Continuous fiber high speed printhead apparatus and high speed printing method

Abstract

The application discloses a continuous fiber high-speed printing head device and a high-speed printing method, and the device comprises a mounting frame, a wire feeding mechanism, a wire cutting mechanism and a hot end assembly. The wire feeding mechanism comprises a wire feeding driving device, a transmission assembly, an extrusion roller and an adjusting assembly. The wire feeding driving device drives the extrusion roller to move towards each other to extrude a prepreg and realize wire feeding. The adjusting assembly is used for adjusting the extrusion force between the two extrusion rollers. The wire cutting mechanism can be quickly disassembled to quickly install and replace the blade. The hot end assembly performs multi-stage heating on the prepreg, and cooperates with the high-speed printing method to realize continuous fiber high-speed printing. By arranging the adjusting assembly, the distance and the clamping force between the extrusion rollers are adjusted, so that the wire feeding mechanism can feed wires of different specifications, and the applicability is wide. The wire feeding mechanism, the wire cutting mechanism and the hot end assembly are optimized, the maintenance difficulty of the printing head is reduced, and the printing stability and the working efficiency are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of additive manufacturing technology, in particular to a continuous fiber high-speed printing head device and a high-speed printing method. BACKGROUND

[0002] With the development of additive manufacturing technology, more and more new materials are used in the field of additive manufacturing, and continuous fiber prepreg is no exception. Continuous fiber reinforced resin matrix composite has the characteristics of high strength, light weight, stable chemical performance, etc., and has extremely wide application in the fields of aerospace, automobile, ship, military industry, etc. The use of additive manufacturing technology makes the manufacturing of continuous fiber reinforced resin matrix material more simple, and it is easier to manufacture complex structures. Compared with the traditional fiber layering process, continuous fiber additive manufacturing technology has become the main development trend in the future.

[0003] The current continuous fiber additive manufacturing technology is not mature enough, especially in the field of continuous fiber high-speed printing. The structure of the printing head is complex and not convenient to maintain, especially the filament feeding and cutting part of the printing head. Different specifications of the filament use different filament feeding and cutting mechanisms. The filament feeding mechanism has high maintenance cost, and there are different degrees of extrusion force deficiency, filament wear and crushing phenomenon during the filament feeding process. The cutting mechanism has complex structure, poor maintenance, poor cutting effect, fast blade wear and cannot quickly replace the blade. In addition, in order to ensure the strength, the speed of continuous fiber printing is at a low level, the production efficiency is low, and the processing time is long. These problems have seriously hindered the development of the industry. SUMMARY

[0004] The purpose of the present application is to solve the problems of the prior art, such as the non-universal filament feeding mechanism, the complex cutting mechanism, the poor cutting effect, and the low overall printing speed. The present application provides a continuous fiber high-speed printing head device and a high-speed printing method.

[0005] Technical scheme: In order to solve the above problems, the present application adopts a continuous fiber high-speed printing head device, which comprises a mounting frame, a filament feeding mechanism, a filament cutting mechanism and a hot end assembly. The filament feeding mechanism comprises a filament feeding driving device, a transmission assembly, an extrusion roller and an adjusting assembly. The filament feeding driving device, the transmission assembly and the adjusting assembly are all mounted on the mounting frame. The transmission assembly comprises a first transmission shaft and a second transmission shaft. Each of the first transmission shaft and the second transmission shaft is provided with an extrusion roller and a driven wheel. The driven wheels of the first transmission shaft and the second transmission shaft are meshed with each other. The first transmission shaft is connected with the filament feeding driving device. The two extrusion rollers are pressed against each other to realize filament feeding. The adjusting assembly is used to adjust the pressing force between the two extrusion rollers.

[0006] The cutting mechanism comprises a cutting drive device, a cutter holder, a push cutter holder installed in the cutter holder, and a moving blade installed on the push cutter holder, the cutting drive device and the cutter holder are installed on the mounting frame, one end of the push cutter holder is connected with the cutting drive device to push the moving blade to cut the fiber;

[0007] The hot end assembly comprises a throat pipe assembly installed on the mounting frame, a multi-stage heating block installed on the outer wall of the throat pipe assembly, and a nozzle installed at the bottom of the throat pipe assembly, the throat pipe assembly is hollow inside, and the mounting frame, the cutter holder and the throat pipe assembly are all provided with an opening for the pre-preg to pass through.

