How to reduce the cost of CNC machining parts through structural design

CNC machining, namely parts processed by CNC equipment, CNC machining, usually refers to the precision machining method controlled by computer digitalization, has become a common machining method. 

CNC processing equipment, called CNC machine tools, also called CNC machine tools, in different areas are also some different names, such as the Yangtze River Delta area is usually called processing center, the Pearl River Delta area is usually called computer gongs. 

Typical TYPES of CNC machining tools:

• CNC Lathes - Lathes work by rotating the material in the lathe chuck.  The tool is then moved along two axes into the workpiece to cut the cylindrical part.  
• CNC milling machines - CNC milling machines are usually used to make flat parts, but more complex machines with more degrees of freedom can create complex shapes;  The material remains stationary, the spindle rotates with the tool, which moves or rotates along three axes (some are 4 or 5) to cut into the material;  In some cases, the spindle is stationary and material will enter it.  
• CNC drilling Machines - These machines are similar to CNC milling machines, but they are specifically designed to cut along only one axis, i.e. the bit only moves down into the material along the Z axis and never cuts along the X and Y axes.  
• CNC grinders - These machines move grinding wheels into the material to produce a high quality surface finish.  They aim to remove small amounts of material from hardened metals;  Therefore, they are used for finishing operations. 

Compared with the traditional machine tool processing method, the advantages and disadvantages of CNC processing are as follows: 

CNC machining is widely used in various industries because of its high precision.  However, CNC processing services can also be more expensive than other manufacturing methods such as injection molding, die-casting, stamping, etc.  The cost of CNC processing parts is mainly affected by the following aspects: 

1, processing equipment

equipment costs include the initial purchase cost, operation cost and maintenance cost, etc., may be there are other costs, such as cutting tools, CNC system using, these costs will affect the cost of each product, so buy, the higher the cost of operation and maintenance of a machine, use the manufacturing parts of the machine are also more expensive.  

Milling machines generally cost more than lathes because they have more complex moving parts;  Harder to set up, operate and maintain;  And can carry out more complex processing.  Therefore, if not necessary, the parts should be designed to adapt to the lathe structure. 

Milling machines come in different types with varying degrees of complexity and capability.  The more shafts a milling machine has, the higher the price.  Most modern CNC machine tools have three or five axes.  While 5-axis machines can create very complex geometric shapes more accurately and faster (and therefore they require less processing time), they are generally more expensive than 3-axis machines. 

2. Design cost

Design cost is the cost generated by preparation for actual processing, mainly including the cost involved in CAD (structure, engineering drawing design), CAE (optimization analysis), CAM (manufacturing programming) process.  The cost that CAD, CAE produces inside this can apportion to spare part cost not necessarily go up, this should see the cooperation way of a b, design cost is fixed at the same time, if quantity is bigger, apportion the design cost of each spare part is lower. 

3. Material cost

The material cost involved in manufacturing parts is one of the most important component costs, which consists of the cost of raw materials, the amount of materials, and the processing time of materials. 

The cost of raw materials: different each are not identical, the market price of the raw materials and different market area of the price is different also, in the choice of raw materials for parts, parts should be based on the purpose and function of choosing appropriate materials, rather than too much beyond the expensive material of performance requirements, such as with stainless steel, 316 stainless steel price is 304 stainless steel price is more expensive. 

Amount of material: When designing part structure and manufacturing process, the amount of material should be considered as little as possible. If necessary, two relatively simple parts can be assembled to form a complex part (requiring more amount of material and processing time) by means of disassembly. 

Material processing time: the cost of parts is directly proportional to the time it takes to process it. The processing time of materials is related to the machinability of materials. Materials with low machinability need more time to process, but also consume more resources, such as cutting fluid, power and cutting tools.  (For example, softer materials like aluminum are easier to cut, which means shorter processing time;  Harder materials, such as stainless steel, require more expensive tools and are more prone to damage and wear, making parts more expensive to process.) 

4. Production capacity

As the number of parts increases, the unit cost of an identical set of parts decreases significantly.  This proportional cost reduction is mainly the result of eliminating duplicate design costs and machine setup debugging.  CAD design, CAM preparation and machine setup are all done once for all parts to be manufactured.  (That is to say, to produce one part, the design cost and machine setup cost are included in that one part, and if 1000 pieces are produced, the design cost and machine setup cost are divided into 1000 pieces.) 

5. Special requirements

CNC machining workpiece before processing, need to clear tolerance requirements, surface roughness requirements, stricter tolerance requirements will lead to more difficult processing, and increase reject rate, which will also lead to higher cost;  Higher surface roughness requirements may lead to CNC milling machine processing can not be done, we must use grinder or even other methods, increase the process, naturally increase the cost. 

CNC workpiece processing after completion, may require some post-processing, such as heat treatment, surface treatment, etc., to improve the function, performance and beauty of parts, these post-processing requirements will increase the cost of parts to a certain extent.  

For finishes, another serious cost driver is the application of different finish requirements for different areas of the part.  Such as local plating, local anodic oxidation, two-color prototype oxidation, oxidation in one area, plating in another area.  Therefore, in order to reduce the cost, if not necessary should try to keep the surface treatment requirements of the whole parts consistent. 

6. Structural design

The more complex the part structure, the more expensive it is to manufacture, and highly complex parts may require more advanced machinery. They also require more processing time, multiple assembly and disassembly and equipment setup, more resources and closer inspection.  All of this affects the cost of parts.  

2) Avoid designing features that cannot be machined by CNC

Not all features can be CNC machined. A typical example is the 90° interior Angle, as all CNC milling tools today have cylindrical shapes that produce a rounded Angle at the edge of the cavity rather than a right Angle or other sharp Angle. 

If the tool must leave a right Angle, the common way to achieve this goal is through EDM (electric discharge machining), a more expensive manufacturing process than CNC machining.  If the rounded corners cannot be left due to assembly only, it is recommended to use the method of cutting the rounded corners, as shown in the figure below. 

5) Reduce the use of curved surface structure features

In the design of CNC processing parts, simple structure should be the principle, should reduce the design of complex surface features, because in order to get a complex surface with appropriate surface finish, need to use small cutting tools, these small cutting takes much longer than the normal cutting, increased a lot of costs.  So to help minimize cost and processing time, minimize or avoid the use of curved surfaces, for example, when chamfering outer edges, bevel rather than fillet if necessary. 

6) Design standard size holes

Holes can be CNC machined quickly and with high precision using standard drills.  From an economic point of view, try to use standard holes. For non-standard holes, end mills must be used to process the holes, which may increase the cost.  

In addition, in general, the larger the hole, the deeper the drill can be, it is recommended that the depth of the drill not exceed 10 times the diameter of the drill bit. 

7) Keep the number of CNC machine Settings to a minimum

Flipping or repositioning parts can add to manufacturing costs because it usually needs to be done manually.  In addition, for complex geometry, custom fixtures may be required, which further adds to the cost.  Particularly complex geometry may require a multi-axis CNC system, further increasing the price.  

Therefore, in order to reduce the number of parts flipping and repositioning, should try to design all the features that need to be machined on a plane;  If unavoidable, consider splitting the parts into features that can be CNC machined in a single setup and then bolted or welded together. 

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