Tips to Reduce CNC Milling Cost
Since the 1960s, CNC milling has been growing in popularity across the globe. The global CNC machine market was worth USD 88 billion in 2022 and is projected to reach USD 131 billion in 2030. These projections show that the market is expanding.
For anyone in this industry or planning to join it, now is the best time to know what contributes to CNC machining costs. Identifying the best CNC milling services nearby can benefit your rapid prototyping business. That’s why we prepared this guide about tips to reduce CNC machining costs. Read on for comprehensive coverage of factors that make the CNC machining process cost-effective.
What is CNC Milling?
CNC milling is a subtractive process based on computer numerical control and special cutting tools that produce CNC machined parts. The process involves the automatic movement of a table holding the workpiece on a variety of planes.
As the table and the workpiece move, the cutting tool is removing material from the workpiece. This creates custom-machined parts that resemble what is contained in the computer-aided design (CAD) software.
CNC milling is ideal for custom parts that are not axially symmetrical. It suits parts that have unique contours and curvatures. CNC milling may also be applicable in the fabrication of manufacturing processes such as 3D molds.
Apart from the table, a CNC machine has the following major parts:
Automatic tool changer
Axes and Columns
Ask for an instant CNC milling quote if you need complex and precise parts with high tolerances within 3 days.
We know that as a business, you may be wondering how you can cut CNC machining costs.
The Factors That Affect the Cost of CNC Milling
For aerospace, oil & gas, hydraulic, or automotive industries, the need for CNC machined parts is perpetually present. Therefore, figuring out how to manage the CNC machining costs element is central to the success of these businesses. Consider the following factors when looking to reduce CNC machining costs:
The size of the CNC machine for custom CNC machining impacts the machining cost. Therefore, inquire about the size of the CNC machines used in the machine shops as you outsource the part manufacturing process.
Some CNC machines are larger and have more axis than others. This difference can bring a cost disparity. The work envelope of the CNC lathe determines the maximum work a machine can handle. It is the area that the CNC milling machine can cover across its Y, X, and Z axes.
This envelope gives the movement limitations for the machine. These limitations determine the maximum size of CNC machined parts that the machine can produce.
From our experience, the machining cost for engineering components is proportional to their tolerances. Custom CNC parts with tight tolerances usually cost more. This is partly because the speed of the CNC machining process is slower in this instance. Tighter tolerances also attract more advanced inspection equipment and higher expertise.
Also impactful on the machining cost is that tighter tolerances mean higher failure rates. Therefore, these cutting tolerances will increase both the machining and inspection costs.
Number of Axes
CNC machines may be categorized as 3-axis and 5-axis. The 3-axis machine handles the less complex parts. For parts with more complex geometry, the 5-axis milling machine is more suited.
Typically, milling operations on a 3-axis CNC machine will be more affordable than on a 5-axis machine. Outsourcing your part manufacturing to a machine shop that uses a smaller but adequate CNC machine may help minimize CNC machining costs.
However, there are instances where the 5-axis machine can present cost savings. For instance, it reduces manual labor costs because it doesn’t require manual repositioning of the workpiece. The milling time is also relatively shorter.
Recommendations on the specific CNC milling job may help you determine which option is less costly.
Part of the CNC machining cost is also related to the time it takes to mill one component or a set of components. Usually, the cost of machining processes is high if the processes take long to complete. We’ve mentioned above the relationship between machining time and CNC machine capability. The machinists can use CAM or related software to estimate the milling time.
Note that you need to also account for the manual processes. For instance, you may require to subject the CNC machined part to assembly or further surface finishing. These can add to the total CNC machining costs. The costs of delivering the products to a different location may also emerge.
It is advisable to analyze the elements contributing to the CNC machining time. Some important ones for consideration are:
Set-up time – this covers the time spent preparing and changing the cutting tools
Cycle time – covers the time spent milling the part
The Efficiency of the milling production process
In the CNC machining world, more complex parts are more difficult to machine, and vice versa. Consequently, the CNC machining cost goes with the complexity of the custom part.
The reason for this relation with the cost is simple. A complex design and geometry need more resources, higher inspection attentiveness, and more machining time. All these add to the machining cost related to labor, electricity, and others.
Some geometry features that could increase the CNC machining cost are thin walls, deep cavities, lettering, and pronounced internal corners.
