When looking at the importance of cutting speed, there are a few key aspects to consider such as optimal material removal, tool life, and surface finish. Of course, like any milling project, achieving optimal performance could be the most important part of determining the cutting speed. For optimal material removal, a properly set cutting speed ensures efficient removal, reducing machining time while maintaining dimensional accuracy and surface finish.

1D mechanical stack-up analysis: This type of analysis is used for simple designs with one-dimensional components that are stacked on top of each other. A 1D stack-up analysis considers the height and placement of each component and the clearance required between components. This type of analysis is often used for evaluating the stack-up of simple mechanical assemblies such as bearings or shafts. However, it is important to note that a limitation of 1D analysis is that representing geometric aspects of a design such as perpendicularity, parallelism, or concentricity is very difficult or even not posible. 2D mechanical stack-up analysis: This type of analysis is used for designs with two-dimensional components that are placed on a flat surface. A 2D stack-up analysis considers the placement and arrangement of the components in the x and y dimensions, the height of each component, and the clearance required between components. This type of analysis is often used for evaluating the stack-up of components on a printed circuit board (PCB) or for evaluating the clearance between components on a two-dimensional surface.1D stack of disks and a housing enclosure? Instead, you’ve got moving cams, levers, and spring components that are all connected. That could be a product that is a part of an appliance, a car, an aircraft, or a medical device. The geometries quickly become complex. The geometric and dimensional tolerances can easily impact more than the fit of the combined components, they can affect the functionality of the product, such as the forces within and output by the product. 3D mechanical stack-up analysis: This type of analysis is used for complex designs with three-dimensional components that require careful placement and routing. A 3D stack-up analysis considers the placement and arrangement of the components in the x, y, and z dimensions, the height of each component, and the clearance required between components. It also considers the effects of thermal and mechanical stress on the system and the clearance required for airflow or other environmental considerations. This type of analysis is often used for evaluating the stack-up of complex assemblies such as aircraft engines or automotive transmissions. More commonly 3D tolerance analysis works best as a validation tool to check for fit related failure modes that would not be easily found with 1D or 2D analysis. You usually do a 3D tolerance validation near the end of detailed CAD modeling.

There are two types of methods to add all variations in tolerance stack-up analysis: worst-case and statistical-based. Worst-case analysis is a tolerance analysis method that adds all maximum values of allocated tolerances, representing the largest possible variation on an assembled product based on allocated tolerance values. On the other hand, statistical-based analysis is a tolerance analysis method that sums all values of allocated tolerances, assuming some degree of confidence on the estimated sum-of-squares total variations. The production processes of products to be analyzed under statistical-based analysis must be under control, and there must be no mean-shift on the production processes of the products. The lower variation values of statistical-based analysis means that the values for allocated tolerance on features can be made larger so that production and inspection costs can be reduced.

Tolerance stack analysispdf

When it comes to the difference between feed rate and cutting speed, not only is there a direct relationship between the two, but a lot of the relationship has to do with the materials being used. Understanding this relationship is essential to completing a successful operation as well as preventing damage to your tools or the part you are working on. The direct relationship in general is to understand that as cutting speed increases, the feed rate also increases to maintain a constant material removal rate. On the other hand, decreasing cutting speed often requires a reduction in feed rate to prevent excessive tool wear and maintain machining precision.

Next up, the type of cutting tool, its geometry, and the depth of cut all play a role in determining the optimal feed rate. Larger diameter tools typically require slower feed rates because they can remove more material per revolution and avoid tool overload. It’s also important to note that a sharp and properly maintained cutting tool is essential for achieving optimal feed rates. Dull or damaged tools may require slower feed rates to compensate for reduced cutting performance.

The analysis carried out in this post can lead to early design corrections and cost savings in product development. Tolerance analysis and allocation are iterative processes that work together to ensure the final variation on the key characteristic is below a certain threshold. The analysis discussed in this case is limited to 2D variation and does not consider rotational variations.

The main goal of mechanical stack up is to determine if the selected tolerances are correct so the fit, form & function of the product is secured.

