Sheet metal parts will inevitably have different degrees of sharp edges and burrs during the manufacturing process. Sharp edges and burrs exceeding a certain limit will affect many aspects, such as product production, turnaround transportation, quality, performance and appearance, even cause harm to production users, such as affecting the processing and assembly positioning, the surface coating due to sharp-edged burrs scratched paint and rust, and scratched the hands of processors and other body parts.
With the continuous improvement of people’s requirements for products, the harmfulness of uncontrolled sharp edges and burrs has draw more and more attention from people.
Causes of Sharp Edges and Burrs on Sheet Metal Parts
Sharp edges are plane intersections that naturally occur during processing.
Sheet punching burr is the separation stage that the material enters after undergoing elastic deformation and plastic deformation in the process of blanking or shearing. When the plunging starts, cracks occur near the cutting edge of the die.
With the increase in the amount of cut, the upper and lower cracks continue to expand into the material. When the cutting edge clearance is set properly, the upper and lower cracks overlap, and the sheet is normally fractured and separated. When the cutting edge gap is not set properly, the upper and lower cracks do not coincide, and punching burrs are caused.
The main reasons for burrs in laser cutting sheet metal parts:
When a laser cutting machine is processing a work piece, the high energy generated by the laser beam irradiating the surface of the work piece causes the cutting part of the work piece to quickly vaporize and evaporate, thereby achieving the purpose of cutting.
In order to ensure the cutting quality, the slag remaining on the surface after gasification of the cutting surface of the work piece needs to be blown off with auxiliary gas.
If auxiliary gas is not used, after the slag is cooled, burrs will form on the cutting surface, which is the main cause of burrs. In addition, the setting of equipment accuracy and processing parameters are also secondary causes of burrs.
Due to process requirements in punching and shearing, the increased micro-connections between tool contacts and parts are another important cause of burrs.
The Necessity to Control Sharp Edges and Burrs
The sharp edges and burrs generated during sheet metal processing not only directly affect the surface quality of the work piece, the appearance of the product, but also cause safety hazards.
Therefore, the research method of how to suppress or reduce burrs is to fundamentally eliminate or reduce the effects of sharp edges and burrs, and ensure the smooth progress of safety production.
Measures to Control Sharp Edges and Burrs
Measures to control sharp edges and burrs can be divided into two categories according to processing technology:
The first type is designed with no sharp edges and burr processing technology, including controlling the height of burrs within the allowable range. For elevator stainless steel sheet metal parts, the product design department considers the burr formation mechanism and removal method at the product and process design stage to minimize burrs.
Using burr-free design such as: Add grooves, cuts, rounded corners, etc. to the edges where burrs may occur to reduce the occurrence of burrs. Change the geometry of the part to make burrs non-functional or to make burrs easier to remove.
The other is deburring technology, such as the following measures in punching and shearing production:
(1) Selecting a reasonable tool clearance during punching and shearing is a key factor which affecting the burrs of products. The size of the edge gap depends on the thickness and strength of the material being punched and sheared. We can refer to Table 1 to select a reasonable gap.
Table 1 Numerical reference of initial bilateral gap Z of blanking die
(2) The roughness and abrasion of the cutting edge of the tool during punching and cutting is another important reason that affects the product burr. Control the cutting edge roughness and wear degree. If the edge wears or damages, it will be rounded, clearance will increase due to side wear, and burrs will increase accordingly.
In production, tools generally undergo three stages of initial wear, normal wear and abnormal wear. The use of various tools before abnormal wear is ideal. However, limited by the accuracy requirements of the product, in many cases the permitted burr height is reached in the normal wear area.
At this point, replacement and grinding must be performed. We must regularly check, maintain and sharpen the cutting edge of the tools to reduce the burr of the material, reduce the shear force of the machine tool and prolong the service life of the machine tool and the tools.
