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ثني المعادن

الوقت المقدر للقراءة: 27 الدقائق

In the process of making sheet metal unfolded drawing correctly, the influence of material thickness should also be considered, that is to say, proper thickness treatment should be carried out. This is because for any sheet metal part, the sheet metal must have thickness, that is, there are inner skin, outer skin and plate thickness center layer. During the processing, they will have different deformation.

As shown , when the sheet metal is bent, the inner skin is shortened due to extrusion and the outer skin is elongated due to stretching. In some cases, the central layer of the sheet thickness will also be deformed, and the length of only one layer of the sheet metal before and after deformation remains unchanged (the neutral layer of the sheet thickness).

Therefore, the position of the neutral layer should be determined when unfolding the blanking, Taking the neutral layer as the standard unfolding length is a problem that must be considered in the unfolding drawing. The corresponding measures to eliminate the influence of plate thickness on the size and shape of components and ensure the processing requirements of sheet metal components are called plate thickness treatment.ثني المعادن

In addition, in the production and processing of unrolled materials and meeting the requirements of the connection and assembly of sheet metal components, machining allowances must also be considered. This is because when the sheet material is cut by gas cutting, due to the need of cutting processing, the machining allowance of the gas cutting gap must be considered in the sheet metal unfolded material, and the riveting, welding and other connection processes of the sheet metal components must be Leave enough connection materials in the unfolded material.

In the actual production and processing, the factors that affect the size of the unfolded blanking material are often multifaceted, not only due to different production equipment and methods, but also due to different processing methods, but the measures to be solved are nothing more than plate thickness treatment and there are two aspects of machining allowance.

How to deal with sheet thickness

Generally, when the accuracy of sheet metal components is not high, the thickness of the sheet with a thickness of less than 1.2mm can be ignored; if the thickness of the sheet is greater than 1.2mm, the sheet will have a certain impact on the size and shape of the workpiece. It must be considered.

Thickness treatment of “curved” shaped components in cross section

When the sheet is bent, due to the compression of the inner skin and the stretching of the outer skin, they all change the original length. Only the length of the neutral layer of the thickness of the plate does not change, but the neutral layer of the same length during bending is affected by many factors. Such as material properties, mold structure, bending methods etc.

Therefore, the bending neutral layer has different positions under different bending methods and different degrees of bending. For a fan gold member with a curved cross section, it is generally considered that r/t ≥3 (where r is the inner angle of the sheet metal bending, and t is the sheet thickness), and the neutral layer of the bending overlaps the center layer of the thickness When, the unfolded size can be calculated according to the length of the central layer of the plate thickness; and when r/t<3, for different bending methods, the bending neutral layer may move inward or outward. For details, see Chapter 5.

Thickness treatment of “bent line” shaped components in cross section

The deformation when the sheet is bent into a broken line shape is different from the deformation when it is bent into an arc shape. As shown in picture, the cross-section is a straight pipe with a square shape. Because the sheet is only sharply bent at the corners, except for the inside In addition to the small change in the length of the skin, the thickness of the central layer and the outer skin have undergone major length changes, so the expanded length of the rectangular section tube should be based on the expanded length of the inner skin. This principle is based on the expansion of the inner skin. The same applies to other components with a broken line cross-section.ثني المعادن

Plate thickness treatment of tapered components

Generally, the height of the central layer of the plate thickness should be taken as the standard when making the unfolded drawing of the tapered sheet metal component.

As shown in Figure 1-3(a), the side surface of the “round sky” component is inclined (all cones are the same), so the edges of the upper and lower mouths are not flat, and the upper and lower mouths are high in outer skin. The lip is low. When making the expanded drawing, the height should be the vertical distance h between the center of the upper and lower plate thickness.

If the plate is not very thick, or trimming will be required in the future, then the total height of the upper and lower edges can be taken; the upper mouth is round Therefore, it is calculated based on the median diameter. Here, the median diameter value is approximately equal to D-t to calculate the expanded graph. The lower mouth is square, so the side length value can be taken to be approximately equal to a-2t to draw the graph ثني المعادن

Plate thickness treatment at the interface of sheet metal components

“Interface” means the junction of different parts of the component. The plate thickness treatment at the interface can be divided into two types : One is no cutting groove ; The other is the groove.

The general guidelines for slab thickness treatment at the interface of intersecting components are : The deployment height of intersecting components , Whether the groove is not , Generally, the size of contact parts shall prevail , If the skin is in contact , The size of the inner skin shall prevail , Contact of the central layer , The size of the center layer shall prevail.

