Did you know? 70% of the manufacturing cost of a part has actually been locked in the design stage? I believe you are committed to providing customers with excellent CNC machining services and customizing various types of parts. However, such a result often leads to gradual increases in costs and reduced profit margins. And what should you do if you want to ensure quality and quantity, and reduce costs and increase efficiency? In fact, the answer lies in your daily work, and the so-called cost trap is completely avoidable.
Additionally, many engineers are shocked when they receive an expensive CNC quote, not because the material chosen is too expensive, but because there are unreasonable parameters on the drawing: unnecessarily tight tolerances, or right angles that the end mill cannot reach, etc. If these problems can be adjusted, you can reduce your costs by 20% or more. In this summary guide, we have also summarized the 10 most practical design for manufacturability (DFM) techniques for you. Whether it’s reducing costs or shortening lead times, these factory-proven rules of thumb can help you.
1. Relax Tolerances
In reality, many designers are accustomed to marking all dimensions with ±0.01mm in their drawings, which will increase the risk of post-testing, adjustment and scrap, thereby significantly increasing costs. In order to avoid this problem, what you need to do is to set the tolerance reasonably according to the function of the part, and only mark the tight tolerance at the mating position (such as shaft hole fit). For non-critical features on the part, you can use standard machining tolerances (such as ISO 2768-m). During this period, you still need to fully communicate your needs with engineers and customers to avoid “over-designing” of part drawings.
Rule of thumb: Standard tolerances are generally ±0.125mm (or ±0.005”). If it is not necessary to be more accurate, don’t mark it smaller.
2. Increase Internal Corner Radii
As you all know, the CNC end mill itself has a certain diameter and corner radius, so the tool cannot cut a perfect right angle (90-degree internal angle). If there is a need for right-angle machining on the drawing, then expensive processes such as electrical discharge (EDM) are required. The way to reduce costs is to add fillets (R corners) to all inner vertical edges, and design the internal fillet radius to be greater than or equal to the conventional tool radius (such as R2, R3, R5, etc.). The larger the R angle, the bigger diameter of the tool you can use, and the faster it will cut, and less money it will cost.
Rule of thumb: It is recommended that the inside corner radius be at least 1/3 of the cavity depth (R ≥ 1/3 D).
3. Minimize Machine Setups
During the CNC machining process, it is a common phenomenon for operators to change tools. However, frequent tool changes and clamping not only waste time, but also increase the probability of errors and scrap. And every time the part needs to be turned over for processing, it also requires manual re-clamping and calibration, which undoubtedly also incurs labor costs (CAM programming + operator time). So to overcome this, you can try to give priority to integrated processing or composite machine tools to complete several links at one time. If the part is too complex, you can also consider splitting it into two simple parts and assembling them with bolts after machining.
Rule of thumb: Before machining, you need to think about “Can this part be machined in one go on a 3-axis machine?” If not, costs will jump.
4. Use Standard Hole Sizes
In the machining industry, it is also quite common to process hole diameter requirements. If you are using a non-standard diameter hole (such as 3.14mm), you will need to customize the tool or use an end mill to spiral the tool, which can be much slower than using a standard tool. Therefore, you should prioritize standard thread/bore diameters and universal tools when machining, which will not only save costs, but also improve supply chain flexibility and responsiveness At the same time, when designing, you can also check the standard drill bit size table, so that it can be directly applied during subsequent processing.
Rule of thumb: If it is a fastener through hole, refer directly to the through hole size of the standard screw (for example, M6 screws correspond to Ø6.6mm holes).
5. Avoid Thin Walls
Those of you who are engaged in the machining industry must know that thin walls are easily deformed and vibrated during processing. In order to maintain the accuracy of the components, the machining speed must be very slow, and even special fixtures are needed to support it. These will certainly prolong the processing time and increase the total production cost.
Regarding the cost issue in this area, you must first design the wall thickness reasonably and increase the wall thickness as much as possible. Secondly, it is to optimize the structural distribution and ensure that structures such as reinforcing ribs and rounded corner transitions are used inside the components to improve the overall rigidity. If the customer has thin-walled parts, you can also customize special fixtures or use step-by-step processing, heat treatment and other processes to increase the success rate of processing.
Rule of thumb: The recommended wall thickness for metal parts is >0.8mm, and for plastic parts >1.5mm.