[0008] Further, a driving gear is sleeved on the output shaft of the feeding drive device, and the transmission assembly further comprises a driven gear sleeved on the first transmission shaft, and the driven gear is engaged with the driving gear.

[0009] Further, the extrusion roller comprises a metal bushing layer on the inner side and a rubber layer on the outer side, and the extrusion roller is further provided with a threaded hole, and a screw is installed in the threaded hole to fix the extrusion roller on the transmission shaft.

[0010] Further, the mounting frame is rotatably provided with a side plate, and the second transmission shaft is installed on the side plate, the adjusting assembly comprises an adjusting bolt and a spring sleeved on the adjusting bolt, the adjusting bolt is installed on the mounting frame through the side plate, and the spring is located between the head of the adjusting bolt and the side plate.

[0011] Further, the cutter holder comprises an upper cutter holder and a lower cutter holder, the upper cutter holder is installed on the lower cutter holder through a rotating shaft pin, the mounting frame is provided with a quick release groove for installing the cutter holder, and the upper cutter holder and the lower cutter holder are installed in the quick release groove.

[0012] Further, the moving blade is provided with symmetrical single-sided circular arc-shaped cutting edges on both sides, and the lower cutter holder is further provided with a fixed blade for cooperating with the moving blade to cut the fiber.

[0013] Further, the cutting drive device is a rudder, and one end of the push cutter holder is connected with the cutting drive device through a rocker arm to convert the rotary motion of the rudder into linear motion.

[0014] Further, the hot end assembly further comprises a radiator and a cooling fan, the radiator is installed on the outer wall of the throat pipe assembly, and the radiator is located between the multi-stage heating block and the mounting frame, and the cooling fan is installed on both sides of the radiator.

[0015] Further, the throat pipe assembly is made of Teflon.

[0016] The application also provides a high-speed printing method of the continuous fiber high-speed printing head device, the density p, the specific heat capacity c, the thermal conductivity λ, the surface heat transfer coefficient h of the printed fiber pre-preg, and the radius R of the pre-preg are determined.

[0017] The expression of printing speed and nozzle temperature is as follows:

[0018]

[0019] According to the steady-state thermal analysis component in the ANSYS-WORHBENCH software, the length of each temperature zone during multi-stage heating is calculated through thermodynamic simulation, and the temperature of the heating block from top to bottom is T1, T2, T3…T n , the temperature of the prepreg sent out of each heating zone is t1, t2, t3…t n , and the length of each heating zone is L1, L2, L3…L n , then the printing speed expression of each heating zone is as follows:

[0020]

[0021]

[0022] According to the principle that the speed of each heating zone during printing must be consistent, V1=V2=V3=V n , a plurality of solutions meeting the requirements can be solved by the exhaustion method, and the solution with the maximum printing speed V is selected, and the temperature of each heating block is set according to the calculated temperature result, so that the maximum speed printing is realized.

[0023] Advantages: compared with the prior art, the present application has the following advantages: (1) by setting the adjusting assembly, the distance between the extrusion rollers and the clamping force are adjusted, so that the wire feeding mechanism can feed wire materials of different specifications, and has wide applicability; (2) the structure of the extrusion roller is optimized, and the rubber material on the surface causes less damage to the wire material; (3) the wire cutting mechanism has a simple structure, and can realize quick fixing and replacement of the blade; (4) the shape of the wire cutting blade is optimized, the convergence of the single-sided edge of the two arc-shaped sides and the wire cutting effect are good, and each blade can be used twice, which reduces the production cost and improves the resource utilization rate; (5) the heating zone structure of the hot end assembly is optimized, the heating temperature zone is prolonged by the gradient multi-stage heating method, the melting speed of the base resin is improved, the risk of plugging is reduced, and the printing speed of the continuous fiber can be greatly improved; (6) a mathematical model of the printing speed and temperature of the prepreg is established, the gradient temperature of the multi-stage heating block and the optimal printing speed can be easily calculated, the fastest printing speed under a certain temperature can be calculated, and theoretical preparation is made for high-speed printing. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 It is the overall structure schematic diagram of the continuous fiber high-speed printing head device of the present application;

