5 things about CNC Machined Aluminium you may not have known
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A CNC (Computer Numerical Control) machine runs on a computer program; it can either be for prototyping or in full item production. Aluminum is the commonly machined material, as it exhibits excellent machinability, and is thus the preferred material in the most manufacturing sector.
Aluminum as a material offers some interesting thermal and mechanical properties. Besides, the aluminum metal is relatively easy to shape, especially in drilling processes, like in CNC aluminum machining. In fact, we highly regard an aluminum alloy compared to other lightweight metals such as magnesium and titanium alloys.
The use of CNC aluminum has grown immensely, the production of CNC automotive parts and other CNC parts that are lightweight has been intense. Below are a few of the things you may not have known.
Aluminum is soft, lightweight, tractable, malleable, and durable metal. Its appearance is silver or dull grey and depends on the roughness of the surface. It lacks magnetic properties and its non-flammable. The aluminum metal melts at 640 degrees, and it’s light with a density of 2.68. It is a good conductor of electricity though not of the same standard as copper on specific cross-section area and is widely used in CNC automotive like ATV, Aerospace and medical industries.
The ultimate choice of the type of aluminum grade you intend to use depends on your machining projects, which allow you to rank each grade according to its characteristic, from the most important to the least. By doing so, you get to choose the aluminum of specific properties and shape as per your needs.
The following are some types with essential facts about Aluminum grade;
Aluminum 6061
: This grade has superb mechanical properties, excellent weldability. Its topical properties make it one of the most extruded grade. This is because of its good toughness, medium and high strength, excellent corrosion resistance on harsh condition, cool anodization, and bending workability. Aluminum 6061 is commonly used for 5 axis CNC machining.Aluminum 7075
: It’s also popular even though not like the 6061. This grade is known for its exceptional fatigue strength. This aluminum grade is not suitable for welding; it’s costly. Hence, it is better for tough parts, such as fuselages, bicycle parts, rock climbing kits, and aircraft wings. This alloy also better in corrosion resistance.Aluminum 2024:
The alloy is predominantly used in military and aerospace sector. This is because of its mechanical properties, like great weariness resistance, and high strength. The aluminum 2024 is terrible in corrosion resistance and not weldable.Aluminum machined prototype are commonly produced according to a variety of alloys. The most used alloy is the 6061-T6, this caters for electronics, transportation, aerospace, military industries among others.
Aluminum alloys are low in density but high in strength. Often CNC aluminum prototype machining has the vast tolerance to control even 0.01MM. The CNC machine can manufacture unique and quality aluminum prototypes. CNC milling is just the perfect choice, the advantages are in the machining process, and that is the high precision and milling aluminum.
The technology of CNC machined aluminum has produced CNC parts and components that aid in a wide range of services (Turning, milling and grinding). Today, well machined CNC aluminum parts are growing in popularity in the engineering sector.
The following are some of the CNC machined aluminum parts:
Aluminum is an essential industrial material, but it has a major undoing. The alloys contain relatively low hardness and their thermal expansion are high, can deform when being machined into a thin part. However, several steps can be taken to avoid the deformation of the material beforehand.
Symmetrical Machining
It’s essential to avoid extreme concentration of heat but rather to create a dissipation of heat to reduce the rate of thermal deformation.
Stratified Multiple Machining
If you have several cavities on some aluminum alloy plate, you can easily twist one cavity wall because of the force distribution. To avoid such an occurrence, you should process all cavities in the same period.
The significant influence on the cutting parameter is the amount of cutting back depth. To maintain efficiency and reduce the number of cutting. A CNC milling can settle the problem, by increasing the speed of the machine and reducing the cutting force.
When the milling cutter is applied to cavity and parts, the cutting is sufficient. The leads to cutting heat, expansion, and deformation. The best way of avoiding this problem is pre-drilling with a bigger tool than the milling cutter and then put the milling cutter and mill.
On the 5-axis machining, the CNC moves while cutting in five angles of the axes simultaneously. This machining process is fast, reliable on designing complex parts, as work is approached in multiple directions.
The 5-axis machining has been adopted widely because of the following:
As we conclude, you are now aware of the various CNC machined aluminum process (milling, drilling, and turning) that unfinished piece of aluminum is taken through until it becomes a complete product. It’s an arduous process that requires experience, accuracy, and powerful machinery. Moreover, these are because of the different aluminum alloy used.
The benefits of aluminum are obvious: fantastic cutting process, the best quality and the demand for a machined aluminum product is on the rise. Industries are snowballing with many specialists to meet your needs, remember to do your research and seek samples to be sure on the quality of the CNC aluminum.
