Design Tips For Reducing CNC Machining Costs
- Gavin Leo
Despite the presence of newer and more advanced technologies, like 3D printing, CNC machining continues to be a cost-effective means of producing goods and products on demand. Of course, the main reason behind this includes the many benefits that it provides to businesses.
Among these benefits are high-quality parts and components, quick lead times, a high level of precision, and low tolerance. The fact that it has quick lead times also means that businesses can get the parts they ordered quickly, thereby significantly decreasing market time.
Note, though, that you should also know how much it would cost to have CNC machining projects. That way, you can readily prepare for it and find ways to reduce CNC machining costs as much as possible.
CNC Machining Defined
To know how much do CNC machines cost, as well as the entire machining procedure, you should delve deeper into the actual process. In general, Computer Numerical Control (CNC) machining refers to a manufacturing strategy that uses high-speed and automated cutting tools to create shapes from certain raw materials, like plastics and metals.
To guarantee quality and precise results, the process utilizes standard CNC machines, like CNC routers, CNC lathe machines and CNC milling machines featuring three, four, and five axes. These CNC lathe and CNC milling machines also work using CAD (computer-aided design) models, thereby providing geometry details for the whole process of machining.
The help of a skilled machinist is necessary in programming the tool paths based on the machined parts’ geometry. What’s great about the CNC milling machine, CNC routers, or any type of CNC machine, is that it is highly versatile in the sense that it is vital across different industries that need custom components for their CNC machines.
Among these industries that proudly use and try to find CNC machines are those in the robotics, aerospace, and medical fields.
How Much Does CNC Machining Cost?
One thing to note about the CNC machining technology is that it is quite a complex process that involves different aspects that directly affect the final cost. If your goal is to optimize the CNC machining operations and manage the associated costs and expenses wisely and effectively, then you should delve deeper into the different factors that might influence the CNC machine cost.
In most cases, the driving factors that result to the increase or decrease of the overall cost include the following:
Machining time
The machining time is a major factor driving the cost of CNC machining. In general, you will spend more if it takes a longer time to operate the machine.
Cost of material
Another major contributor to how much you will spend on CNC machining is the cost of your chosen bulk materials. CNC machining costs may also go up or down depending on how hard or easy it is to process the material in the machine.
Start-up cost
Expect the start-up or initial cost to be the fixed ones in the final CNC machine costs. In most cases, you should set up this cost to cover your spending on product planning and CAD file preparation. Even when used on small volumes, the initial or start-up costs will be extremely significant.
Material finish
If you add finish to your chosen components or parts, then expect the final look to improve. The finish can also improve the ability of the component to resist and withstand harsh environments. Note, though, that this benefit can also greatly increase CNC machining costs.
Other related manufacturing cost
The overall machining costs will also be affected if there are other things you will have to spend related to manufacturing. Note that there are CNC-machined components with special requirements, such as thin walls or tighter tolerances. Such requirements, including raw materials, can affect machining time, which will also end up driving up the cost.
As for the CNC machines, you can expect them to be available in different types and you can choose one depending on your needs. Some of these CNC machines are costlier to operate and run, which is the reason why they also cost higher. For instance, the standard 3-axis CNC machines usually cost around $35 to $40 per hour.
Meanwhile, other CNC machines with multiple axes are more complicated to operate, so expect them to cost higher, usually around $75 to $120 hourly. Overall, the cost of CNC machining varies depending on different factors, like the ones mentioned. It would be great if you contact the company you intend to hire for this service personally, so you can tackle the cost.
Design Tips to Keep CNC Machining Costs Low
Of course, just like everything else, you want to save money when taking advantage of CNC machining. If your goal is to spend less on CNC machining, then here are some design tips that will keep the cost of operating the CNC machine low:
#1 – Add relief to corner pockets
To lower the CNC machining cost, you may want to add relief to corner pockets. This can help introduce a change in design that can speed up the CNC machining and manufacturing process, make it easier, and lower the risk of tool wear. Putting on corner relief can actually help deal with sharp internal corners in pockets that make it harder for CNC machines and tools to operate.
Trying to CNC machine a sharp corner may cause the tool to turn unnaturally, leading to tool wear. It can also be time-consuming. What you should do is add reliefs or radii to the pockets’ sharp corners, giving the CNC machinery the chance to make smoother turns during the machining and manufacturing process.
