CNC Machining ABS

10 Helpful Designing Tips to Reduce CNC Machining Costs

Many methods can help reduce CNC machining costs. Here, this article will introduce 10 helpful designing tips to cut down the cost of CNC machining.

— 1—

Rounding at inner vertical corners


All CNC tools have a cylindrical shape, and when the groove is processed, a fillet consistent with the size of the shape will be generated at the connection between the vertical surface and the surface of the groove.


If the fillet at the joint of the vertical surface of the tank body is too small during product design, it is necessary to use a small tool, which means increased processing man-hours, because the processing efficiency of a small tool is not as good as that of a large tool-this will lead to processing time and cost increases.


To reduce CNC Machining costs:


+ The fillet size is at least 1/3 of the depth of the tank body, the bigger the better;

+ All fillets are of the same size; this allows the same tool to be used for the entire machining;

+ At the root of the tank, design a very small fillet (0.5mm or 1mm), or no rounding.


+ The ideal fillet size should be slightly larger than the radius of the tool, which will reduce the load on the tool during machining, thereby reducing machining costs. For example, the depth of the tank body is 12mm, and the rounded corner is designed to be 5mm or larger, and a tool with a diameter of 8mm (radius 4mm) can be used during processing, which can ensure processing efficiency.


+ If it cannot be rounded due to design requirements, for example, it needs to be matched with another square part, in order to avoid small rounded corners, you can design as follows:



— 2—

Cost Reduction Design #2 – Reduce Tank Depth

Slot machining greatly impacts part cost because of the large amount of material that needs to be machined away, which increases machining time considerably.


The machining depth of CNC tools is limited to a certain extent. When the depth of the groove is 2 to 3 times the diameter of the tool, the machining performance is the best. For example, a milling cutter with a diameter of 12mm can machine the safe depth of the groove body up to 25mm.


Of course, it is also possible to machine deeper grooves, up to 4 times the tool diameter, but this will increase the cost, especially when using multi-axis CNC machine tools.


To reduce CNC machining costs: the depth of the tank body should not exceed 4 times the length.


— 3—

Cost Reduction Design #3 – Avoid Thin Walls

Unless specifically required, thin-walled designs should be avoided, because thin-walled structures are not strong enough and costly to process.


It is easy to deform or even break during thin-wall processing. In order to avoid this situation, more complicated processing paths need to be added, which will consume more processing man-hours. Thin walls are more prone to vibration, and high-precision machining of thin walls is a big challenge.


To reduce CNC Machining costs:


+ For metal parts, the thickness of the wall is at least 0.8mm, the thicker the better.

+ For plastic parts, the thickness of the wall is at least 1.5mm, the thicker the better.

+ The minimum metal parts can be 0.5mm, and the plastic parts can be 1mm minimum, of course, this is not recommended;


When designing holes (including through holes and screw holes) or slots at the edge of a part, thin walls are often present and it is important to ensure that the above design guidelines are followed.



— 4—

Cost Reduction Design #4 – Reduce Thread Depth

Unnecessary thread depth increases CNC machining costs because special tools are required.


Remember: Excessive thread depth (more than 3 times the hole diameter) does not increase the strength of the connection.


To reduce CNC Machining costs:


+ The thread depth can be up to 3 times the diameter of the screw hole.

+ For blind hole tapping, it is best to add at least 1/2 hole thread extra length at the root of the hole


— 5—

Design standard size holes

Using standard drills, holes can be processed quickly and with high precision; for non-standard holes, the use of end mills will increase the cost.


In addition, the depth of the hole should not exceed 4 times its diameter. Deep holes (up to more than 10 times the diameter) can be machined, but this increases costs dramatically due to the difficulty of machining.



— 6—

Cost Reduction Design #6 – Avoiding Close Tolerance Requirements

Close tolerance requirements add cost because they require complex machining operations, increase machining time, and require more inspections.