By the end of this section, you will be able to:
The expansion of alcohol in a thermometer is one of many commonly encountered examples of thermal expansion, the change in size or volume of a given mass with temperature. Hot air rises because its volume increases, which causes the hot air’s density to be smaller than the density of surrounding air, causing a buoyant (upward) force on the hot air. The same happens in all liquids and gases, driving natural heat transfer upwards in homes, oceans, and weather systems. Solids also undergo thermal expansion. Railroad tracks and bridges, for example, have expansion joints to allow them to freely expand and contract with temperature changes.
What are the basic properties of thermal expansion? First, thermal expansion is clearly related to temperature change. The greater the temperature change, the more a bimetallic strip will bend. Second, it depends on the material. In a thermometer, for example, the expansion of alcohol is much greater than the expansion of the glass containing it.
What is the underlying cause of thermal expansion? As is discussed in Kinetic Theory: Atomic and Molecular Explanation of Pressure and Temperature, an increase in temperature implies an increase in the kinetic energy of the individual atoms. In a solid, unlike in a gas, the atoms or molecules are closely packed together, but their kinetic energy (in the form of small, rapid vibrations) pushes neighboring atoms or molecules apart from each other. This neighbor-to-neighbor pushing results in a slightly greater distance, on average, between neighbors, and adds up to a larger size for the whole body. For most substances under ordinary conditions, there is no preferred direction, and an increase in temperature will increase the solid’s size by a certain fraction in each dimension.
The change in length ΔL is proportional to length L. The dependence of thermal expansion on temperature, substance, and length is summarized in the equation ΔL = αLΔT,where ΔL is the change in length L, ΔT is the change in temperature, and α is the coefficient of linear expansion, which varies slightly with temperature.
Table 1 lists representative values of the coefficient of linear expansion, which may have units of 1/ºC or 1/K. Because the size of a kelvin and a degree Celsius are the same, both α and ΔT can be expressed in units of kelvins or degrees Celsius. The equation ΔL = αLΔT is accurate for small changes in temperature and can be used for large changes in temperature if an average value of α is used.
Table 1. Thermal Expansion Coefficients at 20ºC Material Coefficient of linear expansion α(1/ºC) Coefficient of volume expansion β(1/ºC) Solids Aluminum 25 × 10– 6 75 × 10– 6 Brass 19 × 10– 6 56 × 10– 6 Copper 17 × 10– 6 51 × 10– 6 Gold 14 × 10– 6 42 × 10– 6 Iron or Steel 12 × 10– 6 35 × 10– 6 Invar (Nickel-iron alloy) 0.9 × 10– 6 2.7 × 10– 6 Lead 29 × 10– 6 87 × 10– 6 Silver 18 × 10– 6 54 × 10– 6 Glass (ordinary) 9 × 10– 6 27 × 10– 6 Glass (Pyrex®) 3 × 10– 6 9 × 10– 6 Quartz 0.4 × 10– 6 1 × 10– 6 Concrete, Brick ~12 × 10– 6 ~36 × 10– 6 Marble (average) 2.5 × 10– 6 7.5 × 10– 6 Liquids Ether 1650 × 10– 6 Ethyl alcohol 1100 × 10– 6 Petrol 950 × 10– 6 Glycerin 500 × 10– 6 Mercury 180 × 10– 6 Water 210 × 10– 6 Gases Air and most other gases at atmospheric pressure 3400 × 10– 6The main span of San Francisco’s Golden Gate Bridge is 1275 m long at its coldest. The bridge is exposed to temperatures ranging from –15ºC to 40ºC. What is its change in length between these temperatures? Assume that the bridge is made entirely of steel.
Use the equation for linear thermal expansion ΔL = αLΔT to calculate the change in length , ΔL. Use the coefficient of linear expansion, α, for steel from Table 1, and note that the change in temperature, ΔT, is 55ºC.
Plug all of the known values into the equation to solve for ΔL.
[latex]\Delta{L}=\alpha{L}\Delta{L}=\left(\frac{12\times10^{-6}}{^{\circ}\text{C}}\right)\left(1275\text{ m}\right)\left(55^{\circ}\text{C}\right)=0.84\text{ m}\\[/latex]
Although not large compared with the length of the bridge, this change in length is observable. It is generally spread over many expansion joints so that the expansion at each joint is small.
