1: What is a drawing?

Answer: A drawing that accurately expresses the shape, size, and technical requirements of an object.

2: What is a projection drawing?

Answer: It is a method of obtaining a graphic representation on a predetermined plane by a set of rays passing through an object.

3: How many classifications are there for projection methods?

Answer: They can be divided into central projection and parallel projection. Parallel projection is further divided into orthographic projection and oblique projection.

4: What is a sectional view?

Answer: A graphic representation obtained on a projection plane by a set of parallel rays passing through an object.

5: What are the three basic views of object projection?

Answer: They are the front view, top view, and left side view.

6: What are the projection rules for three views?

Answer: The front and top views align in length; the front and left views align in height; the top and left views are equal in width.

7: What are the physical properties of metals?

Answer: These include density, melting point, thermal expansion, electrical conductivity, and thermal conductivity.

8: What is the melting point?

Answer: It is the temperature at which a metal changes from a solid to a liquid state.

9: What are the chemical properties of metals?

Answer: This refers to the ability of a metal material to resist erosion by surrounding chemical media at room temperature or high temperature.

10: What are the chemical properties included?

Answer: These include oxidation resistance and corrosion resistance.

11: What is oxidation resistance?

Answer: The ability to resist oxidation at room temperature or high temperature.

12: What is corrosion resistance?

Answer: The ability to resist corrosion by water vapor and other substances at high temperatures.

13: What are mechanical properties?

Answer: This refers to the ability of a metal material to resist external forces.

14: What are the mechanical properties included?

Answer: These include strength, hardness, plasticity, toughness, and fatigue strength.

15: What is deformation?

Answer: This refers to the change in shape and size of a metal material under external force.

16: What are the types of deformation in metal materials?

Answer: These can be divided into tension, compression, bending, torsion, and shear.

17: What is the elastic limit?

Answer: This refers to the maximum force a material can withstand in the elastic stage.

18: What is yield strength?

Answer: This refers to the maximum stress a material can withstand when yielding occurs.

19: What is tensile strength?

Answer: This refers to the maximum stress a material can withstand before breaking.

20: What is plasticity?

Answer: This refers to the property of a material that allows it to deform easily without breaking.

21: What is the hardness of a material?

Answer: This refers to the ability of a material to resist other objects pressing into its surface.

22: What are the methods for expressing hardness?

Answer: There are Brinell hardness, Rockwell hardness, and Vickers hardness.

23: What are the technological properties of metal materials?

Answer: This refers to whether the properties of metal materials are easy to process and form.

24: What are the technological properties of metals included?

Answer: These include castability, weldability, forgeability, machinability, and heat treatability.

25: What is alloy steel?

Answer: Steel in which some alloying elements are intentionally added to improve certain mechanical properties based on carbon steel.

26: How many categories can alloy steel be divided into?

Answer: It can be divided into alloy structural steel, alloy tool steel, and special-purpose steel.

27: What is cast iron?

Answer: An iron-carbon alloy with a carbon content greater than 2.11% is called cast iron.

28: How many categories can cast iron be divided into?

Answer: White cast iron, gray cast iron, ductile iron, alloy cast iron, malleable cast iron.

29: What are the simple identification methods for steel?

Answer: Spark identification method, fracture identification method, color marking identification method.

30: What are the microstructure of alloys?

Answer: Solid solution, metallic compound, mechanical mixture.

31: What is the critical point?

Answer: The temperature at which a metal undergoes a structural change.

32: What is quenching?

Answer: Heating the steel to an appropriate temperature above the critical temperature, holding it for a period of time, and then rapidly cooling it to obtain a martensitic structure.

33: What is annealing?

Answer: Heat the steel to a certain temperature, hold it for a certain time, and then slowly cool it to room temperature.

34: What is hardenability?

Answer: The ability of steel to obtain a certain temperature of hardened layer after quenching under certain conditions.

35: What is tempering?

Answer: A method in which steel is heated to a certain temperature below Ac1, held for a certain time, and then cooled to room temperature after the organizational transformation is completed.

36: What is normalizing?

Answer: It is a heat treatment method that combines quenching and high-temperature tempering.