Plate thickness treatment without shoveling groove

As shown in picture, there is no plate thickness treatment at the 90° elbow interface of the welded equal diameter round pipe. It is obvious that not only the angle of the elbow is wrong, but there is also a gap in the middle of the interface (commonly known as lack of meat). ), which not only affects product quality, but also increases the difficulty of welding. Picture shows the situation of the interface after the plate thickness treatment. It can be seen from the figure that the two round pipes are completely suitable at the interface.

On the inner side of the elbow, the outer skin of the round pipe is in contact at A, and the outer side of the elbow is round. The inner skin of the pipe is in contact at four places, and the middle O point can be regarded as the contact of the middle diameter of the round pipe; the natural groove formed by the thickness t of the plate, the groove at A is inside, and the groove at four places is outside.

From the above analysis, it is not difficult to get the following conclusions: for the unfolding height of the circular tube, a is the height of the outer skin of the circular tube, B is the height of the inner skin of the circular tube, and O is the height of the central layer of the plate thickness of the circular tube. Therefore, it is concluded that the plate thickness treatment rules are as follows: 1 ~ 8 bisection points on the cross section, 1, 2 and 8 points are drawn on the outer skin, because they are close to point a, 4, 5 and 6 points are drawn on the inner skin, and 3 and 7 points are drawn on the middle diameter. After drawing in this way, the parallel line method can be used to draw the expanded drawing.ثني المعادن

Below picture shows the treatment of the thickness of the T-shaped three-way component without shoveling the bevel. The inner skin of the branch pipe is in contact with the outer skin of the main pipe. Therefore, the height of each branch in the expanded drawing should be drawn based on the inner skin. The expanded view of the main pipe hole should be drawn based on the outer skin. Only in this way can the interface be tight and seamless.ثني المعادن

Thickness treatment of shovel groove

Generally speaking, only thick steel plates are processed with shovel grooves. The purpose of shovel grooves is not only to facilitate welding and improve the strength of the joint, but also an important way to obtain an anatomist joint. The form of the bevel can be divided into two categories: X-shaped bevel and V-shaped bevel according to the difference in plate thickness and specific construction requirements.ثني المعادن

The X-shaped groove is used for double-sided welding, and the V-shaped groove is used for single-sided welding. Their trimming angle α is generally around 60.

Below picture shows a 90° round pipe elbow. After shoveling into an X-shaped groove, it is obvious that the center layer of the plate thickness is in contact. Therefore, only the center layer of the plate thickness is drawn in the expanded view (the double-dotted line in the figure) That is, the height of the expanded view is handled as the center layer of the plate thickness.

ثني المعادن

The picture shows a square tube elbow at any angle. The thickness of the plate is treated with a V-shaped groove. It can be found that the inner skin is in contact at the interface. Therefore, when making the unfolded drawing, you only need to draw the size of the inner skin.ثني المعادن

Treatment of the inclination of welded joints with unequal plate thickness

In the process of welding and processing sheet metal components with different thicknesses, when the thickness of the thinner plate is t<10mm, and the thickness difference between the two plates exceeds 3mm; or when the thickness of the thinner plate is t>10mm, but the thickness difference between the two plates exceeds the thickness of the thin plate When the thickness is 30% or more than 5mm, the edge of the thin plate should be cut on one or both sides according to the requirements shown in picture, or the edge of the thin plate should be welded out of the bevel by the surfacing method according to the same requirements.ثني المعادن

Thickness processing for non-bending forming

There are two types of common wall thickness treatments for non-bending forming.

  • The thickness occupies the effective size of the component. When the thickness of the sheet material occupies the effective size of the component, then the blanking size of its adjacent components should be reduced accordingly. It shows the non-bending forming, due to the thickness of the plate. Several board thickness treatment situations affected. In the picture, the blanking height dimension h of part number 1 should be equal to B-t2; the width dimension b of part number 2 should be equal to A-2t1; Picture (b) the width dimension b of part number 2 Should be equal to H-2t; Picture (c) The width dimension of part number 2 should be L’, L’ can be obtained by graphic method or calculation method.ثني المعادن
  • Thickness treatment of simple inter-poser When the inter-poser without thickness treatment is placed obliquely in the cylinder , it expands into an ellipse, and its short axis b=Dn, long axis a=Dn/cosɑ. When the inter-poser that has undergone plate thickness treatment is placed obliquely in the cylinder , due to the existence of the plate thickness t, at this time, the short axis b of the unfolded ellipse is still equal to Dn, but the length The axis a’ should conform to the calculation result of the following formula. It shows the comparison of the long axis and short axis of the inter-poser with or without plate thickness processing.ثني المعادن

Determination of machining allowance

In the production process of sheet metal parts, due to the needs of blanking,connection and assembly, in the unfolded drawing of the work, it is often necessary to perform processing, that is, to add a certain amount of trimming allowance. This additional trimming allowance amount is called the machining allowance, and the expanded drawing with the machining allowance is called the expanded material. The expanded material is the final basis for marking and setting out in the production process. The types and determination methods of machining allowance are as follows.