(3) Select the appropriate processing tools, equipment and processing status. The material of the tool should be selected to have good wear resistance and high hardness. The higher the hardness of the cutting edge of the tool, the smaller the burr height. The mold structure adopts a high-precision mold guide device, which can ensure a reasonable gap during punching and correspondingly reduce burrs.
As for the accuracy of processing equipment, the higher the static and dynamic accuracy of the equipment, the less chance of plate burrs. Lubricating oil can reduce the friction between the cutting edge of the tool and the processing material, at the same time prevent the temperature rise caused by shear deformation, and prevent the processed material from adhering to the cutting edge of the tool.
Therefore, good lubrication conditions can reduce the occurrence of burrs.
In addition, the following measures can be adopted in laser cutting production:
(1) Select high-quality, high-purity cutting auxiliary gas.
(2) Select reasonable cutting parameters, such as focus position, laser power, air pressure, feed speed, nozzle distance, etc., to optimize cutting quality, reduce or even eliminate burrs.
(3) Adjust the static and dynamic accuracy of the machine tool to ensure the stability of the machine tool.
For micro-connections between tool contacts and parts in punching and shearing, in principle, they should be used as little as possible. Once used, they must be removed by hand or machine.
Control Measures for Sharp Edges and Burrs of Stainless Steel Sheet Metal Parts of Elevators
In addition to taking the above measures to control the minimization of sharp edges and burrs during the punching and shearing process, for the stainless steel sheet metal parts of the elevator, according to the needs of different stages, and the risk of sharp edges and burrs, the priority orders of removing sharp edges and burrs are divided into high risk, medium risk and low risk. Arrange different deburring processes after shearing according to priority.
In the production of elevator sheet metal parts, some products must be deburred before they can be transferred to subsequent processing, and some directly enter the product assembly. Different products are considered from a reasonable economic perspective, and various deburring processes are selected to ensure good product quality, high production efficiency and low cost.
At present, although there are many techniques for removing sharp edges and burrs of sheet metal parts, but most of the stainless steel sheet metal parts of elevators adopt mechanical methods. Generally speaking, for large-to-medium-volume parts such as car walls, hall doors, car doors, and other sheet metal flexible wires and laser cutting, sharp edges and burrs are removed by machine grinding before bending. For single-piece small-batch products that have been bent and formed, manual sharpening and burr methods are used.
Typical Deburring Technology of Stainless Steel Sheet Metal Parts for Elevator
Figure 1 Shows the deburring machine arranged after the punching and shearing center of Salvagnini, which is mainly used for the deburring of hall doors, car doors, and car walls in mass production without bending.
Fig. 1 Deburring machine arranged after punching and shearing processing center
Figure 2 Shows the brush deburring machine arranged after the laser cutting machine, which is mainly used for medium batches such as front wall, door head, car roof, etc., and the burr removal of the unbent products after laser cutting.
Figure 2 Brush deburring machine arranged behind the laser cutting machine
Figure 3 Shows a manual deburring tool, which is mainly used for small batches of products that are not suitable for machine deburring, such as door heads that have been punched and formed.
Figure 3 Manual Deburring
There are many constraints to the reasonable selection of deburring technology. Often, the existing production conditions, the technical quality of the workers and the operating habits must be considered. Reasonable and appropriate deburring process has an important impact on improving product quality and reducing manufacturing costs. Under the premise of ensuring quality, low cost is the basic principle for choosing a deburring process.
The reasonable selection of the deburring process involves the economically more reasonable question of which deburring process to use, especially has a significant impact on the investment in plant, equipment, environmental protection and process equipment.
The reasons and control measures for the formation of sharp edge and burr of sheet metal parts and the process of removing sharp edge and burr of stainless steel sheet metal parts of elevator are described above, but it is difficult to avoid burr completely in general punching and shearing process. However, if we can choose appropriate conditions, control measures and removal processes to maximize efficiency and minimize costs on the premise of ensuring quality, and control the hazards of sharp edges and burrs to a minimum is always an issue for our engineers and technicians.