The general formula for the time taken in all machining operations is as below:
T = L / f * N
Cycle time （T）= L * number of passes / f * N
- L is the length of the workpiece to be machined
- N is the rpm of the workpiece
- f is the feed rate
For a milling operation, the feed rate is per tooth and is given as:
Feed rate (f) = feed per tooth * number of teeth. The length is given by Tool approach length + Job length + Tool over-travel * Number of passes
There are many ways of reducing the production cycle times, and consequently, the cost of CNC machining. Here are some to consider:
Using advanced CAM software to make the cutting path more cost-efficient
Ensuring peak performance for the milling machine
Setting the most optimum cutting parameters
Using advanced CNC cutting tools and techniques
Quick-changing tool methods and other ways of minimizing set-up time
Labor costs include the wages of the engineers and machinists. These unavoidable costs add to the CNC machining process cost. The production process needs the expertise to program for the CNC machining, set up the milling machine and CAD file, and run the machine shop.
There will be variations in these costs depending on the intricacy of the parts and the intensity of labor necessary.
The highest labor costs usually go into programming. It all starts with the preparation of the CAD file. The manufacturing engineer then receives the file and offers improvement suggestions if necessary. For the CNC machine to comprehend the design, the programmer changes the CAD file to a CAM file.
At the set-up stage, a person will typically cut the raw material block and place it in the CNC machine. Loading the tool in the holder may also require manual labor.
Other areas that contribute to the labor costs are the quality assurance process and post-machining activities.
Raw Material Cost
The raw material costs can also affect the CNC machining costs. Again, the specific cost here depends on the quantity of CNC machined components and their complexity.
The experts at the machine shops start with a solid block of the material. According to the rule of thumb, the block should be slightly bigger than the intended finished part. Whether the machine shop is using aluminum alloys, stainless steel, or plastic, this cost can be significant.
There is a reason why plastic and aluminum milling are popular among CNC machining professionals. The material costs for the two tend to be affordable. On the flip side, these materials may not last too long.
Materials that last longer tend to be more expensive. For instance, stainless steel is more durable than aluminum, but it costs about three times more. If your project does not demand the durability qualities of stainless steel, consider using a more affordable material such as aluminum.
Plastic parts are often preferable to metal alloy parts if the project does not require significant rigidity. A good example is Polyethylene, which is relatively affordable and easy to machine.
Manufacturers need to recognize the capabilities and limits of each material. Apart from having different performances on the CNC milling machine, the materials have cost variations. Find a balance between the different elements of raw material cost for the most cost-effective manufacturing process.
How to Reduce CNC Machining Cost?
As the points above suggest, minimizing CNC machining costs in CNC machine shops requires a combination of several approaches. We recommend the following cost-saving measures for your CNC machining project:
Apply DFM(Optimization Design) Strategy
Design for Manufacturing is a popular method of optimizing a product design for the most cost-effective production. The DFM’s goal is to ensure that apart from meeting the functionality requirements, a part is fast and easy to manufacture. The importance of this strategy is cemented by the fact that design decisions determine about 70% of the manufacturing cost.
At Aria, we undertake a comprehensive DFM analysis service for our customers in CNC machining and other areas. When you choose us as your manufacturing partners, we focus on five areas namely:
CNC milling process
Raw material costs etc.
Compliance with existing standards
DFM minimizes CNC milling costs in several ways. The most notable one is the reduction of the number of components in a CNC machining project. Fewer components mean reduced supply chain time, less raw material cost, enhanced processing time, and faster product inspection.
Overall, reducing the number of components minimizes the intensity of activities related to the product during its lifecycle. It also enhances product quality.
Limit the Depth of Cavities
Tools for the milling machine shop operations have limited length. The length of the tools determines how deep the cavities on the part can be. The milling tool steel loses its efficiency when the cavity depth exceeds double or thrice the tool diameter.
Beyond this depth, any milling operation subjects the tool to the risk of fracture or deflection. It may also be more difficult to remove chips at such depths. Due to such challenges, the project lead times can increase significantly. The machinist may even be prompted to look for cutting tools that are more customized for the job.
We recommend a limit to the depth of cavities to minimize the cost of machined parts. If the project must have deep cavities, minimize the depth. Most important, always consider the tool length when determining the depth of cavities.
Reduce the Use of Tight Tolerances
Designing custom production parts with tolerance challenges and limits in mind is an effective way to make the manufacture of CNC parts affordable. It is important to achieve a good balance between tolerance requirements and the cost of the manufacturing process.
Machinists must analyze the cost of tight tolerances. A crucial question to ask is which level of tolerance would be ideal for the proper functioning of the production parts.
