13-)i. 1. deirmen. 2. el deirmeni. 3. fabrika, yapmevi, imalathane. f. 1. deirmende tmek, ekmek. 2. deirmenden geirmek. 3. (parann kenarn) di di yapmak. 4. around k. dili dolanp durmak.
The rising costs for and the possibility for limited availability of electrical energy are emphasizing the continual conflict faced in the selection of comminution circuits used in preparing ores for concentration, namely; capital cost vs. operating cost. Frequently, the circuit with the lowest capital cost is not the most efficient in the use of electrical power and wear resistant materials.
The simplest circuit in terms of flow, pieces of equipment and capital cost is the single stage autogenous or partial autogenous circuit used to grinding primary crusher discharge or run of mine ore to the desired product size. (Fig. 1) From this circuit, complexity increases to multi-stage crushing circuits preparing feed for multi-stage grinding circuits. Fig. 2 showing a three stage rod mill ball mill arrangement is an example of a complex grinding circuit. Stage concentration further complicates the flow. Multi-stage circuits being the most expensive to install, often give the greatest operating flexibility and offer the best possibilities for the most efficient use of available power and wear resistant materials.
Within available grinding circuits, other comparisons such as high speed vs. low speed mills, grate discharge vs. overflow discharge, metal liners vs. rubber liners, high charge vs. low charge, etc. all add to the conflict between capital cost and operating cost as partially reflected by the most efficient use of electrical power and wear resistant materials.
Bench scale and pilot plant scale test work, the cost for which must be within the scope of the project, can be used in establishing the following ore characteristics needed to make an evaluation of the various alternative circuits available.
The current and probably on-going energy availability and cost crisis plus financial considerations demand obtaining the best efficiency from the comminution circuits selected. This calls for designing the comminution circuits so that; instrumentation, data collection and recording and even the use of computer controls can be selected to perform the required measuring and calculating functions.
that influence circuit efficiency, and cause variations in operational factors, such as mass flow in the circuit, circulating load and particle size distribution which when measured reflect changes in the four key variables.
By definition work index is the power required to comminute a short ton of a material from an infinite feed size to 80% passing 100 micrometers. Therefore, by definition, work indices calculated from operating data take the variations in the four key variables in the circuit performance and refer these to a common range of work.
Unless operating work indices are to be compared to work indices obtained from the standard Bond Laboratory procedures for impact and grindability testing, it is not necessary to calculate operating work indices on the basis of short-tons when plant feed data is measured in metric tonnes or long tons.
Circuit feed rate is obtainable by weighing and totalizing the feed going to each comminution stage. Using power measuring equipment, power delivered to the motor driving the comminution machine is obtainable. These two with operating time data gives the power per tonne data needed for the operating work index equation.
Either automatic samplers or manual sampling can be used to collect samples on a regular basis for determination of pulp density and screen analyses. From these, the 80% passing size for the feed and product can be determined.
One of the fundamental parameters of any CNC machining, and 3D machining in particular, is the stepover. It is not a stretch to say that it is the single most important parameter in determining the quality of the finished parts you will produce. A machinist can pick a value by feel, based on previous experience, or do the math and calculate the exact value that will give them the finish required. New users generally dont have the experience and dont know the math so it takes a while to get an intuitive understanding of of the stepover parameter.
The following post focuses mostly on 3D toolpaths so well be assuming the use of a ball mill. Once you understand the basic concepts its easy to apply them to flat end mills and bull mills. Well try to build to some rules of thumb rather than derive equations that most users wont beinterestedin.
Almost all CNC toolpaths are based on the concept of one toolpath being offset from another by some distance; this offset distance is generally called the stepover. Most CAM software, MeshCAM included, uses a couple toolpath styles in particular with these offsets- the raster toolpath (sometimes called a zig-zag toolpath) and a contour offset.
The area in red is the part of the stock leftover on the part in between the toolpath offsets. Its important to understand that these are not good; they are not in the CAD and may need to be removed after machining by sanding or polishing. CNC machinists are almost always trying to reduce the scalloping as much as possible and many man-years of effort have been spent trying to develop toolpath algorithms that minimize them.
A moment spent looking at the image above illustrates at connection between scallop height and the stepover value- increase one and the other increases as well. In the images below well use a stepover equal to 1/10, 1/5, and 1/3 of the tool diameter to show this correlation. To put real numbers on this, that would be equavalent to a .012, .025, and .042 stepover for a .125 ball mill.
It shouldnt be surprising that youll have to givesomethingup if you want to use a really small stepover. In this case youll trade time for quality- you give up machining speed to use a small stepover or give up quality if you want a quick machining time. This is easy to understand when you consider that the total length of a toolpath will approximately double if you cut the stepover in half. The question is, Will cutting the stepover in half double the quality of my part?
It turns out that there is a point of diminishing returns in the time/quality tradeoff. Below is a graph of scallop height vs stepover that illustrates the effect. The graph has been normalized to a tool diameter of 1.0 so its easy to scale it to any tool you happen to be using. (Click on it to see a bigger version)
The important thing to note is the shape of the graph- it tends to flatten out when the stepover goes below about one eighth of the diameter. This means that when you go below this point youre going to take more time to machine without a proportional gain in finish quality. If youre machining a steel injection mold then it may still be worth it but you really need to be sure before doing that.
Heres the other thing we can glean from the math behind the chart above- for a given stepover, a larger tool will give you a smaller scallop. This means that you can get a better finish for free if you can use a larger tool. Obviously, this only works if a bigger tool will fit into all of the parts of your geometry but this is one of the few win-win things we can do get better results if it does work for your geometry.
Before you figure out what stepover you need to get a .0001 scallop, think about what you are going to machine- wood, tooling board, aluminum, steel, etc. I can tell you that in many cases you can do 10 minutes of sanding on a wood part to get a finish that would have taken you an extra hour or two to get straight from the mill. Likewise, tooling board like Renshape can be hand finished quickly enough that it may not be worth doubling the machining time to get a better finish. If youre cutting steel or other hard materials then its probably worth letting the mill do more of the hard work.
The second characteristic of the material to consider is what kind of detail it can hold. MDF will not hold features in the .01 range but metal will. If your material cannot hold a detail that is smaller than your scallop height then you do not need to reduce the stepover; doing so will only waste your time without producing a better finish.
It may be a poor craftsman that blames his tools but we do have to be realistic about the nature of our equipment. In particular, how long do you trust your mill or router to run trouble-free? I started out with a small table-top mill that, while very good, could not be trusted to run for hours without missing a step or hiccuping in some way that gouged a part I had waited half a day to get. If you have a machine like this then its worth thinking about the picking the maximum stepover based more on machining time than finish.
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A cutting force model for ball end milling is developed, the model being based mainly on the assumption that the cutting force is equal to the product of the cutting area and the specific cutting force. The formulation of the cutting area is derived from the geometry of the mill and the workpiece, whilst the specific cutting force is obtained by third-order curve-fitting of data measured in experiments. The model established in this paper predicts the cutting forces in ball-end milling much more accurately than do previous models.Get in Touch with Mechanic