A wire preheating method, a wire feeding control method, and an additive processing device

Abstract

The application discloses a wire preheating method, a wire feeding control method and an additive processing device. A detection current is applied to the wire and the printing base through a current detection loop to obtain a contact signal. In response to the contact signal, a current heating loop is turned on. The current heating loop applies a preheating current to the wire and the printing base. The amplitude of the preheating current is greater than that of the detection current. Joule heat is generated through the resistance of the wire itself, and the wire is preheated through the Joule heat. The detection loop and the heating loop are arranged. The contact state of the wire and the printing base is determined by a constant current small current. After confirming the contact, a preheating large current is applied. The wire itself is preheated by using the resistance to generate Joule heat. The risk of arc or no-load caused by no contact power-on is avoided, and the preheating process is safe and controllable.

Description

Technical Field

[0001] This invention relates to the field of additive manufacturing technology, specifically to a filament preheating method, a filament feeding control method, and an additive manufacturing apparatus. Background Technology

[0002] Wire-feed additive manufacturing technologies (such as laser filament cladding and metal 3D printing) have been widely applied in core manufacturing fields such as aerospace, machinery manufacturing, mold repair, and automotive parts production due to their advantages of high material utilization, excellent forming efficiency, and stable mechanical properties of the formed parts. In this type of processing, real-time monitoring of the filament's position and status, as well as the coordinated timing control of the laser and filament, are crucial to ensuring processing quality. The relative position of the filament to the printing base (substrate or existing layer) directly determines the cladding effect. Any deviation can easily lead to filament pilling and breakage, as well as defects such as porosity, cracks, and dimensional errors in the formed parts, or even processing failure.

[0003] Currently, existing technologies still have the following shortcomings in meeting the processing requirements of the wire material itself:

[0004] First, the laser power requirement is high: In actual production, to achieve stable cladding or welding, the wire is usually fed directly into the molten pool at room temperature. The laser needs to provide all the melting energy; it not only needs to heat the wire from room temperature to its melting point, but also needs to provide additional latent heat of fusion and overcome heat dissipation from the molten pool. For high-melting-point materials (such as titanium alloys and nickel-based alloys), high thermal conductivity materials (such as aluminum and copper), or high wire feeding speeds, the required laser power is often extremely high. When the power of existing lasers is insufficient, current technologies typically employ multiple laser beams combined or directly replace them with higher-power lasers. Both of these solutions significantly increase equipment costs, system complexity, and maintenance difficulty, limiting the widespread application of laser wire feeding technology in small and medium-sized manufacturing enterprises or on-site repair scenarios.

[0005] II. Direct feeding of room temperature wire into the molten pool easily leads to various forming defects: Because the wire enters the high-temperature molten pool without preheating, a huge temperature gradient is formed between the wire and the molten pool. This temperature gradient firstly leads to severe spattering. For example, when the room temperature wire comes into instantaneous contact with the high-temperature molten pool, the moisture and oil adsorbed on the surface vaporize rapidly, and the wire end is also subjected to thermal shock, causing it to crack and generate a large amount of spatter. Secondly, the moisture and crystal water on the surface and inside of the wire decompose at high temperatures, releasing hydrogen gas. When the molten pool solidifies rapidly, the gas does not have time to escape, forming pores; while the sudden cooling of the cold wire causes the molten pool to shrink violently, easily producing shrinkage cavities. Furthermore, once the cold wire enters the molten pool, it rapidly absorbs a large amount of heat, causing the local temperature of the molten pool to drop, resulting in insufficient fusion between the wire and the sidewalls or interlayers of the base material, forming incomplete fusion defects; conversely, the sudden heating of the cold wire easily causes violent disturbance in the molten pool, resulting in messy weld or cladding texture and uneven reinforcement after solidification, affecting the appearance and subsequent processing. Meanwhile, the significant temperature gradient between the wire, the molten pool, and the base material easily generates substantial thermal stress, which can readily induce cold or hot cracks in materials such as high-strength steel, nickel-based alloys, and aluminum alloys. For external assembly equipment, to ensure complete wire melting, the wire feeding speed must be limited to a low range; otherwise, incomplete fusion or wire blockage may occur, hindering the improvement of additive manufacturing efficiency. Furthermore, the intense thermal cycling between the high-temperature molten pool and the cold wire generates significant residual stress, which can easily lead to cracking or dimensional springback during subsequent machining. Regarding the materials themselves, for high thermal conductivity materials (such as aluminum and copper), heat dissipates rapidly after the room-temperature wire is fed in, easily resulting in incomplete welds and insufficient penetration. For dissimilar metal welding, the cold wire struggles to balance the thermal states on both sides, easily leading to compositional segregation and a brittle layer. Moreover, in winter or low-temperature workshop environments, the room-temperature wire temperature is even lower, exacerbating these defects and causing large fluctuations in forming quality under different ambient temperatures for the same process parameters, making it difficult to ensure consistent process throughout the year.

[0006] In summary, existing laser-fed additive manufacturing technologies urgently require a wire preheating solution that can reduce laser power requirements, improve forming quality, broaden the process window, and maintain controllable costs. Therefore, this invention proposes a wire preheating method, a wire feeding control method, and an additive manufacturing apparatus. Summary of the Invention

[0007] In view of the shortcomings of the existing technology, the purpose of this application is to utilize the resistance of the wire itself to achieve controllable preheating while ensuring safe contact, thereby reducing the laser power requirement and reducing the related forming and process defects caused by excessive temperature gradient.

[0008] The above-mentioned objective of this application is achieved through the following technical solution:

[0009] A method for preheating filament includes a current heating circuit. One electrical terminal of the current heating circuit is connected to the filament, and the other electrical terminal is connected to a printing base. When the filament comes into contact with the printing base, the current heating circuit is activated, applying a preheating current to both the filament and the printing base. Joule heating is generated by the resistance of the filament itself, preheating the filament. A current detection circuit is also included, with one electrical terminal connected to the filament and the other electrical terminal connected to the printing base. A detection current is continuously applied to both the filament and the printing base through the current detection circuit. When the filament comes into contact with the printing base, the current detection circuit is activated, generating a contact signal. In response to the contact signal, the current heating circuit is activated. This method primarily utilizes a small detection current to determine physical contact between the filament and the printing base. Once contact is confirmed, a large preheating current is applied, utilizing the filament's own resistance to generate heat. This avoids arcing caused by non-contact energization, achieving safe and controllable resistance preheating.

[0010] Preferably, the detection current is a constant low current with a value ≤100mA; the preheating current is an adjustable high current with a value ≥1A. Furthermore, the amplitude of the preheating current is greater than the amplitude of the detection current, ensuring both detection sensitivity and safety while providing sufficient preheating energy.

[0011] Preferably, the amplitude of the preheating current and / or the preheating duration are set according to at least one of the material, diameter, and feed speed of the filament. Adaptive parameter settings can be used to match different filaments and process conditions.

[0012] Preferably, during the application of the preheating current, the voltage and current of the current heating circuit are monitored in real time, the contact resistance between the filament and the printing base is calculated, and the amplitude of the preheating current is adjusted according to the change in the contact resistance to keep the Joule heat power stable. This closed-loop adjustment method can adaptively compensate for contact resistance fluctuations and ensure the stability of the preheating temperature.