Alongside this point, the manufacturer needs to address a few issues that affect tolerance. For the widely used manufacturing process options, challenges include the following:
Cutting tool breakage
Roughness and other surface finish problems
Tight tolerances for walls, threads, etc. are undesirable because they prompt a slow and expensive CNC machining process. Components with such tolerances also require post-machining analysis using CMM and micrometer.
Complex designs and soft materials are almost impossible to machine to tight tolerances. The part and tools for CNC mills tend to vibrate and flex during the process.
Avoid Multiple Finishes
The surface finish on a custom part helps enhance the visual appeal and protect against elements. Unfortunately, it also increases the CNC machining cost of the component. Using multiple surface finishes on the machined parts can increase the CNC machining costs.
Machine shops that are keen on saving CNC machining costs opt for a single surface finish for the component. Unless it is necessary, request as few surface finishes as possible.
Use Standard Hole Sizes
Various drill bit sizes are available for the swift creation of holes by CNC milling machines. While you may be tempted to experiment with hole sizes, standard sizes will be advantageous to your CNC milling project.
The holes should not be too deep. Limit the depth-to-diameter ratio to 4:1. The problem with deeper holes is that they increase the machining time, and ultimately, the CNC machine cost.
Even when creating the standard hole sizes, it is important to keep them at a safe distance from the edges. This will prevent the creation of thin walls, which can part strength issues.
Increase the Production Volume
The concept of economies of scale applies to the cost of CNC machining processes. According to economics, fewer production parts from the CNC lathe machine go with a higher cost per part or unit. The reverse is also true.
CNC machining may not present impressive economies of scale like 3d molding and casting. However, the cost per part reduces as the production volume increases.
Eliminate Sharp Edges
CNC machine tools are typically cylindrical in shape. When the tool machines a corner, it leaves a rounded edge. So, there are bound to be challenges that may increase the cost of machining processes if your project features sharp edges. Eliminate the sharp edges to avoid the cost of passing the tool many times.
Where possible, make the radius at the edges as wide as possible. For the best results for edges, follow the ratio of 3:1 for length to diameter as the maximum. Consider using the same radius for all the edges in the project to minimize the cost of production parts.
Expand Thin Walls
It is worthwhile to note that thin walls on a machined part tend to chatter. Tool movement and machine vibrations are the possible triggers of this chattering. Thicker walls may not experience this problem.
We recommend that unless product weight is a significant factor in your case, you may want to make the thin walls thicker. There are specific recommendations for wall thickness:
1.0 mm thickness for minimum strength
2.0 mm thickness for medium strength
2.5 mm thickness for maximum strength
In case your metal fabrication project must involve very thin walls, consider using an alternative production process. Sheet metal fabrication is an excellent option that may allow the usage of very thin walls. It is also relatively affordable.
Consider the Machinability of the Material
There are many types of CNC machining materials. The most common raw materials in our milling processes are metal and plastic.
Our CNC parts feature stainless steel, aluminum, metal alloys, bronze, and other common metals. Common plastics include Polypropylene, Polycarbonate, PVC, and ABS. Our CNC milling machines also create parts from reinforced plastic materials such as Polypropylene (PP) 30%GF and PEEK.
Each of these materials has unique machinability levels. This aspect is worth considering when analyzing the cost of your project. The cost aspect comes in the form of hardness, heat impact, and surface finish of the material.
The hardness of CNC parts determines the type of CNC cutting tool and cutting parameters. A special tool may be necessary to mill titanium (a super hard material). The cutting process may also be slower for such a hard material. The additional labor costs and tooling costs can impact overall CNC machining cost.
Polymers and other extremely soft materials can present related challenges. Special tools on the CNC mill and slower milling speeds may be necessary. Such interventions affect the operating costs and overall project cost.
Proper management of manufacturing costs is central to the profitability of a business. Elements such as the variety of surface finish, surface geometries, tolerances, and machinability of the raw material affect the overall cost of the CNC machining service.
Fortunately, you can make your CNC machining projects more affordable with a few considerations. These are optimized designs, correct material selection, avoidance of tighter tolerances, and so on.
We hope this guide helps you reduce the cost of your CNC milling processes. If you are looking for the best CNC machining companies, your search ends here. Start a CNC milling quote today; our online CNC machining service experts will be on hand to help.
Gavin Leo is a technical writer at Aria with 8 years of experience in Engineering, He proficient in machining characteristics and surface finish process of various materials. and participated in the development of more than 100complex injection molding and CNC machining projects. He is passionate about sharing his knowledge and experience.