37: What is the purpose of carburizing?

Answer: It is to allow active carbon atoms to penetrate the surface of the steel to increase the surface carbon content of the steel.

38: What is hot hardness?

Answer: It is the ability of steel to maintain hardness at high temperatures.

39: What are the categories of aluminum alloys?

Answer: They can be divided into wrought aluminum alloys and casting aluminum alloys.

40: What are the categories of copper alloys?

Answer: They can be divided into bronze, copper, and brass.

41: What are the three types of sparks in spark testing?

Answer: Straight sparks, pointed sparks, and foxtail sparks.

42: What are the functions of welding rods?

Answer: They conduct current and provide filler metal to the weld pool.

43: What are the forces acting on the molten droplets?

Answer: Gravity, surface tension, electromagnetic compression force, spot pressure, plasma flow force, and arc gas blowing force.

44: What are the defects that are easily produced when gas welding cast iron?

Answer: The main defects include white spots, cracks, pores, and refractory oxides.

45: What is weldability?

Answer: It refers to the adaptability of metal materials to welding processing, mainly referring to the ease of obtaining high-quality welded joints under certain welding process conditions.

46: What is the main reason for the generation of stress and deformation during welding?

Answer: Uneven heating and cooling.

47: What is primary crystallization?

Answer: The process by which the metal in the welding pool transforms from a liquid state to a solid state.

48: What are the common types of steel with special properties?

Answer: Stainless steel, heat-resistant steel, and corrosion-resistant steel.

49: What are the categories of titanium alloys?

Answer: Type α, Type β, and Type α+β.

50: How many forms of riveting are there generally?

Answer: Mainly lap joint, corner joint, and butt joint.

51: What are the steps in hot riveting?

Answer: Fastening and repairing rivet holes of the riveted parts, heating the rivets, riveting and piercing, heading, and riveting.

52: What is threaded connection?

Answer: It is a detachable fixed connection using threaded parts.

53: What are the common forms of threaded connections?

Answer: Bolt connection, double-headed bolt connection, and screw connection.

54: How many types of washers are there? What is their function?

Answer: They can be divided into three types: general gasket washers, washers to prevent loosening, and special-purpose washers. Their function is to increase the supporting surface, cover larger holes, prevent damage to the surface of parts, and provide a flat surface.

55: What are the washers that prevent loosening?

Answer: Spring washers, round nut lock washers, single-ear lock washers, and double-ear lock washers.

56: What is the important characteristic of a tangent plane?

Answer: All points on the same element line have the same tangent plane.

57: What is a developable surface?

Answer: If a three-dimensional surface can be completely flattened onto a plane without tearing or wrinkling, this surface is called a developable surface.

58: What is a non-developable surface?

Answer: If a three-dimensional surface cannot be naturally flattened onto a plane, it is called a non-developable surface.

59: What are the characteristics of the unfolding method?

Answer: It is to first divide the surface of the part into many small planes according to the nature of the three-dimensional surface, that is, to use these small planes to approximate the surface of the three-dimensional object.

60: What is the principle of the parallel line unfolding method?

Answer: The surface of the three-dimensional object is regarded as being composed of countless mutually parallel element lines. The small area enclosed by two adjacent element lines and their end lines is taken as a plane. As long as the actual size of each small plane is drawn in order on the plane, the unfolded drawing is obtained.

61: What is the principle of radial unfolding?

Answer: The conical surface is divided into several triangles with a common vertex using radial lines. After calculating their actual sizes, they are drawn in the same plane in the form of radial lines in order to obtain the unfolded drawing of the conical surface.

62: What are the steps for unfolding a triangle?

Answer: Draw the necessary views of the component, divide the surface of the object into triangles, find the actual length of each side of the triangle, and draw the unfolded view in the order of the triangles.

63: What is the neutral layer?

Answer: When the sheet metal is bent, the outer layer material is stretched and lengthened, and the inner layer material is compressed and shortened. There is a fiber layer between the elongation and shortening whose length remains unchanged, which is called the neutral layer.

64: Why is plate thickness processing necessary?