[0013] Preferably, the preheating adopts an intermittent preheating mode or a continuous preheating mode; the filament is preheated while the printing base is relatively stationary, and the filament is then conveyed after preheating; or the filament is conveyed forward at a preset speed while maintaining contact with the printing base, and preheating is continuously carried out during the conveying process; the intermittent preheating mode or the continuous preheating mode is selected according to the filament feeding speed or process requirements, or the controller automatically switches according to the filament feeding speed.

[0014] Preferably, during the application of the preheating current, the contact signal is continuously monitored through the current detection circuit; if the contact signal disappears, the preheating current is cut off. This safety interlock mechanism can prevent high-current no-load or arcing caused by accidental detachment of the wire.

[0015] A filament feeding control method for laser filament additive manufacturing involves first maintaining contact between the filament and the printing substrate; then preheating the filament using the filament preheating method described above; subsequently, activating the laser to irradiate the end of the preheated filament; and adjusting the laser output power and / or the filament feeding speed based on the degree of filament preheating. The core of this method lies in using the degree of preheating as a feedback variable to dynamically match the laser energy with the filament supply.

[0016] Preferably, the preheating degree is determined by any of the following methods: the time integral value of the preheating current, the temperature rise of the filament, or the change in contact resistance between the filament and the printing base; based on the determined preheating degree, adjustment commands for the laser output power and / or the filament feed speed are generated.

[0017] Preferably, during or after the preheating process, the filament is fed by a filament feeding mechanism; the timing of laser activation is controlled so that the laser focal point and the end of the filament arrive at the processing position simultaneously, or the end of the filament arrives at the processing position before the laser, or the laser arrives at the processing position before the end of the filament.

[0018] Preferably, after completing single-layer additive manufacturing, the filament preheating method and the filament feeding control method are repeated, and the current forming layer surface is used as a new printing base to perform interlayer repositioning and preheating to achieve multi-layer additive manufacturing.

[0019] An additive manufacturing apparatus employs the filament feeding control method described above, comprising: a filament feeding mechanism for conveying filament, a laser for emitting laser light, a worktable for placing a printing base, and a controller for performing timing control; a detection circuit and a heating circuit connecting the filament and the printing base; and the controller being configured to execute the filament feeding control method. This apparatus integrates the detection circuit, heating circuit, and controller, enabling automatic execution of contact detection, resistance preheating, filament-laser coordination, and preheating feedback adjustment, achieving fully automated additive manufacturing.

[0020] Compared with the prior art, the beneficial effects of the present invention are:

[0021] I. Safe and Controllable Filament Resistance Preheating: This invention establishes a detection circuit and a heating circuit. First, a constant low current is used to determine the contact state between the filament and the printing substrate. Once contact is confirmed, a large preheating current is applied, utilizing the Joule heat generated by the filament's own resistance for preheating. This avoids the risks of arcing or no-load operation that may occur with contactless energization, ensuring a safe and controllable preheating process. Furthermore, because the preheating current amplitude is adjustable, it can be adaptively configured according to the filament material, diameter, and feed speed, achieving high adaptability to different materials and process conditions.

[0022] 2. Reduced laser power requirements and spatter: Through resistance preheating, the wire stores some heat before entering the molten pool, and the laser only needs to provide the remaining melting energy. At the same time, preheating ensures uniform temperature and moderate softening of the wire end, avoiding spatter or incomplete fusion defects caused by cold wire feeding, and improving the stability of the molten pool.

[0023] III. Improved Molding Quality: This invention uses the degree of preheating as a feedback variable to dynamically adjust the laser output power and / or wire feeding speed. When preheating is sufficient, the laser power is automatically reduced or the wire feeding speed is increased; conversely, if preheating is insufficient, the speed is increased or decreased. Even if contact resistance fluctuates due to oxide film, thermal expansion, or vibration, the wire end temperature remains relatively stable, demonstrating strong preheating consistency.

[0024] IV. Adaptable to multiple scenarios: This invention supports both intermittent preheating and continuous preheating modes, and can be flexibly switched according to the wire feeding speed. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the circuit required for the preheating method of the present invention;

[0026] Figure 2 This is a schematic diagram of Embodiment 1 of the present invention;

[0027] Figure 3 This is a flowchart of Embodiment 1 of the present invention;

[0028] Figure 4 This is a schematic diagram of Embodiment 2 of the present invention;

[0029] Figure 5 This is a schematic diagram of Embodiment 3 of the present invention;

[0030] Figure 6 This is a flowchart illustrating one embodiment of the fourth embodiment of the present invention;

[0031] Figure 7 This is a flowchart illustrating another embodiment of the present invention, Embodiment 4.

[0032] Figure 8 This is a flowchart illustrating another embodiment of the present invention, Embodiment 4.

[0033] Figure 9 This is a schematic diagram of the continuous preheating mode in Embodiment 4 of the present invention. Detailed Implementation

[0034] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0035] Example 1. This example provides a method for preheating filament.

[0036] like Figure 1 As shown, this invention employs the following apparatus for filament preheating: a filament feeding mechanism for conveying the filament; a substrate serving as the printing base and carrier for filament deposition; a current heating circuit, with its two ends electrically connected to the filament and the substrate respectively; and a current detection circuit, with its two ends also electrically connected to the filament and the substrate respectively. The filament preheating method is as follows: a current heating circuit and a current detection circuit are pre-set. A detection current is continuously applied to the filament and the substrate through the current detection circuit. When the filament moves to contact the substrate under the drive of the filament feeding mechanism, the current detection circuit is activated and generates a contact signal. In response to this contact signal, the current heating circuit is activated, applying a preheating current to the filament and the substrate. This preheating current flows through the filament's own resistance, generating Joule heat, thereby preheating the filament. The detection current is a constant small current, and the preheating current is an adjustable large current, with the amplitude of the preheating current greater than the amplitude of the detection current. The amplitude of the preheating current and / or the preheating duration can be pre-set based on at least one of the filament's material, diameter, and filament feeding speed.

[0037] Furthermore, such as Figure 2 The diagram illustrates the circuit principle used for wire preheating. The TouchSense board generates a constant current for detecting small currents; its 100mA terminal is electrically connected to the wire via a wire, and its GND terminal is electrically connected to the substrate via a wire. The hot wire driver board outputs an adjustable preheating current; its 100A terminal is electrically connected to the wire via a wire, and its GND terminal is electrically connected to the substrate via a wire. The TouchSense board's OUT terminal is connected to the hot wire driver board's ENABLE or IN terminal via a wire. A 24V power supply powers the TouchSense board, and a 40V / 20A power supply powers the hot wire driver board.

[0038] like Figure 1-2 As shown in the diagram, the line from the 100mA terminal of the TouchSense board to the wire is for detecting the positive output of a small current, while the line from the GND terminal of the TouchSense board to the substrate is for detecting the return current of a small current, i.e., the negative terminal; the two lines together form a current detection loop. The main function of the current detection loop is to continuously apply a constant small current. When the wire contacts the substrate, the loop closes, the TouchSense board detects the voltage change, and generates a contact signal.

