Computer Numerical Control or CNC Machining is the machining method that has been adopted by the industry at large. It deals with the machining process by automating the controls of machining tools as well as 3D printers. With all of its benefits, one of the primaries focuses a company has while using this method, is that of cost-cutting. Certain tweaking here and there during the design process ensures plenty of tips that can come to your aid if you’re aiming to minimize the manufacturing costs. In this article, we are going to go over such tips that can help you minimize the cost of CNC part manufacturing.
First of all, let us make it clear that what actually drives the cost that we are aiming to reduce here. We aim to reduce the cost of the entire process. To break it down, we will have to focus on the parts being used and how the machine is being consumed throughout the process. We will now go through the major factors that control the cost-controlling of CNC part manufacturing.
Material Cost: Obviously the material or the part being used for the manufacturing will have a major impact on the overall cost. We have to focus on the cost of the bulk material. Apart from that, it is important to focus on the efforts that will be required in the machining of that part. The parts having easier and better machinability contribute more in minimizing the cost of a process.
Machining Time: This factor directly arises from our previous point. If a part has poor machinability, it will take up the greater time of a machine. It is important to note that the longer it takes to machine a part, the costlier is the process.
Basic Costs: We are referring to the costs incurred during preparations of CAD files and during process planning. While this may not contribute to the larger part of the costs, it is important to keep them in check to ensure better cost availability for other factors.
Various Manufacturing Costs: Depending on what our final product must be, a process will have to go through various kinds of steps. These steps won’t be general and will depend on what kind of project we are handling. The requirements of this special tool, better and more focused quality control and dedicated processing steps have an impact on the overall costs.
Most Important Tips to Follow for Minimizing Cost of CNC Part Manufacturing
Now that we understand what does the cost of a manufacturing process revolve around broadly, we can go deeper and study the minute or particular tweaks we need to make in order to lower our manufacturing process costs.
Dealing with Thin Walls
It is important to note that the CNC parts having thin walls come with a tendency to chatter, i.e. machining vibrations, movement between the tool we’re having and the workpiece. This is undesired. On the other hand, thick solid sections turn out to be more stable as well as less costly.
It is recommended, unless weight is a major factor in your project, work with parts having relatively thicker walls. The textbook numbers to minimize the costs are:
Design walls thicker than 1 mm when you need the least strength, 2 mm for decent strength & 2.5 mm for the rigid wall.
In case very thin walls are necessarily required for a product, it is better to go ahead with other manufacturing methods like Sheet Metal Fabrication which will prove to be more economical as well.
Avoid Deep Cavities
The parts having deep internal cavities increase the cost of the CNC machining process by a large margin. This is mainly because removal of a comparatively larger amount of material is required which increases machining time which in turn increases the related costs. Apart from that point, the CNC process requires a special kind of tools to deal with such parts. This again results in greater costs.
To deal with this problem, it is recommended to work with parts having a length up to 3-4 times of their depth.
Since all the CNC tools are of cylindrical shape, whenever they cut the edge of a pocket, they leave rounded inside corners. It is optimal that this radius should be wider. A narrow radius will require more passes through a CNC machine and hence will increase costs.
To deal with this, it is recommended to use an inside corner radius that has a length to diameter ratio of 3:1 or less. It is also preferred to use the same radius in all of the internal edges.
Optimizing Threading Sizes
In a CNC process, it is important to ensure that the optimum length of thread is allowed to enter the holes created. While one may argue that with an increase in the length of thread inside a hole, the tightness of hold on a bolt is increased but it is calculated that a hole doesn’t need to be threaded more than 3 times the hole’s diameter. Going deeper can instead cause damage to the part.
It is to be ensured that threads with a maximum length of fewer than 3 times the hole diameter are designed. In case of blind holes, it is recommended to add at least half the length of diameter as unthreaded length at hole’s bottom.
Avoid Specifying Tight Tolerances
What we need to know about tolerances, in this case, is that if we define tight tolerances for each and every surface of our part, it will lead to an increase in machining time as well as the requirement of manual inspection. This is why it is important to filter out the surfaces critical to the function of the part.
When a specific tolerance is not defined in the initial technical drawing, standard tolerance of ∓0.125mm (or better) is used for machining. This tolerance is sufficient for most of the features that are not very critical.
To minimize cost in this case, you need to specify tighter tolerances only for critical parts and only when it’s necessary. Apart from this, you can try defining a single datum. An initial step of a single datum can be the intersection of two sides or intersection with the centre of the hole. Next, everything else is dimensioned from this.
Avoid Text Embossing
While text embossing might feel like an option that makes your product more pleasing in terms of looks, the negatives that it carries with itself might force you to think otherwise. A ball end mill is used to implement this process in CNC machining and it increases the cost of the project significantly because of the requirement of additional time-consuming steps.
Text engraving can be chosen as an alternative method if it is really necessary for a product. Choice of font also makes a difference and it is recommended to go with a Sans-Serif font like Verdana or Arial having at least 20 points size.
Dealing with Holes
If there are holes in the part to be machined, they can be CNC machined rather quickly with great accuracy with the help of standard drill bits. What we need to focus on here for cost minimization, is the depth of those holes.
The depth of all holes should be limited to 4 times their diameter. Deeper holes, while possible to be manufactured, will increase the cost and machining time. Additionally, they could cause more problems for the machine.
Avoid Unnecessary Surface Finishes
While we are aware of how Surface Finishing improves the appearance of a product simultaneously making it possible to enable resistances in different circumstances. Clearly, it comes with its own set of advantages but if we do not use it in a controlled and intelligent manner, the costs of the project can increase exponentially.
It is recommended to go strict with the decisions about surface finishing. Only go for multiple surface finishes when absolutely necessary. Apart from that, the as-machined surface finishes if the most economical method to be used.
Tackling Complex Parts
The problems that arise with working on complex parts are mainly the requirement of special tools, a greater number of machine setups as well as special materials. All of this will increase the cost in a significant manner.
It is recommended that complex parts must go through the process of designing and machining as separate parts. Once these processes are done with, the separate parts can be welded or bolted to form the complete part again. This idea also applies to parts having deep pockets as well as parts that require operating on more than one face.
Avoid Multiple Machine Setups
Taking an example of a part having blind holes on both sides, we will see that it requires two setups because of the need for rotation in order to access both the sides. Such rotating and repositioning of the part increases the manufacturing costs. Again, parts having detailed geometries will require multiple setups leading to an increase in costs.
Just like in our previous factor, it’s important to divide the part into multiple parts that can go through the machining process comparatively easily. These parts can then be assembled together allowing machining of the part in a cheaper way.
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