The result would be a significant reduction in machining time and a lower risk of wear. This also leads to the reduction of the overall cost of machining regardless of the actual raw material cost.
You may use the standard radius, such as 0.125” or 0.5”, depending on the size of the tool. You can also go for a custom radius depending on the pocket’s shape and size. As you add relief, you also get to improve the efficiency of the whole CNC turning and machining process.
Be mindful of your chosen tools, toolpath techniques, and overall design, too. Raw material costs should be low. This helps strike the perfect balance between lowering machining time and ensuring that you get to maintain functional part requirements.
#2 – Deburr edges
You can also deburr the edges of any type of CNC machine on your own. Note that deburring plays a vital role in the entire CNC machining process. However, it may also be costly and time-consuming if you don’t manage it properly. With that said, you should design parts while greatly considering the deburring process as it can significantly lessen the cost and time required for deburring.
Again, let’s talk about sharp edges. If you experience this problem with any type of CNC machine, then note that you may need to do extra deburring to get rid of burrs, which may only increase the amount of labor costs and time during the post-machining process.
To deal with this, you can add chamfers or radii to the sharp edges during the design phase. For example, rather than the 90-degree external or internal corners, you may integrate a small chamfer or radius into the CNC machine.
It may just be a simple and minor change but this will be enough to have a significant effect on how much manual deburring you need to do. The reason is it is actually easier to clean any mess in the chamfered or radiused edges.
Let’s say you are dealing with internal pockets. If that’s the case, a “0.24 or 0.5” radius is necessary to create a huge impact and difference, especially when it comes to minimizing the need for deburring manually.
#3 – Look for alternative materials
You can also stick to your budget and still meet your requirements by looking for alternative materials, specifically those that are cheaper while maintaining quality and are more machine-friendly. Your goal is to select the appropriate materials for your CNC machining project that can significantly affect CNC machining cost as well as the final part’s performance.
Some materials are quicker and easier to machine compared to others, thereby directly influencing the production cost. One example is to use aluminum alloys rather than steel as they are quicker and easier to CNC machine compared to the latter.
Aluminum alloys also have lower hardness and strength. This means that they need less cutting force. You can also process them with faster spindle speeds and higher feed rates.
You can also use plastic materials instead of metals. Aside from being cheaper to CNC machine compared to metals, plastics are also more forgiving, especially when dealing with detailed or intricate parts. Several plastic materials also have good machinability. It is possible to cut them at higher speeds with lower tool wear. Plastic costs lower than other materials, too.
There are other alternative materials you can use in the designing of your CNC machining project that will lower how much you will spend on the process. Just pick one that you can comfortably use and truly fits your budget.
#4 – Limit the cavities’ depth
One thing to take note of about machining deep cavities is that they can have a huge impact on how much you will spend on CNC parts. The reason is that it requires the removal of several materials, which is not only time-consuming but also inefficient and wasteful.
Also, you should remind yourself of the limited cutting length of CNC tools. Expect these tools to work more efficiently when you cut cavities that are twice or thrice as deep as their diameter.
If you want to lower the cost of CNC machining, then limiting the depth of cavities up to four times their actual length can help. It also helps to make appropriate adjustments on the internal corner radii.
#5 – Make the thin walls thicker
If you don’t have to worry about weight, then it would be a great idea to make thin walls thicker as they can also help lower CNC machining cost. What you should do is create thick solid parts as they are cheaper to machine and have a higher level of stability.
To ensure that there won’t be any fractures or deformations on the thin wall when you machine it, you should do several passes using low-cutting depths. Also, take note that thin features are at risk of vibrations. This makes it challenging to machine them correctly while significantly increasing the time required for machining.
If you want to lessen the cost, you should design walls for metal components in a way that they are thicker than 0.8 mm. As for plastics, the wall thickness should be at least 1.5 mm.
#6 – Set limitations on the thread’s length
Avoid using threads longer than what’s required as this may only cause the CNC components to go up. The reason is that this may require special tooling. Keep the cost low by setting a limit of three times max the diameter of the hole when designing threads. As for threads in blind holes, you can add a minimum of one-half the unthreaded length’s diameter at the hole’s bottom part.
