In the equation of Time for Cylindrical Grinding Cut Length of Cut = Length of job + Over-Travel where, Over-Travel equals to 0.5 cm.And Feed/Rev. = w/2 (for rough cut) or w/4 (for finishing cut). Where, w = Width of Grinding Wheel
... in-feed centerless grinding based on a ... be obtained under a lower grinding wheel feed rate, ... and used to draw the profile and calculate the ...calculate spindle rpm in grinding machine ... Stock removal too slow when in feed grinding. Increase in feed rate. Centerless Grinding ...
Ore beneficiation equipment, sand making equipment, crushing equipment and powder grinding equipment, which are widely used in various industries such as metallurgy, mine, chemistry, building material, coal, refractory and ceramics.
Optimize your grinding process using our online calculators built by engineers, for engineers. With just a few clicks you can easily calculate the ideal dressing and coolant parameters and calculate grinding wheel speeds for your specific abrasiveapplication.
The goal of thesecalculatorsis to provide users with starting parameters when truing our products using diamond dressing rolls, tomatch the velocity of the coolant with the velocity of the grinding wheel and to calculate SFPM (Surface Feet Per Minute) and MPS somachine operators don't have to do the conversion.
Cycle time is a contentious topic, not because it doesnt provide value to manufacturers, but because the definition of cycle time is widely debated. Every manufacturer defines and measures it differently, adding to the confusing nature of applying cycle time from one company to another. Let alone the fact that it can be hard to calculate on the floor given all of the factors that contribute.
The Cycle Time Formula is an essential manufacturing KPI to understand in manufacturing. It is used by ERP and MES systems for scheduling, purchasing and production costing. It is also a critical part of the OEE calculation (use our OEE calculator here). Fortunately, it is easy to calculate and understand.
The rest of this resource serves as an explanation of cycle time and why the definition often varies. Then, well dive into using an ideal cycle time on the floor to monitor machines and the production process.
1. Theoretical Max Machine Cycle Maximum number of parts a machine can produce in a particular time period 2. Target Cycle Time Time you would need to hit to deliver a product on time to customers (or downstream processes) 3. Actual Cycle Time Time it takes to produce an actual number of parts or complete a cycle
Using an example to better explain, lets say youre a bottling company. Using custom equipment that bottles beer, you know the machine can theoretically bottle 784 bottles per minute (theoretical max machine cycle) and thats as fast as the filler can go. But, you know you arent actually bottling 784 bottles a minute. How fast does the machine really run over a period of time?
You know you only need to bottle 732 to deliver on time to your customers (target cycle time)but are you hitting that target? Based on production numbers, you determine youre only bottling 711 bottles per minute (actual cycle time).
Thats the difference between the 3 terms. Now, you may begin to understand why using a blanket term of cycle time to describe the production process can be confusing if the KPIs arent clearly defined.
In another example, you are a furniture manufacturer. The company you work for makes desks for elementary schools. If you can make 15 desks an hour, you will be able to deliver on time to the schools (target cycle time). But, in theory, your machines and people are capable of making 20-30 per hour (theoretical max machine cycle).
In the end, you only need to produce 15 to meet demand. But, again, you determine youre making less than the target. In fact, youve only made 10 desks (actual cycle time). This indicates a much larger problem that needs to be addressed in order to meet demand.
There may be other processing problems going on that are slowing things down. Do you have enough products to make a completed desk? Do you have enough people on the line? Is the machine available to run? Do you have boxes to send the desks to the schools in?
A lean expression is that lowering the water level of inventory exposes problems (like rocks in the water) and you have to deal with the problems or sink. Creating flow, whether or materials or of information lowers the water level and exposes inefficient that demand immediate solutions. Everyone concerned is motivated to fix the problems and inefficiencies because the process will shut down if they dont.
Knowing the differences between the terms is only half the battle. Its also important to know which ones you should use and when. This is where its essential to understand what youre actually measuring and why.
Most people think cycle time is actually the same as the machine cycle (again, throwing out more terms, but its important to understand what youre measuring), but a machine cycle does not represent the entirety of a process. Its more important to look at the complete process (aka looking beyond just the machine cycle). This includes the time it takes for an operator to load a job, the time and effort it takes to get the machine up and running, unloading the part or adding finishing touches by hand once the part has been made.
The orange portion for example #1 is likely what you, and many other manufacturers, think represents the cycle time. You could make 200 parts, but you probably didnt take into account the manual actions the operator needs to do to get it up and running in the first place. If thats the case, you will have over-estimated the amount of product that can be made in a given period.