Machining allowance when welding

According to the different welding interface methods, the welding machining allowance is determined as follows.

  • Butt joint as shown in the figure, the machining allowance of sheet Ⅰ and Ⅱ is δ=0ثني المعادن
  • Overlap as shown in the figure, let L be the overlap amount, if A is at the midpoint of L, the machining allowance of sheet material Ⅰ,Ⅱ is δ= L/2ثني المعادن
  • When connecting thin steel plates (1.2~1.5mm) by gas or electric welding, when the butt joint shown in figure (a) is adopted, the machining allowance δ=0, and when connected with figures (b)~(d), the processing The margin δ=5~12mm.
ثني المعادن

Machining allowance when riveting

According to the different riveting forms, the machining allowance of riveting is determined as follows.

  • Connect with splints as shown in the figure, the machining allowance of sheet Ⅰ and Ⅱ δ=0ثني المعادن
  • Lap joint as shown in the figure, suppose the overlap amount is L and A is in the middle, then the machining allowance of sheet material Ⅰ, Ⅱ is δ=L/2ثني المعادن
  • Corner joint as shown in the figure, the machining allowance of sheet I δ=0, then the machining allowance of sheet II δ=L
ثني المعادن

Machining allowance when biting

The bite connection method is to buckle the two ends of the workpiece or the edges of two sheets and press them together to make them into one body. The width of the bite is usually called the single mouth size; it is represented by S.The size of the bite margin is measured by the number of bite width S.The bite width S is related to the plate thickness t, and the relationship can be expressed by the following empirical formula S=(8~12)t In the formula,when t<0.7mm, S should not be less than 6mm.

The bite connection method is mainly suitable for ordinary steel plates with a thickness of less than 1.2mm, aluminum plates with a thickness of less than 1.5mm, and stainless steel plates with a thickness of less than 0.8mm. Different bite forms have different machining allowances. Common bite forms and machining allowances are as follows.

  • The bite shown in flat joint (a) is called a single flat bite. Since A is in the middle of S, the machining allowance of plate I and plate II are equal, δ=1.5S; the bite shown in (b) is also It is called a single flat bite. Since A is on the right of S, the machining allowance of plate I is δ=S, and the machining allowance of plate II is δ=2S; the bite shown in (c) is called a double flat bite, because A The point is on the right of S, so the machining allowance δ of plate I = 2S, and the machining allowance δ of plate II = 3S.ثني المعادن

It can be seen from the figure that the position of point A has a great influence on determining the machining allowance. For example, in (a), if point A is not in the middle of S but at the right end of S, the machining allowance of plate I δ=S, and that of plate II The machining allowance δ=2S, which is different from the original machining allowance.

  • Angle joint bite (a) The bite is called the outer single angle bite, the machining allowance of plate I is δ=2S, and the machining allowance of plate II is δ=S; the bite shown in (b) is called the inner single Angle bite, the machining allowance of plate I δ=2S, the machining allowance of plate II δ=S; the bite shown in (c) is also called the outer single angle bite, the machining allowance of plate I δ=2S+ b, the machining allowance of plate II δ=S+b; the bite shown in (d) is called the joint angle bite, the machining allowance of plate I δ=2S+b, the machining allowance of plate II δ=S, Here b=6~10mm.
ثني المعادن

Machining allowance of round pipe on component edge

The edge of the component is rolled into a round tube for two purposes: one is to increase the rigidity of the component; the other is to avoid the use of flash holes to injure the user. There are two types of coiled tubes: one is hollow coiled tube; the other is coiled wire. As shown in the figure, assuming that the plate thickness is t, the inner diameter (or wire diameter) of the coil is d, and L is the machining allowance of the coil part, then:

L=d/2+2.35(d+t)

In addition, the diameter D of the winding circle should be more than 3 times the plate thickness t.

