In the work-piece machining process, what factors affect the machining parts accuracy?

(1) machining principle error

Machining principle error refers to the error produced by machining with approximate forming movement or approximate shape cutter. In the NC machining of curve or curve. The forming movement of the tool relative to the workpiece is approximate. Furthermore, when the NC machine tool interpolates the straight line or the circular arc, it uses the small straight line segment of the parallel coordinate axis to approach the ideal straight line or the circular arc. There are processing principle errors here.

(2) machine error

The error of machine tool is caused by the manufacture, installation and wear of machine tool. Among all kinds of errors of machine tools, the main ones that affect the machining accuracy of workpieces are the rotary error of main pump and the error of guide rail.

(3) fixture error

The main causes of the fixture error are the low manufacturing accuracy, low assembly accuracy and the wear of the working surface during the use of the fixture. The fixture error will directly affect the position accuracy and dimension accuracy of the workpiece surface, especially the position accuracy of the machined surface.

(4) CUTTING tool error

The manufacturing error and wear in use are the main causes of tool error. The influence of cutter error on machining accuracy varies with the type and material of cutter. For example, the dimensional accuracy of fixed size cutter (such as drill, reamer, etc.) will directly affect the dimensional accuracy of workpiece. For example, the shape accuracy of forming tools (such as forming turning tools, forming milling tools, etc.) will directly affect the shape accuracy of the workpiece.

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Today, we will to introduce the processing methods of aluminum product.

The advantages and characteristics of aluminum are as follows:

1. Low density. The density of aluminum is about 2.7g/cm3. Its density is only 1/3 of iron or copper.
2. High plasticity. Aluminum is malleable and can be made into a variety of supplies by squeezing, stretching and other pressure processing means.
3. Corrosion resistance. Aluminum is a highly charged metal that produces a protective oxide film on the surface of natural conditions or anodization, with much better corrosion resistance than steel.
4. Easy to strengthen. The strength of pure aluminum is not high, but it can be increased by anode oxidation.
5. Easy surface treatment. Surface treatment can further improve or change the surface performance of aluminum. Aluminum anode oxidation process is quite mature, stable operation, in the process of aluminum products has been widely used.
6. Conductelectricity is good, easy to recycle.

PUNCHING OF ALUMINIUM PRODUCT

Cold stamping ALUMINIUM PRODUCT

Use aluminium particles. The extruder table and die are used for one-time forming, which is suitable for cylindrical products or product shapes that are difficult to achieve in drawing process, such as ellipse, square and rectangular products. (Fig. 1 machine, Fig. 2 aluminium particles, Fig. 3 products)

The tonnage of the machine is related to the cross section area of the product. The gap between the upper die punch and the lower die tungsten steel is the wall thickness of the product. The vertical gap between the upper die punch and the lower die tungsten steel is the top thickness of the product when the pressing is completed. (Fig. 4)

Aluminum Cold Stamping Advantages:

Shorter mold making cycle and lower development cost compared with drawing die.

ALUMINUM COLD STAMPING Disadvantage:

The production process is long, the product size fluctuates greatly in the process, and the labor cost is high.

Tensile/DRAWING process for ALUMINIUM PRODUCT

Use aluminium sheet. The continuous punching machine and die are used to deform many times to meet the requirement of shape, which is suitable for non-cylindrical products (aluminium products with bending). (Fig. 5, Fig. 6, Mould, Fig. 7, Fig. 7)

Aluminum tensile or drawing process advantages:

Complicated and multi-deformation products have stable size control and smooth surface in the production process.

ALUMINUM TENSILE OR DRAWING PROCESS Disadvantage:

Die cost is high, development cycle is relatively long, and the selection and precision of machine platform is high.

CNC machining Aluminum product

Aluminum CNC turning and CNC milling is widely used to making aluminum products.

Aluminum CNC turned part, by CNC LATHE can mass making turned parts with low cost, and machined parts have bright and smooth surface.

Aluminum CNC milled part, by CNC machine center or CNC router to making rapid prototype, fixuture, mold and other aluminum products. The cost is expensive, but can got finised parts quickly from design to product.

Aluminum DIe casting

Aluminum die casting product is producing engineered metal parts by forcing molten Aluminum metal under high pressure into reusable steel molds.
Die castings are among the highest volume, mass-produced items manufactured by the metalworking industry, and they can be found in thousands of consumer, commercial, and industrial products. Die cast parts are important components of products ranging from automobiles to toys. Parts can be as simple as a sink faucet or as complex as a connector housing.

aluminium product SURFACE TREATMENT

Sandblasting (shot blasting)

The process of cleaning and roughening metal surface by the impact of high-speed sand flow.

The surface treatment of aluminium parts by this method can obtain a certain degree of cleanliness and different roughness, and improve the mechanical properties of the workpiece surface. Therefore, the fatigue resistance of the workpiece is improved, the adhesion between the workpiece and the coating is increased, the durability of the coating is prolonged, and it is also conducive to the leveling and decoration of the coating. 。 This process is often seen in various products of Apple.