Tolerance stack-up analysis can help answer important questions about the assembly process and the final critical dimensions (KC) of a product before manufacturing, such as the effect on the final assembled product if the location of a hole deviates from the nominal position, how much material needs to be preserved in a machining process, and what happens if the manufactured hole is made larger than its nominal diameter. It can also determine how much the gap or clearance variation between two surfaces of a part changes after an assembly process and how much the optimal temperature of the assembly process should be to maintain the critical dimensions of a micro-scale producto.

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In order to compare the solution developed in this post for 2D tolerance stack up, the following picture shown the result shown from the original maker for this case study (See requirement 3).

The choice of dimensionality of the mechanical stack-up analysis depends on the complexity and requirements of the design. Here are some guidelines for choosing between 1D, 2D, and 3D mechanical stack-up analysis:

Based on this method, the total variation is calculated by summing all the absolute values of based on this method, all manufactured parts (base, support, pulley and rotor) should be inspected to assure that all parts are in tolerance. The total variation, based on worst-case, due to the given tolerances is (based on the tolerance chain and table A:

However, it’s essential to balance cutting speed with factors such as tool material, workpiece material, and desired surface finish to prevent excessive heat generation, tool wear, or even workpiece damage. Now let’s discuss the factors that affect cutting speeds so you can truly understand the difference between cutting speed and feed rate and why that is important.

Tolerance stack analysismethods

Unlike cutting speed, which relates to the rotational motion of the tool, feed rate pertains to the linear motion of the tool along the workpiece. The feed rate directly impacts parameters such as chip thickness, depth of cut, and tool life. Increasing the feed rate can enhance material removal rates and productivity, but it must be carefully controlled to prevent issues like tool breakage, poor surface finish, or excessive load on the machine.

Comprehending the difference between feed rate and cutting speed is crucial for maximizing efficiency and precision in machining operations. While cutting speed determines how fast the cutting tool moves relative to the workpiece material, feed rate controls the rate at which the cutting tool engages with the workpiece. By carefully adjusting these parameters based on material properties, tool characteristics, and desired outcomes, machinists can achieve optimal results in terms of surface finish, dimensional accuracy, and tool life.

A "stack-up" refers to the tolerance stack-up calculations that show the cumulative impact of part tolerances with respect to an assembly requirement. Tolerances "stacking up" involves adding tolerances to determine the total part tolerance and then comparing it to the available gap or performance limits to ensure that the product's functionality is not compromised.

Understanding the difference between cutting speed and feed rate is essential for anyone involved in machining processes. These two parameters play a pivotal role in determining the efficiency, precision, and quality of machining operations across various industries. While both cutting speed and feed rate influence the material removal rate, they operate on distinct principles and affect the machining process differently.

Here are some factors that contribute to the feed rate and why it is so important to understand when performing your CNC milling projects!

Tolerance stackup example PDF

Next, the feed rate significantly influences the surface finish of machined components, a critical factor in determining part quality and functionality. By adjusting the feed rate, machinists can tailor the chip formation process, optimizing chip size and evacuation to achieve smoother surfaces and finer tolerances.

L, D, I, J, K are nominal dimensions so that their variations are zero. C, E, F, G, H, are due to tolerances both dimensional and geometrical tolerances so that the mean value is zero.

Tolerance stackupanalysisExcel

First and foremost, feed rate plays a pivotal role in determining the lifespan and performance of cutting tools in your operations. Optimal feed rates ensure that the tool maintains a consistent level of engagement with the workpiece, minimizing wear and prolonging tool life. Conversely, inadequate feed rates can subject the tool to excessive stress or rubbing, accelerating wear, and potentially leading to premature tool failure.

Table X shows the detailed calculation of the mean (Xn) and variation (Tn) for each point on the tolerance chain in figure X. In table 5, the mean and variation value for each point on the chain are presented. Note that the tolerance format is in equal-bilateral format.

Tolerancestack-up calculator

The following step is defining the tolerance chain, for requirement 3, as mentioned previously this step is part science and part black art due to depend to much of the experience of the people that handle the stack up how to define the tolerance chain, it is a process that improves the more frequently it is performed, and the more knowledge is gained by carrying out tolerance analysis.