Machining allowance when welding thick sheet material or section steel

When welding thick plates or sections, it is necessary to reserve (1~5mm) weld seams. At this time, the machining allowance is no longer a positive value but a negative value.

Machining allowance during cutting

When the blank is cut, the blank will shrink due to the influence of the cutting gap. Therefore, the cutting gap should be considered when blanking to leave a machining allowance. The main processing methods for cutting and blanking are gas cutting, plasma cutting, etc. The cutting gap value is shown in the table below.

Material thickness (mm) Flame cutting
(manual/semi-auto) (mm)
Plasma cutting
(manual/semi-auto) (mm)
≤103/29/6
10~304/711/8
30~505/4 14/10
50~656/416/12
65~1308/520/14
130~200 10/624/16

Lofting of sheet metal parts

In various processing procedures of sheet metal parts, lofting is the prerequisite preparation for blanking processing, and it is also the basis for ensuring the correct blanking. The so-called lofting is based on the analysis of the structural characteristics and manufacturing processes of the sheet metal components that need to be processed, and after appropriate processing of the processed components (such as adding a machining allowance, determining the bending radius of the neutral layer of the bending component, etc.)

Carry out necessary calculations (for parts with too complex calculations, it can also be determined through experiments in production) and expansion, so as to obtain all or part of the expansion drawing of parts that are accurately drawn with a 1:1 ratio during the product manufacturing process (The unfolded picture is the process of setting out the picture), unfolding the data, marking or inspecting the template.

In production, drawing the loft drawing and the marking of the fitter are used to collectively refer to the marking. On the surface, the lofting is only the first process of sheet metal processing. In fact, unfolding and lofting are the core of the entire sheet metal processing, which belongs to the production technology preparation of the component, and the sheet metal processing. The various stages of the production process such as blanking, manufacturing, and quality inspection of gold components are closely related. In production, the process of drawing a lofting diagram is conventionally called lofting, and the unfolding material (through the lofting diagram, scribe template, etc.) or the processing of the position to be processed and the operation of the assembly position line will be drawn on the component or blank to be processed It is also called numbering. In fact, from the essence of its operation, lofting, numbering and fitter’s marking are all markings.

Crossed craft symbols

After the parts on the drawing are marked on the steel, this is only a link in the entire manufacturing process of the parts, and various processing is required. In order to express the nature, content and scope of the following processes after marking, various symbols are often marked on the parts underlined by steel. Common process symbols are shown in the table below.

اسمSymbolIllustration
Cut off lineثني المعادنPut a sample punch or slash on the cut line
Processing lineثني المعادنMake a proof on the line, draw a triangle symbol or add words such as “planing edge”
Center lineثني المعادنThe two ends of the line are marked with punches and marks
Symmetry lineثني المعادنIndicates that the part graphics is completely symmetrical to this line
Corner rolling lineثني المعادنMeans to bend steel into a certain angle or right angle
Round rolling lineثني المعادنMeans that the steel plate is bent into a cylindrical shape
(forward rolling or reverse rolling)
Secant lineثني المعادنDivide the middle part

Cut along the outside of the square hole

Cut along the inside of the square hole

Stakeout tools

In addition to the scribe tools introduced before, the stakeout operation may also use the following stakeout tools when processing large parts.

  • The stone pen is usually made of talc, also known as talc pen. The shape of the stone pen is strip and square, as shown in the figure below. Like the marking needle, the stone pen is also a tool for marking on metal materials. Because the lines can withstand a certain degree of rain erosion, and generally do not sample after marking, it is easy to use, but the marking accuracy is not as high as the marking needle. It is often used for marking large-size steel plates and profiles with low accuracy requirements.ثني المعادن

The method of using the stone pen is the same as that of the drawing needle, but before use, the end should be sharpened to keep the width of the drawn line within 0.5mm or even less. The grindstone pen is usually carried out on an ordinary transparent glass sheet with a certain degree of welding spatter adhered.ثني المعادن

  • Powder line When the length of the drawn line exceeds the length of the steel ruler, the powder line can be used to draw the line. The method of scribed is to pass the powder line through the chalk or powder bag to powder, hold the powder line by hand at both ends of the line to be drawn, and tighten the powder line, and then use your thumb and forefinger in front of the powder line. Pinch the powder line, lift it up vertically, and then quickly loosen it. Then, when the tension-ed powder line is lifted, it will rebound to the steel plate to produce a line that needs to be drawn. When the pink line is longer, two people are required to draw the line.