#7 – Take advantage of standard hole sizes
It is actually quick and easy to CNC machine holes accurately and efficiently with the help of standard drill bits. However, in the case of non-standard sizes, it may be necessary to add a machining step or two, thereby increasing the cost. As much as possible, take advantage of through holes rather than blind holes. The reason is that you can easily machine the former.
It also helps to set limits in terms of how deep the holes are. Stick to a limit of four times the hole’s diameter. Avoid deeper holes as aside from increasing cost, it also takes a lot of time to machine. It also helps to use standard sizes for threads when making the CNC designs to reduce cost and the time needed to machine the parts.
#8 – Indicate tolerances only if needed
One essential tip, if you want to prevent your CNC machining cost to shoot up, is to avoid defining tighter tolerances. Do it only if necessary, especially if you have budget constraints, to avoid considerable waste. An undefined tolerance can lead to the use of standard tolerance when machining the parts. This is enough if you are dealing with non-critical features.
#9 – Limit machine setups
You can also keep the typical costs of CNC machining low if you try to keep the number of setups low. Your goal is to design all components that you can machine using only minimal machine setups (if possible, just one setup).
Let’s say, for instance, the part you will machine features blind holes on two sides. You must then machine them using just two setups since you have to rotate them, making them accessible on both sides.
If you reposition or rotate a component constantly, then you may have to spend more on manufacturing since you can often do it manually. In addition, complex geometries may need a custom fixture, which can also drive up the cost. This is especially true when the complex geometry needs multi-axis machines and CNC systems.
What you can do is try to separate the component into more than one geometry that you can CNC-machine in just a single setup. This means that you should also be able to bold or weld them together later. Note that this tip is also applicable to parts that have extremely deep pockets.
#10 – Stay away from small features that have a high aspect ratio
One thing to note about small features holding a width-to-height aspect ratio that’s considerably high is that it also has a high risk of experiencing vibrations when processed even in advanced machines. This means that they are harder and more challenging to machine correctly, hiking up the cost.
If possible, add bracing support to these small features, especially those with aspect ratios higher than four. You may also try to make them stiffer by connecting them to your wall.
#11 – Take out all lettering and texts
Another design tip that will help reduce the total cost of CNC machining is to take out all lettering and text from the parts. Do not add texts on a CNC-machined component’s surface; otherwise, the cost may go up as you will need to do more steps to complete it, consuming a lot of your time. If you really want to add text, then consider using surface finishing processes and techniques, like painting or silk screening.
#12 – Consider the material’s machinability
If you want to keep the CNC machining cost low, then consider machinability as it plays a huge role in identifying how economical and efficiently you can process the material. In general, machinability refers to the level of ease you can cut, shape, or add finish to such material with the help of machining processes.
Materials that have good machinability need less time, allow quick feed rates, and have minimal tool wear, which can reduce the cost. You will also know that their machinability is good if you can easily cut them and they need less time, effort, and power when processed in the CNC machine.
The materials are also softer. Moreover, they can create fewer burrs and possess consistent grain structures. If you are looking for a machinable metal, then your best option would be aluminum alloy. Aluminum alloy is lightweight and not hard to process on any cutting tool. It also promotes speedy machining, which means you won’t spend too much if you use this material.
You can also use brass and copper alloys – both of which have good machinability. They don’t require too much cutting force, making them easier and quicker to machine. These materials are also perfect for high-precision machining of tiny components.
#13 – Do not use several surface finishes
Yes, surface finishes can make CNC-machined parts more appealing and resistant to difficult environments. However, your use of these finishes, especially if they are more than one, can increase cost. It may also just consume your time. Minimize CNC machining cost by choosing to use the “as machined” finish. Do not use multiple finishes for the surface of any CNC-machined parts when not needed.
#14 – Account for blank sizes
The blank, which refers to the stock material, has a size that may influence the final cost you will be spending on a CNC machine. Follow the general rule of setting at least 3 mm bigger than the end of the blank.
Make the whole process more accurate by removing some materials from the CNC-machined parts’ edges. When designing the parts, the limit for the dimension is 3 mm smaller compared to the standard size of the blank.
Conclusion
There’s no need to worry too much about CNC machining costs for now since there are several ways to reduce them. What you should do is to be meticulous when designing the part. By doing that, you will know exactly which component or feature you should adjust, change, or remove to lower the cost of using CNC machinery.
The good news is that even with the lower cost, you can still expect high-quality and satisfying results once you complete the CNC machining project.