Exercises in Welding Process and Equipment --- Part 4: Cutting Process and Equipment ---

Transcription

1 JICA_OHJI Exercises in Welding Process and Equipment --- Part 4: Cutting Process and Equipment --- Takayoshi OHJI Professor Emeritus, Osaka University Dr. of Engineering VIRTUAL WELD CO.,LTD OK 0912 Classification of cutting processes Many cutting processes are used in industry to cut structural materials. The processes are classified into two types, i.e. thermal cutting and non-thermal cutting processes. In the thermal cutting process, the work-piece is heated and melted locally and the molten metal is blown out and removed from the cutting zone by a high speed gas flow. Gas cutting, powder cutting (Use of thermal energy produced by oxidative reaction) Thermal cutting Plasma cutting (Use of thermal energy produced by arc discharge; Oxidative reaction is also accompanied) Laser cutting (Use of thermal energy of light; Oxidative reaction is also accompanied) Cutting processes Wire-cut discharge cutting (Use of thermal energy of discharge) Non-thermal cutting Water-jet cutting (Use of the kinetic energy of water and hard micro-particles) Mechanical cutting (e.g. sawing machine) (Use of mechanical energy) Classification of cutting processes [Japan Welding Society, Advanced Welding & Joining Technology, Sanpo-pub. 2005] OK

2 Ex. Oxy-fuel gas cutting The figure shows schematically oxy-fuel gas cutting process. Complete the figure with the appropriate words in the list. Gases Cutting direction Work-piece Preheated zone Reaction zone List of words: a.drag line b.cutting tip c.molten pool d.preheating gas flame e.shielding gas f.slag g.filler wire h.cutting oxygen stream Oxy-fuel gas cutting 2,948 2,721 3,043 2, Oxyacetylene flame Preheating gas Cutting tip Cutting oxygen stream Preheating flame Drag line Cutting oxygen Cutting direction Fe+O 2 /2 FeO+ O kJ 2Fe+3O +3O2/2 Fe 2 O kJ 3Fe+2O +2O2 Fe3O4+1,120 20kJ Steel plate Preheated zone Reaction zone Slag Chemical reaction in gas cutting 2

3 Ex. Cutting process Why is the flame (oxy-fuel gas) cutting process difficult to apply to stainless steels and high alloy of steel? Ex. Laser cutting process The figure shows schematically laser cutting process. Complete the figure with the appropriate words in the list. Cooling water Assist gas Cutting direction W: Thickness : t Workpiece List of words: a.plasma stream b.laser beam c.molten pool d.kerf width f.focusing lens g.shielding gas h.reflecting mirror 3

4 Plasma cutting process In plasma cutting, the arc energy, constricted by the nozzle, is concentrated to melt the material locally, and then the molten part is removed by a high speed gas flow to cut the material. The plasma cutting system, similar to plasma arc welding system, consists of plasma torch, power sources and high-frequency generator, as shown in the figure. As to the electrode material, tungsten is used when the plasma gas is non-oxygenated, and zirconium or hafnium embedded cupper sheath is used when the plasma gas is oxygenated. Electrode Plasma gas Plasma arc Power source Pilot arc power source High frequency generator Liner (gas distributor) Nozzle (tip) Arc Current passage Cutting workpiece Ex. Cutting process Pick out at least three (3) items totally among the advantages and disadvantages of the plasma cutting process, comparing to the flame (oxy-fuel gas) cutting process. 4

5 Ex. Thermal cutting process One of the following sentences is correct. Find the correct explanation in the following sentences and circle its symbol. (a)the oxygen-gas flame cutting process can be applied to the cutting of aluminum alloys. (b)the laser cutting process is difficult to apply to the cutting of thin plate stainless steel. (c)the oxygen-gas flame cutting is applied to the cutting of mild steel over 25 mm in thickness. (d)compared with the plasma cutting process, a high speed cutting of thin mild steel plate is possible in the oxygen-gas flame cutting process. (e)the ultrasonic gas flow is obtained by using the straight nozzle in the oxygen-gas flame cutting process. Ex. Straight nozzle and Divergent nozzle Explain briefly the technical term straight nozzle and divergent nozzle in oxy-fuel gas cutting. OK

6 Straight nozzle and Divergent nozzle In order to improve the gas cutting speed and the quality of cut-surface, a high purity and high speed oxygen (99.5% or higher) jet is necessary. In oxy-fuel gas cutting, two types of nozzle are used in industry, as shown in the figure. The straight nozzle has a simple shape but is not applicable to high-speed cutting because the velocity of gas flow cannot be increased much. Nevertheless, this type of nozzle offers easier maintenance, control, and handling. By using the divergent nozzle, the stream of gas can flow expanding towards the exit of the nozzle; hence the velocity of oxygen gas flow can be increased up to a supersonic speed; this type of nozzle is applied to a high-speed automatic cutting. (a) Straight nozzle (b) Divergent nozzle Cutting nozzles in oxy-fuel gas cutting Ex. Abrasive cutting method Explain briefly the technical term abrasive cutting method in water-jet cutting. OK

7 Water jet cutting process In water jet cutting, a high pressure water jet, approximately MPa, is applied to cut the materials. The water jet cutting method is classified into two types i.e. straight water jet method and abrasive-jet method as shown in the figure.water jet cutting can be applied to almost every material including papers, rubbers, and metals. In abrasive-type water jet cutting, the material is abraded by the collision of the abrasive in the water jet stream. this method is used for cutting metals and is suitable for cutting combined materials such as reinforced concrete. High pressure water High pressure water Water nozzle Water jet Abrasive Mixing chamber Abrasive nozzle Jet stream Jet stream with abrasive (a) Straight water jet method (b) Abrasive-jet method Typical water jet cutting torches [Japan Welding Society, Advanced Welding & Joining Technology, Sanpo-pub. 2005] Ex. Cutting process Next sentences describe the thermal cutting processes. Select one (1) or two (2) appropriate word(s) for each among the words in the (a) to (d) below, and put a circle on its alphabetical letter(s). (1) The following plate materials can be cut by flame (oxy-fuel gas) cutting. (a) Low alloy steel (b) Stainless steel (c) Aluminum alloy (d) Copper alloy (2) The following cutting processes can be applied for the cutting of thin concrete plate. (a) Flame (oxy-fuel gas) cutting (b) Plasma cutting of transfer type (c) Plasma cutting of non-transfer type (d) Powder cutting (3) The following gases are used as the plasma gas for plasma cutting process. (a) Air (b) Argon (c) Acetylene (d) Propane (4) The following gasses are used as the assist gas for laser cutting process. (a) Air (b) Nitrogen (c) Acetylene (d) Propane JWES