CNC machining is an integral part of many industries - with its help, you can produce the necessary tools and parts with unparalleled precision. Companies often look for ways to cut budgets - and reducing the cost of CNC machining is no exception. To lower the price of CNC processes and the cost of machining services, one should first understand how they proceed and know the various factors that affect the price. CNC machining has long been widely used in many branches of industry. Considering the wide range of possibilities offered by CNC machines, it is a fact that during machining, complexities, problems, and unnecessary costs can and often do arise. How to improve CNC machining and reduce production costs? Does the machining of parts take longer during economical use of the machine? We write about this below!
What factors influence the price of CNC machining?
In order to eliminate a certain part of the costs, it is necessary to prepare an appropriate design, technical and economic project of the finished product, and to accurately plan and define the machining process itself.
The machining time, which significantly affects its price, largely depends on the complexity of the geometry of the machined object.
Initial costs, including CAD project development and process planning, constitute a large part of the product value in small quantities, but in the case of large or serial quantities, these costs are fixed, so batch sizes can be reduced, raising the price per unit of the product.
The prices of materials and finishes are also factors affecting the total value of the product. In addition, the proportion of the number of finishes on the surface of the product will also have an impact. In some cases, companies using a cheaper production method reduce the final effect of the final product model. How to understand production costs?
How to calculate CNC machining costs?
CNC machining costs will depend on several factors, including the time required to complete the project and specific machines, such as three- and five-axis machines. Companies in the CNC industry often set their own hourly rates for different types of machines. For example, a five-axis usually costs about 400 - 500 PLN per hour, while a three-axis machine usually costs less. It's worth remembering that these are just the operating costs of the CNC device (each CNC milling machine generates costs). They can serve as reference points, although the value of the work will also need to be taken into account. In addition, the price is also influenced by several other factors, which will be presented in the following points of the article. As costs can vary, it is best to contact a potential CNC shop/company before making a decision to order, to see how it will affect the budget we have.
What affects the cost of CNC parts?
Before reducing the costs of CNC machining, one should first understand the factors that affect the cost of CNC parts - machining time, startup costs, material costs, and others. Here are some basic information about each factor that can be used to ultimately reduce production costs:
- Processing time: this is often the main cost factor of CNC processing. Typically, the longer the process takes, the higher the price.
- Startup costs: these are usually fixed. They are intended to cover the preparation of the CAD file and product planning. In small batches, startup costs can be significant.
- Material value: the price of the chosen bulk material and the ease of raw material processing is another important factor in CNC processing costs.
- Other production costs: Some CNC machined parts have special requirements - such as tight tolerances or thin walls. They typically require specific tools, a higher number of additional processing stages, and lower speeds during cutting. All these factors affect processing time and ultimately increase costs.
- Surface finishing of the material: adding a finish to a part can improve its appearance and make it more resistant to harsh conditions. Although this can be beneficial, it significantly increases processing costs.
CNC machine cost
When hiring a company to carry out a project, we can choose from many types of CNC machines. Some of them cost more, which of course can affect the price we ultimately pay for their use. For example, 3-axis machines, which are more standard, can cost from 150 to 200 PLN per hour. Others, such as multi-axis ones, are more complicated to operate, so they will be priced higher — usually from 300 to 500 PLN per hour. The price of a used machine can vary depending on many factors, including the company's prices and how much it has to pay the operator. It is best to talk to representatives to find out the prices of machines before starting a project.
How to reduce CNC machining costs - practical tips
To help reduce costs, changes can be made in CNC machining time, startup costs, material costs, and more. Some product requirements cannot be changed, but taking steps to optimize the design can significantly reduce the required budget. Here are some of our tips on reducing CNC machining costs.
1. Rounded inner corners
A sharp 90-degree angle requires stopping the machine, rotating the part, and continuing the process. As one can imagine, these additional steps consume processing time and often involve extra costs. Changing the design of the internal corners of the part can lower the price of CNC machining. If we adjust the design to include rounded corners, the machine can work continuously, creating the necessary part while reducing the invoice value. Going a step further, it is worth ensuring that the radius of the internal corner is at least 1/3 of the groove depth. A larger radius in the corners means that a larger mill can effectively cut them - a small mill, which has to cut corners with smaller radii multiple times, will not be needed.
2. Avoid deep pockets
Deep pockets can negatively affect the cost of CNC machining, as achieving them means removing a large amount of material. Material removal is time-consuming and may require special tools to achieve the desired depth. It's worth trying to limit the depth of pockets in your project to four times the length. CNC tools have limitations when it comes to grooving - it's best if the depth is two to three times greater than the diameter. You can cut four times the diameter, but it will cost more.
