The automatic torch height control or (THC) is one of the most important elements of the mechanized shape cutter. But it is also the piece of equipment on the cutting machine most likely to be misused, nonfunctional, or even missing. In many fabrication shops you will see the torch operator manually driving the torch up and down while cutting—his eye on the torch and his thumb on a toggle switch. The THC is either not working properly or the operator has not been trained on how to use the equipment. In either case the shop is not getting the most out of its cutting operation.
There are a variety of torch height controls, or "standoff controls," on the market. Each of these automatic THCs has a variety of functions and features. But all use the same basic elements to control position of the torch relative to the material being cut. This "torch to work" distance or "standoff" is critical to both cut quality and parts life.
Elements of the THC
Motor-driven torch positioner. This device moves the torch up and down in response to signals from the control console. Screw drive, rack and pinion, and belt driven mechanisms are used to translate motion.
Control console. This is the brain of the system. It receives input commands from the remote control, sends output commands to the torch positioner, and monitors position feedback and voltage signals.
Plasma system interface. This device usually consists of a voltage divider card that is mounted inside the plasma power supply. The voltage divider card monitors power supply voltage during cutting. It "divides" the voltage signal and sends a smaller signal voltage to the control console.
Remote control. The remote control is the HMI, or human machine interface. This is where the operator sets two critical cutting parameters: initial height and arc voltage. It may be located inside the CNC control or in a separate remote box.
The difference between IHS (initial height sensing) and voltage setting is very important to understand and is often confused.
IHS is an adjustable parameter that determines the height at which the torch will fire and begin piercing through the plate. In order to set the initial height (also called retract distance) the THC must first find the position of the plate. A variety of schemes are used for sensing the plate from simple mechanical devices, to motor stall technology, proximity sensors, and electrical circuits that sense nozzle or shield contact. Regardless of the method used, the most important thing is that the torch finds the plate and accurately retracts to the proper pierce height, whether on thick plate or thin, rusty plate or clean, above water or below.
Figure 1
Correct pierce height is essential. If the torch pierces too low the consumable parts will be damaged. This is the number one cause of premature parts and torch failures (see Fig. 1). If it attempts to pierce too high, the arc will not transfer, causing a misfire. The rule of thumb is to pierce at 150-200 percent of the cut height. Pierce high; cut low.
Torch to Work distance
Torch to Work Distance distance, or standoff, during the cutting process is adjusted by monitoring and controlling the arc voltage. Note that arc voltage is the same thing as power supply output voltage. Plasma power supplies are a current source—they generate a very steady operating current when the torch is cutting.Voltage, on the other hand, varies depending on the distance between the cathode (the electrode in the torch) and the anode (the material being cut). Voltage is directly proportional to resistance (Ohms Law states that V=I*R). The resistance in the arc is a function of the distance. When the torch to work distance increases the voltage goes up; when the torch-to-work decreases the voltage goes down.
The torch height control uses arc voltage to maintain a consistent distance from the plate while the torch is cutting. This allows the system to maintain proper torch height regardless of variations in the material, or flatness of the cutting bed. The operator sets the arc voltage on the remote control according to the cut charts in the plasma system's operations manual. This voltage setting is usually between 100 and 200 VDC.
After the torch height control has completed initial height sensing and the torch has pierced the plate, motion of the cutting machine is enabled and the torch begins to move. Once the cutting begins, the THC starts sampling arc voltage from the power supply and comparing it to the target voltage set by the operator. It adjusts the torch up or down to maintain that target voltage.