[0039] like Figure 1-2 As shown, the line from the 100A terminal of the hot wire driver board to the wire is the positive output of the high-current heating circuit, while the line from the GND terminal of the hot wire driver board to the substrate is the negative output of the high-current heating circuit; these two lines together form the current heating circuit. The main function of the current heating circuit is to receive the enable signal, for example... Figure 2After the signal at the ENABLE port, the hot wire drive board outputs a large current, which flows through the wire's own resistance to generate Joule heat, thus achieving preheating.

[0040] In practice, the electrical connection between the conductor and the wire can be accomplished through the conductive nozzle structure in the prior art. Specifically, one end of the conductor is fixedly connected to the conductive nozzle in the wire feeding mechanism, and the wire passes through the internal channel of the conductive nozzle and maintains sliding contact with the inner wall of the conductive nozzle 4.

[0041] In practice, the filament is initially separated from the substrate, the current detection circuit should be in an open circuit state, and the current heating circuit should be in a standby state. For the current detection circuit, although the TouchSense board continuously outputs a constant 100mA current, the current cannot form a closed loop; the voltage across its internal sampling resistor is zero, and the OUT terminal outputs a low level, i.e., an invalid signal. For the current heating circuit, the ENABLE terminal of the hot wire drive board receives an invalid level, the internal power switch remains off, and there is no preheating current output. The entire device only consumes the power of the detection circuit and does not produce a preheating effect. Only when the filament feeding mechanism drives the filament towards the substrate, causing physical contact between the filament end and the substrate surface, is the electrical isolation between the filament and the substrate eliminated.

[0042] Specifically, such as Figures 1-3 In one specific embodiment of the filament preheating method shown, as the filament comes into contact with the substrate, the current detection loop changes from open to closed. The 100mA constant current source built into the TouchSense board begins to flow steadily through this loop, and its internal sampling resistor generates a clear voltage drop. After processing by the operational amplifier, the OUT terminal of the TouchSense board outputs a high-level enable signal, i.e., a contact signal, and transmits it to the ENABLE terminal of the hot wire driver board. Simultaneously, upon receiving the high-level enable signal, the hot wire driver board switches from standby mode to operating mode, i.e., its internal power switch is turned on, outputting a preset high current, such as 20A, from the 100A terminal through a wire to the filament. The current flows through the filament's own resistance, generating Joule heat, and then returns to the GND terminal of the hot wire driver board via the substrate, forming a complete current heating loop. Thus, the high current continues to flow through the filament, causing its end to heat up to the preset temperature within a few seconds, completing the preheating. When the preset preheating time is reached or the wire temperature reaches the set threshold, the control system sets the OUT signal of the TouchSense board to a low level, or directly cuts off the enable terminal of the hot wire drive board. The hot wire drive board returns to standby mode, and the preheating current returns to zero. At this time, the wire is in a hot state and can proceed to the subsequent wire feeding and cladding process.

[0043] It is worth noting that, to maintain the preheating state, the current detection circuit and the current heating circuit coexist in parallel between the wire and the substrate throughout the preheating process. Since the detection current is less than the preheating current, and the TouchSense board has an internal isolation protection circuit, a large current will not backflow and damage the detection circuit. Simultaneously, as long as the wire and substrate maintain stable contact, the detection circuit continuously outputs a high-level enable signal, keeping the heating circuit conducting.

[0044] In the circuit structure described above, to stably acquire the contact signal, existing structures such as a constant current source can be incorporated into the TouchSense board. For example, the base voltage of the power transistor can be adjusted by an operational amplifier to make the voltage drop across the emitter resistor equal to the reference voltage, thereby maintaining a constant current when the load changes. Alternatively, a sampling resistor can be connected in series in the return path of the constant current source. When the detection loop is open, the loop current is 0, and the voltage difference across the sampling resistor is 0V. When the wire contacts the substrate, a constant current of 100mA flows through the sampling resistor, generating a stable voltage drop of U = 100mA·Rs according to Ohm's law. This voltage drop is independent of the contact resistance and depends only on the constant current value and the sampling resistor value. The contact resistance referred to in this paper refers to the resistance at the contact interface between the wire and the substrate, which, together with the resistance of the wire itself, constitutes the total loop resistance R described later. total .

[0045] It is worth noting that when the wire contacts the substrate, closing the detection circuit, the 100mA constant current source built into the TouchSense board drives the current to flow through the sampling resistor R. s The voltage drop U across the sampling resistor s =I detect Rs, this voltage drop is stable and depends only on the sense current and the sampling resistance value, and is independent of the contact resistance. For example, if R s =10Ω, then U s =100mA·10Ω=1.0V. Since the voltage signal across the sampling resistor is relatively weak and may contain common-mode noise, it needs to be amplified and filtered. Existing technologies such as operational amplifiers can be used, which will not be elaborated here. However, to make the TouchSense board's OUT terminal output a digital level, it needs to be connected to a preset reference voltage V. ref A comparison is made. This embodiment provides two typical implementation methods:

[0046] One implementation method uses a separate voltage comparator chip, and the amplified analog voltage signal is denoted as V. amp Its non-inverting input is connected to V. amp The inverting input terminal is connected to the reference voltage V. ref For example, 2.5V. When V_amp >V refWhen the voltage is low, the comparator outputs a high level, such as 5V; otherwise, it outputs a low level.

[0047] Another implementation method is to denot the amplified analog voltage signal as V. amp V amp The data is fed into the ADC pin of the microcontroller. The microcontroller internally determines through software whether the ADC conversion value is greater than a preset threshold. This threshold must correspond to V. ref If it is greater than 0, then set to high level.

[0048] The above decision result is output through the OUT terminal of the TouchSense board. This terminal is configured as a push-pull output or an open-drain output and can be connected to a logic high level via a pull-up resistor. When the decision result is contact, the OUT terminal outputs a high level, such as 24V or 5V, depending on the enable voltage specification of the subsequent hot wire driver board; when there is no contact, it outputs a low level (0V). This high-level signal is the contact signal, or enable signal, and its electrical characteristics are sufficient to directly drive the ENABLE terminal of the hot wire driver board.

[0049] In the circuit structure described above, once the TouchSense board outputs a high-level enable signal at its OUT terminal, the hot wire driver board immediately conducts the preheating current with a very short response delay, causing the wire to begin heating within the same control cycle after contact detection is completed. When the hot wire driver board receives a low-level or invalid signal, the internal power switch is off. At this time, although the 100A terminal of the hot wire driver board is connected to the wires and GND terminal, the power circuit is open, and no preheating current flows through the wire. However, after the ENABLE terminal receives a high-level enable signal, the internal drive circuit quickly turns on the power switch, forming a low-impedance path between the 100A terminal and the GND terminal, allowing the preheating current to flow. For example, at time T0, the wire contacts the substrate. At time T0+Δt1, the TouchSense board completes signal processing, and the OUT terminal jumps to a high level. At time T0+Δt1+Δt2, the high level reaches the ENABLE terminal of the hot wire driver board. At time T0+Δt1+Δt2+Δt3, the MOSFET is fully turned on, and the preheating current begins to be output from the 100A terminal. Here, Δt2 is the signal transmission delay, and Δt3 is the power switch turn-on time.