Answer: When the plate thickness is greater than 1.5mm and the part size requires accuracy, plate thickness processing must be performed. Otherwise, inaccurate part dimensions, poor quality, or even scrap will result.

65: What are the principles of plate thickness processing?

Answer: The unfolding length is based on the dimensions of the neutral layer of the component, which is obtained through calculation; the curve height in the unfolded view is based on the height at the contact point of the component.

66: What is the main content of plate thickness processing?

Answer: Determine the neutral layer of the bent part and eliminate plate thickness interference.

67: What is blanking? What are the methods?

Answer: Blanking is the process of separating parts or blanks from raw materials. The methods include: shearing and gas cutting.

68: What are the characteristics of shearing processing?

Answer: High productivity, smooth section, and ability to cut plates and various profiles.

69: What is the essence of shearing?

Answer: It is to apply shearing force to the material through upper and lower cutting blades, causing the material to undergo shearing deformation and finally fracture and separate.

70: What are the main measures to improve the quality of the sheared surface?

Answer: Increase the blade strength, choose a reasonable blade gap, and press the material tightly against the lower blade.

71: What is the effect of the shearing front angle on shearing?

Answer: The size of the front angle not only affects the shearing force and shearing quality, but also directly affects the shearing strength.

72: What is the function of the shearing back angle?

Answer: Its function is to reduce friction between the material and the cutting blade. The back angle is usually 1.5～3°.

73: What is the effect of shearing on material properties?

Answer: It can cause material deformation and work hardening at the edges of the material.

74: What are the characteristics of gas cutting?

Answer: Simple equipment, low cost, high production efficiency, and the ability to cut in various spatial positions.

75: What are the stages of the oxygen-acetylene cutting process?

Answer: It consists of three stages: metal preheating, combustion, and oxide removal.

76: What conditions must be met for metal gas cutting?

Answer: (1) The ignition point of the metal must be lower than its melting point. (2) The melting point of the oxide generated by combustion should be lower than that of the metal itself. (3) The combustion of the metal must release a large amount of heat, and the thermal conductivity of the metal itself must be low.

77: Why can't cast iron be gas cut?

Answer: Because its ignition point is higher than its melting point, and it produces high-melting-point SiO2, and the viscosity of the oxide is large and the fluidity is poor, it is difficult for the high-speed airflow to blow it away.

78: What should be noted when using oxygen cylinders?

Answer: Placement must be stable and reliable; at least 5m away from other fire sources; avoid collisions; sun protection in summer; strictly prohibit fire roasting in winter, use hot water to thaw.

79: What is the function of the backfire arrester?

Answer: To intercept the backfire airflow and ensure the safety of the acetylene generator.

80: What is the function of the pressure regulator?

Answer: Pressure reduction and stabilization.

81: What are the equipment preparations before gas cutting?

Answer: Site preparation and inspection of the oxygen flow line (i.e., wind line).

82: What is the preheating flame efficiency?

Answer: It is expressed in units of combustible gas consumption per hour.

83: How many types of preheating flames are there?

Answer: Neutral flame, carburizing flame, and oxidizing flame.

84: What is backfire?

Answer: During cutting, due to overheating of the nozzle or splashing of iron oxide slag, the nozzle is blocked or the acetylene supply is insufficient, causing a backfire with a bang in the nozzle.

85: What measures should be taken in case of backfire?

Answer: Quickly close the preheating oxygen and cutting oxygen valves to prevent oxygen from backflowing into the acetylene pipe and extinguish the backfire.

86: What is plasma arc cutting?

Answer: Using a high-temperature, high-speed plasma arc as a heat source, the metal or non-metal to be cut is locally melted, and at the same time, the melted metal or non-metal is blown away by a high-speed airflow to form a narrow kerf. This is the process.

87: What are the advantages of plasma arc cutting?

Answer: It can cut stainless steel, aluminum, cast iron, and other refractory metals or non-metals; the cutting speed is fast, and the deformation is small; the cost is relatively low.

88: What does part pre-processing include?

Answer: It includes riveting, welding, and drilling, tapping, threading, filing, chiseling, chamfering, and grooving performed on parts to prepare for assembly.

89: What is drilling?