[0025] Figure 2 It is the parts explosion drawing of the wire feeding mechanism of the present application;

[0026] Figure 3 This is an exploded view of the wire-cutting mechanism components of the present invention;

[0027] Figure 4 This is an exploded view of the hot-end component of the present invention;

[0028] Figure 5 This is a schematic diagram of the extrusion roller structure of the present invention;

[0029] Figure 6 This is a schematic diagram of the blade structure of the present invention;

[0030] Figure 7 This is a cross-sectional view of the hot end component of the present invention. Detailed Implementation

[0031] Example 1

[0032] like Figure 1 As shown, a continuous fiber high-speed printhead device in this embodiment includes a mounting frame 07 and a filament feeding mechanism 100, a filament cutting mechanism 200, and a hot end assembly 300 mounted on the mounting frame 07. The mounting frame 07 is provided with an opening 074 for prepreg filaments to pass through, allowing the prepreg filaments to smoothly enter the filament feeding mechanism 100. Figure 2 As shown, the wire feeding mechanism 100 includes a wire feeding motor 01, a back plate 02, a transmission assembly 08, an extrusion roller 03, and an adjustment assembly 05. The wire feeding motor 01 is fixed to the back plate 02 by bolts, and a drive gear 011 is sleeved on its output shaft to provide power to the wire feeding mechanism. The back plate 02 and the front cover plate 07 are locked together by bolts, providing fixed support for the installation position and rotation of the transmission assembly 08 and the extrusion roller 03.

[0033] The transmission assembly 08 includes a first transmission shaft 081, a second transmission shaft 082, and a driven gear (084) sleeved on the first transmission shaft 081. The driven gear 084 is installed between the back plate 02 and the mounting bracket 07, and meshes with the driving gear 011. An adjustment hole is provided on the back plate 2 to adjust the gap between the wire feeding motor and the transmission gear, ensuring smooth transmission.

[0034] Each of the first drive shaft 081 and the second drive shaft 082 is equipped with an extrusion roller 03 and a driven wheel 083. The first drive shaft 081 is mounted on the mounting bracket 07 via a bearing end cover 06. A side plate 04 is rotatably mounted on one side of the mounting bracket 07, and the second drive shaft 082 is mounted on the side plate 04. The driven wheels 083 on the two drive shafts mesh with each other, and the surfaces of the two extrusion rollers 03 contact each other to squeeze and feed the yarn.

[0035] like Figure 5As shown, the extrusion roller 03 includes a metal bushing layer 032 on the inner side, a rubber layer 031 on the outer side, and threaded holes 033 in the extrusion roller 03, and the extrusion roller 03 is fixed on the transmission shaft by screws installed in the threaded holes 033. The flexible rubber layer structure can increase the contact area with the wire, reduce damage such as wire crushing and wear. The screw fixation facilitates maintenance and replacement of the extrusion roller after wear.

[0036] The adjusting assembly 05 includes an adjusting screw and a spring sleeved on the adjusting screw, the adjusting screw is installed on the mounting bracket 07 through the side plate 04, the mounting bracket 07 is provided with a screw hole for the adjusting screw to be screwed into, and the spring is located between the head of the adjusting screw and the side plate 04. By tightening or loosening the screw, the distance and clamping force between the extrusion rollers 03 can be adjusted to adapt to wires of different specifications.

[0037] As shown in Figure 3 The wire cutting mechanism 200 includes a wire cutting steering engine 09, a knife holder, a push knife holder 12, a moving blade 11, and a fixed blade 21. The knife holder includes an upper knife holder 10 and a lower knife holder 13, the upper knife holder 10 is installed on the lower knife holder 13 through a rotating shaft pin, the lower knife holder 13 is made of 6061 aluminum alloy and is the main body of the entire wire cutting mechanism, and is locked with the upper knife holder 10 through a screw to ensure the rigidity of the entire mechanism. The upper knife holder 10 is provided with a fixing hole 101, the mounting bracket 07 is provided with a quick release groove 071 and a locking threaded hole 072 for installing the knife holder, and a screw is installed in the fixing hole 101 and the locking threaded hole 072 to install the upper knife holder 10 and the lower knife holder 13 in the quick release groove 071. The middle part of the upper knife holder 10 and the lower knife holder 13 is provided with an opening 102 for the pre-preg wire to pass through.