The definition of part dimensional tolerances must be taken seriously, avoiding tolerances on any dimension, marking tolerances only when necessary, and marking fine tolerances only as a last resort.


If no tolerances are defined in the part engineering drawing, the parts will be machined to standard tolerances (± 0.2mm or looser), which is sufficient for most non-critical dimensions, which will greatly reduce machining costs.


For those internal features, tight tolerances are more difficult to assure. For example, when machining internally intersecting holes or slots, small defects such as burrs are likely to appear on the edges due to force deformation.


These features require inspection and deburring processes, which can only be performed manually, which is expensive and time-consuming, resulting in high costs.


To reduce CNC machining costs:


+ Define close tolerances only as a last resort.

+ All dimensions are dimensioned from the same datum.

+ Remember: the decimal point in the tolerance is important, it defines the degree of precision and which measurement tool needs to be used. For example, a two-digit decimal point can be measured using a vernier caliper, and a three-digit decimal point can be measured using a micrometer or a three-coordinate measuring instrument. In order to reduce costs, try to avoid adding unnecessary decimal places.


+ Precision tolerance requirements can be avoided by optimizing product design, such as shortening the dimensional chain, using positioning features, etc. For details, please refer to Chapter 7 of “Product Guide for Manufacturing and Assembly”.


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Reduce the number of clamping

Minimize the number of parts clamping, preferably only one clamping.


For example, a part with blind holes on both sides needs to be clamped twice. After one side is processed, it will be rotated and re-clamped before the other side can be processed.


Rotating or repositioning parts adds to machining costs since setup is typically done manually. In addition, for complex part structures, custom clamping fixtures are required, which further increases the cost. Particularly complex part configurations may require multi-axis CNC machines, further increasing costs due to high hourly rates for multi-axis CNC machines.


It can be considered to divide the complex part structure into multiple parts for CNC machining, and then fasten them into one body by threading or welding.


To reduce CNC machining costs:


+ Design parts only need to be clamped once.

+ If not possible, divide complex parts into multiple parts and fasten them into one piece through subsequent processes.


— 8—

Avoid large aspect ratios

During CNC machining, some small features with large aspect ratios tend to vibrate, making it difficult to machine accurately.


In a way to avoid this, these small features should be connected with some thicker walls or supported by some stiffeners.


To reduce cnc machining costs:


+ Avoid designing features with aspect ratios greater than 4.

+ Small features are connected to thicker walls or added ribs for support.


—9—Remove the text and symbols on the surface of the part

Text and symbols on the surface of the part will greatly increase the cost of CNC, because of the need for additional machining operations and more processing time.


Text and symbols can be added to CNC parts using some surface treatment techniques, such as silk screen or painting, which is a more cost-effective method.


To reduce CNC machining costs:


+ Remove text and symbols on all part surfaces;

+ If text and symbols are necessary, choose recessed rather than raised, as the latter requires more material removal.




Consider the processing technology of the material

The processing technology of materials refers to the difficulty of processing materials.


The better the processing technology, the easier the CNC machining of the parts, and the lower the cost.


The processability of a material depends on the physical properties of the material. In general, the softer and more ductile the material, the easier it is to process.


For example, brass C360 has the highest processing technology and can be processed at high speed; aluminum alloys (aluminum 6061 and 7075) can also be processed easily.


The machining process of steel is very low. Compared with aluminum alloy, steel requires more than twice the processing time. Of course, the processing technology is different between different steels. The processing technology index of stainless steel 304 is 45%, while the index of stainless steel 303 is 78%. The latter is easier to process.


The processing performance of plastic materials depends on their stiffness and thermal properties. During CNC processing, plastic materials are easily melted and deformed at high temperatures.


POM is the easiest material for CNC processing, followed by ABS; PEEK and nylon are common engineering plastic materials that are difficult to process.


In order to reduce costs: where possible, try to choose materials with good processing technology.

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