Answer: To machine holes in solid materials using a drill bit.

90: What are the different types of drill bits?

Answer: There are twist drills, flat drills, center drills, etc.

91: What is the function of the shank of a drill bit?

Answer: To clamp and transmit the required torque and axial force during drilling.

92: What is the function of the flat tail in a tapered shank drill bit?

Answer: To increase the transmitted torque and prevent the drill bit from being knocked out of the spindle hole or bushing.

93: What is the function of the guiding part in a drill bit?

Answer: During cutting, it maintains the straight drilling direction of the drill bit. It also has the function of smoothing the hole wall and serves as a backup for the cutting part.

94: What adverse phenomena may occur when the hole is about to be drilled through?

Answer: When the drill bit just drills through the workpiece, the axial resistance suddenly decreases. Due to the clearance and elastic deformation of the drilling machine feed mechanism, the drill bit will automatically cut in with a large feed rate, resulting in drill bit breakage or reduced hole quality.

95: What is the function of cutting fluid during drilling?

Answer: To reduce friction, lower drill bit resistance and cutting temperature, and improve the cutting ability of the drill bit and the surface quality of the hole wall.

96: What is cutting amount?

Answer: It is the general term for cutting speed, feed rate, and cutting depth.

97: What is grinding?

Answer: It is a method of machining the surface of a workpiece using a grinding wheel.

98: What is unfolding?

Answer: The process of sequentially unfolding the surface or part of a metal structure according to its actual shape and size onto a plane is called unfolding.

99: How many methods are there for drawing unfolded drawings?

Answer: There are parallel line method, triangle method, and radial line method.

100: What are the unfolding conditions for the parallel line method?

Answer: The element lines on the surface of the component are parallel to each other, and their true lengths are reflected on the projection plane.

101: What does plate thickness processing include?

Answer: Determine the neutral layer of the bent part and eliminate plate thickness interference.

102: What factors affect the change of the neutral layer position in plate thickness?

Answer: It is related to the bending radius and plate thickness.

103: What is the general principle of plate thickness processing for intersecting parts?

Answer: The unfolding length is based on the neutral layer size of the component, and the curve height in the unfolded drawing is based on the height at the contact point of the component.

104: What is the main content of layout?

Answer: Plate thickness processing, unfolding drawing, and making material templates based on the made component unfolded drawing.

105 What are the commonly used shearing equipment for riveting?

Answer: There are gantry shears, oblique shears, circular shears, and combined punching and shearing machines.

106: According to the number and arrangement of the rollers, rolling machines can be divided into which types?

Answer: They are divided into symmetrical three-roll, asymmetrical three-roll, and four-roll types.

107: According to the structure, punching dies can be divided into which types?

Answer: They are divided into simple dies, dies with guide posts, and compound dies.

108: What are the structural characteristics of a compound punching die?

It has a convex and concave die that acts as both a feeding punch and a punching die.

109: What is punching force?

Answer: It refers to the maximum resistance of the material to the die during punching.

110: What are the stages of the sheet metal separation deformation process during punching?

Answer: It is divided into elastic deformation stage, plastic deformation stage, and shear stage.

111: What is the minimum bending radius?

Answer: The minimum value of the bending radius that can be bent without damaging the material.

112: What are the common methods to reduce the rebound of press-bent parts?

Answer: There are die correction method and pressure correction method.

113: What is the purpose of using a blank holder during stretching?

Answer: It is mainly to prevent wrinkling of the edges of the stretched part.

114: What is the function of the crank connecting rod mechanism of a crank press?

Answer: It not only converts rotary motion into reciprocating linear motion, but also amplifies force.

115: What does manual sheet metal forming include?

Answer: It includes bending, arching, edge pulling, edge rolling, seam biting, and straightening.

116: What are the functions of the unfolded template?

Answer: It can be used for material numbering, making separation dies, and making milling templates.

117: What is edge thinning? What are the forming methods?

Answer: The operation of stretching and thinning the edge material of the deformed part during forming is called edge thinning. The forming methods include thinning and stretching.

118: What is edge pulling?

Answer: Using the methods of edge bending and edge closing, the edge of the sheet metal is processed into a curved workpiece.