[0038] The fixed blade 21 is installed in the lower knife holder 13, the moving blade 11 is installed on the push knife holder 12, and the push knife holder 12 is slidingly installed on the lower knife holder 13. The wire cutting steering engine 09 is fixedly installed on the mounting bracket 07, one end of the push knife holder 12 is connected with the wire cutting driving device 09 through a rocker arm 14 to form a crank slider mechanism to convert the rotary motion of the steering engine into linear motion. As shown in Figure 6 The blade 11 is provided with a center-symmetric single-face circular-arc-shaped cutting edge 111, the circular-arc-shaped cutting edge has a gathering effect during wire cutting, has a converging effect on the broken part, and can effectively reduce the difficulty of re-feeding the wire. The blade is also provided with a screw fixing hole 112 and a fixing groove 113, the lower knife holder 13 and the push knife holder 12 are both provided with a positioning key 131 for positioning the blade, and the blade position is fixed through the cooperation of the positioning key 131 and the fixing groove 113, or the blade position is fixed through a screw. The moving blade 11 cooperates with the fixed blade 21 to cut the wire by pushing the push knife holder 12 through the wire cutting steering engine 09.

[0039] As shown in Figure 4As shown, the hot end assembly 300 includes the throat assembly 19, the heat sink 15, the heat sink fan 16, the multi-stage heating block 17, and the nozzle 18. The throat assembly 19 is located at the bottom of the mounting frame 07, and the inside of the throat assembly 19 is hollow, with the top end communicating with the opening 102 of the filament cutting mechanism for the pre-impregnated filament to pass through. The mounting frame 07 is provided with a bayonet 073, and the heat sink 15 is fixed to the bayonet 073 through the hot end clamp block 20. The throat assembly 19 is fixed to the heat sink 15 through a set screw. The clamping block and the buckle are installed in a cooperative manner to ensure the installation strength of the hot end assembly, and can be quickly disassembled and assembled for easy maintenance. The heat sink 15 surrounds the outer wall of the upper section of the throat assembly 19, and the heat sink 15 is also provided with a fan mounting bracket, and the heat sink fan 16 is installed on both sides of the heat sink 15. The heat sink plays a role in dissipating heat for the throat assembly 19 to avoid overheating of the throat assembly 19 and its internal parts, and also prevents the heat of the heating block from spreading to the filament cutting mechanism and the filament feeding mechanism above to cause damage to the structure. The heat sink fan can accelerate the air convection speed of the heat sink fins to accelerate heat dissipation.

[0040] The multi-stage heating block 17 surrounds the outer wall of the lower section of the throat assembly 19, and the multi-stage heating block 17 includes a plurality of heating blocks, each of which has a thermocouple and a heating rod. The temperature of each heating block can be accurately controlled to ensure the temperature stability of each heating zone and the heating effect of the pre-impregnated material. In addition, the heating blocks have a gradient temperature difference when heating, which not only extends the heating zone and improves the heating efficiency, but also avoids the premature melting of the resin matrix and the sticking of the resin matrix in the throat assembly, causing a blockage. The nozzle 18 is installed at the bottom of the throat assembly 19 to provide a downward pressure for the heated pre-impregnated material to ensure that it can be bonded to the already printed substrate. The throat assembly 19 can be made of Teflon tube, which provides a low-friction channel for the pre-impregnated material to heat evenly in the heating zone, improving the printing quality and reducing the probability of blockage.

[0041] The working principle of the printing head of the present application is as follows: the pre-impregnated filament passes through the opening 074 at the top of the mounting frame 7, passes between the two extrusion rollers 03, and then enters the inside of the throat assembly 19 through the opening 102 of the filament cutting mechanism, and finally is sprayed out from the nozzle 18. The two extrusion rollers 03 are driven by the filament feeding motor 01 to move towards each other and press each other, which brings out the pre-impregnated filament in the middle and completes the filament feeding. According to the different filaments used, the distance and clamping force between the extrusion rollers 03 can be adjusted through the adjusting assembly 05 to adapt to various printing requirements. After the filament is fed into the hot end assembly, it first passes through the heat sink part and then passes through the throat assembly. In the throat assembly, the multi-stage heating block heats the pre-impregnated filament, causing the resin matrix on the pre-impregnated filament to melt and reach a printable state. When cutting the filament is needed, the cutting arm is driven by the cutting steering engine, the cutting arm pushes the cutter holder and the cutter fixed thereto to complete the cutting action of the filament. After cutting the filament, each mechanism returns to its original position to prepare for the next filament feeding and cutting.