Objects expand in all dimensions, as illustrated in Figure 2. That is, their areas and volumes, as well as their lengths, increase with temperature. Holes also get larger with temperature. If you cut a hole in a metal plate, the remaining material will expand exactly as it would if the plug was still in place. The plug would get bigger, and so the hole must get bigger too. (Think of the ring of neighboring atoms or molecules on the wall of the hole as pushing each other farther apart as temperature increases. Obviously, the ring of neighbors must get slightly larger, so the hole gets slightly larger).
For small temperature changes, the change in area ΔA is given by ΔA = 2αAΔT, where ΔA is the change in area A, ΔT is the change in temperature, and α is the coefficient of linear expansion, which varies slightly with temperature.
The change in volume ΔV is very nearly ΔV = 3αVΔT. This equation is usually written as ΔV = βVΔT, where β is the coefficient of volume expansion and β ≈ 3α. Note that the values of β in Table 1 are almost exactly equal to 3α.
In general, objects will expand with increasing temperature. Water is the most important exception to this rule. Water expands with increasing temperature (its density decreases) when it is at temperatures greater than 4ºC (40ºF). However, it expands with decreasing temperature when it is between +4ºC and 0ºC (40ºF to 32ºF). Water is densest at +4ºC. (See Figure 3.) Perhaps the most striking effect of this phenomenon is the freezing of water in a pond. When water near the surface cools down to 4ºC it is denser than the remaining water and thus will sink to the bottom. This “turnover” results in a layer of warmer water near the surface, which is then cooled. Eventually the pond has a uniform temperature of 4ºC. If the temperature in the surface layer drops below 4ºC, the water is less dense than the water below, and thus stays near the top. As a result, the pond surface can completely freeze over. The ice on top of liquid water provides an insulating layer from winter’s harsh exterior air temperatures. Fish and other aquatic life can survive in 4ºC water beneath ice, due to this unusual characteristic of water. It also produces circulation of water in the pond that is necessary for a healthy ecosystem of the body of water.
Differences in the thermal expansion of materials can lead to interesting effects at the gas station. One example is the dripping of gasoline from a freshly filled tank on a hot day. Gasoline starts out at the temperature of the ground under the gas station, which is cooler than the air temperature above. The gasoline cools the steel tank when it is filled. Both gasoline and steel tank expand as they warm to air temperature, but gasoline expands much more than steel, and so it may overflow.
This difference in expansion can also cause problems when interpreting the gasoline gauge. The actual amount (mass) of gasoline left in the tank when the gauge hits “empty” is a lot less in the summer than in the winter. The gasoline has the same volume as it does in the winter when the “add fuel” light goes on, but because the gasoline has expanded, there is less mass. If you are used to getting another 40 miles on “empty” in the winter, beware—you will probably run out much more quickly in the summer.
Suppose your 60.0-L (15.9-gal) steel gasoline tank is full of gas, so both the tank and the gasoline have a temperature of 15.0ºC. How much gasoline has spilled by the time they warm to 35.0ºC?
The tank and gasoline increase in volume, but the gasoline increases more, so the amount spilled is the difference in their volume changes. (The gasoline tank can be treated as solid steel.) We can use the equation for volume expansion to calculate the change in volume of the gasoline and of the tank.
Alternatively, we can combine these three equations into a single equation. (Note that the original volumes are equal.)
[latex]\begin{array}{lll}{V}_{\text{spill}}& =& \left({\beta }_{\text{gas}}-{\beta }_{\text{s}}\right)V\Delta T\\ & =& \left[\left(\text{950}-\text{35}\right)\times {\text{10}}^{-6}/^{\circ}\text{C}\right]\left(\text{60}\text{.}0\text{L}\right)\left(\text{20}\text{.}0^{\circ}\text{C}\right)\\ & =& 1\text{.}\text{10}\text{L}\end{array}\\[/latex]
This amount is significant, particularly for a 60.0-L tank. The effect is so striking because the gasoline and steel expand quickly. The rate of change in thermal properties is discussed in the chapter Heat and Heat Transfer Methods.
If you try to cap the tank tightly to prevent overflow, you will find that it leaks anyway, either around the cap or by bursting the tank. Tightly constricting the expanding gas is equivalent to compressing it, and both liquids and solids resist being compressed with extremely large forces. To avoid rupturing rigid containers, these containers have air gaps, which allow them to expand and contract without stressing them.
Thermal stress is created by thermal expansion or contraction (see Elasticity: Stress and Strain for a discussion of stress and strain). Thermal stress can be destructive, such as when expanding gasoline ruptures a tank. It can also be useful, for example, when two parts are joined together by heating one in manufacturing, then slipping it over the other and allowing the combination to cool. Thermal stress can explain many phenomena, such as the weathering of rocks and pavement by the expansion of ice when it freezes.