Figure 2
Figure 3
Each voltage setting corresponds to a specific height that optimizes the arc characteristics for a clean, straight cut. Torch height has the greatest affect on bevel angle of the plasma cut piece. Setting the voltage too high results in more material being removed from the top of the kerf than the bottom. This causes excessive top rounding and positive bevel (see
ควบคุมความสูงอัตโนมัติไฟฉายหรือ (THC) เป็นหนึ่งในองค์ประกอบที่สำคัญที่สุดของเครื่องตัดรูปทรงยาน แต่ก็เป็นชิ้นส่วนของอุปกรณ์ในเครื่องตัดสามารถนำไปใช้ รุ่น หรือหายไปได้ ในร้านผลิต คุณจะเห็นผู้ประกอบการไฟฉายด้วยตนเองขับรถไฟฉายขึ้นลงในขณะที่ตัด — เขาตาไฟฉายและนิ้วหัวแม่มือของเขาบนสวิตช์ THC อาจทำงานไม่ถูกต้อง หรือตัวดำเนินการไม่ได้รับการฝึกอบรมวิธีการใช้อุปกรณ์ กรณีใด ไม่ได้ประโยชน์จากการตัดมีความหลากหลายของการควบคุมความสูงของหัวเชื่อม หรือ "ควบคุมขัดแย้ง ในตลาด ความหลากหลายของฟังก์ชั่นและคุณสมบัติแต่ละของ THCs เหล่านี้โดยอัตโนมัติได้ แต่ทั้งหมดใช้องค์ประกอบพื้นฐานเดียวกันเพื่อควบคุมตำแหน่งของหัวเมื่อเทียบกับวัสดุถูกตัด ระยะ "ตะเกียงไฟการทำงาน" หรือ "ขัดแย้ง" นี้เป็นสิ่งสำคัญการตัดคุณภาพและอายุการใช้งานของชิ้นส่วนองค์ประกอบของ THCวางเครื่องยนต์ในการขับเคลื่อนมอเตอร์ไฟฉาย อุปกรณ์นี้ย้ายไฟฉายขึ้นลงในการตอบสนองสัญญาณจากคอนโซลควบคุม ไดรฟ์สกรู บังคับ และสายพานขับเคลื่อนกลไกจะใช้การเคลื่อนไหวการควบคุมคอนโซล นี้เป็นสมองของระบบ มันได้รับสัญญาณคำสั่งจากรีโมทคอนโทรล ส่งคำสั่งออกไปวางเครื่องยนต์ไฟฉาย และตรวจสอบสัญญาณแรงและผลป้อนกลับตำแหน่งPlasma system interface. This device usually consists of a voltage divider card that is mounted inside the plasma power supply. The voltage divider card monitors power supply voltage during cutting. It "divides" the voltage signal and sends a smaller signal voltage to the control console.Remote control. The remote control is the HMI, or human machine interface. This is where the operator sets two critical cutting parameters: initial height and arc voltage. It may be located inside the CNC control or in a separate remote box.The difference between IHS (initial height sensing) and voltage setting is very important to understand and is often confused.IHS is an adjustable parameter that determines the height at which the torch will fire and begin piercing through the plate. In order to set the initial height (also called retract distance) the THC must first find the position of the plate. A variety of schemes are used for sensing the plate from simple mechanical devices, to motor stall technology, proximity sensors, and electrical circuits that sense nozzle or shield contact. Regardless of the method used, the most important thing is that the torch finds the plate and accurately retracts to the proper pierce height, whether on thick plate or thin, rusty plate or clean, above water or below.Figure 1Correct pierce height is essential. If the torch pierces too low the consumable parts will be damaged. This is the number one cause of premature parts and torch failures (see Fig. 1). If it attempts to pierce too high, the arc will not transfer, causing a misfire. The rule of thumb is to pierce at 150-200 percent of the cut height. Pierce high; cut low.Torch to Work distanceTorch to Work Distance distance, or standoff, during the cutting process is adjusted by monitoring and controlling the arc voltage. Note that arc voltage is the same thing as power supply output voltage. Plasma power supplies are a current source—they generate a very steady operating current when the torch is cutting.Voltage, on the other hand, varies depending on the distance between the cathode (the electrode in the torch) and the anode (the material being cut). Voltage is directly proportional to resistance (Ohms Law states that V=I*R). The resistance in the arc is a function of the distance. When the torch to work distance increases the voltage goes up; when the torch-to-work decreases the voltage goes down.The torch height control uses arc voltage to maintain a consistent distance from the plate while the torch is cutting. This allows the system to maintain proper torch height regardless of variations in the material, or flatness of the cutting bed. The operator sets the arc voltage on the remote control according to the cut charts in the plasma system's operations manual. This voltage setting is usually between 100 and 200 VDC.After the torch height control has completed initial height sensing and the torch has pierced the plate, motion of the cutting machine is enabled and the torch begins to move. Once the cutting begins, the THC starts sampling arc voltage from the power supply and comparing it to the target voltage set by the operator. It adjusts the torch up or down to maintain that target voltage.Figure 2 Figure 3 Each voltage setting corresponds to a specific height that optimizes the arc characteristics for a clean, straight cut. Torch height has the greatest affect on bevel angle of the plasma cut piece. Setting the voltage too high results in more material being removed from the top of the kerf than the bottom. This causes excessive top rounding and positive bevel (see
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