[0050] It is worth noting that when a preheating current flows through a resistive conductor, electrical energy is converted into internal energy, generating heat. This heating power follows Joule's law: P = I²·R; where P is the heating power, I is the current flowing through the conductor, and R is the conductor's resistance. In this embodiment, this heat acts directly on the end of the wire, causing its temperature to rise rapidly, thus achieving resistive preheating of the wire. The resistance of the wire is determined by its material properties, including resistivity ρ, length L, and cross-sectional area A: R = ρ·(L / A).

[0051] In actual preheating, the heating zone is mainly concentrated at the ends of the wire, such as the section near the contact point. Furthermore, the resistivity of different metals varies significantly. For example, the resistivity of titanium alloy is approximately 1.7 × 10⁻⁻⁻⁻⁻⁶. 6 Ω·m, aluminum alloy approximately 0.4·10⁻ 6 Ω·m, approximately 0.7·10⁻ for stainless steel 6 Ω·m. Under the same geometric dimensions, high resistivity materials have higher intrinsic resistance. The wire diameter directly affects the cross-sectional area. Common additive manufacturing wire diameters range from 0.8 mm to 1.6 mm. The smaller the diameter, the smaller the cross-sectional area, and the higher the resistance. For example, a Φ1.2 mm titanium alloy wire with a 10 mm end has a resistance of approximately 0.5 Ω; while a Φ0.8 mm aluminum alloy wire of the same length has a resistance of approximately 0.15 Ω. In actual preheating, the path length of the current flow is typically several millimeters to several centimeters from the wire end, depending on the distance between the wire feeding mechanism and the substrate; the greater this length, the greater the resistance.

[0052] To further illustrate, if the preheating current I = 20A and the equivalent resistance of the wire R = 0.5Ω, then the heating power P = 20²·0.5 = 200W. This power is sufficient to heat the end of the wire to several hundred degrees Celsius within seconds; for example, the heat required to raise a titanium alloy wire from room temperature (20°C) to 600°C is approximately several hundred joules, which can be provided by heating for 3 seconds at 200W. If R = 0.1Ω and I = 30A, then P = 90W; if higher power is required, the current can be increased or a high-resistance wire can be selected.

[0053] During actual preheating, when a large current continuously flows through the wire, stable heat is generated across the wire's equivalent resistance R according to Joule's law. For example, if the preheating current is 20A and the wire resistance is 0.5Ω, the heating power is 200W. For a 1.2mm diameter titanium alloy wire, if its end is heated from room temperature (25℃) to a preset preheating temperature of 600℃ (60% of its melting point), approximately 300J of heat is required. Therefore, preheating can be completed by continuously applying current for about 1.5 seconds. The preheating temperature can be preset according to the material properties and subsequent laser process requirements, typically controlled between 50% and 80% of the material's melting point. This effectively reduces the energy input required for laser melting and prevents the wire from overheating and softening, leading to wire blockage. When the preset preheating time is reached or the infrared sensor detects that the end temperature has reached a threshold, the control system determines that preheating is complete, and then the preheating current can be cut off or the next wire feeding and cladding process can proceed.

[0054] In actual preheating, to achieve precise control of the preheating time with high current, a fixed preheating time can be preset in the hot wire drive board or controller. When the enable signal triggers the start of preheating, an internal timer is started simultaneously. After the timer reaches the preset value, the enable signal is automatically cut off or the power switch is directly turned off, ending the preheating. This method is simple to implement and suitable for mass production scenarios where the wire material, diameter, and ambient temperature are stable. Alternatively, an encoder can be coaxially mounted on the wire feeding wheel of the wire feeding mechanism. During preheating, the wire may expand thermally or slightly melt at the ends due to heat, resulting in length changes. The control system reads the wire feeding wheel rotation angle fed back by the encoder in real time and converts it into the actual wire feeding or retraction length. When the cumulative movement of the wire towards the substrate reaches a preset threshold, it is determined that the wire end has sufficiently softened and met the preheating requirements, and the preheating current is immediately cut off. This method can adaptively compensate for the expansion differences of different materials and is particularly suitable for high-precision preheating control.

[0055] As a preferred embodiment, to ensure efficient flow of preheating current, the hot wire driver board may further include a power switch. When the ENABLE terminal is low, a negative or zero voltage is output, the MOSFET is turned off, and the drain-source resistance is extremely high, preventing current from flowing. When the ENABLE terminal goes high, the voltage rises above the MOSFET's turn-on threshold, the MOSFET quickly enters the saturation conduction region, the drain-source resistance drops to the milliohm level, and the power loop closes. However, the amplitude of the large preheating current is preset before processing using a potentiometer, DIP switch, or digital communication interface on the hot wire driver board. When the power switch is turned on, the current value is determined by the power supply voltage and the total circuit resistance; the hot wire driver board typically operates in constant voltage output mode. For more precise current control, a constant current driver board can be used, but its basic enable logic remains unchanged.

[0056] As another preferred embodiment, the amplitudes of the detection current and the preheating current must meet the distinguishability requirements to ensure detection safety and efficient preheating. For the detection current, a constant current of 100mA or less can be used. Taking 100mA as an example, when the equivalent resistance of the wire is 0.5Ω, its Joule heat power P=I²·R=(0.1)²·0.5=0.005W. Even if the resistance reaches 1Ω, the power is only 0.01W. This amount of heat is completely insufficient to raise the temperature of the wire; therefore, the detection circuit will not produce any preheating effect on the wire. Simultaneously, a current value of 100mA is sufficient to overcome the weak resistance caused by oxide films, oil stains, etc., on the contact surface, reliably detecting the contact state. For the preheating current, it can be continuously adjusted within the range of 1A to 100A. The lower limit of this range, for example, 1A, can generate a micro-heating power of 0.1W to 1W when the resistance of a typical wire is 0.1Ω to 1Ω, suitable for slow preheating or extremely fine wires. When R=1Ω, the upper limit, for example, 100A, can generate an instantaneous power of up to 10kW, which can meet the rapid preheating requirements of large-diameter, high-melting-point wires. In practical applications, the specific value of the preheating current is determined by the process database based on the wire material, diameter, and required preheating temperature. This embodiment provides two typical examples:

[0057] One implementation involves using a Φ1.2mm titanium alloy wire with relatively high resistivity, requiring a preheating temperature of approximately 600°C. A preheating current of 30A is set, and considering the equivalent resistance of the wire end is approximately 0.3Ω, the heating power P = 30²·0.3 = 270W. At this power, it takes approximately 3 seconds for the wire end to heat from room temperature to 600°C, after which laser cladding can be performed.

[0058] Another implementation involves using 0.8mm aluminum alloy wire, which has relatively low resistivity, requiring a preheating temperature of approximately 400℃. A preheating current of 10A is set, with an equivalent resistance of approximately 0.2Ω and a heating power of P = 10²·0.2 = 20W. Since aluminum alloy conducts heat quickly and the wire diameter is thin, heating to 400℃ takes approximately 2 seconds. Excessive preheating current could easily cause softening and wire blockage at the ends; therefore, 10A is a preferred choice.

[0059] The preheating current amplitude is calculated by the control system based on a table or empirical formula after the operator inputs the wire parameters through the human-machine interface. This value is then written to the internal register of the hot wire driver board via Modbus communication or an analog signal. Upon receiving the enable signal, the hot wire driver board outputs a large current according to the preset value to complete the preheating process.

