The manufacturing process of modern mechanical products, for more complex parts, is usually the use of a variety of different manufacturing methods of organic combination of ways, such as through formative manufacturing technology, and then use subtractive manufacturing technology to improve the accuracy of the final product manufacturing requirements.
1. How are the parts machined?
To perform a certain function, a part in a machine or device must first have a certain shape. These shapes can be achieved based on different forming principles.
According to the change of mass m during the manufacturing process of a part from raw material or blank into a part, there are three principles: Δm < 0, Δm = 0, and Δm > 0. Different principles are used for different forming processes.
- Δm<0, the principle of material removal, as in conventional cutting methods, including CNC turning, CNC milling, grinding, etc., where the desired geometry is obtained by gradual removal of material during the manufacturing process.
- Δm = 0, the principle of fundamental material invariance, such as casting, forging and die forming (injection molding, stamping, etc.) processes, in forming Before and after, the material changes mainly in shape, while the mass remains essentially unchanged.
- Δm>0, the principle of cumulative forming of materials, such as Rapid Prototyping, which emerged in the 1980s, is used to obtain the desired shape by cumulative addition of materials during the forming process.
1) Subtractive manufacturing technology (Δm< 0)
Cutting is achieved by the relative movement of the tool and the workpiece and by the interaction of forces. The workpiece is often mounted on the CNC machine by a fixture, and the machine moves either the tool or the workpiece or both at the same time. During the cutting process, force, heat, deformation, vibration, wear and other phenomena occur, and the combination of these movements determines the final geometry and surface quality of the part.
For parts with particularly high machining accuracy and surface roughness requirements, finishing and super-finishing processes are required. The dimensional accuracy of finishing and superfinishing often reaches the submicron and even nanometer (nm) level. These processes are widely used in aerospace, computer products and other fields.
2) Formative manufacturing technology (Δm = 0)
The process content of the formative manufacturing technology is mainly by means of mould forming, where the quality of the material remains basically the same before and after forming, but only the shape changes. It is worth noting here that statistics show that 40% to 50% of the parts of electromechanical products are formed by moulds, so the role of moulds is obvious. Moulds can be divided into injection moulds, die-casting moulds, forging moulds, stamping moulds, blow moulds and so on. Mold manufacturing accuracy is generally required high, and its production method is often single-piece production. The design of moulds should use a series of technologies such as CAD and CAE, which is a technology-intensive industry.
3) Additive manufacturing technologies (Δm> 0)
Additive manufacturing is the process of joining materials to create objects based on 3D CAD data, which is usually a layer-by-layer process compared to subtractive manufacturing techniques. The advantage of this process is that parts of any complex shape can be formed without the need for special equipment such as tools and fixtures. This process i s called Rapid Prototyping (RP) because of the speed of forming,
but at the beginning of its development, only prototypes could be formed. RP technology and rapid precision casting technology (Quick Casting) and rapid mold manufacturing technology (Rapid Tooling), etc., can be combined for small or large volume production services, so RP technology has become an effective technology to accelerate new product development and achieve parallel engineering.
RP technology has developed several mature process methods and entered the commercialization stage. Currently, the main commercial devices are Stereolithography (SL) , Laminated Object Manufacturing (LOM) , Selective Laser Sintering (SLS) , Fused Deposition Modeling (FDM) , and 3D Printing (3DP, a process that uses a print head to achieve material accumulation). Each of these processes has different
characteristics and is applicable to different applications.
It is important to note that in recent years this additive manufacturing technology has been referred to as 3D printing technology. 3D printing is made directly from engineering materials, and the product or part can be used as a product or functional part directly (or with minimal machining), thus enabling truly rapid manufacturing. 3D printing technology uses a wide range of materials, such as glass fibers, durable nylon materials, gypsum materials, aluminum alloys, titanium alloys, stainless steel, rubber-like materials, biomaterials, food materials, etc.
Nowadays, it is possible to “print” real 3D objects using 3D printing devices, which play an extremely important role in scientific research, production and in the daily life of human beings.