119: What is edge rolling?

Answer: To increase the rigidity and strength of the edge of the workpiece, the edge of the workpiece is curled, which is called edge rolling.

120: What is a bite seam?

Answer: The edges of two sheets or the folded edges of one sheet are interlocked and pressed together, which is called a bite seam.

121: What is plate thickness processing?

Answer: The method used to eliminate the influence of plate thickness on the shape and size of the development drawing.

122: What are the general steps for calculating the unfolded length of a bent part?

Answer: Divide the bent part into straight segments and arc segments; calculate the length of each segment separately; add the calculated lengths together.

123: Under what circumstances is the cutting of steel sections applied?

Answer: Angle steel, channel steel, and I-beam are bent into corners.

124: What are the stages of the entire blanking process?

Answer: It is divided into three stages: elastic deformation stage; plastic deformation stage; shearing stage.

125: What is blanking?

Answer: A stamping process that uses a blanking die to separate part of a sheet from another part along a certain closed line.

126: How many types of bolt connections are there?

Answer: There are two types: connections that bear axial tensile loads; connections that bear transverse loads.

127: What are the anti-loosening measures for bolted joints?

Answer: Increase friction; mechanical anti-loosening.

128: What are the methods of mechanical anti-loosening?

Answer: Cotter pin; lock washer; stop washer; wire rope.

129: What is a welding arc?

Answer: A strong and persistent discharge phenomenon produced in the gaseous medium between two electrodes.

130: What are the components of a welding arc?

Answer: It consists of a cathode region; an anode region and an arc column.

131: What are the three directions of movement of the welding rod?

Answer: Move towards the weld pool; move along the welding direction; make lateral swing.

132: How many types of welds can be classified according to spatial position?

Answer: They are divided into flat welding, vertical welding, horizontal welding, and overhead welding.

133: What are the characteristics of the intersection line?

Answer: It is both the common line and the boundary line of the surfaces of the two bodies; it is always closed in space.

134: What is an intersection line?

Answer: A component formed by the intersection of two or more geometric bodies.

135: What are the factors affecting blanking quality?

Answer: Die gap; misalignment of punch and die centerlines; wear and dulling of the working edge of the die.

136: What are the general principles of die design?

Answer: On the premise of ensuring stamping quality, strive to make the designed die easy to manufacture and simple in process

low cost and easy to use.

137: What is the purpose of calculating the rolling force?

Answer: It is to correctly select the rolling equipment.

138: What is free bending?

Answer: When bending is completed, the punch, blank, and die are in contact with each other and no longer impact.

139: What is correction bending?

Answer: It refers to the punch, blank, and die, after the three are in contact, there is another impact, which plays a correction role on the bent part.

140: What defects are prone to occur when pressing the head?

Answer: Wrinkling and bulging; straight edge scratches and pits; surface microcracks; longitudinal tearing; skew; oval; inconsistent diameter.

141: What is expanding connection?

Answer: A connection method that uses the deformation of pipes and pipe plates to achieve sealing and fastening.

142: What is the purpose of calculating the blanking force?

Answer: To reasonably select the equipment capacity and design the die.

143: What methods can be used to reduce the blanking force?

Answer: Oblique blade die; stepped die; heated die.

144: What is the purpose of calculating the bending force?

Answer: To select the bending press and design the die.

145: What does the degree of tensile deformation include?

Answer: It includes: the degree of die contact; the degree of allowable deformation of the material.

146: How to determine the number of drawing operations of a workpiece?

Answer: Based on the maximum deformation amount of the drawn workpiece and the elongation rate of the material.

147: How to determine the drawing coefficient?

Answer: It depends on the material properties, drawing angle, friction coefficient and whether pre-drawing is used.

148: Which materials are not suitable for cold straightening?

Answer: High carbon steel, high alloy steel, cast iron and other brittle materials.

149: What is the straightening sequence when angle steel has complex deformation?

Answer: Straighten the twist first, then the bend, and finally the corner deformation.

150: What are the causes of deformation of steel structures?

Answer: One is caused by external forces, and the other is caused by internal stress.