[0060] Example 2. This example, based on Example 1 above, further discloses a method for controlling the amplitude of the preheating current and / or the preheating duration. Specifically, it involves adaptive configuration based on at least one of the wire material, diameter, and wire feeding speed.

[0061] like Figure 4 As shown, this embodiment further introduces a PLC, whose IO input is connected to the OUT terminal of the TouchSense board. This terminal outputs a contact signal processed by an operational amplifier. The PLC uses this input signal to determine in real time whether the wire is in contact with the substrate. The PLC's IO output is connected to the ENABLE or similar enable terminal of the TouchSense board. This signal is used to control the opening and closing of the internal detection circuit of the TouchSense board, for example, turning off the constant current source to save energy during non-detection periods. The PLC's IO output is connected to the IN terminal or ENABLE terminal of the hot wire driver board. The PLC can actively send an enable signal to the hot wire driver board according to process requirements, or it can forward the OUT signal from the TouchSense board to the hot wire driver board after processing by the PLC's internal logic; this embodiment does not impose any limitations. The PLC's analog output or communication interface is connected to the current setting terminal of the hot wire driver board, i.e., the 100A port shown in the figure. The PLC calculates the target preheating current value based on parameters such as wire material, diameter, and wire feeding speed. This target value is then written to the hot wire driver board via a 0-10V analog signal or a Modbus digital signal, enabling dynamic setting of the preheating current amplitude. The PLC's power supply is not shown in the diagram, but it can be connected to a 220V power supply or converted via a 24V power module to provide operating power to the PLC.

[0062] One implementation involves matching different preheating currents to the varying resistivity and thermal properties of different materials. For example, for wires with high resistivity and low specific heat capacity, a smaller preheating current and shorter duration are required. For instance, aluminum alloys have a low resistivity, approximately 0.4 × 10⁻⁻⁻⁶. 6 Ω·m, rapid thermal conductivity, requires a relatively large current, such as 30~50A, to overcome heat dissipation. The controller has a built-in database of material resistivity and thermal diffusivity, and calculates the required current based on the Joule heat power demand. A typical relationship is as follows: , where R is calculated from the resistivity of the material and the geometric dimensions of the wire.

[0063] Another implementation involves matching different preheating currents based on the influence of the wire diameter on the cross-sectional area A and the resistance per unit length R. Theoretically, the larger the diameter, the smaller the resistance, i.e., R = ρ·L / A. To achieve the same Joule heat power, since P = I²R, a decrease in R requires a compensation factor of I², necessitating an increase in the preheating current. The PLC calculates the resistance per unit length based on the diameter and sets the current to keep the end-heating power density W / mm³ constant.

[0064] Another implementation involves matching different preheating currents based on the wire feed speed (vfeed). The wire feed speed (vfeed) directly affects the volume of wire entering the molten pool per unit time. The faster the speed, the greater the flow rate of wire requiring preheating; therefore, the preheating current should be increased or the preheating duration extended accordingly, i.e., continuous preheating mode. The controller monitors the wire feed speed fed back via the encoder in real time and dynamically adjusts the preheating current to ensure the wire reaches the target temperature before leaving the contact nozzle. If preheating is completed while the wire is stationary, the wire feed speed is used to determine the waiting time before the next preheating cycle to ensure a match between heat input and wire feed volume.

[0065] It is worth noting that this embodiment provides two preheating modes depending on the wire feeding speed: intermittent preheating mode, suitable for low-speed or dot-matrix wire feeding, and continuous preheating mode, suitable for high-speed continuous wire feeding. Operators can select one according to process requirements, or the controller can automatically switch according to the wire feeding speed.

[0066] The first preferred method is intermittent preheating, also known as static preheating, which is suitable for low wire feeding speeds or lattice processes employing a "wire feed-pause-wire feed" pattern (such as spot welding additive manufacturing of thin-walled parts). Specifically, the wire first contacts the substrate to complete a full preheating cycle. After preheating, it is fed forward at a set speed for cladding. In other words, the wire does not move during the preheating phase, and preheating and wire feeding are separated in time. In this method, the wire feeding speed does not directly change the preheating parameters but is used to determine the interval between two preheating cycles, ensuring that the wire is sufficiently cooled or at the same initial temperature before each static preheating. Its advantages include independently controllable preheating time, precise heat input, and prevention of wire softening and blockage during movement; it is suitable for precision small-size additive manufacturing.

[0067] The second preferred method is continuous preheating, also known as dynamic preheating, suitable for long welds or large-area additive manufacturing processes requiring high wire feed speeds and continuous cladding. Specifically, after the wire contacts the substrate, the preheating current is continuously applied, while the wire feeding mechanism feeds the wire forward at a constant speed (vfeed). The wire end is continuously heated during its movement, reaching the target preheating temperature by the time it leaves the contact nozzle, and then cladding is completed with the laser. In this method, the preheating duration is no longer set separately, but is determined by the time it takes for the wire to travel from the contact nozzle exit to the contact point. Its advantages include no preheating waiting time, high processing efficiency, and real-time linkage between preheating power and wire feed speed, ensuring continuous heat input, making it suitable for high-speed, high-volume additive manufacturing.

[0068] Example 3. Based on Example 1 or 2 above, this example further introduces a real-time contact resistance monitoring and preheating current dynamic adjustment mechanism to achieve stable Joule heat power output.

[0069] During actual preheating, the contact resistance between the filament and the substrate can change due to factors such as surface oxide film, pressure fluctuations, thermal expansion, or fretting. If the preheating current is kept constant, the Joule heat power P will change proportionally with R, leading to unstable filament end temperature and potentially affecting preheating consistency. This embodiment monitors the circuit voltage and current in real time, calculates the contact resistance, and adjusts the preheating current in reverse according to the magnitude of resistance changes to maintain a constant Joule heat power.

[0070] As one implementation method of this embodiment, Figure 5 As shown: This embodiment adds a PoE-enabled Ethernet data acquisition module (hereinafter referred to as the "acquisition module") to the original system. This module is connected to the PoE switch via an Ethernet cable, and the switch provides it with power according to the PoE standard. The acquisition module includes at least two differential analog inputs, with ranges of ±100mV for current sampling and ±50V for voltage sampling. The acquisition module exchanges data in real time with the PLC or host computer through the Ethernet port of the PoE switch.

[0071] like Figure 5 As shown, the voltage between the 100A terminal and the GND terminal of the hot wire driver board is reduced to 0-5V through a voltage divider resistor network and then connected to the VSense terminal of the acquisition module. This signal reflects the total voltage drop U between the wire and the substrate. Simultaneously, a shunt resistor is further connected in series in the 100A output circuit of the hot wire driver board to convert the large current into a millivolt-level voltage signal, which is then connected to another analog input of the acquisition module (not shown separately in the figure, but can be achieved through additional wiring). The acquisition module sends the real-time voltage and current values ​​to the PLC's I / O controller (PLCIO in the figure) via a PoE switch and Ethernet cable using Modbus TCP messages.