2. CNC Machining Services
The use of mechanical processing methods to obtain the shape of the part is the use of machine tools to remove the excess material on the blank to obtain. According to the different machine movements, different tools, can be divided into different machining methods, mainly: CNC turning, CNC milling, grinding, drilling, boring, etc.
1) CNC Turning
The CNC turning method is characterized by the rotation of the workpiece, forming the main cutting motion, so the surface formed after turning is mainly a rotary surface, but also the end face of the workpiece can be machined. Different workpiece shapes can be obtained through different feed movements of the tool relative to the workpiece.
When the tool moves along the axis of rotation parallel to the workpiece, the internal and external cylindrical surface is formed; when the tool moves along the oblique line intersecting with the axis, the tapered surface is formed. With a profiling lathe or CNC lathe, the tool can be fed along a curve to form a specific rotating surface. The rotary surface can also be machined when the shaped turning tool is fed transversely. Turning also Threaded surfaces, end faces and eccentric shafts can be machined. Turning accuracy is generally IT8 to IT7, and surface roughness Ra value is 6.3 ~ 1.6μm. For precision turning, IT6 ~ IT5, the surface roughness Ra value is 0.4 ~ 0.1μm. The productivity of turning is higher, the cutting process is smoother, and the tool is more straightforward.
2) CNC Milling
The main cutting motion in milling is the rotary motion of the tool, and the workpiece is fed through the table of the machine tool. Milling tools are complex, usually multi-edge tools. Different milling methods, the cutting edge of the milling cutter to complete the cutting different, horizontal milling, the formation of the plane is formed by the cutting edge on the outer surface of the milling cutter; vertical milling, the plane is formed by the end of the cutting edge. In vertical milling, the plane is formed by the endface of the cutter. By increasing the speed of the cutter, a higher cutting speed can be achieved, resulting in higher productivity. However, the cutting process is prone to vibration due to the impact of the cutter teeth cutting in and out, thus limiting the improvement of surface quality. This impact also increases the wear and breakage of the tool, often leading to shattering of the carbide insert. When milling, the milling cutter can be cooled to a certain extent during the period of cutting away from the workpiece, so the heat dissipation conditions are better.
According to the direction of the main motion of the milling and the workpiece feed direction of the same or the opposite, and divided into down milling and up milling.
When down milling, the horizontal component of the milling force and the workpiece feed direction is the same, and there is usually a gap between the table feed screw and the fixed nut, so the cutting force is likely to cause the workpiece and the table to move forward together, so that the feed volume increases suddenly, which is likely to cause tool striking. Reverse milling can avoid this phenomenon, therefore, the production of more use of reverse milling. When milling castings or forgings and other workpieces with hard skin on the surface, the teeth of the milling cutter first contact the hard skin of the workpiece, which increases the wear of the milling cutter, while the reverse milling does not have this disadvantage.
However, when up milling, the cutting thickness gradually increases from zero, so the cutting edge starts to experience a period of squeezing and sliding on the machined surface of the cutting hardening, which will also accelerate the wear of the tool.
Milling accuracy can generally reach IT8 ~ IT7, surface roughness Ra value of 6. 3 ~ 0. 8μm. General milling can generally process the plane or groove surface, etc., with forming milling tools can also be processed out of specific surfaces, such as milling gears, etc. CNC milling machine can be controlled by the CNC system several axes according to a certain relationship linkage, milling out complex surfaces, when
the tool is generally used ball milling cutter. CNC milling machines in the processing of mold cores and cavities, impeller machinery, such as the shape of the complex workpiece, the application is very widespread, so the corresponding multi-axis CNC milling machine development is also very fast.
About DFM Rapid
We are a CNC machining China shop in Dongguan. We have 20 CNC milling and turning machines in our shop. We can offer you CNC rapid prototyping and low-volume CNC machining services for plastic and metal parts. Also, surface finish like anodized, powder coating is available. If you need Metal & Plastic parts machined for prototypes or production, please feel free to get a quote online.
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