What pressure would be created in the gasoline tank considered in Example 2, if the gasoline increases in temperature from 15.0ºC to 35.0ºC without being allowed to expand? Assume that the bulk modulus B for gasoline is 1.00 × 109 N/m2.
To solve this problem, we must use the following equation, which relates a change in volume ΔV to pressure:
[latex]\Delta{V}=\frac{1}{B}\frac{F}{A}V_0\\[/latex]
where [latex]\frac{F}{A}\\[/latex] is pressure, V0 is the original volume, and B is the bulk modulus of the material involved. We will use the amount spilled in Example 2 as the change in volume, ΔV.
This pressure is about 2500 lb/in2, much more than a gasoline tank can handle.
Forces and pressures created by thermal stress are typically as great as that in the example above. Railroad tracks and roadways can buckle on hot days if they lack sufficient expansion joints. (See Figure 5.) Power lines sag more in the summer than in the winter, and will snap in cold weather if there is insufficient slack. Cracks open and close in plaster walls as a house warms and cools. Glass cooking pans will crack if cooled rapidly or unevenly, because of differential contraction and the stresses it creates. (Pyrex® is less susceptible because of its small coefficient of thermal expansion.) Nuclear reactor pressure vessels are threatened by overly rapid cooling, and although none have failed, several have been cooled faster than considered desirable. Biological cells are ruptured when foods are frozen, detracting from their taste. Repeated thawing and freezing accentuate the damage. Even the oceans can be affected. A significant portion of the rise in sea level that is resulting from global warming is due to the thermal expansion of sea water.
Metal is regularly used in the human body for hip and knee implants. Most implants need to be replaced over time because, among other things, metal does not bond with bone. Researchers are trying to find better metal coatings that would allow metal-to-bone bonding. One challenge is to find a coating that has an expansion coefficient similar to that of metal. If the expansion coefficients are too different, the thermal stresses during the manufacturing process lead to cracks at the coating-metal interface.
Another example of thermal stress is found in the mouth. Dental fillings can expand differently from tooth enamel. It can give pain when eating ice cream or having a hot drink. Cracks might occur in the filling. Metal fillings (gold, silver, etc.) are being replaced by composite fillings (porcelain), which have smaller coefficients of expansion, and are closer to those of teeth.
Two blocks, A and B, are made of the same material. Block A has dimensions l × w × h = L × 2L × L and Block B has dimensions 2L × 2L × 2L. If the temperature changes, what is
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, assuming the mercury is unconstrained?thermal expansion: the change in size or volume of an object with change in temperature
coefficient of linear expansion: α, the change in length, per unit length, per 1ºC change in temperature; a constant used in the calculation of linear expansion; the coefficient of linear expansion depends on the material and to some degree on the temperature of the material
coefficient of volume expansion: β, the change in volume, per unit volume, per 1ºC change in temperature
thermal stress: stress caused by thermal expansion or contraction
1. 169.98 m
3. 5.4 × 10−6 m
5. Because the area gets smaller, the price of the land DECREASES by ~$17,000.
7. [latex]\begin{array}{lll}V& =& {V}_{0}+\Delta V={V}_{0}\left(1+\beta \Delta T\right)\\ & =& \left(\text{60}\text{.}\text{00 L}\right)\left[1+\left(\text{950}\times {\text{10}}^{-6}/^{\circ}\text{C}\right)\left(\text{35}\text{.}0^{\circ}\text{C}-\text{15}\text{.}0^{\circ}\text{C}\right)\right]\\ & =& \text{61}\text{.}1\text{L}\end{array}\\[/latex]
9. (a) 9.35 mL; (b) 7.56 mL
11. 0.832 mm
13. We know how the length changes with temperature: ΔL = αL0ΔT. Also we know that the volume of a cube is related to its length by V = L3, so the final volume is then V = V0 + ΔV = (L0 + ΔL)3. Substituting for ΔL gives V = (L0 + αL0ΔT)3 = L03(1 + αΔT)3.
Now, because αΔT is small, we can use the binomial expansion: V ≈ L03(1 + 3αΔT) = L03 + 3αL03ΔT.
So writing the length terms in terms of volumes gives V = V0 + ΔV ≈ V0 + 3αV0ΔT, and so ΔV =βV0ΔT ≈ 3αV0ΔT, or β ≈ 3α.
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