[0072] Before preheating begins, the operator sets the target Joule thermal power P via PLC or HMI. target This value is determined by the process database based on the wire material, diameter, and feeding speed. During the preheating process, the PLC operates at a cycle time T. sample =1ms The voltage U and current I are read from the acquisition module via Modbus TCP. The PLC calculates the total loop resistance R in real time. total =U / R. Define the initial total resistance R0 as the resistance value at the first stable sampling point after preheating begins (e.g., the average value within 0.1 seconds after preheating starts). Subsequently, calculate the change amplitude ΔR = |R| at each sampling time. total −R0∣; If ΔR does not exceed the preset threshold δ, for example, δ=0.05Ω, the contact is considered stable and no adjustment is required; if ΔR>δ, the contact resistance is determined to have changed significantly and the preheating current needs to be adjusted.

[0073] During the actual preheating process, the controller adjusts the power P according to the target power. target and the current measured total resistance R total Calculate the required preheating current Then, through the analog output of the PLC, or by writing to the current setting register of the hot wire driver board via Modbus, the preheating current is gradually adjusted from the current value to I. new To avoid splashing or thermal shock caused by sudden current changes, the adjustment process is carried out in steps, for example, each adjustment step is no more than 2A, and the adjustment period is 50ms, until the current reaches the target value.

[0074] This embodiment achieves high-precision remote sampling of voltage and current by adding a PoE-powered Ethernet data acquisition module without increasing the internal complexity of the hot wire driver board. Based on closed-loop adjustment of contact resistance variation, it can adaptively compensate for contact resistance fluctuations caused by thermal expansion, oxide film rupture, vibration, etc., keeping the Joule heat power stable and ensuring consistent wire preheating temperature, thus providing a stable and controllable heat input for subsequent laser cladding. Simultaneously, the PoE power supply simplifies on-site wiring and reduces system costs.

[0075] Example 4. This example further provides a wire feeding control method for laser wire feeding additive manufacturing. Its core lies in dynamically adjusting the laser output power and / or wire feeding speed based on the degree of wire preheating.

[0076] During or after preheating, the filament is fed at a preset feed speed while the laser is activated. This allows the laser spot and the preheated filament end to work together at the processing position, including simultaneous arrival of the filament and laser, filament-first, or laser-first configurations. Throughout this process, the preheating level of the filament is monitored in real time, and the laser output power and / or feed speed are adjusted accordingly to stabilize the cladding process. When the preheated filament reaches the processing position, the laser must be activated at the appropriate time. If the filament is sufficiently preheated, it has stored some heat, so the laser only needs to provide the remaining melting energy; if the preheating is insufficient, the laser needs to provide more energy. In this embodiment, the preheating level is used as an input variable to determine the baseline values ​​for laser power and / or feed speed. The processing position, as referred to herein, is the cladding point specified by the laser, such as the point in front of or at the same location as the filament contact point, where the feed action will move the filament end further to that position.

[0077] One implementation method is as follows Figure 6As shown, when the wire feeding speed is determined by other process requirements and should not be changed, only the laser output power is adjusted: the controller calculates the corresponding laser power based on the preheating degree, such as the preheating energy integral value, by referring to a table or empirical curve. The higher the preheating degree, the lower the laser power; the lower the preheating degree, the higher the laser power. The main purpose of this implementation is to maintain a constant wire feeding speed, but the laser power is adaptively adjusted according to the preheating degree, resulting in a stable molten pool temperature and reduced spatter.

[0078] Specifically, during the wire preheating process, the controller monitors the amplitude and duration of the preheating current in real time and calculates the integrated preheating energy value. This integrated value reflects the total Joule heat absorbed by the wire end, i.e., the degree of preheating, for example, by integrating the square of the current over time or directly accumulating the energizing time. The controller temporarily stores this value in an internal register. When the integrated preheating energy value is 0 (no preheating), the laser power is set to a baseline value P0. When the integrated preheating energy value reaches a certain threshold, such as the amount of heat required to raise the wire to half its melting point, the laser power is reduced to 0.7P0. The higher the degree of preheating, the lower the laser power, but a lower limit should be set to ensure that the wire can still be completely melted.

[0079] Another implementation method is as follows Figure 7 As shown, when the laser is operating at its optimal efficiency point, rated power, or when the light source power is not adjustable, only the wire feed speed is adjusted: the controller determines the wire feed speed based on the preheating level. Higher preheating levels allow for a more appropriate increase in wire feed speed, for example, by 10% to 30%; insufficient preheating reduces the wire feed speed. The change in wire feed speed is achieved by adjusting the rotational speed of the wire feed motor. The main purpose of this implementation is to improve deposition efficiency by matching the heat input to the wire feed amount, while simultaneously avoiding incomplete melting defects caused by cold wire.

[0080] Specifically, similar to the first implementation, the controller first calculates the integral value of preheating energy or the estimated temperature rise based on the amplitude and duration of the preheating current, serving as a measure of the preheating degree. When the preheating degree is 0, the wire feeding speed is taken as a baseline value v0, calibrated by the laser power, wire material, and diameter. When the preheating degree reaches a medium level, the wire feeding speed is increased by 10% to 20%. When the preheating degree is high, the wire feeding speed can be increased to 1.3v0, i.e., an increase of 30%. If the preheating degree is below a certain threshold, the wire feeding speed is reduced to 0.8v0 or lower to prevent cold wire blockage. The controller controls the speed of the wire feeding motor through analog output or pulse direction signal. When the preheating degree is high, the controller increases the motor speed to feed the wire to the processing position faster; when the preheating is insufficient, the motor speed is reduced. The adjustment process adopts a step-by-step method, with each change not exceeding 5mm / s to avoid sudden speed changes that could cause disturbance to the molten pool.

[0081] Another implementation method is as follows Figure 8As shown, the controller can also adjust the laser power and wire feeding speed simultaneously according to the preheating level and preset coordination rules. For example, when the preheating level is high, both the laser power and the wire feeding speed are reduced; when the preheating level is low, both the laser power and the wire feeding speed are increased. The adjustment range is calibrated through process experiments, and a proportional coordination strategy is usually adopted.

[0082] Specifically, the controller not only calculates the integral value of preheating energy, but also optionally incorporates the change in contact resistance or the estimated temperature rise of the wire, forming a comprehensive preheating index H, with a value ranging from 0 to 1, where 0 represents no preheating and 1 represents optimal preheating. A proportional coordination strategy is used as follows: when H=0 (no preheating), the laser power is set to the maximum value Pmax, and the wire feeding speed to the minimum value vmin. When H=0.5, the laser power is set to 0.7Pmax, and the wire feeding speed to vmid. When H=1.0 (optimal preheating), the laser power is set to 0.5Pmax, and the wire feeding speed to vmax. Intermediate values ​​are determined using linear interpolation or piecewise curves. The controller simultaneously sends a power setpoint to the laser and a speed command to the wire feeding motor. To avoid process oscillations caused by simultaneous abrupt changes in both, a strategy of adjusting the laser power first and then the speed, or a strategy of proportional, synchronous, and gradual changes, can be adopted. For example, every 50ms, the laser power can be simultaneously reduced by 5W and the wire feeding speed increased by 1mm / s until the target value is reached.

[0083] In practical applications, the specific values ​​of the three mapping schemes mentioned above need to be calibrated through a small number of process experiments. The experimental method is as follows: under a certain preheating level, different combinations of laser power and wire feed speed are tested, and the set of parameters with the best cladding morphology and the least spatter is selected and entered into the controller database.

