Precautions for stamping design and metal stamping
(1) Stamping material selection and component layout
(1) Material selection
Choose the right material for a variety of applications, depending on your requirements for thickness, strength and elasticity.
(2) Layout of stamping parts
We strive to optimize the design, rational layout, and adopt a lean approach.
(3) Stamp shape
When meeting product requirements, it should be as simple and symmetrical as possible to minimize waste.
(B) Partial thickness and ribs
To guarantee the life of the mold, the quality of the product and the order of the materials on the market, the thickness of the stamping material should be within the following range.
Iron / Stainless Steel: 0.1 ≤ t ≤ 3 (mm)
Copper / Aluminum: 0.1 ≤ t ≤ 4 (mm)
(2) Reinforcement bar
For larger or longer sheet metal parts, the ribs should be properly designed to increase their strength.
In addition, bending is done at the corners of the bend. You can strengthen the ribs.
Strengthen the role of the ribs
Bending is a forming method that relies on the flow of the material, not the separation of the material, and uses bending to change the angle or shape. Most of the parts that need to be formed can be realized by a mold on a conventional press or can be formed by a special device such as a bending machine.
During molding, the material is bent and deformed, and the deformation region is mainly concentrated in the abc region in the following figure. Metals are affected by tensile and stress, and this process can be divided into elastic and plastic deformation stages.
Elastic deformation stage: In the initial stage of molding, the bending force is not large, and the inner and outer layers of the material are elastically deformed under tensile stress without reaching the shrinkage limit to the elastic limit (Fig. A).
Plastic deformation stage: As the bending force continues to increase, the radius of curvature of the material decreases. The inner and outer layers of the material go from the elastic deformation stage to the plastic deformation stage. Next, the plastic deformation zone gradually expands and deforms from the inner and outer layers of the material to the center of the material thickness, and shifts from elastic deformation to plastic deformation (Fig. bc).
Elastic deformation transforms into plastic deformation
(1) General bending type
To extend the life of the mold, the parts are designed to use rounded corners as much as possible.
(2) Bending radius
During the bending process, the inner layer is compressed and the outer layer is stretched. If the R angle is too large or too small, it is not appropriate. If it is too big, it will bounce off. If it’s too small, it will break. As bending continues to improve, many manufacturers can now achieve zero R angles.
(3) Curved straight edge height
When bent at a 90 ° angle, the height of the outer straight edge of the curved fillet area is H 2 2 to ensure its quality.
Height of curved straight edge
(4) Avoid bending on the diagonal side
Prevents cracks and deformation when the side surface (trapezoid) is bent. The design should either hold the groove or change the root to a trapezoid. Groove width K ≧ 2t, groove depth L ≧ t + R + K / 2.
Bending causes cracks and deformation
(5) U bend
In a U-shaped curved member, the lengths of the two curved sides are preferably equal so that they do not move to one side when bent. If not allowed, process positioning holes can be set.
(6) Secure sufficient arc space
<There is a residual arc that passes through the B plane even after the R is bent, but it is necessary to perform ≥R to avoid the remaining arc.
(7) Preliminary incision
Pre-cuts must be designed to prevent rounded corners from being pressed and wrinkled during bending after extrusion.
(1) Minimum pitch diameter and minimum square hole side length
(2) Hole spacing, hole margin, hole bending distance
The above distances are usually C ≥ 3t
(3) Principle of punching gap
Punching should avoid sharp corners as much as possible. Sharp square shapes tend to shorten the life of the mold, and sharp corners are prone to cracking. Therefore, the product design is rounded as much as possible.
(4) Cantilever or groove structure / protrusion or recess
The shape of the blank portion should be as simple as possible to avoid excessive length of the cantilever groove on the blank portion.
General steel A ≥ 1.5 tons, alloy steel ≥ 2 tons, brass or aluminum ≥ 1.2 tons.
(5) Normal self-tapping screw bottom hole, flange hole diameter, flange height
(5) Calculation of punching pressure
F = L t S * 1.3
F = cutting pressure
L = Shear plane boundary
t = material thickness
S = Shear strength of punching shear material (kgf / mm²)
EG: If the material is SPCC, the sheet shear strength is 35kgf / mm² and the minimum shear force is:
F = L t S * 1.3 = [(100 + 50) * 2 + (80 + 30) * 2] * 2.0 * 35 * 1.3 = 47320kgf
Punching pressure calculation
(6) Punching part and burr
(1) Punched part
After the plate is cut by the die, the cross section has two states: a smooth shear surface (bright band) and a shear tear section (section band).
In terms of technical requirements, general drawings rarely specify requirements for punching a cutting surface. Few precision parts specify the range of bright bands.
A-Smooth cut surface (bright band)
B-Tear surface (section belt)
a –Cross section angle
C –Bali height
Punching section and burr
Pay attention to the direction of Bali so as not to hurt people. During the process, burrs can be removed by the imaging process.
(3) Bali height
If the design does not specify trimming requirements, it is typically controlled by the following heights:
Copper / Aluminum: ≤12% t
Iron material: ≤10% t
Stainless steel: ≤8% t
(9) Connection of stamping parts
Spot welding (resistance welding), arc welding, gas shield welding (CO2, Ar), laser welding, gas welding, etc.
(2) Rivet nut
Common rivet nuts are rivet nut columns, rivet nuts, rivet nuts, rivet nuts, and floating rivet nuts.
The main factors that affect the quality of rivets are the characteristics of the board, the size of the drill holes, and the method of riveting.
Therefore, keep the following in mind when using rivet nuts:
a) Do not install steel or stainless steel riveting fasteners before anodizing or surface treating the aluminum sheet.
b) The pressure on the same line is too high. The extruded material does not have a flow position and generates a large stress to bend the work piece in an arc shape.
c) Make sure the surface of the metal plate is plated and attach the rivet fasteners.
d) M5, M6, M8 and M10 nuts are usually spot welded. Nuts that are too large usually require higher strength and can be used for arc welding. M4 (including M4) uses rivet nuts whenever possible. For plated parts, screw nuts can be used.
E) Rivet quality It should be noted that the rivet nut is larger than the bending deformation area at the distance of the bending edge, to ensure that the rivet nut is on the curved edge, from the center of the rivet nut. The inner folded end of the distance L must be larger than the caulking nut, the sum of the radius of the outer cylinder and the inner radius of the bend, ie L> D / 2 + river
(3) Protruding welding nut / spot welding nut
Protruding nuts (spot welded nuts) are widely used in the design of sheet metal parts. It is recommended to use a self-aligned welded hex nut GB / T 13681-92 when welding.
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