Similar to cutting, it is critical to avoid friction and cold work hardening of stainless steel when machining. When machining some stainless steels, in order to make machining more convenient, sulfur or selenium can be added. The main purpose of machining is to drill holes, and the materials for the operation are mostly stainless steel sheets or stainless steel pipes.
Drilling should first minimize cold work hardening. Therefore, it is best not to punch holes before drilling, because punching will cause cold work hardening on the surface of the hole. It is best to use a center drill. If a center drill cannot be used, use a punch to punch the center hole. The same is when drilling with manual feed, it is important that the drilling is not interrupted and that the weight on bit is uniform and continuous.
To use a high-speed steel twist drill, in order to avoid friction, the drill must be sharp, and the best cutting angle, rake angle, clearance angle and cutting speed should be in accordance with the manufacturer's instructions.
Most forming processes are common to all metals. The main difference is the higher strength of stainless steel and its cold work hardening properties. Unlike carbon steel, protecting the stainless steel surface from damage is the most critical. Auxiliary work in this regard needs to be done well.
In addition, some forming processes allow sliding contact between metals, and the local high pressure during the forming process will destroy the passivation film of stainless steel. If this happens, there is a risk of cold welding the unprotected stainless steel surface to the tool surface. When that solder joint breaks in the next slide, the already contaminated tool surface creates a severe scratch on the stainless steel surface. In addition, there is a time loss in terms of downtime caused by the repair tool and the repair tool. Therefore, processors unfamiliar with stainless steel need to consult on the optimal process to use. In many cases, both surface protection and lubrication can be achieved with a suitable plastic film.
Below are some methods of forming.
First of all, let's talk about cold bending, which is widely used in stainless steel sheet and strip to make parts. The punch is basically an open single-action, mechanical or hydraulic transmission, with a relatively long and narrow worktable. It can only produce straight parts, but skilled tool designers can also use the machine to produce parts with complex shapes. Obviously, the length of the parts produced by the machine depends on the type and thickness of the stainless steel material, the power of the machine and the size of the tools that can be installed.
It is very cost-effective to produce small batches of general purpose parts using the general purpose tooling of the cold bending press. In addition, if the cold bending press is also in the production of carbon steel parts, it is also very important to ensure the environment of the cold bending press workshop.
Next is roll forming, which uses a series of continuous stands to roll stainless steel into complex shapes. The rolls are designed in such a way that each stand is shaped to continuously deform the metal until the desired final shape is obtained. If the shape of the part is complex, up to thirty-six racks can be used, but for parts with a simple shape, three or four racks are sufficient.
It is most cost-effective to use roll forming technology to produce long sections in large quantities. The width of stainless steel strip is 2.5-1500mm, and the thickness is 0.25-3.5mm. The shapes of the machined parts range from simple to complex, closed sections.
Usually, because of the high cost of tooling and installation, it is only cost-effective to use the roll forming process when the output is above 30,000 meters. However, the trial production of stainless steel with a roll-former for carbon steel profiles is still unclear. Here, care must be taken to avoid contamination or scratches on the stainless steel surface, and the equipment must be left to withstand cold work hardening of stainless steel and a high springback margin.
The third is stamping, which uses a punch and die to produce the desired shape. The punch press can be not only mechanically driven, but also hydraulically driven, but it is best to use hydraulic transmission when deep drawing, because the hydraulic press can provide full load pressure over the full length of the stroke. Because of the high cost of tooling, this technique is only used for mass production.
The fourth is rubber gasket molding, which can greatly reduce the cost of molds and can be used to produce small batches of products. The forming mechanism used by this technique is made of inexpensive materials, but it is clear that the production of complex shapes using this process is very difficult and there are limits to the maximum depth of the parts produced, generally the process is used for Production of stainless steel components in small batches with thicknesses below 1.5mm.
The fifth is the folding machine, which is a simple bending machine, which can be not only manual, but also motorized. The easiest way is to use a model with a bending radius to firmly fix the steel plate on the machine table. The protruding part of the material is placed on another table, which can be rotated around the center of the bend radius. When the movable table rises, it bends the stainless steel sheet to the desired angle. Because the stainless steel material is easy to slide on the table at this time. Therefore, in order to avoid scratching the stainless steel, the surface of the workbench must be smooth. In the actual processing process, the stainless steel surface is generally protected with a plastic film.
The last method is barrel forming, which generally uses the bending method to produce barrels or barrel sections made of thin sheet for various purposes. The traditional plate rolling machine has a pair of adjustable rollers, which can be adjusted according to the thickness of the stainless steel plate. The third roller, the bending roller, controls the diameter of the forming cylinder. There is also a variant of this type of machine that also uses three rollers, which are configured in a pagoda shape. The bottom roller is a driving roller, and the top roller is rotated by the friction formed between the top roller and the workpiece. The diameter of the bottom roll is generally half the diameter of the top roll.
The minimum diameter of the cylinder produced using the above two equipment is the diameter of the top roll plus 50mm. The maximum diameter of the produced cylinder is affected by factors such as the size of the incoming material, the headroom above the machine and the rigidity of the molded part.