Factors that affect the spinning process and results include equipment, process devices, blanks, machines and other processes. The effects and influences are mutual. With other factors basically unchanged, the selection of process parameters directly determines the deformation process of the material during spinning, and also affects the quality of the spinning workpiece, the amount of spinning force energy, and the efficiency of spinning production.
There are many process factors that affect spinning deformation, mainly the following:
- Spinning direction
- Wall thickness thinning rate
- Spindle or workpiece speed
- Wheel feed ratio or feed speed
- The distance between the wheel and the mandrel
- Working wheel radius and working angle
- Wheel motion trajectory and spinning passes
- Spinning temperature
- Inter-wheel spacing of multi-wheel spinning
On the premise of ensuring the quality of spinning parts, the selection of process parameters is conducive to improving the production efficiency of spinning, the dimensional accuracy and surface quality of spinning parts, and reducing the process cost of spinning. Give examples of the following influencing factors:
1. Determination of spinning direction
In forward rotation, the material flow direction is consistent with the moving direction of the rotating wheel, and the product precision is high. Parts with a step or a bottom at one end can be made, but the length of the product is consistent with the mold.
With anti-rotation, the material flow direction is opposite to the moving direction of the rotating wheel. For tubular parts, the product can be made into a relatively long straight part, and the product length can be longer than the mold length.
2. Wall thickness reduction rate
There is a certain degree of wall thickness thinning rate (5%~12%) during the deep drawing spinning process of ordinary spinning. The size depends on the properties of the material to be formed, the number of passes and the pass rotation (single pass or forward pass). and return trip (i.e. round trip) etc. Some important applications and high-pressure-resistant products have greater restrictions on their wall thickness reduction, which is also an important indicator of product quality. For example, for products such as pressure vessel heads, the maximum thinning rate cannot exceed the upper limit.
During the powerful spinning process, the thinning rate is a major process parameter in the deformation zone, because it directly affects the size of the spinning force and the quality of the spinning parts.
There are two types of wall thickness thinning rates: total thinning rate and pass thinning rate. The total thinning rate is not a simple sum of the thinning rates of each pass, but a combination of the thinning rates of each pass in a certain form, and the relationship is shown in Equation (5-34). The total thinning rate depends on the arrangement of the spinning process. The following mainly introduces the pass thinning rate, that is, the influence of the thinning rate on the spinning deformation during the spinning stroke.
3. Rotary wheel feed ratio (ƒ) or feed speed Uƒ
The wheel feed ratio is related to the spindle speed. The distance that the rotating wheel moves along the bus line of the mandrel for each revolution of the spindle (or mandrel) is called the feed amount or feed ratio (ƒ). The feed speed v of the rotating wheel is the linear speed of the contact point between the rotating wheel and the workpiece moving along its generatrix direction. They are process factors directly related to the spinning deformation process. Through testing and production practice, the following points can be summarized:
- The feed ratio of the wheel during spinning has a significant impact on the spinning deformation. The impact varies with the type of material and depends on the specific situation.
- Under normal circumstances, increasing the feed ratio will reduce the surface quality of the spinning parts. On the one hand, it will increase the surface texture (rolling marks of the rotating wheel) and make the surface roughness worse; on the other hand, The accumulation and bulging of materials increases, which can easily cause surface defects on the workpiece. Too small a feed ratio may also cause “scaly” appearance on the surface of some brittle materials.
- The feed ratio for spinning cylindrical (tubular) parts can be selected in the range of 0.3~2.5mm/revolution. When the surface roughness of the workpiece is not considered and there is a large diameter reduction, a higher feed ratio can be used. In this case, 0.5~3mm/r can be selected.
4. The distance between the rotating wheel and the mandrel
The accuracy of the spindle of the spinning equipment and the accuracy of the tooling mold (especially the mandrel) also have a direct impact on the clearance. The radial and axial runout of the spindle is generally required to be no more than 0.03mm, and the deflection of the mandrel during processing and installation must not exceed 0.02~0.07mm, because the deflection of the mandrel will cause the original gap between the rotating wheel and the mandrel to occur. Significant changes.
Spin forming under heating conditions will increase the number of process factors and complicate the process. Therefore, generally good plastic metals (such as aluminum, copper, low carbon steel and stainless steel, etc.) can be cold spun at room temperature, and hot spinning is generally not needed.
However, for some refractory metals with poor plasticity at room temperature (such as titanium, tungsten, molybdenum, niobium and their alloys, etc.), special product names (such as gas cylinders, heads and aluminum alloy wheels, etc.), extra thick blanks and current When the capacity of the spinning machine is insufficient, heating spinning is used.
To heat thin-walled spinning parts, a spray gun is generally used to locally heat the deformation zone. When the heating temperature is below 500°C, a liquefied petroleum gas spray gun can be used, and when the heating temperature is above 500°C, an oxyacetylene flame spray gun is required. If a hydrogen-oxygen spray gun is used, it can prevent the workpiece from oxidizing when heated. For the spinning of gas bottle closing and bottom sealing, jet heating is often used in the furnace, and then the spray gun is used for supplementary heating while spinning on the spinning machine. For large heads, an open heating furnace is useful for heating and spinning at the same time.
From the above content, we understand that the purpose of heating spinning is to improve the plasticity of the material and reduce its deformation resistance to facilitate spinning deformation. The heating temperature should be determined according to the specific material type and spinning conditions and the thermal deformation temperature range.
Ordinary spinning technology has a long history of development and has been used in various fields. The spinning process is simple, lightweight and applicable, and it is an indispensable spinning forming process for the production of thin-walled products.