151: What are the methods to eliminate welding residual stress?

Answer: Overall high-temperature tempering; local high-temperature tempering; temperature difference stretching method; mechanical stretching method; vibration method.

152: What is overall welding deformation?

Answer: It refers to the change in shape and size of the entire structure.

153: What is the hammer spreading method?

Answer: The fiber structure of the metal sheet is elongated by hammering.

154: How is the length of the rivet rod determined?

Answer: It is determined based on factors such as the total thickness of the connected parts, the gap between the rivet hole and the rivet rod diameter, and the riveting process.

155: What is the reason for the rivet head being too small after riveting?

Answer: Because the rivet rod is too short or the hole diameter is too large.

156: According to the different states of the metal during welding, how many types can it be divided into?

Answer: It can be divided into three types: fusion welding, pressure welding, and brazing.

157: What is fusion welding?

Answer: A method that uses local heating to melt the welding joint.

158: What is clamping?

Answer: It is to use external force to fix the positioned parts so that their positions remain unchanged during processing.

159: What is the six-point positioning rule?

Answer: Using six positioning points to limit the freedom of the part in space to completely determine the spatial position of the part.

160: What is relative parallelism?

Answer: It refers to the parallelism of the line or surface being measured on the part relative to the measuring reference line or surface.

161: What is relative perpendicularity?

Answer: It refers to the degree of perpendicularity of the line or surface being measured on the part relative to the measuring reference line or surface.

162: What are the types of tooling used in assembly?

Answer: Assembly tools; assembly fixtures; assembly lifting devices.

163: What are the commonly used assembly lifting devices?

Answer: There are steel wire ropes, iron chains, hand winches, and special lifting devices.

164: How many guiding forms are there for blanking dies?

Answer: There are two forms: guide posts, bushings, and guide plates.

165: How many parts are there in a blanking die?

Answer: It consists of the working part, material positioning part, unloading part, and die base.

166: What is the function of the gap in the drawing die?

Answer: Reduce friction between the material and the die and control the flow of the material in the die cavity.

167: How many types of bite seams can be divided into according to their structure?

Answer: They can be divided into vertical single bite seam; vertical double bite seam; horizontal flat bite seam; and various corner bite seams.

168: What is the reason for the rebound of the bent part after the external force is removed?

Answer: Because when bending manually, the outer surface of the sheet metal is under tension and the inner surface is under compression, so rebound occurs.

169: How to obtain cold camber and hot camber?

Answer: Cold camber is obtained by shrinking the edges of the sheet metal and expanding the middle of the sheet metal, while hot camber is obtained by heating the sheet metal to cause shrinkage.

170: How many methods are there for edge trimming?

Answer: There are two methods: one is to trim the edges with general-purpose tools, and the other is to trim the edges with a die.

171: What is edge trimming?

Answer: Edge trimming is to first wrinkle the sheet metal, and then flatten the wrinkled part while preventing it from stretching and recovering. In this way, the sheet metal is shortened, and the thickness is increased.

172; What is the basic principle of edge trimming?

Answer: The principle is that the forming of convex curved edge workpieces mainly involves the contraction and thickening of the outer edge material of the flat edge, forcing the upright edge to be curved.

173: What is the purpose of straightening?

Answer: It is to apply external force or local heating to shorten the longer fibers and lengthen the shorter fibers, so that the fibers in each layer tend to be consistent to achieve the purpose of straightening.

174: What is the principle of flame straightening?

Answer: It uses the deformation generated by local heating of the metal to offset the original deformation, achieving the purpose of straightening.

175: What are the factors affecting the effect of flame straightening?

Answer: The rigidity of the workpiece; heating position; flame heat; heating area; and cooling method.

176: What are the heating methods for flame straightening?

Answer: There are point-shaped, line-shaped, and triangular heating.

177: What are the factors that determine the process allowance?

Answer: The influence of layout errors; the influence of errors during parts processing; the influence of assembly errors; the influence of welding deformation; the influence of flame straightening.

178: How many categories can templates be divided into according to their uses?

Answer: They can be divided into material templates, forming templates, positioning templates, and sample rods.

179: What are the methods for drawing templates?