The chalk is usually pressed directly on the chalk line or with the chalk bag. Generally, the powder bag can be modified by bicycle inner tube, and the effective length is 100 ~ 150 mm. The tightening degree of the tie line should be such that there is no obvious resistance to the reciprocating drawing line and no powder leakage. The binding place at both ends should be easy to untie, so as to replace the powder line material.

Pay attention to the following points when using powder line:

  1. In order to ensure the accuracy of the ejected powder thread, the thickness of the powder thread should generally be controlled within 0.8~1 mm. The surface of the powder thread should not be smooth, otherwise it will affect the powdering effect of the powder thread.
  2. During the powdering process, the powder thread must not shake to avoid the powder that has been applied to the powder thread from falling off. This should be especially noticed when playing a long straight line.
  3. When the powder line is used, the powder line and the steel plate must not be wet or wet, and the surface of the powder steel plate should be kept clean.
  4. When springing the powder line in the open, pay attention to the influence of the wind on the powder line, and do not bend the powder line that has not been bounced due to the action of the wind.
  5. The steel plate of the spring line should be straight to avoid the convexity in the middle part, otherwise, after the powder line is ejected, the spring line rebound position will deviate due to the height of the middle part, causing the ejected powder line to be a broken line. This should be paid special attention to the coiled plate after uncoiling.
  6. It is best to use ink thread for stainless steel, aluminum and other materials to facilitate observation and identification.
  7. Because the powder line is scribed by the powder attached to the steel plate, it is not resistant to rain washing, and even can be lost overnight or in dew, heavy fog, etc.Therefore, after the powder line is finished, follow-up processing should be carried out immediately, otherwise , You need to stamp the pink line or re-tracing with a stone pen.ثني المعادن
  • Steel wire When the required straight line is long, it is difficult to use the powder line to stretch the straight line, and the steel wire scribed method can be used. When the steel wire is drawn in a straight line, the steel plate should be straight as a whole, and the degree of local distortion should be strictly controlled to avoid affecting the measurement accuracy of the square ruler. See the figure below for details.ثني المعادن
  • Curve ruler After unfolding the oblique section of cylinder and cone, the curve produced is not a circle. Therefore, it is inconvenient to use a circle to plan out. Although the dot method can be used, it is more troublesome. For this reason, the curve ruler shown in the figure below can be used. The curve ruler is to obtain different curves by adjusting the bolts. When using, the hinged base of the front of the rod and the fixed connection of the elastic steel plate should be adjusted. After adjustment, riveting can be used. After riveting, the adjusted curvature can be stabilized, but it should not be used. Welding, avoid the softening and deformation of the elastic steel plate due to welding heat, and the loss of elasticity, which will affect the use effect.ثني المعادن
  • Template for components with complex shapes, in order to cut materials accurately, conveniently and quickly, templates are generally used. The main types of samples are: blanking samples, forming samples and inspection samples. The sample plate is used when the production and processing batches are large and the number of single pieces is large according to the specific technical requirements of the process drawing. Generally, it is made of 0.5~2 mm thin steel plate (galvanized sheet, tinplate) hard paper, plywood, plastic board can also be used when the requirements are not high. A model is a model drawn according to a 1:1 ratio that reflects the size and real graphics between parts or components. After the sample is made, the drawing number, name, number of pieces, inventory number, etc. must be marked on the sample, and it should be checked and verified by professional inspectors before it can be put into use to ensure the correctness of the stakeout and at the same time facilitate the management of the sample.

Usually the shape of the processed parts is different, the purpose of the produced template is also different. The following table lists the names and uses of several commonly used templates.

Template nameدور
Plane templateScribe and cut the material on a plane on the sheet and profile
Curved templateCheck the curvature of various arcs and circles
Incision templateScribe standards for various angle steels, channel steel cuts, and bends
Expand templateThe actual length and shape of the unfolded parts of various sheets and profiles
Hole line templateDetermine the position of all the holes of the component
Bending templateInspection standards for various bending parts and tire mold parts

The manufacturing tolerance of the template is generally 1/4 to 1/3 of the tolerance of the processed component, and generally should not be less than the dimensional tolerance shown in the following table.

Size nameTolerance
Tolerance between adjacent center lines±0.2
Distance tolerance between plate and adjacent hole center line±0.5
Diagonal tolerance±1.0
Length and width tolerance±0.5
Angle tolerance of template±20′

فكرة واحدة حول "Several Methods of Plate Thickness Treatment"

  1. يقول Mahfuzulo Rajabov:

    Thanks for your share. It is very good

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