In this blog post, we will uncover the fundamental difference between cutting speed and feed rate, explaining their significance and how they impact machining operations. Through understanding these differences, machinists and engineers can optimize their machining strategies to achieve superior results and enhance productivity. Before we compare the difference between feed rate and cutting speed, let’s first go over what is cutting speed and feed rate, and the factors that affect them.

Tolerancestack-upanalysiscourse

Identify the components that make up the assembly and determine their dimensions and tolerances. Define the assembly requirements, including the allowable tolerance range and the functional requirements of the assembly. Determine the tolerance chain and the potential sources of variation in the assembly process. Perform a worst-case analysis or Statistical Method to determine the maximum potential deviation in the assembly due to tolerances. Calculate the stack-up variation by summing up the variations in each component and the variation introduced during the assembly process. Compare the stack-up variation with the allowable tolerance range to determine if the assembly meets the functional requirements. If the assembly does not meet the functional requirements, determine which components or assembly steps need to be adjusted to reduce the variation.

The rigidity of the CNC machine and its spindle, as well as its horsepower, determine the maximum feed rate that can be applied without causing excessive vibration, deflection, or tool chatter. More rigid machines with higher horsepower can generally handle higher feed rates. It’s also essential to have a secure workpiece fixturing to maintain accuracy and stability during milling operations. Poor fixturing can lead to vibrations and chatter, requiring a reduction in feed rate to avoid surface finish issues and dimensional inaccuracies.

Questions to be answered by performing tolerance stack-up analysis by performing tolerance stack-up analysis, important questions regarding the assembly process and the final KC of a product can be answered before manufacturing, for examples:

Lastly, it’s important to utilize your CNC software as this is an invaluable tool when determining your cutting speed and feed rates. Advanced CNC machining software often includes features for simulating machining processes and optimizing cutting parameters, helping machinists streamline the process of finding the optimal balance between cutting speed and feed rate.

What is the effect on a final assembled product when the location of a hole on a bracket deviating few millimetres from the hole nominal position?  How much material need to be preserved in a machining process so that there are still materials for post-processing, for example boring process, to get smooth surface finish or high dimensional accuracy on a feature? What is the effect if a manufactured hole is made larger from its nominal diameter? What is the effect if the number of components constituting an assembly are added? Does the surface of the rotor and stator of a motor touch each other during operation?  How much the gap or clearance variation between two surfaces of a part after an assembly process? How much the optimal temperature of the assembly process of a micro-scale product should be to eliminate or reduce the effect of component thermal expansions during the assembly process so that the KC of the product can be maintained?

Tolerance analysispdf

In summary, the choice of mechanical stack-up analysis depends on the complexity of the design, the number of dimensions of the components, and the design requirements, such as clearance, thermal and mechanical stress considerations, and airflow requirements. A 1D analysis is used for simple designs with one-dimensional components, a 2D analysis is used for more complex designs with two-dimensional components, and a 3D analysis is used for the most complex designs with three-dimensional components that require careful placement and routing.

Another helpful tip is to continuously monitor your cutting tool wear and workpiece surface quality during machining operations. This can provide valuable insights for fine-tuning cutting speed and feed rate settings, helping you to achieve optimal performance with your milling projects.

The case study is the R-A assembly (see pictures bellow); it consists of two nominally parallel shafts (Item 3) mounted into a housing (Item 1). During assembly, the bushings (Item 2) have a slight interference fit with the holes of the housing and a small amount of clearance with the shafts in order to allow the shafts to rotate. Retaining rings (Item 4) do not slide the shaft out of the housing along the axial direction. This assembly is simple, but it represents many common products in industry, such as blowers, gear boxes, and pumps.

To understand the difference between feed rate and cutting speed, we need to explain what feed rate is and the factors affecting it. Feed rate, denoted as F, refers to the rate at which the cutting tool advances along the workpiece in a specific direction, typically measured in inches per minute (IPM) or millimeters per minute (mm/min).

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One key fact is that choosing worst case condition is It is statistically Improbable - The chance that all parts are manufactured to their extremes (maximum tolerance range), and then all those parts are chosen for the same assembly is extremely small. Like 1 in 10 million small. This has a lot to do with the assumption of standard distribution, whereby most of the manufactured parts are going to fall within the range of tolerances around the median. This makes the scenario where all tolerances are at their maximum, together, an outlier on the longtail of a six-sigma graph. Modeling your product and manufacturing on an outlier is going to increase your manufacturing costs exponentially, and only to account for a scenario that will statistically never happen.

