CNC machining, or Computer Numerical Control machining, is digital manufacturing technology. CNC machining is used to manufacture parts that require tight tolerances and high complexity. CNC machining is a subtractive manufacturing technology because parts are created by removing material from a solid block. This block is called the blank or workpiece. Removing material from this blank or workpiece is done by a variety of automated cutting operations.

How does the CNC machining process work?

CNC machining process refers to the entire process from the product or part drawing to the processing into a qualified finished product. Reasonable CNC machining technology is the basis for ensuring machining quality. The process of CNC machining includes:

1. Analyze the pattern of the part

Analyze the geometric shape, size and technical requirements of the parts, and clarify the processing range and processing quality requirements of this process. The specific requirements are:

  • The size of the drawing is complete and the technical requirements are accurate.
  • Determine the appropriate programming origin, and if necessary, according to the requirements of the CNC machining process, convert the dimension of the part drawing and mark it to meet the characteristics of CNC machining. If the absolute coordinate value is used for programming, the position and size of the base point on the drawing should be converted into the form of marking with the programming origin as the base point, or the coordinate value of the base point should be marked directly. Make the design datum, positioning datum, measurement datum, and programming origin coincident as much as possible.

2. Determine the CNC plan and select the CNC machine

Determine which parts on the workpiece need CNC machining, what method to use for machining, and the connection between it and other processes before and after. When choosing a CNC machine, the issues that should be considered include the type of CNC machine (CNC lathe, CNC milling machine or machining center, etc.), the power of the main motion motor, the processing range of the feed movement, the appropriate CNC system, and its programming methods.

3. Determine the content of the processing process

The content includes the selection of positioning datum and the division of processes and steps. CNC machining has a high degree of automation. When arranging CNC machining processes, the principle of process concentration is often adopted, and most similar surfaces are arranged in one process to complete. In the arrangement of working steps, in order to shorten the idle stroke, the machining surface of the same tool is often processed at one time and then transferred to the next tool to process other surfaces. Of course, the principle of separation of roughing and finishing must still be observed, that is, the last finishing of each surface is generally arranged to be completed in the last time.

4. Determine the clamping plan and select the fixture

Ensure that the workpiece is positioned accurately and clamped reliably during machining, and at the same time consider whether the tool setting of the workpiece coordinate system is convenient. CNC machining is generally the processing of products with small batches, so general-purpose fixtures (such as self-centering chucks, single-action chucks, machine pliers, screws-pressing plates, etc.) or combined fixtures should be selected as much as possible.

5. Selection of cutting tools

CNC machining has a high degree of automation, and excessive tool replacement will inevitably reduce processing efficiency, weakening the advantages of high automation and high processing efficiency of CNC machining. Therefore, the machine-clamped indexable tool should be selected as far as possible for CNC machining, and the structural characteristics of the tool should be considered. For example, when milling, choose a flat-bottom end mill as much as possible for rough machining, consider using a rounded end mill (also known as a round nose cutter) for semi-finishing, and only consider using a ball end mill for fine-finishing.

6. Determine the start point and end point of tool setting, tool change and cutting

The tool setting point is the starting point of the movement of the tool relative to the workpiece, and there is a suitable and definite offset relative to the workpiece origin, which is generally the starting point and ending point of the program. The tool change point is the tool change position point of CNC machining. In order to avoid the interference between the tool change action and the workpiece, machine tool, fixture, etc., it is generally far away from the workpiece, and is usually connected with the cutting process by a fast positioning command G00 movement forward/backward connection , which can be the machine reference point, or a fixed point specified during programming. The starting point of cutting processing is the transition point between the rapid movement G00 and the cutting interpolation movement G01 (or G02, G03), such as the tool from the tool setting point (or tool change point) rapidly positioned to the cutting starting point at the speed of G00, and then turned to Machining. The cutting starting point is about 3 to 5 mm away from the workpiece solid cutting point. Return to the tool setting point (or tool change point) at the end of cutting is generally the G00 rapid positioning speed, and its transition point is called the cutting end point, which can be the intersection point of the tool and the workpiece machining surface, but more is to cut out a certain distance and then turn In order to move quickly, it can also be about 1 to 5 mm away from the actual cutting point of the workpiece.

7. Choose the right toolpath

Reasonable toolpath is a comprehensive problem, there are many factors to consider and may restrict each other. When dealing with toolpaths, priority is given to the main issues such as the shortest cutting time, the best machined surface quality, stable cutting forces, no large abrupt changes and fluctuations, etc. When determining the tool path, it is also necessary to consider whether tool radius compensation and tool length compensation are used during machining, and what are the requirements for the machining path.

8. Determine a reasonable cutting amount

When determining the cutting amount of CNC machining, in addition to referring to the parameter selection of ordinary machine tool cutting, it should also be considered that CNC machine tools generally have the characteristics of the adjustment of the spindle speed and feed rate, and the spindle speed and feed rate can be adjusted appropriately. High, in the process of machining, the actual machining cutting amount is determined by controlling the override switch of the spindle speed and the feed speed. Of course, the practicability of the cutting amount provided in the tool manufacturer’s product catalog is better than the value found in the general cutting manual or process manual.

About DFM Rapid

We are a CNC machining China shop in Dongguan. We have 20 CNC milling and turning machines in our shop. We can offer you CNC rapid prototyping and low-volume CNC machining services for plastic and metal parts. Also, surface finish like anodized, powder coating is available. If you need Metal & Plastic parts machined for prototypes or production, please feel free to get a quote online.

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