6. Limit Cavity Depth
A cavity is the hollowed or grooved part of the part. The structure of the cavity is very common in shells, molds, connectors and other parts in the machining industry. For the machining of such cavity components, the length of conventional tools is limited, so deep cavity machining requires extended tools or special tools, which are not only expensive but also prone to vibration and fracture. In order to avoid tool breakage and also ensure the surface quality of the component, the machine can only run slowly, which will double the processing time. Therefore, the suggestion is that you try to avoid designing grooves or holes that are too deep. If the functional requirements of the component do require deep cavities, you can also use layered, segmented, or multi-piece combination structures to minimize the difficulty of deep cavity machining of a single part.
Rule of thumb: You try to keep the pocket depth within 4 times the tool diameter (i.e., a 4:1 diameter ratio). Beyond this ratio, costs will rise exponentially.
7. Avoid Embossed Text
This is something that everyone easily overlooks. Many designers like to add logos and text on parts. If the customer does not need it, this kind of design can be omitted. You should know that embossed requires cutting off all the surrounding material, which is extremely time-consuming and wastes material, while engraved requires the tool to go through the lines. These processes undoubtedly increase the overall cost.
Rule of thumb: The recommended alternative is to add text by laser marking or silk screen after processing, the cost is almost negligible.
8. Select Machinable Materials
Material cost directly affects the manufacturing cost, material hardness affects the machining time. For example, It takes 3 times longer to machine stainless steel parts than aluminum parts, and 10 times longer to machine titanium alloy parts. So, it is recommended that you choose cost-effective and easy to process materials according to the actual needs. If there are no special strength or corrosion resistance requirements, you can preferentially choose aluminum alloys (such as 6061-T6) for processing, and communicate with the supplier on material substitution.
Rule of thumb: 6061 aluminum is the king of value for money. If you are just doing prototypes, you can even use Delrin (POM) plastic, which is extremely fast.
9. Avoid Selective Masking
Surface finishing is a common requirement in machining, but the most significant cost increase is selective masking. It is intended to fulfill certain functions that require special protection of certain areas of the part so that these areas are not covered by the surface treatment. However, this approach will increase the complexity of the production process and prolong the production cycle. In addition, the process is basically manual work. Workers need to use tape or custom plugs to block the threaded holes or contact surfaces one by one, and then remove them one by one after processing. This will greatly increase labor costs (Labor Cost), and it is also very easy to produce defective products.
Therefore, in the design stage, you should try to avoid the need for masking and try to standardize the surface treatment scheme. For some cases where this is required, you can also make design adjustments to make the area to be protected into a structure that is easy to post-process or assemble, thereby reducing the difficulty of processing. Alternatively, if the part still needs to be electrically conductive, you may even consider using a “chemical conversion film” instead of anodizing, or using toothed gaskets to pierce the oxide layer to conduct electricity during assembly, rather than requiring the factory to do the masking.
Rule of thumb: Masking costs more than the finish itself.
10. Mass Production
The unit cost of small batch or single-piece production is high, and CNC machining also has high “start-up costs”, including CAM programming, material preparation, first-piece debugging, etc. This means that whether you produce 1 piece or 200 pieces, the startup cost is the same. It can be seen that for manufacturers, small-batch product manufacturing is not cost-effective. Only mass production can amortize fixed costs such as programming, machine adjustment, and tool wear. In addition, you can also improve batch efficiency and reduce the processing cost of each product through order consolidation and production plan optimization.
Rule of thumb: When increasing from 1 piece to 5-10 pieces, the unit cost decrease curve is steepest (most cost-effective).
In Conclusion
Well, these are the ten golden guidelines for you. Reducing CNC machining costs does not mean sacrificing the performance of parts, but requires you to have higher wisdom and ability to distinguish what is necessary, what is habitual, and what is unnecessary on a component. A part with redundant features removed is not only cheaper, but also lighter, has fewer stress concentrations, and can be delivered faster.After all, complexity is easy, simplicity is difficult.
Don’t think of our DSR company simply as a factory. The goal we have always been committed to achieving for our customers is to use the most reasonable cost and the smartest technology to achieve the most outstanding performance.Really spend money on the blade. At the same time, don’t underestimate every subtle optimization in the components. These may become huge advantages in future market competition.
