WEAR FOR THERMAL STRESS
IN ADDITION TO THE CONTINUOUS HEATING AND COOLING CYCLES FROM THE ROOM TEMPERATURE TO THE RECOMMENDED PRINTING TEMPERATURE, IT IS NECESSARY TO CONSIDER THE PHENOMENA OF LOCAL OVERHEATING (FIG. 1) DUE TO THE DEPOSITION OF THE FIRST SURFACE LAYER.
THIS LAST PHENOMENON WILL ALWAYS DETERMINE THERMAL STRESS WEAR ON THE PRINTING PLATE AND, BETWEEN THE TWO CONSIDERED, THE WORST CONDITION FOR ITS DURATION.
11. RESISTANCE TO HIGH TEMPERATURES
RELATIVE TO THE PREVIOUS POINT, IT’S UNDERSTANDING HOW THE PRINT SURFACE SHOULD NOT RESIST TO THE PRINT TEMPERATURES RECOMMENDED FOR THE VARIOUS MATERIALS BUT TO THE FUSION TEMPERATURES OF THE FILAMENTS.
THEN, WITH RESPECT TO THE MATERIALS PRINTABLES UP TO 300 ° C, LATTER, OR A SIMILAR, MUST BE THE TEMPERATURE OF REFERENCE FOR GOOD DESIGN OF PRINT PLATE.
12. SURFACE THERMAL REFRACTION
ADDING A SURFACE REFRACTION FEATURE OF HEAT TO THE PLATE, CAN IMPROVE THE “MICROCLIMATE” NECESSARY FOR BETTER ADHESION OF THE FIRST LAYERS.
THIS FEATURE, MAY ALSO OFFER OTHER IMPROVEMENTS FOR THE GLOBAL QUALITY OF THE PRINTED MODEL.
EVEN ON MACHINES THAT ARE NOT EXCESSIVELY SUSPHISTICATED, IT CAN MAKE, WITH SOME OTHER SMALL TRICKS, THE FINAL PRODUCT, WITH A QUALITY A LITTLE CLOSER TO THE REFERENCE: THE ONE OBTAINED THROUGH INJECTION MOLDING.
3D FDM Experiments&Innovation 