[0042] The high-speed printing head of the application realizes the adjustment of the distance and clamping force between the extrusion rollers by setting the adjusting assembly, so that the wire feeding mechanism can feed wire materials of different specifications, and is widely applicable; the structure of the extrusion rollers is optimized, and the rubber material on the surface causes less damage to the wire material; the wire cutting mechanism has a simple structure and can realize quick fixing and replacement of the blades; the shape of the wire cutting blades is optimized, the convergence of the single-edged blade on the two sides of the circular arc is good, the wire cutting effect is good, each blade can be used twice, the production cost is reduced, and the resource utilization rate is improved; the structure of the heating area of the hot end assembly is optimized, the heating temperature zone is prolonged by gradient multi-stage heating, the melting speed of the base resin is improved, the risk of plugging is reduced, and the printing speed of the continuous fibers can be greatly improved.

[0043] Example two

[0044] The embodiment provides a high-speed printing method of the high-speed printing head device of the continuous fibers, and comprises the following steps:

[0045] Step one: determine the density p, specific heat capacity c, thermal conductivity λ, surface heat transfer coefficient h, and radius R of the printed fiber prepreg.

[0046] Step two: according to the law of conservation of energy, the expression of the heating time of the prepreg in the nozzle is as follows:

[0047]

[0048] In the above formula, t0 is the initial temperature of the prepreg, which can be replaced by room temperature, t ∞ is the temperature of the prepreg when it is heated, which is equivalent to the temperature of the heating block, t is the target heating temperature, which is equivalent to the melting temperature of the prepreg resin matrix.

[0049] Step three: in the printing nozzle, the expression of the heating time of the prepreg is as follows:

[0050]

[0051] In the above formula, L h is the length of the heating area, and V is the printing speed.

[0052] Step four: according to the expressions of steps two and three, the expressions of the printing speed and the nozzle temperature are further derived as follows:

[0053]

[0054] Step five: according to the steady-state thermal analysis component in the ANSYS-WORHBENCH software, the length of each temperature zone during multi-stage heating is calculated through thermodynamic simulation, such as Figure 7The temperatures of the heating blocks from top to bottom are T1, T2, T3, …, Tn in sequence as shown in the figure. n The temperatures of the prepreg sent out from each heating area are t1, t2, t3, …, tn in sequence. n The lengths of each heating area are L1, L2, L3, …, Ln. n The printing speed expression of each heating area is as follows:

[0055]

[0056] Step six: according to the principle that the speeds of each heating area must be consistent during printing, V1=V2=V3=Vn is set. n A plurality of solutions meeting the requirements can be solved by the exhaustion method, a solution with the maximum printing speed V is selected, and the temperatures of the heating blocks are set according to the solved temperature results, so that the printing with the maximum speed can be realized.

[0057] The printing method of the application establishes a mathematical model of the printing speed and temperature of the prepreg, can conveniently calculate the gradient temperature of the multi-stage heating block and the optimal printing speed, can calculate the fastest printing speed under a certain temperature, and makes a theoretical preparation for the high-speed printing.