3. Limit the use of tight tolerances
When a part is designed with tight tolerances, it increases the cost as it extends the machining time and requires manual inspection. Unfortunately, it is particularly difficult to achieve tight tolerances on the internal surface, as machining holes and other grooves can cause burrs to form on the edges. These defects require an additional step beyond manual inspection - deburring. Deburring is a very time-consuming process, which also increases the cost of CNC machining. If the design does not specify tolerances, a standard tolerance of ± 0.001 or higher is applied. It applies to many elements, so any tight tolerances should be reconsidered and only specified when necessary. If we have advanced design knowledge, we can further reduce CNC machining costs, as they often have smaller tolerances. One final note on tolerances - the numbers representing dimensions are critical as they indicate the level of accuracy required for the part. In CNC machining, this level of precision translates into the tools that will be used for machining. The more decimal places, the more complex the tool and the higher the cost. Remember to remove all unnecessary decimal fractions from the project when it comes to tolerance.
4. Expand Thin Walls
Dealing with thin walls requires time, as they are fragile. They are often processed with a shallow depth of embedding to avoid mistakes or cracks. A common cause of thin walls is the location of holes and threads near the edge of the part. It is best to place them strategically. A thick wall is more stable, and the processing cost is lower. It is worth designing metal parts with a wall thickness above 0.8 mm and plastic parts with a wall thickness above 1.5 mm, as long as weight is not an issue.
5. Limit the length of the thread to reduce costs
Threads that are 1.5 times longer than the diameter of the hole will not strengthen the connection, and threads longer than necessary can be associated with additional costs, as special tools may be required to make them. Save costs by designing components with a maximum length three times the diameter of the hole. Remember that threads in non-through holes should have an additional half of the diameter at the end of the hole, without a thread.
6. Optimization of the threaded hole
Two cost factors of threaded holes are depth and thread size. As we mentioned, increasing the thread length beyond this point will not strengthen the part. "Going" to a depth greater than three times the hole diameter increases the risk of thread tearing and additional time — both of these factors increase the final price. Very small threads also increase costs, as they require manual threading, which increases time and risk. Instead, limiting the depth to three times the hole diameter and sticking to standard thread sizes in the project can help reduce CNC machining costs. It is also worth trying to make threaded holes larger than 2-56 inches.
7. Use the standard drill size
If we plan correctly and ensure that the holes in the part have a standard size, CNC machines can use drills for quick and efficient hole creation. However, non-standard dimensions often require the use of end mills, which can negatively impact costs. The depth of the hole also plays a significant role - although it is possible to make holes with a diameter up to 10 times, they are difficult to process and more expensive. To minimize the cost of CNC machining, with holes up to 10mm in diameter, we should design in increments of 0.1mm. For holes with a diameter larger than 10 mm, increments of 0.5 mm should be used. If we are designing in inches, refer to the fractional bit size and use a fractional part of an inch. Regardless of the size of the hole, let's make sure that the length of the hole does not exceed four times the diameter.
8. Avoid multiple finishes to reduce costs
Finishing CNC machined parts helps protect them from harsh conditions and often improves their appearance. Unfortunately, it also increases costs. Going a step further and requiring multiple finishes on an item will cost more. If we want to save money, consider choosing a complete finish. It's worth asking for multiple finishes only when necessary.
9. Divide complex parts
If we have complex parts — such as intricate geometries, rotation, or position change — machining the part may require custom fixtures, manual rotation, position change, or a multi-axis CNC system. All these actions come with costs. If we can't reduce the complexity of the part, we can still find a way to lower CNC machining costs by dividing the part into two or more individually machined parts that can be assembled into the required whole. By dividing the part into two or more geometries that can be machined in one setup, cost reduction can be achieved.
10. Avoid small parts with large proportions to reduce costs
All fragments with extreme proportions are often difficult to process. For example, small parts with large elongations are difficult to machine due to their tendency to vibrate. As with many other aspects of the process, if it is difficult to machine, it increases the costs.
To reduce costs, let's design all components so that they have proportions smaller than 4 and consider attaching them to the wall or adding reinforcement to increase rigidity.
11. Bulk Order
The quantity of parts ordered has a significant impact on the unit price. So-called economies of scale can be a powerful tool when thinking about how to reduce costs. Increasing the quantity from 1 to 50 can reduce the unit price by over 50%. How to reduce CNC machining costs? There is no one effective way to do this. Certain methods require the use of one type of material to carry out the manufacture of final products according to the order. The development of industrial solutions is useful (especially for using the model to carry out a specific order).