[0084] It is worth noting that the wire feeding method in this embodiment can also be matched with the preheating mode described above.

[0085] One implementation method is the intermittent preheating mode described above: First, a complete preheating process is performed, with the preheating level being a fixed value. Based on this, the controller calculates a set of laser power and / or wire feed speed parameters, and then initiates wire feeding and laser operation. This mode is simple to control and suitable for single-pass cladding or dot-matrix processing.

[0086] Specifically, in this embodiment, the preheating level is a fixed value. After the preheating phase ends, the controller records the cumulative preheating energy integral value or temperature rise estimate during the preheating process. Since the preheating process is completely finished and the preheating level no longer changes, the controller calculates the corresponding laser power and / or wire feeding speed parameters in one go, and then starts the wire feeding mechanism and laser to perform cladding processing. This mode is simple to control, requires no real-time dynamic adjustment, and is suitable for applications with high requirements for heat input consistency, such as single-pass cladding, dot matrix processing, and point-by-point additive manufacturing of thin-walled parts.

[0087] Another implementation method is the continuous preheating mode described above: preheating, wire feeding, and laser processing are performed simultaneously. The controller accumulates preheating energy in real time and dynamically adjusts the laser power and / or wire feeding speed. For example, the preheating level is low and the laser power is high when the wire first contacts the weld; as preheating continues, the laser power gradually decreases and the wire feeding speed gradually increases. This mode has a fast response and is suitable for continuous long welds or high-speed additive manufacturing.

[0088] Specifically, such as Figure 9 In the embodiment shown, the specific preheating level is essentially a quantity that changes continuously over time. From the moment the filament contacts the substrate, the preheating current is continuously applied, while the filament feeding mechanism feeds the filament forward at a certain speed, and the laser is also activated sequentially. The controller uses high-frequency sampling to accumulate the preheating energy in real time and dynamically adjusts the laser power and / or the filament feeding speed to maintain dynamic matching among the three throughout the processing. An exemplary control logic is as follows:

[0089] First, at the initial moment: when the wire just touches the substrate, the preheating level is extremely low (preheating energy integral value ≈ 0), the controller is set to a higher laser power (e.g. 100% of the reference value) and a lower wire feeding speed (e.g. 80% of the reference value) to ensure reliable initial fusion.

[0090] Second, the preheating phase: As the preheating current continuously heats the filament, the integral value of the preheating energy gradually increases. Based on the real-time integral value, the controller gradually reduces the laser power according to the preset mapping relationship described above, while gradually increasing the wire feeding speed. For example, the laser power is reduced by 2W and the wire feeding speed is increased by 1mm / s every 50ms.

[0091] Third, the stabilization stage: When the preheating reaches the target value, for example, when the temperature of the wire end stabilizes at 60%~80% of the melting point, the laser power and wire feeding speed also tend to stabilize, and processing continues under the combination of lower laser power and higher wire feeding speed.

[0092] In this embodiment, the laser's activation timing can be flexibly configured according to process requirements to adapt to different materials, structures, and preheating conditions. Specifically, this includes the following three preferred methods:

[0093] The first implementation involves the laser and the wire arriving at the processing position simultaneously: the controller calculates the laser's pre-start time based on the distance of the wire from the conductive nozzle exit to the processing position, the preset wire feeding speed, and the laser transmission and response delay. As the wire begins to feed, the controller starts a timer, and after a delay, issues a laser start command, ensuring that the laser spot and the wire end arrive at the processing position precisely at the same time. This method achieves instantaneous synchronization of energy and material, and is suitable for conventional cladding scenarios.

[0094] The second implementation involves the wire arriving at the processing position before the laser: After calculating the wire arrival time, the controller adds an extra delay Δt = 50~200ms before starting the laser. The wire end first contacts the substrate or the already formed layer, forming physical support and starting preheating, followed by the laser arrival to melt it. This method is suitable for high melting point materials or thick-walled parts, allowing the wire to adhere in advance and dissipate heat through the substrate, avoiding balling at the end.

[0095] The second implementation involves the controller activating the laser before or at the initial stage of wire feeding, allowing the laser spot to irradiate the processing position for a certain duration, such as 100-500 ms, before preheating the substrate or the already formed layer. After preheating, the wire is then fed to the processing position. This method is suitable for easily oxidized materials or dissimilar metal additive manufacturing, as it can remove surface oxide films, increase local temperatures, and improve fusion quality.

[0096] It is worth noting that the three laser initiation timings can be flexibly combined with the intermittent and continuous preheating modes described above to form six preferred solutions. Generally speaking, in the intermittent preheating mode, the wire first contacts the substrate statically, completing full preheating before wire feeding and laser activation. At this point, the preheating process is complete, the wire tip temperature has stabilized, and the choice of laser initiation timing primarily affects the thermal matching at the moment of molten pool formation. In the continuous preheating mode, preheating, wire feeding, and laser activation occur simultaneously, with the wire continuously heated during movement, and the degree of preheating changing continuously over time. The choice of laser initiation timing needs to be synchronized with the dynamic preheating process in real time.

[0097] The first preferred approach is as follows: After intermittent preheating, the controller simultaneously activates the wire feeding mechanism and the laser, ensuring that the wire end and the laser spot arrive at the processing position exactly at the same time via a preset delay. Since the wire has already been preheated to a certain temperature, the laser only needs to provide the remaining melting energy. The main purpose of this approach is to achieve instantaneous synchronization between energy and material; the preheated wire begins to melt the instant the laser arrives, resulting in rapid molten pool formation and a small heat-affected zone. This approach is suitable for conventional metal additive manufacturing, producing a smooth surface of the formed layer.

[0098] The second preferred approach is to first activate the wire feeding mechanism after intermittent preheating, allowing the preheated wire tip to contact the substrate or the already formed layer in advance. Once the wire has stably adhered and slightly dissipated heat, the laser is then activated. This pre-positioning of the wire avoids direct laser irradiation of the substrate, preventing overheating. Simultaneously, the contact dissipation of the wire tip prevents excessive softening and pilling due to excessively high preheating temperatures. This approach is primarily suitable for high-melting-point materials or thick-walled structural components, improving the bonding strength of the cladding layer.

[0099] The third preferred approach is as follows: After intermittent preheating, the laser is first activated, allowing the laser spot to irradiate the processing position for a certain period of time in advance to locally preheat the substrate. Then, the wire feeding mechanism is activated to deliver the preheated wire to the preheated processing position. Because laser preheating can remove the oxide film on the substrate surface and simultaneously increase the local temperature, it reduces the thermal gradient between the wire and the substrate. This approach is primarily suitable for dissimilar metal additive manufacturing or easily oxidized materials, significantly improving metallurgical bonding quality and reducing porosity and cracks.