Polishing

The surface roughness of workpiece is reduced by mechanical, chemical or electrochemical action to obtain a bright and smooth surface processing method. Polishing technology is mainly divided into: mechanical polishing, chemical polishing, electrolytic polishing. Aluminum parts can approach mirror effect of stainless steel after mechanical polishing and electrolytic polishing. This process gives people a feeling of high-grade, simple and fashionable future.

Wire drawing

Metal wire drawing is a process of repeatedly scraping aluminium sheet out of line with sandpaper. Drawing can be divided into straight wire drawing, screwed wire drawing, screwed wire drawing, screwed wire drawing. Metal wire drawing process can clearly show each fine trace, so that the metal matte gloss in the exudation of fine silk luster, products both fashionable and technological sense.

High-light cutting/Machining

The diamond knife is strengthened on the spindle of the high-speed CNC router to cut the parts, and a local bright area is generated on the surface of the product. It also named: CNC machining. The brightness of cutting highlight is affected by the speed of the milling bit. The faster the bit speed is, the brighter the cutting highlight is. On the contrary, the darker the cutting highlight is and the easier the cutter grain is. In recent years, high-light CNC milling technology has been used in some metal frames of high-end TV sets. In addition, the anodic oxidation and wire drawing technology make TV sets full of fashion sense and sharp sense of science and technology.

Anodic oxidation

Anodic oxidation refers to the electrochemical oxidation of metals or alloys. Under the corresponding electrolyte and specific technological conditions, aluminum and its alloys form an oxide film on the aluminium products (anodes) due to the action of applied current. Anodic oxidation can not only solve the defects of surface hardness and wear resistance of aluminium, but also prolong the service life of aluminium and enhance its beauty. It has become an indispensable part of surface treatment of aluminium. It is the most widely used and very successful technology at present.

Two-color anode

Dual-color anode refers to the process of anodizing a product and giving different colors to a specific area. Dual-color anodizing process is seldom used in TV industry because of its complex process and high cost, but through the contrast between the two colors, it can better reflect the high-end and unique appearance of the product.

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Aluminum Product Processing Technology最先出现在CNC Machining|CNC Milling & Turning Services|CNC turned parts|。

What cause aluminum deformetion?

There are 3mainly reasons:

1. deformation caused by internal stress of blank.
2. deformation caused by cutting force, cutting heat.
3. deformation caused by clamping force.

How to avoid Aluminum deformation?

Technological Measures for Reducing Aluminum Deformation .

1.Reducing the Internal Stress of aluminum rough part

The internal stress of rought part can be partly eliminated by natural or artificial aging and vibration treatment. Pre-processing is also an effective process. For big rough aluminum part, the deformation after machining is also large. If cut the extra aluminum material from rought part, get precise tolerance the deformation can be improved. Also a part of internal stress can be released after stay for a period of time.

2.Improving Cutting Ability of Cutting Tools

Material and geometric parameters of cutting tools have an important influence on cutting force and heat. Correct selection of cutting tools is very important to reduce machining deformation of parts.

1.Reasonable selection of tool geometry parameters.

• Front angle: Under the condition of maintaining the edge strength, the front angle should be selected appropriately larger. On the one hand, it can grind a sharp edge, on the other hand, it can reduce cutting deformation, make chip removal smoothly, and then reduce cutting force and cutting temperature. Never use negative rake tool.

• Back angle: The size of back angle has a direct impact on the wear of the flank and the quality of the machined surface. Cutting thickness is an important condition for choosing rear angle. In rough milling, because of the large feed, heavy cutting load and high heat output, the cutter is required to have good heat dissipation conditions, so the back angle should be selected smaller. In finishing milling, sharp edges are required to reduce friction between the flank and the machined surface and reduce elastic deformation. Therefore, a larger rear angle should be chosen.

• Helix angle: In order to make milling smooth and reduce milling force, the helix angle should be selected as large as possible.

• Principal deviation angle: Appropriate reduction of the main deviation angle can improve the heat dissipation conditions and reduce the average temperature of the processing area.

2. Improve cutting tool structure.

• Reduce the number of milling cutter teeth and increase chip space. Because of the large plasticity of aluminium material and the large cutting deformation in processing, it needs a larger chip space, so the radius of the bottom of the chip groove should be larger and the number of milling cutter teeth should be less.

• Fine grinding of cutter teeth. The roughness of the cutting edge is less than Ra=0.4um. Before using a new cutting tool, a few gentle rubbings should be made on the front and back of the cutter teeth with fine asphalt to eliminate the burrs and slight serrated marks remaining when grinding the tool teeth. In this way, not only cutting heat can be reduced, but also cutting deformation is relatively small.

• Strict control of tool wear standards. After tool wear, the roughness of workpiece surface increases, cutting temperature increases, and workpiece deformation increases. Therefore, in addition to choosing tool materials with good wear resistance, the tool wear standard should not be greater than 0.2 mm, otherwise it is easy to produce chip tumors. When do cutting by CNC Milling or CNC Turning, the temperature of the machining workpiece should not exceed 100 ℃ in order to prevent deformation.