Answer: There are two methods: direct layout method and transition layout method.

180: How is the layout datum line generally selected?

Answer: Using two mutually perpendicular lines or planes; using two centerlines as datum lines; using a plane and a centerline as datum.

181: What is the allowable error in layout?

Answer: In the layout process, due to the influence of factors such as the accuracy of layout tools and instruments and the level of operation, the actual sample drawing will have certain dimensional deviations. Controlling this deviation within a certain range is called the allowable error in layout.

182: What does structural layout include?

Answer: Determine the joining positions and connection methods of each part; make necessary changes according to the actual production and processing capabilities; calculate or measure the actual length of parts and the actual shape of planar parts; design dies or jigs.

183: What are the methods for finding the actual length of a straight segment?

Answer: Rotation method; right-angled triangle method; plane change method; branch line method.

184: What is the drawing rule for finding the actual length of a line segment using the right-angled triangle method?

Answer: It uses the projection of the line segment on any projection plane as one leg of a right-angled triangle, and uses the projection length of the corresponding projection on the axis perpendicular to the plane as the other leg. The hypotenuse is the actual length of the line segment.

185: What is the rotation method for finding the actual length?

Answer: It is to rotate a line segment in a general spatial position around a fixed axis to become parallel lines. Then, the projection of the line on the projection plane parallel to it reflects the actual length.

186: What are the methods for finding the actual length of a curve?

Answer: There are plane change method; unfolding method.

187: What is the plane change method?

Answer: It is to set a new projection plane parallel to the curve, then the projection of the curve on this plane reflects the actual length.

188: What is the unfolding method?

Answer: It is to straighten a length in the curve view while keeping the height in the other view unchanged. The resulting unfolded line is the required length.

189: What are the basic characteristics of the intersection line?

Answer: The intersection line must be a closed plane figure enclosed by straight lines or curves; the intersection line is the common line of the intersecting plane and the surface of the solid, formed by the set of points that are both on the intersecting plane and on the surface of the solid.

190: What are the methods for finding the intersection line of a solid?

Answer: Edge-face method; edge-line method.

191: What are the methods for finding the intersection line of a curved surface solid?

Answer: Generatrix method and latitude line method.

192: What are the characteristics of the intersection line?

Answer: First, it is the common line of the surfaces of the two intersecting solids, and also the boundary line of the two intersecting solids; second, the intersection lines are all closed.

193: What is the essence of finding the intersection line?

Answer: It is to find a certain number of common points on the surfaces of the two solids, and connecting these common points in order is the required line.

194: What is the selection principle for the method of finding the intersection line?

Answer: When using the generatrix method to find the intersection line, at least one projection of the intersection line should be known; when using the auxiliary plane method to find the intersection line, the intersection line should be the simplest geometric figure; the spherical method is only applicable to the intersection of solids of revolution whose axes intersect.

195: Under what conditions is the intersection line a plane curve? The front projection of the curve is the intersection of two straight lines?

Answer: When two solids of revolution that are externally tangent to the same sphere intersect, their intersection line is a plane curve. At this time, when the axes of the two solids of revolution are both parallel to their basic projection plane, the projection of the intersection line on this plane is the intersection of two straight lines.

196: What is a ruled surface?

Answer: It is a surface formed by a straight line as a generatrix.

197: What are the characteristics of a cylindrical surface?

Answer: All generatrices are parallel to each other; when a cylindrical surface is intersected by mutually parallel planes, the cross-sectional figures are the same.

198: What are the characteristics of a conical surface?

Answer: All generatrices intersect at one point; when a conical surface is intersected by mutually parallel planes, the cross-sectional figures are similar; the intersection line passing through the apex of the cone is a triangle.

199: During stretching, into how many stages is the plastic deformation process of the material divided?

Answer: Material bending; material stretching deformation; supplementary stretching.

200: What is stretching?

Answer: It is a forming method in which a sheet metal is plastically deformed under tensile stress to form an ideal curved surface, and overcomes the rebound.

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Address:No. 102-1, Building 1, No. 50, Yingbin Avenue West, Xiquan Street, Huadu District, Guangzhou