![Controlling Wrinkling in Metal Stamping Best Practices Revealed](https://www.machinemfg.com/wp-content/uploads/2023/12/Controlling-Wrinkling-in-Metal-Stamping-Best-Practices-Revealed.jpg)
Have you ever wondered about the fascinating world of metal stamping? In this blog post, we’ll embark on an exciting journey to explore the intricacies of this essential manufacturing process. As an experienced mechanical engineer, I’ll guide you through the key concepts, sharing valuable insights and real-world examples. Get ready to discover how metal stamping shapes our everyday lives and learn the secrets behind its remarkable efficiency and versatility.
Stamping definition
What is stamping?
The definition of stamping: at normal temperature, a metal (or non-metal) sheet is pressed on a stamping press machine by a stamping die to cause separation or plastic deformation, thereby obtaining parts having a certain shape, size and performance.
From the concept of stamping:
(1) Stamping is carried out at room temperature, that is, it does not require heating, so it is called cold stamping.
(2) The objects of stamping processing are all sheets, so it is also called sheet metal stamping.
(3) Stamping is done by equipment and molds. It needs three elements: punch (equipment), mold, and raw materials.
(4) Stamping is one of the basic forms of plastic deformation.
Metal stamping characteristics and applications
(1) High productivity, simple operation, and easy mechanization and automation.
(2) High dimensional accuracy and good interchangeability.
(3) The material utilization rate is high, generally up to 70%~85%, and some up to 95%.
(4) Shape-complex parts that are difficult to machine or cannot be machined by other machining methods, such as thin-shell deep-drawing parts, are available.
(5) Parts with light weight, good rigidity and high strength can be obtained.
(6) No heating is required, energy can be saved, and the surface quality is good.
(7) When the mass is produced, the product cost is low.
It can be seen that stamping can combine high quality, high efficiency, low energy consumption and low cost, which is incomparable with other processing methods.
Therefore, the application of stamping is very extensive. For example, in the automobile and tractor industries, stamping parts account for 60%~70%, instruments and meters account for 60~70%, and including other various stainless steel tableware in daily life.
From fine electronic components, instrument pointers to heavy-duty car covers and girders, as well as aircraft skins, stamping is required.
Disadvantages of stamping
The mold manufacturing cycle is long and the cost is high. Because it uses traditional processing methods and means and traditional mold materials
However, with the advent of advanced mold processing technology and non-traditional mold materials, this shortcoming can be gradually overcome.
Such as:
In short, the mold industry is a country’s basic industry, the level of mold design and mold manufacturing has become a measure of the level of product manufacturing in a country.
Developed countries attach great importance to the development of molds.
Japan believes that “mold is the driving force for entering a wealthy society”;
Germany: “the emperor in the metal processing industry”;
Romania: “the mold is Golden Touch”; the mold is considered to be a stone in the international arena industry.
However, the molds here also include molds, forging dies, die-casting dies, rubber molds, food molds, building materials molds, etc., but currently the cold dies and plastic molds are the most widely used, each accounting for about 40%.
(1)Separation process
During stamping, the material to be processed is deformed by external force.
When the shear stress of the material in the deformation zone reaches the shear strength of the material, the material is sheared and separated to form a part of a certain shape and size.
The separation process mainly includes cutting, punching, blanking, notching, slicing etc.
The separation process is indicated as below:
Separation occurs but does not change the shape of the space.
Table 1-1 Separation process
(2)Metal forming process
During stamping, the material under the action of the external force, the equivalent stress of the material in the deformation zone reaches the yield limit σs of the material, but does not reach the strength limit σb, so that the material only plastically deforms, thus obtaining parts of certain shape and size.
The forming process mainly includes bending, deep drawing, turning, shrinking, bulging, etc.
The forming process is shown as follows:
Only change the shape of the blank, no separation occurs.
Table 1-2 Forming process
Basic requirements for stamping on sheets
Satisfying the performance requirements is the first, and meets the stamping process requirements as much as possible while meeting the performance requirements.
1.3.1 Process requirements for stamping materials
1.Stamping forming performance
Stamping forming performance refers to the ability of the sheet to adapt to the stamping process.
Two kinds of instability:
The former is like the necking phenomenon in the low carbon steel tensile test, and the latter is the instability phenomenon of the pressure bar.
Thus, there is a forming limit, which is divided into an overall forming limit and a local forming limit. The higher the forming limit, the better the press forming performance.
How to measure the stamping forming performance of the sheet?
(1) Crack resistance refers to the ability of a sheet to resist damage during deformation.
(2) Pasteability refers to the ability of the sheet to conform to the shape of the mold during the press forming process.
(3) Shapeability refers to the ability of a part to retain its shape in the mold after demolding.
The stamping forming properties of the sheet can be measured by the mechanical properties of the sheet. Mechanical properties can be obtained through experiments.
Sheet metal forming performance test method:
(1) Direct test method
Like cone cup test(GB/T 15825.6-2008)
(2) Indirect test method
Such as tensile test of low carbon steel, etc.
Mechanical indicators affecting press forming properties
(1) Total elongation δ and uniform elongation δb
δ is good → Allows for large plastic deformation
(2) Yield ratio σs /σb
σs/σb is small → good crack resistance, shape fixing, and good moldability
(3) Modulus of elasticity E
Large elastic modulus E → good shape
(4) Hardening index n
n is large → not easy to crack
(5) Plastic strain ratio γ
γ = εb /εt is big → Good resistance to cracking
(6) Plastic strain specific anisotropy coefficient
Δγ =(γ0 +γ90 – 2γ45 )/2 is big → The more different the anisotropy
1.3.2 Common stamping materials and cutting methods
A.Common stamping materials
Related reading: Ferrous vs Non-ferrous Metals
Metal sheet specifications: steel strip, steel plate, slit steel strip, etc.
Size range of steel plates and strips (GB/T708-2006)
1) The nominal thickness of steel plate and steel strip (including slitting steel strip) is between 0.3mm and 4.0mm, and the steel plate and steel with nominal thickness below 1mm have any size in multiples of 0.05mm; the nominal thickness is above 1mm. Steel plates and steel are available in any size in multiples of 0.1 mm.
2) The nominal width of steel plates and steel strips is between 600mm and 2050mm, and there are any sizes in multiples of 10mm.
3) The nominal length of the steel plate is between 1000mm and 6000mm, and any size in multiples of 50.
4) According to the requirements of the purchaser, steel plates and strips of other sizes can be supplied through negotiation between the supplier and the buyer.
(1) Shearing machine cutting
(2) Disc shearing
(3) Other cutting methods
Selection principle of stamping equipment:
Stamping equipment type:
Working principle and main components of crank press
(1) Working mechanism
Crank and link mechanism: The crank link mechanism is composed of a crankshaft, a connecting rod and a slider. The length of the connecting rod can be adjusted to suit different sizes of molds.
Motor, belt, flywheel, gear, etc.
(3) Operating system
Air distribution system, clutches, brakes, electrical control boxes, etc.
(4) Supporting parts
Body: open, closed
(5) Auxiliary system
Pneumatic system, lubrication system
(6) Attachment
Press model and technical parameters
(1) Model
1) Forging machine type:
2) Crank press code description JB23-63A
(2) Technical parameters
Different materials have different plasticity under the same deformation condition, and the same material will have different plasticity under different deformation conditions.
3 main strain states:
9 types of principal stress states:
Now, let’s dive into the following four different stamping processes.