3.Improving the clamping method of workpiece

For Thin-walled Aluminium workpieces with poor rigidity, the following clamping methods can be used to reduce deformation:

• For thin-wall CNC Machining bushing parts, if three-jaw self-centering chuck or spring chuck is used to clamp from the radial direction. Once it is loosened after machining, the workpiece will inevitably deform. At this time, the method of axial end face compression with better rigidity should be used. A threaded mandrel is made for positioning the inner hole of the part. It is inserted into the inner hole of the part. A cover plate is used to press the end face and a nut is used for back tightening. The clamping deformation can be avoided when the outer circle is machined, and the satisfactory machining accuracy can be obtained.

• When machining thin-wall sheet workpiece, it is better to choose vacuum sucker to obtain uniform clamping force. And then to process with smaller cutting parameters, which can prevent machined workpiece deformation.

• In addition, the filling method can also be used. In order to increase the technological rigidity of thin-walled workpiece, medium can be filled in the workpiece to reduce the deformation of workpiece during clamping and cutting. For example, urea melt containing 3% to 6% potassium nitrate is poured into the workpiece. After processing, the workpiece is immersed in water or alcohol, and the filler can be dissolved and poured out.

4.Reasonable Arrangement of Processes

In high-speed cutting, because of large machining allowance and intermittent cutting, milling process often produces vibration, which affects the processing accuracy and surface roughness. Therefore, the NC high-speed cutting process can be generally divided into roughing, semi-finishing, angle clearing and finishing processes. For parts requiring high precision, it is sometimes necessary to finish them twice and half, and then finish them. After rough machining, the parts can be cooled naturally to eliminate the internal stress and reduce the deformation. The allowance left after roughing should be greater than the deformation, generally 1-2 mm. When finishing, the surface of parts should be kept uniform. Generally, 0.2-0.5mm is the best way to keep the tool in a stable state during the process of finishing, which can greatly reduce the cutting deformation, obtain good surface processing quality and ensure the accuracy of the product.

Operational Skills for Reducing Aluminum Machining Deformation

Except the above reasons, the operation method is also very important in the actual operation.

For parts with large machining allowance

In order to make them have better heat dissipation conditions and avoid heat concentration in machining, symmetrical processing should be adopted. If a 90 mm thick sheet needs to be processed to 60 mm, if the other side is milling immediately after milling one side, and the flatness reaches 5 mm once to the final dimension. If the repeated feed symmetrical processing is used, each side is processed to the final dimension twice, the flatness can be guaranteed to reach 0.3 mm.

If there are more than one cavity in the sheet metal parts

The sequential processing method of one cavity and one cavity should not be adopted in the processing, which is easy to cause uneven force and deformation of the parts. Layered multi-processing is adopted, each layer is machined to all the cavity at the same time, and then the next layer is machined, so that the parts are uniformly stressed and the deformation is reduced.

Reduce cutting force and heat by changing cutting parameters.

Among the three factors of cutting parameters, back feed has a great influence on cutting force. If the machining allowance is too large and the cutting force of the tool is too large. Not only will the parts be deformed, but also will affect the rigidity of the machine tool spindle and reduce the tool durability. If we reduce the amount of knives eaten by the back, the production efficiency will be greatly reduced. However, high-speed milling can overcome this problem in NC machining. At the same time, the cutting force can be reduced and the processing efficiency can be guaranteed as long as the feed is increased correspondingly and the speed of the machine tool is increased.

We should also pay attention to the sequence of cutting tool walking way.

Rough milling emphasizes the improvement of processing efficiency and the pursuit of cutting rate per unit time. Reverse milling can be generally used. That is to say, the superfluous material on the surface of the blank is removed at the fastest speed and in the shortest time, and the geometric contour required for finishing is basically formed. Precision machining emphasizes high precision and high quality, and it is advisable to use forward milling. Because the cutting thickness of the cutter teeth decreases gradually from the maximum to zero, the degree of work hardening is greatly reduced, and the degree of deformation of the parts is also reduced.

The deformation of thin-walled workpiece is inevitable even in finishing because of clamping.

In order to minimize the deformation of the workpiece, it is possible to loosen the pressing part before finishing is about to reach the final dimension, so that the workpiece can be freely restored to its original state, and then slightly compressed, whichever is rigid enough to hold the workpiece (completely by hand), so as to achieve the desired processing effect. In a word, the point of action of clamping force is best on the supporting surface. The clamping force should be applied in the direction of good rigidity of the workpiece. The smaller the clamping force, the better, on the premise of ensuring that the workpiece is not loose.

Don’t use milling cutter like drill

When machining the parts with cavity, try not to let the milling cutter penetrate directly into the parts like a drill bit, resulting in inadequate chip space and unsmooth chip removal of the milling cutter, resulting in overheating, expansion of the parts, tool breaking and other adverse phenomena. First drill the hole with a bit of the same size or size as the milling cutter, and then milling with the milling cutter. Alternatively, the spiral downcutter program can be produced with CAM software.

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How to reduce ALUMINUM Deformation in machining最先出现在CNC Machining|CNC Milling & Turning Services|CNC turned parts|。