Example #2 is good for making estimates because it shows how fast you are capable of running (from start to finish), and will, in turn, give you a target cycle time that is easier to hit and measure. Then, you can use that number to calculate how much product youre actually making and if there are problems or issues that need addressing.
Lets be the devils advocate for a moment. Some manufacturers may only want to look at the machine cycle. Specifically, how close are you getting to removing the blue parts of this cycle? Not to sound repetitive, but this severely limits your ability to measure the process as a whole.
Do you want to measure the time it takes to produce just the part in the machine (machine cycle) or the entirety of the process to determine whats actually possible (cycle time)? If you said the latter, yes, thats what would recommend, too.
At this point, you likely know which metric we believe in measuring, but for the sake of driving the point home, we suggest measuring the entirety of the cycle and referring to that as the ideal cycle time.
Think of it in terms of the bottling example used above. If youre only evaluating the machine cycle, you will know how long it takes to fill the bottle and cork it. This is the work done by only the machine.
But, if youre using complete cycle time of the process, you not only know how long it takes to fill the bottle and cork it, but how long it takes people to load and unload the bottles, box the product, and send it to the delivery area.
If youre truly trying to understand how much beer can be bottled per minute, per hour, or whatever the preferred time frame is, you have to include the role people play in producing the product. That will give you a complete picture of how long it takes to get the product out the door.
When you look at the complete process, this helps you estimate how many parts you can make in a day, realistically. You dont really want to use the machine cycle because it will give you an overly optimistic view that youll never be able to hit.
If 80% is the highest machine performance that can be achieved, this doesnt bode well for morale on the floor. Your employees will never hit their numbers because the goal is based solely on the time it takes for just the machine to run, not all of the other factors that contribute to the production of a part. If theres a goal that can never really be met, employee engagement will decrease leading to negative employee experiences and unfavorable company culture.
In the archetypical Lean organization, manufacturers use cycle time to determine where the production process may be falling short. Thats where the difference between the target and actual cycle time comes into play. Do you need additional help on the line? Can you figure out where the bottlenecks are? Do you need an additional station to meet demand?
The ideal cycle time, not the theoretical maximum of the machine, will help you determine how best to measure and utilize the machine (and people) on your line. Using that knowledge, you can determine you only need to run the job for 2 hours tomorrow and 2 hours the next day to meet demand.
Think about what your timeline looks like at the end of the day. Does it include the setup time or the first 60 minutes of a production run as downtime? Do you estimate the number of parts needed to meet demand?
If youre not including that setup time or any other non-value-added process, in the cycle time, youre missing out on a crucial opportunity. To give yourself and your employees an accurate representation of how much needs to be produced per minute, hour, or shift, measure the whole process.
An example is the best way to drive the point home. If you have 10 hours of operation scheduled, but 1 hour of that is allotted for a changeover, you really only have 9 hours of runtime. Theoretically, the machine can produce 12 parts, but you dont need that many. The target cycle time is 9 parts per shift. With that knowledge, you know you need to create 1 part per hour to meet demand.
All Norton grinding wheels are marked with a maximum operating speed in RPM. Most machines, and especially CNC machines, use Surface Feet Per Minute (SFPM) as an input, which requires operators to do the conversion. This calculator will do this by inputting the wheel diameter in either English units or metric, then inputting the RPM to calculate SFPM or MPS.
In the machining world, turning tools such aslathesandmillsare the flashy stars. In fact, theyaremachining to most people. However, the ability to doprecision centerless grindingin addition to machining is a definite advantage.
Centerless grindingis one of several machining processes that use abrasive cutting to remove material from a part (workpiece). The process involves the part being supported on a workpiece rest blade that sits between two rotating cylinders:
The beauty of centerless grinding is that the workpiece is held in place by the pressure of the rotating wheels. No fixturing is required, so the setup is simple and turnaround times are fast. And because the workpiece is rigidly supported, there is no deflection during the grinding operation.
But despite these and other advantages, centerless grinding has fewer practitioners than machining. And although the centerless grinder has been around for almost a century, a lot of people struggle with the fundamentals of the process and how it works.
What else is helpful to know about this somewhat mysterious process? Lets take a look at8 basic principles of centerless grinding things it is helpful (and we hope, interesting) to know about this mature and yet still somewhat unfamiliar process.