[0100] The fourth preferred solution is as follows: At the instant the filament contacts the substrate, a continuous preheating current is activated, and simultaneously, the filament feeding mechanism begins feeding the filament at an initial speed. The controller calculates the laser lead based on the real-time filament feeding position, ensuring the laser spot and the filament end arrive at the processing position synchronously. Throughout the processing, the controller accumulates preheating energy in real time and dynamically adjusts the laser power and filament feeding speed, always maintaining a simultaneous arrival time. In this solution, the synchronous and continuous preheating of the filament and laser ensures the filament remains in optimal thermal condition throughout its movement, resulting in a stable molten pool temperature. This approach is suitable for high-speed continuous additive manufacturing, offering high forming efficiency and minimal spatter.

[0101] The fifth preferred solution is as follows: After the filament contacts the substrate, a continuous preheating current is applied, and the filament feeding mechanism starts immediately, but the laser is delayed before starting. During the delay period before laser activation, the filament tip continues to heat up under the action of the preheating current and moves forward, reaching the processing position and contacting the substrate first. After laser activation, the laser spot lags behind the filament tip. In this solution, because the filament arrives first and briefly contacts the substrate, its tip temperature can be slightly stabilized due to heat dissipation from contact, avoiding overheating. At the same time, the preheating current continues heating during the delay period, ensuring that the filament tip remains in a good thermal state. This solution is suitable for materials sensitive to overheating and can reduce the risk of tip melting.

[0102] The sixth preferred solution is as follows: After the wire contacts the substrate, the preheating current is turned on, but the wire feeding mechanism starts with a delay. The laser is started immediately or earlier, so that the laser spot first irradiates the processing position. After the substrate has been preheated for a certain period of time, the wire feeding mechanism starts again, so that the end of the wire is preheated during its movement and then arrives at the processing position that has been preheated by the laser. Because the laser arrives first, it can remove the oxide film at the processing position and raise the local temperature. The preheated wire that is fed in later is more likely to spread and fuse at the higher substrate temperature. This solution is suitable for materials that are difficult to wet, such as highly reflective materials like aluminum and copper, or substrates with poor surface conditions during repair processing, and can improve the adhesion rate between the cladding layer and the substrate.

[0103] Example 5. This example also proposes an additive manufacturing apparatus, which includes a wire feeding mechanism for conveying filament, a laser, a worktable, a controller, a detection circuit, and a heating circuit.

[0104] Specifically, the filament feeding mechanism includes conventional components such as a filament feeding motor, filament feeding rollers, and conductive nozzles. This filament feeding mechanism is existing technology in the additive manufacturing field and will not be elaborated upon here. The laser is used to emit a laser beam to clad the filament and the printing base. Its power, start / stop timing control can be adjusted by external commands. The laser itself is also existing technology, and the specific model and optical path structure can be selected according to processing requirements; in addition, the power of the laser itself can be appropriately reduced after the filament has been preheated. The worktable is used to place the printing base and can be configured as a fixed or servo motor-driven motion platform. The worktable and its driving technology are common knowledge and will not be described in detail. The controller adopts a programmable logic controller, embedded microcontroller, or industrial computer. The controller is connected to the filament feeding mechanism, laser, worktable, and various sensors through an electrical interface and is configured to execute any of the technical solutions in Examples 1 to 4. The detection circuit includes, as shown in... Figure 2 , 4 Or, as shown in Figure 5, the TouchSense board is connected to the filament via a conductive nozzle and the printing base through wires. This circuit applies a small detection current of ≤100mA to determine whether the filament and printing base are in contact, and outputs a contact signal to the controller. The heating circuit includes, as shown in Figure 5... Figure 2 , 4 Alternatively, the hot filament drive board shown in Figure 5 connects the filament to the printing base via wires. This circuit responds to an enable signal from the controller or detection circuit, conducting a preheating current of ≥1A to generate Joule heating using the filament's own resistance.

[0105] Furthermore, the detection circuit and the heating circuit are independently connected to the filament and the printing base, respectively. The controller's input receives the contact signal from the detection circuit, and its output is connected to the enable terminal of the heating circuit, the drive motor of the filament feeding mechanism, the control port of the laser, and the motion controller of the worktable. This additive manufacturing device first monitors the contact state between the filament and the printing base through the detection circuit. After confirming contact, it activates the heating circuit for resistance preheating. During or after preheating, it controls the filament feeding mechanism to deliver the filament and activates the laser. Simultaneously, it dynamically adjusts the laser power and / or filament feeding speed according to the degree of preheating to complete single-layer or multi-layer additive manufacturing.

[0106] All the above embodiments merely illustrate implementation methods for relevant practical applications of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for preheating filament, characterized in that, A current heating circuit is set up, with one electrical end connected to the filament and the other electrical end connected to the printing base. When the filament comes into contact with the printing base, the current heating circuit is turned on, and a preheating current is applied to the filament and the printing base. Joule heat is generated by the resistance of the filament itself to preheat the filament.

2. The method for preheating filaments according to claim 1, characterized in that: One electrical terminal of the current detection circuit is connected to the filament, and the other electrical terminal is connected to the printing base; a detection current is applied to the filament and the printing base through the current detection circuit, and the detection current is continuously applied; When the filament comes into contact with the printing base, the current detection circuit is activated and generates a contact signal; In response to the contact signal, the current heating circuit is turned on.

3. The method for preheating filaments according to claim 2, characterized in that: The detection current is a constant small current; the preheating current is an adjustable large current, and the amplitude of the preheating current is greater than the amplitude of the detection current.

4. The method for preheating filaments according to claim 2, characterized in that: The amplitude of the preheating current and / or the preheating duration are set according to at least one of the material, diameter, and wire feeding speed of the filament.

5. The method for preheating filaments according to claim 1, characterized in that: During the application of the preheating current, the voltage and current of the current heating circuit are monitored in real time, the contact resistance between the filament and the printing base is calculated, and the amplitude of the preheating current is adjusted according to the change in the contact resistance to keep the Joule heat power stable.

6. The method for preheating filaments according to claim 4, characterized in that: The filament is preheated while remaining relatively stationary with the printing base, and then the filament is fed in after preheating. Alternatively, the filament is conveyed forward at a preset speed while maintaining contact with the printing base, and preheating is continuously performed during the conveying process.

7. A wire feeding control method for laser wire feeding additive manufacturing, characterized in that, This includes performing the following steps: The wire is preheated using the wire preheating method described in any one of claims 1-6; The laser is activated to irradiate the end of the preheated filament; the output power of the laser and / or the filament feeding speed are adjusted according to the degree of preheating of the filament.

8. The wire feeding control method according to claim 7, characterized in that: The degree of preheating is determined by any of the following methods: The time integral value of the preheating current, the temperature rise of the filament, or the change in contact resistance between the filament and the printing base; Based on the determined preheating level, adjustment commands are generated for the laser output power and / or the wire feed speed.

9. The wire feeding control method according to claim 7, characterized in that: During or after the preheating process, the filament is fed by the filament feeding mechanism; the timing of laser activation is controlled so that the laser focal point and the end of the filament arrive at the processing position simultaneously, or the end of the filament arrives at the processing position before the laser, or the laser arrives at the processing position before the end of the filament.

10. An additive manufacturing apparatus, characterized in that: The wire feeding control method according to any one of claims 7-9 includes: The components include a filament feeding mechanism for conveying filaments, a laser for emitting laser light, a worktable for placing the printing base, and a controller for performing timing control. The current detection circuit and the current heating circuit connect the filament to the printing base; The controller is configured to execute the wire feeding control method.

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