Claims

1. A continuous fiber high-speed printhead device, characterized in that, The assembly includes a mounting frame (07), a wire feeding mechanism (100), a wire cutting mechanism (200), and a hot end assembly (300). The wire feeding mechanism (100) includes a wire feeding drive device (01), a transmission assembly (08), an extrusion roller (03), and an adjustment assembly (05). The wire feeding drive device (01), the transmission assembly (08), and the adjustment assembly (05) are all mounted on the mounting frame (07). The transmission assembly (08) includes a first transmission shaft (081) and a second transmission shaft (082). 2) Each of the first drive shaft (081) and the second drive shaft (082) is equipped with an extrusion roller (03) and a driven wheel (083), and the driven wheel of the first drive shaft (081) and the driven wheel of the second drive shaft (082) mesh with each other. The first drive shaft (081) is connected to the yarn feeding drive device (01). The surfaces of the two extrusion rollers (03) press against each other to achieve yarn feeding. The adjusting component (05) is used to adjust the extrusion pressure between the two extrusion rollers (03). The wire cutting mechanism (200) includes a wire cutting drive device (09), a blade holder, a pusher blade holder (12) installed in the blade holder, and a movable blade (11) installed on the pusher blade holder (12). The wire cutting drive device (09) and the blade holder are installed on the mounting frame (07). One end of the pusher blade holder (12) is connected to the wire cutting drive device (09) to push the movable blade (11) to cut wires. The tool holder includes an upper tool holder (10) and a lower tool holder (13). The upper tool holder (10) is mounted on the lower tool holder (13) by a pivot pin. The mounting bracket (07) is provided with a quick-release slot (071) for mounting the tool holder. The upper tool holder (10) and the lower tool holder (13) are mounted in the quick-release slot (071). The movable blade (11) has symmetrical single-sided arc-shaped cutting edges (111) on both sides, and the lower blade holder (13) is also provided with a fixed blade (21) for cooperating with the movable blade (11) to cut wires; The hot end assembly (300) includes a throat assembly (19) mounted on a mounting bracket (07), a multi-stage heating block (17) mounted on the outer wall of the throat assembly (19), and a nozzle (18) mounted on the bottom of the throat assembly (19). The throat assembly (19) is hollow inside, and the mounting bracket (07), the knife holder, and the throat assembly (19) all have openings for the prepreg to pass through.

2. The continuous fiber high-speed printhead device as described in claim 1, characterized in that, The output shaft of the wire feeding drive device (01) is fitted with a drive gear (011), and the transmission assembly (08) further includes a driven gear (084) fitted on the first transmission shaft (081), the driven gear (084) meshing with the drive gear (011).

3. The continuous fiber high-speed printhead device as described in claim 1, characterized in that, The extrusion roller (03) includes an inner metal bushing layer (032) and an outer rubber layer (031). The extrusion roller (03) also has a threaded hole (033), which is installed in the threaded hole (033) by screws to fix the extrusion roller (03) to the drive shaft.

4. The continuous fiber high-speed printhead device as described in claim 1, 2, or 3, characterized in that, A side plate (04) is rotatably mounted on the mounting bracket (07), and a second drive shaft (082) is mounted on the side plate (04). The adjustment assembly (05) includes an adjustment bolt and a spring sleeved on the adjustment bolt. The adjustment bolt passes through the side plate (04) and is mounted on the mounting bracket (07). The spring is located between the head of the adjustment bolt and the side plate (04).

5. The continuous fiber high-speed printhead device as described in claim 1, characterized in that, The wire cutting drive device (09) is a servo motor. One end of the pusher frame (12) is connected to the wire cutting drive device (09) through a rocker arm (14) to convert the rotational motion of the servo motor into linear motion.

6. The continuous fiber high-speed printhead device as described in claim 1, characterized in that, The hot end assembly (300) also includes a radiator (15) and a cooling fan (16). The radiator (15) is installed on the outer wall of the throat assembly (19) and is located between the multi-stage heating block (17) and the mounting bracket (07). The cooling fan (16) is installed on both sides of the radiator (15).

7. The continuous fiber high-speed printhead device as described in claim 1, characterized in that, The throat assembly (19) is made of Teflon tubing.

8. A high-speed printing method for the continuous fiber high-speed printhead apparatus according to any one of claims 1-7, characterized in that, Determine the density ρ, specific heat capacity c, thermal conductivity λ, surface heat transfer coefficient h, and radius R of the printed fiber prepreg; The expressions for printing speed and printhead temperature are as follows: Based on the steady-state thermal analysis component in ANSYS-WORHBENCH software, the lengths of each temperature zone during multi-stage heating were calculated through thermodynamic simulation. Let the temperatures of the heating blocks from top to bottom be T1, T2, T3…T… n The temperatures of the prepregs delivered from each heating zone are t1, t2, t3...t n The length of each heating zone is L1, L2, L3...L n The printing speed expression for each heating zone is as follows: Based on the principle that the speed of each heating zone must be consistent during printing, let V1 = V2 = V3 = ... = V n By exhaustive search, multiple solutions that meet the requirements can be calculated. The solution with the highest printing speed V is selected. Based on the calculated temperature results, the temperature of each heating block is set to achieve the maximum printing speed.

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