A downside of centerless grinding is, unlike machining, you cant have as manymultiple axes operating on the workpieces. However, there are many parts where the centerless process addresses the limitations of machining in terms of dimensions, materials, and surface finishes.
Thats why we like to say that where machining ends, the centerless grinding process begins. For instance, if you have a part that is out of round from a turning machine and the parts diameter is too small or its center is impossible to mount, you can achieve roundness throughcenterless grinding techniques.
Since they owe much of their functionality to some basic principles of physics, centerless grinders dont have a lot of moving parts. That makes centerless grinding a relatively simple process thats ideal for finishing theoutside diameter of small cylindrical metal parts requiring a tight tolerance.
Centerless grinding is virtually continuous because, compared with grinding between centers, the loading time is small. So, long lengths can be ground continuously. Even large quantities of small parts can be automatically ground by means of various feeder attachments.
In addition, centerless grinders can perform consistently at high speeds. That makes the process a great choice for high-volume applications in aerospace, automotive, military, medical, and other industries.
In-feed grinding also calledplunge grinding is used to grind cylindrical parts with notches or complex shapes, such as gear shafts. Here, the workpiece rest blade needs to be tooled to match the shape of the part, and the grinding and regulating wheels must be dressed to match the parts desired profile cut.
With the in-feed method, the regulating wheel spins the part at one speed while pushing it towards the grinding wheel, which is spinning at a faster speed. The greater the difference in speeds, the faster the removal rate.
In addition to being available in different diameters and widths/thicknesses,centerless grinding wheelscome in different grain types and grit sizes, often using superabrasive materials such as polycrystalline diamond and cubic boron nitride.
Generally, the centers of the regulating and grinding wheels are set at the same height on the machine, and the center of the workpiece is situated higher. However, if the workpiece is set too high, it may exhibit chatter. If the workpiece is set too low, it may be out of round.
The goal is to keep the part (1) in contact with the regulating wheel and (2) rotating at a slower speed, while the faster, larger abrasive grinding wheel applies the force that creates the precise roundness of the part. Using the correct wheel angles helps to ensure that the entire surface of the grinding wheel is in use.
If the angle of the regulating wheel is too acute, it can cause the workpiece to go too far into the grinding zone. This can result in uneven wear, tapering, and reduced wheel life. If the regulating wheel is too close to parallel with the grinding wheel, it can cause the parts to stall between the wheels or, worst-case scenario, cause a workpiece/wheel crash.
But with a wheel width of 6 (152.4 mm) or 8 (203.2 mm), that same angle may generate too much pressure toward the grinding wheel and cause chatter. In this case, changing the angle to 20 or 25 will reduce the pressure and eliminate the chatter on the part.
Centerless grinding requires the use of correctly pressurized coolant to overcome the air barrier created between the grinding wheel and workpiece during the grinding process. This allows the coolant to flow in the space between the two.
The coolant step in centerless grinding is critical to preventing heat from returning to the workpiece or the grinding wheel. Otherwise, it can be difficult to hold tolerances for roundness and straightness, and thermal damage can even cause the grinding wheel to blister and crack.
To increase process efficiency and productivity, CNC programmable controls make it even easier to set up and change the equipment from one job to the next. Other newer technologies are making it possible to:
For example,the latest generation of centerless grinding machinesremove the regulating wheel and replace it with stationary wire supports that have a bushing mode option. This option allows for intricately ground shapes and exotic dimensional features by performing similarly to the guide bushings onSwiss-style automatic lathes.
In addition, advances in software controls, direct drive motors, and robotic loading/unloading of workpieces allow the simple concept of centerless grinding to make complex parts that were previously unthinkable.
For example, from the beginning Metal Cutting has been augmenting our cutting capabilities with centerless grinding for the production of glass-to-metal-seal parts. More than 50 years later, we still perform centerless grinding virtually every day and we continue to stay abreast of industry trends and customer demand by using the latest generation of equipment.
In the right hands, centerless grinding is capable of producing a machined surface that a process such as turning simply cannot match both as an Ra value and also on certain metals that are nearly impossible to turn with a cutting tool.
Almost 100 years after its inception, centerless grinding is still not as common as other metal fabrication methods. Yet, the unique qualities of a ground (vs. turned) finish combined with the innovations and variations available with centerless grinding allow it to produce metal parts that are irreplaceable for their applications.
In circular runout vs. total runout, the first controls variation in circular features of a part while the other controls variation in the entire part surface. Learn the difference and how to measure them here.
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