Next, let’s talk about the importance of cutting speed and tool life. Operating within the recommended cutting speed range extends the lifespan of cutting tools by minimizing wear and reducing the risk of tool breakage. This is crucial for reducing production costs associated with tool replacement and maintenance.

Just like cutting speed, the material type also impacts the feed rate. Different materials have different properties, such as hardness, toughness, and brittleness, which affect the optimal feed rate. Harder materials generally require slower feed rates to prevent excessive tool wear and breakage, whereas softer materials, such as aluminum can have a faster feed rate without damaging the tool.

Finding the optimal balance between cutting speed and feed rate often requires experimentation and optimization. Machinists may need to adjust these parameters based on factors such as material type, tool geometry, machine capabilities, and desired machining outcomes. Over time, you will be able to determine the appropriate parameters needed as you learn more about the factors that contribute to cutting speed and feed rate.

Cutting speed, often denoted as S, refers to the velocity at which the cutting tool moves across the workpiece surface. It’s typically measured in surface feet per minute (SFM) or meters per minute (m/min). Cutting speed is primarily influenced by the rotational speed of the spindle and the diameter of the cutting tool. A higher cutting speed means the tool is moving faster relative to the workpiece, resulting in increased material removal rates.

When examining the factors that affect the cutting speed, you should consider the material type. Different materials have varying hardness and machinability, which directly influences the optimal cutting speed. For instance, the cutting speed for aluminum will be significantly higher than the speed for hardened steel. Since aluminum is softer, the tool encounters less resistance allowing for faster speeds without excessive tool wear. Trying to cut harder materials with a high cutting speed can result in damage to the tool and could compromise the machining accuracy.

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Mechanical stackup analysis is a process of evaluating and determining the total thickness, dimension, and tolerance of a mechanical assembly. It involves assessing the interaction of individual parts in the assembly and the potential impact of their tolerances on the overall functionality of the assembly.

Tolerance stack analysisexample

Next, it’s important to understand how the tool type plays a role in cutting speed. The type of cutting tool, its material composition, and geometry also impact the recommended cutting speed. Carbide tools, for example, can withstand higher cutting speeds compared to high-speed steel tools due to their superior hardness and heat resistance. Going back to our example above, cutting hard steel can quickly wear down cutting tools due to its abrasiveness.

Lastly, the cutting speed directly influences the quality of the surface finish of the machined part. Optimal cutting speeds can produce smoother surface finishes, reducing the need for additional operations such as polishing or grinding. It’s important to highlight that higher cutting speeds typically result in smoother surface finishes, provided that the other parameters are optimized accordingly.

Monte-Carlo (MC) tolerance stack-up analysis is a way to check if parts will fit together correctly in a product. It uses a statistical approach to account for variations that might occur due to design tolerances. Basically, it creates a chain of calculations using matrices to see how these variations might impact the final assembly feature. To do this, it assumes that the variations follow a normal distribution, also called a Gaussian distribution.

For this analysis, the total variation is calculated by root-sum-squared all the safety factor in this analysis is 1.5 considering some parts are made from other manufacturers.

However, the relationship between cutting speed and feed rate can vary based on the material being machined. For example, while softer materials may allow for higher feed rates at increased cutting speeds, harder materials might require lower feed rates to prevent tool damage. Note that moving too slowly can also cause issues like reduced tool life from rubbing and more heat transfer into the material or tool.

Maintaining attention to feed rate is essential for attaining the desired surface finish. Ultimately, feed rate optimization in CNC milling embodies a delicate equilibrium between material removal efficiency, tool longevity, and surface finish quality, underscoring its indispensable role in shaping the outcomes of precision machining processes.

Lastly, the rigidity and power of the CNC machine play a crucial role in determining the maximum cutting speed achievable without compromising the tool’s integrity or the quality of the machined surface. Cutting steel may require slower cutting speeds to maintain precision and avoid vibration or deflection in the machine tool. Materials like aluminum have lower cutting forces which allow for higher cutting speeds without reducing the machine’s accuracy.

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